The study was approved by the hospital's ethics committee. In all, 13 adult cadaver arms (8 left arms and 5 right arms) were used. The donors had no history of deformity or upper extremity surgery. First, the medial epicondyle was palpated, and the skin was cut 3–4 cm proximal to the medial edge of the intermuscular sulcus of the biceps. Then, the gap between the biceps and triceps was determined, the basal vein and the medial cutaneous nerve of the forearm were identified and protected, and the brachial muscle fascia was cut to expose the anteromedial surface of the distal humerus. The brachialis muscle was retracted laterally to protect the anterior blood vessels and nerves, while the triceps brachii protected the posterior ulnar nerve. Then, the pronator teres muscle was retracted medially to expose the upper part of the medial condyle of the humerus and allow steel plate insertion.

The locking compression plate (LCP) was placed on the skin, and the location of the incision at the proximal humerus was determined. By palpation, the gap between the proximal end of the proximal biceps and the deltoid muscle was determined. After the skin was cut, the long head of the biceps brachii tendon was identified, the long head of the biceps brachii tendon was retracted to the outside, and dissection was continued down to the proximal anteromedial surface of the humeral shaft.

The 12-hole LCP was inserted with a locking drill sleeve through the distal incision. Under the brachialis, a soft tissue tunnel was established on the anteromedial side of the humerus. The plate was inserted and positioned with two locking sleeves on the anteromedial surface of the humerus (Fig. 1).

This figure shows proximal (blue arrows) and distal (green arrows) incisions of the right arm and diagrams of the plane of dissection. Red arrows indicate the the medial epicondyle

The relevant measurements were as follows: (1) the mean distance from the medial condyle to the base of the coronal fossa (each specimen was measured three times, and the average was calculated) (Fig. 2); (2) the vertical distance from the vertex of the medial epicondyle to the median nerve (Fig. 3); (3) the length of the humerus from the greater tuberosity to the apex of the lateral condyle; (4) the distance from the medial epicondyle to the lateral epicondyle of the humerus; (5) the distance from the vertex of the epicondyle parallel to the long axis of the humerus to the intersection of the median nerve and the distal end of the underlying steel plate, namely, the safe area for distal screw placement (Fig. 4); (6) parallel to the long axis of the humerus, the distance from the medial base of the humeral head to the intersection of the median nerve and the proximal end of the underlying steel plate, namely, the safe area for proximal screw placement (Fig. 5); (7) located on the medial epicondyle, the distance between the tip of the bicortical screw and the ulnar nerve, which is crossed by the distal end of the plate with four screws; and (8) the distance between the olecranon fossa and the tip of the four screws at the distal end of the plate in the medial humeral epicondyle (Fig. 6 and Tables 1, 2, 3).

This figure shows the distance from the medial condyle to the base of the coronal fossa (a). The green area represents the single-cortical fixation area for screws in the medial epicondyle region of the humerus

This figure shows the vertical distance from the vertex of the medial epicondyle to the median nerve (a). The pentagrams indicate the median nerves. Triangles indicate ulnar nerves

This figure shows the distance from the vertex of the epicondyle to the intersection of the median nerve and the distal end of the underlying steel plate (a). Green areas represent the safe area where the screw is placed at the distal end. The pentagrams indicate the median nerves. The triangles indicate the ulnar nerves. The red arrows indicate the medial epicondyle

This figure shows the distance, parallel to the long axis of the humerus, from the medial base of the humeral head to the intersection of the median nerve and the proximal end of the underlying steel plate (a). The green areas indicate the safe area for screw placement (a and c). The blue arrow indicates the long head of the brachii tendon. Percutaneous screw fixation is not suitable between the distal and proximal incisions (b; the red areas)

A The distal end of the plate with four screws crosses the distance between the tip of the bicortical cortex and the ulnar nerve. B The distance between the olecranon fossa and the tip of the four screws (regions a–d) at the distal end of the plate in the medial humeral epicondyle. The red area (e) represents the olecranon fossa and the articular surface of the olecranon

The study was reviewed and approved by the institutional ethics committee, and informed consent was obtained from all patients. Twelve patients with humeral shaft fractures treated with anteromedial MIPPO from 2017 to 2020 were selected. The mean patient age was 53.67 ± 16.60 years (range 26–82 years). There were 6 males and 6 females, 9 cases on the left and 3 cases on the right. All patients were treated with minimally invasive anteromedial LCP fixation. The inclusion criteria were as follows: (1) diagnosis of unilateral closed humeral shaft fracture by imaging examination; (2) no neurovascular injury; and (3) patient consent to undergo surgery. The exclusion criteria were as follows: (1) pathological fracture; (2) associated nerve injury; (3) open fracture; (4) history of mental illness or cognitive impairment; or (5) severe systemic disease resulting in an inability to tolerate surgery.

Anesthesia was established by supraclavicular nerve block. The patient was placed in the supine position with 90° arm-to-shoulder extension and forearm supination. The proximal and distal incisions were made as described above, and the plate was inserted distally. By palpation, the spaces between the proximal end of the proximal biceps and the pectoralis major were determined.

When the arm is extended 90°, the pectoralis major is parallel to the humeral axis. After the skin is cut, the pectoralis major pulls laterally, the long head of the biceps brachii pulls medially, and there is enough space under the long head of the biceps brachii to place the LCP (Fig. 7). Typical cases are shown in Figs. 8 and 9.

This figure shows the positional relationship between the plate and the biceps brachii in the proximal incision. The blue pentagrams represent the long head of the brachii tendon. The blue arrow represents the LCP

This figure shows a typical case. The patient fell while walking down stairs and sustained a middle fracture of the right humeral shaft. A–B Preoperative X-rays. C–D X-rays taken 3 months after surgery, with full recovery of function. E Proximal (blue arrow) and distal (green arrow) incisions. The incision is on the medial side, so the distal scar from the surgical incision is more hidden. F Three months after surgery, with full recovery of function

A typical case. The patient fell while walking down the stairs and sustained a middle fracture of the humerus (left side). A–B Preoperative X-rays. C–D X-rays taken 4 months after surgery

After surgery, the forearm was suspended for 2 weeks, and the shoulder and elbow joints were moved passively. After 2 weeks, the shoulder and elbow joints were gradually allowed to become active. Strength exercises were performed after X-ray examination showed a bone bridge at the fracture site. None of the patients included in this study developed an iatrogenic nerve injury. X-ray examination was performed within 3 days after the operation, and an outpatient review was performed every 6 months after the operation. The Disability of Arm, Shoulder and Hand (DASH) score was used to evaluate postoperative recovery.

In accordance with the wishes of 1 patient, the internal fixation was purely an elective removed without complications 24 months after surgery. We entered along the original incision and pulled the steel plate from the distal incision. The removal process was smooth and did not cause neurovascular damage; additionally, there were no tissue adhesions that were difficult to remove.

The intraoperative blood loss (ml), operation time (minutes), fracture healing time (months), follow-up time (months), and DASH score were evaluated (Table 4).

IBM SPSS statistics (version 25.0) was used for statistical analysis. Data are presented as the average ± standard deviation (SD).