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Introduction: A previous study demonstrated that performing a total knee arthroplasty through a lateral approach including anterior tibial tuberosity (ATT) osteotomy (refixed in its original position) presented numerous advantages: correcting the preoperative patella lateral tilt and improving postoperative patella tracking. We hypothesized that these improvements in patella centering were, at least in part, due to an increased external rotation of the tibial component. Postoperative scannographic studies were, therefore, undertaken to measure tibial component rotation and analyze the results according the medial and lateral exposure used., Hypothesis: Rotational positioning of the tibial component is influenced by the lateral or medial approach selected at surgery., Materials and Methods: Forty-five CAT scans, performed according to the protocol criteria of the French Hip and Knee Society (SFHG), were studied 3 months postoperatively: 15 knees operated through the lateral approach and 30 knees operated through a standard medial approach. The total knee utilized in all these cases was a posteriorly stabilized, fixed-bearing, design. We measured first the angle formed between the perpendicular to the transverse axis of the tibial component and the axis joining the ATT to the center of the knee; second we also measured the coronal distance between the center of the component and the anterior tibial tuberosity (ATT)., Results: In the group using the medial approach, the lateral position of the ATT was 7 + or - 3mm with a rotation angle of 18 degrees . In the group using the lateral approach these measurements were respectively 1 + or - 4mm and 2 degrees (p<0.0001)., Discussion: External rotation of the tibial component is substantially increased by the lateral approach compared to the medial approach. Better exposure of the lateral tibial plateau is probably responsible of this difference. This increased external rotation improves postoperative patella tracking., Type of Study: Prospective; comparative; non-randomized study; level 3., (2009 Elsevier Masson SAS. All rights reserved.)

Background: Patellofemoral instability following total knee arthroplasty is a very common complication which may result from a defective rotational positioning of the femoral component. However, rotational landmarks for optimal orientation are not unequivocal. Moreover, no proven correlation has yet been established between preexisting rotational malposition and patellofemoral instability occurrence., Hypothesis: Any preexisting distal femoral rotational misalignment is associated with a preop patellofemoral instability in arthritic knees prior to undergoing arthroplasty. A prospective diagnostic study was conducted to test this hypothesis on the basis of morphometric data., Material and Methods: One hundred and eighteen patients were prospectively enrolled in this study. Patellar lateralization was measured on 30 flexion patellofemoral views. Three positionings were arbitrarily defined (less than 3 mm of lateralization, between 3 and 5 mm, over 5 mm). Three angles were preoperatively measured using CT scans: (1) the posterior condylar angle between posterior bicondylar axis and transepiphyseal axis, (2) the anterior trochlear angle between transepicondylar axis and trochlear opening plane, (3) the sum of anterior trochlear and posterior condylar angles finally formed the global trochlear opening angle., Results: The patella was centered in 86 cases and lateralized in 32 cases (less than 5 mm in 25 cases and over 5 mm in seven cases). Independently from the degree of patellar lateralization, the global trochlear opening angle was constant (p=0.41). The value of the posterior condylar angle was statistically inferior when patella was centered (p=0.01; r=0.44). The value of the anterior trochlear angle varied opposite to the posterior condylar angle. Femoral anteversion, position of the anterior tibial tuberosity and tibiofemoral index could not be correlated with patellar positioning. No relationship could be established between patellar lateralization and overall torsional deformities of the lower extremity., Conclusion: The centering of the patella in arthritic knees depends on distal femoral osseous factors which determines the posterior condylar angle and anterior trochlear angle on either side of the transepicondylar axis. Since the trochlear opening angle is constant, the obliquity of the transepicondylar axis appears crucial in patellar lateralization. A better understanding of the influence of distal femoral morphology on patellar positioning will ensure improved positioning of femoral components in total knee arthroplasties or in isolated femoropatellar joint replacements., Level of Evidence Iii: Prospective diagnostic study., (2009 Elsevier Masson SAS. All rights reserved.)