Introduction

Bone loss is a serious problem that can affect any part of the body, both anatomically and functionally, and it must be considered and addressed appropriately. When examining the upper extremity specifically, an area that must be considered extensively is the glenoid and humerus that combine to create the glenohumeral joint. Hantes and Raoulis describe the shoulder as an inherently unstable ball and socket joint that is liable to a multitude of injuries, which makes it highly susceptible to dislocation. In fact, the incidence rate of shoulder dislocations in the United States has been documented to be 23 injuries per 100,000 people. The main cause of the primary shoulder dislocation events is almost always trauma related, due to the traumatic force causing the humeral head to slide out of the glenoid articular arc.

The difficult aspect of glenohumeral dislocation lies in the predisposition for these injuries to become recurrent and lead to an unstable shoulder. Recurrent instability compounds upon itself by creating further attritional bone loss. There are many factors, in addition to trauma, that lead to recurrent glenohumeral instability, such as age, hyperlaxity, glenoid bone loss, humeral head bone loss, and sex. Oftentimes, there are multiple of these factors occurring simultaneously leading to recurrent instability, instead of one isolated factor causing a problem. When determining how to manage shoulder instability several things should be taken into consideration including, osseous defects, experience of the surgeon, and patient-related factors such as participation in athletics and work demands.

Glenoid

The glenoid’s main function is to form a rimmed barrier constraining the humeral head from dislocating. Bony lesions of the glenoid are problematic because they shorten the glenoid arc length and lessen the stability of the joint by reducing the glenoid surface contact area and its concavity ( Fig. 8.1 ). Burkhart and de Beer were able to determine that there was a 4% failure rate for patients not containing a significant glenoid defect, while there was a 67% failure rate in patients with a significant lesion. For the overall prevalence of glenoid defects in cases of recurrent anterior shoulder instability, the rate has been as high as 90%. Of the 90%, 50% of the documented injuries were bony Bankart lesions and 40% were due to erosions from chronic recurrent traumatic anterior instability.

3-Dimensional (3-D) computed tomography en face view of glenoid bone fragment loss. Image has undergone 3-D digital subtraction of the humeral head.

Evaluating the significance of glenoid bone loss has been controversial and indecisive as far as definitive preoperative measurements. The two most commonly used methods for measuring a glenoid defect today are the Pico method and the usage of a preinjury diameter for comparison. The Pico method determines the degree of bone loss by first creating a “normal glenoid circle” from three reference points along the intact rim of the uninjured glenoid. Then, the normal circle is placed on the pathologic glenoid, and the missing part of the normal circle can be divided by area of the inferior glenoid circle to determine the defect as a percent of the entire circle. To find defect size using diameter comparison, the anterioposterior diameter of the injured glenoid is subtracted from the estimated preinjury diameter of the glenoid. Then, that number is divided by the estimated preinjury diameter. A descriptive way of describing a significant glenoid defect, as written by Lo and Burkhart, is to refer to it as an “inverted-pear” shape when viewed arthroscopically from a superior-to-inferior perspective.

The general accepted numerical value for glenoid bone loss is a lesion spanning greater than 25% of the glenoid surface area. However, Gottschalk et al. conducted a systematic review recently and found that 44.7% of the recurrently unstable shoulders studied had glenoid bone loss between 5% and 20%. This means that a large number of shoulders in the past may have been overlooked for potential surgical glenoid augmentation.

Surgical Management

There are several different surgical procedures to stabilize the shoulder, and the correct choice of procedure for each specific patient remains a polarizing topic in the literature. The most common debate in shoulder stabilization surgery is the comparison of the efficacy of arthroscopic and open procedures. In the 1900s and early 2000s, open procedures were thought to be the “gold” standard, but now there is proof in the literature that there are many cases where arthroscopy offers its own advantages.

Arthroscopic Bankart repair is an extremely successful technique for treating soft tissue injuries in the shoulder in conjunction with minimal to zero glenoid bone loss. However, when the glenoid presents a bony defect encompassing 20%–25% of the diameter of the inferior glenoid, the osseous defect must be addressed for a successful surgical outcome. This is because progressive anteroinferior bone loss leads to an increased mean contact pressure and peak pressure. The neglect of the bone loss by performing solely a soft tissue Bankart repair would lead to the bone–soft tissue repair interface having to resist the extra overload, leading to a greater likelihood of repair failure.

Latarjet

One of the most common and effective methods of treating shoulder instability with glenoid bone loss is the Latarjet procedure ( Fig. 8.2 ). The Latarjet is a nonanatomic procedure involving the transfer of the horizontal limb of the coracoid process along with the conjoint tendon to the anterior glenoid rim. The traditional open procedure, which was originally proposed by Latarjet in 1954, is a successful treatment option that has been the standard for the past several decades. However, in 2010, Lafosse and Boyle presented a study that aimed to conduct the Latarjet arthroscopically in order to gain the advantage of minimally invasive surgery. They operated on 100 shoulders, and outcomes revealed 91% excellent scores and 9% good scores. The one limitation of this technique is it is very challenging and places several neurovascular structures at risk. Dumont et al. reported the first long-term (>5 years) results of the arthroscopic Latarjet procedure. They reported results on 64 shoulders with a mean follow-up time of 76.4 months, and they found zero true dislocations and one patient with a subluxation event.

Image of coracoid postharvesting before fixation as part of the Latarjet procedure.

With the fairly recent advent of the arthroscopic Latarjet, there has been debate as to which technique, open or arthroscopic, is the superior method. This year Zhu and colleagues released a comparison study that included 44 patients in the open group and 46 patients in the arthroscopic group. At the final follow-up, they found all of the clinical measurements (American Shoulder and Elbow Surgeons [ASES] score, Rowe score, and range of motion [ROM]) to have no significant differences. Another study by Marion et al. produced similar results in a study with 22 open and 36 arthroscopic Latarjet procedures showing that clinical outcomes between open and arthroscopic procedures were comparable after 2 years’ follow-up. However, the arthroscopic procedure caused significantly less pain for the patients. Both methods are viable and successful options today, so the operative decision lies in the surgeon’s hands.

A new study, by Ersen et al., came out comparing the subscapularis split and subscapularis tenotomy techniques in a Latarjet procedure. They found the internal rotation durability to be significantly higher in the split group ( P = .045) than the tenotomy group. Therefore, when working with the subscapularis during a Latarjet, it should be the preferred method to use the split technique.

Iliac Crest Bone Graft

The Latarjet is a successful technique, but limitations associated with its nonanatomic nature include loss of motion, arthritis, and nonunion. An alternative to the Latarjet is the usage of an iliac crest bone graft (ICBG) to resurface the glenoid defect. Before conducting an ICBG procedure, the doctor must select to use either an allograft or autograft. An allograft is beneficial because it removes the donor-site morbidity from autogenous reconstructions and complications associated with pain and sensory disturbances. On the other hand, an autograft has advantages in that it is osteoinductive and immunogenic. The iliac crest is the most common graft site because of easy access and procurement, low morbidity, and large quantities of both cortical and cancellous bone. Warner et al. described a group of 11 patients who underwent open anatomic reconstruction of the anterior glenoid with an iliac crest allograft and none of the patients reported recurrent instability. Mascarenhas et al. conducted a similar study containing 10 patients who experienced open bone graft reconstruction. Overall, the results showed no recurrent dislocations, no hardware failure, and no joint degeneracy. The open method, as shown in the literature, is a highly successful technique in restoring bony glenoid anatomy.

Similar to the evolution of the Latarjet procedure, arthroscopic reconstruction with the iliac crest graft has begun to gain traction. Taverna and his colleagues recently developed an entirely arthroscopic technique without the usage of screws for anatomic glenoid reconstruction using an iliac crest graft. This technique is important because it lessens the incisions and preserves external rotation, while preventing recurrent instability. The limitation of this procedure is that it does require expert arthroscopic technique and a long learning curve.

The short-term outcomes look very promising, as the procedure has been preventing instability and causing successful union in patients. The one problem is that there has not been any literature published on the long-term outcomes, which is especially problematic because of the potential long-term issues resulting from the allograft.

Distal Tibia Allograft

In cases of glenoid bone loss where the Latarjet technique or ICBG are contraindicated or in the revision setting, distal tibial allograft (DTA) is a viable option ( Fig. 8.3 ). DTAs are advantageous in that they provide chondral restoration of the articular surface defect in addition to osseous restoration, avoid donor-site morbidity, and are not as limited in size as coracoid grafts for reconstructing larger areas of bone loss. DTAs are also dense, weight-bearing corticocancellous bone, allowing for screw fixation with less risk of fracture as was reported in Latarjet procedures. In a cadaveric study, DTA was found to have significantly higher glenohumeral contact areas than Latarjet at 60 degrees of abduction and at the abduction with external rotation (ABER) position, as well as significantly lower glenohumeral peak forces than Latarjet reconstruction in the ABER position.

(A) Distal tibial allograft having Kirschner wires inserted for provisional fixation to the glenoid defect after preparation. (B) Distal tibial allograft after final fixation.

In clinical data, systematic review of 8 studies including 70 shoulders with recurrent anterior instability that were treated with allografts including, iliac crest, femoral head, distal tibia, glenoid, and humeral head, after a mean follow-up of 44.5 months (range 32–90), yielded results that were largely positive, with 93.4% satisfied and a mean final Rowe score of 90.6 (mean improvement of 57.5). Only 9.8% of patients continued to have pain in the shoulder, 7.1% continued to experience instability (dislocation, subluxation, or apprehension), and 2.9% suffered recurrence of glenohumeral dislocation. Bony integration of the graft was achieved in 100% of shoulders without any signs of graft resorption at long-term follow-up. These were excellent results for allografts in general, and the results for DTA specifically are even more encouraging. A separate outcomes study that reported on 27 patients following DTA augmentation of the anterior glenoid with an average follow-up of 45 months (range 30-60) demonstrated significant improvements in ASES score, Western Ontario Shoulder Instability (WOSI) index, and Single Assessment Numerical Evaluation (SANE) score. There were no significant differences in ROM between the affected and nonaffected shoulders in any direction, and there were no signs of apprehension or cases of recurrent instability in any patients at final follow-up. Computed tomography (CT) data showed an allograft healing rate of 89% (range, 80%–100%), average allograft angle of 14.9 (range, 6.6 to 29.3), and average allograft lysis of 3% (range, 0%–25%). Notably, grafts with lesser allograft angles showed superior healing, demonstrating that optimal allograft placement results in superior bony incorporation with the native glenoid. Further investigation is necessary to prove DTA efficacy in larger populations and for longer term follow-up, but initial data are promising.

Hill–Sachs Lesions

The Hill–Sachs lesion is a compression fracture of the posterosuperolateral aspect of the humeral head that occurs when it comes into contact with the dense cortical bone of the anterior glenoid. Throughout the literature, it has been noted that Hill–Sachs defects are prevalent in 67%–93% of primary anterior dislocation events and up to 100% prevalent in recurrent shoulder instability. Recurrent dislocations are a critical issue because they continuously erode and wear down the anatomic glenohumeral constraints, leading to chronic instability. In addition to wearing down the ligaments, the constant abrasion from the anterior glenoid in a dislocation causes the compression fracture on the humeral head to become larger. A larger Hill–Sachs lesion leads to postoperative recurrent instability because of the articular arc deficit, which causes engagement with the anterior glenoid rim.

Grading or defining a Hill–Sachs lesion is a complex task because of the necessity to view and evaluate many different factors, such as length, depth, surface area, volume, and orientation. Consideration of a multitude of factors stems from the hope of finding a valid predictor for when a Hill–Sachs requires surgical intervention. The typical definition of a Hill–Sachs lesion that warrants significance surgically is a bony defect covering 25% of the articular surface. However, this percentage can decrease when considering concomitant injuries, such as a Bankart tear or bipolar bone loss.

In terms of orientation, the Hill–Sachs should be considered for surgical treatment if it lies in a position that forces it to interact with the anterior glenoid in a position of athletic function (i.e., 90 degrees of abduction and 90 degrees of external rotation). Burkhart and de Beer first described the interaction of the humeral head with the glenoid as either “engaging” or “nonengaging.” If the lesion is parallel to the glenoid, it will engage and cause a higher probability of dislocation; if it is diagonal, it will make continuous articular contact and most likely not engage with the rim of the anterior glenoid. Cho et al. noted that engaging lesions are both wider and deeper than nonengaging lesions, showing a correlation between the size of the Hill–Sachs lesion and its engagement.

Glenoid Track Concept

The glenoid track was a concept first described by Yamamoto et al. in 2007. They demonstrated the “track” by showing as a cadaveric arm was lifted, the glenoid shifted from the inferomedial to superolateral of the posterior articular surface of the humeral head. They measured the zone of contact to be 84% of the glenoid articular surface barring any glenoid bone loss, and Omori et al. reaffirmed Yamamoto by finding that the track covers 83% of the articular surface in vivo shoulders using 3-D magnetic resonance imaging (MRI). If the lesion extends too far medially over the medial margin of the glenoid, then the risk of dislocation and engagement becomes high. The glenoid track has been known in the orthopaedic community for several years now, but its functional clinical use is just now being proven and explored in the literature.

Gyftopoulos et al. were the first to relate the on-track off-track method to clinical studies by testing its ability to predict engagement during an MRI. They determined the track method to have an overall accuracy rate of 84.2% when predicting engagement during 2D-MR examination. The negative predictive value of the on-track off-track method was 91.1%, which offers reassurance its accuracy. These findings are important for clinicians because preoperative physical examination findings of increased laxity caused by torn anterior capsulolabral structures could lead to false diagnosis of engagement.

Shaha et al. took the knowledge of the glenoid track to new heights in retrospective review of 57 patients who underwent arthroscopic shoulder stabilization surgery. Eight patients (14%) were documented to be off-track, and 49 patients (86%) were on-track. They determined that 75% of the off-track patients experienced recurrent dislocations postoperatively, while only 8% of the on-track patients dislocated postoperatively. In a subanalysis of 30 patients with bipolar bone loss, they found seven patients with failed treatment, and six of the seven patients (86%) were off-track. The last finding presented was that the glenoid track was accurate in 89% of predictions, while using glenoid bone loss (>20%) as a predictor only offered 29% success. This study is critical to clinical practice because it validates the glenoid track, as the superior method of helping to make proper preoperative decisions in preventing recurrent instability.

The glenoid track can also be defined or measured with an expression created by De Giacomo et al. The equation reads as follows: glenoid track width = 0.83D – d, where D is the diameter of the glenoid and d is the amount of glenoid bone loss (posterior radius–anterior radius). Theoretically, this method would allow the surgeon to preoperatively assess whether a Hill–Sachs lesion needs to be surgically addressed, and it has recently been validated using a biomechanical model. However, the work of the likes of Gyftopoulos and Shaha is what has given clinical proof to the algorithm and theory of the glenoid track as being a necessity in clinical practice.