Abstract:
To investigate the structural/anatomical components of the static stabilisers of the canine glenohumeral joint (GHJ). The GHJ of 22 complete cadaver specimens (44 limbs) were manipulated to estimate laxity at joint angles of 150º, 135º and 90º (palpation study). Following the removal of the peri-articular muscles, laxity was measured in 32 of these limbs after applying a 15N force to the scapula in a variety of directions whilst the humerus was fixed to a jig. This was repeated for the abovementioned angles in intact joints and after venting and flushing to eliminate the limited joint volume and adhesion/cohesion (LJV/AC) mechanisms (biomechanical study). Results of the palpation and biomechanical studies were compared. Anatomical dissections were also performed to better describe the structures constituting the static GHJ stabilisers. The palpation study revealed a marked variation between joints although there was a tendency for progressive laxity as the joint was flexed. This finding was supported by the biomechanical study which also demonstrated no significant difference between intact and vented joints except in a cranio-caudal direction at 135º and 90º, and in a medial/lateral direction at 135º. Static stabilisers contributed to the stability of the GHJ in extension but permitted an ever-increasing range of motion as the joint was flexed. The results of the palpation study did not correlate well with the objective measurements of the biomechanical study. Manipulation is unlikely to be a reliable method for determining subtle joint laxity in the GHJ. The static stabilisers do not appear to play a significant role in providing joint constraint during normal range of motion (except in extension). Diagnoses of pathological laxity attributable to dysfunction of the static stabilisers should be made with caution and surgical treatments should take cognisance of the abovementioned biomechanical features. Anatomical structures providing constraint to joint mobility are described.
