Introduction The purpose of this study was to evaluate the feasibility of the anteromedial minimally invasive plate osteosynthesis (MIPO) approach for distal third humeral shaft fractures and identify neurovascular structures at risk with this approach. Methods Twenty cadaveric arms were fixed with 12-hole precontoured narrow locking compression plates (LCP) with the anteromedial approach using MIPO technique. The proximal approach was done between the biceps and deltoid muscle directly to the bone. The distal approach involved elevating the brachialis from medial intermuscular septum. The plate was inserted beneath the brachialis tunnel from distal to proximal. Three locking screws were fixed at each end through incisions and the rest of screws were inserted percutaneously. The arms were then dissected to identify damage to or direct contact between the screws and brachial artery (BA), median nerve (MN), musculocutaneous nerve (MCN), and radial nerve (RN). The distances from the screws to structures at risk, humeral length, and length of three distal screws in mediolateral (ML) direction were measured. Results The average humeral length was 28.97 cm. The average danger zone for the BA and MN were 20.47%–62.66% of the humeral length from the lateral epicondyle, and 20.47%-75.02% for the MCN. The ulnar nerve was not endangered by this approach as it lies posteromedially to the humerus. The danger zone for the RN averaged 27.07%–43.74%, and the most dangerous screw that either penetrated or touched the nerve was at the fifth hole, which lay at 33.14% of the humeral length. The average length of three distal screws in ML direction were 41.4, 25.0 and 22.5 mm. Conclusions The anteromedial MIPO approach can be performed through the internervous plane beneath the brachialis muscle without exposing any nerves or causing any muscle splitting with a 12-hole plate. Both proximal and distal screw insertion must be done with direct exposure. Insertion of percutaneous screws in the middle part of the plate between the two incisions is not possible. This approach could be an alternative for extra-articular distal third humeral shaft fractures which provides less invasive surgical dissection, allows the use of longer distal screws, and achieves better cosmesis.
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