Context: Hypertrophy of the Infrapatellar Fat Pad (IFP) in idiopathic knee osteoarthritis has been linked to deleterious synovial changes and joint pain related to mechanical tissue impingement; yet, little is known regarding the IFP's volumetric changes following anterior cruciate ligament reconstruction (ACLR).

Objective: To examine changes in IFP volume between 6 and 12 months following ACLR and determine associations between patient-reported outcomes and IFP volume at each time point, as well as volume change over time. In a subset of individuals, we examined inter-limb IFP volume differences 12 months post-ACLR.

Study Design: Prospective cohort study

Setting: Laboratory

Patients or Other Participants: We included 26 participants (13 females, 13 males, 21.88±3.58 years, 23.82±2.21 kg/m2) for our primary aims and 13 of those participants (8 females, 5 males, 21.15±3.85 years, 23.01±2.01 kg/m2) for our exploratory aim.

Main Outcome Measure(s): Using magnetic resonance imaging, we evaluated IFP volume change between 6 and 12 months post-ACLR in the ACLR limb and between-limb differences at 12 months in a subset of participants. International Knee Documentation Committee subjective knee evaluation (IKDC) scores were collected at 6-month and 12-month follow-ups and associations between IFP volume and patient-reported outcomes were determined.

Results: IFP volume in the ACLR limb significantly increased from 6 (19.67±6.30 cm3) to 12 (21.26±6.91 cm3) months post-ACLR. Greater increases of IFP volume between 6 and 12 months significantly associated with better 6-month IKDC scores (r=0.44, P=0.03). IFP volume was significantly greater in the uninjured limb (22.71±7.87 cm3) compared to the ACLR limb (20.75±9.03 cm3) 12 months post-ACLR.

Conclusions: IFP volume increased between 6 and 12 months post-ACLR; however, the IFP volume of the ACLR limb remained smaller than the uninjured limb at 12-months. Additionally, those with better knee function 6 months post-ACLR demonstrated greater increases in IFP volume between 6 and 12 months post-ACLR. This suggests greater IFP volumes may play a role in long-term joint health following ACLR.

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