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Conservative lower back treatment reduces inhibition in knee-extensor muscles: a randomized controlled trial*,**

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Abstract

Background: Knee-joint pathologies, such as anterior knee pain (AKP), are associated with strength deficits and reduced activation of the knee extensors, which is referred to as muscle inhibition (MI). MI is thought to prevent full functional recovery, and treatment modalities that help to reduce or eliminate MI appear necessary for successful rehabilitation. Clinical observations suggest that AKP is typically associated with sacroiliac (SI) joint dysfunction. It is unknown whether Sl-joint dysfunction contributes to knee-extensor deficits and whether correction of SI-joint dysfunction alleviates MI. Objective: The objective of this study was to assess whether conservative low back treatment reduces lower limb MI. Study design: In a randomized, controlled, double-blind study the effects of conservative lower back treatment on knee-extensor strength and MI were evaluated in patients with AKP. Methods: Twenty-eight patients with AKP were randomly assigned to either a treatment or a control group. After a lower back functional assessment, the treatment group received a conservative treatment in the form ofa chiropractic spinal manipulatlon aimed at correcting SI-joint dysfunction. The control group underwent a lower back functional assessment but received no joint manipulation. Before and after the manipulation or the lower back functional assessment, knee-extensor moments, MI, and muscle activation during full effort, isometric knee extensions were measured. Results: Patients showed substantial MI in both legs. Functional assessment revealed SI-joint dysfunction in all subjects (23 symptomatic and 5 asymptomatic). After the SI-joint manipulation, a significant decrease in MI of 7.5% was observed in the involved legs of the treatment group. MI did not change in the contralateral legs of the treatment group or the involved and contralateral legs of the control group. There were no statistically significant changes in knee-extensor moments and muscle activation in either group. Conclusions: The results of this study suggest that SI-joint manipulation reduces knee-extensor MI. Spinal manipulation may possibly be an effective treatment of MI in the lower limb musculature. (J Manipulative Physiol Ther 2000;23:76–80)

Introduction

Clinical observations have shown that anterior knee pain (AKP) often coexists with mechanical dysfunction of the sacroiliac (SI) joint or the lumbar spine. Knee-joint pathologies in general are associated with loss of strength and function of the knee-extensor muscles. 1, 2, 3, 4, 5, 6 This muscle weakness has been attributed to muscle inhibition (MI; ie, the inability to recruit all motor units of a functional muscle group to their full extent during a maximal-effort voluntary contraction). The potential of MI to limit functional recovery of muscles and joints after injury has been recognized, and it has been suggested that one of the early goals in the rehabilitation process should be to reduce or eliminate MI to achieve full recovery of the affected structures.1 There is anecdotal evidence that in patients with combined lower back and knee-joint dysfunction, AKP can be effectively managed through manipulative adjustment of the SI joint. Improved subjective symptoms and increased knee-extensor strength have been reported after manipulation. This result prompts the question of whether SI-joint or lower back dysfunction contribute to the functional deficiencies observed in the knee-extensor muscles of patients with knee-joint pathologies and whether correction of the SI-joint dysfunction may directly affect knee-extensor inhibition.

In a recent pilot study we assessed functional changes of the knee-extensor muscles associated with SI-joint manipulation. We were able to show a significant increase in knee-extensor moment and a significant decrease in MI after SI-joint manipulation.7 The results of this pilot study indicated that SI-joint manipulation may beneficially affect the functional recovery of knee problems. The pilot study was designed as a clinical outcome study and did not include a control group. Although the results are of clinical relevance, they might have contained experimental bias or placebo effects. To establish a scientifically tenable relationship between SI-joint manipulation and reduction of knee-extensor MI, a randomized double-blind study was required.

The purpose of this study was to assess whether conservative lower back treatment reduces knee-extensor MI in a randomized, controlled, double-blind study. The study population consisted of patients with AKP. The spinal manipulation used in all instances was a high-velocity, low-amplitude, side-posture, SI-joint manipulation.

Section snippets

Subjects

Twenty-eight subjects (25 women and 3 men) gave written informed consent to participate in this study. All patients had chief complaints of AKP (either unilateral or bilateral) and were scheduled for treatment at a private chiropractic clinic. Five subjects had previous knee surgery, and 17 subjects had received other forms of therapy before entering the study, such as strengthening exercises or electrical therapy. Descriptive data of the patient population can be found in Table 1.

. Descriptive

Results

Pretreatment values for knee-extensor moments and MI for the treatment and the control group are shown in Figs 1 and 2.

. Knee-extensor moments (mean ± SEM) at baseline for the involved and the contralateral legs of the treatment and the control groups.

. MI (mean ± SEM) at baseline for the involved legs and the contralateral legs of the treatment and control groups. Asterisks indicate a significant difference between involved and contralateral legs. The horizontal line indicates MI values found in

Discussion

MI is thought to prevent full functional recovery of the muscles and the joint after traumatic knee injury.1 Patients with large MI at the onset of a physical rehabilitation program did not show the anticipated improvements during the rehabilitation process. In particular, muscle strength deficits persisted, and there was no significant reduction in MI. Reducing or eliminating MI should therefore be a primary focus of early rehabilitation. Medical and arthroscopic interventions have been

Conclusion

Although the precise mechanisms and the time course of the observed decrease in knee-extensor inhibition are currently unknown, the decrease in MI after manipulation of the SI joint is interesting. The subjects in this study were representative of a typical patient population with AKP complaints. They all showed the expected functional deficiencies, such as weakness and MI, in the knee extensors of the involved and contralateral legs, which is consistent with findings of previous studies. 5, 6

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*

Supported by the Olympic Oval Endowment Fund University of Calgary, the Canadian Chiropractic Association, the Canadian Memorial Chiropractic College, and the College of Chiropractors of Alberta.

**

Submit reprint request to: Esther Suter, PhD, Faculty of Kinesiology, The University of Calgary, 2500 University Dr NW, Calgary, Alberta T2N 1N4, Canada.

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