4.2 Posterior Instability
- In posterior instability there is frequently pain in both sides of the GHJ.
- Pain may be present in the posterior joint line due to pressure of the HH on either the posterior
labrum, capsuloligamentous complex or posterior chondral surface. There can be a tightening
feeling in the posterior musculature due to the posterior cuff guarding against the excessive
posterior HH translation - Posterior instability is often associated with compression pain in the anterior cuff. As the
HH slides posteriorly, the subscapularis is compressed against the HH and the anterior
glenoid fossa. (ref) - With more extensive posterior HH translation the subscapularis can be further traumatised
setting up subscapularis tenopathology or partial thickness tear (refs) - A bony compression injury may occur between the anterior superior HH and the glenoid
(a reverse Bankart lesion) which can also create pain in the front of the joint. - In posterior instability, due to the HH sliding excessively posteriorly, there often can be secondary
stress reactions in the ACJ. This can result in the patient reporting ACJ pain that may or
may not be associated with clicking. On MRI there is often oedema reported on the ACJ or
early development of osteoarthritic change (ref). - Posterior instability of the shoulder is often associated with significant scapula winging (ref)
so it is not uncommon for the patient to resport pain around the shoulder blade, typically
with the arm in combinations of flexion, adduction (horizontal flexion) and internal rotation