Surgical Epicondylar Axis Research Articles

Three-dimensional Analysis of Computed Tomography–Based Navigation System for Total Knee Arthroplasty: The Accuracy of Computed Tomography–Based Navigation System

We evaluated the postoperative alignment of 37 primary total knee arthroplasties performed using a computed tomography–based navigation system (Vector Vision Knee 1.5; Brain Lab, Germany) with a new 3-dimensional analysis. The mean coronal femoral angle was 89.0° ± 1.4° (85.5°-92.8°), and the coronal tibial component was 89.2° ± 1.0° (87.4°-91.6°). The hip-knee-ankle angle was observed to be 178.2° ± 1.5° (173.9°-181.8°). The external rotational alignment of the femoral component relative to the surgical epicondylar axis was −0.5° ± 1.7° (−3.2° to 3.4°). The results demonstrated that a computed tomography–based navigation system provided a reasonably satisfactory component alignment. The discrepancy between the 2-dimensional and 3-dimensional evaluations was 1.0° ± 0.9° (0.1°-3.4°). Three-dimensional analysis is necessary to evaluate the accuracy of the navigation system .

A cadaveric study of relationships among rotational alignment reference axes of distal femur and tibial mechanical axis

To investigate the relationships among rotational alignment reference axes of distal femur and tibial mechanical axis, and determine the safest rotational alignment reference axis. Digital photos were taken of 30 cadaveric lower extremities with knee in extension and flexion at 90 degrees , angles were measured among tibial mechanical axis and a line perpendicular to clinical epicondylar axis, a line perpendicular to surgical epicondylar axis, Whiteside's line and femoral mechanical axis. Statistical analysis of relationships among those axes were performed. The angles among the tibial mechanical axis and a line perpendicular to the clinical epicondylar axis, a line perpendicular to the surgical epicondylar axis, Whiteside's line and femoral mechanical axis were 0.6 degrees varus, 3.9 degrees varus, 0.2 degrees valgus and 3.0 degrees varus respectively. The angle between the femoral mechanical axis and the tibial mechanical axis was significantly larger than the angles among the tibial mechanical axis and a line perpendicular to the clinical epicondylar axis, the Whiteside's line (P < 0.05). There was no significant difference compared with the angle between a line perpendicular to the surgical epicondylar axis and the tibial mechanical axis. Angles of the clinical epicondylar axis, the surgical epicondylar axis and the Whiteside's line between knee extension and flexion were 2.3 degrees valgus, 0.9 degrees varus and 3.1 degrees valgus respectively. The surgical epicondylar axis rather than the clinical epicondylar axis or the Whiteside's line is the safest femoral rotational alignment reference axis intraoperatively.

Relationship between the surgical epicondylar axis and the articular surface of the distal femur: an anatomic study

Many authors presented the epicondylar axis as the fixed axis of rotation of the femoral condyles during flexion of the knee. Positioning of the femoral component of a total knee arthroplasty (TKA) based on the epicondyles has been proposed. This work is a critical analysis of this concept. Metallic bodies were inserted at the level of collateral ligament insertions on 16 dried femurs, allowing us to locate the surgical epicondylar axis. The dried femurs were studied using standard radiographs and CT-scan. CT cuts were made perpendicular to the epicondylar axis. The medial mechanical femoral angle and the epicondylar angle were measured on the radiographs. The posterior and distal epiphyseal rotations relative to the epicondylar axis (Posterior Condylar Angle, PCA, and Distal Condylar Angle, DCA, respectively) were measured on the CT-scans. PCA and DCA values were compared. The centre of the posterior femoral condyles was located on sagittal reconstructions using the tangent method and was confirmed with circular templates, and then compared to the location of the epicondyles. Circle-fitting of the entire femoral condylar contours centred on the epicondyles was also tried. The mechanical femoral axis was nearly perpendicular to the epicondylar axis but with important variations. The average PCA and DCA were 1.9 degrees +/- 1.8 degrees and 3.1 degrees +/- 2.1 degrees , respectively. No relationship could be established between the mechanical femoral angle and the PCA. The individual differences between the PCA and the DCA averaged 2.2 degrees . A significant distance was found between the centre of the condylar contours and the epicondyles: 6.5 mm in average on the lateral side (range 2.3-11.3 mm) and 8.4 mm on the medial side (range 4.0-11.6 mm). Circle-fitting of the entire medial or lateral femoral condylar contours centred on the epicondyles was not possible. The centre of the posterior femoral condyles is significantly different from the epicondylar axis, thus refuting the conclusions of previous authors. Furthermore, considering the differences between the distal and posterior condylar angles shown here, as well as the difficulty of repeatably locating the epicondyles during surgery, using the epicondylar axis as the only landmark to position the femoral component during a first intention TKA is not recommended. The surgical epicondylar axis does not appear to be an adequate basis for the understanding of the shape of the distal femur.

An Additional Reference Axis for Determining Rotational Alignment of the Femoral Component in Total Knee Arthroplasty

No studies have examined the trochlear line connecting the most anterior projections of the lateral and medial femoral condyles in relation to the surgical epicondylar axis. To determine if the trochlear line is more consistent relative to the transepicondylar axis than the posterior condylar axis and the Whiteside's line, the angles between the surgical epicondylar axis and each of the 3 axes in 50 knees of cadavers were measured using computed tomography scans. The results showed that the variability in the trochlear line for referencing the transepicondylar axis was comparable to those of the Whiteside line and the posterior condylar axis. The trochlear line may be considered as an additional reference axis for determining the rotational alignment of the femoral component in total knee arthroplasty.

Radiographic analysis of rotational malalignment between tibial component and femoral component in total knee arthroplasty

To identify possible reasons of rotational mismatch between tibial component and femoral component in total knee arthroplasty and choose a right reference axis for placing the components in the operation and to decrease the complications. Forty normal Chinese knees were studied. There were 20 men and 20 women, and average age was 34 years (range, 18 - 42 years). The images of cross sections of the distal femur were obtained by spiral CT scanning (0.5 mm thickness). Scan direction was aligned to be in the plane perpendicular to the mechanical axis of the tibia. On the images of the distal femur and the proximal tibia, three baselines for the anteroposterior axis of the femoral component were drawn based on the clinical epicondylar axis and the surgical epicondylar axis and 3 degrees lateral rotated to the posterior condylar surfaces of the femur separately, and a baseline for the anteroposterior axis of the tibial component was drawn based on the medial 1/3 of the tibial tuberosity. The rotational mismatch angles were measured between each component by using the Autocad software. The mean rotational mismatch angle between tibial component and femoral component is 2.94 degrees for the clinical epicondylar axis, 6.50 degrees for the surgical epicondylar axis and 6.83 degrees for 3 degrees lateral rotation of the femoral component referenced to the posterior condylar axis separately. Landmarks of each bone were the intrinsic cause of the rotational mismatch in total knee arthroplasty. The clinical epicondylar axis can be chosen for the ideal reference to rotational alignment of the femoral component because of its minimal rotational mismatch between each component.

Femoral component rotation and arthrofibrosis following mobile-bearing total knee arthroplasty

The purpose of this study was to evaluate the femoral component rotation in a small subset of patients who had developed arthrofibrosis after mobile-bearing total knee arthroplasty (TKA). Arthrofibrosis was defined as flexion less than 90 degrees or a flexion contracture greater than 10 degrees following TKA. From a consecutive cohort of 3,058 mobile-bearing TKAs, 49 (1.6%) patients were diagnosed as having arthrofibrosis, of which 38 (86%) could be recruited for clinical assessment. Femoral rotation of a control group of 38 asymptomatic TKA patients matched for age, gender, and body mass index was also evaluated. The surgical epicondylar axis was compared with the posterior condylar axis for the femoral prosthesis. Femoral components in the arthrofibrosis group were significantly internally rotated by a mean of 4.7 degrees (SD 2.2 degrees , range 10 degrees internal to 1 degrees external). In the control group, the femoral component had a mean 0.3 degrees internal rotation (SD 2.3 degrees , range 4 degrees internal to 6 degrees external). Following mobile-bearing TKA, there is a significant correlation between internal femoral component rotation and chronic arthrofibrosis.

The Functional Flexion-Extension Axis of the Knee Corresponds to the Surgical Epicondylar Axis: In Vivo Analysis Using a Biplanar Image-Matching Technique

We investigated the concept that the knee has a fixed flexion-extension axis in the posterior femoral condyles and that this functional axis corresponds to the surgical epicondylar axis in vivo. We used a biplanar image-matching technique to perform the in vivo analysis of 9 normal knees to determine the location of the functional flexion-extension axis of the knee using an optimization technique. The functional flexion-extension axis passed through the sulcus of the medial epicondyle and the prominence of the lateral epicondyle. Flexion and extension of the knee could be represented as a rotation around a fixed axis, and this functional axis corresponded to the surgical epicondylar axis during a 0° to 90° flexion. This study assists more understanding of knee kinematics and provides useful information for the design and positioning of the prostheses used in total knee arthroplasty.

Achieving ligament stability and correct rotational alignment of the femur in knee arthroplasty: A study using the Medial Pivot knee

In a series of 90 Medial Pivot arthroplasties rotational alignment of the femur was achieved by provisionally reconstructing the lateral side of the joint and tensioning the medial side with feeler gauges. Axial CT scans were employed to measure the rotational alignment relative to surgical epicondylar axis. In valgus knees the cutting block was externally rotated to adjust for posterolateral bone loss. The mean rotational alignment of the femur was 0.6° of external rotation (S.D. 1.3, range 3° of ER to 4° of IR). The mean laxity of the medial ligament was 1 mm in flexion (SD 1, range 0–5 mm) and 0.5 mm in flexion (S.D. 0.5, range 0–2 mm) In those knees in which the medial ligament had been released the CT alignment was perfect, but when internally rotated against the hip 3–4 mm of gapping was noted. In valgus knees the mean rotation of the femoral component was 0.8° of internal rotation (S.D. 1.5, range 1° of IR to 4° of ER). In spite of externally rotating the cutting block there was still a tendency to internally rotate the femur in some knees. This simple technique achieves the two goals of ligament stability and correct rotational alignment in a high proportion of cases. It may be applicable to any instrument system which employs posterior referencing.

Can the epicondylar axis be defined accurately in total knee arthroplasty?

As part of a study on rotational alignment of the femoral component in knee replacement, the surgical epicondylar axis was identified in 74 knees and marked with pins. An alternative technique was employed to achieve rotational alignment and in each case the distance between the pins and the cut surface of the posterior condyles was measured. The alignment of the femoral component was measured postoperatively by axial CT scans of the distal femur, allowing an assessment to be made of what would have been achieved if the epicondylar pins had been used for guidance. Only 75% of knees would have been within 3° of the true epicondylar axis using the epicondyles to control rotation. The error range was large (range 6° ER to 11° IR). Our conclusion is that even in experienced hands clinical estimation of the epicondylar axis is inaccurate and should not be relied upon as the sole determinant of femoral rotation.

Linkage guide for rotational alignment during total knee arthroplasty

A linkage guide was devised for use in conjunction with knee arthroplasty instruments to achieve proper component rotation. The femoral component was rotationally aligned to the surgical epicondylar axis using one guide. The other guides were used after all bone surfaces were cut and soft tissue balancing was completed. A Kirschner wire was guided into the proximal tibial aspect parallel to the sagittal plane of the femoral component with the patella in its normal position and the knee in full extension. The wire was used as a reference to determine tibial component rotation. The relative rotational alignment of 21 knees in 19 patients who had undergone cruciate-retaining total knee arthroplasty utilizing this guide was assessed using the modified Eckhoff method. The results of radiographic analysis were compared with those in a control group of 25 knees where the guide was not employed. The external rotation of the femoral component relative to the tibial component was 1.3° ± 2.0° (mean ± SD) in the guided group and 1.1° ± 4.4° in the control group. The relative rotational angle was significantly more consistent using the guide. Implant malrotation can be reduced using our technique.

Relationship between frontal knee alignment and reference axes in the distal femur.

The two transepicondylar axes (the clinical and surgical epicondylar axes), the posterior condylar axis, and the anteroposterior axis were constructed using computed tomography scans in 111 (66 patients) knees with symptomatic arthritis. The relationships between angles made by these reference axes and two angles indicating frontal knee alignment (the tibiofemoral valgus angle and the femoral valgus angle) were investigated. In Y of the knees, the surgical epicondylar axis could not be constructed because the sulcus of the medial epicondyle was not recognizable. The condylar twist angle was almost constant and averaged 6 degrees when the femoral valgus angle was 9 degrees or less, but increased gradually when the angle was greater than 9 degrees. The difference between the condylar twist angle and the posterior condylar angle was constantly 3 degrees. The anteroposterior axis was almost at right angles to the clinical epicondylar axis, and the relationship between these axes was constant, independent of the femoral valgus angle. With 3 degrees to 6 degrees external rotation relative to the posterior condylar axis, the femoral component could be set parallel to the transepicondylar axis in common varus or neutral knees. In cases with a larger femoral valgus angle, the anteroposterior axis would be a more reliable reference axis. Preoperative computed tomography scans are recommended for patients with knees with severe valgus deformity or severe hypertrophic osteoarthritis.

The use of the surgical epicondylaraxis in total knee arthroplasty

When performing total knee arthroplasty, there are many important technical factors to consider to maximize postoperative results. One important factor is the rotational orientation of the femoral component. Improper femoral component rotational positioning can lead to several potential complications, including poor patellofemoral tracking and varus-valgus instability of the knee in flexion. The use of an anatomic landmark, the surgical epicondylar axis, has been developed to aid the surgeon in determining proper rotational orientation of the femoral component in both primary and revision total knee arthroplasty.

Determining the Rotational Alignment of the Femoral Component in Total Knee Arthroplasty Using the Epicondylar Axis

The posterior condylar surfaces of the femur are routinely used as the reference for the rotational orientation of the femoral component during most primary total knee arthroplasties. The purpose of this investigation was to identify a clearly discernible, reproducible secondary anatomic axis useful for determining the rotational orientation of the femoral component when the posterior condylar surfaces cannot be used. Seventy-five embalmed anatomic specimen femurs were studied. A surgical epicondylar axis was defined as the line connecting the lateral epicondylar prominence and the medial sulcus of the medial epicondyle. The posterior condylar angle was measured as the angle between the posterior condylar surfaces and the surgical epicondylar axis. Measurement of the posterior condylar angle referenced from the surgical epicondylar axis yielded a mean posterior condylar angle of 3.5 degrees (+/- 1.2 degrees) of internal rotation for males and a mean posterior condylar angle of 0.3 degree (+/- 1.2 degrees) of internal rotation for females. Thus, rotational alignment of the femoral component can be accurately estimated using the posterior condylar angle. The posterior condylar angle, referenced from the surgical epicondylar axis, provides a visual rotational alignment check during primary arthroplasty and may improve alignment of the femoral component at revision.