Operation times are longer and complication rates are higher (Table 7)thanwith the other two approaches. Kwon and Albert [44] point out that solid fusion does not always correlate with clinical success in other degenerative disorders of the spine. While comparative objective radiographic measurements of the spine after PLIF vs. PLF for lytic spondylolisthesis in adults show better results for PLIF, clinical outcomes were not reported to be markedly different [47, 55, 105]. It is therefore valid to at least critically question whether the benefits engendered by performing a combined approach stand in correlation to the longer, techni- cally more demanding and, from a hardware standpoint, usually more expensive procedure with a higher risk for complications. Fusion to L4 Reduction is facilitated by instrumenting to L4 In children with severe developmental spondylolisthesis at L5/S1 (Meyerding Grades III–V), reduction can be extremely tedious and may be facilitated by instrumentationtoL4( Case Study 2, Fig. 7). This technique allows to distract between L4 and S1, which facilitates the reduction. In selected cases, the L4 screws can be removed at the end of the operation or alternatively 12 weeks later, which leaves the motion segment L4/5 intact [87]. However, the lateral process of L5isoftendysplasticinchildrenanddoesnotallowforareliablefusion.There- fore a fusion to L4 is recommended. This is particularly valid if no interbody fusion is added. In adults the L4/5 disc is often degenerated and requires inclusion in the fusion In adults with marked slips of L5/S1, the adjacent L4/5 segment frequently exhibits significant degenerative changes. In these cases, a fusion of L4 to S1 is indicated because the L4/5 segment often rapidly decompensates after the L5/S1 fusion. Vertebrectomy To achieve good spine realignment, surgical treatment of spondyloptosis, which almost only affects L5/S1, may necessitate vertebrectomy of L5 (Gaines’ proce- dure [26]). This is a two-stage procedure, first incorporating an anterior approach with resection of the entire body of L5 back to the base of the pedicles, as well as the intervertebral discs L4/5 and L5/S1. In a second stage, the posterior approach allows realignment of the spine after L5 pedicles, facets and laminar arch have been removed bilaterally. After transpedicular instrumentation from L4 to S1 and sagittal realignment, nerve roots L5 and S1 exit the spinal canal together over a reconstructed intervertebral foramen. Gaines, who originally described this method in 1985, more recently reported on 30 patients treated with this procedure [26]. Despite the fact that Gaines had a low complication rate and good success, over two-thirds of the patients had neurapraxic injury to one Vertebrectomy for a high-grade slip is prone to complications or both L5 roots and in two this remained permanent. This procedure, which requires a large amount of surgical experience, should only be performed at spe- cifically equipped centers. Complication rates remain very high even in experi- enced hands. Sacral Dome Osteotomy The main risk of reducing high-grade spondylolisthesis and spondyloptosis is related to the stretching of the L5 nerve roots, which often results in neuropraxia. The sacral dome osteotomy helps to avoid this nerve root injury by shortening of the sacrum. This technique consists of a bilateral osteotomy of the sacral dome, which allows the reduction of the slip without distraction ( Fig. 7). The operation is carried out in a single stage. This demanding procedure should be carried out 754 Section Spinal Deformities and Malformations ab cd ef Figure 7. Reduction of high-grade spondylolisthesis with sacrum dome osteotomy a The pedicles of L4, L5 and S1 are instrumented with pedicle screws. b, c The loose posterior arc of L5 is resected and the L5 and S1 nerve root as well as the intervertebral discs are exposed. The dome of the sacrum is osteotomized with a chisel and resected. d A rod is inserted on both sides first connecting the S1 screws with the rods. L4 is then reduced to the rod with a reduction forceps. L4– S1 are slightly distracted. e L5 is pulled back and connected to the rod with a reduction for- ceps. f An interbody fusion is added to L5/S1 and a posterolateral fusion to L4–S1. Spondylolisthesis Chapter 27 755 only with neuromonitoring of the L5 nerve roots. It is important to note that neu- romonitoring is not absolutely reliable, because paresis of the nerve root can occur even hours after the surgery. It is therefore recommended to reduce the slip onlyfarenoughtoallowforagoodsagittalrealignmentandaninterbodybut- tressing by a graft or cage ( Case Study 2). Complications Typical complications encountered are neurologic injuries and non-union As with all surgical procedures, patients surgically managed for spondylolisthe- sis must receive the best outcome with low exposure to problems and complica- tions. It is therefore important to appreciate which complications can occur so as to minimize the occurrence and appreciate the psychologic impact these may have on the patient [79]. Depending on the etiology of the condition and the pro- cedure performed, complication rates differ significantly. In situ fixation for degenerative low-grade slippage in the adult will have a markedly lower risk of attaining neurologic impairment than complex reconstructive surgery of the adolescent spine in spondyloptosis. Common complications after spondylolis- thesis surgery are: neurologic injury (0.3–9.1%) [74, 79, 89, 93] persistent nerve root deficits (2–3%) [15, 38, 74, 89, 102] non-unions (0–39%) [20, 31, 38, 48, 55, 60, 67, 74, 89, 106] progressive slippage (4–11%) [28, 82, 89, 102] revision surgery (7.6%) [48, 67, 89] L5nerverootisathighrisk in high-grade spondylolis- thesis surgery The list of these potential complications indicates that surgery of (high-grade) spondylolisthesis is demanding and very careful preoperative planning is neces- sary before the procedure is performed. As with all neurologic complications, these need to be accurately assessed and diagnostic imaging should occur rap- idly. If there is obvious compression of neural structures, be it from hematoma or misplacement of spinal instrumentation, immediate revision surgery should be the consequence. More complex are the cases where there is no radiographic evidence of com- pression of neural structures. In cases of only minor deficit, an attentive yet merely observational approach may be warranted. The question whether reduc- tion was too ambitious should critically be asked. In general for any surgeon, the decision for or against revision surgery is among the most difficult to make. It is therefore prudent to involve a further, less biased surgeon to assess the patient as well as the radiographic parameters and decide for or against revision together. Adjacent segmen t instability afterinstrumentationmaybeduetoexcessive iatrogenic destabilization of the overlying facet joint and capsule, due to exces- sive thinning or complete removal of the overlying lamina or due to degenerative changes to the adjacent motion segment. While the iatrogenic destabilization of a segment certainly will lead to slippage adjacent to a stabilized segment [109], data concerning adjacent segment degeneration are inconsistent. Incidences are reported to range between less than 3% and 35%. The discussion remains open as to whether these observed degenerative changes reflect the natural history of disc disease or stand in context to the adjacent fusion [66, 83]. As Ogilvie [79] points out, both are probably a factor and therefore as many lumbar levels should be left unfused as are consistent with the goals of surgery. 756 Section Spinal Deformities and Malformations Recapitulation Epidemiology. Lumbar spondylolisthesis can be developmental or acquired. As most slippages are asymptomatic, the true incidence of the condition remains speculative. For developmental spondylo- listhesis, rates of around 3% in the general popula- tion have been estimated, but depending on the ethnic group, the incidence may be significantly higher. Among the acquired slippages, the degen- erative type is the most frequent one. Pathogenesis. Spondylolysis, which is a defect of the pars interarticularis, is the main cause of devel- opmental spondylolisthesis and results from a stress fracture. This causes failure of the posterior stabilizing elements and the disc is confronted with excessive shear. The dissociation of the anterior and posterior column therefore ultimately results in slippage, since the disc cannot withstand the shear forces. Acquired spondylolisthesis mostly oc- curs on the basis of degenerative lumbar disease. Further causes may be iatrogenic destabilization of a motion segment, trauma, tumors, and rare syn- dromes or systemic bone disease. Classification. Only those classifications are of true value that are based on anatomy or distinguish be- tween developmental and acquired forms of the deformity. The two systems which are clinically rele- vant are those of Wiltse/Rothmann and Marchetti/ Bartolozzi. The Marchetti classification is self-ex- planatory and, as it avoids complex terminology, easier to understand. Clinical presentation. Patients seeking medical at- tention do so with a variety of symptoms. Back and/or leg pain may range from merely harassing to severe. Depending on the degree of slippage and onset, neurologic symptoms mayoccur.Inrare cases, spinal canal compromise may be so severe that patients present with a cauda equina syndrome. Adolescents with symptomatic high-grade spondy- lolisthesis may develop a sciatic crisis known as the Phalen-Dixon sign. Tight hamstrings and posture ab- normalities accompany the presentation in the ado- lescent patient. In the adult patient, mechanical low- back pain (worse on motion, better on rest) and radi- culopathy are the prevailing symptoms. Physical ex- amination may show hyperlordosis of the lumbar spine, and in high-grade slippages a step-off be- tween spinous processes.Patientsshouldbeas- sessed for sensory or motor deficits of nerve roots. Diagnostic work-up. Standard anteroposterior and lateral radiographs are the mainstay for the initial as- sessment. Oblique X-rays may visualize a pars defect not already visible on a lateral view. Slippage is quan- tified by either using the method as described by Me- yerding (Grade I–V) or of Taillard (%). Assessment of the sagittal deformity (lumbosacral kyphosis) is cru- cial in high-grade spondylolisthesis. A large slip angle in conjunction with a rounded sacrum increases the risk of slip progression in children. In case of neuro- logic deficit or if surgery is planned, a CT scan or MRI should always be performed. Non-operative treatment. Treatment decision will ultimately be based on the age of the patient, symptoms, etiology as well as the degree of slip- page. General objectives of treatment are to re- lieve pain, reverse neurologic deficit and, in cases of severe slippage, to realign the spine. The vast ma- jority of spondylolisthesis can be treated non-oper- atively. Acute pain should be controlled with initial rest, anti-inflammatory and/or pain-modulating medication as well as administration of a muscle re- laxant. This is followed by a therapeutic exercise program with paraspinal and abdominal muscle strengthening. If pain does not sufficiently subside, the use of a brace or orthoses may be beneficial. Cast treatment may result in a healing of an acute spondylolysis in selected cases. Operative treatment. Surgery is justified in cases of persistent or recurrent back and/or radicular pain, neurologic deficit/neurogenic claudication as well as bladder and/or bowel syndromes. Aim of all sur- gical techniques is to decompress neural struc- tures, prevent progression and achieve stability with subsequent fusion. Generally there are three methods to achieve this goal, i.e. uninstrumented posterolateral fusion (PLF), and instrumented pos- terolateral fusion with or without anterior or poste- rior interbody fusion (ALIF/PLIF). Due to technical innovations and improvement in implants, there is an increasing trend to manage spondylolisthesis by combined approaches. The surgical approach will depend on familiarity with the approach, resources andinfrastructureaswellasback-upexpertisein case of complications. Particularly the manage- ment of high-grade spondylolisthesis is a surgical challenge and technically demanding. In children with high-grade spondylolisthesis,fusiontoL4is often required. Reduction of high-grade spondylo- Spondylolisthesis Chapter 27 757 listhesis is still a matter of debate because of the high complication rates associated with these pro- cedures. Particularly, the L5 nerve root is at risk. The primary goal in adult low-grade spondylolisthesis is not to reduce the slip but this may be necessary in cases with foraminal stenosis. In the latter indica- tion, solid fusion and neural decompression are more important. In cases where reduction and/or distraction of the slipped vertebra was performed, anterior buttressing by an interbody fusion is nec- essary. Frequent complications encountered are non-union and neural compromise. Key Articles Boxall DW, Bradford DS, Winter RB, Moe JH (1979) Management of severe spondylolis- thesis (grade III and IV) in children and adolescents. J Bone Joint Surg (Am) 61:479 – 495 Patients with an L5/S1 spondylolisthesis of 50% or greater were reviewed. Four had been treated non-operatively; 11, by spondylodesis; 18, by decompression and spondylodesis; and 10, by reduction and spondylodesis. The angle of slippage was found to be as impor- tant a measurement as the percentage of slippage in measuring instability and progres- sion. Spondylodesis alone, even in the presence of minor neural deficits, tight ham- strings, or both, gave relief of pain and resolution of neural deficits and tight hamstrings. The study suggests that management by postoperative extension casts may achieve a sig- nificant reduction in percentage and in angle of slippage. Progression of the spondylolis- thesis may occur following a solid spondylodesis. Bradford DS, Boachie-Adjei O (1990) Treatment of severe spondylolisthesis by anterior and posterior reduction and stabilisation. A long-term follow-up study. J Bone Joint Surg (Am) 72:1060 – 1066 Unselected patients (n=22) who had severe spondylolisthesis were treated by a first-stage posterior decompression (Gill procedure) and a posterolateral arthrodesis, followed by haloskeletal traction, and then by a second-stage anterior interbody arthrodesis, followed by immobilization in a cast. At an average 5-year follow-up the corrected slip angle remained much the same. A pseudarthrosis developed in four patients, all of whom had a reoperation. The neurologic deficitsthat had been present in ten patients preoperatively had completely resolved in all but one at follow-up. Alignment in the sagittal plane was restored in most patients, and the back pain and radicular symptoms were resolved in all patients but one. Lenke LG, Bridwell KH, Bullis D, Betz RR, Baldus C, Schoenecker PL (1992)Resultsofin situ fusion for isthmic spondylolisthesis. J Spinal Disord 5:433 – 442 Patients treated with in situ bilateral transverse process fusions utilizing autogenous iliac bone graft yet without decompression or instrumentation are assessed. A surprisingly low fusion rate was found; yet despite this overall clinical improvement was noted in >80% of patients with preoperative symptoms of back pain, leg pain, or hamstring tight- ness. Boos N, Marchesi D, Zuber K, Aebi M (1993) Treatment of severe spondylolisthesis by reduction and pedicular fixation. A 4–6-year follow-up study. Spine 18:1655 – 1661 This paper compares the surgical treatment of severe spondylolisthesis by posterolateral fusion with and without interbody fusion. The majority of patients with single postero- lateral fusion demonstrated loss of reduction, non-union and implant failure. The authors suggest that pedicular fixation systems only allow permanent reduction and sta- bilization of high-grade spondylolisthesis in conjunction with a combined interbody and posterolateral fusion. Moller H, Hedlund R (2000) Instrumented and noninstrumented posterolateral fusion in adult spondylolisthesis: a prospective randomized study: part 2.Spine25:1716 – 1721 This prospective randomized study assesses whether posterolateral fusion in patients with adult isthmic spondylolisthesis results in an improved outcome compared with an exercise program. Pain and functional disability were quantified before treatment and at 1- and 2-year follow-up assessments by visual analog scales (VAS). The data shows that surgical management of adult isthmic spondylolisthesis improves function and relieves pain more efficiently than an exercise program. The results suggest that the use of supple- 758 Section Spinal Deformities and Malformations mentary transpedicular instrumentation does not add to the fusion rate or improve clini- cal outcome. Molinari RW, Bridwell KH, Lenke LG, Baldus C (2002)Anteriorcolumnsupportinsur- gery for high-g rade, isthmic spondylolisthesis. Clin Orthop Rel Res 394:109 – 120 This study compares the outcome of two techniques of surgical management of high- grade isthmic spondylolisthesis. While reduction and circumferential fusion including anterior structural support had no pseudarthrosis, the incidence of non-union in patients treated with in-situ fusion or decompression and reduction with sole posterior instrumentation was 39%. Outcomes regarding pain after treatment, function, and satis- faction were high in those patients who achieved solid fusion regardless of the method. Gaines RW (2005)L5 vertebrectomy for the surgical treatment of spondyloptosis. Thirty cases in 25 years. Spine 30:66 – 70 Thirty cases of vertebrectomy are reviewed over a significant time span. Complication review showed that 23 patients had some temporary clinical deficit in the L5 root for 6 weeks up to 3 years after reconstruction. All but two recovered fully. One patient had retrograde ejaculation, and two patients needed revision surgery for screw breakage due to non-union. No patient had junctional problems and overall patients were clinically sat- isfied with the procedure. McAfee PC, DeVine JG, Chaput CD, Prybis BG, Fedder IL, Cunningham BW, Farrell DJ, Hess SJ, Vigna FE (2005) The indications for interbody fusion cages in the treatment of spondylolisthesis: analysis of 120 cases. Spine 30:60 – 5 The authors review 120 cases of patients with spondylolisthesis of varying etiologies sur- gically managed by 360° instrumentation in respect to their radiographic outcome. Also, complications are assessed. Seven incidental durotomies and three infections were recorded. There was an excellent rate of fusion at 98% and the authors conclude that an important part of the success was regaining neuroforaminal height due to distraction and the interbody spacer. Schlenzka D, Remes V, Helenius I, Lamberg T, Tervahartiala P, Yrjonen T, Tallroth K, Osterman K, Seitsalo S, Poussa M (2006)Directrepairfortreatmentofsymptomatic spondylolysis and low-grade isthmic spondylolisthesis in young patients: no benefit in comparison to segmental fusion after a mean follow-up of 14.8 years. Eur Spine J 15:1437 – 47 Clinical, radiographic and MRI assessment of the long-term clinical, functional, and radiographic outcome of direct repair of spondylolysis using cerclage wire fixation according to Scott in young patients with symptomatic spondylolysis or low-grade isth- mic spondylolisthesis (n=25) as compared to the outcome after uninstrumented pos- terolateral in situ fusion (n=23). In conclusion, the results of direct repair of the spon- dylolysis according to Scott were very satisfactory in 76%. After direct repair, the Oswe- stry Disability Index (ODI) deteriorated with time leading to a clinically moderate but statistically significant difference in favor of segmental fusion. Lumbar spine mobility was decreased after direct repair. Secondary segmental instability above the spinal fusion was not detected. The procedure does not seem to be capable of preventing the olisthetic disc from degeneration. The theoretical benefits of direct repair could not be proven. 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In children with high-grade spondylolisthesis,fusiontoL4is often. percentage of slippage in measuring instability and progres- sion. Spondylodesis alone, even in the presence of minor neural deficits, tight ham- strings, or both, gave relief of pain and resolution of