Kinematic analysis of relative motion within the proximal carpal row.

The motions of the scaphoid and triquetrum relative to the lunate have been studied on cadaver specimens. The helical axis concept was applied. The wrist motions performed were flexion-extension and radial-ulnar deviation. The results showed increased relative motion of the scaphoid towards terminal extension, and to a lesser amount in the case of the triquetrum, towards terminal flexion. The lunate might be considered as a keystone in the proximal carpal row when wrist stability is considered. It is doubly intercalated: longitudinally and transversely. Wrist ligaments co-ordinate the positioning of the bones in the mid-range of carpal motions, and restrict further motion in extreme positions of the wrist joint.

Kinematics of the wrist and its ligaments.

Precise anatomic dissections of unembalmed physiologically intact cadaver specimens were carried out before proceeding with the kinematic investigations on further specimens. Carpal flexor and extensor tendons were used to move the wrist. The analysis of the carpal bone movements was performed according to the finite helical axis motion concept for increments of 10 degrees for each main carpal motion. Separate axes of rotation for each of the bones in the proximal carpal row were found; however, the axes for the lunate and triquetrum bones were close, and the magnitudes of rotation and translation almost equal. One finding was that the axes of rotation of the bones in the proximal carpal row often cross at some particular point. Because the axes of the scaphoid are differently oriented than those of the lunate and triquetrum, shear might occur during wrist motion. This indicates also that the scaphoid and lunate cannot be considered rigidly coupled elements. We also assume that the individual bones of the proximal carpal row self-align themselves as long as they are not constrained by torsion. Several potential mechanisms of flexion motion of the proximal carpal row during radioulnar deviations of the hand were considered. The ligament function is still an unsolved problem. Compensation mechanisms may mask clear correlations between a lesion and the instability pattern associated with it. The proximal carpal row should be studied as one system.

[Arthrosis of the wrist joint due to carpal instability. Therapeutic alternatives]. / Die Arthrose des Handgelenks als Folge der karpalen Instabilität. Therapeutische Alternativen.

A kinematic analysis of the movement of the scaphoid, the lunatum and the triquetrum has shown that their turning axes do not correspond with each other. Without arthritis, and within the range of normal motion, the bones move without imposing any appreciable load on the ligaments. They merely guide the bones and hold them together. In the case of arthritic disorders and in states where abnormal frictional resistance occurs, or following trauma, the ligaments are highly loaded. This could lead to increased wear and ruptured ligaments. A series of 20 arthroscopies has shown that LT and SC ligaments are very prone to this, and are often affected simultaneously. Therefore, there may be certain predisposed sites or "weak points", which should definitely not be further aggravated by inappropriate therapeutic measures. The clinician can classify the carpal dysfunction into five main groups; however, the therapy options cannot be classified in the same way. On the basis of clinical experience and the kinematic study, the following statements can be made: scapho-lunatum (SC) arthrodesis can be considered kinematically unsuitable, while scapho-capitatum (SC) and lunato-capitatum (LC) arthrodeses are both clinically and kinematically acceptable. LC arthrodesis has given good results in cases with advanced carpal collapse. From a mechanical point of view, SC arthrodesis is probably better than scapho-trapezo-trapezoid arthrodesis. In the case of ulnar translocation, radio-ulna-to-scaphoid arthrodesis could be an acceptable alternative to total fusion. Proximal row carpectomy can only be a temporary solution, as can prostheses. Partial prostheses, whether of Silastic or titanium, are also not suitable for permanent use.(ABSTRACT TRUNCATED AT 250 WORDS)