Skin – use axillary crease (extend as necessary)
1st muscle layer – deltoid / pectoral
use of deltopectoral interval anteriorly
5cm deltoid split (n.b. careful re: branches anteriorly)
posteriorly – lift deltoid or release it & go between infra & teres minor
Coracoid = lighthouse; lateral = safe, medial = danger
clavipectoral fascia – (? cephalic vein, lat. pectoral nerves)
CA lig – n.b. preserve to prevent superior migration in cuff tear
Humeroscapular motion interface (I.e. bursa)
separates Deltoid, coracoid muscles, acromion, CA lig from RC, long head of biceps, tuberosities
contains nerves (axillary, musculocutaneous)
N.B. placement of retractors.
Rotator Cuff
rotator interval (between supra and subscap)
biceps tendon (N.B. curves under subscap)
Scapulohumeral ligaments (SGHL, CHL, MGHL, IGHL)
CA lig – restricts superior translation
Glenoid labrum – incision alone does not cause instability, but is contributory
Mechanics of Glenohumeral Stability
- socket shallow – therefore ++mobility, limited neck-rim contact (Contrast – Hip)
- no isometric articular ligaments (ligs only play important stabilizing roles at extremes of motion) (Contrast – Knee)
The mechanics of glenohumeral stability can be most easily understood in terms of teh relationship between the net force acting on the humeral head and the shape of the glenoid fossa.
- no dislocation as long as the net humeral joint reaction force (NHJRF) is directed within the effective glenoid arc
- the humeral head will remain centered in the glenoid fossa if the joint surfaces are congruen and the NHJRF force is directed within the effective glenoid arc.\
- Balance-stability angle = maximal angle that the NHJRF can make with the glenoid center line in a given direction.
NB- dynamic adjustment of NHJRF by components of rotator cuff and posterior/middle deltoid (>anterior deltoid for concavity compression) — therefore n.b. role of strengthening and neuromuscular retraining
? role of LH biceps (controversial, but may contribute as humeral head depressor)
Stability Ratio = tan (balance stability angle) = ratio displacing component (perpendicular to glenoid center line) + compressive component ( // to glenoid center line)
Stability ratio ~= bal. stability angle / 57degrees
clinical correlate = load and shift test.
