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[Effect of distal interphalangeal joint fusion of the index or middle finger on the grip or finger force and load distribution in the hand].

BACKGROUND
Due to the functional coupling of adjacent finger joints and the quadriga effect of the flexor digitorum profundus an influence of the grip pattern of the hand after fusion of a distal interphalangeal joint (DIPJ) is assumed.


PATIENTS AND METHODS
Two patients with DIPJ II- fusion and 8 patients with DIPJ III- fusion due to a posttraumatic osteoarthritis, but without any other pathology of both hands were assessed on average 55 (17-121) months postoperatively by manugraphy. Using three sizes of cylinders the total grip force and the load distribution of the hand and each finger were measured. The grip pattern was analyzed by 2D-graphs. The results of the affected hand were compared to the healthy opposite side. The consolidation of the DIPJ arthrodesis was confirmed and the angle of the joint fusion measured by radiographs. Patients rated their pain in rest or under strain by a visual analogue scale.


RESULTS
The total grip force of the affected hand compared to the opposite side was 93 % for the small cylinder, 97 % for the middle, and 96 % for the large cylinder. Both patients with a DIPJ II- fusion neglected the index finger considerably and had a remarkably weak grip force (68/62/68 % for the 3 cylinders respectively). The grip pattern of all fingers has changed. Eight patients with DIPJ III- fusion averaged 99/106/103 % grip force. In six of them, the affected hand was stronger than the opposite hand when using the middle cylinder. The finger force of the middle and ring finger was reduced, but of the index and little finger increased. Five patients had a striking peak of local pressure at the fused DIPJ III.The angle of the fused DIPJ averaged 6° (0-21°) for all patients. Pain was rated on average 1.4 (0-5) at rest and 2 (0-8) with strain. Both aspects were not found to influence the grip force or the load distribution.


CONCLUSION
After DIPJ- fusion of the middle finger its finger force is reduced; but, the total grip force is compensated by an increased finger force of the index and little finger. Despite limitations due to the small number of patients, a DIPJ II- fusion might have a considerable effect on grip force and load distribution of the hand rather due to omitting this finger than purely biomechanical effects.