Bilateral anatomical variations in the extensor compartment of forearm and hand.

An unusual variation of the extensor muscles was found during the routine dissection of the posterior compartment of the forearm. The left forearm presented an extensor medii proprius muscle, the tendon of which had an unusual trajectory. It passed through the second extensor compartment between the tendons of the extensor carpi radialis longus and extensor carpi radialis brevis muscles. The right forearm presented two muscles for the index finger: one, the extensor indicis et medius communis, the tendon of which was split into three tendons, one radial and one ulnar for the index finger and a rudimentary tendon for the middle finger; the second muscle for the index finger had an unusual origin, common with the extensor carpi radialis brevis, and its tendon ran superficially to the tendon of the extensor indicis et medius communis muscle. Knowledge goes tendon variations can be significant not only for clinicians to misdiagnose a debilitating wrist extensor pain syndrome but also for surgeons to avoid iatrogenic injuries in hand surgery.