Abstract
Introduction
Stiffness of the knee after total knee arthroplasty (TKA) impairs knee function and reduces patient satisfaction. Limited preoperative range of motion (ROM) and a diagnosis of osteoarthritis seem to be associated with postoperative stiffness, and medical comorbidities such as diabetes mellitus have been discussed as predisposing factors. The present study was undertaken in order to analyse both patient-related and surgical factors that could be associated with the need for mobilization under anaesthesia (MUA) after TKA.
Methods
We designed a case-control-study and extracted the study population from our local arthroplasty register. We identified all patients in our register that required MUA following primary TKA (n=35) and then randomly selected 4 control patients for each case of MUA. Incomplete medical records resulted in the exclusion of 18 patients, leaving 157 patients. Univariate analysis was used in order to investigate differences between the two groups with respect to demographics, pre- and postoperative ROM, medical or psychiatric comorbidities, and the type of implant. Variables with a proposed influence on outcome were entered into a binary logistic regression model, and risk ratios (RR) were calculated with 95% confidence intervals (CI).
Results
Regression analysis showed that age at operation, the presence of chronic obstructive lung disease (COLD), and preoperative flexion significantly affected outcome: Increasing age decreased the risk for needing MUA with a RR of 0.88 (CI 0.82–0.94, p<0.001) per year. Patients with COLD had significantly higher risk of needing MUA with a RR of 9.82 (CI 1.84–52.3, p=0.007). Impaired preoperative flexion was an important predictor of postoperative stiffness with a RR of 0.97 (CI 0.95–0.99, p=0.027), implicating that the risk for MUA decreased by approximately 3% for each additional degree of flexion. Gender, BMI, cardiovascular comorbidity, the presence of rheumatoid arthritis, diabetes mellitus, previous knee injury, and the type of implant did not significantly affect the risk for MUA. In univariate analysis, patients requiring MUA had significantly lower knee flexion at discharge than control patients (78° vs. 61°, p<0.001).
Interpretation
We conclude that the presence of COLD, impaired preoperative knee flexion, and younger age increase the risk for needing MUA after primary TKA. The finding that COLD increases the risk for MUA is novel: It is known that patients with COLD have higher systemic levels of inflammatory mediators, and we are tempted to speculate that postoperative arthrofibrosis could be a result of enhanced systemic inflammatory activity. In our hands, the choice of implant and comorbidities other than COLD were not associated with an increased risk for MUA.
