Anatomical study of the deep branch of the ulnar nerve and application to selective neurectomy in the treatment of spasticity of the first web space

Purpose Spasticity of the first web space is common in upper limb spasticity. Selective neurectomy is one of the treatments that can reduce spasticity. The purpose of this study was to describe the variations of the deep motor branch of the ulnar nerve for the adductor pollicis (AP) and the first dorsal interosseous muscle (DIO) to assess the feasibility of selective neurectomy and suggest an ideal surgical approach. Methods The deep branch of the ulnar nerve (DBUN) was dissected in 21 hands. Measurements included the distance between the point of passage of the DBUN between the two heads of the adductor and three anatomical landmarks: the bi-styloid line, the flexor carpi radialis and the pisiform bone, and the number and mode of divisions of each branch. Results The point of passage of the DBUN between the two heads of the adductor is very constant respective to the landmarks. The DBUN gives off 1-3 branches each for the oblique head of the AP, the transverse head, and the first DIO. Muscles receive more than one branch in 95% cases for the oblique head and 62% of cases for the transverse head, and 100% for the DIO. Conclusions This anatomical study suggests that selective neurectomy is feasible for the AP and first DIO muscles in most cases. An ideal approach for selective neurectomy of these muscles should start from the point of passage of the DBUN between the two heads of the AP. This point is easily identified with the help of the described landmarks.