Posterior reference guides do not always maintain the size of posterior femoral condyles in TKA

Abstract

This study showed that posterior femoral condyle bone resection thickness was different for each posterior reference guide. The rotation centre of posterior reference guides influenced the bone resection thickness in the posterior femoral condyle. The size of the posterior femoral condyles increased in some guides but decreased in other guides. The maximum differences in size changes of the posterior femoral condyles between the guides were 1.9 mm at 0° external rotation, 4.1 mm at 3° external rotation, and 6.3 mm at 6° external rotation. To control the size of posterior femoral condyles, the posterior reference guide design should be checked before use.

External rotation of the femoral component increases asymmetry of the posterior condyles

“…The asymmetry of the femoral condyles at the posterior resection plane has been reported in a number of previous studies. 9,16,24 Using intra-operative measurements from 100 consecutive knee arthroplasties aligned to the transepicondylar axis, Poilvache et al 16 found the resected medial condyle to be 2.7 mm thicker than the lateral condyle. Using CT scans of 44 knees, Urabe et al 9 simulated the femoral resections performed during TKA, externally rotated by 3º to the posterior condylar line, and found the medial condyle to be 5.3 mm wider and 3.9 mm longer than the lateral condyle.…”

“…The authors also compared their morphometric measurements with the dimensions of four TKA models and emphasised the risks of prosthetic overhang due to condylar asymmetries. Recently, Minoda et al 24 reported up to 6.3 mm differences in thickness of resected bone using central versus medial referencing guides, when applying 6° of external rotation. However, none of these authors investigated how the extent and technique of Graphs showing digitised points as seen in the coronal view at the posterior resection plane, showing changes in shapes and dimensions of both condyles, in the neutral position (0º), when externally rotating the resection plane by 5º using 'central referencing', and 'medial referencing' techniques.…”

“…11,[21][22][23] The resulting modification of the posterior osteotomy influences the dimensions and asymmetry of the resected condyles. 16,24 Recently, Minoda et al 24 described two main types of posterior cutting guides, depending on the way the rotation is applied. With 'central referencing' guides, the rotation is performed around the intercondylar notch, resulting in both medial over-resection and lateral under-resection.…”

Lateral Distal Femoral Condyle as a Precise Reference for Distal Femoral Resection in Total Knee Arthroplasty for Severe Varus Knee Osteoarthritis

“…The thickness of distal femur resection was set to be consistent with the implant size of 8mm, including the thickness of cartilage and bone (Fig. 2) [11]. Cartilage thickness was set to be consistent with the MRI date.…”

Preoperative Virtual Total Knee Arthroplasty Surgery Using a Computed Tomography-based 3-dimensional Model With Variation in Reference Points and Target Alignment to Predict Femoral Component Sizing

“…The rotation center affects the resection of the posterior femoral condyle even when using the posterior reference guide. Therefore, even if the repair is intended to focus on the medial posterior condyle, different laxity will occur on the medial and lateral sides [ 8 ]. With the anterior reference guide, greater resection should cause a component size difference between the medial and central rotation types.…”