Clinical Anatomy

A thorough understanding of the anatomy and biome-chanics of the elbow is essential to diagnosing and treating injuries of the UCL. The anterior bundle of the UCL is the most discrete of the three portions of the ligament complex (i.e., anterior, posterior, and transverse bundles) (Fig. 7.1). Its margins are readily distinguishable from the surrounding joint capsule, and its fibers often are associated intimately with the deep surface of the flexor mass.16 The posterior bundle consists of a less distinct fan-shaped thickening of the posterior capsule.4 The transverse fibers originate and insert on the ulna, covering a bony depression on the medial portion of the trochlear notch, and they contribute little or nothing to the stability of the elbow.4,16

The anterior bundle is the most important portion of the complex when treating valgus instability of the el bow. The ligament originates from the anteroinferior surface of the medial epicondyle. The width of the origin varies but, in most cases, occupies the middle two-thirds to three-quarters of the epicondyle in the coronal plane (Fig. 7.2).17 A small space remains between the lateral edge of the ligament and the medial crista of the trochlea. This space allows for a synovial reflection in the joint, which the surgeon readily can visualize with magnetic resonance imaging (MRI). In their study, Morrey and An found that the mean length of the anterior bundle is 27.1 ± 4.3 mm and the mean width is 4.7 ± 1.2 mm.4 The anterior bundle inserts on the medial border of the coronoid at the sublime tubercle.4,16

Timmerman and Andrews defined the histology and arthroscopic anatomy of the anterior bundle.16 The medial capsule consists of a synovial lining with two distinct capsular layers between which the anterior and posterior bundles pass (Fig. 7.3).16 The anterior bundle consists of well-defined collagen bundles in parallel arrangement, which is typical of ligaments. In cross section, the bundle consists of two portions: one layer within the two synovial layers of the joint capsule and one layer that is superficial to the capsule and that blends with the deep surface of the flexor muscle mass. The posterior bundle consists of a smaller area of collagen within the capsular layers.

Understanding the functional anatomy of the UCL requires a synthesis of the kinematics of elbow motion with the biomechanics of the throwing mechanism. The ulno-humeral joint is a hinge, or ginglymus, joint that permits flexion and extension. The articulation between the greater sigmoid notch of the olecranon and the trochlea of the humerus is one of the most congruous and constrained joints in the body. With loading, the elbow flexors and extensors tend to seat the olecranon in the trochlea of the humerus, contributing valgus stability under dynamic conditions. Biomechanical studies of the loaded

FIGURE 7.1. The anterior, posterior, and transverse bundles compose the ulnar collateral ligament. The anterior bundle is the primary stabilizer of the elbow when it resists valgus stress.

and unloaded cadaveric elbow by Morrey et al. demonstrated decreased valgus laxity against a gravity valgus stress in the loaded specimens compared with the unloaded specimens both before and after sectioning the anterior bundle of the UCL.8

Researchers have shown that the anterior bundle of the UCL is the primary restraint to valgus stress and that the radial head is a secondary restraint.1'6,8 With anterior bundle sectioning, the resultant instability is greatest between 60° and 70° and is least at full extension and full flexion.6 True lateral radiographs show that the flexion-extension axis, or center of rotation, of the elbow lies in the center of the trochlea and capitellum.1819 The origin of the anterior bundle of the UCL lies slightly posterior

FIGURE 7.2. The anterior part of the medial epicondyle removed by orthogonal osteotomies. On the right, a 2-mm-thick slice through the widest portion of the origin of the anterior bundle of the ulnar collateral ligament. (Mean values are shown.) W, width of medial epicondyle; C, distance from lateral edge of anterior medial collateral ligament origin to medial side of condyle (trochlea); L, width of origin of anterior medial collateral ligament; E, distance from tip of epicondyle to medial edge of anterior band of the medial collateral ligament origin. (From O'Driscoll SW, et al.17)

FIGURE 7.2. The anterior part of the medial epicondyle removed by orthogonal osteotomies. On the right, a 2-mm-thick slice through the widest portion of the origin of the anterior bundle of the ulnar collateral ligament. (Mean values are shown.) W, width of medial epicondyle; C, distance from lateral edge of anterior medial collateral ligament origin to medial side of condyle (trochlea); L, width of origin of anterior medial collateral ligament; E, distance from tip of epicondyle to medial edge of anterior band of the medial collateral ligament origin. (From O'Driscoll SW, et al.17)

FIGURE 7.3. Cross-sectional anatomy of the medial capsule of the elbow at the level of the joint line. A, anterior bundle; M, muscle; P, posterior bundle; S, synovium. (From Tim-merman LA, Andrews JR16)

to the rotational center of the elbow (Fig. 7.4). The anterior bundle is further divided into an anterior band and a posterior band.20 The eccentric origin of these anterior bundle components in relation to the rotational center through the trochlea creates a cam effect during flexion and extension. The anterior band tightens during extension, and the posterior band tightens during flexion. This reciprocal tightening of the two functional components of the anterior bundle allows the ligament to remain taut throughout the full range of flexion (Fig. 7.5).20

Researchers have documented the rupture of the UCL in athletes in many sports; however, most ruptures occur in athletes participating in throwing sports.12,21-23 An understanding of the throwing mechanism and its relationship to injury is essential when treating UCL tears.

The throwing motion is one of the most violent athletic activities. The transition from the late cocking phase to early acceleration places extreme valgus stress on the medial structures of the elbow. Researchers have estimated that between 100 and 120 N • m of varus torque are required to resist the valgus stress that the throwing motion produces in elite-level pitchers.24,25 After comparing the electromyographic data in throwing athletes who had healthy elbows with the data in throwing athletes who had UCL instability, researchers found that the muscles (specifically, the flexor carpi radialis, pronator teres, and flexor carpi ulnaris muscles) that were positioned to function as dynamic stabilizers of the medial elbow did not appear to compensate for UCL laxity. In

FIGURE 7.4. Lateral projection of the distal humerus showing the axis of rotation of the elbow through the center of the humeral trochlea (A) and the origin of the ulnar collateral ligament (B).

FIGURE 7.5. Lateral projections of the elbow demonstrating the reciprocal tightening of the anterior and posterior bands of the anterior bundle of the ulnar collateral ligament. (A) The posterior band tightens during flexion. (B) The anterior band tightens during extension.

FIGURE 7.5. Lateral projections of the elbow demonstrating the reciprocal tightening of the anterior and posterior bands of the anterior bundle of the ulnar collateral ligament. (A) The posterior band tightens during flexion. (B) The anterior band tightens during extension.

fact, they found slightly decreased activity in these muscles in the UCL-insufficient pitchers during throwing.26,27 This finding suggests that the flexor-pronator muscles have limited ability for dynamic stabilization of the elbow in high-demand throwers who have valgus instability.

Cure Tennis Elbow Without Surgery

Cure Tennis Elbow Without Surgery

Everything you wanted to know about. How To Cure Tennis Elbow. Are you an athlete who suffers from tennis elbow? Contrary to popular opinion, most people who suffer from tennis elbow do not even play tennis. They get this condition, which is a torn tendon in the elbow, from the strain of using the same motions with the arm, repeatedly. If you have tennis elbow, you understand how the pain can disrupt your day.

Get My Free Ebook


Post a comment