Background. Finding the anatomical landmarks used for correct femoral rotational alignment can be difficult. The Posterior Condylar Line (PCL) is probably the easiest to find during surgery. The aim of this study was to analyze if a predetermined fixed angle referencing of the PCL could help obtain good femoral alignment in TKA patients. Methods. 2637 CT scans used for preoperative planning and creation of patient-specific instrumentation (PSI) were used to analyze the Posterior Condylar Angle (PCA) between the Surgical Epicondylar Axis (SEA) and the PCL. Results. The mean PCA was 3.99° +/− 1.35° of external rotation. A significant relation was found between more external rotation and more varus of the tibia and more valgus of the femur. In 132 patients bilateral CT's were available and 94 (71%) had rotation within 1° of the opposite side. 96% of patients would receive the right amount of external rotation with 6°. On 105 (4%) CT's external rotation between 7° to 11° was measured and 77 (73%) of those were in varus or neutral alignment. Conclusions. After substracting a correction of 1° for cartilage remnants, a posterior condylar angle of 5° external rotation is proposed which should cover 96% of the population. For 4% of patients, both varus and valgus knees, 5° of external rotation will not be sufficient. The epicondylar axis should be explored during surgery, determined with patient-specific instruments, or a balancer should be used for this group

Introduction. A femoral rotational alignment is one of the essential factors, affecting the postoperative knee balance and patellofemoral tracking in total knee arthroplasty (TKA). To obtain an adequate alignment, the femoral component must be implanted parallel to the surgical epicondylar axis (SEA). We have developed “a superimposable Computed Tomography (CT) scan-based template”, in which the SEA is drawn on a distal femoral cross section of the CT image at the assumed bone resection level, to determine the precise SEA. Therefore, the objective of this study was to evaluate the accuracy of the rotational alignment of the femoral component positioned with the superimposed template in TKA. Patients and methods. Twenty-six consecutive TKA patients, including 4 females with bilateral TKAs were enrolled. To prepare a template, all knees received CT scans with a 2.5 mm slice thickness preoperatively. Serial three slices of the CT images, in which the medial epicondyle and/or lateral epicondyle were visible, were selected. Then, these images were merged into a single image onto which the SEA was drawn. Thereafter, another serial two CT images, which were taken at approximately 9 mm proximal from the femoral condyles, were also selected, and the earlier drawn SEA was traced onto each of these pictures. These pictures with the SEA were then printed out onto transparent sheets to be used as potential “templates” (Fig. 1-a). In the TKA, the distal femur was resected with the modified measured resection technique. Then, one template, whichever of the two potential templates, was closer to the actual shape, was selected and its SEA was duplicated onto the distal femoral surface (Fig. 1-b). Following that, the distal femur was resected parallel to this SEA. The rotational alignment of the femoral component was evaluated with CT scan postoperatively. For convention, an external rotation of the femoral component from the SEA was given a positive numerical value, and an internal rotation was given a negative numerical value. Results. The subjects were 4 knees in 4 males and 26 knees in 22 females. A mean age (for 30 knees) at the operation was 76.7 ± 6.1 years (range from 66.4 to 88.3). The posterior condylar angle was −0.27 ± 1.43, and the outlier, more than 3 degrees, was 1 case. Discussion. Conventionally, the SEA is palpated intraoperatively, however, the sulcus of the medial condyle sometimes cannot be identified precisely in osteoarthritic degeneration at the medial condyle. Also, the SEA is determined from the posterior condylar axis (PCA) by calculating the posterior condylar angle, which is between the SEA and the PCA, with the measurements from the preoperative CT scan. However, the residual cartilage thickness is not considered in this method, and thus, the SEA is possible to be inaccurate. The simple technology of our template allowed us to determine the SEA directly on the femoral surface, without any influence from bone degeneration. The femoral components could be implanted accurately, and therefore, the superimposed template was considered to improve TKA outcomes with the accurate SEA

Aim. The aim of this study is to evaluate the effect of three-dimensional (3D) simulation with 3D planning software ZedKnee® (ZK) in total knee arthroplasty (TKA). Materials and methods. The participants in this study were all TKA patients whose operations were simulated by using ZK. The alignment of all components was evaluated with the ZK valuation software in postoperative computer tomography. Thirty patients (43 knees) met the inclusion criteria. 6 patients were male and 24 patients were female. The mean age of the 30 patients was 72 years old. Diagnoses for surgery were: osteoarthritis- 40 knees, rheumatoid arthritis- 2 knees and osteonecrosis- 1 knee. TKA was performed using the measured resection technique. The distal femur axis where the intramedullary rod would be inserted was drawn manually on the 3D image. Then, the angle between the distal femoral axis and the mechanical axis was measured. The rotational angles of the femoral components were determined from the automatically calculated angle between the posterior condylar axis and the surgical epicondylar axis (SEA) by using ZK. The ZK data used during the operation was the posterior condylar angle, the angle between the distal femoral axis and the mechanical axis and implant size. Results. The angle in coronal plane between the 3D mechanical axis and the distal femoral axis in preoperative planning ranged between 3 degrees and 11 degrees, mean 6.7 (SD 2.2) degrees. The postoperative femoral component alignment was on average 0.7 (SD 1.3) degrees in varus. Outlier of more than 3 degrees in coronal alignment was recognized in 3 cases (7%). The mean posterior condylar angle in preoperative planning was 3.8 (SD 1) degrees. The postoperative femoral component alignment was on average 1.5 (SD 1.6) degrees in external rotation to surgical epicondylar axis. Outlier of more than 3 degrees in rotational alignment was recognized in 6 cases (14%). The concordance rate between the preoperative planning size and the intraoperative selective size was 91%. Discussion. Some errors may be observed in the preoperative TKA X-ray planning, because of the rotational position of the femur while having the X-ray taken or angle of the X-ray beam. Kanekasu et al reported the measurement of the condylar twist angle during the X-ray and it was relatively correct compared with the measurement during CT. Max 1.9 degrees error occurred in the measurements using X-rays. It appeared that preoperative planning using CTs was more accurate than using X-rays. Conclusion. Femoral components with 3D simulation using ZK were fixed perpendicularly against the mechanical axis and parallel to the surgical epicondylar axis with high accuracy. We considered that the ZK 3D simulation in TKA is useful for the accurate alignment of femoral components

Introduction. Instability, loosening, and patellofemoral pain belong to the main causes for revision of total knee arthroplasty (TKA). Currently, the diagnostic pathway requires various diagnostic techniques such as x-rays, CT or SPECT-CT to reveal the original cause for the failed knee prosthesis, but increase radiation exposure and fail to show soft-tissue structures around TKA. There is a growing demand for a diagnostic tool that is able to simultaneously visualize soft tissue structures, bone, and TKA without radiation exposure. MRI is capable of visualising all the structures in the knee although it is still disturbed by susceptibility artefacts caused by the metal implant. Low-field MRI (0.25T) results in less metal artefacts and offers the ability to visualize the knee in weight-bearing condition. Therefore, the aim of this study is to investigate the possibilities of low field MRI to image, the patellofemoral joint and the prosthesis to evaluate the knee joint in patients with and without complaints after TKA. Method. Ten patients, eight satisfied and two unsatisfied with their primary TKA, (NexGen posterior stabilized, BiometZimmer) were included. The patients were scanned in sagittal, coronal, and transversal direction on a low field MRI scanner (G-scan Brio, 0.25T, Esaote SpA, Italy) in weight-bearing and non-weight-bearing conditions with T1, T2 and PD-weighted metal artefact reducing sequences (TE/TR 12–72/1160–7060, slice thickness 4.0mm, FOV 260×260×120m. 3. , matrix size 224×216). Scans were analysed by two observers for:. - Patellofemoral joint: Caton-Descamps index and Tibial Tuberosity-Trochlear Groove (TT-TG) distance. - Prosthesis malalignment: femoral component rotation using the posterior condylar angle (PCA) and tibial rotation using the Berger angle. Significance of differences in parameters between weight-bearing and non-weight-bearing were calculated with the Wilcoxon rank test. To assess the reliability the inter and intra observer reliability was calculated with a two-way random effects model intra class correlation coefficient (ICC). The two unsatisfied patients underwent revision arthroplasty and intra-operative findings were compared with MRI findings. Results. In the satisfied group, a significant difference was found between TT-TG distance in non-weight-bearing and weight-bearing condition (p=0.018), with a good interrater reliability ICC=0.89. Furthermore, differences between weight-bearing and non-weight-bearing were found for the CD ratio, however, not significant (p=0.093), with a good interrater reliability ICC=0.89. The Berger angle could be measured with an excellent interrater reliability (ICC=0.94). The PCA was hard to assess with a poor interrater reliability (ICC=0.48). For one unsatisfied patient a deviation was found for tibial component rotation, according to the perioperative findings as, ‘malposition of the tibial component’. For the other unsatisfied patient revision surgery was performed due to aseptic loosening in which the MRI showed a notable amount of synovitis. Conclusion. It is possible to image the patellofemoral joint and knee prosthesis with low field MRI. Patellofemoral measurements and tibial component rotation measurements can reliably be performed. For the two patients with complaints MRI findings were consistent with intra-operative findings. Further research should focus on a larger group of patients with complaints after TKA to verify the diagnostic capacity of low field MRI for peri-prosthetic knee problems. For any figures or tables, please contact authors directly

Purpose. External rotation of the femoral component is one factor that favors a satisfactory clinical result. New technologies have been developed to precisely implant the components of a total knee arthroplasty, including computer-assisted surgery (CAS) and patient-specific instruments (PSIs). The aim of this study was to compare the precision of CAS and PSIs when determining the orientation of the femoral component. Methods. A total of 65 patients operated on in 2008 with CAS had pre- and post-operative computed tomography (CT) in which the posterior condylar angle (PCA) was measured. The same pre- and post-operative measurements were performed for 27 patients operated on in 2010 with the assistance of PSI. For both populations, the antero-posterior femoral cuts were directed to implant the femoral component 3° of external rotation from the pre-operative posterior condylar line (PCL). Results. The pre-operative parameters for both groups were identical. The post-operative PCA was not significantly different between the CAS and PSI groups, but the pre- to post-operative difference in PCA for the PSI group indicated a diminution of 2 ± 2° compared to no change in the CAS group. A total of 28% of the patients operated on with CAS had their femoral component more internally rotated after the surgery compared to the pre-operative measurements. Conclusion. Both PSI and CAS achieve the same objective of externally rotate the femoral component in the transversal plan, even if CAS, some femoral components still remains less rotated than the plan

Background. Recent anthropometric studies have suggested that current design of total knee arthroplasty (TKA) does not cater to racial anthropometric differences. The purpose of this study was to investigate the exact sizing and rotational landmarks of the distal femur collected from a large group of healthy Southern Chinese using three dimensional computer tomographic measurements, and then compare these measurements to the known dimensions from Caucasian populations. Methods. This study evaluated distal femoral geometry in 125 healthy Southern Chinese, included 58 women (106 knees) and 67 men (134 knees) with a mean age of 35.2±8.11 years, a mean height of 165.5±7.94 cm, and a mean weight of 61.7±9.56 kg. The width of the articular surface as projected onto the transepicondylar line(ML), anteroposterior dimension (AP), the dimensions from medial/lateral epicondyle to posterior condylar (MEP/LEP)were measured. A characterization of the aspect ratio (ML/AP) was made for distal femur[Fig. 1]. The angles between the tangent line of the posterior condylar surfaces, the Whiteside line, the transepicondylar line, and the trochlear line were measured. The sulcus angle and hip center-femoral shaft angle were also measured. Known dimensions from Caucasian populations were compared with the morphologic data collected in this study[Fig. 2]. In analyzing the data, best-fit lines were calculated with use of least-squares regression. The dimensions are summarized as the mean and standard deviation. The differences of rotational landmarks and sizing between the Southern Chinese and Caucasians were assessed with use of the Student t test. A p value of <0.05 indicated a significant effect. Results. Within the Southern Chineses population, males had larger ML and AP values than females (ML: 70.38±3.09 vs. 62.09±2.52mm, P<0.001; AP: 63.68±2.82 vs. 57.83±2.91mm, P<0.001). The results also showed that Southern Chinese knees were generally smaller than Caucasian (ML: 67.27±4.95 vs. 76.8±7.2mm, P<0.001). The femoral aspect ratio of Southern Chinese was significantly smaller than Caucasian (1.09±0.04 vs. 1.28±0.06, P<0.001). In addition, we found a gradual decrease in the aspect ratio corresponding to an increase in anteroposterior dimension in the distal femur of Southern Chinese, as seen in most other studies. The transepicondylar axis was found to be a reliable landmark to properly rotate the femoral component, so we used the femoral condylar MEP and LEP evaluate posterior condylar offset, the values were respectively 28.62±2.18mm and 22.50±2.19mm. From this study, most of the angles were different from Caucasian. Anteroposterior line minus epicondylar line angle was 90.14±1.30° (Caucasian 90.33±2.44°, P>0.05), anteroposterior line minus posterior condylar line angle was 83.18±1.94° (Caucasian 86.82±2.71°, P<0.001), epicondylar line minus posterior condylar line angle was 7.00±1.70° (Caucasian 3.60±2.02°, P<0.001), trochleoepicondylar angle was 12.45±2.34°(Caucasian 4.95±2.15°, P<0.001), sulcus angle was 147.40±4.69° (Caucasian 139.6±6.96°, P<0.001). The angle between mechanical and anatomic axis of the femur was 5.92±0.47°(Caucasian 6.33±2.42°, P<0.001). Conclusion. Because dimensions of the distal femur and the aspect ratio tend to be smaller in Southern Chinese populations, whereas sulcus angles tend to be larger, designs for knee implants should be modified to improve the outcome of surgical treatment in this population. The Larger epicondylar line minus posterior condylar line angles, and the smaller angle between mechanical and anatomic axis seen in Southern Chinese populations also requires us to pay particular attention to surgical technique, in order to ensure patient safety

Purpose. To validate accuracy of transepicondylar axis as a reference for femoral component rotation in primary total knee arthroplasty. Methods. A prospective study done from dec 2010 to dec 2011 at tertiary centre. 80 knees were included (43 females and 21 males). All surgeries were carried out by one senior arthroplasty surgeon. All patients undergoing primary total knee replacement were included and all revision cases were excluded. Intraoperative assessment of TEA was done by palpating most prominent point on lateral epicondyle and sulcus on medial epicondyle and passing a k wire through it. Confirmation is done under image intensifier C arm with epicondylar view. Postoperative TEA was assessed by taking CT scan, measuring condylar twist angle and posterior condylar angle. Also correlation of femoral component rotation with postoperative anterior knee pain was assessed. Results. The mean PCA was around 4° with TEA as reference and only 10% patients required an additional lateral release of which 2% patient had preop patellar maltracking. No postoperative patellar maltracking was seen. Anterior knee pain was present in 8% patients. No postop infection is noted. Alignment ranging from 3° to 9° external rotation. Conclusion. TEA is most accurate reference for femoral component rotation even in severely deformed arthritic knees. Key words – Transepicondylar axis, total knee arthroplasty, femoral component rotation,

Purpose:. To compare accuracy of transepicondylar axis as a reference for femoral component rotation in primary navigated versus non navigated total knee arthroplasty in severely deformed knees. Methods:. A prospective study done from dec 2009 to dec 2011 at tertiary centre. 180 knees were included (124 females and 56 males). All cases were randomly allocated into 2 groups: navigated and non navigated. All surgeries were carried out by two senior arthroplasty surgeons. All patients undergoing primary total knee replacement were included and all revision cases were excluded. Intraoperative assessment of TEA was done by palpating most prominent point on lateral epicondyle and sulcus on medial epicondyle and passing a k wire through it. Confirmation is done under image intensifier C arm with epicondylar view in Non navigated knees. Postoperative TEA was assessed by taking CT scan, measuring condylar twist angle and posterior condylar angle (PCA). Results:. The mean PCA was around 4° with TEA as reference in Navigated and 6° in Non navigated knees and only 7% patients required an additional lateral release of which 2% patient had preop patellar maltracking. No postoperative patellar maltracking was seen. Anterior knee pain was present in 10% patients. No postop infection is noted. Alignment ranging from 4° to 8° external rotation. Conclusion:. Navigation is most accurate measure for TEA as reference, as compared to non navigated TKA, which can lead to excessive external rotation especially in severely deformed knees

Background. The use of Computed Tomography (CT) as a medical imaging tool has widespread applications in the field of knee surgery. Surgeons use a CT scan in a conventional way during the pre-operative stage, to plan the position of the femoral component in the horizontal plane. In the post-operative stage, the use of a CT scan is a routine tool in the evaluation of failed TKA as rotational malalignment of the femoral component has been determined as a cause of poor clinical outcome after TKA. Aim. How accurately can we measure the different angles with importance for alignment on a 3D-image in comparison to a standard CT, 2D, image. Material and methods. This study includes patients above 55 years of age who were scheduled for a TKA at our centre and who had a pre- and postoperative full-leg length computed tomography (CT). These images were analysed using Mimics V 16.0 ® and 3-matic V 8.0 ® (Materialise, Haasrode, Belgium) to create the surface reconstruction and perform the 3D-measurements. Different angles were measured pre- and post-operatively on these images both in 2D as in 3D: condylar twist angle (CTA), posterior condylar angle (PCA), hip-knee-ankle angle (HKA), tibiofemoral rotation angle (TFRA), posterior tilt of the tibial implant (STPA) and the frontal plane angle of the tibial implant (FTPA). A power analysis showed a needed sample size of 18 patients. Pre-operatively 21 patients were included, 18 of them also received a post-operative full-leg CT. Three observers participated in the study and they all performed all analyses twice with a minimum interval of one week for obtaining intra-observer repeatability. Statistical analysis was performed to obtain the intra- and interobserver variability. Results. The intra-and interobserver intra-class coefficients (ICC) were evaluated using the classification of Landis&Koch (see table). Preoperative results: Rotation of femoral component in 3D: ICC CTA=0,73; ICC PCA=0,66. Rotation in 2D: ICC PCA=0,75, ICC CTA=0,84. The highest ICC was found for the HKA: ICC>0,98 both 2D and 3D. Postoperative results. All ICC's are in the highest category (‘almost perfect’) except for the intraobserver ICC PCA in 2D which was ‘substantial’. Conclusions and clinical implications. CT-evaluation is invaluable for the preoperative planning of the position of the femoral component, for the evaluation of the rotation of the femoral component and for accurate assessment of the overall knee alignment,. This study demonstrates low intra- and inter- observer variability in the CT measurement of the pre- and postoperative alignment of the knee. To determine the rotation of the femoral component preoperatively there was no advantage for 3D over 2D. Post-operatively the use of the 3D technique has a lower variability with regard to the assessment of the rotation of the femoral component