Abstract
Introduction The biomechanical properties of biologic cages made of femoral ring allograft in providing immediate stability for lumbar fusion as compared to bovine xenograft, titanium and polyethylether ketone (PEEK) cages are unknown. Biomechanical comparisons were done of lumbar constructs to determine their adequacy in providing immediate stability for fusion mass and demonstrate the need for supplemental posterior fixation.
Methods Fusion constructs were evaluated in 40 Merino sheep as lumbar spine models. Discectomy was performed on multisegmental specimens. Femoral ring allograft, bovine xenograft, titanium cage (Syncage) and Polyethylether ketone / PEEK cage (Plivios) were inserted. Dual X ray absorptiometry assessment of bone mineral content was performed .Testing was one for insertional torque and pullout strengths. Static testing consisted of flexion and extension 2Nm moment and100Nm compression load, bilateral axial rotation pure 5.5 Nm moment and lateral bending pure moments 1.1Nm moment and100Nm compression loads. Dynamic testing was done to detemine long term properties of the construct.
Results Interbody cages performed equivalently to femoral ring allograft. Bovine xenograft had lower stability compared to the rest. Posterior supplemental transpedicular fixation achieved increased stability in flexion, extension & lateral bending. Reduced stability was observed in all contructs with cyclical loading. The stabilizing effects were affected by the disc space distraction and facet joints. The titanium cage had significantly greater median pullout force compared to the others.
Discussion Femoral ring allograft is valid alternative to titanium and PEEK cages. It is able to provide adequate immediate stability. Supplemental posterior fixation resulted in further rigidity of the constructs.
The abstracts were prepared by Assoc Prof Bruce McPhee. Correspondence should be addressed to him at the Division of Orthopaedics, The University of Queensland, Clinical Sciences Building, Royal Brisbane Hospital, Herston, Brisbane, 4029, Australia.
