Factors associated with tibial polyethylene wear in total knee arthroplasty: analysis of inserts retrieved at revision and autopsy

Factors associated with tibial polyethylene wear in total knee arthroplasty: analysis of inserts retrieved at revision and autopsy

Abstracts From the AAHKS Thirteenth Annual Meeting for these wear-related failures are probably multi-factorial. This study emphasizes the potential d...

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Abstracts From the AAHKS Thirteenth Annual Meeting for these wear-related failures are probably multi-factorial. This study emphasizes the potential deleterious effects that small changes in the manufacturing process may have on the outcome of a prosthesis with an initially favorable survivorship. Careful consideration of these effects must be made before any change in the manufacturing process of a successful implant is entertained.

PAPER #20 FACTORS ASSOCIATED WITH TIBIAL POLYETHYLENE WEAR IN TOTAL KNEE ARTHROPLASTY: ANALYSIS OF INSERTS RETRIEVED AT REVISION AND AUTOPSY Matthew B. Collier, MS, C. Anderson Engh, Jr., MD, James P. McAuley, MD, Gerard A. Engh, MD Background: Tibial polyethylene wear contributes to osteolysis and failure of total knee arthroplasty. We identified factors associated with wear by analyzing retrieved cruciate-retaining inserts of one design. Methods: Sixty-eight primary Anatomic Modular Knee total knees were performed for varus osteoarthrosis and retrieved at revision (n⫽49) or autopsy (n⫽19).Wear of each compartment was calculated as the change in minimum polyethylene thickness per year in-vivo. Multiple linear regression analysis assessed relative contributions of 11 variables to wear of the medial (0.36⫾0.30mm/yr) and lateral (0.18⫾0.16mm/yr) compartments: Patient age: 66⫾10yrs Gender: 49% female Weight: 85⫾16 kg Postoperative mechanical axis varus: 4⫾9 mm Tibial component varus: 1⫾2 degrees Femoral component valgus: 6⫾2 degrees Polyethylene resin: 48% 412, 43% 415, 9% 1900 Polyethylene fabrication method: 76% compression-molded sheet, 24% ram-extruded bar Insert shelf age: 1.4⫾1.6 yrs Insert size: 3⫾1 Insert original thickness: 8⫾2 mm

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PAPER #22 HOW PREOPERATIVE MCS AFFECTS POSTOPERATIVE OUTCOME IN JOINT REPLACEMENT SURGERY David C. Ayers, MD, Patricia Durkin Franklin, MD, MBA, MPH, Paula Trief, PhD, Robert Ploutz-Snyder, PhD, Debra Freund, PhD Introduction: We have previously shown that TKR patients who have a low MCS (mental composite score of the SF-36) are less likely to improve physically after TKR. We have proposed that a preoperative intervention targeting low MCS patients might improve post-operative physical outcome; however, traditional mental health correlates (i.e. depression, anxiety, coping skills, social support) of low MCS patients are not known. The purpose of this study was to assess the psychological components represented by low MCS in TJR patients, step one in the process of developing a pre-surgical intervention. Methods: 100 patients scheduled for TJR surgery were assessed 2-3 weeks prior to surgery (mean age⫽62.5, 66% female). They completed the SF-36 (MCS and PCS scored), the Beck Depression Inventory, Spielberger Trait Anxiety Inventory, Coping Strategies Questionnaire, Interpersonal Support Evaluation List and Western Ontario McMaster Questionnaire (WOMAC). First, Pearson’s correlations among all measures were completed. Then, mean scores of high and low MCS subjects on all outcomes were compared using the two-tailed student t-statistic (alpha⫽.05). Finally, Structural Equation Modeling (SEM) techniques were used to test the model that the relationship between psychological predictors (depression, anxiety, support, MCS) and physical outcomes (PCS, WOMAC) is mediated through pain coping strategies employed. Results: Better emotional function (MCS as a continuous variable) significantly correlated with less depression and anxiety, more support and greater use of specific coping strategies. Low MCS subjects had higher depression (p⬍0.001) and anxiety (p⬍0.001) scores; however, they were not clinically depressed. Also, low MCS correlated with lower appraisal (p⬍0.022) and belonging (p⬍0.019) social support, and greater use of catastrophizing (p⬍0.007), praying (p⬍0.039) and reinterpreting pain (p⬍0.002) coping strategies. Conclusion: 25-30% of patients undergoing TJR have a low preoperative MCS and are at higher risk for poor physical outcome following TJR. We have found that low MCS patients report significantly more anxiety and depressive symptoms and are less likely to use specific coping strategies. Thus, a preoperative psychosocial intervention for TJR patients with a low MCS may be warranted. This intervention should teach active coping skills to ameliorate depressive and anxious symptoms, and enhance support. This is part one of an ongoing project funded by the AAHKS and the OREF. Step two will be to develop an appropriate multipronged pre-operative intervention and, step three, to evaluate whether this intervention improves postoperative physical outcomes following TJR.

Results: The 11 factors explained 62% (p⬍0.01, R2⫽0.62) of the variation in medial wear. Shelf age (p⬍0.01, R2⫽0.40), patient age (p⬍0.01, R2 increase⫽0.12), and mechanical axis varus (p⬍0.01, R2 increase⫽0.06) explained 58% (p⬍0.01, R2⫽0.58) alone. The 11 factors explained at least 35% (p⬍0.01, R2⫽0.35-0.39) of the variation in lateral compartment wear, with shelf age explaining 26% (p⬍0.01, R2⫽0.26). Eliminating inserts by shelf age revealed that shelf age and medial/lateral wear were significantly associated until only (43) inserts with shelf ages below 1.3 years remained. Discussion: Medial compartment wear correlated strongest with shelf age, but also increased with decreasing patient age and increasing postoperative mechanical axis varus. Shelf age was the lone variable associated with lateral compartment wear. Minimizing polyethylene shelf age and complete elimination of mechanical axis varus are advised to minimize tibial polyethylene wear in the varus knee.

PAPER #23 THIGH PAIN IN PRIMARY TOTAL HIP REPLACEMENT: THE EFFECTS OF ELASTIC MODULI Carlos Lavernia, MD, Michele Dapuzzo, MD, Victor Hernandez, MD, David Lee, PhD Introduction: Thigh pain after uncemented THA remains a controversial topic. Our objective was to assess the effect of material composition in the development of thigh pain after primary THR. Methods: A cohort of 252 primary THAs was studied. All patients received identically shaped tapered femoral components; an equal number of received cobalt-chrome and titanium stems.

PAPER #21 FIVE-YEAR FOLLOW-UP OF A TANTALUM, MONOBLOCK ACETABULAR COMPONENT S. David Stulberg, MD

Results: One-year incidence of thigh pain was 9.5%. Implant material was unrelated to reported thigh pain one and two years postoperatively. Those patients receiving larger versus smaller stems were more likely to report thigh pain at year one (Relative Risk⫽4.68; 95% Confidence Interval 1.41, 15.50). Conclusions: Material composition of this tapered stem design is unrelated to the incidence of thigh pain.

Introduction: Osteolysis secondary to polyethylene wear is the most serious aseptic long-term complication following THR. Studies have shown that fixation with screws, modularity and lack of extensive bone ingrowth are associated with increased osteolysis. This study examines the initial experience with a cup designed to address these issues. Methods: 127 consecutive primary THRs were performed between 1997 and 1999 using uncemented monoblock, elliptical, tantalum cup without screw holes. The average follow-up time was 50 months (range: 34-71). 79 THRs were performed in females and 48 THRs were performed in males. 48% of the THRs were hybrid fixed, 52% were uncemented. The average age was 61.6 years (range 19-88). Pre and postoperative clinical assessment was conducted with Harris Hip Score (hhs), WOMAC, SF-36. One independent, blinded observer performed zonal radiographic analysis with a modified DeLee and Charnley method. Results: The average hhs at recent follow-up was 93 (range 85-100). All shells appear fixed with bone ingrowth. Dome-gaps were present in 6 cups postoperative; all have filled in since then. Radiolucencies at follow-up 4% zone 1, 8% zone 2; none were greater than 1mm. No cup migration occurred. There were 8 cup related complications: 5 dislocations (4%) 1 subluxation, 2 undisplaced rim fractures (1.7% - no treatment). 3 dislocations, 1 subluxation occurred more than three months postop. Three revisions: 1 deep wound infection, 1 liner exchange (using reaming technique), 1 femoral head exchange. Conclusions: Uncemented monoblock, elliptical tantalum cup without holes provides secure, symptomfree fixation at 5 years. No complications were associated with use of tantalum. An elliptical shape is associated with dome gaps, all of which appeared to fill by 3 months. The monoblock design results in increased polyethylene lip prominence associated with 6 cases of instability. The effect of prominent rim on impingement and long-term wear requires careful follow-up.

PAPER #24 THE EFFECT OF INCISION SIZE ON CLINICAL OUTCOMES AND RECOVERY AFTER TOTAL HIP ARTHROPLASTY WITH THE ANTEROLATERAL APPROACH Isao Asayama, MD, PhD, Tracy L. Kinsey, RN, BS, Ormonde M. Mahoney, MD We evaluated clinical, radiographic, and short-term recovery outcomes in a one-surgeon series of 100 unilateral primary total hip arthoplasties by antero-lateral approach via limited (⬍10 cm) and standard (14-18 cm) size incisions. Anesthesiology estimated significantly lower blood loss with minimum size incisions, but otherwise hematological measures, transfusions, operative time, hospitalization time, narcotic usage, rehabilitation, complications, discharge disposition, and component placement were not significantly different related to approach. Quality of component placement did not appear to be limited by mini-incision approach. We found no objective evidence that minimal incision size benefited these patients, who were blinded to approach type.