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Monday, May 08, 2006

The role of proprioception and low back stability in the incidence and treatment of low back pain.

Mechanical low back pain (LBP) affects 60-80% of the population at some time in their adult lives. Back pain is costly in terms of health care because of lost work days, decreased physical ability and decreased perceived quality of life. Current guidelines for treating LBP include spinal manipulation, non-steroidal anti-inflammatory drugs, active rest, patient education, and exercise (1). The purpose of this paper is to discuss current concepts in the treatment of LBP, focusing mainly on exercise prescription in order to increase lumbar stability and proprioceptive ability. A set of exercises based on the current literature will also be suggested.
Lumbar core stability and proprioception have both emerged as popular concepts in the incidence and treatment of low back pain. Lumbar stability is achieved through a complex interaction between abdominal and paraspinal musculature. Studies indicate that most torso muscles play a large role in stability, depending on the type of activity. These include the multifidus muscles, quadratus lumborum, longissimus and iliocostalis together with the abdominal wall, which includes rectus abdominus, the obliques, and tranversus abdominus (3). The multifidus is likely the main muscle involved in protecting the articular facet joints, due to its unique ability to prevent movements at specific motion segments (9). The multifidus is also responsible for providing segmental stiffness and therefore controls motion in the neutral zone (11). There is strong evidence for the relation between multifidus dysfunction and low back pain (6).
Proprioception is defined as the complex interaction between afferent and efferent input to control body movement and position (2). It is a component of the somatic sense of mechano-receptivity, which encompasses two aspects of position sense (static and dynamic) and allows the body to maintain stability and orientation during both static and dynamic loads2. Proprioception is comprised of 3 main sensations: the sensations of position and movement of joints; the sensations of force, effort, and heaviness associated with muscular contractions; and the sensations of the perceived timing of muscular contractions (6).
Studies have shown that spinal rehabilitation programs that focus on the strengthening of the lumbar musculature through resistance training methods have been shown to increase low back strength as well as reduce pain and improve perceived psychosocial function (4). Furthermore, inefficient muscular stabilization of the low back results in an increased risk of injury to the spine5. Patients with chronic LBP also have been shown to demonstrate low levels of trunk strength compared with healthy subjects. Evidence indicates that the lumbar extensor muscle group plays a primary role in trunk function and dysfunction (4). McGill identifies the importance of the relative endurance of a group of muscles versus the relative strength of that group in maintaining low back stability. He also identifies proposed normal ratios of endurance times for the torso flexors relative to the extensors, as well as the lateral musculature relative to the extensors (0.98 and 0.73 respectively) to assist in the detection of endurance deficits which may cause lumbar ‘instability’* and predispose a patient to low back pain (3,13). However, trunk muscle strength and endurance does not guarantee the relief of painful symptoms (5).

*The term ‘instability’ used here does not imply clinical instability, only a lack of normal lumbar stability.

Several studies have analyzed proprioception and its role in LBP. Reduced proprioception in the spine of patients with chronic LBP has been established for standing posture and four-point kneeling (8). One study performed force plate analysis on LBP and control subjects and found that the subjects with LBP demonstrated significantly greater postural sway, kept their center of force more posteriorly, and were less likely to maintain balance on one foot than subjects without pain (2). It is hypothesized that excessive load to the spine or trunk muscle disuse can result in damage or dysfunction of the muscle spindles. Muscle-tendon vibration and microneurography studies have demonstrated a major role of muscle spindles in proprioception (5). Introducing a vibratory stimulus such as that from a tuning fork, has been shown to cause perceived lengthening of a trunk muscle (if over 40 Hz), as well as a perceived shortening of trunk muscle (if under 40 Hz) (5). This results in an increased righting error, such that when a patient tries to return to neutral position, they can overshoot or undershoot their target. Spinal joints between adjacent vertebrae are rich in mechano-receptor nerve fibers that supply information to the brain. This reflex pathway is necessary for vestibular and ocular righting reflex actions, normal spinal coupling motions, balance and proprioception (10). As a joint is compressed, inflammation results, as well as a decreased mobility of nutrients getting into the joint. Joints are not lubricated or nourished as efficiently, and joint pathology results which destroys the reflex arc to the brain. As the arc is destroyed, the patient will gradually lose his/her expected coupling motion, righting reflex actions and ability to maintain balance and upright posture under gravity (10). This could possibly explain the finding of increased postural sway. The joint capsules are also richly endowed with sensory nerve endings (nociceptors). These nociceptors are sensitized and eventually synapse in the thalamus, where they spill over to the segment’s motor neurons which will cause reflexive muscle spasm of that segment (9), causing pain.
It can therefore be deduced that decreased muscle spindle input could impair spinal proprioception and segmental stability (6). When a joint is injured, there is a decreased mechano-receptor function and proprioceptive feedback to the brain. This deficit will negatively impact coordinated muscle contraction and will result in altered perception of body-space relation (10), which will result in chronic low back problems. This will make the spine more vulnerable to injury or re-injury. To compound this, the ipsilateral multifidus muscle is often decreased in size in a patient with low back pain, and will take time to recover even after cessation of symptoms. The potential mechanisms that have been suggested to account for this include reflex inhibition and perceived pain inhibition (6). Studies have shown that muscle spindle input of the multifidus is crucial for accurate positioning of the pelvis and lumbosacral spine in a sitting posture (6). It is therefore hypothesized that proprioceptive deficits from an inhibited multifidus can cause muscle dysfunction and altered spinal stability (6). It has also been demonstrated in clinical trials that the focused retraining of the deep muscle co-contraction could reverse the inhibition of the multifidus.
Research has shown that both chronic and acute low back pain patients have benefited from some kind of active exercise (1). Carpenter and Nelson (1998) found that lumbar extension exercise using progressive resistance exercises significantly increased strength and decreased pain in chronic LBP patients (12). This was demonstrated with isolated lumbar extension exercise with the pelvis stabilized using specialized equipment. Hides et al (2001) found the subjects with acute, first-episode LBP who received specific exercise therapy in addition to medical management and resumption of normal activity experienced fewer recurrences of LBP in the long-term than subjects who received only medical management and resumed normal activity (11). However, studies have shown that lumbar spine strengthening with traditional equipment is ineffective in strengthening the lumbar spine because of lack of specificity (4). Clearly the use of specific exercises is a high priority.
In most traditional exercise programs for the LBP patient, emphasis is placed on the immediate restoration, or enhancement, of spine range of motion and muscle strength (3). This approach has been shown to be ineffective and evidence suggests that those with greater spine ranges of motion have increased risk of future troubles and that endurance, not strength, is related to reduced symptoms (3). McGill (2001) has performed extensive studies on the loads that a spine undergoes when exercising the muscles involved in low back stability. He has proposed a set of exercises that maximize activation of the involved musculature, while minimizing the load applied to the spine (3). One such example is the side bridge exercise for training the quadratus lumborum (see Appendix A for this exercise as well as other suggested exercises for training low back endurance and proprioception). McGill also suggests exercises for the rectus abdominus, the abdominal obliques, the transverse abdominus, and the back extensors (and stabilizers). McGill contends that a spine must first be stable before moments and forces are produced to enhance performance (3).
Due to the apparent role of proprioception in LBP as discussed above, exercises that train proprioceptive ability would be beneficial in decreasing the incidence of LBP. Brumagne et al contend that interventions in patients with LBP that enhance proprioceptive acuity may aid in recovery and reduce the likelihood or recurrence of chronic LBP (5). Pettibon contends that without re-establishing proprioception, the other components of a rehabilitation program (flexion, strength, endurance) cannot be orchestrated. Without the presence of intact proprioception, chronic problems will result (10). To date, there is very little research on methods of training the proprioceptive system in the lumbar spine. However, Behm et al propose that core stability as well as improved balance and proprioceptive capabilities can be obtained through the use of a stability ball, or ‘Swiss ball’ (14). With regards to the Swiss ball, it is stated that ‘having a client sitting on a gymnastic ball doing almost any exercise will require vestibular and proprioceptive feedback to make the appropriate adaptive responses’ (15).
In summary, the role of both lumbar stability as well as proprioceptive ability appear to play a large role in the incidence and treatment of low back pain. By addressing these aspects in a rehabilitative program, clinicians may obtain more success in effectively treating their LBP patients. It is our contention that exercises such as those prescribed by McGill (3) in combination exercises being researched at Palmer college1 on an exercise ball can target both stability and proprioception. Exercises should be prescribed in order to target muscular endurance as opposed to strength. To accomplish this, the positions of McGill’s exercises should be held for an extended period of time and for multiple repetitions, depending on the capabilities of the patient, and should be steadily increased throughout the progression of the rehabilitative program. It would also be wise to progress from a stable position to an unstable one (as achieved by the exercise ball) when suitable for the patient.
Based on the current literature, we have assembled a set of suggested exercises to improve low back stability and proprioception. See Appendix A.


References:

1. McDonald JC, Lundren, KL. The progressive dynamic lumbar stabilization program for the treatment of musculoskeletal dysfunctions that contribute to mechanical low back pain. Journal of Sports Chiropractic & Rehabilitation; 12(2): 55-64. 1998.
2. Newcomer KL, Laskowski ER, Yu B, Johnson JC, & An K-N. Differences in repositioning error among patients with low back pain compared with control subjects. SPINE; 25(19): 2488-2493. 2000.
3. McGill SM. Low back stability: From formal description to issues for performance and rehabilitation. Exercise and Sport Sciences Reviews; 29(1): 26-31. 2001.
4. Deutsch FE. Isolated lumbar strengthening in the rehabilitation of chronic low back pain. JMPT; 19(2): 124-133. 1996.
5. Brumagne S, Cordo P, Lysens R, Verschueren S, & Swinnen S. The role of paraspinals muscle spindles in lumbosacral position sense in individuals with and without low back pain. SPINE; 25(8): 989-994. 2000.
6. Brumagne S, Lysens R, Swinnen S, & Verschueren S. Effect of paraspinal muscle vibration on position sense of the lumbosacral spine. SPINE; 24(13): 1328-1334. 1999.
7. Jull G, Richardson C. Motor control problems in patients with spinal pain: A new direction for therapeutic exercise. JMPT; 23(2): 115-118. 2000.
8. Gill KP, Callaghan MJ. The measurement of lumbar proprioception in individuals with and without low back pain. JMPT; 21(10): 582. 1998.
9. Schneider MJ. The traction methods of Cox and Leander: The neglected role of the multifidus muscle in low back pain. Journal of Chiropractic Technique; 3(3): 109-116. 1991.
10. Pettibon, B. Spinal biomechanics: Detection and correction of the spinal system’s subluxation; Part 18. Chiropractic Journal; 12(2): 30-32. 1997.
11. Hides J, Jull GA, & Richardson CA. Long term effects of specific stabilizing exercises for first-episode low back pain. SPINE; 26(11): E243-E248. 2001.
12. Carpenter DM, Nelson BW. Low back strengthening for the prevention and treatment of low back pain. Medicine & Science in Sports & Exercise; May 1998: 18-23.
13. McGill SM. Stability: From biomechanical concept to chiropractic practice. JCCA; 43(2): 75-88. 1999.
14. Behm DG, Anderson K, & Curnew RS. Muscle force and activation under stable and unstable conditions. Journal of Strength and Conditioning Research; 16(3): 416-422. 2002.
15. Carriere B. The ‘Swiss Ball’: An effective tool in physiotherapy for patients, families and physiotherapists. Physiotherapy (London); 85(10): 552-561. 1999.


Appendix A:
Assembled from the papers of McGill (3):

Coming soon....

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