AT RHEUMATOLOGY 2016

GLASGOW (FRONTLINE MEDICAL NEWS) Older adults are more than seven times as likely to develop knee osteoarthritis if they had anterior knee pain as adolescents, according to the results of a case-control study.

The adjusted odds ratio for patellofemoral osteoarthritis (PFOA) was 7.5 if there was prior adolescent anterior knee pain. Although the 95% confidence interval was wide (1.51-36.94) the association was significant (P = .014). Adjustment had been made for the potential confounding factors of previous patellar dislocation, prior surgery, and patient-reported knee instability; before this adjustment the OR was 20.2 (95% CI, 3.34-11.67).

Patellar dislocation during adolescence also was found to be a significant risk factor for later PFOA (aOR, 3.2; 95% CI, 1.25-9.18; P = .016).

“Adolescent anterior knee pain represents a constellation of symptoms and had always been thought of as benign and self-limiting,” Henry Conchie, a medical student at the University of Bristol (England), said at the British Society for Rheumatology annual conference.

“I think the take-home message from our research is really that this traditional view of benign pathology associated with adolescent anterior knee pain and patellar dislocation must be challenged and when seen in clinical practice we now encourage the acknowledgment of the potentially severe consequences in the future,” Mr. Conchie said.

A link between adolescent anterior knee pain and later PFOA has previously been suggested but there are few data to support this observation, he explained. So the aim of the current study was to look at this in more detail in a group of patients from the knee arthroplasty database at Southmead Hospital in Bristol.

Questionnaires that asked about a variety of symptoms and knee pain were sent to 190 patients in the database who had undergone patellofemoral arthroplasty and so had severe, isolated, and radiologically confirmed PFOA. Questionnaires also were sent to 445 patients who had undergone arthroplasty for unicompartmental tibiofemoral arthritis to serve as the control group.

A subanalysis was performed to look at the mean age of the first dislocation and the investigators found that patients with PFOA were likely to be much younger than controls, with a 44-year difference observed between the groups.

“This adds some weight to the theory that this process [PFOA] begins much earlier than once thought – at a younger age,” Mr. Conchie suggested.

The study subjects were surveyed 1-4 years after their operation, so patient recall could have affected the results, but the use of the unicompartmental tibiofemoral arthritis patients as controls should have reduced this potential bias, he said. The fact that they had gone through an arthroplasty meant that they would have had very similar experiences to the PFOA group in terms of pain.

Although only severe OA cases and arthritis controls were used, the team believes that the findings are robust as these were clearly defined patient groups, albeit at the end of the disease spectrum.

“Thought can now turn to etiological mechanisms underlying these relationships, and I think it is likely that anatomical etiologies such as patellar outer and trochlear dysplasia can define both the pain and instability in youth as well as the patellofemoral osteoarthritis in later life,” Mr. Conchie proposed. Further research to look at this would be needed in future.

During the Q&A following his presentation, Dr. Eileen Baildam of Alder Hey Children’s Hospital in Liverpool, England, commented that she had looked at the persistence of pain in patients with adolescent anterior knee pain some years ago and found that, 10-20 years later, 60% were still experiencing pain.

The chair of the session, Dr. Joyce Davidson of the Royal Hospital for Sick Children in Glasgow, summed up by saying: “I think we do see lots of patients and maybe we just need to be aware that this may not be as benign as we think, and certainly we should be looking for abnormal patellae and being very aware of it in young people.”

Mr. Conchie and his coauthors had nothing to disclose.

rhnews@frontlinemedcom.com

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