| Background:Humeral shaft fracture means what happens in humerus surgical neck below1~2cmto2cm on the humerus condyle, often in the middle of backbone, followed by the lower,upper fracture happens to a minimum. The main cause of this fracture is direct,conduction, rotational violence. The clinical investigation shows, humeral shaft fracturesare more common in adults around30years old, and they can cause transverse fractures,comminuted fracture or even a multi-stage fracture by high energy injury. In addition,muscle severecontractions can lead to the lower part of humerus fracture in1/3, whichmay cause a typical spiral fracture.At present, the most of the humeral shaft fracture is treated by manual reduction plussmall splint external fixation, elbow flexion long plaster castandorthosis, In addition, theuse of intramedullary nails, steel plate internal fixation has obtained the good effect insurgery, but some drawbacks restrict the use of this methods, such as higher risk forcomplications and highly invasive operations. With the development of minimallyinvasive techniques, minimally invasive plating osteosynthesis（MIPO）has gradually introduced into the treatment of humeral shaft fractures, This treatment also has somecomplications at the same time when it make the better effect. Therefore, our researchfocus on the improvement of the minimally invasive fixation and the surgical operationmethod, in order to reduce the occurrence of complications.Objective:1．To investigate the feasibility of indirect healing model in rats with closed humeralshaft fractures by minimally invasive plating osteosynthesis（MIPO）and bridgingfixation.2．To identify the danger zone for the minimally invasive plate osteosynthesis (MIPO)technique in the treatment of humeral shaft fractures by the anterior approach.3．To observe prospectively the clinical results of the patients with mid-distal humeralshaft fractures by minimally invasive plating osteosynthesis（MIPO）.4．To compare the clinical results of two groups of patients with mid-distal humeral shaftfractures: those treated with minimally invasive plating osteosynthesis（MIPO）and theother treated by conventional open reduction and plating osteosynthesis.Methods:1．By using random Numbers,30mature SD rats were divided into three groupsatrandom.The closed fracture model of humeral shaft fracture for experimental rats wereestablished. A group（n=10）:Humeral shaft fractures were fixed by MIPO; B group（n=10）:the fractures were fixed by intramedullary nailing; C group（n=10）:thefractures were not fixed. At postoperative14and28days, the affected extremity wereexamined by radiograph in order to evaluate the fracture healing. And two animalswere sacrificed in each group, and the affected humerus specimens were cut and sliced.HE staining were used for histological observation.2．18arms of fresh cadavers were fixed with10-hole locking compression plate (LCP) byanterior approach using the MIPO technique，the average length of humerus were29.7±1.2cm. Two locking screws on each end were fixed by the open technique; the rest ofthe screws were inserted percutaneously. The arms were dissected both anterior and posterior to identify musculocutaneous and radial nerve injuries.The length from theposterior tip of the acromion process to the lateral epicondylewhich is commonlyknown as the elbow length determines the size of humerus. According to lateralepicondyle or humeral length，damage or direct contact of the locking screws to themusculocutaneous or radial nerve was recorded.3．34patients with mid-distal humeral shaft fractures were treated by MIPO. Alsorecorded were the fracture union time. At final follow-up, shoulder function wasassessed using the University of California at Los Angeles (UCLA) scoring system.Elbow function was assessed using the Mayo elbow performance index(MEPI).Inaddition, range of motion of affected shoulder and elbow were measured.4．34patients with mid-distal humeral shaft fractures were retrospectively analysed anddivided into two groups. Group A (n=17) patients were treated by MIPO and group B(n=16) by conventional plating. The operative time was collected. Also recorded werethe fracture union time. At final follow-up, shoulder function was assessed using theUniversity of California at Los Angeles (UCLA) scoring system. Elbow function wasassessed using the Mayo elbow performance index(MEPI).In addition, range ofmotion of affected shoulder and elbow were measured.Results:1．At postoperative14days, the occurrence of fracture healing for three group was10%(1/10),10%(1/10) and0%(0/10), respectively. At28days after the surgery, theoccurrence of fracture healing for three group was100%(8/8),75%(6/8) and25%(2/8),respectively. The fracture sites for animals with nonunion showed malformations,pseudarthrosis and abnormal activities. There was a significant difference for theoccurrence of fracture healing during three group（χ2=23.604，P=0.000）. Theoccurrence of fracture healing in C group was lower than B or A group（PAC=0.000,PBC=0.000, respectively）, but statistical difference was not found between B and Agroup （χ2=0.571， P=0.450）. For histological observation, mesenchymal cellproliferation of germinal layer in Periosteum, chondrocytes and osteoblasts gathering around the fracture sites and producing cartilage matrix and osteoid were fond atpostoperative14days. At28days after the surgery, cartilage matrix and osteoidgradually were replaced by the bone tissue in animals with fracture healing; theactivity performance of osteoblasts was reduced，and fibrous tissue hyperplasia shownactive proliferation in animals with nonunion.2．The danger zone for musculocutaneous nerve injury averaged5.5-12.7cm,the averagelength were7.15cm from the lateral epicondyle among the eighteen arms of freshcadavers (18.4%to42.7%of the humeral length，average percentage of27.75%）. Thedanger zone of the radial nerve injury averaged10.8-17.6cm,the average length were15.3cm (36.4%to59.2%of the humeral length, average percentage of51.17%),as thetwo holes with the screws contact of radial nerve injury, the distance from the lateralepicondyle of the humeruswhich is equal to radial nerve injury distance betweenscrews and external humeral epicondylitis, the average length lie14.3–15.8cm,47.2%、53.2%to the average percentage of radial nerve injury distance betweenscrews and external humeral epicondylitis and the humeral length,respectively.3．The mean operation time was85.3±18.6minutes. Iatrogenic radial ormusculocutaneous nerve palsy were not found. The average follow-up time was13.5±3.5months.The mean fracture union time was14.2±3.5weeks (range10–18weeks).All fractures in this group are healing, without infection, internal fixation failure andother complications.The mean UCLA and MEPI was improved from87.5±3.8and31.2±5.6before the surgery to31.6±1.9and97.2±4.1, respectively (tUCLA=3.974,PUCLA=0.000；tMEPI=5.668,PMEPI=0.000).4．The mean operation time in group A was92.4±57.7minutes and103.1±31.1minutesin group B (t=0.662, P=0.513),which means the operating time in group A is shorterthan group B. Iatrogenic radial nerve palsy in group A was0%(0/17) and31.3%ingroup B (5/16(t=6.261, P=0.012). The mean fracture union time in group A was15.3±4.1weeks (range8–24weeks), and21.3±13.7weeks (range10–58weeks) ingroup B (t=1.722, P=0.095). The mean UCLA end-result score in group A was34.8±0.6points (range33–35), and34.4±1.4points (range30–35) in group B (t=1.056, P=0.299). The mean MEPI in group A was99.4±2.4points (range90–100) and99.7±1.3points (range95–100) in group B (t=0.407, P=0.687).Conclusions:1．The MIPO and bridging fixation method can successfully establish the indirect healingmodel in the rats with closed humeral shaft fracture.This animal model is expected tothe use of the experimental study.2．From this cadaveric study, the danger zone for the musculocutaneous and radial nervescould be determined as a percentage of the humeral length or distance from the lateralepicondyle. Since the zone with radial or musculocutaneous nerve injuries may helpsurgeons avoiding nerve injuries during MIPO in the treatment of humeral shaftfractures by the anterior approach.3．Mid-distal humeral shaft fractures in1/3could be safely and effectively treated withthe MIPO, there are shorter fracture union time and lower incidence of iatrogenicradial nerve palsies by this surgery,4．Mid-distal humeral shaft fractures in1/3could be safely and effectively treated withthe MIPO. Compared with ORIF,MIPO have shorter fracture union time and lowerincidence of iatrogenic radial nerve palsies, but the two operations have the samecurative effect. |
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