This article aims to summarize the anatomical characteristics of the medial approach for proximal humeral fractures, of which the study of arteries is the most important. PCHA may play a more important role than ACHA in preventing AVN because of its larger diameter and less variation. Earlier anatomic dissection studies indicated the vascularization of humeral head was mainly through the ACHA while the PCHA vascularized only a small part of the head . But this result could not explain the absence of necrosis in the cases of severe fracture as the ACHA is vulnerable is such cases. Another study shows that humeral head can be completely perfused after ligation of ACHA . In another quantitative assessment of the vascularity, PCHA provided 64% of the blood supply while the ACHA only supply 36% . First, the small diameter of the ACHA (0.3mm-2mm) in comparison to that of the PCHA (1.2-5.5mm) is also funded by other studies [24, 26, 28]. Second, in clinical study of treatment for complex PHFs, no intact ACHA were found in 16 cases except 1 patient But successful fracture healing was achieved in all 17 cases . Last, Natalie Keough et al emphasized the variations exist for the course of the ACHA, which suggest a more significant contribution from the PCHA to the epiphysis . In our study, a separate origin for the ACHA and PCHA was 84.3%. This is consistent with their study. So, the role of the PCHA is revalued as its distinctive branches penetrating the region of the bone cartilage area.
Given the anatomical features of ACHA, we hypothesized that the integrity of ACHA has been lost in complex PHFs as the ACHA was firmly attached to the subscapularis tendon . While the ACHA has been lost, extent dissection of periosteum by deltopectoral approach will increase the risk of necrosis as the vascular supply to the callus area is derived mainly from the surrounding soft tissues. Instead, the medial approach does not require excessive dissection because of its loose subcutaneous tissue. Besides, the longitudinal incisions on the medial side contribute to the concealment of the incisions and have little effect on cutaneous blood supply and cutaneous nerves without any flap. If the ACHA is intact, preoperative localization of ACHA can be of great help to the operation. Method of guiding the quick access to ACHA by landmarks have been proposed . In this study, the distance from ACHA to coracoid was 49.2 mm, which was consistent with our study. This technique provides favorable guidance for preoperative localization of ACHA. CTA can be used to determine the continuity of artery before surgery but is often not used routinely due to its high cost and unclear development (Fig. 7). In addition, Location of the ACHA by intraoperative ultrasound is possible due to the loose subcutaneous tissue in the medial upper arm as using intraoperative ultrasonography in treatment of acute achilleas tendon rupture yield less surgical time .
The entry point of arcuate artery, which regard as an important intraosseous anastomosis, is in the outer upper quadrant of the humeral head . We also find there are no nutrient arteries from PCHA and ACHA in medial side. Based on the above observation, the interval between ACHA and PCHA is practicable for the placement of medial plate. The variation of the origin of PCHA is also noteworthy. According to literature reports, the typical PCHA accounted for 77.1%, PCHA arises from SSA accounted for 12%, PCHA arises from DBA accounted for 8.4% .These data in our observations are 86.8%, 10.5% and 2.6% respectively. When the PCHA arises from the subscapular artery, its origin is located proximal to the typical type. We think it is safer because the deeper course of PCHA. But when it comes from the deep brachial artery, the interval between ACHA and PCHA is limited.
Compared to other nerves, the musculocutaneous nerve is the only nerve that requires special attention in medial approach. The medial brachial cutaneous nerve is away from the incision because it pierce the fascia at about 15 cm proximal to the medial epicondyle . We found that the axillary nerve was generally located behind the PCHA, so the medial approach did not increase the risk of axillary nerve injury. It is reported that shoulder abduction could protect the axillary nerve and radial nerve when working near the latissimus dorsi tendon insertion . The musculocutaneous nerve is the only nerve that normally appears in the surgical area. The exposure of the operative field is influenced by the distance between its origin from the brachial plexus and its afferent coracobrachialis muscle, and by its position with the ACHA. We divide the musculocutaneous nerves into three categories. Type I. The entry point is proximal to the artery. Type II. The entry point is located adjacent to the artery (musculocutaneous nerve intersects with ACHA). Type III. The entry point is located distal to the artery. In this research, 65.8% fits type I. As all the musculocutaneous nerve should be pulled laterally to facilitate the placement of the implant during surgery, so the type I and type III is beneficial to surgery. In a study on the relationship of the musculocutaneous nerve, approximately 83% entry points that musculocutaneous nerve penetrates the coracobrachialis were shorter than 5cm from the humeral head . This is consistent with type I in this article, and the proportion is even higher.
The conjoined tendon of the latissimus dorsi and teres major muscles needs to be cut off. But its function is almost unaffected because Modified L’Episcope procedure have been proposed .The follow-up shows that active internal rotation remained unchanged (7.6 ± 2.0 compared to 7.5 ± 2.4). So, the dissection of the conjoined tendon will not affect the function of the shoulder.
Current implants are not successful in treating complex fractures. 22%-23% failure rate of the locking screw construct has been reported . It is agreed that intraoperative anatomic reduction and restoration of the medial cortical support are the essentials for successful surgical fixation of proximal humerus fractures [22, 41, 42].Without anatomic reduction or inferomedial screws, placing locked plates from a lateral tension-band position may lead to early loss of reduction and cutout of the locking screws can cause severe cartilage damage [21, 43, 44]. The medial approach can reduce the fracture fragments under direct vision. A varus deformity may lead to secondary screw perforations changes the pretension of the rotator cuff .
There are several ways to strengthen the medial column. Michael J et al. provide compressive strength to a comminuted medial column by using a fibula allograft, which showed encouraging results in both clinical and biomechanical. The drawbacks associated with its use are limited supply, high cost, and infection risk, as the axillary nerve need separate from the deltoid for consistently exposure. Dual plate techniques with PHILOS plate and VA-LCP distal radius plate have been used for severely fractures of PHF. However, its clinical prognosis and effects on the posterior rotation brachial artery and axillary nerve are still controversial.
The parallel double plate fixation showed significantly greater integral and stiffness in biomechanical test [23, 46]. The “arch” structure of parallel placement gives the comminuted or osteoporotic bone intrinsic stability . This fixation is also suitable for the treatment of PHF because of its eccentric-load and cancellus-filled structure. The parallel system provided higher stability under physiological load [48, 49]. The perpendicular plating has a lower stress on the deformation of the opposite side, while the parallel system, like i-type curved beam, can compensate for each other.
About indication, unstable medial cortical reconstruction have been proposed . Beside 3- and 4-parts fractures, any medial cortical deficiency can be restored through a medial approach. Poor prognosis with PHILOS is associated with osteoporosis, so the patient's age, gender, job and other factors should be considered. The metaphyseal bone of the humeral head has been described as an egg shell as there is little bone in the center of the head . Tingart et al. found the cortical bone mineral density was 15% higher in the lesser tuberosity region compared to the greater tuberosity region [50, 51]. This provides a theoretical basis for the good purchase of the medial plate. Double plate interlocking also provides higher overall stability. In the case of coracoid process injury, dislocation and other injuries, related tissue repair can also be carried out through the medial approach under direct vision. Short calcar segment (8 mm), Disrupted medial hinge (2 mm dislocation), and some fracture pattern predict of ischemia of humeral head . The imaging evidence is consistent with injury to the ACHA. In such cases, the medial approach is no longer limited by ACHA, and the exposure is more sufficient. If medial support is selected, the medial approach will stimulate the soft tissue less than the deltopectoral approach.
There are still several deficiencies in this research. First, the influence of age, gender, occupation and races affected the anatomical structure is not considered. Other specifications were also ignored for the scope of this study, including how height, weight correlate to the distances measured. Second, the average area of exposure of deltoid-splitting, deltopectoral approaches were 1404.39 mm2, 1325.41mm2 respectively . The extent of exposure from the medial approach remains to be studied. Third, results are limited by the number of specimens and measurement errors. Accurate assessment of risk requires more clinical validation.