March 2016

PFOA prognostication: Sagittal plane factors predict worsening

In the moment: OA

3ITM-OA_iStock_71687689By Jordana Bieze Foster

Sagittal plane mechanics and forces during gait in patients with patellofemoral osteoarthritis (PFOA) can help identify those who are likely to experience worsening pain or cartilage degeneration, according to research presented in February at the annual Combined Sections Meeting of the American Physical Therapy Association in Anaheim, CA.

The predictive potential of sagittal plane variables in individuals with PFOA underscores the biomechanical differences between PFOA and tibiofemoral osteoarthritis and the need to manage the two conditions differently.

“Sagittal plane mechanics during gait may influence the patellofemoral load and disease course, while tibiofemoral OA is more likely to be affected by frontal plane mechanics,” said Alison Chang, PT, DPT, MS, an associate professor of physical therapy and human movement sciences at the Northwestern Feinberg School of Medicine in Chicago.

In one PFOA study, presented at the meeting by Chang, she and her colleagues assessed dynamic joint stiffness—a measure of knee flexion moment versus knee flexion angle as a percentage of the gait cycle—in 204 patients with OA in any compartment of at least one knee. They also assessed magnetic resonance imaging (MRI)-based markers for cartilage degeneration; two years later, they repeated the MRI exams to assess cartilage damage progression.

Tibiofemoral damage progression was detected in 26.5% of participants; patellofemoral damage progression was detected in 13.6%. However, only patello­femoral cartilage damage progression—specifically in the lateral aspect of the patella—was associated with dynamic joint stiffness at baseline. After adjusting for demographics and disease-related covariables, for every unit increase in dynamic joint stiffness at baseline, the odds of patellofemoral cartilage damage progression increased 3.5 times.

Although cartilage damage is not always associated with pain in patients with PFOA, investigators from the University of California, San Francisco (UCSF) reported in a second presentation that peak patello­femoral joint (PFJ) stress during the early stance phase of walking in individuals with PFOA is predictive of pain progression one year later.

The researchers assessed kinematics and kinetics in 50 individuals with PFOA as they walked at a self-selected speed, then used those measures to estimate peak PFJ stress during the first and second half of stance. The study participants also completed the pain and symptoms subscales of the Knee Osteo­arthritis Outcomes Score (KOOS) questionnaire at the time of the gait analysis, and again a year later.

At one year, 10 participants had significant pain progression, defined as a KOOS-Pain score increase above a previously reported minimum detectable change score. Those with pain progression had significantly higher early stance peak PFJ stress at baseline than those whose pain did not progress; every one standard-deviation increase in PFJ stress during early stance resulted in nearly a sixfold higher chance of pain progression at one year.

The higher peak PFJ levels in those with pain progression were largely due to knee flexion moment rather than knee flexion angle, according to Hsiang-Ling (Sharon) Teng, PT, PhD, a postdoctoral scholar in the Department of Radiology at UCSF, who presented the findings.

Pain progression was also associated with higher peak PFJ stress in the second half of stance; that association was not statistically significant, but may be clinically relevant, Teng said.

“Prevention and rehabilitation protocols should focus on patellofemoral joint loading during the entire stance phase,” she said.

Chang and Teng both emphasized the need for PFOA interventions to decrease knee flexion moment, which could include increasing step rate, decreasing walking speed, or wearing flat shoes instead of heels. The Northwestern findings also suggest there could be a benefit to increasing knee joint flexion angle during gait, Chang said, but noted that patients may need neuromotor training to learn to use any additional joint range of motion they achieve.

Sources:

Chang AH, Chmiel JS, Almagor O, et al. Baseline knee sagittal dynamic joint stiffness during gait is associated with 2-year patellofemoral cartilage damage progression in knee osteoarthritis. J Orthop Sports Phys Ther 2016; 46(1):A5.

Teng H-L, MacLeod TD, Nardo L, et al. Association between patellofemoral joint stress during gait and symptomatic progression in people with patellofemoral joint osteoarthritis. J Orthop Sports Phys Ther 2016;46(1):A26.

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