Comparison of Fusion, Subsidence, and Clinical Results Between 3D-Printed Porous Titanium Cage and Polyetheretherketone Cage in Posterior Lumbar Interbody Fusion: A Minimum of 2 Years Follow-Up

Osteoinduction is the process by which osteogenesis is induced. It is a phenomenon regularly seen in any type of bone healing process. Osteoinduction implies the recruitment of immature cells and the stimulation of these cells to develop into preosteoblasts. In a bone healing situation such as a fracture, the majority of bone healing is dependent on osteoinduction. Osteoconduction means that bone grows on a surface. This phenomenon is regularly seen in the case of bone implants. Implant materials of low biocompatibility such as copper, silver and bone cement shows little or no osteoconduction. Osseointegration is the stable anchorage of an implant achieved by direct bone-to-implant contact. In craniofacial implantology, this mode of anchorage is the only one for which high success rates have been reported. Osseointegration is possible in other parts of the body, but its importance for the anchorage of major arthroplasties is under debate. Ingrowth of bone in a porous-coated prosthesis may or may not represent osseointegration.

Spinal interbody fusion is a standard and accepted method for spinal fusion. Interbody fusion devices include titanium (Ti) and polyetheretherketone (PEEK) cages with distinct biomechanical properties. Titanium and PEEK cages have been evaluated in the cervical and lumbar spine, with conflicting results in bony fusion and subsidence. Using Preferred Reporting Items for Systematic reviews and Meta-analyses (PRISMA) guidelines, we reviewed the available literature evaluating Ti and PEEK cages to assess subsidence and fusion rates. Six studies were included in the analysis, 3 of which were class IV evidence, 2 were class III, and 1 was class II. A total of 410 patients (Ti-228, PEEK-182) and 587 levels (Ti-327, PEEK-260) were studied. Pooled mean age was 50.8years in the Ti group, and 53.1years in the PEEK group. Anterior cervical discectomy was performed in 4 studies (395 levels) and transforaminal interbody fusion in 2 studies (192 levels). No statistically significant difference was found between groups with fusion (OR 1.16, 95% C.I 0.59-2.89, p=0.686, I2=49.7%) but there was a statistically significant the rate of subsidence with titanium (OR 3.59, 95% C.I 1.28-10.07, p=0.015, I2=56.9%) at last follow-up. Titanium and PEEK cages are associated with a similar rate of fusion, but there is an increased rate of subsidence with titanium cage. Future prospective randomized controlled trials are needed to further evaluate these cages using surgical and patient-reported outcomes.