Hendrik Delport

Collateral ligament strains during knee joint laxity evaluation before and after TKA

BACKGROUND Passive knee stability is provided by the soft tissue envelope. There is consensus among orthopedic surgeons that good outcome in Total Knee Arthroplasty requires equal tension in the medial/lateral compartment of the knee joint, as well as equal tension in the flexion/extension gap. The purpose of this study was to quantify the ligament laxity in the normal non-arthritic knee before and after Posterior-Stabilized Total Knee Arthroplasty. We hypothesized that the Medial/Lateral Collateral Ligament shows minimal changes in length when measured directly by extensometers in the native human knee during varus/valgus laxity testing. We also hypothesized that due to differences in material properties and surface geometry, native laxity is difficult to reconstruct using a Posterior-Stabilized Total Knee. METHODS Six specimens were used to perform this in vitro cadaver test using extensometers to provide numerical values for laxity and varus-valgus tilting in the frontal plane. FINDINGS This study enabled a precise measurement of varus-valgus laxity as compared with the clinical assessment. The strains in both ligaments in the replaced knee were different from those in the native knee. Both ligaments were stretched in extension, in flexion the Medial Collateral Ligament tends to relax and the Lateral Collateral Ligament remains tight. INTERPRETATION As material properties and surface geometry of the replaced knee add stiffness to the joint, we recommend to avoid overstuffing the joint, when using this type of Posterior-Stabilized Total Knee Arthroplasty, in order to obtain varus/valgus laxity close to the native joint.

Evaluation of Patient Specific Instruments. To measure is to know

Dear Mrs./Mr. With great interest we have read the comments in the Letter to the Editor concerning our article about Patient Specific Instrumentation. First, wewould like to ask if it would be possible to have the name of the author of the Letter to the Editor. It would be more polite if it would not be anonymous. It is stated that post-operative X-ray images are not an accurate measurement tool. However, the pre-operative planning is done, based on an MRI of the knee AND a full leg standing X-ray film. This same, standardized full legX-ray is used to evaluate the overallmechanical axis and its deviation from the pre-operative plan. As this is donewith the leg in a standardized position, the same way as used for the pre-operative planning, we believe that this is an accurate measurement tool for post-operative overall alignment evaluation of the leg. For the tibial slope however, a standardized lateral X-ray was used instead of a full leg lateral view. This was done for cost-saving reasons. Of course, in perspective of costs and irradiation, itwould not be possible to include a post-operative full leg MRI of CT of the leg. Moreover, this kind of examination is never performed in our hospital. The outcome results were indeed compared to the pre-operative planning: there was a standard pre-operative planning of mechanical alignment of the leg of 0° (hip–knee–ankle) in the frontal view and a 3° tibial slope. The outcome results of both study groupswere compared to this standard planning. In Table 6 of our study, it can be seen that the deviation of the actual versus the planned femoral angle was measured. Rotation of the femoral component however was not measured, as no CT-scans were taken post-operatively. It was the aim of our study to compare if the traditional or the PSI technique would give results, closest to the pre-operatively planned values. These results were clearly given in our study. It is stated that comparing postoperative results with the preoperative plan is not the same as evaluating surgical outcome. Of course this is true. But in our study, BOTHweredone, independently! OF COURSE all preoperative plans were created and validated by the surgeon himself. The radiographic outcomeswere compared versus the pre-operative plans and compared between both groups. Also, the functional outcome resultswere compared betweenboth groups, to evaluatewhether traditional instrumentation or PSI scored better, independently from the radiographic outcome. In your last paragraph, you assume that, by using modern technologies, the problem of 20–30% of dissatisfied patients after TKA would be solved! This looks very naive! The aim of studies like ours and the others you mentioned is to investigate if we can get to better results using those techniques. Of course, not every new technology will lead to better results! And if these new technologies are more expensive or more time consuming, their existence has to be questioned. We believe that there is a place for PSI in specific cases (eg posttraumatic, heavily deformed femurs, where no IM guide can be used). But there is no added value for the standard TKA. Also the clinical results are—so far—NOT better! It is our duty, as a researcher, to investigate if results are betterwith a newer technology, not to assume that it is! Sincerely yours, Bart Vundelinckx, MD.

Vibration-based fixation assessment of tibial knee implants: A combined in vitro and in silico feasibility study

The preoperative diagnosis of loosening of cemented tibial knee implants is challenging. This feasibility study explored the basic potential of a vibration-based method as an alternative diagnostic technique to assess the fixation state of a cemented tibia implant and establish the methods sensitivity limits. A combined in vitro and in silico approach was pursued. Several loosening cases were simulated. The largest changes in the vibrational behavior were obtained in the frequency range above 1500 Hz. The vibrational behavior was described with two features; the frequency response function and the power spectral density band power. Using both features, all experimentally simulated loosening cases could clearly be distinguished from the fully cemented cases. By complementing the experimental work with an in silico study, it was shown that loosening of approximately 14% of the implant surface on the lateral and medial side was detectable with a vibration-based method. Proximal lateral and medial locations on the tibia or locations toward the edge of the implant surface measured in the longitudinal direction were the most sensitive measurement and excitation locations to assess implant fixation. These results contribute to the development of vibration-based methods as an alternative follow-up method to detect loosened tibia implants.

Evaluation of predicted knee function for component malrotation in total knee arthroplasty

Soft-tissue balancing for total knee arthroplasty (TKA) remains subjective and highly dependent on surgical expertise. Pre-operative planning may support the clinician in taking decisions by integrating subject-specific computer models that predict functional outcome. However, validation of these models is essential before they can be applied in clinical practice. The aim of this study was to evaluate a knee modelling workflow by comparing experimental cadaveric measures to model-based kinematics and ligament length changes. Subject-specific models for three cadaveric knees were constructed from medical images. The implanted knees were mounted onto a mechanical rig to perform squatting, measuring kinematics and ligament length changes with optical markers and extensometers. Coronal malrotation was introduced using tibial inserts with a built-in slope. The model output agreed well with the experiment in all alignment conditions. Kinematic behaviour showed an average RMSE of less than 2.7mm and 2.3° for translations and rotations. The average RMSE was below 2.5% for all ligaments. These results show that the presented model can quantitatively predict subject-specific knee behaviour following TKA, allowing evaluation of implant alignment in terms of kinematics and ligament length changes. In future work, the model will be used to evaluate subject-specific implant position based on ligament behaviour.

Injuries of the Knee

The knee is one of the body parts most often injured. Sports, falls, and motor vehicle accidents account for the vast majority of injuries to the knee.

Patient-Specific Reconstruction of Large Bone Defects: Clinical Success Due to an Integrated Bioengineering Workflow

Surgical reconstruction of major acetabular defects (Paprosky type IIIb) in view of total hip replacement is a challenge. Existing systems have a documented failure rate between 20% and 50% at five years post-operatively. Our first hypothesis is that this limited success is due to the fact that standard components have to be adapted and assembled intraoperatively to provide a patient solution. Hence our second hypothesis is that a fully personalized solution for acetabular reconstruction will provide an added value for the patient’s outcome.

Postoperative 3D Analysis Based on X-Ray Images

This work presents the results of a postoperative analysis using X-rays images and shows that results reach the same order of accuracy than with CT image.Copyright