Physiologic consequences of surgical lengthening of extensor carpi radialis brevis muscle-tendon junction for tennis elbow.

Sarcomere length was measured intraoperatively using a laser diffraction method before and after surgical lengthening of the human extensor carpi radialis brevis muscle (ECRB) in five subjects treated for lateral epicondylitis. Based on measured sarcomere and filament lengths, we previously established the length-tension curve for this muscle and the normal sarcomere length range as a function of wrist joint angle. Preoperative measurements indicated that the ECRB developed near-maximal isometric force at full wrist extension, decreasing to 20% maximum at full wrist flexion. Stair-step surgical tendon lengthening of the ECRB by 9.1 mm resulted in mean ECRB sarcomere shortening of 0.30 microns. This 0.30 microns shortening was predicted to have two primary biomechanical effects: (1) a 25% decrease in muscle passive tension that could lead to reduced insertional tension and decreased pain and (2) a 25% increase in active muscle force that opposes the notion that tendon lengthening necessarily results in muscle weakness.