Injuries and Conditions Affecting the Elbow Flexor/Pronator Tendons

Key points

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Most patients with medial epicondylitis or flexor-pronator tendon injuries can successfully be treated nonoperatively.
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Operative treatment is reserved for patients with continued symptoms despite adequate nonoperative treatment or in high-level athletes with complete rupture of the common flexor-pronator tendon.
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The physical examination and workup of patients with flexor-pronator tendon injuries should focus on related or concomitant pathologies of the medial elbow, including ulnar collateral ligament injuries, ulnar nerve compression, and the spectrum of injuries associated with valgus extension overload in overhead throwing athletes.
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Surgical treatment of flexor-pronator tendon ruptures or medial epicondylitis includes tendon debridement and reattachment, although alternate techniques have been described in the literature and report favorable functional outcomes.

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Introduction

Relevant Anatomy

A thorough understanding of elbow anatomy is critical to an accurate diagnosis in patients presenting with medial elbow pain. The bony, ligamentous, muscular, and nervous structures of the elbow are all potential sources of elbow pain, and concomitant injuries to these structures are common. The bony articulations of the elbow joint include the proximal radioulnar, radiocapitellar, and ulnohumeral joints, which permit a constrained range of motion between −5° and 140° of flexion-extension and 180° of pronosupination. ^, The physeal anatomy of the elbow is an important consideration in the adolescent patient, as the medial epicondyle of the humerus does not fuse until late 16 to 18 years of age and is a common source of medial elbow pain in teenage overhead athletes. In the skeletally mature patient, pain over the medial epicondyle is typically indicative of soft tissue injury, as it serves as the proximal origin of the ulnar collateral ligament (UCL) and the common flexor-pronator mass. The ulnar nerve travels posterior to the medial epicondyle and can also be a source of medial elbow pain either in isolation or as a concomitant pathology. Most commonly, the ulnar nerve has no branches in the brachium, giving off its first motor branches the heads of flexor carpi ulnaris (FCU). Protection of the ulnar nerve is paramount during any surgical dissection around the medial elbow. The medial antebrachial cutaneous nerve (MACN), which is a direct branch off of the medial cord of the brachial plexus, is also at risk during the surgical exposure of the medial elbow and should be kept in mind as a potential etiology of medial elbow pain in the thrower. ^,

The muscular anatomy of the medial elbow consists of the common flexor-pronator mass, which originates from the medial epicondyle and is the confluence of 5 muscles ( Fig. 1 ): pronator teres (PT), flexor carpi radialis (FCR), palmaris longus (PL), flexor digitorum superficialis (FDS), and FCU. There is an additional origin of the FCU from the medial aspect of the coronoid and proximal medial ulna, giving rise to the 2 heads of the FCU. The ulnar nerve travels into the forearm between these 2 heads of the FCU, which is the most common site of ulnar nerve compression and must be addressed during ulnar nerve decompression or transposition. As the common flexor-pronator tendon crosses the ulnohumeral joint, it gives off attachments to the deeper structure of the UCL ( Fig. 2 ), which together become confluent with the anteromedial joint capsule. The common flexor tendons and the UCL both originate from the medial epicondyle and project distally, with the flexor tendons being oriented and traveling more anteriorly toward various insertions, while the UCL travels slightly more posteriorly to insert onto the sublime tubercle of the ulna ; anatomic distinctions between these 2 medial elbow structures is relevant when assessing for tenderness at specific sites to aid in diagnosis, which will be discussed in subsequent sections. In addition to its motor function in the hand and forearm, the common flexor-pronator mass functions as a dynamic stabilizer to valgus force at the elbow and is susceptible to injury from repetitive tensile stresses such as those seen in overhead throwing. ^, It has been suggested that the FDS and FCU are the predominant musculotendinous units responsible for this dynamic stabilization given their position directly over the UCL in elbow flexion, but biomechanical studies have published mixed results regarding this theory.

The primary mechanism of injury to the common flexor-pronator tendons results from eccentric loading of the musculotendinous units caused by forearm protonation and wrist flexion combined with a valgus force on the elbow. Pathology of the common flexor-pronator mass includes medial epicondylitis and less commonly flexor-pronator tendon avulsion or rupture. The pathology, epidemiology, clinical evaluation, and management of these tendinous pathologies will be discussed in the following sections.

Elbow Flexor-Pronator Mass Pathology

Medial epicondylitis, often referred to as golfer’s elbow, is a common source of elbow pain that typically affects patients in their fourth to sixth decade of life. Although this condition is classically associated with occupational settings that require repetitive upper extremity labor, recent studies have reported an increasing incidence of medial epicondylitis among the general population. Among athletes, medial epicondylitis is most common in overhead throwers and sports requiring repeated wrist flexion, such as baseball players, javelin throwers, weightlifters, golfers, or bowlers. ^, Medial epicondylitis has been reported to be 5 to 20 times less common than lateral epicondylitis. In the occupational setting, medial epicondylitis affects 4% to 5% of individuals, and most these patients (80%) report self-resolving symptoms by 3 years. The etiology of the condition is caused by repetitive stress and eccentric loading of the common flexor tendons, resulting in microtrauma and degeneration. Although most histologic studies focus on lateral epicondylitis, the repeated microtrauma is believed to create damage of the tendon followed by chronic ineffective healing that leads to degeneration and tendinosis. High-level and professional throwing athletes can present with acute strains or ruptures of the flexor pronator mass, and these injuries have been shown to keep athletes away from sport for significant periods of time and found to be a risk factor for subsequent upper extremity injuries including UCL tears. Although overhead throwing athletes may present with an acute injury resulting from avulsion or rupture of the common flexor tendon, most cases are degenerative and are characterized by gradual onset and tendinosis. The clinician should keep in mind that common flexor tendon pathology is rare in a skeletally immature patient; thus alternative etiologies involving the medial epicondylar apophysis should be considered. Evaluating the patient or athlete with medial elbow pain can be a diagnostic challenge, and the spectrum of potential etiologies beyond medial epicondylitis should be considered when making a diagnosis.

Clinical evaluation

History and Differential Diagnosis

When eliciting a patient history, it is important to establish the timing and acuity of symptom onset. The insidious, progressive-onset medial elbow pain without known antecedent trauma is indicative of medial epicondylitis and is typically seen in the general population, whereas the acute onset of pain following a single, distinct injury suggests a common flexor-pronator tendon rupture or avulsion and is more commonly associated with overhead athletes. Symptoms are exacerbated with activity, especially activities requiring wrist flexion and forearm protonation. The pain can radiate distally from the medial epicondyle, and patients may complain of pain with grasping or pulling heavy objects. Symptoms tend to improve with rest and the use of nonsteroidal antiinflammatory drugs (NSAIDs).

Medial elbow pain in the general population or in the athlete can have several different etiologies, and the clinician should be able to differentiate between pathologies based on history, physical examination, and diagnostic imaging. Other than flexor-pronator mass injuries, possible pathologies and associated conditions of medial elbow include ulnar collateral ligament injuries, valgus extension overload, ulnar neuritis or cubital tunnel syndrome, olecranon stress fractures, and medial epicondylar apophysitis or avulsion in skeletally immature throwers. Differentiating between flexor-pronator mass injuries and UCL injuries is critical in overhead athletes, as a UCL injury rarely improves with conservative management may have more serious implications to a player’s future. In contrast to patients with UCL injuries, who typically only experience symptoms during sporting activities that exert a valgus force on the elbow, patients with flexor-pronator mass injuries commonly experience symptoms even with low-demand activities and complain of pain with household activities and activities of daily life. The broad differential diagnosis for medial elbow symptoms can be narrowed down further with physical examination and diagnostic imaging.

Physical Examination

Physical examination begins with inspection and assessment of range of motion in flexion-extension and in pronosupination. Mild loss of terminal extension may be present in patients with valgus extension overload and/or in asymptomatic high level throwers. Landmarks about the elbow are palpated. Patients with medial epicondylitis or flexor-pronator mass avulsion injuries will be tender slightly distal (5–10 mm) to the medial epicondyle along a line orthogonal to the anterior aspect of the epicondyle. ^, Patients with UCL pathology will be more tender over the ligament itself, which is slightly more posterior along a line extending from the posterior aspect of the epicondyle ( Fig. 3 ). The moving valgus stress test should be performed when a UCL injury is suspected and has been reported to have 100% sensitivity with 75% specificity compared with the static valgus stress test. In the authors’ practice, the test is performed with the patient supine with the arm in 90° of abduction; a valgus force is applied to the elbow that maximally externally rotates the shoulder, and the examiner ranges the elbow in an arc of flexion-extension ( Fig. 4 ). Moreover, patients with flexor-pronator mass injuries or medial epicondylitis will have reproduction of symptoms with resisted forearm protonation and wrist flexion, whereas these maneuvers may only elicit mild symptoms in the athlete with UCL pathology. Patients with symptomatic olecranon osteophytes, valgus extension overload, or olecranon stress fractures will be tender to the posterior olecranon process. As mentioned previously, the throwing athlete may also have a mild flexion contracture associated with such pathology. The thrower may have a positive bounce test in which symptoms are reproduced when the elbow is rapidly brought from flexion to full extension. Patients with ulnar neuritis, cubital tunnel syndrome, or subluxation of the ulnar nerve will complain of paresthesias to the ulnar digits and possibly a snapping sensation over the elbow. The clinician should evaluate for a Tinel sign along the course of the ulnar nerve from midmedial arm to midmedial forearm and assess for a subluxing ulnar nerve or a snapping triceps. As the elbow is brought throughout a range of flexion and extension, a subluxing or dislocating ulnar nerve can be palpated and sometimes visualized as it dislocates anteriorly over the medial epicondyle with flexion and reduces with elbow extension. A provocative maneuver such as the elbow flexion test can be performed to assess for ulnar nerve compression at the cubital tunnel by fully flexing the elbow in combination with wrist extension, which may reproduce symptoms. In advanced cases of ulnar nerve pathology with intrinsic muscle weakness, the patient may demonstrate a positive Froment sign.

In summary, the physical examination for a patient with medial epicondylitis or flexor-pronator mass injury is important to rule out other concomitant pathology, more specifically any ulnar nerve pathology, and in the overhead athlete any UCL injury or pathology associated with valgus extension overload. Localizing precise areas of tenderness, whether over the common flexor-pronator tendons or over the UCL itself, is of great diagnostic value. In addition, examination maneuvers such as the moving valgus stress test and provocative maneuvers for ligament or nerve pathology can help in defining the diagnosis.

Imaging and Diagnostic Examinations

Plain radiographs are obtained for patients complaining of medial elbow pain mostly to rule out any bony pathology. For cases of medial epicondylitis or flexor-pronator mass injuries, standard radiographs are most often unremarkable. Calcification may be present along the medial epicondyle, common flexor tendon, or UCL. Posteromedial olecranon osteophytes or loose bodies can sometimes be identified, especially in high-level throwing athletes and should be further evaluated with computed tomography (CT) scan when present. Plain radiographs are also used to evaluate for olecranon stress fractures, but depending on the chronicity of the injury, the fracture may not be visualized acutely. Advanced imaging such as CT or MRI is obtained when suspecting a stress fracture. The most common olecranon stress fracture pattern observed in adult baseball players has been reported to be oblique fractures running from proximal-medial to distal-lateral.

Ultrasound is a cost-effective imaging modality, but requires experienced ultrasound radiologists and technicians. A dynamic or stress ultrasound is useful to evaluate the soft tissue structures about the elbow, namely the common flexor-pronator tendon and the UCL. A few clinical series have evaluated the use of sonography for the diagnosis of epicondylitis in adults, with sensitivity and specificity values ranging from 75% to over 90%. ^,

MRI remains the gold standard for evaluating soft tissues around the elbow and can identify pathology such as medial epicondylitis, common flexor-pronator tendon inflammation or rupture, intra-articular loose bodies, olecranon osteophytes, olecranon stress fractures, and other traumatic causes of elbow pain. An MRI is obtained for overhead throwing athletes with medial elbow pain to differentiate between a flexor-pronator mass and UCL injury ( Fig. 5 ). In suspected cases of ulnar nerve pathology, electromyography (EMG) and nerve conduction studies (NCS) are obtained.