Anterior shoulder dislocation is the commonest dislocation in the body • Makes up 95% of shoulder dislocations
• It occurs in around 2% of individuals at some stage
• Dislocation is more common in the dominant limb
• In young people it is much more common in males
• By the 6th to the 7th decade it is more common in females • Instability is bilateral in around 15%
Two acronyms are used to think about shoulder instability:
1. TUBS: traumatic unidirectional dislocations with a Bankart lesion, often require surgery. 2. AMBRI: Atraumatic multidirectional bilateral shoulder instability, often responds to rehabilitation and occasionally inferior capsular shift may be required.
Anatomy and stability
The shoulder has more movement than any other joint, at the expense of stability
• Shallow cup, deepened by glenoid labrum, 35mm by 25mm.
• Depth 9mm in superoinf, 5mm in AP
i. 50% of depth from glenoid labrum
ii. 50% from configuration of bone and articular cartilage (thicker peripherally) • Superior tilt of 5 degrees (to control inferior instability) • Has retroversion with respect to the body of the scapula of 7 degrees • Overall 30- 40 deg anteverted in coronal plane from body
2. Humeral head
• Surface has 3x articular cartilage of glenoid (and thicker centrally) • Only 25-30% of humeral head cartilage articulating at any time with glenoid • Radius of curvature of the head and glenoid are normally within 2mm (highly congruent)
• Labral attachment in anterior superior quadrant is variable, but any detachment below the glenoid equator is believed to be pathological.
Ligaments act as check reins and are most important at extremes of movement They do not act during mid range activities.
1. SGHL – extends from anterosuperior edge of glenoid, near origin of LHB, runs to top of lesser tuberosity of humerus a. Primarily resists inferior translation and ER of humerus with arm adducted b. Present in 90% and well developed in 50%
2. MGHL – originates from the supraglenoid tubercle, superior labrum or glenoid neck. Runs to the inferior half of the lesser tuberosity. a. Resists anterior translation with the arm abducted to 45 degrees b. Most variable of the ligaments; is poorly defined or absent in 40% of population 3. IGHL – most important complex for GH stability
a. Primary stabilizer of abducted shoulder (increased importance as abd increases) i. At lower abduction subscap SGHL and MGHL contribute to ant stability b. Contributes largely to the anterior lip of the glenoid labrum c. Stabilizes against AP translation (both directions) and supero-inferior instability (inferior) d. Has two bands (thicker anterior and thinner posterior) i. From 3 – 9 O’clock on glenoid separated by an axillary pouch e. Anterior band tight in ER
i. resists forwards translation with arm abducted f. Posterior band tight in IR
i. is a posterior stabilizer with arm flexed and internally rotated 4. Coracohumeral ligament – from horizontal arm of coracoid to transverse humeral ligament (which runs b/w LT and GT) a. Acts in concert with superior glenohumeral ligament 5. Joint capsule
a. Reinforced anteriorly and inferiorly by glenohumeral ligaments (weaker posteriorly)
The rotator cuff and long head of biceps are vital for dynamic stability.
Other factors – these are most important during mid range activities
Negative intra-articular pressure
Adhesion/cohesion of joint fluid (this is not seen in shoulder replacement)
Anterior shoulder dislocation
Usually follows a fall onto upper limb where humerus is...