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Thrower’s elbow
Definition
The term thrower’s elbow covers a spectrum of throwing-related overuse injuries of the elbow. This article focuses on injury to the ulnar (medial) collateral ligament with possible valgus instability. It develops particularly through repeated intensive throwing loads. This is a typical sports injury, affecting especially baseball pitchers, although it also occurs in American football, volleyball, tennis and javelin throwing. In simplified terms, throwing can be divided into wind-up, acceleration and deceleration. High valgus loads at the elbow occur particularly during the late cocking phase and early acceleration phase. These produce tensile loads on the medial structures, compressive loads on the lateral structures and shear loads on the posterior joint structures, with considerable stress on the ulnar collateral ligament (MCL), as the thoracohumeral and scapulohumeral muscles reverse the upper arm’s movement from backward to forward and from external to internal rotation, while the forearm and the thrown object follow the upper arm’s movement only after a delay because of their inertia.
One review reports a valgus moment of approximately 33 Nm for the load-bearing capacity of the isolated medial collateral ligament and moments exceeding 60 Nm during throwing. Another review reports approximately 300 N of medial shear force and up to 500 N of lateral compressive force in the throwing model. These figures, derived from different experimental and biomechanical investigations, indicate orders of magnitude; they are not individual injury thresholds. Ligamentous, bony and muscular stabilizers share the load. The flexor-pronator group, including the wrist flexors, finger flexors and pronator teres, supports dynamic valgus stabilization. If repeated loads exceed the system’s load-bearing capacity and ability to recover, microtrauma and increasing insufficiency of the medial collateral ligament may develop. This may manifest as increased medial opening under valgus stress (medial gapping). This in turn alters the distribution of forces in the joint and can lead to osteoarthritis with osteophyte formation. Medial gapping may also affect the ulnar nerve. The additional loading of the flexor-pronator group originating at the medial epicondyle of the humerus may be accompanied by tendinopathy in the form of golfer’s elbow. Other complications include loose bodies and, owing to lateral compression, radiocapitellar osteochondral lesions. Before skeletal maturity, repetitive traction at the medial epicondyle can cause apophysitis or a bony avulsion. The frequency of 94% cited in a review refers instead to radiographic signs of apophyseal hypertrophy in competitive young baseball players, not to symptomatic apophysitis in 94% of them. Repeated valgus and extension loading may also promote posteromedial impingement changes with olecranon osteophytes and olecranon stress fractures.
Changes in throwing technique can influence mechanical loading but do not necessarily eliminate the problem. Throw count, intensity and recovery time must also be considered, because repeated loading plays a substantial role.
Throwers may develop increased external rotation of the dominant shoulder, partly because of developing joint-capsule laxity, as well as reduced internal rotation. Bony adaptations, particularly altered humeral torsion, and capsular changes may contribute. Such adaptations are not automatically pathological and do not occur exclusively in conjunction with thrower’s elbow. Examination should therefore take account of the total rotational range, side-to-side differences and clinical symptoms.
Causes
- Repeated intensive throwing movements
Predisposing factors
- Existing valgus instability
Symptoms
- Symptoms may initially be absent; structural adaptations or increased medial laxity can also occur in asymptomatic throwers.
- Typical symptoms are load-related pain on the inside of the elbow during throwing; reduced throwing velocity, accuracy or load tolerance may occur.
- Clinically relevant ligament insufficiency may be associated with increased medial opening. This finding must be interpreted in conjunction with symptoms and examination.
Diagnosis
- History covering the sport, performance level, throwing load, onset of symptoms, affected throwing phase and previous injuries.
- Examination of mobility, tenderness, valgus stability and the ulnar nerve; also assess shoulder function and the remainder of the kinetic chain.
- Valgus stress test, milking maneuver and moving valgus stress test as clinical provocation tests; no single test replaces the overall assessment.
- Depending on the findings, radiographs to assess bony changes, dynamic ultrasound to assess joint opening and MRI to investigate the ligamentous structures and possible associated injuries.
Complications
- Golfer’s elbow
- Predominantly lateral osteoarthritis of the elbow joint
- Ulnar nerve irritation
- Loose bodies
- Traction apophysitis
- Radiocapitellar osteochondral lesions
- Olecranon osteophyte formation
Treatment
- Load modification or a temporary break from throwing, avoiding valgus loads that provoke pain or promote progression.
- Finding-dependent conservative rehabilitation to preserve or restore mobility and progressively strengthen the flexor-pronator group as well as the shoulder, scapular and trunk muscles.
- Gradual, criteria-based rebuilding of throwing load following clinical assessment, rather than being guided by time alone.
- Specialist assessment of surgical treatment in the presence of significant persistent instability, suitable higher-grade ligament injuries or failure to return to the desired loading level despite adequate rehabilitation. The procedure depends on the injury pattern and loading requirements.
Differential diagnoses
- Golfer’s elbow or injury of the flexor-pronator group
- Ulnar neuropathy or cubital tunnel syndrome
- Medial epicondylar apophysitis or avulsion injury before skeletal maturity
- Posteromedial impingement or valgus extension overload syndrome
- Olecranon stress fracture
- Osteochondral lesion of the humeral capitellum and loose bodies