BIOMECHANICAL FEATURES OF COMMINUTED HUMERAL SHAFT FRACTURES

Abstract

Humeral shaft fractures make up from 3 to 5 per cent of the general number of fractures. There is a distinct bimodal age distribution of the patients with diaphyseal humeral fractures. Most cases are found among men aged 21-30 years and elderly women aged 60-80 years. Biomechanical peculiarities of bone fragment displacement in the humeral shaft fractures are an important component of the further planning of the patient’s treatment and rehabilitation. The aim of this article is to assess possible variants of bone fragment displacement and determine the role of the muscle component on the displacement vector in the fractures at different levels of the humeral bone shaft. Materials and methods. The study included 50 patients aged from 18 to 78 with comminuted fractures of the humeral shaft. Patients aged from 55 to 78 dominated according to the age distribution, with 68 per cent. In most cases (62 per cent), comminuted fractures were caused by a certain low-energy traumatic factor. 60 per cent of the patients were hospitalized within the first 24 hours after the traumatic injury. According to the A. O. Müller classification, 12B-type fractures constituted 72 per cent of the total number, and 12C made up 28 per cent. Operative treatment was performed on for 76 per cent of the patients, conservative treatment – for 24 per cent. The role of the muscle component on the bone fragment displacement has been determined according to the data of computer-assisted tomography and X-ray photography using the typical muscle insertion chart of the humeral fragment under the study. Reliable individual anatomic properties were determined intraoperatively. Results and discussion. The study included three groups of patients diagnosed with a comminuted humeral shaft fracture. The first group comprised elderly and senile patients with low-energy traumas. The second group included patients aged from 18 to 59 with low-energy traumas. The third group involved the patients with high-energy traumas. As the result, the study has demonstrated key muscles impacting the dislocation of bone fragments in multifragmental humeral shaft fractures including: deltoid, greater pectoral, coracobrachial, triangularis, biceps, brachial, and latissimus dorsi muscles. Based on the analysis of the clinical data, the study has shown the interrelations between the fracture level in low-energy traumas, age, and sex. Elderly and senile female patients have been found out mostly to experience fractures, which are distal to the deltoid muscle attaching point. Individuals aged 18 to 59 typically have the fracture located proximally to the deltoid muscle attaching point. The synergy of the adduction muscles impact on bone fragments in multifragmental fractures has been observed that should be taken into account when performing a closed reduction as well as during an operative intervention.