Acetabular component malalignment remains the single greatest root cause for revision THA with malposition of at least half of all acetabular components placed using conventional methods. These studies repeatedly document that the concept of using local anatomical landmarks has no scientific basis over a breadth of presenting pathology. Traditional navigation and robotics can potentially lead to improved component placement but these technologies have not gained widespread use due to the increase in time of use, complexity, and cost of these systems. Robotic systems have also proven to be potentially hazardous and inaccurate in routine clinical use. The alternative of placing the cup in the supine position, even with the use of arthroscopy, has been proven to have an incidence of inaccuracy equal or greater than that in the lateral position. A smart mechanical instrument system was developed to quickly and easily achieve accurate cup alignment (HipXpert System, Surgical Planning Associates, Boston, MA). The system is based on a low dose, low cost CT study and a customised patient-specific surgery plan. The laterally-based system docks on a patient-specific basis with 3 legs: one through the incision behind the posterior rim, one percutaneously on the lateral side of the ASIS, and a third percutaneously on the surface of the ilium. A direction indicator on the top of the instrument points in the desired cup orientation. The anteriorly-based system also docks on a patient-specific basis with one leg on the anterior ischium and one leg on each ASIS, either to skin or to bone. The lateral system has been proven to be robust, with repeated studies showing accurate cup placement in 100% of cases and an independent study showing accurate cup placement in 98% of cases for both anteversion and inclination. This compares to a recent study of robotic methods that 88% of inclination and 84% for anteversion. Smart mechanical navigation of cup placement offers the optimum combination of accuracy, speed, and simplicity for solving the ubiquitous problem of acetabular component malorientation

Acetabular cup placement in total hip replacement surgery is often difficult to assess, especially in the lateral position and using the posterior approach. On table control X-Rays are not always accessible, especially in the government sector. Conventional techniques and computer assisted surgery (CAS), are currently the two most popular methods for proper placement of the acetabular cup in Lewinnek's safe zone of orientation (anteversion 15°–10° and lateral inclination 40°±10°). We developed a simple way to get accurate cup placement using Smartphone technology. Methods:. A spirit level application was downloaded to the Smartphone. The acetabulum inclination was measured on the pre-operative X-Rays. The phone is placed in a sterile bag and then used intra-operatively, to measure and set our acetabular cup orientation to our pre-operative measurements. The inclination level was measured before and after final placement of the acetabular cup. This was compared to the acetabular cup inclination in our post-operative X-Rays. Results:. In our series of 50 cup placements we found high accuracy. The results show less than 5° deviation between our pre-, intra- and post-operative measurements. Conclusions:. Smartphone technology proves to be good alternative to conventional methods and CAS, to improve Acetabular Cup placement in Total Hip Arthroplasty

Acetabular component malalignment remains the single greatest root cause for revision THA with malposition of at least ½ of all acetabular components placed using conventional methods. The use of local anatomical landmarks has repeatedly proven to be unreliable due to individual variation of these structures. As a result, the use of such landmarks without knowledge of their three-dimensional orientation may actually be a major cause of component malpositioning. Traditional navigation and robotics can potentially lead to improved component placement but these technologies have not gained widespread use due to the increase in time of use, complexity, and cost of these systems. The alternative of placing the cup in the supine position, even with the use of arthroscopy, has been proven to have an incidence of inaccuracy equal or greater than that in the lateral position. A smart mechanical instrument system was developed to quickly and easily achieve accurate cup alignment (HipXpert System, Surgical Planning Associates, Boston, MA). The system is based on a low dose, low cost CT study and a customised patient-specific surgery plan. The laterally-based system docks on a patient-specific basis with 3 legs: one through the incision behind the posterior rim, one percutaneously on the lateral side of the ASIS, and a third percutaneously on the surface of the ilium. A direction indicator on the top of the instrument points in the desired cup orientation. The anteriorly-based system also docks on a patient-specific basis with one leg on the anterior ischium and one leg on each ASIS, either to skin or to bone. The lateral system has been proven to be robust, with repeated studies showing accurate cup placement in 100% of cases and an independent study showing accurate cup placement in 98% of cases for both anteversion and inclination. This compares to a recent study of robotic methods with 88% for inclination and 84% for anteversion. Smart mechanical navigation of cup placement offers the optimum combination of accuracy, speed, and simplicity for solving the ubiquitous problem of acetabular component malorientation

Precision planning with correct sizing and placement of components is critical to proper execution of total hip arthroplasty. While the desire to achieve excellent outcomes has always been a surgeon's goal, value-based care programs such as the Comprehensive Joint Replacement (CJR) program apportion real expenditures for the cost of treating complications such as fracture or dislocation to the participants. Such accountability accentuates the importance of optimizing the planning and execution of joint replacement surgery. Acetabular component sizing and placement in particular remains the single greatest challenge to surgeons. This is simply due to the fact that the requisite spatial information is not available to the surgeon during conventional surgery. Basing component placement on local anatomical landmarks without knowing the patient-specific nature of those landmarks ensures poor component placement in many cases. As a result, studies demonstrate that at least ½ of all acetabular components placed using conventional methods are malpositioned. Potential solutions include the using of intra-operative radiographic analysis, traditional navigation and robotics. Unfortunately, measurements of plain radiographs have repeatedly been shown to be inaccurate due to lack of knowledge of and correction for beam center location, magnification, beam divergence, and position of the pelvis itself on the image. As a result, such quantification of unquantifiable images can systematically lead to poor decisions. Intra-operative radiograph measurement methods have been shown to lead to anteversion measurement errors as high as 27 degrees. Similarly, there is a perception that performing total hip arthroplasty through the anterior exposure can result in reliable cup positioning when fluoroscopy is used, but such procedures have also been shown to have a high incidence of cup malposition. Image-free navigation, image-based navigation, and image-based robotics can potentially lead to accurate component placement. Adoption of these technologies, however, has been limited, possibly due to the increase in time of use, complexity, and cost of these systems. Robotic systems have also proven to be potentially hazardous and inaccurate in routine clinical use. A cloud-based, patient-specific hip surgery planning and smart-tool cup navigation system was developed to address the most common technical problems affecting hip arthroplasty (HipXpert System, Surgical Planning Associates, Boston, MA). The methodology provides the surgeon with a full 3D plan of the surgery including cup size, cup orientation, stem size, head length, femoral anteversion, and planned change in leg length and offset. The application controlling the plan allows the surgeon to instantly change the plan and shows the implants in both 3D and on multiplanar cross-sectional views. The associated smart tool is adjusted specifically for that patient and when docked, provides orientation information to the surgeon. The system has been proven to be robust, with repeated studies showing accurate cup placement in 100% of cases including by an independent study. This compares to a recent study of robotic methods that measured 88% for inclination and 84% for anteversion. Cloud-based 3D planning combined with smart mechanical navigation of cup placement offers the optimum combination of accuracy, speed, and simplicity for solving the ubiquitous problems of acetabular component malorientation and provides critical pre-operative information including acetabular and femoral component sizes, planned femoral anteversion, and planned changes in leg length and offset of the surgery

Introduction. Proper acetabular cup placement is very important factor for successful clinical results in total hip arthroplasty (THA). Malposition of acetabular cup has been linked to increased rates of dislocation, impingement, pelvic osteolysis, cup migration, leg length discrepancy and polyethylene wear. Recently, some authors reported usefulness of navigation systems to set the acetabular cups with correct position. The purpose of this study is to evaluate the accuracy of acetabular cup placement in THA using computed tomography (CT)-based navigation system. Material and Methods. Subjects were 235 hip joints we performed primary THA using CT based navigation system (Stryker® Navigation System, Stryker Corporation, Kalamazoo, MI, USA) from 2008 to 2014 and could assess the implant position by postoperative CT images. Their average age was 65.1 years (range 35–88). In all cases, non-cemented acetabular cups were implanted. TriAD cups (Stryker®) were used in 31 hips, and Tritanium cups (Stryker®) were used in 15 hips, and Trident cups (Stryker®) were used in 189 hips. Registration in this navigation system used surface matching system. We designed cup implantation using preoperative CT images and 3-dimensional (3-D) templates. The planned position of acetabular cup was in principle 40 degrees of inclination and 20 degrees of anteversion. However, we adjusted the better position of the cups according to pelvic tilt and femoral neck anteversion. When we placed acetabular cups, the position, inclination and anteversion, were measured by navigation system. After surgery, the positions of the cups were measured using postoperative CT images, navigation software and 3-D templates. Postoperative position using CT images were adjusted according to preoperative pelvic plane. The discrepancies between intraoperative navigation data and postoperative CT images data were analyzed as accuracy of navigation system in cup placement. Results. No complications related to navigation procedures were encountered. There was no case with acetabular cup displacement obviously. The discrepancies between intraoperative data and postoperative data were an average difference of 1.6 degrees (SD, 1.4 degrees) for inclination and 2.1 degrees (SD, 1.7 degrees) for anteversion. Discussion and Conclusions. In THA, cup position is very important factor of postoperative long-term success. However, it is not easy to place the acetabular cup with proper position using conventional devices. CT-based navigation system was reported that it had many advantages than previous techniques in preoperative planning, setting the implants and analysis of postoperative data. But in registration with surface matching, learning-curve was pointed out and might be a problem for proper placement of implants. Therefore, we performed this study after some navigation THA cases. In the results of this study, the discrepancies between intraoperative and postoperative data were average 1.6 degrees for inclination and 2.1 degrees for anteversion. The accuracy of navigation system was good in inclination and anteversion of the cups, and there was no complication related it. CT-based navigation system is very useful device

Introduction. Lumbar spine fusion in patients undergoing THA (total hip arthroplasty) is a known risk factor for hip dislocation with some studies showing a 400% increased incidence compared to the overall THA population. Reduced spine flexibility can effectively narrow the cup anteversion safe zone while alterations in pelvic tilt can alter the center of the anteversion safe zone. The use of precision cup alignment technology combined with patient-specific cup alignment goals based on preoperative assessment has been suggested as a method of addressing this problem. The current study assess the dislocation rate of THA patients with stiff or fused lumbar spines treated using surgical navigation with patient-specific cup orientation goals. Methods. Seventy-five THA were performed in 54 patients with a diagnosis of lumbar fusion, lumbar disc replacement, and scoliosis with Cobb angles greater than 40 degrees were treated by the senior author (SM) as part of a prospective, non-randomized study of surgical navigation in total hip arthroplasty. All patients were treated using a smart mechanical navigation tool for cup alignment (HipXpert System, Surgical Planning Associates, Inc., Boston, MA). Cup orientation goals were set on a patient-specific basis using supine pelvic tilt as measured using CT. Patients with increased pelvic tilt had a goal for increased cup anteversion and patients with decreased pelvic tilt had a goal for decreased cup anteversion (relative to the anterior pelvic plane coordinate system). Each patient's more recent outpatient records were assessed for history of dislocation, instability, mechanical symptoms, decreased range of motion or progressive pain. Additionally, last clinic radiographs were reviewed to confirm lumbar pathology in the form of spinal surgical hardware. Results. Seventy-five total hip arthroplasties with stiff lumbar spine were reviewed with and average follow up of 6.04 years. The average number of levels of lumbar fusion was 2.3 levels. Since the most recent follow up on all patients in this cohort no hip dislocations had occurred. Discussion and Conclusion. Fusion or stiffness of the lumbar spine is a known risk factor for instability following elective THA. The current study demonstrates that patient-specific planning of cup placement taking abnormal pelvic tilt into consideration combined with the use of accurate intra-operative cup alignment technology can be used to address this problem

The existing image-free Total Hip Arthroplasty (THA) navigation systems conventionally utilise the patient-specific Anterior Pelvic Plane (APP) as the reference to calculate orientations of the implanted cup, e.g. anteversion and inclination angles. The definition of APP relies on the intra-operative digitisation of three anatomical landmarks, the bilateral Anterior Superior Iliac Spine (ASIS) and the pubicum. Due to the presence of the thick soft tissue around the patient's pubic region, however, the landmark on pubic area is hard to be digitised accurately. A novel reference plane called Intra-operative Reference Plane (IRP) was proposed by G. Zheng et al to address this issue. To determine the IRP, bilateral ASIS and the cup center of the operating side instead of the pubicum are digitised intra-operatively. It avoids the error-prone digitisation of pubicum, and the angle between the patient-specific APP and the suggested IRP can be computed pre-operatively by a single X-ray radiograph-based 2D/3D reconstruction approach developed by G. Zheng et al. Based on this angle, the orientation of the APP can be intra-operatively estimated from that of the IRP such that all measurements with respect to IRP can be transformed to measurements with respect to APP. In order to implement and validate this new reference plane for image-free navigation of acetabular cup placement, we developed an IRP-based image-free THA navigation system. All cup placement instruments were mounted with passive markers whose positions could be traced by a NDI Polaris® infrared camera (Northern Digital Inc, Ontario, Canada). The cup center was obtained by first pivoting a tracked impactor with appropriate size of the mounted trial cup and then calculating the pivoting center through a least-squares fitting. The bilateral ASIS landmarks were acquired through the percutaneous pointer-based digitisation. We tested this new IRP-based image-free THA navigation system in our laboratory by conducting twelve studies on two dry cadaver pelvises and two plastic pelvises. The ground truth for each study was established using the conventional APP-based method, i.e., in addition to those landmarks required by our IRP-based method, we also digitised the pubicum on respective pelvic bones and calculated cup orientations on the basis of the digitised APP. The mean and standard deviation of differences between the proposed IRP-based anteversion measurement and the ground truth are 1.0 degree and 0.7 degree, while the maximal and minimal differences are 2.1 degree and 0.3 degree respectively. The mean and standard deviation of differences between the proposed IRP-based inclination measurement and the ground truth are respective 0.2 degree and 0.2 degree. Moreover, the maximum of differences is 0.5 degree and the minimum is 0.0 degree. Our laboratory experimental results demonstrate that the new IRP-based image-free navigation system is accurate enough for acetabular cup placement. In comparison to existing image-free navigation systems that use APP as the reference plane, the newly developed system employs IRP as the reference plane, which has the advantage to eliminate the digitisation of landmarks around the pubic region. The successful validation with the laboratorial study has led us to the next step of clinical trials. We expect to report preliminary clinical cases in the near future

Introduction. Total hip arthroplasty has become an increasingly common procedure. Improper cup position contributes to bearing surface wear, pelvic osteolysis, dislocations, and revision surgery. The incidence of cup malposition outside of the safe zone (40° ± 10° abduction and 15° ± 10° anteversion) using traditional techniques has been reported to be as high as 50%. Our hypothesis is that computer assisted navigation will improve cup placement in total hip arthroplasty compared with traditional techniques. Methods. This study retrospectively evaluated the position of 425 consecutive cups placed during primary total hip arthroplasty performed over a two-year period, from 8/1/2012 to 8/1/2014. All cups were placed with a direct-anterior muscle-sparing approach with computer-assisted imageless navigation by a single surgeon. Real-time intraoperative “screen shots” were taken of cup placement. Standard antero-posterior postoperative radiographs of the pelvis were taken within 6 weeks of surgery in the operating surgeon's office using the same standardized protocol for each patient. The radiographs were evaluated by two separate investigators for final abduction and anteversion utilizing the same method as other studies. Statistics were descriptive in nature. Results. Intraoperative navigation screenshots from 425 hips showed that 100% were within the safe zone for abduction and anteversion. Postoperative radiographic review showed that 97% were within the safe zone for abduction (Mean 41 degrees, Range 29–54 degrees), 96% were within the safe zone for anteversion (Mean 16 degrees, Range 4–38 degrees) and 94% were within the safe zone for both abduction and anteversion. Conclusion. In our series, computer assisted navigation improved cup placement in total hip arthroplasty compared with traditional techniques as reported in current literature. Cup position in our study, was within the safe zone for abduction and version at a comparable rate to similar studies examining THA's performed with navigation

Purpose:. Correct placement of the acetabular cup is a crucial step in hip replacement to achieve a satisfactory result and remains a challenge with free hand techniques. Imageless navigation may provide a viable alternative to freehand technique and improve placement significantly. The purpose of this project was to assess and validate intra-operative placement values as displayed by an imageless navigation system to postoperative measurement of cup position using high resolution CT scans. Methods:. Thirty-two subjects who underwent primary hip joint arthroplasty using imageless navigation were included. The average age was 66.5 years (range 32–87). 23 non-cemented and 9 cemented acetabular cups were implanted. The desired position for the cup was 45 degrees of inversion and 15 degrees of anteversion. A pelvic CT scan using a multi-slice CT was used to assess the position of the cup radiographically. Results:. Two subjects were excluded because of dislodgement of the tracking pin. Pearson correlation revealed a strong and significant correlation (r=0.68; p<0.006) for cup inclination and a moderate non-significant correlation (r=0.53; p=0.45) between intra-operative readings and cup placement for anteversion. Conclusion:. These findings can be explained with the possible introduction of systematic error. Even though the acquisition of anatomic landmarks is simple, they must be acquired with great precision. An error of 1 cm can result in a mean anteversion error of 6 degrees and inclination error of 2.5 degrees. Whilst computer assisted surgery results in highly accurate cup placements for inclination, anteversion of the cup cannot be

Introduction. Optimal alignment of the acetabulum cup component is crucial for good outcome of Total Hip Arthroplasty (THA). A patient-specific instrumentation (PSI) for cup alignment manufactured by 3D printing might improve cup alignment in conventional THAs with patient's lateral decubitus position. In this study, we developed PSI for cup alignment which transferred preoperatively planned cup alignment to the operation room as a linear visual reference(Figure 1), then investigated its accuracy in terms of fitting of PSI on the bony surface and angle deviation between pre- and post-operative cup alignments. Methods. 3-Dimensional bone models created from CT images of both sides of 6 cadaveric specimens were used in the current study. In the first experiment (first 3 specimens and six hips), we designed PSI to fit on the acetabular rim, and we inserted a Kirschner wire (K-wire) through PSI after PSI's fitting. In the second experiment (remaining 3 specimens and six hips), after the same steps like the first experiment were done, we reamed and finally impacted plastic cups with the visual reference of the K-wire. Using postoperative CT images taken after both experiments, we measured deviation of the K-wire placement for the first experiment, and measured deviation of the cup placement from planned cup alignment. Results. The angle deviation of the K-wire alignment on the basis of radiographic inclination and anteversion angles was on average 2.2°±2.5° and 1.0°±1.3° respectively in the first experiment. The angle deviation of the cup alignment with the same definition was on average 2.88°±1.63° and 4.15°±2.56°. For one cadaveric specimen data for the first experiment were missing. Conclusion. We conclude that the accuracy of acetabular cup placement can be improved by the use of patient-specific cup orientation guides

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

Purpose:. Imageless navigation has improved the accuracy of acetabular cup placement but relies on manual identification of pelvic anatomy. Thick soft tissues in obese patients could obscure these landmarks and result in large variances of cup placement. The purpose of this study was to investigate the relationship between BMI, soft tissue thickness, navigated cup and final post-operative cup position. Methods:. Thirty patients with an average age of 66.5 years underwent primary navigated THA. Final intra-operative cup position was recorded. Soft tissue thickness and final post-operative cup alignment were measured on a multi-slice pelvis CT scan. Results:. There were no significant relationships between the variables for inclination. Larger ranges were observed in the obese group. It reached significance for the difference between the desired and final post-operative cup position (p=0.007). There was a moderately significant relationship (r=0.41, p=0.0002) between soft tissue thickness and final cup anteversion and a strong and near significant correlation (r=0.6, p=0.07) for the difference between the desired and final post-operative cup position for anteversion. Similar to inclination larger ranges were observed in the obese group. However, significant differences were only observed for final post-operative cup position (p=0.002) and the difference between the desired and final post-operative cup position (p=0.0003). Conclusion:. Despite the potential introduction of error with acquisition of landmarks, our data suggests that in obese patients the overlying soft-tissue thickness has no significant effect on the accuracy on acetabular cup inclination. In contrast anteversion is influenced by the overlying soft tissue thickness and obesity

Introduction. Cup positioning in total hip arthroplasty (THA) is an important variable for short and long term durability of any hip implant. This novel method utilises internal and external bony landmarks, and the transverse acetabular ligament for positioning the acetabular component. Methods. The cup is placed parallel and superior to the transverse ligament and inside the anterior wall notch of the true acetabulum, and then adjusted for femoral version and pelvic tilt, fixed obliquity, and transverse rotational deformity based on weight bearing pre-operative radiographs. Seventy consecutive THRs (68 patients) were performed using the above technique. The cup radiographic and functional anteversion and abduction angle were measured on post-operative weight bearing pelvic radiographs using EBRA software. Results. The mean follow-up was 8.1 ± 2.4 months (4.3 – 11.8 months). There were no dislocations. The mean anteversion and abduction angle was 41.8 degrees ± 4.6 degrees and 18.5 degrees ± 4.4 degrees, respectively. In 3 hips, the radiographic abduction angle was slightly outside the safe zone of Lewinnek as measured based on the inter-teardrop line. However, when using a weight bearing AP pelvis radiograph to measure functional abduction angle using a horizontal line as a reference, they were all within the normal range. Discussion and Conclusion. The proposed technique utilises intra- and extra-articular bony landmarks, allows for adjustment for lumbosacral angle, abnormal femoral anteversion, and excessive acetabular version. The proposed technique is a reproducible and accurate method for cup placement with posterior exposure

Introduction. Component positioning is of great importance in total hip arthroplasty (THA) and navigation systems can help guide surgeons in the optimal placement of the implants. We report on a newly developed navigation system which employs an inertial measurement unit (IMU) to measure acetabular cup inclination and anteversion. Aims. To assess the accuracy of the IMU when used for acetabular cup placement and compare this with an established optical navigation system (ONS). Methods. At the time of acetabular cup impaction, the IMU and ONS were separately mounted on the impactor handle. Cup inclination and anteversion as measured by each device were recorded. Post-operative CTs were acquired for all patients and used to determine the final cup position. Results. Data were recorded for a total of 100 patients undergoing THA; 51 had a direct anterior approach (DAA) and 49 had a posterior approach (PA). In the DAA group, the mean difference in IMU versus CT measured cup inclination was −0.7°(range −6 to 8º) compared with mean difference of ONS versus CT of −2° (range −8 to 5º). Mean difference in IMU versus CT measured anteversion was − 1.3° (range −10 to 10º) compared with a mean difference of −1.1° (range −23 to 20º) between ONS and CT. In the PA group, mean difference in IMU versus CT inclination was 1.3º (range −8 to 6º) compared with mean difference between ONS versus CT of 1.6° (range −5 to 7º). Mean difference in anteversion was 3.7° (range −7 to 16º) between IMU and CT and 7.3° (range −3 to 19º) between ONS and CT. Conclusion. The novel IMU can be used to accurately determine the position of the acetabular cup at the point of impaction, demonstrating comparable accuracy with an established navigation system in the direct anterior approach, and even greater accuracy in the posterior approach

Background. The accuracy of cup placement in navigated THA depends on the bony landmark registration intraoperatively. The usual patient position for registration is supine, but supine position has some drawbacks such as it's more difficult for femoral canal visualisation. The alternate patient position is lateral decubitus, but registration in this position may be unreliable because of the contralateral ASIS can't be palpated accurately. The other technique is registration in supine position first and then placing the patient in lateral decubitus for operation. The drawbacks of this technique are time consumption and increased risk of contamination. We created a semilateral decubitus position which combined the advantage of supine position for registration and lateral decubitus position for better femoral canal visualisation. We modified the registration technique by compressing the soft tissue above Pubic Symphysis(PS) to the abdomen and registered at the Antero-Superior-Pubic-Symphysis(ASPS). Objective. Evaluate the accuracy of cup placement within the “safe zone” and the accuracy of imageless navigation measurement by comparing the intraoperative values of acetabular cup abduction and anteversion to postoperative computed tomography (CT) values. Method. The prospective study consisted of 30 patients who received short stem navigated THA in semilateral decubitus position from May to October 2012. The abduction and anteversion angle measured on postoperative CT were compared to the intraoperative measurement with a paired t-test and a correlation test at a 0.05 level of significance. Results. The mean CT abduction was 41.37° (range, 37° to 45°, SD 2.01) and the mean navigated abduction was 40.29° (range, 37.6° to 45.5°, SD 1.99). The mean paired difference was 1.26° (range, −0.8° to 4.6°, SD 1.05), this difference was significant (p = 0.02) but considered to be clinically irrelevant. There was a significant correlation between the CT abduction and navigated abduction (p < 0.001). All cases showed a difference of less than 5° between the two measurements and all cases were within the safe zone of CT measurement. The mean CT anteversion was 13.57° (range, 7° to 18°, SD 3.28) and the mean navigated anteversion was 11.18° (range, 5.9° to 15.5°, SD 2.52). The mean paired difference was 3.02° (range, −2.6° to 8.6°, SD 2.33), this difference was significant (p = 0.001) but considered to be clinically irrelevant. There was a significant correlation between the CT anteversion and navigated anteversion (p = 0.005). Twenty-two cases (22/30, 73%) showed a difference of less than 5° between the two measurements and all cases were within the safe zone of CT measurement. Soft tissue thickness overlying the PS and ASIS were measured in axial CT images and averaged 28.53 mm. (range, 11.7 to 54.6, SD 9.97) and 8.03 mm. (range, 3.2 to 26, SD 4.86) respectively. We found no significant correlation between the difference and the thickness of the soft tissue above the PS (p = 0.09) nor above ASIS (p = 0.09). Conclusion. The navigated THA with modified registration technique in semilateral decubitus position offered a more precise cup position. All cases were within the safe zone in both abduction and anteversion angles

Introduction. Optimal orientation of the acetabular cup is vital issue not only for primary but revision total hip arthroplasty (THA). Especially in revision THA, malorientation of the cup is likely to occur because anatomical landmark around acetabular rim often disappeared by the osteolytic bony destruction or the process of cup removal. As a consequence, higher dislocation rate and accelerated wear of bearing surface compared with primary THA, which affect the outcome of revision THA, are concerned. On the other hand, computer aided navigation system has been developed in recent years because of substantial errors of manual technique in cup placement even with experienced surgeon. The purpose of this study was to evaluate the accuracy of the cup orientation in revision cementless THA using CT based navigation system. Materials and Methods. Thirteen patients who underwent revision cementless THA with CT based navigation system (Stryker Japan) were employed for this study. The average age at surgery was 64 years (range, 45–78 years, 3 men and 11 women). Primary surgery was cementless THA in 4 and BHA in 9 hips. Disorder which led to revision THA was loosening of the cup, massive retroacetabular osteolysis, and severe proximal migration of bipolar outer head. In most cases, acetabular rim was not conserved. After removal of the cup or outer head, we revised acetabular components with cementless hemispherical TriAD cups (Stryker Japan) using direct lateral approach in lateral decubitus position. For all the patients, post-operative CT scans were performed and the cup inclination and anteversion angle were measured using 3D image-processing software (Stryker, Japan). The difference between the intra-operative target angle and the angle measured from the post-operative CT image were calculated. Results. The average cup orientation measured by postoperative CT was 39.6±3.8° (range, 34–46°) in inclination and 20.5±5.0° (range, 17–29°) in anteversion. The accuracy (calculated as a mean of the absolute difference between intra-operative target angle and post-operative CT angle) of inclination and anteversion angle were 2.0 ± 1.8° (range, 0–5°) and 2.3±2.2° (range, 0–5°), respectively. The accuracy was within 5° in all cases and there was no postoperative dislocation. Discussion. Our study showed that CT based navigation system provided accurate orientation of the acetabular component even in revision cementless THA as well as in primary THA. Although the basic process of the navigation system in revision THA is same as primary THA, several pitfalls exist. Metal artifact from preexisting hardware such as screws, cup, and head-neck of the stem makes it difficult to do preoperative planning, intraoperative point matching, and surface registration. We have to pay maximum attention to avoid including metal artifact especially around acetabular rim when editing surface of the pelvis at preoperative planning, and also avoid pointing the area around acetabular rim when doing surface registration intraoperatively

Purpose:. Malpositioning of the acetabular cup component in total hip arthroplasty can result in increased wear, early nonseptic loosening and is the most common cause of dislocation. Previous research has defined a safe zone with an inclination of 40±10 degrees and anteversion of 15±10 degrees. The purpose of this study was to compare cup placement using imageless navigation to a matched control group using CT based measurements. Methods:. 30 patients receiving a primary hip replacement were included. Alignment of the implant is based on the acquisition of landmarks (ASIS and pubic tubercle) and placement of tracking pins into the ASIS. The target position for all patients was 45 degrees of inclination and 15 degrees of anteversion. A multi-slice CT scan was used to assess cup position. Results:. There was no significant difference between mean inclination (p=0.11) and anteversion (p=0.24) but a statistically significant difference for mean deviation from the desired position for inclination (p=0.003) and anteversion (p=0.007). There was a significant difference in the percentages of correctly placed cups with inclination (p=0.046) and with anteversion (p=0.006). Combining both anteversion and inclination there was a significant difference (p=0.01). Conclusion:. Computer navigation for total joint arthroplasty, if helpful to the surgeon, has to increase reliability of component placement and show a significant reduction in variation compared to freehand techniques. We demonstrated a significant increase in accuracy of placement of acetabular cups within the desired position and safe zone using imageless navigation

Ideal cup positioning remains elusive both in terms of defining and achieving target.

Our aim is to restore original anatomy by using the Transverse Acetabular Ligament (TAL). In the normal hip TAL and labrum come beyond the equator of the femoral head therefore if the definitive cup is positioned such that: It is cradled by the TAL; Is ideally no more than 4mm greater in diameter than the original femoral head; Sits just deep to the plane of TAL and labrum (this means that normally we leave the fat pad intact and do not ream down to the true floor).

That should restore joint center in terms of height and offset. If the face of the cup is then positioned parallel and just deep to the TAL and psoas groove that should restore original version. We still use TAL for version in dysplasia because we believe the TAL and labrum compensate for any underlying bony abnormality. However in dysplasia the TAL and labrum fall short of original femoral head equator and therefore in such cases we ream down to the true floor if necessary and use a cup which is often smaller than the original head.

Inclination represents a greater challenge and TAL should not be used as an aid to inclination. Our research has shown that errors in postoperative x-ray inclination above 50 degrees are generally caused by errors in patient positioning when in lateral decubitus. Consequently great care needs to be taken when positioning the patient.

The acetabular component is the most troublesome implant. There is more written about acetabular placement than any other anatomical site. The problems are: Maintenance of center of rotation (COR); Coverage of the cup with correct inclination and anteversion; Maintenance of inclination below 50 degrees; Anteversion must be mated to the femur (combined anteversion).

COR is critical for balance of the correct offset and leg length. The inferior-medial metal edge of the cup should lie over the TAL or just proximal to it. No cortical bone of teardrop is palpable.

Coverage: Inclination of the normal bony acetabulum has a mean of 55 degrees (range to 70 degrees) so the posterior-superior edge of the cup may be uncovered in many hips to keep inclination below 50 degrees. 45 degrees is critical for wear and anteinclination. Anteversion of the cup is not independent of the femur (Brown/Callaghan, Hip Society Award paper). Femur anteversion must be known to precisely position the cup. Cup coverage is important here too. The posterior and anterior edges cannot be proud (may need to ream more medial).

Introduction

Total hip arthroplasty is considered to be one of the most successful orthopaedic interventions. Acetabular component positioning has been shown to affect dislocation rates, component impingement, bearing surface wear rates, and need for revision surgery. The safe zones of acetabular component positioning have previously been described by Lewinnek et al. as 5 to 25 degrees of cup version and 30 to 50 degrees of inclination. Callanan et al. later modified the inclination to 30 to 45 degrees. Our aim was to assess whether THA via robotic assisted posterior approach (PA) improves acetabular component positioning compared to fluoroscopic guided anterior approach THA (AA).