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Treatment of recurrent anterior shoulder instability associated with glenoid bone loss: Distal tibial allograft


OVERVIEW

Chapter synopsis

  • Glenoid bone loss is frequently present in patients with recurrent anterior shoulder instability. Key factors indicative of significant glenoid bone loss of more than 20% are instability at midranges of abduction (20–60 degrees) and progressive ease of subluxation with daily activities. Young, highly active patients, especially contact or overhead athletes, should be considered for glenoid bony augmentation to restore glenoid surface area, articular length, and depth. Use of a distal tibia allograft has the advantages of a near congruent articular surface with the native glenoid, dense corticocancellous bone, and a robust cartilage layer. In addition, use of a distal tibia allograft restores the native anatomy without altering mechanical function of surrounding structures and eliminates the risk of donor site morbidity.

Important points

  • Indicated for highly active, young patients with apprehension or instability in midranges of abduction (20–60 degrees) with more than 20% anterior glenoid bone loss measured on three-dimensional (3D) computed tomography (CT).

  • It is not indicated for older, low-demand patients; those with multidirectional instability; voluntary dislocators; or those unable to comply with postoperative restrictions (including smokers).

  • Always perform a CT scan with 3D reconstruction of the glenoid preoperatively with the humeral head digitally subtracted to measure glenoid bone loss on the sagittal oblique images.

  • Use fresh distal tibia allograft for optimal bone and cartilage quality.

  • Allograft is taken from the lateral aspect of the distal tibia, which is nearly identical to the native anterior glenoid radius of curvature.

Clinical and surgical pearls

  • Patient positioning: elevate the back and head to only 40 degrees and ensure the back is well supported with two towels along the medial border of the scapula to facilitate adequate anterior glenoid exposure.

  • Use of a padded mayo stand allows additional arm and shoulder mobility and additional scapular external rotation to expand exposure.

  • Always perform diagnostic arthroscopy first.

  • dentify the subscapularis and capsular plane from lateral to medial, taking care to identify the long head of the biceps tendon before the subscapularis horizontal split.

  • Remove all capsular and labral tissue from the glenoid neck and ensure that the glenoid neck is flat and perpendicular to the articular surface before allograft placement.

  • The allograft is cut from the lateral third of the distal tibia donor.

  • The medial allograft cut is angled 5–10 degrees medially to restore the normal glenoid morphology and fit congruently with a perpendicular cut to the glenoid.

  • Lag screws are inserted perpendicular to the glenoid to ensure bicortical purchase and should be 36–40 mm in length.

Clinical and surgical pitfalls

  • Unrecognized anterior glenoid bone loss of 20%–30% represents a high failure rate with soft tissue stabilization procedures.

  • If the medial border of the scapula is not supported, the scapula may not be externally rotated sufficiently to expose the anterior glenoid. If the glenoid is internally rotated and adequate exposure is not obtained, the pectoralis minor may be released from the coracoid.

  • The axillary nerve is at risk during glenoid preparation. It may be protected with a smooth retractor or a gloved finger.

  • Ensure that the Kirschner wires used for graft positioning are not in the intended path of the cortical screws.

  • If the graft is not drilled perpendicular to the glenoid face, bicortical fixation will not be achieved, which will cause graft migration and inadequate fixation.

Introduction

Glenoid bone loss (GBL) has been reported in up to 90% of patients with recurrent anterior instability. Recognition of anterior glenoid rim fractures is paramount in acute shoulder dislocation as attritional bone loss develops rapidly. Historically, the primary surgical option in the setting of anterior shoulder instability has been open or arthroscopic capsulolabral repair without bone augmentation. However, it has been demonstrated that GBL as low as 13.5% is associated with inferior clinical outcomes, especially in the young, active, male population.

Several bone grafting options are available. The Latarjet technique and its variations is the most commonly used method. The method is suitable when GBL is up to 20% to 25% and offers a hypothetical advantage in that the conjoined tendon serves as a sling, thus adding to the anteroinferior buttress. However, transfer of the coracoid graft with the conjoined tendon alters the anatomy of the neurovascular structures. Although the popularity of the Latarjet procedure has increased, the procedure is technically challenging, and the reported recurrence of instability (dislocation and subluxation) rates following Latarjet is between 7.5% and 11.6%. ,

An iliac crest autograft is another option that has the added benefit of being able to replace larger glenoid bone defects and the method has demonstrated comparable results to the Latarjet technique. An advantage with an iliac crest autograft when using the J-graft method is that the graft can be press-fitted into the glenoid, thus avoiding potential hardware problems. However, some studies reported a high frequency of donor site complications, although the majority of these consist of sensory alternations over the harvest site.

In contrast to the previously described methods, a distal tibial allograft (DTA) offers a cartilage-covered graft alternative. The method was first described in 2009 by Provencher et al., and laboratory and clinical findings with DTA in the primary and revision setting have demonstrated excellent results. , , The curvature of the lateral aspect of the distal tibia matches the curvature of the glenoid, even when the contralateral distal tibia is used. , , Compared to non-anatomic alternatives such as coracoid and iliac crest autografts, it has been shown that DTA provides significantly higher contact area of the glenohumeral articulation. Another unique advantage of the DTA is that the dense corticocancellous bone allows secure fixation and excellent incorporation with the native glenoid.

History

Patient history and demographics are crucial factors to assess in a patient presenting with recurrent anterior instability following a primary shoulder stabilization procedure ( Box 18.1 ). Young, highly active patients and athletes, especially those participating in contact or collision sports, have been found to be a patient population with the greatest risk of experiencing recurrent anterior shoulder instability. , In the setting of multiple recurrent instability events, patients commonly present with osseous defects of the anterior glenoid rim and report instability or apprehension within the midranges of motion and may recall a progressive ease of subluxation or dislocation. , , Those patients presenting with significant GBL have most likely already undergone prior anterior soft tissue stabilization (open or arthroscopic Bankart) and may be unable to perform daily activities or participate in athletics.

BOX 18.1
Pertinent Patient Historical Factors Contributing to Pathologic Instability

  • Multiple recurrent instability events

  • Long duration of instability symptoms (have had prolonged instability over time)

  • Early age at initial subluxation/dislocation

  • Increased ease of dislocation or instability events—meaning less energy is required to cause an instability episode

  • The shoulder coming out in sleep (when muscles of the shoulder girdle are relaxed)

  • High energy mechanism of injury

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