Innervation patterns of the inferior glenohumeral ligament: anatomical and biomechanical relevance.

Although the Inferior Glenohumeral Ligament (IGHL) has a well known mechanical and proprioceptive relevance in shoulder stability, the interrelation of the ligament's anatomical disposition/innervation has not actually been described previously. The purpose of the study was to determine the IGHL innervation patterns and relate them to dislocation. Forty-five embalmed and 16 fresh-frozen human cadaveric shoulders were studied. Masson's Trichrome staining detailed the intraligamentous nerve fiber arrangements. The effect on the articular nerves of an anteroinferior dislocation of the shoulder joint and the position of 60 degrees abduction and 45 degrees external rotation was studied dynamically. The axillary nerve provided IGHL innervation in 95.08% of the cases. We saw two distinct innervation patterns originating from the axillary nerve. In Type 1, one or two collaterals diverged later from the main trunk to enter the ligament. Type 2 showed innervation to the ligament provided by the posterior branch for three to four neural branches. In both cases, these branches enter the ligament near the glenoid rim and at the 7 o'clock position (right shoulder). The radial nerve (Type 3 innervation pattern) provided IGHL innervation in 3.28% of the cases. Microscopic analysis revealed wavy intraligamentous neural branches. The articular branches relaxed and separated from the capsule at the apprehension position and stayed intact after dislocation. These results showed a special predisposition to avoid possible denervation and suggested that the neural arch probably remains unaffected after most dislocations. Knowledge of the neural anatomy of the shoulder will clearly help in avoiding its injury in surgical procedures.