Avulsion Fractures Osteosynthesis in Patients with Normal Bone Mineral Density and Osteoporosis

Objective: to compare the effectiveness of osteosynthesis for avulsion fractures using bioabsorbable versus titanium implants in patients differing in bone mineral density.

Material and Methods. In the experimental phase of study, two groups of bone blocks were singled out from patients' femoral heads to assess the anchoring properties of the implant in osteoporotic and healthy bone. The first group included blocks of 31 patients with osteoporosis, the second one — 27 blocks of patients without osteoporosis. In the first group, cortical bioabsorbable Poly-L-Lactic/ co-glycolic acid (PLGA) screws were implanted into 13 bone blocks, titanium screws — into 10 bone blocks, and bioabsorbable pins (PLGA) — into 8 bone blocks. In the second group, 10 titanium screws, 10 bioabsorbable screws and 7 bioabsorbable pins were implanted. The anchorage of the implant in bone was evaluated by a pull-out test. Then, depending on the anchorage used, the studied bone blocks with osteoporosis, newly obtained from the first group, were divided into three groups for the purpose of evaluating the resistance to the damaging effects of the implant. In experiment, the osteosynthesis for avulsion fracture was simulated on these bone blocks. In the first group (11 bone blocks), the transosseous osteosynthesis of the bone fragment was carried out with a titanium screw, in the second group (9 bone blocks) with a bioabsobable screw, in the third group (11 bone blocks) with a bioabsorbable pin. The results of osteosynthesis were assessed based on how often a small bone fragment was damaged by an implant and on stability of the anchored implant. In the clinical phase of study, a comparative analysis of 65 surgical interventions (38 people with osteoporosis and 27 without osteoporosis) in patients with avulsion fractures was performed. In 24 cases, bioabsorbable screws were used for osteosynthesis, AO/ASIF titanium screws were used in 31 cases, and pins were used in 10 cases.

Results. Experimental studies showed that the resistance to pull-out test of a bioabsorbable screw anchored in osteoporotic bone is 25.7% higher than a titanium screw. No statistically significant difference was found in bone without osteoporosis. Resistance to pull-out test of a bioabsorbable pin is 3% higher than a titanium screw. The model-based experiment with an avulsion fracture in osteoporotic bone using a titanium screw showed lower effectiveness of osteosynthesis: in 27.2% of cases the cortical titanium screw damaged a small bone fragment. Based on the clinical trial findings, no negative results were obtained using bioabsorbable anchorage. In 12.5% cases of osteosynthesis with a titanium screw, migration of a bone fragment was noted. The data obtained during the clinical study correlated with the experimental data. This makes the use of bioabsorbable implants advantageous.

Conclusion. For avulsion fracture osteosynthesis in patients with normal bone mineral density, it is possible to use both titanium and biodegradable fixators with equivalent strength of fragment fixation. n osteosynthesis of fractures in patients with osteoporosis it is preferable to use bioabsorbable implants