Erik Tøndevold

No difference in clinical outcome after posterolateral lumbar fusion between patients with isthmic spondylolisthesis and those with degenerative disc disease using pedicle screw instrumentation: a comparative study of 112 patients with 4 years of follow-up

Abstract. We compared the clinical outcome after spinal fusion between patients with isthmic spondylolisthesis and those with degenerative disc disease of the lumbar spine, using multiple logistic regression analysis. A questionnaire describing medication, pain, vocational status and patient satisfaction was mailed to all the patients at a median interval of 4 years after their operation. Fusion was evaluated on plain radiographs at a minimum of 12 months after surgery, and patients were classified as fused or not fused. The overall satisfaction rate was 70%. The results of the present study showed no difference in the outcome after spinal fusion between the two groups of patients. The factors that significantly increased the likelihood of an optimal result – defined as patient satisfaction, return to work, and reduced medication – were male gender, being in work prior to surgery, and being a non-smoker. Since spinal fusion is an expensive treatment with potentially serious risks, and leaves one-third of the patients with an unsatisfactory result, we believe that more studies focusing on the indications for surgery should be performed.

Nonorganic pain drawings are associated with low psychological scores on the preoperative SF-36 questionnaire in patients with chronic low back pain

Abstract The Short Form 36 questionnaire (SF-36) measures general health and well-being. Within the last 5 years it has been used increasingly to characterise patients in the medical literature. Relatively few studies have used the SF-36 on patients with chronic low back pain undergoing preoperative evaluation, but results suggest that it may be predictive of surgical outcome. Pain drawings are a routine part of evaluation prior to spinal surgery in several centres, since their classification of organic or nonorganic has been shown in some studies to correlate well with psychological characteristics predicting poor outcome. The purpose of the present study was to assess possible correlations between nonorganic pain drawings and the psychological scales in the SF-36. We included 128 patients in the study, all of them referred from other hospitals. Previous spinal surgery had been undergone by 25%, and 59% required daily medication because of low back pain. All patients completed pain drawings using predefined symbols These pain drawings were scored dichotomously as organic or nonorganic based on a brief description of a typical nonorganic characteristics. Patients also completed the Danish version of the SF-36 questionnaire. Statistical analysis was performed using logistic regression analysis. The pain drawing classification was used as the dependent variable and scores on the eight scales of the SF-36 as independent variables. P values of <0.05 were considered significant. The mean scores of the patient population on all eight scales were significantly lower than Danish norms. The only scales that correlated with the presence of nonorganic pain drawings were emotional role (RE) and mental health (MH), both measuring psychological health. The odds ratio (OR) of receiving a nonorganic pain drawing was 22 (95% confidence interval, or CI, 7–65) if the scores on RE and MH were more than 2 standard deviations (SD) below the Danish norm. This is the first study providing evidence that pain drawing ratings are influenced by the psychological scales of the SF-36. The clinical relevance of this observation regarding prediction of outcome after spinal surgery should be assessed in future studies.

Observations on Long Bone Medullary Pressures in Relation to Arterial Po2, PCO2 and pH in the Anaesthetized Dog

To investigate the influence of variations in arterial oxygen tensions (PaO2), arterial carbon dioxide tensions (PaCO2), and arterial pH on long bone medullary pressures, seven anaesthetized dogs were investigated. Comparing the control medullary pressures, i.e. the mean medullary pressures obtained at the normal range of PaO2 (75--110 mmHg) with the mean medullary pressures corresponding to the range of PaO2 of less than 75 mmHg, statistically significant (P less than 0.05) decreases were seen in both epiphyseal, metaphyseal and diaphyseal medullary pressures, from 27.6 +/- 5.0 to 15.5 +/- 3.6 mmHg, from 23.5 +/- 2.9 to 13.9 +/- 2.3 mmHg and from 27.7 +/- 3.9 to 18.3 +/- 2.5 mmHg (all mean values +/- s.e. mean), respectively. Hyperoxia, hypocapnia, hypercapnia or metabolic acidosis had no effect on medullary pressures in any of the regions studied.

Clinical outcome after spinal fusion with a rigid versus a semi-rigid pedicle screw system

Several biomechanical studies have evaluated the quality of fusion obtained with a rigid versus a semi-rigid pedicle screw implant. Some studies indicate that increased rigidity of the implant system results in an increased strength of the fusion mass. Other reports have underlined the risk of stress shielding due to rigid implant systems. Based on these findings some authors have recommended the use of a semi-rigid system. There are, however, few studies focusing on any possible difference in clinical outcome between the two different types of implant systems. Questionnaires were sent to 89 patients who had undergone primary spinal fusion with either a rigid or a semi-rigid pedicle-screw-based implant system. In every case the diagnosis was spondylolisthesis or degenerative lumbar disease. The questionnnaires were analysed using forward stepwise logistic regression analysis. Eighty (90%) of the questionnaires were returned. There was a mean follow-up of 4 years (range 2–8 years). It was not possible to demonstrate any difference in clinical outcome between patients undergoing lumbar fusion with a rigid implant system and those given a semi-rigid system. The overall patient satisfaction rate was 69%, with no difference between the two types of implant. No difference in clinical outcome between the two types of implant was found. Considering the fact that the primary goal of spinal fusion procedure is to obtain a solid fusion mass, biomechanical tests favour the used of a rigid pedicle screw system. This fact combined with the fact that early mobilisation is possible with rigid implants justifies the use of rigid implant systems, although no difference in clinical outcome could be demonstrated in this study.

Decreased blood perfusion in canine tibial diaphysis after filling with acrylic bone cement compared with inert bone wax.

Sixteen dogs had one tibia filled with acrylic PMMA bone cement and the opposite, control tibia filled with inert bone wax. After 1, 4, and 12 weeks, the blood perfusion in diaphyses was measured with Sc-46 labeled microspheres. The blood flow rates increased from 1 to 4 weeks and dropped to about the 1-week level after 12 weeks on both sides, with the acrylic side lower than the control side. On both sides, Disulphine Blue staining of the bones showed severe endosteal avascularity after 1 and 4 weeks and massive periosteal apposition after 4 and 12 weeks. The initial increase in blood flow is considered due to periosteal apposition, and the differences in blood flow rates are attributed to avascularity caused by the polymerization heat and toxicity of the acrylic cement.

Observations on Long Bone Medullary Pressure in Relation to Mean Arterial Blood Pressure in the Anaesthetized Dog

To study the influence of variations in mean arterial pressures (MAP) on long bone medullary pressures, seven anaesthetized dogs were investigated. The medullary pressures were measured in the epiphyseal, the metaphyseal and the diaphyseal regions and remained rather constant when MAP was above 80 mmHg. Below this level of MAP a statistically significant (P less than 0.01) reduction of the medullary pressures was seen. Comparing the mean medullary pressures obtained with ranges of MAP of 81--100 mmHg (the control medullary pressures) and of 61--80 mmHg, the greatest decline was seen in the epiphyseal and the diaphyseal regions, from 25.2 mmHg to 8.1 mmHg and from 26.7 mmHg to 8.3 mmHg, respectively. The corresponding decrease in the metaphyseal region was from 18.9 mmHg to 10.9 mmHg. The mean values of intraosseous pressure measured by our technique were between 20--30 mmHg and this is in accordance with measurements in normal humans found by other authors.

Relationships Between Oxygen and Carbon Dioxide Tensions and Acid-Base Balance in Arterial Blood and in Medullary Blood from Long Bones in Dogs

By means of an invasive technique the relations between arterial and medullary gas tensions PO2 and PCO2), and arterial and medullary acid-base balance (pH and standard bicarbonate) were determined in long bones in seven anaesthetized dogs. A semilogarithmic correlation was found between the arterial oxygen tension and the oxygen tension in the medullary blood. Between the arterial carbon dioxide tension and the medullary blood carbon dioxide tension a linear correlation was demonstrated A linear correlation was also found between arterial pH and standard bicarbonate values and the corresponding values obtained from medullary blood. With regard to the parameters investigated no difference was demonstrated between epiphyseal, metaphyseal or diaphyseal medullary blood.

Regional Vascular Volumes and Dynamic Haematocrit Compared to Regional Perfusion in Canine Cancellous and Cortical Bone

Regional vascular volumes in different areas of long bones in dogs were measured with 125I-fibrinogen and 51C-r erythrocytes. According to the volumes determined, the dynamic small vessel haematrocrit was calculated to be 50 per cent of the arterial cortical bone. The perfusion rate in the same regions was determined with 99Tcm-labelled microspheres (size 15 mu +/- 5 mu). A linear relation between perfusion rate and blood volume was demonstrated. The data obtained showed that the perfusion rate and blood volume in the red marrow in the femoral neck are 25 times greater than values obtained from tibial and femoral cortical bone. A thorough testing of the plasma indicators showed that the distribution volume in the tissue for albumin and transferrin is twice the value determined with fibrinogen. The degrees of the indicators seems to be correlated with molecular weight.

The Cotrel-Dubousset instrumentation for unstable sacral fractures:Report of 3 patients

We present a new operative procedure using the Cotrel-Dubousset (C-D) instrumentation in unstable sacral fractures, where the vertebral column is dissociated from the pelvis. This technique is based on screw fixation in the ileum and in the first sacral and the fifth lumbar vertebrae or the fifth and fourth lumbar vertebrae, with help of interconnecting rods. 3 patients were successfully treated.