Concept of the “biceps box”: a tool to improve understanding of anterosuperior impingement of the shoulder when the intra-articular biceps is normal
Background: Anterior shoulder pain is frequently attributed to pathology of the long head of the biceps tendon (LHBT), leading to the common surgical practice of tenotomy or tenodesis during rotator cuff repair. However, the routine sacrifice of a macroscopically normal LHBT remains controversial due to potential postoperative complications and a lack of consensus regarding the precise nosological origin of pain when intrinsic tendon damage is absent.
Objective: This article describes the "biceps box" concept, a functional geometric model designed to map the anatomical environment of the LHBT and differentiate between intrinsic tendon lesions and extrinsic damage to adjacent stabilizing structures.
Key Points: The LHBT is modeled within a rectangular cuboid representing the rotator interval. The posterior wall comprises the five-layered supraspinatus tendon, while the superior wall consists of the coracohumeral complex and superior glenohumeral ligament (SGHL). The subscapularis and SGHL form the anterior wall, and the lateral wall is defined by the biceps pulley and semicircular humeral ligament. This tissue continuum maintains LHBT stability through interconnected structures, including the fasciculus obliquus and rotator cable. Clinical studies indicate that interobserver reliability in diagnosing LHBT instability is often low, potentially leading to unnecessary surgical intervention. Furthermore, the model accounts for sensory innervation of the rotator interval by the lateral pectoral nerve, suggesting that anterosuperior humeral head decentering may result in nerve entrapment and referred pain.
Conclusion: The biceps box model provides a framework for identifying anterior shoulder pain arising from extrinsic structural or neurological involvement. This approach encourages conservative management, such as dynamic humeral centering and targeted nerve blocks, when the LHBT appears healthy.
