Matthew L. Vopat, MD; Liam A. Peebles, BA; Maj. Travis J. Dekker, MD, MC, USAF; and Matthew T. Provencher, MD, MC, USNR
As the osseous architecture of the glenohumeral joint allows for a large arc of motion as well as rotation, it is inherently predisposed to an elevated risk of instability. The incidence of glenohumeral instability events has been estimated to be 0.08 per 1000 person-years in the general US population, and is significantly greater in active, contact/collision sport, and military populations.1–5 Moreover, recent reports in the literature suggest that military personnel specifically are at a 20 times greater risk of experiencing shoulder instability compared to the general US population in the form of either subluxation or dislocation.3,6 It has been found that these patients are commonly younger athletes who are highly active because this population is at the greatest risk of recurrent instability; furthermore, their risk of recurrent instability increases directly with patient activity level.4,5 It is important to identify the specific patient populations that are at risk for not only primary events of instability but recurrent instability as well, as numerous clinical studies have reported a significant correlation between the rate of recurrence following surgical treatment and the presence and severity of glenoid bone loss (GBL).7–10
In cases of recurrent glenohumeral instability, numerous studies have cited occurrence rates of bony glenoid injury ranging from 36% to 93.7% because higher rates of bone loss are associated with a greater number of instability events.11–14 Furthermore, it has been reported that patients with as little as 13.5% GBL experience worse functional outcomes following primary surgical stabilization procedures.15,16 In attempts to mitigate this risk of recurrent instability through the restoration of natural glenohumeral joint anatomy and function, numerous types of osseous grafts and bony-augmentation procedures have been proposed, including 1) the iliac crest bone graft (ICBG), 2) the distal tibia allograft (DTA), and 3) the distal clavicular allograft. Although the Latarjet procedure, which uses a coracoid autograft, has long been considered to be the gold standard for anterior shoulder stabilization in the setting of significant GBL, these more recent bone grafting options have demonstrated early success in avoiding some of the potential complications commonly seen following a Latarjet and providing excellent clinical outcomes in highly active and athletic populations.
PREOPERATIVE ASSESSMENT OF INSTABILITY AND BONE LOSS
Although recurrent anterior instability commonly results from a Bankart tear of the glenoid labrum, in cases of recurrent subluxation or dislocation patients will frequently present with bony defects of the glenoid. Following initial traumatic dislocation or subluxation of the shoulder, the static capsulolabral restraints of the joint may be compromised due to the presence of a glenoid rim fracture or attritional bone loss, making recurrent instability more likely in the future. The accurate assessment of these potential osseous defects given a patient’s history and physical exam findings in a clinical setting is critical to the overall success of a surgeon’s treatment algorithm. An in-depth understanding of the clinical factors that contribute to anterior glenohumeral instability such as age, sex, level activity, and events of recurrent instability may also help the surgeon accurately predict and diagnose the presence of such osseous deficiencies of the glenoid prior to imaging.
In patients who present after sustaining contact or collision injuries, namely if the arm was axially loaded and abducted 70 degrees or more with extension of 30 degrees or more, the diagnosis of GBL may be suspected if further supported by physical exam findings.17,18 These patients are commonly younger and highly active athletes because this population is at the greatest risk of recurrent instability, which has been found to increase directly with patient activity level.4,5 In patients that have a history and physical examination indicative of potential GBL, it is commonly noted that they will also report a longer duration of instability symptoms, experience a progressive ease in subluxation or dislocation of the glenohumeral joint as well as a mechanical “clunk” on manipulation of the symptomatic shoulder. Prior treatments, whether operative or nonoperative, and their respective outcomes should be assessed along with previous operative reports and imaging studies to clearly delineate the initial pattern of injury and adequacy of proposed treatment for the patient’s pathology. These crucial pieces of information extracted from a patient’s history provide a basis from which a surgeon can tailor their physical exam of both the patient’s defective and contralateral shoulders.
During the physical examination, it is crucial that both shoulders be inspected to identify abnormal physical deformity, prior surgical scarring, scapular dyskinesia, and/or potential atrophy of the rotator cuff on the pathologic shoulder vs the contralateral shoulder.9,18 This comparison can also aid in quantifying the direction and magnitude of glenohumeral laxity by performing physical manipulations of the shoulder such as the Jobe relocation test,19 Gagey hyperabduction sign,20 apprehension sign,21 and sulcus sign.22 Along with the aforementioned tests to assess glenohumeral laxity, the primary physical examination should also incorporate a careful neurovascular evaluation of the entire upper extremity, testing of active and passive shoulder motion, assessment of rotator cuff strength, and provocative labral signs. In the presence of mild to severe anterior GBL, patients will typically demonstrate a positive apprehension test in 90 degrees of shoulder abduction (AB) and 90 degrees of external rotation, and may also exhibit significant anterior or inferior translation of the of the humeral head over the glenoid rim. Physical findings of this nature may be indicative of GBL that is compromising glenohumeral stability and should be further investigated with diagnostic imaging.
DIAGNOSTIC IMAGING MODALITIES
Two-Dimensional and 3-Dimensional Computed Tomography
Numerous methodologies for quantifying the extent and severity of GBL have been proposed in the literature. These techniques are most commonly derived from either surface area- or diameter-based measurement methods. The methodology of measuring GBL stems from the notion that the inferior aspect of the glenoid in the en-face view has a similar shape and curvature to a true circle, from which the degree of bone loss can be calculated by measuring the total surface area of bone loss or comparing the ratio of measurements taken to a healthy, contralateral shoulder.11,23 Although there is a lack of consensus and heterogeneity in reporting persists in the literature, this section describes these measurement techniques and their clinical implications.
The percentage of GBL can be calculated with the use of surface area techniques, which require measuring the area of the superimposed circle not occupied by the glenoid surface and dividing this area by the total area of the best-fit circle.24 Sugaya et al23 first described the “circle method” to determine percentage of bone loss area, which was further expanded on by Baudi and colleagues25 and referred to as the ‘Pico’ method. This method involves superimposing a circle with a horizontal diameter from 3 o’clock to 9 o’clock on the inferior part of the healthy glenoid, and the circle area is measured, most commonly in millimeters squared. That same circle is then transferred to the contralateral, defective glenoid and the area of bone loss outlined, allowing surgeons to calculate percent total bone loss.
Recent studies have found that quantification of GBL using bilateral computed tomography (CT) scans, such as the Glenoid Index, produce the most accurate assessment of GBL. This method consists of comparing the ratio of the measured widths of the injured glenoid to the healthy glenoid.26 In a clinical study, Altan et al27 reported no statistically significant differences between Glenoid Index calculations and the surface area–based measurement technique in patients with more than 6% GBL. It was noted that, although insignificant, as the amount of bone loss increased, the differences in measurements increased as well.27 However, a unilateral affected shoulder CT is the senior author’s preferred method because it exposes the patient to far less radiation and maintains high accuracy.
It has been reported that the location of the glenoid defect is also a fundamental variable in the overall accuracy of bone loss quantification for linear measurement techniques.28 This is primarily because linear measurements are hindered in their ability to represent defects outside the anteroposterior (AP) plane. This results in a significant underestimation of defects that are located in the anteroinferior portion of the glenoid. This was highlighted in a study conducted by Provencher et al,17 who reported that diameter-based measurements are the most inaccurate when the defect is located anteroinferiorly at a 45-degree angle relative to the long axis of the glenoid.
Recent studies that have employed 3-dimensional (3D) CT imaging have called into question the use of diameter-based measurements as a whole. This is primarily because these measurements have been reported to significantly overestimate GBL, which has the potential to misguide a surgeon’s treatment algorithm.24 In regards to the best-fit circle technique, it has been proposed that its inaccuracy arise from the use of incorrect geometric formulas that more closely applies to calculating the area of a square, rather than a circle.29 In a study by Bhatia and colleagues,29 these inaccuracies were most prominent in bony defects that range between 15% and 25%. Therefore, these studies have suggested that unnecessary bony augmentation may be performed because of the overestimation of bone loss that appears to exceed the critical threshold of 20% to 21% for recurrent instability.29–31
Magnetic Resonance Imaging
The primary benefits of using magnetic resonance imaging (MRI) to diagnose and quantify GBL include its ability to evaluate both soft-tissue and bony pathologies concurrently and the avoidance of a patient’s exposure to excessive radiation.32 However, scapular tilt and difficult visualization of the glenoid rim in the presence of soft tissue have been reported to be innate factors that limit the accuracy of MRI in the assessment of GBL.33 These inherent limitations lead to inaccurate measurements because of the difficulty of obtaining a true en face slice of the glenoid as well as in determining the exact edge of the glenoid rim, which is critical when quantifying bone loss via width-length methods.
Although inconsistency in the literature persists regarding whether MRI is a viable substitute for CT, previous studies have reported that MRI does not produce significantly different measurements when comparing the 2 modalities.33,34 Gyftopoulos et al33 concluded that MRI measurements can be as equally accurate to those produced via 3D CT with small margins of error when using the best-fit circle method. Similarly, Huijsmans and colleagues34 reported minimal, insignificant differences in accuracy using the best-fit circle method. Although other studies have reported high accuracy and strong correlations between MRI and 3D CT measurements,35,36 MRI has ultimately proved to be less sensitive and less reliable than 3D CT.37 Overall, 2-dimensional measurements such as the width-length ratio may be less reliable than surface area measurements because of the disadvantages described previously.38 Therefore, when using MRI to preoperatively assess GBL, surface area measurements such as the Pico method or other best fit-circle techniques are suggested to be more clinically applicable.32,34
Because routine plain radiographs are commonplace in the first steps of patient diagnostic workup, the assessment for bony lesions of the glenoid with this modality may be favorable to clinicians because it offers an efficient, low-cost, and low-radiation diagnostic alternative to other aforementioned imaging modalities.39 Although numerous studies have advocated for the use of plain radiographs for these reasons, diagnostic sensitivity, specificity, and accuracy can be drastically influenced by patient positioning.30 When discussing optimal patient positioning for plain radiographs, the axillary view, West Point View, true AP radiographs, and the Bernageau view have been recommended. Of these methods, recent studies have reported the Bernageau view to be the most accurate and reliable when referenced to 3D CT imaging,30,39,40 although using this method makes it difficult to evaluate inferior bony lesions.30 However, true AP radiographs may still provide utility in determining whether there is a loss of contour, or disruption of the sclerotic line, along the anteroinferior glenoid rim. The West Point view has demonstrated potential efficacy in identifying bone loss, but may not be sufficiently accurate in clinical settings to ultimately guide operative decision making.30
BONE GRAFTING VARIATIONS FOR GLENOID BONE LOSS
Patient Positioning for Open-Shoulder Stabilization
After induction of anesthesia with use of an interscalene regional nerve block when possible, the patient is placed into a beach-chair position with 30 degrees of head elevation (Figure 11-1). A small bump or towels are placed under the medial border of the scapula to prevent anterior and internal rotation. The arm can be placed into an armholder of choice or remain free for manipulation with the use of a padded Mayo stand for resting the extremity.67
Standard Deltopectoral Approach for Bone Grafting Procedures
A standard Bankart-type incision with a No. 10 scalpel is made from the tip of the coracoid toward the axillary fold measuring 8 to 10 cm in length. The deltopectoral interval is identified and the cephalic vein is mobilized and protected laterally.41 Deep blunt dissection occurs followed by the identification of the short head of the biceps muscle belly adjacent to the conjoint tendon. A Gelpi or Weitlaner retractor is used to expose the fascia overlying the conjoint tendon, which when identified is then incised, and the lateral aspect of the conjoint tendon is retracted medially with a Kolbel retractor placed beneath the deltoid laterally. A Fukuda retractor is placed just behind the glenoid to retract the humeral head and deltoid laterally. The subscapularis insertion is identified and cleared of adhesions. The junction between the superior two-thirds and inferior one-third is identified and, using this junction, a sharp incision is made in line with the fibers of the subscapularis, taking care to not go medially to the coracoid to prevent iatrogenic nerve injury. However, in revision settings, the quality of subscapularis tissue may make this impossible and instead the subscapularis tendon may be taken down. If this is done, then the subscapularis tendon is tagged with a 2 Fiberwire Suture (Arthrex) for ease of later identification and repair. After clearance of the subscapularis off of the glenohumeral capsule, a medial T-shaped capsulotomy is used for glenohumeral joint exposure with a No. 15 scalpel. The capsule is then elevated off the glenoid neck sharply in a medial and subperiosteal fashion. In the revision setting, hardware, scar tissue, and prior implants are removed with the use of a rongeur and elevators of choice. While remaining perpendicular to the face of the glenoid, the anterior glenoid neck and rim are prepared with a high-speed burr to create a uniform bed of bleeding bone to complete the preparation of the recipient site. One should also evaluate the humeral head for an engaging Hill-Sachs lesion; this can be identified with the prior diagnostic arthroscopy.41
Iliac Crest Bone Graft
Use of bone graft for anterior glenoid bone augmentation to extend the arc and effective articulation with the humeral head has occurred for more than a century. Although Eden42 and Hybbinette43 originally described augmentation with distal tibia, both authors almost immediately switched to the use of the iliac crest autograft (ICBG). The original procedure describes the use of bicortical iliac crest graft but more modern approaches have used tricortical iliac crest.44,45 The iliac crest remains a main source of autograft because of its ease in harvest, more than ample amounts of graft that would be necessary for augmentation, as well as flexibility to give both tricortical and bicortical graft that can be used per surgeon preference. Multiple variations exist, from implant free J-bone graft to bicortical screws to more recent descriptions of cortical suspensory devices.46–52 The iliac crest is most often used in revision procedures but can be used as a primary procedure in the setting of large anterior GBL defects where the Latarjet coracoid transfer would be insufficient (> 30% GBL). This section discusses surgical indications, a variety of ICBG glenoid augmentation techniques, and the associated outcomes to date.
Indications and Contraindications
Debates continue about the quantity and setting of GBL that should lead a surgeon to perform a bone augmentation procedure in the setting of anterior shoulder instability. Most recently, Shaha et al defined bone loss of 13.5% as being a critical number to identify because it leads to unacceptable clinical results and thus would require a bone augmentation procedure.15 Traditionally, biomechanical models and clinical studies have identified the normal cutoff of performing a soft-tissue only repair to a bony augmentation procedure at 20% to 25%.7,9,10,17,31,53–55 Furthermore, the concept of the glenoid track has revolutionized treatment because it aids the surgeon in identifying Hill-Sachs lesions that will engage based on location alone and not necessarily size of either the GBL or the Hill-Sachs lesion. The on-track, off-track concept uses a mathematical equation based on the size and location of the Hill-Sachs lesion and compares it to the amount of remaining glenoid bone stock. If the lesion is “off-track,” the patient has an engaging lesion that will portent to worse outcomes if soft-tissue–only repairs are performed.56,57 At present, the senior author uses tricortical or bicortical ICBG in patients requiring a revision technique procedure (ie, after a failed Latarjet) or those that have extensive attritional bone loss exceeding 30%.
Preoperative workup is similar to that of a Latarjet in that patients should demonstrate anterior instability and apprehension on physical exam. Preoperative imaging should consist of standard shoulder radiographs (AP/Grashey/scapular Y/axillary lateral) along with advanced imaging of a 3D CT scan to quantify GBL (Figure 11-2). The senior author uses the en face view of the reformatted CT and uses the circle method to quantify GBL.23,25
Both open and arthroscopic techniques have been described in the setting of anterior glenoid bone augmentation for anterior shoulder instability with associated bone loss. Arthroscopic techniques have been described with purported benefits that the procedure is completely subscapularis sparing, with smaller incisions along with ease of access to the ICBG harvest site. Pitfalls include that with all new arthroscopic techniques, that there is a steep learning curve, possible increased risk of neuropraxia to the musculocutaneous nerve and axillary nerve, and possible graft harvest site complications.47,49,50,52 Fortun and colleagues47 describe their arthroscopic technique that places the ICBG in an extra-articular fashion along with being able to perform a large capsular shift. Furthermore, they advocate the routine use of a 70-degree arthroscope to facilitate complete visualization of the anterior glenoid rim and neck. Giannakos et al used a double-barreled cannula through a low anterior “J portal” to aid in ease of passage and bicortical graft fixation.48 Authors have also used both screw fixation with bicortical purchase through the glenoid as well as bicortical suspensory devices in an arthroscopic fashion to provide firm and reliable iliac crest cortical abutment.49
The open technique for ICBG for anterior glenoid deficiency has also been described with benefits of direct visualization of the graft/glenoid interface but known technical challenges in revision exposure after failed Latarjet.45,51 The senior author uses the open technique and exposure in the setting of ICBG for anterior GBL.
Iliac Crest Bone Graft Harvest
Starting 2 cm posteriorly to the anterior superior iliac spine, a 5-cm curvilinear incision is made sharply with a No. 10 blade along the iliac crest. A plane between the tensor fascia lata and the external abdominal obliques is created with the use of electrocautery, ensuring the insertion of the abductors remain intact. After complete exposure of the superior iliac crest, blunt retractors are placed on the inner and outer table of the crest to facilitate full exposure for graft harvest. The dimensions of the graft are measured and marked with electrocautery (typically 3 cm long by 2 cm wide). Using a small 1 cm oscillating saw followed by the use of small straight and curved osteotomes, the graft harvesting is completed. The inner table is contoured to approximate the correct contour of the native glenoid, which will eventually articulate with the native humeral head.
After contouring and shaping has been completed, two 4.0 mm cannulated screws with suture washers initially positioned with appropriately sized K-wires are placed for graft fixation (Figure 11-3). The goal for screw trajectory is to be within 10 degrees of parallel to the face of the glenoid with the screws as far medially on the graft as possible to avoid articulation with the native humeral head. Small adjustments and recontouring of the graft/glenoid interface can occur to ensure a perfectly smooth transition from glenoid to the graft with the use of a small burr. The humeral head retractor is removed and articulation along with stability is retested at this time. The high-strength sutures from the washers are then used to repair the capsulolabral ligamentous complex back to the edge of the graft. The lateral limbs of the capsule can often not be repaired in the setting of revision procedures or chronic bone loss. The lateral subscapularis can effectively extend the lateral capsule by fixing the capsule to the undersurface of the subscapularis with the humerus in 30 degrees of external rotation.45 The procedure is then completed with a dermis closure of 2-0 Vicryl followed by a running resorbable 3-0 monofilament suture. The incision is dressed and placed into an immobilizer.