Work Relative Value Units Do Not Adequately Support the Burden of Infection Management in Revision Knee Arthroplasty.

BACKGROUND: Revision total knee arthroplasty for infection is challenging. Septic revisions, whether 1-stage or 2-stage, may require more time and effort than comparable aseptic revisions. However, the burden of infection may not be reflected by the relative value units (RVUs) assigned to septic revision compared with aseptic revision. The purposes of this study were to compare the RVUs of aseptic and septic revision total knee arthroplasties and to calculate the RVU per minute for work effort. METHODS: The American College of Surgeons National Surgical Quality Improvement Program (ACS NSQIP) database was analyzed for the years 2006 to 2017. The Current Procedural Terminology (CPT) code 27487 and the International Classification of Diseases, Ninth Revision (ICD-9) code 996.XX, excluding 996.6X, were used to identify all aseptic revision total knee arthroplasties (n = 12,907). The CPT code 27487 and the ICD-9 code 996.6X were used to determine all 1-stage septic revision total knee arthroplasties (n = 891). The CPT codes 27488 and 11981 were used to identify the first stage of a 2-stage revision (n = 293). The CPT codes 27447 and 11982 were used to identify the second stage of a 2-stage revision (n = 279). After 4:1 propensity score matching, 274 cases were identified per septic cohort (aseptic single-stage: n = 1,096). The RVU-to-dollar conversion factor was provided by the U.S. Centers for Medicare & Medicaid Services (CMS), and RVU dollar valuations were calculated. RESULTS: The septic second-stage revision was used as the control group for comparisons. The RVU per minute for the aseptic 2-component revision was 0.215, from a mean operative time of 148.95 minutes. The RVU per minute for the septic, 2-component, 1-stage revision was 0.199, from a mean operative time of 160.6 minutes. For septic, 2-stage revisions, the first-stage RVU per minute was 0.157, from a mean operative time of 138.1 minutes. The second-stage RVU per minute was 0.144, from a mean operative time of 170.0 minutes. Two-component aseptic revision total knee arthroplasty was valued the highest. CONCLUSIONS: Despite the increased complexity and worse postoperative outcomes associated with revision total knee arthroplasties for infection, the current physician reimbursement does not account for these challenges. This inadequate compensation may discourage providers from performing these operations and, in turn, make it more difficult for patients with periprosthetic joint infection to receive the necessary treatment. Therefore, the CPT code revaluation may be warranted for these procedures.

Automated detection & classification of knee arthroplasty using deep learning.

BACKGROUND: Preoperative identification of knee arthroplasty is important for planning revision surgery. However, up to 10% of implants are not identified prior to surgery. The purposes of this study were to develop and test the performance of a deep learning system (DLS) for the automated radiographic 1) identification of the presence or absence of a total knee arthroplasty (TKA); 2) classification of TKA vs. unicompartmental knee arthroplasty (UKA); and 3) differentiation between two different primary TKA models. METHOD: We collected 237 anteroposterior (AP) knee radiographs with equal proportions of native knees, TKA, and UKA and 274 AP knee radiographs with equal proportions of two TKA models. Data augmentation was used to increase the number of images for deep convolutional neural network (DCNN) training. A DLS based on DCNNs was trained on these images. Receiver operating characteristic (ROC) curves with area under the curve (AUC) were generated. Heatmaps were created using class activation mapping (CAM) to identify image features most important for DCNN decision-making. RESULTS: DCNNs trained to detect TKA and distinguish between TKA and UKA both achieved AUC of 1. Heatmaps demonstrated appropriate emphasis of arthroplasty components in decision-making. The DCNN trained to distinguish between the two TKA models achieved AUC of 1. Heatmaps showed emphasis of specific unique features of the TKA model designs, such as the femoral component anterior flange shape. CONCLUSIONS: DCNNs can accurately identify presence of TKA and distinguish between specific arthroplasty designs. This proof-of-concept could be applied towards identifying other prosthesis models and prosthesis-related complications.

Current practice of orthopaedic surgical skills training raises performance of supervised residents in total knee arthroplasty to levels equal to those of orthopaedic surgeons.

AIM: To investigate whether the current, generally accepted practice of orthopaedic surgical skills training can raise the performance of supervised residents to levels equal to those of experienced orthopaedic surgeons when it comes to clinical outcomes or implant position after total knee arthroplasty. METHODS: In a retrospective analysis of primary total knee arthroplasty outcomes (minimum follow-up of 12 months) procedures were split into two groups: supervised orthopaedic residents as first surgeon (group R), and experienced senior orthopaedic surgeons as first surgeon (group S). Outcome data that were compared 1 year postoperatively were operation times, complications, revisions, Knee Society Scores (KSS) and radiological implant positions. RESULTS: Of 642 included procedures, 220 were assigned to group R and 422 to group S. No statistically significant differences between the two groups were found in patient demographics. Operation time differed significantly (group R: 81.3 min vs. group S: 71.3 min (p = 0.000)). No statistically significant differences were found for complications (p = 0.659), revision rate (p = 0.722), femoral angle (p = 0.871), tibial angle (p = 0.804), femoral slope (p = 0.779), tibial slope (p = 0.765) and KSS (p = 0.148). DISCUSSION AND CONCLUSION: Supervised residents needed 10 minutes extra operation time, but they provided the same quality of care in primary total knee arthroplasty as experienced orthopaedic surgeons concerning complication rates, revisions, implant position on radiographs and KSS. The currently used training procedure in which the supervising surgeon and the resident decide if the resident is ready to be first surgeon is safe for patients.

Definitional Differences of 'Outpatient' Versus 'Inpatient' THA and TKA Can Affect Study Outcomes.

BACKGROUND: There has been great interest in performing outpatient THA and TKA. Studies have compared such procedures done as outpatients versus inpatients. However, stated "outpatient" status as defined by large national databases such as the National Surgical Quality Improvement Program (NSQIP) may not be a consistent entity, and the actual lengths of stay of those patients categorized as outpatients in NSQIP have not been specifically ascertained and may in fact include some patients who are "observed" for one or more nights. Current regulations in the United States allow these "observed" patients to stay more than one night at the hospital under observation status despite being coded as outpatients. Determining the degree to which this is the case, and what, exactly, "outpatient" means in the NSQIP, may influence the way clinicians read studies from that source and the way hospital systems and policymakers use those data. QUESTIONS/PURPOSES: The purposes of this study were (1) to utilize the NSQIP database to characterize the differences in definition of "inpatient" and "outpatient" (stated status versus actual length of stay [LOS], measured in days) for THA and TKA; and (2) to study the effect of defining populations using different definitions. METHODS: Patients who underwent THA and TKA in the 2005 to 2014 NSQIP database were identified. Outpatient procedures were defined as either hospital LOS = 0 days in NSQIP or being termed "outpatient" by the hospital. The actual hospital LOS of "outpatients" was characterized. "Outpatients" were considered to have stayed overnight if they had a LOS of 1 day or longer. The effects of the different definitions on 30-day outcomes were evaluated using multivariate analysis while controlling for potential confounding factors. RESULTS: Of 72,651 patients undergoing THA, 529 were identified as "outpatients" but only 63 of these (12%) had a LOS = 0. Of 117,454 patients undergoing TKA, 890 were identified as "outpatients" but only 95 of these (11%) had a LOS = 0. After controlling for potential confounding factors such as gender, body mass index, functional status before surgery, comorbidities, and smoking status, we found "inpatient" THA to be associated with increased risk of any adverse event (relative risk, 2.643, p = 0.002), serious adverse event (relative risk, 2.455, p = 0.011), and readmission (relative risk, 2.775, p = 0.010) compared with "outpatient" THA. However, for the same procedure and controlling for the same factors, patients who had LOS > 0 were not associated with any increased risk compared with patients who had LOS = 0. A similar trend was also found in the TKA cohort. CONCLUSIONS: Future THA, TKA, or other investigations on this topic should consistently quantify the term "outpatient" because different definitions, stated status or actual LOS, may lead to different assignments of risk factors for postoperative complications. Accurate data regarding risk factors for complications after total joint arthroplasty are crucial for efforts to reduce length of hospital stay and minimize complications. LEVEL OF EVIDENCE: Level III, therapeutic study.

Total Knee Arthroplasty for Posttraumatic Osteoarthritis: Is it Time for a New Classification?

BACKGROUND: Total knee arthroplasty (TKA) is often the best answer for end-stage, posttraumatic osteoarthritis after intra-articular and periarticular fractures about the knee. Although TKA in this setting is often considered more technically demanding, outcomes are typically worse for patients. This study examines the intraoperative differences and 30-day outcomes in posttraumatic vs primary TKA cohorts. METHODS: Patients undergoing TKA were selected from the National Surgical Quality Improvement Program database from 2010 to 2013. Patients were stratified on the basis of concurrent procedures and administrative codes indicating posttraumatic diagnoses. Thirty-day complications were recorded, and multivariate analyses were performed to determine whether posttraumatic arthritis was a risk factor for poor outcomes. RESULTS: A total of 67,675 primary and 674 posttraumatic TKAs were identified. Posttraumatic TKA patients were on average younger and healthier than the primary TKA population. The posttraumatic TKA group had higher rates of superficial surgical site infections and bleeding requiring transfusion. History of posttraumatic knee osteoarthritis was found to be an independent risk factor for prolonged operative time, increased length of hospital stay, and 30-day hospital readmission. CONCLUSION: We have demonstrated increased intraoperative times, heightened transfusion requirements and surgical site infections, and higher readmission rates after conversion TKA in the posttraumatic cohort. In contrast to total hip arthroplasty, current diagnosis and reimbursement schemes do not differentiate posttraumatic patients from primary osteoarthritis groups undergoing TKA. We believe that classification reform would improve medical documentation and improve patient care.

Effect of age on cost-effectiveness of unicompartmental knee arthroplasty compared with total knee arthroplasty in the U.S.

BACKGROUND: Trade-offs between upfront benefits and later risk of revision of unicompartmental knee arthroplasty compared with those of total knee arthroplasty are poorly understood. The purpose of our study was to compare the cost-effectiveness of unicompartmental knee arthroplasty with that of total knee arthroplasty across the age spectrum of patients undergoing knee replacement. METHODS: Using a Markov decision analytic model, we compared unicompartmental knee arthroplasty with total knee arthroplasty with regard to lifetime costs, quality-adjusted life-years (QALYs), and incremental cost-effectiveness ratios (ICERs) from a societal perspective for patients undergoing surgery at forty-five, fifty-five, sixty-five, seventy-five, or eighty-five years of age. Transition probabilities were estimated from the literature; survival, from the Swedish Knee Arthroplasty Register; and costs, from the literature and the Healthcare Cost and Utilization Project (HCUP) database. Costs and QALYs were discounted at 3.0% annually. We conducted sensitivity analyses to test the robustness of model estimates and threshold analyses. RESULTS: For patients sixty-five years of age and older, unicompartmental knee arthroplasty dominated total knee arthroplasty, with lower lifetime costs and higher QALYs. Unicompartmental knee arthroplasty was no longer cost-effective at a $100,000/QALY threshold when total knee arthroplasty rehabilitation costs were reduced by two-thirds or more for these older patients. Lifetime societal savings from utilizing unicompartmental knee arthroplasty in all older patients (sixty-five or older) in 2015 and 2020 were $56 to $336 million and $84 to $544 million, respectively. In the forty-five and fifty-five-year-old age cohorts, total knee arthroplasty had an ICER of $30,300/QALY and $63,000/QALY, respectively. Unicompartmental knee arthroplasty became cost-effective when its twenty-year revision rate dropped from 27.8% to 25.7% for the forty-five-year age group and from 27.9% to 26.7% for the fifty-five-year age group. CONCLUSIONS: Unicompartmental knee arthroplasty is an economically attractive alternative in patients sixty-five years of age or older, and modest improvements in implant survivorship could make it a cost-effective alternative in younger patients.

Feasibility and safety of performing outpatient unicompartmental knee arthroplasty.

PURPOSE: Unicompartmental knee arthroplasty (UKA) has a faster short-term recovery than total knee arthroplasty (TKA). The purpose of this study was to determine the feasibility and safety of performing outpatient UKAs in a consecutive group of patients presenting with unicompartmental knee osteoarthritis. METHODS: A total of 105 consecutive patients underwent unicompartmental arthroplasty before noon with the intention of being discharged as an outpatient. All patients followed an established rapid recovery pathway to facilitate a same-day discharge. Post-operative complications and hospital readmissions were retrospectively recorded for all patients at one week and at three months after surgery. RESULTS: All of the 105 patients (100 %) indicated for outpatient UKA could be discharged home on the same day of surgery. No patients required readmission within the first week post-operatively, while one patient required readmission between week one and week 12. The single patient who required readmission developed a post-operative infection requiring irrigation/debridement with polyethylene liner exchange and intravenous antibiotics. CONCLUSION: Using an established, multidisciplinary, rapid recovery protocol, outpatient UKA is safe and feasible in the vast majority of patients.

Lateral unicondylar knee arthroplasty (UKA): contemporary indications, surgical technique, and results.

Unicompartmental femoro-tibial osteoarthritis usually affects the medial compartment of the knee, but in 10%, the lateral compartment is primarily involved. Femoral osteotomy is attractive to avoid TKA in younger patients with low-grade unicompartmental osteoarthritis and a valgus deformity. However, only limited functional results can be expected for patients with Ahlback grade 2 or greater osteoarthritis. Moreover, because of previous skin incisions and hardware removal, TKA after femoral osteotomy remains a complex procedure with poor functional results. Unicompartmental knee arthroplasty for both the medial and the lateral compartments has been performed since the 1970s. In a patient with involvement of only one compartment, a medial or a lateral UKA can provide a quicker recovery and enhanced function when compared to TKA. In addition, it preserves bone stock and can be "easily" revised by a TKA. Technical improvements, combined with strict patient selection, have resulted in ten year survivorships greater than 90%. However, lateral UKA is technically more challenging than medial UKA due to the lower number of indications, as well as the functional anatomy of the lateral compartment. The goals of this article are to present up-to-date information concerning indications, patients' selection, surgical technique and results of lateral compartment UKA.

Computer-assisted unicompartmental knee arthroplasty using dedicated software versus a conventional technique.

PURPOSE: The aim of this study was to retrospectively compare the results of two matched-paired groups of patients who had undergone a medial unicompartmental knee arthroplasty (UKA) performed using either a conventional or a non-image-guided navigation technique specifically designed for unicompartmental prosthesis implantation. METHODS: Thirty-one patients with isolated medial-compartment knee arthritis who underwent an isolated navigated UKA were included in the study (group A) and matched with patients who had undergone a conventional medial UKA (group B). The same inclusion criteria were used for both groups. At a minimum of six months, all patients were clinically assessed using the Knee Society Score (KSS) and the Western Ontario and McMaster Osteoarthritis Index (WOMAC) index. Radiographically, the frontal-femoral-component angle, the frontal-tibial-component angle, the hip-knee-ankle angle and the sagittal orientation of components (slopes) were evaluated. Complications related to the implantation technique, length of hospital stay and surgical time were compared. RESULTS: At the latest follow-up, no statistically significant differences were seen in the KSS, function scores and WOMAC index between groups. Patients in group B had a statistically significant shorter mean surgical time. Tibial coronal and sagittal alignments were statistically better in the navigated group, with five cases of outliers in the conventional alignment technique group. Postoperative mechanical axis was statistically better aligned in the navigated group, with two cases of overcorrection from varus to valgus in group B. No differences in length of hospital stay or complications related to implantation technique were seen between groups. CONCLUSION: This study shows that a specifically designed UKA-dedicated navigation system results in better implant alignment in UKA surgery. Whether this improved alignment results in better clinical results in the long term has yet to be proven.

Revision rates after knee replacement. Cumulative results from worldwide clinical studies versus joint registers.

OBJECTIVE: To assess revision rates after knee arthroplasty by comparing the cumulative results from worldwide clinical studies and arthroplasty registers. We hypothesised that the revision rate of all clinical studies of a given implant and register data would not differ significantly. METHODS: A systematic review of clinical studies in indexed peer-reviewed journals was performed followed by internal and external validation. Parameters for measurement of revision were applied (Revision for any reason, Revisions per 100 observed component years). Register data served as control group. RESULTS: Thirty-six knee arthroplasty systems were identified to meet the inclusion criteria: 21 total knee arthroplasty (TKA) systems, 14 unicondylar knee arthroplasty (UKA) systems, one patello-femoral implant system. For 13 systems (36%), no published study was available that contained revision data. For 17 implants (47%), publications were available dealing with radiographic, surgical or technical details, but power was too weak to compare revision rates at a significant level. Six implant systems (17%) had a significant number of revisions published and were finally analysed. In general, developers report better results than independent users. Studies from developers represent an overproportional share of all observed component years. Register data report overall 10-year revision rates of TKA of 6.2% (range: 4.9-7.8%), rates for UKA are 16.5% (range: 9.7-19.6%). CONCLUSION: Revision rates of all clinical studies of a given implant do not differ significantly from register data. However, significant differences were found between the revision rates published by developers and register data. Therefore the different data need to be interpreted in the context of the source of the information.

Evaluation of centers of excellence program for knee and hip replacement.

BACKGROUND: Medicare and private plans are encouraging individuals to seek care at hospitals that are designated as centers of excellence. Few evaluations of such programs have been conducted. This study examines a large national initiative that designated hospitals as centers of excellence for knee and hip replacement. OBJECTIVE: Comparison of outcomes and costs associated with knee and hip replacement at designated hospitals and other hospitals. RESEARCH DESIGN: Retrospective claims analysis of approximately 54 million enrollees. STUDY POPULATION: Individuals with insurance from one of the sponsors of this centers of excellence program who underwent a primary knee or hip replacement in 2007-2009. OUTCOMES: Primary outcomes were any complication within 30 days of discharge and costs within 90 days after the procedure. RESULTS: A total of 80,931 patients had a knee replacement and 39,532 patients had a hip replacement of which 52.2% and 56.5%, respectively, were performed at a designated hospital. Designated hospitals had a larger number of beds and were more likely to be an academic center. Patients with a knee replacement at designated hospitals did not have a statistically significantly lower overall complication rate with an odds ratio of 0.90 (P=0.08). Patients with hip replacement treated at designated hospitals had a statistically significant lower risk of complications with an odds ratio of 0.80 (P=0.002). There was no significant difference in 90-day costs for either procedure. CONCLUSIONS: Hospitals designated as joint replacement centers of excellence had lower rates of complications for hip replacement, but there was no statistically significant difference for knee replacement. It is important to validate the criteria used to designate centers of excellence.

Resource utilization and costs before and after total joint arthroplasty.

BACKGROUND: The purpose of this study was to compare pre- and post-surgical healthcare costs in commercially insured total joint arthroplasty (TJA) patients with osteoarthritis (OA) in the United States (U.S.). METHODS: Using a large healthcare claims database, we identified patients over age 39 with hip or knee OA who underwent unilateral primary TJA (hip or knee) between 1/1/2006 and 9/30/2007. Utilization of healthcare services and costs were aggregated into three periods: 12 months "pre-surgery," 91 days "peri-operative," and 3 to 15 month "follow-up," Mean total pre-surgery costs were compared with follow-up costs using Wilcoxon signed-rank test. RESULTS: 14,912 patients met inclusion criteria for the study. The mean total number of outpatient visits declined from pre-surgery to follow-up (18.0 visits vs 17.1), while the percentage of patients hospitalized increased (from 7.5% to 9.8%) (both p < 0.01). Mean total costs during the follow-up period were 18% higher than during pre-surgery ($11,043 vs. $9,632, p < 0.01), largely due to an increase in the costs of inpatient care associated with hospital readmissions ($3,300 vs. $1,817, p < 0.01). Pharmacotherapy costs were similar for both periods ($2013 [follow-up] vs. $1922 [pre-surgery], p = 0.33); outpatient care costs were slightly lower in the follow-up period ($4338 vs. $4571, p < 0.01). Mean total costs for the peri-operative period were $36,553. CONCLUSIONS: Mean total utilization of outpatient healthcare services declined slightly in the first year following TJA (exclusive of the peri-operative period), while mean total healthcare costs increased during the same time period, largely due to increased costs associated with hospital readmissions. Further study is necessary to determine whether healthcare costs decrease in subsequent years.

Development of a new Knee Society scoring system.

BACKGROUND: The Knee Society Clinical Rating System was developed in 1989 and has been widely adopted. However, with the increased demand for TKA, there is a need for a new, validated scoring system to better characterize the expectations, satisfaction, and physical activities of the younger, more diverse population of TKA patients. QUESTIONS/PURPOSES: We developed and validated a new Knee Society Scoring System. METHODS: We developed the new knee scoring system in two stages. Initially, a comprehensive survey of activities was developed and administered to 101 unilateral TKA patients (53 women, 48 men). A prototype knee scoring instrument was developed from the responses to the survey and administered to 497 patients (204 men, 293 women; 243 postoperatively, 254 preoperatively) at 15 medical institutions within the United States and Canada. Objective and subjective data were analyzed using standard statistical and psychometric procedures and compared to the Knee Injury and Osteoarthritis Score and SF-12 scores for validation. Based on this analysis, minor modifications led to the new Knee Society Scoring System. RESULTS: We found the new Knee Society Scoring System to be broadly applicable and to accurately characterize patient outcomes after TKA. Statistical analysis confirmed the internal consistency, construct and convergent validity, and reliability of the separate subscale measures. CONCLUSIONS: The new Knee Society Scoring System is a validated instrument based on surgeon- and patient-generated data, adapted to the diverse lifestyles and activities of contemporary patients with TKA. This assessment tool allows surgeons to appreciate differences in the priorities of individual patients and the interplay among function, expectation, symptoms, and satisfaction after TKA.

The validity of using administrative claims data in total joint arthroplasty outcomes research.

The purpose of this study was to evaluate concordance between administrative and clinical diagnosis and procedure codes for revision total joint arthroplasty (TJA). Concordance between administrative and clinical records was determined for 764 consecutive revision TJA procedures from 4 hospitals. For revision total hip arthroplasty, concordance between clinical diagnoses and administrative claims was very good for dislocation, mechanical loosening, and periprosthetic joint infection (all kappa > 0.6), but considerably lower for prosthetic implant failure/breakage and other mechanical complication (both kappa < 0.25). Similarly, for revision total knee arthroplasty diagnoses, concordance was very good for periprosthetic fracture, periprosthetic joint infection, mechanical loosening, and osteolysis (all kappa > 0.60), but much lower for implant failure/breakage and other mechanical complication (both kappa < 0.24). Concordance for TJA-specific procedure codes was very good only for revision total knee arthroplasty patellar component revisions and tibial insert exchange procedures. Total (all-component) revisions were overcoded for hips (00.70) and undercoded for knees (00.80). Improved clinical documentation and continued education are needed to enhance the value of these codes.

Risk classification for primary knee arthroplasty.

We devised a 4-group classification for primary TKA patients: C0, fit patient, simple arthritis; CI, fit patient, complex arthritis; CII, medically unfit patient with simple pattern; and CIII, unfit patient with complex arthritis. Patient fitness and arthritis complexity were based on the literature. One hundred twenty-two patients, operated on by the senior author, were retrospectively placed into one of these 4 groups. We found the following: significantly increased cumulative complication risk in CII and CIII incomparison with C0 (P < .001), increased length of stay in CII and CIII (P < .001), and similar trends between C0 and CI and between CI and CII. This system is useful in preoperative planning, risk counseling, and surgeon selection. It identifies patients with a higher risk of complications and inpatient stay.

An application of the Dempster-Shafer theory of evidence to the classification of knee function and detection of improvement due to total knee replacement surgery.

This paper utilises a novel method for the classification of subjects with osteoarthritic and normal knee function. The classification method comprises a number of different components. Firstly, the method exploits the Dempster-Shafer theory of evidence allowing for a degree of ignorance in the subject's classification, i.e., a level of uncertainty as to whether a gait variable indicates osteoarthritis or not. Secondly, the inclusion of simplex plots allows both the classification of a subject, and the contribution of each associated gait variable to that classification, to be represented visually. As a result, the method is further able to highlight periodic changes in a subject's knee function due to total knee replacement surgery and subsequent recovery. The visual representation enables a simple clinical interpretation of the results from the quantitative analysis.

[Revision surgery for knee prostheses using the DRG system]. / Wechseloperationen in der Kniegelenkendoprothetik im DRG-System.

Due to an increasing life expectancy and earlier primary implantation of total knee replacements, the number of patients requiring revision surgery in Germany is increasing by 7% every year. These revision cases belong to the most treatment and cost intensive operations in joint replacement surgery. Presently, the description of these procedures in the German DRG system, which defines the financial reimbursement for the hospitals, is changing yearly with the development of new catalogues. The changes made from 2003 to 2005 are outlined in the following article. A correct depiction of the treatment and procedures required in such cases is a prerequisite for an adequate reimbursement. In the long-term, hospitals will only be able to offer such complex treatment forms if the financial compensation correctly reflects the costs incurred.

Rates of revision knee replacement in Ontario, Canada.

BACKGROUND: The present study was designed to measure the longevity of knee replacements and to assess the determinants of revision knee replacements in order to enhance the potential for informed decision-making. METHODS: Data on all hospitalizations for knee replacement that occurred in Ontario, Canada, between April 1, 1984, and March 31, 1991, were acquired. To calculate the rates of revision knee replacement, two algorithms were developed: one distinguished primary knee replacements from revision knee replacements, and the second linked revision knee replacements to primary knee replacements. The Kaplan-Meier method was used to assess survivorship (absence of a revision) for primary knee replacement. A proportional-hazards regression model was estimated to assess the role of independent variables on the survival of primary knee replacements. RESULTS: During the period of the study, 7.0 percent (1301) of 18,530 knee replacements were classified as revisions. Significant differences were identified between hospitalizations for primary and revision knee replacements in terms of the patient and hospital characteristics. Patients who were more than fifty-five years old, lived in a rural area, or had a diagnosis of rheumatoid arthritis had a significantly (p < 0.05) longer duration before revision than did other patients. Primary knee replacements performed in a teaching or specialty hospital had a significantly (p < 0.05) shorter duration before revision than did those performed in a non-teaching hospital. The long-term rates of revision were uniformly low. Estimates of the proportion of knee replacements that would need to be revised within seven years ranged from a low of 4.3 percent, with use of the algorithm for the longest time to revision, to a high of 8.0 percent, with use of the algorithm for the shortest time to revision. CONCLUSIONS: Revision of a primary knee replacement was a rare event that depended on a patient's age, gender, and place of residence as well as on the hospital where the primary knee replacement was performed. Estimates of the rates of revision knee replacement after almost seven years ranged from a low of 4.3 percent to a high of 8.0 percent.