Is lumbar facet fusion biomechanically equivalent to lumbar posterolateral onlay fusion?
OBJECTIVE This study was designed with the following research objectives: 1) to determine the efficacy of facet fusion with recombinant human bone morphogenetic protein-2 (rhBMP-2) on an absorbable collagen sponge (ACS) in an ovine lumbar facet fusion model; 2) to radiographically and histologically compare the efficacy of lumbar facet fusion with rhBMP-2/ACS to facet fusion with an iliac crest bone graft (ICBG); and 3) to biomechanically compare lumbar facet fusion with rhBMP-2/ACS to lumbar posterolateral fusion (PLF) with ICBG. METHODS The efficacies of the 3 treatments to induce fusion were evaluated in an instrumented ovine lumbar fusion model. Eight sheep had 10 cm3/side ICBG placed as an onlay graft for PLF at L2-3. At the adjacent L3-4 level, 0.5 cm3/side ICBG was placed for facet fusion. Finally, 0.5 cm3/side rhBMP-2/ACS (0.43 mg/ml) was placed for facet fusion at L4-5. CT scans were obtained at 2, 4, and 6 months postoperatively with 2 reviewers conducting an evaluation of the 6-month results for all treated spinal levels. All 8 sheep were killed at 6 months, and all posterolateral instrumentation was removed at this time. The spines were then sectioned through L3-4 to allow for nondestructive unconstrained biomechanical testing of the L2-3 and L4-5 segments. All treated spinal levels were analyzed using undecalcified histology with corresponding microradiography. Statistical comparisons were made between the treatment groups. RESULTS The PLF with ICBG (ICBG PLF group) and the rhBMP-2 facet fusion (rhBMP-2 Facet group) treatment groups demonstrated similar levels of stiffness, with the rhBMP-2 Facet group having on average slightly higher stiffness in all 6 loading directions. All 8 levels in the autograft facet fusion treatment group demonstrated CT radiographic and histological fusion. All 8 levels in the rhBMP-2 Facet group showed bilateral CT radiographic and histological fusion. Six of 16 rhBMP-2/ACS-treated facet defects demonstrated small intraosseous hematomas or seromas. Four of the 8 levels (50%) in the ICBG PLF treatment group demonstrated bilateral histological fusion. Three of 8 levels in the ICBG PLF treatment group showed unilateral fusion. One of the 8 levels in the ICBG PLF treatment group demonstrated bilateral histological nonfusion. CONCLUSIONS Both rhBMP-2/ACS and autograft demonstrated 100% efficacy when used for facet fusion in the instrumented ovine model. However, the ICBG PLF treatment group only demonstrated a 50% bilateral fusion rate. Biomechanically, the ICBG PLF and rhBMP-2 Facet groups demonstrated similar stiffness in all 6 loading directions, with the rhBMP-2 Facet group having on average slightly higher stiffness in all directions.
Department of Orthopaedic Surgery, The Medical College of Wisconsin Inc., Milwaukee, Wisconsin.
Jeffrey M
JM
Toth
Department of Neurosurgery, University of Tennessee Health Science Center, Memphis, Tennessee.
Kevin T
KT
Foley
Department of Orthopaedic Surgery, The Medical College of Wisconsin Inc., Milwaukee, Wisconsin.
Mei
M
Wang
Department of Clinical Sciences, Colorado State University, Fort Collins, Colorado.
Howard B
HB
Seim
Department of Clinical Sciences, Colorado State University, Fort Collins, Colorado.
A
A
Simon Turner
D020341:Absorbable Implants; D000818:Animals; D001696:Biomechanical Phenomena; D050071:Bone Density Conservation Agents / Q000008:administration & dosage*; D055396:Bone Morphogenetic Protein 2 / Q000008:administration & dosage*; D016025:Bone Transplantation / Q000009:adverse effects; D003094:Collagen; D004343:Drug Implants; D005260:Female; D007085:Ilium / Q000637:transplantation*; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000187:drug effects / Q000601:surgery*; D008852:Microradiography; D023421:Models, Animal; D011994:Recombinant Proteins / Q000008:administration & dosage; D012756:Sheep; D013123:Spinal Fusion / Q000009:adverse effects / Q000379:methods*; D014057:Tomography, X-Ray Computed; D016212:Transforming Growth Factor beta / Q000008:administration & dosage*; D016896:Treatment Outcome
D050071:Bone Density Conservation Agents; D055396:Bone Morphogenetic Protein 2; D004343:Drug Implants; D011994:Recombinant Proteins; D016212:Transforming Growth Factor beta; C499469:recombinant human bone morphogenetic protein-2; D003094:Collagen
ACS = absorbable collagen sponge; ICBG = iliac crest bone graft; PLF = posterolateral fusion; bone morphogenetic proteins; degenerative; facet fusion; lumbar; onlay grafting; posterolateral fusion; recombinant human bone morphogenetic protein–2; rhBMP-2 = recombinant human bone morphogenetic protein–2; sheep; spinal fusion