Severity of patellofemoral joint disease is associated with increased functional limitations and lower limb impairments in patients with coexisting tibiofemoral osteoarthritis

Purpose: Although the knee joint is comprised of both the tibiofemoral and the patellofemoral joints, knee osteoarthritis (OA) has primarily been viewed as a disorder of the tibiofemoral joint alone. Therefore, the potential impact of coexisting patellofemoral joint disease has gone largely unconsidered. As such, it is currently unclear to what extent the severity of patellofemoral joint disease is associated with the symptoms, functional limitations, and lower limb physical impairments attributed to knee OA. The purpose of the present study was to compare the knee related functional limitations and lower limb physical impairments between individuals with tibiofemoral OA who have minimal patellofemoral joint disease and those presenting with tibiofemoral OA who have more advanced patellofemoral joint disease. Methods:Asecondaryanalysis of baseline data for 167 subjects (55men; 112 women) participating in a randomized clinical trial of exercise therapy for knee OA was performed. Subjects were included in the analysis if they met the American College of Rheumatology clinical criteria for knee OA as well as having a Kellgren & Lawrence (KL) radiographic grade of 2 or greater for tibiofemoral OA. Subjects with tibiofemoral OA were subsequently divided into two groups of minimal patellofemoral joint disease (KL grade 0-2 for patellofemoral joint; N1⁄496), mean age 63.8 9.1 yr, height 168.0 9.6 cm, body mass 84.2 19.0 kg, body mass index 29.8 6.4; or moderate to severe patellofemoral joint disease (KL grade 3-4 for patellofemoral joint; N1⁄471) age 63.8 8.7 yr, height 167.8 9.3 cm, body mass 89.6 17.4 kg, body mass index 31.9 6.1. The 24-itemWesternOntario andMcMaster Universities (WOMAC)OA Index and the 14-itemActivities of Daily Living Scale of the Knee Outcome Survey (ADLS) were used to gather information on pain and limitations during performance of specific functional tasks. Pain and functional limitations reported on the individual WOMAC and ADLS items were then dichotomized as normal/mild or moderate/extreme. The association of eachWOMAC and ADLS individual itemwith severity of patellofemoral disease was examined by multiple logistic regression adjusted for age and BMI. Additionally, independent sample t-testswere used to evaluate between-group differences in quantitative knee extension strength and knee range of motion. Results: More severe patellofemoral joint disease was associated with moderate/extreme limitations with going down stairs (OR 1⁄4 2.8; 95% CI: 1.4 to 5.6) and kneeling on the front of the knee (OR1⁄4 2.6; 95%: CI 1.2 to 5.8). In addition, moderate/extreme pain with going up and down stairs (OR 1⁄4 2.2; 95% CI: 1.1 to 4.0) was associated with more advanced patellofemoral joint involvement. Patients with severe patellofemoral joint disease also demonstrated decreased knee extension strength (4.0 1.8 Nm/BMI vs. 5.0 1.8 Nm/BMI; p<0.001) along with more pronounced range of motion limitations in Knee flexion (126.8 10.9 vs. 132.9 10.3 ; p<0.001) and knee extension (-6.0 6.1 vs. -4.4 5.7 ; p1⁄40.04). Conclusions: Coexistence of moderate to severe patellofemoral joint disease along with tibiofemoral OA appears to be associated with increased pain and difficulty with negotiating stairs and kneeling, as well as decreased knee extension strength and range of motion. Thus, specific treatment strategies targeting the patellofemoral joint may be needed if these specific functional problems and lower limb impairments are to be mitigated. Further efforts on clinical recognition of coexisting patellofemoral and tibiofemoral OA may be warranted.