Morbid Obesity in Revision Total Knee Arthroplasty: A Significant Risk Factor for Re-Operation.

BACKGROUND: The purpose of this study is to compare surgical and clinical outcomes between matched groups of morbidly obese (body mass index [BMI] >40 kg/m2) and non-morbidly obese (BMI <40 kg/m2) patients undergoing first-time revision total knee arthroplasty with a minimum 5-year follow-up. METHODS: Two groups of 87 patients (BMI >40 or <40 kg/m2) were matched 1:1 based on age at the time of revision, gender, and diagnosis for revision (aseptic or septic causes). RESULTS: The morbidly obese group had a significantly greater incidence of re-operation (34.5% [30/87] vs 16.1% [14/87], P = .005) and re-revision (27.6% [24/87] vs 12.6% [11/87], P = .014) with a significantly lower 10-year survivorship for re-operation (P = .05) and subsequent revision (P = .014). In particular, the aseptic sub-group had a greater incidence of re-operation (29.9% [20/67] vs 13.4% [9/67], P = .021) and re-revision (26.9% [18/67] vs 11.9% [8/67], P = .029). The non-morbidly obese group demonstrated higher final Western Ontario and McMaster Universities Index scores (63.1 ± 19.5 vs 55.5 ± 22.5, P = .030) and a greater change between pre-operative and final KSS (45.6 ± 44.3 vs 39.7 ± 48.4, P = .040) and SF-12 Mental component (3.6 ± 10.8 vs -1.4 ± 10.3, P = .013). CONCLUSION: Morbidly obese patients undergoing revision total knee arthroplasty have a greater risk of re-operation and re-revision while experiencing lower clinical outcome scores compared to non-morbidly obese patients. These patients should be informed of the higher potential for re-operation and the possibility of poor results.

Current Total Knee Designs: Does Baseplate Roughness or Locking Mechanism Design Affect Polyethylene Backside Wear?

BACKGROUND: Tibial baseplate roughness and polyethylene-insert micromotion resulting from locking-mechanism loosening can lead to polyethylene backside wear in TKAs. However, many retrieval studies examining these variables have evaluated only older TKA implant designs. QUESTIONS: We used implant-retrieval analysis to examine if there were differences in: (1) backside damage scores, (2) backside damage modes, and (3) backside linear wear rates in five TKA implant designs owing to differing baseplate surface roughness and locking mechanisms. Additionally, we examined if (4) patient demographics influence backside damage and wear. METHODS: Five TKA implant models (four modern and one historical design) were selected with different tibial baseplate and/or locking mechanism designs. Six tibial inserts retrieved at the time of revision from each TKA model were matched for time in vivo, age of the patient at TKA revision, BMI, sex, revision number, and revision reason. Each insert backside was analyzed for: (1) visual total damage score and (2) individual visual damage modes, both by two observers and with an intraclass correlation coefficient of 0.66 (95% CI, 0.39-0.92), and (3) linear wear rate measured by micro-CT. Median primary outcomes were compared among the five designs. For our given sample size among five groups we could detect with 80% power a 10-point difference in damage score and an 0.11-mm per year difference in wear rate. RESULTS: The polished tibial design with a partial peripheral capture locking mechanism and anterior constraint showed a lower total damage score compared with the nonpolished tibial design with only a complete peripheral-rim locking mechanism (median, 12.5; range, 9.5-18.0; 95% CI, 9.58-16.42 versus median, 22.3; range, 15.5-27.0; 95% CI, 17.5-26.5; p = 0.019). The polished baseplate with a tongue-in-groove locking mechanism showed more abrasions than the nonpolished baseplate with a peripheral-rim capture and antirotational island (median, 7.25; range, 0.5-8.0; 95% CI, 2.67-8.99 versus median, 0.75; range, 0-1.5; 95% CI, 0.20-1.47; p = 0.016)). Dimpling was a unique wear mode to the nonpolished baseplates with the peripheral-rim capture and antirotational island (median, 5.5; range, 2.0-9.0; 95% CI, 2.96-8.38) and the peripheral-rim capture alone (median, 9.0; range, 6.0-10.0; 95% CI, 7.29-10.38). Overall, the linear wear rate for polished designs was lower than for nonpolished designs (0.0102 ± 0.0044 mm/year versus 0.0224 ± 0.0119 mm/year; p < 0.001). Two of the polished baseplate designs, the partial peripheral capture with anterior constraint (median, 0.083 mm/year; range, 0.0037-0.0111 mm/year; 95% CI, 0.0050-0.0107 mm versus median, 0.0245 mm/year; range, 0.014-0.046 mm/year; 95% CI, 0.0130-0.0414 mm; p = 0.008) and the tongue-in-groove locking mechanism (median, 0.0085 mm/year; range, 0.005-0.015 mm/year; 95% CI, 0.0045-0.0138 mm; p = 0.032) showed lower polyethylene linear wear rates compared with the nonpolished baseplate design with only a peripheral-rim capture. CONCLUSIONS: Total damage scores and linear wear rates were highest involving the nonpolished design with only a peripheral rim capture. There were no differences among the other TKA designs regarding damage and wear, but this finding should be considered in the setting of a relatively small sample size. CLINICAL RELEVANCE: Our study showed that in the complex interplay between baseplate surface finish and locking mechanism design, a polished baseplate with a robust locking mechanism had the lowest backside damage and linear wear. However, improvements in locking mechanism design in nonpolished baseplates potentially may offset some advantages of a polished baseplate. Further retrieval analyses need to be done to confirm such findings, especially analyzing current crosslinked polyethylene. Additionally, we need mid- and long-term studies comparing TKA revisions attributable to wear and osteolysis among implants before understanding if such design differences are clinically relevant.

Differences in Trochlear Surface Damage and Wear Between Three Different Total Knee Arthroplasty Designs.

INTRODUCTION: Trochlear design plays a role in patellofemoral kinematics. Little is known regarding differences in the contact properties between modern designs. The purpose of the present study was to analyze patellofemoral joint contact by identifying areas of joint surface damage and wear in retrieved femoral components of 3 modern designs. MATERIALS: Eighteen retrieved femoral components featuring 3 different modern designs (Triathlon, SIGMA, and GENESIS II) were matched based on time-in-vivo, age, gender, and body mass index. Trochlear wear and surface damage were assessed using visual inspection, light microscopy, and light profilometry. RESULTS: Visual inspection of the femoral components showed evidence of surface damage in all implant types. No significant differences between the groups were found with respect to surface damage and wear on visual inspection. Light profilometry of retrieved components showed that retrieved Triathlon (P = .002) and SIGMA (P = .009) components were significantly rougher than the corresponding reference components. The GENESIS II retrieved components were not substantially rougher than the reference components (P = .48). Light profilometry analysis showed significantly increased roughness of retrieved SIGMA components compared with Triathlon or GENESIS II components, particularly in the proximal trochlear groove and the medial trochlea. CONCLUSION: As the volume and patient demands for total knee arthroplasty increase, a greater understanding of the patellofemoral joint is warranted. Patellofemoral kinematics can have an effect on the surface characteristics of total knee arthroplasty components. Retrieved SIGMA components appeared to have increased roughness compared with Triathlon or GENESIS II components. The etiology and long-term effects of increased trochlear roughness require further investigation.

Transitioning to the Direct Anterior Approach in Total Hip Arthroplasty: Is It Safe in the Current Health Care Climate?

BACKGROUND: The direct anterior approach for total hip arthroplasty has recently gained interest for its quicker short-term recovery despite concerns about increased complications and operative time, especially during the steep learning curve period. The primary goal of this study was to determine if the transition from a posterior approach to a direct anterior approach for total hip arthroplasty can be achieved without harming patient safety. METHODS: This is a retrospective cohort single-surgeon study of consecutive primary total hip arthroplasties performed over a transition period from posterior to direct anterior (DA) approach. RESULTS: A total of 412 patients (211 anterior, 201 posterior) were included with no significant demographic differences between cohorts. There were no significant differences between the DA and posterior group in 30-day readmission rates (2.84% vs 2.49%, P = .823), 90-day readmission rates (4.27 vs 5.97, P = .432), complication rate (6.16% vs 3.48%, P = .206), or revision rate (1.90% vs 2.99%, P = .535). The DA group had a significantly lower percentage of cases outside the goal abduction angle range (35°-50°) than the posterior group (9.52%, n = 20 vs 19.6%, n = 39, P < .01). The number of cases outside the goal leg length discrepancy range (±10 mm) was not significantly different (P = .846) between the DA (12.9%) and posterior (13.6%) groups. CONCLUSION: This single-surgeon study demonstrates that the DA approach can be transitioned to safely with no significant increase in complications or readmissions over a high-volume experienced surgeon's first 200 cases. Furthermore, our results endorse the consistency of the DA approach during the learning curve period in regard to component positioning compared to posterior approach.

The 72-Hour Medicare Mandate After Total Joint Arthroplasty: Is This Medically Necessary?

INTRODUCTION: Currently, Medicare total joint arthroplasty patients are required to stay postoperatively 3 days in the hospital before discharge to a skilled nursing facility (SNF). We evaluated Medicare's mandated 3-night hospital stay rule to find out how many total joint arthroplastic patients are safe for discharge to SNFs on postoperative day 2 (POD2). METHODS: This is a retrospective case series analyzing Medicare primary total hip or total knee arthroplastic patients at a single hospital over 1 year. Patients meeting 15 separate criteria by POD2 were considered safe for discharge home rather than to a SNF. RESULTS: Of 259 patients, 47.88% met discharge criteria to SNF POD2. 31.66% did not meet 1, 13.13% did not meet 2, and 6.95% did not meet ≥3 criteria on POD2. Common criteria delaying discharge were blood pressure abnormalities, increasing or elevated white blood cell count, cardiac abnormalities, and fever. Thirty-day readmission rate for patients in the group safe for discharge POD2 was 1.75%. CONCLUSION: Of the total, 47.88% of patients required to stay by the Medicare 3-night stay rule were safe for discharge to SNF on POD2 without an increase in readmission rate at 30 days when compared to our institutional mean.