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Spine:
Randomized Trial

Trunk Muscle Strength, Cross-sectional Area, and Density in Patients With Chronic Low Back Pain Randomized to Lumbar Fusion or Cognitive Intervention and Exercises

Keller, Anne MD*; Brox, Jens I. MD, PhD†; Gunderson, Ragnhild MD‡; Holm, Inger PT, PhD†; Friis, Astrid PT†; Reikerås, Olav MD, PhD†

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Abstract

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.

Lumbar fusion rates for chronic low back pain have increased markedly over the last 20 years, but variations between countries do exist. 1 One randomized study reported that lumbar fusion mitigated pain and disability better than usual care within the primary health system. 2 Exercise therapy for chronic low back pain is recommended by several guidelines. 3–5 According to recent systematic reviews, there is strong evidence for exercises and cognitive therapy being more effective than normal care provided by general practitioners, although evidence in favor of any specific exercise is lacking. 6,7

Studies have reported that patients with chronic low back pain have reduced muscle strength and greater atrophy of the back muscles compared with healthy persons. 8,9 An increase in muscle strength and the cross-sectional area of the back muscles has been reported after various exercise programs. 10–12 In contrast, reduced muscle strength and atrophy of the back muscles have been demonstrated after lumbar fusion. 13–15

We have previously reported results of two randomized studies comparing cognitive intervention and exercises with instrumental lumbar fusion. At the 1-year follow-up examination, no differences between groups were found for disability, the main outcome variable (Oswestry Disability Index), 16,17 or for pain, a secondary outcome variable. 18,19

The purpose of the present study was to investigate the differences in muscle strength, cross-sectional area, and density of the back muscles in patients with chronic low back pain and disc degeneration and in patients with postlaminectomy syndrome, randomized to either lumbar fusion or cognitive intervention and exercises.

© 2004 Lippincott Williams & Wilkins, Inc.

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