Anterior Glenoid Reconstruction With Distal Tibial Allograft: Biomechanical Impact of Fixation and Presence of a Retained Lateral Cortex.

BACKGROUND

Glenoid reconstruction with distal tibial allograft (DTA) is a known surgical option for treating recurrent glenohumeral instability with anterior glenoid bone loss; however, biomechanical analysis has yet to determine how graft variability and fixation options alter the torque of screw insertion and load to failure.

HYPOTHESIS

It was hypothesized that retention of the lateral cortex of the DTA graft and the presence of a washer with the screw will significantly increase the maximum screw placement torque as well as the load to failure.

STUDY DESIGN

Controlled laboratory study.

METHODS

Whole, fresh distal tibias were used to harvest 28 DTA grafts, half of which had the lateral cortex removed and half of which had the lateral cortex intact. The grafts were secured to polyurethane solid foam blocks with a 2-mm epoxy laminate to simulate a glenoid with an intact posterior glenoid cortex. Grafts underwent fixation with 4.0-mm cannulated drills, and screws and washers were used for half of each group of grafts while screws alone were used for the other half, creating 4 equal groups of 7 samples each. A digital torque-measuring screwdriver recorded peak torque for screw insertion. Constructs were then tested in compression with a uniaxial materials testing system and loaded in displacement control at 100 mm/min until at least 3 mm of displacement occurred. Ultimate load was defined as the load sustained at clinical failure.

RESULTS

The use of a washer significantly improved the ultimate torque that could be applied to the screws (+cortex and +washer = 12.42 N·m [SE, 0.82]; -cortex and +washer = 10.54 N·m [SE, 0.59]) ( < .0001), whereas the presence of the native bone cortex did not have a significant effect (+cortex and -washer = 7.83 N·m [SE, 0.40]; -cortex and -washer = 8.03 N·m [SE, 0.56]) ( = .181).

CONCLUSION

In a hybrid construct of fresh cadaveric DTA grafts secured to a foam block glenoid model, the addition of washers was more effective than the retention of the lateral distal tibial cortex for both load to failure and peak torque during screw insertion.

CLINICAL RELEVANCE

This biomechanical study is relevant to the surgeon when choosing a graft and selecting fixation options during glenoid reconstruction with a DTA graft.