Clinical examination using the patellofemoral grind test can help predict which patients with knee pain are most likely to progress to osteoarthritis requiring arthroplasty.

A large study of more than 4,000 participants from the National Institutes of Health Osteoarthritis Initiative found about 16% had a positive patellofemoral grind test – assessed as pain on distal force at the superior border of the patella with a contracted quadriceps.

The study found those patients had a higher rate of cartilage loss assessed by MRI over four years from baseline than other patients without patellofemoral grind.

In addition, patients with patellofemoral grind at any timepoint had a significantly higher risk of knee replacement at six years.

The odds ratio of needing a knee replacement was 1.55 for those with fluctuating patellofemoral grind (present at either baseline or at one year) and 2.10 for persistent patellofemoral grind (present at both baseline and one year).

There was no similar association between assessment of joint line tenderness and either cartilage loss or need for knee replacement.

Lead author Professor Flavia Cicuttini, from the School of Public Health and Preventive Medicine at Monash University, told the limbic the study highlighted the value of simple clinical tests to provide helpful extra information.

“We keep advising people to lose weight and exercise and they are still the mainstays of our treatment offerings for osteoarthritis. We know that it’s really hard to keep people motivated to do these things. It’s a recurrent theme and we’re not really winning.”

“We also know that osteoarthritis is really common in the community and the natural history can fluctuate a lot; not everybody is exactly the same in the way that their disease progresses. The opportunity to identify ways to pick those more likely to do badly is very attractive.”

“We found no effect of joint line tenderness but we found that the people that had patellofemoral grind did worse, even adjusting for their levels of pain.”

She said the knowledge that they were at higher risk for surgery might be a helpful motivator for people to do the ‘hard things’ of weight loss and exercise.

“We would still advise all people to lose weight and exercise – we are not suggesting that you don’t advise others the same – but if there is patellofemoral grind present then we have the opportunity to say to the person they have close to double the risk of needing knee replacement in the next six years. It’s just a bit of extra information to try and motivate people.”

While it was an easy test to do, Professor Cicuttini said it probably wasn’t routinely checked in the context of busy clinics.

The study found no significant association between patellofemoral grind and worsening radiographic osteoarthritis (ROA).

“It is likely that the presence and persistence of patellofemoral grind are associated with articular cartilage damage rather than subchondral bone changes, providing a potential explanation for the association of patellofemoral grind with cartilage volume loss and risk of total knee replacement but not worsening of ROA,” the study said.