A biomechanical analysis of strength and motion following total shoulder arthroplasty

BACKGROUND: The primary goal of total shoulder arthroplasty (TSA) has traditionally been pain relief and motion improvement. The literature contains multiple studies that have documented the restoration of motion and consistent pain relief following the procedure. However, there has been little attention placed on strength following TSA. Therefore, the purpose of this study was to determine in an objective manner whether strength and motion improve with shoulder arthroplasty and over what time course this may occur. MATERIALS AND METHODS: Between April 2002 and January 2004, 15 patients who underwent TSA for osteoarthritis had biomechanical strength testing preoperatively, at 6 and 12 months postoperatively. The mean age at the time of TSA was 66 years (range, 52-82). None of the patients had full thickness rotator cuff tears at the time of surgery. Peak forces for shoulder flexion, extension, abduction, internal rotation and external rotation strength were recorded. In addition, patients had shoulder range of motion measurements performed. FINDINGS: Range of motion improved significantly with TSA from preoperative to 6 months postoperative: flexion 104° to 147° (P = 0.0034), abduction 86° to 145° (P = 0.0001), internal rotation 43° to 54° (P = 0.0475) and external rotation 25° to 50° (P = 0.0008). There was minimal improvement in range of motion from 6 to 12 months. In contrast, there continued to be improvements in strength from the 6 month to the 12 month postoperative time frame: extension 18.3 kg to 22.4 kg (P = 0.006), abduction 11.3 kg to 12.8 kg (0.0474) and external rotation 8.8 kg to 10.1 kg (P = 0.016). Despite these improvements, compared to normative values, there continued to be relative weakness of the shoulder following TSA. INTERPRETATION: The data from this study suggest that recovery of strength and motion follow different time frames after TSA. The results of this study may allow the surgeon to more accurately discuss with the patient over what time course strength and motion may return. In addition, this study raises important questions in regard to the current rehabilitation program used after shoulder arthroplasty and whether development of new protocols may improve the functional outcome from surgery. LEVEL OF EVIDENCE: Level 2