Glenoid Labral Tears are associated with increased neurofilament innervation

Background

The glenoid labrum is a fibrocartilaginous structure that runs circumferentially around the rim of the glenoid fossa. It provides stability to the glenohumeral joint and is an attachment site for the glenohumeral ligaments and the long head of biceps tendon. Tears can occur in the anterior labrum, superior labrum, posterior labrum or any combination of the three. Pain is a common presenting feature of symptomatic labral tears, particularly superior anterior to posterior (SLAP) tears. The cause of pain in symptomatic labral tears is unknown. We aimed to determine if there is a differential expression of nerve fibres around the glenoid labrum and if torn labra have increased neuronal expression compared to untorn labra.

Methods

Labral tissue was collected at 3, 5, 9 and 12 o’clock during total shoulder arthroplasty. Samples were also collected at 3, 5 and 12 o’clock during rotator cuff repair, anterior labral repair, type II superior labral anterior to posterior (SLAP) repair and capsular release for idiopathic capsulitis. Sections were immunostained with antibodies to neurofilament, a specific neuronal marker which is used to identify central and peripheral nerve fibers, and the concentration and intensity of immunostained-positive nerves assessed.

Results

The concentration of neurofilament staining was similar in the superior, anterior, posterior and inferior glenoid labrum in untorn labra (8 nerves/mm2, p > 0.05). Torn labra exhibited a 3-4-fold increase in neuronal expression which was isolated to the location of the tear in SLAP (p = 0.09) and anterior labral tears (p = 0.02). The concentration of nerves in torn glenoid labrum samples were comparable to the glenoid labrum of adhesive capsulitis samples (p > 0.05).

Conclusions

This study showed that there is little variation of nerve expression between the superior, anterior, posterior and inferior glenoid labrum in untorn labra. Torn labra exhibited increased neuronal expression throughout the glenoid labrum, particularly at the site of the tear. This study supports the hypothesis that following a traumatic tear of the anterior or superior labrum, the labrum in that region becomes populated with new nerve fibres and that these fibres are likely to be responsible for many of the symptoms, particularly pain noted by patients with SLAP and/or Bankart tears.