Paper 72: How Much Glenoid Bone Loss Needs to be Restored with a Latarjet?

Abstract

Objectives:Significant anterior glenoid bone loss in the setting of recurrent instability may warrant a coracoid transfer (Latarjet). However, the amount of glenoid width that must be restored with a Latarjet in order to reestablish glenohumeral stability has not been studied.We hypothesize that restoration of greater than 90% of glenoid width with a Latarjet will be necessary to restore glenohumeral stability. We also hypothesize that there will be significant increases in anterior humeral head translation when 90% or less of the native glenoid width is restored and that contact pressures on the coracoid graft will increase.Methods:Seven cadaveric specimens were prepared and mounted on an established shoulder simulator, which loads shoulder tendons through a system of pulleys and weights. A motion tracking system to record glenohumeral translations was placed on the scapula and humerus and registered based on a computed tomography (CT) scan. Contact pressures were mapped and recorded using a TekScan secured to the glenoid face and coracoid graft transfer (Figure 1). The humerus was placed in 90 degrees of humerothoracic abduction.Coracoid osteotomy was performed, and the coracoid graft was sized to a depth of 10mm. A lesser tuberosity osteotomy (LTO) was performed to allow accurate removal of glenoid bone. The amount of bone loss needed to re-establish 110%, 100%, 90% and 80% of native glenoid width after Latarjet was calculated by directly measuring the widest point of the glenoid and confirming accuracy based on the CT scan. Glenoid bone loss was established using a burr and the coracoid graft transfer was secured to the anteroinferior glenoid with two screws. The conjoined tendon was passed through a subscapularis split and the LTO was repaired with multiple Kirshner wires prior to each testing condition (Figure 2). Additionally, the rotator interval was closed and the capsule was repaired prior to each testing condition.The supraspinatus, subscapularis, infraspinatus and conjoined tendons were each loaded with 22N. Testing conditions included native glenohumeral joint, LTO, Bankart tear, and then 110%, 100%, 90% and 80% of glenoid width restoration with Latarjet. Glenohumeral translations and contact pressures were recorded with an anteroinferior load of 0 or 44N at 0 degrees of glenohumeral external rotation.Results:Progressive increases in anterior humeral head translation occurred with an anteroinferior load as the amount of glenoid width restored decreased (Figure 3). An anteroinferior load created an average of 5.5mm, 9.6mm, 3.3mm, 3.6mm, 9.2mm and 10.2mm of anterior translation in the LTO, Bankart, 110%, 100%, 90% and 80% of glenoid restoration cohorts, respectively. Greater glenoid bone loss also led to more contact pressure on the coracoid graft after Latarjet (Figure 4). An anteroinferior load produced 26.4%, 46.9%, 86.2% and 94.4% of the contact pressures on the coracoid graft relative to the native glenoid with glenoid width restored to 110%, 100%, 90% and 80%, respectively.Conclusions:There is an increase in anterior humeral head translation and contact pressure on the coracoid graft when 90% or less of the native glenoid width is restored with Latarjet. By determining the goals for glenoid width restoration after Latarjet, the findings of this study may provide guidance for patient-specific size requirements for the coracoid based on preoperative imaging. When greater than 90% of glenoid width cannot be restored with a Latarjet, surgeons may consider alternative graft sources.