Scaphoid Excision with Four-Corner Fusion: A Biomechanical Study

Abstract

Purpose Partial wrist arthrodesis is a commonly performed procedure for the treatment of posttraumatic wrist arthritis because of its ability to provide pain relief without sacrificing complete wrist motion. The purpose of this study was to evaluate the redistribution of force after fourcorner fusion and scaphoid excision, and to correlate the findings with the reported clinical outcomes. Methods Fifteen cadaveric wrists were used to study the biomechanics of the four-corner fusion. Pressure-sensitive film (super-low-pressure-indicating film-Pressurex, Sensor Products Inc, Madison, NJ) was inserted into the radiocarpal joint. Using the MTS 858 Mini Bionix (MTS System, Eden Prairie, MN), 50-kg loads (220 N) were applied to the wrists before and after simulated four-corner fusion and scaphoid excision. Statistically, we compared the pressure in the normal (intact) wrists versus four-corner fusion and scaphoid excision. The pressure measurements across the scaphoid fossa, lunate fossa, and triangular fibrocartilage complex (TFCC) were compared. Results There is a statistical significant difference between scaphoid, lunate, and TFCC mean total force when pre and post-fusion were compared (p=0.0001). Our study revealed a statistical significant decrease in the mean scaphoid total force after scaphoid excision and four-corner fusion (p=0.0001). We also found a subsequent increase in mean total force after scaphoid excision and four-corner fusion for the lunate fossa that did not reach statistical significance (p=0.08), and no difference in load across the TFCC area (p=0.995). Conclusions Our findings suggest that load is preferentially transferred to the radiolunate joint after scaphoid excision with four-corner fusion.

Results of a Method of 4-Corner Arthrodesis Using Headless Compression Screws

“…17 Arthritis can develop in the radiolunate joint secondary to the increased forces across the joint or to pre-existing or new cartilage damage. 4,5,8,18 Although the distal to proximal capitolunate fixation still creates a 1-mm guide wire hole in the lunate and the radius, it avoids the larger screw-head-sized holes that are created if the screw placement is performed in a proximal to distal direction.…”

Intercarpal fusions: indications, treatment options and techniques

“…The position of the lunate has been demonstrated biomechanically to be predictive of the total active motion of the wrist following midcarpal arthrodesis. 8,9,10 Intercarpal arthrodesis requires up to six weeks of wrist immobilisation in either a cast or a plastic splint before initiation of the rehabilitation period. Assessment of bone healing can be difficult, and only a CT-scan at this time can reveal the bone bridging trabeculae.…”

Scaphocapitolunate Arthrodesis and Radial Styloidectomy: A Treatment Option for Posttraumatic Degenerative Wrist Disease

“…A study of cadaveric wrists confirmed an increase in the mean total load in the lunate fossa after scaphoid excision and 4CF with no difference in the load across the triangular fibrocartilage complex (TFCC) area. 5 Theoretically, degenerative osteoarthritis could occur as a consequence of the 4CF or PRC due to the smaller articular contact area. In contrast, an SCL fusion model demonstrated an increase in scaphoid contact areas by 42% accompanied by a slight decrease in the lunate contact area (by 12%).…”

“…This leads to an increased load across the lunate fossa, as the scaphoid fossa is no longer articulating with the carpus. 5 Therefore, osteoarthritis is a risk, particularly in PRC. 6 The rates of osteoarthritis in 4CF were recently reported at 1% by a meta-analysis, 3 but only one of the eight studies included in the analysis had a greater than 5-year follow up.…”