Volume 52, Issue 5

The aim of this cadaveric study was to describe the kinematics of the anterior cruciate ligament (ACL)-intact, posterolateral (PL) bundle-deficient and ACL-deficient knee by applying a protocol for computer-assisted evaluation of knee kinematics. The hypothesis that the PL bundle functions mainly at low knee flexion angles was tested. An optical tracking system was used to acquire knee joint motion on 10 knees during clinical evaluations by tracking markers rigidly attached to the bones. The protocol included acquisition of anterior-posterior (AP) translations and internal-external (IE) rotations, and evaluation of three clinical knee laxity tests (anterior drawer, manual and instrumented Lachman). The data demonstrated no significant contribution to AP translation and IE laxity from the PL bundle over the entire range of motion. The clinical knee laxity tests showed no significant differences between the ACL-intact and PL bundle-deficient states. The hypothesis could not be proven. Current clinical knee laxity measurements may not be suited for detecting subtle changes such as PL bundle deficiency in the ACL anatomy. The computation of knee laxity might be a step towards a more precise kinematic test of knee stability not only in the native and torn ACL state of the knee but also in the reconstructed knee. Zusammenfassung Ziel der Kadaverstudie war, die Kinematik von Kniegelenken mit intaktem, PL-Bündel-defizientem und defizientem VKB mit Hilfe eines Protokolls für Computer-assistierte Beurteilung von Gelenkkinematiken zu untersuchen. Die Hypothese war, dass das PL-Bündel primär bei niedrigen Flexionsgraden das Kniegelenk stabilisiert. Ein optisches Positionsmesssystem wurde benutzt, um Bewegungen von 10 verschiedenen Kniegelenken während der klinischen Tests zu dokumentieren. Das Protokoll beinhaltete die Erfassung von anteriorposteriorer Translation, Innen- und Außenrotation, manuellem und instrumentiertem Lachman-Test sowie vorderer Schublade. Die Daten zeigten keinen signifikanten Anteil des PL- Bündels für anteriorposteriore Translation und Innen- und Außenrotation über das gesamte Bewegungsausmaß des Kniegelenkes. Die klinischen Tests zeigten ebenso keine signifikanten Unterschiede zwischen VKB-intakten und PL-Bündel-defizienten Kniegelenken. Die Hypothese konnte somit nicht bestätigt werden. Gegenwärtige klinische Knietests sind möglicherweise nicht geeignet, um kleine Unterschiede in der VKB-Anatomie wie PL-Bündel-Läsionen zu beurteilen. Die Dokumentation der Kniegelenklaxizität mit dem Computer mag ein Schritt für eine präzisere kinematische Gelenkbeurteilung, nicht nur bei intaktem und defizientem VKB, sondern auch bei verschiedenen Rekonstruktionen sein.

Introduction : The kinematics of a robotic device significantly determines its installation space when it comes to technical realisation. With regard to the deployment of robotic manipulators in surgery, manipulators with a preferably small installation space are needed. Materials and methods : This study describes six versions of novel epicyclic kinematics with six degrees of freedom (DOF). At first, the kinematics functionality was analysed using Gruebler's formula. Subsequently, the quantitative determination of the relation of workspace and installation space was performed using Matlab algorithms. To qualitatively describe the shape of the workspace, the Matlab visualisation features were utilised. For comparison, the well-known Hexapod was used. Results : The assessed kinematics had 6-DOF-functionality. It became apparent that one version of the epicyclic kinematics having two 3-DOF disk systems mounted in a parallel way featured a particularly good relation of workspace and installation space. Compared to the Hexapod, this is approximately four times better. The shape of the workspaces of all epicyclic kinematics assessed was convex and compact. Conclusion : It could be shown that a novel epicyclic kinematics has a notably advantageous relation of workspace and installation space. Apparently, it seems to be well suited for the deployment in robotic machines for surgical procedures.

Navigation systems have been successfully established in spine surgery over the past years. Although there is rather good intraoperative support, preoperative planning still lacks a technologically mature software basis. In particular, the computation of the effect of intervention would be of great importance to the surgeon, which would allow him to choose the right strategy. For the patient, this would result in reduced trauma and optimized postoperative mobility. For a correct simulation of the behavior of the cervical spine, a patient individual finite element model is needed which would precisely reflect the geometrical and biomechanical properties of the spine. Therefore, a modeling process starting from tomographic data and ending in an applicable finite element model must be elaborated. A possible solution will be presented in this paper.

The aim of our study was to develop a femoral component for total hip arthroplasty that would exclusively anchor in the metaphysis of the femoral neck. To forego trochanteric fixation, the load needs to be transferred to the metaphysis at as many points as possible. A computer simulation model suggested that an implant with a central cylinder and 16 rods aligned along a thread would be the preferable solution. To evaluate primary implantation stability, 14 fresh frozen cadaver femora were used. A special instrument set was developed to allow for centered implantation of the prosthesis without the need to dissect the greater trochanter. For our tests, we used two prototype implants: one made from titanium and the other from a CoCrMo alloy. For the measurement of micromotions at the medial proximal femur, sinusoid dynamic loading with a force between 300 N and 1700 N and a frequency of 1 Hz was employed. In a neutral position of 16 degrees adduction and 9 degrees antetorsion, the average micromotions measured were 119 μm. Despite these convincing in vitro results with regards to primary stability, circular cut-out of the implant, followed by aseptic osteonecrosis, loosening might still occur in a clinical situation. Animal experiments are therefore required to further evaluate this new implant design.

Introduction : The novel ultrasonic osteotomy technique (Piezosurgery ® ) is an alternative to conventional osteotomy devices. The aim of the present study was to carry out morphological comparison of the bone surface using conventional osteotomy techniques in comparison to the rather new ultrasonic osteotomy technique by means of a reflected-light microscopic examination. Materials and methods : Following the sacrifice of 12 rabbits, 24 standardized bone samples were removed from the skull. The osteotomy devices used were a rotating instrument (Lindemann bur), an oscillating micro-saw, and an ultrasonic osteotomy device (Piezosurgery ® ) with insert tips OT6 and OT7. The times needed for osteotomy were measured. The bone surfaces were examined using a reflected-light microscope with a magnification of 40× and 100×. Results : Osteotomy with Piezosurgery ® is significantly more time consuming than osteotomy with conventional methods (p<0.05). Following osteotomy with the ultrasonic device, the reflected-light microscopic examinations of the unmodified bone samples revealed typical bone structure of the calvaria, including compacta externa, diploe and compacta interna. On the contrary, following osteotomy with the conventional devices, the diploe structure presented distinct modifications. The cancellous spaces were filled with bone debris, and the cancellous structure was demolished. The samples prepared by the micro-saw technique showed a superficially condensed and grooved surface. Conclusion : In the present study, well-defined differences were observed following osteotomy with conventional devices and osteotomy with the ultrasonic device. The integrity of the bony structure observed after the ultrasonic technique could benefit the bone healing process. Further studies dealing with the bone healing process after using different osteotomy techniques are recommended.

A sudden failure of implantable pulse generators used for spinal cord stimulation occurred in two patients. To identify the cause of this failure, an intensive destructive analysis of the explanted devices was carried out. A functional diagnosis was carried out by inspecting amplitude, pulse width and frequency on each output channel of the implantable pulse generators. Later, the titanium case of the pulse generators was opened by laser cutting to minimise any additional mechanical stress during the opening procedure. The functional test for both pulse generators showed faultless behaviour. Using light and electron microscopy, hairline cracks could be identified in the electrical connection between battery and electronic circuit. In both devices, the cracks spread through the whole bond wire in the connection to the plus pole of the battery and partially also to the minus pole. The analysis showed that both devices failed by broken bond wires. The electrical connection to the battery exists just by the spring characteristic of the wires. A push to the implant causes a short-term disconnection, resulting in a power on reset of the device. Manufacturing or design issues, allowing micromotion between battery and the hybrid part, may be the reason for this problem. Zusammenfassung Ein plötzlicher Ausfall von implantierten Pulsgebern zur Rückenmarkstimulation ereignete sich bei zwei Patienten. Die Implantate wurden einer gründlichen zerstörenden Untersuchung unterzogen, um die Ursache des Fehlers identifizieren zu können. Die Stimulationsamplitude, Pulsbreite und Frequenz jedes einzelnen Stimulationsausgangs wurden innerhalb eines Funktionstests überprüft. Anschließend wurden die Titangehäuse der Pulsgeneratoren durch einen Laser geöffnet, um jede zusätzliche mechanische Belastung innerhalb der Bearbeitung zu minimieren. Der Funktionstest zeigte ein fehlerloses Verhalten der Stimulatoren. Mittels Licht- und Elektronenmikroskopie konnten Haarrisse in den Verbindungsdrähten zwischen Batterie und dem elektronischen Schaltkreis erkannt werden. Die Bonddrähte wiesen in beiden Implantaten durchgehende Bruchstellen in der Verbindung zum Pluspol und teilweise zum Minuspol der Batterie auf. Die Analyse zeigte, dass der plötzliche Ausfall beider Pulsgeneratoren durch gebrochene Bonddrähte hervorgerufen wurde. Die elektrische Verbindung zur Batterie bestand nur noch durch die Federcharakteristik der Drähte. Ein mechanischer Stoß am Implantat bewirkte eine kurzzeitige Trennung von der Batterie, wodurch das Implantat in den Resetzustand versetzt wurde. Bedingt durch die Herstellung oder Konstruktion ist eine geringfügige Bewegung zwischen Batterie und Schaltkreis möglich, welche als Ursache dieses Problems angesehen werden kann.