Congenital unilateral absence of the long head of the biceps tendon: A diagnostic challenge in shoulder pain evaluation

INTRODUCTION

Shoulder pain is a common musculoskeletal complaint, frequently attributed to rotator cuff pathology, adhesive capsulitis, or subacromial impingement.^[1,2] The glenoid labrum and supraglenoid tubercle give rise to the long head of the biceps tendon (LHBT), which is frequently assessed on magnetic resonance imaging (MRI) and is essential for anterior shoulder stability.^[2] Only 35 examples of congenital lack of the LHBT have been documented in the literature to date, making it an incredibly uncommon anatomical variation.^[3] Both unilateral and bilateral occurrences are possible, and it is occasionally linked to congenital diseases such as Silver-Russell syndrome.^[4] In addition, isolated unilateral agenesis or cases linked to anatomical differences like a shallow bicipital groove or a large subscapularis insertion have been reported in a number of case studies.^[5-7] To differentiate acquired tendon rupture from agenesis, MRI characteristics such as a flattened or non-existent bicipital sulcus are crucial.^[1] A systematic review found that anterior instability was evident in 37.1% of cases of LHBT agenesis, while shoulder discomfort was observed in 85.7% of cases.^[3] We present a rare case of unilateral LHBT agenesis in a 52-year-old male with persistent shoulder pain, initially misdiagnosed as adhesive capsulitis. MRI played a crucial role in detecting this unusual condition and directing the proper course of treatment.

CASE REPORT

A 52-year-old right-handed male presented with a 6-month history of chronic right shoulder pain and progressively restricted range of motion. The pain was constant, dull in character, and exacerbated by overhead activities, particularly abduction and external rotation. There was no preceding history of trauma, repetitive overuse, or prior similar complaints. The left shoulder was asymptomatic.

On physical examination, both active and passive movements of the right shoulder were painful and limited, particularly in forward flexion, external rotation, and abduction. Mild tenderness was elicited over the anterior aspect of the shoulder. Neer’s and Hawkins’ impingement signs were mildly positive, while Speed’s and O’Brien’s tests were negative. Neurovascular examination of the right upper limb was normal, and vital signs were stable. A provisional diagnosis of adhesive capsulitis was made based on clinical findings, and an MRI was organized to evaluate this.

However, MRI of the right shoulder showed absence of the LHBT, with a shallow bicipital groove seen on axial and coronal sequences, indicating congenital etiology. The short head of the biceps tendon was intact, inserting into the coracoid process [Figure 1]. The rotator cuff tendons and glenoid labrum were normal, with no tears or degeneration. Mild acromioclavicular joint degeneration was noted. There was no subacromial or subdeltoid bursitis. He was managed symptomatically with analgesics and physiotherapy.

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Figure 1:

Magnetic resonance imaging of the right shoulder. (a) Proton density fat-suppressed axial, (b) coronal, (c) sagittal, and (d) coronal, showing absence of long head of biceps tendon with shallow groove (arrow) (a) and intact short head of biceps (arrow) (b). Note the synovitis (arrow) in the axillary recess (c and d).

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DISCUSSION

The rotator cuff is made up of the four muscles that surround the shoulder joint: The supraspinatus, infraspinatus, teres minor, and subscapularis. These muscles allow smooth arm abduction and rotation and are essential for preserving glenohumeral stability.^[1] Shoulder pain is frequently caused by rotator cuff problems, such as tendinopathy and tears, especially in older persons.^[1,2] There is a close anatomical and functional link between the rotator cuff and the LHBT, which passes through the bicipital groove.^[3] It frequently plays an integral part in shoulder disease, particularly when anterior discomfort or instability is present.^[4-6]

The LHBT emerges from the superior labrum and supraglenoid tubercle, travels intra-articularly over the humeral head, and then leaves through the rotator interval to run in the bicipital groove before distally joining the short head.^[4,5] It supports anterior shoulder stability, especially during overhead and rotational movements, and is held in place by the coracohumeral and transverse humeral ligaments.^[6] The tendon develops embryologically from mesenchymal tissue in the glenohumeral area between 6 and 8 weeks of gestation, and a disruption in this process may result in congenital absence.^[3]

The biceps brachii can have both acquired and congenital abnormalities. Congenital variations such as the absence of the long head tendon and the presence of supernumerary heads have been reported.^[7] The LHBT may arise anomalously from structures such as the joint capsule, coracobrachialis, pectoralis major tendon, or greater tuberosity,^[7] and distal anomalies such as bifid or dual insertions have also been observed.^[8,9]

Congenital absence of the LHBT is exceedingly unusual and can occur unilaterally or bilaterally. A shallow or absent bicipital groove is commonly linked to it, which can help with radiological diagnosis.^[10,11] Clinically, it is frequently overlooked during initial MRI interpretation and might resemble common shoulder disorders such adhesive capsulitis, rotator cuff tendinopathy, or biceps tendon rupture.^[11] Particularly for patients who have no history of trauma or overuse, MRI is still the most effective way to confirm the diagnosis.^[12] In addition, certain cases may exhibit related anomalies such as labral hypoplasia or large subscapularis insertion.^[3,13] Our case underlines the importance of considering LHBT agenesis as a rare but significant differential in patients with chronic shoulder pain and restricted motion, particularly when typical diagnoses like frozen shoulder are suspected. Meticulous imaging review is essential to avoid misdiagnosis and unnecessary treatment.^[14]

Overuse injuries, including tendinopathy, tendinitis, and tenosynovitis, which are frequently linked to impingement beneath the coracoacromial arch, are examples of acquired illnesses.^[15] Injury to the subscapularis or pulley system is frequently associated with mechanical instability, either subluxation or dislocation, of the tendon from the bicipital groove.^[15,16] Ruptures can also be partial or complete; the iconic “Popeye” deformity is usually the result of complete tears.^[15] Awareness of these anomalies and pathologies is critical for accurate diagnosis, especially in rare presentations like ours involving congenital absence. Several clinical and diagnostic imaging findings, previously reported and reaffirmed in our case, include the lack of a “Popeye” deformity and a shallow or underdeveloped bicipital groove. Given the absence of agreement on the long head of the biceps (LHB) tendon’s contribution to shoulder function and pain, it is uncertain whether its congenital absence could act as a source of pain or lead to microinstability,^[17] as proposed in earlier case reports. A possible association may exist between LHB tendon absence and increased risk of developing shoulder pain and instability, though this connection is not yet established. Future studies on larger cohort would be needed to clarify this potential relationship.

CONCLUSION

Congenital absence of the LHBT is exceedingly rare and sometimes neglected because there is no history of injury, and the symptoms match common shoulder disorders such as frozen shoulder or rotator cuff tendinopathy. In our example, the patient was initially diagnosed with a frozen shoulder, but an MRI showed that the real cause was a shallow bicipital groove and absent LHBT. To prevent needless therapies (such as aggressive therapy or surgery aimed at the wrong condition), it is imperative to recognize this anomaly. Although uncommon, LHBT agenesis is rare; it should be diagnosed as it can aid in management of shoulder pathology.