Abstract. Purpose. Intracanal rib head penetration is a well-known entity in dystrophic scoliotic curves in neurofibromatosis type 1. There is potential for spinal cord injury if this is not recognised and managed appropriately. No current CT-based classification system is currently in use to quantify rib head penetration. This study aims to propose and evaluate a novel CT-based classification for rib head penetration primarily for neurofibromatosis but which can also be utilised in other conditions of rib head penetration. Materials and methods. The grading was developed as four grades: normal rib head (RH) position—Grade 0, subluxed ext-racanal RH position—Grade 1, RH at pedicle—Grade 2, intracanal RH—Grade 3. Grade 3 was further classified depending on the head position in the canal divided into thirds. Rib head penetration into proximal third (from ipsilateral side)—Grade 3A, into the middle third—Grade 3B and into the distal third—Grade 3C. Seventy-five axial CT images of Neurofibromatosis Type 1 patients in the paediatric age group were reviewed by a radiologist and a spinal surgeon independently to assess interobserver and intraobserver agreement of the novel CT classification. Agreement analysis was performed using the weighted Kappa statistic. Results. There was substantial interobserver correlation with mean Kappa score (k = 0.8, 95% CI 0.7–0.9) and near perfect intraobserver Kappa of 1.0 (95% CI 0.9–1.0) and 0.9 (95% CI 0.9–1.0) for the two readers. Conclusion. The novel CT-based classification quantifies rib head penetration which aids in management planning

Background. Accurate acetabular cup positioning is considered to be essential to prevent postoperative dislocation and improve the long-term outcome of total hip arthroplasty (THA). Recently various devices such as navigation systems and patient-specific guides have been used to ensure the accuracy of acetabular cup positioning. Objectives. The present study evaluated the usefulness of CT-based three-dimensional THA preoperative planning for acetabular cup positioning. Methods. This study included 120 hips aged mean 68.3 years, who underwent primary THA using CT-based THA preoperative planning software ZedHip® (LEXI, Tokyo Japan) and postoperative CT imaging (Fig.1). The surgical approach adopted the modified Watson-Jones approach in the lateral decubitus position and Trident HA acetabular cups were used for all cases. Preoperatively the optimum cup size and position in the acetabular were decided using the ZedHip® software, taking into consideration femoral anteversion and to achieve the maximum range of motion in dynamic motion simulation. Radiographic inclination (RI) was selected in the range between 40°∼45° and radiographic anteversion (RA) in the range between 5°∼25°. Three-dimensional planning images of the cup positioning were obtained from the ZedHip® software, and the distances between the edge of the implant and anatomical landmarks such as the edge of the anterior or superior acetabular wall were measured on the three-dimensional images and recorded (Fig.2). Intraoperatively, the RI and RA were confirmed by reference to these distances and the acetabular cup was inserted. Relative positional information of the implant was extracted from postoperative CT imaging using the ZedHip® software and used to reproduce the position of the implant on preoperative CT imaging with the software image matching function. The difference between the preoperative planning and the actual implant position was measured to assess the accuracy of acetabular cup positioning using the ZedHip® software. Results. Actual cup size corresponded with that of preoperative planning in 95% of cases (114 hips). Postoperative mean RI was 42.3° ± 4.2° (95% confidence interval (CI), 41.5° ∼ 43.0°) and mean RA was 16.1° ± 5.9° (95%CI, 15.0° ∼ 17.1°). Deviation from the target RI was 4.2° ± 3.7° (95%CI, 3.5° ∼ 4.9°) and deviation from the target RA was 4.0° ± 3.6° (95%CI, 3.4° ∼ 4.7°). Overall 116 hips (96.7%) were within the RI safe zone (30° ∼ 50°) and 108 hips (90.0%) were within the RA safe zone (5° ∼ 25°), and 105 hips (87.5%) were within both the RI and RA safe zones (Fig.3). Mean cup shift from preoperative planning was 0.0mm ± 3.0mm to the cranial side in the cranio-caudal direction, 2.1mm ± 3.0mm to the anterior side in the antero-posterior direction, and 1.7mm ± 2.1mm to the lateral side in the medio-lateral direction. Conclusion. The accuracy of acetabular cup positioning using our method of CT-based three-dimensional THA preoperative planning was slightly inferior to reported values for CT-based navigation, but obviously superior to those without navigation and similar to those with portable navigation. CT-based three-dimensional THA preoperative planning is effective for acetabular cup positioning, and has better cost performance than expensive CT-based navigation. For any figures or tables, please contact the authors directly

Introduction. Total Knee Arthroplasty (TKA) is highly successful in treatment of end-stage degenerative arthritis of the knee. CT-based Patient-Specific Instrumentation (PSI) utilizes a CT scan of the lower extremity to create a three-dimensional model of the patient's anatomy, plan the surgery, and provide unique patient-specific resection blocks for the surgery. There are few published studies utilizing CT-PSI. The present study prospectively evaluates clinical, operative, and radiographic outcomes from 100 CT-based TKAs using this technology (MyKnee®, Medacta International S.A., Castel San Pietro, Switzerland). Materials and Methods. 100 consecutive eligible knees (94 patients) of the senior author underwent TKA using CT-based PSI technology. The primary outcome of the study was to compare the planned pre-operative femoral and proximal tibial resections to the actual intra-operative measured resections. Clinical outcomes included pre- and post-operative Knee Society Scores, Range-of-Motion (ROM, measured by goniometer), and complication data. Pre- and 6-week post-operative long-leg standing radiographs were obtained to assess HKA alignment. The femoral component angle (FCA) in the coronal plane, the tibial component angle (TCA), and posterior slope of the tibia were also assessed. Additionally, 10 patients were selected at random to undergo a post-operative CT scan for comparison to radiographic measurements. Results. 94 patients were enrolled representing 51 left and 49 right TKAs. Average follow up was 3.9 years (range 3.5 – 4.4 years). Average Knee Society Score (KSS) improved from 44.3 to 81.8 while KSS Function Score improved from 59.1 to 81.8 at 1 year. ROM arc of the patients was 110.5 (range 0–130) pre-operatively and was 111.3 (range 0–130) post-operatively. Two patients had a post-operative infection requiring surgical intervention. There were no thromboembolic complications and no revisions in study patients. No patient required a manipulation under anesthesia for post-operative stiffness. No intraoperative complications occurred nor were there any cases of abandoning the PSI blocks for standard technique. The actual bony resections achieved during surgery were strongly correlated to the planned resections of all 6 bone fragments measured. Each achieved statistical significance (p<0.001). Average post-operative alignment was 179.36° (range 175°–186°). Alignment was 180 ± 3° in 94% of patients post-operatively. Ten patients underwent a post-operative CT scan for HKA verification. The average post-operative HKA was 179.9° (range, 176.9°–180.9°) with a standard deviation of 1.31°. When comparing our pre-operative alignment by x-ray vs. CT, we found only 0.09° (p<0.001) average difference between them. Post-operatively, we continued to show very similar results showing x-ray HKA measurement of 180.1° vs. CT measurement of 179.9° (p<0.001). Discussion. The pre-operative CT reconstruction can accurately predict the intra-operative resection depths as demonstrated here. All 6 bony resections measured to within 1mm of the predicted value in the aggregate of our series. The restoration of mechanical axis to 179.9° as measured by CT scans demonstrates the efficacy of the blocks. Conclusion. The present study demonstrates efficacy in the use of CT-based PSI - showing that the planning can accurately predict bony resections, be used safely, and achieve precise radiographic outcomes. Consequently, we routinely support the use of CT-based PSI in TKA

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:. 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. 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

Introduction. Surgeons fixing scaphoid fractures need to be familiar with its morphological variations and their implications on safe screw placement during fixation of these fractures. Literature has limited data in this regard. The purpose of this CT-based study was to investigate scaphoid morphometry and to analyse the safe trajectories of screw placement in scaphoid. Methods. We measured the coronal and Sagittal widths of scaphoid in CT-scans of 60 patients using CT based data from 50 live subjects with intact scaphoid. Safe placements for screws with diameters of 1.7mm, 2.4mm, 3.5mm and 4mm were studied using trajectories with additional 2mm safety corridor. Results. The mean width of proximal segment in coronal and sagittal plane were 6.39mm (4.5–8.7) and 11.44mm (8.4–14.1) respectively. For the waist region, the mean coronal, sagittal width were 8.03mm (6.3–10.2mm) and 9.02mm (7–11.4mm) respectively. For distal segment, the mean coronal and sagittal width were 10.58mm (8.2–14.6mm) and the 9.59mm (7.3–11.9mm) respectively. The coronal and sagittal widths were significantly different from each other in all three zones. All scaphoid were capable of safely containing single 4mm screw and two parallel 1.7mm screws. Conclusion. Our study shows that there is considerable variation in scaphoid morphometry. Among the parameters, the waist region measurements show the least variation. The screw lengths do not always correlate to the overall longitudinal extent of scaphoid and can be planned preoperatively using CT-scans. Surgeons treating these fractures should opt for a CT-based analysis regarding the screw direction and length and need to be familiar with the variations in scaphoid morphometry

Background. Accuracy of implantation is a recognized prognostic factor for the long-term survival of TKA. The purpose of this study was to analyze the accuracy of component orientation and post-operative alignment of the leg following CT-based navigation-assisted TKA and to compare these parameters with those of a conventional surgical technique. Methods. We retrospectively compared the alignment of 130 total knee arthroplasties performed with a CT-based navigation system with that of 130 arthroplasties done with a conventional alignment guide system. The knee joints were evaluated using full-length weight-bearing antero-posterior and lateral radiographs. Results. The mean hip-knee-ankle angle, the frontal femoral component angle and the frontal tibial component angle were 180.7° (normal angle: 180.0°), 88.8° (90.0°) and 90.6°(90.0°), respectively, for the navigation-assisted arthroplasties and 180.9°(180.0°), 89.8°(90.0°) and 89.3°(90.0°), respectively, for conventional arthroplasties. The mean lateral femoral component angle and the femoral tibial component angle were 0.99° and 89.9°, respectively, for the navigation group and 2.62° and 88.5°, respectively, for the conventional group. All pre-operative leg axes of 10 outliers (HKA<177 or HKA>183) in the navigation group were over 193°, while in the conventional group, 23 outliers’ data were scattered. Conclusions. Our retrospective study with randomly assigned cases (consecutive patients in two separate hospitals) demonstrates significant improvements in component positioning with the CT-based navigation system compared to the conventional alignment guide system. Furthermore, we found that when analyzing cases within each group with pre-operative hip-knee-ankle angles lower and equal 192°, no outliers were found in the navigation group indicating a high level of alignment accuracy in this group. However, in cases with pre-operative hip-knee-ankle angles larger or equal 193°, outliers were found in both groups and no significant difference between the two groups was observed (p = 0.24). A detailed analysis of the outlier cases in the navigation group revealed that the femoral component was placed in the varus position. We thought that pre-operative underestimation of osteophytes of the medial femoral condyle might have led to a lateral shift of the femoral component during its intra-operative placement and was one of the contributing factors causing lower alignment accuracy

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

Patella resection has been the least controlled element of total knee arthroplasty (TKA). We have developed an intraoperative guide system involving a custom-made surgical template designed on the basis of a three-dimensional computer simulation incorporating computed tomography (CT) data for several years. This time we have applied this intraoperative guide system for the patella resection in TKA. We investigated the accuracy of CT-based patient-specific templating (PST) for patella resection using cadaveric knee joints in vitro. To plan the corrective patella resection, we attempted to simulate a three-dimensional patella resection with the use of computer models of the patella. From CT images of the patella we obtained three-dimensional surface models of the patella by performing a three-dimensional surface generation of the bone cortex. After the patella resection using CT-based custom-made surgical templating instrumentation, CT scan was performed again and we compared the patella shape in three-dimensional patella bone model reconstructed from pre and after cut from CT data. We compared the accuracy of patella cut using three-dimensional patella bone model reconstructed from pre and after cut from CT data. Statistical analysis was performed using paired t test. The difference between patella cut with CT-based custom-made surgical templating instrumentation and pre-operative planning were 0.8±1.2mm (medial side) and 0.1±1.4mm (lateral side). More than 60% resulted within 2mm from the pre-operative planning. There were significant differences both in flexion/extension, external/internal rotation and bone cut depth between CT-based custom-made surgical templating instrumentation and conventional instrument. The results in this study demonstrated the usefulness of CT-based custom-made surgical templating instrumentation for patella resection in TKA

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

Introduction:. Alignment of the initial femoral guidewire is critical in avoiding technical errors that may increase the risk of failure of the femoral component. A novel alternative to conventional instrumentation for femoral guidewire insertion is a computed tomography (CT) based alignment guide. The aim of this study was to assess the accuracy of femoral component alignment using a CT-based, patient specific femoral alignment guide. Methods:. Between March 2010 and January 2011, 25 hip resurfacings utilizing a CT-based femoral alignment guide were performed by three surgeons experienced in hip resurfacing. Stem-shaft angle (SSA) accuracy was assessed using minimum 6 week post-operative digital radiographs. A benchside study was also conducted utilizing six pairs of cadaveric femora. Each pair was divided randomly between a group utilizing firstly a conventional lateral pin jig followed by computer navigation and a group utilizing a CT-based custom jig. Guidewire placement accuracy for each alignment method was assessed using AP and lateral radiographs. Results:. In the clinical series, the post-operative SSA differed from the planned SSA by a mean of 1.3° (SD 4.8, range −9–14). The final SSA measured within ± 5° of the planned SSA in 20 of 24 cases (83%). There was no significant difference between surgeons in post-operative SSA accuracy (p = 0.697). In the benchside study, the custom jig (mean error 6.4°, SD 2.9) provided a comparable level of accuracy to that of the conventional jig (mean error 5.5°, SD 3.6, p = 0.851). Guidewire version using the custom jig (mean error 1.0°, SD 0.4) was comparable to computer navigation (mean error 3.9°, SD 2.1, p = 0.101) and was superior to the conventional jig (mean error 5.6°, SD 2.9, p = 0.008). Conclusion:. CT-based, patient specific guidewire alignment jigs provide a satisfactory level of accuracy for alignment of the femoral component. A custom guidewire alignment jig is comparable to computer navigation and may be a better alternative to conventional instrumentation for placement of the initial femoral guidewire in hip resurfacing. Accuracy results of the device approach those previously established for imageless computer navigation in hip resurfacing (1)

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

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

We have used CT-based total hip navigation system from 2003, to set the acetabular socket in optimal position. At first, we had used CT-based land-mark matching system. It needs matching procedure during surgery, touching paired points in surgical exposure. From 2006, we started to use new navigation system, called CT-based fluoroscopy-matching system, which was developed by BrainLAB Company (Vector-vision 2.7.1., 3.5.1.). For this new system, pre-surgical image matching procedure is need. Fluoroscopic images with 2 different directions must be taken in operation room. Then fluoroscopic images and CT reconstructive images were matched in computer with special program. Matching procedure was done before surgical incision. We compared the advantage of these two systems about technical problem, radiation exposure, time need for procedure, and accuracy. And then we discussed how to use these two different systems for THA patients. Accuracy was compared for 241 THA patients using these navigation systems. 152 cases were with CT-based land-mark matching system and 89 patients with CT-based fluoroscopy matching system. Final verification angle of acetabular socket setting in navigation during surgery was recorded for each case. The operative angle, which is referred from Murray, is used to show the socket setting angle (inclination and anteversion) in these navigation systems. Post-operative CT scan was taken to evaluate the actual socket setting angle. The values between verification angle during surgery and post-operative CT measured angle were calculated and compared statistically. Results were followed. New CT-based fluoroscopy matching method (F method): Average setting angle (operative angle) of socket in these 89 cases were 42.9 +/− 5.1 degree in inclination angle, and 28.5 +/− 7.9 degree in anteversion angle. The absolute difference in 89 cases between final verification angle and post-operative CT measurement angle was 2.9 degree (on average) +/− 2.5 degree in inclination angle, and 2.8 degree (on average) +/− 2.6 degree in anteversion angle. Conventional CT-based land-mark matching method (L method): The absolute difference in 152 cases between final verification angle and post-operative CT measurement angle was 4.2 degree (on average) +/− 3.2 degree in inclination angle, and 4.4 degree (on average), +/− 3.7 degree in anteversion angle. Absolute differences of setting angle in fluoroscopy matching groups showed statistically low compared with land-mark matching groups (P<0.01). Technical problems: L method is difficult to learn actual procedure. F method is easy to learn procedure. Image matching was done automatically by computer program. Radiation exposure during surgery: L method needs no additional radiation. F method needs radiation to get 2 fluoroscopic images. Total amount time need for navigation: L method needs extra 10 minutes during surgery in case of skilled-doctor. F method needs extra 20 minutes before starting surgery in case of all kind doctors. The accuracy of acetabular socket setting: Absolute errors in socket setting with theses two systems were within 5 degree together on average. These results showed the usefulness of both systems. Compared the accuracy between these 2 systems, F methods showed high accuracy. The accuracy of F methods is always high. It has no influence with deformity around hip joint, because fluoroscopic image matching was done with lower part of pubic bone, especially around symphysis pubis. For ordinary THA cases with skilled-doctor, CT-based land-mark matching system is useful, because this system is very convenient and needs only extra 10 minutes during surgery. For severe deformed cases with all kind doctors, CT-based fluoroscopy matching system is useful, because this system showed high accuracy even for severe deformed cases. Before surgical incision, fluoroscopic matching procedure has finished. This system needs no extra time after surgery starts

The present IRB approved study evaluates the early results of 100 TKAs using CT-based Patient-Specific Instrumentation (PSI) (MyKnee®, Medacta International, SA, Castel San Pietro, Switzerland). For this technique, a CT scan of the lower extremity is obtained, and from these images, the knee is reconstructed 3-dimensionally. Surgical and implant-size planning are performed according to surgeon preference, with the goal to create a neutral mechanical axis. Once planned and approved, the blocks are made. Outcomes measured for the present study include surgical factors such as Tourniquet Time (TT) as a measure of surgical efficiency, the actual intraoperative bony resection thicknesses to be compared to the planned resections from the CT scan, and complication data. Furthermore, pre- and post-operative long standing alignment and Knee Society Scores (KSS) were obtained. During surgery, the PSI cutting block is registered on the femur first and secured with smooth pins. No osteophytes are removed as the blocks use the positive topography of the osteophytes for registration. The distal femoral resection is performed directly through the block. An appropriate sized 4-in-1 block is placed and the remaining resections are performed. The tibial resection block is registered and resection performed. Final bone preparation, patella resurfacing, and trialing is performed as is standard to all surgical techniques. There were 50 Left and 50 Right TKA's performed in 61 females and 39 males. All patients had diagnosis of osteoarthritis. The average BMI was 31.1 and average age was 64.5 (range 41–90). 79 patients had pre-operative varus deformities with Hip Knee Angle (HKA) average of 174.7° (range 167°–179.5°). 19 patients had pre-operative valgus deformities averaging 184.4° (range 180.5°–190°). Three patients were neutral. Average TT was 31.2 minutes (range 21–51 minutes). With regard to the bony resections, the actual vs. planned resections for the distal medial femoral resection was 8.7 mm vs. 8.9 mm respectively. Further actual vs. planned femoral resections include distal lateral 7.2 vs. 6.7 mm; posterior medial 8.3 vs. 8.9 mm; and posterior lateral 6.2 vs. 6.8 mm. The actual vs. planned tibial resections recorded include medial 6.4 vs. 6.3 mm and lateral 8.3 vs. 8.2. The planned vs. actual bony cuts are strongly correlated, and highly predictive for all 6 measured cuts (p=<.001). No intraoperative complications occurred. Average KSS improved from 45.9 to 81.4, and KSS Function Score improved from 57.7 to 73.5 at 6 weeks postoperative visit. There were no thromboembolic complications. Two patients had a post-operative infection requiring surgical intervention. Post-operative alignment was 179.36° (range 175°–186°) for all patients. Alignment was neutral, within 3° in 95.9% of patients. There were only 4 outliers with maximal post-operative angulation of 6°. In conclusion, these early results demonstrate efficacy of CT-based PSI for TKA. The surgery can be performed efficiently, accurately, and safely. Furthermore, excellent short term clinical and radiographic results can be achieved

The present IRB approved study evaluates the early results of 100 TKAs using CT-based Patient-Specific Instrumentation (PSI) (MyKnee®, Medacta International, SA, Castel San Pietro, Switzerland). For this technique, a CT scan of the lower extremity is obtained, and from these images, the knee is reconstructed 3-dimensionally. Surgical and implant-size planning are performed according to surgeon preference, with the goal to create a neutral mechanical axis. Once planned and approved, the blocks are made [Fig. 1]. Outcomes measured for the present study include surgical factors such as Tourniquet Time (TT) as a measure of surgical efficiency, the actual intraoperative bony resection thicknesses to be compared to the planned resections from the CT scan, and complication data. Furthermore, pre- and post-operative long standing alignment and Knee Society Scores (KSS) were obtained. During surgery, the PSI cutting block is registered on the femur first and secured with smooth pins. No osteophytes are removed as the blocks use the positive topography of the osteophytes for registration. The distal femoral resection is performed directly through the block. An appropriate sized 4-in-1 block is placed and the remaining resections are performed. The tibial resection block is registered and resection performed. Final bone preparation, patella resurfacing, and trialing is performed as is standard to all surgical techniques. There were 50 Left and 50 Right TKA's performed in 61 females and 39 males. All patients had diagnosis of osteoarthritis. The average BMI was 31.1 and average age was 64.5 (range 41–90). 79 patients had pre-operative varus deformities with Hip Knee Angle (HKA) average of 174.7° (range 167°–179.5°). 19 patients had pre-operative valgus deformities averaging 184.4° (range 180.5°–190°). Three patients were neutral. Average TT was 31.2 minutes (range 21–51 minutes). With regard to the bony resections, the actual vs. planned resections for the distal medial femoral resection was 8.7 mm vs. 8.9 mm respectively. Further actual vs. planned femoral resections include distal lateral 7.2 vs. 6.7 mm; posterior medial 8.3 vs. 8.9 mm; and posterior lateral 6.2 vs. 6.8 mm. The actual vs. planned tibial resections recorded include medial 6.4 vs. 6.3 mm and lateral 8.3 vs. 8.2. The planned vs. actual bony cuts are strongly correlated, and highly predictive for all 6 measured cuts (p=<.001) [Fig. 3]. No intraoperative complications occurred. Average KSS improved from 45.9 to 81.4, and KSS Function Score improved from 57.7 to 73.5 at 6 weeks postoperative visit. There were no thromboembolic complications. Two patients had a post-operative infection requiring surgical intervention. Post-operative alignment was 179.36° (range 175°–186°) for all patients. Alignment was neutral, within 3° in 95.9% of patients. There were only 4 outliers with maximal post-operative angulation of 6° [Fig. 2]. In conclusion, these early results demonstrate efficacy of CT-based PSI for TKA. The surgery can be performed efficiently, accurately, and safely. Furthermore, excellent short term clinical and radiographic results can be achieved

Hardware in or about the knee joint presents a number of challenges to the surgeon in performance of Total Knee Arthroplasty (TKA). Conventional instrumentation usually requires a modification of technique or removal of the metallic implants. Computer-Assisted TKA (CAOS) is another option, but adds complexity and time to the procedure. MRI-based Patient-Specific Instrumentation (PSI) cannot be used as metal causes unwanted artifact and renders the images for planning, useless. However, CT scans are not affected by metal and thus CT-based PSI can be used in TKA patients with pre-existing hardware. The present IRB approved study evaluates 12 consecutive knees (10 patients) with pre-existing hardware using CT-based PSI (MyKnee®, Medacta International, SA, Castel San Pietro, Switzerland). In this technique, CT scan of the lower extremity is obtained, and from these images, the knee is reconstructed 3-dimensionally. Surgical and implant-size planning are performed according to surgeon preference, with the goal to create a neutral mechanical axis. Once planned and approved, the blocks are made [Fig 1]. During surgery, the PSI cutting block is registered on the femur first and secured with smooth pins. The distal femoral resection is performed directly through the block. An appropriate sized 4-in-1 block is placed and the remaining femoral resections are performed. The tibial resection block is registered and resection performed. Final bone preparation, patella resurfacing, and trialing is performed as is standard to all surgical techniques. Of the 12 TKAs, there were 5 left and 7 right knees performed in 6 females and 6 males. The average BMI was 33.19 and average age was 53 (range 44–63). All diagnoses were either osteoarthritis or post-traumatic osteoarthritis. Follow-up averaged 59 weeks (range 18.6–113.7). Nine patients had pre-operative varus deformities with HKA deformities average of 171.9° (range 154°–178.5°). One patient had pre-operative valgus deformity of 184.5°. Two patients were neutral (180°). Post-operative alignment for all patients (n = 11) was 179° (range 177°–180°). All patients were within 3° neutral, post operatively. Four patients measured 180°, 4 measured at 179°, 2 measured at 178°, and only one at 177°. Hardware consisted of 5 patients with femur or tibia staples, 3 with plate(s) and screws [Fig. 2], 3 patients with ACL interference screws, and one titanium rod. No hardware was removed unless necessary for implantation. Only 3 patients required some hardware removal. The pre-operative Range of Motion (ROM) averaged 2.9° to 98.3° (Extension range 0–15° and flexion range 30–115°). Post-operative ROM was 2.9° to 101.3°. (Extension range 0–5° and flexion range 65–125°). Knee Society Score (KSS) improved from 42.3 to 82.3, and KSS Function Score improved from 52.1 to 77.5. No intraoperative complications were recorded. Average tourniquet time was 42.1 minutes (range 28–102). Regardless of the deformity, the patient's post-operative mechanical axes HKA averaged 179° (range 177–180). Clinical scores were typical for TKA patients with improvement in both KSS and ROM. In conclusion, early results using PSI in patients with pre-existing hardware in or about the joint, is safe, efficient, and accurate in performance of TKA

Hardware in or about the knee joint presents a number of challenges to the surgeon in performance of Total Knee Arthroplasty (TKA). Conventional instrumentation usually requires a modification of technique or removal of the metallic implants. Computer-Assisted TKA (CAOS) is another option, but adds complexity and time to the procedure. MRI-based Patient-Specific Instrumentation (PSI) cannot be used as metal causes unwanted artifact and renders the images for planning, useless. However, CT scans are not affected by metal and thus CT-based PSI can be used in TKA patients with pre-existing hardware. The present IRB approved study evaluates 12 consecutive knees (10 patients) with pre-existing hardware using CT-based PSI (MyKnee®, Medacta International, SA, Castel San Pietro, Switzerland). In this technique, CT scan of the lower extremity is obtained, and from these images, the knee is reconstructed 3-dimensionally. Surgical and implant-size planning are performed according to surgeon preference, with the goal to create a neutral mechanical axis. Once planned and approved, the blocks are made. During surgery, the PSI cutting block is registered on the femur first and secured with smooth pins. The distal femoral resection is performed directly through the block. An appropriate sized 4-in-1 block is placed and the remaining femoral resections are performed. The tibial resection block is registered and resection performed. Final bone preparation, patella resurfacing, and trialing is performed as is standard to all surgical techniques. Of the 12 TKAs, there were 5 left and 7 right knees performed in 6 females and 6 males. The average BMI was 33.19 and average age was 53 (range 44–63). All diagnoses were either osteoarthritis or post-traumatic osteoarthritis. Follow-up averaged 59 weeks (range 18.6–113.7). Nine patients had pre-operative varus deformities with HKA deformities average of 171.9° (range 154°–178.5°). One patient had pre-operative valgus deformity of 184.5°. Two patients were neutral (180°). Post-operative alignment for all patients (n=11) was 179° (range 177°–180°). All patients were within 3° neutral, post operatively. Four patients measured 180°, 4 measured at 179°, 2 measured at 178°, and only one at 177°. Hardware consisted of 5 patients with femur or tibia staples, 3 with plate(s) and screws, 3 patients with ACL interference screws, and one titanium rod. No hardware was removed unless necessary for implantation. Only 3 patients required some hardware removal. The pre-operative Range of Motion (ROM) averaged 2.9° to 98.3° (Extension range 0–15° and flexion range 30–115°). Post-operative ROM was 2.9° to 101.3°. (Extension range 0–5° and flexion range 65–125°). Knee Society Score (KSS) improved from 42.3 to 82.3, and KSS Function Score improved from 52.1 to 77.5. No intraoperative complications were recorded. Average tourniquet time was 42.1 minutes (range 28–102). Regardless of the deformity, the patient's post-operative mechanical axes HKA averaged 179° (range 177–180). Clinical scores were typical for TKA patients with improvement in both KSS and ROM. In conclusion, early results using PSI in patients with pre-existing hardware in or about the joint, is safe, efficient, and accurate in performance of TKA