Patient-reported outcomes (PROs) are an important endpoint in orthopedics providing comprehensive information about patients' perspectives on treatment outcome. Computer-adaptive test (CAT) measures are an advanced method for assessing PROs using item sets that are tailored to the individual patient. This provides increased measurement precision and reduces the number of items. We developed a CAT version of the Forgotten Joint Score (FJS), a measure of joint awareness in everyday life. CAT development was based on FJS data from 580 patients after THA or TKA (808 assessments). The CAT version reduced the number of items by half at comparable measurement precision. In a feasibility study we administered the newly developed CAT measure on tablet PCs and found that patients actually preferred electronic questionnaires over paper–pencil questionnaires.
patient-reported outcomes; forgotten joint score; electronic data capture; computer-adaptive testing; total knee arthroplasty; total hip arthroplasty
We used Medicare administrative data to examine trends in primary and revision THA utilization and hospital volume. Between 1991 and 2005 primary and revision THA utilization increased by 40.9% and 16.8% respectively. The percentage of primary THA procedures performed in high volume hospitals (those in the highest quintile of volume) increased slightly from 58.0% of all procedures in 1991 to 58.7% in 2005 (P-value < 0.01). The percentage of revisions performed in high volume hospitals increased from 60.9% to 62.4% (P-value < 0.01). The percentage of primary THA procedures performed by low volume hospitals remained relatively stable (P-value = 0.36) while the percentage of revision THA performed by low volume hospitals declined (P-value < 0.001). In aggregate these results suggest minimal evidence that regionalization of THA is occurring.
Axial torsional loads representative of gait and stair climbing conditions were applied to transverse sections of 8 uncemented postmortem retrievals and a high-resolution imaging system with digital image correlation was used to measure local micromotion along the bone-implant interface. For seven components that were radiographically stable, there was limited micromotion for gait loading (1.42±1.33 μm) that increased significantly (p=0.0032) for stair climb loading (7.32±9.96 μm). A radiographically loose component had motions on the order of 2.3 mm with gait loading. There was a strong inverse relationship between the amount of bone-implant contact (contact fraction) (p=0.001) and micromotion. The uncemented components had greater contact fraction (41.8±14.4% vs. 11.5±10.2%, p=0.0033) and less median micromotion (0.81±0.79μm vs. 28.8±51.1μm) compared to a previously reported study of cemented retrievals.
Ceramic acetabular liners may exhibit a small, sharp crest - an artifact of discontinuous machining steps - at the junction between the concave spherical surface and the interior edge. On three ceramic liners, this crest was found to form a 9–11° deviation from tangency. Edge loading wear tests were conducted directly on this crest and on a smoother region of the edge. The crest elicited 2–15 times greater volumetric wear on the femoral head. The propensity of the crest to rapidly (<2000 wear cycles) cause elevated wear under low contact force (200 N) suggests that the crest artifact of prevailing machining protocols might be a root cause of stripe wear and squeaking in ceramic acetabular bearings.
This study aims to identify whether patient-level or provider-level characteristics are most influential on a patient’s length of stay in the acute care hospital.
Materials and Methods
A dataset containing a nationally representative sample of inpatient discharge abstracts was used. Multi-level linear regression models were used to evaluate the associations between patient- and provider-level characteristics on patients’ lengths of stay.
The target population included 322,894 discharges with a primary procedure code for primary total knee arthroplasty and 193,553 discharges for total hip arthroplasty. The variables associated with the greatest increases in length of stay were a higher co-morbidity level among patient level attributes (+17.4%) and low surgeon volume among provider-level characteristics (+18.8%).
Provider-level characteristics, particularly provider volume, had a greater impact on length of stay.
The purpose was to explore the responsiveness of both patient-report and performance-based outcome measures to determine functional changes during the acute and long-term postoperative recovery after total knee arthroplasty (TKA). One hundred patients scheduled for unilateral TKA underwent testing preoperatively, 1 month, and 12 months postoperatively using the Delaware Osteoarthritis Profile. All physical performance measures decreased initially after surgery then increased in the long term, however the perceived function did not follow the same trend and some showed an increase immediately after surgery. Patient-report measures were variable with no to small response early, but had excellent long-term responsiveness that was twice as large as performance measures. Patient perception fails to capture the acute functional declines after TKA and may overstate the long-term functional improvement with surgery.
Nine cross-linked UHMWPE acetabular liners were retrieved at revision surgery. Eight of the liners were fully intact and functional at retrieval. Six cases contained shallow initiated cracks at the root of rim notches; one crack had propagated several millimeters. Optical and electron microscopic inspection of the crack surfaces revealed clam shell markings, which are characteristic of fatigue crack initiation. Crack initiation at notches has been identified in reports of catastrophic cross-linked liner failures, with cracks initiation sites exhibiting similar morphology and clam shell markings. Thus, we believe the shallow cracks identified in this case series are precursors to catastrophic rim fracture. The results of this study recommend further investigations to clarify the etiology and prevalence of crack initiation in cross-linked acetabular liners.
Acetabular liner; total hip arthroplasty; fracture; UHMWPE; crosslinked UHMWPE; crack initiation
The aim of this study was to better understand how in vivo oxidation contributes to fatigue damage in total knee arthroplasty (TKA). 119 tibial inserts were consecutively collected after revision surgery. Of the 119 polyethylene retrievals, 29 were gamma sterilized in air (historical), while the remaining 90 were gamma sterilized in nitrogen (conventional). Surface damage assessment and characterization of oxidation were performed on all the retrievals. Delamination was significantly more prevalent and extensive in the longer-term, highly oxidized, historical tibial inserts. Pitting damage, in contrast, appeared to be equally prevalent between both retrieval groups, and was not correlated with in vivo oxidation. Our findings support our hypothesis that in vivo oxidation is a contributing factor to delamination, but not pitting, in TKA. Despite the lower oxidation displayed by conventional retrievals, this study provides strong evidence that delamination secondary to in vivo oxidation may occur during the second decade of implantation.
ultra-high molecular weight polyethylene; total knee arthroplasty; in vivo oxidation; pitting; delamination; fatigue
Recent reports have noted higher rates of heterotopic ossification (HO) with surface replacement arthroplasty (SRA) than with traditional total hip arthroplasty in the absence of postoperative HO prophylaxis. This study reports rates and grades of HO in 44 SRA patients with at least 1 year of follow-up. Heterotopic ossification prophylaxis was used in 32 (73%) of 44 cases. Heterotopic ossification prophylaxis consisted of radiotherapy (22/32), nonsteroidal anti-inflammatory drugs (8/32), or both (2/32). One case of clinically significant HO was documented in the no-prophylaxis group. This strategy of selective HO prophylaxis in patients felt by orthopedic surgeons to be at high risk of HO resulted in low rates of clinically relevant HO after SRA (1/44, 2.3%). Further study is needed to establish optimal selection criteria for HO prophylaxis after SRA.
surface replacement arthroplasty; heterotopic ossification; prophylactic radiation
We assessed whether higher Body Mass Index (BMI) is associated with higher risk of moderate-severe knee pain 2- and 5-years after primary or revision Total Knee Arthroplasty (TKA). We adjusted for gender, age, comorbidity, operative diagnosis and implant fixation in multivariable logistic regression. BMI (reference, <25 kg/m2) was not associated with moderate-severe knee pain at 2-years post-primary TKA (odds ratio (95% confidence interval): 25-29.9, 1.02 (0.75,1.39), p=0.90; 30-34.9, 0.93 (0.65,1.34), p=0.71; 35-39.9, 1.16 (0.77,1.74), p=0.47; ≥40, 1.09 (0.69,1.73), (all p-values ≥0.47). Similarly, BMI was not associated with moderate-severe pain at 5-year primary TKA and at 2- and 5-yr revision TKA follow-up. Lack of association of higher BMI with poor pain outcomes post-TKA implies that TKA should not be denied to obese patients for fear of suboptimal outcomes.
The purpose of this investigation was to determine whether functional performance and self-report outcomes are related to body mass index (BMI) after total knee arthroplasty (TKA). We hypothesized that higher BMIs would negatively affect functional performance as assessed by the timed up-and-go test, stair climbing test, 6-minute walk test, and self-report questionnaires. A total of 140 patients with BMIs ranging from 21.2 to 40.0 kg/m2 were followed over the first 6 months after unilateral TKA. Hierarchical linear regression was used to evaluate the impact of BMI on functional performance at 1, 3, and 6 months after TKA, while taking into account preoperative functional performance. There were no meaningful relationships between BMI and functional performance in the subacute (1 and 3 months) and intermediate (6-month) stages of recovery.
total knee arthroplasty; body mass index; obesity; functional performance
Over a ten-year period, we prospectively evaluated the reasons for revision for contemporary and highly crosslinked polyethylene formulations in a multicenter retrieval program. 212 consecutive retrievals were classified as conventional gamma-inert sterilized liners (n=37), annealed (Crossfire™, n=72), or remelted (Longevity™, XLPE, Durasul; n=93). The most frequent reasons for revision were loosening (35%), instability (28%) and infection (21%) and were not related to polyethylene formulation (p = 0.17). Annealed and remelted liners had comparable linear penetration rates (0.03 and 0.04 mm/y, respectively, on average) and were significantly lower than conventional retrievals (0.11 mm/y; p ≤ 0.0005). This retrieval study including first-generation highly crosslinked liners demonstrated lower wear than conventional polyethylene. While loosening remained the most prevalent reason for revision, we could not demonstrate a relationship between wear and loosening. The long-term clinical performance of first-generation highly crosslinked remains promising, based on the mid-term outcomes of the components documented in this study.
Ultra-high molecular weight polyethylene; UHMWPE; revision; total hip replacement; total hip arthroplasty; crosslinking; wear
Sixty Crossfire (Stryker Orthopaedics, Mahwah, NJ) liners were consecutively revised after an average of 2.9 years (range: 0.01 – 8.0 years) for reasons unrelated to wear or mechanical performance of the polyethylene. Femoral head penetration was measured directly from 42 retrievals implanted for over 1 year. Penetration rate results (0.04 mm/y, on average; range: 0.00-0.13 mm/y) confirmed decreasing wear rates with longer in vivo times. Overall, we observed oxidation levels at the bearing surface of the 60 liners (0.5, on average; range: 0.1-1.7) comparable to those of non-implanted liners (0.5, on average; range: 0.3-1.1) and preservation of mechanical properties. We also measured elevated oxidation of the rim (3.4, on average; range: 0.2-8.8) that was correlated with implantation time. Rim surface damage, however, was observed in only 3/60 (5%) cases. Retrieval analysis of the three rim-damaged liners did not reveal an association between surface damage and the reasons for revision.
Mechanical properties; oxidation; wear; hip arthroplasty; highly crosslinked ultra-high molecular weight polyethylene
This study was performed to explore the cost-effectiveness of total hip replacement compared with hemiarthroplasty in the treatment of displaced femoral neck fractures in active otherwise healthy older patients in whom the optimum treatment is believed to be an arthroplasty procedure.
A Markov decision model was used to determine whether total hip arthroplasty or hemiarthroplasty was most cost-effective for the management of a displaced femoral neck fracture in this patient population.
Total hip arthroplasty was associated with an average cost $3,000 more than hemiarthroplasty, and the average quality-adjusted life year gain was 1.53. The incremental cost-effectiveness ratio associated with the total hip replacement treatment strategy is $1960 per quality-adjusted life-year.
Currently available data support the use of total hip arthroplasty as the more cost-effective treatment strategy in this specific population. The increased upfront cost appears to be offset by the improved functional results when compared with hemiarthroplasty in this select patient group.
The purpose of this study was to evaluate the functional outcomes of persons who underwent simultaneous bilateral total knee arthroplasty (TKA) compared to subjects who underwent unilateral TKA and a healthy control group. Fifteen subjects who underwent primary bilateral TKA and 15 sex, age, and body mass index-matched subjects who underwent primary unilateral TKA were observed prospectively for 2 years. Subjects in both surgical groups showed significant improvement in Knee Outcome Scores, Short Form 36 physical component scores, Timed Up and Go, and stair-climbing tasks (P ≤ .004). No differences in final outcomes were found between surgical groups. In addition, most 2-year clinical measures were no different between the surgical and control groups. Subjects medically appropriate for bilateral TKA should be afforded this option.
bilateral; knee; arthroplasty; outcomes; function
Eliminating post-irradiation melting and stabilizing the residual free radicals of radiation crosslinked ultra-high molecular weight polyethylene (UHMWPE) with Vitamin-E resulted in improved fatigue crack propagation resistance without compromising wear resistance. We designed a cantilever post bending test to determine the bending fatigue resistance of vitamin E-doped, irradiated UHMWPE (α-TPE) in comparison to conventional UHMWPE. The bending fatigue behavior of α-TPE was comparable to conventional UHMWPE. Upon accelerated aging the fatigue resistance of α-TPE was substantially better than that of conventional UHMWPE. α-TPE has shown improved wear and oxidation resistance, migration stability of vitamin E, and improved mechanical properties. The use of this material may be beneficial in total knee arthroplasty where its improved fatigue properties may be an advantage under high stresses.
Total knee arthroplasty; highly cross-linked polyethylene; oxidation resistance; fatigue resistance; vitamin E; biomaterials
In impaction grafting for revision joint arthroplasty, the morselized cancellous bone (MCB) ideally remodels into a new contiguous lattice. However, the use of biologically active factors may sometimes be indicated to enhance fusion. The purpose of this study was to determine the stability of femoral impaction graft constructs for which either only the proximal or distal half of the MCB volume was modeled as fused. Fusing the proximal half of the impaction graft volume resulted in a higher femoral stem stability than did fusing the distal half. This proximal graft fusion also resulted in a stem stability that was similar to that of fusing the entire graft. These results emphasize the importance of proximal fixation of an impaction grafted femoral stem.
Our hypothesis was that cross-linked UHMWPE stabilized with vitamin-E would be wear and fatigue resistant. Acetabular liners were radiation cross-linked, doped with vitamin E and γ-sterilized. Hip simulator wear rate of vitamin E-stabilized UHMWPE was approximately 1 and 6 mg/million-cycles in clean serum and in serum with third-body bone cement particles, respectively; a four to ten-fold decrease from that of conventional UHMWPE. The ultimate strength, yield strength, elongation-at-break and fatigue resistance of vitamin E-stabilized UHMWPE were significantly higher than that of 100-kGy irradiated and melted UHMWPE and were unaffected by accelerated aging. Rim impingement testing with 3.7 mm-thick acetabular liners up to 2 million-cycles showed no significant damage of the cross-linked liners compared to conventional, gamma-sterilized in inert UHMWPE vitamin-E stabilized liners. The data indicate good wear properties and improved mechanical and fatigue properties for vitamin-E stabilized cross-linked UHMWPE.
Total hip arthroplasty; highly cross-linked polyethylene; oxidation resistance; fatigue resistance; vitamin E; biomaterials
This study reports on detailed analyses of retrieved, annealed crosslinked liners. Twelve crosslinked liners (Crossfire, Stryker Orthopaedics, Mahwah, NJ) of the same Omnifit design were retrieved at revision surgery by one institution after an average 1.9 years (0.02 to 4.8 years) in vivo. In each case, the revision surgery was performed for reasons unrelated to wear. The mechanical properties and extent of oxidation of all inserts were characterized using a standard small punch test and measurement of the oxidation index. Results indicated that there was no association between implantation time and either mechanical properties or extent of oxidation for the inserts near the worn bearing surface. Slight variation in properties was observed as a function of sampling location, with the properties near the unworn surface displaying the greatest relative variability. We conclude that the variability in polyethylene properties observed in this small study was not clinically significant for these short term-implanted, annealed crosslinked liners.
Mechanical properties; oxidation; wear; hip arthroplasty; highly crosslinked ultra-high molecular weight polyethylene