T. Mendel

CT-based 3-D visualisation of secure bone corridors and optimal trajectories for sacroiliac screws

Sacroiliac screw (SI) fixation represents the only minimally invasive method to stabilise unstable injuries of the posterior pelvic ring. However, it is technically demanding. The narrow sacral proportions and a high inter-individual shape variability places adjacent neurovascular structures at potential risk. In this study a CT-based virtual analysis of the iliosacral anatomy in the human pelvis was performed to visualise and analyse 3-D bone corridors for the safe placement of SI-screws in the first sacral segment. Computer-aided calculation of 3-D transverse and general SI-corridors as a sum of all inner-bony 7.3-mm screw positions was done with custom-made software algorithms based on CT-scans of intact human pelvises. Radiomorphometric analysis of 11 CT-DICOM datasets using the software Amira 4.2. Optimal screw tracks allowing the greatest safety distance to the cortex were computed. Corridor geometry and optimal tracks were visualised; measurement data were calculated. A transverse corridor existed in 10 pelvises. In one dysmorphic pelvis, the pedicular height at the level of the 1st neural foramina came below the critical distance of 7.3mm defined by the outer screw diameter. The mean corridor volume was 45.2 cm3, with a length of 14.9cm. The oval cross-section measured 2.8 cm2. The diameter of the optimal screw pathway with the greatest safety distance was 14.2mm. A double cone-shaped general corridor for screw penetration up to the centre of the S1-body was calculated bilaterally for every pelvis. The mean volume was 120.6 cm3 for the left side and 115.8 cm3 for the right side. The iliac entry area measured 49.1 versus 46.0 cm2. Optimal screw tracks were calculated in terms of projected inlet and outlet angles. Multiple optimal screw positions existed for each pelvis. The described method allows an automated 3-D analysis with regard to secure SI-screw corridors even with a high number of CT-datasets. Corridor visualisation and calculation of optimal screw tracks trains the visual thinking of the surgeon and can improve pre-operative planning. Prospectively, the introduced method can be implemented in computer-assisted surgery applications involving pelvic trauma.

Cup positioning in total hip arthoplasty: spatial alignment of the acetabular entry plane

PurposeCorrect cup positioning is one of the keys for successful total hip replacement. There are mechanical and computer assistant guides for correct cup positioning in the market. To optimize the cup positioning, the use of navigation systems is recommended. The aim of this study was to compare spatial orientation of the acetabulary entry plane in relation to tables plane which is used by mechanical guides as well as anterior pelvic plane used for cup orientation by navigation systems.MethodsCT raw data of 80 Caucasians (160 acetabuli) (done in supine position) with osteoartritic hips were collected. 3-D pelvic reconstruction was generated using Amira® software (Visage Imaging Berlin, Germany). Anterior pelvic plane and acetabulary entry plane were defined by reliable anatomical landmarks. Spatial orientation were calculated by a custom made program code for the Amira® software.ResultsThere were no differences between anterior pelvic plane and table’s plane as well as spatial orientation of acetabulary entry plane of both acetabuli in relation to anterior pelvic plane or table’s plane. Furthermore, there was no correlation between age, sex or body mass index and spatial orientation of the acetabulary entry plane as well.ConclusionsThe use of mechanical alignment guides for cup orientation during total hip arthroplasty based on table’s plane in patient’s supine position is a successful method to achieve proper cup orientation.

A Method for Computing General Sacroiliac Screw Corridors Based on CT Scans of the Pelvis

Sacroiliac (SI) joint dislocations and sacral fractures of the pelvis can be stabilized by SI screws; however, screw insertion into a sacral isthmus region is risky for the adjacent neurovascular structures. Therefore, shape analyses of general SI screw corridors or safety zones are of great surgical interest; however, before such analyses can be conducted, a method for computing 3D models of general SI corridors from routine clinical computed tomography (CT) scans has to be developed. This work describes a method for determining general corridors in pelvic CT data for accurate screw placement into the first sacral body. The method is implemented with the computer language C++. The pelvic CT data are preprocessed before the presented algorithm computes a model of the 3D corridor volume. Additionally, the two most important parameters of the algorithm, the raster step and the virtual SI screw diameter, have been characterized. The result of the work is an algorithm for computing general SI screw corridors and its implementation. Additionally the influences of two important parameters, the raster step and the SI screw diameter, on corridor volume precision and computation time have been quantified for the test sample. We conclude that the method can be used in further corridor shape analyses with a large number of pelvic CT data sets for investigating general SI screw corridors and clinical consequences for the placements of the screws. Implementation of the presented software algorithm could also enhance performance of computer-assisted surgery in the near future.

Micro-computed tomography, scanning electron microscopy and energy X-ray spectroscopy studies of facet joint degeneration: A comparison to clinical imaging

Segmental degeneration in the human lumbar spine affects both the intervertebral discs and facet joints. Facet joint degeneration not only affects the cartilage surface, but also alters the cellular properties of the cartilage tissue and the structure of the subchondral bone. The primary focus of this study is the investigation of these microstructural changes that are caused by facet joint degeneration. Microstructural analyses of degenerated facet joint samples, obtained from patients following operative lumbar interbody fusion, have not previously been extensively investigated. This study analyzes human facet joint samples from the inferior articular process using scanning electron microscopy, micro-computed tomography, and energy dispersive X-ray spectroscopy to evaluate parameters of interest in facet joint degeneration such as elemental composition, cartilage layer thickness and cell density, calcification zone thickness, subchondral bone portion, and trabecular bone porosity. These microstructural analyses demonstrate fragmentation, cracking, and destruction of the cartilage layer, a thickened calcification zone, localized calcification areas, and cell cluster formation as pathological manifestations of facet joint degeneration. The detailed description of these microstructural changes is critical for a comprehensive understanding of the pathology of facet joint degeneration, as well as the subsequent development and efficacy analysis of regenerative treatment strategies.

Aggravated reduction of the posterior malleolar fracture due to incarceration of the flexor digitorum longus tendon

The indications for stabilization of the posterior malleolus (Volkmann triangle) while fixing ankle fractures are controversially discussed. Detailed descriptions of possible obstacles to reduction are scarce. The following case describes the difficulty of reduction of the posterior malleolus caused by interposition of the flexor digitorum longus tendon. The fracture line of the posterior malleolus passed in an atypical manner vertically to the posterior-medial tibial margin with direct contact to the anatomical pathway of the tendon. The impaction of the tendon was already present in the computed tomography (CT) scan taken preoperatively but the tendon hindering malleolar reduction was first realized during surgery after several unsuccessful attempts at repositioning.

Repositionshindernis des hinteren Volkmann-Dreiecks durch Interposition der Sehne des M. flexor digitorum longus@@@Aggravated reduction of the posterior malleolar fracture due to incarceration of the flexor digitorum longus tendon

The indications for stabilization of the posterior malleolus (Volkmann triangle) while fixing ankle fractures are controversially discussed. Detailed descriptions of possible obstacles to reduction are scarce. The following case describes the difficulty of reduction of the posterior malleolus caused by interposition of the flexor digitorum longus tendon. The fracture line of the posterior malleolus passed in an atypical manner vertically to the posterior-medial tibial margin with direct contact to the anatomical pathway of the tendon. The impaction of the tendon was already present in the computed tomography (CT) scan taken preoperatively but the tendon hindering malleolar reduction was first realized during surgery after several unsuccessful attempts at repositioning.

Gelenkerhaltende Korrektureingriffe nach distaler Radiusfraktur

ZusammenfassungFrakturen des distalen Radius zählen zu den häufigsten ossären Verletzungen. Bei signifikanten intra- und/oder extraartikulären Fehlstellungen oder Pseudarthrosen nach konservativer bzw. operativer Therapie, die von persistierenden Beschwerden und funktioneller Einschränkung begleitet werden, sollte die Indikation für einen korrigierenden Eingriff geprüft werden. Öffnende Osteotomien mit Defektauffüllung mittels Beckenkammspan oder autologer Spongiosa haben sich gemeinhin bewährt und sind als Standardverfahren etabliert. Wann immer möglich, sollte das Ziel der Korrektur in einer Rekonstruktion möglichst anatomischer Verhältnisse mit Rekonstruktion der radialen Länge, des palmaren Tilt sowie der Ulnarinklination liegen. Hierbei sind das Radiokarpalgelenk und das distale Radioulnargelenk grundsätzlich als funktionelle Einheit zu betrachten. Letztlich besteht eine klare Korrelation zwischen dem klinischen und radiologischen Ergebnis nach erfolgter Korrektur.AbstractFractures of the distal radius are one of the most frequent bony injuries. Corrective surgery should be considered in cases of significant malpositioning of intra-articular or extra-articular fractures as well as malunions after conservative or surgical treatment associated with persistent pain and functional impairment. Open wedge osteotomy combined with an iliac crest graft or autologous cancellous bone is the most widely recommended technique and has become established as the standard method. Whenever possible, an anatomical reduction with reconstruction of the radial length, palmar tilt and ulnar inclination should be performed. In so doing, the radiocarpal and the distal radioulnar joints have to be considered as one functional unit. The functional outcome after corrective osteotomy shows a clear correlation with the radiological result.

Möglichkeiten und Grenzen von Repositionstechniken bei distaler Radiusfraktur

ZusammenfassungDistale Radiusfrakturen gehören zu den häufigsten Frakturen des Menschen. Der überwiegende Teil wird heutzutage osteosynthetisch versorgt. Das Ziel ist die anatomische Rekonstruktion im Radiokarpalgelenk und distalen Radioulnargelenk (DRUG) zum Erreichen einer schmerzfreien vollumfänglichen Funktion des Handgelenkes sowie Verhinderung einer frühzeitigen posttraumatischen Arthrose. Die korrekte Reposition als das entscheidende Element der Osteosynthese kann dabei über ein offenes oder geschlossenes Vorgehen sowie direkte und indirekte Techniken erfolgen. Zur adäquaten Behandlung der jeweiligen Fraktursituation sollte der Operateur die verschiedenen Retentions- und Repositionsmöglichkeiten beherrschen sowie kombinieren können.AbstractDistal radius fractures are the most common fractures of long bones. The majority of these fracture types are nowadays indications for osteosynthetic treatment. The aim is the anatomical reconstruction of the radiocarpal joint and the distal radioulnar joint to achieve a painless full range of motion of the wrist and to prevent early posttraumatic osteoarthritis. The correct repositioning as the main part of osteosynthesis can be carried out by open or closed reduction and by direct or indirect methods. To achieve the most suitable therapy for each individual fracture type the orthopedic surgeon should have the ability to use these different tools and repositioning procedures and also know how to combine them.

Repositionshindernis des hinteren Volkmann-Dreiecks durch Interposition der Sehne des M. flexor digitorum longus

The indications for stabilization of the posterior malleolus (Volkmann triangle) while fixing ankle fractures are controversially discussed. Detailed descriptions of possible obstacles to reduction are scarce. The following case describes the difficulty of reduction of the posterior malleolus caused by interposition of the flexor digitorum longus tendon. The fracture line of the posterior malleolus passed in an atypical manner vertically to the posterior-medial tibial margin with direct contact to the anatomical pathway of the tendon. The impaction of the tendon was already present in the computed tomography (CT) scan taken preoperatively but the tendon hindering malleolar reduction was first realized during surgery after several unsuccessful attempts at repositioning.

Periimplantäre Frakturen – assoziiert mit Plattenosteosynthese

ZusammenfassungUrsachen des Versagens einer PlattenosteosyntheseDas Versagen einer Plattenosteosynthese stellt für den Operateur nicht selten eine Herausforderung dar. Zunächst muss die zugrundeliegende Ursache erkannt und im Rahmen der gewählten Therapiestrategie korrekt adressiert werden. So führen periimplantäre Frakturen am Plattenende, aber auch Schraubenlockerungen oder eben Plattenbrüche auf Höhe der ehemaligen Fraktur zu einem Versagen des Konstrukts. Plattennahe Frakturen werden außer nach adäquaten Unfallereignissen bei zumeist männlichen Patienten im erwerbstätigen Alter in zunehmendem Maß auch bei geriatrischen Patienten infolge einer generalisierten osteoporosebedingten Schwächung des Knochens im Rahmen von inadäquaten Traumen gesehen. Am häufigsten jedoch ist ein mechanisches Versagen durch Bruch der Platte oder Schraubenauslockerungen auf Basis einer verzögerten Frakturheilung. TherapieDie Möglichkeiten einer operativen Stabilisierung sind mannigfaltig. Sie reichen von zusätzlichen Platten über den Wechsel auf ein intramedulläres Verfahren bis hin zur Konversion auf einen endoprothetischen Ersatz bei entsprechend gelenknaher Lokalisation. Die Versorgungsstrategie sollte immer individuell, abhängig von der Ursache und der Art des Versagens der einliegenden Plattenosteosynthese unter Berücksichtigung der Knochenqualität gewählt werden. Sollte eine verzögerte Frakturheilung Ursache des Versagens sein, sollte dieser mit adäquaten Mitteln zwingend Rechnung getragen werden, um den Bruch letztlich zur Ausheilung bringen zu können.AbstractReasons for failure of plate osteosynthesisNot uncommonly, the management of plate fixation failure can pose a challenge for the surgeon. Therefore it is first necessary to recognize the underlying reason and to address it in the context of a correct therapy strategy. Peri-implant fractures at the end of the plate, screw breakage or loosening as well as plate breakage at the site of the initial fracture line can lead to failure of the plate fixation construct. Commonly, a secondary fracture at the end of the plate is caused by an adequate force impact in mostly younger male patients in an employable age. On the other hand, in geriatric patients brittle fractures due to a low impact in inadequate accidents are seen at an increasing rate resulting from a generalized fragility of osteoporotic bone. However, in most cases the mechanical failure of plate osteosynthesis is the result of plate breakage or screw loosening based on a delayed bone fracture union. TherapyNumerous options for internal fixation are available to readdress the instability, ranging from additional plating through intramedullary nailing to conversion to endoprosthetic arthroplasty at an appropriate fracture location near a joint. The choice of treatment should depend on the type of plate failure as well as the individual bone quality. In cases of delayed fracture union, the surgical treatment should imperatively focus on measures to support fracture healing.