Summary of main findings
In this analysis of data from an arthroplasty registry in Australia, we found high overall rates of post-operative complications, with 9.5% of THA and 14.4% of TKA patients having experienced a major complication by 6 months post-surgery; 34.0% of THA and 46.6% of TKA patients experienced a minor complication over the same time frame.
Comparison with previous studies
Complication rates in our registry were higher than those reported by NSQIP, which reported major and minor 30-day complication rates at 4.2% and 2.17% for THA and 1.83% and 3.20% for TKA, respectively6,18. However, our registry follows patients to 6 months rather than 30 days; this longer follow-up period may account for at least part of the difference in complication rates. Our time period was chosen to allow adequate time for improvement in function and complications to surface24.
We found higher rates of surgical site infections to those in the literature. In our TKA cohort, for example, 4.2%% and 0.2% of patients reported SSI requiring oral or IV antibiotics, respectively. A Hong Kong study analysing elective unilateral TKA by a single surgeon over 10 years observed rates of SSI requiring oral antibiotics at 0.66%, whilst a slightly larger Taiwanese study reported a rate of 1.52%25,26. A large UK prospective study showed superficial SSI at 2.23% for THA patients compared to our rates of 1.6% and 0.5% requiring oral and IV antibiotics, respectively27. Surgical site infections are important as they can lead to prosthetic joint infections (PJI) which require revision surgery28. Rates of PJI requiring revision surgery have been observed in large international studies including the US, Europe, Australia and New Zealand at 0.6%-1.6% for THA and 0.7%-1.5% for TKA12,29–33 which is higher than the rates found in this study (THA=0.4%, TKA=0.1%). However, this is unsurprising as most studies investigating PJI observed a period of 12- to 24-months post-operatively compared to the 6-month period in this study. Our high rates of oral antibiotic use may reflect low prescribing thresholds rather than an underlying difference in superficial infections.
We found DVT rates of 0.8% and 1.8% for THA and TKA. These are higher than reported in previous studies using inpatient data in the US (0.24% and 0.45% for THA and TKA, respectively) and China (0.24% vs 0.71%), but lower than 90-days post-operatively in Korea (2.4% vs 3.4%) %)15,34,35, whilst a meta-analysis of patients receiving chemoprophylaxis following THA and TKA published rates of VTE at 1% for TKA and 0.5% for THA, again limited to the inpatient stay16. The variability seen in these rates may be due to both patient factors including comorbidities and cultural factors, and clinical factors, as such as mechanical and chemoprophylaxis. Previous studies have found higher rates of DVT in patients undergoing TKA compared to THA, and this was reflected in our study with higher rates of both PE and DVT in TKA patients compared to THA. This may be explained by the involvement of smaller calf veins that are affected in TKA compared to larger veins in THA which would take longer to become occluded and therefore symptomatic16. Tourniquet use may also contribute to the higher rate of DVT in TKA36.
Mortality and readmission
At 6 months, all-cause mortality rates were 0.2% for both procedures, which falls within the range of published 30- and 90-day rates of 0.05%-1.1% in the US, UK, Australia and Denmark37–42. Compared to readmission rates from US Medicare data, we found lower readmission rates at 6 months than the 30-day rates for THA and 90-day rates for TKA8,9,43. We found that infection was overall the most common reason for arthroplasty-related readmission in both procedures, followed by periprosthetic fracture and dislocation for THA and cellulitis for TKA. A single centre study at a US orthopaedic specialty hospital reported significantly lower rates of 0.33% and 0.21% for THA and TKA, respectively, at 30 days17. However, those numbers are limited to patients who re-present to the same hospital, and therefore those who present to different centres may not have been captured using this metric. Our data is advantageous in this regard as data are collected directly from patients and do not rely on re-presentation to the same institution.
Minor complications overall
We found significantly higher rates of minor complications in this study at 34.0% for THA and 46.6% for TKA compared to published rates of 2.7% for THA and 3.2% for TKA from NSQIP data6,18. The NSQIP data use hospital medical charts documented by medical staff to capture complications, whereas our registry used a combination of hospital data for the acute stay along with patient-reports collected by telephone interview at 6 months. In addition to ACORN registering a larger range of patient-reported minor complications, including hypotension, swelling and paraesthesia, it is possible that patients and surgeons have different conceptions of what constitutes a complication. For example, stiffness may indicate patients’ subjective experience, whilst rates of MUA may suggest an objective measurement by surgeons that indicates stiffness severe enough to require intervention. Disagreement in complication reporting rates between clinicians and patients has already been established following orthopaedic and general surgery44–48. Although minor complications such as stiffness, swelling and paraesthesia do not necessarily indicate procedure failure, they represent legitimate patient experience, and the absence of measurement standards to characterise their severity may impact the accuracy and reliability of complications data. Further, minor complications may reflect quality of care delivery. For example, high rates of pressure sores may reflect a lack of attention to early ambulation, while high rates of hypotension may reflect too high a dose of intra-operative opioid. Even minor complications are costly to the health system and may be important to patients thus are worth preventing.
Patient characteristics associated with complications
Our study found low back pain to be an independent predictor for major complications following either THA or TKA, and BMI as a risk factor for major complications following THA. BMI, longer operative time and higher American Society of Anaesthesiologist scores have been identified as independent predictors of postoperative complications overall in both THA and TKA patients13,49. Bleeding disorder and anaemia have further been identified as risk factors for major complications following THA, and low back pain has been shown to influence functional outcomes following arthroplasty procedures6,18,50,51. Further, in separate risk-adjusted models we found increasing age to be associated with reduced odds of reoperation, and female gender to be associated with decreased odds of readmission. These associations may reflect the selection of patient groups who have lower comorbidity load as eligible and appropriate for surgery. Geriatric patients aged over 85 are significantly less likely to receive TKA than their younger counterparts; it may be that among patients who do undergo arthroplasty, increased age reflects the selection process of appropriate surgical candidates rather than being a protective factor, as only patients with limited comorbidities who are likely to experience long term benefits would be considered for total arthroplasty procedures6. Increased BMI in THA was the single patient factor that was consistently positively associated with major complications, including infection, reoperation and readmission which is in accordance with previous studies which showed BMI to have strong associations with dislocation, infection and revision52,53. A study using the New Zealand Joint Registry also reported an OR of 3.73 for PJI in patients with BMI >40 compared to patients with BMI <3554.
Increased age, female gender and previous knee arthroplasty were associated with decreased odds of experiencing a minor complication for TKA patients. Although male gender has been identified in the literature as an independent predictor for postoperative complications due to higher rates of comorbidities such as diabetes, hypertension and smoking, we found increased odds of minor complications among women undergoing THA55.
Strengths and limitations
A strength of this study is that it is a large cohort with high rates of long-term follow up. Further, contacting patients directly means that complications managed in the community or a different healthcare facility would have been captured which is a potential limitation of studies relying on single centre administrative data16. Limitations of our study include potential recall bias, accuracy of patient reports and although not necessarily a drawback of this study, we were unable to make fair comparisons with other similar studies due to differences in follow up time and complication definitions. We did not capture the timing of complications that occurred after hospital discharge, so were not able to determine whether they happened shortly after discharge or later in the 6-month follow-up period. Although complications such as bladder infection or retention and respiratory infection may be expected during the acute hospital admission, after discharge, particularly after the first 30 days, they are less likely to be arthroplasty-related. Depending on timing, it is possible that some of these complications were not related to surgery and thus may overestimate their true incidence in relation to the procedure. ACORN also did not capture care characteristics, for example, type of VTE or infection prophylaxis received, thus we are unable to provide complication outcomes according to care received.