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The Effect of Capitate Position on Coronal-Plane Wrist Motion After Simulated Four-Corner Fusion
Steve K. Lee, MD; Alexia Marie Hernandez-Soria, MD; Soumen Das De, MD, MPH; Zina Model, MD; Scott W. Wolfe, MD
Hospital for Special Surgery, New York, NY

Introduction: Scaphoid excision and four corner fusion (4CF) is most often performed when the radiolunate articulation is spared in conditions such as scapholunate advanced collapse (SLAC) and scaphoid nonunion advanced collapse (SNAC). In particular, the position of the lunate in the sagittal plane is a determining factor of post 4CF wrist flexion and extension and is considered by some to be the most important step of the procedure. To our knowledge, the coronal relationship between the lunate and capitate, however, has not been studied. The objective of this study was to examine the effect of altering the capito-lunate relationship on coronal-plane wrist motion after scaphoidectomy 4CF.
Materials and Methods: Eight human cadaveric limbs were disarticulated at the elbow and mounted on a custom jig. The baseline position of the wrist was recorded with no load applied, followed by sequential loads of 44.4N, 89N and 125N applied to the FCR, ECRL and ECRB tendons to simulate maximal radial deviation (RD) and to the FCU and ECU tendons to simulate ulnar deviation (UD). A scaphoidectomy was then performed and 2 methods of simulated 4CF were studied in random order (figure 1). Range of motion (ROM) was compared using one-way ANOVA and bonferroni correction.
Results: The resting position of the “capitate covered” wrist was in significantly greater radial deviation than the pre-operative wrist position (p < 0.01). Under 44.4N radial load, the capitate covered position had significantly greater radial deviation than the pre-operative radial deviation at the same radial load (p = 0.01). The anatomic position wrist did not differ significantly from the pre-operative wrist at any position.
Conclusions: To our knowledge, this is the first study to evaluate the coronal position of the capito-lunate articulation following scaphoid excision and four-corner fusion. In this cadaveric model, the resting position of the wrist as well as the coronal arc of motion was not significantly changed from the pre-operative state when the remaining carpal bone positions are maintained after scaphoid excision. In contrast, complete covering of the capitate head by the lunate, as recommended in the literature (1-5), placed the wrist in excessive radial deviation. The extra radial deviation may be due to over tensioning of the radioscaphocapitate ligament and may clinically result in a perceptible deformity and affect function.

Figure 1

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