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.