Motor Points for the Neuromuscular Blockade of the Subscapularis Muscle

Abstract 

Harrison TP, Sadnicka A, Eastwood DM. Motor points for the neuromuscular blockade of the subscapularis muscle.

Objective

To locate the motor points of the subscapularis muscle in relation to palpable anatomic landmarks and hence suggest a technique for botulinum toxin injection into subscapularis applicable to patients of all ages.

Design

Anatomic dissection of the innervation of 20 subscapular muscles.

Setting

University dissecting room.

Cadavers

Ten formalin-preserved cadavers.

Interventions

Not applicable.

Main Outcome Measure

The location of motor points in relation to anatomic landmarks.

Results

The median number of motor points for the subscapularis was 5 (range, 3−6). All motor point measurements were related to surface points and converted into proportional values along reference lines. Motor points from the 20 dissections showed clustering in a band. A line of best fit was calculated (y=1.48x–0.743).

Conclusions

We describe an injection technique that would deliver botulinum toxin close to the motor points of the subscapularis, a surrogate marker of the motor endplate zones. By using proportional distances, this technique is applicable to an adult and pediatric population. This should lead to an increased efficacy and decreased side-effect profile in clinical practice, although clinical trials will need to confirm this.

Key Words: Botulinum toxins, Muscle spasticity, Rehabilitation, Shoulder