Comparison of CT scan muscle measurements and isokinetic trunk strength in postoperative patients

Trunk muscle strength, cross-sectional area, and density in patients with chronic low back pain randomized to lumbar fusion or cognitive intervention and exercises

STUDY DESIGN

A randomized study.

OBJECTIVES

To compare muscle strength, cross-sectional area, and density of the back muscles in two categories of patients with chronic low back pain, randomized to either lumbar fusion or cognitive intervention and exercises.

SUMMARY OF BACKGROUND DATA

In two clinical trials, patients with chronic low back pain plus disc degeneration and postlaminectomy syndrome, respectively, were randomized to either lumbar fusion or cognitive intervention and exercises. We have previously reported that results for the primary outcome were similar at the 1-year follow-up examination.

METHODS

As the treatment alternatives and test procedures were identical, the two trials were merged into one. A total of 124 patients 25 to 60 years of age were included. Muscle strength, measured by isokinetic test device and by the Biering-Sørensen Test, was measured in 112 patients, and the cross-sectional area and density of the back muscles were measured in 61 patients at the inclusion and at the 1-year follow-up examination.

RESULTS

The exercise group performed significantly better in muscle strength than did the lumbar fusion group, with the mean difference at 184 Nm (95% confidence interval, 64-303 Nm; P = 0.003) and for the Biering-Sørensen Test 21 seconds (95% confidence interval, 6-36 seconds; P = 0.006). The density at L3-L4 decreased in the lumbar fusion group but remained unchanged in the exercise group. The mean difference was 5.3 HU (95% confidence interval, 1.1-9.5 HU; P = 0.01). The cross-sectional area was unchanged in both groups.

CONCLUSIONS

Patients with chronic low back pain who followed cognitive intervention and exercise programs improved significantly in muscle strength compared with patients who underwent lumbar fusion. In the lumbar fusion group, density decreased significantly at L3-L4 compared with the exercise group.

Atrophy of the abdominal wall muscles after extraperitoneal approach to the aorta

OBJECTIVE

We retrospectively assessed computed tomography (CT) scans to determine degree of anterolateral abdominal muscle atrophy in patients who underwent infrarenal aortic repair with 2 kinds of incisions for the extraperitoneal approach.

METHODS

CT scans obtained before surgery and final scans obtained 2 to 100 months after surgery were assessed in 12 patients with paramedian incision (PM group) and 27 patients with flank incision (F group) who could be followed up at our hospital. We considered muscle thickness before surgery on the incision side to be 100% thickness (baseline value), and we calculated, by measuring the incision side after surgery, the corrected percent thickness (CPT%), which represents percentage of remaining muscle thickness that has escaped incision-induced atrophy. CT scans obtained at the level of the third (L3) and fifth (L5) lumbar vertebrae and the center of the sacrum (S) were selected for CPT% measurement.

RESULTS

Duration from surgery to final CT scan was 2 to 65 months (mean +/- SD, 34.33 +/- 21.38 months) in PM group and 3 to 96 months (27.85 +/- 20.74 months) in F group. In PM group, mean CPT% values of the rectus abdominis muscle were 55.83 +/- 21.65% at L3, 35.50 +/- 10.79% at L5, and 31.92 +/- 11.00% at S; these values were statistically much smaller than baseline (P <.01). Mean CPT% values of the lateral abdominal muscles were not statistically different from baseline. In F group, mean CPT% values of the rectus abdominis muscle were 82.19 +/- 23.15% at L5 and 64.41 +/- 31.34% at S; these values were statistically smaller than baseline (P <.01). Mean CPT% values of the lateral abdominal muscles were 87.59 +/- 22.30% at L3 and 84.59 +/- 26.90% at L5; these values were statistically smaller than baseline (P <.05).

CONCLUSIONS

Paramedian incision induced severe rectus abdominis muscle atrophy. Although flank incision induced various degrees of atrophy in both muscles, some patients had no muscle atrophy. These data indicate that further anatomic investigation into the relation between flank incision and abdominal wall innervation may contribute to prevention of muscle atrophy after flank incision.

Minimally invasive lumbar fusion

STUDY DESIGN

Review article.

OBJECTIVES

To provide an overview of current techniques for minimally invasive lumbar fusion.

SUMMARY OF BACKGROUND DATA

Minimally invasive techniques have revolutionized the management of pathologic conditions in various surgical disciplines. Although these same principles have been used in the treatment of lumbar disc disease for many years, minimally invasive lumbar fusion procedures have only recently been developed. The goals of these procedures are to reduce the approach-related morbidity associated with traditional lumbar fusion, yet allow the surgery to be performed in an effective and safe manner.

METHODS

The authors' clinical experience with minimally invasive lumbar fusion was reviewed, and the pertinent literature was surveyed.

RESULTS

Minimally invasive approaches have been developed for common lumbar procedures such as anterior and posterior interbody fusion, posterolateral onlay fusion, and internal fixation. As with all new surgical techniques, minimally invasive lumbar fusion has a learning curve. As well, there are benefits and disadvantages associated with each technique. However, because these techniques are new and evolving, evidence to support their potential benefits is largely anecdotal. Additionally, there are few long-term studies to document clinical outcomes.

CONCLUSIONS

Preliminary clinical results suggest that minimally invasive lumbar fusion will have a beneficial impact on the care of patients with spinal disorders. Outcome studies with long-term follow-up will be necessary to validate its success and allow minimally invasive lumbar fusion to become more widely accepted.

Reliability of computed tomography measurements of paraspinal muscle cross-sectional area and density in patients with chronic low back pain

STUDY DESIGN

A reliability study was conducted.

OBJECTIVE

To estimate measurement errors related to equipment and the observer in computed tomography measurements of cross-sectional area and density of paraspinal muscles. Interobserver reliability was not investigated in the current study.

SUMMARY OF BACKGROUND DATA

Computer tomography (CT) had been used to measure the cross-sectional area and degeneration of the back muscles in patients with low back pain.

METHODS

This study included 31 patients, mean age 47 years, with chronic low back pain. The measurements comprised cross-sectional area (cm2) and density (Hounsfield units [HU]) of the paraspinal muscles at Th12-L1, L3-L4, and L4-L5. To measure the reliability of the equipment and the observer (total reliability), two independent CT scans were performed for each patient. The radiologist traced the cross-sectional area twice within 2 weeks for measurement of the intraobserver reliability.

RESULTS

There were no significant differences in the assessments between the first and second CT scans, or between the radiologist's two measurements of the identical slices. The critical difference for the total reliability ranged from 11.3 to 22.8 for the density and from 10.0 to 16.0 for the cross-sectional area. For the cross-sectional area, the measurement error associated with the observer was higher than for the equipment. For the density, the measurement error related to the equipment was higher. The main measurement error was associated with the radiologist for the cross-sectional area and with the CT scanner for the density.

CONCLUSIONS

The reliability of the CT scan for measuring the cross-sectional area and density of the back muscles is acceptable. The authors do not know definitely whether their results can be generalized because the interobserver and intermachine reliabilities were not investigated.

The effect of comprehensive group training on cross-sectional area, density, and strength of paraspinal muscles in patients sick-listed for subacute low back pain

The effect of exercise on back muscle cross-sectional area (CSA), density, and strength was evaluated in patients sick-listed for subacute low back pain. Twenty-four patients were randomized into an exercise (n = 11) or a control (n = 13) group. Patients in the exercise group followed a biweekly exercise protocol for 15 weeks. Control patients received usual care. Muscle CSA and density were measured by computed tomography before and after intervention. Isokinetic test of back extensors was conducted simultaneously. Results showed a tendency to increased muscle CSA and density in patients in the exercise group, a significant decrease in muscle CSA at L4-L5 in control group patients, and a significant difference in change between groups in muscle CSA at L4-L5. Back extension strength increased in patients in the exercise group, but the improvement was not significant compared with control group patients. In conclusion, there was a tendency for reversal of muscle atrophy after exercise.

Nuclear factor-kappaB-regulated cyclooxygenase-2 expression in surgery-associated paraspinal muscle injury in rats

OBJECT

Paraspinal muscle injury is a common but neglected complication of posterior spinal surgery. Evidence suggests that surgical retraction places mechanical and oxidative stress on the paraspinal muscles and that inflammation is a major postoperative pathological finding in the muscles. The roles of cyclooxygenase (COX)-2 and nuclear factor (NF)-kappaB in the inflammatory processes after retraction remain to be clarified.

METHODS

In the control group, paraspinal muscles were dissected from the spine via a posterior incision and then laterally retracted. Paraspinal muscle specimens were harvested before as well as at designated time points during and after persistent retraction. The time course of NF-kappaB activation was determined by gel shift assay. Expression of COX-2 was examined using Western blot analysis and immunohistochemistry. The severity of inflammation was evaluated based on histopathology and myeloperoxidase (MPO) activity. The NF-kappaB activation was inhibited by the administration of pyrrolidine dithiolcarbamate (PDTC) in the PDTC-treated group. Retraction induced early activation of NF-kappaB in paraspinal muscle cells. The expression of COX-2 could not be detected until 1 day postoperativley, reaching a peak at 3 days. The time course of COX-2 expression correlated with that of inflammatory responses and MPO activity. Pretreatment with PDTC inhibited intraoperative NF-kappaB activation and greatly downregulated postoperative COX-2 expression and inflammation in the muscles. Postinflammation fibrosis was also abolished by PDTC administration.

CONCLUSIONS

Both NF-kappaB-regulated COX-2 expression and inflammation play an important role in the pathogenesis of surgery-associated paraspinal muscle injury. The therapeutic strategy of NF-kappaB inhibition may be applicable to the prevention of such injury.

The impact of self-retaining retractors on the paraspinal muscles during posterior spinal surgery

STUDY DESIGN

This was a prospective pilot study examining pre-, intra- and postoperative measures.

OBJECTIVES

The aim of the study was to investigate the effect of muscle retractors on the posterior spinal muscles during posterior spinal surgery.

SUMMARY OF BACKGROUND DATA

Previous studies have identified changes in the structure and function of the back extensor mechanism as a result of low back pain. However, the effect of surgery on the functioning of these muscles, particularly surgical retraction, has received less attention.

METHODS

Twenty patients undergoing posterior spinal surgery were recruited into this study, and recordings of intramuscular pressure during surgery were performed using a pressure-monitoring system before insertion of retractors, 5, 30, and 60 minutes into surgery, and on removal of retractors. Before and following use of the retractors, muscle biopsies were taken from the multifidus muscle for analysis using birefringence techniques.

RESULTS

A significant increase in intramuscular pressure (P < 0.001) was observed during surgery. On removal of retractors, this pressure returned to or near to the original value. Analysis of muscle biopsies using calcium activated adenosine triphosphatase birefringence revealed a reduction in muscle function following prolonged use of self-retaining retractors.

CONCLUSIONS

A substantial rise in pressure in the erector spinae muscle during posterior spinal surgery was observed, and this appeared to be associated with marked changes in the function of the muscles. This could be an important factor in the generation of operative scar tissue and postoperative dysfunction of the spinal muscles.

Microendoscopic Decompressive Laminotomy for the Treatment of Lumbar Stenosis

OBJECTIVE

By modifying existing microendoscopic discectomy techniques, we previously developed a novel surgical treatment of lumbar stenosis and validated its ability to achieve a thorough decompression in a cadaveric study. We now describe our clinical experience with this new, minimally invasive microendoscopic decompressive laminotomy (MEDL) technique.

METHODS

A MEDL was performed in 25 patients with classic features of lumbar stenosis. By use of a fluoroscopically guided percutaneous technique, the working portal was docked on the lamina with minimal soft-tissue injury. With the angle of the endoscope combined with an oblique entry, a bilateral bony and ligamentous decompression was achieved under the midline, thereby preserving the supraspinous–interspinous ligaments and contralateral musculature. A second group of 25 patients treated with open decompression was used for comparison.

RESULTS

Effective circumferential decompression was achieved in the majority of patients. The results for the MEDL group were as follows: operative time, 109 minutes per single level; blood loss, 68 ml; and postoperative stay, 42 hours. The results for the open-surgery group were as follows: operative time, 88 minutes; blood loss, 193 ml; and postoperative stay, 94 hours. The MEDL group needed significantly less narcotic medication after surgery. Overall, 16% of the MEDL patients reported resolution of their back pain, 68% improved symptomatically, and 16% remained unchanged. The outcome of the open group was very similar.

CONCLUSION

Compared with an equivalent open technique, MEDL appears to offer a similar short-term clinical outcome with a significant reduction in operative blood loss, postoperative stay, and use of narcotics. This lower surgical stress, decreased tissue trauma, and quicker recovery are particularly important in this elderly population of patients.

Minimally Invasive Percutaneous Posterior Lumbar Interbody Fusion

OBJECTIVE

The wide exposure required for a standard posterior lumbar interbody fusion (PLIF) can cause unnecessary trauma to the lumbar musculoligamentous complex. By combining existing microendoscopic, percutaneous instrumentation and interbody technologies, a novel, minimally invasive, percutaneous PLIF technique was developed to minimize such iatrogenic tissue injury (MIP-PLIF).

METHODS

The MIP-PLIF technique was validated in three cadaveric torsos with six motion segments decompressed and fused. Preoperative variables measured from imaging included interpedicular distance, pedicular height and width, interspinous distance, lordosis, intervertebral height, Cobb angle, and foraminal height and volume. Using the METRx and MD spinal access systems (Medtronic Sofamor Danek, Memphis, TN), bilateral laminotomies were performed using a hybrid of microsurgical and microendoscopic techniques. The intervertebral disc spaces were then distracted and prepared with the Tangent (Medtronic Sofamor Danek) interbody instruments. Either a 10 or 12 by 22 mm interbody graft was then placed. Using the Sextant (Medtronic Sofamor Danek) system, percutaneous pedicle screw-rod fixation of the motion segment was completed. We then applied MIP-PLIF in three patients.

RESULTS

For segments with preoperative intervertebral/foraminal height loss, MIP-PLIF was effective in restoring both heights in all cases. The amount of improvement (9.7 to 38% disc height increase; 7.7 to 29.9% foraminal height increase) varied directly with the size of the graft used and the original degree of disc and foraminal height loss. Segmental lordosis improved by 29% on average. Graft and screw placement was accurate in the cadavers, except for a single Grade 1 screw violation of one pedicle. The average operative time was 3.5 hours per level. In our three clinical cases, the MIP-PLIF procedure required a mean of 5.4 hours, estimated blood loss was 185 ml, and inpatient stay was 2.8 days, with no intravenous narcotic use after 2 days in any of the patients. All screw and graft placements were confirmed.

CONCLUSION

A complete PLIF procedure can be safely and effectively performed using minimally invasive techniques, thereby potentially reducing the pain and morbidity associated with standard open surgery. Prospective, randomized outcome studies will be required to validate the efficacy of this exciting new surgical technique.

Oxidative stress and heat shock protein response in human paraspinal muscles during retraction

OBJECT

The need for wide dissection and forceful retraction of paraspinal muscles often required for posterolateral lumbar fusion and fixation may severely jeopardize the muscles, structurally and functionally. The underlying pathophysiology of muscle damage may involve both mechanical and ischemic mechanisms. On the other hand, the surgery-related stress may trigger certain protective responses within the insulted paraspinal muscles. This study was conducted to assess the relationship between the oxidative stress and the stress response mediated by heat shock protein 70 (HSP70) induction within paraspinal muscles being retracted.

METHODS

Multifidus muscle specimens were surgically obtained before, during, and after retraction in patients with lumbar spondylolisthesis undergoing posterolateral lumbar fusion, pedicle fixation, and laminectomy. Muscle samples were analyzed to determine HSP70 and malondialdehyde (MDA) levels. Both HSP70 expression and MDA production within multifidus muscle cells were increased significantly by retraction. Expression of HSP70 then decreased after a peak at 1.5 hours of retraction, whereas MDA levels remained elevated even after release of retractors for reperfusion of the muscles. Analysis of histopathological and immunohistochemical evidence indicated that the decline of HSP70 synthesis within muscle cells after prolonged retraction was the result of severe muscle damage.

CONCLUSIONS

Results of this study highlight the deleterious effect of intraoperative retraction on human paraspinal muscles at the cellular and molecular levels. The authors also found that intraoperative maneuvers aimed at reducing the oxidative stress within the paraspinal muscles may help to attenuate surgery-related paraspinal muscle damage.

Aggressive exercise as treatment for chronic low back pain

Exercise has long been a standard of treatment for back pain. Over the last 2 decades, the use of intense, non-pain-contingent exercises for treatment of chronic back pain has received increased advocacy. The main goals of these treatments are to improve functioning of painful lumbar soft tissue and to decrease the fears and concerns of patients about using their backs for daily activities. The methodology of an aggressive quota-based exercise approach to back pain is outlined in this article. This approach relies on objective quantification of physical capabilities, treatment directed at altering these parameters, and repeat quantification for determination of treatment efficacy and positive feedback. By eliminating impairments in back function, altering fears and beliefs about pain, and reducing disability, patients with chronic low back pain can achieve meaningful improvements in their quality of life.

A minimally invasive technique for decompression of the lumbar spine

STUDY DESIGN

The technical feasibility of percutaneous microendoscopic bilateral decompression of lumbar stenosis via a unilateral approach was evaluated in a human cadaver model.

OBJECTIVES

The purpose of this study was to determine the feasibility of using a microendoscopic laminotomy technique to treat spinal stenosis.

SUMMARY AND BACKGROUND DATA

Minimally invasive surgery is an important means of reducing tissue trauma and patient morbidity. This may prove to be essential in improving pain and in reducing postoperative stress responses and delayed sequelae that can lead to unfortunate complications after otherwise uneventful procedures. To date, minimally invasive lumbar endoscopic techniques have not been used to decompress the lumbar spinal canal.

METHODS

In each of four cadavers, the laminae of L1 through L4 were subjected to one of four procedures consisting of unilateral microendoscopic laminotomy, bilateral microendoscopic laminotomy, unilateral open laminotomy, and bilateral open laminotomy. Every procedure was performed once at all levels. Computed tomography was performed before and after laminotomy to establish the extent of decompression of the spinal canal, and measurements of the midsagittal, interpedicular, and decompression diameters were taken.

RESULTS

The four procedures were successfully performed at every level. Satisfactory decompression of the spinal canal was achieved regardless of the approach used. The exiting nerve roots were well visualized when any one of these techniques was used. Complications, including dural tears and facet complex instability, were independent of the procedure performed.

CONCLUSION

Microendoscopic laminotomy can be used to decompress the spinal canal as effectively as an open laminotomy and may prove to be beneficial in decreasing the complications and morbidity of standard treatments for lumbar stenosis.

Effects of three different training modalities on the cross sectional area of the lumbar multifidus muscle in patients with chronic low back pain

OBJECTIVES

To determine the effect of different training schedules on the cross sectional area (CSA) of the lumbar multifidus muscle in patients with chronic low back pain.

METHODS

Each of 59 nine patients was randomly assigned to one of three programmes: 10 weeks of stabilisation training (group 1; n = 19); 10 weeks of stabilisation training combined with dynamic resistance training (group 2; n = 20); 10 weeks of stabilisation training combined with dynamic-static resistance training (group 3; n = 20). Before and after 10 weeks of training, multifidus CSAs were measured from standard computed tomography images at three different levels (upper end plate of L3 and L4, and lower end plate of L4).

RESULTS

The CSA of the multifidus muscle was significantly increased at all levels after training in group 3. In contrast, no significant differences were found in groups 1 and 2.

CONCLUSIONS

General stabilisation exercises and dynamic intensive lumbar resistance training have no significant effect on the CSA of the lumbar multifidus muscle in patients with chronic low back pain. The static holding component between the concentric and eccentric phase was found to be critical in inducing muscle hypertrophy during the first 10 weeks. Treatment consisting of stabilisation training combined with an intensive lumbar dynamic-static strengthening programme seems to be the most appropriate method of restoring the size of the multifidus muscle.

Current techniques of decompression of the lumbar spine

Lumbar spinal decompression is a commonly performed procedure. Although the conventional open techniques of decompression remain the gold standard of treatment, problems with paraspinal musculature denervation and resultant lumbar instability have focused attention on less invasive techniques. A multitude of spinal instrumentation systems have been developed to stabilize the spine and improve arthrodesis rates. A stronger emphasis on restoration of anterior column height and stability has increased the use of anterior interbody fusion devices. Developing technology is allowing for better visualization and possibly improved outcomes with minimally-invasive techniques. The results of all lumbar decompressive and stabilization procedures however, remain closely related to careful patient selection.

Optimal sagittal motion axis for trunk extension and flexion tests in chronic low back trouble

OBJECTIVE

To find the optimal height for sagittal motion axis for trunk strength test in chronic low back trouble.

DESIGN

Cross-sectional study.

BACKGROUND

The strength of trunk muscles of low back pain patients is decreased. The measured strength depends on the height of the sagittal motion axis but the differences between patients and controls are not known.

METHODS

114 (67 female) patients with chronic low back trouble are classified according to Quebec Task Force, 50 (31 female) patients with rheumatic disorder, but without low back trouble, and 33 (22 female) healthy controls, no appreciable physical differences but clear differences in Oswestry score. Isometric trunk extension-flexion test with different heights for the pelvic fulcrum.

RESULTS

Force decreased in extension, increased in flexion, and torque increased both in flexion and extension in every group (P<0.001) as the fulcrum was moved caudally. The male controls were stronger than patients with low back trouble (P<0.01). The female controls were stronger only if the fulcrum was set at the hip joint level (P<0.05). There were no differences between patients with rheumatic disorder and low back trouble, except in extension if the fulcrum was at the hip joint level (P<0.02).

CONCLUSIONS

The rotation axis in trunk extension-flexion strength test should be set at the level of the hip joint.

RELEVANCE

Trunk muscle weakness is a common sign of different rheumatic disorders. Proper setting of sagittal motion axis and concomitant measurement of trunk and hip extensor or flexor muscles increases the specificity of the strength test for low back trouble.

Postoperative changes in paraspinal muscle thickness after various lumbar back surgery procedures

Damage to the paraspinal muscle after various lumbar back surgery procedures was evaluated by measuring the paraspinal muscle thickness preoperatively and postoperatively in 89 patients, 61 males and 28 females. There were 42 single interlaminar level procedures (SL group), 13 multiple interlaminar level procedures (ML group), and 34 posterolateral fusion procedures (PLF group). Changes in paraspinal muscle thickness were evaluated at more than 10 months after surgery, because muscle swelling continued as long as 10 months after surgery, and then reduced as the edema subsided. Postoperative serum creatine phosphokinase (CPK) level on postoperative day 2 was also measured. The decrease of paraspinal muscle thickness was significantly larger in the PLF group than in the SL group (-12.9% and -2.7%, respectively, p < 0.02). There was no significant correlation between postoperative serum CPK level and decrease of paraspinal muscle thickness. However, the postoperative elevation of serum CPK level was significantly higher in the PLF group than in the SL and ML groups (979 +/- 114 vs. 292 +/- 45 and 410 +/- 44 IU/l, respectively, p < 0.001). In conclusion, posterolateral fusion is the most invasive procedure of the paraspinal muscles in various lumbar back surgery procedures. Paraspinal muscle damage during lumbar back surgery may be one of the most important factors that causes atrophy of the muscles.

An experimental study of the effects of nerve root retraction on the posterior ramus

STUDY DESIGN

The histologic and ultrastructural changes in the posterior ramus after posterior lumbar surgery were studied in rabbits.

OBJECTIVE

To investigate the structural changes in the posterior ramus after posterior lumbar surgery that may cause injury to the posterior ramus after the procedure.

SUMMARY OF BACKGROUND DATA

Investigators in previous studies have pointed out that low back discomfort after lumbar discectomy relates to neurogenic changes and/or myogenic changes of paravertebral muscle. However, no previous study has demonstrated the effects of excessive nerve root retraction on spinal posterior rami.

METHODS

Eighteen male Japanese White rabbits were used. The posterior ramus arising from the S1 nerve root was examined after exposure of the lamina only, fenestration, or retraction of the S1 nerve root, with light microscopy and transmission electron microscopy at 2, 4, and 6 weeks after the procedure. Results were compared with a those in control specimens that did not undergo the procedure.

RESULTS

In the exposed group, no distinct difference was found compared with the control specimen. In the fenestration group, especially at 6 weeks, some attenuation and splitting of myelin sheaths was observed. In the retraction group, the structural alteration was most severe. Even at 2 weeks, fragmentation of many myelin sheaths was detected. Examination of specimens by electron microscopy indicated phagocytosis of myelinated fibers at 4 and 6 weeks.

CONCLUSIONS

Findings showed that posterior lumbar procedures, including retraction of paravertebral muscle, fenestration of the lamina, and retraction of the nerve root affect the posterior ramus. Excessive retraction of the nerve root has an especially disastrous effect on the posterior ramus. Such a violent maneuver within the spinal canal must be avoided.

Microdecompression for lumbar spinal canal stenosis

STUDY DESIGN

A description of the technique for lumbar microdecompression and a prospective study of the outcomes.

OBJECTIVE

To describe and analyze a technique that affords an excellent decompression while minimizing damage to surrounding tissues.

SUMMARY OF BACKGROUND DATA

Commonly used techniques of lumbar decompression that include bilateral takedown of paraspinal musculature and aggressive bony resection can result in significant iatrogenic sequelae. A less destructive alternative is needed.

METHODS

Unilateral limited takedown of multifidus was undertaken, and ipsilateral decompression performed. The contralateral side then was addressed under the midline structures with microscopic visualization--thereby preserving the supra-/interspinous ligament complex and the contralateral musculature. Thirty consecutive patients undergoing the procedure were analyzed prospectively and after a follow-up period by independent observers using a modified validated functional outcome score and patient satisfaction measures.

RESULTS

The technique affords an excellent decompression while minimizing destruction to tissues not directly involved in the pathologic process. Functional outcome scores doubled, and 87% of patients reported high satisfaction rates.

CONCLUSIONS

Lumbar microdecompression is a minimally invasive technique that appears to provide excellent functional outcomes.

Serial changes in trunk muscle performance after posterior lumbar surgery

STUDY DESIGN

Serial changes in trunk muscle performance were prospectively studied in 20 patients who underwent posterior lumbar surgery.

OBJECTIVE

To evaluate the influence of back muscle injury on postoperative trunk muscle performance and low back pain, to clarify the significance of minimization of back muscle injury during surgery.

SUMMARY OF BACKGROUND DATA

The current investigators have reported examination of iatrogenic back muscle injury in an animal model and in humans. However, definite impairment caused by such back muscle injury has not been clarified.

METHODS

The patients were divided into a short-retraction-time group (< 80 minutes; n = 12) and a long-retraction-time group (> or = 80 minutes; n = 8). Before surgery and 3 and 6 months after surgery, the degree of back muscle injury was estimated by magnetic resonance imaging, and trunk muscle strength was measured. In addition, the incidence and severity of low back pain were serially analyzed.

RESULTS

Back muscle injury was directly related to the muscle retraction time during surgery. The damage to the multifidus muscle was more severe, and the recovery of extensor muscle strength was delayed in the long-retraction-time group. In addition, the incidence of postoperative low back pain was significantly higher in the long-retraction-time group.

CONCLUSIONS

Postoperative trunk muscle performance is dependent on the muscle retraction time. Thus, it is beneficial to shorten the retraction time to minimize back muscle injury and subsequent postoperative low back pain.

Volume of ankle dorsiflexors and plantar flexors determined with stereological techniques

The validity of the methods used for determination of muscle mass has not been evaluated previously. We determined muscle mass by estimating muscle volume with assumption-free stereological techniques applied to magnetic resonance imaging (MRI) in 18 healthy untrained subjects (6 women, 12 men) aged 41 yr (29-64 yr; median, range). Muscle mass was also estimated by measuring leg circumference and cross-sectional muscle areas (CSA) from MRIs at three predetermined levels. Power [peak torque (PT)] of the ankle dorsiflexors and plantar flexors was estimated by using isokinetic dynamometry. Dorsiflexor volume (r2 = 0.76, P < 5 x 10(-6)) and CSA (r2 = 0.73, P < 5 x 10(-5)) were related to PT, whereas circumference was not (r2 = 0.17, not significant). Correspondingly, a relationship to plantar PT was established for plantar flexor volume (r2 = 0.69, P < 5 x 10(-5)) and CSA (r2 = 0.46, P < 5 x 10(-3)) but not leg circumference (r2 = 0.15, not significant). SDs of the residuals were smaller for the relationship between dorsiflexor PT and volume than between PT and CSA (0.42 vs. 0.45) for plantar flexors (1.5 vs. 2.0). By using the Cavalieri method, six MRI sections and 15 min of point counting are sufficient to obtain a valid estimate of the volume of the muscles of the lower leg.

Predictors of isokinetic back muscle strength in patients with low back pain

STUDY DESIGN

Testing for trunk muscle strength was performed on 105 patients with chronic low back pain.

OBJECTIVES

To investigate prediction of isokinetic back muscle strength in patients with low back pain.

SUMMARY OF BACKGROUND DATA

The clinical evaluation of patients with chronic low back pain often in difficult because of discrepancy between disability and impairment. The isokinetic trunk device was developed as a tool for objective assessment of back muscle strength. However, the performance of patients depends on radiologic abnormalities of the spine, conditions of the back muscles, and various psychosocial factors. Studies are warranted that address how these variables influence back muscle strength.

METHODS

The patients with chronic low back pain were tested by an isokinetic trunk muscle strength test (Cybex TEF, Ronkonkoma, NY). In addition, the following variables were recorded: gender, age, body mass index, emotional distress, pain on exertion, self-efficacy for pain, degenerative changes of the lumbar spine, cross-sectional area, and density of the erector spinae muscles. The three latter variables were estimated by computed tomography scans. The sum of the total work performed during isokinetic extension strength test was the dependent variable in a multiple regression analysis, and anthropometric, demographic, psychological, and radiologic factors were independent variables.

RESULTS

Gender, cross-sectional muscle area, and pain on exertion were the most powerful predictors of isokinetic back muscle strength. The final regression model, which included these variables, could account for approximately 40% of the variability in back muscle strength.

CONCLUSION

For assessing the results of an isokinetic trunk muscle strength test, cross-sectional muscle area, gender, and pain on exertion should be taken into account.

Rehabilitation: what do we do with the chronic patient?

Neurologists are often called on to see patients who have low back pain presenting with significant chronicity and disabling pain. Even in situations of chronic low back pain, it has been estimated that a structural diagnosis is made only 60% of the time. Even when a physical diagnosis is made in these cases, it may be irrelevant to the primary causes of persistent pain and disability. This article is designed to point out that, when nonstructural factors are adequately rehabilitated, even in a worst-case occupational injury cohort, remarkable outcomes can be anticipated irrespective of the structural pathology, patient age, or postoperative impairment.

Spinous process osteotomies to facilitate lumbar decompressive surgery

STUDY DESIGN

A technique for lumbar decompression using spinous process osteotomies is described, and the outcomes are studied prospectively.

OBJECTIVE

To describe a technique that affords a wide exposure for decompression while minimizing damage to surrounding tissues, and to analyze the outcomes formally using the technique.

SUMMARY OF BACKGROUND DATA

Commonly used techniques of lumbar decompression, which include bilateral takedown of paraspinal musculature and aggressive bony resection, can result in significant iatrogenic sequelae, whereas minimally invasive techniques often provide inadequate visualization and/or decompression.

METHOD

Unilateral limited takedown of the multifidus is undertaken, followed by spinous process osteotomies at the involved levels. The spinous processes with the attached interspinous/supraspinous ligaments are then retracted. A complete "trumpeted" decompression is then undertaken. Fifty consecutive patients undergoing the procedure were analyzed prospectively and at follow-up by an independent observer using a validated functional outcome measure, a visual analog pain scale, and a patient satisfaction score.

RESULTS

Functional outcome scores improved on average by 47%, pain levels were reduced by 66%, and high satisfaction rates were reported by 83% of patients.

CONCLUSIONS

The technique affords excellent visualization and a wide area available for Kerrison use and angulation while minimizing destruction to tissues not directly involved in the pathologic process, including the paraspinal musculature as well as the interspinous/supraspinous ligament complex and facets. Additionally, it minimizes dead space and improves the cosmetic result.

The effects of external compression by three different retractors on pressure in the erector spine muscles during and after posterior lumbar spine surgery in humans

STUDY DESIGN

An experimental study on patients undergoing posterior lumbar spine surgery.

OBJECTIVES

To study the relation between external compression and muscle strain induced by spinal retractors and intramuscular pressure in the dorsolumbar compartment during posterior spinal surgery.

SUMMARY OF BACKGROUND DATA

Pressures were studied as a function of the distance between the retractor blades during surgery.

METHODS

Intramuscular pressure was measured bilaterally in the erector spinae muscle with intermittent microcapillary infusion technique in 12 patients undergoing posterior lumbar spine surgery during 271 (range 90-420) minutes. Three self-retaining retractors were tested; the McCulloch, the Viking, and the Richard retractors.

RESULTS

Intramuscular pressure was 7.7 mm Hg before surgery. It varied between 35 mm Hg and 69 mm Hg during surgical exposure of the laminas and facet joints. Intramuscular pressure varied between 61 mm Hg and 158 mm Hg depending on which retractor was used and on the distance between the retractor blades. Intramuscular pressure never exceeded 30 mm Hg at rest after the operation.

CONCLUSIONS

External compression and muscle strain from retractor blades during surgery increased intramuscular pressure in the paravertebral muscles to levels that, according to other studies, induce ischemia in the muscles.

Determinants of isokinetic and psychophysical lifting strength and static back muscle endurance: a study of male monozygotic twins

STUDY DESIGN

Retrospective cohort.

OBJECTIVES

To determine the relative contributions of anthropometric factors, physical activity, back and neck pain, overall health, and familial aggregation (the combined effects of genetics and childhood environment) to different measurements of adult back muscle function.

SUMMARY OF BACKGROUND DATA

Many methods of muscle testing are employed in the attempt to predict, prevent, treat, and rehabilitate low back pain. Poor correlations between the test results suggest that they are measuring different attributes and have different determinants.

METHODS

Muscle function tests, magnetic resonance images, and a detailed interview were obtained in 65 pairs of monozygotic male twins.

RESULTS

Familial aggregation was the strongest determinant of isokinetic and psychophysical lifting and static back endurance, explaining 56%, 32%, and 15% of the variances, respectively, beyond that which age alone predicted. Back pain and physical loading in work and leisure explained 2%, 0%, and 23% of the variances.

CONCLUSIONS

The combined effects of genetics and childhood environment play a dominant role in determining adult back muscle function. Physical loading at work and leisure, back and neck pain history, overall health, and anthropometric factors had a comparatively minor role, suggesting that the potential of interventions to increase and sustain back muscle function in healthy adults, measured through these tests, may be limited. The relative contributions of constitutional, behavioral, and environmental factors differ substantially in the three tests, and provide insights into what these commonly used tests actually reflect or measure. This knowledge can be used to guide more appropriate selection and interpretation of results of back muscle function tests.

Fibre type characteristics of the lumbar paraspinal muscles in normal healthy subjects and in patients with low back pain

A knowledge of the alteration in the fibre type profile of paraspinal muscle associated with low back pain is essential for the design of successful rehabilitation programmes. In attempting to compare the muscles of patients with low back pain with those of controls, few previous studies have considered factors such as gender, age, and size of the subjects, each of which can potentially confound interpretation of the results. We obtained samples of lumbar paraspinal muscle during spinal surgery from 21 patients with low back pain and, using the percutaneous biopsy technique, from 21 control volunteers matched for gender, age, and body mass. The samples were subject to routine histochemical analysis to determine characteristics of muscle fibre type. Compared with controls, the muscle of the patients had a significantly higher proportion of type-IIB (fast-twitch glycolytic) fibres than type-I (slow oxidative) fibres. The mean size of a given fibre type did not differ between the patients and the controls. Consequently, the relative area of the muscle occupied by type-IIB fibres was higher and that by type-I fibres was lower in the patients. The patients had a greater number of muscle samples with more than 1% type-IIC fibres, and abnormalities that could be described as pathological were more marked in the patients than in the controls. In conclusion, the paraspinal muscles of patients who have low back pain display a more glycolytic (faster) profile; this can be expected to render them less resistant to fatigue.

Objectification of functional improvement after nonoperative care

STUDY DESIGN

In this article, the authors review the three broad categories of measures that have been used to objectify functional improvement after nonoperative care of painful spinal disorder patients-physical, psychological, and socioeconomic. For each of the three categories, the major measures used are discussed, as well as research relating to the efficacy of the measures.

OBJECTIVE

To point out the many differences that still exist among research studies regarding which functional outcome measures to use and when to use them.

SUMMARY OF BACKGROUND DATA

During the past few decades, it has been made abundantly clear that painful spinal disorders, particularly when associated with work disability and/or financial benefits, result from a complex interaction of medical, psychological, and social factors. This has resulted in frequent confusion regarding what constitutes the primary roots of the disabling process. Currently, a more comprehensive biopsychosocial perspective of chronic pain and disability has emerged that has significant implications for diagnostic and treatment philosophies of practitioners.

METHODS

Identifying the measures frequently used to address the important biopsychosocial factors, and evaluating their relative benefits and drawbacks.

RESULTS AND CONCLUSIONS

It is demonstrated that there has been an overall trend in recent years toward using more objective, quantifiable instruments, encompassing the physical, psychological, and socioeconomic parameters of outcomes research in painful spinal disorders. These changes will certainly improve the ability of researchers to tease out which factors tap more directly into such tissue as physical impairment, as well as create greater uniformity of measures that will permit direct comparisons between studies.

Changes in serum creatine phosphokinase MM isoenzyme after lumbar spine surgery

STUDY DESIGN

Serum concentrations of creatine phosphokinase and its isoenzyme were measured serially in 47 patients who underwent lumbar surgery.

OBJECTIVE

To analyze the significance of postoperative creatine phosphokinase MM levels as indicators of muscle trauma after lumbar surgery.

SUMMARY OF BACKGROUND DATA

The authors of the present study previously have reported on iatrogenic back muscle injury in an animal model and in man. However, the relationship between the change of the creatine phosphokinase MM isoenzyme level and muscle injury after surgery has not been clarified.

METHODS

Peripheral venous blood samples were collected serially before surgery, just after surgery, and at 1, 3, 7, 14, and 21 days after surgery. The serum concentration of total creatine phosphokinase and its isoenzymes was measured by agarose gel electrophoresis. The serial postoperative change of the creatine phosphokinase MM isoenzyme concentration was evaluated with respect to age, gender, body weight, types and levels of surgery, and surgery time.

RESULTS

Creatine phosphokinase MM activity increased after surgery and reached a maximum value 1 day after surgery, followed by recovery to the normal value 1 week after surgery. The maximum concentration of creatine phosphokinase MM isoenzyme in posterior lumbar surgery was significantly higher than that in anterior surgery (P = 0.04). It was significantly higher in men than in women (P = 0.02). Serum concentration of creatine phosphokinase MM isoenzyme showed no significant correlation to the extent of muscle exposure and surgery time.

CONCLUSION

The time course of postoperative serum creatine phosphokinase MM isoenzyme activity is correlated with the histologic changes of the back muscles after surgery. The concentration of creatine phosphokinase MM isoenzyme in posterior lumbar surgery was significantly higher than that in anterior surgery. It was also significantly higher in men than in women.

Back muscle injury after posterior lumbar spine surgery. Topographic evaluation of intramuscular pressure and blood flow in the porcine back muscle during surgery

STUDY DESIGN

Intramuscular pressure and blood flow of the back muscles were evaluated topographically during posterior lumbar spine surgery. The topographic damage of the back muscle after surgery was studied.

OBJECTIVE

To investigate the relationship between intramuscular pressure or blood flow during posterior lumbar surgery and the back muscle injury after surgery.

SUMMARY OF BACKGROUND DATA

Latrogenic back muscle injury in an animal and human model has been reported previously. Changes of intramuscular pressure and blood flow during surgery might be related to the muscle injury. No previous study on this issue has been published.

METHODS

The contact pressure between the retractor blade and muscle tissue was monitored in 10 pigs during posterior surgery of the lumbar spine. On one side, intramuscular pressure at 5, 10, and 20 mm lateral to the retractor and on the other side blood flow of the back muscle at 5 and 20 mm during surgery were measured. Histologic changes of the back muscle at 5, 10, and 20 mm to the midline were evaluated 3 hours after surgery.

RESULTS

The contact pressure decreased exponentially with time. Intramuscular pressure 5 mm lateral to the retractor was 114 +/- 31 mm Hg and was significantly higher than at 10 mm and 20 mm. Blood flow markedly decreased during surgery and recovered incompletely after releasing the retractor at 5 mm and 20 mm lateral to the retractor. Blood flow at 5 mm was significantly lower than at 20 mm throughout surgery. The muscle damage 3 hours after surgery was more severe near the retractor blade.

CONCLUSIONS

The back muscles were exposed to pathophysiologic condition by a retractor during posterior lumbar spine surgery. External compression by a retractor increases intramuscular pressure to levels that impede local muscle blood flow. The muscle degeneration after surgery could be explained by direct mechanical damage and by the increased intramuscular pressure of muscle tissue by the retractor.

Density of lumbar muscles 4 years after decompressive spinal surgery

Results of decompressive surgery for lumbar spinal stenosis vary. We evaluated the density of lumbar muscles by computed tomography (CT) at the L2-L4 levels in patients 4 years after they had undergone surgery for lumbar spinal stenosis. Twenty of these patients had an excellent outcome clinically, and 16 patients had very poor outcome. The residual stenosis and density of lumbar muscles in Hounsfield units were measured on CT images. The clinical evaluation of outcome also included the Oswestry questionnaire and a walking test. The density of lumbar flexors was higher in the group with excellent results than in the group with poor results. The density of lumbar extensors showed a marked decrease in the operated area. These results suggest that the decrease of muscular density can be partially explained by disuse or inactivity. The decrease in the operated area probably reflects muscular atrophy caused by muscle denervation.

Back muscle injury after posterior lumbar spine surgery. A histologic and enzymatic analysis

STUDY DESIGN

Back muscle injury after posterior lumbar surgery was studied by muscle histology and serum creatine phosphokinase MM isoenzyme activity.

OBJECTIVES

To investigate intraoperative factors influencing the magnitude of back muscle injury after posterior lumbar surgery.

SUMMARY OF BACKGROUND DATA

The authors previously have reported iatrogenic back muscle injury in an animal model and in humans. Serious injury of the back muscle has been shown by short-term and long-term follow-up evaluation.

METHODS

The retraction pressure was monitored, and the retraction pressure-time products were calculated in 24 patients. Early histologic changes of multifidus muscle, which were taken at completion of surgery, and serum creatine phosphokinase MM isoenzyme activity changes were examined.

RESULTS

The magnitude of back muscle injury was significant as the pressure-time product increased. Creatine phosphokinase MM isoenzyme activity increased after surgery and reached a plateau 1 day after surgery, followed by recovery to the normal value 1 week after surgery. Creatine phosphokinase MM isoenzyme activity tended to be high in cases with multilevel exposure and with high pressure-time product.

CONCLUSIONS

Back muscle injury occurs in all patients who underwent posterior lumbar surgery, and these injuries are related to the retraction pressure, time, and extent of exposure.

Cross-sectional areas of lumbar muscles after surgical treatment of lumbar disc herniation. A study with magnetic resonance imaging after microdiscectomy or percutaneous nucleotomy

We assessed in this study the potential development of postoperative muscle atrophy in the operation area in 39 patients treated by either microdiscectomy or percutaneous nucleotomy for lumbar disc herniation. The cross-sectional areas of the lumbar muscles were measured on magnetic resonance images created on the day preceding the operation and 6 months postoperatively. The cross-sections of the lumbar muscles remained unchanged during the observation period in all treated patients indicating that no muscle atrophy had developed in the operation area. Since peroperative tissue trauma may correlate with subsequent muscle denervation and atrophy, this finding may be due to the tissue sparing nature of microdiscectomy and percutaneous nucleotomy, thus encouraging the use of these techniques in the treatment of lumbar disc herniation.

Recent advances in lumbar spinal mechanics and their clinical significance

Of the many problems associated with low back pain, those which are most amenable to biomechanical investigation are identified. Recent advances in lumbar spinal mechanics are then reviewed in five sections dealing with mechanical function, mechanisms of failure, movements in vivo, loading in vivo, and the biological consequences of mechanical loading. The discussion suggests that mechanical fatigue damage may frequently be the underlying cause of low back pain, even when degenerative changes are evident in the tissues, and the review ends by suggesting some priority areas for future research.

Influence of repeated measurements on isokinetic lifting strength

The aim of the study was to evaluate the effect of repeated measurements on isokinetic lifting strength in a smaple of patients with low back pain. The measures were performed in series of five consecutive lifts on two occasions 1-13 days apart, and the patients continued their normal living during this period. A group of healthy subjects was used as a control. The hypothesis was that a mere repetition of the lifting procedure would increase the performance, and that the increase would be bigger in the patient group that in the non-patient group. In addition, grip strength was measured on both occasions. It was supposed that grip strength would not change from trial 1 to trial 2. The results showed an increase in lifting strength from first to second trial in the patient group by an average of 28%, and in the control group by an average of 16%. Grip strength did not increase in either group. The last of five consecutive lifts was the best one in a majority of the cases in both trials. Neither five consecutive lifts nor measurements on two different occassions seem enough to define a reliable baseline for maximal lifting capacity. Other factors than an increase in muscle strength influence the performance, one being a repetition of the lifting procedure. This must be accounted for when defining a baseline for isokinetic lifting capacity.

Gender variation of human spinal and paraspinal structures

To investigate the effects of gender on the dimensions of spinal and paraspinal structures, anthropometric assessments were made on 92 patients (39 female and 53 male, aged 20-55 years) suffering low back pain which required computerized tomography for further investigation. During routine scans cross-sectional areas (CSA) of L4 and paraspinal and psoas muscles were measured at the level of the upper table of L4. The results indicated significantly greater cross-sectional areas of all structures in males who were significantly heavier. For both sexes there were significant, linear relationships between L4 and paraspinal and psoas muscle cross-sectional areas and bodyweight. Gender differences were apparent since for each structure regression lines were, although parallel, separated according to sex, with males having significantly greater muscle and bone cross-sectional areas than females. The gender difference between the lines was much greater for psoas than for paraspinal muscles, suggesting the influence of biomechanical, in addition to hormonal, differences between the sexes.

Isokinetic trunk muscle performance characteristics of classical ballet dancers

Presented at the Sports Physical Therapy Section Team Concept Meeting, December 1991, New Orleans, LA. Recent availability of trunk isokinetic dynamometers has created a need for documented normative data. The purpose of this initial investigation was to determine isokinetic norms for trunk flexion and extension in classical ballet dancers. Strength levels were determined by peak torque. A fatigue index was derived from 20 reciprocal contractions. Twenty-three dancers were tested - 17 females (F) and six males (M). Female dancers were further divided into professional (FP) and semiprofessional (FSP) groups. A questionnaire regarding dance background, training habits, and back pain was administered. Means and ranges for peak torque and fatigue were calculated for each group. T-tests were performed on peak torque and fatigue data grouped by gender and dance status. Peak torque analysis indicated trends of M > F and FP > FSP. A statistically significant (p < 0.05) difference existed for trunk extension between FP and FSP dancers, a possible sport-specific adaptation. Fatigue levels were lower than expected, and possible explanations are considered. J Orthop Sports Phys Ther 1992;15(2):99-106.

Electro and acoustic myography for noninvasive assessment of lumbar paraspinal muscle function

In 31 normal subjects (17 male), aged 19-48 years, and 8 patients with chronic low back pain (4 male), aged 37-55 years, the repeatability of surface recordings of acoustic myography (AMG) and electromyography (EMG) were examined in the lumbar paraspinal muscles. Five isometric test positions were examined. In 21 of the normal subjects, four positions tested were: quiet standing, half extension from prone lying, full extension from prone with and without resistance. In 10 of the normal subjects and the 8 back pain patients, a standardised, unsupported horizontal position with the upper body over the end of a couch was tested. The AMG and EMG signals were full-wave rectified and integrated (iAMG and iEMG). The variability of recordings during repeated 5-s isometric contractions was assessed by analysis of variance (ANOVA) and the coefficient of variation (CV) was calculated from the ANOVA. Both recording techniques produced the most repeatable results during the unsupported, horizontal hold position. In the normal subjects, CV were, iAMG 5.6%, iEMG 4.9%; and in the patients, iAMG 4.4%, iEMG 2.6%. The CV for the other four isometric test positions ranged from 15.3% to 29.4% for iAMG, and 8% to 15.7% for iEMG. These results demonstrated that a controlled test manoeuvre for examining AMG and EMG of the paraspinal muscles was vital for repeatable recordings. The CV for the standardised, horizontal position were lower than for previously published results.(ABSTRACT TRUNCATED AT 250 WORDS)

Isokinetic muscle testing (IMT) in neuromuscular diseases. Preliminary report

Isokinetic muscle testing (IMT) allows precise and reliable measurement of the force produced by the skeletal muscle during exercise at constant velocity and accommodating resistance. This study reports on some clinical situations that illustrate the difference between manual muscle testing (MMT) and IMT in neuromuscular patients. IMT was performed by a special method (continuous passive motion plus gravity compensation) which allowed the measurement of very weak forces, such as in the four patients described in this study. It is important to note that for the same MMT grading the corresponding isokinetic force values were very different. Therefore there is an obvious correspondence between the isokinetic measurement of muscle strength and the morphological change in the muscle on the CT scan of the thigh, which did not show up on MMT. IMT could be extremely important for research into neuromuscular disorders, where the detection of even the tiniest variations in strength is relevant.

Lumbar muscularity and its relationship with age, occupation and low back pain

This paper considers an internal standard of lumbar muscularity. The cross-sectional areas (Acs) of the intervertebral disc and paraspinal muscles were measured in 147 working men from an axial magnetic resonance image passing through the L3-4 disc. Lumbar muscularity was expressed by two ratios; the ratio between the Acs of the right psoas and the Acs of the intervertebral disc (P:disc), and the ratio between the combined Acs values of the right erector spinae and quadratus lumborum and the Acs of the disc (ESQL:disc). When the subjects were divided into two age groups (76 aged 20-30 years and 71 aged 31-58 years) lumbar muscularity was found to be significantly greater (P less than 0.001) in the younger age group (P:disc = 0.8, SD 0.2; ESQL:disc = 2.0, SD 0.3) than in the older age group (P:disc = 0.7, SD 0.2; ESQL:disc = 1.8, SD 0.3). Lumbar muscularity was not significantly affected by occupation or by a history of low back pain.