Abstract
To evaluate the efficacy of using a novel button-suture construct in place of traditional screws to provide bone block fixation for the Latarjet procedure.
Four paired cadaveric shoulders (n=8) were denuded, with the exception of the conjoint tendon on the coracoid, and were potted. A 15% anterior glenoid bone defect was simulated. Right and left specimens were randomised into two groups: double-screw versus quadruple-button Latarjet reconstruction techniques. A uniaxial mechanical actuator loaded the Latarjet reconstructed glenoid articular surface via a 47mm diameter metallic hemisphere. Cyclic loading between 50–200N was applied to the glenoid at a rate of 1Hz for 1000 cycles. Testing was repeated three times for conjoint tendon loads of 0N, 10N and 20N. The relative positions of three points on the inferior, central and superior edges of the coracoid bone fragment were optically tracked with respect to a glenoid coordinate system throughout testing. Screw and button constructs were compared on the basis of maximum relative displacement at these points (RINF, RCENT, RSUP). Statistical significance was assessed using a paired-samples t-test in SPSS.
When conjoint tendon loading was not present the double screw and quadruple button constructs were not significantly (P>0.779) different (0N: RINF: 0.11 (0.05)mm vs. 0.12 (0.03)mm, RCENT: 0.12 (0.04)mm vs. 0.12 (0.03)mm, RSUP: 0.13 (0.04)mm vs. 0.12 (0.03)mm). Additionally, the double screw construct was not found to differ (P>0.062) from the quadruple button in terms of resultant coracoid displacement for all central and superior points, regardless of conjoint loading (10N: RCENT: 0.11 (0.03)mm vs. 0.19 (0.05)mm, RSUP: 0.11 (0.01)mm vs. 0.18 (0.04)mm; 20N: RCENT: 0.13 (0.01)mm vs. 0.30 (0.13)mm, RSUP: 0.13 (0.03)mm vs. 0.26 (0.14)mm). It was only for the inferior point with conjoint loading of 10N and 20N that the double screw construct began to produce significantly lower displacements than the quadruple button (10N: RINF: 0.11 (0.03)mm vs. 0.23 (0.05)mm, P=0.047; 20N: RINF: 0.12 (0.02)mm vs. 0.39 (0.15)mm, P=0.026).
The results of the screw and button constructs when conjoint tendon loading was absent suggest that the button may be a suitable substitute to the screw when the coracoid is used as a bone block. Due to the small resultant displacements (max: screw = 0.19mm, button = 0.52mm), it is suggested that buttons may also act as a substitute to screws for Latarjet procedures, provided conjoint tendon overloading is minimised during the post-operative graft healing period. These in-vitro results support the in-vivo results of Boileau et al (2015) that demonstrated the suture-button technique to be an excellent alternative to screw fixation Latarjet, with graft healing in 91% of their subjects.
