HIGH DEGREE SPONDYLOLISTHESIS IN ADULTS: MONOSEGMENTAL REDUCTION AND FIXATION ESPONDILOLISTESE DE ALTO GRAU EM ADULTOS: REDUÇÃO E FIXAÇÃO MONOSSEGMENTAR ESPONDILOLISTESIS DE ALTO GRADO EN ADULTOS: REDUCCIÓN Y FIJACIÓN MONOSEGMENTARIA

Objective: To evaluate a method to reduce high degree spondylolisthesis in adults with monosegmental fixing preserving the adjacent level and the improvement of sagittal balance. Methods: A prospective study, with 12 adult patients with high degree spondylolisthesis (III and IV) in adults who underwent surgery by the same team. We included 7 women and 5 men with a mean age of 37 years and lombosciatalgy that had no improvement with conservative treatment. The surgical technique used was total or partial reduction by Spondylolisthesis Reduction Instrument (SRI) system, with instrumentation only in the affected level, thus sparing the adjacent level, associated with 360o fusion. Results: The L5-S1 level was involved in nine patients, L4-L5 in two, and VT-S1 in one patient. The isthmic type predominated in nine patients, followed by dysplastic type in two, and one iatrogenic spondylolisthesis. These patients were assessed by the Oswestry scale, which showed a preoperative average of 59% and postoperative average of 12.4% (P<0.05). A significant improvement in the average slip angle from 54.66% to 9.5% (35% to 0%) was found. No major complications such as infection, neurological damage or material breaks were observed. Conclusion: The reduction of high degree listhesis instrumenting only the affected level produces good results, with good control of pain and functional improvement of patients. However, a larger follow-up is required to better evaluation.


InTRODUCTIOn
Spondylolisthesis, which is characterized by the slippage of one vertebra over another, was first observed by Herbiniaux, 1 a Belgian obstetrician, in 1782, and described by Killian 2 in 1854.
Five classifications are mentioned in the literature; however, two of them are more commonly used: that of Wiltse et al., 3 who identify five types (Type I: Dysplastic; Type II: Isthmic; Type III: Degenerative; Type IV: Traumatic; Type V: Pathological; and Type VI: Iatrogenic), and that of Marchetti and Bartolozzi, 4 which is more complete in terms of prognosis and response to treatment. There is also the Meyerding radiological scale, which differentiates the percentage of slippage as Grade I from 0% to 25% (GI), Grade II from 26% to 50% (GII), Grade III from 51% to 75% (GIII), and Grade IV from 76% to 100% (GIV), with GI and GII considered low grade and GIII and GIV considered high grade. 5 Low and high grade spondylolistheses are totally distinct entities with different treatments. In the high grade type, the greatest concerns are sagittal balance, which can completely alter the biomechanics of the spine, and the risks of neurological lesions and pseudoarthrosis, which can be decisive in the choice of surgical method. In the low grade type, arthrodesis in situ is considered the procedure of choice, as it does not involve the abovementioned concerns. 6,7 There is agreement as to the surgical treatment for high grade symptomatic spondylolisthesis, 7-9 but the surgical technique to be used is still much debated. There are several types described in the literature with great similarity in the outcomes. Among the different techniques, we can cite posterior arthrodesis in situ, posterior decompression and postero-lateral arthrodesis without reduction, antero-posterior circumferential arthrodesis in situ, a combination of anterior reduction and posterior stabilization, vertebrectomy of L5 with posterior stabilization of L4 to S1, reduction with posterior instrumentation associated with decompression, and posterior arthrodesis. [10][11][12][13] The objective of the study is to report on the surgical treatment of high grade symptomatic spondylolisthesis performed via a posterior approach associated with reduction and monosegment arthrodesis.

MATERIALS AnD METHODS
A prospective study was conducted from 2003 to 2010, evaluating 12 patients over the age of 21 years with spondylolisthesis, who did not respond to clinical treatment. There were 5 men and 7 women, with an average age of 37 years (ranging from 21 to 52 years). The average follow-up was 29.1 months (ranging from 6 to 65). All patients had high grade spondylolisthesis, classified as grade III or IV according to the Meyerding classification system. 5 (Table 1). Based on the Wiltse et al. classification, 3 nine patients were of the Isthmic type, two of the Dysplastic type, and one of the Iatrogenic type.
All patients had lower back pain that worsened with physical exertion. Sciatic pain was present in 10 patients, one of whom had a motor deficit of the root of L5. Seven patients had sensory deficits associated with lower back pain. None of them had cauda equina syndrome.
The criteria for inclusion of patients in the study were: high grade spondylolisthesis, severe lower back pain without improvement after clinical treatment, progression of subluxation, progressive motor deficit, or cauda equina syndrome. Patients with less than six months of follow up, and those who had been operated on by another surgical team or with another type of surgical technique, were excluded from the study. All were informed of the type of surgery they would undergo, and the associated surgical risks.
The surgical team consisted of three surgeons, always present at all the surgeries, using the same system.
The surgical technique used was total laminectomy associated with a complete or partial reduction of the spondylolisthesis with the S.R.I. system (Spondylolisthesis Reduction Instrument), performing translation and distraction of the segment followed by intersomatic arthrodesis using the P.L.I.F. (Posterior Lumbar Interbody Fusion) technique with a cage or bone graft, associated with postero-lateral arthrodesis with SOCON type (Aesculap ® ) pedicle screws, with instrumentation of only one level, thereby preserving the adjacent level ( Figure 1a). This system enables the reduction of the vertebral body that is uneven due to the translation of the upper vertebra over the lower vertebra with a low risk of radicular trauma (Figures 1b-d). An autologous graft from the iliac crest was used in all patients.
The patients were clinically evaluated using the Oswestry Disability Index (ODI) scale. This evaluation method takes both pain and physical activity into account. The first version was published in 1980, 14 followed by a modification in 1989. 15 The ODI has been validated in numerous countries, facilitating comparison between its results among researchers. 16 Vigatto et al. 17 developed a Brazilian version of the instrument in Portuguese. The values are classified as minimum capacity (0% to 20%), moderate incapacity (21% to 40%), severe incapacity (41% to 60%), invalid (61% to 80%), and bedridden or exaggerating their symptoms (81% to 100%). 16 The patients were evaluated radiographically for loss of reduction, sacral angle, angle of the slippage, complications from the instrumentation, and consolidation of the arthrodesis. In the pre-operative, immediate post-operative, and late follow-up periods, the Wiltse and Winter method 18 radiographic parameters were used to measure the sacral angle, angle of slippage, and percentage of slippage.  All patients were mobilized on the second post-operative day, following removal of the suction drain. Neither intra-operative evoked potential nor post-operative orthoses were used.

RESULTS
The Wiltse et al. 3 classification was used for the 12 patients in the series: nine with the isthmic type, two with the dysplastic type, and one with the iatrogenic type of spondylolisthesis. The most often affected level was L5-S1 in nine patients, followed by L4-L5 in two patients and VT-S1 in only one patient.
The average initial percentage of slippage was 55% (15% to 76%) and after surgery it dropped to 9.5% (0% to 35%) with p<0.05. The angle of slippage improved from 25º (20º -35º) to 3º (0º -7º) in the post-operative period. There was an increase in this angle in only one patient, from 2º in the immediate post-operative period to 7º in the 6 th month of follow-up; however, it remained stable over the next two years. This patient had no clinical pain, and both radiography and tomography showed consolidation of the arthrodesis. There was an average improvement of the sacral angle of from 20º (18º -36º) to 44º (39º -52º) after surgery, which was maintained in follow-up.
All 10 patients showed improvement in radicular pain. There was a great improvement in lower back pain in six patients. Four patients continued to have mild lower back pain related to physical exertion. One patient continued to have lower back pain unrelated to activity and used NSAIDs (Non-steroidal anti-inflammatory drugs) sporadically and physiotherapy. One patient presented an improvement in the L5 motor deficit.
No partial or total lesion of the nerve root was observed during surgery or in the post-operative period. Four years after surgery, one patient developed listhesis in the level above, and underwent a new surgery using the same technique, with good results. An accidental lesion of the dura mater was repaired during surgery, with a good outcome. All 12 patients were monitored by computed tomography after six months of evolution, and all of them showed bone consolidation. None of the patients developed pseudoarthrosis. (Figure 2)

DISCUSSIOn
High grade spondylolisthesis is a very debilitating clinical condition for the patient. It is a major challenge for the spine surgeon, because of the divergence between the best surgical techniques and the complexity of its classification. As it is not common in our clinics, only a few surgeons have a large case series to report. The objectives of the treatment of high grade symptomatic spondylolisthesis include resolution of lower back pain and improvement of the radicular symptoms associated with arthrodesis of the affected levels and restoration of sagittal balance. 8,9,19 The current methods for achieving these objectives include a range of surgeries that vary from isolated posterior fusions in situ to aggressive antero--posterior combinations with circumferential procedures, including vertebrectomy. [7][8][9][10]12,13,19 The level most affected by high grade spondylolisthesis in adults is L5-S1, occurring in rare cases in L5-VT and L4-L5. 20 In our case series, the high predominance of level L5-S1 was in agreement with the literature, 19,20,21 but due to the small number of patients in the studies, reliable comparison is difficult. The Wiltse classification shows that the isthmic type of spondylolisthesis is predominant, 19,20,21 particularly in adults, which occurred in our statistics. No cases of iatrogenic spondylolisthesis were reported in any of the studies reviewed.
It is known that today, bone fusion in situ is the surgical procedure used in children. 22,23 However, it has the following problems: a high rate of pseudoarthrosis, ranging from 0% to 19%; the fact that fusion is extended to the level above it; and the progression of all the parameters of deformity, especially the angle of slippage. On the other hand, instrumented and non-instrumented reductions followed by fusion have been reported with rates of pseudoarthrosis of 0% to 8%. 22,24 In adults, posterior fusion in situ is not a viable situation. The inability of most isolated posterior procedures to achieve stabilization of the anterior spine may contribute to the increased rates of pseudoarthrosis, with rates of 17% to 50% being reported. 10,25 Boos et al. 10 report on 10 patients with high grade spondylolisthesis, 50% of whom had pseudoarthrosis. They conclude that there needs to be anterior support to complement the arthrodesis, and that this was correlated with biomechanical laboratory tests. 26 There is still significant controversy concerning reduction in spondylolisthesis in adult patients. This procedure should be considered in patients with evidence of an unstable segment, or when there is a change in sagittal balance. 8,9,20,21 It has already been recognized that to improve sagittal balance, a partial reduction of the angle of slippage is more important than the percentage of translation. 11

2B
Bradford and Brochie 11 mention several advantages of reduction in high grade spondylolisthesis, among them, the reduction of the angle of slippage, which allows for neurological decompression, improvement of the lumbosacral sagittal orientation, and an improvement in the patient's overall condition. This partial correction of the lumbosacral angulation not only enables greater anterior compression (improving the probability of arthrodesis), but also improves both the overall sagittal balance and the cosmetic appearance, through the spontaneous correction of thoracic hypokyphosis and lumbar hyperlordosis. When the overall sagittal balance of the patient is improved, this enables erect posture and better biomechanical conditions of the spine. Other advantages are low rates of pseudoarthrosis as compared to arthrodesis in situ, and better neurological decompression. The disadvantages of reduction are the greater surgical time, higher neurological risk, and loss of reduction. 10,11,19 Harms 27 reported excellent results in 112 patients, using a one--level reduction arthrodesis technique and only L4 for the reduction. He showed an improvement of the angle of slippage in 92.5%, and of the degree in 92%. There was a lower percentage of restoration of the sacral angle as compared to the other parameters, with a 62% improvement, obtaining smaller sacral angles than the norm of 35º. Shufflebarger and Geck 28 showed an improvement similar to that of Harms 27 in 18 patients using the same technique, with an improvement in the sacral angle, which remained above 35º. One patient evolved with an increase of the progression, stabilizing in six months, and no cases of pseudoarthrosis were reported.
The objective of the procedural technique used here is to restore sagittal balance, making the absorption of the mechanisms of force in the lumbosacral junction more favorable. This procedure also aims to preserve the adjacent disc, thereby reducing new disc degenerations resulting from the arthrodesis of a segment, and maintaining a greater range of movement. In most of the patients, the percentage of slippage was reduced to less than 25% and was associated with 360º arthrodesis. This may explain why no cases of pseudoarthrosis were encountered. Neurological injury, though not found in our case series, is common in patients in whom the grade of spondylolisthesis is reduced; however some factors, such as the surgeon's experience, better exposure with laminectomy, and visualization of the roots during the reduction, may help reduce these risks, ensuring that there is no distraction of the nerve elements. 19

COnCLUSIOn
The method of high grade spondylolisthesis reduction with instrumentation only at the affected level is a treatment option with good results, with control of the pain profile and functional improvement in patients. It has the advantages of saving levels and improving sagittal balance.
All authors declare no potential conflict of interest concerning this article.