Computed Tomography Analysis of Postsurgery Femoral Component Rotation Based on a Force Sensing Device Method versus Hypothetical Rotational Alignment Based on Anatomical Landmark Methods: A Pilot Study

Abstract

Rotation of the femoral component is an important aspect of knee arthroplasty, due to its effects on postsurgery knee kinematics and associated functional outcomes. It is still debated which method for establishing rotational alignment is preferable in orthopedic surgery. We compared force sensing based femoral component rotation with traditional anatomic landmark methods to investigate which method is more accurate in terms of alignment to the true transepicondylar axis. Thirty-one patients underwent computer-navigated total knee arthroplasty for osteoarthritis with femoral rotation established via a force sensor. During surgery, three alternative hypothetical femoral rotational alignments were assessed, based on transepicondylar axis, anterior-posterior axis, or the utilization of a posterior condyles referencing jig. Postoperative computed tomography scans were obtained to investigate rotation characteristics. Significant differences in rotation characteristics were found between rotation according to DKB and other methods (P < 0.05). Soft tissue balancing resulted in smaller deviation from anatomical epicondylar axis than any other method. 77% of operated knees were within a range of ±3° of rotation. Only between 48% and 52% of knees would have been rotated appropriately using the other methods. The current results indicate that force sensors may be valuable for establishing correct femoral rotation.

A CT Based assessment of femoral component external rotation in TKA for osteoarthritic varus knees

“…Inaccurate implantation of the TKA prosthesis leads to instability, patella-femoral mal-tracking, accelerated poly wear, loosening, and overall poor outcomes 1,[6][7][8][9][10][11] . Using conventional techniques of surface referencing in TKA only about 75% of the femoral components are likely to be placed within the desired femoral external rotation of 3 degrees 12,13 . It is well reported in the literature that about 10-15% of the patients are unhappy after TKA [14][15] , TKA instrumentation sets are equipped with tools to align the TKA component placement in the correct mechanical axis in the sagittal and coronal planes however the axial rotation is usually at the surgeons own discretion based on surface landmarks, and are thereby prone to high inter observer error, and could be directly linked to a poor outcome in TKA patients; with this background it is reasonable to deduce if the accuracy rate of femoral component placement in axial rotation is improved it can reduce a certain percentage of unhappy patients after TKA.…”

“…Various conventional surface referencing methods use the posterior condylar axis (PCA), "Whiteside's line" (AP-axis), trans-epicondylar axis (TEA) or the gap balancing technique to decide the femoral component rotation 11,20,21 however, it is not yet clear which method is superior for femoral rotational component axial rotation 2 and is also highly prone to inter-observer errors 22 . With no standard parameter to follow and multiple variables at the time of surgery affecting femoral component rotation, the number of outliers in postoperative axial alignment of the femoral component with respect the desired femoral external rotation are likely to be high 12,13,23 and has long been overlooked 1 . This degree of mismatch in the femoral component placement can have a graded, multifaceted, subtle or subclinical effect on the tibiofemoral and patella-femoral biomechanics and stresses and may contribute significantly towards 10 to 20% unhappy patients after TKA 24 .…”

“…This excessive combined internal rotation was directly proportional to the severity of the patella-femoral complication 11 . Data is sparse on the aspect of actual femoral component rotation achieved in TKA using the conventional reference methods for the implantation of femoral component with respect to the desired distal femoral anatomy 1,5,12,27,28 . In a PS fixed bearing design the significant influence of distortion of the proximal tibial anatomy is neutralized by a perpendicular coronal proximal tibial cut 22 , however the distal femoral anatomy alterations specially the femoral rotation in patients of OA for TKA is still not fully addressed.…”

Computed tomography is not necessary to assess rotation of the femoral component in navigation-assisted total knee replacement

“…The transepicondylar axis is regarded as a consistent reference for identifying the coronal plane. 17 , 18 The so-called clinical epicondyles were used as references in the present study. These are defined as the greatest protrusion of the lateral and medial epicondyles and conform to the anatomical transepicondylar axis.…”

The Effect of Patellar Positioning on Femoral Component Rotation when Performing Flexion Gap Balancing Using a Tensioning Device for Total Knee Arthroplasty

“…13 One such device is the eLIBRA Dynamic Knee Balancing System (Zimmer Biomet, Warsaw, IN), which was developed to determine objective intraoperative measurements of the tension forces in the medial and lateral knee compartments, allowing the surgeon to adjust them by modifying the femoral rotation. 14 15 While this device provides more accuracy and repeatability, the balance is still determined without considering the influence of the patella position. 2 16 Therefore, the purpose of this study was to determine the relationship between component femoral rotation and position of the patella (i.e., reduced, dislocated, and dislocated and everted patella) when performing flexion gap balancing during TKA.…”