[Dynamic stabilisation and compression without fusion using Dynesys for the treatment of degenerative lumbar spondylolisthesis: a prospective series of 25 cases].

PURPOSE OF THE STUDY: We used the Dynesys stabilization to treat degenerative lumber spondylolysis by decompression without fusion with the objective of decreasing the morbidity related to instrumented arthrodesis in older patients yet preventing progression of the displacement.

MATERIAL AND METHODS: This was a prospective study of 25 patients with symptomatic degenerative lumber spondylolysis associated with degenerative spinal canal stenosis documented by saccoradiculography. For inclusion, static anteroposterior intervertebral displacement had to be at least 3mm in the upright position, irrespective of the displacement on the stress films. The series included 19 women and six men, mean age 71 years (range 53-83). The level was L4-L5 in all 25 cases. Instrumentations involved a single level (L4-L5) or two levels (L3-L5). All patients were explored with computed tomography and saccoradiculography. An MRI was obtained in 12 patients. Pre- and postoperative stress images and views of the entire spinal column in the upright position were used to study pelvic parameters and sagittal spinal balance before and after surgery. Lumbar incidence and lordosis was used to divide the patients into three groups. Outcome was assessed with the Beaujon classification at minimal follow-up of 24 months, mean 34, range 24-72 months.

RESULTS: Very good results were obtained in 72% of patients (relative gain greater than 70%) and good results in 28% (relative gain 40-70%). There were not outcomes considered fair or poor. There were two complications: aggravation of preoperative crural paresia with complete recovery and replacement of one neuroaggressive pedicular screw with no consequence thereafter. The stress films confirmed the residual mobility of the instrumented level when the preserved disc was of sufficient height. Postoperative pelvic parameters after Dynesys instrumentation showed improvement in sagittal tilt for T9 by accentuated suprajacent lordosis, even in the event of anterior spinal imbalance preoperatively.

DISCUSSION: Theoretically, solicitation of the pedicular anchors of a rigid instrumentation on a poorly balanced spine would rapidly lead to failure, while fibrous non-union on a globally well balanced spine would be tolerated much longer or even definitively without development of clinical symptoms. In our opinion, the Dynesys instrumentation enables a real restabilization of the spine by adapting to the patients particular spinal balance intra-operatively and postoperatively without imposing a definitive curvature as would a rigid fixation. The ultimate objective is to accompany the aging spine without brutally changing the stress forces. This semi-rigid instrumentation without fusion enables an adapted evolution of the overall spinal degeneration without imposing excessive local forces, which could be sources of stenosis or junctional instability.

CONCLUSION: The most logical indication for this instrumentation is the older subject aged at least 65 years with degenerative lumber spondylolysis and a predominantly self-reducible angular displacement and satisfactory disc height. This context (group 3 in our series) occurs in patients with a weak sacral slope and incidence, as well as minimal lordosis adapted to the pelvic parameters. The Dynesys instrumentation can be a palliative alternative to fusion for more advanced degenerative lumber spondylolysis occurring on spines with anterior imbalance where fusion would be technically difficult in terms of correction of the kyphosis or because of the general risk factors.