New intervertebral disc respacing biomaterial: open porous, hydroxyapatite filled polymethylmethacrylate

In order to prevent secondary intervertebral joint arthrosis of the lumbar spine and to minimize scar tissue formation close to the nerve roots due to micro movements following a microsurgical discotomy, a blocking and open porous biomaterial has been developed. It is intended to adapt the implant stiffness to the bone stiffness. The spacer implant has to fulfill the following additional requirements: 1. easy to inject into the intervertebral disc space immediately following nucleotomy and within the same surgical procedure, 2. polymerizing and achieving primary segment stability within 10 minutes, 3. preventing excessive heat during polymerization, 4. controlled open porosity enabling bone ingrowth into the intervertebral disc spacer from the upper and lower terminal plates of the vertebrae. Therefore a polymethylmethacrylate bone cement (PMMA, Sulfix 6) was modified with a viscoelastic, non miscible water phase. Structural and/or mechanical results are compared with hydroxyapatite (poly D,L-lactide acid (PDLA) coated) filled bone cement and with a porous gel cement. The mechanical compression behavior of the stable artificial intervertebral disc (SAD) has been analyzed in a FEM model.