The quadriga phenomenon: a review and clinical relevance.

The flexor digitorum profundus tendons are markedly interconnected, making them less able to move independently than the tendons of the flexor digitorum superficialis. This difference is often attributed to the common muscle belly of the profundus, but also, more importantly, to cross-connections between the tendons of the profundus. The effect of this quadriga phenomenon is important in several clinical situations, including testing for strength, assessing movement of the tendons, and when deciding which exercises to teach the patient after a tendon injury. The anatomy and biomechanics of this phenomenon are reviewed in this article to help explain why certain conditions occur, and to improve the diagnosis and treatment of some conditions in rehabilitation medicine.