Highly cross-linked polyethylene (HXLPE) is the most commonly used bearing surface in total hip arthroplasty (THA) because of its superior wear properties, but long-term results in young patients are limited. We report on the clinical outcome, radiographic wear patterns and survivorship of 72 patients ≤50 years old who had a 28-millimeter cobalt-chromium femoral head on HXLPE acetabular liner. Mean and median true linear wear rates at average ten-year follow-up were 0.0104 and 0.016 mm per year +/− 0.07 mm. Mean and median two-dimensional volumetric wear rates were 12.79 mm3 and 5.834 mm3 per year +/− 26.1mm3 as determined by Martell analysis. As a result of the minimal wear profile, there was no evidence of radiographic osteolysis and no wear-related revisions.
This study aimed at identifying preoperative predictors of patient-reported outcomes after total knee arthroplasty (TKA) and at investigating their association with the outcomes over time.
We used data from 2080 patients from the Knee Arthroplasty Trial who received primary TKA in the United Kingdom between July 1999 and January 2003. The primary outcome measure was the Oxford knee score (OKS) collected annually over 10 years after TKA. Preoperative predictors included a range of patient characteristics and clinical conditions. Mixed-effects linear regression model analysis of repeated measurements was used to identify predictors of overall OKS, and pain and function subscale scores over 10 years, separately.
Worse preoperative OKS, worse mental well-being, body mass index greater than 35 kg/m2, living in the most deprived areas, higher American Society of Anesthesiologists grade, presence of comorbidities, and history of previous knee surgery were associated with worse overall OKS over 10 years after surgery. The same predictors were identified for pain and function subscale scores, and for both long-term (10 years) and short-to-medium-term outcomes (1 and 5 years). However, fitted models explained more variations in function and shorter-term outcomes than in pain and longer-term outcomes, respectively.
The same predictors were identified for pain and functional outcomes over both short-to-medium term and long term after TKA. Within the factors identified, functional and shorter-term outcomes were more predictable than pain and longer-term outcomes, respectively. Regardless of their preoperative characteristics, on average, patients achieved substantial improvement in pain over time, although improvement for function was less prominent.
epidemiology; osteoarthritis; knee arthroplasty; patient-reported outcome; Oxford knee score
“ Off-label use” refers to medical device utilization for purposes or subpopulations other than those approved by the United States Food and Drug Administration. The primary goal of this study was to determine the current epidemiology of off-label total hip and knee arthroplasty (THA and TKA, respectively) in the United States and to project further off-label use through 2040. Over the past decade, the prevalence of off-label THA and TKA was 30.4% and 37.0%, respectively, growing ~70% from 2000 2010. By 2040, the majority of THA (86.1%) and TKA (91.5%) could be off-label. The high prevalence of off-label arthroplasty and the dramatically shifting patient profile illustrated by these results highlight the need for continued medical device surveillance among on-and off label patients.
The purpose of this study was to evaluate changes in movement patterns during a sit-to-stand (STS) task before and after total hip arthroplasty (THA), and to compare biomechanical outcomes after THA to a control group. Forty-five subjects who underwent THA and twenty-three healthy control subjects participated in three-dimensional motion analysis. Pre-operatively, subjects exhibited inter-limb movement asymmetries with lower vertical ground reaction force (VGRF) and smaller moments on the operated limb. Although there were significant improvements in movement symmetry 3 months after THA, patients continued to demonstrate lower VGRF and smaller moments on the operated limb compared to non-operated and to control limbs. Future studies should identify the contributions of physical impairments and the influence of surgical approach on STS biomechanics.
sit to stand; lateral trunk angle; biomechanics; total hip arthroplasty; joint moment
This review of the Nationwide Inpatient Sample (1998-2011) examined trends in solid organ transplant patients who received a total knee arthroplasty (TKA) to determine whether length of stay (LOS), cost, and perioperative complications differed from non-transplant peers. Primary TKA patients (n=5,870,421) were categorized as: (1) those with a history of solid organ transplant (n=6,104) and (2) those without (n=5,864,317). Propensity matching was used to estimate adjusted effects of solid organ transplant history on perioperative outcomes. The percentage of TKA patients with a transplant history grew during the study period from 0.069% to 0.103%. Adjusted outcomes showed patients with a transplant had a 0.44 day longer LOS, $962 higher cost of admission, and were 1.43 times more likely to suffer any complication (p=0.0002).
total knee arthroplasty; solid organ transplant; complication; length of stay; Nationwide Inpatient Sample
Contemporary total knee designs incorporating highly porous metallic surfaces have demonstrated promising clinical outcomes. However, stiffness differences between modular and monoblock porous tantalum tibial trays may affect bone ingrowth. This study investigated effect of implant design, spatial location and clinical factors on bone ingrowth in retrieved porous tantalum tibial trays. Three modular and twenty-one monoblock tibial trays were evaluated for bone ingrowth. Nonparametric statistical tests were used to investigate differences in bone ingrowth measurements by implant design, spatial location on the tray, substrate depth and clinical factors. Modular trays (5.3±3.2%) exhibited higher bone ingrowth than monoblock trays (1.6±1.9%, p=0.032). Bone ingrowth in both designs was highest in the initial 500 μm from the surface. Implantation time was positively correlated with bone ingrowth for monoblock trays.
The hypothesis of this study was that the rotational orientation of femoral head damage would greatly affect the volumetric wear rate of the opposing polyethylene (PE) liner. Damage on twenty retrieved cobalt-chromium femoral heads was simulated in a validated damage-feature-based finite element model. For each individual retrieval, the anatomic orientation of the femoral head about the femoral neck axis was systematically varied, in 30° increments. The PE wear rate differential between the maximum-versus minimum-wear orientations was often sizable, as high as 7-fold. Knowing the correct femoral head anatomic orientation is therefore important when analyzing the effects of femoral head damage on PE liner wear. Surgeons retrieving modular femoral heads should routinely mark the anatomic orientation of those components.
Damage; femoral head; finite element analysis; retrieval analysis; total hip arthroplasty; wear
Knee forces are highly relevant to performance after total knee arthroplasty especially during high flexion activities such as squatting. We constructed subject-specific models of two patients implanted with instrumented knee prosthesis that measured knee forces in vivo. In vivo peak forces ranged from 2.2 to 2.3 times bodyweight but peaked at different flexion angles based on the type of squatting activity. Our model predicted tibiofemoral contact force with reasonable accuracy in both subjects. This model can be a very useful tool to predict the effect of surgical techniques and component alignment on contact forces. In addition, this model could be used for implant design development, to enhance knee function, to predict forces generated during other activities, and for predicting clinical outcomes.
Total knee arthroplasty; squatting; computer model; knee contact force; patient-specific
The aims of this study were to assess damage on the surface of retrieved oxidized zirconium metal (OxZr) femoral heads, to measure surface roughness of scratches, and to evaluate the extent of surface effacement using scanning electron microscopy (SEM). Ceramic zirconia-toughened alumina (ZTA) heads were analyzed for comparison. OxZr femoral heads explanted for recurrent dislocation had the most severe damage (p<0.001). The median surface roughness of damaged OxZr femoral heads was 1.49μm, compared to 0.084μm for damaged ZTA heads and 0.052μm for undamaged OxZr (p<0.001). This may be of clinical concern because increased surface roughness has the potential to increase the wear of polyethylene liners articulating against these OxZr heads in THA.
The purpose of our study is to investigate the impact of incremental perioperative practice changes and the introduction of rapid recovery protocols on hospital LOS and readmission rates associated with primary THAs. 1,751 cases were assigned to one of four protocol cohorts across 13 years: traditional, enhanced pain management, early mobility, and rapid recovery (RR). LOS significantly decreased by 52% between the traditional and RR pathways (IRR=0.48; 95% CI 0.44, 0.53; p<0.0001) and differed significantly between all sequential eras (p<0.001) without an overall increase in thirty-day readmission rates (p=0.13). The odds of readmission for THAs performed under the RR pathway are almost one-third of the traditional era (OR=0.36; 95% CI 0.14, 0.93; p=0.04). Accelerated clinical care protocols should be considered for patients undergoing primary THA.
Pelvic tilt (PT) affects the functional anteversion and inclination of acetabular components in total hip arthroplasty (THA). One-hundred and thirty-eight consecutive patients who underwent unilateral primary THA were reviewed. Most cases had some degree of pre-operative PT, with 17% having greater than 10° of PT on standing pre-operative radiographs. There was no significant change in PT following THA. A computer model of a hemispheric acetabular component implanted in a range of anatomic positions in a pelvis with varying PT was created to determine the effects of PT on functional anteversion and inclination. Based on the study results, tilt-adjustment of the acetabular component position based on standing pre-operative imaging will likely improve functional component position in most patients undergoing THA.
Preoperative planning for patient-specific guides (PSGs) in total knee arthroplasty (TKA) requires identification of anatomic landmarks on three-dimensional imaging studies. The aim of this study was to assess the accuracy and precision with which landmarks commonly used to determine rotational alignment in TKA can be identified on magnetic resonance imaging (MRI). Two orthopaedic surgeons and two musculoskeletal radiologists independently reviewed a sequential series of 114 MRIs of arthritic knees. The magnitude of interobserver variability was high, suggesting an inherent risk of inconsistency when these landmarks are used in PSG fabrication. Additionally, there was a high degree of physiologic variation among patients, indicating that assuming standard relationships among anatomic landmarks when placing TKA components may lead to rotational malalignment relative to each patient's native anatomy.
Patient-specific TKA; rotational alignment
The purpose of this study was to determine the percentage of time that patients are subtherapeutic, therapeutic, and supratherapeutic based on the recommended INR for therapeutic efficacy when prescribed warfarin for chemical thromboprophylaxis following a hip or knee arthroplasty procedure. One hundred eighty-four patients receiving warfarin for 4 weeks postoperatively, dosed using a web-application accounting for patient demographics, INR levels, and concomitant medication use, were included for analysis. On average, patients with a target INR range between 1.7-2.7 were therapeutic for only 54.4% of the time (32.5% subtherapeutic, 13.0 supratherapeutic) while patients with a target INR range between 2.0 and 3.0 were therapeutic for only 45.9% of the time (39.2% subtherapeutic, 14.8% supratherapeutic) of their warfarin regimen. This study confirms that patients receiving warfarin for chemical thromboprophylaxis are within their targeted INR range for only a limited period of time during their postoperative course.
total knee arthroplasty; warfarin; coumadin; thromboprophylaxis
Recent studies suggest the ‘Lewinnek safe zone’ for acetabular component position is outdated. We used a large prospective institutional registry to determine if there is a ‘safe zone’ exists for acetabular component position within which the risk of hip dislocation is low and if other patient and implant factors affect the risk of hip dislocation. Patients who reported a dislocation event within six months after hip replacement surgery were identified, and acetabular component position was measured with anteroposterior radiographs. The frequency of dislocation was 2.1% (147 of 7040 patients). No significant difference was found in the number of dislocated hips among the zones. Dislocators <50 years old were less active preoperatively than nondislocators (p=0.006). Acetabular component position alone is not protective against instability.
Perioperative blood loss leading to blood transfusion continues to be an issue for total knee arthroplasty (TKA) patients. The US Nationwide Inpatient Sample (NIS) was used to determine annual trends in allogenic blood transfusion rates, and effects of transfusion on in-hospital mortality, length of stay (LOS), costs, discharge disposition, and complications of primary TKA patients. TKA patients between 2000 and 2009 were included (n=4,544,999) and categorized as: (1) those who received a transfusion of allogenic blood, and (2) those who did not. Transfusion rates increased from 7.7% to 12.2%. For both transfused and not transfused groups, mortality rates and mean LOS declined, while total costs increased. Transfused patients were associated with adjusted odds ratios of in-hospital mortality (AOR 1.16; p = 0.184), 0.71 ± 0.01 days longer LOS (p < 0.0001), and incurred ($1,777 ± 36; p < 0.0001) higher total costs per admission.
The purpose of this study was to characterize the prevalence of taper damage in modular TKA components. 198 modular components were revised after 3.9±4.2y (range: 0.0–17.5y). Modular components were evaluated for fretting corrosion using a semi-quantitative 4-point scoring system. Flexural rigidity, stem diameter, alloy coupling, patient weight, age and implantation time were assessed as predictors of fretting corrosion damage. Mild-to-severe fretting corrosion (score≥2) was observed in 94/101 of the tapers on the modular femoral components and 90/97 of the modular tibial components. Mixed alloy pairs (p=0.03), taper design (p<0.001), and component type (p=0.02) were associated with taper corrosion. The results from this study supported the hypothesis that there is taper corrosion in TKA. However the clinical implications of fretting and corrosion in TKA remain unclear.
TKA; Corrosion; Modular
Aseptic loosening of Total Knee Arthroplasty (TKA) components is the foremost cause of implant failure in the long term. While tibial component loosening is of primary concern, femoral loosening may become a clinical problem due to younger, more active patients seeking TKA, and also high-flexion designs. In this study, we analyzed the fixation for 19 non-revised, postmortem retrieved, femoral components of TKA with time in service ranging from 1–22 years. We found that average total contact fraction for cemented components was 9.5% and had a power law response with years in service. The average initial interdigitation depth was 0.7mm, and the average current interdigitation depth was 0.13mm. Loss of interdigitation was 81%. Over all, minimal fixation seems necessary for long term success of TKA.
Total Knee Arthroplasty; fixation; aseptic loosening; cementation; interdigitation depth
Data regarding the posterior slope of the tibia (PTS) is limited and sometimes conflicting. The purpose of this study was to determine the native posterior tibial slope in patients undergoing a medial or lateral UKA. A retrospective review was performed on 2,395 CT scans in patients indicated for UKA, and the PTS of the osteoarthritic compartment was measured relative to a plane set perpendicular to the sagittal, tibial mechanical axis. The mean pre-operative PTS in patients undergoing medial UKA was 6.8° ± 3.3°, with 34.3% between 4° to 7°. The mean pre-operative PTS in patients undergoing lateral UKA was 8.0° ± 3.3°, with 27.5% between 4° to 7°. If attempting to recreate a patient's pre-operative tibial slope, a routine target of 5° to 7° will produce a posterior slope less than the patient's native anatomy in 47% of patients undergoing UKA. This is the first, large CT-based review of posterior slope variation of the proximal tibia in patients undergoing UKA.
unicondylar; knee; arthroplasty; posterior slope
Range of motion (ROM) is an important component of the assessment of total knee replacement (TKR) outcome. We compared patient-reported versus clinically observed ROM in a prospective cohort. Clinically observed ROM was measured using a goniometer by a trained research assistant. Self-reported ROM was estimated using a set of lateral knee photographs depicting varying levels of flexion and extension. All measures were taken pre-operatively, three, and six months postoperatively. We found statistically significant associations between self-reported ROM and clinically observed ROM for flexion and extension (all P<0.001). We dichotomized flexion at 90 degrees and found that self-report had a specificity of 94% and sensitivity of 65%. We conclude that patient-reported ROM may be a useful outcome measure for TKR.
total knee replacement; self-reported outcomes; range of motion; knee osteoarthritis; rehabilitation
Total knee arthroplasty has provided dramatic improvements in function and pain for the majority of patients with knee arthritis, yet a significant proportion of patients remain dissatisfied with their results. We performed a prospective analysis of 215 patients undergoing TKA who underwent a comprehensive array of evaluations to discover whether any preoperative assessment could predict high pain scores and functional limitations postoperatively. Patients with severe pain with a simple knee range-of-motion test prior to TKA had a 10x higher likelihood of moderate to severe pain at 6 months. A simple test of pain intensity with active flexion and extension preoperatively was a significant predictor of postoperative pain at 6 months after surgery. Strategies to address this particular patient group may improve satisfaction rates of TKA.
Administrative data are commonly used to evaluate total joint arthroplasty, but analyses have historically been limited by the inability to capture which conditions were present-on-admission (POA). In 2007 Medicare began allowing hospitals to submit POA information. We used Medicare Part A data from 2008-2009 to examine POA coding for three common complications (pulmonary embolism [PE], hemorrhage/hematoma, and infection) for primary and revision total knee arthroplasty (TKA). POA information was complete for 60%-75% of complications. There was no evidence that higher TKA volume hospitals or major teaching hospitals were more likely to accurately code POA data. The percentage of complications coded as POA ranged from 6.4% (PE during index admission for primary TKA) to 68.8% (infection during index admission for revision TKA). Early experience suggests that POA coding can significantly enhance the value of Medicare data for evaluating TKA outcomes.
The purpose of this study was to use 3-dimensional, weight-bearing images corrected for rotation to establish normative data of limb alignment and joint line orientation in asymptomatic, adult knees. One hundred adults (200 lower extremities) were recruited to receive weight-bearing, simultaneous biplanar imaging of both lower extremities. Multiple radiographic parameters were measured from 3D images, corrected for limb rotation. 70.0% of knees were in neutral, 19.5% in varus, and 10.5% in valgus overall alignment. Only 31 % of knees possessed both a neutral mechanical axis and the absence of joint line obliquity. There was substantial agreement between the 2D and 3D images for overall mechanical alignment (κ=0.77), but only a moderate agreement for joint line obliquity (κ=0.58). A substantial portion of asymptomatic adults possess either a varus or valgus mechanical alignment and joint line obliquity,
This study investigated the hypothesis that wear particle-induced oxidative stress initiates osteolysis after total hip replacement (THR). Patient radiographs were scored for osteolysis and periprosthetic tissues were immunostained and imaged to quantify polyethylene wear, inflammation, and five osteoinflammatory and oxidative stress-responsive factors. These included high mobility group protein-B1 (HMGB1), cyclooxygenase-2 (COX2), inducible nitric oxide synthase (iNOS), 4-hydroxynonenal (4-HNE), and nitrotyrosine (NT). The results show wear debris correlated with inflammation, 4-HNE, NT and HMGB1, whereas inflammation only correlated with NT and HMGB1. Similar to wear debris and inflammation, osteolysis correlated with HMGB1. Additionally, osteolysis correlated with COX2 and 4-HNE, but not iNOS or NT. Understanding the involvement of oxidative stress in wear-induced osteolysis will help identify diagnostic biomarkers and therapeutic targets to prevent osteolysis after THR.
osteolysis; high mobility group protein-B1 (HMGB1); cyclooxygenase-2 (COX2); inducible nitric oxide synthase (iNOS); 4-hydroxynonenal (4-HNE); nitrotyrosine (NT)