Effect on force transmission across the carpus in procedures used to treat Kienböck's disease.

A simplified two-dimensional articulating force analysis (rigid body spring model) examined how different surgical procedures used for treating Kienböck's disease modify the force distribution across the carpus. A two-dimensional model of a carpus was loaded through the metacarpals by forces of up to 143 Newtons. The resulting intercarpal displacement and joint loadings were calculated for the intact wrist and for different simulated surgical procedures. The predicted total amount of force transmitted through the radio-lunate joint of the intact wrist averaged a 32% of the total radio-ulno-carpal joint load. Limited intercarpal fusions were found to reduce compressive loading at the radio-lunate joint by no more than 15% of the original load. Capitate shortening was successful in relieving radio-lunate forces, however, it dramatically overloaded the adjacent scapho-trapezial and triquetral-hamate joints. By contrast, a 4 mm lengthening of the ulna (or shortening of the radius) resulted in a 45% reduction of radio-lunate load with only moderate changes in force at the midcarpal and radio-scaphoid joints. On the basis of this study, radial shortening or ulnar lengthening significantly unload the lunate and are rationale procedures in the treatment of Kienböck's disease. Limitations regarding direct clinical application of this mathematical model are also discussed.