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1.  Labral Refixation: Current Techniques and Indications 
HSS Journal  2012;8(3):240-244.
Labral tears have been associated with femoroacetabular impingement, instability, sports-related activity or trauma, capsular laxity or hypermobility, dysplasia, and degeneration. Disruption of the labrum increases the rate of acetabular cartilage compression and the contact stress between the femoral and acetabular cartilage. If left untreated, these lesions will alter normal hip joint function and may eventually lead to osteoarthritis.
For the labrum with adequate tissue (>7 mm), the labrum is repaired if it is detached or torn. If the labrum is bruised, a rim reduction and repair is performed, especially in the presence of cartilage damage and the labral–chondral junction. Labri are debrided only if there is enough substance to maintain the function of the labrum. Care must be taken to fix the labrum so that it provides adequate seal with the femoral head.
Two-year outcome on 122 patients who underwent arthroscopic treatment for femoroacetabular impingement and chondrolabral dysfunction showed that, overall, most patients showed an improvement in symptoms and function and were satisfied with the results. Independent predictors of improved outcomes were joint space >2 mm and repair of labral pathology instead of debridement. Several other studies have shown excellent results following labral refixation and repair.
Labral tears have been associated with femoroacetabular impingement, instability, sports-related activity or trauma, capsular laxity or hypermobility, dysplasia, and degeneration. Untreated labral tears can result in premature osteoarthritis of the hip. Debridement only used to be the standard of care, but excellent results reveal arthroscopic labral repair and refixation are an option with good outcomes.
PMCID: PMC3470662  PMID: 24082867
labral tear; labral refixation; femoroacetabular impingement; acetabular rim
2.  MR-based Parameters as a Supplement to Radiographs in Managing Developmental Hip Dysplasia 
Clinics in Orthopedic Surgery  2011;3(3):202-210.
Some dysplastic hips with favorable radiographic parameters fail to develop normally, suggesting that we should consider cartilaginous or soft tissue structures for further information regarding the condition of the hip. The purpose of this study was to provide a clear definition of concentric reduction in developmental dysplasia of the hip (DDH) based on magnetic resonance imaging (MRI), and to determine how radiographic and MR-based parameters could be used together to treat dysplastic hips.
We studied range of motion (ROM)-MRI of 25 patients with unilateral hip dysplasia (mean age at the time of MR imaging, 44.1 months). Each ROM-MRI consisted of a set of bilateral hip scans in the following positions: neutral; abduction; abduction- internal rotation; abduction-internal rotation-flexion; and adduction. Before MR scanning, the 25 patients received the following primary treatments: closed reduction (n = 15; at a mean age of 14.5 months); and open reduction (n = 10; at a mean age of 10.0 months). The following new parameters appear to be useful in treating DDH: 1) the labral angle, the angle the labrum makes with the acetabulum; 2) the uncorrected labral deformity (ULD), the "residual deformity" (deflection of the labrum) when the affected labrum is freed from pressure in abduction; and 3) the zone of compressive force (ZCF), the region of the acetabulum through which the body weight acts on the femoral head.
A concentrically-reduced hip is one in which the labrum points downward in the neutral position, at the same angle as that of the normal side; and in which the ZCF is zone 3, the inner acetabular zone as defined herein. The ULD and the ZCF may be determined precisely as we have done, or the physician may simply observe the changes in the orientation of the labrum and compare the changes qualitatively to the unaffected side, and likewise for the medial joint space.
Detailed analysis of the labrum as permitted by ROM-MRI, together with acetabular index and other parameters measured from radiographs, provides important information for physicians treating childhood hip dysplasia.
PMCID: PMC3162200  PMID: 21909467
Developmental hip dysplasia; Dysplastic hip; Magnetic resonance imaging; Concentric reduction; Labrum
3.  The labrum: structure, function, and injury with femoro-acetabular impingement 
The recognition of the importance of femoro-acetabular impingement (FAI) as a potential cause of hip pain has been stimulated by major efforts to salvage hip joints by reconstruction to prevent or delay the need for replacement. A previous review addressed the nature of FAI, the various types, and how to make the diagnosis. When FAI occurs, the structure between the femur and acetabular rim, the labrum, is initially impinged upon and subsequently injured.
Injury to the labrum should be recognized when treating the osseous causes of FAI. Preserving or recovering labral function, enhancing hip stability and protecting the articular surface, is critical to restoring the hip to normal or near-normal mechanical and physiologic function. The present review collected the varied essential information about the labrum in a succinct manner, independent of treatment algorithms.
Advanced knowledge of the labrum is presented, including the anatomy, circulation, histology, embryology, and neurology, as well as how the labrum tears, the types of tears, and how to make the diagnosis. The advantages and limitations of diagnostic magnetic resonance techniques are discussed, including magnetic resonance imaging (MRI), indirect magnetic resonance arthrography (i-MRA), and direct magnetic resonance arthrography (d-MRA). The review recognizes the complexity of the labrum and provides a greater understanding of how the labrum is capable of stabilizing the joint and protecting the articular surface of the hip. This information will act as a guide in developing treatment plans when treating FAI.
PMCID: PMC3468736  PMID: 24082951
Labrum; Magnetic resonance imaging; MRI; Magnetic resonance arthrography; MRA; Consolidation
4.  Cartilage Thickness in the Hip Measured by MRI and Stereology Before and After Periacetabular Osteotomy 
Untreated hip dysplasia can result in a degenerative process joint and secondary osteoarthritis at an early age. While most periacetabular osteotomies (PAOs) are performed to relieve symptoms, the osteotomy is presumed to slow or prevent degeneration unless irreparable damage to the cartilage has already occurred.
We therefore determined (1) whether changes in the thickness of the cartilage in the hip occur after PAO, and (2) how many patients had an acetabular labral tear and whether labral tears are associated with thinning of the cartilage after PAO.
Patients and Methods
We prospectively followed 22 women and four men with hip dysplasia with MRI before PAO and again 1 year and 2½ years postoperatively to determine if cartilage thinning (reflecting osteoarthritis) occurred. The thickness of the femoral and acetabular cartilage was estimated with a stereologic method. Three and one-half years postoperatively, 18 of 26 patients underwent MR arthrography to investigate if they had a torn acetabular labrum.
The acetabular cartilage thickness differed between 1 and 2½ years postoperatively (preoperative 1.40 mm, 1 year postoperatively 1.47 mm, and 2½ years postoperatively 1.35 mm), but was similar at all times for the femoral cartilage (preoperative 1.38 mm, 1 year postoperatively 1.43 mm, and 2½ years postoperatively 1.38 mm.) Seventeen of 18 patients had a torn labrum. The tears were located mainly superior on the acetabular rim.
Cartilage thickness 2½ years after surgery compared with preoperatively was unchanged indicating the osteoarthritis had not progressed during short-term followup after PAO.
PMCID: PMC2882008  PMID: 20232180
5.  The Biomechanical Case for Labral Débridement 
Labral repair is increasingly performed in conjunction with open and arthroscopic surgical procedures used to treat patients with mechanically related hip pain. The current rationale for labral repair is based on restoring the suction-seal function and clinical reports suggesting improved clinical outcome scores when acetabular rim trimming is accompanied by labral repair. However, it is unclear whether available scientific evidence supports routine labral repair.
The questions raised in this review were: (1) does labral repair restore normal histologic structure, tissue permeability, hip hydrodynamics, load transfer, and in vivo kinematics; and (2) does labral repair favorably alter the natural course of femoroacetabular impingement (FAI) treatment or age-related degeneration of the acetabular labrum?
An electronic literature search for the keywords acetabular labrum was performed. Three hundred fifty-five abstracts were reviewed and 52 selected for full-text review that described information concerning pertinent aspects of labral formation, development, degeneration, biomechanics, and clinical results of labral repair or resection.
Several clinical studies support labral repair when performed in conjunction with acetabular rim trimming. Little data support or refute the use of routine labral repair for all patients with symptomatic labral damage associated with FAI. It is not known whether or how labral repair affects the natural course of FAI.
Based on the current understanding of labral degenerative changes associated with mechanical hip abnormalities, the low biologic likelihood of restoring normal tissue characteristics, and mechanical data suggesting minimal consequence from small labral resections, routine labral repair over labral débridement is not supported.
PMCID: PMC3492648  PMID: 22744205
6.  Arthroscopic Labral Repair of the Hip, Using a Through-Labral Double-Stranded Single-Pass Suture Technique 
Arthroscopy Techniques  2014;3(5):e615-e619.
The normal labrum is crucial to the biomechanical function of the hip joint, not only increasing the surface area and depth of the acetabulum but also maintaining a suction seal to assist in normal synovial fluid flow from the peripheral to the central compartment. Simple loop suture repairs of the labrum may evert the labrum, thus losing the optimal seal, as well as causing abrasion of the articular cartilage. Vertical mattress suture and labral base fixation techniques aim to leave the free edge of the labrum intact and undisturbed, therefore improving the contact of the labrum to the femoral head and neck to improve the seal of the acetabulum. We aim to describe a double-stranded single-pass vertical mattress suture technique that may allow greater versatility to the surgeon in repairing thinner labrums while still achieving a free and continuous free edge.
PMCID: PMC4246392  PMID: 25473617
7.  The innervation of the human acetabular labrum and hip joint: an anatomic study 
The aim of the current study was to evaluate the innervation of the acetabular labrum in the various zones and to understand its potential role in nociception and proprioception in hips with labral pathology.
A total of twenty hip labrums were tagged and excised intraoperatively from patients undergoing a total hip replacement. After preparation, the specimens were cut to a thickness of 10 μm and divided into four quadrants (zones) using a clock face pattern. Neurosensory structure distribution was then evaluated using Hematoxylin and Eosin (H and E), and immunoreactivity to S-100.
All specimens had abundant free nerve endings (FNEs). These were seen predominantly superficially and on the chondral side of the labrum. In addition, predominantly three different types of nerve end organs (NEOs) were identified in all twenty specimens. FNEs and NEOs were more frequently seen in the antero-superior and postero-superior zones. Four specimens had abundant vascularity and disorganised architecture of FNEs in the deeper zones of the antero-superior quadrant suggestive of a healed tear. Myofibroblasts were present in abundance in all the labral specimens and were distributed uniformly throughout all labral zones and depth.
The current study shows that the human acetabular labrum has abundant FNEs and NEOs. These are more abundant in the antero-superior and postero-superior zones. The labrum, by virtue of its neural innervation, can potentially mediate pain as well as proprioception of the hip joint, and be involved in neurosecretion that can influence connective tissue repair.
PMCID: PMC3927620  PMID: 24529033
Labrum; Innervation; Femoro-acetabular impingement; Hip arthroscopy; Labral tear
8.  Finite Element Prediction of Cartilage Contact Stresses in Normal Human Hips 
Journal of Orthopaedic Research  2011;30(7):1133-1139.
Our objectives were to determine cartilage contact stress during walking, stair climbing and descending stairs in a well-defined group of normal volunteers and to assess variations in contact stress and area among subjects and across loading scenarios. Ten volunteers without history of hip pain or disease with normal lateral center-edge angle and acetabular index were selected. Computed tomography imaging with contrast was performed on one hip. Bone and cartilage surfaces were segmented from volumetric image data, and subject-specific finite element models were constructed and analyzed using a validated protocol. Acetabular contact stress and area were determined for seven activities. Peak stress ranged from 7.52±2.11 MPa for heel-strike during walking (233% BW) to 8.66±3.01 MPa for heel-strike during descending stairs (261% BW). Average contact area across all activities was 34% of the surface area of the acetabular cartilage. The distribution of contact stress was highly non-uniform, and more variability occurred among subjects for a given activity than among activities for a single subject. The magnitude and area of contact stress were consistent between activities, although inter-activity shifts in contact pattern were found as the direction of loading changed. Relatively small incongruencies between the femoral and acetabular cartilage had a large effect on the contact stresses. These effects tended to persist across all simulated activities. These results demonstrate the diversity and trends in cartilage contact stress in healthy hips during activities of daily living and provide a basis for future comparisons between normal and pathologic hips.
PMCID: PMC3348968  PMID: 22213112
Hip; Finite Element; Biomechanics; Cartilage Contact Stresses; Cartilage Pressure
9.  Arthroscopic Hip Labral Repair 
Arthroscopy Techniques  2013;2(2):e73-e76.
Labral tears in the hip may cause painful clicking or locking of the hip, reduced range of motion, and disruption to sports and daily activities. The acetabular labrum aids stabilization of the hip joint, particularly during hip motion. The fibrocartilaginous structure extends the acetabular rim and provides a suction seal around the femoroacetabular interface. Treatment options for labral tears include debridement, repair, and reconstruction. Repair of the labrum has been shown to have better results than debridement. Labral refixation is achieved with sutures anchored into the acetabular rim. The acetabular rim is trimmed either to correct pincer impingement or to provide a bleeding bed to improve healing. Labral repair has shown excellent short-term to midterm outcomes and allows patients to return to activities and sports. Arthroscopic rim trimming and labral refixation comprise an effective treatment for labral tears with an underlying diagnosis of femoroacetabular impingement and are supported by the peer-reviewed literature.
PMCID: PMC3716192  PMID: 23875153
10.  Anterior Hip Joint Force Increases with Hip Extension, Decreased Gluteal Force, or Decreased Iliopsoas Force 
Journal of biomechanics  2007;40(16):3725-3731.
Abnormal or excessive force on the anterior hip joint may cause anterior hip pain, subtle hip instability and a tear of the acetabular labrum. We propose that both the pattern of muscle force and hip joint position can affect the magnitude of anterior joint force and thus possibly lead to excessive force and injury. The purpose of this study was to determine the effect of hip joint position and of weakness of the gluteal and iliopsoas muscles on anterior hip joint force. We used a musculoskeletal model to estimate hip joint forces during simulated prone hip extension and supine hip flexion under 4 different muscle force conditions and across a range of hip extension and flexion positions. Weakness of specified muscles was simulated by decreasing the modeled maximum force value for the gluteal muscles during hip extension and the iliopsoas muscle during hip flexion. We found that decreased force contribution from the gluteal muscles during hip extension and the iliopsoas muscle during hip flexion resulted in an increase in the anterior hip joint force. The anterior hip joint force was greater when the hip was in extension than when the hip was in flexion. Further studies are warranted to determine if increased utilization of the gluteal muscles during hip extension and of the iliopsoas muscle during hip flexion, and avoidance of hip extension beyond neutral would be beneficial for people with anterior hip pain, subtle hip instability, or an anterior acetabular labral tear.
PMCID: PMC2580726  PMID: 17707385
acetabular labral tear; groin pain; hip instability; hip joint force; hip pain
11.  Hip Capsule Dimensions in Patients With Femoroacetabular Impingement: A Pilot Study 
Joint-preserving hip surgery, either arthroscopic or open, increasingly is used for the treatment of symptomatic femoroacetabular impingement (FAI). As a consequence of surgery, thickening of the joint capsule and intraarticular adhesions between the labrum and joint capsule and between the femoral neck and the joint capsule have been observed. These alterations are believed to cause persistent pain and reduced range of motion. Because the diagnosis is made with MR arthrography, knowledge of the normal capsular anatomy and thickness on MRI in patients is important. To date there is no such information available.
The purpose of this study was to establish thickness, length of the hip capsule, and the size of the perilabral recess in patients with FAI.
We reviewed the preoperative MR arthrography of 30 patients (15 men) with clinical symptoms of FAI. We measured capsular thickness and made observations on the perilabral recess.
The joint capsule was thickest (6 mm) anterosuperiorly between 1 and 2 o’clock. The average length from the femoral head-neck junction to the femoral insertion of the capsule ranged from 19 to 33 mm. A perilabral recess was present circumferentially, even across the acetabular notch, where the labrum is supported by the transverse acetabular ligament. The shortest recess occurred superiorly.
Knowledge of the capsular anatomy in patients with FAI before surgery is important to judge the postoperative changes and to plan potential further therapy including arthroscopic treatment of intraarticular adhesions.
PMCID: PMC3492636  PMID: 22810156
12.  Histological study of the fetal development of the human acetabulum and labrum: significance in congenital hip disease. 
Seventy-four acetabula from a total of 140 normal human fetuses, obtained from abortions and deaths in the prenatal period, were used. The fetuses ranged from 9.1 to 40 cm in crown-rump length and are believed to be between 12 weeks and term. Acetabula were decalcified embedded in paraffin or celloidin, sectioned, and stained using conventional histologic techniques. Sections from the superior one-quarter of the acetabulum were examined for the initial appearance and later spread of osseous tissue. Throughout the fetal period bone was present only in the floor of the acetabulum and did not extend into the socket walls. Ossification was detected initially more posteriorly in the socket floor, and at all ages, ossification was more prominent on the ischial side of the socket. Despite the lack of osseous tissue a well-formed hyaline cartilage socket was present. The fetal labrum was composed of fibrous tissue with the density of fibers increasing with age. Typical-appearing chondrocytes were detected at only the inner articular margin of the labrum. Contributing from one-fifth to one-half of the socket depth, the labrum may play a greater role in containing the femoral head at birth than it does in the mature joint. In seven acetabula, from joints that were neither subluxated nor dislocated, an area of areolar tissue with capillaries was detected at the hyaline cartilage-labrum junction. Such defects may weaken the labrum and contribute to neonatal hip instability.
PMCID: PMC2595965  PMID: 7324504
13.  A New Discrete Element Analysis Method for Predicting Hip Joint Contact Stresses 
Journal of biomechanics  2013;46(6):1121-1127.
Quantifying cartilage contact stress is paramount to understanding hip osteoarthritis. Discrete element analysis (DEA) is a computationally efficient method to estimate cartilage contact stresses. Previous applications of DEA have underestimated cartilage stresses and yielded unrealistic contact patterns because they assumed constant cartilage thickness and/or concentric joint geometry. The study objectives were to: 1) develop a DEA model of the hip joint with subject-specific bone and cartilage geometry, 2) validate the DEA model by comparing DEA predictions to those of a validated finite element analysis (FEA) model, and 3) verify both the DEA and FEA models with a linear-elastic boundary value problem. Springs representing cartilage in the DEA model were given lengths equivalent to the sum of acetabular and femoral cartilage thickness and joint space in the FEA model. Material properties and boundary/loading conditions were equivalent. Walking, descending, and ascending stairs were simulated. Solution times for DEA and FEA models were ~7 seconds and ~65 minutes, respectively. Irregular, complex contact patterns predicted by DEA were in excellent agreement with FEA. DEA contact areas were 7.5%, 9.7% and 3.7% less than FEA for walking, descending stairs, and ascending stairs, respectively. DEA models predicted higher peak contact stresses (9.8–13.6 MPa) and average contact stresses (3.0–3.7 MPa) than FEA (6.2–9.8 and 2.0–2.5 MPa, respectively). DEA overestimated stresses due to the absence of the Poisson’s effect and a direct contact interface between cartilage layers. Nevertheless, DEA predicted realistic contact patterns when subject-specific bone geometry and cartilage thickness were used. This DEA method may have application as an alternative to FEA for pre-operative planning of joint-preserving surgery such as acetabular reorientation during peri-acetabular osteotomy.
PMCID: PMC3623562  PMID: 23453394
Hip; cartilage; cartilage mechanics; contact stress; discrete element analysis; finite element analysis; computational modeling
14.  Interventions for Hip Pain in the Maturing Athlete 
Sports Health  2014;6(1):70-77.
Femoroacetabular impingement (FAI) alters hip mechanics, results in hip pain, and may lead to secondary osteoarthritis (OA) in the maturing athlete. Hip impingement can be caused by osseous abnormalities in the proximal femur or acetabulum. These impingement lesions may cause altered loads within the hip joint, which result in repetitive collision damage or sheer forces to the chondral surfaces and acetabular labrum. These anatomic lesions and resultant abnormal mechanics may lead to early osteoarthritic changes.
Evidence Acquisition:
Relevant articles from the years 1995 to 2013 were identified using MEDLINE, EMBASE, and the bibliographies of reviewed publications.
Level of Evidence:
Level 4.
Improvements in hip arthroscopy have allowed FAI to be addressed utilizing the arthroscope. Adequately resecting the underlying osseous abnormalities is essential to improving hip symptomatology and preventing further chondral damage. Additionally, preserving the labrum by repairing the damaged tissue and restoring the suction seal may theoretically help normalize hip mechanics and prevent further arthritic changes. The outcomes of joint-preserving treatment options may be varied in the maturing athlete due to the degree of underlying OA. Irreversible damage to the hip joint may have already occurred in patients with moderate to advanced OA. In the presence of preexisting arthritis, these patients may only experience fair or even poor results after hip arthroscopy, with early conversion to hip replacement. For patients with advanced hip arthritis, total hip arthroplasty remains a treatment option to reliably improve symptoms with good to excellent outcomes and return to low-impact activities.
Advances in the knowledge base and treatment techniques of intra-articular hip pain have allowed surgeons to address this complex clinical problem with promising outcomes. Traditionally, open surgical dislocations for hip preservation surgery have shown good long-term results. Improvements in hip arthroscopy have led to outcomes equivalent to open surgery while utilizing significantly less invasive techniques. However, outcomes may ultimately depend on the degree of underlying OA. When counseling the mature athlete with hip pain, an understanding of the underlying anatomy, degree of arthritis, and expectations will help guide the treating surgeon in offering appropriate treatment options.
PMCID: PMC3874222  PMID: 24427445
hip pain; joint preservation; hip arthroscopy; femoroacetabular impingement
15.  Inside Out: A Novel Labral Repair and Advancement Technique 
Arthroscopy Techniques  2014;3(2):e241-e244.
Labral tears are a significant cause of hip pain and are currently the most common indication for hip arthroscopy. Compared with labral debridement, labral repair has significantly better outcomes in terms of both daily activities and athletic pursuits in the setting of femoral acetabular impingement. The techniques described in the literature all use anchor placement on the capsular aspect of the acetabular rim, which can be difficult especially anteriorly, where the rim is very thin, and has the potential for significant complications. Anchor breakage, anchor slippage into the surrounding (capsular side) soft tissue, and penetration of the cartilage surface are among the most common complications. We describe an intra-articular anchor placement technique for labral repair from inside out. This technique, because of the location of the anchor and direction of suture pull, can assist in labral advancement in cases in which the native labrum fails to create a seal because of its location away from the femoral head.
PMCID: PMC4044508  PMID: 24904768
16.  Magnetic resonance arthrography for femoroacetabular impingement surgery: is it reliable? 
Magnetic resonance arthrography (MRA) is commonly used to demonstrate injury to the labrum and hyaline cartilage in patients with femoroacetabular impingement (FAI). The purpose of this study was to assess the diagnostic correlation between MRA and findings at arthroscopic and open surgery.
Materials and methods
MRA reports of 41 hips with symptomatic FAI were reviewed and compared with subsequent intraoperative findings (n = 21 surgical dislocations and n = 20 therapeutic hip arthroscopies). Each case was assessed for the presence of a cam deformity, a cartilage lesion of the femoral head, an os acetabuli, an injury to the labrum and injury to the acetabular cartilage. Results were collected prospectively in a cross-table and analysed retrospectively for sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV).
The sensitivity, specificity, PPV and NPV in the presence of reported cam-type deformity or an os acetabuli were 100 %. In the presence of cartilage lesions of the femoral head, the values were 46, 81, 55 and 73 %, respectively. For labral tears, the values were 91, 86, 97 and 67 %. In the presence of acetabular cartilage injuries, the values were 69, 88, 78 and 81 %, respectively.
MRA appears to be an efficacious imaging modality in the evaluation of labral tears, cam-type impingement lesions and os acetabuli of the hip. MRA is less efficacious in the diagnosis of cartilage abnormalities in the hip, both femoral and acetabular. Researchers should focus on further improvements in imaging techniques in order to give reliable preoperative information to the surgeon.
PMCID: PMC3751278  PMID: 23397418
Femoroacetabular impingement; ArthroMRI; Hip
17.  Acetabular Tilt Correlates with Acetabular Version and Coverage in Hip Dysplasia 
The rotational position of the acetabulum to the pelvis (acetabular tilt) may influence acetabular version and coverage of the femoral head. To date, the pathologic significance of acetabular tilt in hip dysplasia is unknown.
We determined whether acetabular tilt in hip dysplasia is different from that in normal hips and whether this correlates with acetabular version and coverage.
We measured the acetabular tilt angle on the lateral view of three-dimensional pelvic CT images of 40 patients (72 hips) with hip dysplasia. Forty normal hips from 40 patients were used as controls. The acetabular sector angle was measured as an index for acetabular coverage of the femoral head.
The mean acetabular tilt angle was increased in dysplastic hips compared with controls. In dysplastic hips, a posteriorly rotated acetabulum (increased acetabular tilt) was associated with increased acetabular anteversion and with decreased anterior and anterosuperior acetabular coverage. No correlation was found in controls. In dysplastic hips with a posterior acetabular deficiency, the acetabulum was rotated anteriorly (decreased acetabular tilt) compared with hips with anterior and lateral deficiencies.
We observed a correlation between the rotational position of the acetabulum in the pelvis with acetabular version and coverage in hip dysplasia. Our observations confirmed anterior rotation of the acetabular fragment during periacetabular osteotomies is an anatomically reasonable maneuver for hips with anterolateral acetabular deficiencies, while the maneuver can exacerbate posterior coverage and should be avoided in hips with a posterior acetabular deficiency.
Level of Evidence
Level IV, diagnostic study. See the Guidelines for Authors for a complete description of levels of evidence.
PMCID: PMC3441999  PMID: 22544668
18.  Is the Damage of Cartilage a Global or Localized Phenomenon in Hip Dysplasia, Measured by dGEMRIC? 
The mechanism of damage in osteoarthritis is believed to be multifactorial where mechanical and biological factors are important in its initiation and progression. Hip dysplasia is a classic model of increased mechanical loading on cartilage attributable to insufficient acetabular coverage that leads to osteoarthritis. If the damage is all attributable to direct mechanical damage then one initially would expect only local, not global changes.
We hypothesize that in hip dysplasia although the elevated cumulative contact stresses are localized, the damage to cartilage is biologically mediated, therefore, biochemical changes will be global.
Thirty-two patients with symptomatic hip dysplasia were scanned using a 1.5-T MRI scanner. We used a high-resolution three-dimensional dGEMRIC technique to characterize the distribution of cartilage damage in dysplastic hips. High-resolution isotropic acquisition was reformatted around the femoral neck axis and the dGEMRIC index was calculated separately for femoral and acetabular cartilages. Joint space widths also were evaluated in each reformatted slice. Each hip was characterized by the presence or absence of joint migration and by Tönnis grade.
The global dGEMRIC index correlated with the dGEMRIC indices of individual regions with the highest correlations occurring in the anterosuperior to posterosuperior regions. The corresponding correlations for joint space width were uniformly lower, suggesting that tissue loss is a more local phenomenon. Higher Tönnis grades and hips with joint migration were associated with lower dGEMRIC indices.
The dGEMRIC index shows a global decrease, whereas tissue loss is more localized. This suggests that hip osteoarthritis in acetabular dysplasia is a biologically mediated event that affects the entire joint.
PMCID: PMC3528925  PMID: 23079789
19.  Metal-on-Metal Total Hip Resurfacing Arthroplasty 
Executive Summary
The objective of this review was to assess the safety and effectiveness of metal on metal (MOM) hip resurfacing arthroplasty for young patients compared with that of total hip replacement (THR) in the same population.
Clinical Need
Total hip replacement has proved to be very effective for late middle-aged and elderly patients with severe degenerative diseases of the hips. As indications for THR began to include younger patients and those with a more active life style, the longevity of the implant became a concern. Evidence suggests that these patients experience relatively higher rates of early implant failure and the need for revision. The Swedish hip registry, for example, has demonstrated a survival rate in excess of 80% at 20 years for those aged over 65 years, whereas this figure was 33% by 16 years in those aged under 55 years.
Hip resurfacing arthroplasty is a bone-conserving alternative to THR that restores normal joint biomechanics and load transfer. The technique has been used around the world for more than 10 years, specifically in the United Kingdom and other European countries.
The Technology
Metal-on-metal hip resurfacing arthroplasty is an alternative procedure to conventional THR in younger patients. Hip resurfacing arthroplasty is less invasive than THR and addresses the problem of preserving femoral bone stock at the initial operation. This means that future hip revisions are possible with THR if the initial MOM arthroplasty becomes less effective with time in these younger patients. The procedure involves the removal and replacement of the surface of the femoral head with a hollow metal hemisphere, which fits into a metal acetabular cup.
Hip resurfacing arthroplasty is a technically more demanding procedure than is conventional THR. In hip resurfacing, the femoral head is retained, which makes it much more difficult to access the acetabular cup. However, hip resurfacing arthroplasty has several advantages over a conventional THR with a small (28 mm) ball. First, the large femoral head reduces the chance of dislocation, so that rates of dislocation are less than those with conventional THR. Second, the range of motion with hip resurfacing arthroplasty is higher than that achieved with conventional THR.
A variety of MOM hip resurfacing implants are used in clinical practice. Six MOM hip resurfacing implants have been issued licences in Canada.
Review Strategy
A search of electronic bibliographies (OVID Medline, Medline In-Process and Other Non-Indexed Citations, Embase, Cochrane CENTRAL and DSR, INAHTA) was undertaken to identify evidence published from Jan 1, 1997 to October 27, 2005. The search was limited to English-language articles and human studies. The literature search yielded 245 citations. Of these, 11 met inclusion criteria (9 for effectiveness, 2 for safety).
The result of the only reported randomized controlled trial on MOM hip resurfacing arthroplasty could not be included in this assessment, because it used a cemented acetabular component, whereas in the new generation of implants, a cementless acetabular component is used. After omitting this publication, only case series remained.
Summary of Findings
Health Outcomes
The Harris hip score and SF-12 are 2 measures commonly used to report health outcomes in MOM hip resurfacing arthroplasty studies. Other scales used are the Oxford hip score and the University of California Los Angeles hip score.
The case series showed that the mean revision rate of MOM hip resurfacing arthroplasty is 1.5% and the incidence of femoral neck fracture is 0.67%. Across all studies, 2 cases of osteonecrosis were reported. Four studies reported improvement in Harris hip scores. However, only 1 study reported a statistically significant improvement. Three studies reported improvement in SF-12 scores, of which 2 reported a significant improvement. One study reported significant improvement in UCLA hip score. Two studies reported postoperative Oxford hip scores, but no preoperative values were reported.
None of the reviewed studies reported procedure-related deaths. Four studies reported implant survival rates ranging from 94.4% to 99.7% for a follow-up period of 2.8 to 3.5 years. Three studies reported on the range of motion. One reported improvement in all motions including flexion, extension, abduction-adduction, and rotation, and another reported improvement in flexion. Yet another reported improvement in range of motion for flexion abduction-adduction and rotation arc. However, the author reported a decrease in the range of motion in the arc of flexion in patients with Brooker class III or IV heterotopic bone (all patients were men).
Safety of Metal-on-Metal Hip Resurfacing Arthroplasty
There is a concern about metal wear debris and its systemic distribution throughout the body. Detectable metal concentrations in the serum and urine of patients with metal hip implants have been described as early as the 1970s, and this issue is still controversial after 35 years.
Several studies have reported high concentration of cobalt and chromium in serum and/or urine of the patients with metal hip implants. Potential toxicological effects of the elevated metal ions have heightened concerns about safety of MOM bearings. This is of particular concern in young and active patients in whom life expectancy after implantation is long.
Since 1997, 15 studies, including 1 randomized clinical trial, have reported high levels of metal ions after THR with metal implants. Some of these studies have reported higher metal levels in patients with loose implants.
Adverse Biological Effects of Cobalt and Chromium
Because patients who receive a MOM hip arthroplasty are shown to be exposed to high concentrations of metallic ions, the Medical Advisory Secretariat searched the literature for reports of adverse biological effects of cobalt and chromium. Cobalt and chromium make up the major part of the metal articulations; therefore, they are a focus of concern.
Risk of Cancer
To date, only one study has examined the incidence of cancer after MOM and polyethylene on metal total hip arthroplasties. The results were compared to that of general population in Finland. The mean duration of follow-up for MOM arthroplasty was 15.7 years; for polyethylene arthroplasty, it was 12.5 years. The standardized incidence ratio for all cancers in the MOM group was 0.95 (95% CI, 0.79–1.13). In the polyethylene on metal group it was 0.76 (95% CI, 0.68–0.86). The combined standardized incidence ratio for lymphoma and leukemia in the patients who had MOM THR was 1.59 (95% CI, 0.82–2.77). It was 0.59 (95% CI, 0.29–1.05) for the patients who had polyethylene on metal THR. Patients with MOM THR had a significantly higher risk of leukemia. All patients who had leukemia were aged over than 60 years.
Cobalt Cardiotoxicity
Epidemiological Studies of Myocardiopathy of Beer Drinkers
An unusual type of myocardiopathy, characterized by pericardial effusion, elevated hemoglobin concentrations, and congestive heart failure, occurred as an epidemic affecting 48 habitual beer drinkers in Quebec City between 1965 and 1966. This epidemic was directly related the consumption of a popular beer containing cobalt sulfate. The epidemic appeared 1 month after cobalt sulfate was added to the specific brewery, and no further cases were seen a month after this specific chemical was no longer used in making this beer. A beer of the same name is made in Montreal, and the only difference at that time was that the Quebec brand of beer contained about 10 times more cobalt sulphate. Cobalt has been added to some Canadian beers since 1965 to improve the stability of the foam but it has been added in larger breweries only to draught beer. However, in small breweries, such as those in Quebec City, separate batches were not brewed for bottle and draught beer; therefore, cobalt was added to all of the beer processed in this brewery.
In March 1966, a committee was appointed under the chairmanship of the Deputy Minister of Health for Quebec that included members of the department of forensic medicine of Quebec’s Ministry of Justice, epidemiologists, members of Food and Drug Directorate of Ottawa, toxicologists, biomedical researchers, pathologists, and members of provincial police. Epidemiological studies were carried out by the Provincial Ministry of Health and the Quebec City Health Department.
The association between the development of myocardiopathy and the consumption of the particular brand of beer was proven. The mortality rate of this epidemic was 46.1% and those who survived were desperately ill, and recovered only after a struggle for their lives.
Similar cases were seen in Omaha (Nebraska). The epidemic started after a cobalt additive was used in 1 of the beers marketed in Nebraska. Sixty-four patients with the clinical diagnosis of alcoholic myocardiopathy were seen during an 18-month period (1964–1965). Thirty of these patients died. The first patient became ill within 1 month after cobalt was added to the beer, and the last patient was seen within 1 month of withdrawal of cobalt.
A similar epidemic occurred in Minneapolis, Minnesota. Between 1964 and 1967, 42 patients with acute heart failure were admitted to a hospital in Minneapolis, Minnesota. Twenty of these patients were drinking 6 to 30 bottles per day of a particular brand of beer exclusively. The other 14 patients also drank the same brand of beer, but not exclusively. The mortality rate from the acute illness was 18%, but late deaths accounted for a total mortality rate of 43%. Examination of the tissue from these patients revealed markedly abnormal changes in myofibrils (heart muscles), mitochondria, and sarcoplasmic reticulum.
In Belgium, a similar epidemic was reported in 1966, in which, cobalt was used in some Belgian beers. There was a difference in mortality between the Canadian or American epidemic and this series. Only 1 of 24 patients died, 1.5 years after the diagnosis. In March 1965, at an international meeting in Brussels, a new heart disease in chronic beer drinkers was described. This disease consists of massive pericardial effusion, low cardiac output, raised venous pressure, and polycythemia in some cases. This syndrome was thought to be different from the 2 other forms of alcoholic heart disease (beriberi and a form characterized by myocardial fibrosis).
The mystery of the above epidemics as stated by investigators is that the amount of cobalt added to the beer was below the therapeutic doses used for anemia. For example, 24 pints of Quebec brand of beer in Quebec would contain 8 mg of cobalt chloride, whereas an intake of 50 to 100 mg of cobalt as an antianemic agent has been well tolerated. Thus, greater cobalt intake alone does not explain the occurrence of myocardiopathy. It seems that there are individual differences in cobalt toxicity. Other features, like subclinical alcoholic heart disease, deficient diet, and electrolyte imbalance could have been precipitating factors that made these patients susceptible to cobalt’s toxic effects.
In the Omaha epidemic, 60% of the patients had weight loss, anorexia, and occasional vomiting and diarrhea 2 to 6 months before the onset of cardiac symptoms. In the Quebec epidemic, patients lost their appetite 3 to 6 months before the diagnosis of myocardiopathy and developed nausea in the weeks before hospital admission. In the Belgium epidemic, anorexia was one of the most predominant symptoms at the time of diagnosis, and the quality and quantity of food intake was poor. Alcohol has been shown to increase the uptake of intracoronary injected cobalt by 47%. When cobalt enters the cells, calcium exits; this shifts the cobalt to calcium ratio. The increased uptake of cobalt in alcoholic patients may explain the high incidence of cardiomyopathies in beer drinkers’ epidemics.
As all of the above suggest, it may be that prior chronic exposure to alcohol and/or a nutritionally deficient diet may have a marked synergistic effect with the cardiotoxicity of cobalt.
MOM hip resurfacing arthroplasty has been shown to be an effective arthroplasty procedure as tested in younger patients.
However, evidence for effectiveness is based only on 7 case series with short duration of follow-up (2.8–3.5 years). There are no RCTs or other well-controlled studies that compare MOM hip resurfacing with THR.
Revision rates reported in the MOM studies using implants currently licensed in Canada (hybrid systems, uncemented acetabular, and cemented femoral) range from 0.3% to 3.6% for a mean follow-up ranging from 2.8 to 3.5 years.
Fracture of femoral neck is not very common; it occurs in 0.4% to 2.2% of cases (as observed in a short follow-up period).
All the studies that measured health outcomes have reported improvement in Harris Hip and SF-12 scores; 1 study reported significant reduction in pain and improvement in function, and 2 studies reported significant improvement in SF-12 scores. One study reported significant improvement in UCLA Hip scores.
Concerns remain on the potential adverse effects of metal ions. Longer-term follow-up data will help to resolve the inconsistency of findings on adverse effects, including toxicity and carcinogenicity.
Ontario-Based Economic Analysis
The device cost for MOM ranges from $4,300 to $6,000 (Cdn). Traditional hip replacement devices cost about $2,000 (Cdn). Using Ontario Case Costing Initiative data, the total estimated costs for hip resurfacing surgery including physician fees, device fees, follow-up consultation, and postsurgery rehabilitation is about $15,000 (Cdn).
Cost of Total Hip Replacement Surgery in Ontario
MOM hip arthroplasty is generally recommended for patients aged under 55 years because its bone-conserving advantage enables patients to “buy time” and hence helps THRs to last over the lifetime of the patient. In 2004/2005, 15.9% of patients who received THRs were aged 55 years and younger. It is estimated that there are from 600 to 1,000 annual MOM hip arthroplasty surgeries in Canada with an estimated 100 to 150 surgeries in Ontario. Given the increased public awareness of this device, it is forecasted that demand for MOM hip arthroplasty will steadily increase with a conservative estimate of demand rising to 1,400 cases by 2010 (Figure 10). The net budget impact over a 5-year period could be $500,000 to $4.7 million, mainly because of the increasing cost of the device.
Projected Number of Metal-on-Metal Hip Arthroplasty Surgeries in Ontario: to 2010
PMCID: PMC3379532  PMID: 23074495
20.  Rehabilitation after Arthroscopy of an Acetabular Labral Tear 
Over the past few years, arthroscopy of the hip joint is becoming more common as a technique in both the diagnosis and treatment of hip pain. A frequent cause of hip and groin pain is a tear of the acetabular labrum. Patients with labral tears complain of pain in the groin region and pain with clicking in the hip without a history of pain prior to the original onset. Once a patient presents with signs and symptoms of hip pain that are greater than four weeks in conjunction with indicative findings of a labral tear by way of MRI, he or she may be considered a good candidate for arthroscopy of the hip joint. Little evidence exists in the current literature on rehabilitative procedures performed after arthroscopy of the acetabular labrum. The purpose of this clinical commentary is to suggest a rehabilitation protocol after acetebular labral debridement or repair.
PMCID: PMC2953303  PMID: 21509143
21.  Finite Element Analysis Examining the Effects of Cam FAI on Hip Joint Mechanical Loading Using Subject-Specific Geometries During Standing and Maximum Squat 
HSS Journal  2012;8(3):206-212.
Cam femoroacetabular impingement (FAI) can impose elevated mechanical loading in the hip, potentially leading to an eventual mechanical failure of the joint. Since in vivo data on the pathomechanisms of FAI are limited, it is still unclear how this deformity leads to osteoarthritis.
The purpose of this study was to examine the effects of cam FAI on hip joint mechanical loading using finite element analysis, by incorporating subject-specific geometries, kinematics, and kinetics.
The research objectives were to address and determine: (1) if hips with cam FAI demonstrate higher maximum shear stresses, in comparison with control hips; (2) the magnitude of the peak maximum shear stresses; and (3) the locations of the peak maximum shear stresses.
Using finite element analysis, two patient models were control-matched and simulated during quasi-static positions from standing to squatting. Intersegmental hip forces, from a previous study, were applied to the subject-specific hip geometries, segmented from CT data, to evaluate the maximum shear stresses on the acetabular cartilage and underlying bone.
Peak maximum shear stresses were found at the anterosuperior region of the underlying bone during squatting. The peaks at the anterosuperior acetabulum were substantially higher for the patients (15.2 ± 1.8 MPa) in comparison with the controls (4.5 ± 0.1 MPa).
Peaks were not situated on the cartilage, but instead located on the underlying bone. The results correspond with the locations of initial cartilage degradation observed during surgical treatment and from MRI.
Clinical Relevance:
These findings support the pathomechanism of cam FAI. Changes may originate from the underlying subchondral bone properties rather than direct shear stresses to the articular cartilage.
PMCID: PMC3470675  PMID: 24082862
hip; impingement; cam femoroacetabular impingement; finite element analysis; subject-specific; finite element model
22.  Biomechanical Factors in Planning of Periacetabular Osteotomy 
Objective: This study addresses the effects of cartilage thickness distribution and compressive properties in the context of optimal alignment planning for periacetabular osteotomy (PAO).
Background: The Biomechanical Guidance System (BGS) is a computer-assisted surgical suite assisting surgeon’s in determining the most beneficial new alignment of a patient’s acetabulum. The BGS uses biomechanical analysis of the hip to find this optimal alignment. Articular cartilage is an essential component of this analysis and its physical properties can affect contact pressure outcomes.
Methods: Patient-specific hip joint models created from CT scans of a cohort of 29 dysplastic subjects were tested with four different cartilage thickness profiles (one uniform and three non-uniform) and two sets of compressive characteristics. For each combination of thickness distribution and compressive properties, the optimal alignment of the acetabulum was found; the resultant geometric and biomechanical characterization of the hip were compared among the optimal alignments.
Results: There was an average decrease of 49.2 ± 22.27% in peak contact pressure from the preoperative to the optimal alignment over all patients. We observed an average increase of 19 ± 7.7° in center-edge angle and an average decrease of 19.5 ± 8.4° in acetabular index angle from the preoperative case to the optimized plan. The optimal alignment increased the lateral coverage of the femoral head and decreased the obliqueness of the acetabular roof in all patients. These anatomical observations were independent of the choice for either cartilage thickness profile, or compressive properties.
Conclusion: While patient-specific acetabular morphology is essential for surgeons in planning PAO, the predicted optimal alignment of the acetabulum was not significantly sensitive to the choice of cartilage thickness distribution over the acetabulum. However, in all groups the biomechanically predicted optimal alignment resulted in decreased joint contact pressure and improved acetabular coverage.
PMCID: PMC4126379  PMID: 25152876
periacetabular osteotomy; preoperative planning; articular cartilage thickness; cartilage compressibility; biomechanical analysis
23.  MRI of Hip Cartilage: Joint Morphology, Structure, and Composition 
Accurate, reproducible, and noninvasive assessment of hip cartilage is clinically relevant and provides a means by which to assess the suitability of candidates for arthroscopic or open surgical procedures and the response to such interventions over time. Given the relatively thin cartilage of the hip and the complex spherical anatomy, however, accurately assessing the cartilage poses a challenge for traditional MRI techniques.
We assessed the current status of imaging articular cartilage of the hip through a comprehensive review of recent literature.
We performed a literature review using PubMed. Topics included quantitative MRI, imaging of the hip cartilage and labrum, femoroacetabular impingement syndrome, and osteoarthritis of the hip.
Where Are We Now?
With the use of high in-plane and through-plane resolution, reproducible assessment of hip cartilage and labrum is clinically feasible. More recent quantitative MR techniques also allow for noninvasive assessment of collagen orientation and proteoglycan content in articular cartilage, thus providing insight into early matrix degeneration. These techniques can be applied to cohorts at risk for osteoarthritis, helping to predict cartilage degeneration before symptoms progress and osteoarthritic changes are visible on radiographs.
Where Do We Need to Go?
Prospective longitudinal data registries are necessary for developing predictive models of osteoarthritis and subsequent joint failure to assess the results of surgical intervention and predict the timing of arthroplasty.
How Do We Get There?
By establishing more hip cartilage registries, a correlation can be made between subjective measures and morphologic MRI to assess the cartilage, labrum, bone, and synovial lining of the hip.
PMCID: PMC3492599  PMID: 22723242
24.  Hip Damage Occurs at the Zone of Femoroacetabular Impingement 
Although current concepts of anterior femoroacetabular impingement predict damage in the labrum and the cartilage, the actual joint damage has not been verified by computer simulation. We retrospectively compared the intraoperative locations of labral and cartilage damage of 40 hips during surgical dislocation for cam or pincer type femoroacetabular impingement (Group I) with the locations of femoroacetabular impingement in 15 additional hips using computer simulation (Group II). We found no difference between the mean locations of the chondrolabral damage of Group I and the computed impingement zone of Group II. The standard deviation was larger for measures of articular damage from Group I in comparison to the computed values of Group II. The most severe hip damage occurred at the zone of highest probability of femoroacetabular impact, typically in the anterosuperior quadrant of the acetabulum for both cam and pincer type femoroacetabular impingements. However, the extent of joint damage along the acetabular rim was larger intraoperatively than that observed on the images of the 3-D joint simulations. We concluded femoroacetabular impingement mechanism contributes to early osteoarthritis including labral lesions.
Level of Evidence: Level II, diagnostic study. See the Guidelines for Authors for a complete description of levels of evidence.
PMCID: PMC2505146  PMID: 18196406
25.  Endoscopic Shelf Acetabuloplasty Combined With Labral Repair, Cam Osteochondroplasty, and Capsular Plication for Treating Developmental Hip Dysplasia 
Arthroscopy Techniques  2014;3(1):e185-e191.
In addition to the underlying shallow acetabular deformity, a patient with hip dysplasia has a greater risk of development of a labral tear, a cam lesion, and capsular laxity. This combination of abnormalities exacerbates joint instability, ultimately leading to osteoarthritis. Unsurprisingly, only repairing the acetabular labrum remains controversial, and the outcome is unpredictable. In this technical note, with video, we demonstrate an entirely endoscopic approach for simultaneously repairing the most common mechanical abnormalities found in moderate hip dysplasia: labral repair, cam osteochondroplasty, capsular plication, and shelf acetabuloplasty using an autologous iliac bone graft.
PMCID: PMC3986493  PMID: 24749043

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