Vita TU, Occupational Therapist and Project Manager
Sunshine Social Welfare Foundation
Post-burn hand deformities are complex by nature, affecting different joints in different ways, and requiring different intervention goals. Take claw hand deformity as an example. It presents as hyperextension of metacarpophalangeal (MP) joints and flexion of proximal interphalangeal (PIP) joints. Both MP and PIP joints present deformity, but the direction of deformity is different.
When planning our rehabilitation goals and interventions, we ideally want to achieve maximum impact. If addressing one problem can help solve or lessen other issues at the same time, this is rather efficient. So, in the case of claw hand deformity, what will be the rehabilitation priorities? With which joint deformity should we start? Should the problem of the MP joint be dealt with first? Or should the problem of the PIP joint be dealt with first? In terms of intervention effectiveness, which joint should we prioritize for maximum impact?
From our point of view, dealing with MP joint problems comes before dealing with PIP joint problems. This is based on two considerations: functional and anatomical. We’ll explain both considerations below.
To perform normal grasp, the MP, PIP and even the DIP joints must tend towards flexion. However, in the case of claw hand, the MP joint is in hyperextension, which is a completely opposite direction of normal grasp movement. From a functional perspective, if the MP joint hyperextension problem can be reduced and the ability to perform MP flexion improves, even if PIP joint still has some limitations, the hand can still maintain basic grasp ability. Therefore, when dealing with claw hand, we can start by dealing with the MP hyperextension problem before dealing with PIP flexion.
The MP joints and PIP joints of the fingers are linked to each other through the anatomical structure of tendons and ligaments. In the case of claw hand deformity, when MP joints are pulled into hyperextension, this is more likely to cause PIP joint flexion.
The lateral bands and the central slip at the end of the extensor digitorum communis (EDC) are connected to the lumbrical and interossei muscles. In terms of function, the central slip and the lateral bands can be regarded as the tendons of the lumbrical and interossei muscles.EDC contraction mainly produces MP extension, while IP extension is produced by lumbrical and interossei muscle contraction.Therefore, when the MP joint is in hyperextension, the moment arm of the EDC up to the PIP joint will be shortened, and the force acting on IP extension will be weakened, resulting in an increase in the relative force of the flexor muscles FDS and FDP, resulting in greater flexion of IP. Therefore, if we prioritize reducing MP hyperextension, as MP flexion increases, this in turn will promote PIP extension, which will help improve the problem of excessive PIP flexion of claw hand deformity.
Whether it is from functional or anatomical considerations, prioritizing the MP hyperextension problem in our intervention plan makes more sense in terms of “efficiency” of intervention. That is because we can create more gains not just in terms of improving the MP joint problem, but also improving the PIP flexion problem.