Restored flexor carpi ulnaris function after mere tenotomy explains the recurrence of spastic wrist deformity

Objective. To prove that fibrous restoration of the continuity of a cut tendon may cause recurrence of flexion deformity of the wrist after mere tenotomy of the spastic flexor carpi ulnaris muscle. Background. Mere tenotomy of the flexor carpi ulnaris tendon is insufficient to prevent recurrence of acquired spastic flexion deformity of the wrist. Subsequent restoration of the continuity of the tendon by fibrous interposition may result in the recurrence. We examined whether a previously tenotomised muscle is strong enough to cause the deformity. Methods. Active and passive force–length characteristics of the flexor carpi ulnaris muscle were measured intraoperatively in a patient with recurrent spastic flexion wrist deformity. The observed characteristics were compared with the average in vivo force–length characteristics of 14 spastic flexor carpi ulnaris muscles that had not previously been operated. Results. The previously tenotomised flexor carpi ulnaris muscle was able to maximally exert 110 N force. Its active force–length curve and passive force at maximal extension were similar to those of non-operated spastic flexor carpi ulnaris muscles. Conclusions. A previously tenotomised flexor carpi ulnaris muscle is strong enough to cause recurrence of spastic flexion deformity of the wrist in case functional fibrous restoration of the tendon occurs after mere tenotomy.