[Post-traumatic palmar instability of the thumb metacarpophalangeal joint. The "other skier's thumb"].

"Passive" and "active" stabilizers give the thumb metacarpophalangeal (MP) joint the necessary palmar stability. It is possible to temporarily stabilize the joint by means of the flexor muscles in cases where there is an injury to the palmar ligaments due to hyperextension trauma. However, sudden severe or prolonged strain may lead to palmar instability and/or stress-related pain. In an experimental study, the MP joints of 40 specimen thumbs were hyperextended to varying degrees. The extent of tissue damage was evaluated during dissection. Between 1984 and 1992, in 72 cases with acute hyperextension injury of the thumb MP joint, we X-rayed the thumb under stress during primary examination. Habitual instability was excluded by comparing X-ray films under stress of the opposite uninjured thumb. The treatment of the lesion depends on the degree of instability documented by the X-ray films. Experimentally, we found only partial lesions or ruptures with only slight dislocation of the ligament ends in cases where the MP joint was hyperextended up to 30 degrees. In cases with hyperextension of 60 degrees or more, there was usually a complete rupture of the ligaments or a fracture of the sesamoid bones with dislocation of the ligament ends as well as partial rupture of the thenar muscles. This injury pattern was also observed in clinical cases during surgery. Partial lesions of the palmar ligaments of the thumb MP joint can be treated conservatively with good results. In cases of complete palmar instability due to trauma, we saw better results after surgical reconstruction of the ligaments particularly in manual workers.