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Flexion-Relaxation Ratio in Sitting: Application in Low Back Pain Rehabilitation

Mak, Joseph N. F., MMedSc, PhD*; Hu, Yong, PhD*; Cheng, Aldous C. S., MSc; Kwok, H. Y., FRCSE(Ortho), FHKCOS, FHKAM(Orthopaedic Surgery)*; Chen, Y. H., PhD; Luk, Keith D. K., FRACS, FRCSEd, FRCS(Glas), FHKCOS, FHKAM(Ortho Surg)*

doi: 10.1097/BRS.0b013e3181ba021e
Biomechanics
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Study Design. A multiple-comparative study between normal and low back pain (LBP) patients before and after rehabilitation.

Objective. To examine whether there is a change in flexion-relaxation phenomenon in sitting in LBP patient following a rehabilitation treatment.

Summary of Background Data. There is an association between LBP and seated spine posture. Previous study has reported an absence of flexion-relaxation phenomenon in LBP patients during sitting. However, it is unknown whether there is a difference in flexion-relaxation phenomenon in sitting in LBP patients before and after rehabilitation treatment.

Methods. A total of 20 normal subjects and 25 chronic LBP patients who underwent a 12 weeks rehabilitation program were recruited. Surface electromyography recordings during upright sitting and flexed sitting were taken from the paraspinal muscles (L3) bilaterally from the normal subjects, and in the LBP patients before and after the rehabilitation treatment. The main outcome measures for patients include the visual analogue scale, Oswestry disability index, subjective tolerance for sitting, standing and walking, trunk muscle endurance, lifting capacity, and range of trunk motion in the sagittal plane. Flexion-relaxation phenomenon in sitting, expressed as a ratio between the average surface electromyography activity during upright and flexed sitting, was compared between normal and patients; and in LBP patients before and after rehabilitation.

Results. Flexion-relaxation ratio in sitting in normal subjects (Left: 6.83 ± 3.79; Right: 3.45 ± 2.2) presented a significantly higher (Left: P < 0.001; Right: P < 0.05) value than LBP patients (Left: 3.04 ± 2.36; Right: 2.02 ± 1.49). An increase in flexion-relaxation ratio in sitting was observed in LBP patients after rehabilitation (Left: 4.69 ± 3.94, P < 0.05; Right: 3.58 ± 2.97, P < 0.001), together with a significant improvement (P < 0.05) in subjective tolerance in sitting and standing, abdominal and back muscle endurance, lifting capacity, and range of motion. There were no significant changes in disability and pain scores, and subjective tolerance in walking.

Conclusion. Flexion-relaxation ratio in sitting has demonstrated its ability to discriminate LBP patients from normal subjects, and to identify changes in pattern of muscular activity during postural control after rehabilitation.

This study compared the flexion-relaxation ratio in sitting between normal and low back pain (LBP) patients before and after rehabilitation. Flexion-relaxation ratio in sitting in normal subjects presented a significantly higher value than LBP patients. An increase in flexion-relaxation ratio in sitting was observed in LBP patients after rehabilitation, together with a significant improvement in self-reported measures and physical assessment outcomes.

From the *Department of Orthopaedics and Traumatology, The University of Hong Kong, Pokfulam, Hong Kong; †Department of Physiotherapy, Duchess of Kent Children's Hospital, Sandy Bay, Hong Kong; and ‡Department of Mechanical Engineering, The University of Hong Kong, Pokfulam, Hong Kong.

Acknowledgment date: November 26, 2008. First revision date: April 26, 2009. Second revision date: June 16, 2009. Acceptance date: June 22, 2009.

The manuscript submitted does not contain information about medical device(s)/drug(s).

Foundations funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.

Supported by grants from the Research Grants Council of the Hong Kong SAR, China (CERG 712408E) and S.K. Yee Medical Foundation (207210/203210).

Address correspondence and reprint requests to Yong Hu, PhD, Research Office, Duchess of Kent Children's Hospital, 12 Sandy Bay Rd, Pokfulam, Hong Kong; E-mail: yhud@hkusua.hku.hk

© 2010 Lippincott Williams & Wilkins, Inc.