Cartilage assessment using preoperative planning MRI for femoral component rotational alignment

BackgroundSurgical planning of posterior referencing total knee arthroplasty (TKA) using computed tomography (CT) might lead to over-rotation of the femoral component because CT could not detect cartilage thickness of the posterior femoral condyle. The purpose of this study was to examine the rotational alignment difference of the femoral component between magnetic resonance imaging (MRI) and CT.MethodsFor elderly varus osteoarthritic patients, 66 varus osteoarthritic knee patients that underwent primary TKA were selected. Twenty-seven young patients who underwent primary anterior cruciate ligament reconstruction were selected as control. After the transepicondylar axis (CEA), the surgical epicondylar axis (SEA) and the posterior femoral condylar line (PCL) were drawn on CT and on MRI at the same angles as CT. Then, the practical PCL was drawn on MRI considering the cartilage thickness (the cartilage PCL). The angle between the SEA and the cartilage PCL (the cartilage posterior condylar angle (PCA)) was measured as preoperative planning. To investigate the accuracy of preoperative MRI measurement, the cartilage thickness on posterior femoral condyles was directly measured during TKA.ResultsThe cartilage PCA for varus osteoarthritic patients averaged 1.3 ± 1.3°. The cartilage PCA was 1.8 ± 1.0° significantly smaller than the bone PCA (the PCA measured on CT). Meanwhile, the cartilage PCA was 0.2 ± 0.4° significantly larger than the bone PCA in young people. The preoperative angle measurement on MRI strongly correlated with the direct measurement of cartilage thickness during TKA.ConclusionThere was 1.8° of divergence between MRI and CT in varus osteoarthritic patients due to cartilage degeneration of the medial femoral condyle. Cartilage assessment using MRI was useful for femoral component rotational alignment.     

数字技术在全膝关节置换术股骨旋转控制中的应用

目的 探讨在人工全膝关节置换术（TKA）中采用数字技术进行个体化股骨旋转定位的准确性及可行性。方法 选择上海市东方医院关节外科2012年5月—2013年11月68例膝关节严重退变病例纳入观察组进行回顾性分析,全部病例x线检查均符合Kellgren＆Lawrence分级法Ⅲ级以上,且合并严重的膝关节疼痛及活动受限。术前CT扫描下肢采集数据后利用数字化软件Mimicsl4．01在建立的3D立体模型中测量股骨后髁角,在TKA中参照该角度进行个体化截骨,术后再次测量股骨后髁角。选择2010年9月—2012年10月统一采用外旋3°截骨的62例患者作为对照组。比较两组手术前后股骨后髁角以及股骨假体旋转不良率。结果 观察组68例采用数字技术的患者术前测得股骨后髁角5．14°±1．59°（1．05°-8．26°）,术后0．83°±0．44°（0．03°～2．28°）;对照组中62例采用传统技术的患者术前测得股骨后髁角5．47°±1．23°（1．97°-8．41°）,术后3．82°±0．41°（0．08°-6．93°）。两组患者术前的股骨后髁角差异无统计学意义（t=1．349,P〉0．05）,观察组术后股骨后髁角明显小于对照组,差异有统计学意义（t=39．973,P〈0．01）。观察组股骨假体旋转不良率为10．3％（7／63）,对照组为38．7％（24／62）,两组比较差异有统计学意义（χ^2=14．420,P〈0．01）。结论 TKA术前应用数字化技术测量股骨后髁角,并根据测量结果进行个体化股骨外旋截骨,可以获得良好的股骨旋转力线。     

滑车线与股骨远端假体旋转轴线关系及其稳定性的影像学研究

目的 探讨滑车线在全膝关节置换手术中作为股骨远端假体旋转对线标志物的可靠性,为临床提供指导。方法 从2013年10月—2014年5月在同济大学附属第十人民医院行膝关节CT检查的患者中,选取符合纳入标准的膝关节影像学资料,共75例75侧进行回顾性分析。其中男36名,女39名;年龄23～60岁,平均(44.7±11.5)岁。在CT图像上定位外科经股骨上髁轴、前后轴、后髁轴、滑车线,以外科经股骨上髁轴为参照,测量前后轴、后髁轴、滑车线相对于该轴线的旋转角度,分别表示为APSA、PCA、ATSA,比较APSA、PCA、ATSA在不同性别间的差异,并比较三条轴线相对于外科经股骨上髁轴旋转角度的稳定性。结果 75例75侧膝关节中,APSA为86.38°±2.40°,男性86.73°±2.51°、女性86.06°±2.26°;PCA为3.89°±1.67°,男性3.62°±1.72°、女性4.13°±1.45°;ATSA为8.17°±2.01°,男性8.42°±1.89°,女性7.94°±2.08°。不同性别间ATSA、PCA、APSA比较,差异均无统计学意义(P值均＞0.05)。F检验提示,分别与前后轴、后髁轴相比较,滑车线相对于外科经股骨上髁轴的角度的稳定性差异均无统计学意义(P值均>0.05)。结论 通过对正常膝关节的影像学测量分析,滑车线作为全膝置换术中股骨远端假体旋转对位参考线的稳定性较好,可以为临床手术提供参考。     

Femoral component rotation in mobile-bearing total knee arthroplasty

The surgical technique utilized for the LCS mobile-bearing since 1977 has been a tibial cut first method which requires determination of femoral rotation with tension spacing. We evaluated 38 randomly selected mobile-bearing TKA in which this technique was utilized. All cases had satisfactory clinical results. Spiral computed tomography scans measured the posterior condylar angle which is the angle of the femoral component posterior condyles in relation to the surgical transepicondylar axis. The mean femoral component alignment was 0.3 degrees of internal rotation to the transepicondylar axis (S.D.=2.2 degrees ; range=6 degrees internal to 4 degrees external). Four cases (10%) were outside of 3 degrees from the TEA. Lateral patellar tilt and subluxation was identified in one female who had a femoral component position of 5 degrees internal rotation. In 90% of cases, the posterior condylar angle was within 3 degrees of the surgical transepicondylar axis which is regarded as the functional ideal for conventional methods.     

Posterior condylar cartilage may distort rotational alignment of the femoral component based on posterior condylar axis in total knee arthroplasty

Purpose

Among several anatomical references, the posterior condylar axis is the most apparent landmark to decide the femoral rotation for total knee arthroplasty. External rotation based on the posterior condylar axis requires condylar twist angle in order to set the femoral component parallel to trans-epicondylar axis although the angle is not constant. The angle during surgery differs from the pre-operative measurement on epicondylar view, because X-rays do not show the posterior condylar residual cartilage thickness. The thickness should be measured for the accurate femoral rotation.

Methods

We investigated the two twist angles on preoperative X-ray and during surgery, and the impact of residual cartilage on the setting of rotational angle of the femoral component in 184 knees in 112 patients with varus osteoarthritis (mean femorotibial angle: 185?±?6.9 from 169 to 205°).

Results

The twist angle during surgery was 5.2?±?1.3° (1.5–8.5°) and the angle on X-ray was 6.5?±?2.3° (0.6–13.5°). The rotational angle influenced by the residual cartilage was calculated to be 1.7?±?1.3° (0.0–4.6°). The discrepancy in the two twist angles was close to the rotational angle. There were, however, wide variations in all angles.

Conclusion

The results suggested the importance of considering the influence of the residual cartilage and the individual variation in determining the femoral component setting. Multiple reference frames for femoral component rotation or combination with gap technique may help to minimize malalignment which may lead to poor clinical outcome.     

A computed-tomography-scan-based template to place the femoral component in accurate rotation with respect to the surgical epicondylar axis in total knee arthroplasty

Background

Femoral rotational alignment is considered an essential factor for total knee arthroplasty because malrotation of femoral components results in poor outcomes. To obtain proper alignment, we developed a superimposable computed tomography (CT) scan-based template to intraoperatively determine the accurate surgical epicondylar axis (SEA), and evaluated the effectiveness of this CT template.

Preoperative rotational assessment of the distal femur with CT may cause femoral component malrotation in TKA

BackgroundBefore total knee arthroplasty (TKA), rotational assessment of the distal femur can be performed using either magnetic resonance imaging (MRI) or computed tomography (CT). Until now, there has been no study comparing the two modalities regarding rotational assessment of the distal femur in the same patients.MethodsWe retrospectively reviewed the preoperative CT and MRI images of 110 knees in 110 patients who underwent TKA. In the axial planes of CT and MRI scan, the posterior condylar axis (PCA), anatomical transepicondylar axis (aTEA), and perpendicular line to anteroposterior axis (pAPA) were identified; the angles between these studied lines were calculated. During TKA, the angles measured on the preoperative CT and MRI were compared with the measurements obtained in the intraoperative field.ResultsThe mean aTEA-PCA angle was 6.2 ± 1.9° with CT and 5.1 ± 1.8° with MRI. The mean pAPA-PCA angle was 4.7 ± 2.1° with CT and 3.5 ± 2.0° with MRI. The mean aTEA-PCA (1.1 ± 1.3°, p = 0.001) and pAPA-PCA (1.2 ± 1.2°, p = 0.012) angles significantly differed between CT and MRI. Intra-operatively, the mean aTEA-PCA angle was 4.7 ± 1.1° and the mean pAPA-PCA angle was 3.2 ± 0.9°. Reliability analysis between the preoperative CT/MRI and the intraoperative measurements gave kappa values of 0.72 for aTEA-PCA and 0.66 for pAPA-PCA with CT, and 0.82 for aTEA-PCA and 0.84 for pAPA-PCA with MRI.ConclusionsPreoperative rotational assessment of the distal femur with CT may cause higher external rotation of femoral component in TKA.     

人体膝关节股骨后髁角度的MRI测量

背景：全膝关节置换过程中股骨假体旋转力线良好非常重要,研究显示后髁角度是确定力线的重要依据,后髁角度为股骨后髁轴与股骨手术髁上轴之间角度,MRI测量可清晰显示后髁软骨、外上髁突起及内上髁凹陷,从而保证测量数据的准确。 目的：测量保定北部地区人群中膝关节后髁角度,为临床实施全膝关节置换过程中确定股骨假体旋转力线提供影像学依据。 方法：应用核磁共振机对入选中青年人群膝关节进行扫描,取膝关节伸直中立位,扫描平面垂直于膝关节机械轴,选择T1像上最佳膝关节轴位平面,由两名观察者独自分析图像,通过Bravo viewer 6.0影像软件观察股骨内上髁存在率,画出股骨髁上轴线及后髁线并测量两条轴线之间角度,即股骨后髁角度。 结果与结论：入选人群男性股骨后髁角度为(2.73±1.28)°,女性股骨后髁角度为(2.35±1.37)°,不同性别间差异无显著性意义。提示MRI测量股骨后髁角具有较大优越性,人工全膝关节置换过程中髁上轴线变异性较小,可参照后髁角度定位安装股骨假体,避免膝关节置换后并发症发生。中国组织工程研究杂志出版内容重点：人工关节;骨植入物;脊柱;骨折;内固定;数字化骨科;组织工程全文链接：     

Correlation between posterior offset of femoral condyles and sagittal slope of the tibial plateau

The aim of this study was to address, in normal knees, the variability of posterior offset of femoral condyles and tibial slope, and the presence of any correlation between the two that might be needed to achieve an adequate joint motion in flexion. Magnetic resonance images of normal knees of 80 subjects, 45 males and 35 females, with a mean age of 38.9 years, were analysed. Measurements were performed by two independent observers using an imaging visualization software. The tibial slope averaged 8 and 7.7 °, on the medial and lateral sides, respectively (P = 0.2); the mean posterior offset of femoral condyles was 27.4 and 25.2 mm on the two sides, respectively (P = 0.0001). The variation coefficient of the condylar offset and tibial slope was 11.5 and 38%, respectively. In the medial compartment, a significant correlation was found between the femoral condylar offset and the tibial slope, while the same was not observed in the lateral compartment of the knee. Magnetic resonance imaging allows the assessment of tibial slope and femoral condylar offset in the medial and lateral side separately, taking into account any difference between the two compartments. The sagittal tibial slope exhibits a greater variability compared with the posterior offset of femoral condyles. The correlation found, in the medial compartment, between the tibial slope and femoral condylar offset suggests that the reconstitution of the proper morphology of the posterior part of the knee joint may be necessary to obtain a full range of motion in flexion after total knee replacement.     

Can the epicondylar axis be defined accurately in total knee arthroplasty?

As part of a study on rotational alignment of the femoral component in knee replacement, the surgical epicondylar axis was identified in 74 knees and marked with pins. An alternative technique was employed to achieve rotational alignment and in each case the distance between the pins and the cut surface of the posterior condyles was measured. The alignment of the femoral component was measured postoperatively by axial CT scans of the distal femur, allowing an assessment to be made of what would have been achieved if the epicondylar pins had been used for guidance. Only 75% of knees would have been within 3 degrees of the true epicondylar axis using the epicondyles to control rotation. The error range was large (range 6 degrees ER to 11 degrees IR). Our conclusion is that even in experienced hands clinical estimation of the epicondylar axis is inaccurate and should not be relied upon as the sole determinant of femoral rotation.     

Relationship of the posterior femoral axis of the “kinematically aligned” total knee arthroplasty to the posterior condylar,transepicondylar, and anteroposterior femoral axes

BackgroundA recent proposed modification in surgical technique in total knee arthroplasty (TKA) has been the introduction of the “kinematically aligned” TKA, in which the angle and level of the posterior joint line of the femoral component and joint line of the tibial component are aligned to those of the “normal,” pre-arthritic knee. The purpose of this study was to establish the relationship of the posterior femoral axis of the “kinematically aligned” total knee arthroplasty (TKA) to the traditional axes used to set femoral component rotation.MethodsOne hundred and fourteen consecutive, unselected patients with preoperative MRI images undergoing TKA were retrospectively reviewed. The transepicondylar axis (TEA), posterior condylar axis (PCA), antero-posterior axis (APA) of the trochlear groove, and posterior femoral axis of the kinematically aligned TKA (KAA) were templated on axial MRI images by two independent observers. The relationships between the KAA, TEA, APA, and PCA were determined, with a negative value indicating relative internal rotation of the axis.ResultsOn average, the KAA was 0.5° externally rotated relative to the PCA (minimum of − 3.6°, maximum of 5.8°), − 4.0° internally rotated relative to the TEA (minimum of − 10.5°, maximum of 2.3°), and − 96.4° internally rotated relative to the APA (minimum of − 104.5°, maximum of − 88.5°). Each of these relationships exhibited a wide range of potential values.ConclusionsUsing a kinematically aligned surgical technique internally rotates the posterior femoral axis relative to the transepicondylar axis, which significantly differs from current alignment instrument targets.     

Computed tomographic study of the posterior condylar angle in arthritic knees: its use in the rotational positioning of the femoral implant of total knee prostheses

The epicondylar axis is a reliable reference to check the rotation of the femoral implant in total knee prostheses (TKPs). However, during the operation it seems easier to use the posterior condylar axis as a landmark. The angle between these two axes is called the posterior condylar angle (PCA). The aim of this study was to measure the PCA in arthritic knees to assess the reliability of the posterior condylar axis as a reference for the control of the rotation of the femoral implant and to look for correlation with other radiological measurements. This prospective study consisted of 103 arthritic knees (81 varus, 22 valgus) before a TKP had been done in 103 patients (75 women, 28 men). The assessment of the PCA was made by computed tomographic scanning (CT). The HKA, HKS and HKT angles were measured on the pangonogram. The posterior condylar axis was internally rotated with respect to the epicondylar axis. The average value for all the patients was 2.65° degrees with a range from 0° to 7°. The PCA was significantly increased in the valgus knees. There was no correlation between the angles on the pangonogram and the posterior condylar axis. While the preoperative assessment of the PCA by CT scanning is reliable, the results obtained indicate the marked variability in its value. If one wishes to use the posterior condylar axis as a guide for rotation, it is therefore necessary to assess the PCA for each patient using adjustable jigs according to the value obtained. No measurement on standard radiographs allowed an extrapolation of the value of the PCA, and CT scanning seems to be the preferable radiological examination.

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Electronic Supplementary Material The french version of this article is available in the form of electronic supplementary material and can be obtained by using the Springer Link server located at

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Etude tomodensitométrique de l'angle condylien postérieur dans les genoux arthrosiques. Intérêt dans le positionnement en rotation de l'implant fémoral dans les prothèses totales de genou

Résumé L'axe épicondylien est une référence fiable pour le contrôle de la rotation de l'implant fémoral dans les prothèses totales de genou (PTG). Mais, lors de l'intervention, il semble plus facile d'utiliser l'axe condylien postérieur comme repère. L'angle entre ses deux axes est appelé angle condylien postérieur (ACP). Le but de cette étude était de mesurer l'ACP dans les genoux arthrosiques, d'évaluer la fiabilité de l'axe condylien postérieur comme référence pour le réglage de la rotation de l'implant fémoral, de rechercher une corrélation avec d'autres mesures radiologiques. Une étude prospective comportant 103 genoux arthrosiques (81 varus et 22 valgus), avant PTG a été effectuée, chez 103 patients (75 femmes et 28 hommes). L'évaluation de l'ACP a été faite par examen tomodensitométrique (TDM). Les angles HKA, HKS et HKT ont été mesurés sur le pangonogramme. L'axe condylien postérieur était en rotation interne par rapport à l'axe épicondylien. La valeur moyenne pour tous les patients était de 2.65°, avec des valeurs de 0 à 7°. La valeur de l'angle CP augmentait avec une différence significative dans le groupe des genu valgum. Il n'y avait pas de corrélation entre les angles du pangonogramme et l'ACP. Si l'évaluation pré-opératoire de l'ACP par TDM est fiable, les résultats obtenus mettent en évidence une variabilité importante de sa valeur. Il faut donc, si l'on veut utiliser l'axe condylien postérieur comme repère de rotation, évaluer pour chaque patient l'ACP, et utiliser un ancillaire réglable reportant la valeur obtenue. Aucune mesure sur des radiographies standard ne permettant d'extrapoler la valeur de l'ACP, la TDM semble l'examen radiologique de choix.

     

Kellgren–Lawrence grade of osteoarthritis is associated with change in certain morphological parameters

BackgroundTo compare selected morphological parameters between normal and osteoarthritic (OA) knees, as well as to evaluate differences in these parameters between Kellgren–Lawrence (K-L) grades of OA.MethodsKnee joint morphology was evaluated using magnetic resonance (MR) images of 200 participants with knee OA (50 each of K-L grades 1–4) and 50 without knee OA, matched for age, body mass index, sex, and tibiofemoral angle. Knees with a coronal alignment within five degrees of neutral and no apparent bone loss on radiographs were included. Twenty-one morphologic parameters of the distal femur and proximal tibia were measured on MR images. Correlation between the K-L grade and measured parameters and differences in measured parameters across the K-L grades and between the OA and control groups were evaluated.ResultsThe K-L grade was significantly correlated with multiple distal femur measurements including the posterior condylar angle (PCA), lateral epicondyle to posterior condylar cartilage (LEPC) length, medial epicondyle to posterior condylar cartilage (MEPC) length, medial epicondyle to distal cartilage (MEDC) length, medial tibial slope angle, femoral condylar cartilage height difference (FCHDc), and femoral condylar bone height difference (FCHDb) (P < 0.05). A significant difference was identified between the different K-L grades with regard to PCA, LEPC, MEPC, MEDC, and FCHDc (P < 0.05). There was no correlation between K-L grade and measured proximal tibial parameters.ConclusionsAmong knees without significant angular deformity, progression of knee OA is associated with a change in the morphology of the femoral condyles but not of the proximal tibia.     

Transepicondylar axes for femoral component rotation might produce flexion asymmetry during total knee arthroplasty in knees with proximal tibia vara

BackgroundAdequate rotation of the femoral component in total knee arthroplasty is mandatory for prevention of numerous adverse sequelae. Therefore, we investigate whether there is the distal femoral deformity in knees with tibia vara. The purpose of this study was to evaluate the reliability of the transepicondylar axis as a rotational landmark in knees with tibia vara.MethodsWe retrospectively reviewed and selected 101 osteoarthritic knees with proximal tibia vara and 150 osteoarthritic knees without tibia vara for inclusion in this study. The transepicondylar axis (TEA), anteroposterior (AP) axis and posterior condylar (PC) line were measured using the axial image from magnetic resonance imaging axial images. We compared the external rotation angle of the TEA relative to the PC line between groups in order to investigate the presence of distal femoral anatomical adaptation in the tibia vara group.ResultsThe TEA in the tibia vara group had 6.1º of external rotation relative to the PC line, which was not significantly different from the 6.0º of external rotation in the non-tibia vara group. The line perpendicular to the AP axis in the tibia vara group had 6.1º of external rotation relative to the PC line, which was not significantly different from the 5.4º of external rotation in the non-tibia vara group. Distal femoral geometry was unaffected by the tibia vara deformity.ConclusionsThe use of transepicondylar axes in determining femoral rotation may produce flexion asymmetry in knees with tibia vara.Level of evidenceLevel III     

Comparison of medial and lateral posterior femoral condyle articular cartilage wear patterns

Background

While degenerative changes to the articular cartilage of the anterior and distal portions of the femoral condyles have been well studied in the literature, the changes that occur on the posterior femoral condyle are not as clear. The purpose of this study was to assess the difference in articular cartilage thickness between the medial and lateral posterior femoral condyles in knees undergoing unicompartmental knee arthroplasty.

Rotational mismatch between femoral and tibial components should be avoided in JOURNEY II bi-cruciate stabilized total knee arthroplasty

BackgroundJOURNEY II bi-cruciate stabilized (BCS) knee system, a guided motion total knee arthroplasty (TKA), has been reported to reproduce physiological knee kinematic motion with good clinical outcomes. However, this guided system may be sensitive to the femorotibial rotational alignment.MethodForty-four patients (50 knees) who underwent JOURNEY II BCS TKA were included in this retrospective study. The 2011 Knee Society Score (KSS) and range of motion were assessed pre-operatively and one year postoperatively. The femoral component rotational angle relative to the surgical epicondylar axis and the tibial component rotational angle relative to Akagi’s line were measured postoperatively. The absolute difference between the femoral and tibial component rotational angles was defined as femorotibial component rotational mismatch. The correlation between the parameters of these rotational alignments and postoperative clinical outcomes was evaluated. Additionally, receiver operating characteristic curve analysis was performed to determine the optimal cut-off point of the femorotibial component rotational mismatch.ResultsMean femoral and tibial component rotational angles were 0.4° (internal rotation) and 0.7° (external rotation), respectively. The rotational mismatch of the femorotibial component was 3.2°. There were negative correlations between femorotibial rotational mismatch and clinical outcomes, including objective knee indicators, patient satisfaction, functional activities, and total 2011 KSS. The area under the curve of the femorotibial component rotational mismatch was 0.768 and the cut-off value identified by the Youden index was 2.8°.ConclusionsExcessive rotational mismatch between the femoral and tibial components can negatively influence the clinical outcomes of JOURNEY II BCS TKA.     

Optimized functional femoral rotation in navigated total knee arthroplasty considering ligament tension

Femoral malrotation in total knee arthroplasty is correlated to an increased number of revisions. Anatomic landmarks such as Whiteside line, posterior condyle axis and transepicondylar axis are used for determining femoral component rotation. The femoral rotation achieved with the anatomical landmarks is compared to the femoral rotation achieved by a navigated ligament tension-based tibia-first technique.Ninety-three consecutive patients with gonarthritis were prospectively enrolled. Intraoperatively the anatomical landmarks for femoral rotation and the achieved femoral rotation using a navigated tension-based tibia-first technique were determined and stored for further comparison. A pre- and postoperative functional diagram displaying the extension and flexion and varus or valgus positions was also part of the evaluation.Using anatomical landmarks the rotational errors ranged from 12.2° of internal rotation to 15.5° of external rotation from parallel to the tibial resection surface at 90° flexion. A statistical significant improved femoral rotation was achieved using the ligament tension-based method with a rotational error ranged from 3.0° of internal rotation to 2.4° of external rotation. The functional analyses demonstrated statistical significant lower varus/valgus deviations within the flexion range and an improved maximum varus deviation at 90° flexion using the ligament tension-based method.Compared to the anatomical landmarks a balanced, almost parallel flexion gap was achieved using a navigation technique taking the ligament tension of the knee joint into account. As a result the improved femoral rotation was demonstrated by the functional evaluation. Unilateral overloading of the polyethylene inlay and unilateral instability can thus be avoided.     

Fracture of titanium nitride-coated femoral component after total knee arthroplasty

We report a case of fracture of a titanium nitride-coated femoral component 3 years after primary total knee arthroplasty (TKA). The fracture was at the medial condylar area just posterior to the medial peg of the femoral component. The backside of the broken medial condylar portion of the femoral component was devoid of cement. Debonding of the component is a possible cause of the stress fracture. To our knowledge, this is the first case report of the fracture of the femoral component manufactured from titanium alloy.Level of evidenceIV     

Femoral rotational asymmetry is a common anatomical variant

The sulcus line (SL) is a three‐dimensional landmark that corrects for individual variation in the coronal alignment of the trochlear groove in contrast to the traditional Whiteside's line (WL). Femoral rotational asymmetry (FRA) is an anatomical variation in which the posterior condyles and trochlear groove are not perpendicular to each other. This study aims to measure the SL and assess its reliability relative to WL, in addition to measuring and classifying the FRA. A retrospective analysis of a series of 191 CT scans of nonarthritic knees was performed. Measurements were taken of rotational landmarks in three‐dimensional reconstructions. The variability and outlier rate of SL was less than WL (P < 0.05), however, it was also greater than the posterior condylar line (PC) (P < 0.05). Averaging the PC + 3° and the SL did not change the rate of femoral malrotation relative to the surgical epicondylar axis (SEA) (P > 0.05), however it decreased the rate of change of the rotational alignment of the trochlear groove between the native knee and the prosthetic knee from 31% to 5% (P < 0.05). FRA was classified and was >5° in 56/191 (29%) of cases. The SL technique is more accurate than WL for determining the rotational alignment of the trochlear groove. Nonarthritic femora have a high rate of rotational asymmetry. Identifying and classifying FRA in individual cases allows the femoral component to be inserted in a position which gives the best possible match to both the native posterior condyles and trochlear groove. Clin. Anat. 31:551–559, 2018. © 2018 Wiley Periodicals, Inc.     

Accuracy of 2D CT-Based Measurements of Rotational Alignment of the Femoral Component for Total Knee Arthroplasty

PurposeWe aimed to investigate the accuracy of two-dimensional computed tomography (2D-CT)-based methods for measuring rotational alignment of the femoral component during total knee arthroplasty in comparison to reference values for three-dimensional (3D) reconstruction.Materials and MethodsWe selected the “most protruding transepicondylar axis section,” “most protruding posterior condylar line section,” and “distal femoral cut section” on 2D-CT images for 100 knees. We investigated posterior condylar angle (PCA) and condylar twist angle (CTA) values using three different methods on 2D-CT and compared to these values to those obtained using a 3D model.ResultsThe mean PCA and CTA values were 2.8° and 7.0° on the 3D model and 2.0° to 2.1° and 5.9° to 6.0° on 2D-CT, respectively. Errors in PCA and CTA measurement included internal rotation of 0.8° and 1.1° with the 1-plane and 2-plane methods and 0.9° and 1.0° with the assumed resection method, respectively.ConclusionMean errors in PCA and CTA values measured using three different methods on 2D-CT were not significantly different. However, PCA and CTA values measured on 2D-CT were approximately 1° smaller than their 3D values. Thus, we suggest that adding 1° to the mean PCA and CTA values obtained from a single plane of 2D-CT would provide values similar to those obtained from 3D reconstruction.