JR vertebral body prosthesis: A modular, anatomical and expandable device, with cage function and plate dual designed ad hoc for spine stabilization after corpectomy

Abstract

Introduction: due to the unsatisfactory results obtained with posterior instrumentations in cases of vertebral tumors and to the economical limitations of our patients for acquiring the systems available in the market, a vertebral body prosthesis to stabilize the spine after corpectomy was designed. Objective: to describe the structural and functional characteristics of the JR prosthesis, the biomechanical assays in cadaver and the surgical technique on the patient. Methods: firstly, it was performed a detailed anatomical study of the vertebral bodies. A design of a modular, anatomical and expandable device was obtained. Its components once assembled make an implant with expandable cage and plate dual function. Afterwards, a biomechanical assay was performed in a cadaver and the device was implanted in a patient with vertebral body metastasis. Results: the radiographs extracted from the cadaver after implant location did not show loss of fixation. When the cadaver was raised, flexion moments were generated laterally with levers 80 cm long; therefore, the prosthesis was demanded in its most vulnerable point with a force of approximately 588 N. With rotation, flexion and extensions forced, stability was preserved and no movement was observed. The device was implanted in a 50-year-old woman with metastatic thyroid cancer affecting L3. Pain improved in the postoperative immediate, as well as its motor function, which allowed her to walk with a stable and painless spine for seven years. No implant failure was observed. Conclusion: the dual cage function and plate integrated in a single device offers a mechanical advantage, compared with the cages and plates used separately, since the prosthesis design permits to apply a distraction axial force with lateral fixation at the same time, through one implant. The results of the implant placement in the patient were satisfactory.