Medial Tibial Stress Shielding: A Limitation of Cobalt Chromium Tibial Baseplates.

BACKGROUND: Stress shielding is a well-recognized complication associated with total knee arthroplasty. However, this phenomenon has not been thoroughly described. Specifically, no study to our knowledge has evaluated the radiographic impact of utilizing various tibial component compositions on tibial stress shielding. METHODS: We retrospectively reviewed 3 cohorts of 50 patients that had a preoperative varus deformity and were implanted with a titanium, cobalt chromium (CoCr), or an all polyethylene tibial implant. A radiographic comparative analysis was performed to evaluate the amount of medial tibial bone loss in each cohort. In addition, a clinical outcomes analysis was performed on the 3 cohorts. RESULTS: The CoCr was noted to have a statistically significant increase in medial tibial bone loss compared with the other 2 cohorts. The all polyethylene cohort had a statistically significantly higher final Knee Society Score and was associated with the least amount of stress shielding. CONCLUSION: The CoCr tray is the most rigid of 3 implants that were compared in this study. Interestingly, this cohort had the highest amount of medial tibial bone loss. In addition, 1 patient in the CoCr cohort had medial soft tissue irritation which was attributed to a prominent medial tibial tray which required revision surgery to mitigate the symptoms.

Metal or Modularity: Why Do Metal-Backed Tibias Have Inferior Outcomes to All-Polyethylene Tibial Components in Patients With Osteoarthritis.

BACKGROUND: Biomechanical studies have suggested improved stress distribution in metal-backed (MB) compared to all-polyethylene (AP) tibias, but such potential benefits have not been realized clinically. The purpose of this investigation was to analyze the outcomes of AP components in patients with primary osteoarthritis and compare the results to those obtained with MB tibial components in total knee arthroplasty (TKA). METHODS: We reviewed 11,653 patients undergoing primary TKA for osteoarthritis. There were 9999 (86%) MB (8470 modular and 1529 monoblock) and 1654 (14%) AP tibial components. All patients had at least 2 years of clinical follow-up with mean follow-up of 8 years (range, 2-30 years). RESULTS: Mean survivorship for all primary TKAs at the 5-year, 10-year, 15-year, and 20-year time points was 97%, 92%, 86%, and 78%. AP tibial components were found to have improved survivorship when compared to modular and monoblock MB counterparts (P < .0001). Likewise, AP tibial components were found to have lower rates of tibial component loosening (P < .0001), tibial osteolysis, and component fracture. Furthermore, the AP group had improved survival rates in most age-groups except <55 years where there was no difference. AP tibial components demonstrated improved survival for all body mass index (BMI) groups except in patients with a BMI ≤25 kg/m2 where there was no difference. CONCLUSION: AP tibial components had significantly improved implant survival across all age-groups and most BMI categories in patients who underwent TKA for osteoarthritis. Given these outcomes, AP tibias are a reasonable option, regardless of patient age and BMI.

All-Polyethylene Tibial Components: An Analysis of Long-Term Outcomes and Infection.

BACKGROUND: There is debate regarding tibial component modularity and composition in total knee arthroplasty (TKA). Biomechanical studies have suggested improved stress distribution in metal-backed tibias; however, these results have not translated clinically. The purpose of this study was to analyze the outcomes of all-polyethylene components and to compare the results to those with metal-backed components. METHODS: We reviewed 31,939 patients undergoing a primary TKA over a 43-year period (1970-2013). There were 28,224 (88%) metal-backed and 3715 (12%) all-polyethylene tibial components. The metal-backed and all-polyethylene groups had comparable demographics with respect to gender, age and body mass index (BMI). Mean follow-up was 7 years. RESULTS: The mean survival for all primary TKAs at the 5-, 10-, 20- and 30-year time points was 95%, 89%, 73%, and 57%, respectively. All-polyethylene tibial components were found to have a significantly improved (P < .0001) survivorship when compared with their metal-backed counterparts. All-polyethylene tibial components were also found to have a significantly lower rate of infection, instability, tibial component loosening, and periprosthetic fracture. The all-polyethylene group had improved survival rates in all age groups, except in patients 85 years old or greater, where there was no significant difference. All-polyethylene tibial components had improved survival for all BMI groups except in the morbidly obese (BMI ≥ 40) where there was no significant difference. CONCLUSION: All-polyethylene tibial components had significantly improved implant survival, reduced rates of postoperative infection, fracture, and tibial component loosening. All polyethylene should be considered for most of the patients, regardless of age and BMI.

Morbidly Obese vs Nonobese Aseptic Revision Total Hip Arthroplasty: Surprisingly Similar Outcomes.

BACKGROUND: We aimed to compare the outcomes between matched morbidly obese (BMI ≥ 40 kg/m(2)) and nonobese (BMI <30 kg/m(2)) patients undergoing first-time aseptic revision THA with at least 4 years of follow-up. METHODS: Groups were matched 1:1 using sex, age, and date of revision surgery (123 patients in each group). RESULTS: The overall incidence and risk of complication, reoperation, and re-revision were similar between groups. Morbidly obese patients were more likely to dislocate (odds ratio [OR], 3.3; P = .03), but were less likely to develop polyethylene wear (OR, 0.1; P = .04) and aseptic loosening (OR, 0.3; P = .03). CONCLUSION: Quality outcome measures such as hospital readmission were not addressed by this study and could be the basis for future studies. LEVEL OF EVIDENCE: level III, prognostic study.

Anatomic Hip Center Decreases Aseptic Loosening Rates After Total Hip Arthroplasty with Cement in Patients with Crowe Type-II Dysplasia: A Concise Follow-up Report at a Mean of Thirty-six Years.

UNLABELLED: We previously reported the two to twenty-two-year results of 145 total hip arthroplasties (THAs) with cement performed from 1969 to 1980 in 117 patients with Crowe type-II dysplasia. The purpose of the present study was to update the long-term effects of a nonanatomic hip center on component loosening and aseptic revision in this cohort. Forty-nine patients (sixty hips) were alive at a mean of thirty-six years. The overall cumulative incidence of aseptic revision at thirty-five years was 32% for acetabular cups and 21% for femoral stems. Acetabular loosening was less likely with a hip center placed within the true acetabular region (TAR), <15 mm superior to the approximate femoral head center (AFHC), <35 mm superior to the interteardrop line (ITL), or within zone 1. Femoral loosening and revision were less likely with the hip center placed <35 mm superior to the ITL and within zone 1. An anatomic hip center was associated with significantly lower loosening and aseptic revision rates for both acetabular and femoral components. The current study supports the placement of acetabular components in an anatomic position to promote long-term durability after THA with cement. LEVEL OF EVIDENCE: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.