The Radial Arc technique: A systematic ultrasound method to imaging the distal biceps brachii tendon from a medial approach with anatomical insights

Abstract

Introduction: Distal biceps brachii tendon disorders predominantly result from repetitive use and eccentric loading. High-resolution ultrasound has emerged as a preferred diagnostic tool due to its dynamic imaging capabilities, accessibility, and cost-effectiveness.

Topic description: This paper introduces the Radial arc technique, a didactic and systematic ultrasound scanning method from a medial approach designed to facilitate the identification of the distal biceps brachii tendon insertion in the long-axis view. The technique is a five-step sonographic approach navigating sonographers and clinicians through a series of landmarks to address the often-complex sonographic examination of the distal biceps brachii tendon insertion. The paper also provides detailed anatomical insights into the biceps brachii muscle and the distal tendinous complex, highlighting key morphological features critical for accurate ultrasound interpretation.

Discussion: The proposed approach is tailored to support the educational development of undergraduate and postgraduate students specialising in musculoskeletal sonography and enhance the practical skills of early-career and experienced sonographers and clinicians utilising point-of-care ultrasound. The anatomical framework provided offers a deeper understanding of the distal biceps brachii tendinous complex, supporting diagnostic accuracy for distal biceps brachii tendon-related conditions that are critical for guiding patient management.

Conclusion: The systematic nature of the Radial arc technique aims to standardise practices not only in clinical settings but also in the design and execution of research studies involving the assessment of the distal biceps brachii tendon integrity with ultrasound. Future research should focus on assessing the reproducibility of the Radial arc technique in diverse clinical settings and among different practitioners and operators, crucial for its adoption in sonographic diagnostics.

Keywords: Point-of-care-ultrasound; elbow anatomy; sonographic technique; tendon pathology; ultrasound imaging.

Figure 1.

The distal biceps brachii tendinous complex (DBBTC). (a) Schematic drawing of the DBBTC components from the anterior aspect of the elbow, with coloured rectangles indicating probe positions corresponding to ultrasound views in panels (b)-(f). (b) Short-axis view of the hyperechoic, flat appearance of the internal bicipital aponeurosis (IBA) within the biceps brachii muscle (BBm). (c) Short-axis view showing the short head (SH) and long head (LH) of biceps brachii tendon, and external bicipital aponeurosis (EBA) arising from the IBA. (d) Short-axis view of the SH and LH approximating as they descend distally. (e) Short-axis view showing the 90° rotation, with the SH sliding to a superficial position over the LH. (f) Long-axis view of the EBA, travelling medially and superficial to the brachial artery (BrA), and merging with the ulnar flexor muscles; note the distinct superficial, middle, and deep layers of the EBA. DBBTC, distal biceps brachii tendinous complex; IBA, internal bicipital aponeurosis; EBA, external bicipital aponeurosis; DBBT, distal biceps brachii tendon; BBm, biceps brachii muscle; BRm, brachialis muscle; BrA, brachial artery; H, humerus; yellow arrows, IBA; BRRm, brachioradialis muscle; SH, short head of biceps tendon; LH, long head of biceps tendon; CFP, coronoid fat pad; S/DBRN, superficial and deep branches of radial nerve; HT, humeral trochlea; HhPT, humeral head of pronator teres muscle; MN, median nerve; red arrows, long axis view of EBA; SL-EBA, superficial layer of EBA; ML-EBA, middle layer of EBA; DL-EBA, deep layer of EBA.

Figure 2.

Patient positioning. (a) Patient seated facing the clinician, left elbow on cushion at 30° flexion for optimal probe access and distal biceps brachii tendon visualisation. (b) Left forearm in a near-neutral position, close to halfway between pronation and supination. (c) Patient lying on side with the left arm slightly off the plinth and the distal humerus supported for comfort and accessibility.

Figure 3.

Step 1. (a) Probe on medial epicondyle, aligned horizontally. (b) View includes the medial epicondyle (ME), humeral trochlea (HT), and coronoid process (CP), excluding ulnar shaft. AOL, anterior oblique ligament of the medial collateral ligamentous complex; CP, coronoid process; CFT, common flexor tendon; FDSm, flexor digitorum superficialis muscle; HT, humeral trochlea; IEA, inferior epicondylar aspect; ME, medial epicondyle; asterisk (*), humero-ulnar joint.

Figure 4.

Step 2. (a) Distal slide of the probe in a true horizontal direction. (b) Medial epicondyle (ME) and inferior epicondylar aspect (IEA) exit sonogram, while the humeral trochlea (HT) and coronoid process (CP) are now situated on the left side of the sonogram. BRm, brachialis muscle; BRt, brachialis tendon; CP, coronoid process; FDSm, flexor digitorum superficialis muscle; HT, humeral trochlea; UhPT, ulnar head of pronator teres; asterisk (*), humero-ulnar joint.

Figure 5.

Step 3. (a) Anterior sweep of the probe towards forearm's midline. (b) The radial head (RH) appears with hyperechoic signal, while the humeral trochlea (HT), resembling a cliff, remains visible. BRt, brachialis tendon; CFT, common flexor tendon; DhBRm, deep head of brachialis muscle; FCR, flexor carpi radialis; HT, humeral trochlea; HhPT; humeral head of pronator teres; RH, radial head; RN, radial neck; ShBRt, superficial head of brachialis muscle; asterisks (*), hyaline cartilage.

Figure 6.

Step 4. (a) Further distal slide of the probe in a true horizontal direction. (b) Radial arc: view includes the radial head (RH) as a hill on the left, radial neck (RN) as a valley in the centre, and radial tuberosity (RT) as a hill on the right side of the sonogram. BRt, brachialis tendon; BrA, brachial artery; DhBRm, deep head of brachialis muscle; FCR, flexor carpi radialis; HhPT; humeral head of pronator teres; MN, median nerve; RH, radial head; RN, radial neck; RT, radial tuberosity; ShBRt, superficial head of brachialis muscle; asterisks (*), hyaline cartilage; yellow arrows, distal biceps brachii tendon.

Figure 7.

Step 5. (a) The proximal end of the probe is upwardly rotated by about 15°. (b) Long-axis view of the long head of biceps brachii tendon (LH) insertion showing a subtle convexity – raised contour – along its superficial layer, with insertional fibres extending proximally and deeply into the radial tuberosity (RT). (c) Long-axis view of the short head of biceps tendon (SH) insertion displaying a flat, straight superficial layer, with fibres confined to the uppermost, distal part of the footprint. BrA, brachial artery; FCR, flexor carpi radialis; HhPT, humeral head of pronator teres; RT, radial tuberosity; yellow arrows, distal biceps brachii tendon; LH, long head of biceps tendon; red arrow, proximal and deep insertional fibres of LH on tuberosity; curved green arrow, raised contour of LH’s superficial layer; SH, short head of biceps tendon; purple arrow, SH footprint lacks proximal fibres; curved orange arrow, flat and straight superficial layer of SH.