No sex differences exist in posterior condylar offsets of the knee.

BACKGROUND: Restoration of posterior condylar offset during TKA is believed to be important to improving knee kinematics, maximizing ROM, and minimizing flexion instability. However, controversy exists regarding whether there are important anatomic differences between sexes and whether a unisex knee prosthesis can restore the anatomy of knees in males and females. QUESTIONS/PURPOSES: The purposes of our study were to determine if sex differences exist in (1) absolute posterior condylar offset size, (2) relative posterior condylar offset size in relation to total condylar height, and (3) posterior condylar articular cartilage thickness. METHODS: We identified 100 patients (50 men and 50 women) without a history of arthritis, deformity, dysplasia, osteochondral defect, fracture, or surgery about the knee who had MRI of the knee performed. All MR images were ordered by primary care medical physicians for evaluation of nonspecific knee pain. Using a previously described three-dimensional MRI protocol, we measured posterior condylar offset, total condylar height, and articular cartilage thickness at the medial and lateral femoral condyles and compared values to evaluate for potential sex differences. We performed an a priori power calculation using a 2-mm posterior condylar offset difference as the minimum clinically important difference; with 2n = 100, our power to detect such a difference was 99.8%. RESULTS: Compared with females, males had greater medial posterior condylar offset (30 mm [95% CI, 29.3-30.7 mm; SD, 2.5 mm] vs 28 mm [95% CI, 27.0-28.5 mm; SD, 2.7 mm]), lateral posterior condylar offset (27 mm [95% CI, 26.2-27.3 mm; SD, 2.0 mm] vs 25 mm [95% CI, 24.2-25.4 mm; SD, 2.0 mm]), medial condylar height (63 mm [SD, 3.2 mm] vs 57 mm [SD, 4.4 mm]), and lateral condylar height (71 mm [SD, 5.2 mm] vs 65 mm [SD: 4.0 mm]) (all p values < 0.001). However, the mean ratio of medial posterior condylar offset to medial condylar height (0.48 [SD, 0.04] vs 0.49 [SD, 0.05]) and the mean ratio of lateral posterior condylar offset to lateral condylar height (0.38 [SD, 0.05] vs 0.38 [SD, 0.03]) were not different between sexes (p = 0.08 and p = 0.8, respectively). There also was no sex difference in mean articular cartilage thickness at either condyle (medial condyle: 2.7 mm [SD, 0.5 mm] vs 2.5 mm [SD, 0.7 mm]; lateral condyle: 2.6 mm [SD, 0.6 mm] vs 2.5 mm [SD, 0.8 mm]) (both p values ≥ 0.1). CONCLUSIONS: Results of our study showed that knees in males exhibited greater posterior condylar offset and greater total condylar height at the medial and lateral femoral condyles, however, there were no sex differences in the ratio of posterior condylar offset to condylar height at either condyle. CLINICAL RELEVANCE: These findings suggest that a unisex knee prosthesis design is adequate to recreate the normal posterior condylar offsets for men and women.

Prevalence and Costs of Rehabilitation and Physical Therapy After Primary TJA.

This study evaluated the trends in discharge patterns and the prevalence and cost of post-discharge PT. The 5% Medicare database (1997-2010) was used to identify 50,886 primary THA and 107,675 TKA patients. More than 50% of patients were discharged from hospital to an inpatient facility. There were an increase in discharges to skilled nursing units and a reduced rate to rehabilitation facilities. In contrast to hospital, surgeon reimbursement, and implant costs, the average annual PT cost per patient rose through the study period. Approximately 25% of PT costs were used on less common modalities. PT costs more than $648 million a year. With the increased pressure to control costs for primary TJA, these patterns may change unless PT effectiveness can be demonstrated.

Does chondrocalcinosis affect Knee Society scores and range of motion after TKA?

BACKGROUND: Chondrocalcinosis is manifested by crystalline deposits of calcium commonly found during primary TKA for osteoarthritis. Its frequency among patients undergoing TKA is poorly defined, as is its influence on pain or function after TKA. QUESTIONS/PURPOSES: The purposes of this study are to (1) determine the prevalence of chondrocalcinosis in patients undergoing TKA for osteoarthritis; (2) evaluate the effect of chondrocalcinosis on ROM and The Knee Society scores; (3) determine if patients with chondrocalcinosis and severe synovitis who underwent synovectomy are at risk for lower postoperative Knee Society scores and less ROM; and (4) assess if chondrocalcinosis is associated with increased rates of revision surgery. METHODS: We retrospectively reviewed the medical records of 1500 primary TKAs performed by one surgeon. The minimum followup for patients was 24 months (average, 57 months; range, 24-120 months). There were 511 men and 934 women with an average age of 70 years. Fifty-five patients underwent bilateral knee replacements. Crystal deposition was graded prospectively during surgery using a subjective visual scale. A thorough synovectomy was performed on patients with severe synovitis and apparent crystalline deposition suggestive of calcium pyrophosphate dihydrate (CPPD) deposition (n = 50). The Knee Society scores, ROM, and revision rates were compared between patients with visible chondrocalcinosis with those without and between patients with mild chondrocalcinosis with those with severe chondrocalcinosis. RESULTS: Chondrocalcinosis was found in 173 male patients (34%) undergoing TKAs during this period compared with 224 female patients (24%) (p < 0.001). The Knee Society scores for knee rating and function were similar in patients with or without chondrocalcinosis undergoing TKA. However, patients with visible CPPD deposition who underwent synovectomy for proliferative synovitis had diminished final ROM and Knee Society knee rating scores (107(o) versus 115(o) knee flexion, p < 0.001 and 87 versus 94 points, p = 0.001). We cannot determine whether this result is because of the synovectomy or severity of the disease, and therefore we cannot recommend a synovectomy at this time. Revision rates were no different among patients with chondrocalcinosis compared with those without it (3.6% versus 2.2%, p = 0.2). CONCLUSIONS: Chondrocalcinosis is common among patients undergoing TKA for osteoarthritis. The presence of CPPD deposition does not appear to affect the ROM and Knee Society scores of patients with CPPD but without severe synovitis. However, patients with severe synovitis and visible CPPD who underwent thorough synovectomy may be at risk for having decreased postoperative ROM and pain develop. LEVEL OF EVIDENCE: Level III, therapeutic study. See the Instructions for Authors for a complete description of levels of evidence.

Plain radiographs underestimate the asymmetry of the posterior condylar offset of the knee compared with MRI.

BACKGROUND: Restoration of posterior condylar offset (PCO) during total knee arthroplasty is essential to maximize range of motion, prevent impingement, and minimize flexion instability. Previously, PCO was determined with lateral radiographs, which could not distinguish the asymmetries between the femoral condyles. MRI can independently measure both medial and lateral PCO. QUESTIONS/PURPOSES: The purpose of this study is to determine the normal PCO of the knee, to establish the differences in medial and lateral PCO, and to compare PCO measurements obtained from radiographs versus those obtained from MRI. METHODS: We identified 32 patients without a history of prior knee pathology who had both plain radiographs and MRI scans of the same knee performed. The PCO was measured on lateral radiographs and compared with MRI measurements using a novel three-dimensional protocol. RESULTS: By MRI, the mean medial PCO was 29 (± 3) mm and the mean lateral PCO was 26 (± 3) mm; both values were greater (p < 0.001 and p = 0.03, respectively) than the mean radiographic PCO of 25 (± 2) mm. The medial PCO, as measured by MRI, was significantly greater than the lateral PCO (p < 0.001). CONCLUSIONS: Plain radiographs underestimate PCO as well as the asymmetry of the medial and lateral PCO compared with MRI. This discrepancy is the result of both articular cartilage thickness and the anatomic differences between medial and lateral condyles. Designers of knee prostheses and instrumentation should take these differences into account.

Can surgeons predict what makes a good TKA? Intraoperative surgeon impression of TKA quality does not correlate with Knee Society scores.

BACKGROUND: Surgeons generally agree on what they want to achieve when performing TKA. However, we do not know which technical quality goals are correct, important, or irrelevant to achieve adequate function or durability. QUESTIONS/PURPOSES: We asked whether a surgeon can predict postoperative Knee Society scores (KSSs) of TKAs at the time of surgery based on perceived technical quality of surgery. PATIENTS AND METHODS: We reviewed all 1050 patients undergoing 1193 primary TKAs performed by a single surgeon between 2000 and 2004. The surgeon intraoperatively recorded his impression of the technical quality of surgery based on 15 factors (on a 1-10 scale, with 10 being highest quality) and degree of difficulty (on a 1-10 scale, with 10 being most difficult). We correlated these impressions to KSSs. One hundred thirty-nine of the 1050 patients had technical quality scores of less than 8, including 15 knees with major technical downgrades with clear deficiencies we presumed would affect outcomes. Minimum followup was 24 months (mean, 48 months; range, 24-60 months). RESULTS: We found no difference in mean KSSs between the 1054 TKAs with technical quality scores of more than 8 and the 124 knees with technical quality scores of less than 8. However, mean KSSs were lower in the 15 knees with technical quality scores of less than 6.5 than in the 124 knees with technical quality scores of less than 8, but these 15 knees also had a higher degree of difficulty than the 124 knees. CONCLUSIONS: The surgeon's subjective view of technical quality of surgery did not predict KSSs unless the technical quality score was extremely low. More than one technical problem was associated with lower scores. It is unclear whether this is a question of the subjective ratings or our inability to define quality.

Porous tantalum patellar components in revision total knee arthroplasty minimum 5-year follow-up.

Revision total knee arthroplasty can be complicated by severe patellar bone loss, precluding the use of standard cemented patellar components. This study evaluated the midterm outcomes of porous tantalum (PT) patellar components. Twenty-three PT components were used in 6 men and 17 women (average age, 62 years). All patellae had less than 10-mm residual thickness. The PT shell was secured to host bone, and a 3-peg polyethylene component was cemented onto the shell. In 2 patients, the PT component was sutured directly to extensor mechanism. Average follow-up was 7.7 years (range, 5-10 years). At follow-up, the Knee Society scores for pain and function averaged 82.7 and 33.3, respectively, whereas the mean Oxford knee score was 32.6. Four patients underwent revision surgery. Survivorship was 19 (83%) of 23 patients. Porous tantalum patellar components can provide fixation where severe bone loss precludes the use of traditional implants. Failures were associated with avascular residual bone and fixation of components to the extensor mechanism.

Management of intraoperative medial collateral ligament injury during TKA.

BACKGROUND: Intraoperative injuries to the medial collateral ligament are often unrecognized and failure to appropriately manage ligament loss may result in knee instability and loosening. QUESTIONS/PURPOSES: We compared the functional scores in patients with iatrogenic injury to the medial collateral ligament (MCL) treated with additional constraint to those without. METHODS: We retrospectively reviewed the records of all 1478 patients (1650 knees) who underwent primary TKA between 1998 and 2004. Thirty-seven patients (2.2%) had recognized intraoperative injury to the MCL; the remaining 1441 patients (1613 knees) served as controls. We attempted to repair the ligament in 14 patients; increased prosthetic constraint over that planned was used in 30 of the 37 patients. We determined Knee Society scores (KSS) in all patients. Three patients were lost to followup. The minimum followup was 36 months (average, 54 months; range, 36-120 months). RESULTS: The mean KSS for all MCL injury knees for pain and function averaged 81 and 74 points, respectively, compared with 91 and 87 for the control group. However, in the 30 knees in which the MCL insufficiency was treated with increased constraint, the mean scores for pain and function increased to 88 and 83 points, respectively. Four of the seven patients treated without increased prosthetic constraint were revised for instability; no revisions for instability were performed in the 37 patients treated with additional constraint. CONCLUSIONS: Recognition of MCL injury during TKA is crucial, since using nonstabilizing inserts was associated with residual instability requiring revision. LEVEL OF EVIDENCE: Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Rivaroxaban versus enoxaparin for thromboprophylaxis after total knee arthroplasty (RECORD4): a randomised trial.

BACKGROUND: Prophylaxis for venous thromboembolism is recommended for at least 10 days after total knee arthroplasty; oral regimens could enable shorter hospital stays. We aimed to test the efficacy and safety of oral rivaroxaban for the prevention of venous thromboembolism after total knee arthroplasty. METHODS: In a randomised, double-blind, phase III study, 3148 patients undergoing knee arthroplasty received either oral rivaroxaban 10 mg once daily, beginning 6-8 h after surgery, or subcutaneous enoxaparin 30 mg every 12 h, starting 12-24 h after surgery. Patients had mandatory bilateral venography between days 11 and 15. The primary efficacy outcome was the composite of any deep-vein thrombosis, non-fatal pulmonary embolism, or death from any cause up to day 17 after surgery. Efficacy was assessed as non-inferiority of rivaroxaban compared with enoxaparin in the per-protocol population (absolute non-inferiority limit -4%); if non-inferiority was shown, we assessed whether rivaroxaban had superior efficacy in the modified intention-to-treat population. The primary safety outcome was major bleeding. This trial is registered with ClinicalTrials.gov, number NCT00362232. FINDINGS: The primary efficacy outcome occurred in 67 (6.9%) of 965 patients given rivaroxaban and in 97 (10.1%) of 959 given enoxaparin (absolute risk reduction 3.19%, 95% CI 0.71-5.67; p=0.0118). Ten (0.7%) of 1526 patients given rivaroxaban and four (0.3%) of 1508 given enoxaparin had major bleeding (p=0.1096). INTERPRETATION: Oral rivaroxaban 10 mg once daily for 10-14 days was significantly superior to subcutaneous enoxaparin 30 mg given every 12 h for the prevention of venous thromboembolism after total knee arthroplasty. FUNDING: Bayer Schering Pharma AG, Johnson & Johnson Pharmaceutical Research & Development.

Prevention of symptomatic pulmonary embolism in patients undergoing total hip or knee arthroplasty.

This clinical practice guideline is based on a systematic review of published studies on the management of adult patients undergoing total hip replacement (THR) or total knee replacement (TKR) aimed specifically at preventing symptomatic pulmonary embolism (PE). The guideline emphasizes the need to assess the patient's risk for both PE and postoperative bleeding. Mechanical prophylaxis and early mobilization are recommended for all patients. Chemoprophylactic agents were evaluated using a systematic literature review. Forty-two studies met eligibility criteria, of which 23 included patients who had TKR and 25 included patients who had THR. The following statements summarize the recommendations for chemoprophylaxis: Patients at standard risk of both PE and major bleeding should be considered for aspirin, low-molecular-weight heparin (LMWH), synthetic pentasaccharides, or warfarin with an international normalized ratio (INR) goal of < or =2.0. Patients at elevated (above standard) risk of PE and at standard risk of major bleeding should be considered for LMWH, synthetic pentasaccharides, or warfarin with an INR goal of < or =2.0. Patients at standard risk of PE and at elevated (above standard) risk of major bleeding should be considered for aspirin, warfarin with an INR goal of < or =2.0, or none. Patients at elevated (above standard) risk of both PE and major bleeding should be considered for aspirin, warfarin with an INR goal of < or =2.0, or none.

Lateral retinacular release during primary total knee arthroplasty: effect on outcomes and complications.

Intraoperative lateral retinacular release performed during primary total knee arthroplasty (TKA) can improve patellar tracking. This study compares the outcomes of patients who did and did not have lateral retinacular release during primary TKA. One thousand one hundred eight consecutive primary TKAs were reviewed. Lateral release was performed on 314 patients; 794 patients did not undergo release. Comparisons of range of motion, Knee Society Score, and postoperative complications were made between the 2 groups. At an average follow-up of 4.7 years, no statistically significant difference in range of motion, Knee Society Score, or postoperative complications of patella fracture, subluxation, postoperative manipulation, or wound complications was demonstrated. Lateral retinacular release to achieve improved patellar tracking does not compromise the clinical outcomes or complication rate of primary TKA.

Postthrombotic syndrome after asymptomatic deep vein thrombosis following total knee and hip arthroplasty.

Lower extremity deep vein thrombosis (DVT) is relatively common after total knee arthroplasty (TKA) and total hip arthroplasty (THA). In this study, we sought to identify whether post-thrombotic syndrome is a significant risk in patients with asymptomatic DVT after TKA and THA. Included in the study were 186 patients (203 lower extremities) who had undergone routine lower extremity venography after TKA or THA between 1989 and 1993. Patients were contacted a minimum of 7 years after surgery. Postoperative varicose veins occurred in 8% of limbs without DVT compared with 12% of limbs with DVT. Hyperpigmentation occurred in 13% of limbs without DVT and in 16% and 18% of limbs with proximal and distal DVT, respectively. Swelling occurred in 6% of limbs without DVT, in 8% of limbs with proximal DVT, and in 12% of limbs with distal DVT. None of these differences was statistically significant, and there were no differences for proximal versus distal DVT. There was no significant increase in risk for postthrombotic syndrome after asymptomatic proximal or distal DVT after TKA or THA.

Stiffness after total knee arthroplasty.

BACKGROUND: Stiffness is an uncommon but disabling problem after total knee arthroplasty. The prevalence of stiffness after knee replacement has not been well defined in the literature. In addition, the outcomes of revision surgery for a stiff knee following arthroplasty have not been evaluated in a large series of patients, to our knowledge. The purposes of this study were to define the prevalence of stiffness after primary total knee arthroplasty and to evaluate the efficacy of revision surgery for treatment of the stiffness. METHODS: We defined a stiff knee as one having a flexion contracture of 15 degrees and/or <75 degrees of flexion. Two separate groups were evaluated. First, the results of 1000 consecutive primary total knee replacements were reviewed to determine the prevalence of stiffness. Second, the results of fifty-six revisions performed because of stiffness, sometimes associated with pain or component loosening, after primary total knee arthroplasty were evaluated. RESULTS: The prevalence of stiffness was 1.3%, at an average of thirty-two months postoperatively. The patients with a stiff knee had had significantly less preoperative extension and flexion than did those without a stiff knee (p < 0.0001). There were no significant differences in age, gender, implant design, diagnosis, or the need for lateral release between the patients with and without stiffness. The second cohort, of knees revised because of stiffness, were followed for an average of forty-three months. The mean Knee Society score improved from 38.5 points preoperatively to 86.7 points at the time of follow-up; the mean Knee Society function score, from 40.0 to 58.4 points; and the mean Knee Society pain score, from 15.0 to 46.9 points. The mean flexion contracture decreased from 11.3 degrees to 3.2 degrees , the mean flexion improved from 65.8 degrees to 85.4 degrees , and the mean arc of motion improved from 54.6 degrees to 82.2 degrees . The arc of motion improved in 93% of the knees, and flexion increased in 80%. Extension improved in 63%, and it remained unchanged in 30%. CONCLUSIONS: The prevalence of stiffness in our series of 1000 primary knee arthroplasties was 1.3%. Revision surgery was a satisfactory treatment option for stiffness, as the Knee Society scores improved, the flexion contractures diminished, and 93% of the knees had an increased arc of motion. However, the results suggest that the benefits are modest.

Ximelagatran versus warfarin for the prevention of venous thromboembolism after total knee arthroplasty. A randomized, double-blind trial.

BACKGROUND: Warfarin is used for prophylaxis of venous thromboembolism in patients undergoing total knee arthroplasty. However, it is associated with rates of deep venous thrombosis (DVT) of approximately 38% to 55% and requires routine coagulation monitoring and frequent dose adjustment. Ximelagatran, an oral direct thrombin inhibitor, has shown promising efficacy and tolerability in patients undergoing total hip or knee arthroplasty. OBJECTIVE: To compare the efficacy and safety of ximelagatran and warfarin for prophylaxis of venous thromboembolism after total knee arthroplasty. DESIGN: Randomized, double-blind, parallel-group trial. SETTING: 74 North American hospitals. PATIENTS: 680 patients who had undergone total knee arthroplasty. INTERVENTION: 7 to 12 days of treatment with oral ximelagatran, 24 mg twice daily, starting on the morning after surgery, or warfarin (target international normalized ratio, 2.5 [range, 1.8 to 3.0]), starting on the evening of the day of surgery. MEASUREMENTS: Principal end points were asymptomatic DVT on mandatory venography; symptomatic DVT confirmed by ultrasonography or venography; symptomatic, objectively proven pulmonary embolism; and bleeding. All were assessed by blinded adjudication locally and at a central study laboratory. RESULTS: On central adjudication, incidence of venous thromboembolism was 19.2% (53 of 276 patients) in the ximelagatran group and 25.7% (67 of 261 patients) in the warfarin group (difference, -6.5 percentage points [95% CI, -13.5 to 0.6 percentage points]; P = 0.070). On local assessment, incidence was 25.4% in the ximelagatran group and 33.5% in the warfarin group (P = 0.043). In the ximelagatran and warfarin groups, respectively, major bleeding occurred in 1.7% and 0.9% of patients and minor bleeding occurred in 7.8% and 6.4% of patients. No variables related to bleeding differed significantly between the two groups. CONCLUSIONS: For prophylaxis of venous thromboembolism, fixed-dose ximelagatran started the morning after total knee arthroplasty is well tolerated and at least as effective as warfarin, but it does not require coagulation monitoring or dose adjustment.

Stiffness after total knee arthroplasty. Prevalence of the complication and outcomes of revision.

BACKGROUND: Stiffness is an uncommon but disabling problem after total knee arthroplasty. The prevalence of stiffness after knee replacement has not been well defined in the literature. In addition, the outcomes of revision surgery for a stiff knee following arthroplasty have not been evaluated in a large series of patients, to our knowledge. The purposes of this study were to define the prevalence of stiffness after primary total knee arthroplasty and to evaluate the efficacy of revision surgery for treatment of the stiffness. METHODS: We defined a stiff knee as one having a flexion contracture of >/=15 degrees and/or <75 degrees of flexion. Two separate groups were evaluated. First, the results of 1000 consecutive primary total knee replacements were reviewed to determine the prevalence of stiffness. Second, the results of fifty-six revisions performed because of stiffness, sometimes associated with pain or component loosening, after primary total knee arthroplasty were evaluated. RESULTS: The prevalence of stiffness was 1.3%, at an average of thirty-two months postoperatively. The patients with a stiff knee had had significantly less preoperative extension and flexion than did those without a stiff knee (p < 0.0001). There were no significant differences in age, gender, implant design, diagnosis, or the need for lateral release between the patients with and without stiffness. The second cohort, of knees revised because of stiffness, were followed for an average of forty-three months. The mean Knee Society score improved from 38.5 points preoperatively to 86.7 points at the time of follow-up; the mean Knee Society function score, from 40.0 to 58.4 points; and the mean Knee Society pain score, from 15.0 to 46.9 points. The mean flexion contracture decreased from 11.3 degrees to 3.2 degrees, the mean flexion improved from 65.8 degrees to 85.4 degrees, and the mean arc of motion improved from 54.6 degrees to 82.2 degrees. The arc of motion improved in 93% of the knees, and flexion increased in 80%. Extension improved in 63%, and it remained unchanged in 30%. CONCLUSIONS: The prevalence of stiffness in our series of 1000 primary knee arthroplasties was 1.3%. Revision surgery was a satisfactory treatment option for stiffness, as the Knee Society scores improved, the flexion contractures diminished, and 93% of the knees had an increased arc of motion. However, the results suggest that the benefits are modest.

Response bias: effect on outcomes evaluation by mail surveys after total knee arthroplasty.

BACKGROUND: Mail survey questionnaires are increasingly being used for follow-up evaluations to gauge satisfaction and performance after total joint arthroplasty. Responses to questionnaires are subject to a variety of possible biases. We evaluated response behavior in a mail survey of patients who had had a total knee arthroplasty. METHODS: A ten-question survey that evaluated satisfaction, general health, and Knee Society knee function and clinical scores was mailed to 472 patients who had undergone consecutive primary total knee arthroplasties from 1996 to 1998. The 83% who responded were stratified as early, late, and repeat-mailing responders. The 17% who failed to respond after two mailings were considered nonresponders. All of the nonresponders were eventually contacted. The groups were compared with regard to their scores at the preoperative office visit, at the most recent office visit, and on the mail survey. RESULTS: In the mail survey, the patients who responded earliest gave the highest satisfaction ratings and the nonresponders gave the poorest ratings (p < 0.001). Similarly, the mean Knee Society knee score (and standard deviation) was significantly higher for the early responders (82.7 +/- 19.0) than for the nonresponders (66.9 +/- 16.0), as was the mean function score (68.8 +/- 24.1 compared with 48.4 +/- 12.5) and the mean pain score (39.8 +/- 13.9 compared with 27.0 +/- 9.7) (all p < 0.0001). The change between the preoperative and mail survey Knee Society knee scores was significantly higher for the early responders (46.12 +/- 25.71) than for the nonresponders (28.45 +/- 23.62), as was the change in the mean function scores (18.87 +/- 22.52 compared with 5.34 +/- 20.05) and the change in the mean pain scores (23.57 +/- 17.76 compared with 10.67 +/- 12.93) (all p < 0.0001). CONCLUSIONS: Patients who do not respond to mail surveys used for follow-up are unique in that they report significantly poorer outcomes than do responders. This potential response bias should be considered in all follow-up analyses. Because it may be difficult to attain 100% response rates in very large series of patients, division of the study cohort into more manageable segments is advised to achieve a more complete response rate. The assessment of patients who are lost to follow-up is an important and necessary component in the accurate analysis of outcomes after arthroplasty.