Imaging structural abnormalities in the hip joint: instability and impingement as a cause of osteoarthritis

Osteoarthritis is thought to be caused by a combination of intrinsic vulnerabilities of the joint, such as anatomic shape and alignment, and environmental factors, such as body weight, injury, and overuse. It has been postulated that much of osteoarthritis is due to anatomic deformities. Advances in surgical techniques such as the periacetabular osteotomy, safe surgical dislocation of the hip, and hip arthroscopy have provided us with effective and safe tools to correct these anatomical problems. The limiting factor in treatment outcome in many mechanically compromised hips is the degree of cartilage damage which has occurred prior to treatment. In this regard, the role of imaging, utilizing plain radiographs in conjunction with magnetic resonance imaging, is becoming vitally important for the detection of these anatomic deformities and pre-radiographic arthritis. In this article, we will outline the plain radiographic features of hip deformities that can cause instability or impingement. Additionally, we will illustrate the use of MRI imaging to detect subtle anatomic abnormalities, as well as the use of biochemical imaging techniques such as dGEMRIC to guide clinical decision making.

T2 mapping in the knee after microfracture at 3.0 T: correlation of global T2 values and clinical outcome - preliminary results

OBJECTIVE: The aim of our study was to correlate global T2 values of microfracture repair tissue (RT) with clinical outcome in the knee joint. METHODS: We assessed 24 patients treated with microfracture in the knee joint. Magnetic resonance (MR) examinations were performed on a 3T MR unit, T2 relaxation times were obtained with a multi-echo spin-echo technique. T2 maps were obtained using a pixel wise, mono-exponential non-negative least squares fit analysis. Slices covering the cartilage RT were selected and region of interest analysis was done. An individual T2 index was calculated with global mean T2 of the RT and global mean T2 of normal, hyaline cartilage. The Lysholm score and the International Knee Documentation Committee (IKDC) knee evaluation forms were used for the assessment of clinical outcome. Bivariate correlation analysis and a paired, two tailed t test were used for statistics. RESULTS: Global T2 values of the RT [mean 49.8ms, standards deviation (SD) 7.5] differed significantly (P<0.001) from global T2 values of normal, hyaline cartilage (mean 58.5ms, SD 7.0). The T2 index ranged from 61.3 to 101.5. We found the T2 index to correlate with outcome of the Lysholm score (r(s)=0.641, P<0.001) and the IKDC subjective knee evaluation form (r(s)=0.549, P=0.005), whereas there was no correlation with the IKDC knee form (r(s)=-0.284, P=0.179). CONCLUSION: These findings indicate that T2 mapping is sensitive to assess RT function and provides additional information to morphologic MRI in the monitoring of microfracture.

Steady state free precession magnetization transfer imaging

The formerly proposed concept for magnetization transfer imaging (MTI) using balanced steady-state free precession (SSFP) image acquisitions is in this work extended to nonbalanced protocols. This allows SSFP-based MTI of targets with high susceptibility variation (such as the musculoskeletal system), or at ultra-high magnetic fields (where balanced SSFP suffers from considerable off-resonance related image degradations). In the first part, SSFP-based MTI in human brain is analyzed based on magnetization transfer ratio (MTR) histograms. High correlations are observed among all different SSFP MTI protocols and thereby ensure proper conceptual extension to nonbalanced SSFP. The second part demonstrates SSFP-based MTI allowing fast acquisition of high resolution volumetric MTR data from human brain and cartilage at low (1.5T) to ultra-high (7.0T) magnetic fields.

Hip damage occurs at the zone of femoroacetabular impingement

Although current concepts of anterior femoroacetabular impingement predict damage in the labrum and the cartilage, the actual joint damage has not been verified by computer simulation. We retrospectively compared the intraoperative locations of labral and cartilage damage of 40 hips during surgical dislocation for cam or pincer type femoroacetabular impingement (Group I) with the locations of femoroacetabular impingement in 15 additional hips using computer simulation (Group II). We found no difference between the mean locations of the chondrolabral damage of Group I and the computed impingement zone of Group II. The standard deviation was larger for measures of articular damage from Group I in comparison to the computed values of Group II. The most severe hip damage occurred at the zone of highest probability of femoroacetabular impact, typically in the anterosuperior quadrant of the acetabulum for both cam and pincer type femoroacetabular impingements. However, the extent of joint damage along the acetabular rim was larger intraoperatively than that observed on the images of the 3-D joint simulations. We concluded femoroacetabular impingement mechanism contributes to early osteoarthritis including labral lesions. LEVEL OF EVIDENCE: Level II, diagnostic study. See the Guidelines for Authors for a complete description of levels of evidence.

Prevalence of bone attrition on knee radiographs and MRI in a community-based cohort

OBJECTIVES: Bone attrition probably constitutes remodeling of the bone, resulting in flattening or depression of the articular surfaces. Defining bone attrition is challenging because it is an accentuation of the normal curvature of the tibial plateaus. We aimed to define bone attrition on magnetic resonance imaging (MRI) of the knee using information from both radiographs and MRIs, and to assess whether bone attrition is common prior to end stage disease osteoarthritis (OA) in the tibio-femoral joint. METHODS: All knees of participants in the community-based sample of the Framingham OA Study were evaluated for bone attrition in radiographs and MRIs. Radiographs were scored based on templates designed to outline the normal contours of the tibio-femoral joint. MRIs were analyzed using the semi-quantitative Whole-Organ Magnetic Resonance Imaging Scoring (WORMS) method. The prevalence of bone attrition was calculated using two different thresholds for MRI scores. RESULTS: Inter-observer agreement for identification of bone attrition was substantial for the radiographs (kappa=0.71, 95% CI 0.67-0.81) and moderate for MRI (kappa=0.56, 95% CI 0.40-0.72). Of 964 knees, 5.7% of the radiographs showed bone attrition. Of these, 91% of MRIs were also read as showing bone attrition. We selected a conservative threshold for bone attrition on MRI scoring (> or = 2 on a 0-3 scale) based on agreement with attrition on the radiograph or when bone attrition on MRI co-occurred with cartilage loss on OA. Using this threshold for bone attrition on MRI, bone attrition was common in knees with OA. For example, in knees with mild OA but no joint space narrowing, 13 of 88 MRIs (14.8%) showed bone attrition. CONCLUSIONS: Using MRI we found that many knees with mild OA without joint narrowing on radiographs had bone attrition, even using conservative definitions. The validity of our definition of bone attrition should be evaluated in further studies. Bone attrition may occur in milder OA and at earlier stages of disease than previously thought.

Subcellular distribution of the insulin-like growth factor (IGF) binding proteins (IGFBPs) 2 and 3 in articular chondrocytes

The insulin-like growth factor (IGF) is a major anabolic regulator in articular cartilage. The IGF-binding proteins (IGFBPs) are increased during osteoarthritis (OA), but the function of the later proteins remains unknown. In general, the IGFBPs are pluripotential effectors capable of IGF regulation and of acting on their own to control key cell functions, including survival and proliferation. The independent functions are often associated with their cell location, and therefore this study explores the distribution of IGFBP-2 and IGFBP-3 in articular chondrocytes. Immunohistochemistry was used to localize IGFBP-2 in normal human articular cartilage. Bovine chondrocytes were used for subcellular fractionation (hypotonic cell lysis) under nonreducing conditions and nuclear purification (centrifugation on sucrose cushions). Cell fraction markers and IGFBPs were assayed in the subcellular fractions by Western immunoblot. The IHC results showed association of IGFBP-2 with chondrocytes, but not with the nuclei. Subcellular fractionation of isolated chondrocytes yielded intact nuclei as assessed at the light microscopic level; the nuclear marker histone H1 was exclusively associated with this fraction. More than 90% of the cytoplasmic marker GAPDH and all the detectable IGFBP-2 were in the cytoplasmic fraction. Immunoreactive IGFBP-3 was found in the cytoplasmic and peri-nuclear/nuclear fractions. Chondrocytes contain intracellular IGFBP-2 and IGFBP-3 but only IGFBP-3 is associated with nuclei. This suggests the hypothesis that the actions of these IGFBPs in articular cartilage extend beyond the classic modulation of IGF receptor action.

Accelerated hypertrophic chondrocyte kinetics in GDF-7 deficient murine tibial growth plates

The Growth/Differentiation Factors (GDFs) are a subgroup of the Bone Morphogenetic Proteins (BMPs) well known for their role in joint formation and chondrogenesis. Mice deficient in one of these signaling molecules, GDF-5, have recently been shown to exhibit a decreased rate of endochondral bone growth in the proximal tibia due to a significantly longer hypertrophic phase duration. GDF-7 is a related family member, which exhibits a high degree of sequence identity with GDF-5. The purpose of the present study was to determine whether GDF-7 deficiency also alters the endochondral bone growth rate in mice and, if so, how this is achieved. Stereologic and cell kinetic parameters in proximal tibial growth plates from 5-week-old female GDF-7 -/- mice and wild type control littermates were examined. GDF-7 deficiency resulted in a statistically significant increase in growth rate (+26%; p = 0.0084) and rate of cell loss at the chondrosseous junction (+25%; p = 0.0217). Cells from GDF-7 deficient mice also exhibited a significantly shorter hypertrophic phase duration compared to wild type controls (-27%; p = 0.0326). These data demonstrate that, in the absence of GDF-7, the rate of endochondral bone growth is affected through the modulation of hypertrophic phase duration in growth plate chondrocytes. These findings further support a growing body of evidence implicating the GDFs in the formation, maturation, and maintenance of healthy cartilage.

Effect of reduced oxygen tension and long-term mechanical stimulation on chondrocyte-polymer constructs

We have investigated the influence of long-term confined dynamic compression and surface motion under low oxygen tension on tissue-engineered cell-scaffold constructs. Porous polyurethane scaffolds (8 mm x 4 mm) were seeded with bovine articular chondrocytes and cultured under normoxic (21% O(2)) or hypoxic (5% O(2)) conditions for up to 4 weeks. By means of our joint-simulating bioreactor, cyclic axial compression (10-20%; 0.5 Hz) was applied for 1 h daily with a ceramic ball, which simultaneously oscillated over the construct surface (+/-25 degrees; 0.5 Hz). Culture under reduced oxygen tension resulted in an increase in mRNA levels of type II collagen and aggrecan, whereas the expression of type I collagen was down-regulated at early time points. A higher glycosaminoglycan content was found in hypoxic than in normoxic constructs. Immunohistochemical analysis showed more intense type II and weaker type I collagen staining in hypoxic than in normoxic cultures. Type II collagen gene expression was slightly elevated after short-term loading, whereas aggrecan mRNA levels were not influenced by the applied mechanical stimuli. Of importance, the combination of loading and low oxygen tension resulted in a further down-regulation of collagen type I mRNA expression, contributing to the stabilization of the chondrocytic phenotype. Histological results confirmed the beneficial effect of mechanical loading on chondrocyte matrix synthesis. Thus, mechanical stimulation combined with low oxygen tension is an effective tool for modulating the chondrocytic phenotype and should be considered when chondrocytes or mesenchymal stem cells are cultured and differentiated with the aim of generating cartilage-like tissue in vitro.

Evaluation of early tissue reactions after lumbar intertransverse process fusion using CT in a rabbit

OBJECTIVE: The objective of the study was to evaluate tissue reactions such as bone genesis, cartilage genesis and graft materials in the early phase of lumbar intertransverse process fusion in a rabbit model using computed tomography (CT) imaging with CT intensity (Hounsfield units) measurement, and to compare these data with histological results. MATERIALS AND METHODS: Lumbar intertransverse process fusion was performed on 18 rabbits. Four graft materials were used: autograft bone (n = 3); collagen membrane soaked with recombinant human bone morphogenetic protein-2 (rhBMP-2) (n = 5); granular calcium phosphate (n = 5); and granular calcium phosphate coated with rhBMP-2 (n = 5). All rabbits were euthanized 3 weeks post-operatively and lumbar spines were removed for CT imaging and histological examination. RESULTS: Computed tomography imaging demonstrated that each fusion mass component had the appropriate CT intensity range. CT also showed the different distributions and intensities of bone genesis in the fusion masses between the groups. Each component of tissue reactions was identified successfully on CT images using the CT intensity difference. Using CT color mapping, these observations could be easily visualized, and the results correlated well with histological findings. CONCLUSIONS: The use of CT intensity is an effective approach for observing and comparing early tissue reactions such as newly synthesized bone, newly synthesized cartilage, and graft materials after lumbar intertransverse process fusion in a rabbit model.

MicroRNA-140 is expressed in differentiated human articular chondrocytes and modulates interleukin-1 responses

OBJECTIVE: MicroRNA (miRNA) are a class of noncoding small RNAs that act as negative regulators of gene expression. MiRNA exhibit tissue-specific expression patterns, and changes in their expression may contribute to pathogenesis. The objectives of this study were to identify miRNA expressed in articular chondrocytes, to determine changes in osteoarthritic (OA) cartilage, and to address the function of miRNA-140 (miR-140). METHODS: To identify miRNA specifically expressed in chondrocytes, we performed gene expression profiling using miRNA microarrays and quantitative polymerase chain reaction with human articular chondrocytes compared with human mesenchymal stem cells (MSCs). The expression pattern of miR-140 was monitored during chondrogenic differentiation of human MSCs in pellet cultures and in human articular cartilage from normal and OA knee joints. We tested the effects of interleukin-1beta (IL-1beta) on miR-140 expression. Double-stranded miR-140 (ds-miR-140) was transfected into chondrocytes to analyze changes in the expression of genes associated with OA. RESULTS: Microarray analysis showed that miR-140 had the largest difference in expression between chondrocytes and MSCs. During chondrogenesis, miR-140 expression in MSC cultures increased in parallel with the expression of SOX9 and COL2A1. Normal human articular cartilage expressed miR-140, and this expression was significantly reduced in OA tissue. In vitro treatment of chondrocytes with IL-1beta suppressed miR-140 expression. Transfection of chondrocytes with ds-miR-140 down-regulated IL-1beta-induced ADAMTS5 expression and rescued the IL-1beta-dependent repression of AGGRECAN gene expression. CONCLUSION: This study shows that miR-140 has a chondrocyte differentiation-related expression pattern. The reduction in miR-140 expression in OA cartilage and in response to IL-1beta may contribute to the abnormal gene expression pattern characteristic of OA.

Impingement-free hip motion: the 'normal' angle alpha after osteochondroplasty

Femoroacetabular impingement is considered a cause of hip osteoarthrosis. In cam impingement, an aspherical head-neck junction is squeezed into the joint and causes acetabular cartilage damage. The anterior offset angle alpha, observed on a lateral crosstable radiograph, reflects the location where the femoral head becomes aspheric. Previous studies reported a mean angle alpha of 42 degrees in asymptomatic patients. Currently, it is believed an angle alpha of 50 degrees to 55 degrees is normal. The aim of this study was to identify that angle alpha which allows impingement-free motion. In 45 patients who underwent surgical treatment for femoroacetabular impingement, we measured the angle alpha preoperatively, immediately postoperatively, and 1 year postoperatively. All hips underwent femoral correction and, if necessary, acetabular correction. The correction was considered sufficient when, in 90 degrees hip flexion, an internal rotation of 20 degrees to 25 degrees was possible. The angle alpha was corrected from a preoperative mean of 66 degrees (range, 45 degrees - 79 degrees) to 43 degrees (range, 34 degrees - 60 degrees) postoperatively. Because the acetabulum is corrected to normal first, the femoral correction is tested against a normal acetabulum. We therefore concluded an angle alpha of 43 degrees achieved surgically and with impingement-free motion, represents the normal angle alpha, an angle lower than that currently considered sufficient.

Capital realignment for moderate and severe SCFE using a modified Dunn procedure

Moderate to severe slipped capital femoral epiphysis leads to premature osteoarthritis resulting from femoroacetabular impingement. We believe surgical correction at the site of deformity through capital reorientation is the best procedure to fully correct the deformity but has traditionally been associated with high rates of osteonecrosis. We describe a modified capital reorientation procedure performed through a surgical dislocation approach. We followed 40 patients for a minimum of 1 year and 3 years from two institutions. No patient developed osteonecrosis or chondrolysis. Slip angle was corrected to 4 degrees to 8 degrees and the mean alpha angle after correction was 40.6 degrees. Articular cartilage damage, full-thickness loss, and delamination were observed at the time of surgery, especially in the stable slips. This technique appears to have an acceptable complication rate and appears reproducible for full correction of moderate to severe slipped capital femoral epiphyses with open physes.

Hip MRI and its implications for surgery in osteoarthritis patients

Osteoarthritis (OA) of the hip joint stems from a combination of intrinsic factors, such as joint anatomy, and extrinsic factors, such as injuries, diseases, and load. Possible risk factors for OA are instability and impingement. Different surgical techniques, such as osteotomies of the pelvis and femur, surgical dislocation, and hip arthroscopy, are being performed to delay or halt OA. Success of salvage procedures of the hip depends on the existing cartilage and joint damage before surgery. The likelihood of therapy failure rises with advanced OA. For imaging of intra-articular hip pathology, MRI represents the best technique because it enables clinicians to directly visualize cartilage, it provides superior soft tissue contrast, and it offers the prospect of multidimensional imaging. However, opinions differ on the diagnostic efficacy of MRI and on the question of which MRI technique is most appropriate. This article gives an overview of the standard MRI techniques for diagnosis of hip OA and their implications for surgery.

MRI of hip osteoarthritis and implications for surgery

Osteoarthritis of the hip joint is caused by a combination of intrinsic factors and extrinsic factors. Different surgical techniques are being performed to delay or halt osteoarthritis. Success of salvage procedures of the hip depends on the existing cartilage and joint damage before surgery; the likelihood of therapy failure rises with advanced osteoarthritis. For imaging of intra-articular hip pathology, MR imaging represents the best technique because of its ability to directly visualize cartilage, superior soft tissue contrast, and the prospect of multidimensional imaging. This article gives an overview on the standard MR imaging techniques used for diagnosis of hip osteoarthritis and their implications for surgery.

Radiologische Diagnose des femoroazetabuläre Impingements [Radiological diagnosis of femoroacetabular impingement]

Femoroacetabular impingements (FAI) are due to an anatomical disproportion between the proximal femur and the acetabulum which causes premature wear of the joint surfaces. An operation is often necessary in order to relieve symptoms such as limited movement and pain as well as to prevent or slow down the degenerative process. The result is dependent on the preoperative status of the joint with poor results for advanced arthritis of the hip joint. This explains the necessity for an accurate diagnosis in order to recognize early stages of damage to the joint. The diagnosis of FAI includes clinical examination, X-ray examination and magnetic resonance imaging (MRI). The standard X-radiological examination for FAI is carried out using two X-ray images, an anterior-posterior view of the pelvis and a lateral view of the proximal femur, such as the cross-table lateral or Lauenstein projections. It is necessary that positioning criteria are adhered to in order to avoid distortion artifacts. MRI permits an examination of the pelvis on three levels and should also include radial planned sequences for improved representation of peripheral structures, such as the labrum and peripheral cartilage. The use of contrast medium for a direct MR arthrogram has proved to be advantageous particularly for representation of labrum damage. The data with respect to cartilage imaging are still unclear. Further developments in technology, such as biochemical-sensitive MRI applications, will be able to improve the diagnosis of the pelvis in the near future.