Quantifying the Functional Impact of Chronic Patellofemoral Pain and Its Relationship to Perceived Duty-related...

Chronic patellofemoral pain (PFP) is a heterogeneous pain condition that may significantly burden active duty service members, whose rigorous physical training demands include activities such as running and heavy load carriage. While chronic PFP is often defined by its pathoanatomical characteristics, evidence from other pain conditions (e.g., chronic low back pain) suggests classifying pain by its functional impact on work, social, and self-care activities may better inform personalized treatment approaches. As this approach has not been previously undertaken in chronic PFP or younger populations with chronic pain, this study aimed to characterize the global impact of PFP on day-to-day function and evaluate its relationship with perceived duty-related medical readiness among young, active service members.

Institutional Review Board approval was obtained at Naval Medical Center San Diego. Electronic health records were retrospectively reviewed among 295 service members referred to physical therapy for "knee pain" from April 2021 to April 2022. For service members with chronic PFP (i.e., anterior knee pain present for at least 3 months and on at least half the days in the past 6 months), demographic, pain-related, and standardized outcome measure data were extracted from physical therapy intake documentation. Knee function was quantified using the validated Anterior Knee Pain Scale, scored from 0 to 100 (100 = highest function). Patient-reported Outcomes Measurement Information System Computer Adaptive Tests for physical function and pain interference were collected and subcategorized from 0 (within normal limits) to 3 (severe limitation) based on t-score cut-points, then summed to create a Pain Impact Score (0 = no impact to 6 = severe impact). Finally, perceived duty-related medical readiness was averaged across 2 questions assessing confidence in performing deployment and military duties with well-managed pain, each scored from 0 to 100 (100 = highest readiness). Relationships between Pain Impact Scores and perceived duty-related medical readiness were evaluated using linear regression after controlling for age, sex, symptom chronicity, and knee function.

Overall, 56 active duty service members, of whom 66% were males, met the criteria for chronic PFP and had outcome measures documented in their electronic health records. Most service members were classified as having mildly impaired physical function (46%) and moderately impaired pain interference (41%), while only 12 (21%) fell within normal limits for both physical function and pain interference domains. Median (25th-75th percentile) Pain Impact Scores were 2 (1-3). The overall regression model was statistically significant (R2 = 0.540, F(5,50) = 11.76, P < .001). Beyond covariates, Pain Impact Scores explained an additional 21.0% of the variance in perceived duty-related medical readiness (P < .001).

Service members with chronic PFP frequently report impaired physical function and pain interference, opposing assumptions that PFP is a mild, self-limiting condition. As each 1-point increase in Pain Impact is associated with a 10-point decrease in perceived duty-related medical readiness, functional pain impact should be evaluated alongside other condition-specific factors (e.g., knee function) to identify rehabilitation targets among service members with chronic PFP. Future work should explore whether similar associations are found between functional pain impact and other objective readiness measures (e.g., physical fitness tests).