A 20-year-old man had a history of multiple subluxation/dislocation episodes of the shoulder joint for several years and he could voluntarily dislocate his shoulder. Six months ago, his shoulder pain increased after strenuous exercise. He had full range of motion of the shoulder joint. The physical examination showed the sulcus sign (grade 2), a positive anterior drawer test (grade 2) and a positive posterior drawer test (grade 2). The anterior and posterior apprehension test was also positive.

Preoperatively, the Rowe score was 35 and the American Shoulder and Elbow Surgeons (ASES)/University of California, Los Angeles (UCLA) score was 80 and 25 respectively. The simple radiologic findings showed no bony abnormalities. MRI of the left shoulder demonstrated a multiseptated cyst in the inferior aspect of the glenoid neck and a suspected labral tear (arrows) (Fig. 1). The electromyogram findings showed non-specific findings. We initially recommend physical therapy such as stretching and strengthening exercise. However, his symptoms were not improved after 6 months of rehabilitation.

Shoulder instability is divided voluntary and involuntary instability. For the case of involuntary instability, surgical treatment is necessary, but for the case of voluntary instability, the surgical indications should be strict because of secondary compensation such as military issues and the occupational worker's gain. If there is a pathologic condition such as labral tear, cyst and/or rotator cuff injury, then surgical treatment should be considered.

A paralabral cyst of the shoulder joint can be observed in 2% to 4% of the general population, and particularly in men during the third and fourth decades. On average, these cysts measure 10 mm to 20 mm in diameter and they are preferentially located on the postero-superior aspect of the glenoid.1)

The cysts may or not be observed to communicate with a labral tear. Westerheide et al.2) and Westerheide and Karzel3) advocated that labral pathology was the main cause of periarticular cysts. On the contrary, Piatt et al.4) reported that paralabral cysts spontaneously resolved in 2 patients, as assessed on MRI. Youm et al.5) reported that repair of a labral tear, without cyst excision, resulted in successful outcomes for all 10 patients who had spinoglenoid cysts associated with superior labral tears. They advocated that the treatment given for intra-articular disease was the key component of the surgical management.

The symptoms of a paralabral cyst may be the result of rotator cuff disease, labral disease, entrapment syndrome from compression of the suprascapular nerve, instability or a combination of these conditions.1,4,6,7) The most common complication is the suprascapular nerve entrapment syndrome, which leads to pain and supraspinatus and/or infraspinatus atrophy. In the shoulder, a labral tear can cause mechanical symptoms and instability symptoms. The English medical literature shows only 3 reports of the paralabral cyst of the shoulder associated with glenohumeral instability.8-10) Our current report is a rare case of inferior paralabral cyst combined with multidirectional instability. The previous reports only describe anterior, posterior and superior paralabral cyst with shoulder instability. Ferrick and Marzo9) reported that suprascapular entrapment neuropathy with ganglion is related to posterior shoulder instability. Dietz et al.8) reported that anterior-inferior labral cyst with an anterior labral tear was related with non-traumatic shoulder instability, and Yukata et al.10) also reported that paralabral cyst of the shoulder was associated with recurrent anterior dislocation. Tirman et al.11) reported that labral cysts may be an indicator of labrocapsular injury and instability, and so taking a careful history and a thorough physical examination to detect instability should be considered. In that report, the physical examination showed glenohumeral instability in the direction of the labral tear and a cystic-appearing mass in 11 patients (11/20, 55%); the instability pattern was multidirectional in three patients and unidirectional in eight patients. Our case was an inferior paralabral cyst with an inferior labral tear. We performed inferior labroplasty combined with rotator interval closure. This cyst was just nearby the axillary nerve, but the postoperative deltoid function was unaffected. So, we suspected that repetitive microtrauma was the main cause of the inferior labral tear and the paralabral cyst. The relationship between shoulder instability and labral tears is well known, yet the association of shoulder instability with a paralabral cyst is rare. We considered that there was the cyclic correlation of shoulder instability, labral tear and paralabral cyst. In the future, we will study the direct relationship between shoulder instability and paralabral cyst.

Shoulder instability may cause labral injury, or labral injury may cause shoulder instability, and then the injured tear labrum develops a paralabral cyst. In our patient, the inferior paralabral cysts may have been associated with inferior labral tears and instability.