Introduction: Hyperlipidemia is related to hypercoagulability and hypofibrinolysis, which may cause a tendency to intravascular thrombosis and result in osteonecrosis (ON). Recently PPARs were confirmed to induce adipocyte differentiation, and fatty acids were identified as the transcriptional effectors for PPARs, which may cause the hyperlipidemia and fatty marrow. The aim of this study was to identify whether the adipocytic differentiation was increased in the bone marrow obtained from the femoral head in patients with osteonecrosis.

Materials and Methods: A lipid profile (cholesterol, triglyceride, LDL, and free fatty acid) was performed for patients with osteonecrosis of the femoral head. The PPARγ2 expression was checked as to whether the mesenchymal stem cells differentiate toward adipocytes rather than osteogenic cells. RT-PCRs were completed using the bone marrow stroma cells obtained during THA from 11 patients with osteonecrosis and 9 control patients. As not all of alcoholics and steroid users develop osteonecrosis, genetic differences may relate to susceptibility to the osteonecrosis. Therefore, we determined the polymorphism of the PPARγ2 gene for 34 osteonecrosis patients and 76 controls.

Results: Among 89 cases of osteonecrosis, increased free fatty acid (above 580mg%) was the most frequent finding (40.8%), and triglyceride was the next (29.6%). Cholesterol was increased in only 9.0%. Seven of the osteonecrosis cases (63.6%) and 4 of the control cases (44.4%) expressed PPARγ2. Pro/Ala (C/G) polymorphism was found in seven (20.6%) ON cases and four control cases (5.3%), and Ala/Ala (G/G) polymorphism was found in only 1 case in the control group. The numbers of patients with elevated triglyceride among osteonecrosis were much higher (71.4%) in polymorphism (C/G) than osteonecrosis (21.5%) without polymorphism.

Discussion: In conclusion, hyperlipidemia and higher expression of the PPARγ2 were found in ON, and Pro/Ala PPARγ2 polymorphism was more common in ON.

Introduction: Proton magnetic resonance spectroscopy (¹H MRS) is a powerful non-invasive technique used to identify and quantify chemical compounds. In a recent study, the early histopathologic findings of osteonecrosis showed marrow edema and hemorrhage, and the late findings were fibrous marrow transformation with new bone formation. The purpose of this study was to apply ¹H MRS to the bone marrow of osteonecrosis and bone marrow edema syndrome by measuring the amount of lipid relative to water of the femoral head and greater trochanter.

Materials and Methods: Magnetic Resonance (MR) imaging and MR spectroscopy were performed in twenty-five patients (male: female = 17:8, age = 29–69 years) who were diagnosed with osteonecrosis and bone marrow edema syndrome and compared with three normal control patients. Twenty-three cases were osteonecrosis and two were bone marrow edema syndrome. Ficat stages of osteonecrosis in the femoral heads were 1 patient with stage I, 8 patients with stage II, and 14 patients with stage III disease. Osteonecrosis developed in 14 patients with steroid therapy after kidney transplantation, in 6 alcoholics, and 3 were idiopathic. After routine hip MRI, spectroscopy was obtained from T2 weighted images by the 3-dimensional localization technique. Locations of voxels were the center of the osteonecrotic zone verified by T2-weighted MR images and from the fat marrow in the greater trochanter of femur. The values of the [Lipid/Water] ratios were calculated for all patients.

Results: The average Lipid/Water ratio of the osteonecrotic area was 3.15, those of the greater trochanter was 6.45, compared with 10.28 in the normal control group. The MRS pattern for osteonecrosis could be divided into 4 patterns: A, Lipid/Water > 10 ; B, 3 < Lipid/Water ≤ 10; C, 0.3 ≤ Lipid/Water < 3; and D, Lipid/Water ≤ 0.3. The numbers of cases for each pattern were 1 in A, 6 in B, 10 in C, and 6 in D. Interestingly, in one patient with Ficat stage I osteonecrosis diagnosed by only bone scintigraphy, ¹H MR spectroscopy revealed a much higher lipid/water peak ratio compared to the normal control group. The average Lipid/Water ratio of the bone marrow edema syndrome patients was 0.71.

Discussion: This study revealed the decreasing pattern of lipid content as osteonecrosis progresses, which correlates with histopathologic results. In bone marrow edema syndrome, a reverse pattern to the normal control group was found. Further study is needed for the change of Lipid/Water ratio in early change of osteonecrosis.