TO THE EDITOR:
We read with interest "Simulated Bennett Fracture Treated with Closed Reduction and Percutaneous Pinning. A Biomechanical Analysis of Residual Incongruity of the Joint" (79-A: 413—420, March 1997), by Cullen et al., which showed the unloading effect of articular incongruity after imperfect reduction of the palmar beak fragment. However, because the authors referred only to medium-term studies regarding outcome even though the results of a long-term study (average duration of follow-up, 26.4 years) has been published4, their conclusions are flawed.
Cullen et al. chose to study the biomechanics of the joint with use of lateral pinch-testing; however, this function was found to be only slightly impaired after a Bennett fracture. In the long-term study by one of us (P. J. L.), more severe impairment was noted in pinch grip strength4. This activity may place a greater load across the area of incongruity and thereby lead to long-term degeneration of the joint. Similarly, although static loading of the joint may not reveal a biomechanical cause for joint degeneration, this does not rule out the possibility of dynamic loading doing so.
Many studies have shown that there is little impairment after these injuries1-3, regardless of the treatment modality, but all of those studies had only medium-term follow-up. However, the previously mentioned long-term study demonstrated marked symptoms and functional impairment after nonoperative treatment4. The prevalence of posttraumatic osteoarthritis in the long-term study (fifteen of seventeen patients) was also higher than that in other series, suggesting that imperfect reduction led to progressive degeneration of the joint, often compounded by persistent subluxation as well as malunion.
Until an adequate long-term study of the results of indirect reduction and percutaneous pinning is published, it will remain unknown whether imperfect reduction within the two-millimeter limit is acceptable and whether marked degeneration of the joint is the final outcome after this fracture.
Julian Chell, F.R.C.S; S. Surendran, F.R.C.S.; Peter J. Livesley, F.R.C.S. (Orth): Department of Orthopaedics and Trauma, The King's Mill Centre for Health Care Services, Mansfield Road, Sutton-in-Ashfield, Nottinghamshire NG17 4JL, England
Dr. Cullen, Dr. Parentis, Dr. Chinchilli, and Dr. Pellegrini reply:
We thank our colleagues from the United Kingdom for their insightful comments concerning the simulated Bennett fracture-dislocation described in our biomechanical study. We agree nearly entirely with their observations and conclusions.
On the basis of the long-term study of seventeen patients who had a Bennett fracture-dislocation4, Livesley concluded that "in light of the poor long-term outcome, this injury should not be managed conservatively but by some operative means." Livesley went on to describe a characteristic clinical subluxation in a dorsoradial direction in twelve hands and a corresponding radiographic subluxation of the metacarpal base in thirteen hands. Osteoarthritic changes were common in these hands.
These characteristics are the result of displacement of the metacarpal shaft fragment away from the beak with its attached stabilizing palmar beak ligament. In our biomechanical study, this displacement was directly addressed with simulated closed reduction and percutaneous pinning in order to achieve tight apposition of the osseous fragments and to eliminate subluxation of the metacarpal shaft fragment. The attention to reduction of this shaft fragment successfully restored stability to the joint while unloading the palmar compartment, where osteoarthritic changes most frequently develop. We agree with Livesley that operative treatment of this injury is indicated4. His findings relative to the association of osteoarthritic changes with persistent metacarpal subluxation support our hypothesis that the primary lesion in need of operative treatment is the subluxation of the shaft fragment rather than the residual incongruity of the joint surface.
We chose to study lateral pinch because this is the most common functional use of the thumb in activities of daily living. Moreover, this position places the greatest load on the palmar compartment of the trapeziometacarpal joint. In contrast, Livesley noted the greatest decrease in pinch grip strength4; this finding probably was due to the loss of rotation of the thumb about its axis, namely pronation-abduction, secondary to persistent subluxation of the metacarpal shaft. Compromise of the first web space, with diminished ability to pronate and oppose the thumb, directly compromises the pinch grip strength and may be the principal variable responsible for the reduction in this parameter as noted by Livesley. Likewise, both static and dynamic testing in our biomechanical model yielded similar results of unloading of the palmar beak fragment after the Bennett fracture.
We agree with Chell et al. that long-term clinical follow-up studies are necessary to assess the importance of a two-millimeter articular step-off in determining the ultimate outcome and the development of posttraumatic osteoarthritis after this injury. However, to date, all of the published reports, notably that of Livesley4 in concert with our biomechanical study, indicate that persistent subluxation of the metacarpal shaft fragment is the primary lesion in need of operative treatment to prevent degenerative disease after a Bennett fracture-dislocation.
Joseph P. Cullen, M.D.: Prevea Clinic, 1551 Dousman Street, P.O. Box 19070, Green Bay, Wisconsin 54303-9070
Michael A. Parentis, M.D.; Vernon M. Chinchilli, Ph. D; Vincent D. Pellegrini, Jr., M.D.: Departments of Orthopaedics and Rehabilitation (M. A. P. and V. D. P., Jr.,) and Biostatistics (V. M. C.), Milton S. Hershey Medical Center, Pennsylvania State University, Box 850, Hershey, Pennsylvania 17033