Glenoid Bone Defects—Open Latarjet with Congruent Arc Modification

Recurrent anterior shoulder instability is commonly associated with glenoid bone defects. When the defect is significant, bony reconstruction is typically necessary. The congruent arc modification of the Latarjet procedure uses the concavity of the undersurface of the coracoid to optimally reconstruct the glenoid. Outcomes are maximized and complications minimized.

Recurrent anterior shoulder instability is commonly associated with glenoid bone defects. Significant untreated glenoid bone defects are one cause of failed instability repairs. It is, therefore, important to recognize and treat glenoid bone defects appropriately. The size of the defect together with concomitant pathologies and patient demands determine the significance of the bone loss. When the glenoid bone defect is deemed significant, the authors recommend treating it with the congruent arc modification of the Latarjet procedure.

Bony reconstruction of the glenoid

Bony reconstruction of the glenoid was popularized in English-speaking countries after the publication of the Bristow procedure by Helfet in 1958. He described a technique that was taught to him by Rowley Bristow approximately 19 years previously. The technique involved “transplanting the terminal half-inch of the coracoid.” This was affixed adjacent to an area of roughened glenoid neck with sutures through a split in the subscapularis. This technique was modified to fixation of the coracoid with a screw. This modification was first described by McMurray in 1961. The technique and results were then published by May in 1970. Only the terminal portion of the coracoid was used, however. May also described that the stabilizing mechanism of this procedure was attributable to the bracing role played by the conjoined tendon and the subscapularis tendon in abduction and external rotation rather than by the bone block itself.

Michel Latarjet, however, first described his procedure in 1954. Latarjet described affixing the horizontal limb of the coracoid process with a screw flush to the anteroinferior margin of the glenoid, making a horizontal incision through the fibers of the subscapularis.

The Latarjet procedure has undergone some modifications over the years. Patte and Debeyre suggested modifying the procedure by suturing the anterior joint capsule to the stump of the coracoacromial ligament. They termed this the “triple-blocking procedure.” The term, blocking , is misleading, however, because articular incongruity with this procedure should be avoided to prevent rapid-onset arthropathy.

The triple effect described was as follows. The first effect was the glenoidplasty effect with restoration or lengthening of the glenoid arc. The second effect was the hammock effect of the sling created by the intact lower third of the subscapularis, which is inferiorized by the positioning of the block with its intact conjoint tendon. This is especially evident as the arm is brought into abduction and external rotation. The third effect was the Bankart effect, from resuturing the capsule to the coracoacromial ligament. In addition, the conjoint tendon has a tensioning effect on the inferior part of the subscapularis, adding to the stabilization effect and virtually counteracting the ligamentous laxity, which is often part of the instability.

In order for the coracoid to be used in the manner described by Latarjet, the inferior surface of the coracoid must be decorticated to encourage bony union. Once placed, a graft may need to be contoured with a burr to ensure articular congruity and to prevent articular overhang. It has been shown, although not published, that the radius of curvature of the inferior surface of the coracoid is an excellent match for the radius of curvature of the glenoid. It is, therefore, possible by rotating the coracoid through 90° about the axis to match the 2 surfaces. By removing the pectoralis tendon with a sliver of bone, a ready decorticated surface is obtained for optimum integration of the bone block. These modifications have created the congruent arc Latarjet.

Critical to long-term success of bony reconstruction of the glenoid is optimization of glenohumeral contact forces. Rotation of the coracoid in this modification of the traditional technique has been shown to optimize these contact forces. The optimal position for the graft is flush with the glenoid surface. Grafts placed medially result in increased pressures with high edge loading. Bone grafts placed in a proud position not only increase the peak contact forces anteroinferiorly but also increase the posterosuperior glenoid pressure, indicating a shift posteriorly. An accurately placed graft using this technique should, therefore, minimize the rate of late-onset arthropathy.

Patient selection

The Latarjet procedure is generally reserved for patients with significant bone loss. The significance of any glenoid bone loss is dependant, to some degree, on patient demand. There is an inverse relationship between the amount of bone loss tolerated and the demands placed on the shoulder (ie, the higher the demand, the less bone loss that is tolerated). The authors, therefore, feel that even small bony deficiencies in contact athletes are often significant.

Previous work has identified a high failure rate associated with bone loss in contact athletes, leading to the inverted pear glenoid concept. This represents a 25% bone loss of the inferior pole of the glenoid. The effect of sizeable glenoid defects on shoulder instability has been confirmed in cadaveric studies. Itoi and colleagues performed sequential glenoid osteotomies to determine their effect on humeral head translation. They determined that glenoid deficiencies of a width greater 21% of the glenoid length may be best served by restoration of the glenoid arc for reasons of stability and range of movement. The same was found by Yamamoto and colleagues, who performed a biomechanical cadaver study on anterior glenoid defects.

The size of the defect can be determined by CT, MRI, or arthroscopy. Preoperative CT scanning also helps with the operative planning. Although it is most common for the cleavage plane of the bone loss to be perpendicular to the plane of the glenoid, this is not always the case. If the cleavage plane is shallower, then it may be necessary to burr this flat or modify the pectoralis minor osteotomy to compensate.

Balg and Boileau have provided a useful index to further clarify the decision-making process as to who would most likely benefit from a Latarjet procedure. The instability severity index score takes into account 6 significant preoperative factors: age under 20 (2 points), competitive sports (2 points), contact or forced overhead activity (1 point), anterior or inferior hyperlaxity (1 point), and on the anteroposterior radiograph a visible Hill-Sachs lesion in external rotation (2 points) and loss of normal inferior glenoid contour (2 points). A score of 3 or less is associated with a recurrence rate of 5% with arthroscopic stabilization and 6 or less with a 10% recurrence rate; with a score greater than 6, the recurrence rate escalates to 70%. The investigators suggested that a patient with a score of more than 6 is better served by open surgery (ie, a Latarjet procedure).

An arthroscopic evaluation provides invaluable information that may prove crucial to the final decision as to which procedure to perform if the other evaluations, especially the static imaging results, are inconclusive. If a patient has a moderate Hill-Sachs with small glenoid bone loss but the Hill-Sachs engages ( Fig. 1 ) on air arthroscopy, then a Latarjet is more appropriate than a soft tissue arthroscopic reconstruction.

The Latarjet procedure, however, is not a panacea. It is not a substitute for sound clinical judgment. Patients with multidirectional instability, muscle patterning, and voluntary dislocators are not suitable for this procedure.

Patient selection

The Latarjet procedure is generally reserved for patients with significant bone loss. The significance of any glenoid bone loss is dependant, to some degree, on patient demand. There is an inverse relationship between the amount of bone loss tolerated and the demands placed on the shoulder (ie, the higher the demand, the less bone loss that is tolerated). The authors, therefore, feel that even small bony deficiencies in contact athletes are often significant.

Previous work has identified a high failure rate associated with bone loss in contact athletes, leading to the inverted pear glenoid concept. This represents a 25% bone loss of the inferior pole of the glenoid. The effect of sizeable glenoid defects on shoulder instability has been confirmed in cadaveric studies. Itoi and colleagues performed sequential glenoid osteotomies to determine their effect on humeral head translation. They determined that glenoid deficiencies of a width greater 21% of the glenoid length may be best served by restoration of the glenoid arc for reasons of stability and range of movement. The same was found by Yamamoto and colleagues, who performed a biomechanical cadaver study on anterior glenoid defects.

The size of the defect can be determined by CT, MRI, or arthroscopy. Preoperative CT scanning also helps with the operative planning. Although it is most common for the cleavage plane of the bone loss to be perpendicular to the plane of the glenoid, this is not always the case. If the cleavage plane is shallower, then it may be necessary to burr this flat or modify the pectoralis minor osteotomy to compensate.

Balg and Boileau have provided a useful index to further clarify the decision-making process as to who would most likely benefit from a Latarjet procedure. The instability severity index score takes into account 6 significant preoperative factors: age under 20 (2 points), competitive sports (2 points), contact or forced overhead activity (1 point), anterior or inferior hyperlaxity (1 point), and on the anteroposterior radiograph a visible Hill-Sachs lesion in external rotation (2 points) and loss of normal inferior glenoid contour (2 points). A score of 3 or less is associated with a recurrence rate of 5% with arthroscopic stabilization and 6 or less with a 10% recurrence rate; with a score greater than 6, the recurrence rate escalates to 70%. The investigators suggested that a patient with a score of more than 6 is better served by open surgery (ie, a Latarjet procedure).

An arthroscopic evaluation provides invaluable information that may prove crucial to the final decision as to which procedure to perform if the other evaluations, especially the static imaging results, are inconclusive. If a patient has a moderate Hill-Sachs with small glenoid bone loss but the Hill-Sachs engages ( Fig. 1 ) on air arthroscopy, then a Latarjet is more appropriate than a soft tissue arthroscopic reconstruction.

The Latarjet procedure, however, is not a panacea. It is not a substitute for sound clinical judgment. Patients with multidirectional instability, muscle patterning, and voluntary dislocators are not suitable for this procedure.

Technique

The patient is placed in a beach chair position and brought to the edge of the table, or a table with a shoulder cutout is used. The scapula must be well supported but overprotracting the scapula avoided because this makes exposure and graft positioning and fixation more difficult. The head is supported and the arm is draped free.

An examination of the shoulder is performed to confirm the degree of anterior laxity. Any posterior laxity and laxity of the other shoulder are also noted.

An initial arthroscopic evaluation of the shoulder is performed. The arthroscope is introduced through a standard posterior portal and a 20-mL syringe is connected to the inflow tap on the scope and 20 to 40 mL of air is introduced into the joint. The joint is examined arthroscopically and special attention is paid to the glenoid, anterior labrum (Bankart lesion), and degree of bone loss. The humeral head is examined for the Hill-Sachs lesion, and if the latter is difficult to view, the arm is externally rotated. Most importantly, the absence or presence of a humeral avulsion of the glenohumeral ligaments (HAGL) lesion is noted. The arm is then moved into abduction and external rotation and the Hill-Sachs lesion is followed to note if engagement of the defect takes place over the edge of the glenoid (see Fig. 1 ). This dynamic view is one of the most decisive factors to confirm that a deficient articular arc is present and that bone augmentation is indicated.

The scope is then moved to the anterosuperior portal and air is again introduced into the joint because the air pressure may have been lost with the changeover of the scope to the anterior portal. Through this portal the anterior edge of the glenoid can be viewed better than through the posterior portal ( Fig. 2 ). Bone loss from the glenoid can be evaluated most accurately from this portal, and it is this view that led the authors to first describe the inverted pear appearance of the glenoid. The glenoid is measured as described by Lo and colleagues. The presence of an HAGL lesion is also best appreciated through the anterior portal.