Biomechanical effects of a novel hollow pedicle screw in the minimally invasive treatment of Kümmell disease: a finite element study

Abstract

Background Vertebral augmentation is the preferred treatment for Kümmell disease (KD), but there exists a risk of cement displacement resulting in severe back pain and exacerbation of kyphosis. The study aimed to investigate and evaluate the biomechanical behavior of a novel hollow pedicle screw in the minimally invasive treatment of Kümmell disease by finite element (FE) analysis. Methods A finite element model of the thoracolumbar T12-L2 vertebral bodies of a KD patient treated with PKP was established. Part of the bone tissue of the T12 vertebral body was removed to simulate the intravertebral vacuum cleft in the injured vertebra. Based on these, the FE model of KD was established. The finite element model was used to simulate the treatment of KD with three surgical methods. Including six models: Model 1 is the osteoporotic vertebral compression fracture vertebra with IVC; Model 2 is simply unilateral PKP; Model 3 is unilateral PKP combined with pediculoplasty; Model 4 is bilateral PKP combined with pediculoplasty; Model 5 is unilateral PKP combined with a hollow pedicle screw (PKP-HPS); Model 6 is bilateral PKP-HPS. In addition, under certain loading conditions, the maximum von Mises stress, and stress distribution of bone cement, vertebral bodies, intervertebral discs of the six models, and the bone cement displacement of the postoperative models were analyzed and compared. Results Finite element analysis showed that the maximum von Mises stress of the T12 vertebra was reduced by almost 50% after the operation. Under the same conditions, the stresses of the bilateral operation models were less than those of the unilateral operation models, and the stress distribution of the bilateral operation models was more symmetrical than that of the unilateral operation model in discs, vertebral bodies, and bone cement. In addition, PKP-HPS models are superior to PKP combined with pediculoplasty models in reducing the stress on adjacent vertebral bodies and intervertebral discs after operation compared with the preoperative model and PKP alone. Besides, the M2 and M3 models showed significantly greater displacement than the other models, and M6 showed the smallest displacement. Conclusion Bilateral PKP-HPS has better stability in the treatment of KD, and can effectively avoid the loosening or displacement of bone cement. It can take advantage of simple PKP and PKP combined with pediculoplasty at the same time and can reduce the risk of vertebral re-fracture or collapse, adjacent vertebral fracture, and bone cement instability.