Labral tears are a common complication of shoulder injuries, particularly among young patients ^[1]. These injuries often present with vague, deep shoulder pain that is exacerbated by overhead activities. Patients may also experience locking sensations if a loose fragment of the labrum impinges on the joint. Among superior labrum anterior to posterior (SLAP) lesions, type II is the most prevalent, accounting for 41% of cases ^[2]. Type II lesions involve fraying and detachment of the labrum, along with the biceps tendon, from the superior glenoid tubercle. These tears can function as one-way valves, leading to joint fluid leakage and the formation of paralabral glenoid cysts ^[3]. As these cysts enlarge, they may exert pressure on the suprascapular nerve, resulting in weakness in both the supraspinatus and infraspinatus muscles ^[4]. Compression at the spinoglenoid notch specifically can cause isolated weakness of the infraspinatus muscle. Early identification of muscle weakness during physical examinations is crucial, as prolonged nerve compression can lead to irreversible damage. Despite their clinical significance, para-labral cysts are often missed or misdiagnosed due to their relative rarity. The advent of high-resolution magnetic resonance imagings (MRIs) has significantly improved the detection of paralabral cysts associated with labral tears. Surgical intervention remains the gold standard for treating symptomatic patients ^[5]. Early identification and treatment are essential for optimal recovery outcomes. This case series examines isolated infraspinatus muscle weakness caused by suprascapular nerve palsy due to a paralabral glenoid cyst associated with a labral tear.

This case series presents four patients with shoulder pain and weakness related to a SLAP tear and paralabral cyst, causing compression of the suprascapular nerve and subsequent infraspinatus denervation. All patients underwent arthroscopic labral repair and cyst decompression, followed by a standard rehabilitation protocol.

Patient profiles

Two of the patients were active males involved in sports: A 41-year-old (Case 1, Fig. 1) who played badminton and football and lifted weights, and a 22-year-old (Case 2, Fig. 2) who was a dedicated gym goer. Their pain, exacerbated by overhead activities, developed after specific incidents: The 41 years old had a history of trauma a year prior, while the 22 years old reported no significant injury. Conversely, the other two patients, a 37-year-old male (Case 3, Fig. 3) and a 29-year-old female (Case 4, Fig. 4), reported more gradual symptom onset. The 37-year-old male mentioned difficulty opening sliding doors and the 29-year-old female, a surgical resident, reported issues affecting her patient care due to her shoulder pain.

Clinical findings

All four patients exhibited pain during active shoulder movement. A common finding was weakness in external rotation, specifically infraspinatus weakness of varying grades (3 or 4), alongside supraspinatus strength typically maintained at grade 5. All cases also showed wasting over the scapular area and were positive on O’Brien’s test. All cases had some form of restriction and pain in the active range of motion.

Imaging

MRI revealed consistent findings across all cases: A SLAP tear with a paralabral cyst extending to the spinoglenoid notch. Varying degrees of denervation edema in the infraspinatus muscle were also noted, with the extent to teres minor in one instance. The cyst was directly compressing the suprascapular nerve at the notch in all four cases.

Surgical intervention and post-surgery rehabilitation

All patients underwent the same surgical procedure involving an arthroscopic repair of the labral tear and cyst decompression. The cyst was accessed and decompressed through the labral tear using a probe and shaver, confirmed by drainage of thick cyst content into the joint. Labrum was then debrided and repaired using all suture anchors. Postoperatively, all patients followed a standard rehabilitation program, including 3 weeks of shoulder immobilization, followed by pendulum exercises and peri-scapular strengthening starting from the 3^rd week. Rotator cuff strengthening with resistance bands was implemented by the 3^rd month and sports were allowed by the 6-month mark. All patients reported complete pain relief, full range of motion, and restoration of infraspinatus muscle strength to grade 5 by the end of the 6-month follow-up period. No post-surgical complications were reported Fig 5.

The suprascapular nerve, a mixed nerve arising from the superior trunk of the brachial plexus with contributions from the C5 and C6 nerve roots, has both motor and sensory functions. It innervates the supraspinatus and infraspinatus muscles while providing sensory input to structures such as the glenohumeral and acromioclavicular joints, coracohumeral and coracoacromial ligaments, and the subacromial bursa ^[6]. The nerve originates in the posterior triangle of the neck and then traverses the suprascapular notch beneath the superior transverse scapular ligament to innervate the supraspinatus muscle. From there, it continues through the spinoglenoid notch, positioned between the scapular spine and glenoid cavity, and terminates in the infraspinatus muscle ^[7]. Due to its anatomical proximity (18–21 mm from the glenoid rim), the suprascapular nerve is highly susceptible to compression by small paralabral cysts, particularly at the suprascapular and spinoglenoid notches ^[7]. Compression at the suprascapular notch affects both the supraspinatus and infraspinatus muscles, whereas compression at the spinoglenoid notch primarily impacts the infraspinatus. Factors such as anatomical variations, repetitive overhead activities, and athletic overuse increase the risk of suprascapular nerve dysfunction [8, 9]. Paralabral cysts are commonly associated with labral tears, which allow joint fluid to escape through labral defects [10, 11]. These cysts form as the fluid leaks through the labrum forming a well-defined collection adjacent to it [12, 13]. These cysts are then perpetuated by a one-way valve mechanism that prevents fluid re-entry, leading to cyst growth ^[13]. When located near the spinoglenoid notch, these cysts can compress the suprascapular nerve, causing denervation edema and, over time, irreversible muscle atrophy if left untreated [14-17]. MRI plays a pivotal role in diagnosing these conditions, with its superior soft tissue contrast providing detailed visualization of labral tears and associated paralabral cysts. It has a sensitivity and specificity for detecting labral lesions of 60% and 92.5%, respectively ^[18]. These tears are best identified in the coronal plane, appearing as increased signal intensity in the labrum with possible separation from the glenoid cartilage ^[19]. Paralabral cysts, typically well-defined fluid collections within 1 cm of the labrum, strongly correlate with labral tears and can indirectly indicate the presence of a tear when not clearly visualized ^[10]. Treatment strategies for symptomatic paralabral cysts and SLAP lesions range from conservative approaches, such as physiotherapy and ultrasound-guided cyst aspiration, to surgical interventions like open or arthroscopic labral repair with cyst decompression. While ultrasound-guided aspiration can provide relief [4, 20, 21, 22], combining labral repair with cyst decompression has demonstrated superior outcomes, particularly in restoring external rotator strength. Jodoin et al. documented complete resolution of infraspinatus weakness 1 year after arthroscopic labral repair and cyst decompression ^[23]. Studies have shown that early intervention with arthroscopic labral repair and cyst decompression can reverse denervation edema and prevent long-term muscle atrophy ^[24].

Our study highlights the crucial importance of comprehensive clinical examinations and advanced diagnostic investigations for the timely identification and management of shoulder pain and functional limitations. By employing meticulous examination techniques and utilizing high-resolution imaging modalities, we accurately diagnosed and characterized labral tears associated with paralabral cysts and isolated infraspinatus weakness in our patients. Arthroscopic techniques for labral repair and cyst decompression proved to be effective, yielding favorable outcomes and demonstrating the efficacy of surgical intervention in restoring shoulder function and alleviating symptoms. Early identification and intervention are pivotal in optimizing patient outcomes, enhancing functional recovery, and minimizing the risk of recurrent injury in individuals with similar shoulder pathologies. Supervised rehabilitation and targeted muscle training are essential for optimizing recovery and restoring shoulder function. Regular follow-up visits allow for ongoing monitoring and adjustments to treatment plans, promoting long-term shoulder health and functionality.

Early diagnosis and treatment of such cases are necessary as it yields better clinical results. Chronic compressive neuropathy can lead to irreversible neuromuscular denervation which can lead to poor surgical outcomes. Arthroscopic cyst decompression and labral repair are safe and yield excellent outcomes for patients, enhancing both function and recovery.