A flexor-pronator mass injury or common flexor-pronator muscle injury is a muscle injury most commonly a muscle tear or strain of flexor-pronator muscles of the elbow joint.
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Epidemiology
A flexor-pronator mass injury is an uncommon injury seen in athletes practising throwing sports. It can rarely occur in the setting of an acute injury e.g. an elbow dislocation.
Associations
A flexor-pronator mass injury might be associated with the following clinical conditions 1-3:
Diagnosis
Diagnostic clues
Flexor-pronator mass injury is a primarily clinically based diagnosis. Imaging is done to rule out possible associated injuries e.g ulnar collateral ligament injury.
Clinical presentation
The typical clinical presentation of a flexor-pronator mass injury consists of clinically significant elbow pain, which might present in a similar way as an ulnar collateral ligament complex injury. However medial elbow pain is typically experienced during a wide variety of activities enabling this muscle group including gripping movements or opening a jar 1.
Complications
Flexor-pronator muscle injuries might contribute and lead to valgus instability, especially in the setting of continued unrestricted valgus stress associated with the throwing activity.
Pathology
Flexor-pronator mass injuries comprise muscle tears/strain or avulsion injuries of the flexor-pronator muscle group usually distal to the medial epicondyle. This can be the result of an acute or acute-on-chronic injury.
Radiographic features
Ultrasound
Ultrasound can show ill-defined hyper- or hypoechoic lesions within the flexor-pronator muscle group with varying degrees of fiber disruption.
MRI
MRI can demonstrate and confirm as well as grade a common flexor-pronator muscle injury, differentiate it from medial epicondylitis and most important rule out any associated injuries such as a tear of the ulnar collateral ligament indicating valgus instability 1.
Radiology report
The radiological include a description of the following:
- muscle injury including type and extent
- associated injuries
- ulnar collateral ligament injury
- bony avulsions
Treatment and prognosis
For isolated common flexor-pronator muscle injuries the treatment is conservative with pain control and an active resting period with functional rehabilitation involving a stepwise and structured program returning athletes to their activity.
Persisting pain or recurrent symptoms should prompt a suspicion for valgus instability 1.
Differential diagnosis
Conditions that might mimic the clinical presentation or imaging appearance of a flexor-pronator mass injury include: