Alterations in Hoffa's fat pad induced by an inflammatory response following idealized anterior cruciate ligament surgery.

ABSTRACT

OBJECTIVE: To determine whether inflammation following anterior cruciate ligament (ACL) reconstruction leads to long-term pathological changes in the infrapatellar fat pad (IPFP or Hoffa's fat pad) which could compromise the integrity of the knee joint. MATERIALS AND METHODS: Sixteen mature sheep underwent anatomic idealized ACL reconstruction surgery (ACL-R) and were sacrificed at 2 weeks (n = 9) and 20 weeks (n = 7) post-ACL-R. Five additional animals served as unoperated controls. A histological grading protocol was developed to quantify the changes in the IPFP post-injury. mRNA expression levels for key markers of inflammation, angiogenesis and tissue regeneration were assessed by qPCR. RESULTS: The IPFP exhibited altered cellularity and fibrosis at 2 and 20 weeks post-ACL-R. Immunohistochemistry detected macrophage-like cells in the IPFP which were increased at 20 weeks. Specific pro-inflammatory cytokines and IPFP specific adipokines exhibited changes indicating early inflammation mediated alterations. Elevations in CD105 mRNA levels at 2 weeks corroborated the increases in neovascularization observed in the IPFP following injury. CONCLUSIONS: Sustained long-term pathological changes stemming from inflammation are present in IPFP tissue after ACL-R surgery and may compromise the long-term integrity of the knee joint.