Changes in clinical symptoms and functional disability in patients with coexisting patellofemoral and tibiofemoral osteoarthritis: a 1-year prospective cohort study

Abstract

Background: This 1-year prospective cohort study aimed to compare the changes in clinical symptoms and functional disability between patients with coexisting patellofemoral (PF) and tibiofemoral (TF) osteoarthritis (OA) and those with isolated TFOA.

Methods: Seventy-two patients with medial knee OA were enrolled. Knee pain and functional disability were assessed at baseline and at 1-year follow-up using the Japanese Knee Osteoarthritis Measure (JKOM) and a visual analog scale (VAS). We performed two-way analysis of covariance for the clinical outcome variables to examine, time (baseline and follow-up), group (coexisting PFOA and isolated TFOA), and time-group interaction effects. Furthermore, we conducted post-hoc exploratory analysis to address the possibility that dividing patients according to location of PFOA (i.e., isolated lateral, isolated medial, and mixed [bilateral]) may identify a distinct subgroup with different changes in clinical outcomes at 1-year follow-up.

Results: We detected group effects only in scores of the JKOM pain subscale (P = 0.012) and VAS (P = 0.033), adjusted for age, sex, and body mass index. Patients with coexisting PFOA have stable moderate level knee pain and functional disability throughout the year which is significantly worse than that in those with isolated TFOA. Post-hoc subgroup analysis demonstrated that change of knee pain likely varied with location of PFOA. Patients with isolated lateral PFOA had mild/moderate level knee pain, and their VAS scores were likely to improve, whereas those with mixed PFOA exhibited stable to worsening moderate/severe knee pain.

Conclusions: Although we did not detect differences in changes in clinical symptoms and functional disability between patients with coexisting PFOA and those with isolated TFOA, our findings indicate that patients with coexisting PFOA had worse clinical symptoms and functional disability than those with isolated TFOA. The results of the exploratory analysis suggested that patients with coexisting PFOA might have heterogeneous clinical outcomes, and presence of mixed PFOA might be an indicator of severe clinical knee OA.

Keywords: Disability; Knee pain; Patellofemoral osteoarthritis; Tibiofemoral osteoarthritis.

Fig. 1

Changes in VAS in the subpopulation of patients with coexisting PFOA at 1 year follow-up. a, Trajectories of VAS scores. Categorized pain scale grades are also shown in the same panel (no, mild, moderate, and severe). The clinically important borderline between mild and moderate pain (VAS score = 30 mm) is displayed as a solid horizontal line. Other borderline values on the categorized pain scale are displayed as dotted horizontal lines. White squares connected with dotted lines represent the mean change in VAS score of each group. ^*Significantly different (P < 0.05) after adjusting for age, sex, and body mass index in a post-hoc analysis of two-way repeated analysis of covariance (time effect: adjusted P-value = 0.385, group effect: adjusted P-value = 0.033, time-group interaction: adjusted P-value = 0.167, as shown in Table 4). b, Numbers and percentages of patients with moderate or more severe pain (i.e., moderate [30 mm < VAS ≤ 60 mm] and severe [VAS > 60 mm]) corresponding to a state with unacceptable symptoms and considered a clinically relevant treatment target [31, 34, 35]. Unadjusted P-values were calculated using the chi-square test. ^† P-values corresponding to significant differences are displayed in bold