Relationship between the surgical epicondylar axis and the articular surface of the distal femur: An anatomic study
Service de Chirurgie Orthopédique, Centre Livet, Hôpital de la Croix-Rousse, 8, rue de Margnolles, 69300 Caluire, Lyon, France. Knee Surgery Sports Traumatology Arthroscopy
(Impact Factor: 3.05).
08/2008; 16(7):674-82. DOI: 10.1007/s00167-008-0551-9
Many authors presented the epicondylar axis as the fixed axis of rotation of the femoral condyles during flexion of the knee. Positioning of the femoral component of a total knee arthroplasty (TKA) based on the epicondyles has been proposed. This work is a critical analysis of this concept. Metallic bodies were inserted at the level of collateral ligament insertions on 16 dried femurs, allowing us to locate the surgical epicondylar axis. The dried femurs were studied using standard radiographs and CT-scan. CT cuts were made perpendicular to the epicondylar axis. The medial mechanical femoral angle and the epicondylar angle were measured on the radiographs. The posterior and distal epiphyseal rotations relative to the epicondylar axis (Posterior Condylar Angle, PCA, and Distal Condylar Angle, DCA, respectively) were measured on the CT-scans. PCA and DCA values were compared. The centre of the posterior femoral condyles was located on sagittal reconstructions using the tangent method and was confirmed with circular templates, and then compared to the location of the epicondyles. Circle-fitting of the entire femoral condylar contours centred on the epicondyles was also tried. The mechanical femoral axis was nearly perpendicular to the epicondylar axis but with important variations. The average PCA and DCA were 1.9 degrees +/- 1.8 degrees and 3.1 degrees +/- 2.1 degrees , respectively. No relationship could be established between the mechanical femoral angle and the PCA. The individual differences between the PCA and the DCA averaged 2.2 degrees . A significant distance was found between the centre of the condylar contours and the epicondyles: 6.5 mm in average on the lateral side (range 2.3-11.3 mm) and 8.4 mm on the medial side (range 4.0-11.6 mm). Circle-fitting of the entire medial or lateral femoral condylar contours centred on the epicondyles was not possible. The centre of the posterior femoral condyles is significantly different from the epicondylar axis, thus refuting the conclusions of previous authors. Furthermore, considering the differences between the distal and posterior condylar angles shown here, as well as the difficulty of repeatably locating the epicondyles during surgery, using the epicondylar axis as the only landmark to position the femoral component during a first intention TKA is not recommended. The surgical epicondylar axis does not appear to be an adequate basis for the understanding of the shape of the distal femur.
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ABSTRACT: Rotational malalignment still accounts for an unacceptable number of failures in total knee arthroplasty (TKA). This paper presents a literature review of previously published papers describing rotational alignment of the distal femur and discussing different techniques in obtaining correct rotational alignment of the femoral component in TKA. Based on the published values, the following mean angular relationships between the rotation axes of the distal femur in the axial plane can be calculated: the posterior condylar line is on average 3 degrees internally rotated relative to the surgical transepicondylar axis (TEA), 5 degrees relative to the anatomical TEA and 4 degrees relative to the perpendicular to the trochlear anteroposterior axis. The greatest interindividual variability is described for the trochlear AP axis. The worst track record regarding inter- and intraobserver variability is for the TEA. Given the large ranges and standard deviations of all reference axes, and the important inter- and intraobserver variability in the surgical location of the TEA, the use of a preoperative CT scan is recommended.
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ABSTRACT: Les erreurs de rotation fémorale engendrent un nombre inacceptable d’échecs après prothèse totale du genou (PTG). Ce travail est une revue de la littérature des articles publiés décrivant l’orientation en rotation du composant fémoral et discutant les différentes techniques qui permettent d’obtenir une rotation correcte du composant fémoral au cours des PTG. En se fondant sur les valeurs publiées, il est possible de calculer les angles moyens entre les axes de rotation du fémur distal dans le plan horizontal : la ligne condylienne postérieure est en rotation interne de 3° en moyenne par rapport à l’axe transépicondylien (ATE) chirurgical, 5° par rapport à l’ATE anatomique et 4° par rapport à la perpendiculaire à l’axe antéropostérieur (AP) de la trochlée. La plus grande variabilité entre individus a été décrite pour l’axe trochléen AP et la plus grande variabilité inter- et intra-observateur pour le repérage de l’ATE. Etant données les importantes variations individuelles et déviations standard des axes de références et la grande variabilité inter et intra-observateur du repérage peropératoire de l’ATE, nous recommandons d’utiliser un scanner préopératoire pour mesurer de façon fiable l’angle condylien postérieur.
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ABSTRACT: The femoral shaft (FDA) and transepicondylar (TA), anterior-posterior (WL) and posterior condylar (PCL) axes are fundamental quantities in planning knee arthroplasty surgery. As an alternative to the TA, we introduce the anatomical flexion axis (AFA). Obtaining such axes from image data without any manual supervision remains a practical objective. We propose a novel method that automatically computes the axes of the distal femur by processing the femur mesh surface.
Surface data were processed by exploiting specific geometric, anatomical and functional properties. Robust ellipse fitting of the two-dimensional (2D) condylar profiles was utilized to determine the AFA alternative to the TA. The repeatability of the method was tested upon 20 femur surfaces reconstructed from CT scans taken on cadavers.
At the highest surface resolutions, the relative median error in the direction of the FDA, AFA, PCL, WL and TA was < 0.50 degrees, 1.20 degrees, 1.0 degrees, 1.30 degrees and 1.50 degrees, respectively. As expected, at the lowest surface resolution, the repeatability decreased to 1.20 degrees, 2.70 degrees, 3.30 degrees, 3.0 degrees and 4.70 degrees, respectively. The computed directions of the FDA, PCL, WL and TA were in agreement (0.60 degrees, 1.55 degrees, 1.90 degrees, 2.40 degrees) with the corresponding reference parameters manually identified in the original CT images by medical experts and with the literature.
The proposed method proved that: (a) the AFA can be robustly computed by a geometrical analysis of the posterior profiles of the two condyles and can be considered a useful alternative to the TA; (b) higher surface resolutions leads to higher repeatability of all computed quantities; (c) the TA is less repeatable than the other axes.
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