and Uwe Spetzger1
Department of Neurosurgery, Klinikum Karlsruhe, Karlsruhe, Baden-Württemberg, Germany
In cases of secondary dislocation of disc or vertebral body replacements, it is usually necessary to perform an anterior and/or posterior fusion during revision surgery. Material failure of cervical implants is observed very rarely. Especially in cases of osteoporosis, secondary subsidence of disc or vertebral body replacements is not an unusual complication. The aimed maintenance of motion after the relatively expensive total disc replacement can be completely neutralised by heterotopic ossification. The latter is evoked by excessive drilling during primary surgery. The implant safety of cages and prostheses has been significantly improved by stop devices at the insertion instruments. Complications like accidental injuries of the dura, blood vessels, trachea or oesophagus are usually treated surgically.
10.1 Dislocation of Implants
Dislocation of implants is observed after total disc replacement as well as vertebral body replacement (Figs. 10.1 and 10.2). Since there is always a damage to the adjacent endplates due to the removal of a dislocated prosthesis, it is not reasonable to reimplant a prosthesis because of the high risk of heterotopic ossification. The safest solution is a classical fusion with interposition of an iliac crest bone graft and additional anterior plating (Fig. 10.1).
Secondary dislocation of a cervical prosthesis Discover™, lateral X-ray image before (a) and after (b) revision surgery with interposition of an iliac crest bone graft and anterior plating. Both endplates of the partially dislocated implant showed bony fixation in the adjacent vertebral bodies and had to be removed by drilling out of the surrounding vertebral body
Secondary surgical complication with breaking out of screws and dislocation of an iliac crest bone graft after anterior plating. Preoperative situation with degenerative instability, sagittal CT scan (a). Lateral X-ray image 1 day after surgery with adequate position of implants (b). Lateral X-ray image 3 months after surgery with breaking out of screws and dislocation of the bone graft (c). Sagittal CT scan after revision surgery with adjustable titanium vertebral body replacement ADD™ (d)
10.2 Breaking of Implants
Nowadays, the cages, prostheses, plates and screws show a high measure of reliability due to ongoing biomechanical testing. In the lumbar spine, breaking of screws in overweight individuals is occasionally observed, but in the cervical spine, this is unlikely due to much less biomechanical stresses. It is more likely that screws break out of the bone due to poor bone quality (Fig. 11.1c). In the authors’ patient population of a few hundred individuals with cervical implants, there was only one case with a broken DCI implant after a car accident (Fig. 10.3). In such a case in the authors’ opinion, it is reasonable to fuse the affected level analogue to cases of implant dislocation (Fig. 10.1) by using iliac crest bone graft and anterior plating.
Secondary breaking of a DCI implant after an accident. Primary surgery with cage fusion at C4/5 and DCI implant at C5/6, lateral X-ray image (a). Breaking of the DCI after a car accident with persisting neck pain, lateral X-ray image (b). Sagittal CT scan after revision surgery with replacement of the DCI by a PEEK cage and anterior plating (c)
10.3 Subsidence of Implants and Heterotopic Ossification
For total disc replacement, intact bony endplates of the adjacent vertebral bodies are a ‘conditio sine qua non’ for avoiding heterotopic ossification which would lead to a loss of function due to bony fusion of the relatively expensive implant. Therefore, the use of a drill has to be avoided when aiming total disc replacement. Nevertheless, heterotopic ossification occasionally occurs despite correct surgical technique (Fig. 10.4).
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