Pain at Multiple Locations Associated With Increased Knee OA Pain

Pain at Multiple Locations Associated With Increased Knee OA Pain

Emma Hitt, PhD

November 24, 2010 — Patients with osteoarthritis (OA) of the knee who also have pain in other joints are more likely to experience greater knee pain, according to new research.

Pradeep Suri, MD, with the New England Baptist Hospital, in Boston, Massachusetts, and colleagues reported their findings in Arthritis Care & Research, published in the December 2010 print issue. Specifically, lower back, foot, and elbow pain on the same side as the affected knee were associated with more severe knee pain.

According to the researchers, previous studies have suggested that concurrent low back pain may be associated with more severe symptoms of knee OA. "Pain in other musculoskeletal locations, including the hip and the foot, may also be associated with symptoms in the knee," the study authors write.

This may have several explanations. For example, lower back pain and other joint pains may "directly cause increased knee pain due to the biomechanical interrelationship of joints in the kinetic chain," the study authors note.

In this study, the researchers analyzed data from the Osteoarthritis Initiative, a database including 1389 individuals aged 45 to 79 years with symptomatic tibiofemoral knee OA. Musculoskeletal pain in other areas, including the lower back, neck, shoulder, elbow, wrist, hand, hip, knee, ankle, or foot, was also documented by the patients.

Of the participants, 57.4% reported having lower back pain. A pain score (Western Ontario McMaster Universities Osteoarthritis Index [WOMAC], possible range, 0 - 20), applied to the more symptomatic knee, averaged 6.5 ± 4.1 in participants with low back pain vs 5.2 ± 3.4 in participants without low back pain (P < .0001).

Multivariate analyses found that only low back pain, but not pain at other locations, was significantly associated with increased WOMAC knee pain score (P < .0001). However, when all locations were considered simultaneously, only ipsilateral elbow (P = .02), ipsilateral foot (P = .02), and low back pain (P = .002) correlated significantly with knee pain.

In addition, pain at more than 1 location was associated with greater WOMAC knee pain, especially in those with 4 or more pain locations (P < .0001).

According to the researchers, understanding these associations "may help to identify patients who are at risk for poor outcomes following (total knee arthroplasty), and patients who may benefit from co-interventions to treat musculoskeletal pain in other locations."

"Our findings suggest that pain external to the knee may exert small but clinically significant effects on WOMAC pain score, even when the WOMAC is applied in a knee-specific manner," the study authors conclude. "...stratification by musculoskeletal pain comorbidity may be a factor worth considering in trial design." They add that interventions that simultaneously target knee and nonknee pain may improve overall knee-related outcomes.

"These findings highlight an important consideration in osteoarthritis diagnosis and treatment assessment, which is that many of our outcome metrics, such as the commonly used WOMAC pain, are subject to a great deal of noise," said independent commentator Janie Astephen Wilson, PhD, with Dalhousie University, in Halifax, Nova Scotia, Canada. "They are highly influenced by a variety of factors including comorbidity," she told Medscape Medical News.

According to Dr. Astephen Wilson, scores such as the WOMAC do not reflect the structural state of the disease and have been shown to be unrelated to the measures of mechanical loading of the knee joint (which presumably relate to the progression of the disease). "If our aim is to capture the symptomatic state of the disease, then we must consider all of the factors (such as comorbidity and LBP [low back pain]) that may be influencing our metrics," she said.

"There have been a number of studies that have related pain in other lower extremity joints to knee pain, but few studies consider pain outside of the lower extremity," she said. "This study further supports the results of these previous studies by additionally relating upper extremity and low back pain to knee pain, and would support the hypothesis of a less biomechanical association between these comorbidities."

The study was supported by the National Institutes of Health as well as commercial funding from Merck Research Laboratories, Novartis Pharmaceuticals Corp, GlaxoSmithKline, and Pfizer, Inc. Dr. Astephen Wilson has disclosed no relevant financial relationships.

Arthritis Care Res. December 2010. Abstract

Medscape Medical News © 2010 WebMD, LLC
Send press releases and comments to news@medscape.net.