Background/Purpose: Anterior knee pain (AKP) may be a precursor to patellofemoral osteoarthritis (PFOA). Cross-sectionally, frequent AKP has been associated with MRI features of PFOA; however, longitudinal evidence to support the temporal nature of AKP and PFOA is lacking. Understanding the relationship between frequent AKP and PFOA could inform the development of treatments to prevent or slow disease progression. The purpose of this study was to examine the association between frequent AKP and worsening of patellofemoral cartilage morphology over 2 years.

Methods: Participants were from the NIH-funded Multicenter Osteoarthritis (MOST) study. At the 144-month clinic visit (baseline for the current analysis), a new cohort without established OA was recruited, offering an opportunity to study early AKP and PFOA development. At baseline, subjects were asked about knee pain, including its location and frequency, and weight-bearing radiographs and MRIs were obtained. Participants had a follow up visit 2 years later including repeat MRIs of their knee. Participants were excluded if they had radiographic PFOA at baseline. Anterior knee pain was defined using a knee pain map. The presence of AKP in combination with frequent knee pain (pain on most days of the last month) was our primary exposure variable (frequent AKP). Frequent isolated AKP, defined as answering ‘yes’ to frequent pain and reporting pain only in the anterior region of the knee, was also used to group participants. Two musculoskeletal radiologists assessed cartilage damage using the MOAKS scale in four PF subregions (medial and lateral patella and trochlea). Worsening PF cartilage damage was defined by any increase in MOAKS score over 2 years. Since risk factors for medial and lateral PFOA are different, worsening was evaluated in the medial and lateral PF compartments separately. Worsening was present if either the patella or trochlea had worsening cartilage damage. Logistic regression was used to evaluate the relation of frequent AKP to worsening PF cartilage in the medial and lateral compartments separately, adjusting for age, sex, BMI, race, and radiographic tibiofemoral OA.

Results: One knee from 1082 participants was included with a mean (standard deviation) age and body mass index (BMI) of 56.7 (6.6) and 28.0 (4.9), respectively; 57% were female. Frequent AKP and frequent isolated AKP was present in 15% and 4% of participants, respectively. Cartilage worsening was present in 11% and 14% of the lateral and medial PF, respectively. Compared to knees without frequent AKP, those with frequent AKP had 1.9 (95% CI: 1.2, 3.1) and 1.1 (95% CI: 0.7, 1.8) times the odds of lateral and medial PF cartilage worsening, respectively. Compared to knees without frequent isolated AKP, those with frequent isolated AKP had 1.7 (95% CI: 0.7, 4.0) and 1.3 (95% CI: 0.6, 3.0) times the odds of lateral and medial PF cartilage worsening, respectively.

Conclusion: Among those without radiographic PFOA, frequent AKP increased the odds of worsening cartilage damage in the lateral PF. AKP may be an indicator of future PFOA and used as a measure to identify individuals at risk of future OA who may benefit from targeted treatments to prevent future PFOA.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/anterior-knee-pain-is-associated-with-2-year-compartment-specific-patellofemoral-cartilage-worsening-the-most-study/