Marc Puls

Pathomorphologic alterations predict presence or absence of hip osteoarthrosis.

Abnormal morphology of the hip has been associated with primary osteoarthrosis. We evaluated the morphology of 464 consecutive hips contralateral to hips treated by THA. We excluded all hips with known diagnoses leading to secondary osteoarthritis and all hips with advanced arthrosis to eliminate the effect of arthritic remodeling on the morphologic measurements. Of the remaining 119 hips, 25 were in patients aged 60 years or older who had no or mild arthrosis (Tönnis Grade 0 or 1) and 94 hips had Tönnis Grade 2 osteoarthrosis. We quantified morphologic parameters on plain radiographs and CT images and simulated range of motion using virtual bone models from the CT data. The nonarthritic hips had fewer pathomorphologic findings. High alpha angles and high lateral center edge angles were strongly associated with the presence of arthritis; decreased internal and external rotation in 90° flexion showed lesser correlation. The data confirm previous observations that abnormal hip morphology predates arthrosis and is not secondary to the osteoarthritic process. Hips at risk for developing arthrosis resulting from pathomorphologic changes may potentially be identified at the cessation of growth, long before the development of osteoarthrosis.Level of Evidence: Level II, diagnostic study. See the Guidelines for Authors for a complete description of levels of evidence.

LCPD: Reduced Range of Motion Resulting From Extra- and Intraarticular Impingement

BackgroundLegg-Calvé-Perthes disease (LCPD) often results in a deformity that can be considered as a complex form of femoroacetabular impingement (FAI). Improved preoperative characterization of the FAI problem based on a noninvasive three-dimensional computer analysis may help to plan the appropriate operative treatment.Questions/purposesWe asked whether the location of impingement zones, the presence of additional extraarticular impingement, and the resulting ROM differ between hips with LCPD and normal hips or hips with FAI.MethodsWe used a CT-based virtual dynamic motion analysis based on a motion algorithm to simulate the individual motion for 13 hips with LCPD, 22 hips with FAI, and 27 normal hips. We then determined the motion and impingement pattern of each hip for the anterior (flexion, adduction, internal rotation) and the posterior impingement tests (extension, adduction, external rotation).ResultsThe location of impingement zones in hips with LCPD differed compared with the FAI/normal groups. Intra- and extraarticular impingement was more frequent in LCPD (79% and 86%, respectively) compared with normal (15%, 15%) and FAI hips (36%, 14%). Hips with LCPD had decreased amplitude for all hip motions (flexion, extension, abduction, adduction, internal and external rotation) compared with FAI or normal.ConclusionsHips with LCPD show a decreased ROM as a result of a higher prevalence of intra- and extraarticular FAI. Noninvasive assessment of impingement characteristics in hips with LCPD may be helpful in the future for establishment of a surgical plan.

Size and shape of the lunate surface in different types of pincer impingement: theoretical implications for surgical therapy

OBJECTIVE Acetabular rim trimming is indicated in pincer hips with an oversized lunate surface but could result in a critically decreased size of the lunate surface in pincer hips with acetabular malorientation. There is a lack of detailed three-dimensional anatomy of lunate surface in pincer hips. Therefore, we questioned how does (1) size and (2) shape of the lunate surface differ among hips with different types of pincer impingement? METHOD We retrospectively compared size and shape of the lunate surface between acetabular retroversion (48 hips), deep acetabulum (34 hips), protrusio acetabuli (seven hips), normal acetabuli (30 hips), and hip dysplasia (45 hips). Using magnetic resonance imaging (MRI) arthrography with radial slices we measured size in percentage of the femoral head coverage and shape using the outer (inner) center-edge angles and width of lunate surface. RESULTS Hips with retroversion had a decreased size and deep hips had normal size of the lunate surface. Both had a normal shape of the outer acetabular rim. Protrusio hips had an increased size and a prominent outer acetabular rim. In all three types of pincer hips the acetabular fossa was increased. CONCLUSION Size and shape of the lunate surface differs substantially among different types of pincer impingement. In contrast to hips with protrusio acetabuli, retroverted and deep hips do not have an increased size of the lunate surface. Acetabular rim trimming in retroverted and deep hips should be performed with caution. Based on our results, acetabular reorientation would theoretically be the treatment of choice in retroverted hips.

The Equidistant Method – a novel hip joint simulation algorithm for detection of femoroacetabular impingement

Introduction: A novel computerized algorithm for hip joint motion simulation and collision detection, called the Equidistant Method, has been developed. This was compared to three pre-existing methods having different properties regarding definition of the hip joint center and behavior after collision detection. It was proposed that the Equidistant Method would be most accurate in detecting the location and extent of femoroacetabular impingement. Materials and Methods: Five plastic pelves and ten plastic femora with modified acetabula and head-neck junctions, allowing for 50 different morphologic combinations, were examined, along with six cadaver hips. First, motions along anatomically relevant paths were performed. These motions were tracked by a navigation system and impingement locations were digitized with a pointer. Subsequently, previously generated 3D models of all the specimens, together with the recorded anatomic motion paths, were applied to all four simulation algorithms implemented in a diagnostic computer application. Collisions were detected within the motion paths, and the linear and angular differences regarding the location as well as the size of the detected impingement areas were compared and analyzed. Results: The Equidistant Method detected impingement with significantly higher linear and angular accuracy compared to the other methods (p < 0.05). The size of the detected impingement area was smaller than that detected with the other methods, but this difference was not statistically significant. Conclusions: The increased accuracy of the Equidistant Method is achieved by implementing a dynamic hip joint center, more closely resembling the natural characteristics of the hip joint. Clinical application of this algorithm might serve as a diagnostic adjunct and support in the planning of joint-preserving surgery in patients with femoroacetabular impingement.

Computer-Assisted Femoral Head-Neck Osteochondroplasty Using a Surgical Milling Device An In Vitro Accuracy Study

Surgical navigation might increase the safety of osteochondroplasty procedures in patients with femoroacetabular impingement. Feasibility and accuracy of navigation of a surgical reaming device were assessed. Three-dimensional models of 18 identical sawbone femora and 5 cadaver hips were created. Custom software was used to plan and perform repeated computer-assisted osteochondroplasty procedures using a navigated burr. Postoperative 3-dimensional models were created and compared with the preoperative models. A Bland-Altmann analysis assessing α angle and offset ratio accuracy showed even distribution along the zero line with narrow confidence intervals. No differences in α angle and offset ratio accuracy (P = 0.486 and P = 0.2) were detected between both observers. Planning and conduction of navigated osteochondroplasty using a surgical reaming device is feasible and accurate.

Automated detection of the osseous acetabular rim using three-dimensional models of the pelvis

An automated algorithm for detection of the acetabular rim was developed. Accuracy of the algorithm was validated in a sawbone study and compared against manually conducted digitization attempts, which were established as the ground truth. The latter proved to be reliable and reproducible, demonstrated by almost perfect intra- and interobserver reliability. Validation of the automated algorithm showed no significant difference compared to the manually acquired data in terms of detected version and inclination. Automated detection of the acetabular rim contour and the spatial orientation of the acetabular opening plane can be accurately achieved with this algorithm.

MARVIN: a medical research application framework based on open source software

This paper describes the open source framework MARVIN for rapid application development in the field of biomedical and clinical research. MARVIN applications consist of modules that can be plugged together in order to provide the functionality required for a specific experimental scenario. Application modules work on a common patient database that is used to store and organize medical data as well as derived data. MARVIN provides a flexible input/output system with support for many file formats including DICOM, various 2D image formats and surface mesh data. Furthermore, it implements an advanced visualization system and interfaces to a wide range of 3D tracking hardware. Since it uses only highly portable libraries, MARVIN applications run on Unix/Linux, Mac OS X and Microsoft Windows.

Calibration of C-arm for orthopedic interventions via statistical model-based distortion correction and robust phantom detection

In this paper, we present a novel C-arm calibration approach for orthopedic applications that is based on a distortion correction plate with fiducials arranged in a single-plane and a novel mobile phantom. The former is designed to be rigidly attached to the image intensifier and is used together with a statistical model of the geometrical image distortion pattern for intra-operative image distortion correction. The latter can be placed to anywhere close to the patient anatomy being imaged. A simulation based method is then proposed for a robust detection of the phantom from an intra-operatively acquired image in order to compute both the intrinsic and the extrinsic parameters of the acquired image. Validation study performed on 20 cadaver images demonstrated an average calibration accuracy of 0.8 ± 0.4 mm.

Determination of pelvic orientation from ultrasound images using patch-SSMs and a hierarchical speed of sound compensation strategy

In the field of computer assisted orthopedic surgery (CAOS) the anterior pelvic plane (APP) is a common concept to determine the pelvic orientation by digitizing distinct pelvic landmarks. As percutaneous palpation is - especially for obese patients - known to be error-prone, B-mode ultrasound (US) imaging could provide an alternative means. Several concepts of using ultrasound imaging to determine the APP landmarks have been introduced. In this paper we present a novel technique, which uses local patch statistical shape models (SSMs) and a hierarchical speed of sound compensation strategy for an accurate determination of the APP. These patches are independently matched and instantiated with respect to associated point clouds derived from the acquired ultrasound images. Potential inaccuracies due to the assumption of a constant speed of sound are compensated by an extended reconstruction scheme. We validated our method with in-vitro studies using a plastic bone covered with a soft-tissue simulation phantom and with a preliminary cadaver trial

SIMULATION OF HIP MOTION FOR IMPINGEMENT DETECTION: A COMPARISON OF FOUR STRATEGIES

In literature, several strategies exist that describe techniques for hip motion simulation and its effects on the amplitude of range of motion, mainly in the field of gait analysis, prosthetics, or surgical planning and navigation [Piazza, 2001] [Teschner, 1998]. However, none of these methods have been used for diagnosis of femoro-acetabular impingement (FAI), a recently described mechanical cause of pre-arthritic joint degeneration. The aim of this study was to validate and compare three established and one specifically developed novel method for possible FAI detection.