Exercises for the distal interphalangeal joint? Use caution and avoid passive flexion exercises!

Vita TU, Occupational Therapist, Sunshine Social Welfare Foundation

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When dealing with hand burns, exercises are one of the intervention strategies that therapists use to prevent or minimize complications like contractures that can lead to severe deformity. As part of their “arsenal”, therapists can use various types of exercises: passive, active, stretching, muscle strengthening, etc. But the type, frequency and intensity of exercise must be carefully considered based on the location and the extent of injury to avoid causing secondary damage. This is especially true in the case of the distal interphalangeal (DIP) joints.

Anatomical explanation

At the level of the proximal interphalangeal (PIP) joint, the common extensor tendon (EDC) splits into two lateral bands, which finally merge as the terminal tendon at the level of the distal interphalangeal joint. The terminal tendon of the common extensor tendon is primarily responsible for DIP extension [1]. The flattened terminal tendon attaches to the base of the distal phalanx and blends with the joint capsule. Because its excursion is only about 4mm, even a very small gap can lead to a lack of extension, therefore causing an extension lag [2].

In a study done by Satoshi et al., computed tomography images were used to analyze the grasping movements of the thumb and index finger, and the flexion of MP, PIP and DIP joints when picking up objects of different sizes. The study found that the MP and PIP joints significantly adjusted their flexion angle and posture according to the size of objects, while the DIP flexion angle and posture didn’t change much and tended to be fixed [4]. For the overall performance of hand function, the range of motion requirements for DIP joints is not as high as for PIP and MP joints. This means that even with some DIP limitation, hand function will not be significantly affected and the