3.17 Spondylolisthesis and spondylolysis

Spondylolisthesis is the forward slip of a vertebra on another. The most common cause is degenerative spondylolisthesis which is seen in the older population as a result of disc and facet joint degeneration. In the young, the majority of vertebral slips are of the isthmic type in which an interruption (spondylolysis) or elongation of the pars interarticularis (isthmus) of the vertebral arch is present (Figures 3.17.1–3.17.3). Dysplastic spondylolisthesis develops because of congenital changes in the upper part of the sacrum and the vertebral arch of L5. Subluxation of the facet joints is always present in this form. True dysplastic spondylolisthesis is extremely rare. According to the classification of Newman and Wiltse (Table 3.17.1), additional types of spondylolisthesis are traumatic spondylolisthesis in acute fractures and pathological spondylolisthesis caused by infection or tumour destruction of parts of the vertebral arch. Iatrogenic spondylolisthesis after excessive resection of posterior vertebral elements should be added. The Wiltse classification has been critisised rightly for being inconsistent and mixing aetiologic (e.g. dysplastic) and anatomic (e.g. isthmic) terms. As its inventors already realised, the distinction between isthmic and dysplastic forms is not always possible. And no specific treatment guidelines are derived. To overcome these shortcomings, improved classification systems have been proposed by Marchetti and Bartolozzi (1997) and Mac-Thiong and Labelle (2006). They are rather complex and do still not yet allow a clear scientifically based distinction between dysplastic and isthmic slips. Furthermore, their treatment recommendations are not validated in clinical series so far. For clinical decision making at present, the essential factors are the degree of slip, the sagittal alignment (lordosis/kyphosis) at the level of the slip, patient’s age, and symptoms. In this context, it is of secondary interest whether a slip is to classify e.g. as dysplastic or not.

Spondylolysis is a fatigue fracture of the isthmus of the vertebral arch with the histological characteristics of a fibrocartilaginous pseudarthrosis. The lysis may heal, resulting in a normal or elongated isthmus (Figure 3.17.4).

Spondylolisthesis affects only humans. It has never been described in animals except in an experimental study.

Spondylolysis has never been found in a newborn. The youngest reported patient with spondylolisthesis reported in the literature was 3.5 months old, and a case reported of unilateral spondylolysis with 4-mm slip in a 10-month-old girl. In Caucasians the prevalence of spondylolysis is 4.4–5% at early school age. It increases during growth, and is 6–7.2% in adults. In some ethnic groups the prevalence is much higher (Alaskan Inuit, 32.9%; Japanese Aino, 41%). Isthmic spondylolisthesis is more common in males, but severe slips occur more frequently in females. Lumbar spondylolysis affects the fifth lumbar vertebra in 90% of cases, the fourth in 5%, and the third in 3%. Symptomatic spondylolysis is more likely if it occurs in the segments above L5. Spondylolysis may be present without vertebral slip. In most cases, however, it leads to spondylolisthesis. In the majority of individuals the slip is mild (10–20% of vertebral body length). The slipping occurs during the growth period, and slip progression is rare after growth is complete.

Risk factors for the progression of spondylolisthesis in young individuals are a high degree of slip and age before growth spurt.

The trapezoidal shape of the slipped vertebral body and rounding of the upper endplate of the sacrum are secondary changes.

According to Laurent and Einola (1961), slip is measured as the ratio of the sagittal slip to the sagittal length of the slipped vertebral body expressed as a percentage (Figure 3.17.5A). The lumbosacral kyphosis seen in more severe slip is assessed from the same radiograph and measured as the angle between the posterior border of the first sacral vertebral body and the anterior or posterior border of the fifth vertebral body (Figures 3.17.5B and 3.17.6A).

Spondylolysis is related to the erect posture of humans and to lumbar lordosis. A higher incidence has been found in individuals practising sporting activities with repeated hyperextension movements of the lumbar spine and/or lifting (e.g. gymnasts, divers, javelin throwers, weight lifters, ballet dancers). The possible role of particular sagittal profiles and pelvic parameters (including elevated pelvic incidence) is emerging.

Marty et al (2002) found that individuals with spondylolisthesis have a higher pelvic incidence, a steeper sacral slope and a greater sacral kyphosis than control persons. The concept of abnormal pelvic morphology and disturbed spino-pelvic balance in spondylolisthesis is supported also by other authors. However, Huang et al (2003) could not confirm increased pelvic incidence as a predictor of slip progression. Based on an anthropological study, Whitesides et al. (2005) stated that increased pelvic incidence in spondylolisthesis appears to be secondary to changes in the sacral table angle (i.e. the angle between the superior endplate and the posterior wall of S1) caused by the slip.

The condition can also be inherited. The primary site of the inborn error has not yet been identified. It may in the bony structures (isthmus dysplasia), or in the soft tissues (intervertebral disc, ligaments), or in both leading to a particular sagittal profile with a high pelvic incidence and a high lumbar lordosis.

The disc below the slipped vertebra is pathological even in young individuals whether or not they have pain. Degeneration of the adjacent disc above the slipped vertebra is common in symptomatic patients. Symptomatic disc hernia at the level of the slip is rare in patients with isthmic spondylolisthesis.

Lumbar scoliosis is seen as a secondary phenomenon to spondylolisthesis. ‘Sciatic’ scoliosis is due to pain and muscle spasm, and usually disappears after relief of symptoms. Structural (‘olisthetic’) curves are caused by rotational displacement of the slipped vertebra. Lumbosacral fusion is indicated if progression occurs (Figure 3.17.7).

Thoracic scoliosis in a patient with lumbar spondylolisthesis is managed as a separate entity according to the normal procedure for scoliosis management (see Chapter 3.10).

The natural history of isthmic spondylolisthesis is benign in the majority of cases. The affected segment stabilizes itself. Even so, isthmic spondylolisthesis is the most important cause of low back pain and radiating leg pain in children and adolescents. The prognosis of back pain and working ability of adults with isthmic spondylolisthesis is no different from the rest of the population. Back pain symptoms in adults are related to the following:

There is no explanation yet as to why some people with spondylolysis or isthmic spondylolisthesis become symptomatic while the majority remain symptom free. It is also unknown why slips above L5 seem to cause relatively more pain symptoms than L5 slips. The proposed sources of the pain include the lytic defect itself, the intervertebral disc, and the ligaments. This is not yet resolved.

The onset of the symptoms is often spontaneous. In young patients there is often a history of sports activities. Sometimes acute trauma is reported.

The main symptoms are as follows:

In severe slip (>50%) symptoms may include:

There is no direct relationship between severity of subjective symptoms and the amount of slip.

Gait and posture are normal unless radicular symptoms are present or the slip is severe. The mobility of the lumbar spine is free or decreased due to muscle spasm and pain. There is local tenderness during palpation and in most cases a step can be felt between the spinous processes at the level of the slip. Hamstring tightness is common in younger patients. The Laségue test is usually negative. Muscle power, reflexes, and skin sensation of the lower extremities are normal in the majority of patients.

In severe slips, the posture of the patient is abnormal (Figure 3.17.8). The sacrum is in a vertical position due to retroversion of the pelvis. There is a short kyphosis at the lumbosacral junction and a compensatory hyperlordosis of the lumbar spine, usually reaching up into the thoracic region. The spine is scoliotic and often out of balance. The patient is unable to extend hips and knees fully during standing and he or she walks with a typical pelvic waddle. The hamstrings are extremely tight and signs of neural impairment (muscle weakness, disturbances of skin sensation, incontinence) may be present. Astonishingly, even in very severe slips, neurological findings are rare and many patients are often free of pain despite significant posture changes and hamstring tightness.

The vertebral slip is diagnosed from a plain lateral radiograph of the lumbar spine taken in standing position and centred on the lumbosacral junction. In most cases the lysis can be seen from the lateral radiograph. If there is doubt, oblique radiographs will show the defect (Figure 3.17.9). A computed tomography (CT) scan with tilted gantry is the most reliable imaging mode for demonstrating the spondylolysis (Figure 3.17.10).

Magnetic resonance imaging (MRI) demonstrates the shape of the spinal canal and possible compression of neural structures (Figure 3.17.11) and shows degenerative disc changes in and above the olisthetic segment (Figure 3.17.12). However, the clinical relevance of disc degeneration seen on MRI is unclear and therefore in this respect MRI is uncertain.

Technetium scintigraphy is used in patients where fresh (tra umatic) spondylolysis is suspected with normal radiographs. The impending lysis may be seen in the scintigram (Figure 3.17.13). It also helps to judge the possible healing of the defect.

Electroneuromyography may be indicated in cases with clinical neurological signs. Discography can be used for preoperative assessment of the condition of the disc(s) above the slipped vertebra.

Symptomatic spondylolysis or mild spondylolisthesis (up to 25% slip) is treated non-operatively by decreasing the level of physical activities, strengthening of back and abdominal muscles, and sometimes a brace or plaster of Paris jacket.

At this stage it is very important to explain to the patient and his or her parents that the natural course of the condition is benign and that the symptoms resolve, usually after several months, without any special treatment. Sports players are advised to modify their training program to avoid pain-causing exercises. There is no reason to stop all physical activities. Younger patients before or during the growth spurt should be followed up with radiographs at 6- to 12-month intervals because of the risk of progression at this age.

Indications for operation in children and adolescents are:

The choice of operative procedure depends on the amount of slip and on the personal experience and preferences of the surgeon. Table 3.17.2 represents the author’s policy and is used as a guideline for decision-making. The final decision is an individual one depending on the patient’s skeletal maturity, gender, anatomical features of the slip, ability to cooperate, and the aspirations of the patient and his or her parents.

Uninstrumented segmental posterolateral fusion in situ using autogenous bone from the posterior iliac crest is the method of choice for cases with slip up to 50% (Figure 3.17.14). The segment above the slipped vertebra is not usually included in the fusion in young patients even if it shows signs of degeneration in discography or on MRI. The patient is mobilized 2 or 3 days after the operation wearing a soft brace for 3 months. Sports activities are forbidden for about a year. There are no restrictions on physical activities after solid healing of the fusion. This method is safe and effective, and there are no specific complications. In this young age group, bony fusion is achieved in almost 90% of cases, and subjective results are good or satisfactory in 82–96%. Symptoms disappear in most cases even when solid fusion is not achieved.

If there is a lysis without a slip or a very mild slip, direct repair of the isthmic defect is recommended. Different methods of internal fixation (screws, cerclage wires, butterfly plates, hook plates) have been described. The author prefers Scott’s wiring technique (Figure 3.17.15). Postoperative immobilization with a plastic thoracolumbosacral orthosis is recommended for 3–6 months. Equivalent results to the results of posterolateral fusion can be expected in the mid-term. Schlenzka et al (2006) were not able to prove the benefit of direct repair in comparison to segmental fusion in a long-term study.

If the slip exceeds 50%, the physiological lumbosacral lordosis decreases and a progressive kyphotic deformity develops. For biomechanical reasons, posterior or posterolateral fusion is not sufficient to prevent progression without anterior support. Anterior interbody fusion through a transperitoneal approach using autogenous tricortical iliac crest grafts is preferred (Figure 3.17.16). Combined anterior and posterolateral (circumferential) fusion is necessary to stop progression in slips with significant lumbosacral kyphosis (more than 10–20 degrees) (Figure 3.17.17). There is no need to include more than the olisthetic segment into the fusion. After anterior or combined procedures the patient is mobilized at the second or third postoperative day and wears a plastic thoracolumbosacral orthosis for 3–6 months. The clinical results of anterior and combined fusion in severe slip are comparable to the results of posterior or posterolateral fusion. The risk of complications is obviously higher in anterior fusion. Massive intraoperative bleeding, postoperative thrombosis, and retrograde ejaculation in male patients may occur. However, in experienced hands these complications are rare.

Reduction of the slipped vertebra is technically possible. So far no benefit has been shown for reduction procedures compared with fusion in situ. There is a high risk of complications related to these procedures. At this stage of knowledge, the author would consider slip reduction in children and adolescents only for cases of spondyloptosis (slip of 100% or more).

Decompressive laminectomy is indicated in young patients only in rare cases where there is true impingement of neural structures. If decompression is performed during growth, segmental fusion always has to be added to prevent subsequent progression of the slip.

The primary treatment of a symptomatic spondylolysis or isthmic spondylolisthesis is non-operative. Load reduction, stabilizing exercises of abdominal and back muscles, local injections of steroids/local anaesthetics, physiotherapy, a soft brace, and pain-relieving drugs should be tried first. In some cases changes to the working environment of the patient may be necessary. It is very important to give the patient objective understandable information. One should not underestimate the psychological effect on a non-medical person of being told that a vertebral arch in his or her back has ‘broken’ and has caused ‘slipping’ of the vertebra. The natural history of this condition has to be explained to the patient with special emphasis on the benign course and the tendency of the process to self-stabilize in the long term.

Indication for operation is severe low back and/or radiating pain which does not respond to the measures described earlier and interferes significantly with the patient’s daily activities.

Decision-making is much more difficult than in the treatment of young patients. The older the patient, the more likely it is that changes outside the lytic/olisthetic segment are responsible for the symptoms, i.e. one has to clarify whether the radiological finding of spondylolysis or isthmic spondylolisthesis is really the sole cause of the patient’s symptoms. In addition to the patient’s history and physical examination, a thorough analysis of all aspects of the individual case is mandatory. Pain analysis (pain drawing, visual analogue scale, Oswestry Questionnaire) and assessment of the patient’s psychosocial situation are performed. Radiological investigations include flexion–extension views and discography to identify the actual source of pain. Diagnostic pars blocks can be very useful and may identify the spondylolysis as an isolated source of pain and pars repair could be considered.

The choice of the operative procedure depends on the results of the preoperative work-up. Posterolateral fusion augmented with transpedicular instrumentation (Figure 3.17.18) is performed in patients who suffer mainly from low back pain. If root symptoms are predominant, decompression (Gill’s operation) is indicated. During this procedure the loose lamina and the pseudarthrotic tissue of the lysis are carefully removed bilaterally. The nerve roots have to be totally free after this resection. In some patients the roots are caught under the pedicle. Additional resection of the medial and inferior parts of the pedicle is necessary to achieve complete nerve root decompression. Gill’s operation alone is sufficient only if the olisthetic disc is severely degenerated and the segment is stable. Otherwise, instrumented posterolateral fusion is added.

The extension of the fusion proximally (one or more segments) depends on the condition of the segment(s) above the slipped vertebra.

Direct repair of the spondylolysis may be performed in young adults with symptomatic spondylolysis or mild slip if the condition of the disc is satisfactory on MRI investigation. The author uses this procedure in adults mainly at the L4 level because in the L5 slip the disc below is almost invariably abnormal.

Slip reduction is not usually indicated in adult patients. Adult patients with a severe slip (>50%) should be treated by decompression and instrumented fusion in situ to the sacrum. Sometimes the fusion will need to extend to L4 depending on the slip angle, the disc/facet status, and the slip angle.

In cases of spondyloptosis with severe symptoms and impairment of patient’s posture, L5 vertebra resection and fusion of L4 onto the sacrum may be considered. This is a high-risk procedure and should be performed only by very experienced spine surgeons (Figure 3.17.19).

The results of operative treatment of isthmic spondylolisthesis in adult patients are as unpredictable as all low back pain operations. The literature is unhelpful because of different approaches to patient selection and the influence of the specific socioeconomic environment in different countries. One study reported a fusion rate of 88% after uninstrumented posterolateral in situ fusion and a clinical success rate of 55% in 45 adult patients. Risk factors for a poor outcome were compensation cases and pseudarthrosis. A trend towards unsatisfactory result was seen in males, middle-aged individuals, smokers, and patients with preoperative radicular symptoms. Another study used transpedicular fixation and achieved a 94% fusion rate. They reported numerous instrumentation-related complications (malposition of screws with and without neurological damage, screw loosening, and breakage). There is no evidence that the addition of interbody spacers would improve patients’ outcome. Most of the complications were of no clinical importance, but the potential danger of implants is obvious. They should be used only by well-trained spine surgeons.

Spondylolysis occurs in 4.4% of children and about 6% in the adult population. In general it is a benign condition. The majority of individuals that develop mild or moderate isthmic vertebral slip remain free of symptoms for their whole life or show only mild symptoms.

In children and adolescents with mild slip, primary treatment of pain symptoms is non-operative. Young children before growth spurt need radiographic follow-up to check for progression. If the slip exceeds 25% in a child, segmental fusion should be considered. Uninstrumented posterolateral fusion is the method of choice for treatment of pain symptoms not responding to conservative measures in slips up to 50%. In severe slips (>50%) anterior or combined fusion is necessary to prevent further progression of lumbosacral kyphosis. The clinical results of in situ fusion in this age group are satisfactory in 80–90%. Slip reduction has not yet been shown to be superior to in situ fusion. It may be performed in cases with spondyloptosis and severe impairment of neurological function and sagittal malalignment of the spine.

In adults, careful analysis of the patient’s problems is crucial to identify the source of pain and the importance of non-organic factors and the environment. If pain is moderate, non-operative treatment is indicated. If symptoms persist and interfere with daily activities, operation may be necessary. Decompression (Gill’s operation) is indicated if radicular symptoms are dominant. Posterolateral spondylodesis augmented by transpedicular fixation leads to solid fusion in over 90% of patients. Subjective outcome depends very much on patient selection. Slip reduction is not indicated in adult patients. Vertebra resection may be considered in adult patients with severe subjective and objective symptoms due to spondyloptosis.