Gait adjustment a possible explanation for pain in regions outside the knee
by
Contributing Writer, MedPage Today
Results of a new study confirm that patients with painful knees are more likely to develop pain in other joints.
Since multiple musculoskeletal comorbidities are disabling and potentially preventive, it’s important to investigate causes of pain to develop preventive strategies, said the authors, led by David T Felson, MD, Professor of Medicine and Public Health, Clinical Epidemiology Research and Training Unit, Boston University School of Medicine.
“Prevention opportunities might exist if those with knee pain alone can be identified at an early point in their disease,” they wrote in Arthritis & Rheumatology.
The authors used two large cohort studies of patients with or at risk of knee pain and osteoarthritis (OA): the Multicenter Osteoarthritis (MOST) Study, which recruited subjects aged 50-79 years from Birmingham and Iowa City, and the Osteoarthritis Initiative (OAI), which recruited subjects aged 45-69 years from Columbus, Ohio, Providence, R.I., Baltimore, and Pittsburgh.
In both studies, participants were asked about frequent pain or discomfort in or around each knee. They were also asked about frequent pain or discomfort in other joints.
Knee X-rays were acquired using the same technique in both studies. Subjects were characterized as having symptomatic knee OA if they had frequent knee pain and a Kellgren and Lawrence grade greater than 2 on radiograph of that knee.
Researchers compared those who had knee pain recorded for the first time at the first follow-up examination (index visit) to those who did not have knee pain at baseline or the first follow-up visit.
They defined incident pain as development of pain at any of the follow-up visits (starting after the index visit) up to the 84-month visit in the MOST study or the 72-month visit in the OAI Study.
Researchers assessed the frequency and distribution of painful sites in patients with index knee pain and those without it. They looked at 14 joints (two each of the feet, ankles, hips, hands, wrists, elbows, shoulders), and adjusted for age, body mass index (BMI), sex, depressive symptoms, number of painful joints at the index visit, and the cohort (MOST or OAI).
In MOST, 281 patients had index knee pain and 852 did not have knee pain at the index visit, while in the OAI study, 412 subjects had knee pain at the index exam and 1,941 did not.
In both cohorts, prevalent pain in joint regions outside the knee was common at the index exam. The mean number of joint regions outside the knee that were painful was 2.3 in those with knee pain compared to 1.3 in those without it (P <0.001).
Those with bilateral knee pain had more painful joint regions (2.9) than those with unilateral knee pain (1.9) For those with bilateral knee pain, 79.6% had pain outside the knee whereas 63.8% of those with unilateral pain had pain elsewhere. This compared to 49.9% of those without index knee pain.
After excluding subjects with widespread pain at the index visit, those with index knee pain still had more sites of pain than those without.
Pain in other regions could be because OA patients make modifications in their gait, which gradually causes damage to other joints such as hips and ankles.
“Since damage to other joints is likely cumulative, evidence that these account for multi-joint pain in those with knee OA would constitute a powerful argument for early treatment of knee OA to prevent this damage,” wrote the authors.
However, they pointed out that study findings don’t necessarily support the argument that in patients with knee pain, aberrant loading by altered movement patterns induces pain only in nearby joints.
“Our findings suggest that the sites affected are more than just the hip and ankle and that there is no special predilection for pain in these locations.”
And, according to the authors, reports of pain in other joint regions do not necessarily represent arthritis in these regions. For example, they said, hip pain may be due to trochanteric bursitis.
One limitation of the study is that the researchers can’t be sure that what they labeled as incident joint pain is, in fact, new onset.
Commenting on the study for MedPage Today, Lynn Webster, MD, vice president of Scientific Affairs, PRA Health Sciences, and a past president of the American Academy of Pain Medicine, said it confirms what most clinicians intuitively know.
“Arthritis is a systemic disease, so it would not be uncommon to find multiple joints with pain and disease in people with very advanced knee arthritis. ”
The suggestion by the authors that abnormal gait due to the pathology in one knee might cause other joints to develop arthritis “is certainly possible,” said Webster.
He noted that the paper omitted the potential involvement of genetics in multiple site involvement of arthritis.
“I suspect the individuals who develop arthritis at early ages and more advanced arthritic changes are more likely to have a genotype associated with early onset arthritis,” Webster said.
“We need to keep in mind that arthritis is not just about a worn out tire, but is a connective tissue disease and can involve all of our connective tissue.”
This research was supported by the National Institutes of Health.
The authors have no conflicts of interest.
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