Abstract:In residual hip dysplasia periacetabular osteotomy (PAO) can improve insufficient coverage of the femoral head. It requires a broad dissection of the pelvic bones and detachment of muscle insertions, however. We have developed a modification of the Bernese periacetabular osteotomy with reduced soft tissue exposure. It uses two small skin incisions and offers therefore the perspective of nicer scars but also increases the risk of technical complications due to impaired vision. To be able to draft these risks, the clinical and radiographic results of 23 patients with PAO through the modified Smith-Petersen approach of Ganz (group A) and 24 patients with our two-incision modification (group B) have been reviewed retrospectively with an average follow-up of 19 (group A) and 12 (group B) months postoperatively.Functional improvement (Harris Hip Score) and center-edge-angle normalization did not differ significantly in both groups. Scars of patients in group B were significantly shorter. However, the overall patient satisfaction (as measured with a visual analogous scale) was the same in both groups. 4 patients in group A and one patient in group B developed superficial or deep wound infections.In conclusion, the experience with our cohort study showed that approach-related morbidity can be reduced without increasing the risk for the individual patient. This observation clearly holds a promise for further minimal invasive approaches as well as for further morbidity reduction of PAO.Level of Evidence: Retrospective comparative study (Level III).

Background Appropriate three-dimensional imaging of the hip joint is a substantial prerequisite for planning and performing surgical correction of deformities. Although surgeons still use computed tomography (CT), modern and fast acquisition techniques of volumetric imaging using magnetic resonance imaging (MRI) for pelvic measurements enable similar resolution. Purpose This study was designed to determine if already described measures of acetabular morphology are comparable in both techniques and if assessment can be performed with equal intra-observer and inter-observer reliability. Material and Methods Thirty-two hips (16 patients) were examined with a pelvic CT and a MRI with 3-T. Pelvic orientation was standardized by each observer in coronal, axial, and sagittal planes. Acetabular version as well as seven acetabular sector angles were measured by two observers twice with a minimum of four weeks between sessions. Results Inter-rater reliability showed excellent results for intra- and inter-rater reliability for CT (0.977-0.999) and MRI (0.969-0.998) measuring acetabular version and sector angles. Evaluating the reliability of CT and MRI for each observer revealed excellent results (0.972-0.998). Evaluating the Bland-Altman plots for intra-observer reliability showed an equal distribution of angles, within acceptable 95% limits of agreement. The same results were observed for inter-observer reliability evaluating CT and MRI as well as inter-method reliability. Conclusion Modern MRI scans are equally applicable to assess the bony pelvis as CT scans. In addition, MRI would enable the examination of soft tissues such as chondrolabral structures and muscle in the same examination. Since hip-preserving surgery is mostly conducted in younger patients, the reduction of radiation exposure is a benefit.

Bone fragility due to osteopenia, osteoporosis or debilitating focal skeletal dysplasias is a frequent observation in the Mendelian disease Neurofibromatosis type 1 (NF1). To determine the mechanisms underlying bone fragility in NF1 we analyzed two conditional mouse models, Nf1Prx1 (limb knock-out) and Nf1Col1 (osteoblast specific knock-out), as well as cortical bone samples from individuals with NF1. We examined mouse bone tissue with micro-computed tomography, qualitative and quantitative histology, mechanical tensile analysis, small-angle X-ray scattering (SAXS), energy dispersive X-ray spectroscopy (EDX), and scanning acoustic microscopy (SAM). In cortical bone of Nf1Prx1 mice we detected ectopic blood vessels that were associated with diaphyseal mineralization defects. Defective mineral binding in the proximity of blood vessels was most likely due to impaired bone collagen formation, as these areas were completely devoid of acidic matrix proteins and contained thin collagen fibers. Additionally, we found significantly reduced mechanical strength of the bone material, which was partially caused by increased osteocyte volume. Consistent with these observations, bone samples from individuals with NF1 and tibial dysplasia showed increased osteocyte lacuna volume. Reduced mechanical properties were associated with diminished matrix stiffness, as determined by SAM. In line with these observations, bone tissue from individuals with NF1 and tibial dysplasia showed heterogeneous mineralization and reduced collagen fiber thickness and packaging. Collectively, the data indicate that bone fragility in NF1 tibial dysplasia is partly due to an increased osteocyte-related micro-porosity, hypomineralization, a generalized defect of organic matrix formation, exacerbated in the regions of tensional and bending force integration, and finally persistence of ectopic blood vessels associated with localized macro-porotic bone lesions.