Décompression et stabilisation dynamique sans fusion avec le système Dynesys® dans le traitement des spondylolisthésis dégénératifs lombaires (à propos d’une série prospective de 25 cas)

Nous avons traité les spondylolisthésis dégénératifs lombaires par une décompression associée à une stabilisation sans fusion avec le système Dynésys^® dans le but de diminuer la morbidité des arthrodèses instrumentées chez ces patients âgés tout en évitant l’évolution vers une aggravation du glissement. Il s’agissait d’une série prospective de 25 patients ayant un âge moyen de 71 ans. Des clichés dynamiques pré-et postopératoires selon la méthode de Putto, ainsi que des grands clichés du rachis entier en charge pour l’étude des paramètres pelviens et sagittaux du rachis avant et après l’intervention ont également été réalisés chez tous les patients. Les résultats ont été revus selon la classification de Beaujon, avec un recul minimum de 24 mois et moyen de 34 mois. Nous obtenons 72 % de très bons résultats (gain relatif supérieur à 70 %) et 28  % de bons résultats (gain relatif entre 40 et 70 %), nous n’avons pas de résultats moyens ou mauvais (100 % de bons et très bons résultats). L’étude des paramètres pelviens postopératoires après instrumentation par Dynésys^® a montré une amélioration de la gîte sagittale en T9 par une accentuation de lordose sus-jacente à l’instrumentation, même dans les cas de déséquilibre antérieur du rachis. Le système Dynésys^® permet d’obtenir dans cette indication les mêmes résultats que ceux des arthrodèses avec une morbidité péri-opératoire moindre.

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 3 mm 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.