The use of retrograde femoral intramedullary nails in children for deformity correction is controversial. It is unknown if the injury to the central part of the growth plate results in premature bony union, leading to limb deformities or discrepancies. The aim of this study was to assess physeal healing and bone growth after insertion of a retrograde femoral nail thorough the centre of the physis in a skeletally immature experimental porcine model. Eleven immature pigs were included in the study. One leg was randomised for operation with a retrograde femoral nail (diameter 10.7 mm), whilst the non-operated contralateral remained as control. All nails were inserted centrally in coronal and sagittal plane under fluoroscopic guidance, and the nails spanned the physis. The nails were removed at 8 weeks. Both femora in all animals underwent MRI at baseline (pre-operatively), 8 weeks (after nail removal) and 16 weeks (before euthanasia). Femoral bone length was measured at 5 sites (anterior, posterior, central, lateral and medial) using 3d T1-weighted MRI. Growth was calculated after 8 weeks (growth with nail) and 16 weeks (growth without nail). Physeal cross-sectional area and percentage violated by the nail was determined on MRI. Operated side was compared to non-operated. Corresponding 95% confidence intervals were calculated. No differences in axial growth were observed between operated and non-operated sides. Mean growth difference was 0,61 mm [−0,78;2,01] whilst the nail was inserted into the bone and 0,72 mm [−1,04;1,65] after nail removal. No signs of angular bone deformities were found when comparing operated side to non-operated side. No premature bony healing at the physis occurred. Histology confirmed fibrous healing. Mean physeal violation was 5.72% [5.51; 5.93] by the femoral nail. The insertion of a retrograde femoral nail through the centre of an open physis might be a safe procedure with no subsequent growth arrest. However, experiments assessing the long term physeal healing and growth are needed

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