Analysis of porous ingrowth in intervertebral disc prostheses: a nonhuman primate model.
METHODS
A study was conducted to investigate the biomechanical, histochemical, and biologic ingrowth characteristics of the most widely used total disc prosthesis, the hydroxyapatite-coated SB Charité prosthesis.


OBJECTIVE
To compare the porous ingrowth, linear apposition, or bony ingrowth in total disc replacement with published reports of porous ingrowth prostheses in the appendicular skeleton.


METHODS
Seven mature baboons (Papio cynocephalus) underwent L5-L6 total disc replacement through an anterior transperitoneal approach. The SB Charité prosthetic vertebral endplates (n = 14) were cobalt-chrome covered by two layers of thin titanium with a hydroxyapatite coating, which was electrochemically bonded to the implant surface.


RESULTS
At 6 months after surgery, the range of motion exhibited by the SB Charité and the nonoperative control subjects under axial compression, flexion-extension, and lateral bending showed no statistical difference (P > 0.05). Plain film radiographic analysis showed no lucencies or loosening of any prosthetic vertebral endplate. Gross histopathologic analysis of the hydroxyapatite-coated SB Charité prosthesis demonstrated excellent ingrowth at the level of the implant-bone interface, without evidence of fibrous tissue or synovium. Histochemical assays showed no accumulation of particulate wear debris (no titanium, ultrahigh molecular weight polyethylene, or cobalt-chrome) nor cytokines (tumor necrosis factor-alpha, prostaglandin E2, interleukin-1, -2, or -6). Total endplate area showed a mean ingrowth (volume fraction) of 47.9% +/- 9.12% and a total ingrowth range of 35.5% to 58.8%.


CONCLUSIONS
The porous ingrowth (percentage of pore ingrowth coverage at the bone-metal interface) was more favorable for total disc replacement than for cementless total joint components in the appendicular skeleton (range, 10-30%). The reason for the improved degree of porous ingrowth in total disc replacement prostheses probably is that ligamentotaxis causes sustained compression across the metal-bone interface.
McAfee
Paul C
PC
Scoliosis and Spine Center, St. Josephs Hospital, and the Biomechanics Laboratory at Union Memorial Hospital, Baltimore, Maryland 21204-7737, USA.
Cunningham
Bryan W
BW
Orbegoso
Carlos M
CM
Sefter
John C
JC
Dmitriev
Anton E
AE
Fedder
Ira L
IL
D000818:Animals; D001696:Biomechanical Phenomena; D017886:Durapatite / Q000494:pharmacology; D007403:Intervertebral Disc / Q000502:physiology / Q000601:surgery*; D008297:Male; D023421:Models, Animal; D009068:Movement / Q000502:physiology; D016348:Osseointegration / Q000187:drug effects / Q000502:physiology*; D010215:Papio; D019736:Prostheses and Implants
D017886:Durapatite