Pectoralis minor length measurements in three different scapula positions.

Muhle A Komati,Francina E Korkie,Piet Becker

doi:10.4102/sajp.v76i1.1487

Muhle A Komati, Francina E Korkie + Show 1 more

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https://doi.org/10.4102/sajp.v76i1.1487

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Abstract

BackgroundThe pectoralis minor (PM) muscle is commonly regarded as a contributor to abnormal scapula positioning. Subsequently, the muscle length of the scapular stabilising muscles may be affected, as these muscles assume a lengthened position, which over time causes weakness. There are inconsistencies regarding PM muscle length values because of the different techniques and positions used when the length of the PM muscle is measured.ObjectiveTo determine the PM muscle length in participants aged 18−24 using a Vernier® caliper and expressed as pectoralis minor index (PMI), with the scapula in three different positions.MethodThe PM muscle length of 144 participants was measured with a Vernier® caliper (intraclass correlation coefficient 0.83−0.87). Measurements were made with the scapula in the resting position, in an active and a passive posterior tilt position.ResultsSignificant differences were observed in PMI between the resting scapula position – 10.04 (confidence interval, CI 9.93–10.14) and active posterior tilt – 10.19 (CI 10.09–10.30) (p < 0.001); the resting position – 10.04 (CI 9.93–10.14) and passive posterior tilt – 10.77 (10.66–10.87) (p < 0.001) and active – 10.19 (CI 10.09–10.30) and passive posterior tilt 10.77 (10.66–10.87) (p < 0.001). The dominant side had lower PMI values than the non-dominant side.ConclusionThe significant differences between the active and posterior tilt positions suggested that optimal muscle length of PM was affected by the inner range strength of the lower fibres of Trapezius.Clinical implicationsIt is important that in clinical practice not only the length of PM in scapular misalignment but also the strength of the antagonistic muscles is considered.

Highlights

Pectoralis minor (PM) muscle shortening has been attributed to sustained postures involving anterior tilting and protraction of the scapula (Borstad 2006; Rosa et al 2016)
The effect of an anteriorly tilted and protracted scapula on gleno-humeral function is threefold: the orientation of the glenoid to the humeral head is affected and may result in altered gleno-humeral arthrokinematics; the space between the acromion and humeral head is decreased and this may lead to compression of the sub-acromial structures and the scapula stabilising muscle may weaken as a result of the prolonged elongated position (Lee, Im & Kim 2020; Morais & Cruz 2016; Umehara et al 2018)
As PM is identified as a muscle that affects scapula positioning and gleno-humeral function, the effective measurement of PM length is important for rehabilitation purposes, to prevent and manage any upper limb dysfunction that may be caused by PM shortening

Summary

Introduction

Pectoralis minor (PM) muscle shortening has been attributed to sustained postures involving anterior tilting and protraction of the scapula (Borstad 2006; Rosa et al 2016). In studies where PM length was measured in standing, the scapula could be in an anteriorly tilted position because of the influence of gravity on posture, demonstrating poor diagnostic accuracy and may provide inaccurate values for PM muscle length (Borstad 2006, 2008; Borstad & Ludewig 2005; Finley et al 2017; Ko et al 2016; Lee et al 2015; Rosa et al 2016, 2017). There are inconsistencies regarding PM muscle length values because of the different techniques and positions used when the length of the PM muscle is measured

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