New precontoured long locking plate for proximal metadiaphyseal fractures of the humerus: a cadaveric study for its use with the minimally invasive technique

BACKGROUND: The purpose of this study was to identify nerves at risk when using a minimally invasive plate osteosynthesis precontoured long proximal humerus locking plate and to evaluate the risk of injury to deltoid insertion and brachialis muscle. METHODS: Ten cadaveric upper limb specimens were used. A transdeltoid anterolateral approach was performed proximally and a second anterior approach was performed distally. A 14-hole “low” long precountored ALPS locking plate (Biomet Trauma; Zimmer Biomet, Warsaw, IN, USA) was used. Subsequently, anatomic dissection to measure the anatomic relationship of the plate with the deltoid insertion, with the brachialis muscle, and with the axillary, radial, and musculocutaneous nerves was performed. RESULTS: The mean humeral length was 302 mm (standard deviation 52.3, 99% confidence interval: 259.3-344.6). In 6 specimens, the axillary nerve was located at the level of the third row of holes of the plate; in 3 specimens, at the level of the fourth row; and in one specimen, at the level of the second row. The distance between the plate and the musculocutaneous nerve was on average 10.2 mm (standard deviation 4, 99% confidence interval: 6.9-13.5) and between the plate and the radial nerve was on average 7.9 mm (standard deviation 4.7, 99% confidence interval: 4-11.8). The plate pierced the anterior distal fibers of the deltoid in all specimens. In 8 specimens, no brachialis muscle fibers were located under the plate. CONCLUSIONS: The use of the long precontoured 14-hole ALPS locking plate with the minimally invasive plate osteosynthesis technique, previously identifying the axillary and musculocutaneous nerves, is feasible; however, the distances between the plate and the nerves remain low, so caution should be maintained. Despite the curved design of the plate, the deltoid insertion is partially compromised in all cases.