College of Massage Therapists of British Columbia (CMTBC) Practice Exam

What typically causes the hyper-extension of the PIP joint in Swan Neck Deformity?

1. Weak extensor tendons

2. Intrinsic muscle contraction

3. Ruptured flexor tendons

4. Overstretching of ligaments

The correct answer is: Intrinsic muscle contraction

The hyper-extension of the PIP (proximal interphalangeal) joint in Swan Neck Deformity is primarily caused by intrinsic muscle contraction. This condition arises when there is an imbalance in the muscles and tendons that control the movements of the fingers. In Swan Neck Deformity, the intrinsic muscles—such as the lumbricals and interossei—become overactive or excessively tight, while the extrinsic flexor tendons are often stretched or weakened. This muscle imbalance leads to a hyper-extension of the PIP joint and a corresponding flexion at the distal interphalangeal (DIP) joint. Understanding this pathology is critical, as it provides insight into the mechanics involved in joint alignment and function. The intrinsic muscles play a pivotal role in finger positioning, and their contraction can pull the PIP joint into an extended position while simultaneously causing the DIP joint to flex. This characteristic posture exemplifies the deformity, commonly linked with conditions such as rheumatoid arthritis. The other factors listed, while they may contribute to hand dysfunction generally, do not directly cause the hallmark hyper-extension seen in Swan Neck Deformity. For example, weak extensor tendons might affect movement but are not the primary source of this specific deformity