Introduction. In the evaluation of patients with pre-arthritic hip disorders, making the correct diagnosis and identifying the underlying bone pathology is of upmost importance to achieve optimal patient outcomes. 3-dimensional imaging adds information for proper preoperative planning. CT scans have become the gold standard for this, but with the associated risk of radiation exposure to this generally younger patient cohort. Purpose. To determine if 3D-MR reconstructions of the hip can be used to accurately demonstrate femoral and acetabular morphology in the setting of femoroacetabular impingement (FAI) and development dysplasia of the hip (DDH) that is comparable to CT imaging. Materials and Methods. We performed a retrospective review of 14 consecutive patients with a diagnosis of FAI or DDH that underwent both CT and MRI scans of the same hip with 3D reconstructions. 2 fellowship trained musculoskeletal radiologists reviewed all scans, and a fellowship trained hip preservation surgeon separately reviewed scans for relevant surgical parameters. All were blinded to the patients' clinical history. The 3D reconstructions were evaluated by radiologists for the presence of a CAM lesion and acetabular retroversion, while the hip preservation surgeon also evaluated CAM extent using a clock face convention of a right hip, location of femoral head blood supply, and morphological anterior inferior iliac spine (AIIS) variant. The findings on the 3D CT reconstructions were considered the reference standard. Results. Of 14 patients, there were 9 females and 5 males with a mean age 32 (range 15–42). There was no difference in the ability of MRI to detect the presence of a CAM lesion (100% agreement between 3D-MR and 3D-CT, p=1), AIIS morphology (p=1, mode=type 1 variant), or acetabular retroversion (85.7%, p=0.5). 3D-MR had a sensitivity and specificity of 100 in detecting a CAM lesion relative to 3D-CT. Four CT studies were inadequate to adequately evaluate for presence of a CAM. Five CT studies were inadequate to evaluate for location of the femoral head vessels, while MRI was able to determine location in those patients. In the 10 remaining patients for presence of CAM, and nine patients for femoral head vessel location, there was no statistically significant difference between 3D-MR and 3D-CT in determining the location of CAM lesion on a clock face (p=0.8, mean MRI = 12:54, mean CT: 12:51, SD = 66 mins MR, 81 mins CT) or in determining vessel location (p=0.4, MR mean 11:23, CT mean 11:36, SD 33 mins for both). Conclusion. 3D MRI reconstructions are as accurate as 3D CT reconstructions in evaluating osseous morphology of the hip, and may be superior to CT in determining other certain clinically relevant hip parameters. 3D-MR was equally useful in determining the presence and extent of a CAM lesion, acetabular retroversion, and AIIS morphologic variant, and more useful than 3D CT in determining location of the femoral head vessels. In evaluating FAI or hip dysplasia, a 3D-MR study is sufficient to evaluate both soft tissue and osseous anatomy, sparing the need for a 3D CT scan and its associated radiation exposure and cost

Introduction

Kinematics analyses of the spine have been recognized as an effective method for functional analysis of the spine. CT is suitable for obtaining bony geometry of the vertebrae but radiation is a clinical concern. MRI is noninvasive but it is difficult to detect bone edges especially at endplates and processes where soft tissues attach. Kinematics analyses require tracking of solid bodies; therefore, bony geometry is not always necessary for kinematics analysis of the spine. This study aimed to develop a reliable and robust method for kinematics analysis of the spine using an innovative MRI-based 3D bone-marrow model.

Purpose: Partial epiphysiodesis of the growth plate due to physeal aggression is a common problem in paediatric patients. Surgical management requires precise imaging. We recall other imaging techniques currently employed and describe a novel method for studying the characteristic features of epiphysiodesis bridges of the growth plate: 3D-magnetic resonance imaging (3D-MRI).

Material and methods: We analysed retrospectively MRI series of 27 epiphysiodesis bridges in 23 children (ten boys and thirteen girls) aged 11.3 years (range 2.5 – 15). We recorded information concerning the cause of the physeal aggression, the joint involved, the type of bony bridge (Ogden classification), the clinical deformation, and the proposed treatment. The 27 bridges were studied on coronal MRI acquired with echo-gradient and fat suppression sequences. Data were processed with a manual 3D reconstruction program in 15 minutes to precisely define the localisation, the volume, and the morphology of the bony bridge and the active physis.

Results: The epiphysiodeses were caused by trauma (65%), iatrogenic aggression (17%), ischemia-infection (purpura fulminans) (9%), juxta-physeal essential cyst (4.5%), and unknown causes (4.5%). Eighty-seven percent involved a lower limb joint, 75% of which involved the tibia. The surface of the epiphysiodesis bridge covered 20% of the physis. The bridges were peripheral (46.5%), central (46.5%), and linear (7%).

Discussion: It is difficult to determine the position and the 3D relations of an epiphysiodesis bridge in a healthy active physis with imaging techniques such as plain x-rays, scintigraphy, tomography and computed tomography. The 3D-MRI method described here provides a sure way to distinguish the active growth plate which gives a high intensity signal and the epiphyseal bridge which gives a low intensity signal. Morphological (size, form) and topographic characteristics of the bony bridge and the physis can be described with precision facilitating therapeutic decision making and guiding surgery. The lack of radiation risk is also an advantage of MRI.

Conclusion: The quality of the images obtained, the safety of MRI and the easy interpretation of 3D reconstructions makes this imaging technique an excellent method for pre-therapeutic analysis of epiphysiodesis bridges.

Computer-assisted surgery (CAS) is a tool developed to allow accurate limb and implant alignment in total knee arthroplasty [TKA]. The strength of the technology is that it allows the surgeon to assess soft tissue balance and ligament laxity in flexion and extension. The accuracy of this ligament balancing technology depends upon an accurate determination of femoral component size. This size is established with intraoperative surface registration techniques. Customised instrumentation (CI) is a measured resection technique in which component size is established on preoperative 3D MRI reconstructions. The purpose of this study is to determine how these two computer-based technologies compare with regard to the accuracy with which femoral component size is established in TKA. 67 TKA were performed using CI and 30 TKA were performed using CAS by a single surgeon. CI-predicted and CAS-predicted femoral component size were compared to actual component selection. The process by which CI and CAS perform an anatomic registration was evaluated. The CI and CAS systems accurately predicted surgeon-selected femoral component size in 89% and 43% of cases, respectively (p<0.001). The discrepancy between predicted and actual femoral component size with CI and CAS was 0.1 and 0.8 sizes, respectively (p<0.001). The maximum deviation between predicted and actual femoral component size was greater in CAS than in PMI (three sizes versus one size, respectively). The anterior cortex cut was flush in 92% of CI cases. The rotation profile was consistent with Whiteside's line in 95% of CI cases. The CI system was both more accurate and more precise than the CAS navigation system in predicting femoral component size in TKA. CI utilises preoperative MR imaging to generate femoral component sizing based on optimizing medial-lateral fit with a measured posterior femoral bone resection. CAS utilises surface registration techniques based on anatomic site registration that may be subject to intraoperative measurement error due to difficult visualization (femoral epicondyles), inherent subjectivity (Whiteside's line) or anatomic variation (hypoplastic posterior condyles). CI bases implant sizing solely on reproducing an anatomical fit and a measured resection technique, whereas CAS attempts to balance an anatomic fit with optimal soft tissue balancing. In this study, the surgeon's final component selection was more likely to be in accordance with the CI rather than the CAS sizing algorithm. The CI system was capable of accurate femoral component placement in TKA. This study suggests that intraoperative surface registration may not be as accurate as preoperative 3D MRI reconstructions for establishing optimal femoral component sizing. Surgeons using intraoperative navigation based surface registration need to be aware of this when making femoral component size selection, establishing ligament balance, and determining femoral rotation

Introduction. Computer-assisted surgery (CAS) is a tool developed to allow accurate limb and implant alignment in TKA. The strength of the technology is that it allows the surgeon to assess soft tissue balance and ligament laxity in flexion and extension. The accuracy of this ligament balancing technology depends upon an accurate determination of femoral component size. This size is established with intraoperative surface registration techniques. Customized instrumentation (CI) is a measured resection technique in which component size is established on preoperative 3D MRI reconstructions. The purpose of this study is to determine how these two computer-based technologies compare with regard to the accuracy with which femoral component size is established in TKA. Methods. 67 TKA were performed using CI and 30 TKA were performed using CAS by a single surgeon. CI-predicted and CAS-predicted femoral component size were compared to actual component selection. The process by which CI and CAS perform an anatomic registration was evaluated. Results. The CI and CAS systems accurately predicted surgeon-selected femoral component size in 89% and 43% of cases, respectively (p<0.001). The discrepancy between predicted and actual femoral component size with CI and CAS was 0.1 and 0.8 sizes, respectively (p<0.001). The maximum deviation between predicted and actual femoral component size was greater in CAS than in PMI (three sizes versus one size, respectively). Discussion. The CI system was both more accurate and more precise than the CAS navigation system in predicting femoral component size in TKA. CI utilizes preoperative MR imaging to generate femoral component sizing based on optimizing medial-lateral fit with a measured posterior femoral bone resection. CAS utilizes surface registration techniques based on anatomic site registration that may be subject to intraoperative measurement error due to difficult visualization (femoral epicondyles), inherent subjectivity (Whiteside's line) or anatomic variation (hypoplastic posterior condyles). CI bases implant sizing solely on reproducing an anatomical fit and a measured resection technique, whereas CAS attempts to balance an anatomic fit with optimal soft tissue balancing. In this study, the surgeon's final component selection was more likely to be in accordance with the CI rather than the CAS sizing algorithm. This study suggests that intraoperative surface registration may not be as accurate as preoperative 3D MRI reconstructions for establishing optimal femoral component sizing. Surgeons using intraoperative navigation based surface registration need to be aware of this when they are making femoral component size selection, establishing ligament balance, and determining femoral rotation

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

Purpose of the study: There are limited data on the behaviour of intervetebral discs below arthrodesis for scoliosis. We have developed a reproducible MRI protocol for measuring the volume of the different components of the intervertebral disc and an original method for measuring disc hydration (ratio between the volume of the nucleus and the global volume). The discs studied were below fusions. The purpose of this study was to search for correlations between the disc volume and hydration and clinical outcome assess on standard x-rays. Material and method: This was a prospective study conducted from 2005 to 2008. The series included 46 children with idiopathic scoliosis requiring arthrodesis (41 girls, 5 boys, mean age 15 years). The protocol included anteroposterior and lateral x-rays and MRI pre- and postoperatively and at 3 months and 1 year. 3D MRI reconstruction relied on a standard protocol validated in our research laboratory. These reconstructions produced a measurement of disc volume and its state of hydration. Two groups were identified using the plain x-rays: group A with what was considered to be a good result, well balanced spine and a horizontal disc subjacent to the arthrodesis; group B with what was considered a poor result with an unbalanced spine or oblique subjacent disc. Two groups were also defined as a function of postoperative reduction of the COBB angle. Group A’, reduction > 65% and group B’ reduction < 65%. Student’s t test was used for the statistical analysis. Results: MRI series were obtained in 46 patients at 3 months and 28 at 1 year. At 3 months, there was an increase in nuclear volume (9.3%, p=0.056), global volume (5.2%, p=0.0017) and hydration (4.6%, p=0.056). At 1 year, the significant increases were, respectively, 15.4, 5.3 and 11.6%. At 3 months, there was a significant increase in disc volume in the groups A and A’. In group B, increase in disc volume (4.%, p=0.02) and hydration (13.9%, p=0.07) was only seen at 1 year. Conclusion: This work enabled us to establish a significant correlation between increased disc volume and hydration as measured on the MRI and clinical outcome as assessed on the plain x-rays

A new hinge knee system (LEGION HINGE, Smith & Nephew, Memphis, TN) was designed to treat gross knee instability resulting from loss of collateral ligament function, femoral and/or tibial bone loss, or from comminuted fractures of the proximal tibia or distal femur. The knee system is offered with an insert that guides the motion of the implant for kinematic improvement. The purpose of this study was to evaluate kinematic and wear performance of this novel hinge knee replacement system. The kinematics and kinetics of the Guided Motion (GM) hinge knee were assessed for a deep knee bend using a numerical lower leg simulator. Measurements of A/P translation and I/E rotation were compared to 3D MRI data of healthy weight bearing knees and measurements of M/L patella shear forces were compared to a standard primary knee implant. Three GM knee systems were tested for wear performance. All metal components were fabricated from cobalt chrome except for the Ti-6Al-4V insert locking screw. All plastic components were fabricated from UHMWPE. Wear testing was conducted on an AMTI 6-station force controlled knee simulator for approximately 5 million cycles under ISO 14243-1 load/motion profiles and soft tissue constraints. Simulation results showed that up to 130° of flexion the anterior/posteror (A/P) translation and internal/external (I/E) rotation followed a similar path over the flexion range compared to the MRI data. The magnitude of A/P translation at 130° was 9.5 mm for the GM design compared to 15.7 mm for the MRI data. The magnitude of I/E rotation at 130° was 18° for the GM design compared to 20.8° for the MRI data. The GM design showed a maximum M/L patella shear force of 456.8 N compared to 1152.4 N for a standard primary knee design over the flexion range. All constructs successfully completed wear testing and were fully functional with no issues for binding of the mating parts. All polyethylene components showed only burnishing on the articulating surfaces. The volumetric wear rate of polyethylene components was 17.54±1.24 mm3/Mcycle. The volumetric wear rate of the metal components (excluding femoral and tibial tray) was 0.045±0.01 mm3/Mcycle. Testing showed the GM design has A/P and I/E kinematics that are similar to those seen in a normal healthy knee and good patella tracking as evidenced by the low M/L patella shear forces. The wear rate of the polyethylene parts was within the range of wear rates published in the literature for primary knee designs (up to 35.8 mm3/Mcycle). The low metal wear rate indicates that fretting and corrosion of the components was minimal. We conclude the GM design more closely replicates the kinematics of the natural knee without compromising the wear characteristics. This could lead to better outcomes for the patient population that requires a hinge knee implant

Aims

Recurrent dislocation is both a cause and consequence of glenoid bone loss, and the extent of the bony defect is an indicator guiding operative intervention. Literature suggests that loss greater than 25% requires glenoid reconstruction. Measuring bone loss is controversial; studies use different methods to determine this, with no clear evidence of reproducibility. A systematic review was performed to identify existing CT-based methods of quantifying glenoid bone loss and establish their reliability and reproducibility

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