UKA假体后倾角安装位置对衬垫磨损的影响

目的 研究单髁膝关节置换(unicompartmental knee arthroplasty, UKA)假体不同后倾角度安装对膝关节承载、运动及衬垫磨损的影响。方法 联合UKA骨肌多体动力学模型、有限元模型和磨损模型,分析固定式UKA假体5种后倾角安装位置情况对术后膝关节力和运动、衬垫接触应力、线性磨损深度和体积磨损量的影响。结果 后倾角0°时,衬垫的最大von Mises等效应力为24.84 MPa,接触应力为47.61 MPa, 5百万次循环(million cycle, MC)周期的磨损量为47.29 mm³。随着UKA胫骨假体后倾角的增加,步态周期内旋和后移运动均增大,摆动相的内侧关节力增大,5 MC磨损周期后衬垫von Mises等效应力与接触应力显著减小,衬垫的磨损面积、最大线性磨损深度和体积磨损量随之减少。相对于后倾角0°,后倾角为3°、5°、7°时衬垫的线性磨损深度分别减小了17.8%、19.2%、20.6%;衬垫体积磨损量分别下降了24.5%、30.9%、34.3%。结论 UKA假体考虑后倾角安装超过3°时会显著增加步态周期内旋运动和后移运动,...     

Effects of tibial slope changes in the stability of fixed bearing medial unicompartmental arthroplasty in anterior cruciate ligament deficient knees

Patients with anterior cruciate ligament (ACL) deficiency may have increased failure rates with UKA as a result of abnormal contact stresses and altered knee kinematics. Variations in the slope of the tibial component in UKA may alter tibiofemoral translation, and affect outcomes. This cadaveric study evaluated tibiofemoral translation during the Lachman and pivot shift tests after changing the slope of a fixed bearing unicondylar tibial component. Sectioning the ACL increased tibiofemoral translation in both the Lachman and pivot shift tests (P<0.05). Tibial slope leveling (decreasing the posterior slope) of the polyethylene insert in a UKA decreases anteroposterior tibiofemoral translation in the sagittal plane to a magnitude similar to that of the intact knee. With 8° of tibial slope leveling, anterior tibial translation during the Lachman test decreased by approximately 5mm. However, no variation in slope altered the pivot shift kinematics in the ACL deficient knees.     

单髁置换术应用于骨关节炎合并前交叉韧带缺失的三维有限元研究

目的采用有限元方法比较前交叉韧带(anterior cruciate ligament,ACL)完整与缺失的骨关节炎患者单髁关节置换(unicompartmental knee arthroplasty,UKA)术后膝关节生物力学特性,分析ACL缺失对膝关节单髁置换术后的运动和应力的影响。方法根据膝关节CT、MRI图像,建立有限元模型。采用逆向工程技术重建活动衬垫单髁假体,加载入该正常膝关节三维有限元模型。在不同屈膝角度(0°、30°、60°、90°、120°)加载载荷,观察在ACL完整(ACL-intact,ACLI)和缺失(ACL-deficiency,ACLD)情况下,膝关节的最大接触压和位移程度。结果 UKA-ACLI与UKA-ACLD模型在膝关节屈膝各角度,各部位(外侧股骨软骨、胫骨软骨、半月板、股骨假体、胫骨假体、衬垫)最大应力无明显差异,ACLD模型在膝关节屈膝0°和30°位前后位移明显大于ACLI模型,在膝关节屈膝0°位股骨相对内旋减小,在膝关节屈膝30°位股骨相对外旋增加。结论标准位置假体植入情况下,ACL缺失并不会导致UKA术后应力异常增大,会导致在膝关节伸直位时位移增加。     

Differences in impact on adjacent compartments in medial unicompartmental knee arthroplasty versus high tibial osteotomy with identical valgus alignment

BackgroundIt is unclear why medial unicompartmental knee arthroplasty (UKA) with postoperative valgus alignment causes adjacent compartment osteoarthritis more often than high tibial osteotomy (HTO) for moderate medial osteoarthritis of the knee with varus deformity. This study used a computer simulation to evaluate differences in knee conditions between UKA and HTO with identical valgus alignment.MethodsDynamic musculoskeletal computer analyses of gait were performed. The hip–knee–ankle angle in fixed-bearing UKA was changed from neutral to 7° valgus by changing the tibial insert thickness. The hip–knee–ankle angle in open-wedge HTO was also changed from neutral to 7° valgus by opening the osteotomy gap.ResultsThe lateral tibiofemoral contact forces in HTO were larger than those in UKA until moderate valgus alignments. However, the impact of valgus alignment on increasing lateral forces was more pronounced in UKA, which ultimately demonstrated a larger lateral force than HTO. Valgus alignment in UKA caused progressive ligamentous tightness, including that of the anterior cruciate ligament, resulting in compression of the lateral tibiofemoral compartment. Simultaneously, patellofemoral shear forces were slightly increased and excessive external femoral rotation against the tibia occurred due to the flat medial tibial insert surface and decreased lateral compartment congruency. By contrast, only lateral femoral slide against the tibia occurred in excessively valgus-aligned HTO.ConclusionsIn contrast to extra-articular correction in HTO, which results from opening the osteotomy gap, intra-articular valgus correction in UKA with thicker tibial inserts caused progressive ligamentous tightness and kinematic abnormalities, resulting in early osteoarthritis progression into adjacent compartments.     

膝关节单髁置换术胫骨假体不同后倾角对假体磨损和功能的影响

目的 建立单髁置换术胫骨假体后倾3°和7°膝关节不同屈膝角度三维有限元模型,研究两种后倾角膝关节生物力学特性和假体磨损及其对功能的影响.方法 结合人体膝关节CT与MRI图像和第3代Oxford假体,建立胫骨假体后倾3°和7°下屈膝单髁置换术有限元模型,在股骨内外侧髁中心点上施加1 kN载荷模拟人体站立相负重,分析不同屈...     

External rotation of the tibial component should be avoided in lateral unicompartmental knee arthroplasty

BackgroundLateral unicompartmental knee arthroplasty (UKA) leads to good clinical outcomes for isolated lateral osteoarthritis. However, the impact of the tibial component position on postoperative outcomes in lateral UKA is yet to be determined.PurposeThis study investigated the influence of tibial component malposition on clinical outcomes in lateral UKA.MaterialsThis was a retrospective study of 50 knees (mean age 73.5 years) who underwent lateral UKA between September 2013 and January 2019. The Oxford Knee Score (OKS), Knee Society Score – Knee (KSSK), and Knee Society Score – Function (KSSF) were evaluated. The coronal alignment, posterior slope of tibial component, tibial component rotation relative to Akagi’s line (angle α), and femoral anteroposterior (AP) axis (angle β) were measured postoperatively. The average follow up period was 2.3 (range, 1–4.9) years.ResultsClinical scores were significantly improved after lateral UKA. The mean coronal alignment was 0.9° ± 3.2° varus (range, 9.1° varus to 5.5° valgus), the mean posterior slope was 6.8° ± 3.8° (range, 0.8° to 14.8°). The mean α and β angles, were 4.1° ± 5.8° (range, −9.7° to 16.5°) and 6.7° ± 7.1° (range, −7.0° to 20.5°) external rotation. The angle α had significant negative correlations with postoperative OKS (r = −0.36), KSSK (r = −0.28), and KSSF (r = −0.39), and angle β had significant negative correlations with postoperative OKS (r = −0.34) and KSSK (r = −0.46).ConclusionExcessive external rotation of the tibial component could negatively influence the postoperative outcomes of lateral UKA.     

Catastrophic failure of biconcave unicompartmental polyethylene bearings

BackgroundA biconcave polyethylene (PE) bearing was developed for mobile-bearing unicompartmental knee arthroplasties (UKA) to reduce PE dislocation.MethodsA modification of the BalanSys Unicompartmental knee system with a biconcave PE and convex tibial component was used in 32 prostheses in 28 patients. Clinical outcomes and five cases of PE fracture are reported and extensively analyzed ex vivo.ResultsVisual Analogue Score of pain and satisfaction, and Knee Society Scores improved for all patients. The passive range of motion was 130°. No PE bearings dislocated. Five bearings fractured with oxidation, cracking and delamination at the thinnest central region of the PE. The combination of increased stress and decreased poly thickness was associated with increased creep. PE oxidation caused embrittlement and contributed to fractures in the thin waist of the implant.ConclusionsThe unforeseen consequence of a novel design of a UKA that resulted in a specific mechanical and tribological mode of failure is reported. We conclude the PE failed due to a biconcave design that increased stress on the implant at its region of risk combined with a decrease of the polyethylene thickness by 1 mm in the central area.     

单髁置换胫骨假体后倾角对关节接触应力影响

目的 建立活动平台膝关节单髁置换(mobile-bearing unicompartmental knee arthroplasty, MB-UKA)术前、术后膝关节有限元模型,研究MB-UKA胫骨假体后倾角对关节接触应力影响。方法 基于健康受试者计算机断层(computed tomography, CT)及磁共振(magnetic resonance, MR)影像,构建健康膝关节有限元模型,并验证MB-UKA术前、术后模型的有效性。模拟MB-UKA胫骨假体后倾7°手术,将三维运动捕捉系统及力平台相关参数作为有限元模型输入条件,分别计算外侧间室胫骨平台软骨和聚乙烯衬垫的最大接触应力。结果 与现有文献结果进行对比验证表明,健康膝关节和MB-UKA术后膝关节有限元模型计算结果较为合理。MB-UKA术后胫股关节接触应力变化较大,聚乙烯衬垫接触应力远大于对侧间室胫骨平台软骨接触应力。结论 本文所建MB-UKA术前、术后有限元模型较为合理。研究结果为MB-UKA的评估提供了一个可参考的方法。     

How does the inclination of the tibial component matter? A three-dimensional finite element analysis of medial mobile-bearing unicompartmental arthroplasty

Background

Medial unicompartmental knee arthroplasty (UKA) using Oxford mobile-bearing prosthesis is performed in the treatment of medial compartmental arthritis of the knee. However, little is known about the stress distributions for mobile-bearing UKA on the medial tibial plateau.

Ipsilateral ACL injured patients with Segond fractures demonstrate increased posterior tibial slope

BackgroundThe anterolateral complex has been demonstrated to assist with rotational stability and prevention of anterior tibial translation during the pivot shift. In this study the Segond fracture is used as a surrogate for an anterolateral complex injury to determine if there is an association between Segond fracture and increased posterior tibial slope.MethodsPatients’ charts and radiographs were analyzed retrospectively for the presence of Segond fractures on injury radiographs. These patients, the Segond cohort, were then age and gender matched to a control cohort. Demographic as well MRI measurements of medial and lateral posterior tibial slope and lateral-to-medial slope asymmetry were collected for each cohort. Secondary outcome of anterior cruciate ligament reconstruction failure data was also collected.ResultsThe Segond group demonstrated a statistically significantly greater lateral posterior tibial slope (8.42° versus 6.55°, P = 0.003) as well as medial posterior tibial slope (6.57° versus 5.34° degrees, P = 0.045). There was no significant differences between lateral-to-medial asymmetry (2.18°versus 1.83°, P = 0.246).ConclusionPatients with Segond fractures at the time of anterior cruciate ligament injury have increased medial and lateral posterior tibial slope. This may relate to increased rotational and translational instability associated with anterolateral complex injuries. Surgeons treating these patient may use this information to counsel their patients on the risks of associated pathology at the time of arthroscopy such as lateral meniscal posterior root tears.     

Influence of cartilage and menisci on the sagittal slope of the tibial plateaus

We analyzed the magnetic resonance studies of the knee in 80 subjects, 45 men and 35 women with a mean age of 38.9 years, who showed no pathological condition of the joint. Using an imaging visualization software, the sagittal longitudinal axis of the tibia was identified. The angle between this axis and a line tangent to the bone profile of the tibial plateau (bone slope) and to the superior border of the menisci (meniscal slope) were calculated. Thickness of anterior and posterior portion of menisci and underlying cartilage were also measured. The bone slope averaged 8° and 7.7° on the medial and lateral sides, respectively. The mean meniscal slope was 4.1° and 3.3° on the medial and lateral sides, respectively, with a significant difference compared with the bone slope. Menisci and underlying cartilage were significantly thicker in their posterior than their anterior portion (7.6 and 5.2 mm, respectively, in the medial compartment; 8.6 and 5.2 mm, respectively, in the lateral compartment). The presence of cartilage and menisci implies a significant decrease in the posterior tibial slope. In the lateral compartment, the greater the bone slope, the larger the difference between bone and meniscal slope, which means that a marked posterior tilt of the lateral tibial plateau is decreased by the cartilage and meniscus. These findings should be taken into account in planning surgical procedures which affect the slope of the articular tibial surface. Clin. Anat. 26:883–892, 2013. © 2012 Wiley Periodicals, Inc.     

Achievement of Targeted Posterior Slope in the Medial Opening Wedge High Tibial Osteotomy: A Mathematical Approach

High tibial osteotomy (HTO) for medial compartment knee osteoarthritis is preferred in the activity patient since it allows patients to return to sports and recreational activities similar to the preoperative level. The purpose of this study was to mathematically formulate medial and anteromedial opening gaps in the medial opening wedge HTO to achieve a targeted tibial posterior slope. The change of posterior slope angle was mathematically derived in terms of the medial and anteromedial opening gaps, and the medial opening angles. The derived equations were validated by comparing them with those directly measured by performing simulated HTOs. In the triangular geometries of osteotomy planes, measured from three-dimensional osteotomy models of 30 knee patients, the mean anteromedial, medial, and lateral included angles were 92.4°, 53.9°, and 33.7°, respectively, and the mean lateral–medial edge length was 53.3 mm. The ratio of the anteromedial opening gap to the posterior opening gap should be “sin(the medial included angle) × cos(the lateral included angle)/sin(the anteromedial included angle)” to maintain an intact posterior tibial slope angle. With the derived equations, surgeons can estimate the opening gaps and opening angles to get a targeted posterior tibial slope with a medial opening angle.     

Finite element analysis of unicompartmental knee arthroplasty

Concerns over accelerated damage to the untreated compartment of the knee following unicompartmental knee arthroplasty (UKA), as well as the relatively poor success rates observed for lateral as opposed to the medial arthroplasty, remain issues for attention. Finite element analysis (FEA) was used to assess changes to the kinematics and potential for cartilage damage across the knee joint in response to the implantation of the Oxford Mobile Bearing UKA. FE models of lateral and medial compartment arthroplasty were developed, in addition to a healthy natural knee model, to gauge changes incurred through the arthroplasty. Varus–valgus misalignments were introduced to the femoral components to simulate surgical inaccuracy or over-correction. Boundary conditions from the Stanmore knee simulator during the stance phase of level gait were used. AP translations of the tibia in the medial UKA models were comparable to the behaviour of the natural knee models (±0.6 mm deviation from pre-operative motion). Following lateral UKA, 4.1 mm additional posterior translation of the tibia was recorded than predicted for the natural knee. IE rotations of the medial UKA models were less consistent with the pre-operative knee model than the lateral UKA models (7.7° vs. 3.6° deviation). Varus misalignment of the femoral prosthesis was more influential than valgus for medial UKA kinematics, whereas in lateral UKA, a valgus misalignment of the femoral prosthesis was most influential on the kinematics. Resection of the cartilage in the medial compartment reduced the overall risk of progressive OA in the knee, whereas removing the cartilage from the lateral compartment, and in particular introducing a valgus femoral misalignment, increased the overall risk of progressive OA in the knee. Based on these results, under the conditions tested herein, both medial and lateral UKA can be said to induce kinematics of the knee which could be considered broadly comparable to those of the natural knee, and that even a 10° varus–valgus misalignment of the femoral component may not induce highly irregular kinematics. However, elevated posterior translation of the tibia in lateral UKA and large excursions of the insert may explain the higher incidence of bearing dislocation observed in some clinical studies.     

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.

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.

Kinematics of a cementless mobile bearing posterior cruciate ligament-retaining total knee arthroplasty

Mobile bearing (MB) total knee arthroplasty (TKA) was developed to provide low contact stress and unconstrained joint motion. We studied a consecutive series of 41 knees with mobile-bearing, posterior cruciate-retaining (CR) TKAs to determine if kinematics resembled normal knees or if kinematics changed over time. Patients were studied at 3 and 21 months average follow-up with weight-bearing radiographs at full extension, 30° flexion and maximum flexion. Shape-matching techniques were used to measure TKA kinematics. Implant hyperextension, maximum flexion and total ROM increased with follow-up. Tibial rotation and condylar translations did not change with time. The medial condyle did not translate from extension to 30°, but translated 5 mm anteriorly from 30° to maximum flexion. Lateral condylar translation was 3 mm posterior from extension to 30°, with no translation from 30° to maximum flexion. Tibiofemoral kinematics in CR-MB-TKAs were stable over time, but did not replicate motions observed in healthy knees. The mobile tibial insert showed rotation and translation at both follow-up examinations, but the patterns of translation were not predictable.     

Spherical center axial hinge knee prosthesis causes lower contact stress on tibial insert and bushing compared with biaxial hinge knee prosthesis

BackgroundMotion axial system may affect contact stress of hinge knee prosthesis. However, it is unclear which axial system provides the better biomechanical effect. Therefore, the aim of this study was to compare the contact stress and stress distribution on the tibial insert and the bushing of hinge knee prostheses with a biaxial (BA) system and a spherical center axial (SA) system during a gait cycle.MethodsThree-dimensional finite-element (FE) models of the prostheses with different motion systems were included. The comparisons between experimental tests and FE analyses were performed to verify the models. Dynamic implicit FE analyses were performed to investigate the peak contact stresses and stress distributions on the tibial insert and the bushing.ResultsThe peak contact stresses on the tibial insert and the bushing of the BA prosthesis were higher than those of the SA prosthesis during most gait cycles. The contact time on the bushing is short in the SA prosthesis. The stress distributions on the superior surface of the tibial insert in the BA prosthesis were at the posterior side, but of the SA prosthesis were not fixed.ConclusionThe SA prosthesis has a lower peak contact stress on tibial insert and bushing than the BA prosthesis; in addition, the SA prosthesis has a ‘self-adjustment’ mechanism which could disperse high stress on the tibial insert to decrease the risk of wear and damage. The comparison could help designers and surgeons to better understand the future design of rotating hinge knee prostheses which should be able to achieve multiaxial motion and complete weight bearing by the tibial condylar to transmit the axial force better.     

The influence of tibial slope on the graft in combined high tibial osteotomy and anterior cruciate ligament reconstruction

Background

Young patients with severe medial osteoarthritis, varus malalignment and insufficiency of the anterior cruciate ligament (ACL) are difficult to treat. The tibial slope has gained attention with regard to osteotomies and ligamentous instability. The purpose was to evaluate the outcome of combined high tibial osteotomy (HTO), ACL reconstruction and chondral resurfacing (CR, abrasion plus microfracture), and to analyse graft failure rates with regard to the tibial slope.

Intraoperative assessment of midflexion laxity in total knee prosthesis

BackgroundSoft-tissue balancing of the knee is fundamental to the success of a total knee arthroplasty (TKA). In posterior-stabilized TKA, there is no stabilizer of the anterior–posterior translation in the midflexion range in which the cam-post mechanism does not engage yet. Therefore, instability in the midflexion range is suspected to occur in posterior-stabilized TKA. The purpose of this study was to measure the joint gap throughout a full range of motion and to analyze the joint gap laxity in the midflexion range after implantation of a mobile-bearing posterior-stabilized total knee prosthesis.MethodsJoint gap kinematics in 259 knees with varus osteoarthritis were measured during TKAs using a tensor device with the same shape of a total knee prosthesis of the same design was used. After the implantation of a mobile-bearing posterior-stabilized prosthesis and the reduction of the patellofemoral joint, the joint gap was measured at 0°, 30°, 60°, 90°, 120°, and 145° of flexion.ResultsThe center size of the joint gap was tight in extension and deep flexion and loose at midflexion ranges, especially at 30° of flexion (p < 0.001). The symmetry of the joint gap was varus at 0° and 145° of flexion (p < 0.001).ConclusionsOur results showed the joint gap laxity in the midflexion range after the implantation of a mobile-bearing posterior-stabilized prosthesis. Our new tensor device, which can attach the polyethylene insert trial, will provide the important information about the joint gap kinematics after implantation of total knee prostheses.Level of evidenceIV.     

How does asymmetric tibial insert affect tibiofemoral kinematics and contact stresses in total knee Arthroplasty?

BackgroundAsymmetric tibial insert design is expected to restore normal knee kinematics better than symmetric design. A tri-condylar implant has asymmetric and symmetric tibial inserts with a ball-and-socket joint to replace the post-cam mechanism. The purpose of this study was to compare the knee kinematics of the two designs and to measure tibiofemoral contact stresses, including that of the ball-and-socket joint.MethodsUsing a computer simulation, the anteroposterior position and axial rotation of the femoral component were simulated during a weight-bearing deep knee bend for six validated models. Contact forces were simultaneously simulated in the medial, lateral, and ball-and-socket compartments. The relative position and the magnitude and direction of each contact force were applied to aforce/displacement control knee simulator. The contact stresses were measured individually using a pressure sensor.ResultsThe asymmetric tibial insert demonstrated a more posterior position of the femoral component in the lateral compartment during the entire range of motion and greater external rotation of the femoral component, compared to the symmetrical tibial insert. The mean peak contact stress of the medial and lateral compartments was < 9 Mpa, with no significant differences between the two designs except at 0°. The contact stress of the ball-and-socket joint was < 5 MPa.ConclusionsAsymmetry of the tibial insert shows significant kinematic difference and has little influence on the peak contact stress, which is considerably lower than the yield strength of polyethylene. The asymmetric tibial insert can lead to clinical benefits owing to its kinematic and kinetic properties.