Utility of the Pectoralis Major Index in the Diagnosis of Structurally Significant Pectoralis Major Tears

Abstract

Background: Diagnosis of pectoralis major tears early in the acute phase is important for optimizing surgical repair and outcomes. However, physical examination of pectoralis major injuries can be misleading, often resulting in a potentially detrimental delay in surgical treatment.

Purpose: To establish and validate a quantifiable clinical diagnostic test for structurally significant pectoralis major tears.

Study design: Cohort study (diagnosis); Level of evidence, 2.

Methods: A total of 50 healthy male participants (mean age, 43.3 ± 11.9 years) with normal uninjured pectoralis major anatomy were examined. Digital photographs of all participants were taken in the "military press" starting position (90° of shoulder abduction, 90° of shoulder external rotation). The length between the ipsilateral nipple and the apex of the pectoralis major muscle curvature along the anterior axillary fold, known as the pectoralis major distance, was measured bilaterally. Two orthopaedic surgeons measured all photographs on 2 separate occasions. The pectoralis major index (PMI) was calculated as a ratio of pectoralis major distance values to establish normal values. The PMI was also calculated in a cohort of 19 male patients (mean age, 33.8 ± 6.8 years) with a pectoralis major rupture to assess the diagnostic utility of this novel quantifiable physical examination technique.

Results: Mean (± standard deviation) PMI for the uninjured group was 1.0 ± 0.07. A diagnostic threshold of a PMI <0.9 resulted in a sensitivity of 79%, specificity of 98%, and overall accuracy of 93% in identifying structurally significant pectoralis major ruptures. There was no correlation between PMI and age or activity level, including participation in sports and/or weight training. The PMI technique demonstrated good to excellent intrarater reliability (intraclass correlation coefficient [ICC] = 0.82, 0.74) and interrater reliability (ICC = 0.63, 0.76).

Conclusion: The PMI technique is a simple, quantifiable, and accurate clinical diagnostic test for structurally significant pectoralis major tears. Routine application of the PMI technique by clinicians may improve accurate identification of structurally significant rupture and expedite referral to a surgical specialist for optimal treatment and outcome.

Keywords: diagnosis; pectoralis major; shoulder; tendon rupture.

Figure 1.

Preoperative photograph of a chronic right pectoralis major rupture 84 days after injury. Alteration due to a structurally significant rupture is apparent in the visual appearance of the anterior axillary fold on the injured side (arrow).

Figure 2.

Description of the technique to determine the pectoralis major index (PMI). (A) The patient positions both arms in the “military press” starting position (shoulders in 90° abduction, 90° external rotation). (B) Both nipples are marked. (C) The pectoralis major contour is followed along the anterior axillary fold and the most laterally prominent apex is marked on both sides. (D) The distance along a straight line between the nipple and the apex (the pectoralis major distance [PMD]) is measured to 1 decimal place, and the PMI is calculated as the injured-side PMD over the uninjured-side PMD.