It’s the Patellofemoral Height, Stupid!

Patella baja (abnormally lying patella) or patella alta (a high patella)? In terms of patient outcomes, cartilage health or malalignment, how the patella lies may be more consequential than previously thought—according to a new study.

The researchers, from the University of Pennsylvania, Hospital for Special Surgery (HSS), and Northwestern University in Chicago, designed a retrospective cohort study of patellofemoral arthroplasty patients from 2012 to 2020.

The results, “Effect of Patellofemoral Arthroplasty on Patellar Height in Patients with Patellofemoral Osteoarthritis,” was published in the September 1, 2022, Journal of Knee Surgery.

Co-author Sabrina M. Strickland, M.D., an orthopedic surgeon with HSS, told OTW, “We know that any type of knee surgery, especially an arthrotomy, can cause scarring and patella baja (an abnormally low lying patella, which is associated with restricted range of motion). I hypothesized that after a patellofemoral arthroplasty, patients may have scarring of their patellar tendon and/or fat pad leading to a decrease in patellar height.”

The team measured patellar heights on X-ray images before and after patellofemoral arthroplasty and collected patient-reported outcome measures (International Knee Documentation Committee score, Kujala Anterior Knee Pain Score, and Veterans RAND 12-Item Health Survey for mental and physical health).

Of 133 knees, 73% presented with patella alta and 61% had patellar heights that decreased after patellofemoral arthroplasty. The authors wrote, “Compared with patients who did not present with patella alta, patients with patella alta reported similar outcomes with respect to knee function, pain, and general physical and mental health. Compared with patients whose patellar heights decreased after patellofemoral arthroplasty, patients whose knees did not decrease in height reported greater improvements in pain and function.”

“I think the most important finding of this study,” stated Dr. Strickland to OTW, “was that 73% of patients undergoing patellofemoral arthroplasty actually had patella alta. We know this is a risk factor for patellofemoral arthritis and this is just another data point that suggests that potentially, realignment at a young age may prevent this.”

“I was surprised by how many patients with end-stage patellofemoral arthritis still were patella baja as I would have guessed that their patellar tendons would have contracted over time. We did not observe significant postop reduction in patellar height which suggests that those with severe patella alta may benefit from tibial tubercle distalization to optimize tracking.”