Filip Leszko

Patellofemoral joint forces

In this review of patellofemoral joint forces as they might apply to implant design, methodologies for estimating forces on the patella and estimates of the forces, as reported in the literature, are summarized. Two methodologies exist for studying joint loads; one that measures kinematics in-vivo and uses analysis to estimate the joint loads and another that measures ground reaction forces and uses analysis to estimate the joint loads. In both these analyses many assumptions are required with varying degrees of uncertainty; here, those assumptions are examined with data from the published literature. The topics covered include: relationships between quadriceps forces and patellofemoral forces or patella ligament forces, relationships between knee joint moments and quadriceps forces, knee joint moments in various gaits, relationships between patellofemoral forces and lateral subluxation forces, and relationships between patella forces and inferior-superior forces. In many cases, there is little data on patella forces during normal activities, in other cases, there are some discrepancies in reported patella forces, i.e. during squat.

In Vivo Normal Knee Kinematics: Is Ethnicity or Gender an Influencing Factor?

BackgroundIn vivo studies have suggested Caucasians achieve lower average knee flexion than non-Western populations. Some previous studies have also suggested gender may influence condylar AP translation and axial rotation, while others report an absence of such an influence.Questions/purposesWe determined whether different ethnic and gender groups residing in the United States had different knee translations and rotations.MethodsThree-dimensional knee rotations and translations were determined for 72 healthy subjects (24 Caucasian men, 24 Caucasian women, 13 Japanese men, 11 Japanese women) from full extension to maximum flexion using a fluoroscopic technique, under in vivo, weightbearing conditions.ResultsAlthough we observed substantial variability in all groups, small differences between groups were found, especially in deep flexion. Japanese women and men and Caucasian women achieved higher maximum flexion (153°, 151°, and 152°, respectively) than Caucasian men (146°). External rotation was higher for these three groups than for Caucasian men. The medial condyle remained more anterior for Caucasian women and all Japanese subjects than for Caucasian men, possibly leading to greater axial rotation and flexion, observed for these three groups.ConclusionWe identified small differences in maximum flexion between genders and ethnic groups. While no differences were identified in the lateral condyle translation, the medial condyle remained more stationary and more anterior for the groups that achieved highest (and similar) maximum flexion. Therefore, it may be important for future implant designs to incorporate these characteristics, such that only the lateral condyle experiences greater posterior femoral rollback, while the medial condyle remains more stationary throughout flexion.

In Vivo Kinematics of the Salto Total Ankle Prosthesis

Background: Recent technological advancements in total ankle arthroplasty (TAA) have included the introduction of the mobile bearing concept. This bearing has several advantages, but researchers have questioned whether or not increased mobility sacrifices joint stability or durability of the implant. The present study evaluated the kinematics of this type of prosthesis implanted in patients. Materials and Methods: Fluoroscopy and 3D-to-2D registration techniques were used to determine the in vivo kinematics for 20 TAA subjects performing two activities: gait and step-up. The motion of the prostheses was described in terms of clinical rotations and as rotation about the helical (screw) axis. Then, the anterior-posterior translation and axial rotation of the mobile bearing insert were determined. Results: Among the clinical rotations, the dorsi-/plantarflexion was the most dominant, revealing the greatest pattern change and the largest magnitude. During gait, the orientation of the prosthetic components changed smoothly from plantarflexion to dorsiflexion. The average range of this motion was 9.2 degrees. For step-up activity, the range was 8.0 degrees. However, between 33% and 66% of stance phase, the talar components orientation changed from dorsiflexion to plantarflexion. The average absolute range of anterior-posterior translation of the mobile bearing insert was 1.5 mm and 2.3 mm for gait and step-up, respectively. Conclusion: These measured translations were relatively small and may suggest that the rotational portion of the motion was more dominant than translational and provided sufficient mobility. Level of Evidence: IV, Retrospective Case Series

Comparison of In Vivo Patellofemoral Kinematics for Subjects Having High-Flexion Total Knee Arthroplasty Implant With Patients Having Normal Knees

This study compares the in vivo patellar kinematics of high-flexion posterior cruciate ligament-retaining and posterior-stabilized total knee arthroplasty (TKA) implants with that of the healthy knee. Twenty-seven subjects performing weight-bearing deep knee bends were analyzed under fluoroscopic surveillance from full extension to maximum flexion. The patellofemoral contact positions and patellar flexion were similar for both TKAs. At low flexion, the patellofemoral contact was significantly more distal on the healthy patella than on the TKA patella, but in deeper flexion, there was no difference among the 3 groups. The tibiopatellar angle was similar for all 3 groups, except at deep flexion where the healthy patella rotated significantly more than the implanted ones. Patellofemoral separation was observed in some TKA knees, whereas it was absent in the healthy knees.

In Vivo Determination of Cam-Post Engagement in Fixed and Mobile-bearing TKA

BackgroundKinematics vary, sometimes in important ways, among the different types of total knee arthroplasty (TKA) designs, yet differences between the in vivo mechanisms of cam-post engagement in rotating-platform posterior-stabilized (PS) TKA, bicruciate-stabilized TKA, and fixed-bearing PS TKA designs remain largely uncharacterized.Questions/purposesThe objective of this study was to determine the cam-post mechanism interaction for subjects implanted with three different TKA designs.MethodsIn vivo, analysis was conducted for patients implanted with nine rotating-platform PS TKAs, five knees with a fixed-bearing PS TKA, and 10 knees with a bicruciate-stabilized TKA while performing a deep knee bend. Three-dimensional kinematics of the implant components were determined by analysis of fluoroscopic images during flexion. The distances between the interacting surfaces were measured throughout flexion and instances and locations of contact were identified.ResultsSeven of the 10 bicruciate-stabilized knees analyzed had the femoral component engaged with the anterior aspect of the tibial post at full extension. Posterior cam-post engagement occurred at 34° for the bicruciate-stabilized (range, 17°–68°), 93° for the fixed-bearing PS (range, 88°–100°), and at 97° (range, 90°–104°) for rotating-platform PS TKA. In bicruciate-stabilized and fixed-bearing PS knees, the contact initially occurred on the medial aspect of the posterior surface of the tibial post and then moved centrally and superiorly with increasing flexion. For rotating-platform PS TKA, it was located centrally on the posterior surface of the post at all times.ConclusionsThis study suggests that mobility of the polyethylene might play an important role in ensuring central cam-post interaction in PS TKA. The polyethylene insert rotates axially in accordance with the rotating femur, maintaining central cam-post contact. This phenomenon was not observed in the fixed-bearing PS TKAs analyzed in this study.Clinical RelevanceWe speculate that this centralized symmetrical contact between the cam and posterior surface of the post could be beneficial clinically in terms of reducing wear of the posterior surface and particularly at the medial extremes of it.Level of EvidenceLevel III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.