Injury to the brachialis muscle is a rare phenomenon and is infrequently described in literature [1, 2]. This may promote misdiagnosis of this injury. Furthermore, there are conflicting thoughts on the anatomy and the precise function of the brachialis muscle. Gray's Anatomy describes a normal variant with two or more parts , while Leonello et al. suggest that all brachialis muscles consist of a superficial and a deep head . The rarity of brachialis muscle injury and the conflicting thoughts on the normal morphology and function of the muscle make diagnosing and treating a brachialis muscle injury a real challenge. The first case report, by Van Den Berghe, presented a male who was clinically diagnosed with a tear of the biceps brachii muscle after lifting a heavy object. However, a MRI revealed a tear in the distal aspect of the brachialis muscle. He was treated conservatively in an outpatient setting and regained full function in 10 months .
Nishida et al. described two cases in which the patients were referred for evaluation of a possible muscular neoplasm. Both patients complained of pain and a loss of active extension in the elbow 1 week after the injury. MRI showed a brachialis muscle tear, mimicking an intramuscular tumor. Active mobilization was initiated on both patients with eventual full restoration of function after 3 months .
The fourth patient, reported by Winblad et al, was diagnosed with a brachialis muscle tear after a hyperextension injury of the elbow. MRI sequencing confirmed the diagnosis. The patient was treated conservatively with full restoration of function .
The final case report was published by Wasserstein and involves a hyperextension injury of the elbow, resulting in a brachialis muscle rupture, confirmed by MRI. Their patient was treated non-operatively and regained full function .
To summarize, expensive diagnostic modalities, such as MRI, are too often felt to be needed to definitely diagnose brachialis muscle injury. In our hospital, ultrasound is the first modality of choice if additional studies are needed for diagnosing tendon or muscle ruptures In the case of equivocal findings from the ultrasound imaging, a MRI sequencing is done for the definitive diagnosis. In our experience, we believe that most brachialis muscle ruptures can be treated conservatively with early active mobilization.