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1.  Complications in Brief: Quadriceps and Patellar Tendon Tears 
Effective treatment of knee extensor mechanism disruptions requires prompt diagnosis and thoughtful decision-making with surgical and nonsurgical approaches. When surgery is chosen, excellent surgical technique can result in excellent outcomes. Complications and failures arise from missed or delayed diagnoses and from technical problems in the operating room. In particular, inappropriate surgical timing (especially late surgery), misplaced patellar drill holes, and failure to address concomitant injuries can result in complications seen when repairing a patellar or quadriceps tendon tear. We review the complications that can occur during treatment of these injuries (Table 1).Table 1Errors and complications in the treatment of quadriceps and patellar tendon tearsError/complicationClinical effectPreventionDetectionRemedyJudgment errors Missed diagnosis: patella tendon tearPatient seen in the emergency room, presumed to have a patella dislocation; sent home; delay in treatment leads to chronic extensor mechanism disruption, which can cause disability and be more difficult to treatCareful history and physical examination(1) Physical examination Infrapatellar pain Infrapatellar gap Inability to maintain full active extension Unable to perform straight leg raise Gait abnormalities: stiff knee gait or exaggerated hip elevation for swing through circumduction(2) Radiographs Abnormal patella height (alta)(3) MRI/ultrasoundEducation of physicians and ancillary staff; high index of suspicion; thorough history and physical examination Missed diagnosis: quadriceps tendon tearVery common, especially in obese patients; delay in treatment leading to chronic extensor mechanism disruption, which can cause disability and be more difficult to treatCareful history and physical examination(1) Physical examination Suprapatellar pain Suprapatellar gapInability to maintain full active extension Gait abnormalities: stiff knee gait or exaggerated hip elevation for swing through circumduction(2) Radiographs Abnormal patella height (baja)(3) MRI/ultrasoundEducation of physicians and ancillary staff; high index of suspicion; thorough history and physical examination Missed diagnosis: intact retinaculum but torn quadriceps tendonPatient able to perform weak straight leg raise as a result of intact retinaculum, but quadriceps tendon actually completely torn; lack of power leading to altered gait and joint kinematics, joint breakdown and potential subsequent traumatic injuries(1) Careful physical examination: check for extensor lag(2) Aspirate blood from knee and inject with lidocaine; then reexamine(3) Additional imaging: MRI(1) Palpable defect in soft tissues proximal to patella(2) MRIEducation of physicians and ancillary staff; high index of suspicion Missed diagnosis: multiligament knee injury, failure to recognize extensor mechanism disruptionWith severe traumatic knee injuries, clinicians may focus on ligament/bony injury and may miss extensor mechanism disruption, leading to incomplete care of injuries and significant disability(1) Careful review of imaging, particularly sagittal views(2) Thorough physical examination(1) Palpable defect in soft tissues proximal/distal to patella(2) MRIEducation of physicians and ancillary staff; high index of suspicion; thorough history and physical examination; careful review all imaging Delayed diagnosis: delayed surgeryOperating too late after injury; tendon becomes scarred down and retracted; may be difficult to perform primary repair; may require tissue grafting and multiple surgeriesPerforming surgery as soon as possible, preferably within first weekProper detection and early management; if noted too late, consider V-Y or Scuderi technique Incorrect diagnosis: partial tendon tearTendon only partially disrupted (< 10 mm separation of the tendon from bone); will heal without surgery; in one study, nonsurgical management resulted in 93% success rate [5](1) MRI(2) Ultrasound(3) Physical examination(1) Patient should be able to maintain full active extension(2) Radiographs: normal patellar heightThis individual can be treated nonoperatively with immobilization until the tendon has healed Incorrect diagnosis: retinaculum torn, but quadriceps tendon intactAs long as the tendon is intact, the retinaculum should heal nonoperatively(1) Careful physical examination(2) Aspirate blood from knee and inject with lidocaine; then reexamine(3) Additional imaging: MRI or ultrasound Incorrect diagnosis: inability to extend knee or perform straight leg raise, but extensor mechanism is intactMultiple reasons:(1) Femoral nerve palsy(2) Pain(3) Intraarticular pathology: locked knee (loose body, bucket handle meniscal tear, etc)(1) Thorough history and careful physical examination(2) Additional imaging: MRIConsider aspiration/injection of local anesthetic and reexaminationPotential judgment errors Performing definitive surgery in open injuryConsider staged procedure if contaminated wound(1) Irrigation and debridement(2) Definitive fixationThorough history and careful physical examinationSingle stage management of contaminated or chronically open injuries potentially leads to infection and repair failure Failure to account for diabetesPoor tissue quality that should be accounted for. Delayed wound and tendon healingThorough history and careful physical examination. Tight perioperative glycemic controlLaboratory studies. Patient’s glycemic historyConsultation with patient’s primary care provider/internal medicineAdequate diseased tendon debridement.Delayed postoperative motion to account for expected delayed healingTechnical errors Positioning and preparing(1) Supine, bump under ipsilateral hip to internally rotate lower extremity(2) Consider full muscle paralysis to aid in reduction Inadequate exposureGenerous midline incision needed to see extent of injury (retinacular injury) and define injury pattern (midsubstance tear versus avulsion from patella) Failure to identify correct injury pattern: patellar tendonThree injury patterns based on location:(1) Avulsion (with/without bone) from inferior pole patella(2) Midsubstance rupture(3) Distal avulsion from tibial tubercle(1) Preoperative imaging(2) Adequate exposureCorrectly identifying injury pattern will dictate fixation method Failure to identify correct injury pattern: quadriceps tendonThree injury patterns based on location:(1) Avulsion (with/without bone) from superior pole patella(2) Midsubstance rupture(3) Mixed(1) Preoperative imaging(2) Adequate exposureCorrectly identifying injury pattern will dictate preoperative planning and fixation method Failure to débride patella/quadriceps tendon stumpFailure to débride scar or devascularized tissue may predispose to failure of the repair and/or chronic weaknessRongeur scar tissue from patellaPrepare bleeding bone bed: curette or burr a trough Failure to débride/prepare patella bone bedFailure to débride patella bone bed may predispose to poor healingRongeur scar tissue from patellaPrepare bleeding bone bed: curette or burr a trough Tendon repair: inadequate tissue for repair of midsubstance rupturesCan be challenging, especially with severely disrupted patella tendonsConsider augmentation with contralateral hamstring autograft or allograft; role for other biologics (dermal patches, etc)? Tendon repair: appropriate tension for midsubstance rupturesCan be challenging, especially with severely disrupted patella tendonsLateral radiograph of contralateral leg can help determine appropriate tension Transosseous tendon repair: divergent tunnelsDivergent tunnels lead to asymmetric reduction of tendon to bone; may lead to poor contact and therefore poor healing or maltracking(1) Adequate exposure of entire patella(2) Parallel pin drill guide(3) Consider use of fluoroscopy Transosseous tendon repair: tunnel penetration into articular surfaceIatrogenic articular cartilage injury(1) Adequate exposure of entire patella(2) Parallel pin drill guide Transosseous tendon repair: drill breakageBroken drill bit in tunnel(1) Careful drilling technique(2) Do not attempt to change direction of drill hole once started drilling(3) Do not torque drill(4) Use stout drill bit Transosseous tendon repair: anterior placement of tunnelsMay lead to downward tilting of the patella and increase patellofemoral contact forces and pain(1) Place drill holes in center of patella (with respect to AP)(2) If have to cheat, cheat toward articular surface Transosseous tendon repair: overtightening repairMay lead to patella alta or baja(1) Prepare opposite leg to assist with tensioning(2) Obtain intraoperative radiograph and compare with contralateral side Transosseous tendon repair: undertightening repair(1) May lead to patella alta or baja(2) Poor tendon to bone contact may interfere with healing(1) When tying knots, make sure to remove all the slack and that the tendon is pulled snuggly into patella bone trough(2) Adequate retinacular repair Transosseous tendon repair: prominent proximal suture knotsMay lead to skin irritationAttempt to bury knots and cover with surrounding soft tissue Suture anchor tendon repairAdvantages:(1) Less dissection(2) Decreased surgical time(3) More accurate suture placement(4) Low profile Suture anchor tendon repair: anchor pulloutCauses:(1) Poorly placed anchors(2) Poor bone quality(3) Weak anchors(1) Anchors should be placed in center of patella [2](2) Not to be used in osteoporotic bone(3) Two 5.0-mm corkscrew titanium anchors (equivalent pullout to transosseous tunnels) [1] Suture anchor tendon repair: proud anchorsProud anchors will not allow the tendon edge to be pulled into the bone trough in the patella, possibly leading to a gap at the bone-tendon junction and poor healingAnchors should be slightly countersunk to pull tendon firmly into bone trough in patella Failure to repair retinacular tissueMay lead to increased stress on central repair(1) Adequate exposure(2) Suture medial and lateral retinaculumAdditional complications Infection(1) Open injury(2) Comorbidities  Diabetes  Smoking  Chronic disease(1) Irrigation and debridement (consider delayed repair)(2) Timely administration preoperative antibiotics(3) Tight glucose control(4) Smoking cessation Wound complications(1) Open injury(2) Comorbidities  Diabetes  Smoking  Chronic disease(3) Prominent sutures(1) Irrigation and débridement (consider delayed repair)(2) Timely administration preoperative antibiotics(3) Tight glucose control(4) Smoking cessation Nerve injuryExtremely rareRehabilitation complications Prolonged immobilizationLeads to stiffness and decreased ROMIntraoperative assessment of maximum flexion before gapping between bone and tendon is observedEarly ROM (10–14 days): active flexion, passive extension to limits determined intraoperatively Inadequate immobilization(1) Wound complications(2) Failure of repairROM bracing locked in extension Overly aggressive physical therapyNeed time for tendon-to-bone healing to occurNo forced flexion or active extension in first 6 weeks
PMCID: PMC3916631  PMID: 24338040
2.  Intratendinous Tophaceous Gout Imitating Patellar Tendonitis in an Athletic Man 
Orthopedics  2011;34(3):223.
Patellar tendon-related pain is common in the athletic patient. When it occurs in skeletally mature patients participating in running, jumping, or kicking sports, the diagnosis of jumper’s knee patellar tendonitis is usually made. If patellar tendon pain is associated with a mass, the differential diagnosis should be broadened to include crystalline arthropathy.
This article presents a case of a highly athletic 45-year-old man with a history of gout, anterior knee pain, and an enlarging mass in the region of the patellar tendon. Conservative management failed, and an excisional biopsy found it to be an intra-tendinous gouty tophus. To our knowledge, only 1 report exists documenting a patellar tendon mass secondary to gout, and no case report exists documenting this problem in an athlete. The interplay between athletics and gout has not been well described. Despite the long-term protective nature of fitness, transient elevations in uric acid associated with athletic endeavors may contribute acutely to manifestations of gout in some athletes. Resultant intra- or extra-articular pathology may present as, and easily be mistaken for, a sports-related injury. Without appropriate medical management, tophaceous deposition may continue to occur and treatment of the resultant mass may require surgical intervention.
PMCID: PMC3784320  PMID: 21410111
3.  Surgical Treatment of Chronic Patellar Tendinitis in a Collegiate Football Player 
Journal of Athletic Training  1995;30(4):342-344.
In the competitive athlete, there are many causes of anterior knee pain, one of which is patellar tendinitis. Repetition of explosive movements can cause microtrauma to the tendon and its insertion, resulting in patellar tendinitis and occasional tearing, either partial or total. Due to its refractory nature, the treatment of this disorder can be quite frustrating to all involved. A 20-year-old collegiate football player with patellar tendinitis was treated conservatively for more than 2 years. Despite aggressive training regimens, including quadriceps stretching, eccentric strengthening, and therapeutic modalities, the athlete was unable to participate at his preinjury level. Physical examination of his knee revealed inflammation and crepitation. Radiographs demonstrated an avulsion fragment from the inferior pole of the patella and magnetic resonance imaging showed cystic degeneration of the tendon. These findings confirmed the diagnosis of chronic patellar tendinitis. The patient underwent surgical debridement of the patellar tendon without complications. His postoperative rehabilitation was divided into three phases: passive range of motion, active strengthening, and sport-specific activities. At 14 weeks post-surgery, the athlete was able to return to his previous level of activity without pain. Follow-up 30 weeks postoperatively revealed no return of symptoms. At 40 weeks postsurgery, the athlete was participating at his preinjury level. This case report demonstrates the successful outcome of the surgical treatment of chronic patellar tendinitis, which was unresponsive to conservative treatment, in a competitive collegiate football player.
PMCID: PMC1318006  PMID: 16558360
4.  High prevalence of jumper's knee and sonographic changes in Swedish elite junior volleyball players compared to matched controls 
Background: Jumper's knee is a common and troublesome condition among senior volleyball players, but its prevalence among elite junior players compared to matched non-sports active controls is not known.
Objective: To clinically, and by sonography, examine the patellar tendons in elite junior volleyball players (15–19 years) at the Swedish National Centre for volleyball and in matched controls.
Methods: The patellar tendons in the 57 students at the Swedish National Centre for high school volleyball and in 55 age, height, and weight matched not regularly sports active controls were evaluated clinically and by grey scale ultrasonography (US) and power Doppler (PD) sonography.
Results: There were no significant differences in mean age, height, and weight between the volleyball players and the controls. In the volleyball group, jumper's knee was diagnosed clinically and by US in 12 patellar tendons (10 male and two female). In 12/12 tendons, PD sonography demonstrated a neovascularisation in the area with structural tendon changes. In another 10 pain free tendons, there were structural tendon changes and neovessels. In the control group, no individual had a clinical diagnosis of jumper's knee. US demonstrated structural tendon changes in 11 tendons, but there was no neovascularisation on PD sonography.
Conclusions: A clinical diagnosis of jumper's knee, together with structural tendon changes and neovascularisation visualised with sonography, was seen among Swedish elite junior volleyball players but not in matched not regularly sports active controls. Structural tendon change alone was seen in 10% of the control tendons.
PMCID: PMC1725221  PMID: 15849296
5.  Superior results with eccentric compared to concentric quadriceps training in patients with jumper's knee: a prospective randomised study 
British Journal of Sports Medicine  2005;39(11):847-850.
Background: A recent study reported promising clinical results using eccentric quadriceps training on a decline board to treat jumper's knee (patellar tendinosis).
Methods: In this prospective study, athletes (mean age 25 years) with jumper's knee were randomised to treatment with either painful eccentric or painful concentric quadriceps training on a decline board. Fifteen exercises were repeated three times, twice daily, 7 days/week, for 12 weeks. All patients ceased sporting activities for the first 6 weeks. Age, height, weight, and duration of symptoms were similar between groups. Visual analogue scales (VAS; patient estimation of pain during exercise) and Victorian Institute of Sport Assessment (VISA) scores, before and after treatment, and patient satisfaction, were used for evaluation.
Results: In the eccentric group, for 9/10 tendons patients were satisfied with treatment, VAS decreased from 73 to 23 (p<0.005), and VISA score increased from 41 to 83 (p<0.005). In the concentric group, for 9/9 tendons patients were not satisfied, and there were no significant differences in VAS (from 74 to 68, p<0.34) and VISA score (from 41 to 37, p<0.34). At follow up (mean 32.6 months), patients in the eccentric group were still satisfied and sports active, but all patients in the concentric group had been treated surgically or by sclerosing injections.
Conclusions: In conclusion, eccentric, but not concentric, quadriceps training on a decline board, seems to reduce pain in jumper's knee. The study aimed to include 20 patients in each group, but was stopped at the half time control because of poor results achieved in the concentric group.
PMCID: PMC1725058  PMID: 16244196
6.  Neovascularisation and pain in jumper's knee: a prospective clinical and sonographic study in elite junior volleyball players 
Background: The nature of tendon neovascularisation associated with pain over time has not been studied.
Objective: To prospectively study the patellar tendons in elite junior volleyball players.
Methods: The patellar tendons in all students at the Swedish National Centre for high school volleyball were evaluated clinically and by ultrasonography (US) and Power Doppler (PD) sonography.
Results: Altogether 120 patellar tendons were followed for 7 months. At inclusion, jumper's knee was diagnosed clinically in 17 patellar tendons. There were structural changes on US in 14 tendons, in 13 of which PD sonography showed neovascularisation. There were 70 clinically normal tendons with normal US and PD sonography, 24 clinically normal tendons with abnormal US but normal PD sonography, and nine clinically normal tendons with abnormal US and neovascularisation on PD sonography. At 7 month follow up, jumper's knee was diagnosed clinically and by US in 19 patellar tendons, in 17 of which there was neovascularisation. Three of nine clinically normal tendons with structural changes and neovascularisation at inclusion developed jumper's knee. Two of 24 tendons clinically normal at inclusion, with abnormal US but normal PD sonography, developed jumper's knee with abnormal US and neovascularisation on PD sonography. A total of 20 clinically normal tendons with normal US and PD sonography at inclusion developed structural tendon changes and 12 of these also developed neovascularisation.
Conclusions: The clinical diagnosis of jumper's knee is most often associated with neovascularisation in the area with structural tendon changes. The finding of neovessels might indicate a deterioration of the condition.
PMCID: PMC1725252  PMID: 15976162
7.  Infrapatellar Straps Decrease Patellar Tendon Strain at the Site of the Jumper’s Knee Lesion 
Sports Health  2011;3(3):296-302.
The impetus for the use of patellar straps in the treatment of patellar tendinopathy has largely been based on empirical evidence and not on any mechanistic rationale. A computational model suggests that patellar tendinopathy may be a result of high localized tendon strains that occur at smaller patella–patellar tendon angles (PPTAs).
Infrapatellar straps will decrease the mean localized computational strain in the area of the patellar tendon commonly involved in jumper’s knee by increasing the PPTA.
Study Design:
Controlled laboratory study.
Twenty adult males had lateral weightbearing and nonweightbearing radiographs of their knees taken with and without 1 of 2 infrapatellar straps at 60° of knee flexion. Morphologic measurements of PPTA and patellar tendon length with and without the straps were used as input data into a previously described computational model to calculate average and maximum strain at the common location of the jumper’s knee lesion during a simulated jump landing.
The infrapatellar bands decreased the predicted localized strain (average and maximum) in the majority of participants by increasing PPTA and/or decreasing patellar tendon length. When both PPTA and patellar tendon length were altered by the straps, there was a strong and significant correlation with the change in predicted average localized strain with both straps.
Infrapatellar straps may limit excessive patella tendon strain at the site of the jumper’s knee lesion by increasing PPTA and decreasing patellar tendon length rather than by correcting some inherent anatomic or functional abnormality in the extensor apparatus.
Clinical Relevance:
The use of infrapatellar straps may help prevent excessive localized tendon strains at the site of the jumper’s knee lesion during a jump landing.
PMCID: PMC3445162  PMID: 23016021
infrapatellar straps; patellar tendon strain; patellar tendinopathy; patella–patellar tendon angle; computational model
8.  Reproducibility and clinical utility of tendon palpation to detect patellar tendinopathy in young basketball players 
Background—Palpation is an important clinical test for jumper's knee.
Objectives—To (a) test the reproducibility of palpation tenderness, (b) evaluate the sensitivity and specificity of palpation in subjects with clinical symptoms of jumper's knee, and (c) determine whether tenderness to palpation may serve as a useful screening test for patellar tendinopathy. The yardstick for diagnosis of patellar tendinopathy was ultrasonographic abnormality.
Methods—In 326 junior symptomatic and asymptomatic athletes' tendons, palpation was performed by a single examiner before ultrasonographic examination by a certified ultrasound radiologist. In 58 tendons, palpation was performed twice to test reliability. Tenderness to palpation was scored on a scale from 0 to 3 where 0 represented no pain, and 1, 2, and 3 represented mild, moderate, and severe tenderness respectively.
Results—Patellar tendon palpation was a reliable examination for a single examiner (Pearson r = 0.82). In symptomatic tendons, the positive predictive value of palpation was 68%. As a screening examination in asymptomatic subjects, the positive predictive value of tendon palpation was 36–38%. Moderate and severe palpation tenderness were better predictors of ultrasonographic tendon pathology than absent or mild tenderness (p<0.001). Tender and symptomatic tendons were more likely to have ultrasound abnormality than tenderness alone (p<0.01).
Conclusions—In this age group, palpation is a reliable test but it is not cost effective in detecting patellar tendinopathy in a preparticipation examination. In symptomatic tendons, palpation is a moderately sensitive but not specific test. Mild tenderness in the patellar tendons in asymptomatic jumping athletes should be considered normal.
Key Words: patellar tendon; ultrasound; palpation; reliability; athletes
PMCID: PMC1724272  PMID: 11157466
9.  Reconstruction of medial patellofemoral ligament for chronic patellar instability 
Indian Journal of Orthopaedics  2012;46(4):447-454.
Disruption of the capsule, medial patellar retinaculum, and/or vastus medialis obliqus has been associated with recurrent patellar instability. Biomechanical studies have shown that the medial patellofemoral ligament (MPFL) is the main restraint against lateral patella displacement and reconstruction of the MPFL has become an accepted surgical technique to restore patellofemoral stability in patients having recurrent patellar dislocation. We report a prospective series of patients of chronic patellar instability treated by reconstruction of medial patellofemoral ligament.
Materials and Methods:
Twelve patients (15 knees) with recurrent dislocation of patella, were operated between January 2006 and December 2008. All patients had generalised ligament laxity with none had severe grade of patella alta or trochlear dysplasia. The MPFL was reconstructed with doubled semitendinosus tendon. Patients were followed up with subjective criteria, patellar inclination angle, and Kujala score.
The mean duration of followup after the operative procedures was an average of 42 months (range 24–60 months) 10 knees showed excellent results, 3 knees gave good results, and 2 knees had a fair result. The average patellar inclination angle decreased from 34.3° to 18.6°. The average preoperative Kujala functional score was 44.8 and the average postoperative score was 91.9.
MPFL reconstruction using the semitendinosus tendon gives good results in patients with chronic patellar instability without predisposing factors like severe patella alta and high-grade trochlear dysplasia, and for revision cases.
PMCID: PMC3421936  PMID: 22912521
Hamstring tendon; medial patellofemoral ligament; patellofemoral instability
10.  Patellar tendinosis as an adaptive process: a new hypothesis 
Background: Patellar tendinosis (PT), or "jumper's knee" is a common condition in athletes participating in jumping sports, and is characterised by proximal patellar tendon pain and focal tenderness to palpation. Hypoechoic lesions observed in the proximal patellar tendon associated with the tendinosis are typically described as being a result of degenerative change or "failed healing". We propose a new model for the development of the hypoechoic lesion observed in PT, in which the aetiology is an adaptive response to differential forces within the tendon.
Methods: We assessed the clinical, histopathological, and biomechanical literature surrounding the patellar tendon and integrated this with research into the response of tendons to differential forces.
Results and conclusions: We propose that the hypoechoic lesion commonly described in PT is the result of adaptation or partial adaptation of the proximal patellar tendon to a compressive load. We postulate that the biomechanics of the patellar–patellar tendon interface creates this compressive environment. Secondary failure of the surrounding tensile adapted tendon tissue may result in tissue overload and failure, with resultant stimulation of nociceptors. We believe that this "adaptive model" of patellar tendinosis is consistent with the clinical and histological findings.
PMCID: PMC1725001  PMID: 15562176
11.  Normal clinical and ultrasound findings indicate a low risk to sustain jumper's knee patellar tendinopathy: a longitudinal study on Swedish elite junior volleyball players 
Jumper's knee patellar tendinopathy is well known to be a common and difficult injury in volleyball. Knowledge about its aetiology and pathogenesis is sparse.
To prospectively follow clinical status, tendon structure and vascularity in elite junior volleyball players.
22 volleyball players (44 patellar tendons) beginning their first grade at the Swedish National Centre for high school volleyball were continuously evaluated clinically and by ultrasonography (US) and power Doppler (PD) over the 3 school years.
At inclusion, there were 44 tendons being assessed. Jumper's knee was diagnosed clinically in eight patellar tendons (seven of eight had structural changes and vascularity on US+PD). There were 27 normal (clinical and US+PD) tendons. At 3 years, there were 36 tendons still being assessed. Four individuals (eight tendons) had been excluded. Jumper's knee had developed in 2 of 25 (2 were excluded) tendons that were normal (clinical and US+PD) at inclusion. Jumper's knee (clinical and US+PD) was also present in six tendons.
Normal clinical tests and ultrasound findings at the start indicated a low risk for these elite junior volleyball players to sustain jumper's knee during three school years with intensive training and playing.
PMCID: PMC2658958  PMID: 17127723
12.  The TOPGAME-study: effectiveness of extracorporeal shockwave therapy in jumping athletes with patellar tendinopathy. Design of a randomised controlled trial 
Patellar tendinopathy is a major problem for many athletes, especially those involved in jumping activities. Despite its frequency and negative impact on athletic careers, no evidence-based guidelines for management of this overuse injury exist. Since functional outcomes of conservative and surgical treatments remain suboptimal, new diagnostic and therapeutic strategies have to be developed and evaluated.
Extracorporeal shockwave therapy (ESWT) appears to be a promising treatment in patients with chronic patellar tendinopathy. ESWT is most often applied after the known conservative treatments have failed. However, its effectiveness as primary therapy has not been studied in athletes who keep playing sports despite having patellar tendon pain.
The aim of this study is to determine the effectiveness of ESWT in athletes with patellar tendinopathy who are still in training and competition.
The TOPGAME-study (Tendinopathy of Patella Groningen Amsterdam Maastricht ESWT) is a multicentre two-armed randomised controlled trial with blinded participants and outcome assessors, in which the effectiveness of patient-guided focussed ESWT treatment (compared to placebo ESWT) on pain reduction and recovery of function in athletes with patellar tendinopathy will be investigated. Participants are volleyball, handball and basketball players with symptoms of patellar tendinopathy for a minimum of 3 to a maximum duration of 12 months who are still able to train and compete. The intervention group receives three patient-guided focussed medium-energy density ESWT treatments without local anaesthesia at a weekly interval in the first half of the competition. The control group receives placebo treatment. The follow-up measurements take place 1, 12 and 22 weeks after the final ESWT or placebo treatment, when athletes are still in competition. Primary outcome measure is the VISA-P (Victorian Institute of Sport Assessment - patella) score. Data with regard to pain during function tests (jump tests and single-leg decline squat) and ultrasound characteristics are also collected. During the follow-up period participants also register pain, symptoms, sports participation, side effects of treatment and additional medical consumption in an internet-based diary.
The TOPGAME-study is the first RCT to study the effectiveness of patient-guided ESWT in athletes with patellar tendinopathy who are still in training and competition.
Trial registration
Trial registration number NTR1408.
PMCID: PMC2831826  PMID: 20144188
13.  Open Patellar Tendon Debridement for Treatment of Recalcitrant Patellar Tendinopathy 
Sports Health  2013;5(3):276-280.
Patellar tendinopathy can be treated surgically for patients that have failed at least 1 year of nonoperative treatment who continue to have debilitating symptoms. Patellar tendinopathy can cause significant functional deficits, yet little has been reported about the operative treatment of patellar tendinopathy.
A combined arthroscopic and open surgical technique for the treatment of recalcitrant patellar tendinopathy results in an improvement in function and pain at a minimum 2-year follow-up. The purpose of this study was to present the indications, combined surgical technique, rehabilitation protocol, and the 2-year minimum follow-up results of the operative treatment of recalcitrant patellar tendinopathy.
Study Design:
Retrospective case series.
A retrospective review was performed of all patients who underwent a surgical primary patellar tendon debridement for recalcitrant patellar tendinopathy by a single surgeon between July 1999 and December 2005. Every patient failed at least 1 year of nonoperative treatment. Patients were excluded from the study if they had previous open knee surgery. Validated patient-reported outcome scores were used to assess function and pain levels pre- and postoperatively (Lysholm, International Knee Documentation Committee, Tegner activity, and visual analog pain score).
Thirty-four consecutive patients (37 consecutive cases) with mean follow-up 3.8 ± 1.6 years (range, 2-7.6 years) underwent the procedure with no complications. The mean age at surgery was 29 years (range, 14-51 years). Postoperatively, the visual analog score decreased by an mean of 6 points (range, 1 to −10, P < 0.001), and patients were able to return to their preinjury Tegner activity level. When asked if they were satisfied by the overall outcome of their surgery, 28 patients (82%) were completely or mostly satisfied with their surgical outcome on a particular knee; 6 (18%) were somewhat satisfied; and 2 (6%) were dissatisfied. Twenty-seven patients (79%) said they would have the surgery again.
The combined arthroscopic and open surgical technique described for chronic recalcitrant patellar tendinopathy successfully reduces knee pain and allows return to preinjury level of activity.
PMCID: PMC3658401  PMID: 24427403
patellar tendinopathy; microfracture; fenestration; clinical outcomes
14.  High Tibial Valgus Osteotomy: Closing, Opening or Combined? Patellar Height as a Determining Factor 
According to the literature, closing and opening wedge high tibial valgus osteotomies can raise or lower the patella, and diffèrent methods of patella height measurement show similarly conflicting results. Clarification of this was thought to be important because there is much literature describing morbidity secondary to patella alta or patella infera (baja). Effects on tibial slope and patellar tendon length are not well delineated and the influence of sex and age is unknown.
A group of patients who underwent high tibial valgus osteotomy was investigated to determine how surgical technique influenced postoperative (1) patellar height and (2) tibial slope and patellar tendon length, and (3) whether age or gender independently influenced postoperative patellar height. To eliminate the often conflicting results seen when several ratio methods are used, patellar height was measured by one method, before and after surgery, shown previously to be reliable.
Patellar height was measured on radiographs using the plateau-patella angle in a retrospective case series consisting of three cohorts: 18 patients with closing wedge osteotomies, 26 with opening wedge osteotomies, and 32 with combined osteotomies. The indication for surgery in all three cohorts was medial osteoarthritis with secondary varus. Before surgery there were no significant differences in patellar height, femorotibial angle, age, or gender among the three groups, and no patients were lost to followup during the 8-week study period after surgery. Seven of the 76 patients (9.2%), all in the opening wedge cohort, had concomitant ACL reconstruction at the time of the tibial osteotomy. No other surgery, except arthroscopy, was performed at the time of osteotomy. Patellar tendon length was assessed by the Insall-Salvati index and tibial slope by the angle between the posterior tibial cortex and the medial tibial joint line. Postoperative measurements were made between 6 and 8 weeks. The influence of sex and age was calculated using patellar height measurements made before any surgery.
All closing wedge osteotomies produced patellar ascent by an average of 13% (p < 0.001), all opening wedges produced descent by an average of 21% (p < 0.001), and the combined osteotomy mean showed minimal change (p = 0.0034). The absolute consistency of the changes and their direction allow suggested guidelines for selection of osteotomy type. There were only slight changes in tibial slope. A significant change in patellar tendon length was seen in seven knees of the opening wedge cohort that had concomitant ACL reconstruction. All had a mean reduction of the Insall-Salvati index of 0.05 (approximately 5%), p = 0.0002. New findings showed higher patellae in female and older patients, unrelated to the surgery.
If it is accepted that patella baja and patella alta should be avoided, then closing wedge osteotomies should be performed only when the patella is low riding, and opening wedge osteotomies should be done only for patients with preexisting patella alta. The combined osteotomy minimizes changes in patellar height. Patellar tendon contractures and tibial slope changes can be avoided. The plateau-patella angle should be measured preoperatively to help decide the type of osteotomy.
Level of Evidence
Level III, therapeutic study. See the Instructions for Authors for a complete description of levels of evidence.
PMCID: PMC4182389  PMID: 25070919
15.  Changes in Morphological and Elastic Properties of Patellar Tendon in Athletes with Unilateral Patellar Tendinopathy and Their Relationships with Pain and Functional Disability 
PLoS ONE  2014;9(10):e108337.
Patellar tendinopathy (PT) is one of the most common knee disorders among athletes. Changes in morphology and elasticity of the painful tendon and how these relate to the self-perceived pain and dysfunction remain unclear.
To compare the morphology and elastic properties of patellar tendons between athlete with and without unilateral PT and to examine its association with self-perceived pain and dysfunction.
In this cross-sectional study, 33 male athletes (20 healthy and 13 with unilateral PT) were enrolled. The morphology and elastic properties of the patellar tendon were assessed by the grey and elastography mode of supersonic shear imaging (SSI) technique while the intensity of pressure pain, self-perceived pain and dysfunction were quantified with a 10-lb force to the most painful site and the Victorian Institute of Sport Assessment-patella (VISA-P) questionnaire, respectively.
In athletes with unilateral PT, the painful tendons had higher shear elastic modulus (SEM) and larger tendon than the non-painful side (p<0.05) or the dominant side of the healthy athletes (p<0.05). Significant correlations were found between tendon SEM ratio (SEM of painful over non-painful tendon) and the intensity of pressure pain (rho  = 0.62; p = 0.024), VISA-P scores (rho  = −0.61; p = 0.026), and the sub-scores of the VISA-P scores on going down stairs, lunge, single leg hopping and squatting (rho ranged from −0.63 to −0.67; p<0.05).
Athletes with unilateral PT had stiffer and larger tendon on the painful side than the non-painful side and the dominant side of healthy athletes. No significant differences on the patellar tendon morphology and elastic properties were detected between the dominant and non-dominant knees of the healthy control. The ratio of the SEM of painful to non-painful sides was associated with pain and dysfunction among athletes with unilateral PT.
PMCID: PMC4193737  PMID: 25303466
16.  A cross sectional study of 100 athletes with jumper's knee managed conservatively and surgically. The Victorian Institute of Sport Tendon Study Group. 
OBJECTIVES: Jumper's knee causes significant morbidity in athletes of all standards. However, there are few reference data on the clinical course of this condition in a large number of patients, and the aim of this study was to rectify this. METHODS: A retrospective study of the course of jumper's knee in 100 athletes who presented to a sports medicine clinic over a nine year period was carried out. Subjects completed a questionnaire designed to collect details of sport participation, symptoms, and time out of sport. Ultrasonographic results were recorded from the radiologists' reports. Histopathological results were obtained for patients who had surgery. RESULTS: Forty eight subjects recalled that symptoms of jumper's knee began before the age of 20 years. Symptoms prevented 33 from participating in sport for more than six months, and 18 of these were sidelined for more than 12 months. Forty nine of the subjects had two or more separate episodes of symptoms. Ultrasonography showed a characteristics hypoechoic region at the junction of the inferior pole of the patella and the deep surface of the patellar tendon. Histopathological examination showed separation and disruption of collagen fibres on polarisation light microscopy and an increase in mucoid ground substance consistent with damage of tendon collagen without inflammation. CONCLUSIONS: Jumper's knee has the potential to be a debilitating condition for a sports person. About 33% of athletes presenting to a sports medicine clinic with jumper's knee were unable to return to sport for more than six months.
PMCID: PMC1332572  PMID: 9429013
17.  The John Insall Award: Control-matched Evaluation of Painful Patellar Crepitus After Total Knee Arthroplasty 
Patellar crepitus (PC) is reported in up to 14% of subjects implanted with cruciate-substituting total knee arthroplasty (TKA). Numerous etiologies of PC have been proposed.
We determined when painful PC typically occurs postoperatively and compared patients undergoing primary TKA who developed painful PC requiring subsequent surgery with a matched group without this complication to identify clinical, radiographic, and surgical variables associated with this complication.
From the databases of two institutions (greater than 4000 TKAs), we identified 60 patients who required surgery for painful PC from 2002 to 2008. This group was then compared with an identified control group of 60 TKA subjects without PC who were matched for the key variables of age, gender, and body mass index to determine clinical, radiographic, and surgical factors associated with the development of PC.
The mean time to presentation of PC was 10.9 months. The incidence of PC correlated with a greater number of previous knee surgeries, decreased patellar component size, decreased composite patellar thickness, shorter preoperative and postoperative patellar tendon length, increased posterior femoral condylar offset, use of smaller femoral components and thicker tibial polyethylene inserts, and placement of the femoral component in a flexed posture.
Many of the factors associated with an increased incidence of postoperative PC such as shortened patellar tendon length, use of smaller patellar components, decreased patellar composite thickness, and increased posterior femoral condylar offset may all increase quadriceps tendon contact forces against the superior aspect of the intercondylar box, increasing the risk of fibrosynovial proliferation and entrapment within the intercondylar region of the femoral component. Based on these findings, the authors recommend use of larger patellar components when possible, avoid oversection of the patella or increasing posterior femoral condylar offset, and advising patients preoperatively who have had previous knee surgery or demonstrate a shortened patellar tendon length of an increased risk of development of postoperative patellar crepitus.
Level of Evidence
Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
PMCID: PMC3008897  PMID: 20706813
18.  Use of platelet-rich plasma for the treatment of refractory jumper’s knee 
International Orthopaedics  2009;34(6):909-915.
The aim of this study was to evaluate the efficacy of multiple platelet-rich plasma (PRP) injections on the healing of chronic refractory patellar tendinopathy after previous classical treatments have failed. We treated 15 patients affected by chronic jumper’s knee, who had failed previous nonsurgical or surgical treatments, with multiple PRP injections and physiotherapy. We also compared the clinical outcome with a homogeneous group of 16 patients primarily treated exclusively with the physiotherapy approach. Multiple PRP injections were performed on three occasions two weeks apart into the site of patellar tendinopathy. Tegner, EQ VAS and pain level were used for clinical evaluation before, at the end of the treatment and at six months follow-up. Complications, functional recovery and patient satisfaction were also recorded. A statistically significant improvement in all scores was observed at the end of the PRP injections in patients with chronic refractory patellar tendinopathy and a further improvement was noted at six months, after physiotherapy was added. Moreover, comparable results were obtained with respect to the less severe cases in the EQ VAS score and pain level evaluation, as in time to recover and patient satisfaction, with an even higher improvement in the sport activity level achieved in the PRP group. The clinical results are encouraging, indicating that PRP injections have the potential to promote the achievement of a satisfactory clinical outcome, even in difficult cases with chronic refractory tendinopathy after previous classical treatments have failed.
PMCID: PMC2989009  PMID: 19641918
19.  Eccentric decline squat protocol offers superior results at 12 months compared with traditional eccentric protocol for patellar tendinopathy in volleyball players 
Background: Conservative treatment of patellar tendinopathy has been minimally investigated. Effective validated treatment protocols are required.
Methods: This was a prospective randomised controlled trial of 17 elite volleyball players with clinically diagnosed and imaging confirmed patellar tendinopathy. Participants were randomly assigned to one of two treatment groups: a decline group and a step group. The decline group were required to perform single leg squats on a 25° decline board, exercising into tendon pain and progressing their exercises with load. The step group performed single leg squats on a 10 cm step, exercising without tendon pain and progressing their exercises with speed then load. All participants completed a 12 week intervention programme during their preseason. Outcome measures used were the Victorian Institute of Sport Assessment (VISA) score for knee function and 100 mm visual analogue scale (VAS) for tendon pain with activity. Measures were taken throughout the intervention period and at 12 months.
Results: Both groups had improved significantly from baseline at 12 weeks and 12 months. Analysis of the likelihood of a 20 point improvement in VISA score at 12 months revealed a greater likelihood of clinical improvements in the decline group than the step group. VAS scores at 12 months did not differ between the groups.
Conclusions: Both exercise protocols improved pain and sporting function in volleyball players over 12 months. This study indicates that the decline squat protocol offers greater clinical gains during a rehabilitation programme for patellar tendinopathy in athletes who continue to train and play with pain.
PMCID: PMC1725109  PMID: 15665207
20.  Comparative study between mono-bundle bone-patellar tendon-bone, double-bundle hamstring and mono-bundle bone-patellar tendon-bone combined with a modified Lemaire extra-articular procedure in anterior cruciate ligament reconstruction 
International Orthopaedics  2012;37(2):193-199.
The aim of the study was to compare three different procedures performed by the same surgeon: mono-bundle patellar tendon reconstruction (bone-patellar tendon-bone, BPTB), double-bundle hamstring reconstruction (DBH) and mono-bundle patellar tendon combined with extra-articular reconstruction (Lemaire) (BPTB + L).
A total of 75 patients (25 in each group) were evaluated at a mean follow-up of 25 months. Laxity was assessed pre- and post-operatively with Telos™ stress radiographs (15 kg). The amount of anterior tibial translation (ATT) corrected by the surgery was quantified. Secondary outcomes were International Knee Documentation Committee (IKDC) scores, pivot shift grading, pain complaints, sensory deficits, subsequent surgical procedures, return to sports and patients’ ability to kneel or squat on their affected knee.
Absolute correction of ATT for the internal compartment was not statistically significant [analysis of variance (ANOVA), p = 0.377]. For the external compartment BPTB + L (8.2 mm) showed superiority over DBH (5.6 mm) and BPTB (4.1 mm) (ANOVA, p = 0.0001, Tukey’s test). Kneeling was better in the DBH group (ANOVA, p = 0.0001, Tukey’s test). In 22 patients it felt normal, while only in seven in the BPTB and eight in the BPTB + L groups. Sensory deficits were present in 11 patients from the DBH group, while in 17 in the BPTB and 19 in the BPTB + L groups (ANOVA, p = 0.052). Mean IKDC values, presence of anterior knee pain, subsequent operations, ability to squat and return to sports were not statistically different between groups.
Absolute correction of ATT was not statistically different for the medial compartment, but the patellar tendon reconstruction combined with the extra-articular procedure achieved the best lateral compartment ATT correction. Sensory deficits and kneeling seem to be worse in the groups where the patellar tendon is harvested.
PMCID: PMC3560891  PMID: 23180103
21.  Recalcitrant Infrapatellar Tendinitis and Surgical Outcome in a Collegiate Basketball Player: A Case Report 
Journal of Athletic Training  2001;36(2):174-181.
To present the history, surgery, rehabilitation management, and eventual functional and surgical outcomes of a collegiate basketball player with recalcitrant jumper's knee.
A 21-year-old, male collegiate basketball player had a 2-year history of anterior knee pain.
Differential Diagnosis:
Injuries that often mimic symptoms of infrapatellar tendinitis include infrapatellar fat pad irritation, Hoffa fat pad disease, patellofemoral joint dysfunction, mucoid degeneration of the infrapatellar tendon, and, in preadolescents and adolescents, Sinding-Larsen-Johannsson disease.
After conservative treatment failed to improve his symptoms, the athlete underwent surgical excision of infrapatellar fibrous scar tissue and repair of the infrapatellar tendon.
This patient's case was unique in 3 distinct ways: (1) outcome surveys helped me to understand how this injury affected various aspects of this patient's life and how he viewed himself as he progressed through rehabilitation; (2) a modified functional test was used to help determine whether the athlete was ready to return to sport; and (3) the athlete progressed rapidly through rehabilitation and returned to competitive athletics in 3 months.
This patient was able to return to sport without functional limitations. The surgical outcome was also considered excellent.
PMCID: PMC155530  PMID: 12937459
jumper's knee; tendinitis; tendinosis; rehabilitation
22.  Can Arthroscopically Assisted Treatment of Chronic Patellar Tendinopathy Reduce Pain and Restore Function? 
Patellar tendinopathy is a common source of pain in athletes, especially those involved in sports with a high incidence of jumping and cutting. Changes in training programs and exercises based on eccentric quadriceps contractions often relieve patients’ symptoms. For athletes unresponsive to this treatment, some authors suggest open and arthroscopic procedures débriding either the tendon alone, or the tendon and bone.
We asked whether an arthroscopically assisted approach to débride not only the tendon, bone, but also the peritenon could relieve pain and allow athletes to return to their former activities.
Patients and Methods
We retrospectively reviewed 23 patients with a history of at least 6 months of painful patellar tendinopathy unresponsive to nonoperative treatment treated with an arthroscopic technique that débrided the tendon, inferior pole of the patella, and peritenon: 22 males and one female. Mean age was 29 years. Patients were evaluated using the anterior knee pain score of Kujala et al. The minimum followup was 12 months (mean, 58 months; range, 12–121 months).
Twelve patients scored 100, one 99, one 98, five 97, two 94, one 90, and one 64. The Kujala et al. mean score was 96 (range, 64–100). All but four patients returned to their former sports activities. We observed no complications.
Arthroscopic treatment can relieve the pain of refractory chronic patellar tendinopathy. Our observations were comparable with those previously reported for open techniques and a high percentage of patients returned to their previous activity level.
Level of Evidence
Level IV, observational study. See Guidelines for Authors for a complete description of levels of evidence.
PMCID: PMC3293969  PMID: 21461867
23.  A randomised clinical trial of the efficacy of drop squats or leg extension/leg curl exercises to treat clinically diagnosed jumper's knee in athletes: pilot study 
Objectives—To compare the therapeutic effect of two different exercise protocols in athletes with jumper's knee.
Methods—Randomised clinical trial comparing a 12 week programme of either drop squat exercises or leg extension/leg curl exercises. Measurement was performed at baseline and after six and 12 weeks. Primary outcome measures were pain (visual analogue scale 1–10) and return to sport. Secondary outcome measures included quadriceps and hamstring moment of force using a Cybex II isokinetic dynamometer at 30°/second. Differences in pain response between the drop squat and leg extension/curl treatment groups were assessed by 2 (group) x 3 (time) analysis of variance. Two by two contingency tables were used to test differences in rates of return to sport. Analysis of variance (2 (injured versus non-injured leg) x 2 (group) x 3 (time)) was also used to determine differences for secondary outcome measures.
Results—Over the 12 week intervention, pain diminished by 2.3 points (36%) in the leg extension/curl group and 3.2 points (57%) in the squat group. There was a significant main effect of both exercise protocols on pain (p<0.01) with no interaction effect. Nine of 10 subjects in the drop squat group returned to sporting activity by 12 weeks, but five of those subjects still had low level pain. Six of nine of the leg extension/curl group returned to sporting activity by 12 weeks and four patients had low level pain. There was no significant difference between groups in numbers returning to sporting activity. There were no differences in the change in quadriceps or hamstring muscle moment of force between groups.
Conclusions—Progressive drop squats and leg extension/curl exercises can reduce the pain of jumper's knee in a 12 week period and permit a high proportion of patients to return to sport. Not all patients, however, return to sport by that time.
Key Words: knee; patellar tendon; tendinopathy; tendinosis; eccentric strengthening; strength training
PMCID: PMC1724276  PMID: 11157465
24.  The effect of mild symptomatic patellar tendinopathy on the quadriceps contractions and the Fente motion in elite fencers 
To investigate how mild symptomatic patellar tendinopathy (PT) affects quadriceps contractions and the Fente motion, this case-control study examined elite fencers who continue to train and play fully with mild tendon pains. Twenty-four elite fencers (10 women) with mild symptomatic PT and 24 controls (10 women) participated in the study. Concentric/eccentric isokinetic strength of the quadriceps was tested, and peak torque and total work were recorded. Kinematic data from the knee during the Fente motion were collected. The first analysis period (P1) was after heel contact to the maximal flexion of the knee, and the second (P2) was right after P1 to heel-off. Normalized peak torque and work of concentric/eccentric contractions were not significantly different. Affected fencers demonstrated significantly reduced angular velocities at P2 (p = 0.042). The male fencers did not demonstrate any differences. The affected female fencers demonstrated significantly weaker concentric peak torque at 60°·s-1 (p = 0. 009) and 180°·s-1 (p = 0.047) and less concentric work at 60°·s-1 (p = 0.020). They also demonstrated significantly reduced average angular velocities at P2 (p = 0.001). Therefore, mild symptomatic PT seems to have an effect on the isokinetic concentric contraction of the quadriceps and the angular velocity of the knee during the backward Fente motion in elite female fencers who are participating fully in training and competition.
Key pointsIt is likely that even mild symptomatic patellar tendinopathy could affect the athletic performances in elite fencers.Elite female fencers are more likely to be affected substantially by symptomatic patellar tendinopathy in their sporting ability than male fencers.Because weak concentric knee extensors may affect the performance in fencing, not only eccentric training for symptomatic patellar tendinopathy but also proper concentric training of the quadriceps may be helpful in a rehabilitation program of elite female fencers who are participating fully in their training and competition.
PMCID: PMC3761502  PMID: 24149561
Patellar tendinopathy; elite fencers; isokinetic; kinematics
25.  Relationship between landing strategy and patellar tendinopathy in volleyball 
The aetiology of patellar tendinopathy (jumper's knee) remains unclear. To see whether landing strategy might be a risk factor for the development of this injury, this study examined whether landing dynamics from drop jumps differed among healthy volleyball players (CON) and volleyball players with a jumper's knee. The patients with jumper's knee were divided into an asymptomatic group with a previous jumper's knee (PJK) and a symptomatic group with a recent jumper's knee (RJK).
Inverse dynamics analyses were used to estimate lower extremity joint dynamics from 30, 50 and 70 cm drop jumps in the three groups (CON, n = 8; PJK, n = 7; RJK, n = 9). A univariate repeated measures analysis of variance was used to compare the different landing techniques.
Data analysis of the landing dynamics revealed that PJK showed higher knee angular velocities (p<0.01), and higher ankle plantar flexion moment loading rate (p<0.01). Furthermore, strong tendencies of higher loading rate of vertical ground reaction force (p = 0.05) and higher knee extensor moment loading rate (p = 0.08) were found compared with CON. Higher values for peak knee moment, peak knee power and knee work (all p<0.01) were found for CON compared with RJK. The comparison of the two jumper's knee groups yielded higher knee angular velocities (p<0.01), together with higher ankle plantar flexion and knee extensor moment loading rate (p<0.01 and p<0.05, respectively).
Where RJK used a landing technique to avoid high patellar tendon loading, PJK used a stiffer landing strategy, which may be a risk factor in the development of patellar tendinopathy.
PMCID: PMC2465350  PMID: 17224437

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