Factors affecting sagittal malalignment due to cage subsidence in standalone cage assisted anterior cervical fusion

• Published in: European spine journal 2007-09, Vol.16 (9), p.1395-1400
• Main Authors: Barsa, Pavel, Suchomel, Petr
• Format: Article
• Language: English
• Subjects: Adult; Cervical Vertebrae - diagnostic imaging; Cervical Vertebrae - surgery; Diskectomy - methods; Equipment Failure Analysis; Female; Humans; Male; Middle Aged; Original; Orthopedic Fixation Devices - adverse effects; Prospective Studies; Prosthesis Failure; Radiography; Risk Factors; Spinal Curvatures - etiology; Spinal Curvatures - surgery; Spinal Fusion - instrumentation; Spinal Fusion - methods; Treatment Outcome
• ISSN: 0940-6719; 1432-0932
• DOI: 10.1007/s00586-006-0284-8

Fusion of cervical spine in kyphotic alignment has been proven to produce an acceleration of degenerative changes at adjacent levels. Stand-alone cages are reported to have a relatively high incidence of implant subsidence with secondary kyphotic deformity. This malalignment may theoretically lead to adjacent segment disease in the long term. The prospective study analysed possible risk factors leading to cage subsidence with resulting sagittal malalignment of cervical spine. Radiographic data of 100 consecutive patients with compressive radiculo-/myelopathy due to degenerative disc prolapse or osteophyte formation were prospectively collected in those who were treated by anterior cervical discectomy and implantation of single type interbody fusion cage. One hundred and forty four implants were inserted altogether at one or two levels as stand-alone cervical spacers without any bone graft or graft substitute. All patients underwent standard anterior cervical discectomy and the interbody implants were placed under fluoroscopy guidance. Plain radiographs were obtained on postoperative days one and three to verify position of the implant. Clinical and radiographic follow-up data were obtained at 6 weeks, 3 and 6 months and than annually in outpatient clinic. Radiographs were evaluated with respect to existing subsidence of implants. Subsidence was defined as more than 2 mm reduction in segmental height due to implant migration into the adjacent end-plates. Groups of subsided and non-subsided implants were statistically compared with respect to spacer distance to the anterior rim of vertebral body, spacer versus end-plate surface ratio, amount of bone removed from adjacent vertebral bodies during decompression and pre- versus immediate postoperative intervertebral space height ratio. There were 18 (18%) patients with 19 (13.2%) subsided cages in total. No patients experienced any symptoms. At 2 years, there was no radiographic evidence of accelerated adjacent segment degeneration. All cases of subsidence occurred at the anterior portion of the implant: 17 cases into the inferior vertebra, 1 into the superior and 1 into both vertebral bodies. In most cases, the process of implant settling started during the perioperative period and its progression did not exceed three postoperative months. There was an 8.7 degrees average loss of segmental lordosis (measured by Cobb angle). Average distance of subsided intervertebral implants from anterior vertebral rim was fou