The ESP prosthesis is a one-piece deformable but cohesive interbody spacer. it provides 6 full degrees of freedom about the 3 axes including shock absorption (fig1). The prosthesis geometry allows limited rotation and translation with resistance to motion (elastic return property) aimed at avoiding overload of the posterior facets. The rotation center can vary freely during motion in this “silentblock” implant. It thus differs substantially from current prostheses. Surgeries were performed by 2 senior surgeons in 54 women and 34 men (1level in 72 cases, 2 levels in 3 cases, hybrid construct in 13 cases). Average age was 42 (SD: 7). Average BMI was 24.2kg/m2 (SD: 3,4). Clinical data and X-rays were collected at the preoperative time and at 3, 6, 12, 24, and 60 months post-op. The analysis was performed by a single observer independent from the selection of patients and from the surgical procedure. The radiological analysis at 60 months follow-up could be realized in only 76 cases because the quality of the dynamic Xrays was not sufficient in 12 patients. We measured the ROM and the location of mean center of rotation (MCR) of the implanted and adjacent levels using the Spineview® software. The MCR is considered to reflect the quality of movement of a segment; it is localized thanks its co-ordinates. X is expressed as a percentage of the length of the vertebral end plate, and Y as a percentage of the height of the posterior wall. The usual location of the MCR is in a circle, whose center is placed between 30 and 50% of the superior vertebral endplate of the vertebra below, and whose diameter is 70% of the vertebral endplate size.Introduction
Material and methods
