Oh-Ryong Kwon

Comparative Outcomes of Open-Wedge High Tibial Osteotomy With Platelet-Rich Plasma Alone or in Combination With Mesenchymal Stem Cell Treatment: A Prospective Study

PURPOSE This study compared the clinical results and second-look arthroscopic findings of patients undergoing open-wedge high tibial osteotomy (HTO) for varus deformity, with or without mesenchymal stem cell (MSC) therapy. METHODS This prospective, comparative observational study was designed to evaluate the effectiveness of MSC therapy. The patients were divided into 2 groups: HTO with platelet-rich plasma (PRP) injection only (n = 23) or HTO in conjunction with MSC therapy and PRP injection (n = 21). Prospective evaluations of both groups were performed using the Lysholm score, Knee Injury and Osteoarthritis Outcome Score (KOOS), and a visual analog scale (VAS) score for pain. Second-look arthroscopy was carried out in all patients at the time of metal removal. RESULTS The patients in the MSC-PRP group showed significantly greater improvements in the KOOS subscales for pain (PRP only, 74.0 ± 5.7; MSC-PRP, 81.2 ± 6.9; P < .001) and symptoms (PRP only, 75.4 ± 8.5; MSC-PRP, 82.8 ± 7.2; P = .006) relative to the PRP-only group. Although the mean Lysholm score was similarly improved in both groups (PRP only, 80.6 ± 13.5; MSC-PRP, 84.7 ± 16.2; P = .357), the MSC-PRP group showed a significantly greater improvement in the VAS pain score (PRP only, 16.2 ± 4.6; MSC-PRP, 10.2 ± 5.7; P < .001). There were no differences in the preoperative (PRP only, varus 2.8° ± 1.7°; MSC-PRP, varus 3.4° ± 3.0°; P = .719) and postoperative (PRP only, valgus 9.8° ± 2.4°; MSC-PRP, valgus 8.7° ± 2.3°; P = .678) femorotibial angles or weight-bearing lines between the groups. Arthroscopic evaluation, at plate removal, showed that partial or even fibrocartilage coverage was achieved in 50% of the MSC-PRP group patients but in only 10% of the patients in the PRP-only group (P < .001). CONCLUSIONS MSC therapy, in conjunction with HTO, mildly improved cartilage healing and showed good clinical results in some KOOS subscores and the VAS pain score compared with PRP only. LEVEL OF EVIDENCE Level II, prospective comparative study.

Biomechanical comparison of fixed- and mobile-bearing for unicomparmental knee arthroplasty using finite element analysis.

Unicomparmental knee arthroplasty (UKA) is a popular alternative to total knee arthroplasty (TKA) and high tibial osteotomy for unicompartmental knee conditions, especially in young patients. However, failure of UKA occurs due to either progressive osteoarthritis (OA) in the other compartment or wear on the polyethylene (PE) insert. This study used finite element (FE) analysis to investigate the effects of PE insert contact pressure and stress in opposite compartments for fixed‐ and mobile‐bearing UKA. Analysis was performed using high kinematics displacement and rotation inputs, which were based on the kinematics of the natural knee. ISO standards were used for axial load and flexion. The mobile‐bearing PE insert had lower contact pressure than the fixed‐bearing PE insert. With the mobile‐bearing UKA, lower stress on the opposite compartment reduces the overall risk of progressive OA in the knee. The fixed‐bearing UKA increases the overall risk of progressive OA in the knee due to higher stress on the opposite compartment. However, the PE insert of mobile‐bearing showed pronounced backside stress at the inferior surface.

Importance of joint line preservation in unicompartmental knee arthroplasty: Finite element analysis.

Unicompartmental knee arthroplasty (UKA) is an effective surgical technique for pain relief and functional restoration in patients with localized osteoarthritis of the knee joint. However, the role of the joint line in UKA, especially its biomechanical effect, has not been previously investigated. This study numerically evaluates the effects of the joint line on the contact stresses in polyethylene (PE) inserts, articular cartilage, and lateral meniscus using the finite element (FE) analysis. The FE model for joint line was modeled as the orthogonal projection line from the medial tibial plateau to the anatomical axis. The joint line was varied from −6 to +6 mm in 2 mm intervals, and the seven FE models were analyzed and compared under ISO gait loading conditions. The contact stresses in the PE insert, articular cartilage, and lateral meniscus matched those of the reference joint line (0 mm) in the ±2 and ±4 mm joint line cases but significantly differed from the reference in the ±6 mm joint line cases. On the +6 mm joint line, the contact stress was greater on the PE insert than on the articular cartilage, whereas the reverse occurred on the −6 mm joint line. This study confirms the post‐operative significance of joint line preservation in UKA implantation surgery.

Wear predictions for UHMWPE material with various surface properties used on the femoral component in total knee arthroplasty: a computational simulation study

The wear of ultrahigh-molecular weight polyethylene (UHMWPE) tibial inserts in total knee arthroplasty (TKA) remains a major limitation that hinders the longevity of clinically successful devices. Surface properties significantly affect the overall performance of TKA, and surface modification with mechanically and chemically stable materials is an effective method for overcoming the wear of TKA. However, wear tests are not cost-efficient or time-efficient; thus, the effects of geometric, loading, and alignment perturbations are often evaluated via parametric studies. Computational wear prediction using a finite element (FE) model followed by validation through comparison with experimental data is effective for assessing new prosthetic designs or surface change methods prior to functional testing and surgical implementation. The aim of this study was to evaluate the weight loss, wear depth, and kinematics for different surface properties, including nanostructured diamond (NSD), diamond-like carbon (DLC), titanium-nitride (TiN), and oxidized zirconium (OxZr) on femoral components in TKA using FE analysis under gait-cycle loading conditions. Weight loss and wear depth were lowest with OxZr followed by TiN, NSD, and DLC. However, the DLC femoral component did not show any improvement in wear rate compared to an uncoated cobalt–chromium (Co–Cr) femoral component. Not all surface changes applied in this study did lead to improvement in wear performance. However, this study demonstrates the potential of OxZr and TiN for reducing UHMWPE wear and offers new insights into the effects of wear on TKA.Graphical Abstract

The Effect of Femoral Cutting Guide Design Improvements for Patient-Specific Instruments

Although the application of patient-specific instruments (PSI) for total knee arthroplasty (TKA) increases the cost of the surgical procedure, PSI may reduce operative time and improve implant alignment, which could reduce the number of revision surgeries. We report our experience with TKA using PSI techniques in 120 patients from March to December 2014. PSI for TKA were created from data provided by computed tomography (CT) scans or magnetic resonance imaging (MRI); which imaging technology is more reliable for the PSI technique remains unclear. In the first 20 patients, the accuracy of bone resection and PSI stability were compared between CT and MRI scans with presurgical results as a reference; MRI produced better results. In the second and third groups, each with 50 patients, the results of bone resection and stability were compared in MRI scans with respect to the quality of scanning due to motion artifacts and experienced know-how in PSI design, respectively. The optimized femoral cutting guide design for PSI showed the closest outcomes in bone resection and PSI stability with presurgical data. It is expected that this design could be a reasonable guideline in PSI.

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.

Morphometry of femoral rotation for total knee prosthesis according to gender in a Korean population using three-dimensional magnetic resonance imaging

BACKGROUND We aimed to evaluate differences in femoral arthometric data for 700 osteoarthritic knees (587 females and 113 males) with respect to gender in a Korean population. METHODS We identified and measured the mediolateral (ML) and anteroposterior (AP) lengths, femoral aspect ratio (ML/AP), surgical epicondylar axis (SEA), and Whitesides line (WL). In addition, the anterior, posterior, and distal bone resections of the implanted femurs were evaluated using SEA and WL as references using a three-dimensional analysis method. RESULTS ML and AP lengths significantly differed according to gender. ML dimension and aspect ratio were greater in males than in females for a given AP dimension in the femur. No statistically significant differences in femoral rotation with SEA as a reference were observed between male and female knees; however, a significant difference was shown using WL as a reference and both affected the amount of bone resection irrespective of gender. CONCLUSION This study provides important guidelines for gender-specific femoral prosthesis design with different ML and AP aspect ratios and femoral rotation based on SEA and WL for Korean populations.

Femoral component alignment in unicompartmental knee arthroplasty leads to biomechanical change in contact stress and collateral ligament force in knee joint

BackgroundIn recent years, the popularity of unicompartmental knee arthroplasty (UKA) has increased. However, the effect of femoral component positioning in UKA continues to invite a considerable debate. The purpose of this study involved assessing the biomechanical effect of mal-alignment in femoral components in UKA under dynamic loading conditions using a computational simulation.MethodsA validated finite element model was used to evaluate contact stresses in polyethylene (PE) inserts and lateral compartment and force on collateral ligament in the femoral component ranging from 9° of varus to 9° of valgus.ResultsThe results indicated that contact stress on the PE insert increased with increases in the valgus femoral alignment when compared to the neutral position while contact stress on the lateral compartment increased with increases in the varus femoral alignment. The forces on medial and lateral collateral ligaments increased with increases in valgus femoral alignments when compared to the neutral position. However, there was no change in popliteofibular and anterior lateral ligaments with respect to the malpositioning of femoral component.ConclusionThe results of the study confirm the importance of conservation in post-operative accuracy of the femoral component since the valgus and varus femoral malalignments affect the collateral ligament and lateral compartment, respectively. Our results suggest that surgeons should avoid valgus malalignment in the femoral component and especially malalignment exceeding 9°, which may induce higher medial collateral ligament forces.

Effects of measurement methods for tibial rotation axis on the morphometry in Korean populations by gender

BACKGROUND There have been arguments for methodology in tibial rotation axis measurement, which accordingly determines the morphometry of the proximal tibia in total knee arthroplasty. The morphometry of the proximal tibia for the Korean population is determined by gender, based on the anatomical tibial axis and reliable rotational orientation in knee replacements, to evaluate the size suitability of the currently available prostheses in Korea. METHODS This study reconstructed the MRI images in three-dimensions for identification and measurement of the mediolateral (ML) and anteroposterior (AP) lengths of the proximal tibia and the tibial aspect ratio (ML/AP) using proximal tibial anthropometric data for 700 osteoarthritic knees (587 females and 113 males). The ML and AP lengths were measured using tibial rotation axis techniques based on the medial one-third tibial tubercle and Cobbs method. RESULTS Significant differences (P<0.05) in ML, medial anteroposterior (MAP), lateral anteroposterior (LAP) lengths, and aspect ratio (ML/LAP) were observed for males and females with respect to different measurement techniques for the tibial rotation axis. However, the measured aspect ratio (ML/MAP) of tibiae for the Korean population did not show significance. The measured aspect ratio (ML/AP) ratio of tibiae for the Korean population was higher than that of currently available tibial components. CONCLUSIONS Results from this study can guide development of gender-specific tibial prosthesis designs with different ML and AP aspect ratios based on the tibial anatomical rotation axis for the Korean population.

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.