Another reason why radiographic disease should not guide OA treatment

People with knee osteoarthritis and a complete or partial ACL tear in one knee do not report more severe symptoms in the ACL-deficient knee compared to the ACL-intact knee.

A small study of 37 patients from the Osteoarthritis Initiative (OAI) used the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and Knee Injury and Osteoarthritis Outcome Score (KOOS) to compare knees.

Patients had an average age of 61 years, radiographic evidence and symptoms of OA and most (94.6%) reported a history of a previous knee injury.

The study found average WOMAC scores for pain, stiffness and disability and KOOS scores for pain, overall symptoms, catching, clicking or grinding, swelling, bending and straightening were similar between knees with an ACL tear and those without.

While the index knee was more likely to exhibit symptoms of knee swelling (OR 1.91), catching (OR 2.13), clicking (OR 2.12), pain with knee straightening (OR 2.05) and functional disability (OR 1.97), none of these approached statistical significance.

However when the radiographic assessment of the knees was compared to knee symptoms, reduced knee function as indicated by WOMAC disability score was significantly associated with radiographic severity (p=0.04).

The study authors, from the Institute of Bone and Joint Research at the University of Sydney’s Kolling Institute, said loss of ACL integrity would be expected to translate to changes in both the dynamic and static loading patterns in the affected knees.

“Thus it would be expected that these changes in knee kinematics would result in worsening of knee symptoms and disability.”

“A possible reason why there was no significant difference in symptoms between the two knees is that radiographic knee OA was present in both the control and index knees, thus individuals reported symptoms and disability in both knees even though the underlying pathology of the OA and location of the joint damage may have been different.”

“Given these altered knee kinematics secondary to a loss of ACL integrity, it is unsurprising that increasing joint-space narrowing on knee radiographs correlates positively with reduced overall knee function and difficulty with knee bending, which is likely secondary to mechanical obstruction from osteophytes on the joint margins.”

They said the relationship between structural OA pathology and knee symptoms has long been contentious.

“These findings further underline the fact that the structural radiographic correlates of OA such as joint-space narrowing, osteophyte formation, and subchondral bone sclerosis may not correlate significantly to the overall pain experience of an individual, particularly at mild to moderate radiographic disease.”

“This is an important finding as many clinicians currently rely on radiographic disease as seen on X-ray to dictate disease treatment. ”

First author Dr Victoria Johnson, a rheumatology advanced trainee at the Prince of Wales Hospital, told the limbic that as radiographs were not accurate in providing insight into which of the structural pathologies are contributing significantly to an individual’s knee pain, knee MRIs could be useful to tease out extra information for patients who might require surgical management.

“But MRI is only useful if the knee has become unstable and you want to know which structures are damaged,” she said.

“MRIs shouldn’t be ordered otherwise. You don’t need a MRI to diagnose OA and it doesnt direct care.”

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