Intraoperative passive kinematics of osteoarthritic knees before and after total knee arthroplasty.

Total knee arthroplasty is a successful procedure to treat pain and functional disability due to osteoarthritis. However, precisely how a total knee arthroplasty changes the kinematics of an osteoarthritic knee is unknown. We used a surgical navigation system to measure normal passive kinematics from 7 embalmed cadaver lower extremities and in vivo intraoperative passive kinematics on 17 patients undergoing primary total knee arthroplasty to address two questions: How do the kinematics of knees with advanced osteoarthritis differ from normal knees?; and, Does posterior substituting total knee arthroplasty restore kinematics towards normal? Osteoarthritic knees displayed a decreased screw‐home motion and abnormal varus/valgus rotations between 10° and 90° of knee flexion when compared to normal knees. The anterior–posterior motion of the femur in osteoarthritic knees was not different than in normal knees. Following total knee arthroplasty, we found abnormal varus/valgus rotations in early flexion, a reduced screw‐home motion when compared to the osteoarthritic knees, and an abnormal anterior translation of the femur during the first 60° of flexion. Posterior substituting total knee arthroplasty does not appear to restore normal passive varus/valgus rotations or the screw motion and introduces an abnormal anterior translation of the femur during intraoperative evaluation. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 24:1607–1614, 2006     

固定平台后稳定型假体全膝关节置换术后的运动学研究

 目的 探讨固定平台后稳定型假体全膝关节置换(total knee arthroplasty,TKA)术后膝关节在负重屈膝下蹲时的运动学特征。方法 选取10名健康志愿者和10例固定平台后稳定型假体TKA术后患者。制作骨骼及膝关节假体三维模型,在持续X线透视下完成负重下蹲动作,膝关节屈曲度每增加15°截取一幅图像。通过荧光透视分析技术完成三维模型与二维图像的匹配,再现股骨与胫骨在屈膝过程中的空间位置,通过连续的图像分析比较正常与固定平台后稳定型假体TKA术后膝关节在负重下蹲时股骨内、外髁前后移动及胫骨内外旋转幅度。结果 负重下蹲时,正常膝关节平均屈曲136°,股骨内、外髁分别后移(7.3±1.2) mm和(19.3±3.1) mm,胫骨平均内旋23.8°±3.4°;TKA术后膝关节平均屈曲125°,股骨内、外髁分别后移(1.4±1.6) mm和(6.4±1.7) mm,胫骨平均内旋8.5°±3.4°。结论 固定平台后稳定型假体TKA术后膝关节运动与正常膝关节相似,均表现出股骨内、外髁后移及胫骨内旋运动,但幅度小于正常膝关节,且在屈膝过程中存在股骨矛盾性前移及胫骨外旋现象。     

Kinematics of medial osteoarthritic knees before and after posterior cruciate ligament retaining total knee arthroplasty

Total knee arthroplasty (TKA) is a widely accepted surgical procedure for the treatment of patients with end‐stage osteoarthritis (OA). However, the function of the knee is not always fully recovered after TKA. We used a dual fluoroscopic imaging system to evaluate the in vivo kinematics of the knee with medial compartment OA before and after a posterior cruciate ligament‐retaining TKA (PCR‐TKA) during weight‐bearing knee flexion, and compared the results to those of normal knees. The OA knees displayed similar internal/external tibial rotation to normal knees. However, the OA knees had less overall posterior femoral translation relative to the tibia between 0° and 105° flexion and more varus knee rotation between 0° and 45° flexion, than in the normal knees. Additionally, in the OA knees the femur was located more medially than in the normal knees, particularly between 30° and 60° flexion. After PCR‐TKA, the knee kinematics were not restored to normal. The overall internal tibial rotation and posterior femoral translation between 0° and 105° knee flexion were dramatically reduced. Additionally, PCR‐TKA introduced an abnormal anterior femoral translation during early knee flexion, and the femur was located lateral to the tibia throughout weight‐bearing flexion. The data help understand the biomechanical functions of the knee with medial compartment OA before and after contemporary PCR‐TKA. They may also be useful for improvement of future prostheses designs and surgical techniques in treatment of knees with end‐stage OA. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29:40–46, 2011     

Correlation between preoperative and postoperative knee kinematics in total knee arthroplasty using cruciate retaining designs

The authors evaluated the relationships between preoperative and postoperative kinematics in 50 osteoarthritic knees scheduled for cruciate retaining total knee arthroplasty with regards to posterior femoral roll back and external femoral rotation using a navigation system from 10° to 120° of knee flexion. Although posterior femoral roll back was maintained, external femoral rotation was significantly decreased compared to those of the preoperative knee after total knee arthroplasty. However, the amount of posterior roll back and external femoral rotation after total knee arthroplasty were found to be significantly positively related to those measured preoperatively (r = 0.62 and 0.57, respectively). These significant kinematic correlations may explain why preoperative range of knee motion influences range of motion after total knee arthroplasty.     

Posterior cruciate ligament removal contributes to abnormal knee motion during posterior stabilized total knee arthroplasty

Abnormal anterior translation of the femur on the tibia has been observed in mid flexion (20–60°) following posterior stabilized total knee arthroplasty. The underlying biomechanical causes of this abnormal motion remain unknown. The purpose of this study was to isolate the effects of posterior cruciate ligament removal on knee motion after total knee arthroplasty. We posed two questions: Does removing the posterior cruciate ligament introduce abnormal anterior femoral translation? Does implanting a posterior stabilized prosthesis change the kinematics from the cruciate deficient case? Using a navigation system, we measured passive knee kinematics of ten male osteoarthritic patients during surgery after initial exposure, after removing the anterior cruciate ligament, after removing the posterior cruciate ligament, and after implanting the prosthesis. Passively flexing and extending the knee, we calculated anterior femoral translation and the flexion angle at which femoral rollback began. Removing the posterior cruciate ligament doubled anterior translation (from 5.1 ± 4.3 mm to 10.4 ± 5.1 mm) and increased the flexion angle at which femoral rollback began (from 31.2 ± 9.6° to 49.3 ± 7.3°). Implanting the prosthesis increased the amount of anterior translation (to 16.1 ± 4.4 mm), and did not change the flexion angle at which femoral rollback began. Abnormal anterior translation was observed in low and mid flexion (0–60°) after removing the posterior cruciate ligament, and normal motion was not restored by the posterior stabilized prosthesis. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:1494–1499, 2008     

Comparison of tibial rotation in fixed and mobile bearing total knee arthroplasty using computer navigation

Tibial rotation is an important aspect of knee function and can be altered after total knee arthroplasty (TKA). These alterations include decreased internal rotation with knee flexion as compared to the normal state and paradoxical external rotation with flexion. Mobile bearing total knee prostheses may allow greater unconstrained tibial rotation. I compared tibial rotation after fixed bearing or mobile bearing total knee arthroplasty in 82 patients who underwent TKA with the tibia cut first technique to ascertain any differences. Using intraoperative imageless computer navigation, measurements included the determination of tibial rotation from extension to 90° flexion before and after prosthetic implantation with non-weight-bearing range of motion. I found that tibial rotation was significantly reduced after fixed bearing total knee replacement as compared to mobile bearing. In addition, the tibial position compared to the distal femur in extension was more external in fixed bearings compared to mobile bearings. Placing the fixed tibial tray with increased internal rotation could explain this difference.

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Résumé  La rotation du tibia est un élément important sur le plan fonctionnel. Elle peut être altérée après une prothèse totale du genou. Ces altérations de la rotation portent sur une diminution de la rotation interne et paradoxalement une augmentation de la rotation externe en flexion. Une prothèse totale du genou à plateau mobile permet une libération plus importante de la rotation tibiale. Nous avons comparé cette rotation à partir de prothèses à la plateau fixe et à plateau mobile sur une série de 82 patients ayant bénéficie de cette arthroplastie avec une coupe première du tibia. Nous avons utilisé pour cela un système de navigation per opératoire. Nous avons trouvé à l’issue de cette étude que les rotations tibiales étaient significativement réduites après prothèse totale à plateau fixe versus prothèses à plateau mobile. Par ailleurs, la position du tibia en extension est en rotation externe par rapport au fémur distal. Cette rotation est plus importante dans les prothèses à plateau fixe que dans les prothèses à plateau mobile. Le positionnement du plateau tibial en rotation interne lors de l’intervention peut expliquer cette différence.

     

A comparative study of weight-bearing and non-weight-bearing 3-dimensional lower extremity alignment in knee osteoarthritis

BackgroundLower extremity alignment is an important variable with respect to the development and progression of knee osteoarthritis. It is very essential for the preoperative planning of realignment surgeries such as total knee arthroplasty and high tibial osteotomy. Nevertheless, there have been no reports comparing 3D lower extremity alignment between weight-bearing upright and non-weight-bearing horizontal states in osteoarthritic knees in the same subject. Therefore, we determined whether the alignment of the lower extremity in the weight-bearing upright state differed from that in the non-weight-bearing horizontal or supine position in patients with knee osteoarthritis.MethodsAdduction–abduction, flexion–extension, and rotational angle of osteoarthritic knees were assessed in weight-bearing upright and non-weight-bearing supine positions. Knee alignment in the supine position was determined from preoperative computed tomography data. In the weight-bearing upright state, alignment was determined using a technique that utilized 2D-3D image-matching with biplanar computed radiography and 3D bone models of the complete lower extremity rebuilt using computed tomography-based information.ResultsWe assessed 81 limbs from osteoarthritic knee patients (74 women, 7 men; mean age 75.3 years, range 59–86 years). In the coronal plane, there were varus deformities in both the supine and standing positions, while there was flexion in both the supine upright state and position at the sagittal plane. In the axial plane, the rotation of the tibia to the femur was neutral in the supine position and internal in the upright state.ConclusionPatient position significantly affects lower extremity alignment in osteoarthritic knees. This study provides important data regarding the preoperative evaluation of realignment surgery in total knee arthroplasty and high tibial osteotomy. We believe that these results are an important contribution to the knowledge regarding knee osteoarthritis.     

Robotic total knee arthroplastyThe accuracy of CT-based component placement

Background?Accurate alignment of the components in total knee arthroplasty is important. By use of postoperative CT controls, we studied the ability of a robotic effector to accurately place and align total knee arthroplasty (TKA) components according to a purely CT-based preoperative plan.Patients and methods?Robotic TKA was performed in 13 patients (6 men) with primary gonarthrosis. Locator screws were placed into femur and tibia under spinal anesthesia. A CT-scan including the femoral head, knee and ankle was performed. In the preoperative planning software, virtual components were positioned into the CT volume. In a second operation, the robot milled femur and tibia with a high-speed milling tool according to the preoperative plan. On the 10th day, CT controls were performed following the same protocol as preoperatively.Results?The mean deviation of the postoperative from the preoperatively planned mechanical axis was 0.2° (95% CI: ?0.1° to 0.5°). The accuracy of angular component placement in frontal, sagittal and transverse planes was within±1.2°, and the accuracy of linear component placement in mediolateral, dorsoventral and caudocranial directions was within±1.1 mm.Interpretation?Robotic TKA allows placement of components with unparalleled accuracy, but further development is mandatory to integrate soft-tissue balancing into the procedure and make it faster, easier and cheaper.     

Intra-articular correction of extra-articular tibial deformities with total knee arthroplasty

INTRODUCTIONExtra-articular leg deformities may occur in the femur or tibia from mal-unions from previous trauma or metabolic bone disease. Secondary osteoarthritis at the knee occurs due to loss of mechanical alignment of the limb. At surgery for total knee arthroplasty, mechanical alignment can be restored intra-articularly with appropriate bone cuts and soft tissue balancing.PRESENTATION OF CASEWe describe 2 case studies with extra-articular tibial deformities (9° and 24° varus deformity) which were corrected with a 1 stage procedure of total knee arthroplasty with intra-articular deformity correction.DISCUSSIONPatient selection, pre-operative considerations and surgical technique are discussed with reference to the literature.CONCLUSIONOne stage intra-articular correction of extra-articular deformity is suitable for mild degrees of varus deformities (<30°). Staged corrective procedures with larger deformities in the tibia or femur can be performed with extra-articular osteotomies on top of intra-articular corrections. Consideration should be given to the use of computer navigation when conventional jigs cannot be applied to deformed bone.     

Longitudinal measurement of tibial motion relative to the femur during passive displacements in the cat before and after anterior cruciate ligament transection

Passive anterior-posterior displacement and medial-lateral rotation of the tibia on the femur in the feline knee were assessed before transection of the anterior cruciate ligament, immediately after transection, and 2 and 4 months after transection. Four anaesthetized experimental and three sham-operated control animals were positioned in a stereotaxic frame. Motions of the tibia relative to the femur were measured with use of 60-Hz video motion analysis, while a strain-gauged system allowed measurement of forces and moments applied to the tibia. Displacement at 15 N of anterior force and 30° of knee flexion increased by an average of 6 mm following transection, and stiffness decreased by an average of 6 N/mm. At 2 and 4 months following transection, there were statistically significant reductions in this abnormal displacement. Stiffness during anterior displacement of the tibia at 30° increased significantly from immediately after transection to 4 months. At 90°, mean anterior displacement decreased from 5.1 mm immediately after transection to 2.9 mm at 4 months. Media rotation at 30° of knee flexion was significantly decreased from a mean of 16.5° after transection to a mean of 10.7° at 4 months. Changes in medial rotation at 90°, lateral rotation at 90°, and lateral rotation at 30° were not statistically significant. These results indicate a significant change in secondary constraints to tibial motion in response to knee instability.     

Die Extension-First-Technik bei der Knie-TEP-Implantation

Objective

Surgical technique in total knee arthroplasty (TKA) to combine the femur first and tibia first techniques in order to reduce surgical mistakes regarding rotation and alignment.

Indications

Symptomatic arthritis of the knee.

Contraindications

General contraindications for TKA.

Surgical technique

Osseous preparation starting with a distal femur cut. Then the proximal tibia cut is accomplished and the knee is balanced in extension after checking for correct alignment. Bone-referenced positioning of the femoral cutting block for further preparation of the femur. Finally, the rotation of the femur is checked in 90° of flexion by means of ligament tension. If required, the rotation is checked and the flexion gap balanced, respectively.

Postoperative management

Mobilization with weight bearing and range of motion as tolerated.

Results

In a prospective study, 267?knees (160 women, 107 men, average age of 69.3 [46?C89]?years) were followed up preoperatively and after 6 weeks. The clinical results were based on the American Knee Society score. The scores were 48.9 (32?C68) preoperatively and 86.5?(75?C100) at follow-up. Radiologically 92.1% of the knees showed a malposition <3°.     

Patellofemoral joint after total knee arthroplasty: Effect on contact area and contact stress

Compressive contact stress between the patella and the anterior femur and between the quadriceps tendon and anterior femur was measured before and after total knee arthroplasty in 5 cadaver knee specimens using a digital electronic sensor. Contact stresses were measured in the normal knee and after total knee arthroplasty with an unresurfaced patella, a dome-shaped patella, and a conforming patella. Patellofemoral contact stresses did not change significantly after total knee arthroplasty when the patella was not resurfaced, but they increased significantly after the patella was resurfaced with both the dome-shaped and the conforming components. The conforming patella had the highest contact stresses because it tilted at flexion angles greater than 90° and applied load to a small area on the superior portion of the patellar component. The conforming patella markedly decreased tendofemoral contact force because the thicker superior pole of the patella tented the quadriceps tendon at flexion angles greater than 120°. This further increased patellofemoral contact force in deep knee flexion.     

The posterior condylar angle in osteoarthritic knees

The posterior condylar angle is formed by the transepicondylar axis and the tangent line to the posterior condyles. It is an important relationship to determine rotational alignment of the femoral component in total knee arthroplasty. We measured this angle directly in 107 osteoarthritic knees undergoing total knee arthroplasty. The posterior condylar angle was significantly greater in valgus knees than in other osteoarthritic knees. Given the standard deviations and ranges of values noted, the posterior condyles are potentially unreliable references for femoral component rotation in some knees.     

骨性关节炎患者人工膝关节假体旋转定位标志研究

目的探讨对合并内、外翻畸形的膝关节骨性关节炎行人工全膝关节置换术，以股骨内外上髁外科轴（surgical epicondylar axis，SEA）作为股骨假体旋转参考轴，以胫骨结节内1／3作为胫骨假体旋转定位的骨性标志，判断股骨假体和胫骨假体的旋转对线情况。方法2004年7月～2005年1月，对32例（62膝）拟行人工全膝关节置换术的膝关节骨性关节炎患者（病例组），男2例，女30例；年龄58～80岁，平均68．9岁；内翻畸形55膝，胫股角平均内翻-8．23°；外翻畸形7膝，胫股角平均外翻＋15．48°。于术前行伸膝旋转中立位CT扫描，测量膝关节股骨后髁角（posterior condylar angle，PCA），并以10个正常膝关节作为对照组，测量SEA中点C与髌腱内1／3连线（BC）和经SEA中点C的垂线（AC）之间的夹角，即α角。结果病例组80％以上膝关节CT图像显示股骨内上髁陷凹；PCA中位数为＋2．36°（0～＋7．5°）；对照组膝关节α角为＋6．45±3．68°（0～＋11．8°）；病例组内翻畸形患者膝关节α角为＋10．85±10．47°（0～＋28．1°），与对照组比较差异有统计学意义（P〈0．05），病例组外翻畸形患者膝关节α角为＋11．6±7．3°（-6．5～＋26．8°），与对照组比较差异有统计学意义（P〈0．05）。结论以胫骨结节内1／3作为胫骨假体旋转参考轴线，胫骨假体相对于股骨假体处于轻度外旋位；合并内、外翻畸形患者的胫骨假体外旋角度明显增大，容易使股骨假体和胫骨假体间出现旋转对线不良。     

腘肌腱与腘腓韧带重建对控制膝关节外旋不稳定的作用

 目的 探讨腘肌腱与腘腓韧带重建对控制膝关节外旋不稳定的作用。方法 取6个非配对下肢标本,分别对腘肌腱和腘腓韧带进行选择性切断和重建。在屈膝0°、30°、45°、60°、90°和120°时向胫骨施加5 N?m的外旋力矩,使用导航系统测量完整状态、不同切断状态和不同重建状态下胫骨相对股骨的外旋角度。结果 单纯切断腘腓韧带导致屈膝30°到屈膝120°时胫骨外旋增加2.1°±0.7°(2.0°~2.3°),单纯切断腘肌腱导致屈膝30°到屈膝120°时胫骨外旋增加1.3°±1.2°(0.5°~2.0°),两组比较差异无统计学意义;同时切断腘肌腱与腘腓韧带导致胫骨外旋增加4.1°±1.6°(2.8°~5.0°),与单纯切断腘腓韧带及单纯切断腘肌腱比较差异有统计学意义。腘肌腱重建或腘肌腱+腘腓韧带联合重建后,从屈膝30°到屈膝90°胫骨外旋角度与完整膝关节及腘腓韧带重建比较差异有统计学意义。结论 对于外侧副韧带完整的膝关节后外复合体损伤,腘肌腱和腘腓韧带作为一个整体发挥着控制膝关节外旋稳定性的作用。三种重建技术均能恢复膝关节的外旋稳定性,腘腓韧带重建与膝关节正常状态无异,而包含腘肌腱的重建技术会造成外旋受限。     

Endosteal referencing in revision total knee arthroplasty

A method of orienting the femoral and tibial bone cuts relative to the endosteal cortex of the femur and tibia was used in 32 patients who underwent revision total knee arthroplasty. The mean orientation of the femoral component was 96.74° ± 1.03°, mean orientation of the tibial baseplate was 90.71° ± 1.10°, mean anatomic tibiofemoral alignment was 7.42° ± 1.69° of valgus, and mean mechanical tibiofemoral alignment was 1.09° ± 1.83° of valgus. Mean tibial bowing was 1.63° ± 1.57° of valgus, and mean femoral bowing was 0.58° ± 1.53° of varus. Valgus tibial bowing was correlated with valgus orientation of the tibial component (r = .86, P < .000001), and varus femoral bowing was correlated with orientation of the femoral component (r = .54, P = .0054). Referencing the implant position from the endosteal cortex of the intramedullary canals provides a reliable method of achieving satisfactory alignment in most revision total knee arthroplasties; however, bowing of the femur or tibia can affect alignment.     

Five to eight year results of the Johnson-Elloy (Accord) total knee arthroplasty

Between February 1982 and December 1985, 133 knees in 107 patients were replaced with a cemented Johnson-Elloy (Accord) total knee arthroplasty. Thirty-five knees were lost during the follow-up period because of death in 29, revision in 3, infection in 1, and refusal of follow-up evaluation in 2. The results of the remaining 98 knees in 76 patients with a 5–8 year follow-up period are presented. The procedure was carried out in all cases presenting for surgery, irrespective of pathology and degree of deformity. The range of flexion achieved as a mean of 93.5° in the osteoarthritic group and 100° in the rheumatoid arthritic group. Eighty-seven percent of the osteoarthritic group and 95% of the rheumatoid arthritic group achieved between 10° and 50° of rotation at 90° of flexion, which was maintained for the duration of the study. Adequate stability in both groups, valgus-varus and rotation in extension, and anteroposterior in flexion was achieved. Survivorship was 97.7% at 80 months.     

Influence of Posterior Tibial Slope on Kinematics After Cruciate-Retaining Total Knee Arthroplasty

Background

The purpose of this study was to investigate the influence of posterior tibial slope (PTS) on knee kinematics after cruciate-retaining total knee arthroplasty (CR-TKA). These influences were evaluated using a prosthesis designed with high geometric conformity to the medial articular surface under the weight-bearing condition of deep knee bending.

Total knee arthroplasty for arthritis of the knee with extra-articular deformity

BACKGROUND: Simultaneous corrective osteotomy of angular deformity and total knee arthroplasty has been considered the treatment of choice for patients with arthritis of the knee associated with ipsilateral extra-articular deformity. However, this procedure is technically demanding, and the functional outcome of the total knee arthroplasty may be jeopardized if the osteotomy fails. This retrospective study was performed to evaluate the clinical results of total knee arthroplasty combined with intra-articular bone resection, without osteotomy, in patients with extra-articular deformity and arthritis of the knee. METHODS: Fifteen patients with arthritis of the knee and extra-articular deformity underwent total knee arthroplasty with bone resection and soft-tissue balancing. All deformities had resulted from fracture malunion. There were ten uniplanar, three biplanar, and two triplanar deformities. The deformity was in the tibia in eight patients and in the femur in seven. The average angle of the femoral deformities was 15.1 degrees in the coronal plane and 8.1 degrees in the sagittal plane. Two femora had a rotational deformity, consisting of 20 degrees of internal rotation in one and 10 degrees of external rotation in the other. The average angle of the tibial deformities was 19 degrees in the coronal plane. RESULTS: The duration of follow-up averaged thirty-eight months. The average Knee Society knee score improved from 22.3 points preoperatively to 91.7 points at the time of the last follow-up, and the average Knee Society function score improved from 28.0 points preoperatively to 87.3 points at the time of the last follow-up. The average arc of knee motion improved from 77.7 degrees preoperatively to 103.7 degrees postoperatively. The average mechanical axis of the knee improved from 22.7 degrees of varus preoperatively to 0.3 degrees of varus at the time of the last follow-up. Two patients had an unsatisfactory clinical result, which was not related to the total knee arthroplasty. There were no complications such as infection, ligament instability, or component loosening. CONCLUSIONS: Total knee arthroplasty in conjunction with intra-articular bone resection is an effective procedure for patients with arthritis of the knee and extra-articular varus deformity of <20 degrees in the femur or 30 degrees in the tibia in the coronal plane.     

Anterior border of the tibia as a landmark for extramedullary alignment guide in total knee arthroplasty for varus knees

A disadvantage to using extramedullary alignment guides of the tibia for total knee arthroplasty (TKA) is difficulty in correctly identifying the ankle center. The anterior border of the tibia is easily palpable, as it is not covered by muscles and its shape is convex anteriorly. We hypothesized that appropriate points exist along the anterior border that can be used as landmarks for extramedullary guides. Prior to TKA, computed tomographic images of the entire tibia were obtained from 101 osteoarthritic knees with varus deformities. The relationship between the lines connecting two points on the anterior border and the mechanical axis was evaluated using 3D imaging software. The mean angles between each of 10 determined axes and the mechanical axis varied from 3.2° varus to 2.1° valgus in the coronal plane. In the sagittal plane, all axes referencing the anterior border of the tibia showed anterior inclination to the mechanical axis. The line connecting the medial one‐third of the patellar tendon attachment and the distal one‐fourth of the anterior border, however, was highly consistent and parallel to the mechanical axis in the coronal plane. This axis can be effectively used as a landmark for extramedullary guides during TKA. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 29:919–924