Pectoralis minor tendon in the rotator interval: arthroscopic, magnetic resonance imaging findings, and clinical significance

Anatomical Variations in the Pectoralis Minor Muscle Origin and Insertion: A Systematic Review

The pathology of the shoulder is among the most widespread medical presentations and may be a result of existing anatomical variations. Therefore, the knowledge of the variations is vital for physicians and clinicians, tasked with treating patients presenting similar complaints to minimize misdiagnosis and prevent iatrogenic injuries. Therefore, the main objective of the present systematic review the variations in pectoralis minor muscle origin and insertion/attachment point. The study also seeks to better inform physicians and clinicians of the task of treating patients with various pathology problems and to ascertain that, upon identification, the pectoralis minor muscle variants are aptly appreciated. The search method used in this systematic review entails the use of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) protocol, and the searching of several online databases, for studies focusing on variations in pectoralis minor muscles. The author reviewer evaluated the studies for eligibility, and the selection criteria for the studies used are described below. This systematic review has disclosed that, in some individuals, the pectoralis minor muscles have their origins in the second, third, and fourth ribs, even as others have their origin in the third and fourth ribs. Still, the systematic review has disclosed that, in certain individuals, the insertion of the pectoralis minor muscle occurs at the supraspinatus tendon, even as there are anomalies in the pectoralis minor insertion points linked to subacromial impingement, possible compression of the brachial plexus anteromedial and the axillary artery, and the subcoracoid impingement.

Variant pectoralis minor muscle: a case study with clinical relevance

The pectoralis minor (PMn) muscle originates from the third, fourth, and fifth ribs near the costochondral junctionusually and gets inserted on the medial margin and upper surface of the coracoid process of the scapula. To look at the morphological insertion patterns and sites of attachment of the PMn muscle in the donated cadavers. Over all 19 limbs were included in the study (9 right and 10 left). Out of 19 limbs, 10 belonged to female and 9 belonged to male cadavers. The cadavers were meticulously dissected to determine the morphological insertion types and location of the attachment of the muscle. Unusual pattern of insertion was observed in 6 limbs (31.6%) out of total 19 limbs included in the study. The variations we observed does not fall completely in the classification by Le Double, hence variations we observed can be considered as new and rare variant which to our knowledge is not reported in literature. We propose this new variant to be type 4 of Le Double classification. The potential of ectopic PMn tendon should be taken into consideration and tested out, especially in patients with shoulder discomfort and stiffening who have ruled out the more frequent diseases. For proper surgical planning, a preoperative magnetic resonance imaging or USG examination of the shoulder joint is required considering the prevalence of variation in the insertion pattern of PMn muscle. Preoperative identification of any abnormal PMn insertion can help to reduce the risk of iatrogenic tendon injury and post-operative problems.

The clinical anatomy of variations of the pectoralis minor

Shoulder pathology is a very common medical presentation and can be due to anatomical variations. Therefore, knowledge of variants is important for the clinician treating patients with such complaints so that misdiagnosis is minimized and iatrogenic injury prevented. A review of the literature was performed of the variant anatomy of the pectoralis minor muscle. The aim of this review is to better inform clinicians who might treat patients with shoulder pathology so that if identified, variants of the pectoralis minor muscle are better appreciated.

Prevalence of anomalous or ectopic insertion of pectoralis minor: a systematic review and meta-analysis of 4146 shoulders

INTRODUCTION

The proximal insertion beyond coracoid process of pectoralis minor is considered as hidden culprit of rotator cuff disorders. The ectopic insertion is also associated with thoracic outlet syndrome. The current review was conducted to provide a comprehensive evidence-based assessment of the anatomical characteristics of ectopic insertion of pectoralis minor.

MATERIALS AND METHODS

A through systematic search was conducted on the major electronic database, PubMed, EMBASE, Google Scholar and Journals of Anatomy, orthopedics, plastic surgery, sports medicine. The primary outcome was to measure the prevalence of ectopic insertion of pectoralis minor tendons. The data extraction was conducted for pooled estimation and metanalysis.

RESULTS

A total of 25 studies were included for systematic review. The overall pooled estimate of ectopic insertion of Pectoralis Minor was 19.27% (95% CI 15-24%). The prevalence rate in dissected specimen was 21% (CI 15-28%) and in arthroscopic evaluation was 22% (95% CI 5-59%) which was marginally higher with wide confidence interval due small sample size. The prevalence rate in MRI and USG were 15 and 12%, because MRI and USG have almost similar sensitivity in the detection of anomalous insertion of Pectoralis Minor. The distribution of subtypes of anomalous or ectopic insertion based on Le Double classification was 34% for type I, 42 and 9% for Type III. The incidence of ectopic insertion of pectoralis minor was highest in Japanese population. The female and left side have slightly higher incidence at insignificant level.

CONCLUSION

The preoperative MRI or at least USG evaluation of shoulder joint must be conducted for appropriate surgical planning, because the prevalence of ectopic insertion is around 20%. The preoperative detection of anomalous insertion of pectoralis minor can be crucial in minimizing the incidences of iatrogenic injuries of tendon or post-operative complications.

Ectopic tendons of the pectoralis minor muscle as cause for shoulder pain and motion inhibition-Explaining clinically important variabilities through phylogenesis

OJECTIVE

Clinical consequences of ectopic tendons of the pectoralis minor muscle (PMM) for shoulder pain and range-of-motion limitation have been demonstrated. For better understanding the existence of such ectopic tendons, a phylogenetic hypothesis is proposed.

METHODS

Forty-five shoulders of anatomical specimens were dissected and examined. Insertions areas of PMM were measured and occurring aberrant tendons were identified. Their relationship with the coracohumeral ligament (CHL) described and samples of the ligament were collected and histologically stained.

RESULTS

The prevalence of PMM variations was 37.84%. Shoulders with variations showed a statistically significant smaller coracopectoral distance (p<0.001) and larger insertion areas (p<0.003) than shoulders without. A strong negative correlation between these two variables (p<0.001, r = -0.620) was shown.

CONCLUSIONS

The presented results prompted the conclusion that the CHL may be in fact the remnant of the pectoralis minor tendon (PMT), which migrated from the humerus to the coracoid process through the process of phylogenetic evolution. Variations of PMTs are significantly more common than in previous studies. Imaging techniques appear to be insufficiently sensitive for reliably detecting ectopic tendons. Especially in patients experiencing shoulder pain and stiffness in whom the commoner pathologies have been ruled out the possibility of ectopic PMT should be kept in mind and ruled out.

Classification of unusual insertion of the pectoralis minor muscle

PURPOSE

The pectoralis minor muscle (PMi) generally originates from the third, fourth, and fifth ribs and inserts on the medial and superior margins of the anterior portion of the coracoid process. Variations in the shape and attachment point of the PMi could cause discomfort in the shoulders. The aim of this study was to observe the types of morphological insertion patterns and attachment sites of the PMi.

METHODS

Seventy-four sides of fresh, embalmed Korean (42 sides; mean age 78 years) and Thai (32 sides; mean age 78 years) cadavers were dissected to analyze the morphological insertion types and attachment sites of the PMi.

RESULTS

Unusual insertion patterns were evident in about 23% of the samples. When the portion of the PMi tendon ran over the coracoid process, the most common attachment site was the glenohumeral joint capsule. We also confirmed the attachment of the PMi to the clavicle. Costal attachments of the PMi that extend from the second rib to the fourth rib were observed frequently as well.

CONCLUSIONS

Unusual insertion patterns of the PMi are common. Some authors consider that tendon attachment to the joint capsule can cause shoulder pain. In addition, the PMi tendon could be utilized in acromioclavicular joint reconstruction. Surgeons need to be aware of the possibility of a PMi variant being found during surgery even when this is not visible in magnetic resonance or ultrasound imaging.