Is the Tendon-to-Groove Ratio Associated with Elevated Risk for LHB Tendon Disorders?-A New Approach of Preoperative MR-Graphic Analysis for Targeted Diagnosis of Tendinopathy of the Long Head of Biceps

Abstract

Background: Pathologies of the long head of the biceps (LHB) tendon are a common cause of anterior shoulder pain. While the influence of the anatomical morphology of the intertubercular groove (ITG) on the development of LHB tendon instability has been investigated with ambiguous results, the relationship of the LHB to ITG anatomy has not yet been considered in this context. The objective of this study was to reliably extract the tendon-to-groove ratio from MRI scans of symptomatic patients and examine its potential influence on the occurrence of certain causes for LHB-associated symptoms. Methods: In this retrospective study, preoperative MRI scans of 35 patients (mean age of 46 ± 14 years) presenting with anterior shoulder pain and clinical indications of LHB tendinopathy were analyzed in transversal planes. Long and short diameters of the LHB tendon and ITG were measured, cross-sectional areas of the LHB tendon and ITG were calculated from these measurements, and the ratio of cross-sectional areas (LHB/ITG) was introduced. All measurements were repeated independently by three investigators and inter-rater reliability was assessed using intraclass correlation coefficient (ICC). Thereafter, tendon-to-groove ratios were compared in patients with and without intraoperative signs of LHB tendon instability. Results: All patients exhibited intraoperative signs of LHB tendinitis, with additional findings including pulley lesions and SLAP lesions. Analysis revealed variations in the dimensions of the LHB tendon and ITG cross sections, with the tendon-to-groove ratio decreasing from 37% at the pulley to 31% at the deepest point of the sulcus. Very good inter-rater reliability was observed for all measurements. The tendon-to-groove ratio did not significantly differ (p > 0.05) in patients with or without pulley lesions or SLAP lesions. Conclusions: Our study introduced the novel parameter of the tendon-to-groove ratio of cross-sectional areas as a reproducible parameter for the description of local anatomy in the field of targeted diagnosis of LHB tendon disorders. While our findings do not yet support the predictive value of the tendon-to-groove ratio, they underscore the importance of further research with larger cohorts and control groups to validate these observations.

Keywords: arthroscopy; biceps tendon; intertubercular groove; pulley lesions; shoulder.

Figure 1

Inclusion and exclusion criteria of the study cohort.

Figure 2

Dimensions that were extracted from axial PD images at both measuring points: Long axis of the LHB tendon (a) and short axis of the LHB tendon (b). For the measurement of the dimensions of the ITG various straight lines and points were defined: First, a straight line was created that was tangent to both edges of the ITG. The point of contact of the tangent at the lesser tuberosity was labeled A and the point of contact at the greater tuberosity was labeled B. A second parallel straight line was then drawn and shifted in parallel so that it was tangent to the deepest point of the ITB. The point of contact of the second tangent with the base of the ITG was labeled C. The depth of the ITG was measured as the distance between the two straight lines (d). The distance between points A and B was used to measure the width of the ITG (e) and depth of the ITG (d); the cross-sectional areas of both the LHB tendon (c) and the ITG (f) were calculated from the above measurements.

Figure 3

The medial wall angle (MWA, a) was determined by measuring the angle formed between a straight-line connecting points A and B and a second line intersecting points A and C. This measurement indicates the inclination of the medial wall of the ITG as it transitions towards the lesser tuberosity. The adapted opening angle (AOA, b) was assessed as an angle originating from the center of the best-fit circle of the humeral head and extending from point A to point B. This angle provides information about the degree of opening from the center of the humeral head to the indicated points.

Figure 4

Visualization of the area ratio between the LHB tendon and the intertubercular grove. While the cross-sectional area of the LHB tendon is calculated under the assumption of an elliptic tendon shape (dark blue), the area of the groove was calculated under the assumption of a half-elliptic shape (light blue). Both cross-sectional areas (A–C) were calculated as explained in Figure 2.