Andrej Maria Nowakowski

Measurement of knee joint gaps without bone resection: "physiologic" extension and flexion gaps in total knee arthroplasty are asymmetric and unequal and anterior and posterior cruciate ligament resections produce different gap changes

General agreement is that flexion and extension gaps should be equal and symmetrical in total knee arthroplasty (TKA) procedures. However, comparisons using a standard TKA approach to normal knee joints that have not undergone bone resection are currently unavailable. Since bony preparation can influence capsule and ligament tension, our purpose was to perform measurements without this influence. Ten normal cadaveric knees were assessed using a standard medial parapatellar TKA approach with patellar subluxation. Gap measurements were carried out twice each alternating 100 and 200 N per compartment using a prototypical force‐determining ligament balancer without the need for bony resection. Initial measurements were performed in extension, followed by 90° of flexion. The ACL was then resected, and finally the PCL was resected, and measurements were carried out in an analogous fashion. In general, the lateral compartment could be stretched further than the medial compartment, and the corresponding flexion gap values were significantly larger. ACL resection predominantly increased extension gaps, while PCL resection increased flexion gaps. Distraction force of 100 N per compartment appeared adequate; increasing to 200 N did not improve the results.

Assessment of knee implant alignment using coordinate measurement on three-dimensional computed tomography reconstructions.

The rapid development of navigation systems designed to improve implant alignment calls for precise methods to verify positioning. One new approach to assess knee implant alignment is coordinate measurement (CM) using reference objects on 3-dimensional reconstructions of computed tomographic (CT) image sequences. The objectives of this study were to determine whether implant alignment can be accurately and precisely examined with CT-based CM, and whether correct positioning of a transversal support implant can be attained using a specially developed aiming instrument. Average deviation of CT measurements from those made with a digital caliper remained within the caliper’s range of error. This level of accuracy was observer independent. CT-based CM can be used for accurate and precise alignment verification. As well, precise alignment of transversal support can be achieved during implantation with a conventional aiming device, assuming the bony landmarks are appropriately recognized.

Computer tomographic evaluation of talar edge configuration for osteochondral graft transplantation

To successfully surgically reconstruct osteochondral lesions of the talus, the exact three‐dimensional (3D) configuration of the upper articular surface of the talus has to be respected. We assessed the talar geometry by measuring the coronal and sagittal talar edge radius and the frontal talar profile in multiplanar reconstructions of computer tomographic (CT) studies of 79 patients (83 feet) with a healthy ankle joint. An image visualization software designated for coordinate measurement was used to perform the measurement. In the coronal plane, the mean lateral talar edge radius was 4.0 mm and the medial 4.5 mm. In the sagittal planes the mean lateral talar edge radius was 20.3 mm, the radius of the sulcus 20.7 mm and the medial talar edge radius 20.4 mm. The talus showed a concave shape in coronal cuts. These results show a significant difference between medial and lateral talar edge configuration in coronal planes. The measurements of the lateral and medial sagittal radius and the mid‐sagittal radius in the sulcus tali show no statistically significant difference. The depth of the talar sulcus shows no correlation to age or sex. Different sizes of custom‐made tissue‐engineered grafts according to the location of the osteochondral lesion at the talus are needed for exact surgical reconstruction of the anatomy. Osteochondral lesions are three dimensional; therefore, a 3D preoperative planning tool by CT scan or MRI is mandatory. Clin. Anat. 25:773–780, 2012.

Investigating the primary stability of the transversal support tibial plateau concept to retain both cruciate ligaments during total knee arthroplasty.

PURPOSE The important roles of the anterior cruciate ligament regarding knee stability, physiologic kinematics, and proprioception are unquestioned. Thus, various efforts have been made to retain the ACL during total knee arthroplasty (TKA). Neither of the existing solutions to this problem, i.e. bicruciate retaining prostheses and implantation of two unicondylar prostheses, has been successful because of concept-specific problems as well as general difficulties with implant fixation. The new transversal support tibial plateau concept is a prosthesis of two individual joint surfaces reinforced beneath the articular line by joint surface supports and buttressed by a single transversal support. This configuration, which enables retention of both cruciate ligaments, should provide good bone fixation and ensure long-term alignment of the individual joint surfaces. METHODS In the current study, four prototypes based on this novel concept were developed and the resulting primary stability was analyzed using adapted load testing. The test set-up, with the model-loading of specially prepared Sawbones® and a sinusoidal oscillating load transmission with 25 000 cycles over 10 increasing load levels, achieved subsidence, which enabled comparison of the four different model variants regarding primary stability in view of bone anchoring. RESULTS The model variant (TSmobile) that allowed transverse glide of the joint surface supports along the transversal support revealed the largest subsidence. CONCLUSIONS A rigid attachment of the joint surface supports of the transversal support tibial plateau thus appears to offer increased primary stability regarding bone anchoring.

Surgical approach for a new knee prosthesis concept (TSTP) retaining both cruciate ligaments

The transversal support tibial plateau (TSTP) concept was developed to retain both cruciate ligaments during total knee arthroplasty. TSTP design consists of two individual joint surfaces, reinforced beneath the joint line by two joint surface supports and buttressed by a single transversal support (TS). This configuration is devised to provide good bony anchoring especially for the TS, and to ensure long‐term alignment of the individual joint surfaces. TS insertion requires a small extra incision. This study assessed techniques to implant the TS into the tibia. Using a specially designed aiming device, TS insertion from each side was evaluated in 13 human cadaveric knees (10 formalin‐fixed, two Thiel embalmed, one fresh) at defined intervals of 15, 25, and 35 mm beneath the joint line. Particular attention was paid to potentially endangered structures, e.g., the medial collateral ligament (MCL), pes anserinus, and common peroneal nerve, as well as impediments to insertion, e.g., the fibula. TS implantation was successfully performed using both medial and lateral approaches. From medial, the TS was inserted safely at the 15 mm interval with the knee in maximum flexion and external rotation. With increasing intervals, however, the MCL and pes anserinus became progressively more susceptible to injury. In contrast, with the lateral approach, the operative field was quite close to the fibular head for the 25 mm interval. However, with the knee in extension, no other important structures were at risk. Clin. Anat. 23:985–991, 2010.

Comparison of the primary stability of different tibial baseplate concepts to retain both cruciate ligaments during total knee arthroplasty

BACKGROUND A novel tibial baseplate design (Transversal Support Tibial Plateau) as a new treatment concept for bi-cruciate retaining total knee arthroplasty is evaluated for mechanical stability and compared to other tibial baseplate designs. This concept should provide better primary stability and thus, less subsidence, than implantation of two separate unicondylar tibial baseplates. METHODS Different baseplates were implanted into synthetic bone specimens (Sawbones® Pacific Research Laboratories, Inc., Washington, USA), all uncemented. Using a standardized experimental setup, subsidence was achieved, enabling comparison of the models regarding primary stability. FINDINGS Overall implant subsidence was significantly increased for the two separate unicondylar tibial baseplates versus the new Transversal Support Tibial Plateau concept, which showed comparable levels to a conventional tibial baseplate. Reduced subsidence results in better primary stability. INTERPRETATION Linking of two separate baseplates appears to provide increased primary stability in terms of bony fixation, comparable to that of a conventional single tibial baseplate.

Comparison of knee joint orientation in clinically versus biomechanically aligned computed tomography coordinate system

Background Preoperative planning of total knee arthroplasty is usually performed using knee-centred computed tomography (CT) data sets. The disadvantage of these data sets is having no account of the biomechanical axis of the lower extremity, known as Mikulicz line. It aligns the femoral head to the middle of the talocrural joint. For optimal prosthesis arrangement, the knee CT data set must therefore be brought in congruency with this line of loading to achieve the best results and eliminate rotational malalignments. This study aims to establish a relation between the knee-centred clinical coordinate system (CCS) and a biomechanical coordinate system (BCS) based on the Mikulicz line. Methods CT data sets of 45 lower extremities were evaluated. Using VG Studio Max, a visualisation and measurement software program; each CT data set was aligned according to the CCS and BCS. After superimposing both the aligned data sets, the deviations of both coordinate systems in all three planes were measured with the centre of the knee defined as the origin. Results For the coronal plane, the CCS was demonstrated to be 2.54° in adduction compared to the BCS [standard deviation (SD) = 1.8°]. In sagittal view, the CCS was demonstrated to be 0.3° retroversed (SD = 3.27°). Finally, the deviation in the axial plane showed an outward rotation of 3.39° (SD = 1.99°). The alignment as well as the measurements demonstrated high intraobserver and interobserver reproducibility. Conclusion Both coordinate systems can be established in knee-centred CT data sets in a reproducible manner. Clearly, the CCS differs significantly from the BCS describing the biomechanical axis, but mathematical-based adaptations and corrections can be performed. The translational potential of this article The findings of this study allow a mathematical conversion of a knee CT to the biomechanical axis of the leg.

Comparison of 2 plating techniques for lateral clavicle fractures, using a new standardized biomechanical testing setup

Background: Conservative treatment of lateral clavicle fractures (Neer type II) often ends with unsatisfactory results for patients. Operative treatment is thus gaining acceptance. A retrospective study found success using a double plate technique for these injuries. For the current study, a standardized testing setup was developed to compare the mechanical properties of single versus double plate technique for lateral clavicle fractures. Methods: Six synthetic bones were tested for each technique. Neer type IIB fractures were created using computer-aided design (CAD). Fatigue testing was carried out with a cantilever bending test. Parameters measured were cycles undergone, failure load and stiffness at the point of failure. Results: The standardized testing setup was able to provide reproducible failures. The double plate technique lasted about 16,000 more cycles and withstood an additional 22.4 N on average. Conclusions: The new modified standardized testing setup produced reproducible fixation failures for both clavicle fracture fixation techniques. The double plate technique seems to be mechanically superior to the single plate technique.

True Angle between Anterior-Posterior Impingement in Total HipArthroplasty: Why Common Constrained Cups have to Fail

Background: Dislocation after total hip arthroplasty is a common complication and partially based on impingement. Questions/purposes: (1) The purpose of this study was to investigate the angle between anterior and posterior impingement in current hip cup designs. (2) Furthermore, the aim was to design a model of an acetabular cup with sparing gaps that match to impact areas. Methods: The range of motion was simulated with Maple R8 software using standard parameters in hip arthroplasty. Afterwards, a preliminary model for an optimized acetabular cup was designed in order to avoid impingement and dislocation. Results: (1) Anterior and posterior areas of impingement were not opposite but twisted by an angle of 108.3°. (2) The two main trajectories of motion were identified and areas with corresponding reductions and elevations were appropriate modified. The improvement resulted in a “bidirectional total hip prosthesis” with a combination of a snapfit acetabular cup and a reduced cup profile. Conclusion: The improvements of the described hip prosthesis are based on a simulation and are most likely to prevent impingement and subsequent dislocation. In addition, simulation with standard implantation parameters resulted in a rotational asymmetric implant design. Clinical relevance: Our data provide evidence that conventional hip cup designs fail to prevent impingement due to (1) The incorrect assumption of diagonally arranged impingement areas and the diagonal arranged sparing gaps (2) The sparing gap design itself that technically is not reducing the rim of the cup but instead only has an elevated coverage relative to the center of motion.