We found little consistent evidence for an important relation between provider volumes and early outcomes of elective primary TJR in Ontario. Our results are largely in keeping with previous Ontario research11,12
but conflict with several American studies, which have consistently reported volume–outcome relations for TJR.7–9,18–21
One possible explanation is that surgeon and hospital procedure volumes are relatively greater and exhibit less variation in Ontario. For instance, whereas half of US joint replacements are performed in hospitals with fewer than 100 procedures per year,19,22
fewer than 20% are performed in such hospitals in Ontario.
Importantly, we found that rates of complications, even among lower-volume providers, were generally low and, where comparable, similar to or less than those in the United States. Overall, about 6 per 1000 Ontarians died within 90 days of joint replacement. This is roughly the same rate reported by Katz and colleagues19
and Soohoo and colleagues21
in US Medicare knee replacement patients, and about two-thirds that observed in a 1995 hip replacement cohort.7
Our 1-year revision rates (about 1.5% for THR and 1% for TKR) are similar to those observed in the United States, United Kingdom, Australia and Sweden.9,23,24
Taken together, our findings provide little support for regionalizing joint replacement surgery in Ontario. Even if consistent volume–outcome effects were observed, the small absolute improvements potentially achievable through regionalization would have to be weighed against other important considerations. Regionalization could make joint replacement procedures less accessible, particularly to rural patients, and could contribute to longer waiting times, neither of which would benefit patients.
Several of our findings were unexpected. In-hospital complications were more frequent with THR than with TKR, and complication rates increased with comorbidity for hip but not knee replacement. Similarly, THR (but not TKR) patients admitted to teaching hospitals had higher odds of readmission for amputation, fusion or excision relative to those admitted to nonteaching hospitals. Higher-volume surgeons had relatively shorter ALOSs after both procedures, but no such associations were observed for hospital volume. Previously, Kreder and colleagues11,12
studied in-hospital complications and found associations with age and comorbidity for both THR and TKR. The fact that we excluded a greater proportion of patients than Kreder and colleagues11,12
may have contributed to the absence of such findings in our study. Age and comorbidity were important predictors of outcome in other studies of THR.22,25–27
There are several possible explanations for why teaching hospitals may have relatively higher complication rates. Patients referred to teaching hospitals may be surgically complex in ways that are not captured by standard measures of comorbidity. For example, teaching hospital surgeons may be more likely than others to operate on patients who have poor peripheral circulation, severe dysplasia, previous joint infection or metabolic bone disease. In addition, some complications in teaching hospitals may be attributable to physician trainees. In the only other Ontario study to consider TJR outcomes as a function of hospital teaching status, Coyte and colleagues28
also found relatively higher revision rates in teaching hospitals. That multiple studies22,23,29
have reported surgeon- but not hospital-volume effects on hip-replacement outcomes lends support to the notion that THR outcomes are particularly sensitive to surgical technique.
Relations between provider volume and length of hospital stay are complex. In earlier Ontario studies,11,12
both higher-volume surgeons and higher-volume hospitals had relatively shorter average ALOSs. In a recent study of TJR in the United Kingdom, Judge and colleagues30
also found relatively shorter lengths of stay in higher-volume trusts. These findings are consistent with the idea that higher-volume providers are more likely to employ policies or have access to resources (e.g., home care and rehabilitation services) that promote shorter ALOSs. As expected, we found that patients who were discharged to rehabilitation units or facilities had significantly shorter ALOSs. The fact that we did not observe a hospital-volume effect on ALOS is therefore most likely because of simultaneous adjustment for discharge destination. Future studies should consider whether joints replaced by higher-volume surgeons are less costly.
Strengths and limitations
To our knowledge, this is the largest Canadian study of TJR outcomes and the only one to report results for THR and TKR simultaneously. Whereas American studies have been confined largely to US Medicare recipients (who are aged 65 years and older), we included adults of all ages. This is important because several studies (including ours) have shown that younger age groups are at higher risk for revision arthroplasty, particularly after TKR. 27
Further, because most studies of joint failure have not had access to information about procedure laterality and have not excluded patients who had prior joint replacement, it has been impossible for these studies to definitively link outcomes to the index procedures. Here we reduced the potential for such misclassification by studying the first joint replaced during the accrual period and by excluding those who had prior or subsequent joint replacement.
Like most researchers who use administrative data, we had limited clinical information with which to assess patient outcomes, surgical complexity and comorbidity, and no information about patients’ pain or functional status. Suboptimal patient-focused outcomes do not always result in surgical intervention. In fact, Katz and colleagues31
found that patients who had TKR performed by low-volume surgeons in low-volume hospitals were twice as likely to have poor functional status as those operated on by high-volume surgeons in high-volume settings. This is an important dimension that is absent from studies of administrative data. Importantly, we also had no data about the reasons for revision procedures or cause of death.
Second, although evidence suggests that relations between provider volume and joint failure disappear after about 1 year,9,10,23
we cannot comment on longer-term outcomes because we followed patients for only 1 year. Third, owing to the rarity of the clinical outcomes, we used a composite outcome measure for in-hospital complications, as well as for amputation, fusion or excision at 1 year. Despite the increased power, the CIs around the adjusted ORs were wide. Fourth, the large number of comparisons increased the probability of finding differences by chance. Thus, marginally significant differences should be viewed skeptically. Finally, we studied elective primary TJR. Our findings may not be generalizable to urgent procedures, revision procedures or partial joint replacements. Although adverse outcomes are relatively more frequent after revision arthroplasty,7,10,22
in one study, volume–outcome associations with revision THR were less striking than with primary THR.7
Given the growing burden of revision arthroplasty in Ontario, volume–outcome studies of these procedures are warranted.