Association Between Infrapatellar Fat Pad And Knee Pain And Joint Structural Changes In Patients With Knee Osteoarthritis

Background With the hastened progress of aging and obesity, the incidence and prevalence of osteoarthritis(OA),the most common chronic and low inflammatory joint disease in the world, present a markedly increase trend. The main pathological characteristics of knee OA are articular cartilage defects and osteophytes, resulting in knee pain, stiffness and disability, so that it can severely affect the health and life quality of elderly. So far, the diagnosis of OA depends on radiological examination such as X-ray, which is unable to observe OA early abnormal joint structural changes. With the development of radiological technology, magnetic Resonance Imaging(MRI) can identify the early and small joint structural changes and more and more articular disease can be diagnosed by MRI. Infrapatellar fat pad(IPFP) is the intra-articular normal joint structure and its relationship with OA is still unclear. Recently, a few studies reported the association between IPFP and knee structural changes, but the findings are still controversial. The research about the association between IPFP size, quality and knee pain and abnormal joint structure is rarely reported in China.Objective The main aim of this study is to examine the associations between IPFP volume, signal intensity alteration and knee pain, knee structural changes, so that to improve the understanding of IPFP and explore the possible early diagnostic criteria and potential targeted treatment of OA.Methods A total of 206 symptomatic patients with knee OA were recruited from the Outpatient and Inpatient Department of Rheumatology and Immunology in the First Affiliated Hospital of Anhui Medical University, from January 2012 to November 2013.According to the exclusion criteria, 174 participants remained in the study with recorded clinical symptom and laboratory index. The Western Ontario and Mc Master Universities Osteoarthritis Index(WOMAC) was used to estimate knee pain. The classification of osteophytes and joint space narrowing and knee radiographic severity were assessed respectively according to Osteoarthritis Research Society International(OARSI) atlas and Kellgren-Lawrence(K-L) grades. IPFP volume, cartilage volume and cartilage defects were measured on MRI T1-weighted fat saturation 3D spoiled gradient recall acquisition, using the software program Osiri X. IPFP signal intensity alteration and bone marrow lesions(BMLs) were assessed on T2-weighted fat saturation fast spin echo MRI.Results1. Relationship between IPFP volume, signal intensity alteration and clinical indicators of patients with knee OA: IPFP volume was associated with weight, height and age(all P < 0.05). IPFP volume between male and female had obvious difference(P < 0.05).IPFP signal intensity alteration was associated with age(r = 0.286, P < 0.001) and there was also a significant difference between non-ROA and ROA(P = 0.045).2. Relationship between IPFP volume, signal intensity alteration and knee pain: After adjustment for potential confounders, IPFP volume and signal intensity alteration all were no significantly associated with total WOMAC knee pain, pain when standing,pain walking on flat surface, pain in bed, pain when sitting and pain going up/down stairs.3. Association between IPFP volume, signal intensity alteration and cartilage volume:After adjustment for potential confounders, IPFP volume was positively and significantly associated with medial and lateral tibial and patellar cartilage volume(β:0.016-0.076, all P<0.05). Greater IPFP signal intensity alteration was associated with smaller patellar cartilage volume(β:-0.127, 95%CI:-0.216,-0.037).4. Association between IPFP volume, signal intensity alteration and articular cartilage defects: IPFP volume between different meidial femoral cartilage defects groups(F=3.796,P=0.012) and patellar cartilage defects groups(F=4.876,P=0.003) had obvious difference. After adjustment for potential confounders, IPFP volume was negatively association with cartilage defects at all sites(OR: 0.876-0.909, all P<0.05),including medial and lateral tibia, medial and lateral femer, and patella. Compared IPFP signal intensity alteration between different grades of cartilage defects groups, IPFP signal intensity alteration between different classifications of cartilage defects at medial and lateral femoral,medial tibial and patellar compartment had significant difference(all P<0.05). After adjustment for potential confounders, Higher IPFP signal intensity alteration was associated with greater cartilage defects at all sites, excluding lateral tibia(OR: 1.456-1.540, all P<0.05).5. Association between IPFP volume, signal intensity alteration and bone marrow lesions(BMLs): IPFP volume had obvious difference between different grades of BMLs at lateral tibia and femer(all P<0.05).The logistic regression analysis indicated that there were negative and significant associations between IPFP volume and lateral tibia BMLs(OR: 0.882, 95%CI: 0.799,0.975) and medial femoral BMLs(OR: 0.911,95%CI: 0.832, 0.998). IPFP signal intensity alteration had appearent difference between different classifications of BMLs at medial and lateral tibia and medial femer(all P<0.05). After adjustment for potential confounders, IPFP signal intensity alteration was positively and significantly associated with the presence of BMLs at lateral tibia(OR: 1.611, 95%CI: 1.081, 2.399), medial femer(OR: 1.562, 95%CI: 1.068, 2.284) and lateral femer(OR: 1.502, 95%CI: 1.037, 2.179).6. Association between IPFP volume, signal intensity alteration and osteophytes and joint space narrowing: there was a significant difference in IPFP volume between different lateral femoral osteophytes groups(F=3.574, P=0.03). Greater IPFP volume was associated with fewer lateral femoral osteophytes(OR: 0.782, 95%CI: 0.689,0.886). There were no significant associations between IPFP volume and osteophytes at other sites and joint space narrowing. There were significant differences in IPFP signal intensity alteration between different grades of osteophytes at lateral tibia and medial and lateral femer(all P<0.05). IPFP signal intensity alteration was positively and significantly associated with lateral tibia OP(OR: 1.452, 95%CI: 1.014, 2.079), medial femoral OP(OR: 1.775, 95%CI: 1.232, 2.557) and lateral femoral OP(OR: 1.587,95%CI: 1.097, 2.296). The associations between IPFP signal intensity alteration and joint space narrowing were not significant.Conclusions1. IPFP volume was associated with cartilage volume and abnormal knee structures in patients with knee OA, suggesting that IPFP size may play a protective role in knee OA.2. IPFP signal intensity alteration was associated with knee structural changes in patients with knee OA, suggesting that IPFP signal intensity alteration may be an important pathological change of knee OA and may have dignosis value of early knee OA. Thus, abnormal IPFP may have a detrimental role in the development and progression of knee OA.3. Our results suggest that it could be avoided to resect normal IPFP in knee surgery.