ABSTRACT
Objective:To investigate the effect of a degradable high-purity magnesium screw in fixing the greater trochanter bone flap of a lateral circumflex femoral artery transverse branch in the treatment of ischemic necrosis of femoral head in young and middle-aged adults.Methods:From February 2017 to February 2019, 12 cases (15 hips) of young and middle-aged patients with avascular necrosis of femoral head were treated in the Department of Orthopaedic of Affiliated Zhongshan Hospital of Dalian University. The age of patients was 30-53 years old. According to Association Research Circulation Osseous (ARCO), 2 hips were graded in stage II b, 4 in ARCO II c, 1 in ARCO III a, 5 in ARCO III b, 2 in ARCO III c and 1 in ARCO IV. The greater trochanter bone flap with a lateral circumferential vascular branch was used to fill the necrotic area, and fixed by a biodegradable high purity magnesium screw in the bone flap transfer. At 3, 6 and 12 months postoperation, the patient came to the hospital outpatient clinic for follow-up, and then were reviewed once a year. Imaging efficacy was evaluated by comparing preoperative and postoperative imaging. The Harris score and Visual Anoalogue Scale (VAS) score were tested at 12 and 24 months after surgery. The Harris score and VAS score before and after surgery were compared by Friedman test, and P<0.05 was considered statistically significant. Results:All 12 patients (15 hips) were entered in the 24-36 months of follow-up. At 12 and 24 months after surgery, Harris score was found at 87 (86, 92) and 90 (87, 92) respertively, which were both higher than that before surgery [59 (52, 74)] with a significant statistical difference ( Z=-3.743, Z=-4.473, P<0.05). However, there was no significant difference in Harris scores between 12 and 24 months after the surgery ( Z=-0.730, P>0.05). At the 12 and 24 months after surgery, VAS score was found at 3 (2, 3) and 2 (1, 3) respertively, which were both lower than that before surgery [6 (5, 6) ] with a significant statistical difference ( Z=-3.560, Z=-4.656, P<0.05). There was no statistical difference in VAS scores between 12 and 24 months after surgery ( Z=-1.095, P>0.05). X-ray and CT scan showed that the bone flaps healed well and the areas of osteonecrosis were repaired. Thirteen femoral heads were in good shape, and 2 femoral heads had further collapse of hips. No patients underwent joint replacement surgery at the time of last follow-up. Conclusion:Fixation of the greater trochanter flap of lateral circumflex femoral artery transverse branch with a degradable high-purity magnesium screw can ensure the healing of the flap at the implantation site and avoid the displacement and shedding of the flap. It is a new therapeutic option to treat the avascular necrosis of femoral head of young and middle-aged people.
ABSTRACT
Objective To compare the in vivo degradation rates of two different kinds of high purity magnesium bone screws by animal experiments, so as to make some suggestions on structural design of high purity magnesium bone screws. Methods High purity magnesium bone screws with threads and without threads were implanted into femoral condyles of New Zealand rabbits separately. Twenty-four rabbits were randomly divided into 3 groups. They were euthanized at 8, 12 and 16 weeks after operation, respectively. The in vivo degradation rates of bone screws with two different shapes were compared through micro-CT scanning and Skyscan CT-analyser software, and the stress changes during the progress of bone screw degradation were analyzed. Results The initial surface area of threaded screws ［(31.70±0.06) mm2］ was significantly greater than that of the non-threaded ones ［(29.56±0.22) mm2］. After 8, 12 and 16 weeks, the volume loss ratios of the threaded screws were (26.01±3.44)%, (33.35±5.05)%, (36.84±6.99)%, respectively, and the volume loss ratios of the non-threaded screws were (22.53±4.78)%, (31.12±6.59)%, (43.22±9.31)%, respectively. At the same time point, there were no significant differences in the volume loss ratio between two kinds of screws. The relationship between the volume reduction and the implantation time was linear for non-threaded screws and gradually decreasing for threaded screws. Conclusions Under the low-bearing condition, different structural design for high purity magnesium screws has no obvious effect on their degradation rate in vivo.
ABSTRACT
Objective To study the effects of mechanical load on in vivo degradation performance of high-purity magnesium (HP Mg, 99.99 wt.%) quantitatively. Methods Cylindrical Mg specimens, with a 2 mm diameter and a 14 mm length, were mounted in polyetheretherketone (PEEK) rings to bear compressive stresses ［（6.2±0.6） MPa］, tensile stresses ［（4.6±0.1） MPa］ or no stress (as control). The specimens under different stress states were implanted subcutaneously in dorsal abdominal regions of SD rats for 4 weeks. The mass loss, residual volume and surface morphology of the specimens and staining of surrounding soft tissues were used to analyze the degradation rate of HP Mg. Results Specimens and rings were completely encapsulated by membranous tissues after implantation for 4 weeks. No significant differences in the degradation rates were noted between specimens bearing stress and the control. The corrosion layers of specimens under each stress state were uniform. Conclusions The compressive and tensile stresses (4-6 MPa) could not affect significantly HP Mg degradation performance in vivo. The research findings provide theoretical references for the design and clinical application of Mg-based degradable implants.