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

Good long-term results of total knee replacement (TKR) are reliant upon accurate positioning of the femoral component for both lexion 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 Abstract


Introduction
Good long-term results of total knee replacement (TKR) are reliant upon accurate positioning of the femoral component for both lexion 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 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 dif icult to recognize intraoperatively and via computed tomography (CT) scan. More than 25% of reported cases of osteoarthritis of the knees were classi ied 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.

Materials and methods
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 inal 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 ilm cassette was set at 100 cm. The obtained x-ray images were used to measure, irst, 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 pro ile 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 patientderived outcome measure to better characterize post-TKR satisfaction, expectations, and abilities for physical activities [15,16].

Results
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 lexion, balancing the posterior cruciate ligament, and minimizing mid-lexion 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 lexion for the irst 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 unsatis ied with the TKR.

Discussion
Four methods are available to select the right rotation of the femoral component during TKR in our hospital. The irst usually involves choosing the rotation according to the Whiteside's line (i.e. trans-sulcus line); this line should be constructed from the lowest part of the intercondylar Figure 1: Flexion-relaxed X-ray of with the 15° of higher x-ray lamp, set to X-ray to miss the avoid soft tissue overlap. The clinical epicondylar axis (two values CEA) and posterior condylar axis (PCA) were measured to have determined the exact outer rotation of the femoral component FC of the total knee replacement TKR; here, the outer rotation was -here measured 6.32°.
sulcus to the intercondylar notch. The second involves the transepicondylar axis, which is parallel to the Whiteside line. The third involves the resection block oriented for the resections to be carried out at 3° outer rotation to the posterior condyles. The fourth method uses the tibial resection block, which is oriented parallel to the biomechanical limb axis. Applications of the four methods are presented in igure 4.
To balance a varus knee in lexion (having hyperplastic medial condyle of the femur), a greater degree is required to correct the lexion space. In a valgus knee, it is important to irst balance in lexion and then in extension. The valgus deformity is usually caused by hypoplasia that is distal to and on the posterior part of the femur. For varus knees, the medial pinhole is almost always moved upward, to provide more medial space in lexion. For valgus knees, owing to the hypoplastic lateral femoral condyle, the lateral hole in usually moved downward.
It is rare for a knee to require internal rotation off the posterior condylar axis to achieve lexion gap symmetry; we can recommend such for only two types of cases. The irst is a severe varus knee that has suffered erosion of the posterior medial femoral condyle. The second is a post-osteotomy knee that has the tibial joint line in excessive valgus axis. For good balance of the femoral popliteal joint, we use the reverse cruciform release to achieve full popliteal balance in extension. We seldom use the lateral collateral ligament release technique or the popliteal and biceps tendon release technique in lexion. For the most severe deformities that cannot be balanced, we use the constraint modular system.

Conclusion
Malrotation of a femoral component in TKR is a cause of persistent pain and poor function postoperatively. The malrotation has been reported to produce patellofemoral problems, lexion instability, ultra-high molecular weight polyethylene wear, stiffness, and abnormal patterns. The optimal setting of the femoral rotation is different for every knee. It should, however, always be in outer rotation of not more than 7°, to counter any worsened balance in the lexion space postoperatively. Inner rotation of the femoral component leads to malfunction of the femoro-patellar line, and eventually arthro ibrosis and lateral impingement. We recommend the application of Whiteside's balancing of the lexion position of the femoral component in TKR, or use of the transepicondylar axis. Before operation, x-ray Kanekasu balancing can provide additional data to better balance the knee. Still, the development of other parameters for knee balance will provide important forensic value for patients who undergo TKR, improving operative success and individual satisfaction. Our recommendation to have good results in TKR is to do x-rays before and postoperatively. 3 views are essential: 1) antero-posterior, 2) lateral, and 3) Kanekasu projection to know the rotation after TKR. These projections seem to be basic to have good output of the TKR. Other cases without stability in lexion are nor very rarely planed for revision surgery, which is much more expensive, and burdens overall health system.