Identification of spastic muscles involved in abnormal joint posture in patients with upper motor neuron syndrome: a narrative review

Few studies have specifically investigated which muscles are involved in abnormal joint posture (AJP) due to muscle spasticity and should therefore be targeted for botulinum toxin injections. This gap has significant implications for treatment efficiency, safety, health economics, and sustainable healthcare. A 2000 to 2025 (July) PubMed search identified 3,488 articles, but only 7 articles met the criteria for providing a method to determine the muscles involved in AJP due to muscle spasticity. Of these, just 2 have proposed how to measure each muscle contribution and only 1 focused on identifying the muscle actually responsible for the observed AJP. There are many strategies for determining the muscles involved in spasticity-related AJP, but they are primarily based on inference. They draw on clinical skills, which incorporate descriptive and functional anatomy, knowledge of different muscle and joint structures, simple rules of biomechanics, determination of the exact phase of the movement involved, consideration of compensatory AJP in these motor control deficient patterns, and, of course, the patient's goals. Achieving the authors' proposed objective would enable the standardization of clinical practices, confirm the effectiveness of treatments for spasticity, particularly botulinum toxin, and ensure that the correct dose is injected in the right muscle.