INTRODUCTION: People with sedentary work often suffer from low back pain. High spinal loads, sitting in one position for a long period of time, and whole‐body vibration are reasons for low back pain. However, sitting can vary greatly. One may sit on different types of seats such as stool, chair, physiotherapy ball or knee‐stool. The posture may also vary. The back may be leaned against a backrest, and the arms may be placed on armrests, on the thighs, on a desk or hanging laterally. The upper body may be relaxed or erected as well as inclined or declined. In a vehicle, the seat may vibrate at different intensity levels, frequencies and directions. All these parameters influence the spinal load. The aim of this study was not only to measure the loads on a vertebral body replacement (VBR) while sitting but also to determine the influence of several parameters on the implant force.
METHODS: Telemeterized VBR were implanted into 5 patients with a compression fracture of a lumbar vertebral body. The loads on the implant were measured while the patients were sitting on different types of seats in various postures.
RESULTS: Compared to sitting on a stool, the force was on the average 7% higher when sitting on a physiotherapy ball and 19% lower when sitting on a knee‐stool. Without leaning at a backrest, the force was less than 10% lower for sitting on a chair, an office chair or a bench. A padded wedge on a stool reduced the force by 10%. Leaning against the backrest led to a force reduction of 36%. Placing the arms on the thighs reduced the load on the average by 19% compared to when arms were hanging. An inclination of the upper body by 15° increased the force by 20%, while whole‐body vibration increased it by approximately 50%.
DISCUSSION: The measured force varied considerably during sitting, depending on the type of seat and the posture. Leaning against a backrest, declining the upper body, and supporting the body with the arms strongly reduced the loads.