Introduction. Malrotation following total knee replacement is directly related to poor outcome. The knowledge of proximal and distal rotational axes and angles of the femur is therefore of high importance. The aim of the study was to determine whether the most used proximal and distal femoral angles; femoral anteversion angle (FAA) and posterior condylar angle (PCA) were different within individuals, between right, left and gender. As well, we studied whether the “inferior condylar angle” is correlated to the PCA and therefore useful in determining the rotation of the distal femur. Material and Methods. From 36 cadavers the femora were obtained and after removing the soft tissue a Computed Tomography (CT) scan was made. Three angles were measured: (i) the FAA between femoral columnar line (FHNL) and posterior condylar line (PCL), (ii) the PCA between anatomical transepicondylar line (TEL) and PCL, (iii) the inferior condylar angle (ICA) between the TEL and inferior condylar line (ICL). Statistical analysis of comparative relationships between the different angles was examined by calculating correlation coefficients and a paired t-test. Results. The mean FAA, PCA and ICA for the whole group were respectively 12.0 degrees (range 0.2–31.6, SD 8.3, 95% CI 9.6–14.4), 4.8 degrees (range 0.9–9.6, SD 2.3, 95% CI 4.1–5.4) and 4.5 degrees (range 0.1–9.8, SD 2.1, 95% CI 3.9–5.1). A strong correlation of the FAA was found within the total group and left versus right (r = 0.82; p = 0.00). A weaker relationship was found for the total group of the PCA measurements (r = 0.59; p = 0.00). When FAA compared to the PCA subdivided in only sexes, there is a weak correlation for the female group (r = 0.54; p = 0.00) Despite the small mean difference of the mean ICA and PCA, there was no correlation between these two angles. Conclusion. Considering the weak correlation of the FAA and PCA within the group but also individuals, the importance of development of more individual approaches for determining the optimal rotation of the components in total knee surgery is essential. As a result, one should be aware that the widely used, current guidelines for knee rotation of 3 degrees of external rotation in placing total knee arthroplasties shows variation between individuals. A more individual approach in total knee arthroplasty seems essential for future knee prosthesis implantations

Prosthetic impingement after THA is to different for the angle and shape of the implant. Purpose of this study is examine the range of motion(ROM) on a computer when angle and shape of the implant are changed. The 3D implant models were created on a computer. The angle was measured in the flexion, extension, adduction direction byevery 0.1 degrees. There are three kinds of acetabular abduction angle, two kinds of acetabular anteversion angle and two kinds of femoral anteversion angle. There are three kinds of the radius of neck and the neck shaft angle. All 324 patterns of the above model were measured. When the radius of neck decreased, the ROM increased in all cases. When the neck shaft angle decreased, the ROM increased by almost all cases. When the acetabular anteversion angle increased, the ROM of flexion direction increased and adduction direction decreased, and as for the extension direction, all the factors had influenced the change in the ROM. When the acetabular angle increased, the ROM of the extension direction increased and the flexion directions decreased. As for adduction direction, femoral anteversion angle, acetabular anteversion angles, and the radius of neck had influenced the ROM. When the femoral anteversion angle increased, the ROM of flexion direction increased and extension, adduction direction decreased. The clinical ROM is affected by the impingement of non-implant and the strain of the soft tissue. Therefore, It’ s considered that the clinical ROM is smaller than the ROM which was investigated in this study in many cases. When the radius of neck and the neck shaft angle decrease, the increase of the ROM expected. However the radius of the neck should not be decreased too much to avoid the decrease of the neck strength

Background. High tibial osteotomy is a common procedure to treat symptomatic osteoarthritis of the medial compartment of the knee with varus alignment. This is achieved by overcorrecting the varus alignment to 2–6° of valgus. Various high tibial osteotomy techniques are currently used to this end. Common procedures are medial opening wedge and lateral closing wedge tibial osteotomies. The lateral closing wedge technique is a primary stable correction with a high rate of consolidation, but has the disadvantage of bone loss and change in tibial condylar offset. The medial opening wedge technique does not result in any bone loss but needs to be fixated with a plate and may cause tibial slope and medial collateral ligament tightening. Purpose. The purpose of this article is to examine correlation between femoral rotational angle and subjective satisfaction of high tibial osteotomy outcome of the range of motion of knee joint. Materials and methods. The subjects were 15 patients (6 males, 9 females) with primary osteoarthritis undergoing high tibial osteotomy from June of 2004 to August of 2008. They were CT tested on the knee joint before and after high tibial osteotomy. TEA and Akagi's line are analysed as percentages. The Kendall's and Spearman's nonparametric correlation coefficient were used for the statistical tests with 0.5 level of significance. Results. We observed a negative linear relationship (p = 0.0001) between the femoral component external rotation (measured by TEA) and active and passive ROM. Pearson Coefficient was −0.80, −0.57, respectively. We can find a negative linear relationship (p=0.001) between Akagi's line and passive ROM, and Pearson coefficient was −0.863. Preoperative flexion contracture, age, tibiofibula angle, pain, and other factors do not influence the ROM of the patient. Follow up duration do not influence the ROM of the patient. Conclusion. The result reveals that femoral rotational angle correlates with not the range of motion of knee joint but subjective satisfaction of the patients. In HTO, beside deformity correction in coronal plane, rotation of the femur contributes postoperative pain relief

Purpose. Computer navigation system has been reported as a useful tool to obtain the proper alignment of lower leg and precise implantation in TKA. This system alsoãζζhas shown the accurate gap balancing which was lead to implants longevity and optimal knee function. The aim of this study was determine that the postoperative acquired deep knee flexion would be influenced by intraoperative kinematics on navigated TKA even under anesthesia. Materials & methods. Forty knees from 40 patients, who underwent primary TKA (P.F.C. sigma RPF, DePuy Orhopaedic International, Leed, UK) with computer-navigation system (Ci Knee, BrainLAB / DePuy Inc, Leeds, UK), were recruited in this study. These patients were classified into two groups according to the recorded value of maximum knee flexion at three month after surgery: 15 patients who obtained more than 130 degrees of flexion in Group A, and 25 patients less than 130 degrees in Group B. We retrospectively reviewed about intraoperative kinematics in each group, to obtain the clue for post operative deep-flexion. The measurements of intraoperative kinematics were consisted of 3 points: femoral rotation angle (degree) and antero-posterior translation (mm), which were measured as the translation of the lowest points of femoral component to tibial cutting surface, and the joint gap difference between the medial and lateral components gap (mm). All joint kinematic data were recorded at every 10 degrees of flexion from maximum extension to flexion under anesthesia. Results. There were no significant differences between two groups about preoperative diagnosis, sex, age, BMI, and preoperative range of motion. At 3 months, the recorded mean value of maximum knee flexion was 134.7 degrees in Group A, and 112.0 degrees in Group B. Femoral components were rotated internally up to 90 degrees flexion, and then rotated externally with flexion to the tibial plateau in the axial plane. There was no significant difference in femoral rotation angle between two groups, but slightly greater in Group A. Regarding to antero-posterior translation, femoral component had an anterior translation up to 50 degrees in both groups. The posterior translation was started at more than 50 degrees, and total amount of posterior displacement was significantly greater in Group A. The gap difference of lateral side was significantly greater in Group A than that in Group B especially at more than 110 degrees of flexion. Discussion. We found two parameters that can obtain greater knee flexion at more than 130 degrees in the early postoperative period. There were significant differences between two groups about the femoral rollback at more than 50 degrees of flexion, and the gap difference at more than 110 degrees of flexion. Navigation system would only suggest that intraoperatively optimal knee kinematics for femoral rollback and slight laxity at more than 110 degrees of flexion to lead the medial pivot motion. The surgeon can keep it in mind for soft tissue release to obtain the ideal postoperative function. Conclusion. This study showed that the axial rotation and posterior translation of femoral component were important factors for acquisition of postoperative deep flexion

Patello-femoral tracking and polyethylene wear are strongly dependent on rotational alignment of the components in total knee arthroplasty. In the current literature four methods to obtain correct axial femoral alignment are reported: the transepicondylar axis method, Whiteside’s method, the tibial axis method and 3° external rotation of posterior condyles method. Because of its simplicity the last of these is the most popular method used at present. But it is also the most accurate? The purpose of this study was to investigate the accuracy of the 3° external rotation method, comparing it to the transepicondylar axis and the White-side’s A-P line. We performed a CT scan examination of the hip and the knee of 40 patients scheduled to undergo a total knee arthroplasty. Seven cases of valgus deformity were excluded from the study, leaving 34 cases. The mean age was 72.4 and the left knee was involved in 23 cases. The mean height was 159 cm and the mean weight was 76.6 kg. The mean varus deformity was 14° (min 5° – max 30°). CT scan was conducted using a Picker PQCT machine. Two axial images were obtained in all the patients: one of the femoral neck and one of the knee with good visualisation of the posterior aspect of the condyles of the femur and epicondyles. We measured the following angles: the femoral anteversion angle (between the femoral neck line and the posterior condylar line), the posterior condylar angle (between the posterior condylar line and the transepicondylar axis) and the Whiteside’s angle (between the posterior condylar line and the perpendicular line to the White-side’s A-P line). The mean femoral anteversion angle was 5.5°± 13.7° (min -24°; max 33°). The mean posterior condylar angle was 6.1°± 2.5° (min 1°; max 14°). In 20 cases (60.6%) the posterior condylar angle was greater than 5°. The mean Whiteside’s angle was 6°±3.5° (min 1°; max 16.5°). In 17 cases (51.5%) it was greater than 5°. Both the posterior condylar angle and the White-side’s angle showed average values, which doubled the 3° proposed as standard for external rotational alignment of the femoral component, with maximum values of 14° and 16.5° respectively. More than 50% of the cases showed a posterior condylar angle grater than 5°. The two methods (transepicondylar and Whiteside’s line) are complementary. The posterior condylar axis and the Whiteside’s line were not altered by severe varus deformity or femoral neck retro- or anteversion. The 3° external rotation of the posterior condyle line is not recommended as a standard procedure to determine the degree of external rotation of the femoral component in total knee arthroplasty

There are few studies that have compared between continuous flexion activities and extension activities of normal knees. The purpose of this study is to compare in vivo kinematic comparison of normal knees between flexion activities and extension activities. Total of 8 normal male knees were investigated. We evaluated in vivo three-dimensional kinematics using 2D/3D registration technique. We compared femoral rotation angle relative to tibia, anterior/posterior (AP) translation of medial femoral sulcus (medial side) and lateral femoral epicondyle (lateral side) onto tibial plane perpendicular to tibial functional axis between flexion activities (F groups) and extension activities (E groups). Femoral external rotation was observed with the knee bending during both groups. The external rotation angle of F group was larger than that of E group significantly from 20 to 30 degrees with flexion (p < 0.05). Regarding medial side, anterior translation was observed up to 40 degrees in F group. From 40 to 140 degrees, posterior translation was observed. In E group, anterior translation was observed from 140 to 40 degrees with extension. From 40 degrees, posterior translation was observed. From 30 to 40 degrees, F group located anterior than E group (p < 0.05). Regarding lateral side, posterior translation was observed with flexion in F group. On the other hand, anterior translation was observed with extension in E group. Regarding AP location with flexion angle, there was no significant difference between two groups. In conclusion, there were different kinematics between flexion activities and extension activities

Introduction. One of the objectives of total hip arthroplasty is to restore femoral and acetabular combined anteversion. It is desirable to reproduce both femoral and acetabular antevesions to maximize the acetabular cup fixation coverage and hip joint stability. Studies investigated the resultant of implanted femoral stem anteversion in western populations showed that the implanted femoral stems had only a small portion can meet the desirable femoral anteversion angle. 1. , and anteversion angle increases after the implantation of an anatomical femoral stem with anteverted stem neck comparing to anatomical femoral neck. 2. The purpose of this study was to anatomically measure the anteversion angular difference between metaphyseal long axis and femoral neck in normal Chinese population. The metaphyseal long axis represents the coronal fixation plane of modern cementless medial-lateral cortical fitting taper stem. This angular difference or torsion Δ angle provides the estimation of how much the neck antevertion angle of femoral stem would be needed to match for desirable anatomical femoral neck version. Methods. 140 (77 male and 63 female) anonymous normal adult Chinese CT data with average age of 54.6 (male 54.6, female 54.5, P=0.95) were segmented and reconstructed to 3D models in Trauson Orthopeadic Modeling and Analytics (TOMA) program. Femoral head center, femoral neck axis and center point of diaphyseal canal 100mm bellow calcar formed the femoral neck plane. The metaphyseal stem implantation plane was determined by the center point of medial calcar, proximal canal central axis formed by femoral neck plane and the center point of diaphyseal canal 100mm bellow calcar. [Fig. 1] The angle between two planes was the torsion Δ angle between femoral placement plane and anatomical femoral neck. [Fig. 2] The torsion Δ angles were measured for all 140 cases. The traditional anteversion angle for anatomical femoral neck was also measured by Murphy's method. Student T test was perform to compare the angles for male and female. The 98% confidence level was assumed. Results. The average torsion Δ angle for whole population was 4.9°(0.04°-15.6°), SD=3.52°, male: 4.6° (0.42°-13.9°), SD=3.09°; female: 5.3° (0.04°-15.6°), SD=3.98°. There was no statistical significant difference between genders. P=0.28. All metaphyseal stem placement planes were less anteverted than anatomical femoral neck plane. [Fig. 3] The average anatomical femoral neck anteversion angle for total population was 18.6° (0.27°-42.6°), SD=7.54°; male: 18.6° (0.27°-32.9°), SD=7.37°; female: 18.7° (1.74°-42.6°), SD=7.81°. There was no statistical significance between male and female P=0.92. Only 26% of study population or 37 cases with unadjusted implant neck version had normal anteversion angle of 10°-15° (Tönnis). Discussion. The study suggested femoral stem neck anteversion angle adjustments up to 11° was necessary to match anatomical femoral neck for 94% of cases in Chinese population. And the adjustments of 0°-7° represented the 76% majority of population. This finding was in agreement with the published data in western population. 2. . Significance. Variable femoral stem neck anteversion angles up to 11° are necessary to reproduce the anatomical anteversions for 94% of normal Chinese population. For any figures or tables, please contact the authors directly

The pourpose of this study was to investigate the variability of the posterior condylar angle and the whiteside’s angle to establish if three degrees of external rotation of the femoral component produce the correct rotational alignment, in varus knee. 33 patients (33 knee) affected by varus osteoarthritic knee (5°–30°)underwent a preoperative CT scan examination of the knee and the hip. On the axial views, we have evaluated the femoral anteversion, the posterior condylar angle and the whitesiede’s angle. The mean femoral anteversion angle was 5.5°±13.7° (−24°;33°). The mean posterior condylar angle was 6.1°±2.5° (1°;14°). The mean intraobserver error was 0.9°. In 60.6% of the cases the angle was greater than 5°. The mean Witheside’s angle was 6°±3.5° (1°;16.5°). The mean intraobserver error was 0.8°. In 51.5% of the cases the angle was greater than 5°. Both the posterior condylar angle and the Whiteside’s angle showed values almost double than three degrees proposed as standard rotation for the femoral component. The method of three degrees standard of external rotation lead to relative internal rotation of the femoral component in TKR also for varus knee

Aims

This study was designed to develop a model for predicting bone mineral density (BMD) loss of the femur after total hip arthroplasty (THA) using artificial intelligence (AI), and to identify factors that influence the prediction. Additionally, we virtually examined the efficacy of administration of bisphosphonate for cases with severe BMD loss based on the predictive model.

Purpose. The complication of patellofemoral compartment was quite often in total knee arthroplasty. One of the impotant factors in these complications would be the femoral component rotation in TKA. To determine the rotation of the femoral component, the reference of the surgical epicondylar axis (SEA), posterior condylar axis (PCA), AP axis with three dimensional model achieved from computed tomography data were considered. There are some limitations with pre-oprerative CT-based planning such as radio exposure, cost, time and detection of the depth of cartilage. We evaluate the determination of the femoral component rotation with image-free registration method to compare with three-dimensional template system. Material and Methods. Thirty six knees were evaluated to determine the femoral component rotation. The reference points were marked to measure the PCA (posterior condylar axis), SEA (surgical transepicondylar axis), and APA (anteroposterior axis, Whiteside line) intra-operatively and calculated the angle from PCA to SEA and PCA to APA with Image free navigation system (BrainLAB). Those knees were preoperatively evaluated the angle deviation from SEA to PCA with three dimensional template system. These angle deviations, which suggested the femoral component rotation obtained from preoperative template system, were statistically compared with the femoral rotation angle in clinical situation. Results. The mean angle from PCA to SEA was external rotated 2.7 degrees (SD=1.8 degrees) with the template system. During image- free system in TKA, the mean angle from PCA to SEA was external rotated 2.2 degrees (SD=4.5 degrees), and the mean angle from APA to SEA was 0.5 degrees (SD=4.4 degrees). Discussion. The preoperative 3 dimensional template system showed the small ranges and standard deviations in PCA and SEA even when the residual cartilage of the surface at the femur was not considered to evaluate. Meanwhile, the three reference axes obtained from image free navigation system showed the large amount of deviations and thus the variability in these references was difficult to decide the rotation of the femoral component. Now navigation system provided the appropriate gap balance during knee motion. This gap-navigation technique would be one of the keys to obtain the proper rotation of the component

Combined anteversion angle of acetabular component and femeral neck is an important factor for total hip arthroplasty (THA) as it may affect impingement and dislocation. Previous studies have collected data mainly from direct measurements of bone morphology or manual measurements from 2D or 3D radiolographic images. The purpose of this study was to electronically measure the version angles in native acetabulum and femur in matured normal Caucasion population using a novel virtual bone database and analysis environment named SOMA™. 221 CT scans from a skeletally mature, normal Caucasian population with an age range of 30–95 years old. The population included 135 males and 86 females. CT data was converted to virtual bones with cortical and cancellous boundaries using custom CT analytical sofware. (SOMA™ V.3.2) Auxillary reference frames were constructed and measurements were performed within the SOMA™ design environment. Acetabular Anteversion (AA) angle as defined by Murray. 1. was measured. The acetabular rim plane was constructed by selecting 3 bony land marks from pubis, ilium and ischium. A vector through acetabular center point and normal to the rim plane defined the plane for the AA measurement. The AA was defined as the angle of this plane relative to the frontal (Coronal) plane of the pelvis. The Femoral Neck Anteversion (FNA) angle was measured from the neck axis plane to the frontal (Coronal) plane as defined by the posterior condyles. The neck axis plane was constructed to pass through femoral neck axis perpendicular to the transverse plane. The combined anteversion angle was computed as the summation of acetabular and femoral anteversion angles. Student's t tests were performed to compare gender difference with an assumed 95% confidence level. The mean AA angle for total population was 25.8°, SD=7.95°. The mean AA for male was 24.8°, SD=5.93° and for female was 27.3°, SD=7.14°. P=0.009. The mean FNA angle for total population was 14.3°, SD=6.52°. The mean FNA for male was 13.5°, SD=7.97° and for female was 15.5°, SD=7.80°. P=0.058. The mean combined anteversion angle for total population was 40.1°, SD=10.76°. The mean combined anteversion angle for male was 38.3° SD=10.39 ° and for female was 42.8° SD=10.83 °. P=.0002. The plot of AA as a function of FNA shows weak correlation for both male and female. (Figure 1) The frequency distribution is shown in Figure 2. The results showed the both AA, FNA and combined anteversion angles were significantly smaller in male population than that in female population. The FNA angle of the cementless femoral stem can be smaller than with the natural femur, therefore a higher AA or higher posterior build up may be required for the acetabular component for optimal function of a THA

INTRODUCTION The ability to evaluate the alignment of total knee arthroplasty using postoperative radiographs might be confounded by limb rotation. The aim of the presented study was therefore to measure the effect of limb rotation on postoperative radiographic assessment and to introduce a mathematical correction to calculate the true axial alignment in cases of a confounded radiograph. METHODS A synthetic lower left extremity (Sawbones®, Inc,Vashon Island, WA) was used to create a total knee arthroplasty of the Interax I.S.A.® knee prosthesis system (Stryker, Limerick, Ireland). Laser guided measurement of the tibia showed a femoral valgus angle of 6.5° postoperatively. The model was fixed in an upright stand which positioned the limb in varying degrees of rotation. Four series of 10 antero-posterior (AP) radiographs were taken with the knee in full extension, with femoral limb rotation ranging from 20° external rotation to 20° internal rotation in respect to the x-ray beam, in 5° increments. After digitizing each radiograph, four observer independently measured the femoral valgus angle for each series of the long leg radiographs using a digital measurement software (MEDICAD®, Hectec, Altfraunhofen, Germany). Each observer was instructed to determine the femoral valgus angle following the software’s guidelines. In addition each observer measured the geometrical distances of the femoral component figured on the radiographic film. Using a student t-test, the effect of femoral limb rotation on the measured femoral valgus angle and a correlation between femoral rotation and femoral valgus angle was established. Then for each limb rotation the distances ratio was determined to calculate the limb rotation. RESULTS Without an application of femoral rotation the femoral valgus angle was measured radiographically to be 6.5° (SD 0.4°). With external femoral rotation the measured femoral valgus angle linearly decreased to a minimum of 4.5° (SD 0.2°) at 20° femoral rotation. The linear regression (R2=0.94) calculated a 0.09° change of radiographically measured femoral valgus angle per femoral rotation angle. With the femoral rotation the radiographically measured ratio decreased linearly (R2=0.98) with further internal rotation. DISCUSSION The results of the presented study suggest a significant influence of femoral rotation during radiographic evaluation of limb alignment after total knee arthroplasty. With further external femoral rotation the radiographically apparent femoral valgus angle decreases. As the apparent femoral valgus angle changes linearly, a calculation of the distances of the particular femoral component could be used to determine the real femoral valgus angle in cases of femoral limb rotation

Introduction: It is difficult to measure the knee kinematics after TKA, navigation system can measure the knee kinematics during TKA operation. The purpose of this study is to describe the knee kinematic analysis in TKA using navigation system. Patients and methods: TKA kinematics was measured in 24 patients (7 men and 17 women) 27 knees (7 rheumatoid arthritis knees and 20 osteoarthritis knees) in this study. Mean age was 72.8 (55–81). The TKA implant was Vanguard PS (Biomet, Warsaw) and navigation system was Vector Vision Knee ver. 1.6 (BrainLab Inc). All patients were operated using navigation system. This system was CT-based navigation system. We cut the bone independently and released medial collateral ligament, joint capsule and other tight structures to equal the joint balance. Femoral component was implanted parallel to clinical epicondylar line. Kinematic Analysis: We measured the joint gap (mm), coronal alignment (degree), antero-posterior translation (mm) and femoral rotation angle (degree) using navigation workstation just after all prostheses implantation and closure of joint capsule. The patient’s leg was held by operator and moved passively. All joint kinematic data were recorded at every 10 degrees in full range of motion (0 to 130 degrees). The joint gap is the distance between proximal tibial cut surface and that of distal femur (extension range: 0–40) and posterior femur (flexion range: 50–130). Medial and lateral distances were measured. Results: In extension range, medial joint gap was 21.7mm at 0 degrees and decreased to 15.2mm with knee flexion. Lateral joint gap was 22.1mm at 0 knee extension, slightly decreased up to 40 degrees. Coronal alignment was 0.47 varus at 0 deg. and increased to 6.64 varus at 40 flexion. In flexion range, medial and lateral joint gap were increased 20.7 to 25.3, 17.2 to 31.2mm. Coronal alignment was c hanged from 4.94 valgus (60 flexion) to 8.94 varus (130 full flexion). Regarding to AP translation, femoral component was once moved 7.4 mm forward in early knee flexion and 15.2mm backward with flexion. Femoral components were rotated internally to 50 degrees flexion and then rotated externally with flexion. Conclusion: The balance of TKA was still varus alignment after soft tissue release. Femoral components were moved backward and external rotation. Our results demonstrated that femoral rollback movement and medial pivot knee motion were recognized. The limitation of this study was the situation of under anesthesia and no muscle strain were loaded during the measurement of knee kinematics. However navigation system is available not only for the accurate implantation but also the measurement of intra operative knee kinematics

For radiographic assessment of THA, we must estimate a 3-D structure with 2-D images. Basically, it has been good. But even after a successful surgery, sometimes we encountered an undersized stem in radiograph. Interestingly, it was more frequent after we introduced surgical robot for primary THA. It sometimes brought a huge dilemma during planning and evaluating the surgery. We performed this study to elucidate the cause of this problem. We used image data of 30 consecutive THAs using ROBODOC (ISS, USA). The measurement was made with the built-in tool in the Orthodoc, which is for the CT-based preoperative planning, and digital imaging system (PiView, Infinitt, Korea). We measured femoral anteversion, tilting angle at corresponding level, the longest and shortest diameters of femoral canal and their ratio. Also we measured anteversion and alignment of the stem. The canal filling of the stem was measured in projected images with CT and postoperative radiographs. The mean femoral anteversion was 21.1±10.2°. The canal tiling angle was 39.3±7.9°(p< 0.01). The long and short diameters were 19.3±2.6° and 14.3±1.8°. The mean ratio between them was 0.8±0.08°. Canal filling at AP and lateral dimensions were 88.25±9.8% and 85.7±6.9%. In postoperative radiographs, they were 85.4±7.3%(p=0.05) and 88.0±6.1%(p=0.06). This result suggests that the femoral canal at this particular or more distal level is elliptically shaped constantly. It tilts (in axial plane) to the same direction but not to the same degrees with femoral anteversion. Because of this tilt, relatively well-fixed round femoral stem can be considered as undersized in plane radiograph. Therefore, rather than using two plain radiographs alone for postoperative evaluation, adding postoperative CT may provide appropriate accuracy for assessment. And surgeon should keep in mind this axial tilt during planning and evaluating a robotic THA, especially not to remove too much healthy cortical bones to obtain full distal filling