Biomechanical comparison between various screw fixation angles for Latarjet procedure: a cadaveric biomechanical study

Latarjet procedure: biomechanical evaluation of 2-screw coracoid fixation

BACKGROUND

Coracoid nonunion is a relevant complication following the Latarjet procedure and is influenced by multiple factors, including the method of graft fixation. The purpose of this study was to evaluate and characterize the biomechanical properties of various two-screw fixation constructs used for coracoid graft fixation in the Latarjet procedure.

METHODS

Forty model scapulae (Sawbones Inc., Vashon, WA, USA) were used for this study. A 15% anterior inferior glenoid bone defect was created. The coracoid was osteotomized at the juncture of the vertical and horizontal aspects, transferred to the anterior-inferior edge of the glenoid, and fixed with either two 3.5 mm fully threaded cannulated cortical screws, two 3.5 mm fully threaded solid cortical screws, two 3.5 mm partially threaded cannulated screws, or two 4.5 mm partially threaded malleolar screws (MS). Biomechanical testing was performed with an Instron material testing machine (Instron Corp., Norwood, MA, USA) by applying loads to the lateral aspect of the transferred coracoid graft. The constructs were preconditioned with nondestructive cyclical loading (0N-20N) to determine construct stiffness. After 100 cycles of dynamic loading, the construct was loaded to failure to determine ultimate failure load, yield displacement, and mode of failure.

RESULTS

All failures were associated with plastic deformation of the screws and coracoid graft fracture. There was a significantly lower initial stiffness for partially threaded cannulated screws compared to MS (186 ± 49.3 N/mm vs. 280 ± 65.5 N/mm, P = .01) but no significant differences among the other constructs. There was no difference in ultimate failure load (P = .18) or yield displacement (P = .05) among constructs.

CONCLUSION

Two screw coracoid fixation of the coracoid in a simulated classic Latarjet procedure with 3.5 mm fully threaded cortical and cannulated screws is comparable to 4.5 mm MS in strength, stiffness, and displacement at failure. On the other hand, partially threaded 3.5 mm cannulated screws provide inferior fixation stiffness and could potentially affect clinical outcomes.

Sutures, Screws, Buttons, and Anchors: A Review of Current Bone Graft Fixation Devices for Glenoid Bone Loss in the Unstable Shoulder

PURPOSE OF REVIEW

Anterior shoulder instability is associated with concomitant injury to several stabilizing structures of the shoulder, including glenoid bone loss. While instability is most common in young athletes and patients with predisposing conditions of hyperlaxity, recurrent shoulder instability can occur throughout various age ranges and may lead to longer term effects including pain and shoulder arthritis. Glenoid bone loss exceeding certain thresholds is generally treated by glenoid reconstruction via bone block augmentation to adequately stabilize the glenohumeral joint. These procedures increase the width of the articular surface on which the humeral head can translate before dislocation and, based on the procedure performed, provide a sling effect via the conjoined tendon, and increase tension to support the anterior capsule. The purpose of this review is to summarize the available literature regarding bone block fixation techniques.

RECENT DEVELOPMENTS

Various fixation techniques have been utilized to secure bone block transfers. Though screw fixation has traditionally been used for bone block fixation, suture buttons, suture anchors, and all-suture techniques have been utilized in attempts to avoid complications associated with the use of screws. Biomechanical studies report variable force-resistance, displacement, and mode of failure when comparing screw to suture button-based fixation of glenoid bone blocks. Clinical and radiographic studies have shown these novel suture-based techniques to be comparable, and in some cases advantageous, to traditional screw fixation techniques. While screw fixation has long been the standard of care in glenoid bone block procedures, it is associated with high complication rates, leading surgeons to endeavor toward new fixation techniques. In available biomechanical studies, screw fixation has consistently demonstrated high maximal load-to-failure and displacement with cyclic loading. Studies have reported similar clinical and radiographic outcomes in both screw and suture-based fixation methods, with evidence of reduced bone resorption with suture fixation. While suture button fixation is associated with a higher rate of recurrent instability, overall complication rates are low. Future research should address biomechanical shortcomings of suture-based fixation techniques and continue to assess long-term follow-up of patients treated with each fixation method.

Screw Fixation for the Latarjet Procedure May Reduce Risk of Recurrent Instability but Increases Reoperation Rate Compared to Suture-Button Fixation: A Systematic Review

PURPOSE

To perform a systematic review to compare clinical outcomes, complications, and reoperation rates of patients undergoing the Latarjet procedure with screw vs suture-button fixation.

METHODS

A systematic review was performed by searching PubMed, the Cochrane Library, and Embase to identify clinical studies directly comparing screw vs suture-button fixation for the Latarjet procedure. The search terms used were shoulder screw suture button. Patients were evaluated based on reoperation rate, complication rate, recurrent instability, radiologic outcomes, and patient-reported outcomes. Graft and screw position were assessed via computed tomography.

RESULTS

Seven studies (1 Level II, 6 Level III) met inclusion criteria, with 845 patients undergoing the Latarjet procedure with screw fixation (screw group) and 279 patients with suture-button fixation (suture-button group). Mean patient age ranged from 21.2 to 29.6 years. Mean follow-up time ranged from 6.0 to 40.8 months. The recurrent instability rate ranged from 0% to 2.5% in the screw group and 0% to 8.3% in the suture-button group. The reoperation rate ranged from 0% to 7.7% in the screw group compared to 0% to 1.9% in the suture-button group. One study reported significantly lower visual analog scale pain scores in the suture-button group compared with the screw group (1.5 vs 1.2, P = .003). No other studies reported significant differences in any patient-reported outcomes. There was no significant difference in horizontal or vertical graft position, graft union rate, or complication rate between groups in any study.

CONCLUSIONS

The Latarjet procedure with screw fixation may result in a lower risk of recurrent instability compared to suture-button fixation, although screw fixation may also have a higher reoperation rate due to hardware-related complications.

LEVEL OF EVIDENCE

Level III, systematic review of Level II to III studies.

Stability of novel cow-hitch suture button coracoid bone graft fixation in Latarjet procedures: a biomechanical study

BACKGROUND

The Latarjet procedure is widely used to address anterior shoulder instability, especially in case of glenoid bone loss. Recently, cortical suture button fixation for coracoid transfer has been used to mitigate complications seen with screw placement. The aim of this biomechanical study was to evaluate the stability of a novel and cost-effective cow-hitch suture button technique, designed to be performed through a standard open deltopectoral approach, and compare this to a well-established double suture button technique.

MATERIALS AND METHODS

We randomly assigned 12 fresh frozen cadaveric shoulders to undergo the Latarjet procedure with either 4 suture button (S&N EndoButton) fixations (SB group; n = 6, age 72 ± 9.8 years) or cow-hitch suture button technique using a 1.7-mm FiberTape looped sequentially in 2 suture buttons (Arthrex Pectoralis Button) placed from anterior on the posterior glenoid (CH-SB group; n = 6, age 73 ± 9.3 years). After fixation, all shoulders underwent biomechanical testing with direct loading on the graft via a material testing system. Cyclic loading was performed for 100 cycles (10-100 N) to determine axial displacement with time; each graft was then monotonically loaded to failure.

RESULTS

The maximum cyclic displacement was 4.3 ± 1.6 mm for the cow-hitch suture button technique and 5.0 ± 1.7 mm for the standard double suture button technique (P = .46). Ultimate load to failure and stiffness were, respectively, 190 ± 82 N and 221 ± 124 N/mm for the CH-SB technique and 172 ± 48 N and 173 ± 34 N/mm for the standard double SB technique (P = .66 and .43). The most common failure mode was suture cut-through at the anteroinferior aspect of the glenoid for both fixation groups.

CONCLUSIONS

The cow-hitch suture button technique resulted in a similar elongation, stiffness, and failure load compared to an established double suture button technique. Therefore, this cost-effective fixation may be an alternative, eligible for open approaches, to the established double suture button techniques.