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This study aimed to understand the ability of fixed-bearing posterior cruciate ligament (PCL)-retaining implants to maintain functionality of the PCL in vivo. To achieve this, elongation of the PCL was examined in six subjects with good clinical and functional outcomes using 3D kinematics reconstructed from video-fluoroscopy, together with multibody modelling of the knee. Here, length-change patterns of the ligament bundles were tracked throughout complete cycles of level walking and stair descent. Throughout both activities, elongation of the anterolateral bundle exhibited a flexion-dependent pattern with more stretching during swing than stance phase (e.g., at 40 degrees flexion, anterolateral bundle experienced 3.9% strain during stance and 9.1% during swing phase of stair descent). The posteromedial bundle remained shorter than its reference length (defined at heel strike of the level gait cycle) during both activities. Compared with loading patterns of the healthy ligament, postoperative elongation patterns indicate a slackening of the ligament at early flexion followed by peak ligament lengths at considerably smaller flexion angles. The reported data provide a novel insight into in vivo PCL function during activities of daily living that has not been captured previously. The findings support previous investigations reporting difficulties in achieving a balanced tension in the retained PCL., Journal of Clinical Medicine, 9 (7), ISSN:2077-0383

The primary aim of this study was to assess the effects of total knee arthroplasty (TKA) implant design on collateral ligament elongation patterns that occur during level walking, downhill walking, and stair descent. Using a moving fluoroscope, tibiofemoral kinematics were captured in three groups of patients with different TKA implant designs, including posterior stabilized, medial stabilized, and ultra-congruent. The 3D in vivo joint kinematics were then fed into multibody models of the replaced knees and elongation patterns of virtual bundles connecting origin and insertion points of the medial and lateral collateral ligaments (MCL and LCL) were determined throughout complete cycles of all activities. Regardless of the implant design and activity type, non-isometric behavior of the collateral ligaments was observed. The LCL shortened with increasing knee flexion, while the MCL elongation demonstrated regional variability, ranging from lengthening of the anterior bundle to slackening of the posterior bundle. The implant component design did not demonstrate statistically significant effects on the collateral elongation patterns and this was consistent between the studied activities. This study revealed that post-TKA collateral ligament elongation is primarily determined by the knee flexion angle. The different anterior translation and internal rotation that were induced by three distinctive implant designs had minimal impact on the length change patterns of the collateral ligaments., Frontiers in Bioengineering and Biotechnology, 7, ISSN:2296-4185

Figure S2. Averaged values of the knee moment in the sagittal plane [Nm/Kg] as a function of the knee flexion angle [°] in the experienced cohort with the wooden bar (e) and with extra load on the barbell (e+) for all nine positions. (PDF 176 kb)

Video-fluoroscopic analysis can provide important insights for the evaluation of outcome and functionality after total knee arthroplasty, allowing the in vivo assessment of tibiofemoral kinematics without soft tissue artefacts. To enable measurement of the knee throughout activities of daily living such as gait, robotic systems like the moving fluoroscope have been developed that follow the knee movement and maintain the joint in front of the image intensifier. Since it is unclear whether walking while being accompanied by moving fluoroscope affects normal gait, the objective of this study was to investigate its influence on gait characteristics in healthy subjects. In addition, the impact of the motors’ noise was analysed. By means of skin markers analysis (VICON MX system, Oxford Metrics Group, UK) and simultaneous measurement of ground reaction forces (Kistler force plates, Kistler, Switzerland), gait characteristics when walking with and without the moving fluoroscope as well as with and without ear protectors in combination with the moving fluoroscope, were obtained in young (n = 10, 24.5y ± 3.0y) and elderly (n = 9, 61.6y ± 5.3y) subjects during level gait and stair descent. Walking with the moving fluoroscope significantly decreased gait velocity in level gait and stair descent over the respective movement without the fluoroscope. Statistical analysis, including gait velocity as a covariate, resulted in no differences on the ground reaction force parameters. However, some kinematic parameters (ankle, knee and hip ranges of motion, minimal knee angle in late stance phase, maximal knee angles in stance and swing phase) seemed to be modified by the presence of the moving fluoroscope, but statistical comparison was limited due to velocity differences between the conditions. Wearing ear protectors to avoid the influence of motor sound during walking with the moving fluoroscope caused no significant difference. Walking with the moving fluoroscope has been shown to decrease gait velocity and small alterations in kinematic parameters were observed. Therefore, gait and movement alterations due to the moving fluoroscope cannot completely be excluded. However, based on the absence of differences in ground reaction force parameters (when adjusted for velocity within ANCOVA), as well as based on the comparable shape of the angular curves to the slow control condition, it can be concluded that changes in gait when walking with the moving fluoroscope are small, especially in comparison to natural slow walking. In order to allow assessment of joint replacement with the moving fluoroscope, including an understanding of the effects of joint pain, clinical analyses can only be compared to gait activities showing similarly reduced velocities. Importantly, the reduced gait speeds observed in this study are similar to those observed after total knee arthroplasty, suggesting that analyses in such subjects are appropriate. However, the moving fluoroscope would likely need to be optimized in order to detect natural gait characteristics at the higher gait velocities of healthy young subjects. The moving fluoroscope can be applied for comparisons between groups measured with the moving fluoroscope, but care should be taken when comparing data to subjects walking at self-selected speed without the moving fluoroscope., PLoS ONE, 13 (7), ISSN:1932-6203

Videofluoroscopy has been shown to provide essential information in the evaluation of the functionality of total knee arthroplasties. However, due to the limitation in the field of view, most systems can only assess knee kinematics during highly restricted movements. To avoid the limitations of a static image intensifier, a moving fluoroscope has been presented as a standalone system that allows tracking of the knee during multiple complete cycles of level- and downhill-walking, as well as stair descent, in combination with the synchronous assessment of ground reaction forces and whole body skin marker measurements. Here, we assess the ability of the system to keep the knee in the field of view of the image intensifier. By measuring ten total knee arthroplasty subjects, we demonstrate that it is possible to maintain the knee to within 1.8 ± 1.4 cm vertically and 4.0 ± 2.6 cm horizontally of the centre of the intensifier throughout full cycles of activities of daily living. Since control of the system is based on real-time feedback of a wire sensor, the system is not dependent on repeatable gait patterns, but is rather able to capture pathological motion patterns with low inter-trial repeatability., PLoS ONE, 12 (10), ISSN:1932-6203

Background The posterior cruciate ligament (PCL) is the strongest ligament of the knee, serving as one of the major passive stabilizers of the tibio-femoral joint. However, despite a number of experimental and modelling approaches to understand the kinematics and kinetics of the ligament, the normal loading conditions of the PCL and its functional bundles are still controversially discussed. Objectives This study aimed to generate science-based evidence for understanding the functional loading of the PCL, including the anterolateral and posteromedial bundles, in the healthy knee joint through systematic review and statistical analysis of the literature. Data sources MEDLINE, EMBASE and CENTRAL Eligibility criteria for selecting studies Databases were searched for articles containing any numerical strain or force data on the healthy PCL and its functional bundles. Studied activities were as follows: passive flexion, flexion under 100N and 134N posterior tibial load, walking, stair ascent and descent, body-weight squatting and forward lunge. Method Statistical analysis was performed on the reported load data, which was weighted according to the number of knees tested to extract average strain and force trends of the PCL and identify deviations from the norms. Results From the 3577 articles retrieved by the initial electronic search, only 66 met all inclusion criteria. The results obtained by aggregating data reported in the eligible studies indicate that the loading patterns of the PCL vary with activity type, knee flexion angle, but importantly also the technique used for assessment. Moreover, different fibres of the PCL exhibit different strain patterns during knee flexion, with higher strain magnitudes reported in the anterolateral bundle. While during passive flexion the posteromedial bundle is either lax or very slightly elongated, it experiences higher strain levels during forward lunge and has a synergetic relationship with the anterolateral bundle. The strain patterns obtained for virtual fibres that connect the origin and insertion of the bundles in a straight line show similar trends to those of the real bundles but with different magnitudes. Conclusion This review represents what is now the best available understanding of the biomechanics of the PCL, and may help to improve programs for injury prevention, diagnosis methods as well as reconstruction and rehabilitation techniques.

Designing orthopaedic implants to reconstruct native anatomy and function continues to be a major challenge in the development of new products. This thesis provides insights and suggestions for designing next generation knee arthroplasty with a focus on native joint kinematics. Like in many other specialties, biomimetics is the ultimate objective in joint reconstruction. Knee arthroplasty is the most successful treatment option for severe osteoarthritis, providing patients with a reliable solution to relief pain and regain mobility. However, native joint function is not fully restored and for an aging population with growing interest in demanding activities, several limitations are present. Particularly, existing total knee arthroplasty (TKA) delivers kinematic deficits, associated with abnormal feeling of the knee, following joint surgery. These limitations are related to sacrificed ligaments, and none-anatomic geometries of current implant designs. Mostly, the anterior cruciate ligament (ACL) is sacrificed and its function is lost. Therefore, a biomimetic process was implemented to reverse engineer articular surfaces, by directly incorporating native knee kinematics. For the first aim, we designed a biomimetic implant that would preserve all major ligaments of the native knee joint. Therefore, an anatomically designed femoral component was virtually moved through native knee kinematics, to carve out a tibial articular surface, through the biomimetic process. This anatomical surface was incorporated into a novel implant, specifically designed to preserve the native ACL. For the second aim, we established a dynamic simulation platform to reliably evaluate implant design variations and the effect of ligaments. Knee kinematics, driven by ligament function and contacting implant geometry, allowed for comparison of different knee arthroplasty systems, against in vivo and simulated native knee motion. The first computational study revealed that a biomimetic, bi-cruciate retaining (BCR) implant provides activity dependent kinematics, similar to healthy knees in vivo, during deep knee bend, chair sit and level walking. This was in contrast to symmetric BCR systems, which nonetheless showed kinematic improvements over ACL-sacrificing implants. This indicates that restoring anatomic knee geometry together with ACL preservation is required for optimal implant function. The second computational study showed that a novel ACL-substituting mechanism could improve kinematic deficits of contemporary PCL-retaining (ACL-sacrificing) implants. ACL-substituting and ACL-retaining implants both provided similar improvements over the ACL-sacrificing implant in comparison to a native knee model. This was shown during walking, stair-ascent, chair-sit and deep knee bend simulations, indicating that ACL-substitution may be a valuable treatment option when ACL preservation is not feasible. For the third aim, we evaluated an extended treatment indication for unicompartmental knee arthroplasty (UKA), via in vivo kinematic analysis, using a moving fluoroscope. UKA is known for better functionality over TKA due to ACL retention and partial preservation of the native articulation. An ACL-deficient population, undergoing an altered surgical technique, with appropriate adaptation of implant placement, was compared against conventional UKA patients, with an intact ACL. The first in vivo study showed kinematic similarities between ACL-deficient and conventional UKA patients, in contrast to TKA. A posterior femoral shift was observed with ACL-deficient UKA, while kinematic trends and range of motion were similar during deep knee bend, downhill walking, level walking and stair descent. Based on kinematics, this confirms that the indication for UKA can be extended to include selected ACL-deficient patients. The second kinematic study revealed no differences in ground reaction forces between ACL-deficient and conventional UKA patients. Adequate kinematic and kinetic symmetries among implanted and contralateral leg indicate that UKA may not always be a contraindication due to ACL deficiency. In summary, this thesis outlines the importance of biomimetic implants for the objective of “forgotten knees”, following joint arthroplasty. Native knee function may be restored with anatomic geometries and ligament retention. Preservation or substitution of either the articular geometry or the ACL, results in kinematic improvements over conventional TKA. Long-term clinical outcome studies will be required for the ultimate proof of this concept.