A predictive model for hip abductor strength and knee extensor strength 12 months after total hip arthroplasty with an interaction term.

BACKGROUND: Identifying populations with poor muscle recovery after total hip arthroplasty (THA) is important for postoperative physical therapy. Preoperative muscle strength is a strong factor that determines postoperative muscle strength. However, this effect may depend on other factors. Thus, predictive models with interaction terms are important for accurately predicting postoperative muscle strength. This study aimed to develop a predictive model for lower muscle strength 12 months after THA which incorporates interaction terms. METHODS: Subjects were female patients with hip osteoarthritis who underwent unilateral THA. Patients with locomotor disorders, neurological disorders, or postoperative complications were excluded. Hip abductor and knee extensor strength were measured, and a generalized linear model approach with preoperative muscle strength, age, body weight, height, disease duration, physical activity, and leg extension as explanatory variables was used to identify factors that determine muscle strength 12 months after THA. Models with interaction terms between preoperative muscle strength and other explanatory variables were also examined. RESULTS: A total of 82 patients were analyzed. Preoperative muscle strength, age, body weight, physical activity, and disease duration were extracted as factors that significantly and independently determine hip abductor and knee extensor strength. The interaction term between preoperative muscle strength and age was identified as a factor that significantly determines knee extensor strength. Regression coefficients for preoperative knee extensor strength and postoperative muscle strength were significant when age was +1 SD, but not when age was -1 SD. CONCLUSIONS: The predictive model demonstrated that lower muscle strength 12 months after THA is determined by preoperative muscle strength, age, weight, physical activity, disease duration, and preoperative muscle strength, with the effect of preoperative muscle strength on knee extensor strength being dependent on age. When predicting postoperative knee extensor strength using preoperative muscle strength, it is important to consider the effect of age.

Sports activity participation after curved periacetabular osteotomy for acetabular dysplasia.

BACKGROUND: Curved periacetabular osteotomy (CPO) was developed to treat acetabular dysplasia. Given that CPO can improve physical function in the early post-operative period, patients might be able to participate in sports activities post-operatively. Therefore, this study examined the post-operative sports activity participation and characteristics of acetabular dysplasia patients who have undergone CPO. METHODS: A total of 52 patients who underwent CPO for acetabular dysplasia were given a questionnaire on pre- and post-operative sports activities; 43 patients responded. We surveyed patients' sports activities, satisfaction, and physical function. Patients were divided according to whether they participated in sports activities after CPO. Physical function was compared before and after CPO. RESULTS: The pre- and post-operative sports activity participation rates were 55.8 and 72.1%, respectively. Patients mostly performed low-impact sports activities. Moreover, patients who participated in sports activities post-operatively had smaller pre-operative range of motion of hip flexion and returned to full weight bearing earlier. CONCLUSIONS: Among acetabular dysplasia patients who underwent CPO, 72.1% participated in sports activities post-operatively. Post-operatively, patients participated not only in low-impact sports activities, but also in high-impact ones. These findings might be useful for advising patients who are concerned about participating in sports activities after CPO.

Increased medial laxity of the elbow in preadolescent baseball players with or without medial elbow apophysitis.

BACKGROUND: Medial elbow apophysitis is a traction apophysitis observed in the medial epicondyle of the elbow in preadolescent baseball players. The purpose of this study was to determine the relationship between medial elbow apophysitis and elbow valgus instability in preadolescent baseball players. METHODS: The participants were classified into a control group and an injury group; the injury group included participants diagnosed with a medial elbow injury (inclusion criteria were only symptoms of the elbow joint or positive findings on physical examinations, or both). Elbow valgus instability was assessed by measuring the differences in ulnohumeral joint gapping width, with and without gravity stress induced by weight loading of the forearm using ultrasonography. RESULTS: The control and injury groups consisted of 81 and 23 preadolescent baseball players, respectively. In the throwing elbow, valgus instability in the injury group was significantly greater than that in the control group (1.07 vs. 0.57 mm, P = .001). In the non-throwing elbow, valgus instability in the injury group was significantly greater than that in the control group (0.57 vs. 0.37 mm, P = .011). The area under the curve for valgus instability of the throwing elbow was 0.89 mm (95% confidence interval, 0.64-0.77), and the cut-off value for elbow pain appearance was 0.80 mm. CONCLUSION: The increased elbow valgus instability in the injury group was associated with a medial elbow injury. For the elbow valgus instability of the non-throwing side in the injury group, we considered that players with medial elbow apophysitis inherently have elbow laxity.