Factors Affecting Supination Strength Following a Distal Biceps Rupture

14 FACTORS AFFECTING SUPINATION STRENGTH FOLLOWING A DISTAL BICEPS RUPTURE Christopher C. Schmidt, MD, Brandon Brown, Prasad J. Sawardeker, MD, Martin deGravelle, Mark C. Miller, PhD, Allegheny General Hospital, Pittsburgh and the University of Pittsburgh, Pittsburgh, Pennsylvania, USA Introduction:Advocates for the non-operative treatment of distal biceps ruptures emphasize the limited functional loss. Isometric supination loss of 26%-40% has been reported in a neutral forearm testing position. The amount of strength loss in other forearm positions, i.e. pronation and/or supination, has not been published to date. Biomechanical studies have demonstrated that the native biceps moment arm, the ability of the biceps to generate a torque, changes significantly with forearm position. The purpose of this study is to quantify the effects of a complete distal biceps rupture compared to the uninjured limb in 60 of supination, (0 ) neutral and 60 of pronation. We hypothesize that supination strength loss will be significant, vary with forearm position, and be independent of arm dominance. Furthermore, strength will positively correlate with time from injury and negatively correlate with high perception of pain and low reported disability. Methods: Twentythree consecutive adult males with an average age of 50 6 11 years suffered a complete distal biceps avulsion. There were 12 dominant and 11 non-dominant arm injuries. The patients underwent prospective isometric supination strength testing using a custom-made torque-measuring device and a previously published protocol. The average time of injury to evaluation was 518 days (median of 24), ranging from 4 days to 30 years. Peak torque was recorded for each arm at three forearm positions: 60 of supination, (0 ) neutral and 60 of pronation. Strength loss was expressed as the ratio of the injured side to the uninjured side. Pain level was assessed using a numeric visual analog pain scale (VAPS), ranging from 0-10. Functional outcomes were measured using the DASH questionnaire. Strength data was compared to arm dominance, test angle, and biceps injury using a 3-way ANOVA, while relationships to strength were analyzed using linear regression (significance set at p1⁄40.05). Results: Peak torque values in the injured arm were statistically less than the uninjured arm (p 0.002), but not in supination (p1⁄40.157). The average VAPS score was 5 6 2 and DASH score was 38 6 21. Strength was not related to VAPS or DASH scores at any test angle (p>0.105). Time from injury and the VAPS score were negatively correlated (p1⁄40.029), while time from injury and DASH were not (p1⁄40.244). Discussion: The study clearly shows that a patient can expect to lose 60% of their supination strength in neutral. The loss of supination strength is independent of forearm position. However, patients were strongest in pronation and weakest in supination with or without an intact distal biceps. This finding maybe due in part to the co-contraction of the brachioradialis muscle; which acts as a supinator of a pronated forearm, and a pronator of a supinated forearm. Surprisingly, perceived disability and pain associated with the injury were not indicative of reduced strength. However the strength improved over time in pronation and neutral, but not in supination. We speculate that supination strength from pronation to neutral can improve as one strengthens the brachioradialis, but that strength deficits from neutral to supination will be more difficult to overcome.