Should isolated superolateral Hoffa's fat pad edema identified by MRI be reported or ignored in adolescent patients?

BACKGROUND AND OBJECTIVE: The presence of superolateral Hoffa's fat pad (SHFP) edema is associated with several morphometric measurements related to patellar alignment and trochlear morphology. Our aim is to evaluate management implications in adolescent patients with isolated superolateral Hoffa's fat pad edema on MRI.

MATERIALS AND METHODS: Retrospective review of 117 adolescents with knee MRI (mean 14.8 years old) with isolated superolateral Hoffa's fat pad edema. Patients with edema were separated into two groups based on the number of MRI axial slices involved with edema: group 1 (G1) of 27 patients with 1 slice vs group 2 (G2) of 90 patients with 2 or more slices. A comparison control group was used (45 patients who had normal MRI knees). Data points included % referral for physical therapy (PT) or surgery, Hoffa's fat pad edema, tibial tubercle-trochlear groove (TT-TG) distance and lateral trochlear inclination (LTI) angle. Fisher's exact and independent t-tests, ANOVA and regression models were used for statistical analysis.

RESULTS: There is statistically significant difference between Hoffa's fat pad edema patients and control regarding PT referral with G1: 70%, G2: 76%, and control: 53% (p = 0.03). There is statistically significant difference between these groups regarding TT-TG measurements with higher values in edema groups; G1: 11.9 mm±4.1, G2 13 mm ±4.1, and control 8.7 mm±3.6, (p = 0.001). There was a statistically significant association between edema and increased TT-TG distance (p = 0.001) but not LTI angle (p = 0.2).

CONCLUSION: MRI identification of isolated superolateral Hoffa's fat pad edema is positively associated with TT-TG distance and its presence is associated with higher referral rates to physical therapy for patella maltracking.