The effect of valgus/varus malalignment on load distribution in total knee replacements

Valgus or varus malpositioning of the tibial component of a total knee implant may cause increased propensity for loosening or implant wear and eventually may lead to revision surgery. The aim of this study was to determine the effect of valgus/varus malalignment on tibio-femoral mechanics during surgical trial reduction and simulated gait loading. In seven cadaver legs, posterior cruciate sparing total knee replacements were implanted and tibial inserts representing a neutral alignment and 3 degrees and 5 degrees varus and valgus alignments were sequentially inserted. Each knee with each insert was loaded in a manner representative of a trial reduction performed during knee surgery and loaded in a physiological knee simulator. Simulated gait performed on the simulator demonstrated that internal/external and adduction/abduction rotations showed statistical changes with some of the angled inserts at different points in the walking cycle. Neither medial/lateral nor anterior/posterior translations changed statistically during simulated walking. The pressure distribution and total load in the medial and lateral compartments of the tibial component changed significantly with as little as a 3 degrees variation in angulation when loaded in a manner representative of a trial reduction or with a knee simulator. These results support the need for precise surgical reconstruction of the mechanical axis of the knee and proper alignment of the tibial component. These results further demonstrate that tibial contact pressures measured during a trial reduction method may be predictive of contact mechanics at the higher loading seen in the knee simulator.     

Effect of varus/valgus malalignment on bone strains in the proximal tibia after TKR: an explicit finite element study

Malalignment is the main cause of tibial component loosening. Implants that migrate rapidly in the first two post-operative years are likely to present aseptic loosening. It has been suggested that cancellous bone stresses can be correlated with tibial component migration. A recent study has shown that patient-specific finite element (FE) models have the power to predict the short-term behavior of tibial trays. The stresses generated within the implanted tibia are dependent on the kinematics of the joint; however, previous studies have ignored the kinematics and only applied static loads. Using explicit FE, it is possible to simultaneously predict the kinematics and stresses during a gait cycle. The aim of this study was to examine the cancellous bone strains during the stance phase of the gait cycle, for varying degrees of varus/valgus eccentric loading using explicit FE. A patient-specific model of a proximal tibia was created from CT scan images, including heterogeneous bone properties. The proximal tibia was implanted with a commercial total knee replacement (TKR) model. The stance phase of gait was simulated and the applied loads and boundary conditions were based on those used for the Stanmore knee simulator. Eccentric loading was simulated. As well as examining the tibial bone strains (minimum and maximum principal strain), the kinematics of the bone-implant construct are also reported. The maximum anterior-posterior displacements and internal-external rotations were produced by the model with 20 mm offset. The peak minimum and maximum principal strain values increased as the load was shifted laterally, reaching a maximum magnitude for -20 mm offset. This suggests that when in varus, the load transferred to the bone is shifted medially, and as the bone supporting this load is stiffer, the resulting peak bone strains are lower than when the load is shifted laterally (valgus). For this particular patient, the TKR design analyzed produced the highest cancellous bone strains when in valgus. This study has provided an insight in the variations produced in bone strain distribution when the axial load is applied eccentrically. To the authors' knowledge, this is the first time that the bone strain distribution of a proximal implanted tibia has been examined, also accounting for the kinematics of the tibio-femoral joint as part of the simulation. This approach gives greater insight into the overall performance of TKR.     

Effects of femoral component placement on the balancing of a total knee at surgery

Misalignment and soft-tissue imbalance in total knee arthroplasty (TKA) can cause discomfort, pain, inadequate motion and instability that may require revision surgery. Balancing can be defined as equal collateral ligament tensions or equal medial and lateral compartmental forces during the flexion range. Our goal was to study the effects on balancing of linear femoral component misplacements (proximal, distal, anterior, posterior); and different component rotations in mechanical alignment compared to kinematic alignment throughout the flexion path. A test rig was constructed such that the position of a standard femoral component could be adjusted to simulate the linear and rotational positions. With the knee in neutral reference values of the collateral tensions were adjusted to give anatomic contact force patterns, measured with an instrumented tibial trial. The deviations in the forces for each femoral component position were then determined. Compartmental forces were significantly influenced by 2 mm linear errors in the femoral component placement. However, the errors were least for a distal error, equivalent to undercutting the distal femur. The largest errors mainly increase the lateral condyle force, occurred for proximal and posterior component errors. There were only small contact force differences between kinematic and mechanical alignment. Based on these results, surgeons should avoid overcutting the distal femur and undercutting the posterior femur. However, the 2–3 degrees varus slope of the joint line as in kinematic alignment did not have much effect on balancing, so mechanical or kinematic alignment were equivalent.     

Anserina Bursitis—A Treatable Cause of Knee Pain in Patients with Degenerative Arthritis

The anserina bursa is located on the medial surface of the tibia deep to the tendons of the sartorius, gracilis, and semimembranosus muscles and superficial to the insertion of the tibial collateral ligament. Knee pain, a palpable swelling of the bursa, and tenderness over the medial anterior aspect of the tibia just below the knee are the hallmarks of anserina bursitis.In a three-year period, 24 patients with anserina bursitis were seen in a rheumatology clinic. All but one were women, 18 were obese, and only four were under 50 years old. Knee x-ray studies showed degenerative arthritis in 20 of the 24 patients. In ten, varus knee deformities were present, while three had valgus deformities.Ultrasound or local steroid injections gave dramatic relief in all but one patient.     

Useability of an image based nagivation system in reconstruction of leg alignment in total knee arthroplasty - results of a propsective study]

Accurate leg alignment is one important factor for long term survival in total knee arthroplasty (TKA). The aim of this study was to determine the accuracy of a CT-based navigation system in restoration of the leg axis. 80 TKA (P.F.C.-Sigma--DePuy) were implanted either using a CT-based navigation-system or the conventional technique. There were no significant differences between the groups according to the preoperative leg deformity. Accuracy of implantation was determined on postoperative long-leg coronal and lateral x-rays. A postoperative leg axis between 3 degrees varus and 3 degrees valgus was obtained in 35/40 patients (88%) in the computer assisted and 28/40 patients (70%) in the conventional operated group. A higher precision in the sagittal plane was seen for the tibial (computer assisted: 3.9 +/- 2.2 vs. conventional TKA 1.3 +/- 5.8) and the femoral component (computer assisted: 3.5 +/- 2.3 vs. conventional TKA 6.9 +/- 3.6). The use of the CT-based VectorVision-System allows a significant improvement in the accuracy of implantation in TKA. The CT-based module has the advantage of a precise preoperative planning and a useful documentation and control tool for each important step. On the other hand there are additional costs and time consuming logistics.     

Epiphyseal-based designs for tibial plateau components--II. Stress analysis in the sagittal plane

A two-dimensional, finite element study was undertaken to establish the stresses in the proximal tibia before and after total knee arthroplasty. Equivalent-thickness models in a sagittal plane were created for the natural, proximal tibia and for the proximal tibia with two different types of tibial plateau components. All components simulated bony ingrowth fixation, i.e. no cement layer existed between component and bone. In addition, the interface between component and bone was assumed to be intimately connected, representing complete bony ingrowth and a rigid state of fixation. Two load cases were considered: a joint reaction force acting in conjunction with a patellar ligament force, simulating the knee at 40 degrees of flexion; and a joint reaction force directed along the long axis of the tibia. For the natural tibia model, the pattern of principal stresses for loadcase 1 more closely corresponds to the epiphyseal plate geometry and trabecular morphology than do the principal stress patterns for loadcase 2. Judging from the distribution of principal stresses, loadcase 1 represents a more severe test of implant design than does loadcase 2. The model of the component with a peg predicted that the trabecular bone near the tip of the peg will experience higher than normal stresses, while the bone stresses near the posterior aspect adjacent to the metal tray will be reduced. A component without pegs that incorporates a posterior chamfer and an anterior lip lead to stress distributions closer to those existing in the natural tibia. The interface geometry for this design is based upon the contour of the epiphyseal plate.     

Trigonometric analysis of the mechanical axis deviation induced by telescopic intramedullary femoral lengthening nails

Femoral lengthening with intramedullary nails can create alterations in the mechanical axis of the limb. This is based on the relationship of the anatomic femur axis to the mechanical femur axis, which is typically 5-9 degrees valgus. We developed trigonometric formulas to calculate the predicted change, using the lengths of the tibia, femur, and whole limb; the amount of lengthening; and the angle between the anatomic and the mechanical axis of the femur. We recognized three patterns depending on whether the overall limb mechanical axis is lateral (valgus), medial (varus), or straight through the center of the knee. The varus and valgus patterns lead to similar formulas. When the mechanical axis goes directly through the center of the knee joint, the formula simplifies. These formulas could be incorporated into digital radiographic programs to predict the change in mechanical axis deviation that will develop from lengthening along the anatomic femur axis with an intramedullary lengthening nail.     

腓骨近端截骨术与胫骨高位截骨术治疗内侧间室性膝关节骨关节炎的比较研究

目的:对比内侧间室性膝关节骨关节炎(KOA)患者应用腓骨近端截骨术与胫骨高位截骨术治疗的疗效。方法:选取2016年11月到2017年12月在我院接受治疗的内侧间室性KOA患者32例,采用随机数字表法将所有患者分为腓骨近端截骨组与胫骨高位截骨组各16例,比较两组患者的手术时间、住院时间、术中出血量和住院费用,比较两组患者术前、术后3个月、术后6个月的美国特种外科医院膝关节评分(HSS)、美国膝关节协会评分(KSS)、视觉模拟疼痛评分(VAS)和股胫角(FTA),比较两组患者术后出现的并发症的发生率。结果:腓骨近端截骨组患者的手术时间、住院时间短于胫骨高位截骨组,术中出血量和住院费用均显著少于胫骨高位截骨组(P0.05);术后3个月、术后6个月两组患者的HSS评分、KSS评分均明显高于术前,VAS评分、FTA均明显低于术前(P0.05);术前、术后3个月、术后6个月两组患者的HSS评分、KSS评分、VAS评分、FTA比较均无统计学差异(P0.05);两组患者的并发症发生率比较无统计学差异(P0.05)。结论:腓骨近端截骨术和胫骨高位截骨术均可有效治疗内侧间室性KOA,改善患者的膝关节功能和疼痛感,纠正内翻畸形,但腓骨近端截骨术手术时间和住院时间更短,术中出血量和住院费用更少。     

Failure locus of the anterior cruciate ligament: 3D finite element analysis

Anterior cruciate ligament (ACL) disruption is a common injury that is detrimental to an athlete's quality of life. Determining the mechanisms that cause ACL injury is important in order to develop proper interventions. A failure locus defined as various combinations of loadings and movements, internal/external rotation of femur and valgus and varus moments at a 25(o) knee flexion angle leading to ACL failure was obtained. The results indicated that varus and valgus movements were more dominant to the ACL injury than femoral rotation. Also, Von Mises stress in the lateral tibial cartilage during the valgus ACL injury mechanism was 83% greater than that of the medial cartilage during the varus mechanism of ACL injury. The results of this study could be used to develop training programmes focused on the avoidance of the described combination of movements which may lead to ACL injury.     

A finite element model of the human knee joint for the study of tibio-femoral contact

As a step towards developing a finite element model of the knee that can be used to study how the variables associated with a meniscal replacement affect tibio-femoral contact, the goals of this study were 1) to develop a geometrically accurate three-dimensional solid model of the knee joint with special attention given to the menisci and articular cartilage, 2) to determine to what extent bony deformations affect contact behavior, and 3) to determine whether constraining rotations other than flexion/extension affects the contact behavior of the joint during compressive loading. The model included both the cortical and trabecular bone of the femur and tibia, articular cartilage of the femoral condyles and tibial plateau, both the medial and lateral menisci with their horn attachments, the transverse ligament, the anterior cruciate ligament, and the medial collateral ligament. The solid models for the menisci and articular cartilage were created from surface scans provided by a noncontacting, laser-based, three-dimensional coordinate digitizing system with an root mean squared error (RMSE) of less than 8 microns. Solid models of both the tibia and femur were created from CT images, except for the most proximal surface of the tibia and most distal surface of the femur which were created with the three-dimensional coordinate digitizing system. The constitutive relation of the menisci treated the tissue as transversely isotropic and linearly elastic. Under the application of an 800 N compressive load at 0 degrees of flexion, six contact variables in each compartment (ie., medial and lateral) were computed including maximum pressure, mean pressure, contact area, total contact force, and coordinates of the center of pressure. Convergence of the finite element solution was studied using three mesh sizes ranging from an average element size of 5 mm by 5 mm to 1 mm by 1 mm. The solution was considered converged for an average element size of 2 mm by 2 mm. Using this mesh size, finite element solutions for rigid versus deformable bones indicated that none of the contact variables changed by more than 2% when the femur and tibia were treated as rigid. However, differences in contact variables as large as 19% occurred when rotations other than flexion/extension were constrained. The largest difference was in the maximum pressure. Among the principal conclusions of the study are that accurate finite element solutions of tibio-femoral contact behavior can be obtained by treating the bones as rigid. However, unrealistic constraints on rotations other than flexion/extension can result in relatively large errors in contact variables.     

Discrepancies in knee joint moments using common anatomical frames defined by different palpable landmarks

The aim was to investigate the effects of three anatomical frames using palpable anatomical landmarks of the knee on the net knee joint moments. The femoral epicondyles, femoral condyles, and tibial ridges were used to define the different anatomical frames and the segment end points of the distal femur and proximal tibia, which represent the origin of the tibial coordinate system. Gait data were then collected using the calibrated anatomical system technique (CAST), and the external net knee joint moments in the sagittal, coronal, and transverse planes were calculated based upon the three anatomical frames. Peak knee moments were found to be significantly different in the sagittal plane by approximately 25% (p 相似文献   

Detecting condylar contact loss using single-plane fluoroscopy: A comparison with in vivo force data and in vitro bi-plane data

Knee contact mechanics play an important role in knee implant failure and wear mechanics. Femoral condylar contact loss in total knee arthroplasty has been reported in some studies and it is considered to potentially induce excessive wear of the polyethylene insert.Measuring in vivo forces applied to the tibial plateau with an instrumented prosthesis is a possible approach to assess contact loss in vivo, but this approach is not very practical. Alternatively, single-plane fluoroscopy and pose estimation can be used to derive the relative pose of the femoral component with respect to the tibial plateau and estimate the distance from the medial and lateral parts of the femoral component towards the insert. Two measures are reported in the literature: lift-off is commonly defined as the difference in distance between the medial and lateral condyles of the femoral component with respect to the tibial plateau; separation is determined by the closest distance of each condyle towards the polyethylene insert instead of the tibia plateau.In this validation study, lift-off and separation as measured with single-plane fluoroscopy are compared to in vivo contact forces measured with an instrumented knee implant. In a phantom study, lift-off and separation were compared to measurements with a high quality bi-plane measurement.The results of the in vivo contact-force experiment demonstrate a large discrepancy between single-plane fluoroscopy and the in vivo force data: single-plane fluoroscopy measured up to 5.1 mm of lift-off or separation, whereas the force data never showed actual loss of contact. The phantom study demonstrated that the single-plane setup could introduce an overestimation of 0.22 mm±±0.36 mm. Correcting the out-of-plane position resulted in an underestimation of medial separation by −0.20 mm±±0.29 mm.In conclusion, there is a discrepancy between the in vivo force data and single-plane fluoroscopic measurements. Therefore contact loss may not always be determined reliably by single plane fluoroscopy analysis.     

Failure locus of the anterior cruciate ligament: 3D finite element analysis

Anterior cruciate ligament (ACL) disruption is a common injury that is detrimental to an athlete's quality of life. Determining the mechanisms that cause ACL injury is important in order to develop proper interventions. A failure locus defined as various combinations of loadings and movements, internal/external rotation of femur and valgus and varus moments at a 25^o knee flexion angle leading to ACL failure was obtained. The results indicated that varus and valgus movements were more dominant to the ACL injury than femoral rotation. Also, Von Mises stress in the lateral tibial cartilage during the valgus ACL injury mechanism was 83% greater than that of the medial cartilage during the varus mechanism of ACL injury. The results of this study could be used to develop training programmes focused on the avoidance of the described combination of movements which may lead to ACL injury.     

UKA与TKA治疗膝关节内侧单间室骨性关节炎的临床对比

目的:探究膝关节单髁置换术(UKA)与全膝关节置换术(TKA)治疗膝关节内侧单间室骨性关节炎的临床治疗效果。方法:将2011年4月-2015年7月期间因膝关节单间室骨性关节炎入院接受治疗的89例患者纳入本研究,随机分为研究组和对照组,研究组44例,行UKA手术,对照组45例,采用TKA手术方式治疗。对两组患者进行术后随访,对比临床治疗效果。结果:两组术前均有明显膝关节疼痛,术后膝关节疼痛均明显改善,组间差别无显著统计学意义(X2=1.323,P=0.2500.05);术后膝关节屈曲角度、HSS评分相对于术前均显著改善,研究组术后膝关节屈曲角度(111.2±18.8)度高于对照组的(98.6±14.7)度,差异有统计学意义(P0.05);HSS评分(87.6±13.7)分高于对照组的(73.2±16.8)分,差异有统计学意义(P0.05);研究组膝关节屈曲至90度时间比对照组短,数据差异有统计学差异(t=-2.303,P=0.0240.05)。结论:膝关节内侧单间室骨性关节炎采用UKA与TKA均能取得一定临床效果,减轻患者痛苦,改善膝关节功能,但UKA临床疗效较好,手术创伤较小,术后恢复较快。     

Surgeon variability in total knee arthroplasty component alignment: a Monte Carlo analysis

Component mal-alignment in total knee arthroplasty has been associated with increased revision rates and poor clinical outcomes. A significant source of variability in traditional, jig-based total knee arthroplasty is the performance of the surgeon. The purpose of this study was to determine the most sensitive steps in the femoral and tibia arthroplasty procedures. A computational model of the total knee arthroplasty procedure was created, and Monte Carlo simulations were performed that included surgeon variability in each step of the procedure. The proportion of well-aligned components from the model agrees with clinical literature in most planes. When components must be aligned within ±3° in all planes, component alignment was most sensitive to the accuracy of identifying the lateral epicondyle for the femoral component, and to the precision of the transverse plane alignment of the extramedullary guide for the tibial component. This model can be used as a tool for evaluating different procedural approaches or sources of variability to improve the quality of the total knee arthroplasty procedure.     

A method to quantify alteration of knee kinematics caused by changes of TKR positioning

Few in-vitro studies have investigated changes in kinematics caused by total knee replacement (TKR) implantation. The advent of surgical navigation systems allows implant position to be measured accurately and the effects of alteration of TKR position and alignment investigated. A test rig and protocol were developed to compare the kinematics of TKR-implanted knees for different femoral component positions. The TKR was implanted and the component positions documented using a navigation system. The quadriceps was tensed and the knees were flexed and extended manually. Torques and drawer forces were applied to the tibia during knee flexion–extension, while recording the kinematics with the navigation system. The implant was removed and replaced on an intramedullary fixation that allowed proximal–distal, and internal–external rotation of the femoral component without conducting a repeated arthrotomy on the knee. The implant was repositioned using the navigation system to reproduce the previously achieved normally navigated position and the kinematics were recorded again. The recorded kinematics of the knee were not significantly different between both normal implantation and intramedullary remounting for tibial internal–external rotation, varus–valgus angulation, or posterior drawer, at any angle of knee flexion examined. Anterior drawer was increased approximately 2.5 mm across the range 20–35° knee flexion (p<0.05), but was otherwise not significantly different. This method of navigating implant components and of moving them within the closed knee (thus avoiding artefactual effects of repeated soft tissue manipulations) can now be used to quantify the effect on kinematics of alteration of the position of the femoral component.     

Contact forces in several TKA designs during squatting: A numerical sensitivity analysis

Total knee arthroplasty (TKA) is a very successful procedure, but pain or difficulties during activities still persist in patients. Patient outcomes in TKA surgery can be affected by implant design, alignment or patient-related anatomical factors. This paper presents a numerical sensitivity analysis of several TKA types: a fixed bearing, posterior stabilized prosthesis, a high flexion fixed bearing guided motion prosthesis, a mobile bearing prosthesis and a hinge prosthesis. Each prosthesis was virtually implanted on the same cadaver leg model and it underwent a loaded squat, in 10s, between 0° and 120°, similar to several previous experimental tests performed on knee kinematics simulators. The aim of this examination was to investigate the sensitivity of the patello-femoral (PF) and tibio-femoral (TF) contact forces to patient-related anatomical factors, and component position in the different implant types. The following parameters were used for the sensitivity study: the proximo-distal patellar position, the patellar component tilting, the tibial component position and orientation, the locations of the medial and lateral collateral ligaments with respect to femur and tibia and the patellar tendon length. The sensitivity analysis showed that PF contact forces are mostly affected by patella height (increases up to 67% for one TKA type in patella-alta configuration), by an anterior tibial component translation (increases up to 30%), and by patellar component tilting (increases up to 29%); TF contact forces are mostly affected by the anterior displacement of the insertion points of the medial collateral ligament with respect to the reference position (increases up to 48%).     

Influence of patellar position on tibial rotation after total knee arthroplasty]

AIM: Common total knee arthroplasty leads to resection of the anterior cruciate ligament. Lacking the ligamentous guidance, tibial rotation depends on different factors, i.e., muscle vectors. The present study measured the influence of the knee extensor mechanism determined by the mediolateral patella position on tibial rotation after implantation of two different knee prostheses. MATERIALS AND METHODS: Physiologic tibial rotation and mediolateral patella translation were measured in ten fresh-frozen knee specimens. After implantation of the Interax- and Genesis II-prosthesis in each five of the ten specimens, kinematic measurements were made again with a determination of significant alterations. RESULTS: The maximal medial patella position relative to the centre of the tibia was -6.6 mm (representing lateralisation); the maximal external tibial rotation was 4.1 degrees. After implantation of the Genesis II-prosthesis the external tibial rotation was reduced (p=0.03) with a relatively medialised patella (p=0.01), whereas after implantation of the Interax-prosthesis the external tibial rotation was increased (p=0.01) while the patella was measured to be lateralised similar to physiologic conditions. CONCLUSION: The results of the current study revealed a potential influence of mediolateral patella position on tibial rotation following total knee arthroplasty, while both prosthesis systems were not able to reproduce physiologic joint kinematics.     

In vivo kinematic evaluation and design considerations related to high flexion in total knee arthroplasty

In designing a posterior-stabilized total knee arthroplasty (TKA) it is preferable that when the cam engages the tibial spine the contact point of the cam move down the tibial spine. This provides greater stability in flexion by creating a greater jump distance and reduces the stress on the tibial spine. In order to eliminate edge loading of the femoral component on the posterior tibial articular surface, the posterior femoral condyles need to be extended. This provides an ideal femoral contact with the tibial articular surface during high flexion angles. To reduce extensor mechanism impingement in deep flexion, the anterior margin of the tibial articular component should be recessed. This provides clearance for the patella and patella tendon. An in vivo kinematic analysis that determined three dimensional motions of the femorotibial joint was performed during a deep knee bend using fluoroscopy for 20 subjects having a TKA designed for deep flexion. The average weight-bearing range-of-motion was 125 degrees . On average, TKA subjects experienced 4.9 degrees of normal axial rotation and all subjects experienced at least -4.4 mm of posterior femoral rollback. It is assumed that femorotibial kinematics can play a major role in patellofemoral kinematics. In this study, subjects implanted with a high-flexion TKA design experienced kinematic patterns that were similar to the normal knee. It can be hypothesized that forces acting on the patella were not substantially increased for TKA subjects compared with the normal subjects.     

The effects of knee joint kinematics on anterior cruciate ligament injury and articular cartilage damage

This study determined which knee joint motions lead to anterior cruciate ligament (ACL) rupture with the knee at 25° of flexion. The knee was subjected to internal and external rotations, as well as varus and valgus motions. A failure locus representing the relationship between these motions and ACL rupture was established using finite element simulations. This study also considered possible concomitant injuries to the tibial articular cartilage prior to ACL injury. The posterolateral bundle of the ACL demonstrated higher rupture susceptibility than the anteromedial bundle. The average varus angular displacement required for ACL failure was 46.6% lower compared to the average valgus angular displacement. Femoral external rotation decreased the frontal plane angle required for ACL failure by 27.5% compared to internal rotation. Tibial articular cartilage damage initiated prior to ACL failure in all valgus simulations. The results from this investigation agreed well with other experimental and analytical investigations. This study provides a greater understanding of the various knee joint motion combinations leading to ACL injury and articular cartilage damage.