Innervation of the subscapularis muscle and implications for treatment of spasticity

Spasticity of the muscles in the shoulder girdle, frequently observed in upper motor neuron syndromes, leads to an internal rotation deformity with associated functional limitation. Selective neurectomy (SN) of motor branches can offer targeted relief whilst preserving glenohumeral joint stability.

To provide detailed anatomical mapping of motor branches to the subscapularis muscle and assess the feasibility of SN in the management of shoulder spasticity.

Twenty shoulders from ten formalin-fixed cadavers were dissected via an infraclavicular approach. The number, diameter, length of the motor branches were documented, as was the distance of the emergence point of the nerves referenced from the inferior border of the clavicle. Anatomical variations were recorded.

The mean number of motor branches to the subscapularis was 2.55 (± 0.89). The average length of each branch was 44.9 mm, with an average diameter of 1.9 mm. Branches emerged on average 36 mm below the inferior edge of the clavicle, with 7.9% emerging more proximally. An origin from the axillary nerve was identified in 35% of cadavers, typically supplying the lower segment of the muscle. A common trunk with the thoracodorsal nerve was observed in 10% of dissections.

This study provides an anatomical map of the innervation to the subscapularis, with a mean of 2.55 branches emerging on average 36mm below the inferior edge of the clavicle. This information is useful when considering performing selective neurectomy to this muscle in the setting of upper motor neuron syndrome.