The relationship of the lateral cord of the brachial plexus to the coracoid process during arthroscopic coracoid surgery: a dynamic cadaveric study.

BACKGROUND: Arthroscopic coracoid decompression is performed for coracoid impingement and has also been advocated for arthroscopic repair of tears of the subscapularis tendon, placing the lateral cord or the musculocutaneous nerve at risk of injury. The dynamic relationship of the lateral cord to the coracoid while the upper limb is in abduction and traction in the shoulder arthroscopy position is not clear.

PURPOSE: The purpose of this study was to evaluate the dynamic relationship of the lateral cord of the brachial plexus to the coracoid process during varying degrees of upper limb abduction in traction.

STUDY DESIGN: Descriptive laboratory study.

METHODS AND MATERIALS: The musculocutaneous nerves of 15 fresh-frozen cadaveric shoulders were carefully dissected and identified without mobilization of the nerve. The musculocutaneous nerve was then injected with radiopaque contrast mixed with methylene blue. The contrast would infiltrate retrogradely into the lateral cord, minimizing mobilization of the lateral cord. The specimens were mounted in the lateral decubitus position with 4.5 kg of traction to the forearm and anteroposterior radiographs were taken at 30 degrees and 60 degrees of abduction. The nearest distance of the lateral cord to the coracoid process was measured off the radiographs and the displacement with increase in shoulder abduction was determined.

RESULTS: The mean nearest distance between the lateral cord and the coracoid tip at 30 degrees of shoulder abduction was 26.6 +/- 5.2 mm and it moved nearer at 60 degrees of abduction to 23.4 +/- 5.1 mm; the difference of 3.2 mm was statistically significant (P < .0005, 95% confidence interval, 2.5-3.9 mm). The shortest distance measured was 14.4 mm in 1 specimen at 60 degrees of abduction.

CONCLUSION: The lateral cord moved closer to the coracoid process at 60 degrees than at 30 degrees of abduction under traction during simulated shoulder arthroscopy position using the lateral decubitus position.

CLINICAL RELEVANCE: The margin of safety for lateral cord injury during arthroscopic surgery around the coracoid process is improved with lower abduction angles in the lateral decubitus position.