Does SLAC IV Exist? A Radiographic and Magnetic Resonance Imaging Analysis

Introduction The progression of scapholunate advanced collapse (SLAC) and scaphoid nonunion advanced collapse (SNAC) was originally described in three stages that spared the radiolunate joint. A fourth stage of the continuum, which includes progression into the radiolunate joint, has been proposed; however, rigorous analysis of its prevalence has not been performed using standard or advanced imaging protocols. The purpose of our study is to evaluate the radiolunate joint on radiographs and cartilage sensitive MRI in a cohort of patients with SLAC or SNAC arthritis. We hypothesize that stage IV SLAC/SNAC arthritis exists due to degeneration of the radiolunate joint.

Materials and Methods A retrospective cohort of 32 patients with SLAC or SNAC arthritis was studied with radiographs and cartilage-sensitive MRI. Two board-certified hand surgeons and a board-certified musculoskeletal radiologist read the blinded radiographs and MRIs. The styloid-scaphoid, radioscaphoid, midcarpal, capito-lunate, and radiolunate (RL) joints were independently graded using the Kelgren-Lawrence scale, and an overall SLAC/SNAC grade was assigned to each patient. Depth of cartilage wear on the volar, middle, and dorsal aspects of the radiolunate joint was graded on MRI.

Results Both surgeons graded 3 of 32 wrists (9%) as SLAC/SNAC IV on radiographs. MRI identified 2 of the 3 patients as having deep or full thickness cartilage wear of the dorsal RL joint. MRI evaluation yielded grade 3 (deep wear) or 4 (full thickness) cartilage wear of the RL joint in 9 of 32 (28%) wrists, all of which was on the dorsal one-third of the joint only. No wrists showed a grade > 2 (superficial wear) in the middle or volar aspect of the joint. Five of 32 (16%) wrists had normal radiolunate joints radiographically and grade 3 or 4 cartilage loss on the dorsal one-third of the radiolunate joint.

Conclusion Although mainly limited to the dorsal aspect, the radiolunate joint is involved in SLAC/SNAC wrists in approximately one out of four cases. We recommend MRI with cartilage sensitive sequencing in the workup of SLAC/SNAC arthritis, to more accurately grade cartilage involvement as the findings and location of radiolunate cartilage loss may influence treatment decisions. The amount of radiolunate cartilage loss and its effect on clinical outcome is the subject of ongoing study.

References

References

1 Watson HK, Ballet FL. The SLAC wrist: scapholunate advanced collapse pattern of degenerative arthritis. J Hand Surg Am 1984;9(3):358–365

2 Black DM, Watson HK, Vender MI. Scapholunate gap with scaphoid nonunion. Clin Orthop Relat Res 1987;(224):205–209

3 Kitay A, Wolfe SW. Scapholunate instability: current concepts in diagnosis and management. J Hand Surg Am 2012;37(10):2175–2196

4 Mack GR, Bosse MJ, Gelberman RH, Yu E. The natural history of scaphoid non-union. J Bone Joint Surg Am 1984;66(4):504–509

5 Ruby LK, Stinson J, Belsky MR. The natural history of scaphoid non-union. A review of fifty-five cases. J Bone Joint Surg Am 1985;67(3):428–432