Trimming the Fat (Pad) in Knee OA

This post comes from Fred Nelson, MD, an orthopaedic surgeon in the Department of Orthopedics at Henry Ford Hospital and a clinical associate professor at Wayne State Medical School. It has been sent to >3,000 members of the Orthopaedic Research Society (ORS). For more information about the ORS, visit www.ors.org. 

The knee joint is comprised of cartilage, fibrocartilage, bone, synovium, ligaments, a fibrous capsule, and adipose tissue, the last of which includes the large anterior infrapatellar fat pad (IFP). The role of synovial inflammatory cells and cytokines in knee osteoarthritis (OA) has been well studied. The IFP is also rich in stem cells and inflammatory cells. Because Hartley guinea pigs naturally develop a form of knee OA that is similar to human disease, researchers recently used them as a model for elucidating a possible role of the IFP in knee OA.¹

Ten 3-month-old guinea pigs had a unilateral IFP excision from one knee, with sham surgery performed on the opposite knee. Hartley guinea pigs typically develop OA after three months, and this intervention sought to determine whether IFP excision protected against OA. Gait analysis data were collected prior to surgery and then monthly until the animals were harvested at 7 months of age, at which point researchers performed microcomputed tomography (microCT) and histopathology on all 20 knee joints.

In knees with IFP resection, fibrous connective tissue replaced the adipose tissue. Stride length was not statistically different for either hindlimb throughout the study. Joints with resected IFPs had a decreased microCT score compared to contralateral intact knees (p <0.0001), indicating healthier cartilage. Histopathologically, the mean modified Mankin score of knees with IFPs removed was 2.556 versus 12.56 in contralateral knees (p <0.0004).

Surgeons commonly resect the fat pad during reconstructive knee surgery in humans, with no known reports of adverse effects beyond decreased range of motion due to local fibrosis. A recent review of the contribution of the IFP and synovium to knee OA pain² suggests that synovial tissue and adipose tissue may act as a “functional unit” and have a combined effect on OA pathogenesis and, in all probability, OA pain and progression.

References

1. Afzali MF, Radakovich LB, Pixler ZC, Campbell MA, Sanford JL, Marolf AJ, Donahue T, Santangelo, Kelly S. Early removal of the infrapatellar fat pad beneficially alters the pathogenesis of primary osteoarthritis in the Hartley guinea pig ORS 2020 Annual Meeting Paper No.0166
2. Belluzzi E, Stocco E, Pozzuoli A, Granzotto M, Porzionato A, Vettor R, De Caro R, Ruggieri P, Ramonda R, Rossato M, Favero M, Macchi V. Contribution of Infrapatellar Fat Pad and Synovial Membrane to Knee Osteoarthritis Pain. Biomed Res Int. 2019 Mar 31;2019:6390182. doi: 10.1155/2019/6390182. eCollection 2019.PMID: 31049352