The Effect of Scaphoid Overstuffing on Radiocarpal Contact Pressures

The medial femoral trochlea flap is used for treating recalcitrant scaphoid proximal pole nonunions. Although this requires resecting a substantial portion of the scapholunate interosseous ligament, the intercarpal angular relationships are preserved. Studies have demonstrated that lunate alignment is preserved despite loss of the scapholunate ligament because the scaphoid is reconstructed with an osteochondral flap that is larger than the resected nonunited proximal scaphoid. The technique of purposeful expansion of the scaphoid height has been termed scaphoid overstuffing. The purpose of this study is to characterize the effect of scaphoid overstuffing on force transmission across the scaphoid and lunate facets of the radius.

Eleven fresh frozen cadaveric upper extremities without ligament instability were selected. The radiocarpal joint was exposed via a dorsal approach, and electronic pressure sensors were introduced. Three different states of the wrist were evaluated: native, scapholunate dissociation (SLD), and overstuffed (OS). Pressures were measured in 4 positions: 30° flexion, full wrist extension, 30° extension, and clenched fist. Pressures were measured in kPa and contact areas in mm².

In all functional positions, the OS state had higher peak pressures across the scaphoid facet. This included 30° wrist flexion (OS 383 ± 221 kPa, P = .033), full wrist extension (OS 1068 ± 767 kPa, P = .022), 30° wrist extension (OS 880 ± 518 kPa, P < .001), and clenched fist (OS 1040 ± 736 kPa, P = .02).

In functional wrist positions, overstuffing the scaphoid increases scaphoid facet peak contact pressures. Further study is needed to examine the long-term clinical consequences of these changes and the potential for accelerated cartilage degeneration.