Contributed by:  Dr. Ken McLeod, Sonostics Chief Science Officer

Joint pain is the second most common complaint that people have when they visit a physician. Over 50 million individuals in the U.S. are afflicted, and approximately one-third of the population over age 45.  Joint pain results in over 40 million physician visits each year.  In addition, joint pain is the leading cause of disability in the U.S., affecting approximately 18% (8 million) of the adult population.  Direct and indirect costs of joint pain were estimated at over $65 billion in 1992 (Yelin, et al, 1992) and have grown considerably since that time.

Of the various joint pains, knee pain dominants, accounting for more than 14 million physician visits each year in the U.S.  In fact, knee pain is the third most common complaint of individuals seeking the advice of a physician (Table 1) (CDC 2009).

Table 1. Most common complaints of ambulatory care patients who are not seeing a physician for a regular physical, pregnancy check-up, or post-surgical follow-up.

When a patient with joint pain visits a physician they will usually be told they have a form of arthritis. Arthritis is a general term for a variety of joint diseases. There are three types of arthritis:  the most common by far is osteoarthritis, which is often referred to as ‘wear and tear’ arthritis, and is commonly thought to be a natural outcome of aging.  In addition, there are the more rare conditions of rheumatoid arthritis (an autoimmune disease), and ankylosing spondylitis (general associated with spinal pain, and is thought to be genetic in origin).

Most ambulatory care visits for arthritis involve persons over age 45 and over (75%) and predominantly women (66%).  Individuals with joint pain most commonly visit a primary care provider (52%), followed by orthopaedic surgeons (20%), and rheumatologists (17%).  The standard of care for patients who visit a physician is pharmacologic treatment (anti-inflammatories and pain medications).  In a recent study of 36.5 million physician visits for joint pain, over 70% of patients were given a total of 59 million drug prescriptions.  The most commonly administered drug was non-steroidal anti-inflammatory (NSAIDS), followed by analgesics (both topical, non-narcotic and narcotic), and corticosteroids (Hootman, et al 1997).

This standard approach to the treatment of arthritis is currently undergoing close scrutiny as it does not at all address the underlying cause of the pain. Rather, the pharmacologic approach simply allows the individual to mask the pain until joint degradation reaches a point where the knee has to be replaced (total knee arthroplasty – TKA).  Previously, it was believed that nothing else could be done, but studies such as the Arthritis Foundation’s “Arthritis Self-Management Study” have shown that simple preventative approaches, such as exercise, can be as effective as pharmacologic treatment (Lorig, et al, 1993).  Unfortunately, such approaches are severely underutilized.

The difficulty in pursuing preventative approaches to arthritis, and more specifically, exercise interventions, is that, historically, there has been no means for identifying the specific exercises which need to be undertaken by the individual to relieve the pain of arthritis.  As a result, a broad range of exercises have been provided to the individual, and after a short time, most individuals abandon their exercise routine, both because it is so time consuming, and since there is no feedback on whether progress was being made.

Yet, the basis for exercise intervention is well established. Since the beginning of the 20th century it has been recognized that specific muscle imbalances (either among complementary or agonist/antagonist muscle pairs) results in inappropriate distribution of forces in a joint, resulting in inflammation and eventually degradation (Truslow, 1909) – note that trauma and congenital defects can also lead to inappropriate joint loading, though these situations are far more rare.  Correspondingly, restoration of muscle balance corrects the joint loading, allowing the joint tissue to heal and the pain will disappear.

The challenge that has faced the healthcare community since the early 20th century has been one of identifying the specific muscle imbalances.  With the advent of electronic technology in the 1920 and 1930s, the technique of measuring the electrical potentials in contracting muscles (electromyography – EMG) began to be developed and it was widely hoped that this technology would permit accurate muscle assessment. EMG started to be utilized in the late 1960s, but EMG techniques could not be found which would permit comparisons between muscles or over time, and given the difficulty of application, was never widely accepted in the primary care clinic.  Integrated circuit technology developed in the 1980s did produce developments in EMG technology which allowed it effective use during neurosurgery.

In the 1970s and 1980s, feedback control muscle dynamometry was developed, and again, there was great hope that a means for assessing muscle activity would be available in the clinic. However, dynamometry requires that any exercise activity used in an assessment be open-chain so that the application to functional activity is unclear.  Moreover, muscle dynamometers report torque generated at a joint, rather than the activity of a specific muscles, so that direct application to a muscle training regimen was always indirect. The inability for muscle dynamometers to assess closed-chain activities resulted in insurance companies removing this assessment technique as a reimbursable evaluation, and their presence in clinics has been greatly reduced over the past decade.

Starting in the 1990s, a research group in Italy began to pursue the phenomenon of “muscle sound” as an alternative means for assessing the activity of specific muscles.  This research progressed from using microphones to record the sounds that muscles create when they contract, to small accelerometers to record the actual muscle body vibrations at the surface of the skin.  This new recording technique has been called mechano-myography (MMG) in order to distinguish the technique from EMG, but more accurately, the technique should be called vibromyography, or VMG, as it is the muscle vibrations on the surface of the skin which are being recorded.

Recent work out of the State University of New York at Binghamton, has shown that advanced signal processing techniques can be applied to a recorded VMG signal from a muscle undergoing contraction during a functional activity, resulting in a reflection of the absolute force being generated by the muscle.  This approach works for muscles in either isometric contraction or in isotonic contraction.  Moreover, the repeatability of the recording permits comparisons between different muscles, between different people, or comparisons in the change of a person’s muscles over time.  In other words, there now exists a convenient and reliable technique available for assessing muscle balance during closed-chain functional activity.

Arthritis has not attracted as much attention as other chronic health conditions such as diabetes, cancer and heart disease, perhaps because the associated rates of mortality and hospitalization are relatively low.  However, the burden of arthritis on individuals and society is extremely high.  Indeed, given the high prevalence of arthritis, the impact on the workplace, the healthcare system, and the quality of life for the affected population, the impact of joint pain is widely considered to be higher than that of other chronic diseases.   The goal of Sonostics Inc. is to provide communities throughout the U.S. (and perhaps eventually the world) with the resources necessary to indentify the specific muscle imbalances existing in individuals with joint pain as early as possible, and then help these individuals address their imbalances.  The company is starting with a focus on knee pain – evaluating both those with knee pain, and those who want to ensure that no muscle imbalance exists which could result in future knee pain and joint damage.  It is expected that there will then be progressive developments in the technology permitting additional joint assessments, such as elbow, hip, back and neck.  The development of VMG technology for the non-invasive assessment of muscle balance appears to be extensive, and the impact on the healthcare will be immense.

References
CDC. Summary health Statistics for U.S. Adults. National Health Inverview Survey 2009.

http://www.cdc.gov/nchs/fastats/docvisit.htm

Hootman JM, Helmick CG, Schappert SM. Magnitude and characteristics of arthritis and other rheumatic conditions on ambulatory medical care visits in the U.S.  Arthritis and Rheumatism 47:571-581, 2002.

Hurley MV, The role of muscle weakness in the pathogenesis of osteoarthritis. Rheum dis Clin North Am. 25:283-286, 1999.

Lorig KR,  Mazonson PD, Holman HR. Evidence suggesting that health education for self-management in patients with chronic arthritis has sustained health benefits while reducing health care costs.  Arthritis Rheum 36:439-446, 1993.

Turslow W. The principles of muscle balance as applied to orthopedic practice.  J. Bone and Joint Surgery, 1909.

Yelin E, Callahan LF for the National Arthritis Data Work Group. The economic cost and social and psyghological impact of musculoskeletal conditions. Arthritis Rheum 38:1351-1362, 1992.