Uninstrumented segmental posterolateral fusion in situ using autogenous bone from the posterior iliac crest is the method of choice for cases with a percentage of slip up to 50 % (Fig. 24.8). The operation is performed through the bilateral paraspinal muscle split approach as recommended by Wiltse [146, 147]. The segment above the slipped vertebra is usually not included into the fusion even if the disc shows signs of dehydration in MRI. The patient is mobilised 1–2 days after the operation wearing a soft brace for 3 months’ time. Sports activities are forbidden for 6–12 months depending on the radiologic development of the fusion. There are no restrictions of physical activities after solid bony healing. The method is very safe and effective. There are no specific complications. In this young age group it leads to bony fusion in 80–90 %. Subjective results and functional outcome are good or satisfactory in 82–96 % of the patients [62, 65, 116, 117, 126]. A recent long-term study in 107 children and adolescents with a mean age at operation of 15.9 years (range, 8.1–19.8) and a mean follow-up of 20 years has proven the lasting effectiveness and reliability of this method [58]. The mean Oswestry Disability Score [25] was 7.6 (range, 0–68) at last follow-up. It was in the normal range (0–20) in 100 out of 107 patients (93 %). Six (6 %) out of 107 patients had an Oswestry score of 20–40 (moderate disability); one patient had a score of 68 (crippled). Pseudarthrosis (17 % after posterolateral fusion) and adjacent disc degeneration on plain radiographs (12 %) did not correlate with poor outcome. The Scoliosis Research Society outcome instrument [35] yielded a mean of 94.0 points (range, 44–114 points) at follow-up [40]. Degenerative changes in MRI at follow-up did not have any significant influence on patients’ outcome [105].

In low-grade slips, decompressive laminectomy is indicated in young patients only in rare cases with true impingement of neural structures. However, this has not been seen by the author in a low-grade slip during a period of over 30 years. Pseudoradicular symptoms (radiating pain to the posterior aspect of the thigh) and hamstring tightness resolve without laminectomy due to stabilisation of the segment by fusion. If decompression is performed during growth segmental fusion has to be added always to prevent subsequent progression of the slip [95].

The use of instrumentation has not been shown to give any advantages in low-grad slips in this age group. Nor is there any reason for reduction of low-grade slips. The author agrees fully with this statement published by Wiltse and Jackson in 1976 [146]. Internal fixation, with or without reduction, is connected with longer operation time, more severe muscle trauma, an increased risk of complications, and higher costs. It would probably increase the fusion rate. But the disadvantages mentioned above would not countervail this, as pseudarthrosis does not have a measurable negative effect on the outcome in this group of patients [58, 65, 119, 124].

In cases of spondylolysis without a slip or with a slip of less than 25 %, the direct repair of the isthmic defect is recommended by some authors reporting favourable results using different methods of internal fixation (screws, cerclage wire, butterfly plate, hook plate, pedicle screws and rods) [16, 33, 48, 51, 67, 86, 91]. Several authors reported favourable outcome especially in younger patients [14, 39, 46, 91]. There are no series published dealing exclusively with children. At the author’s institution Scott’s wiring technique with autologous bone grafting has been used [91]. For postoperative treatment a plastic TLSO was applied for 3–6 months. In a comparative study in children and adolescents, the results after mid-term and long-term follow-up were very good in the majority of cases, but not better than the results of uninstrumented segmental fusion. Thus, the benefit from saving the lytic-olisthetic motion segment could not be demonstrated so far [116, 117]. At present, the direct repair is used by the author only in cases of spondylolysis or minimal slips in the segments above L5.

If the slip approaches 50 % the biomechanical situation changes profoundly with far reaching consequences for the sagittal alignment of the entire spine [66]. The physiologic lumbosacral lordosis decreases and, dependent of the amount of displacement, a kyphosis develops due to absence of anterior support for the slipping vertebra (Fig. 24.9). In the growing patient, this kyphotic deformity has a risk for progression in almost 100 %. Operation should be considered even in patients with minimal subjective symptoms or no symptoms at all [146]. There is no data showing that non-operative measures (exercises, bracing) or restriction of sports activities would stop the progression. One should not wait and see too long. Proceeding progression makes the necessary operation technically more difficult, increases the risk of complications, and leads possibly to an inferior result. It has, however, to be noted that in some cases even patients with high-grade slips or even spondyloptosis remain subjectively symptom-free. The author agrees with Bridwell that there is no “right way” to treat all high-grade slips [15]. But overtreatment for the sake of radiologic correction should be avoided. The methods applied should be assessed critically for their benefit for the patient in the long run in terms of clinical outcome and function.

A considerable variety of methods for operative treatment of high-grade slips has been published: uninstrumented posterior or posterolateral fusion from L3 or L4 to S1 [34, 41, 45, 59, 65, 106, 122, 146], uninstrumented anterior interbody fusion [41, 102, 103, 136], uninstrumented combined fusion [57], uninstrumented posterolateral fusion L4-S1 and anterior fusion L5-S1 with cast immobilisation after preoperative gradual conservative reduction [59, 138], uninstrumented posterolateral fusion L3 or L4 to S1 with postoperative cast reduction [17], anterior reduction with anterior screw fixation and interbody fusion, posterior pedicle screw reduction with or without decompression and posterior or combined fusion using bone graft or cages [24, 77, 84, 88, 102, 103, 108, 110] or the Bohlman technique utilising a transsacral fibular strut graft [10, 36, 128], or a special titanium cage [2, 127], and anterior and posterior reduction with decompression, and double-plating [139].

According to Bradford, the goals of treatment for high-grade spondylolisthesis are to prevent progression, to relieve pain, to improve function and to reverse the neurologic deficit if there is any [13]. These goals can be achieved in the vast majority of cases safely by in situ fusion which wrongly is of bad repute. The reason for the negative attitude of many surgeons towards in situ fusion seems to be that many of them have seen symptomatic adult patients with a high-grade slip up to spondyloptosis who had a posterior or posterolateral “in situ” fusion of a more or less severe slip as teenagers. Usually, in the early years after the primary operation, they were symptom free. But with time, posture deteriorated and symptoms reappeared, sometimes they became even worse than before the operation. When analysing the radiographs, one sees that slow progression of the slip and the kyphosis happened over the years despite a solid-looking fusion mass. Retrospectively, one can say that although in situ fusion was attempted it was not achieved. Several of such cases with slow progression after posterior or posterolateral so-called in situ fusion L4 to S1are are shown in the very instructive papers by Taillard and Burkus et al. [17, 134]. The cause for the failure is misunderstanding of the biomechanics of a high-grade slip which in fact is a progressive kyphosis. Anterior bony support is insufficient or missing totally. The disc below the significantly slipped vertebra is always severely damaged. The disk will degenerate further and atrophy due to loss of functional motion after fusion. This all together induces increasing flexion moments on the posterior fusion mass which will bend and elongate. It must be stressed here that in the author’s language successful in situ fusion does mean that a solid bony fusion is achieved and even after long-term follow-up the position of the fused vertebra is not significantly worse than before the operation.

Biomechanically, the most reasonable procedure to stop the progression of a kyphotic deformity is to provide anterior support. This is the rationale for anterior fusion. At the author’s institution, uninstrumented anterior interbody fusion in situ without decompression is the method of choice for high-grade slips with no ore minimal (up to 10–20°) lumbosacral kyphosis (Fig. 24.10). The operation is performed through a transperitoneal or retroperitoneal approach using two to three autogenous tricortical iliac crest grafts. Uninstrumented combined anterior and posterolateral fusion in situ without decompression is preferred for slips with greater lumbosacral kyphosis (more than 20°). Combined fusion has been shown to be more effective in preventing the postoperative progression of the lumbosacral kyphosis, i.e. to achieve a true and lasting in situ fusion without late deterioration [41, 106]. Using this technique there is no need to include more than the olisthetic segment into the fusion. After anterior or combined procedures the patient is mobilised at the second or third postoperative day wearing a plastic TLSO for 3–6 months. Hamstring tightness disappears and spinal balance is regained within a few weeks although no decompression has been performed (Figs. 24.11, 24.12, and 24.13). The clinical short- and mid-term results of anterior and combined fusion in the severe slip are comparable to the results of posterior or posterolateral fusion [49, 59, 64, 122, 125, 136]. In a recent long-term follow-up study (67 patients, slip 50–100 %, mean age at operation 14.4 years, range 8.9–19.6, follow-up of 10.7–26 years.), the outcome after three different uninstrumented in situ fusion techniques (posterolateral, anterior, combined) without decompression was compared. At final follow-up, 14 % in the posterolateral and in the anterior fusion group reported low-back pain at rest often or very often, but none in the circumferential fusion group. The mean Oswestry index was 9.7 (0–62), 8.1 (0–32) and 2.3 (0–14) respectively, indicating combined fusion being slightly but not significantly superior. Radiographs showed some progression of the mean lumbosacral kyphosis during follow-up in the posterolateral and in the anterior only fusion group. No progression of the lumbosacral kyphosis was detected after combined fusion [106]. A comparison of the three groups using the Scoliosis Research Society questionnaire yielded the same kind of results with a slightly better outcome in the circumferential fusion group [40, 57]. It has, however to be noted that those patients are still in their thirties. And no data is available showing what happens when they reach midlife and seniority.