Mark P Arts and Jasper FC Wolfs
Object: Neuroforaminal stenosis has been documented frequently in patients with degenerative lumbar scoliosis. Pedicle screw fixation with posterior lumbar interbody fusion is usually performed although a debate has been started on the need for unilateral or bilateral screws, or interbody fusion only. Trabecular Metal is a porous tantalum biomaterial with good osteoconductive properties, which may be suitable for unilateral interbody fusion aiming at enlargement of neuroforamen.
Methods: From July 2011 until January 2013, 20 consecutive patients with degenerative scoliosis-related foraminal stenosis were treated with unilateral stand-alone Trabecular Metal cages (Zimmer TM 500) without additional pedicle screw fixation. All patients presented with leg pain, with or without low back pain. Patients underwent CT and MRI to confirm neuroforaminal stenosis on the concave side of the degenerative scoliosis. All patients were followed-up and examined at 2 months after surgery (follow-up moment 1). Long-term follow-up (moment 2; mean 36 months) was available of 17 patients; 2 patients died of unrelated disease and 1 patient was lost to follow-up. On both follow-up moments, neutral and dynamic flexion-extension images were documented. Based on these images, the position of the cage was determined and the Cobb’s angle of the segmental scoliosis (angle between the cranial endplate of the upper vertebral body and the caudal endplate of the lower vertebral body) was measured. The clinical outcome was measured by the patients’ global perceived recovery according to the 7-point Likert scale; “complete recovery” and “almost complete recovery” were determined as good results.
Results: Most of the patients were operated on L3L4 and L4L5 (70%). The mean duration of surgery was 56 ± 15 minutes. Surgical complications occurred in 5 patients, namely cerebrospinal fluid leakage (4 patients) and nerve root injury (1 patient) with sensory deficit. Good outcome (Likert 1 or 2) was reported by 14 patients (70%) on the shortterm follow-up (moment 1), and by 9 patients (53%) on the long-term follow-up (moment 2). Whenever Likert 1-3 was dichotomized, 95% of the patients on the short-term and 83% of the patients on the long-term reported at least some benefit from the operation. The mean Cobb’s angle improved significantly from 13.4 ± 5.1º pre-operatively, to 6.1 ± 3.5º at moment 1, and 7.1 ± 3.6º at moment 2 (P < 0.001). On follow-up moment 1 and 2, radiographic examination showed subsidence in 3 and 9 patients, respectively. Pseudarthrosis around the stand-alone cage was only seen at follow-up moment 2 in 3 patients.
Conclusions: Instrumented fusion with bilateral pedicle screw fixation and interbody fusion may not always be necessary in patients with scoliosis-related foraminal stenosis. Unilateral stand-alone TM cages could be an alternative strategy in a subgroup of patients leading to correction of Cobb’s angle and improvement of symptoms in most cases. However, the long-term result is moderately satisfying and could be explained by the development of cage subsidence over time.
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