Anatomy of the Shoulder and Elbow
Anatomy and Approaches
Anatomy of the Shoulder and Elbow
Anatomy and Approaches
OVERVIEW OF SHOULDER AND ELBOW SURGERY
In order to diagnose and treat problems of the shoulder and elbow, one must fully understand the anatomy of the region and appreciate how this translates to functional derangements.
There is no line of demarcation between the shoulder and elbow regions. Pain in the arm may originate at the neck or shoulder and refer down the arm. Less often, pain noted by patients at the elbow or forearm has local origin. If the slightest doubt exists as to the etiology of the pain, the patient is examined from neck to fingers.
The upper extremity functions to position and move the hand in space. The upper extremities are attached to the body by the sternoclavicular joint. Otherwise, they are suspended from the neck and held fast to the torso by soft tissues (muscles and fascia).
The upper extremity gains leverage against the posterior aspect of the thorax by virtue of the broad, flat body of the scapula.
The elbow is a complex modified hinge articulation. Unlike the shoulder, the elbow has much more intrinsic stability based on its bony architecture. The primary purpose of the elbow is to position the hand in space.
An increasing knowledge of the pathoanatomy and biomechanics of the shoulder and elbow has guided development of new and innovative surgical techniques and devices that have allowed more effective treatment of a number of disorders.
Arthroscopic surgery, in particular, has significantly increased our ability to surgically manage conditions and reduce morbidity. The Sports Medicine portion of this textbook handles the arthroscopic management of shoulder and elbow disorders.
The art of any surgery lies in the reconstruction of diseased or injured tissues with minimal additional destruction. Skillful handling of the soft tissues is the hallmark of all upper extremity surgery, including surgery about the shoulder and elbow. Knowledge of anatomy defines the precision and safety of surgery. Approaches to any joint in the body are developed on this foundation, with particular emphasis on the exploitation of internervous planes. Familiarity with the intricate anatomy and multiple approaches to the shoulder and elbow allows the surgeon to confidently embark on the repair or reconstruction of the injury or disorder of the joint.
ANATOMY OF THE SHOULDER
The shoulder has the greatest mobility of any joint in the body and therefore the greatest predisposition to dislocation.
This great range of motion is distributed to three diarthrodial joints: the glenohumeral, the acromioclavicular, and the sternoclavicular.
The last two joints, in combination with the fascial spaces between the scapula and the chest, are known
collectively as the scapulothoracic articulation.
OSTEOLOGY
Clavicle
This is a relatively straight bone when viewed anteriorly, whereas in the transverse plane, it resembles an italic S (FIG 1).
There are three bony impressions for ligament attachment to the clavicle:
On the medial side is an impression for the costoclavicular ligament, which at times may be a rhomboid fossa.
At the lateral end of the bone is the conoid tubercle.
Just lateral to the conoid tubercle is the trapezoid tubercle.
Muscles that insert on the clavicle are the trapezius on the posterosuperior surface of the distal end and the subclavius muscle, which has an insertion on the inferior surface of the middle third of the clavicle.
The clavicle serves as a site of muscular attachment and a strut for the shoulder girdle.
Although historical literature discussed the clavicle as predominantly as a site of muscular attachment, recent work, especially regarding displaced clavicle fractures, has demonstrated an important structural function of the clavicle as a strut for the shoulder girdle, maintaining the position of the scapulothoracic articulation and glenohumeral joint in space.
Four muscles take origin from the clavicle: deltoid, pectoralis major, sternocleidomastoid, and sternohyoid. Important relations to the clavicle are the subclavian vein and artery and the brachial plexus inferiorly.
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FIG 1 • The clavicle. AC, acromioclavicular; SC, sternoclavicular.
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Scapula
This is a thin sheet of bone that functions mainly as a site of muscle attachment (FIG 2A).
It is thicker at its superior and inferior angles in its lateral border, where some of the more powerful muscles
are attached.
It is also thick in forming its processes: coracoid, spine, acromion, and glenoid.
The coracoid process comes off the scapula at the upper base of the neck of the glenoid and passes anteriorly before hooking to a more lateral position.
Functions as the origin of the short head of the biceps and the coracobrachialis tendons
Serves as the insertion of the pectoralis minor muscle and the coracoacromial, coracohumeral, and coracoclavicular ligaments
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FIG 2 • A. The scapula. B. The supraspinatus and infraspinatus fossa.
The spine of the scapula functions as part of the insertion of the trapezius on the scapula as well as the origin of the posterior deltoid.
Also serves to suspend the acromion in the lateral and anterior directions to serve as a prominent lever arm for function of the deltoid
The posterior surface of the scapula and the presence of the spine create the supraspinatus and infraspinatus fossa (FIG 2B).
The acromion is the most studied process of the scapula because of the amount of pathology involving the acromion and the rotator cuff.
Three types of acromion morphologies have been defined by Bigliani and Morrison1 (FIG 3).
Type 1, with its flat surface, provided the least compromise of the supraspinatus outlet, whereas type 3, which has a hook, was associated with the highest rate of rotator cuff pathology in a series of cadaver dissections.
The glenoid articular surface is within 10 degrees of being perpendicular to the blade of the scapula, with the mean being 6 degrees of retroversion.
More caudad portions face more anteriorly than cephalad.
Three processes—the spine, the coracoid, and the glenoid— create two notches in the scapula.
Suprascapular notch is at the base of the coracoid.
Spinoglenoid, or greater scapular notch, is at the base of the spine.
Major ligaments that take origin from the scapula are as follows:
Coracoclavicular
Coracoacromial Acromioclavicular Glenohumeral Coracohumeral
Blood supply to the scapula derives from vessels in the muscles that take fleshy origin from the scapula.
Vessels cross these indirect insertions and communicate with bony vessels.
Humerus
The articular surface of the humerus at the shoulder is spheroid, with a radius of curvature of about 2.25 cm.
With the arm in the anatomic position (ie, with the epicondyles of the humerus in the coronal plane), the head of humerus has retroversion of about 30 degrees, with a wide range of normal values.
The intertubercular groove lies about 1 cm lateral to the midline of the humerus (FIG 4).
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FIG 3 • Acromion morphologies.
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FIG 4 • The humerus.
The axis of the humeral head crosses the greater tuberosity at about 9 mm posterior to the bicipital groove.
The lesser tuberosity lies directly anterior, and the greater tuberosity lines up on the lateral side.
The lesser tuberosity is the insertion for the subscapularis tendon.
The greater tuberosity bears the insertion of the supraspinatus, infraspinatus, and teres minor in a superior
to inferior order.
Greater and lesser tuberosities make up the boundaries of the intertubercular groove through which the long head of the biceps passes from its origin on the superior lip of the glenoid.
The intertubercular groove has a peripheral roof referred to as the intertubercular ligament or the
transverse humeral ligament, which has varying degrees of strength.
In the coronal plane, the head-shaft angle is about 135 degrees.
The space between the articular cartilage and the ligamentous and tendon attachments is referred to as the
anatomic neck of the humerus.
Below the level of the tuberosities, the humerus narrows in a region that is referred to as the surgical neck of the humerus because of the frequent occurrence of fractures at this level.
Historically, the humeral head was thought to be perfused predominantly by the ascending branch of the anterior humeral circumflex artery, traveling along the biceps groove. Recent work, however, has demonstrated that the posterior humeral circumflex artery has a vital function in perfusing the humeral head.
STERNOCLAVICULAR JOINT
This is the only skeletal articulation between the upper limb and the axial skeleton.
Ligaments
The major ligaments of the sternoclavicular joint are the anterior and posterior sternoclavicular ligaments. The most important ligament of this group, the posterior sternoclavicular ligament, is the strongest.
Blood Supply
Blood supply of the sternoclavicular joint derives from the clavicular branch of the thoracoacromial artery, with additional contributions from the internal mammary and the suprascapular arteries.
Nerve Supply
Arises from the nerve to the subclavius, with some contribution from the medial suprascapular artery
ACROMIOCLAVICULAR JOINT
Only articulation between the clavicle and the scapula
Ligaments
Ligaments about the acromioclavicular articulation include the superior and inferior acromioclavicular ligaments and the coracoclavicular ligaments (the trapezoid and the conoid ligaments (FIG 5).
The anteroposterior stability of the acromioclavicular joint is controlled by the acromioclavicular ligaments, and the vertical stability is controlled by the coracoclavicular ligaments.
Blood Supply
Blood supply derives mainly from the acromial artery, a branch of the deltoid artery of the thoracoacromial axis.
There are rich anastomoses between the thoracoacromial artery, suprascapular artery, and posterior
humeral circumflex artery.
The acromial artery comes on to the thoracoacromial axis anterior to the clavipectoral fascia and perforates back through the clavipectoral fascia to supply the joint.
Nerve Supply
Innervation of the joint is supplied by the lateral pectoral, axillary, and suprascapular nerves.
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FIG 5 • Acromioclavicular joint.
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SHOULDER LIGAMENTS: CAPSULOLIGAMENTOUS AND LABRAL ANATOMY
Superior Glenohumeral Ligament
Arises near the origin of the long head of the biceps brachii
If the glenoid had the markings of a clock, with the 12 o'clock position superiorly and the 3 o'clock position
anteriorly, the origin of the superior glenohumeral ligament (SGHL) would correspond to the area from the 12 o'clock to the 2 o'clock positions (FIG 6).
SGHL runs inferiorly and laterally to insert on the humerus, superior to the lesser tuberosity.
Middle Glenohumeral Ligament
Usually arises from the neck of the glenoid just inferior to the origin of the SGHL and inserts into the humerus just medial to the lesser tuberosity. Arthroscopically, it can be easily identified as it crosses the superior boarder of the subscapularis at a 90-degree angle.
Presence of the middle glenohumeral ligament (MGHL) is the most variable of any shoulder ligament.
Inferior Glenohumeral Ligament
Most important ligament for providing anterior and posterior shoulder stability
Inferior glenohumeral ligament (IGHL) has been described as having an anterior and posterior band, with an axillary pouch between the bands.
With abduction and external rotation, the anterior band fans out and the posterior band becomes cordlike.
Likewise, with internal rotation, the posterior band fans out and the anterior band appears cordlike.
Anterior band of the IGHL arises from various areas corresponding to the 2 o'clock to 4 o'clock positions on the glenoid.
Insertion site of this ligament has two attachments, one to the glenoid labrum and the other directly to the anterior neck of the glenoid.
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FIG 6 • Shoulder ligaments.
Posterior band originates at the 7 o'clock to 9 o'clock positions.
With the arm at the side, both the anterior and the posterior bands pass through a 90-degree arc and insert on the humerus.
Labrum
Surrounds the periphery of the glenoid and is a site of attachment of the capsuloligamentous structures
It is composed of dense fibrous connective tissue, with a small fibrocartilaginous transition zone at the anteroinferior attachment of the osseous glenoid rim.
The labrum acts as a load-bearing structure for the humeral head and serves to increase the surface area of the glenoid.
Howell and Galinat2 showed that the labrum deepened the glenoid socket by nearly 50%.
Lippitt and coworkers3 have shown that removal of the labrum decreases the joint's stability to sheer stress by 20%.
Triangular cross-section of the labrum allows it to act as a chock-block to help prevent subluxation.
SCAPULOTHORACIC MUSCLES
Trapezius
Largest and most superficial of scapulothoracic muscles Takes origin from spinous process of C7-T12 vertebrae
Insertion of the upper fibers is over the distal one-third of the clavicle.
Lower cervical and upper thoracic fibers of the trapezius have their insertion over the acromion and spinous scapula.
Lower portion of the muscle takes insertion at the base of the scapular spine.
Acts as a scapular retractor, with the upper fibers used mostly for elevation of the lateral angle Spinal accessory nerve is the motor supply.
Arterial supply is derived from transverse cervical artery.
Rhomboids
Similar in function to the midportion of the trapezius, with origin from the lower ligamentum nuchae, C7 and T1 for the rhomboid minor, and T2-T5 for the rhomboid major
Rhomboid minor inserts on the posterior portion of the medial base of the spine of the scapula.
Rhomboid major inserts to the posterior surface of the medial border, from where the minor leaves off down to the inferior angle of the scapula.
Action of the rhomboids is retraction of the scapula, and because of their oblique course, they also participate in elevation of the scapula.
Innervation is the dorsal scapular nerve (C5), which may arise off the brachial plexus in common with the nerve to the subclavius or with the C5 branches of the long thoracic nerve.
Dorsal scapular artery provides arterial supply to the muscles through their deep surfaces.
Levator Scapula and Serratus Anterior
The levator scapula and the serratus anterior are often discussed together because of their close relationship anatomically and functionally.
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The levator scapula takes origin from the posterior tubercles of the transverse process from C1 through C3 and sometimes C4.
Inserts on the superior angle of the scapula
Acts to elevate the superior angle of the scapula
In conjunction with the serratus anterior, produces upward rotation of the scapula Innervation is from the deep branches of C3 and C4.
Serratus anterior takes origin from the ribs on the anterior lateral wall of the thoracic cage.
Bounded medially by the ribs and intercostal muscles and laterally by the axillary space
Protracts the scapula and participates in upward rotation of the scapula
More active in flexion than in abduction because straight abduction requires some retraction of the scapula
Absence of serratus activity, usually because of paralysis, produces a winging of the scapula with forward flexion of the arm and loss of strength in that motion.
Innervation is supplied by the long thoracic nerve (C5-C7).
Blood supply is from the lateral thoracic artery, with a large contribution from the thoracodorsal artery.
Pectoralis Minor
Takes fleshy origin anteriorly on the chest wall, and second through fifth ribs, and has its insertion onto the base of the medial side of the coracoid
Function is protraction of the scapula if the scapula is retracted and depression of the lateral angle or downward rotation of the scapula if the scapula is upwardly rotated.
Innervation is from the medial pectoral nerve (C8 and T1).
Blood supply is through the pectoral branch of the thoracoacromial artery.
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FIG 7 • A,B. Glenohumeral muscles.
GLENOHUMERAL MUSCLES
Deltoid
Largest and most important of the glenohumeral muscles, consisting of three major sections:
Anterior deltoid takes origin off the lateral third of the clavicle, middle third of the deltoid takes origin off the acromion, and posterior deltoid takes origin from the spine of the scapula (FIG 7).
The deltoid is supplied by the axillary nerve (C5 and C6), which enters the posterior portion of the shoulder through the quadrilateral space and innervates the teres minor in this position.
Nerves to the posterior third of the deltoid enter the muscle very close to their exit from the quadrilateral space, traveling in the deltoid muscle along the medial and inferior borders of the posterior deltoid.
Branch of the axillary nerve that supplies the anterior twothirds of the deltoid ascends superiorly and then travels anteriorly, about 5 cm inferior to the rim of the acromion.
Vascular supply to the deltoid is largely derived from the posterior humeral circumflex artery, which travels with the axillary nerve through the quadrilateral space and on the deep surface of the muscle.
Deltoid is also supplied by the deltoid branch of the thoracoacromial artery.
Supraspinatus
Lies on the superior portion of the scapula
It takes origin from the supraspinatus fossa and overlying fascia and inserts into the greater tuberosity. Its tendinous insertion is in common with the infraspinatus posteriorly.
It is active in any motion involving elevation.
It exerts maximum effort at about 30 degrees of elevation.
Innervation of the supraspinatus is supplied by the suprascapular nerve (C5, C6). Arterial supply is the suprascapular artery.
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Nerve comes through the suprascapular notch and is bound above by the transverse scapular ligament.
Artery travels above this ligament.
Suprascapular vessels and nerve supply the deep surface of the muscle.
Infraspinatus
Second most commonly torn rotator cuff muscle
Its tendinous insertion is in common with the supraspinatus anterosuperiorly and the teres minor inferiorly at the greater tuberosity.
One of the two main external rotators of the humerus and accounts for as much as 60% of external rotation force
Also functions as a depressor of the humeral head
Even in a passive state, it is an important stabilizer against posterior subluxation. Innervated by the suprascapular nerve
Blood supply is from two large branches of the suprascapular artery.
Teres Minor
One of the few external rotators of the humerus
It provides up to 45% of the external rotation force.
Innervated by the posterior branch of the axillary nerve (C5 and C6)
Blood supply is derived from several vessels in the area, especially the posterior humeral scapular circumflex artery.
Subscapularis
Makes up the anterior portion of the rotator cuff
Takes origin from the subscapularis fossa, which covers most of the anterior surface of the scapula
Its upper 60% inserts through a cartilaginous tendon into the lesser tuberosity of the humerus, and its lower 40% has a fleshy insertion into the humerus below the lesser tuberosity cupping the head and neck.
Functions as an internal rotator and passive stabilizer to anterior subluxation and serves in its lower fibers to depress the humeral head
Innervation is usually supplied by two sources:
Upper subscapular nerve (C5) and lower subscapular nerve (C5 and C6)
Upper subscapular nerve usually comes off the posterior cord of the brachial plexus.
Blood supply originates from the axillary and subscapular arteries.
Teres Major
Takes origin from the posterior surface of the scapula along the inferior portion of the lateral border
It has a muscular origin and a common tendinous insertion with the latissimus dorsi into the humerus along the medial lip of the bicipital groove.
In their course, both the latissimus dorsi and the teres major undergo a 180-degree spiral; thus, the formerly posterior surface of the muscle is represented by fibers on the anterior surface of the tendon.
Function is internal rotation, adduction, and extension of the arm. Innervation is supplied by the lower subscapular nerve C5 and C6. Blood supply is derived from the subscapular artery.
Coracobrachialis
Originates from the coracoid process, in common with and medial to the short head of the biceps, and inserts onto the anteromedial surface in the midportion of the humerus
Action is flexion and adduction of the glenohumeral joint.
Innervation supplied by small branches from the lateral cord and the musculocutaneous nerve
Because the larger musculocutaneous nerve's entrance to the muscle may be situated as high as 1.5 cm from the tip of the coracoid to as low as 7 to 8 cm, it must be protected during certain types of repair.
Major blood supply is usually off the axillary.
MULTIPLE JOINT MUSCLES
Pectoralis Major
Consists of three portions
Upper portion takes origin from the medial one-half to two-thirds of the clavicle and inserts along the lateral lip of the bicipital groove.
Middle portion takes origin from the manubrium and upper two-thirds of the body of the sternum and ribs 2
through 4.
It inserts directly behind the clavicular portion and maintains a parallel fiber arrangement.
Inferior portion of the pectoralis major takes origin from the distal body of the sternum, the fifth and sixth ribs, and the external oblique muscle fascia.
Action
Clavicular portion participates somewhat in flexion with the anterior portion of the deltoid while the lower fibers are antagonistic.
Is active in internal rotation against resistance and will extend the shoulder from flexion until the neutral position is reached
Powerful adductor of the glenohumeral joint Innervation is supplied by two sources:
Lateral pectoral nerve (C5-C7) innervates the clavicular portion of the muscle.
Loop contribution from the lateral to the medial pectoral nerve carrying C7 fibers into the upper sternal portion
Major blood supply derives from two sources:
The deltoid branch of the thoracoacromial artery supplies the clavicular portion and the pectoral artery supplies the sternocostal portion of the muscle.
Latissimus Dorsi
Takes origin by the large and broad aponeurosis from the dorsal spines of T7-L5, a portion of the sacrum, and the crest of the ilium
Wraps around the teres major and inserts into the medial crest and floor of the bicipital or intertubercular groove
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Actions are inward rotation and adduction of the humerus, shoulder extension, and indirectly through its pull on the humerus downward rotation of the scapula.
Innervation is through the thoracodorsal nerve (C6 and C7). Major blood supply is derived from the thoracodorsal artery.
Biceps Brachii
There are two origins of the biceps muscle in the shoulder:
The long head takes origin from the bicipital tubercle at the superior rim of the glenoid.
The short head takes origin from the coracoid tip.
Has two distal tendinous insertions
Lateral insertion is to the posterior part of the tuberosity of the radius.
Medial insertion is aponeurotic (lacertus fibrosus), passing medially across and into the deep fascia of the muscles of the volar forearm.
Loss of the long head attachment expresses itself mainly as loss of supination strength (20%), with a smaller loss (8%) of elbow flexion strength.
Actions of the biceps are flexion and supination at the elbow. Main action is at the elbow rather than the shoulder.
Innervation is supplied by branches of the musculocutaneous nerve (C5 and C6).
Blood supply derives from a single large bicipital artery from the brachial artery (35%), multiple very small arteries
(40%), or combination of two types.
Triceps Brachii
Long head takes origin from the infraglenoid tubercle. Major action of the muscle is extension at the elbow.
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FIG 8 • The brachial plexus.
Innervation is supplied by the radial nerve with root innervation C6-C8.
Arterial supply is derived mainly from the profunda brachial artery and the superior ulnar collateral artery.
BRACHIAL PLEXUS
The brachial plexus is generally made up of distal distribution of the anterior rami of spinal nerve roots C5-C8 and T1. The plexus has contributions from C4 and T1 (FIG 8).
Trunks, Divisions, and Cords
The roots combine to form trunks: C5 and C6 form the superior trunk; C7 forms the middle trunk; and C8 and T1 form the inferior trunk.
The trunks then separate into anterior and posterior divisions.
The posterior divisions combine to form the posterior cord, the anterior division of the inferior trunk forms the medial cord, and the anterior division of the superior and middle trunks forms the lateral cord.
These cords give off the remaining largest number of the terminal nerves of the brachial plexus, and roots from the lateral and medial cords come together to form the median nerve.
The brachial plexus leaves the cervical spine and progresses into the arm through the interval between the anterior and middle scalene muscles.
The subclavian artery follows the same course. The plexus splits into cords at or before it passes below the clavicle.
As the cords enter the axilla, they become closely related to the axillary artery, attaining positions relative to the artery indicated by their names: lateral, posterior, and medial.
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Terminal Branches
Plexus gives off some terminal branches above the clavicle.
The dorsal scapular nerve comes off C5 with some C4 fibers and penetrates the scalenus medius and the levator scapulae, sometimes contributing with C4 fibers to the latter.
The dorsal scapular nerve accompanies the deep branch of the transverse cervical artery or the dorsal scapular artery on the undersurface of the rhomboids and innervates them.
Rootlets of the nerves C5-C7 immediately adjacent to the intravertebral foramina contribute to the formation of the long thoracic nerve, which immediately passes between the middle and posterior scalene muscles or penetrates the middle scalene.
Next most proximal nerve is the suprascapular nerve.
It arises from the superolateral aspect of the upper trunk shortly after its formation at Erb point.
The lateral cord generally contains fibers of C5-C7 and gives off three terminal branches:
Musculocutaneous
Lateral pectoral
Lateral root of the median nerve
Posterior cord supplies most of the innervations of the muscles of the shoulder, in this order:
Upper subscapularis, thoracodorsal, lower subscapular, axillary, and radial
Medial cord has five branches, in the following order:
Medial pectoral nerve, medial brachial cutaneous, medial antebrachial cutaneous, medial root of the median nerve, and ulnar nerve
ARTERIES
Subclavian Artery
Blood supply to limb begins with the subclavian artery, which ends at the lateral border of the first rib. Divided into three portions in relation to the insertion of the scalenus anterior muscle
Vertebral artery takes origin in the first portion, and the costocervical trunk and thyrocervical trunk take origin in the second portion.
There are usually no branches in the third portion of the artery.
Two vessels encountered more frequently by the shoulder surgeon are the transverse cervical artery and the suprascapular artery.
Come off the thyrocervical trunk in 70% of dissections
In the remaining cases, they come off directly or in common from the subclavian artery.
Axillary
Is the continuation of the subclavian artery
It begins at the lateral border of the first rib and continues along the inferior border of the latissimus dorsi, at which point it becomes the brachial artery.
This artery is traditionally divided into three portions:
First portion is above the superior border of the pectoralis minor.
Second portion is deep to the pectoralis minor.
Third portion is distal to lateral border of the pectoralis minor.
Usual number of branches for each of the three sections corresponds to the name of the section: one branch in the first portion, two in the second, and three in the third.
First section gives off the superior thoracic artery.
Second portion gives off the thoracoacromial artery and the lateral thoracic artery. Third portion gives off the following:
Largest branch is the subscapular artery, and this is the largest branch of the axillary artery.
Next branch is the posterior humeral circumflex artery, and the third branch is the anterior humeral circumflex artery.
Anterior humeral circumflex artery is an important surgical landmark because it travels laterally at the inferior border of the subscapularis tendon, marking the border between the upper tendinous insertion of the subscapularis and the lower muscular insertion.
VEINS
Axillary Vein
Begins at the inferior border of the latissimus dorsi as the continuation of the basilic vein, continues along the lateral border of the first rib, and becomes the subclavian vein
Cephalic
Cephalic vein is the superficial vein in the arm that lies deep to the deep fascia after reaching the deltopectoral groove and finally pierces the clavipectoral fascia, emptying into the axillary vein.
ANATOMY OF THE ELBOW
OSTEOLOGY
Distal Humerus
The distal humerus consists of two condyles, which form the articular surfaces of the trochlea and capitellum (FIG 9A).
Trochlea
Hyperbolic, pulley-like surface that articulates with the semilunar notch of the ulna, covered by articular cartilage over an arc of 300 degrees
Medial margin is large and projects more distally than does the lateral margin.
The prominent medial and lateral margins are separated by a groove that courses in a helical manner from an anterolateral to the posteromedial direction.
Capitellum
Capitellum is almost spheroidal in shape and is covered with hyaline cartilage, which is about 2-mm thick anteriorly.
Posteromedial limit of the capitellum is marked by a prominent tubercle.
A groove separates the capitellum from the trochlea, and the rim of the radial head articulates with this groove throughout the arc of flexion and during pronation and supination.
Joint Surface Orientation
In the sagittal plane, the orientation of the articular surface of the distal humerus is located anteriorly about 30 degrees with respect to the long axis of the humerus (FIG 9B).
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The center of the concentric arc formed by the trochlea and capitellum is on a line that is coplanar with the anterior and distal cortex of the humerus.
In the transverse plane, the articular surface is rotated inwardly about 5 degrees, and in the frontal plane, it is tilted about 6 degrees in valgus (FIG 9C).
Epicondyles of Humerus
Medial epicondyle serves as the source of attachment of the ulnar collateral ligament and the flexor-pronator group of muscles.
Lateral epicondyle is located just above the capitellum and is much less prominent than the medial epicondyle. The lateral collateral ligament and the supinator extensor muscle group originate from the flat, irregular
surfaces of the lateral epicondyle.
Anterior Surface of Humerus
Anteriorly, the radial and coronoid fossae accommodate the radial head and coronoid, respectively, during flexion.
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FIG 9 • The distal humerus. A. Bony landmarks of the anterior aspect. B. Anterior rotation of the articular condyles respective to the long axis. C. Valgus tilt of the articulations relative to the long axis. D. Bony landmarks of the posterior aspect.
Posterior Surface of Humerus
Posteriorly, the olecranon fossa receives the tip of the olecranon in extension (FIG 9D).
Radius
The proximal radius includes the radial head, which articulates with the capitellum and exhibits a cylindrical depression in the midportion to accommodate the capitellum.
Hyaline cartilage covers the depression of the radial head. The outside circumference of the radial head articulates with the ulna at the lesser sigmoid notch.
About 240 degrees of the circumference of the radial head is covered with cartilage. With the arm in neutral rotation, the anterolateral third of the circumference of the radial head is void of cartilage.
This part of the radial head lacks subchondral bone and thus is not as strong as the part that supports the articular cartilage.
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FIG 10 • The proximal radius. A. Bony landmarks. B. Angle of the radial neck relative to long axis.
This part has been demonstrated to be the portion most often fractured.
The disc-shaped head is held against the ulna by the annular ligament distal to the radial head.
The head and neck of the radius are not colinear with the rest of the bone. The head and neck are offset by an angle of about 15 degrees with respect to the shaft of the radius opposite to the radial tuberosity (FIG 10).
The neck of the radius is tapered, and the angular relationship between the head and neck has been implicated in the etiology of radial neck fractures.
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FIG 11 • The ulna. A. Anterior aspect. B. Lateral view. C. Radial collateral ligament complex.
Ulna
The proximal ulna provides the major articulation of the elbow that is responsible for its inherent stability (FIG 11A,B).
The broad, thick, proximal aspect of the ulna consists of the greater sigmoid notch (incisura semilunaris), which articulates with the trochlea of the humerus.
The sloped cortical surface of the coronoid process serves as the site of insertion of the brachialis muscle.
The olecranon comprises the posterior portion of the articulation of the ulnohumeral joint and is the site of attachment for the triceps tendon.
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On the lateral aspect of the coronoid process, the lesser sigmoid or radial notch articulates with the radial head and is oriented roughly perpendicular to the long axis of the bone.
On the lateral aspect of the proximal ulna, a tuberosity, the crista supinatoris, is the site of the insertion of the lateral ulnar collateral ligament (FIG 11C).
This stabilizes the humeroulnar joint to resist varus and rotational stresses.
The medial aspect of the coronoid process (sublime tubercle) serves as the site of attachment of the anterior bundle of the medial collateral ligament.
SURVEY OF TOPICAL ANATOMY
Landmarks
Lateral Landmark
The tip of the olecranon, the lateral epicondyle, and the radial head form an equilateral triangle, providing an important landmark for entry into the elbow for such things as joint aspiration.
Flexion Crease
The flexion crease of the elbow is in line with the medial and lateral epicondyles. It is actually 1 to 2 cm proximal to the joint line when the elbow is extended.
Antecubital Fossa
Inverted triangular depression on the anterior aspect of the elbow that is just distal to the epicondyles
Topographical Regions of the Elbow and Corresponding Musculature
Lateral Margin of Antecubital Fossa
Extensor forearm musculature originates from the lateral epicondyle and has been termed the mobile wad.
This forms the lateral margin of the antecubital fossa and the lateral contour of the forearm and comprises the brachioradialis and the extensor carpi radialis longus and brevis muscles.
Medial Margin of the Antecubital Fossa
Muscles making up the contour of the medial anterior forearm include the pronator teres, flexor carpi radialis, palmaris longus, and flexor carpi ulnaris.
Dorsum
The dorsum of the forearm is contoured by the extensor musculature, consisting of the anconeus, extensor carpi ulnaris, extensor digitorum quinti, and extensor digitorum communis.
Cutaneous Innervation
Proximal Elbow
Skin about the proximal elbow is innervated by the lower lateral cutaneous (C5, C6) and the medial cutaneous (radial nerve, C8, T1, and T2) nerves of the arm.
Forearm
Forearm skin is innervated by the medial (C8, T1), lateral (musculocutaneous, C5, C6), and posterior (radial nerve, C6-C8) cutaneous nerves of the forearm.
Elbow Joint Structure
Joint Articulation
The elbow joint consists of two types of articulations:
The ulnohumeral joint resembles a hinge (ginglymus), allowing flexion and extension.
The radiohumeral and the proximal radioulnar joint allow actual rotation or pivoting type of motion.
Because of this joint articulation, the elbow is classified as a trochoginglymoid joint and is one of the most congruent joints of the body.
Carrying Angle
Angle formed by the long axis of the humerus and the ulna with the elbow fully extended
In males, mean carrying angle is 11 to 14 degrees.
In females, mean carrying angle is 13 to 16 degrees.
Joint Capsule
The anterior capsule inserts proximally above the coronoid and radial fossae.
Distally, the capsule attaches to the anterior margin of the coronoid medially and to the annular ligament laterally.
Posteriorly, the capsule attaches just above the olecranon fossa, distally along the supracondylar bony columns, and then down along the medial and lateral margins of the trochlea.
Distally, the attachment is along the medial and lateral articular margin of the sigmoid notch; laterally, it occurs along the lateral aspect of the sigmoid notch and blends with the annular ligament.
Normal capacity of the fully extended joint capsule is 25 to 30 mL.
The joint capsule is innervated by branches from all major nerves crossing the joint, including contributions from the musculocutaneous nerve.
LIGAMENTS OF THE ELBOW
Ligaments of the elbow consist of specialized thickening of the medial and lateral capsule that forms medial and lateral collateral ligament complexes.
Medial Collateral Ligament Complex
The medial collateral ligament consists of three parts: anterior, posterior, and transverse segments. Anterior bundle is the most discrete component.
The posterior portion, being a thickening of the posterior capsule, is well defined only in about 90 degrees of flexion.
The transverse component appears to contribute a little or nothing to elbow stability.
Clinically and experimentally, the anterior bundle is clearly the major portion of the medial ligament complex.
Lateral Collateral Ligament Complex
Unlike the medial collateral ligament complex, with a rather consistent pattern, the lateral ligaments of the elbow joint are less discrete and some individual variation is common.
Several components make up the lateral ligament complex: radial collateral ligament, the annular ligament, a variably present accessory lateral collateral ligament, and the lateral ulnar collateral ligament.
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Lateral Ulnar Collateral Ligament
This structure originates from the lateral epicondyle and blends with the fibers of the annular ligament but arching superficial and distal to it.
Insertion is through the tubercle of the crest of the supinator on the ulna.
The function of this ligament is to provide stability to the ulnohumeral joint; it has been shown to be deficient in posterolateral rotary instability of the joint.
This ligament represents the primary lateral stabilizer of the elbow and is taut on flexion and extension.
Accessory Lateral Collateral Ligament
Its function is to further stabilize the annular ligament during varus stress.
VESSELS
Brachial Artery and Its Branches
The brachial artery descends in the arm, crossing in front of the intramuscular septum to lie anterior to the medial aspect of the brachialis muscle.
The median nerve crosses in front of and medial to the artery at this point, near the middle of the arm. The artery continues distally at the medial margin of the biceps muscle and enters the antecubital space medial to the biceps tendon and lateral to the nerve.
At the level of the radial head, it gives off its terminal branches, the ulnar and radial arteries, which continue into the forearm.
Radial Artery
Usually, the radial artery originates at the level of the radial head, emerges from the antecubital fossa between the brachioradialis and the pronator teres muscle, and continues down the forearm under the brachioradialis muscle.
Ulnar Artery
The ulnar artery is the larger of the two terminal branches of the brachial artery.
The artery traverses the pronator teres between its two heads and continues distally and medially behind the flexor digitorum superficialis muscle.
It emerges medially to continue down the medial aspect of the forearm under the cover of the flexor carpi ulnaris.
NERVES
Musculocutaneous Nerve
Originates from C5 through C8 nerve roots and is a continuation of the lateral cord
Innervates the major elbow flexors and the biceps and brachialis and continues through the brachial fascia lateral to the biceps tendon, terminating as the lateral antebrachial cutaneous nerve
Motor branch enters the biceps about 15 cm distal to the acromion; it enters the brachialis about 20 cm below the tip of the acromion.
Median Nerve
Median nerve arises from C5 through C8 and T1 nerve roots.
The nerve enters the anterior aspect of the brachium, crossing in front of the brachial artery as it passes across the intramuscular septum.
It follows a straight course into the medial aspect of the antecubital fossa, medial to the biceps tendon and the brachial artery.
It then passes under the bicipital aponeurosis.
There are no branches of the median nerve in the arm.
The first motor branch is given to the pronator teres, through which it passes.
In the antecubital fossa, a few small articular branches are given off before the motor branches to the pronator teres, the flexor carpi radialis, the palmaris longus, and the flexor digitorum superficialis.
Anterior Interosseous Nerve
Arises from the median nerve near the inferior border of the pronator teres and travels along the anterior aspect of the interosseous membrane in the company of the anterior interosseous artery
Innervates the flexor pollicis longus and the lateral portion of the flexor digitorum profundus
Radial Nerve
Is a continuation of the posterior cord and originates from the C6 to C8 nerve roots, with variable contributions of the C5 and T1 roots
In the midportion of the arm, the nerve courses laterally just distal to the deltoid insertion to occupy the groove in the humerus that bears its name.
It then emerges in a spiral path inferiorly and laterally to penetrate the lateral intramuscular septum.
Before entering the anterior aspect of the arm, it gives off the motor branches to the medial and lateral heads of the triceps, accompanied by the deep branch of the brachial artery.
After penetrating the lateral intramuscular septum in the distal third of the arm, it descends anterior to the lateral epicondyle behind the brachioradialis.
It innervates the brachioradialis with a single branch to this muscle.
In the antecubital space, the nerve divides into the superficial and deep branches. The superficial branch is the continuation of the radial nerve and extends into the forearm to innervate the mid-dorsal cutaneous aspect of the forearm.
Motor branches of the radial nerve are given off to the triceps above the spiral groove, except for the branch to the medial head of the triceps, which originates at the entry to the spiral groove.
This branch continues distally through the medial head to terminate as a muscular branch to the anconeus.
In the antecubital space, the recurrent radial nerve curves around the posterolateral aspect of the radius, passing deep through supinator muscle, which it innervates. During its course through the supinator muscle, the nerve lies over the bare area, which is distal to and opposite to the radial tuberosity. The nerve is believed to be at risk at this site with fractures of the proximal radius. It emerges from the muscle
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as the posterior interosseous nerve, and the recurrent branch innervates the extensor digitorum minimi, the extensor carpi ulnaris, and occasionally the anconeus.
The posterior interosseous nerve is accompanied by the posterior interosseous artery and sends further muscle branches distally to supply the abductor pollicis longus, the extensor pollicis longus, the extensor pollicis brevis, and the extensor indicis on the dorsum of the forearm.
Ulnar Nerve
The ulnar nerve is derived from the medial cord of the brachial plexus from roots C8 and T1. In the mid-arm, it passes posteriorly through the medial intramuscular septum and continues distally along the medial margin of the triceps in the company of the superior ulnar collateral branch of the brachial artery and the ulnar collateral branch of the radial artery.
There are no branches of this nerve in the brachium.
The ulnar nerve may undergo compression as it passes behind the medial epicondyle, emerging into the forearm through the cubital tunnel.
The roof of the cubital tunnel has been defined by a structure termed the cubital tunnel retinaculum.
The first motor branch is the single nerve to the ulnar origin of the pronator and another one to the epicondylar head of the flexor carpi ulnaris. Distally, the nerve sends a motor branch to the ulnar half of the flexor digitorum profundus.
Two cutaneous nerves arise from the ulnar nerve in the distal half of the forearm to innervate the skin of the wrist and the hand.
MUSCLES
Elbow Flexors
Biceps
Covers the brachialis muscle in the distal arm and passes into the cubital fossa as the biceps tendon, which attaches to the posterior aspect of the radial tuberosity
Bicipital aponeurosis or lacertus fibrosus is a broad, thin band of tissue that is a continuation of the anterior, medial, and distal muscle fascia. It runs obliquely to cover the median nerve and the brachial artery and inserts into the deep fascia of the forearm and possibly into the ulna as well.
The biceps is a flexor of the elbow that has a large crosssectional area but an intermediate mechanical advantage because it passes relatively close to the axis of rotation.
In the pronated position, the biceps is a strong supinator of the forearm.
Brachialis
Largest cross-sectional area of any of the elbow flexors but suffers from a poor mechanical advantage because it crosses so close to the axis of rotation
Origin consists of the entire anterior distal half of the humerus, and it extends medially and laterally to the respective intermuscular septa.
Crosses the anterior capsule, with some fibers inserting into the capsule that are said to help retract the capsule during elbow flexion
Insertion of the brachialis is along the base of the coronoid and into the tuberosity of the ulna.
More than 95% of the cross-sectional area is muscle tissue at the elbow joint, a relationship that may account for high incidence of trauma to this muscle with elbow dislocation.
Brachioradialis
Has a lengthy origin along the lateral supracondylar column that extends proximally to the level of the junction
of the middle and distal humerus
Origin separates the lateral head of the triceps and the brachialis muscle.
Lateral border of the cubital fossa is formed by this muscle, which crosses the elbow joint with the greatest mechanical advantage of any elbow flexor. It progresses distally to insert into the base of the radial styloid.
Protects and is innervated by radial nerve (C5 and C6) as it emerges from the spiral groove Major function is elbow flexion.
Extensor Carpi Radialis Longus
Originates from the supracondylar bony column joint just below the origin of the brachioradialis
As it continues into the midportion of the dorsum of the forearm, it becomes largely tendinous and inserts to the dorsal base of the second metacarpal.
Innervated by the radial nerve
Functions as wrist extensor and possibly an elbow flexor
Extensor Carpi Radialis Brevis
Originates from the lateral superior aspect of the lateral epicondyle
Its origin is the most lateral of the extensor group and is covered by the extensor carpi radialis longus. This relationship is important as the most commonly implicated site of lateral epicondylitis.
Extensor carpi radialis brevis shares the same extensor compartment as the longus as it crosses the wrist under the extensor retinaculum and inserts into the dorsal base of the third metacarpal.
Function of the extensor carpi radialis brevis is pure wrist extension, with little or no radial or ulnar deviation.
Extensor Digitorum Communis
Originating from the anterior distal aspect of the lateral epicondyle, the extensor digitorum communis accounts for most of the contour of the extensor surface of the forearm.
Extends and abducts fingers
Innervation is from the deep branch of the radial nerve, with contributions from the sixth through eighth cervical nerves.
Supinator
This flat muscle is characterized by the virtual absence of tendinous tissue and has a complex origin and insertion.
It originates from three sites above and below the elbow joint: the lateral anterior aspect of the lateral epicondyle; the lateral collateral ligament; and the proximal anterior crest of the ulna along the crista supinatoris, which is just anterior to the depression for the insertion of the anconeus.
Form of the muscle is roughly that of a rhomboid as it runs obliquely, distally, and radially to wrap around and insert diffusely on the proximal radius, beginning lateral and proximal to the radial tuberosity and continuing distal to the
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insertion of the pronator teres at the junction of the proximal middle third of the radius.
The radial nerve passes through the supinator to gain access to the extensor surface of the forearm.
This anatomic feature is clinically significant with regard to exposure of the lateral aspect of the elbow joint and the proximal radius and in certain entrapment syndromes.
Functions as a supinator of the forearm, but it is a weaker supinator than the biceps
Unlike the biceps, however, the effectiveness of the supinator is not altered by the position of the elbow flexion.
Innervation is derived from the muscular branch given off by the radial nerve just before and during its course through the muscle.
Elbow Extensors
Triceps Brachii
Comprises the entire musculature of the arm posteriorly
Two of its three heads originate from the posterior aspect of the humerus.
The long head has a discrete origin from the infraglenoid tuberosity of the scapula.
The lateral head originates in a linear fashion from the proximal lateral intramuscular septum on the posterior surface of the humerus.
The medial head originates from the entire distal half of the posteromedial surface of the humerus, bounded laterally by the radial groove and medially by the intramuscular septum.
Each head originates distal to the other with progressively larger areas of origin.
The long and lateral heads are superficial to the deep medial head, blending in the midline of the humerus to form a common muscle that then tapers into the triceps tendon and attaches to the tip of the olecranon with Sharpey fibers.
The tendon is usually separated from the olecranon by the subtendinous olecranon bursa.
Innervated by the radial nerve, the long and lateral heads are supplied by branches that arise proximal to the entrance of the radial nerve into the groove.
The medial head is innervated distal to the groove with a branch that enters proximally and passes through the entire medial head to terminate by innervating the anconeus.
Anconeus
This muscle has little tendinous tissue because it originates from a rather broad site on the posterior aspect of the lateral epicondyle and from the lateral triceps fascia and inserts into the lateral dorsal surface of the proximal ulna.
Innervated by the terminal branch of the nerve to the medial head of the triceps Function of this muscle has been the subject of considerable speculation.
Some suggest that the primary role is that of a joint stabilizer.
Covers the lateral portion of the annular ligament and the radial head
For the surgeon, the major significance of this muscle is its position as a key landmark in various lateral and posterolateral exposures, and it is used for some reconstructive procedures.
Flexor-Pronator Muscle Group
Pronator Teres
This is the most proximal of the flexor-pronator group.
There are usually two heads of origin; the larger arises from the anterosuperior aspect of the medial epicondyle and the second from the coronoid process of the ulna, which is absent in about 10% of individuals.
Two origins of the pronator muscle provide an arch through which the median nerve typically passes to gain access to the forearm.
This anatomic characteristic is a significant feature in the etiology of median nerve entrapment syndrome.
The common muscle belly proceeds radially and distally under the brachioradialis, inserting at the junction of the proximal middle portion of the radius by a discrete broad tendinous insertion into a tuberosity on the lateral aspect of the bone.
A strong pronator of the forearm, it also is considered a weak flexor of the elbow. Innervated by two motor branches from the median nerve
Flexor Carpi Radialis
The flexor carpi radialis originates inferior to the origin of the pronator teres and the common flexor tendon at the anteroinferior aspect of the medial epicondyle.
It continues distally and radially to the wrist, where it can be easily palpated before it inserts into the base of the second and sometimes third metacarpal.
Chief function is as a wrist flexor.
Innervation is from one or two branches of the median nerve.
Palmaris Longus
When present, it arises from the medial epicondyle and from the septa it shares with the flexor carpi radialis and flexor carpi ulnaris.
It becomes tendinous in the proximal portion of the forearm and inserts into and becomes continuous with the palmar aponeurosis.
Absent in about 10% of the extremities Innervated by a branch of the median nerve
Flexor Carpi Ulnaris
Most posterior of the common flexor tendons originating from the medial epicondyle
Second and largest source of origin is from the medial border of the coronoid and the proximal aspect of the ulna.
Ulnar nerve enters and innervates the muscle between these two sites of origin with two or three motor branches given off just after the nerve has entered the muscle. The muscle continues distally to insert into the pisiform, where the tendon is easily palpable, because it serves as a wrist flexor and ulnar deviator.
With an origin posterior to the axis of rotation, weak elbow extension may also be provided by the flexor carpi ulnaris.
Flexor Digitorum Superficialis
The flexor digitorum superficialis muscle is deep to those originating from the common flexor tendon but superficial to the flexor digitorum profundus; thus, it is considered the intermediate muscle layer.
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This broad muscle has a complex origin.
Medially, it arises from the medial epicondyle by way of the common flexor tendon and possibly from the ulnar collateral ligament and medial aspect of the coronoid.
The lateral head is smaller and thinner and arises from the proximal two-thirds of the radius.
The unique origin of the muscle forms a fibrous margin under which the median nerve and ulnar artery emerge as they exit from the cubital fossa.
The muscle is innervated by the median nerve with branches that originate before the median nerve enters the pronator teres.
Action of the flexor digitorum superficialis is flexion of the proximal interphalangeal joints.
Flexor Digitorum Profundus
Originates from the proximal ulna distal to the elbow joint and is involved in flexion of the distal interphalangeal joints
REFERENCES
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Bigliani LU, Morrison DS, April EW. The morphology of the acromion and its relationship to rotator cuff tears. Orthop Trans 1986; 10:228.
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Howell SM, Galinat BJ. The glenoid-labral socket. A constrained articular surface. Clin Orthop Relat Res 1989;(243):122-125.
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Lippitt SB, Vanderhooft JE, Harris SL, et al. Glenohumeral stability from concavity-compression: a quantitative analysis. J Shoulder Elbow Surg 1993;2(1):27-35. doi:10.1016/S1058-2746(09)80134-1.