Novel concepts in the evaluation and treatment of high-dysplastic spondylolisthesis

Abstract

The classification system of spondylolisthesis proposed by Marchetti and Bartolozzi is the most practical regarding prognosis and treatment and includes the description of both low- and high-dysplastic developmental spondylolisthesis (HDDS). Unfortunately, it does not provide strict criteria on how to differentiate between these two subtypes. The accepted treatment for HDDS is surgical. However, there is no consensus on how to surgically stabilize this subtype of spondylolisthesis, and although the concept of reducing spinal deformity before fusion is attractive, the issue of surgical reduction versus in situ fusion remains controversial, especially for HDDS (Meyerding Grades III and IV). The purpose of this study was (1) to describe the severity index (SI) as a simple method that can be used in the identification of low-dysplastic developmental spondylolisthesis from HDDS allowing earlier surgical stabilization to prevent slip progression, (2) to provide guidelines for using the unstable zone for the inclusion of L4 in stabilization, and (3) to describe a surgical technique in the reduction and stabilization of this challenging surgical entity in an attempt to decrease the risk of iatrogenic L5 neurologic injury. The concepts of SI and unstable zone in the evaluation and treatment of HDDS are relatively new. In our study, patients with an SI value >20% were classified as having HDDS and surgical stabilization was offered. In addition, all vertebrae that were contained in the defined unstable zone were surgically instrumented and fused with attempts at anatomic reduction. This case series involved the retrospective radiological review of 25 consecutive patients surgically treated for HDDS between April 2000 and September 2004 by two senior surgeons. All 25 patients had a minimum 3-year follow-up. Reduction of slip, lumbosacral kyphosis, sacral inclination, fusion rate, maintenance of reduction, and iatrogenic L5 neurologic injury were evaluated. Twenty-two patients underwent a single-level L5-S1 fusion. Three patients had extension of the L5-S1 fusion to include L4 because it fell into the unstable zone. Slip improved from 67.2 to 13.6%, focal L5-S1 kyphosis improved from +17.5 degrees to -6.4 degrees . There were no pseudoarthroses and all patients had radiographic evidence of solid bony fusion at latest follow-up. To date, there have been no re-operations secondary to progression of deformity or loss of fixation. Two re-operations were performed, one for a superficial wound infection, the other for further laparoscopic decompression for continued L5 nerve root symptoms after the index surgery. One patient developed an iatrogenic L5 radiculopathy with dysaesthesiae 3 days postoperatively which completely resolved over 6 weeks. HDDS is best treated surgically. Early identification and stabilization of this challenging surgical entity could prevent the progression of slip and deformity making the index surgery less technically demanding. Vertebrae that are contained in the unstable zone can be instrumented and stabilized so that progression of the deformity and re-operation might be avoided. The authors suggested surgical technique can provide a way to restore sagittal balance, provide an environment for successful fusion, and decrease the risk of iatrogenic L5 neurologic injury.

Fig. 1

In normal subjects, the standing lateral radiograph demonstrates a minor torque. Also in low-dysplastic spondylolisthesis patients, a minor torque is present. In high-dysplastic spondylolisthesis patients, an abnormal spinopelvic alignment creates a major torque

Fig. 2

In this 12-year-old patient, the diagnosis of high-dysplastic spondylolisthesis can be difficult without SI calculation. One year later, a severe evolution occurs

Fig. 3

MRI and standing lateral radiograph showing high-dysplastic developmental spondylolisthesis. The square indicates the unstable zone and includes both L5 and L4. The unstable zone always includes the slipped L5 and sometimes L4, if there is a large torque (SI >20%) on L4 due to high pelvic retroversion. Postoperative radiograph showing reduction of the L5 slip and the inclusion of L4 in the instrumented fusion

Fig. 4

In this 13-year-old patient, preoperative imbalance is due to the pelvic retroversion, which causes hip and knee flexion and a high torque (SI = 54%). After pelvic retroversion reduction, no hip and knee flexion and the SI is normal

Fig. 5

In this 26-year-old patient with spondyloptosis, SI is normal in L4; for this reason, the instrumented and fusion area includes only L5. Reduction technique allows a minimal distraction of the L5–S1 segment

Fig. 6

Two rods are mounted to L5 Schanz screws and locked to S1 screws. The arrows show the distance between the clamps and the L5 transverse process

Fig. 7

In this 27-year-old patient with spondyloptosis, since SI is normal in L4 the instrumented and fusion area includes only L5. ALIF with cage was performed due to the risk of L5 root over distraction during the posterior cages insertion