Static stabilizers are the non-contractile tissue of the glenohumeral joint. They are very important in shoulder stability at end-range ROM and/or when there is a dysfunction of the dynamic stabilizers. These static stabilizers set the base of support for the shoulder joint.
The articular surface is much like the meniscus of the knee joint. It thicker at the periphery, provides foundation for concativy-compression effect of RTC.
The labrum is a firbrous connective tissue which increases articular surface area for the humeral head by deepening the glenoid fossa. Provides attachment of the glenohumeral ligaments, long head biceps tendon, capsule, and scapular neck. Contributes to approximately 50% of depth of shoulder joint. Stretches out anteriorly with external rotation, stretches out posteriorly with internal rotation. A loss of labrum integrity has been shown to decrease the resistance to translation by 20%.
The capsule is twice the size of the humeral head. Has most extensibility anteriorly and inferiorly. “Winds up” in abduction and external rotation. The joint capsule and glenohumeral ligaments are intimately adherent anatomically and mainly function as stabilizers at the extremes of motion. This static end-range stabilization is very important when all other stabilizing mechanisms are overwhelmed.
The joint capsule has an inherit negative intra-articular pressure that holds the joint together. The osmotic action of the synovium removes free fluid, keeping a slightly negative pressure within the joint. This slightly negative intra-articular pressure holds the joint together much like “2 wet microscopic slides placed together” (Terry GC et al 2000).
There are 3 main ligaments in the glenohumeral joint:
- The Superior Ligament limits inferior translation and parallels the course of the coracohumeral ligament.
- The Middle Ligament limits ER at 45° of abduction, anterior translation in 60-90° of abduction.
- The Inferior Ligament is the thickest of the ligaments and has 3 different portions: anterior band, posterior band, and the axillary pouch.
It is important to consider that the anterior band of the inferior ligament is the primary stabilizer against anterior translation in the throwing position of abduction and external rotation.
Limits anterior and inferior translation. Is taught at lower levels of elevation, extension, and extension with adduction (Izumi et al 2011).
“Circle Stability Concept”
For a full dislocation to occur, both sides of the capsule and ligaments must be damaged. The capsule preventing the direction of location would be considered the primary restraint and the opposite side would be considered the secondary restraint.
Using the sulcus test and the drawer/load and shift tests at different angles of abduction, the clinician can differentiate between these 3 different ligaments to determine the specific structure involved. Consider the magnitude of translation and primary and secondary restraints involved with these movements.
Position the patient in a relaxed seated position with the arms at the side resting on the thighs. An inferior translation force is applied through the humerus. Assessment of the amount of inferior translation will determine if there is a positive “sulcus sign”.
- 0-20° Abduction = Primary Restraint is Superior Glenohumeral Ligament
- 45° Abduction = Primary Restraint is Anterior Band of the Inferior Glenohumeral Ligament
- 90° Abduction = Primary Restraint is Posterior Band of the Inferior Glenohumeral Ligament
Anterior Drawer / Load and Shift Test
Patient is positioned in the same position as the sulcus test. Stabilize the scapula with one hand and genlty shift the humeral head obliquely forward in the plane of the scapula. A “normal” shoulder reaches a firm end point with only slight anterior displacement and no clunking, popping, or pain. This test can also be performed supine if the patient has difficulty relaxing.
- 0° Abduction = Primary Restraint is Superior and Middle Glenohumeral Ligament
- 45° Abduction = Primary Restraint is Middle Glenohumeral Ligament
- 90° Abduction = Primary Restraint is Inferior Glenohumeral Ligament
Understanding the static stability of the shoulder allows the clinician to assess the baseline stability independent of dynamic support. Finding the direction of impaired static stability will also help to reveal which dynamic stability structures need to be emphasized in the plan of care.
Shoulder Stability – Osteo-Arthrokinematics
Static Shoulder Stability
Dynamic Shoulder Stability