The implications of stress patterns in the vertebral body under axial support of an artificial implant.

Clinical studies show an association between changed load patterns both in the disc and its adjacent vertebral body, with painful degenerated discs. This suggests that failure to restore the normal loading pattern on implantation of a disc replacement could be a cause of lower clinical success rate. In the present study the variations of load patterns in the vertebra after disc implantation was studied using a simplified finite element models of natural and artificial discs. The effect of implant size and presence of voids at the implant-bony endplate interface were studied, for the worst case scenario of no bone remodelling. An altered stress pattern was observed in the vertebrae of implanted segments. The use of smaller size implants and presence of voids at the interface caused localized stress concentration in the endplate and adjacent cancellous bone. The study results support the hypothesis that current implants fail to restore normal loading patterns in the vertebral body, and the localized high stress regions could be the source of pain, and the cause of low success rate of TDRs.

The myth of lumbar instability: the importance of abnormal loading as a cause of low back pain.

Spinal fusion became what has been termed the "gold standard" for the treatment of mechanical low back pain, yet there was no scientific basis for this. Operations of fusion for low back pain were initially done at the beginning of the last century for back pain thought to be related to congenital abnormalities or for past spinal infection. The recognition of the disc as a cause of sciatica, commonly associated with back pain, and the recognition that a degenerate disc led to abnormal movement suggested the concept that this abnormal movement was the cause of pain, and this abnormal movement came to be called "instability". Much biomechanical expertise confirmed the fact that degenerate discs led to abnormal movement, there were many hypothesis as to why this caused pain. However clinical results of fusion for back pain were unpredictable. The failure of pedicle screws and cage fusion to improve the clinical results of fusion despite near 100% fusion success, and the introduction of "flexible stabilization" and artificial discs, which demonstrated that despite the often unpredictable movement permitted by of these devices, clinical success was similar to fusion, directed attention to the other role of the disc, that of load transfer, which these devices also affected. Abnormal load transfer was already known to be critical in other joints in the body and had led to the use of osteotomy to realign joints. The relevance of load transfer to the future design of spinal implants used in the treatment of low back pain is discussed, and some finite element studies are reported demonstrating the likely effect of abnormal loading beneath an incompletely incorporated plate of an artificial disc, perhaps explaining in part the somewhat disappointing clinical results to date of the implantation of artificial discs.

Scientific basis for the treatment of low back pain.

Disc degeneration causes back pain because the function of the disc as a load transferring structure is abnormal, producing abnormal patterns of load which cause pain. Fusion has been unpredictable because it only fortuitously addresses loading. A fusion may be in such a position that it takes load from the disc, and this may be reflected in the way the fusion models, demonstrating a weight bearing pattern, but this is unpredictable. Recognition that we are dealing with a problem of load transfer allows us to design any surgical implant to solve this problem, without stopping movement.

Cages: outcome and complications.

The coincidental development of minimal intervention techniques for carrying out anterior lumbar spinal fusion and the introduction of cages to provide mechanical support of introduced bone graft led to the development of a type of cage suitable for both minimal intervention use (laparoscopic) and for the standard open procedure (the BAK cage). Reported results concentrated in the main on feasibility, safety and fusion rate achieved, rather than clinical outcome. Laparoscopic insertion at the lumbosacral level was as safe as if the procedure was an open one, although there was a slighter higher incidence of retrograde ejaculation. Immediate post-operative morbidity was less with the laparoscopic procedure and discharge home and return to work was earlier. There was no long-term benefit from the laparoscopic procedure. Laparoscopic insertion at the L4/5 level was attended by a greater incidence of complications, and had a longer learning curve.

Lumbar disc high-intensity zone: the value and significance of provocative discography in the determination of the discogenic pain source.

Disagreement still exists in the literature as to the significance of the high-intensity zone (HIZ) demonstrated on magnetic resonance imaging (MRI) as a potential pain indicator in patients with low back pain. A prospective blind study was therefore conducted to evaluate the lumbar disc high-intensity zone with the pain provocation response of lumbar discography. Consecutive patients with low back pain unresponsive to conservative treatment and being considered for spinal fusion were subjected to MRI followed by lumbar discography as a pre-operative assessment. The discographer was blinded to the results of the MRI scans. We used the chi-squared test to analyse our results. Ninety-two HIZs were identified in 73 patients, mainly occurring at L4/5 (48%) and L5/S1 (35%). Significant correlation was found between abnormal disc morphology and the HIZ (P < 0.001). In morphologically abnormal discs (grades 3, 4 and 5), there was a significant correlation between the HIZ and exact or similar pain reproduction (P < 0.001). The sensitivity, specificity and positive predictive value for pain reproduction were high, at 81%, 79% and 87% respectively. The nature of the HIZ remains unknown, but it may represent an area of secondary inflammation as a result of an annular tear. We conclude from our study that the lumbar disc HIZ observed on MRI in patients with low back pain is likely to represent painful internal disc disruption.

Medical decompression of vertebral hydatidosis.

STUDY DESIGN: A case report from one of the longest follow-up studies of survivors with spinal hydatid disease. This patient was treated with a combination of albendazole and praziquantel chemotherapy; the results of this form of treatment are reported. OBJECTIVES: To demonstrate the efficacy of combination albendazole and praziquantel drug treatment for spinal hydatidosis. SUMMARY OF BACKGROUND DATA: Although echinococcal infestation in humans is a world-wide problem, it is rarely seen in the United Kingdom. Between 1% and 2% of all cases involve bone, and 50% of these involve the spine. The condition has a reported mortality rate of more than 50%. The average length of survival of patients with echinococcal infestation in Britain after the onset of symptoms is 5 years, and the average age at death is 41 years. METHODS: The patient in this report had undergone multiple spinal debridement operations alongside internal fixation and presented with increasing paraparesis from recurrent disease. Surgery for disease recurrence carries a high risk of mortality. The patient was treated with a preoperative combination of albendazole and praziquantel drug therapy, a novel combination for this condition. RESULTS: Response to treatment was monitored clinically, biochemically, and with serial computed tomography. No serious side effects were observed. Results were very encouraging. After 2 months of treatment she had improved and was able to walk with the aid of a walking frame; therefore, surgery was deferred. CONCLUSION: The combination of albendazole and praziquantel drug therapy appears to be effective in the conservative treatment of patients with inoperable spinal hydatidosis.

The effects of posterior fixation on internal intervertebral disc mechanics.

Posterior fixation of intervertebral discs is used to treat, and occasionally diagnose, discogenic pain since it is thought that it will reduce the internal loading of the discs in vitro. We measured the internal loading of ten intervertebral discs using stress profilometry under simulated physiological loads and then after posterior fixation. Partial discectomies were performed to simulate advanced disc degeneration and the sequence repeated. Posterior fixation had very little effect on the magnitude of the loads acting on the disc and none when disc degeneration was simulated. It did, however, reduce bulging of the anterior annulus under combined bending and compression (p < 0.03). Recent experiments in vivo have shown that discogenic pain is associated with abnormal bulging of the annulus which suggests that the clinical benefit of fixation may be due to this.

Temporary external fixation for low back pain: is it worth doing?

Thirty-three patients with low back pain underwent spinal fusion following a positively predicting external fixation test. Thirty-two spinal fusions and one sacroiliac joint fusion were performed. The complications following the use of the external fixator were significant. The results following spinal fusion were not related to the positive response to the external fixator. Multiple variables affect the results of spinal fusion. We feel that the external fixator test in low back pain management is very invasive, and its use cannot be justified.

In vivo stress measurement can predict pain on discography.

STUDY DESIGN: An in vivo experimental investigation of internal disc mechanics and discogenic pain. OBJECTIVES: To test the hypotheses: 1) The pattern of internal loading of intervertebral discs in vivo is similar to that measured previously in vitro; 2) stress concentrations also are found in clinically degenerate discs in vivo; and stress concentrations are associated with discogenic pain. SUMMARY OF BACKGROUND DATA: Stress concentrations corresponding to potentially painful loading patterns of the intervertebral disc and endplate have been observed in vitro. METHODS: The distribution of stress within the lumbar intervertebral discs of patients with chronic discogenic pain was measured using stress profilometry. The severity of their pain was assessed using provocative discography. RESULTS: Discogenic pain was found to be associated with anomalous loading of the posterolateral anulus (P < 0.001) and nucleus (P < 0.01). Painful discs were found to have a 38% wider posterolateral anulus (P < 0.023) than painless discs and to have a 63% lower mean nuclear stress (P < 0.017). CONCLUSIONS: Stress profilometry is an effective investigation of the mechanics of intervertebral discs in vivo. Discogenic pain is caused by changes in the pattern of loading of the posterolateral anulus or nucleus pulposus.

Sir William Gowers 1845-1915.

This is a brief review of the life and contributions to neurologic science of Sir William Gowers. He was a neurologist in England in the late 19th century who, before the availability of modern diagnostic aids, established the importance of clinical examination, including history and physical signs, in the diagnosis of neurologic disorders. He was the first neurologist to identify a removable spinal tumor. He arranged for his colleague, Sir Victor Horsley, to remove it and the operation was completely successful. He invented the patella hammer and his book "Manual of Diseases of the Nervous System" (in two volumes) was the standard reference until early in the 20th century.

Adolescent disc protrusions. A long-term follow-up of surgery compared to chymopapain.

STUDY DESIGN: This study compared chymopapain with primary surgery in the treatment of 60 radiologically proven adolescent lumbar disc protrusions and symptoms of low back pain and sciatica; the failures of intradiscal therapy were treated by surgical discectomy. OBJECTIVES: To establish whether chymopapain is as good as primary surgery in treating adolescents with proven lumbar disc protrusions. SUMMARY OF BACKGROUND DATA: Symptomatic lumbar disc protrusions are rare in white adolescents; the reported incidence varies from 0.8% to 3.2% of all lumbar disc protrusions. This is the largest study with long-term follow-up in the world literature. METHODS: Forty-two patients between the ages of 13 and 19 years with proven lumbar disc protrusions were initially treated with chymopapain; the failures of intradiscal therapy were treated by surgical discectomy. Eighteen patients were treated with surgical discectomy. After initial review at 1, 3, 6, and 12 months, the patients were assessed using a postal questionnaire and telephone interview at a minimum of 5 years' follow-up (means: 8.5 years for chymopapain group, 7.2 years for surgery group). RESULTS: Full replies were received from 16 of 18 (89%) in the surgery group and 42 of 42 (100%) in the chymopapain group. The long-term outcome is classed as good or excellent in 81% of the surgical group and 64% in the chymopapain group. If chymopapain is used as a first-line treatment, with surgery reserved for the failures, the long-term outcome is good or excellent in 82%. The chymopapain group had a shorter hospital stay. The surgical group were more likely to be unemployed and were less able to perform manual work and less able to engage in sporting activity. CONCLUSIONS: Back pain, radicular pain, and tension signs are common, but neurologic signs are less frequent in this age group. Long-term results of surgery are no better than the results of first-line chymopapain treatment with surgery being reserved for the failures. In 60% to 70% of patients, the morbidity, cost, and hospital stay were lessened. The patient is more likely to be in satisfactory employment after chemonucleolysis than after primary surgery.

Chronic contained rupture of an aortic aneurysm mimicking infective spondylitis.

Chronic contained rupture of an abdominal aortic aneurysm is rare. These aneurysms are small and affected patients are usually normotensive. The resultant pseudoaneurysmal sac may cause extensive vertebral erosion. Diagnosis is often delayed as the condition may present with symptoms referable to the lumbar spine. This report is of two cases where the initial diagnosis was infective spondylitis.

Automated percutaneous lumbar discectomy. An outcome study.

We treated 137 patients with symptomatic lumbar disc prolapse by automated percutaneous lumbar discectomy (APLD). Seventeen (12%) required further operation. At a mean follow-up of 55 months, the success rate was 45%. Of those who had APLD alone, 52% were graded as either excellent or good. In this group, 76% were employed, and the mean Oswestry score was 28.2%. One-third of those patients initially rated as successful had deterioration in symptoms and increased disability from back pain. The Short Form 36 health survey questionnaire revealed that these patients had a chronic ill-health profile.

The Graf stabilisation system: early results in 50 patients.

The results of the first 50 consecutive patients using the Graf stabilisation system are presented. The average age of the patients was 41 years; there were 32 women and 18 men in the group. All patients suffered from intractable symptomatic degenerative disc disease which could be localised to one or more levels. All patients gave a history of chronic back pain, but the mean period of severe disability was 24 months. The mean preoperative disability score (Oswestry questionnaire) was 59%. The average period of follow-up was 24 months (range 19-36 months). At the latest review, the mean disability score was 31%. The clinical results were classified as "excellent" or "good" in 72% of patients, "fair" in 10%, "the same" in 16% and "worse" in 2%. All but three patients felt that surgery was worthwhile. The results have not deteriorated over the period of follow-up.

Femoral nerve palsy. An unusual complication of anterior lumbar interbody fusion.

SUMMARY OF BACKGROUND DATA: Compression neuropathy of the femoral nerve has been reported as an uncommon complication of bleeding into the iliopsoas muscle. OBJECTIVE: The authors detected anatomic reasons of direct injury to the femoral nerve at the lower lumbar level. METHODS: Keeping the hip in extension during the course of carrying out anterior fusion on a previously failed posterior fusion was considered another causative factor of femoral nerve injury. Anatomical dissection confirmed the likelihood of this injury being produced in this situation. RESULTS: Femoral nerve traction and compression can occur after prolonged compression of the nerve within the psoas muscle stretched between an immobile lower lumbar spine and the lesser trochanter when the hip is kept in extension. In the patients described no other reasons for direct or indirect injury were identified. CONCLUSION: Although uncommon, the complication should be kept in mind. It can be avoided by intraoperative hip flexion.