Effectiveness of surgical reconstruction to restore radiocarpal joint mechanics after scapholunate ligament injury: an in vivo modeling study

Abstract

Disruption of the scapholunate ligament can cause a loss of normal scapholunate mechanics and eventually lead to osteoarthritis. Surgical reconstruction attempts to restore scapholunate relationship show improvement in functional outcomes, but postoperative effectiveness in restoring normal radiocarpal mechanics still remains a question. The objective of this study was to investigate the benefits of surgical repair by observing changes in contact mechanics on the cartilage surface before and after surgical treatment. Six patients with unilateral scapholunate dissociation were enrolled in the study, and displacement driven magnetic resonance image-based surface contact modeling was used to investigate normal, injured and postoperative radiocarpal mechanics. Model geometry was acquired from images of wrists taken in a relaxed position. Kinematics were acquired from image registration between the relaxed images, and images taken during functional loading. Results showed a trend for increase in radiocarpal contact parameters with injury. Peak and mean contact pressures significantly decreased after surgery in the radiolunate articulation and there were no significant differences between normal and postoperative wrists. Results indicated that surgical repair improves contact mechanics after injury and that contact mechanics can be surgically restored to be similar to normal. This study provides novel contact mechanics data on the effects of surgical repair after scapholunate ligament injury. With further work, it may be possible to more effectively differentiate between treatments and degenerative changes based on in vivo contact mechanics data.

Figure 1

Sample MRI images of the normal wrist of Subject 1. Left shows a high resolution slice of the unloaded wrist used for model construction, while right shows a lower resolution slice acquired during functional loading for image registration.

Figure 2

Example wrist of a subject with the grip device in the active grasp position. The wrist was also braced for consistent loaded positions.

Figure 3

Normal (left), injured (center) and postoperative (right) surface models of the radiocarpal joint in the unloaded position, for Subject 5, from a dorsal/posterior view. Radius, lunate and scaphoid bones are colored green, red and yellow respectively.

Figure 4

Normal (A), injured (B) and postoperative (C) contact locations of Subject 5, for radioscaphoid (RS) and radiolunate (RL) articulations, shown on the radius cartilage. Magnitude of contact pressures vary linearly from white (minimum) to dark red (maximum) for each articulation. Peak pressure (PP) values are also shown. The images for this particular subject illustrate clear separation of the scaphoid and lunate in the injured wrist, primarily due to scaphoid motion. After repair, the scaphoid moves medially to a position approaching the normal contact location. While this grossly illustrates the typical overall behavior, not all subjects exhibited these contact patterns.

Figure 5

Means (± standard errors) of radioscaphoid (RS) and radiolunate (RL) peak contact pressures for normal (N), injured (I) and postoperative (P) wrists. * indicates significant difference from injured.

Figure 6

Means (± standard errors) of radioscaphoid (RS) and radiolunate (RL) mean contact pressures for normal (N), injured (I) and postoperative (P) wrists. * indicates significant difference from injured.