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Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_IX | Pages 86 - 86
1 Mar 2012
Page S Pinzuti J Payne AP Picard F
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Purpose

To evaluate the normal bony profiles of the anterior surface of the distal femoral cortex, its relation to the posterior condylar plane and assess the implications of these findings to anterior femoral referencing.

Methods and Results

Fifty well preserved adult, cadaveric femora were studied. Different points on the proximal and distal femur were recorded using an optoelectronic system based around a commercial navigation system. Definitions were: anterior femoral plane (AFP) derived from nine points on the anterior cortex of the distal femur; posterior condylar plane (PCP) as the plane parallel to the sagittal mechanical axis of the femur and containing the PCA. The anterior femoral cortex was divided into lateral, median and medial areas. Average heights of each of these areas from the PCP were calculated, as were the angles between the PCP and AFP.

Four distinct anterior cortex profiles were seen. In 28 specimens the lateral side had the highest mean height and the medial side had the lowest mean height (Group 1). For 13 specimens the lowest mean height was in the median area (Group 2) but 7 specimens had highest mean height here (Group 3). Only 2 specimens had the highest mean height on the medial side with the lowest mean height on the lateral side (Group 4). The average angle between the AFP and the PCP was 1.3° of external rotation. In Group 1 the AFP angle was more internally rotated (-10° to -2°) compared to the other groups, in particular Group 4 which showed the most external rotation (3° and 4°).


Orthopaedic Proceedings
Vol. 93-B, Issue SUPP_IV | Pages 528 - 528
1 Nov 2011
Picard F Page S Willcox N Deakin A Pinzuti J Payne A
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Purpose of the study: Rotation of the tibial implant is an important factor for the functional outcome of total knee arthroplasty (TKA). Any rotational malposition will cause eccentric loading of the plateau. Several techniques have been recommended to avoid malposition, but none has proven superior over the others in terms of reliability or reproductibility. The landmark used to establish rotation must meet two prerequisites: easy identification and reliable representation of the anatomic rotation of the proximal tibia. This study was conducted to compare seven different techniques for landmarking used for choosing the rotation of the tibial base in TKA.

Material and methods: An optoelectronic method was used to measure 50 tibia selected among a collection of 600 skeletons. A palper was used to locate 34 distinct landmarks and institute each reference system. The groups of anatomic points were reconstructed to form lines and plans depending on the comparisons to make: posterior condylar alignment (PCA), transversal alignment (TA), anterior condylar alignment (ACA), alignment of the anterior tibial tuberosity (ATT), the transmalleolar alignment (TMA), the line of the tibial crest (LTC) and a new line, the anterior distal line (ADL). The PCA was used as the reference.

Results: Intra-observer variation was determined in a preliminary study using ten consecutive measurements. The standard deviation was 0.5° with a distribution of 1.8°. Angle: mean [-:internal rotation; +external rotation], standard deviation: difference between the minimum and the maximum. TA: −5.13; 9.2; 38.03; ACA: −12.81; 6.7; 41.74; ATT: 68.72; 8.6; 58.46; TMA: −22.68; 11.6; 72.84; LTC: 67.56; 10.3; 46.11; ADL: 16.61; 13.2; 74.93.

Discussion: This study did not prove convincingly that any one of the tibial alignments was better than another; which demonstrates that use of a single reference is probably inappropriate to determine the rotational alignment of the tibial base for TKA. It was noted however that the anterior condylar line (mean external rotation 12.8°-SD< 7° relative to the PCA) could be pertinent for future research since this line is easily accessible and palpable, particularly during navigated surgery.