High Prevalence of Patellofemoral Osteoarthritis Detected in China

Approximately half of people with knee pain or knee osteoarthritis (OA) have patellofemoral (PF) joint involvement. PFOA commonly coexists with tibiofemoral osteoarthritis (TFOA), and it's been proposed that PFOA increases the risk of TFOA, but by far the bulk of OA research has focused on TFOA.

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Yuqing Zhang, DSc, director of Epidemiological and Biostatistical Methods at the Division of Rheumatology, Allergy and Immunology at Massachusetts General Hospital, and Zhanglai Li and Qiang Liu, MD, of Peking University, and colleagues have conducted the first epidemiologic study of OA in China that focused on PFOA in nonurban populations. In Clinical Rheumatology, they report a high prevalence of PFOA in northern China, where most residents do manual labor.

Study Design

This cross-sectional study was conducted in 2014 in three suburban and rural areas in northern China. In each region, six to eight villages or communities were randomly selected and all residents age ≥50 were recruited. Recruitment continued until all residents willing to participate were included.

At participants' homes, a health professional administered a standardized questionnaire about knee symptoms, function and risk factors for knee OA. Participants underwent skyline-view radiography of the PF joint at their local hospital.

Participant Characteristics

The recruitment rates in each region were 72% to 80%. There were 1,276 men and 2,170 women, average age 62. Most reported moderate or heavy occupational activity (87% of men, 82% of women).

Prevalence of Knee Injury and PFOA

• 9% of participants reported a history of a knee injury that limited their walking ability for at least a week
• The prevalence of radiographic PFOA was 24% (21% in men, 26% in women)
• One-third of participants with PFOA reported knee pain on most days of the previous month when going up and down stairs
• The prevalence of lateral PFOA was 17% versus 3.8% for medial PFOA
• Grades of osteophytes and joint space narrowing in the lateral PF compartment were higher than those in the medial compartment (all P values < .001)

Predictive Factors

Female gender, older age, higher body mass index and fewer years of education were significantly associated with a higher prevalence of PFOA, osteophytes and joint space narrowing.

Addressing Key Knowledge Gaps

As well as being conducted in nonurban populations, this is the first study to describe the compartment involvement pattern of PFOA in China. Such knowledge will shed light on the etiology of PFOA and guide the development of prevention and treatment strategies tailored to compartment-specific PFOA.

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