I. Shoulder
A. Osteology
1. Clavicle
a. The clavicle is the first bone to ossify (5th week of gestation); it is the only long bone to ossify by intramembranous ossification.
b. The medial (sternal) epiphysis is the last ossification center to fuse, at age 20 to 25 years.
c. The primary blood supply is periosteal; there is no nutrient artery.
2. Scapula—The scapula has only one true diarthrodial articulation, the acromioclavicular (AC) joint.
a. Body
i. Ossification begins at the 8th week of gestation.
ii. Shoulder motion is two thirds glenohumeral and one third scapulothoracic.
b. Spine
i. The spine is an osseous ridge that separates the supraspinatus and infraspinatus fossae.
ii. The spinoglenoid notch is a potential site of suprascapular nerve tethering or compression.
iii. Nerve compression at the spinoglenoid notch leads to selective denervation of the infraspinatus muscle. Suprascapular nerve compression at the suprascapular notch causes denervation of both the supraspinatus and the infraspinatus.
c. Acromion
i. The acromion has three ossification centers: the meta-acromion (base), the mesoacromion (mid), and the pre-acromion (tip).
ii. Failure of fusion results in os acromiale.
d. Coracoid process
i. The coracobrachialis muscle and the short head of the biceps tendon originate from the coracoid process.
ii. The pectoralis minor muscle inserts into the coracoid process.
iii. The coracoid process is an anatomic landmark for the deltopectoral approach to the shoulder.
e. Glenoid
i. The subchondral bone of the glenoid is relatively flat; the articular concavity is augmented by cartilage and a circumferential labrum.
ii. The glenoid averages 5° of retroversion in relation to the axis of the scapular body.
f. Superior shoulder suspensory complex (SSSC)
i. The SSSC provides stable connection of the scapula to the axial skeleton (
Figure 1).
ii. The SSSC is composed of the glenoid, the coracoid process, the coracoclavicular ligaments, the distal clavicle, the AC joint, and the acromion.
iii. The superior strut comprises the middle clavicle; the inferior strut comprises the lateral scapular border/spine of the scapula.
3. Proximal humerus
a. There are three primary ossification centers, which fuse to the shaft at age 17 to 20 years.
i. Humeral head (4 to 6 months)
ii. Greater tuberosity (1 to 3 years)
iii. Lesser tuberosity (3 to 5 years)
b. The humeral head averages 19° of retroversion and 41° of inclination (neck-shaft angle).
c. The greater and lesser tuberosities serve as attachment sites for the rotator cuff.
[Figure 1. Lateral view of the bone-soft-tissue ring of the superior shoulder suspensory complex.]
d. The anterolateral ascending branch of the anterior humeral circumflex artery provides the primary blood supply to the humeral head. It travels proximally in the lateral aspect of the intertubercular groove. The terminal intraosseous portion of the artery enters at the proximal aspect of the intertubercular groove as the arcuate artery.
B. Joints/ligaments
1. Sternoclavicular (SC) joint
a. The SC joint is the only true diarthrodial articulation between the upper appendicular and axial skeletons.
b. The posterior SC joint capsule and ligaments are the primary stabilizers to both anterior and posterior translation of the medial clavicle.
2. AC joint
a. The AC joint is a small diarthrodial joint with an interposed fibrocartilagenous disk.
b. The superior and posterior AC ligaments are the primary stabilizers to anterior and posterior (horizontal) translation of the clavicle.
c. The coracoclavicular ligaments (conoid: medial, trapezoid: lateral) are the primary stabilizers to superior (vertical) translation of the distal clavicle.
3. Glenohumeral joint
a. Dynamic stabilizers—The rotator cuff stabilizes the joint via joint compression. Positioning of the scapulothoracic joint also contributes to dynamic stability.
b. Static stabilizers include articular congruity, glenoid labrum, concavity-compression, negative intra-articular compression, and the glenohumeral capsule and ligaments. The glenoid labrum provides concavity and up to 50% of marginal glenoid socket depth.
c. Rotator interval
i. The rotator interval is defined medially by the base of the coracoid, superiorly by the supraspinatus tendon, and inferiorly by the subscapularis tendon.
ii. It contains the coracohumeral (CH) ligament, the superior glenohumeral ligament, and the intra-articular portion of the long head of the biceps tendon.
iii. Laxity can result in increased inferior glenohumeral laxity (sulcus sign).
iv. Contracture is seen in adhesive capsulitis (frozen shoulder).
v. The CH ligament restricts external rotation in adduction, and it is a static restraint to inferior translation in 0° of abduction and external rotation.
d. Glenohumeral ligaments
i. The superior glenohumeral ligament (SGHL) is a primary static restraint against anterior translation with the arm at the side. With the CH ligament, the SGHL forms a pulley that provides restraint against medial subluxation of the long head of the biceps tendon.
ii. The middle glenohumeral ligament (MGHL) is a primary static restraint against anterior translation with the arm in external rotation and 45° of abduction.
iii. The anterior inferior glenohumeral ligament (IGHL) is a primary static restraint against anterior-inferior dislocation of the glenohumeral joint in 90° of abduction and external rotation (position of apprehension).
iv. The posterior IGHL is a primary static restraint against posterior-inferior translation in internal rotation and adduction.
4. Intrinsic scapular ligaments
|
a. |
Superior transverse scapular ligament |
|
|
i. Arises from the medial base of the coracoid overlying the suprascapular notch.
ii. The suprascapular artery runs superior to the ligament; the nerve runs deep to the ligament.
iii. Entrapment of the suprascapular nerve here causes denervation of both the supraspinatus and the infraspinatus. |
[
Table 1. Musculature of the Shoulder Girdle]
|
b. |
Spinoglenoid ligament |
|
|
i. The spinoglenoid ligament overlies the distal suprascapular nerve at the spinoglenoid notch.
ii. Entrapment or compression here causes denervation of the infraspinatus alone. |
|
c. |
Coracoacromial ligament—The ligament originates from the lateral coracoid to insert on the anterior and lateral acromion. |
C. Musculature of the shoulder girdle (Table 1)
D. Nerves
1. The brachial plexus is organized into roots, trunks, divisions, cords, and branches (
Figure 2).
2. Axillary nerve (posterior cord)
a. The axillary nerve splits into the posterior and anterior branches at the 6 o'clock position on the glenoid.
b. It exits posteriorly with the posterior humeral circumflex artery through the quadrilateral space (medial: long head of triceps, lateral: humeral shaft, superior: teres minor, inferior: teres major) (
Figure 3).
c. The posterior branch terminates into a muscular branch to the teres minor and a sensory branch to the skin overlying the lateral deltoid (superior-lateral brachial cutaneous nerve). Loss of sensation over the lateral deltoid can signify palsy of the teres minor.
d. The anterior branch innervates and courses along the undersurface of the deltoid.
e. On average, the anterior branch is located 5 cm from the lateral acromial edge, but it can be found as close as 3.5 cm.
f. The lateral deltoid should not be split more than 3.5 cm from the lateral acromial edge to avoid axillary nerve injury and anterior deltoid denervation.
3. Musculocutaneous nerve (lateral cord)
a. The main trunk penetrates the coracobrachialis muscle 3 to 8 cm distal to the tip of the coracoid.
b. It innervates the biceps brachii and the brachialis.
c. It terminates as the lateral antebrachial cutaneous nerve to the anterolateral forearm.
4. Suprascapular nerve (preclavicular branch)
a. This nerve transverses through the suprascapular
[Figure 2. Drawing of the brachial plexus and its terminal branches.]
notch (under the superior transverse scapular ligament), where it innervates the supraspinatus.
b. It transverses the spinoglenoid notch to innervate the infraspinatus.
c. It is found approximately 1.5 cm medial to the posterior rim of the glenoid.
5. Long thoracic nerve (preclavicular branch)—Injury (axillary dissection, aggressive retraction of middle scalene muscle) results in serratus anterior palsy and medial winging of the scapula (superior elevation of the scapula with medial translation and medial rotation of the inferior pole of the scapula).
6. Spinal accessory nerve (cranial nerve XI)—Injury (cervical lymph node biopsy or radical neck dissection) results in trapezius palsy and lateral winging of the scapula (depression of scapula with lateral translation and lateral rotation of the inferior pole of scapula).
E. Arteries—The axillary artery is divided into three segments by the pectoralis minor muscle.
1. First part
a. Found medial to the pectoralis minor muscle
b. Has one branch: the supreme thoracic artery
2. Second part
a. Found deep to the pectoralis minor muscle
b. Has two branches: the thoracoacromial trunk and the lateral thoracic artery
3. Third part
a. Found lateral to the pectoralis minor muscle
b. Has three branches: the subscapular artery (the circumflex scapular branch runs through the triangular space), the anterior humeral circumflex artery (the anterolateral ascending branch is the major blood supply to the humeral head), and the posterior humeral circumflex artery (accompanies the axillary nerve
[Figure 3. View of the posterior aspect of the shoulder with respect to the axillary nerve, quadrilateral space, triangular space, and triangular interval.]
[
Figure 4. Illustration showing the vascularity of the anterior shoulder.]
and exits posteriorly through the quadrilateral space) (Figure 4)
F. Surgical approaches
1. Deltopectoral approach
a. This is the "workhorse" approach to the shoulder.
b. It uses the internervous plane between the deltoid (axillary nerve) and the pectoralis major (medial and lateral pectoral nerves) muscles.
c. The cephalic vein is usually present in the interval.
d. The clavipectoral fascia overlies the conjoined tendon (coracobrachialis and short head of the biceps) and the subscapularis.
e. The musculocutaneous nerve is at risk for traction injury.
f. The axillary nerve (posterior cord of the brachial plexus) can be palpated on the anteroinferior surface of the subscapularis, medial to the coracoid.
g. The anterior circumflex humeral artery travels along the inferior subscapularis between the upper two thirds and the inferior one third (muscular portion).
2. Posterior approach
a. The posterior approach is commonly used in surgery to repair posterior capsular shift and glenoid fractures.
b. Identification of the quadrilateral space protects the axillary nerve and the posterior circumflex humeral artery.
c. This approach uses the internervous plane between the teres minor (axillary nerve) inferiorly and the infraspinatus (suprascapular nerve) superiorly.
3. Lateral approach
a. The lateral approach is commonly used in surgery to repair the rotator cuff and greater tuberosity fractures.
b. A mini-open approach to the shoulder utilizes a deltoid split between the middle and anterior raphe.
c. Alternatively, the deltoid is detached from the anterior lateral acromion for open rotator cuff repair.
G. Important biomechanical features of the shoulder
1. The SC joint permits three degrees of freedom in movement (ball-and-socket mechanics).
2. The clavicle rotates 50° along its long axis during shoulder motion, mainly through the AC joint. Clavicular rotation accounts for up to 50% of scapulothoracic elevation.
3. The glenohumeral-to-scapulothoracic ratio varies through elevation, but it averages 2:1.
H. Arthroscopic anatomy of the shoulder
1. The long head of the biceps brachii exits the joint in the lateral aspect of the rotator interval and is stabilized against medial subluxation by a pulley composed of the coracohumeral ligament and the SGHL.
2. The superior biceps-labral anchor complex is anchored to the supraglenoid tubercle. The normally mobile superior glenoid labrum associated with the rim of articular cartilage on the supraglenoid tubercle must be differentiated from a traumatic disruption of the superior labrum (superior labral anterior-to-posterior [SLAP] tear) from bone.
3. The region of the anterosuperior labrum and MGHL origin has wide anatomic variability (
Figure 5).
a. The most common anatomy is an attached labrum with a broad MGHL.
b. A sublabral hole is often associated with a cordlike MGHL.
c. A cordlike MGHL with absent anterosuperior labrum is a rare variant known as the Buford complex.
4. A central bare spot on the glenoid and a bare area on the posterior humeral head are normally devoid of cartilage and are not representative of trauma or arthritis.
II. Arm and Elbow
A. Osteology
1. Humeral shaft
a. The deltoid inserts in a V shape at the deltoid tubercle.
b. The radial nerve lies within the spiral groove, distal to the deltoid insertion.
c. A supracondylar process, present in 1% to 3% of individuals, is located 5 to 7 cm proximal to the medial epicondyle and is a potential site of median nerve entrapment.
2. Distal humerus
a. The distal humerus is composed of an articular cylinder (spool) between the lateral and medial metaphyseal flares (columns) of the distal humerus.
b. The articular surface has approximately 30° of anterior tilt, 5° of internal rotation, and 6° of valgus.
i. The capitellum articulates with the radial head and is the site of idiopathic osteonecrosis (Panner disease) and osteochondritis dissecans lesions.
ii. The trochlea has a high degree of articular congruency with the greater sigmoid notch of the olecranon.
iii. The olecranon fossa receives the tip of the olecranon during terminal extension, the coronoid fossa receives the coronoid tip in flexion, and the radial fossa receives the radial head in flexion.
iv. The lateral condyle provides for origin of the lateral ulnar collateral ligament.
v. The medial epicondyle provides for origin of the medial collateral ligament.
3. Proximal radius
a. The radial head functions as an important secondary stabilizer to valgus stress, particularly in medial collateral ligament-deficient elbows.
b. Cartilage encircles approximately 240° of the marginal radial head, with the lateral 120° ("safe zone") devoid of cartilage. This is an important consideration for placement of internal fixation for radial head and neck fractures.
c. The proximal radial tuberosity provides the insertion site for the distal biceps tendon.
4. Proximal ulna—The ulnohumeral joint is the major osseous stabilizer of the elbow joint.
[Figure 5. Normal anatomic variation of the anterosuperior labrum. A, Normal shoulder. The anterosuperior labrum is firmly attached to the glenoid rim and the MGHL is flat or sheetlike. B, Sublabral foramen with normal MGHL. C, Sublabral foramen with cordlike MGHL. D, Absence of anterosuperior labrum with cordlike MGHL originating from superior biceps-labral anchor. MGHL = middle glenohumeral ligament; IGHL = inferior glenohumeral ligament.]
a. The coronoid acts as an anterior buttress to posterior dislocation.
b. The transverse sulcus at the midportion of the articular surface of the olecranon is normally devoid of cartilage.
c. The crista supinatoris (supinator crest) provides for insertion of the lateral ulnar collateral ligament and the origin of the supinator muscle.
d. The sublime tubercle provides insertion for the anterior bundle of the medial collateral ligament.
B. Joint/ligaments
1. The elbow is a trochoginglymoid joint with three articulations: the ulnohumeral joint, the radiohumeral joint, and the proximal radioulnar joint.
a. The ulnohumeral joint is highly congruous and is nearly hingelike.
b. The radiohumeral and proximal radioulnar joints allow rotation.
2. Stability is provided by dynamic and static constraints.
a. Dynamic (muscular) stabilizers provide a variable degree of compression, with a resultant posterior vector.
b. Static stabilizers include bone, capsule, and ligaments.
3. Ligaments (
Figure 6)
a. Annular ligament—Stabilizes the proximal radioulnar joint.
b. Radial collateral ligament
c. Lateral ulnar collateral ligament—Acts as the primary stabilizer to posterolateral rotatory instability.
d. Medial collateral ligament (
Figure 7)
i. Anterior band—Acts as the primary stabilizer to valgus stress.
[Figure 6. Illustration of the lateral collateral ligament complex.]
ii. Posterior band—Forms the floor of the cubital tunnel; it limits flexion when contracted.
iii. Transverse bundle
C. Musculature (
Table 2)
D. Nerves
1. Lateral antebrachial cutaneous nerve
|
a. |
This nerve is the terminal branch of musculocutaneous nerve (lateral cord). |
|
b. |
The musculocutaneous nerve runs between the biceps and brachialis and emerges lateral to the distal tendon of the biceps brachii as the lateral antebrachial cutaneous nerve. |
[Figure 7. Illustration of the medial collateral ligament complex.]
[Table 2. Musculature of the Elbow]
|
c. |
The lateral antebrachial cutaneous nerve is at risk for injury during distal biceps repair (oneincision anterior approach). |
2. Radial nerve (posterior cord)
a. The radial nerve exits the triangular interval (teres major, medial humeral shaft, long head of the triceps).
b. It travels with the profunda brachii artery, lateral to the deltoid insertion, into the spiral groove of the humerus.
c. It pierces the lateral intermuscular septum to enter the anterior compartment of the arm at the junction of the middle and distal thirds of the humerus.
d. It courses superficial to the elbow joint capsule, anterior to the radiocapitellar joint, where it is vulnerable to injury during arthroscopy or open anterior capsular release.
e. Radial nerve palsy is most commonly associated with middle-third humeral fractures.
3. Ulnar nerve (medial cord)
a. The ulnar nerve enters the posterior compartment of the brachium through the medial intermuscular septum at the arcade of Struthers.
b. It passes through the cubital tunnel posterior to the medial epicondyle.
c. The first motor branch to the flexor carpi ulnaris arises distal to the cubital tunnel.
4. Median nerve (lateral and medial cords)
a. The median nerve courses distally medial to the brachial artery.
b. It overlies the brachialis muscle at the elbow joint.
E. Arteries
1. Brachial artery
a. The brachial artery descends in the anterior compartment of the arm with the median nerve.
b. Proximally, the nerve is medial to the artery.
c. Distally, the artery is medial to the nerve.
d. At the level of the elbow joint, the brachial artery branches into the radial and ulnar arteries.
2. The inferior ulnar collateral artery provides the only direct supply of oxygenated blood to the ulnar nerve proximal to the cubital tunnel.
3. The vascular supply to the lateral condyle is from the posterior aspect.
F. Surgical approaches—Humeral shaft
1. Anterior/anterolateral approach
a. Proximally, the deltopectoral interval is used.
b. Distally, the superficial interval is between the biceps brachii (musculocutaneous nerve) and the brachialis (the musculocutaneous nerve medially and the radial nerve laterally).
c. The lateral antebrachial cutaneous nerve, located between the biceps and the brachialis, is retracted medially with the biceps.
d. The radial nerve is identified in the deep interval between the lateral brachialis (radial nerve) and the brachioradialis (radial nerve).
e. The brachialis is split (anterior approach) or subperiosteally reflected from the humerus and retracted medially and laterally (anterolateral approach).
2. Posterior approach
a. This approach allows exposure of the distal two thirds of the humerus and the radial nerve.
b. The superficial interval is between the long and lateral heads of the triceps.
c. The radial nerve and the profunda brachii artery are identified in the spiral groove.
G. Surgical approaches—Elbow
1. Lateral approaches are used for radial head surgery, capsular release/excision, and lateral collateral ligament repair/reconstruction.
a. Kocher approach
i. The Kocher approach uses the plane between the anconeus (radial nerve) and the extensor carpi ulnaris (posterior interosseous nerve).
ii. Access to the joint anterior to the midplane of the radial head preserves the lateral ulnar collateral ligament.
iii. The approach can be extended proximally to the lateral column approach.
b. The lateral column approach uses the plane along the lateral supracondylar ridge between the triceps posteriorly and the brachioradialis/extensor carpi radialis longus anteriorly.
2. Medial approach
a. The medial approach is used for medial capsular release/excision, coronoid fracture, and medial collateral ligament repair/reconstruction.
b. Identification and/or transposition of the ulnar nerve is required.
[
Figure 8. Location of the anterior portals used in arthroscopic surgery of the elbow. A, Lateral view of the elbow showing the proximal anterolateral, anterolateral, and midlateral (soft spot) portals in relation to the radial nerve. B, Medial view of the elbow showing the anteromedial and proximal anteromedial portals in relation to the median, ulnar, and medial antebrachial cutaneous nerves.]
c. The medial antebrachial cutaneous nerve is also identified and protected in the distal aspect of the incision.
3. Posterior approach
a. The posterior approach is a utilitarian extensile exposure for concomitant medial and lateral surgery, elbow arthroplasty, and distal humerus fractures.
b. Posterior exposure is obtained by split or reflection of the triceps or by osteotomy of the olecranon.
H. Biomechanical features of the elbow
1. Articular congruity contributes greatly to varus stability.
2. Valgus stability is equally divided among the medial collateral ligament, the anterior joint capsule, and the osseous articulation in elbow extension.
3. In 90° of flexion, the medial collateral ligament is the primary valgus stabilizer.
4. The carrying angle of the elbow is 11° of valgus.
5. Axial loading of the extended elbow is transmitted 40% through the ulnohumeral joint and 60% through the radiohumeral joint.
6. Most activities of daily living require elbow range-of-motion arcs comprising 100° (30° to 130°) of flexion/extension and 100° (50°/50°) of pronation/supination.
7. The center of rotation approximates a line through the isometric points on the capitellum and trochlea.
I. Arthroscopic anatomy of the elbow
1. The close proximity of neurovascular structures places them at risk during arthroscopy (Figure 8).
a. The proximal anterolateral portal is close to the radial nerve.
b. The proximal anteromedial portal is close to the medial antebrachial cutaneous nerve.
2. The radial nerve lies adjacent to the anterior capsule at the mid aspect of the capitellum.
3. The ulnar nerve lies directly superficial to the joint capsule in the posteromedial gutter.
4. The most common neurologic complication after elbow arthroscopy is transient ulnar nerve palsy.
Top Testing Facts
Anatomy of the Shoulder
1. The clavicle is the first bone to ossify, and the medial (sternal) epiphysis of the clavicle is the last ossification center to fuse, at age 20 to 25 years.
2. The primary blood supply to the humeral head is the anterolateral ascending branch of the anterior circumflex artery, terminating as the intraosseous arcuate artery.
3. With the CH ligament, the SGHL forms a pulley that provides restraint against medial subluxation of the long head of the biceps tendon.
4. The anterior IGHL is a primary static restraint against anterior-inferior dislocation of the glenohumeral joint in 90° of abduction and external rotation (position of apprehension).
5. Loss of sensation over the lateral shoulder indicates injury to the posterior branch of the axillary nerve and signifies possible teres minor palsy.
6. The lateral deltoid should not be split more than 3.5 cm from the lateral acromial edge to avoid axillary nerve injury and anterior deltoid denervation.
7. Injury to the long thoracic nerve (serratus anterior) causes medial scapular winging, and injury to the spinal accessory nerve (trapezius) causes lateral scapular winging.
Anatomy of the Arm/Elbow
1. The lateral ulnar collateral ligament is the primary elbow stabilizer to posterolateral elbow rotatory instability. The anterior band of the medial collateral ligament is the primary valgus stabilizer in elbow flexion.
2. The radial nerve pierces the lateral intermuscular septum to enter the anterior compartment of the arm at the junction of the middle and distal thirds of the humerus.
3. Most activities of daily living require elbow range-of-motion arcs comprising 100° (30° - 130°) of flexion/extension and 100° (50°/50°) of pronation/supination.
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