6 shoulder muscles converge from scapula ¨ humerus to surround the joint: deltoid, subscapularis, teres major, teres minor, supraspinatus & infraspinatus.
- three of them (supraspinatus, infraspinatus, teres minor) extend from posterior surface of scapula to 3 impressions of the greater tubercle of the humerus
Arises: medial 2/3 of supraspinous fossa of scapula (multipennate)
- bare area at lateral scapula has a bursa which communicates with the shoulder jt
Inserts: tendon blends with capsule ¨ lesser tubercle of humerus (Pl 392).
Nerve supply: C5-6, upper and lower subscapular nerve (posterior cord)
Action: Medial Rotator. Also stabilises shoulder, fixates upper humerus during hand/elbow motion.
Test: none satisfactory.
Arises: medial 2/3 of supraspinous fossa; bursal laterally; bulky bipennate muscle.
Inserts: tendon blends with capsule of shoulder ¨ upper facet of gr tuberosity.
Nerve supply: suprascapular nerve (C5-6) from upper trunk of BP
Action: Abductor. Also braces head of humerus into glenoid, stabilising other muscles
Test: Abduct arm against resistance and palpate it.
Arises: medial 2/3 infraspinous fossa, under infraspinous fascia (over muscle, attaches scapular edges)
Inserts: tendon blends with capsule of shoulder ¨ central facet of gr tuberosity.
Nerve supply: suprascapular nerve (C5-6), passing down from notch ¨ around lat border of spine.
Action: Lateral rotator. Braces head of humerus against glenoid fossa.
Test: flex elbow, hold it to the side; move forearm outward against resistance. Palpate
Arises: dorsal axillary border of scapula. Passes laterally under border of infraspinatus and over major.
Inserts: goes behind long head of triceps (cf teres maj passes in front) ¨ blends with capsule then ¨ lowest facet of gr tuberosity.
Nerve supply: posterior branch of axillary nerve (C5,6).
Action: Lateral rotator and weak adductor. Holds down humeral head during shoulder abduction.
This ÔoffspringÕ of subscapularis has migrated around to the posterior surface of the scapula.
Arises: dorsal surface of scapula at inferior angle.
Inserts: passes in front of triceps tendon to runs edge to edge with subscapularis, ¨ reaches medial lip of inter-tubercular sulcus
- lat dorsi binds around its lower border ¨ lies in front of its upper part at insertion.
Nerves: C5,6 via lower subscapular nerve (off posterior cord)
Action: Adducts & medial rotates and helps extend the flexed arm. Steadies humeral head.
- with teres minor helps hold down humeral head during should abduction.
- If lateral rotators paralysed, can be transplanted posteriorly.
Test: adduct abducted arm against resistance.
Contains teres minor & infraspinatus (and haematomas due to scapular #).
- firmly attached to bone at the border of these muscles
Covers shoulder convexly like a cape.
Arises: lateral 1/3 of clavicle, acromion, inferior lip of scapular spine
- four fibrous septae pass from its acromial portion to those muscle.
Inserts: deltoid tuberosity; three septa pass upwards from here to interdigitate with the above.
- this arrangement is essentially multipennate ¨ strong pull though little range
- ant and post fibres from clavicle and scapula are not multipennate greater range but less pull.
Nerve supply: axillary n. (C5,6) (post cord); runs round the surgical neck of the humerus (through quadrangular space) ¨ enters deltoid from deep surface (397). Vertically splitting deltoid will not damage this nerve.
Action: multipennate fibres abduct; anterior fibres assist pec major in flexing / medially rotating; posterior fibres assist lat dorsi in extending arm & laterally rotate.
Test: abduct arm against resistance
Injections: use lateral side of bulge, <4cm below lower acromion border (nerve is 5cm below this).
Below teres major, b/n humerus and long head triceps (obliquely)
B/n teres major and minor (with subscapularis), and between long head triceps & humerus.
(1) Dorsal scapular artery (from 3rd part of subclavian; or branch of transverse cervical)
- accompanies dorsal scapular nerve down vertebral border of scapula
(2) Suprascapular artery (from thyrocervical trunk)
- passes through supraspinous fossa (passes over the superficial transverse scapular ligament), then around lateral spine to infraspinous fossa
(3) Subscapular artery (from 3rd part of axillary)
- supplies subscapularis then ¨ circumflex branch to infraspinous fossa
All vessels anastomose ¨ connection of 1st part of subclavian with axillary arteries ¨ collaterals.
Veins: veins companion arteries ¨ corresponding anastomoses.
Ball-and-socket synovial jt. Glenoid fossa is 1:4 smaller than humeral head, but deepened by ring of fibrocartilage called the glenoid labrum.
Capsule: attaches to labrum margins, and scapula beyond supraglenoid tubercle. Thick and strong but necessarily lax in a mobile joint.
- attaches to humerus around articular margins except inferiorly where it meets the surgical neck one-finger-breadth below the articular margin
- continues across intertubercular sulcus as transverse humeral ligament.
- communicates with the subscapularis bursa anteriorly through a small gap.
- a similar posterior gap sometimes meets the infraspinatus bursa.
- It is thickened by the tendons of the short scapula muscles
- Remember the long head of biceps is intracapsular.
Synovial membrane attaches around the labrum and lines the capsule meeting humerus at articular margins.
- herniates through the above bursal orifices
- invests the intracapsular head of biceps in a long sleeve that reflects back to the floor of the intertubercular sulcus, gliding with ab/adduction of the shoulder.
3 bands between labrum and humerus, reinforcing capsule anteriorly (middle, inferior, superior)
- communication with subscapular bursa is through the upper two of these.
Strong. From coracoid to front of greater tubercle, blending with capsule.
Runs from named structures, supports head of humerus, subacromial bursa separates it from the cuff.
Large. Attached to coracoacromial lig above and supraspinatus below.
- rolled in under the acromion when arm abducted
- bursitis thus palpably tender under deltoid during adduction, disappears in abduction.
Only communicates with the joint space when the supraspinatus is badly torn.
Nerve supply: (Hilton): branches of axillary, musculocutaneous and suprascapular nerves.
- overhanging coracoacromial arch processes prevent displacement of the humeral head; this will never #, rather the clavicle or humerus itself would go first.
Rotator Cuff: tendons of subscapularis, supraspinatus, infraspinatus & teres min fuse with posterior aspect of shoulder joint, and attach near it onto the humerus.
- adds great stability & prevents ÔnippingÕ of joint capsule.
- Supraspinatus is prone to impingement, and a critical area of diminished vascularity 1cm proximal to its insertion may also contribute to its tendonitis rate.
- Leads to a painful arc between 60-120o.
- easily done if abducted >90o, extended and laterally rotated, drives head through inferior, less-well-supported capsule, frequently tearing the labrum as well
- may damage the axillary nerve and then prone to recurrent dislocation.
- May need reinforcing with overlapping repair/rearrangement of anterior muscles
Long head of biceps from supraglenoid tubercle ¨ strong support across head of humerus.
Long head of triceps important when arm abducted; lies immediately below joint in that position.
Ball and socket, free in many axes, often with associated scapula and thus clavicle movements.
Flexion: brings arm forward and inward across body
- clavicular head of pec major, anterior deltoid, coracobrachialis, short head of biceps
Extension: lat dorsi, teres major, posterior deltoid
- sternocostal pec major can extend the fully flexed arm and flex the fully extended arm
Abduction: mainly multipennate deltoid fibres
- supraspinatus critical in initiation while other cuff muscles exert a downward pull
- Only 90o is possible at the articular surface; further 30o from lateral rotation of the humerus bringing additional articular surface into effect. Further needs scapular rotation (makes glenoid face upwards (trapezius and serratus anterior)
- Actually beyond 30o all of these motions occur at once.
Adduction: gravity, aided by pec major, lat dorsi and teres major.
Rotation: largely short scapular muscles:
- infraspinatus and teres minor for lateral rotation
- subscapularis and teres major for medial rotation
Tests: place both hands behind the head tests lateral rotation, behind the back tests medial rotation.
- with arm abducted to 90o and elbow flexed, should achieve 90o of each.
Expose from front or back.
Front: via deltopectoral groove; ligate cephalic tributaries but preserve vein itself
- detach tip of coracoid, turn it medially with coracobrachialis and short head of biceps attached
- do not damage the musculocutaneous nerve on entering coracobrachialis
- divide subscapularis to expose the joint cavity
- anterior circumflex humeral vessels at the lower border of this muscle.
Back: detach deltoid from spine of scapula
- cut infraspinatus and teres minor to expose capsule
- avoid axillary nerve and posterior circumflex humeral vessels.
Injection & Aspiration: below the acromion at the side
- below the spine-acromion jx at the back (in direction of coracoid)
- through deltopectoral groove then below & medial to the coracoid tip at the front.