Continuous passive motion applications can help patients with low back pain function again.

Despite our best clinical efforts and technological advances, low back pain remains a health problem of epidemic proportions. The fact that most adults suffer from back pain at some time in their lives is astounding by itself. But consider the additional factors of a high recurrence rate and the associated costs of medical care, days lost from work, and liability/compensation. You can see why estimates of annual United States’ expenditures for low back pain top billions of dollars.

Functional Restoration

Helping people disabled by spinal pain to get back on their feet has been the principal goal of the Spine Institute of New England and the Work Enhancement and Rehabilitation Center (WERC) in Williston, Vt. While surgery and a variety of traditional therapies are available, functional restoration remains the most successful approach for improving the flexibility, strength, and endurance required by the patients’ work and activities of daily living (ADL) goals. Functional restoration combines education and counseling with progressive exercise guided by frequent measurements of physical capacity. The culmination of this treatment program comes when the patients’ measured capacities are matched with the physical requirements of their desired jobs and ADL.

The functional restoration program has been very successful in helping people recover sufficiently to return to work, and it has also illustrated a special problem for people with back pain—sitting down hurts.1,2 

Back pain during sitting is an ironic problem in rehabilitation. Many people who cannot achieve enough flexibility, strength, and endurance to return to their former activities and work look for more sedentary pastimes and occupations. Many jobs involve prolonged sitting in office, assembly, and motor-vehicle settings. Most people have to commute. So the fact that sitting is commonly painful for people with back pain becomes a significant issue for rehabilitation practitioners who are trying to help them make functional recoveries. Together, they face two critical questions: identifying the source of the pain, and identifying the physical limitations associated with intolerance of sitting.

Functional Limitations and Sitting Discomfort

Despite radiography, computed tomography scanning, and magnetic resonance imaging, the anatomic source of a patient’s low back pain is usually not known. This makes it all the more difficult to explain how sitting might be painful for an individual, and how this effect might be reduced. Recognizing that we cannot usually make an anatomic diagnosis and intervention, our research team looked for functional limitations that might be associated with painful sitting. We compared patients in our functional restoration program who complained of back pain during sitting to those who did not. Comparison variables included lumbar spinal and pelvic flexion and extension, isokinetic trunk strength, lifting capacity, and cardiovascular fitness.

Unfortunately, none of these physical-capacity parameters could distinguish the patients with painful sitting very accurately. Therefore, we could not identify specific physical attributes we might improve with rehabilitation to reduce sitting symptoms.3 

Biomechanics of Sitting

Without a clear way to determine the anatomic and physiologic cause and cure of most individual patients’ back pain while sitting, we turned our attention from the sitter to the seat. The biomechanical effects of sitting on the spine have been studied primarily through pressure-sensing probes, spinal imaging, and electromyography. First, sitting increases the intervertebral disc pressure due to a forward shifting of the center of gravity.⁴ Second, the nucleus pulposus shifts posteriorly when you sit with kyphosis.⁵ Finally, paraspinal muscles contract to counter the forward pull of the upper body.⁶ All of these actions have been blamed for the pain of sitting and can be reduced by lumbar support. These biomechanical advantages of lordosis have been ratified by a careful clinical trial demonstrating reduced back and leg complaints with use of a lumbar support.7 

Another way to reduce lumbar spinal compression is to recline the seat backward. However, reclining is usually not possible during task seating such as driving or working at a desk. A common observation is the fact that not everyone sits with lumbar lordosis. In fact, if you look at a group of people sitting, you will notice that some sit with lordosis and some with kyphosis. Look again several minutes later, and you will very likely see that many of them have changed from one position to the other. The fact that people try to shift positions periodically when they sit explains in part why many seat designs are available, but no single posture or seat design works for everyone all the time. 

Several years ago, while driving on vacation, I was able to relieve my own back pain for a while by placing a lumbar pillow behind my back. After about 10 minutes, my back began to hurt again, so I took out the pillow, and that felt better for a while. After several trials of replacing and removing the pillow, a light bulb went on in my head. The key to sitting comfortably is to keep the spine moving back and forth through greater and lesser degrees of lordosis. This continuous passive motion (CPM) is similar to the mobilization provided after knee surgery. More specific to the lumbar spine, it resembles the repetitive lordosis achieved with the extension exercises popularized by Robin McKenzie, RPT.8,9 The best way to do this would be with an air bladder that could be slowly inflated and deflated by a pump and valve. How would variations in body size, spinal compliance, clothing, and position in the seat pan be accommodated? Adding a pressure sensor and a microprocessor would allow the user to set just the right amount of inflation pressure.

Lumbar Motion: Pie in the Sky?

Next came 10 years of research at the Vermont Rehabilitation and Engineering Research Center, with funding from the National Institute on Disability and Rehabilitation Research. Once the optimal bladder sizes and shapes, pump and valve characteristics, inflation-cycle times, and pressure ranges were established, we were ready to do efficacy testing.

First, people without back pain were tested with and without the CPM system in a tightly controlled laboratory setting. They sat in a car seat vibrated vertically at 4.5 Hz to simulate highway driving. Visual analogue scores for back discomfort, stiffness, and fatigue were dramatically better during 2-hour sessions with the CPM compared to the control periods.¹⁰ Likewise, subsequent testing showed that people with clinical back problems had much better comfort, stiffness, and fatigue self-assessment ratings on days when they used CPM in their motor vehicles than on days when they did not.10 This research won first prize from the International Society for the Study of the Lumbar Spine.

The next question was: How did the CPM system work? In our original laboratory experiments, we used an instrumented flexible ruler called the lordosimeter to measure lordotic excursions. The lordosimeter was applied to the user’s lumbar skin, and electronic output from implanted strain gauges quantified the lordotic angle changes during inflation and deflation of the CPM bladder. While there was much more movement with the CPM than without it, some readers of our publications wanted more direct evidence. Furthermore, our efforts with  McKenzie and his research group in New Zealand taught us that there were significant problems in measuring lordosis angle changes with surface techniques.11 

So the next step was to document spinal motion with lateral fluoroscopic movies of subjects during CPM use under customary inflation specifications. These movies demonstrated that, instead of some relatively superficial soft-tissue effect of massage or vibration, the CPM system functioned by slowly moving the spine through the ranges of lordosis that might be expected when rising from an unsupported (bench) sitting position to standing.

Since the discovery that pneumatic CPM supports could help people with back problems when they sit, the devices have been used in a variety of settings around the world. CPM systems have been installed in automobiles and buses in places as far away as Thailand and in recliners and office seats here in the United States. United Airlines has equipped about 10,000 of its airplane seats with the commercial version of the CPM system. The seats have received the highest ratings in the company’s passenger surveys. Most recently, Good Housekeeping magazine (September 2001) gave the commercial system a four-star rating—the best among the products for back pain. But how could these commercial products help our low back pain patients at the Spine Institute of New England and the WERC?

A Federal Catch-22

First, we needed approval from the US Food and Drug Administration, which classified the system as a Class II and then a Class I device based on equivalency with a powered therapy table that could be used only in a medical facility. Subsequently, our application to the Health Care Financing Administration (HCFA) for a billing code number was rejected due to low sales volumes. This was a real eye-opener about the difficulties in entering the medical marketplace. Essentially, without major corporate financing and detailing, a small company could not pass the HCFA’s-sales volume criteria no matter how good its product was—a true catch-22. 

Rehab and CPM

When patients are disabled by low back pain, and the traditional medical models of anatomic diagnosis and cure fail to restore comfort and function, rehabilitation is often the critical pathway to recovery. This is particularly true for people whose goals include returning to the physical activities of work, leisure, and daily life. When the ability to tolerate sitting is a part of those desired activities, rehabilitation should include education about postural strategies, and frequent changing of positions and stretching. When these approaches are not enough, and sitting is still limited or uncomfortable, CPM can provide a new adjunct to a total program for patients with low back pain.

Rowland G. Hazard, MD, is a professor of orthopedics and rehabilitation. He can be reached via email: rghazardmd@aol.com.

References

1. Hazard RG, Fenwick JW, Kalisch SM, et al. Functional restoration with behavioral support: a 1-year prospective study of patients with chronic low back pain. Spine. 1989;14:157–161.

2. Hazard RG. Functional restoration of patients with chronic low back pain. In: Frymoyer JW, ed. The Adult Spine. New York: Raven Press; 1995.

3. Hazard RG, Koelbel S. Correlations between sitting intolerance and other physical impairments in people with chronic low back pain. In: Abstracts of the International Society for the Study of the Lumbar Spine; June 1994; Seattle.

4. Nachemson AL. Disc pressure measurements. Spine. 1981;6:93–97.

5. Shah JS, Hampson WGH, Jayson MIV. The distribution of surface strain in the cadaveric lumbar spine. J Bone Joint Surg. 1978;60B:246–250.

6. Andersson GBJ, Chaffin DB, Pope MH. Occupational biomechanics of the lumbar spine. In: Pope MH, Andersson GBJ, Frymoyer JWF, Chaffin DB, eds. Occupational Low Back Pain: Assessment, Treatment and Prevention. St Louis: Mosby; 1991:20–43.

7. Williams MW, Hawley JA, McKenzie RA, van Wijmen PM. A comparison of the effects of two sitting postures on back and referred pain. Spine. 1991;16:1185–1191.

8. McKenzie RA. The Lumbar Spine: Mechanical Diagnosis and Therapy. Waikenae, New Zealand: Spinal Publications; 1981.

9. Hazard RG, McKenzie RA, Mooney V. Helping your back pain patients make the most of spinal motion. J Musculoskeletal Med. 1994;11:24–35.

10. Reinecke SM, Hazard RG, Coleman K. Continuous passive motion in seating: a new strategy against low back pain. J Spinal Disord. 1994;7:29–35.

11. Hazard RG, Williams MM, McKenzie RA. Reliability of three methods for measuring prone lumbar extension. N Z J Phys Ther. 1994;22:11–13.