Between October 1997 and October 2001, circumferential spinal fusion using Diapason® pedicle screw instrumentation (Stryker) and Brantigan® anterior interbody fusion cages (DuPuy) was performed on 43 patients with chronic low back pain. These patients were selected for surgery by the senior author (NB) from his private and public (National Health Service - NHS) practices. The same selection criteria were used for all patients. All patients were operated on by the senior author who is an orthopaedic surgeon specialising in spinal surgery (Table 1).

Figure 1

Table 1: Patient demographics

Patients had clinical and radiographic evaluation in a spinal clinic for a minimum of two years. Follow-up was at six weeks, three, six, twelve and twenty-four months post-operatively at which a full clinical evaluation was carried out and plain antero-posterior (AP) and lateral standing radiographs were taken. The x-rays from the two-year follow-up clinic visit were independently reviewed by two orthopaedic surgeons to determine whether fusion was present. The criteria used to establish fusion in patients with radiolucent interbody implants in conjunction with pedicle screw instrumentation are those described by Brantigan and Steffee.₄

• Trabeculae seen bridging the interbody gap with isodense bone in the cage and the adjacent vertebral bodies

• Anterior and/or posterior sentinel signs

• No lucencies around the pedicle screws

• No lucencies around the cages

• Integration of the cage with the endplates and silhouetting of the cage

• No detectable movement on flexion and extension lateral x-rays

All six of these criteria needed to be met to allow the observers to conclude that there was fusion.

The final follow up was by postal questionnaire and outcome measures used were:

• Low Back Outcome Score 13

• The Prolo Economic Score (after Schnee) 14

• A Patient Satisfaction Score composed of the

• • A subjective pain-relief assessment 15

  • • NASS Patient Satisfaction Index 16 modified to include an assessment of whether the patient would recommend the operation to a friend or family member

    • An assessment of the patient’s level of satisfaction with the process of their care before and after surgery 17

Analysis of the outcome data was by descriptive statistics.

Patients were selected by fulfilling a number of strict criteria that are thought to have a positive influence on the clinical and radiological outcomes of spinal fusion. These are listed in Table 2.

When patients were initially seen in the spinal clinic a full history and examination was carried out including an assessment of disability using the Waddell and Main Disability Index and Abnormal Illness Behaviour Scores .₁₈,₁₉ Patients who failed to meet selection criteria 1 and 6 – 11 were not considered for circumferential fusion and were treated in other ways. If patients were obese at presentation, but otherwise fulfilled the criteria for investigation possibly leading to surgery, they were given time and encouragement to lose weight and if they achieved a body mass index (BMI) of less than 30 within twelve months of their initial assessment they were further investigated.

Figure 2

Table 2: Selection criteria for circumferential fusion

If patients were smokers they were given the opportunity to stop, with appropriate pharmacological and psychological support. Abstinence was required for three months before surgery and patients were encouraged to maintain their abstinence for at least six months after surgery. Only one reformed smoker started smoking again in the post-operative period.

The biopsychosocial model has become the most powerful discriminative tool in our practice in selecting patients for any intervention for back pain. Patients with considerable abnormal illness behaviour and a mismatch between their physical symptoms and signs and their disability scores were not considered for elective surgery for chronic back pain. They are offered education, functional restoration and drug therapy for their pain. Occasionally they are referred to the pain clinic for minimally invasive treatments. However, the psychosocial profile as exemplified by abnormal illness behaviour symptoms and signs was not used to penalise patients if they had a genuine organic cause for their pain.₂₀ Rather it guided pre-intervention therapy and in some cases, when the profile improved with non-interventional techniques, allowed the patient to become a candidate for surgical intervention.

Using this triage system, 50% of patients were selected out of the intention-to-treat (by surgery) group by the end of their initial assessment. Those remaining underwent non-invasive treatment consisting of progressive walking and swimming programmes and remedial exercise supervised by a physiotherapist or remedial therapist. After a further six months of treatment, 50% of this group were excluded from consideration for surgery, either because they had improved sufficiently to not need an operation, or because they had not complied with the rehabilitation programme and therefore would be unlikely to cope with a similar post-operative regime.

Of the 25% of the original group of patients left, more than a third declined further investigation when they were asked directly if they would have surgery should the investigations suggest it would be appropriate. 15% of patients then went on to have x-rays and MRI scans, of whom half had multiple levels of degenerative change that immediately precluded them from single or two-level surgical intervention. Of the remainder, facet joint injections and discography were used as minimally invasive tests. The patients were made aware that the injections were tests to try to identify possible pain sources in the lumbar spine and to try to establish a correlation between their MRI findings and their symptoms. If there was a therapeutic benefit, that was a bonus. However, we have found that about 60% of patients who have positive, concordant discograms who are concurrently treated with intra-discal steroids and those with good initial relief from facet injections, will go on to have lasting pain relief and do not need surgery. If there is a good result from these investigations, further physiotherapy is prescribed in the anticipation that clinical improvement will occur if a patient has a pain-free spine and can make their muscles function well irrespective of the appearances of the intervertebral discs on MRI.

Patients who had a good first response to injections, but had a recurrence of pain, were offered a second injection of the same kind to ensure that the first result was not the result of a placebo effect. If they had a second good, but ultimately temporary, result they were offered either intra-discal electro-thermo-coagulation (IDET) or facet joint rhyzolysis, followed by further exercise therapy. By the time this investigatory process had been completed, fewer that 1% of the original cohort of patients who presented to the clinic were candidates for surgery.

Although eventually all patients had back pain for more than two years by the time of surgery, for many when they presented, it had been present for a shorter time. However, the timetable for investigations and conservative treatment was such that by the time they had completed a comprehensive course of physiotherapy and gone through the various diagnostic blocks to establish the correlation between MRI findings and symptoms, more than two years had passed from the first onset of pain.

A further full clinical assessment was made of patients in the weeks prior to surgery to ensure that during the investigatory phase of their treatment they had not developed inappropriate disability or abnormal illness behaviour. If they had deteriorated psychosocially to a significant extent, they were excluded from surgery and offered further cognitive behavioural therapy based functional restoration.

Circumferential fusion was used for those patients who had low back pain with neurological deficit and no significant static radicular pain or whose radicular pain came on with axial loading of a degenerate disc. These patients did not need to have intra-canal surgery and indirect decompression by distraction and anterior interbody stabilisation was thought to be sufficient to relieve radicular symptoms.

A Wiltse posterior approach was used in all cases. Diapason pedicle screws were inserted and were connected with contoured rods, under bi-planar image intensifier control and Neurosign 800 (Magstim Company) active motor nerve monitoring (Figure 1). Distraction was applied to restore the normal sagittal profile. The posterior bony structures were decorticated and autograft from the iliac crest was used to provide the fusion mass. Part of the harvested bone was put aside for the anterior interbody fusion.

Figure 3

Figures 1a & 1b: Neurosign 800 motor-neurone monitoring

Figure 4

The anterior fusion was carried out through a trans-peritoneal approach for single level L5/S1 operations and a retroperitoneal approach for all other procedures. The relevant discs were fully excised except for the peripheral annulus and all the cartilage was removed from the end plates to reveal bleeding bone. The Brantigan ALIF instrumentation was used to assess the size of the interbody space and an appropriate cage was packed with autograft and impacted into the space. Residual bone chips were used to fill the annulotomy defect anterior to the cage.

The senior author had used the Diapason pedicle screw instrumentation for several years prior to the start of this study and therefore was familiar with its technical demands. The Brantigan ALIF cage was chosen as the anterior implant on biomechanical grounds as the modulus of elasticity of the cage is close to cortical bone and therefore load-sharing between the bone graft and the cage is much more likely than when threaded metal cages are used. In addition, the Brantigan cage is radiolucent and in the mid to late 1990’s it was thought that fusion could be adequately assessed using plain radiographs with radiolucent interbody devices.

Postoperatively, patients were mobilised within 24 - 48 hrs and after discharge from hospital wore a rigid lumbo-sacral, custom-built orthosis for 3 months. Their rehabilitation consisted of a progressive walking programme for 6 weeks followed by intensive physiotherapy to restore core stability, flexibility and spinal muscular stamina lasting for up to a further three months.

Formal clinical review of patients was at regular intervals of 6 weeks, 3 months, 6 months, 1 year and 2 years after the surgery. Symptoms of pain and disability were recorded as well as sexual function for men. All the patients were examined for range of motion of the spine, neural tension, presence of an abdominal wall hernia, presence of a sympathectomy effect in the left leg and peripheral neural deficits.

Final review was by postal questionnaire at least six months after the two-year clinical follow up. The mean follow up was 3.5 years (range 2.5 – 6.0 years).

Standing AP and lateral radiographs of the lumbo-sacral spine were taken at each clinic visit with additional flexion and extension lateral views at the two year visit. The final follow up radiographs were evaluated independently by two orthopaedic surgeons for fusion using the criteria listed above. In patients with operations at multiple levels, assessment of fusion included all the levels operated on.

35 fusions were performed at a single level and eight performed at two levels (Table 1).

L5/S1 fusion alone was performed in 24 (55.8%) patients, L4/5 fusion alone in nine (20.9%) and L3/4 fusion in two (4.7%). Eight patients had an L4-S1 fusion (18.6%). There were no fusions above the L3/4 segment. Analysis of the post-operative radiographs at the two-year follow up revealed that spinal fusion was present in all of the 43 cases, at all operated levels (100%) according to the Brantigan and Steffee criteria (Figures 2a & 2b). Further investigations were carried out in the six patients with poor outcomes on the LBOS, including fine-cut CT scanning of operated levels. These scans confirmed that a solid interbody fusion was present in each case thus supporting the validity of the radiological assessments.

Figure 5

Figures 2a & 2b: Antero-posterior and lateral x-rays of an L5/S1 360° fusion showing a solid arthrodesis

Figure 6

The complication rate at final follow-up was 4.7%. The most common early complication was sympathetic dysfunction in the left leg (eight cases – 18.6%), none of which lasted greater than four months. One incisional hernia (2.3%) required repair using a mesh four years after the index procedure, with a very satisfactory outcome for the patient. Six patients (14%) had persistent bone-graft site pain up to one year after surgery, but only one (2.3%) had symptoms beyond one year due to pain felt over the Cluneal nerves. There were no cases of deep infection, clinical deep vein thrombosis or pulmonary embolus. There were no cases of retrograde ejaculation in the men or permanent neurological injury in the whole group.

The mean duration of hospital stay post-operatively was nine days (range 8 -12).

42 patients returned the questionnaires (97.7%). Analysis of the results showed that there was a disparity between the patients’ satisfaction rating and the LBOS score (Table 3). 36 (83.7%) patients were rated as having ‘good’ or ‘excellent’ outcomes according to the LBOS and 39 respondents (90.7%) rated themselves as having “complete” or “good” relief of their presenting pain (Tables 2 and 3).

40 patients (93%) stated that they would opt to have a circumferential fusion again, for the same symptoms, if guaranteed the same post-operative result. 40 patients (93%) stated they would recommend the treatment to a friend or family member with similar trouble.

Figure 7

Table 3: Summary of Outcomes

41 (95.3%) patients returned to full-time normal work or full-time work that was lighter than their pre-operative occupation (E4 and E5 on the Prolo scale defining “success”). One patient did not return to work and assuming the non-responder did not, two patients had failed outcomes using this score.

Five patients had a “fair result” and one had a “poor result” based on the LBOS. One patient was lost to follow-up and was presumed to have a poor outcome. Of the seven detectable failures, two had evidence of a more generalised osteoarthritis causing significant musculoskeletal pain outside of the lumbar spine in the years after their spinal operations and as a result scored badly on the LBOS three and four years after their lumbar surgery. One of these did not return to work, whilst the other was able to return to a lighter job compared to his pre-morbid occupation. One male patient had had three previous posterior spinal operations (two decompressions and an attempted fusion), but was still running his own business before surgery although on regular narcotic medication. Although he said that he had a worthwhile result from his surgery, he scored relatively low on the LBOS as he was not able to regain pain-free spinal motion, although he did return to full-time work within eight weeks of surgery. One woman developed intractable, bilateral leg pain in the S1 distribution in the few weeks prior to surgery without obvious static compression of the nerves on MRI in addition to her constant severe low back pain. Despite having a complete decompression of the roots by front and back surgery (as shown on a post-operative MRI) she was unable to get measurable pain relief and scored badly on the LBOS. Another had only a fair outcome with a borderline acceptable psychosocial profile before surgery, although all of her provocative tests indicated a genuinely painful post-discectomy instability at L5/S1. She developed worsening abnormal illness behaviour in the months after her surgery as a result of adverse life events and her back pain recurred despite good evidence on CT and plain films twelve months after surgery that she had solidly fused. When reviewed five years after operation she was found to be as bad as she was before her operation, hence her low LBOS. The last patient who did not have a successful result had an L5/S1 post-discectomy instability that on provocation was painful with normal discs cephalad. He did not disclose to us, even on direct questioning, that he was involved in active litigation. On this basis he would have been excluded from surgery and offered functional restoration rather than an invasive procedure. Although he had some improvement after surgery his LBOS at final follow-up was less than 25/75 indicating a “poor” outcome. Confounding this score, he was able to return to work albeit doing a less vigorous job than before the onset of his back trouble. At his last review, the litigation had still not been settled.

• A retrospective study of the outcome of 360° lumbar spinal fusion using validated clinical and radiological outcome measures.

• A better correlation exists between subjective satisfaction scores and radiological results that between physician-derived, disease-specific outcome scores and x-rays.

• In conjunction with other recent studies using similar outcome instruments, evidence is presented that it is the careful selection of patients, not the radiological result that most significantly influences the outcome of lumbar spinal fusion.