Early failure of bioabsorbable anterior cervical fusion plates: case report and failure analysis.
METHODS
Case report with forensic failure analysis.


OBJECTIVE
To determine the failure modes of 3 explanted 70:30 PLDLA Mystique (Medtronic Sofamor Danek, Memphis, TN) graft containment plates retrieved from revision surgery for early device failure.


BACKGROUND
To reduce the problems of stress-shielding and radiopacity associated with metallic systems, bioabsorbable polymers have been used in anterior cervical discectomy and fusion procedures. Degradation of mechanical properties in vivo is a major concern when using bioabsorbable systems. Three of 6 patients who underwent anterior cervical discectomy with instrumented fusion, using Mystique graft containment systems experienced early failure requiring revision to alternate hardware.


METHODS
Devices were retrieved after failure and analyzed by light microscopy and environmental scanning electron microscopy. Simulations were performed with an unused plating system to induce damage for comparison with the retrieved devices. A detailed case review was performed to identify possible sources of extraordinary loading or damage.


RESULTS
One plating system failed at 6 weeks postimplantation due to fatigue fracture of the screws. Crack initiation sites were identified at the interface of the thread root and mold line of the screw. Another plating system failed at 16 weeks postimplantation due to the coalescence of radial microcracking between holes in the plate, leading to catastrophic failure of the plate. The final plating system failed during the implantation surgery, when the screw fractured in torsion.


CONCLUSIONS
Stress concentrations at the screw head-shaft interface and thread-shaft interface reduce the fatigue performance of bioabsorbable screws. Hydrolysis of the polymer may also play a role in the reduction of resistance to crack initiation and propagation.
Brkaric
Mario
M
Department of Orthopedic Surgery, William Beaumont Hospital, Royal Oak, MI, USA.
Baker
Kevin C
KC
Israel
Raj
R
Harding
Trevor
T
Montgomery
David M
DM
Herkowitz
Harry N
HN
D020341:Absorbable Implants / Q000009:adverse effects* / Q000592:standards; D000328:Adult; D001863:Bone Screws / Q000009:adverse effects / Q000592:standards; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D017586:Diskectomy / Q000009:adverse effects* / Q000295:instrumentation / Q000379:methods; D004868:Equipment Failure; D019544:Equipment Failure Analysis / Q000379:methods; D005260:Female; D006801:Humans; D016268:Internal Fixators / Q000009:adverse effects* / Q000592:standards; D007403:Intervertebral Disc / Q000601:surgery; D007405:Intervertebral Disc Displacement / Q000601:surgery; D008855:Microscopy, Electron, Scanning; D008875:Middle Aged; D010969:Plastics / Q000009:adverse effects / Q000592:standards; D011108:Polymers / Q000009:adverse effects / Q000592:standards; D011183:Postoperative Complications / Q000209:etiology* / Q000473:pathology / Q000503:physiopathology; D011859:Radiography; D013123:Spinal Fusion / Q000009:adverse effects* / Q000295:instrumentation / Q000379:methods; D013314:Stress, Mechanical; D013997:Time Factors
D010969:Plastics; D011108:Polymers