Posterior shoulder instability in the contact athlete: a review of the diagnosis, management and outcomes

Introduction

Posterior instability of the glenohumeral joint is gaining increasing attention as a significant source of pain and recurrent injury in athletes that engage in high-risk sports, such as contact athletes (football, wrestling and rugby), overhead and throwing athletes and military servicemembers. While anterior shoulder instability is a much more commonly encountered pathology, posterior shoulder instability is often underdiagnosed, as patients frequently present with more vague symptoms of pain and without an acute traumatic injury. These vague symptoms often overlap with other common shoulder pathologies, which can lead to a delay in diagnosis and management. Posterior shoulder instability is typically the result of some combination of an acute traumatic injury, in addition to repetitive microtrauma and stress across the posterior capsule and glenohumeral ligaments. Timely diagnosis and appropriate treatment are crucial, especially for contact athletes, as recurrent instability and persistent pain can result in poor patient-reported outcomes, decreased shoulder function, limited rate of return-to-play, and, in some cases, premature retirement from sport (1-4). Comprehensive evaluation and individualized treatment strategies are necessary for optimizing patient outcomes and return to pre-injury level of activity in the contact athlete. Significant strides have been made in the last decade with an increasing body of literature focused on defining, treating and monitoring recurrence in patients with posterior shoulder instability. This clinical review describes the complex interplay between injury patterns, anatomical considerations and diagnostic criteria, as well as surgical and rehabilitation strategies to timely diagnosis and treat posterior shoulder instability in the contact athlete with the goal of optimizing patient-reported outcomes, functional performance and rates of return to sport.

Prevalence in contact athletes

Overall, past literature has reported posterior labral tears to account for only 2–5% of shoulder instability cases (1,2,5,6). However, this has been challenged more recently, specifically with the higher rates of posterior shoulder instability reported in the United States (US) military population, which is a high-risk population often engaging in combat arms, weapons training, parachuting, heavy load carrying and weightlifting. A 2021 review of the incidence of posterior shoulder instability in the US military population found the total incidence of all shoulder instability to be 1.84 per 1,000 person-years, with posterior instability accounting for 5.2% of total cases (3). This overall incidence is higher than previously reported, which is likely reflective of the young, active population and due to increased awareness of posterior instability as a concern in shoulder pain in the contact athlete. Furthermore, the overall unadjusted incidence was 0.032 per 1,000 person-years for posterior dislocation, 0.064 per 1,000 person-years for posterior subluxations, and 0.096 per 1,000 person-years for all cases of posterior shoulder instability (3).

Mannava et al. (4) reported on the prevalence of posterior labral tears in collegiate football players competing in the National Football League (NFL) Combine. The authors found that linebackers and linemen were most likely to demonstrate labral pathology. Magnetic resonance imaging (MRI) demonstrated that 34% of patients with labral tears had posterior labral pathology compared to 30% with an anterior labral tear, 34% with combined anterior and posterior labral tears and 31% with a superior labral anterior-posterior (SLAP) tear. They also demonstrated that 53% of shoulders with an identified labral tear also demonstrated evidence of prior shoulder surgery in this contact athlete population. Offensive lineman, tight ends and long snappers, all positions that are commonly involved in blocking maneuvers, demonstrated the highest rate of posterior labral tears. Similarly, a retrospective review of military service members who underwent shoulder stabilization procedures found that 24% had isolated posterior labral tears, while 43% had combined anterior and posterior labral tears (7). This higher than previously reported rate of posterior shoulder instability in the contact athlete is further supported by a United Kingdom study focusing on a cohort of predominantly young, male patients among the general population undergoing arthroscopic labral repair (8). In this study, Javed et al. (8) found a 17% rate of posterior labral tears and 34% rate of combined anteroposterior labral tears in the athletic population, predominantly comprised of rugby players, which was significantly higher compared to the non-athletic population (12% rate of posterior labral tear and 18% rate of combined anteroposterior labral tear) (8).

Injury mechanism and pathoanatomy

Posterior glenohumeral instability can result from two general mechanisms. In the overhead throwing athlete, SLAP tears can propagate in a posteroinferior direction, classified as a SLAP type VIII tear. In the contact athlete, posteroinferior tears in the labrum generally occur due to repetitive microtrauma resulting from a posteriorly directed axial force. Posterior loading typically occurs in the provocative position of forward-flexion, adduction and internal rotation of the shoulder. Chronic repetitive microtrauma leads to attenuation of the posterior capsule and associated posterior labral tear. Although much more common in anterior shoulder instability, acute traumatic posterior subluxation or dislocation can also occur, which results in posterior capsulolabral detachment.

The glenohumeral joint is inherently the most unstable joint in the body due to the small osseous static restraint. The labrum increases the depth of the glenoid socket and functions as a static stabilizer. The posterior inferior capsule and inferior glenohumeral ligament (IGHL) provide the primary restraint to posterior instability with the shoulder in 90 degrees of abduction. A balance between dynamic and static stabilizers is critical to maintain posterior shoulder stability. In the setting of posterior instability, the static and dynamic stabilizers include the posterior labrum and capsule, glenoid and humeral head morphology, rotator cuff and rotator interval, deltoid function, and coordinated scapulothoracic motion (2).

Only one third of the humeral head articulates with the glenoid fossa throughout the arc of shoulder motion. Therefore, abnormalities in bony morphology such as posterior acromial height, glenoid hypoplasia, posterior glenoid rim erosion, and excessive glenoid or humeral retroversion can predispose patients to posterior instability (9-11). Insidious-onset patulous posterior capsule is also a common phenomenon in posterior instability and has been reported in up to 20% of shoulder patients with posterior instability (12). Additional concomitant pathology in the setting of posterior shoulder instability may include a reverse Hill-Sachs lesion or impaction fracture of the humeral head (9%), bony glenoid abnormalities (2%), such as posterior glenoid fracture or glenoid dysplasia, and excessive glenoid or humeral retroversion (12). A cadaveric study by Imhoff et al. (13) suggested that the labrum contributed more significantly to stability at higher degrees of glenoid retroversion, specifically in retroversion greater than 10 degrees. Furthermore, with every additional 1 degree of glenoid retroversion, the risk of posterior instability increased by 17% (14). These anatomic variations must be considered when combining the patient’s clinical presentation and ultimately determining a treatment plan, especially when considering retroversion in the setting of posterior glenoid bone loss. Wolfe and colleagues (15) reported posterior shoulder instability with moderate glenoid bone loss, defined as greater than 13.5%, was associated with higher rates of increased glenoid retroversion.

Clinical presentation

A thorough patient history, comprehensive physical exam and imaging modalities are key in timely and accurate diagnosis, in addition to optimization of the treatment plan. As compared to anterior shoulder instability, posterior instability is less common in the contact athlete and harder to diagnose as patients often have variable clinical presentation with vague symptoms. Typically, there is not a classically described event of a traumatic dislocation event. The most common presenting symptom of posterior shoulder instability is shoulder pain located deep and posterior within the joint, often lacking accompanying mechanical symptoms. In a comparative study by Bernhardson et al. (16), the primary presenting complaint of posterior shoulder instability was pain alone (90.7%) without an identifiable mechanism of injury versus joint instability (80%) with an identifiable mechanism of injury for anterior shoulder instability. Contact athletes will often complain of difficulty with push-up and bench press positioning. Football lineman and linebackers often describe the provocative shoulder position to be during blocking motion (4). On the other hand, overhead throwing athletes may describe a decline in pitch accuracy and decreased pitch velocity in posterior shoulder instability (17).

Physical exam findings are often subtle, and both active and passive range-of-motion (ROM) of the shoulder are typically normal. However, overhead throwing athletes with posterior instability commonly demonstrate increased physiologic external rotation and posterior capsular laxity at the expense of decreased internal rotation and compensatory scapular winging to antevert the glenoid (18). Physical exam maneuvers specific for posterior instability include the Kim test, jerk test, posterior load and shift test, and the dynamic posterior instability test (DPIT), which are defined in Table 1 (19-21). The Kim test has been shown to be more sensitive in detecting predominantly inferior labral lesions, while the jerk test has been shown to be more sensitive in detecting predominantly posterior labral lesions (22). When combining both the Kim and Jerk tests as part of the physical exam, there is 97% sensitivity in detecting posteroinferior labral pathology (22). The DPIT has been described by Arner et al. (21) as an adjunct to diagnosing posterior instability with the patient simulating an overhead throwing position while the examiner holds the forearm and forward flexes the shoulder to 140 degrees. A positive test, in which the patient’s symptoms of pain are recreated, or instability is felt, demonstrated a sensitivity and specificity of 94% and 95%, respectively.

A comprehensive physical examination and evaluation for anterior and superior labral tears, as well as concomitant rotator cuff pathology is required, as these conditions can often coexist (23). Arner et al. (23) found 43% of overhead throwing athletes had concomitant rotator cuff tears in addition to posterior capsulolabral pathology. Further comprehensive physical examination techniques of the biceps-labrum complex include the crank test, shear test and resisted throwing maneuver (24). The crank test is performed with forward elevation of the shoulder to 160 degrees with application of axial load through the shoulder with internal and external rotation of the humerus. This maneuver can be performed in the supine or seated position, with pain indicating a positive test, suggestive of labral pathology. The dynamic labral shear test is performed with the patient standing upright and the examiner positioned behind. The patient’s arm is placed in external rotation and elevation in the plane of the body. The examiner supports the patient’s wrist with one hand and applies an anterior force to the proximal humerus at the level of the glenohumeral joint with the other. The arm is then abducted from 90 to 120 degrees. A positive test is indicated by pain or a palpable click in the posterior shoulder. In the resisted throwing test, the shoulder is abducted to 90 degrees and the elbow flexed to 90 degrees, with the arm placed in maximal external rotation. The examiner, standing behind the patient, applies resistance as the patient mimics the late cocking phase of throwing. The patient then steps forward with the opposite leg, simulating the early acceleration phase. Pain reproduced during this maneuver is most specific for pathology at the biceps-labrum junction.

Imaging

Plain radiographs—Grashey, anteroposterior, scapular Y and axillary views—aid with identification of significant glenoid bone loss, glenoid rim fracture or reverse Hill-Sachs lesion. Optimal advanced imaging studies include MRI and magnetic resonance arthrograms (MRA). MRI is essential for the diagnosis of posterior inferior capsulolabral injuries with a sensitivity that is increased with intra-articular gadolinium contrast. MRA will increase the sensitivity of MRI in identification of a purely soft tissue injury of the posterior labrum and capsule. In the acute setting, the labrum may be well visualized without intra-articular contrast due to hemarthrosis. As compared to the anterior labrum, the posterior labrum tends to be more homogenous with less variable anatomy in the population. Preoperative MRI/MRA has a lower sensitivity when identifying posterior labral pathology, highlighting the importance of clinical suspicion and physical exam findings (25,26). A Kim lesion presents a variant of posterior shoulder instability in which an incomplete avulsion of the posterior inferior labrum occurs from the glenoid articular cartilage with an intact superficial portion of the labrum. Though rare, Kim lesions are more frequently seen in young, active individuals, particularly overhead or contact athletes, and require careful evaluation on MRI as failure to identify and treat them may lead to persistent shoulder instability (27). Typical treatment in the setting of a Kim lesion includes converting the partial tear into a complete tear and incorporating the posterior band of the IGHL into the repair (28).

A high clinical suspicion for posterior glenoid bone loss should be considered in instances of recurrent instability or traumatic dislocation (Figure 1). Computed tomography (CT) of the shoulder is the modality of choice for evaluation of bony morphology to include glenoid retroversion or dysplasia, as well as bone loss. CT is also utilized for quantifying the location and degree of attritional posterior glenoid bone loss. Although the well-established threshold that guides treatment for anterior bone loss has not been established for posterior bone loss, irregularities in bony morphology may further dictate the surgical approach.

Figure 1 Pre-operative imaging of a left shoulder including (A) Grashey and (B) axillary lateral plain films demonstrating an irregular contour of the posterior glenoid rim (arrow), as well as magnetic resonance imaging T2-weighted (C) axillary and (D) sagittal cuts confirming posterior capsulolabral pathology (arrow) with posterior glenoid bone loss of 30% measured by the best-fit circle technique.

Posterior glenoid bone loss

There are several structural differences characteristic of posterior instability compared to anterior instability. Bone loss occurs 30 degrees from the long axis of the glenoid, as compared to 90 degrees to the long axis of the glenoid, as is seen in anterior glenoid bone loss. In a review of three-dimensional reconstructed computed tomography (3D-CT) scans of patients with recurrent posterior shoulder instability, Dekker et al. (29) identified a predictable pattern of posterior bone defect localized to the posteroinferior quadrant extending from 6:44 to 9:28 on the clockface, which corresponded to an average of 81 total degrees of bone loss arc. Sequelae of posterior instability include loss of glenoid concavity and changes in slope leading to acquired glenoid retroversion, which is associated with failure of nonoperative therapy and posterior shoulder stabilization.

Nearly 25% of posterior shoulder instability may be associated with posterior glenoid bone loss, and noticeable bone loss can be demonstrated in as few as one traumatic dislocation event (12). Bedrin et al. (30) showed that the average single posterior shoulder instability event was associated with 5% of glenoid bone loss, and greater than 10 degrees of glenoid retroversion increased the amount of posterior inferior bone loss after a posterior instability event. A clearly established critical or subcritical threshold for posterior glenoid bone loss has not been defined, similar to the ongoing lack of consensus in the anterior shoulder instability literature. However, a cadaveric study with greater than 20% bone loss suggests a high risk of failure of arthroscopic posterior shoulder stabilization alone (31). Similarly, in a retrospective case-control study, Arner et al. (32) suggested that even a small threshold of 11% posterior glenoid bone loss led to a tenfold higher failure rate, while 15% bone loss resulted in a 25-fold higher failure rate following arthroscopic posterior shoulder stabilization alone.

Treatment strategies

There is no gold standard treatment algorithm for posterior shoulder instability, and treatment overall is highly individualized based on patient-specific and morphology-specific factors. First-line management is centered around nonsurgical treatment with activity modification and physical therapy including proprioceptive training, dynamic stabilization and strengthening of the posterior shoulder musculature. Physical therapy further focuses on strengthening the dynamic stabilizers of the shoulder including the rotator cuff and deltoid, as well as scapulothoracic mechanics. Orthobiologics, such as platelet-rich plasma (PRP) injection therapy, may be considered for use in the nonoperative treatment of posterior shoulder instability. However, sparse literature exists to support the use of PRP in the treatment of labral pathology, with data extrapolated from anecdotal experience and existing data from other uses in the shoulder (33,34). Arthroscopic posterior labral repair with or without capsular plication is a reliable treatment option in patients who fail nonoperative management. A comprehensive assessment of all anatomical considerations for instability should be addressed at the index procedure to decrease recurrence, as failure to address combined pathology, excessive glenoid retroversion or posterior glenoid bone loss increases the risk of recurrence after arthroscopic stabilization (1). Subsequently, posterior osseous glenoid augmentation is considered in the setting of a failed arthroscopic posterior stabilization or in the setting of abnormal posterior glenoid morphology (increased glenoid retroversion or significant glenoid bone loss). Treatment plans are highly individualized, especially in the contact athlete, and care should be taken to consider factors such as age, severity of symptoms, level of competition, in-season versus off-season play, position, and desired longevity in sport in the shared decision making. The authors’ preferred treatment algorithm for posterior shoulder instability in the contact athlete, adapted from Trivellas et al. (35), is outlined in Figure 2.

Figure 2 Preferred treatment algorithm for posterior shoulder instability in the contact athlete. pGBL, posterior glenoid bone loss.

Arthroscopic all-soft tissue stabilization

Arthroscopic posterior shoulder stabilization is the gold standard in the absence of substantial posterior glenoid bone loss (Figure 3), with generally excellent clinical outcomes reported. Arthroscopic repair can be performed in either the lateral or beach chair position based on the surgeon’s preference. In addition to soft tissue labral repair with fixation at the chondrolabral junction, tensioning of the IGHL is an important consideration. Capsular plication can also be performed at the time of labral repair to reduce capsular volume and further limit glenohumeral translation.

Figure 3 Arthroscopic images of a posterior shoulder stabilization of a left shoulder in the lateral decubitus position viewing from the anterior portal, beginning with (A) identification of the isolated posteroinferior capsulolabral lesion (*), and followed by (B,C) preparation and elevation of the capsulolabral disruption with the combination of a labral elevator, rasp and arthroscopic shaver in preparation of the bone-labrum interface for repair. (C) A posterolateral portal placed under spinal-needle direct visualization is key to the success of the (D) inferior anchor placement at the 6 o’clock position on the glenoid face. (E,F) Soft anchors are spaced approximately 10–15 mm apart in the inferior to superior direction to complete the posterior labral repair with capsular shift. G, glenoid; HH, humeral head.

In the early 1990s, thermal capsulorrhaphy was popularized as an alternative to the traditional open capsular shift pioneered by Neer and Foster (36). Despite early success, higher than expected long term failure rates and recurrent instability led to a shift to all-arthroscopic labral repair with posterior capsular shift in the setting of traumatic unidirectional recurrent posterior instability of the shoulder. The lateral decubitus position is typically the position of choice for instability; however, the beach chair position can also be employed. Standard posterior, anterior and anterosuperior portals are created with the addition of a 7 o’clock percutaneous portal placed under spinal needle localization for an appropriate angle to access the posteroinferior glenoid rim. Complete elevation and preparation of the posterior labrum from the glenoid is a critical step in facilitating a superior capsular shift combined with a posterior labral repair. A posterior-based repair typically starts with an anchor placed at the 6 o’clock position as a critical step in anatomic repair with a minimum of 3–4 anchors spaced 10–15 mm apart on the face of the glenoid, as Bradley et al. have demonstrated that too few suture anchors as a potential risk factor for arthroscopic failure (37). Additionally, arthroscopic failure may be the result of poor quality capsular tissue, underestimation of capsular laxity and the inability to recognize associated pathology at the index procedure, compromising the outcome of the arthroscopic posterior stabilization procedure (38).

A systematic review and meta-analysis of patients undergoing arthroscopic treatment for unidirectional posterior glenohumeral instability demonstrated superior clinical outcomes when treated arthroscopically (27 studies) versus treatment with open stabilization procedures (26 studies) with respect to shoulder stability, clinical recurrence of instability, patient satisfaction, return to sport and return to previous level of play (39). This finding is also supported by Bottoni et al. (5), who reported statistically significant higher outcome scores in the arthroscopic versus open group, although similar recurrence rates, in the setting of posterior shoulder stabilization among a retrospective comparison of 30 military servicemembers. Additionally, arthroscopic stabilization procedures utilizing suture anchors resulted in fewer recurrences and revision procedures than anchorless repairs in the young contact and overhead throwing athletes (39). There is strong evidence to support the use of modern-day suture anchors in the setting of arthroscopic repair versus anchorless repair to establish more reliable outcomes, specifically in terms of lower failure and quicker return to sport rates. Several studies have reported higher rates of recurrent instability in posterior shoulder repairs performed with capsulolabral plication alone compared to techniques that use suture anchors (39-41). In the largest study to date of contact and overhead throwing athletes undergoing arthroscopic posterior shoulder stabilization with an average of 36 month follow-up, capsulolabral plication with suture-anchors showed significantly greater improvement in American Shoulder and Elbow Surgeons (ASES) scores (P<0.001) and a higher rate of return to play (P<0.05) when compared with anchorless capsulolabral plications (40).

Posterior glenoid reconstruction

Glenoid bone loss is a known significant risk factor for recurrent posterior shoulder instability and failure after posterior labral repair, which has led to the development of intracapsular posterior bone block reconstruction. As compared to anterior instability, posterior shoulder instability with large glenoid bone loss is a rare entity. While there is no consensus on the amount of bone loss necessitating posterior glenoid reconstruction, stability of the glenohumeral joint is compromised with bone loss exceeding 20–25% (32). The current literature suggests bone block reconstruction for glenoid defects involving more than 25% bone loss of the inferior glenoid, with possible consideration of an even lower threshold in contact athletes and in revision settings (42). Free bone block augmentation for posterior glenoid reconstruction most commonly includes iliac crest autograft and distal tibial allograft options. Techniques either include an open procedure or arthroscopic delivery of the graft traditionally described through the infraspinatus using a 3 cm incision parallel to the posterior glenoid rim (Figure 4). It is important to consider the technical challenges of the bone block procedure, with an overall high complication rate reported in early-to-mid-term follow-up, including residual instability and post-traumatic osteoarthritis. Similarly, biomechanical data suggested that a posterior bone block could overconstrain the posterior glenohumeral joint and lead to joint incongruity, particularly when using an extracapsular bone block technique (43).

Figure 4 Arthroscopic images of a left shoulder with 30% posterior glenoid bone loss demonstrating (A) a distal tibial allograft bone block after fixation to the posterior glenoid rim with solid screws, followed by (B) final fixation of the bone block in an extra-articular fashion (*) with a 6 o’clock and 11 o’clock anchor. Immediate post-operative (C) Grashey and (D) scapular Y plain films of a left shoulder demonstrate fixation after undergoing open posterior glenoid bone augmentation. G, glenoid; HH, humeral head.

Short-to-mid-term results are mixed in the setting of a bicortical iliac crest autograft bone block. In one study, Servien et al. (44) demonstrated improved subjective patient-reported outcomes at a 6-year follow-up, with 71% (15/21) of patients returning to sport at their preinjury level and only three reported clinical failures. Meuffels et al. (45) demonstrated a high rate of progression to post-traumatic osteoarthritis and inconsistent patient reported outcomes at 18-year follow-up, with all patients demonstrating radiographic glenohumeral joint osteoarthritis and overall worse clinical outcomes at 18-year compared to 6-year follow-up after iliac crest autograft. More contemporary techniques focus on contouring the iliac crest autograft to match the arc of motion of the glenohumeral joint, optimizing contact forces between the humeral head and the bone graft, positioning the graft flush or slightly overhanging the glenoid rim at the posteroinferior quadrant, and creating an extra-articular bone block by repairing the native capsular interface (46,47). In a more recent multicenter review of 66 cases with 3.7-year follow-up, iliac crest autograft led to improved functional and satisfaction scores with a 12% recurrence rate and 18% occurrence of persistent post-operative pain with one-third of patients experiencing major lysis of the bone block (48).

The osteochondral distal tibial allograft was first described in 2013 by Millett et al. (42) as an intracapsular or extracapsular technique for anatomic reconstruction of the posterior glenoid. Advantages of distal tibial allograft include eradication of donor site morbidity and similar matched congruity of the glenohumeral arc of motion. Frank et al. (49) have demonstrated that iliac crest bone autograft and fresh distal tibial allograft offer similar joint contact pressures and joint peak forces in cadaveric specimens, with distal tibial allograft demonstrating the potential advantage of restoring joint congruity of the glenoid articular surface due to the geometry of its articulation with the humeral head. While both open and arthroscopic techniques have been reported, long-term results are lacking and access to distal tibial allograft may not be readily available in all practice settings. In a study involving a cohort of 10 patients undergoing distal tibial allograft for posterior glenoid reconstruction, Gilat et al. (50) reported that 7 patients had previously undergone stabilization procedures, with an average preoperative bony Bankart lesion involving 26% of the glenoid diameter. At 1-year follow-up, 1 patient reported recurrent instability, and 2 patients underwent revision for hardware-related issues.

Outcomes and recurrence

Generally, clinical outcomes are excellent after arthroscopic posterior stabilization. Overall, arthroscopic posterior shoulder stabilization has been shown to be effective in restoring stability and function in symptomatic, unidirectional posterior instability. Bradley et al. (40) showed no significant differences in ASES scores, shoulder stability, strength, or ROM among contact athletes when compared to the entire cohort of athletes undergoing arthroscopic posterior shoulder stabilization, which included both contact and non-contact athletes. On further comparison of overhead throwing athletes versus contact athletes, excellent results were achieved in 89% of overhead throwing athletes and 93% of contact athletes (51). While there was no difference reported in ASES scores, stability, ROM, strength, pain or function between both groups, overhead throwing athletes were less likely to return to their preinjury level of sport (55%) compared with contact athletes (71%). The lower dynamic glenohumeral demands of the contact athlete compared to the overhead throwing athlete may allow for a higher rate of return to sport and previous level of play among contact athletes.

In a meta-analysis of posterior shoulder instability, the overall rate of recurrent instability after the index procedure among the athletic population (513 shoulders) was 8.58% (SD, 64.82%) (39). Among these athletes, a recurrence rate of 5.06% (SD, 62.35%) was noted in contact athletes, with a two-fold higher recurrence rate of 12.12% (SD, 61.53%) in overhead throwing athletes. Additionally, a revision rate of 6.82% (SD, 63.98%) was reported in the athletic population, 6.18% (SD, 62.86%) among contact athletes. At a minimum of 1 year follow-up, athletes returned to sport at any level at a rate of 91.81% (SD, 645.43%). Among contact athletes, 89.33% (SD, 642.39%) and 71.91% (SD, 632.56%) returned to any level of sport and previous level of play, respectively, after index procedure. This was noticeably lower in overhead throwing athletes, who returned to any level of sport and previous level of play at a rate of 83.87% (SD, 612.50%) and 58.06% (SD, 67.94%), respectively, after index procedure. In this same study, overall patient satisfaction was 93.17% (SD, 660.38%), with 92.35% (SD, 652.52%) of contact athletes reporting satisfaction with their procedure and considering it worthwhile.

Bradley et al. (37) identified significant risk factors for contact athletes requiring revision arthroscopic posterior labral repair which included female sex, dominant shoulder, concomitant rotator cuff injury, fewer than four anchors used and smaller glenoid bone width. The authors also demonstrated that while all patients showed improvement in patient-reported and functional outcome scores, those undergoing revision surgery demonstrated significantly less improvement in outcome scores, shoulder stability scores and return to sport rates. In this athletic cohort, 64% of contact athletes returned to sport at the same level in the non-revision group versus 15% of contact athletes in the revision group, while 78% of the non-revision group and 61% of the revision group returned to sport at some level. At short and mid-term follow-up of active-duty servicemembers, often compared to contact athletes, treated arthroscopically for posterior shoulder instability, a 17.2% failure rate was reported at 5-year follow-up with only a 1.5% rate of revision surgery and an 83% rate of return to military duty. In this cohort, there was no statistically significant risk factor for recurrence identified, including age, tear size, insidious onset, male sex, anchor position or intraoperative positioning (52).

The current literature reporting on outcomes of posterior glenoid bone block stabilization demonstrates improved patient reported outcomes in the short-term follow-up but still reports a moderate rate of recurrent instability requiring revision surgery and complications (48,53,54). A systematic review of 11 studies by Mojica et al. (54) reported 9.8% recurrent instability after posterior glenoid bone block with a 13.8% complication rate, led by hardware complications (11.1%) and 11.6% of patients with residual, persistent pain. Furthermore, Wolfe and colleagues reported a higher rate of clinical failure requiring reoperation in 44.4% of patients with moderate posterior glenoid bone deficiency, compared to only 10.5% in those with minimal bone loss. The authors demonstrated a higher clinical failure requiring reoperation in 44.4% of patients with moderate posterior bone deficiency versus 10.5% of patients with minimal posterior bone deficiency. As a relatively new technique, posterior glenoid augmentation with free bone block procedures have not been around long enough for long-term data or comparative studies.

Outcomes following posterior shoulder stabilization can be challenging to compare and interpret, which is attributed to the high heterogeneity among the population studies, lack of consistency on the definition of failed stabilization procedures and recurrence, as well as the subtle differences among surgical techniques. Furthermore, rates of return to sport are inconsistent throughout the literature, especially in the throwing athlete.

Conclusions

While posterior shoulder instability has traditionally been a less common diagnosis, especially compared to anterior shoulder instability, prevalence in contact athletes is likely underdiagnosed, and can be challenging to treat. Contact athletes are at high risk for this injury due to position requirements, young age and high activity demand. Overall, arthroscopic labral repair with suture anchors for the treatment of unidirectional traumatic posterior shoulder instability has demonstrated excellent results, high patient satisfaction and low recurrent rates in eliminating symptoms of pain and instability in contact athletes. Further advantage of the arthroscopic approach allows tailoring for pathology-specific treatment and can allow the surgeon to address all encountered intra-articular pathology in the same setting. While research over the last decade has demonstrated overall good success following arthroscopic posterior stabilization, ongoing research is required to optimize treatment, standardize the definition of clinical failure and recurrence, and improve return to sport, especially for the high-risk contact athlete. Posterior bone block stabilization techniques should generally be reserved for patients with significant posterior glenoid bone loss or retroversion, or who have failed previous arthroscopic soft tissue procedure.

Acknowledgments

None.

Footnote

Provenance and Peer Review: This article was commissioned by the Guest Editor (Justin W. Arner) for the series “Care of the Contact Athlete’s Shoulder” published in Annals of Joint. The article has undergone external peer review.

Peer Review File: Available at https://aoj.amegroups.com/article/view/10.21037/aoj-25-26/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://aoj.amegroups.com/article/view/10.21037/aoj-25-26/coif). The series “Care of the Contact Athlete’s Shoulder” was commissioned by the editorial office without any funding or sponsorship. N.N.D. serves as an unpaid editorial board member of Annals of Joint from August 2024 to December 2026. M.T.D. reports serving on the editorial board of Arthroscopy and on the boards or committees of the American Academy of Orthopaedic Surgeons and the Society of Military Orthopaedic Surgeons, all outside the submitted work. T.J.D. reports serving on the editorial board of Arthroscopy and on the board or committee of the Society of Military Orthopaedic Surgeons, outside of the submitted work. The views expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Department of Defense or the US Government. The authors have no other conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All clinical procedures described in this study were performed in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patients for the publication of this article and accompanying images.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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