Summary

During the Latarjet procedure, coracoid fixation with a mini-plate demonstrates superior biomechanical properties compared to standard fixation with screws.

Abstract

Background

The use of a mini-plate for coracoid fixation during the Latarjet procedure has recently been described, with encouraging radiographic outcomes. The purpose of this study was to determine the biomechanical properties of mini-plate fixation for the Latarjet procedure, and to compare these findings to various screw fixation configurations.

Methods

Eight fixation groups (n=5 specimens per group) were tested at a screw insertion angle of 0° including I) 3.75mm single-screw, II) 3.75mm double-screw, III) 3.75mm double-screw with washers, IV) 3.75mm double-screw with mini-plate, V) 4.00mm single-screw, VI) 4.00mm double-screw, VII) 4.00mm double-screw with washers, and VIII) 4.00mm double-screw with mini-plate. In addition, for groups I-III and V-VII, 30 additional specimens (n=5 per group) were tested at a screw insertion angle of 15° (groups IX-XIV). To maintain specimen uniformity, rigid polyurethane foam blocks were used (30pcf, Sawbones, Pacific Research Laboratories Inc., WA, USA). For all specimens, testing parameters included a preload of 214N for 10 seconds, cyclical loading from 184-736N at 1Hz for 100 cycles, and failure loading at a rate of 15mm/min until 10mm of displacement or specimen failure occurred (ElectroPuls E10000, Instron, UK). Maximum load to failure and failure mode were the primary outcomes of interest. In addition, a full-field stereo-optical measurement system (ARAMIS, GOM mbH, Germany) was utilized to evaluate graft strain, graft displacement, and screw displacement and rotation. Statistical analysis was performed via 1-way analysis of variance utilizing SigmaPlotversion 12.0, Systat Software Inc., USA.

Results

All specimens in Groups I and V (single screw constructs) as well as 77% of specimens within groups IX-XIV (screw insertion angle of 15°) failed prior to the completion of cyclical loading; all but 1 of the other specimens survived and underwent maximum load to failure testing (1 specimen in group VII failed). Across all groups, Group VIII (4.00mm; plate) demonstrated the highest maximum failure load (P<0.001), averaging loads 770N higher than the next highest group (P<0.001). There was no significant difference in displacement during cycling between specimens with plate fixation (groups V and VIII, P>0.05). There were no differences in failure loads among specimens in with single-screw fixation (groups I, V, IX, and XII; P>0.05). All specimens in groups IX, X, XI, XII, XIII, XIV (insertion angle of 15°) had significant lower maximum loads to failure compared to their specimens in Groups II, II, IV, VI, VII, and VIII, respectively (P<0.001 for all).

Conclusions

This is the first study to report on the biomechanical properties of the mini-plate for coracoid fixation in the Latarjet procedure. The results indicate significantly superior failure loads with the mini-plate compared to all other constructs, which may have clinical implications, particularly in the high-demand contact athlete. Clinical studies with analysing patient outcomes and failure rates are necessary to determine the clinical implications of these biomechanical findings.