j.otsr.2009.06.003

Orthopaedics & Traumatology: Surgery & Research (2010) 96, 325

LETTER TO THE EDITOR

Comments on: ‘‘Does lateral versus medial exposure influence total knee tibial component final external rotation? A scannographic appraisal’’ published in Orthop Traumatol Surg Res doi:10.1016/j.otsr.2009.06.003 Dear Editor, It was with great interest that I read the article by Passeron et al. (doi:10.1016/j.otsr.2009.06.003) titled ‘‘Does lateral versus medial exposure influence total knee tibial component final external rotation? A scannographic appraisal.’’ The statistical analysis seems to confirm the hypothesis advanced in the abstract: ‘‘positioning the tibial component in rotation is influenced by the lateral or medial approach.’’ However, in the explanation of the surgical technique, the authors state that ‘‘we sought to position the trial tibial implant parallel to the femoral component, with the knee in complete extension.’’ This leads us to believe that tibial implant rotation is provided by the rotation of the femoral implant component in relation to the femoral epiphysis, ‘‘rotation which was adapted by navigation to the posterior condylar angle measurement obtained with preoperative CT.’’ Since the preoperative femoral torsions were undoubtedly different for cases of genu varum and genu valgum, it would seem that the implant posterior condylar angles differed in the lateral approaches, particularly those performed in cases of genu valgum, and in the medial approaches, particularly those performed in cases of genu varum. This could explain that the tibial implant rotations differed in the lateral and medial approaches. Unfortunately, the preoperative femoral torsion and external rotation values of the femoral implants in relation to femoral epiphyses were not noted and not correlated with the external rotation values of the tibial implant. Moreover, in TKA, the postprosthetic tibial tuberosity—trochlear groove distance, which governs the centering, patellar tilt, and coronal stability of the

patellofemoral joint, is only modified by femoral implant rotation: its external rotation in relation to the femoral epiphysis reduces the tibial tuberosity—trochlear groove distance and reduces its lateral condyle slope, making its lateral edge less prominent [1]. The tibia, which is maintained under the femur by the surrounding ligaments, does not turn (and therefore the coronal position of the tibial tuberosity is not modified), unless the implant is constrained in rotation and if the tibial implant does not ‘‘fall’’ under the femoral implant (which the technique suggested by the authors prevents). In conclusion, without complementary data, tibial implant rotation may not depend on the side of the surgical approach. • Goutallier D, Van Driessche S. Articulation fémoropatellaire et appareil extenseur dans la prothèse du genou. In: Prothèses totales du genou, Lemaire R et Witvoet J, editors; Cahiers d’enseignement de la SOFCOT, 2002, Éditions scientifiques et médicales Elsevier SAS. 149—165.

Reference [1] Boisrenoult P, Scemama P, Fallet L, Beaufils P. La torsion épiphysaire distale du fémur dans le genou arthrosique. Rev Chir Orthop Reparatrice Appar Mot 2001;87: 469—76.

D. Goutallier ∗ S. Van Driessche Service de chirurgie orthopédique et traumatologique, hôpital Henri-Mondor, Assistance publique—Hôpitaux de Paris, faculté de médecine de Créteil (Université Paris XII), Paris, France

DOI of original article:10.1016/j.otsr.2009.06.003. 1877-0568/$ – see front matter © 2010 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.otsr.2010.03.004

∗ Corresponding author. E-mail address: [email protected] (D. Goutallier).