Midcarpal Structure Effect on Force Distribution through the Radiocarpal Joint

Abstract

Background Wrist structure is complicated by distinct anatomical patterns. Previous studies defined radiographic wrist types based on lunate and capitate shape within the midcarpal joint. We hypothesized that these disparate structural patterns will transfer forces differently through the wrist. Objective This study aims to correlate force transferred to the distal radius and ulna with morphological measurements in cadaver arms. Methods Radiographs from 46 wrists, previously tested for force transfer between the radius and ulna, were examined. The percentage of compressive force through the distal ulna was determined by mounting load cells to the radius and ulna, while 22.2 Newton (N) tensile forces were individually applied to multiple tendons. Each wrist was tested in a neutral flexion–extension and radial-ulnar deviation position. Results Wrist type and lunate type were associated with percentage of force transfer through the ulna (p = 0.002, p = 0.0003, respectively). Percentage of force transfer was correlated with capitate circumference (p = 0.02, r = 0.34). Conclusions This study supports distinct force transfer between morphological wrist types. Clinical Relevance Understanding the mechanical significance of different structural variations in the wrist bones will improve our ability to understand wrist function and the distinctive development of wrist pathology. Level of Evidence This is a Level II study.

Force Transfer through the Scaphotrapeziotrapezoid (STT) Joint

“…Most studies have suggested that there is a more stable midcarpal joint in type 2 wrists and that a type 2 joint transfers forces more radially toward the scaphoid and scapholunate ligament than a type 1 wrist. 3,14,15 This study found that type 2 wrists experience increased force transfer (as inferred by motion that is predicted by the model) both in the coronal (medial-to-lateral) and axial (proximal-to-distal) planes. Since this will transfer forces in the direction of the scapholunate ligament, it is likely that there is more load on the scapholunate ligament in a type 2 wrist while performing certain tasks.…”

A Preliminary Model of the Wrist Midcarpal Joint

“…In a cadaver study, Wollstein et al found similarly that a type 1 wrist transferred more force ulnarly in the radiocarpal joint than a type 2 wrist. 6 This finding is counterintuitive in that we expect the type 2 midcarpal joint to be more stable due to the lunate hamate articulation and therefore to transfer forces more ulnarly, i.e., less toward the scapholunate joint. A kinetic in vivo study by Abe et al found more triquetral motion and lunate-triquetrum motion with increased shearing forces to the lunotriquetral interosseous ligament, as well as increased hamate lunate shear in type 2 lunates.…”

“…4,5 This variation has been shown to affect load transfer in between the ulna and radius. 6 Assuming that these structural disparities will affect load transfer through the midcarpal joint, the purpose of this study was to:…”

Does Midcarpal Joint Structure Affect Development of Arthritis in the Wrist

“…A cadaver study examining the difference in distribution of forces to the radiocarpal joint demonstrated that a wrist type 2 transfers forces radially to the SL joint and radius while a wrist type 1 transfers the forces differentially in a more ulnar direction. 19 This differential transfer radially in type 2 wrists can explain failure of the SL ligament with repeated trauma or significant one-time injury and the development of the typical SLAC pattern with initial wear at the radial styloid-scaphoid joint followed by involvement of the whole radial-scaphoid joint. This disparate transfer of forces may also explain why in a type 1 wrist the radial-scaphoid joint remains relatively spared and the wrist tends to develop wear in just the midcarpal joint.…”