Biomechanical study of weightlifting behavior in L5 lumbar spondylolysis using finite element simulation

Lumbar spondylolysis is related to weightlifting. The biomechanics of lumbar spondylolysis in weightlifting and the connection between lumbar spondylolysis and muscles are still unclear. Therefore, this study clarified the influence of decreased muscle strength on lumbar spondylolysis through finite element (FE) analysis. We used computed tomography to scan the L1-S1 segment of the patient and constructed a three-dimensional FE model. Apply a moment of 7.5 N·m and a weight of 280 N at the top of L1 after fixing the sacroiliac joint. The dumbbell weight was set to 15 kg. Apply muscle strength and follower loads representing the muscles of the back and abdomen in the FE model. The back muscle strength was reduced to 50%. The results showed that L4 with incomplete lumbar spondylolysis under decreased muscle strength and L5 with incomplete lumbar spondylolysis under normal muscle strength had the higher range of motion (ROM) in the flexion stage (45°). The ROM of L4 was affected by the decreased muscle strength, and the ROM of L5 was affected by the lumbar movement. L4 and L5 of incomplete lumbar spondylolysis showed the greatest stress range changes in the lifting and the final stage, respectively. Stresses at L4 and L5 are affected by the defect and decreased muscle strength. This study shows that the ROM of incomplete spondylolysis is vulnerable to flexion during weightlifting. Decreased muscle strength leads to increased stress on the defect and adjacent segments in the lifting and final stages, which might aggravate the fracture.