‘Rotational alignment on patients’ clinical outcome of total knee arthroplasty: Distal femur axillary X-ray view to qualify rotation of the femoral component

Background: Rotation of the femoral component in total knee replacement (TKR) is very important for good long-term results. Malrotation of the femoral component usually requires subsequent reimplantation. We performed X-ray projections of the knee at 90° to determine proper rotation of the femoral component without use of computed tomography.

Methods: The axial projection of the distal femur was measured in post-TKR cases. During the TKR operation, Whiteside’s method had been used to provide symmetrical flexion space. The exact outer rotation of the femoral component was measured by x-ray determination of the middle condylar twist angle, from the central epicondylar axis and posterior condylar axis.

Results: The middle condylar twist angle was in outer rotation, with an average of 3.36° (range: 1-7.6), similar to the literature. Six of the patients underwent bilateral TKR. In total, the case series included 18 women and 15 men, with average age of 71.34 years-old (range: 56-85). As a clinical evaluation we used Knee Society Score (2011). From results 2 patients were not very satisfied with the instability TKR. Axially X-ray seemed to be only which could distribute these patients.

Summary: X-ray values have the same evaluation as computed tomography. The results were 2 patients in pattern of 48, which were sufficient to extrapolate to whole population according to the statistical methods. This corresponds to 4% which we can add to evaluate satisfaction of all patients after TKR and eventually lower the total of unsatisfactory patients which is total of ¼ of total. It is also forensic reason for all patients. Our recommendation to have good results and patient satisfaction in TKR is to do x-rays before and after operation. Important are x-rays antero-posterior, lateral, and Kanekasu projection to know the rotation after TKR. Other cases without stability in flexion are nor very rarely planed for revision surgery, which is much more expensive, and burdens overall health system.

Good long-term results of total knee replacement (TKR) are reliant upon accurate positioning of the femoral component for both flexion and extension movements. For osteoarthritis cases, the TKA reduces pain for up to 15 years in 90% of the patients [1]. The remaining patients report incomplete satisfaction with their post-TKR clinical outcome [2,3], and revision rates among these patients exceed 35% within 2 years of the primary TKR [4,5]. The reported cases of loosening are mostly related to aseptic, polyethylene wear, infection, periprosthetic fracture, and joints instability.

Rotation of the femoral component in the transverse plane is a primary factor affecting post-TKR flexion stability and alignment in flexion [6-8]. Bone resection is necessary for component stability, and needs to be performed perpendicular to the preoperative biomechanical stability of the limb. Gap-balancing and measured resection are the two most commonly used methods for determination of the femoral rotation. The goal of kinematically-aligned TKR is to restore the native alignment of the limb, the knee, and the joint lines, in order to restore knee function to its native state and without ligament release. The femoral component, itself, achieves kinematic alignment when the thickness of the distal and posterior resections of the femoral condyles are equal to the thicknesses of the corresponding portions of the femoral component [9,10].

The center of knee rotation is often considered the surgical epicondylar axis (commonly referred to as the SEA), which is in effect the line connecting the sulcus of the medial epicondyle with the prominence of the lateral epicondyle [15]. The femoral component is usually implanted parallel to this line, based on anatomical landmarks [11]. For accurate determination of the SEA and proper alignment of the femoral component, the surface-delivered bony landmarks as well as the posterior condyle line and the anteroposterior trochlea axis (i.e. the Whiteside’s line) must be utilized [12]. Unfortunately, sulcus of the medial epicondyle is sometimes difficult to recognize intraoperatively and via computed tomography (CT) scan. More than 25% of reported cases of osteoarthritis of the knees were classified as type 3; meaning that the medial sulcus is not recognizable on CT scans [13]. In some cases, however, the bony landmarks technique alone can be imprecise for determining the femoral rotation alignment.

All patients involved in this study provided informed consent for participation. In total, we enrolled 50 patients, representing 48 TKR and 2 nonresponders. Six of the patients received bilateral TKR. The period of assessment was 12 months from 2017 through 2018. The sex distribution was 1.2:1, with 18 men and 15 women. The average age was 71.34 years-old (range: 56 – 85 years). All TKR were carried out in our clinic; the clinic population is representative of the population of the geographical region, increasing the likelihood that our results are transferable to the region’s whole population. The TKR method was designed and carried out according to that described by Kanekasu, et al. 2004 [14].

CT was carried out following each TKR to verify the rotation of the femoral component. The CT measurements were based upon the condylar twist angle (a line between the condylar and transepicondylar lines), and SEA (a line connecting the sulcus of the medial epicondyle with the prominence of the lateral epicondyle). The CT scans were conducted with the patient on a wooden table 70 cm high; this allowed for setting the x-ray lamp about 15° higher, in order to avoid soft tissue overlap on the final x-rays (Figure 1).

On this 70-cm high wooden table, it was important to have the patient’s post-TKR knee in neutral rotation, to obtain resting x-rays. The position of the knee was then adjusted so that the central ray of the x-ray beam would be directed to the center of the patella. The distance between the x-ray tube and the film cassette was set at 100 cm. The obtained x-ray images were used to measure, first, the axis between the clinical epicondylar prominences and, second, the posterior condylar axis. These two axes form the middle twist angle. Ultimately, these data were compared to the related data in the literature to determine the failure data profile that when applied will allow for avoidance of failures in future implantations.

To assess the patients’ satisfaction with the clinical results after TKR, the Knee Society Score (also known as the KSS) was employed. The KSS was developed in 2011 as a patient-derived outcome measure to better characterize post-TKR satisfaction, expectations, and abilities for physical activities [15,16].

The average middle twist angle for all study participants was 3.36° (range: 1° - 7.6°). This result was similar to that in the literature. Our data presented herein is all for outer rotation. We prefer to perform the femoral sizing from the posterior upward, as this is most reliable for restoring the joint line in flexion, balancing the posterior cruciate ligament, and minimizing mid-flexion laxity. To create more external rotation, either the medial pinhole has to be moved upward or the lateral pinhole has to be moved downward.

The average KSS for all study participants was average 45% – 85%. Three patients gave KSS that corresponded to poor outcome (44.8%, 29% and 22%; Figure 2), x-rays showing discrepancy in flexion for the first two patients, respectively, are provided in figure 3. The third patient, with 22% KSS, showed no difference on the axial x-ray and was most probably generally unsatisfied with the TKR.