Recently, femoroacetabular impingement has been recognised as a cause of early osteoarthritis. There are two mechanisms of impingement: 1) cam impingement caused by a non-spherical head and 2) pincer impingement caused by excessive acetabular cover. We hypothesised that both mechanisms result in different patterns of articular damage. Of 302 analysed hips only 26 had an isolated cam and 16 an isolated pincer impingement. Cam impingement caused damage to the anterosuperior acetabular cartilage with separation between the labrum and cartilage. During flexion, the cartilage was sheared off the bone by the non-spherical femoral head while the labrum remained untouched. In pincer impingement, the cartilage damage was located circumferentially and included only a narrow strip. During movement the labrum is crushed between the acetabular rim and the femoral neck causing degeneration and ossification. Both cam and pincer impingement lead to osteoarthritis of the hip. Labral damage indicates ongoing impingement and rarely occurs alone

Summary. The dGEMRIC index correlates more strongly with the pattern of radiographic joint space narrowing in hip osteoarthritis at five year follow-up than morphological measurements of the proximal femur. It therefore offers potential to refine predictive models of hip osteoarthritis progression. Introduction. Longitudinal general population studies have shown that femoroacetabular impingement increases the risk of developing hip osteoarthritis, however, morphological parameters have a low positive predictive value. Arthroscopic debridement of impingement lesions has been proposed as a potential strategy for the prevention of osteoarthritis, however, the development of such strategies requires the identification of individuals at high risk of disease progression. We investigated whether delayed Gadolinium-Enhanced MRI of Cartilage (dGEMRIC) predicts disease progression. This imaging modality is an indirect measure of cartilage glycosaminoglycan content. Patients and Methods. 34 asymptomatic individuals from a longitudinal cohort study (sibkids) were assessed at baseline with the collection of Patient Reported Outcome Measures (PROMs), anteroposterior and cross-table lateral radiographs, 3D morphological MRI, and dGEMRIC at 3T of their index hip. A dGEMRIC index was calculated as a ratio of the anterosuperior acetabular cartilage T1 relaxation time and the total femoral and acetabular cartilage T1 relaxation time. 29 individuals were followed up at 5 years for repeat assessment (average age 51 years and range 36 to 67). Radiological measurements were made by a single observer using in house Hipmorf software. Radiographic disease progression was assessed using minimum joint space width (JSW), lateral sourcil JSW, and medial sourcil JSW. These were measured on baseline and five year follow-up anteroposterior radiographs with an intra-observer ICC of 0.916. Alpha angle measurements were made by the same observer on radiographs and MRI radial slices with an intra-observer ICC of 0.926. Results. Mean minimum JSW for the cohort fell by 0.16mm over five years (p=0.024). Baseline dGEMRIC index did not correlate with change in minimum JSW (r=0.031 p=0.873). There was a moderate correlation between baseline dGEMRIC and the direction of JSW loss (change in JSW at the lateral sourcil minus change in JSW at the medial sourcil) (r=0.561 p=0.002). There was a weak correlation between the change in Non-Arthritic Hip Score and baseline dGEMRIC (r=0.256 P=0.180). Maximum alpha angle measured on baseline MRI radial slices did not correlate with change in minimum JSW and weakly correlated with the direction of JSW narrowing (r=0.273 p=0.160). Conclusion. A low dGEMRIC index indicates reduced glycosaminoglycan concentration in the anterosuperior acetabular cartilage compared with the total femoral and acetabular cartilage. This correlates with lateral JSW narrowing relative to medial JSW narrowing as osteoarthritis progresses. The dGEMRIC index correlates better with osteoarthritis progression than alpha angle measurements and offers the potential to refine a predictive model for osteoarthritis progression to aid patient selection for clinical trials

Introduction. Modification in joint loading, and specifically shear stress, is found to be an important mechanical factor in the development of osteoarthritis (OA). Cartilage shear stresses can be investigated using finite element (FE) modelling, where typically in vivo joint loading as measured by an instrumented hip prosthesis is used as boundary condition. However, subject-specific gait characteristics substantially affect joint loading. The goal of this study is to investigate the effect of subject-specific joint loading as calculated using a subject-specific musculoskeletal model and integrated motion capture data on acetabular shear stress. Methods. Three healthy control subjects walked at self-selected speed while measuring marker trajectories (Vicon, Oxford Metrics, UK) and force data (two AMTI force platforms; Watertown, MA). A subject-specific MRI-based musculoskeletal model consisting of 14 segments, 19 degrees of freedom and 88 musculotendon actuators, and including wrapping surfaces around the hip joint, was used. All analyses were performed in OpenSim 3.1. The model was scaled to the dimensions of each subject using the marker positions of a static pose. A kalman smoother procedure was used to calculate joint angles. Muscle forces were calculated using static optimization, minimizing the sum of squared muscle activations, and hip contact forces (HCF) were calculated and normalized to body weight (BW). To calculate shear stress, HCFs and joint angles calculated during the stance phase of gait were imposed to a hip finite element model (hip_n10rb) using FFEbio 2.5. In the model, femoral and acetabular cartilage were represented using the Mooney-Rivlin formulation (c1=6.817, bulk modulus=1358.86) and the pelvis and femur bones as rigid bodies. Peak HCF as well as maximal acetabular shear stress, magnitude and location, and the HCF at the time of maximal shear stress were compared between subjects. Results. Maximal shear stress was lower for S3 compared to S1 and S2 (9.14, 9.48 and 7.14 MPa for S1, S2 and S3 respectively). Nevertheless, HCF at the time instance of peak stress as well as peak HCF were highest for S3 (S1: 2.40/4.54 BW, S2: 2.97/4.78 BW and S3: 3.13/6.46 BW respectively). Maximal shear stress also occurred earlier in the stance phase for S3 compared to S1 and S2 (31, 26 and 11% of the stance phase for S1, S2 and S3 respectively). In addition, the location of the peak maximal shear stress was found to be more superior for S3. Discussion. Subject-specific loading patterns clearly influence the calculated maximal shear stress in the acetabular cartilage, affecting both the magnitude and the location of the stress. In addition, higher shear stresses are not coinciding with higher HCFs. This finding highlights the need of subject-specific rather than generic loading patterns when assessing cartilage shear stresses and associated risk in OA development in individual patients

The use of a composite osteochondral device for simulating partial hemiarthroplasty was examined. The device was composed of a polyvinyl alcohol hydrogel and a titanium fibre mesh, acting as artificial cartilage and as porous artificial bone, respectively. The titanium fibre mesh was designed to act as an interface material, allowing firm attachment to both the polyvinyl alcohol gel (through injection moulding) and the femoral joint surface (through bony ingrowth). We implanted 22 of these devices into canine femoral heads. Histological findings from the acetabular cartilage and synovial membrane, as well as the attachment of the prosthesis to bone, were examined up until one year after operation. No marked pathological changes were found and firm attachment of the device to the underlying bone was confirmed. The main potential application for this device is for partial surface replacement of the femoral head after osteonecrosis. Other applications could include articular resurfacing and the replacement of intervertebral discs

Objectives

An experimental piglet model induces avascular necrosis (AVN) and deformation of the femoral head but its secondary effects on the developing acetabulum have not been studied. The aim of this study was to assess the development of secondary acetabular deformation following femoral head ischemia.

Acetabular dysplasia was produced in 24 immature white rabbits. A rotational acetabular osteotomy was then carried out and radiological and histological studies of the articular cartilage were made.

In the hips which did not undergo osteotomy, radiographs at 26 weeks showed that residual subluxation remained and arthritic changes such as narrowing of the joint space or dislocation were still seen. However, in the operated group there was a remarkable increase in cover, but arthritic changes were not observed. After 24 weeks, the Mankin grading score in the operated group was significantly lower than that in the non-operated group. The latter hips showed an irregular surface of the cartilage, exfoliation and proliferation of synovial tissue. In those undergoing osteotomy, primary cloning of chondrocytes or hypercellularity was seen and at 24 weeks after operation and metaplasia of the cartilage in the fibrous tissue was observed in the boundary between the medial area of the acetabulum and the acetabular fossa.