Aims. This study aimed to investigate whether the use of CT-based navigation enhances: 1) the accuracy of cup placement; and 2) the achievement rate of required range of motion (ROM). Additionally, we investigated the impact of using a large femoral head and dual-mobility liner on the achievement rates. Methods. This retrospective study analyzed 60 manual and 51 CT-based navigated primary total hip arthroplasties performed at a single facility. Postoperative CT scans and CT-based simulation software were employed to measure the cup orientation and to simulate the ROM. We compared the absolute errors for radiological inclination (RI) and radiological anteversion (RA) between the two groups. We also examined whether the simulated ROM met the required ROM criteria, defined as flexion > 110°, internal rotation > 30°, extension > 30°, and external rotation > 30°. Furthermore, we performed simulations with 36 mm femoral head and dual-mobility liner. Results. The absolute errors of RI and RA from the preoperative plan were significantly smaller in the CT-based navigation group (3.7° (SD 3.5°) vs 5.1° (SD 3.5°); p = 0.022, and 3.9° (SD 3.5°) vs 6.8° (SD 5.0°); p = 0.001, respectively). The proportion of cases achieving the required ROM in all directions was significantly higher in the CT-based navigation group (42% vs 63%; p = 0.036). The achievement rates of the required ROM were significantly higher with the use of a 36 mm ball or dual-mobility liner compared to the use of a 32 mm ball (65% vs 51%; p = 0.040 and 77% vs 51%; p ≤ 0.001, respectively). Conclusion. CT-based navigation enhanced required ROM achievement rates by > 20%, regardless of the ball diameter. The improved accuracy of cup placement through CT-based navigation likely contributed to the enhancement. Furthermore, the use of large femoral heads and dual-mobility liners also improved the required ROM achievement rates. In cases with a high risk of dislocation, use of these devices is preferred. Cite this article: Bone Jt Open 2025;6(2):155–163

Rotational acetabular osteotomy (RAO), one of periacetabular osteotomies, is an effective joint-preserving surgical treatment for developmental dysplasia of the hip. Since 2013, we have been using a CT-based navigation for RAO to perform safe and accurate osteotomy. CT-based navigation allows precise osteotomy during surgery but cannot track the bony fragment after osteotomy. Thus, it is an issue to achieve successful reorientation in accordance with preoperative planning. In this presentation, we introduce a new method to achieve reorientation and evaluate its accuracy. Thirty joints in which CT-based navigated RAO was performed were included in this study. For the first 20 joints, reorientation was confirmed by tracing the lateral aspect of rotated fragment with navigation and checked if it matched with the preoperative planning. For the latter 10 joints, a new method was adopted. Four fiducial points were made on lateral side of the acetabulum in the preoperative 3-dimensional model and intraoperatively, rotation of the osteotomized bone was performed so that the 4 fiducial points match the preoperative plan. To assess the accuracy of position of rotated fragment in each group, preoperative planning and postoperative CT were compared. A total of 24 radial reformat images of postoperative CT were obtained at a half-hour interval following the clockface system around the acetabulum. In every radial image, femoral head coverage of actual postop- and planned were measured to evaluate the accuracy of acetabular fragment repositioning. The 4-fiducial method significantly reduced the reorientation error. Especially in the 12:00 to 1:00 position of the acetabulum, there were significantly fewer errors (p<0.01) and fewer cases with under-correction of the lateral acetabular coverage. With the new method with 4 reference fiducials, reorientation of the acetabulum could be obtained as planned with lesser errors

Introduction. Robotic-assisted hip arthroplasty helps acetabular preparation and implantation with the assistance of a robotic arm. A computed tomography (CT)-based navigation system is also helpful for acetabular preparation and implantation, however, there is no report to compare these methods. The purpose of this study is to compare the acetabular cup position between the assistance of the robotic arm and the CT-based navigation system in total hip arthroplasty for patients with osteoarthritis secondary to developmental dysplasia of the hip. Methods. We studied 31 hips of 28 patients who underwent the robotic-assisted hip arthroplasty (MAKO group) between August 2018 and March 2019 and 119 hips of 112 patients who received THA under CT-based navigation (CT-navi group) between September 2015 and November 2018. The preoperative diagnosis of all patients was osteoarthritis secondary to developmental dysplasia of the hip. They received the same cementless cup (Trident, Stryker). Robotic-assisted hip arthroplasty were performed by four surgeons while THA under CT-based navigation were performed by single senior surgeon. Target angle was 40 degree of radiological cup inclination (RI) and 15 degree of radiological cup anteversion (RA) in all patients. Propensity score matching was used to match the patients by gender, age, weight, height, BMI, and surgical approach in the two groups and 30 patients in each group were included in this study. Postoperative cup position was assessed using postoperative anterior-posterior pelvic radiograph by the Lewinnek's methods. The differences between target and postoperative cup position were investigated. Results. The acetabular cup position of all cases in both Mako and CT-navi group within Lewinnek's safe zone (RI: 40±10 degree; RA: 15±10 degree) in group were within this zone. Three was no significant difference of RI between Mako and CT-navi group (40.0 ± 2.1 degree vs 39.7± 3.6 degree). RA was 15.0 ± 1.2 degree and 17.0 ± 1.9 degree in MAKO group and in CT-navi group, respectively, with significant difference (p<0.001). The differences of RA between target and postoperative angle were smaller in MAKO group than CT-navi group (0.60± 1.05 degree vs 2.34± 1.40 degree, p<0.001). The difference or RI in MAKO group was smaller than in CT-navi, however, there was no significance between them (1.67± 1.27 degree vs 2.39± 2.68 degree, p=0.197). Conclusions. Both the assistance of the robotic arm and the CT-based navigation system were helpful to achieve the acetabular cup implantation, however, MAKO system achieved more accurate acetabular cup implantation than CT-based navigation system in total hip arthroplasty for the patients with OA secondary to DDH. Longer follow-up is necessary to investigate the clinical outcome

Introduction. CT-based navigation system in total hip arthroplasty (THA) is widely used to achieve accurate implant placement. Now, we developed our own CT-based navigation system originally, and since then we have been conducting various analysis in order to use the system more effectively. We compared the accuracy of registration with this navigation system and land mark matching type navigation system. In this study, we evaluated the influence of the surgical approach to the accuracy of registration. Methods. Between June 2015 and February 2016, 28 consecutive uncemented THAs were performed in 26 patients. The preoperative diagnosis was osteoarthritis in 20 hips, osteonecrosis of the femoral hips in 5, and rheumatoid arthritis in 3. The newly developed navigation system was a CT based, surface matching type navigation system. We used newly developed navigation system and commercially available land-mark type CT-based navigation system in the setting of acetabular sockets under the same condition. After we fixed the cementless cup, we measured the cup setting angle of inclination and anteversion on each navigation system. Postoperative assessment was performed using CT one week after the operation, and measured the actual angle of the cup. Approach of operations were performed via posterolateral approach in 14 hips, and Hardinge approach in 14 hips. We calculated the absolute value of the cup angle difference between intra-operative value and post-operative value with each navigation system and compared the accuracy between each navigation system and surgical approach. Results. The mean inclination using the Land-mark type navigation(group L) was 38.3±3.8°, using our navigation system (group S) was 38.7±5.7 °, the mean anteverion on group L was 25.8±5.6°, and group S was 27.3±10.2°. The mean of actual inclination of the implants calculated by postoperative CT was 38.4±7.1°, the mean of actual anteversion was 25.8±8.3°. In comparison with the absolute value of the difference between intra-operative and post-operative date, the mean difference of inclination on group L was 6.5±5.7°, and group L was 3.7±3.1 °, the difference was significant (p<0.05). The mean difference of anteversion of group L was 4.7±4.6 °, group S was 4.0±3.3°. In group L, the mean of absolute value of the difference between intra-operative and post-operative date of inclination via Hardinge approach was 6.0±6.8°, and posterior approach was 7.9±4.5°. In group S, The mean difference of inclination via Hardinge approach was 3.0±1.8°, and posterior approach was 4.5±4.1°. In group L, The mean difference of anteversion of Hardinge approach was 4.2±4.1°, and posterior approach was 5.3±5.3°. In group S, The mean difference of anteversion of Hardinge approach was 3.8±3.5°, and posterior approach was 4.2±3.3°. Discussion. N-navi was superior on inclination of the acetabular socket setting. Considering surgical approach, the accuracy was not good via posterior approach. We should take surface matching points widely around the acetabulum, however, to take points of anterior the acetabulum via posterior approach was difficult because of the femur. It was the reason of decrease the accuracy via posterior approach. We should choose the area of surface matching points according to surgical approach to make the registration more accurate

Objectives. Few reports were shown about the position of the cup in total hip arthroplasty (THA) with CT-based navigation system. We use minimally invasive surgery (MIS) technique when we perform cementless THA and the correct settings of cups are sometimes difficult in MIS. So we use CT-based navigation system for put implants with correct angles and positions. We evaluated the depth of cup which was shown on intra-operative navigation system. Materials and Methods. We treated 30 hips in 29 patients (1 male and 28 females) by navigated THA. 21 osteoarthritis hips, 6 rheumatoid arthritis hips and 3 idiopathic osteonecrosis hips were performed THA with VectorVision Hip navigation system (BrainLAB). Implants were AMS HA cups and PerFix stems (Japan Medical Materials, Osaka). Appropriate angles and positions of cups were decided on the 3D model of pelvis before operation. According to the preoperative planning, we put the implants with navigation system. We correct the pelvic inclination angle and measured the depth of cups with 3D template software. Results. The average distance from the surface of the cup to the edge of medial wall of pelvis was 3.4mm (0.0–8.0mm) on the axial plane which include the center of femoral head on postoperative CT. The average distance from the surface of the cup to the edge of medial wall of pelvis was 6.4mm (1.5–15.0mm) on intraoperative navigation. The average error was 2.9mm (0.0–9.0mm). The cup positions of post operative CT were deeper than that of intraoperative navigation in twenty six hips (86%). Conclusions. The shallow setting of cups caused the instability of cups. Deep setting caused damage of acetabular fossa. The positions of cups on the navigation system tend to be shown shallower than actual positions, so we should take care of deeper setting

Accurate cup placement in total hip arthroplasty (THA) for the patients with developmental dysplasia of the hip (DDH) is one of the challenges due to distinctive bone deformity. Robotic-arm assisted system have been developed to improve the accuracy of implant placement. This study aimed to compare the accuracy of robotic-arm assisted (Robo-THA), CT-based navigated (Navi-THA), and manual (M-THA) cup position and orientation in THA for DDH. A total of 285 patients (335 hips) including 202 M-THAs, 45 Navi-THAs, and 88 Robo-THA were analyzed. The choice of procedure followed the patient's preferences. Horizontal and vertical center of rotation (HCOR and VCOR) were measured for cup position, and radiographic inclination (RI) and anteversion (RA) were measured for cup orientation. The propensity score-matching was performed among three groups to compare the absolute error from the preoperative target position and angle. Navi-THA showed significantly smaller absolute errors than M-THA in RI (3.6° and 5.4°) and RA (3.8° and 6.0°), however, there were no significant differences between them in HCOR (2.5 mm and 3.0 mm) or VCOR (2.2 mm and 2.6 mm). In contrast, Robo-THA showed significantly smaller absolute errors of cup position than both M-THA and Navi-THA (HCOR: 1.7 mm and 2.9 mm, vs. M-THA, 1.6 mm and 2.5 mm vs. Navi-THA, VCOR:1.7 mm and 2.4 mm, vs. M-THA, 1.4 mm and 2.2 mm vs. Navi-THA). Robo-THA also showed significantly smaller absolute errors of cup orientation than both M-THA and Navi-THA (RI: 1.4° and 5.7°, vs. M-THA, 1.5° and 3.6°, vs. Navi-THA, RA: 1.9° and 5.8° vs. M-THA, 2.1° and 3.8° vs. Navi-THA). Robotic-arm assisted system showed more accurate cup position and orientation compared to manual and CT-based navigation in THA for DDH. CT-based navigation increased the accuracy of cup orientation compared to manual procedures, but not cup position

Objectives. Few reports were shown about the position of the cup in total hip arthroplasty (THA) with CT-based navigation system. We use minimally invasive surgery (MIS) technique when we perform cementless THA and the correct settings of cups are sometimes difficult in MIS. So we use CT-based navigation system for put implants with correct angles and positions. We evaluated the depth of cup which was shown on intra-operative navigation system. Materials and Methods. We treated 30 hips in 29 patients (1 male and 28 females) by navigated THA. 21 osteoarthritis hips, 6 rheumatoid arthritis hips and 3 idiopathic osteonecrosis hips were performed THA with VectorVision Hip 2.5.1 navigation system (BrainLAB). Implants were AMS HA cups and PerFix stems (Japan Medical Materials, Osaka). Appropriate angles and positions of cups were decided on the 3D model of pelvis before operation. According to the preoperative planning, we put the implants with navigation system. We correct the pelvic inclination angle and measured the depth of cups with 3D template software. Results. The average distance from the surface of the cup to the edge of medial wall of pelvis was 3.4mm (0.0-8.0mm) on the axial plane which include the center of femoral head on postoperative CT. The average distance from the surface of the cup to the edge of medial wall of pelvis was 6.4mm (1.5-15.0mm) on intraoperative navigation. The average error was 2.9mm (0.0-9.0mm). The cup positions of post operative CT were deeper than that of intraoperative navigation in twenty six hips (86%). Conclusions. The shallow setting of cups caused the instability of cups. Deep setting caused damage of acetabular fossa. The positions of cups on the navigation system tend to be shown shallower than actual positions, so we should take care of deeper setting

Background. CT-based navigation system in total hip arthroplasty(THA) is widely used to achieve accurate implant placement. The purpose of this study was to evaluate the influence of initial error correction according to the differences in the shape of the acetabulum, and correction accuracy associated with operation approach after localization of registration points at anterior or posterior area of the acetabulum. Methods. We set the anterior pelvic plane(APP) as the reference plane, and defined the coordinates as follows: X-axis for external direction, Y-axis for anterior direction, and Z-axis for proximal direction. APP is defined by the anterior superior iliac spines and anterior border of the pubic symphysis. We made a bone model of bilateral acetabular dysplasia of the hip, after rotational acetabulum osteotomy(RAO) on one side, and performed registration using infrared-reflective markers. At first, we registered the initial error on navigation system, and calculated the accuracy of the error correction based on each shape of the acetabulum as we increased the surface matching points. Based on the actual operation approach, we also examined the accuracy of the error correction when concentrating the matching points in anterior or posterior areas of the acetabulum. Results. For the rotational acetabular osteotomy model, the range of possible initial error correction increased as the surface matching points increased on both X-axis and Y-axis: On the X-axis, the range increased from 6mm to 10mm as the surface matching point increased from 10 to 20; and on the Y-axis, the range increased from 2mm to 10mm as the point increased 10 to 50. The range did not increase on the Z-axis. For the acetabular dysplasia model, the range of possible initial error correction increased on the X-axis(the range increased from 2mm to 8mm as the point increased from 10 to 50); however, no increase was observed for the Y- and Z-axis. Furthermore, concentrating the surface matching points in the posterior area around the acetabulum was more effective for the correction of the initial rotational error. Discussion. Because of the different anatomical shapes of the acetabulum, the error directions that were difficult to correct tended to vary between dysplasia and post-RAO. The error correction of Z-axis was difficult on both shapes of the acetabulum. Thus, the careful initial setting on Z-axis is important to minimize the error. Surface matching point on the posterior part of the acetabulum is more effective in correcting the initial rotational error compared with the anterior part of the acetabulum. It was shown that the difference in the error correction was affected by the localization of the registration points around the acetabulum. We presumed that using surface matching points on posterior area of the acetabulum improves the accuracy of the CT-based navigation system on the anterior approach. When using the system, it is important to understand the tendency that the shape of the acetabulum and the localization of the surface matching points have influence on correction of the initial error

Aims: Various studies could show that computer assisted pedicle screw insertion can reduce pedicle perforation rate. We conducted this study to verify if pedicle screw navigation can also avoid neurological complications. Methods: Within 20 months 112 patients were stabilised with 584 pedicle screws in the thoracolumbar spine (Th1-L5). 333 screws were inserted using a CT-based navigation system, 251 srews with conventional technique. Postoperatively, screw positons were assessed by an independent radiologist using CT-scans. Neurological complications and revision surgery were noted. Results: 47 (14.1%) of navigated screws perforated pedicle wall, 13 (28%) to medial side with 2 screws more than 4 mm. One screw (0.3%) had to be changed due to medial perforation of 6 mm in Th4. In the conventional group 60 (29.9%) screws perforated pedicle wall, 13 (22%) to medial side with 3 screws more than 4 mm. One patient had to be reoperated due to radicular deficit caused by a medial perforated screw in L1 (0.4%)Conclusion: CT-based navigation of pedicle screws decreased pedicle perforation rate significantly. However, considerable medial perforations up to 6 mm could not be avoided entirely. The rate of neurologic complicatons and revision surgery was the same in both computer assisted and conventional group

Accurate evaluation of lower limb coronal alignment is essential for effective pre-operative planning of knee arthroplasty. Weightbearing hip-knee-ankle (HKA) radiographs are considered the gold standard. Mako SmartRobotics uses CT-based navigation to provide intra-operative data on lower limb coronal alignment during robotic assisted knee arthroplasty. This study aimed to compare the correlation between the two methods in assessing coronal plane alignment. Patients undergoing Mako partial (PKA) or total knee arthroplasty (TKA) were identified from our hospital database. The hospital PACS system was used to measure pre-operative coronal plane alignment on HKA radiographs. This data was correlated to the intraoperative deformity assessment during Mako PKA and TKA surgery. 443 consecutive Mako knee arthroplasties were performed between November 2019 and December 2021. Weightbearing HKA radiographs were done in 56% of cases. Data for intraoperative coronal plane alignment was available for 414 patients. 378 knees were aligned in varus, and 36 in valgus. Mean varus deformity was 7.46° (SD 3.89) on HKA vs 7.13° (SD 3.56) on Mako intraoperative assessment, with a moderate correlation (R= 0.50, p<0.0001). Intraoperative varus deformity of 0-4° correlated to HKA measured varus (within 3°) in 60% of cases, compared to 28% for 5-9°, 17% for 10-14°, and in no cases with >15° deformity. Mean valgus deformity was 6.44° (SD 4.68) on HKA vs 4.75° (SD 3.79) for Mako, with poor correlation (R=0.18, p=0.38). In this series, the correlation between weightbearing HKA radiographs and intraoperative alignment assessment using Mako SmartRobotics appears to be poor, with greater deformities having poorer correlation

Objectives. The setting angle of the cup is important for achieving the stability and avoiding the dislocation after total hip arthroplasty (THA). It is difficult to set the cup at correct angle in minimally invasive THA by modified Watson-Jones approach. So we use CT-based navigation system. We evaluated the accuracy of with post-operative CT data. Materials and Methods. We treated 30 hips in 30 patients (7 male and 23 females) by navigated THA. 26 osteoarthritis hips, 2 rheumatoid arthritis hips and 2 idiopathic osteonecrosis hips were performed THA with VectorVision Hip 3.5.2 navigation system (BrainLAB). Implants were AMS HA cups and PerFix stems (Kyocera Medical, Osaka). Appropriate angles and positions of cups were decided on the 3D model of hip joint before operation. According to the preoperative planning, we put the cups with navigation system and stems without navigation system. We measured the anteversion angle with post-operative CT data and 3-dimensional template software. Results. The average angle of cup inclination was 35.2 degrees on navigation system in operation. The average angle was 37.4 degrees in post-operative CT data. We calculated the deference between the inclination angle of intra-operative navigation data and the angle of post-operative CT data. The average of error was 2.2 degrees. The average angle of cup anteversion was 24.2 degrees on navigation system in operation. The average angle was 27.5 degrees in post-operative CT data. The average of error was 3.5 degrees. Conclusions. There are some reports of complications in minimally invasive THA by modified Watson-Jones approach. Anteversion angle of cup are tend to insert from relative anterior direction with this approach. We could make the error of cup setting minimize with CT-based navigation system

Cup orientation of total hip arthroplasty (THA) is critical for dislocation, range of motion, polyethylene wear, pelvic osteolysis, and component migration. But, substantial error under manual technique has been reported. Therefore, various navigation systems were introduced to reduce outliers. CT based navigation (CTN) was reported to reduce outliers in cup orientation. Recently, a noble technique, fluoroscopy-CT-based navigation (FCTN), has recently been developed using 2D-3D matching technique. Because of much less registration points, FCTN might be friendly to MIS THA and cases with sever bone deformity. Between October 2006 and April 2008, 33 THAs were performed through MIS approach with navigations.

We prospectively randomized those into two groups, CTN and FCTN groups. We implanted cementless hemispherical cups in 18 hips using CTN (VectorVision CT Hip 3.1) and in 15 hips using FCTN (VectorVision CT Hip 3.5). For all the patients, volumetric post-operative CT scan was performed to measure 3D cup orientation. using 3D image-processing software (JMM, Japan). The difference from target angles of anteversion was 2.7 ± 2.4 degrees in FCTN group, and 12.1 ± 5.7 degrees in CTN group (p < 0.001). The absolute value of difference from target angles of inclination was 2.7 ± 2.4 degrees in FCTN group, and 6.5 ± 4.5 degrees in CTN group (p = 0.006). FCTN does not need surface registration around acetabulum, which is great advantage to MIS THA. Our study clearly showed that FCTN significantly improved a cup orientation to CTN.

Purpose: Minimally invasive surgery (MIS) total knee arthroplasty (TKA) makes faster rehabilitation in many cases, but it was sometimes difficult to performed the precise osteotomy and place the implants correctly due to loss of view or orientation for its small exposure. The computer-assisted navigation TKA system (CAS) was reported to achieve the optimal alignment and placement. However, it had disadvantages of longer operation time and wider exposure to acquire the reference points than these of the conventional method. Now MIS technique needs the accuracy of implant placement, on the other hand, CAS needs less-invasive methods. Among CAS methods, CT-based navigation system would have the potential for MIS because it would be referred to preoperative CT images. This study examined the accuracy of the registration with CT-based navigation system and the possibility of its application for MIS. Material and Methods: CT data were obtained from the femur and tibia of “Sawbone” (synthetic bone, Pacific Research Laboratories, Vashon, WA, USA) with a slice thickness of 1 mm. These data were transferred to Vector Vision Knee 1.5 (BrainLab Inc, Heimstettenm, Germany) and reconstructed to three-dimensional model. Two registrations were performed by a surface-matching algorithm. One is the conventional method as Vector Vision protocol; another is MIS approach which was allowed the limited area around the femoral notch and joint surface of tibia for registration. The accuracy of registration with these two methods was evaluated by Vector Vision Knee. And these registration points of these different methods were measured using a coordinate measuring machine, 3D surface scanner (Mitsutoyo, JAPAN) and were analyzed and calculated the distribution of points. Results and Discussion: There was a high degree of reproducibility of the MIS approach compared with the conventional method in the femur. However, the reference points in the distal tibia were deviated 1.5 cm to medial and thus 2.39 degree in varus would be happened at the proximal tibia in both methods. Now this software should be improving to be more accurate

Objectives. Many reports were shown about the angle of the cup in total hip arthroplasty (THA) with CT-based navigation system. However, there are few reports about the position of the stem. We investigated the position of the stem in navigated THA. We evaluated the position and alignment of stem which were shown on intra-operative navigation system. Materials and Methods. We treated 10 hips in 10 patients (1 male and 9 females) by navigated THA. 7 osteoarthritis hips and 3 idiopathic osteonecrosis hips were performed THA with VectorVision Hip 2.5.1 navigation system (BrainLAB). Implants were AMS HA cups and PerFix stems (Japan Medical Materials, Osaka). The positions of stem were decided on the 3D model of femur before operation. According to the preoperative planning, we put the implants with navigation system and recorded the position. We measured the position and alignment of stem with 3D template software after operation. We checked for complications. Results. The average error of stem alignment was 0.9 degrees in anteroposterior direction, 1.2 degrees in mediolateral direction and 3.5 degrees in rotation. The average error of the distance between the tip of greater trochanter and the shoulder of stem was 1.6mm on postoperative CT. Though there were no infections and fractures, 7 cases had postoperative pain on the lesion where we insert tracker pin. Conclusions. The accuracy of longitudinal stem alignment was correct but the anteversion varies widely. We usually perform THA by minimally invasive technique. Therefore the reference points of proximal femur were restricted at narrow area for registration and the landmarks for deciding the rotational alignment were difficult to be picked up correctly

The ligament balance as well as the alignment is essential for successful total knee arthroplasty (TKA). However it is usually assessed and adjusted only at 0? and 90?. In order to evaluate the ligament balance at the other angles we have used a navigation system. Twenty-one patients underwent posterior stabilised mobile bearing TKA using a CT-based navigation system were included in this study. Immediately post-operation and still under anaesthesia, varus and valgus stresses were applied on operated knees manually at 0?, 30?, 60?, 90? and 120?. The ligament balance was calculated based on the angles under varus and valgus stress displayed on the navigation screen, presenting a relationship between the femoral and tibial cutting planes. The mean ligament balance angle at 0?, 30?, 60?, 90? and 120? were −2? ± 3.6?, −5.8? ± 7.9?, 5.0? ± 6.9?, −1.3? ± 5.4?, 7.9? ± 7.2?, respectively. At 0? and 90? balance was well adjusted, however in the other angles, it was quite varied. At 30? and 120?, the lateral side was loose, on the other hand, medial side was looser at 60? knee flexion angle. The good balance at 0? and 90? is understandable because the balance is assessed and adjusted in these angles. Regarding the other angles, the 30? and 120? results corresponded with previous studies; however, the 60? results did not correlate. Although the reason is unknown, it must be aware the mid-flexion and deep flexion instability is quite common. Further investigations about the impact on clinical outcomes of such instabilities and how to adjust them if they are critical are needed

Introduction. We have used CT-based navigation system for THA from 2004 (Fig, 1). The purpose is to set acetabular socket in optimal position. We have used two different matching methods in these navigation THA surgeries. The old one is Land-mark matching method (L-method), using conventional paired point matching procedure during surgery. The new one is CT-based fluoroscopy-matching system (F-method), that is new technology of image matching procedure before starting surgery (Fig. 2). We compared the accuracy of socket setting angle with these two systems and discuss the usefulness of navigation system. Material. Materials were 477 THA patients using these navigation systems. 273 cases were with L method and 204 patients were with F method. The values between verification angle by navigation system during surgery and post-operative measured angle (by X-ray or CT scan) were calculated and compared. Results. The absolute difference in L method (273 cases) was on average 3.9 +/− 3.1 degree in inclination, and 4.0 +/− 3.4 degree in anteversion. The absolute difference in F method (204 cases) was on average 2.8 +/− 2.3 degree in inclination, and 2.9 degree +/− 2.6 in anteversion. The values in F method groups showed high accuracy (P<0.01). Discussion. Accurate socket setting in THA is essential for preventing dislocation and ensuring long term usage of prosthesis. Absolute errors in socket setting with theses two navigation systems were within 4 degree on average. These results showed the usefulness of both navigation systems. F method is new technology using image matching procedure of fluoroscopy and CT-scan doing on computer (Fig. 3). F method is easy to learn actual procedure and showed high accuracy. L method is conventional procedure and needs skill to use correctly. But it needs short additional time and so it is convenient for skilled-doctor

Introduction. Deformity after femoral osteotomy varies between patients. Some researchers reported good results when using cemented stems for the hips after femoral osteotomy, but there are many disadvantages that obstruct ideal fixation using cemented stems. Therefore, we developed cementless custom-made stems and inserted those using a computed tomography (CT) –based navigation system. Methods. Eighteen dysplastic hips of 15 patients after intertrochanteric osteotomy were investigated in the present study. Individual computed tomography data were used to manufacture cementless custom-made femoral stems out of Ti-6Al-4V. The proximal 1/3 of each stem was coated using porous coating covered with hydroxyapatite coating. The stems were inserted using a CT-based fluoro navigation system for accuracy of insertion. The average patient age at time of surgery was 66 years, and the average follow-up period was 3.5 years. Results. No fracture was observed during any surgery or follow-up period. The average preoperative Harris Hip Score was 44 points, and the average postoperative score was 85 points. No patient complained of postoperative thigh pain. The average difference between preoperatively planned anteversion and postoperative anteversion was 2° (range 0–5°). According to Engh's radiological classification system, there was bone ingrowth fixation in all hips. Conclusions. The technique of inserting the custom-made stems using a computed tomography-based navigation system was useful; however, there was an associated increase in manufacture time and cost

Introduction:. Since2007, we have used CT-based fluoroscopy-matching navigation system (Vector Vision Hip Ver.3.5.2, BrainLAB, Germany) in revision total hip arthroplasty. This system completes the registration procedure semi-automatically by matching the contours of fluoroscopic images and touching 3 adequate points to the contours of 3D bone model created in the computer. Registration procedure using fluoroscopic figures has finished before making surgical incision. It needs no elongation time during the operation. The objective of this study was to evaluate the accuracy of CT-based fluoroscopy-matching navigation system in revision THA. Material and method:. We analysed the acetabular cup in consecutive 33 hips with both intra-operative and post-operative alignment data (based on navigation system and CT evaluation) We further compared these measurements with results from primary THA. Data for primary THA were therefore obtained from 40 consecutive patients who underwent primary THA between August 2007 and May 2013 using the same navigation system by postero-lateral approach. We aimed the cup angle for Revision THA as following, the inclination: 40 degrees, the anteversion: 20 degrees Anteversion on the navigation system must be adjusted by the pelvic tilt. Results:. There was one dislocation in 33 Revision THAs. There was no other obvious complication (nerve palsy, VTE and Infection). The all cup alignments were within 7 degrees from the preoperative orientation. In the Revision THA group the differences between the intra- and post-operative measurement of cup inclination were 2.3 ± 1.9 degrees. The differences of cup anteversion were 2.7 ± 2.5 degrees. In the primary THA group, the differences between the intra- and post-operative measurement of cup inclination were 1.9 ± 2.1 degrees. The differences of cup anteversion were 2.1 ± 2.5 degrees. There was no significant difference with two groups. Discussion:. CT-based navigation THA is very useful for severe deformity of hip osteoarthritis. We had used CT-based navigation system (landmark matching) since 2003. It needs some technical skills to improve the accuracy of landmark matching. The registration with CT-based fluoroscopy-matching navigation system is much easier and more simple than with landmark matching navigation system. CT images of revision patients included metal artifacts caused by implants. However this system is not so affected by metal artifacts. And we found this system provided high accuracy even in revision THA

Introduction. Since2007, we have used CT-based fluoroscopy-matching navigation system (Vector Vision Hip Ver.3.5.2, BrainLAB, Germany) in Total hip arthroplasty. This system completes the registration procedure semi-automatically by matching the contours of fluoroscopic images and touching 3 adequate points to the contours of 3D bone model created in the computer. Registration procedure using fluoroscopic figures has finished before making surgical incision. It needs no elongation time during the operation. The accuracy of navigation system depends on the techniques of registration used for the navigation and secure fixation of the dynamic reference markers. These could be affected by the different type of approaches. The objective of this study was to evaluate the accuracy of CT-based fluoroscopy-matching navigation system in THA and compare the cup position by anterolateral and posteolateral approaches. Material and method. We analysed the acetabular cup in consecutive 132 hips with both intra-operative and post-operative alignment data (based on navigation system and CT evaluation), including 65 cases with anterolateral approach(Modified Watson Jones) (Group AL) and 67 cases with posterolateral approach(Group PL). We aimed the cup angle for THA as following, the inclination: 40 degrees, the anteversion: 20 degrees. Anteversion on the navigation system must be adjusted by the pelvic tilt. Results. The average of the operative time were 84.8 ± 13.5 in group AL and 89.3 ± 15.1 minutes in group PL. There was one dislocation in group AL. There was no other obvious complication (nerve palsy, VTE and Infection) in these two groups. The all cup alignments were within 8 degrees from the preoperative orientation. The differences between the intra- and post-operative measurement of cup inclination were 1.9 ± 1.6 degrees in group AL and 2.1 ± 1.1 degrees in group PL(N.S.). The differences between the intra- and post-operative measurement of cup anteversion were 2.3 ± 1.4 degrees in group AL and 2.2 ± 1.3 degrees in group PL (N.S.). Discussion. CT-based navigation THA is very useful for severe deformity of hip osteoarthritis. We had used CT-based navigation system(landmark matching) since 2003. It needs some technical skills to improve the accuracy of landmark matching. The registration with CT-based fluoroscopy-matching navigation system is much easier and more simple than with landmark matching navigation system. And we found this system provided high accuracy even in severe deformity cases. There was no significant difference with anterolateral and posterolateral approaches by using CT-based fluoroscopy-matching navigation system

Introduction. Orientation of the acetabular component in total hip arthroplasty has been shown to influence component wear, stability, and impingement. Freehand placement of the component can lead to widely variable radiographic outcomes. Accurate abduction, in particular, can be difficult in the lateral decubitus position due to limited ability to appreciate and control positional obliquity of the pelvis. A CT-based mechanical navigation device has been shown to decrease cup placement error. This is an independent report of a single-surgeon's radiographic results using the device to control cup abduction. Patients and Methods. Sixty-four (64) consecutive elective THRs in 58 patients were performed via a supercapsular percutaneously-assisted (SuperPATH) surgical approach. Intraoperatively, the acetabular components were aligned with the aid of the CT-based mechanical navigation device (HipXpert; Surgical Planning Associates, Medford, MA). The cup orientation was then further adjusted to ensure that the anterior rim of the acetabular component was not prominent to avoid psoas impingement. Postoperatively, radiographic abduction was measured on standing postoperative radiographs. Results. Measured on standing postoperative radiographs, the cup radiographic abduction angle averaged 42.7° with a standard deviation of ± 3.9° and a range of 35° to 51°. Conclusions. Total hip arthroplasty using a CT-based navigation device as a guide for abduction led to cup implantation within a very narrow abduction range. This navigation device deserves more widespread interest and study, as acetabular component malposition remains a major concern in THR