Sae Kwang Kwon

The increase in posterior tibial slope provides a positive biomechanical effect in posterior-stabilized total knee arthroplasty

PurposeThis study aims to clarify the influence of the posterior tibial slope (PTS) on knee joint biomechanics after posterior-stabilized (PS) total knee arthroplasty (TKA) using a computer simulation.MethodsA validated TKA computational model was used to evaluate and quantify the effects of an increased PTS. In order to conduct a squat simulation, models with a − 3° to 15° PTS using increments of 3° were developed. Forces on the quadriceps and collateral ligament, a tibial posterior translation, contact point on a polyethylene (PE) insert, and contact stress on the patellofemoral (PF) joint and post in a PE insert were compared.ResultsThe maximum force on the quadriceps and the PF contact stress decreased with increases in the PTS. The kinematics on the tibiofemoral (TF) joint translated in an increasingly posterior manner, and the medial and lateral contact points on a PE insert were located in posterior regions with increases in the PTS. Additionally, increases in the PTS decreased the force on the collateral ligament and increased the contact stress on the post in a PE insert. A higher force on the quadriceps is required when the PTS decreases with an equivalent flexion angle.ConclusionsA surgeon should be prudent in terms of determining the PTS because an excessive increase in the PTS may lead to the progressive loosening of the TF joint due to a reduction in collateral ligament tension and failure of the post in a PE insert. Thus, we support a more individualized approach of optimal PTS determination given the findings of the study.

The impact of generalized joint laxity on clinical outcomes of total knee arthroplasty

PurposeThe aim of this study was to investigate whether the severity of generalized joint laxity influences preoperative and postoperative clinical outcomes and if patients with severe generalized joint laxity would require a thicker polyethylene (PE) liner during total knee arthroplasty (TKA).MethodsA total of 338 female patients undergoing TKA were divided into two groups according to generalized joint laxity. Preoperative and postoperative (at 3 years) patellofemoral scale, AKS, WOMAC, ROM, and satisfaction VAS were compared between the two groups. Additionally, PE liner thickness was compared.ResultsPreoperatively, flexion contracture and WOMAC stiffness scores in the severe laxity group were significantly lower than those in the no to moderate laxity group (p < 0.001 for both). There was no significant difference in postoperative clinical outcomes of patellofemoral scale, AKS, WOMAC, or ROM or in satisfaction VAS between the two groups. There was a significant difference in PE liner thickness between the two groups (10.3 ± 1.3 versus 11.4 ± 1.2, p = 0.043).ConclusionsThere was no significant difference of clinical outcomes between the patients with and without severe generalized joint laxity after 3 years of follow-up after TKA, even though preoperative clinical outcomes indicated that the patients with severe generalized joint laxity showed significantly smaller flexion contraction and better WOMAC stiffness score. Since patients with generalized joint laxity require a thicker PE liner, care should be taken to avoid cutting too much bone from patients with severe generalized joint laxity.Level of evidenceRetrospective comparative study, Level III.

Biomechanical Effects of Posterior Condylar Offset and Posterior Tibial Slope on Quadriceps Force and Joint Contact Forces in Posterior-Stabilized Total Knee Arthroplasty

This study aimed to determine the biomechanical effect of the posterior condylar offset (PCO) and posterior tibial slope (PTS) in posterior-stabilized (PS) fixed-bearing total knee arthroplasty (TKA). We developed ±1, ±2, and ±3 mm PCO models in the posterior direction and −3°, 0°, 3°, and 6° PTS models using a previously validated FE model. The influence of changes in the PCO and PTS on the biomechanical effects under deep-knee-bend loading was investigated. The contact stress on the PE insert increased by 14% and decreased by 7% on average as the PCO increased and decreased, respectively, compared to the neutral position. In addition, the contact stress on post in PE insert increased by 18% on average as PTS increased from −3° to 6°. However, the contact stress on the patellar button decreased by 11% on average as PTS increased from −3° to 6° in all different PCO cases. The quadriceps force decreased by 14% as PTS increased from −3° to 6° in all PCO models. The same trend was found in patellar tendon force. Changes in PCO had adverse biomechanical effects whereas PTS increase had positive biomechanical effects. However, excessive PTS should be avoided to prevent knee instability and subsequent failure.

Is Electrocautery of Patella Useful in Patella Non-Resurfacing Total Knee Arthroplasty?: A Prospective Randomized Controlled Study

There is controversy over the need for electrocauterization of the patella in non-resurfacing total knee arthroplasty (TKA). We investigated whether this procedure is beneficial through a prospective randomized controlled trial. Fifty patients who underwent electrocautery were compared with 50 patients who did not undergo this procedure. We determined cartilage status, preoperative and postoperative American Knee Society (AKS) score, the Western Ontario and McMaster Universities score (WOMAC) and the Patellofemoral (PF) scores for a minimum of 5 years. The two groups did not differ significantly in demographics, intraoperative cartilage status, or preoperative or postoperative outcomes. No complications were detected in either group. We found no benefits of electrocautery of the patella in patellar non-resurfacing TKA up to 5 years.

Effect of femoral component position on biomechanical outcomes of unicompartmental knee arthroplasty.

BACKGROUND The positions of unicompartmental femoral components do not always follow the neutral center of the medial distal femoral condyle. The biomechanical effect of the center of the distal femoral condyle has not yet been evaluated, and the optimal femoral position in unicompartmental knee arthroplasty (UKA) is yet to be biomechanically justified. The purpose of this study was to evaluate, using finite element analysis, the effect of the center of the distal femoral component on the biomechanical outcomes of UKA with respect to the contact stresses in the polyethylene (PE) insert and articular cartilage. METHODS Five models in which the centers of the distal femoral components were translated by three millimeters and five millimeters to the medial and lateral sides, respectively, from the neutral position were modeled and analyzed in a gait loading condition. RESULTS The contact stresses on the PE insert increased as the center of the femoral component translated to the lateral side and, in contrast, the contact stresses decreased as it translated to the medial side. For the articular cartilage the contact stresses increased and decreased as the center of the femoral component translated to the medial and lateral sides. CONCLUSION This study implied that the best position for the femoral component in UKA could be the center of the distal femoral condyle. Femoral component position could be one of the sensitive factors that influenced the contact stresses on the PE insert and articular cartilage, and the postoperative significance of the femoral component position in UKA.

Effects of posterior condylar offset and posterior tibial slope on mobile-bearing total knee arthroplasty using computational simulation

BACKGROUND Postoperative changes of the femoral posterior condylar offset (PCO) and posterior tibial slope (PTS) affect the biomechanics of the knee joint after fixed-bearing total knee arthroplasty (TKA). However, the biomechanics of mobile-bearing is not well known. Therefore, the aim of this study was to investigate whether alterations to the PCO and PTS affect the biomechanics for mobile-bearing TKA. METHODS We used a computational model for a knee joint that was validated using in vivo experiment data to evaluate the effects of the PCO and PTS on the tibiofemoral (TF) joint kinematics, patellofemoral (PF) contact stress, collateral ligament force and quadriceps force, for mobile-bearing TKA. The computational model was developed using ±1-, ±2- and ±3-mm PCO models in the posterior direction and -3°, 0°, +3°, and +6° PTS models based on each of the PCO models. RESULTS The maximum PF contact stress, collateral ligament force and quadriceps force decreased as the PTS increased. In addition, the maximum PF contact stress and quadriceps force decreased, and the collateral ligament force increased as PCO translated in the posterior direction. This trend is consistent with that observed in any PCO and PTS. CONCLUSIONS Our findings show the various effects of postoperative alterations in the PCO and PTS on the biomechanical results of mobile-bearing TKA. Based on the computational simulation, we suggest that orthopaedic surgeons intraoperatively conserve the patients own anatomical PCO and PTS in mobile-bearing TKA.

Multi-objective design optimization of high tibial osteotomy for improvement of biomechanical effect by using finite element analysis: DESIGN OPTIMIZATION OF HTO USING FINITE ELEMENT ANALYSIS

Medial opening wedge high tibial osteotomy (HTO) makes the proximal tibia a highly unstable structure and causes plates and screws to be the potential sources for mechanical failure. However, asymmetrical callus and incomplete bone formations underneath the plates (TomoFix) have been recent concerns in clinical and experimental studies related to HTO due to the high stiffness. The purpose of this study was to evaluate the biomechanical effect of the TomoFix plate system with respect to changes in design using a computational simulation. A parametric three‐dimensional model of HTO was constructed from medical image data. The design parameters for the HTO plate were evaluated to investigate their influence on biomechanical effects, and the most significant factors were determined using Taguchi‐style L27 orthogonal arrays. Multi‐objective optimization was used to identify the wedge micromotion stability without the stress shielding effect that occurs in the bone plate. The initial design showed that the high stiffness of the plate caused stress shielding on the bone and plate. However, the optimal design led to sharing the stress and load with the bone plate to eliminate stress shielding. In addition, the stability required for the plate could be found in the micromotions of the wedge for the optimal design. The optimal condition of design parameters was successfully determined using the Taguchi and multi‐objective optimization method, which was shown to eliminate stress shielding effects. The results showed that an optimal design demonstrated the feasibility of design optimization and improvements in biomechanical stability for HTO.

Effect of Post-Cam Design for Normal Knee Joint Kinematic, Ligament, and Quadriceps Force in Patient-Specific Posterior-Stabilized Total Knee Arthroplasty by Using Finite Element Analysis

The purpose of this study is to investigate post-cam design via finite element analysis to evaluate the most normal-like knee mechanics. We developed five different three-dimensional computational models of customized posterior-stabilized (PS) total knee arthroplasty (TKA) involving identical surfaces with the exception of the post-cam geometry. They include flat-and-flat, curve-and-curve (concave), curve-and-curve (concave and convex), helical, and asymmetrical post-cam designs. We compared the kinematics, collateral ligament force, and quadriceps force in the customized PS-TKA with five different post-cam designs and conventional PS-TKA to those of a normal knee under deep-knee-bend conditions. The results indicated that femoral rollback in curve-and-curve (concave) post-cam design exhibited the most normal-like knee kinematics, although the internal rotation was the closest to that of a normal knee in the helical post-cam design. The curve-and-curve (concave) post-cam design showed a femoral rollback of 4.4 mm less than the normal knee, and the helical post-cam design showed an internal rotation of 5.6° less than the normal knee. Lateral collateral ligament and quadriceps forces in curve-and-curve (concave) post-cam design, and medial collateral ligament forces in helical post-cam design were the closest to that of a normal knee. The curve-and-curve (concave) post-cam design showed 20% greater lateral collateral ligament force than normal knee, and helical post-cam design showed medial collateral ligament force 14% greater than normal knee. The results revealed the variation in each design that provided the most normal-like biomechanical effect. The present biomechanical data are expected to provide useful information to improve post-cam design to restore normal-like knee mechanics in customized PS-TKA.

Comparison of Kinematics in Cruciate Retaining and Posterior Stabilized for Fixed and Rotating Platform Mobile-Bearing Total Knee Arthroplasty with respect to Different Posterior Tibial Slope

Reconstructed posterior tibial slope (PTS) plays a significant role in kinematics restoration after total knee arthroplasty (TKA). However, the effect of increased and decreased PTS on prosthetic type and design has not yet been investigated. We used a finite element model, validated using in vitro data, to evaluate the effect of PTS on knee kinematics in cruciate-retaining (CR) and posterior-stabilized (PS) fixed TKA and rotating platform mobile-bearing TKA. Anterior-posterior tibial translation and internal-external tibial rotation were investigated for PTS ranging from -3° to 15°, with increments of 1°, for three different designs of TKA. Tibial posterior translation and external rotation increased as the PTS increased in both CR and PS TKAs. In addition, there was no remarkable difference in external rotation between CR and PS TKAs. However, for the mobile-bearing TKA, PTS had less effect on the kinematics. Based on our computational simulation, PTS is the critical factor that influences kinematics in TKA, especially in the CR TKA. Therefore, the surgeon should be careful in choosing the PTS in CR TKAs.