Introduction. Cup malpositioning remains a common cause of dislocation, wear, osteolysis, and revision. The concept of a “Safe Zone” for acetabular component orientation was introduced more than 35 years ago1. The current study assesses CT studies of replaced hips to assess the concept of a safe zone for acetabular orientation by comparing the orientation of acetabular components revised due to recurrent instability and to a series of stable hip replacements. Methods. Cup orientation in 50 hips revised for recurrent instability was measured using CT. These hips were compared to a group of 184 stable hips measured using the same methods. Femoral anteversion in the stable hips was also measured. Images to assess femoral anteversion in the unstable group were not available. An application specific software modules was developed to measure cup orientation using CT (HipSextant Research Application 1.0.13 Surgical Planning Associates Inc., Boston, Massachusetts). The cup orientation was determined by first identifying Anterior Pelvic Plane Coordinate system landmarks on a 3D surface model. A multiplanar reconstruction module then allowed for the creation of a plane parallel with the opening plane of the acetabulum. The orientation of the cup opening plane in the AP Plane coordinate space was calculated according to Murray's definitions of operative anteversion and operative inclination2. Both absolute cup position relative to the APP and tilt-adjusted cup position3 were calculated. Results. Supine tilt-adjusted Operative anteversion for the anteriorly unstable hips was significantly higher than in the stable hips (p< .0001). Supine tilt-adjusted Operative anteversion for the posteriorly unstable hips was significantly lower than in the stable hips (p<.01). Alt in the supine position, all unstable hips had operative anteversion of less than 22.9 or more than 38.6 degrees or operative inclination of less than 30.6 or more than 55.9 degrees or both. The center of the “safe zone” is 30.7 +/− 7.8 degrees of tilt-adjusted operative anteversion and 42.4 +/− 13.5 degrees of operative inclination (Figure 1). Conclusions. The current study demonstrates that most conventionally placed acetabular components are malpositioned but not all malpositioned acetabular components are associated with dislocation. Using acetabular revision for recurrent instability as the end point, a safe zone for acetabular component orientation does exist. The range is narrower for anteversion than for inclination. Improved methods of defining component positioning goals on a patient-specific basis and accurately placing the acetabular component may reduce the incidence of cup mal-position and its associated complications. For figures and tables, please contact authors directly

Introduction. Proper acetabular component orientation is an important part of successful total hip replacement surgery. Poorly positioned implants can lead to early complications, such as dislocation. Mal-positioned acetabular components can also generate increase wear debris due to edge loading which can cause pre-mature loosening. It is essential to be able to measure post-operative implant orientation accurately to assure that implants are positioned properly. It is difficult and potentially inaccurate to manually measure implant orientation on a post-op radiograph. This is particularly true for the immediate post-op radiograph where the patient is not as well aligned relative to the x-ray beam. However, the best time to determine if an acetabular component is mal-aligned is immediately following surgery so the patient could be taken back to the OR for immediate revision. Taking post-op CT scans is expensive and subjects the patient to increased radiation exposure, so using CT post-operatively is not done routinely. With the increased use of robotics and computer navigation at surgery there are often pre-op CT scans for total hip replacement patients. Current radiological tools do not take advantage of this pre-op CT scan for assessment of acetabular component orientation. A new software module for Mimics medical imaging software (Materialise, Leuven, Belgium) is able to overlay 3D CT data onto radiographs. We used this x-ray module to see if we could measure acetabular component orientation using the pre-op CT scan and the routine post-op x-ray that is taken immediately following total hip arthroplasty at our institution. Methods. From a prior study, we had pre-op, and post-op CT scans of a group of twenty patients who received a total hip replacement. The post-op scan was used to measure the actual acetabular component orientation, both inclination and anteversion (Figure 1). We then measured component orientation using only the pre-op CT scan and the initial post-op x-ray using the Mimics x-ray module. We created a 3D model of the pelvis from the pre-op CT using Mimics. Then, the x-ray module was used to import the post-op radiograph into the Mimics file. Using the software, the x-ray was registered to the pre-op 3D pelvis. A 3D .stl file of the acetabular component used at surgery was then imported into the Mimics file and also registered according to the post-op radiograph (Figures 2 and 3). Once the cup and pelvis were both registered to the post-op radiograph, they were exported as .stl files and the acetabular anteversion and inclination were measured using the same method we used for the post-op scan. We then compared the results of our measurements from the post-op 3D reconstruction to the 2D overlay method to determine the accuracy of this new measurement technique. Results. The average error for anteversion and inclination was 1.5±1.5 and −0.8±1.6 degrees respectively. Maximum error for anteversion and inclination was 5.7 and −5.0 degrees respectively. Conclusion. The x-ray module could be a powerful tool in the assessment of post-operative orientation of the acetabular component in total hip arthroplasty

Introduction. Cup malpositioning remains a common cause of dislocation, wear, osteolysis, and revision. The concept of a “Safe Zone” for acetabular component orientation was introduced more than 35 years ago1. The current study assesses CT studies of replaced hips to assess the concept of a safe zone for acetabular orientation by comparing the orientation of acetabular components revised due to recurrent instability and to a series of stable hip replacements. Methods. Cup orientation in 21 hips revised for recurrent instability was measured using CT. These hips were compared to a group of 115 stable hips measured using the same methods. Femoral anteversion in the stable hips was also measured. Images to assess femoral anteversion in the unstable group were not available. An application specific software modules was developed to measure cup orientation using CT (HipSextant Research Application 1.0.13 Surgical Planning Associates Inc., Boston, Massachusetts). The cup orientation was determined by first identifying Anterior Pelvic Plane Coordinate system landmarks on a 3D surface model. A multiplanar reconstruction module then allowed for the creation of a plane parallel with the opening plane of the acetabulum. The orientation of the cup opening plane in the AP Plane coordinate space was calculated according to Murray's definitions of operative anteversion and operative inclination2. Both absolute cup position relative to the APP and tilt-adjusted cup position3 were calculated. Results. Operative anteversion for the anteriorly unstable hips was significantly higher than in the stable hips (p < .001). Operative anteversion for the posteriorly unstable hips was significantly lower than in the stable hips (p=.01). Adjusting for pelvic tilt in the supine position, all unstable hips had operative anteversion of less than 22.9 or more than 38.6 degrees or operative inclination of less than 28.9 or more than 55.9 degrees or both. The center of the “safe zone” is 30.7 +/− 7.8 degrees of tilt-adjusted operative anteversion and 42.4 +/− 13.5 degrees of operative inclination. Conclusions. The current study demonstrates that most conventionally placed acetabular components are malpositioned but not all malpositioned acetabular components are associated with dislocation. Using acetabular revision for recurrent instability as the end point, a safe zone for acetabular component orientation does exist. The range is narrower for anteversion than for inclination. Improved methods of defining component positioning goals on a patient-specific basis and accurately placing the acetabular component may reduce the incidence of cup malposition and its associated complications

INTRODUCTION. Cup malpositioning remains a common cause of dislocation, wear, osteolysis, and revision. The concept of a “Safe Zone” for acetabular component orientation was introduced more than 35 years ago. 1. The current study assesses CT studies of replaced hips to assess the concept of a safe zone for acetabular orientation by comparing the orientation of acetabular components revised due to recurrent instability and to a series of stable hip replacements. METHODS. Cup orientation in 30 hips revisedin 27patients for recurrent instability was measured using CT. These hips were compared to a group of 115 stable hips measured using the same methods. Femoral anteversion in the stable hips was also measured. Images to assess femoral anteversion in the unstable group were not available. An application specific software modules was developed to measure cup orientation using CT (HipSextant Research Application 1.0.13 Surgical Planning Associates Inc., Boston, Massachusetts). The cup orientation was determined by first identifying Anterior Pelvic Plane Coordinate system landmarks on a 3D surface model. A multiplanar reconstruction module then allowed for the creation of a plane parallel with the opening plane of the acetabulum. The orientation of the cup opening plane in the AP Plane coordinate space was calculated according to Murray's definitions of operative anteversion and operative inclination. 2. Both absolute cup position relative to the APP and tilt-adjusted cup position. 3. were calculated. RESULTS. Operative anteversion for the anteriorly unstable hips was significantly higher than in the stable hips (p < 0.001). Operative anteversion for the posteriorly unstable hips was significantly lower than in the stable hips (p < 0.01). Adjusting for pelvic tilt in the supine position, all unstable hips had operative anteversion of less than 21.8 or more than 42.6 degrees or operative inclination of less than 30.6 or more than 55.9 degrees or both. The center of the “safe zone” is 32.2 ± 10.4 degrees of tilt-adjusted operative anteversion and 45.3 ± 8.7 degrees of operative inclination (Figure 1). CONCLUSIONS. The current study demonstrates that most conventionally placed acetabular components are malpositioned but not all malpositioned acetabular components are associated with dislocation. Using acetabular revision for recurrent instability as the end point, a safe zone for acetabular component orientation does exist. The range is narrower for anteversion than for inclination. Improved methods of accurately placing the acetabular component placement may reduce the incidence of cup malposition and its associated complications

Introduction:. Wear, wear-associated osteolysis, and instability are the most common reasons for revision total hip arthroplasty. These failures have been shown to be associated with acetabular component malpositioning. However, optimal acetabular component orientation on a patient-specific basis is currently unknown. The current study uses CT to assess acetabular orientation in a group of unstable hips as compared to a control group of stable hips. Methods:. Our institutional database of CT studies performed in the region of the hip beginning in February of 1998 (41,975 CT studies) was compared against our institutional database of revision total hip arthroplasties beginning in August of 2003 (2262 Revision THA) to identify CT studies of any hip treated for recurrent instability by revision of the acetabular component. Twenty hips in 20 patients with suitable CT studies were identified for the study group. Our control group consisted of 99 hips in 93 patients who had CT studies either for computer-assisted surgery on the contralateral side or for assessment of osteolysis. Using the CT data, the AP plane (APP) was defined, supine pelvic tilt was measured, and cup orientation was calculated by fitting a best fit plane to 6 points on the rim of the acetabular component. Cup orientation was calculated in degrees of operative anteversion and operative inclination according to the definitions of Murray. Both absolute cup position relative to the APP and tilt-adjusted cup position. 1. were calculated. Results:. The study group of 20 hips treated for instability showed a mean operative anteversion of 30.3 degrees (SD 17.6, range 1.0 to 58.1), a mean operative inclination of 35.9 degrees (SD 8.4, range 25.1 to 55.9), and a mean tilt-adjusted operative anteversion of 29.7 (SD 14.2, range 1.8 to 53). The control group of 99 hips showed a mean operative anteversion of 30.5 degrees (SD 10.7, range −1.9 to 57.5), a mean operative inclination of 37.7 degrees (SD 8.0, range 18.4 to 68.1), and a mean tilt-adjusted operative anteversion of 26.7 (SD 10.8, range −0.2 to 47.3). Most interestingly. all of the hips treated for instability had an operative anteversion of either 22.9 degrees or less or 38.67 degrees or more of tilt-adjusted operative inclination of either 30.5 degrees or less or 55.9 degrees or more, or both. The center of the safe zone in this study is 30.7 of tilt-adjusted operative anteversion and 43.2 degrees of operative inclination (Figure 1). There was no discernable safe zone in the non tilt-adjusted group. Discussion and Conclusion:. Most conventionally placed acetabular components are malpositioned but not all malpositioned acetabular components are associated with dislocation. The hip dislocation safe zone appears to be narrower in operative anteversion than in operative inclination. Improved methods of improving the accuracy and reliability of acetabular component placement may reduce the incidence of cup malposition and its associated complications

Introduction. The optimal acetabular component orientation in general or on a patient-specific basis is currently unknown. In order to answer this question, the current study uses CT to assess acetabular orientation in a group of unstable hips as compared to a control group of stable hips. Methods. Our institutional database of CT studies performed in the region of the hip beginning in February of 1998 (41,975 CT studies) was compared against our institutional database of revision total hip arthroplasties beginning in August of 2003 (2262 Revision THA) to identify CT studies of any hip treated for recurrent instability by revision of the acetabular component. Twenty hips in 20 patients with suitable CT studies were identified for the study group. Our control group consisted of 101 hips in patients who had CT studies either for computer-assisted surgery on the contralateral side or for assessment of osteolysis. Using the CT data, the AP plane (APP) was defined, supine pelvic tilt was measured, and cup orientation was calculated by fitting a best fit plane to 6 points on the rim of the acetabular component. Cup orientation was calculated in degrees of operative anteversion and operative inclination according to the definitions of Murray. Both absolute cup position relative to the APP and tilt-adjusted cup position were calculated. Results. The study group of 20 hips treated for instability showed a mean operative anteversion of 29.6 degrees (SD 14.3, range 1.8 to 58) and a mean operative inclination of 35.8 degrees (SD 8.3, range 25.1 to 55.9). The control group of 101 hips showed a mean operative anteversion of 26.7 degrees (SD 10.7, range 0.2 to 47.3) and a mean operative inclination of 37.7 degrees (SD 7.9, range 18.4 to 68.1). Most interestingly. all of the hips treated for instability had a tilt-adjusted operative anteversion of either 22.9 degrees or less or 38.6 degrees or more or operative inclination of either 28.9 degrees or less or 55.9 degrees or more, or both. The center of the safe zone in this study is 30.7 degrees of tilt-adjusted operative anteversion and 42.4 degrees of operative inclination. Discussion and Conclusion. Most conventionally placed acetabular components are malpositioned but not all malpositioned acetabular components are associated with dislocation. The hip dislocation safe zone appears to be narrower in operative anteversion than in operative inclination and so the safe zone is better represented graphically as an oval as opposed to a box. The safe zone identified in the current study relates only to instability. Optimal positioning for reducing wear may narrow the safe zone further, particularly as it relates to the upper limit of operative inclination. Improved methods of achieving better accuracy and reliability of acetabular component placement may reduce the incidence of cup malposition and its associated complications

Background. The current orthopaedic literature demonstrates a clear relationship between acetabular component positioning, polyethylene wear and risk of dislocation following Total Hip Arthroplasty (THA). Problems with edge loading, stripe wear and squeaking are also associated with higher acetabular inclination angles, particularly in hard-on-hard bearing implants. The important parameters of acetabular component positioning are depth, height, version and inclination. Acetabular component depth, height and version can be controlled with intra-operative reference to the transverse acetabular ligament. Control of acetabular component inclination, particularly in the lateral decubitus position, is more difficult and remains a challenge for the Orthopaedic Surgeon. Lewinnek et al described a ‘safe zone’ of acetabular component orientation: Radiological acetabular inclination of 40 ± 10° and radiological anteversion of 15 ± 10°. Accurate implantation of the acetabular component within the ‘safe zone’ of radiological inclination is dependent on operative inclination, operative version and pelvic position. Traditionally during surgery, the acetabular component has been inserted with an operative inclination of 45°. This assumes that patient positioning is correct and does not take into account the impact of operative anteversion or patient malpositioning. However, precise patient positioning in order to orientate acetabular components using this method cannot always be relied upon. Hill et al demonstrated a mean 6.9° difference between photographically simulated radiological inclination and the post-operative radiological inclination. The most likely explanation was felt to be adduction of the uppermost hemipelvis in the lateral decubitus position. The study changed the practice of the senior author, with target operative inclination now 35° rather than 40° as before, aiming to achieve a post-operative radiological inclination of 42° ± 5°. Aim. To determine which of the following three techniques of acetabular component implantation most accurately obtains a desired operative inclination of 35 degrees:. Freehand. Modified (35°) Mechanical Alignment Guide, or. Digital inclinometer assisted. Methods. 270 patients undergoing primary uncemented THA were randomised to one of the three methods of acetabular component implantation. Target operative inclination for all three techniques was 35°. Operative inclination was measured intra-operatively using both a digital inclinometer and stereophotogrammetric system. For both the freehand and Mechanical Alignment Guide implantation techniques, the surgeon was blinded to intra-operative digital inclinometer readings. Results. The freehand implantation technique had an operative inclination range of 25.2 – 43.2° (Mean 32.9°, SD 2.90°). The modified (35°) Mechanical Alignment Guide implantation technique had an operative inclination range of 29.3 – 39.3° (Mean 33.7°, SD 1.89°). The digital inclinometer assisted technique had an operative inclination range of 27.5 – 37.5° (Mean 34.0°, SD 1.57°). Mean unsigned deviation from target 35° operative inclination was 2.92° (SD 2.03) for the freehand implantation technique, 1.83° (SD 1.41) for the modified (35°) Mechanical Alignment Guide implantation technique and 1.28° (SD 1.33) for the digital inclinometer assisted technique. Conclusions. When aiming for 35° of operative inclination, the digital inclinometer technique appears more accurate than either the freehand or Mechanical Alignment Guide techniques. In order to improve accuracy of acetabular component orientation during Total Hip Arthroplasty, the surgeon should consider using such a technique

Mal-positioning of the acetabular component is associated with increased dislocation rate, increased wear and component impingement. Navigation provides real time feedback to the surgeon and allows the accurate position of implants. Compared to conventional techniques of total hip replacement; use of the imageless navigation system has shown to improve accuracy of implant positioning. When impacting uncemented acetabular components under navigation, there is often a deviation from the planned abduction and anteversion measurement due to deflection of the implant in the reamed cavity. Although there exists the ability to navigate the reaming of the acetabular cavity; this is not widely performed. The ability to ream the acetabular cavity in the exact orientation of the planned acetabular component may provide some theoretical advantage on the final acetabular position. The purpose of this study was to compare the effect of navigated Vs free hand acetabulum reaming on achieving the planned orientation of acetabular component. In a retrospective study we reviewed two groups of patients who underwent computer navigated placement of the acetabular component with reference to the anterior pelvic plane. We used an imageless computer navigation system for all cases (Brainlab, Munich). All procedures were performed by single surgeon (ETD) through a standard posterior approach. The patients were divided into two groups depending on the availability of the navigated reamer. In the first group (n = 57), acetabulum reaming was done under navigation and in the second group (n = 37) a non-navigated reamer was used. The acetabular cavity was reamed “line to line” or under reamed by 1 or 2mm. Intra-operative acetabular abduction and anteversion angles were planned using navigation at the discretion of the surgeon. Results of planned acetabular abduction and anteversion angles were compared with intra-operative verification using the navigation system. In the navigated reamer group, the mean error from the planned to verified abduction angle was 1.7 degrees (SD 2.1 degrees) and in the non-navigated reamer group the mean error was 2 degrees (SD 2.6 degrees). In the navigated reamer group, the mean error from the planned to verified anteversion angle was 0.5 degrees (SD 2.8), and in the non-navigated reamer group the mean error was 0.1 degrees (SD 1.6). There was no statistically significant difference in the mean error between the navigated and non-navigated reaming groups for abduction angle (p = 0.54) or anteversion angle (p = 0.24). There was no statistical difference between the mean acetabular component size in the navigated (mean 53mm) and non-navigated (53mm) reamer groups (p = 0.8). There was no statistical difference in the mean difference in reamer size and the acetabular component size in the navigated (0.8mm) and non-navigated reamer groups (0.8mm, p = 0.52). This study appears to show that performing reaming of the acetabular cavity under navigation does not improve the final orientation of the acetabular component when compared to using conventional non-navigated reamers. However, this study only considered the abduction and anteversion orientation of the component. The move to a range of movement or kinematic orientation of the acetabular component in hip arthroplasty requires control over the off-set of the acetabular component which may be more easily achieved when the reaming is performed under navigation. This study used a conventional posterior approach rather than a minimal incision technique, where the use of navigated reaming may also provide some theoretical advantage when visibility is limited. Further study is required in these two areas. There appears to be a slightly higher standard deviation for the anteversion measurement in the navigated reamer group when compared to the non navigated reamer group, although this is not significant. It is difficult to account for this as it appears to be opposite of what one would predict. One explanation for this may come in the difference in the angled geometry of the navigated reamer when compared to the straight non navigated reamer. The angled reamer can be more difficult to control forming a cavity in the correct orientation but with the possibility for the cavity to not been perfectly hemispherical. When using navigation to insert the acetabular component in a planned abduction and anteversion position during hip arthroplasty through a standard incision, navigating the reaming of the acetabular component does not appear to provide any advantage over the use of conventional non-navigated reamers in the final acetabular orientation

Metal on Metal hip resurfacing (MoM HR) can be an effective operation for the young arthritic hip population. However, errors in cup orientation have been associated with increased wear, circulating blood metal ions, and soft tissue abnormalities that can lead to premature failure of the bearing surface and subsequent revision surgery. While image free computer guidance has been shown to increase surgical accuracy in total hip arthroplasty, the role of image based technology in MoM HR is unclear. In this study, we compared the accuracy of cup orientation in MoM HR performed by either freehand technique or CT based navigation.

Seventy five patients (81 hips) underwent either freehand (n=42) or navigation (n=39) surgery, both requiring a three dimensional (3D) CT surgical plan. Surgery was conducted by hip specialists blind to the method of cup implantation until the operation. Deviation in inclination and version from the planned orientation, as well as, number of cups within a 10° safe zone and 5° optimal zone of the target position was calculated using post operative 3D CT analysis.

Error in inclination was significantly reduced with navigation compared to freehand technique (4° vs 6°, p=0.02). We could not detect a difference between the two groups for version error (5° vs 7°, p=0.06). There was a significantly greater number of hips within a 10° (87% vs 67%, p=0.04) and 5° (50% vs 20%, p=0.06) safe zone when navigated.

Image based navigation can substantially improve accuracy in cup orientation. The results of our freehand group appear better than historic controls, suggesting the use of a 3D plan may help to reduce technical error and improve the learning curve in this technically demanding procedure. We advocate the use of image based navigation in MoM hip resurfacing arthroplasty.

In order to avoid complications of hip arthroplasty such as dislocation, impingement and eccentric liner wear accurate acetabular orientation is essential. The three-dimensional assessment of acetabular cup orientation using two-dimensional plain radiographs is inaccurate. The aim of this study was to develop a CT-based protocol to accurately measure postoperative acetabular cup inclination and anteversion establishing which bony reference points facilitate the most accurate estimation of these variables.

An all-polyethylene acetabular liner was implanted into a cadaveric acetabulum. A conventional pelvic CT scan was performed and reformatted images created in both functional and anterior pelvic planes. CT images were transferred to a Freedom-Plus Graphics software package enabling an identical, virtual, three dimensional model of the cadaveric pelvis to be created. Using a computer interface this model could be ‘palpated’, bony landmarks accurately identified and definitive acetabular cup orientation established. Using original CT scans, acetabular cup inclination and anteversion were measured on five occasions by eight radiographers using differing predetermined bony landmarks as reference points. The intra- and inter-observer variation in measurement of acetabular cup orientation using varying bony reference points was assessed in comparison to the previously elucidated definitive cup position. Statistical analysis using appropriate ANOVA models was performed in order to assess the significance of the results obtained.

Virtually derived definitive acetabular cup orientation was measured showing cup inclination and anteversion as 41.0 and 22.5 degrees respectively. Mean CT-based measurement of cup inclination and anteversion by eight radiographers were 43.1 and 20.8 degrees respectively. No statistically significant difference was found in intra- and inter-observer recorded results. No statistically significant differences were found when using different bony landmarks for the measurement of inclination and anteversion (p= 0.255 and 0.324 respectively).

CT assessment of acetabular component inclination and anteversion is accurate, reliable and reproducible when measured using differing bony landmarks as reference points. We recommend measuring acetabular inclination and anteversion from the inferior acetabular wall/teardrop and posterior ischium respectively. The Perth CT hip protocol is easily reproducible in the clinical setting both in the routine assessment of hip arthroplasty patients and as research tool. In our unit its initial application will be to validate commercially available hip navigation systems.

BACKGROUND. Cup malpositioning remains a common cause of dislocation, wear, osteolysis, and revision. The concept of a “Safe Zone” for acetabular component orientation was introduced more than 35 years ago. The current study assesses CT studies of replaced hips to assess the concept of a safe zone for acetabular orientation. PURPOSE. We assessed the orientation of acetabular components revised due to recurrent instability and compared the results to a series of stable hip replacements. METHODS. Cup orientation in 21 hips revised for recurrent instability was measured using CT. These hips were compared to a group of 115 stable hips measured using the same methods. Femoral anteversion in the stable hips was also measured. Images to assess femoral anteversion in the unstable group were not available. RESULTS. Operative anteversion for the anteriorly unstable hips was significantly higher than in the stable hips (p=.01). Operative anteversion for the posteriorly unstable hips was significantly lower than in the stable hips (p<.001). Operative inclination was not significantly different between the control and dislocating groups. Adjusting for pelvic tilt in the supine position, all unstable hips had operative anteversion of less than 22.9 or more than 38.6 degrees or operative inclination of less than 28.9 or more than 55.9 degrees or both. The center of the “safe zone” is 30.7 ± 7.8 degrees of tilt-adjusted operative anteversion and 42.4 ± 13.5 degrees of operative inclination. CONCLUSION. Using acetabular revision for recurrent instability as the end point, a safe zone for acetabular component orientation does exist. The range is narrower for anteversion than for inclination

This session will be practically oriented, focusing on important surgical decisions and on technical tips to avoid complications. The panel will be polled concerning individual preferences as regards the following issues in primary total hip arthroplasty: 1. Perioperative antibiotics; 2. Blood management and tranexamic acid protocols; 3. Surgical indications: high BMI patients; 4. Surgical approach for primary total hip arthroplasty: indications or preferences for direct anterior, anterolateral, posterior; 5. Acetabular fixation; 6. Tips for optimizing acetabular component orientation; 7. Femoral fixation: (a) Indications for cemented and uncemented implants. Case examples will be used.; (b) Is there still a role for hip resurfacing?; 8. Femoral material and size: (a) Preferred head sizes and materials in different situations.; (b) Is there a role for dual mobility implants in primary THA?; 9. Bearing surface: present role of different bearings. Case examples will be used. 10. Tips for optimizing intraoperative hip stability; 11. Tips for optimizing leg length; 12. Postoperative venous thromboembolism prophylaxis; 13. Heterotopic bone prophylaxis; 14. Postoperative pain management; 15. Hospital discharge: is there a role for outpatient surgery?; 16. Postoperative rehabilitation protocol: weight bearing, role of physical therapy; 17. Postoperative activity restrictions; hip dislocation precautions; 18. Is there value to physical therapy as outpatient after THA?; 19. Long-term antibiotic prophylaxis for procedures

This session will be practically oriented, focusing on important surgical decisions and on technical tips to avoid complications. The panel will be polled concerning individual preferences as regards the following issues in primary total hip arthroplasty: 1.) Peri-operative antibiotics; 2.) Blood management and tranexamic acid protocols; 3.) Surgical indications: High BMI patients; 4.) Surgical approach for primary total hip arthroplasty: indications or preferences for direct anterior, anterolateral, posterior; 5.) Acetabular fixation; 6.) Tips for optimizing acetabular component orientation; 7.) Femoral fixation: Indications for cemented and uncemented implants. Is there still a role for hip resurfacing?; 8.) Femoral material and size: Preferred head sizes and materials in different situations. Is there a role for dual mobility implants in primary THA?; 9.) Bearing surface: Present role of different bearings; 10.) Tips for optimizing intra-operative hip stability; 11.) Tips for optimizing leg length; 12.) Post-operative venous thromboembolism prophylaxis; 13.) Heterotopic bone prophylaxis; 14.) Post-operative pain management; 15.) Hospital discharge: Is there a role for outpatient surgery?; 16.) Post-operative rehabilitation protocol: weight bearing, role of physical therapy; 17.) Post-operative activity restrictions; hip dislocation precautions; 18.) Is there value to physical therapy as outpatient after THA?; 19.) Long-term antibiotic prophylaxis for procedures

This session will be practically oriented, focusing on important surgical decisions and on technical tips to avoid complications. The panel will be polled concerning individual preferences as regards the following issues in primary total hip arthroplasty: Perioperative antibiotics/blood management/preferred anesthetics, Surgical approach for primary total hip arthroplasty, Acetabular fixation, Tips for optimizing acetabular component orientation, Femoral fixation, Femoral head size, Bearing surface, Tips for optimizing intraoperative hip stability, Tips for optimizing leg length, Postoperative venous thromboembolism prophylaxis, Heterotopic bone prophylaxis, Postoperative pain management, Postoperative rehabilitation protocol, Postoperative activity restrictions, and Postoperative antibiotic prophylaxis for procedures

This session will be practically oriented, focusing on important surgical decisions and on technical tips to avoid complications. The panel will be polled concerning individual preferences as regards the following issues in primary total hip arthroplasty: Perioperative antibiotics/blood management/preferred anesthetics; Surgical approach for primary total hip arthroplasty: indications or preferences for direct anterior, anterolateral, posterior; Acetabular fixation; Tips for optimizing acetabular component orientation; Femoral fixation: Indications for cemented and uncemented implants. Case examples will be used. Is there still a role for hip resurfacing?; Femoral head size: Preferred head sizes and materials in different situations. Is there a role for dual mobility implants in primary THA?; Bearing surface: Present role of different bearings. Case examples will be used.; Tips for optimizing intra-operative hip stability; Tips for optimizing leg length; Post-operative venous thromboembolism prophylaxis; Heterotopic bone prophylaxis; Post-operative pain management; Post-operative rehabilitation protocol: weight bearing, role of physical therapy; Post-operative activity restrictions; Post-operative antibiotic prophylaxis for procedures

This session will be practically oriented, focusing on important surgical decisions and on technical tips to avoid complications. The panel will be polled concerning individual preferences as regards the following issues in primary total hip arthroplasty: 1.) Peri-operative antibiotics; 2.) Blood management and tranexamic acid protocols; 3.) Surgical indications: High BMI patients; 4.) Surgical approach for primary total hip arthroplasty: indications or preferences for direct anterior, anterolateral, posterior; 5.) Acetabular fixation; 6.) Tips for optimizing acetabular component orientation; 7.) Femoral fixation: (a) Indications for cemented and uncemented implants. (b) Is there still a role for hip resurfacing?; 8.) Femoral material and size: (a) Preferred head sizes and materials in different situations. (b) Is there a role for dual mobility implants in primary THA?; 9.) Bearing surface: Present role of different bearings. 10.) Tips for optimizing intra-operative hip stability; 11.) Tips for optimizing leg length; 12.) Post-operative venous thromboembolism prophylaxis; 13.) Heterotopic bone prophylaxis; 14.) Post-operative pain management; 15.) Hospital discharge: Is there a role for outpatient surgery?; 16.) Post-operative rehabilitation protocol: weight bearing, role of physical therapy; 17.) Post-operative activity restrictions; hip dislocation precautions; 18.) Is there value to physical therapy as outpatient after THA?; and 19.) Long-term antibiotic prophylaxis for procedures

This session will be practically oriented, focusing on important surgical decisions and on technical tips to avoid complications. The panel will be polled concerning individual preferences as regards the following issues in primary total hip arthroplasty: 1. Peri-operative antibiotics/blood management/preferred anesthetics; 2. Surgical approach for primary total hip arthroplasty: indications or preferences for direct anterior, anterolateral, posterior; 3. Acetabular fixation; 4. Tips for optimizing acetabular component orientation; 5. Femoral fixation: (a) Indications for cemented and uncemented implants. (b) Role of hip resurfacing; 6. Femoral head size: Preferred head sizes in different situations; 7. Bearing surface: Present role of different bearings; 8. Tips for optimizing intra-operative hip stability; 9. Tips for optimizing leg length; 10. Post-operative venous thromboembolism prophylaxis; 11. Heterotopic bone prophylaxis; 12. Post-operative pain management; 13. Post-operative rehabilitation protocol: weight bearing, role of physical therapy; 14. Post-operative activity restrictions; and 15. Post-operative antibiotic prophylaxis for procedures

Introduction. Navigation of acetabular component orientation is still not commonly performed despite repeated studies that show that more than ½ of acetabular components placed during hip arthroplasty are significantly mal-positioned and that intra-operative radiographic assessment is unreliable. The current study uses postoperative CT to assess the accuracy of a smart mechanical navigation instrument system for cup alignment. Patients and Methods. Thirty seven hip replacements performed using a smart mechanical navigation device (the HipXpert System) had post-operative CT studies available for analysis. These post-operative CT studies were performed for pre- operative planning of the contralateral side, one to three years following the prior surgery. An application specific software module was developed to measure cup orientation using CT (HipXpert Research Application, Surgical Planning Associates Inc., Boston, Massachusetts). The method involves creation of a 3D surface model from the CT data and then determination of an Anterior Pelvic Plane coordinate system. A multiplaner image viewer module is then used to create an image through the CT dataset that is coincident with the opening plane of the acetabular component. Points in this plane are input and then the orientation of the cup is calculated relative to the AP Plane coordinate space according to Murray's definitions of operative anteversion and operative inclination. The actual cup orientation was then compared to the goal of cup orientation recorded when the surgery was performed using the system for acetabular component alignment. Results. For the thirty seven hips replacements, mean operative anteversion error was 1.1 degrees (SD 3.6, range −5.5 to 8.2). Mean operative inclination error was − 1.7 degrees (SD 3.0, range −8.0 to 5.6). There were no outliers in either anteversion or inclination. Conclusion. The current study demonstrates that the mechanical navigation system produces accurate cup alignment results as measured by post-operative CT and confirms the prior accuracy study performed using 2D/3D matching. This improved accuracy compared to robotic systems may be due to the wide-based nature of the docking mechanism and the elimination of the cumulative errors of registration and tracking inherent to more complex systems

This session will be practically oriented, focusing on important surgical decisions and on technical tips to avoid complications. The panel will be polled concerning individual preferences as regards the following issues in primary total hip arthroplasty. Perioperative antibiotics/blood management/preferred anesthetics; Surgical approach for primary total hip arthroplasty: indications or preferences for direct anterior, anterolateral, posterior; Acetabular fixation; Tips for optimising acetabular component orientation; Femoral fixation: indications for cemented and uncemented implants, role of hip resurfacing; Femoral head size: preferred head sizes in different situations; Bearing surface: present role of different bearings; Tips for optimising intraoperative hip stability; Tips for optimising leg length; Postoperative venous thromboembolism prophylaxis; Heterotopic bone prophylaxis; Postoperative pain management; Postoperative rehabilitation protocol: weight bearing, role of physical therapy; Postoperative activity restrictions; Postoperative antibiotic prophylaxis for procedures

This session will be practically oriented, focusing on important surgical decisions and on technical tips to avoid complications. The panel will be polled concerning individual preferences as regards the following issues in primary total hip arthroplasty: Peri-operative antibiotics/blood management/preferred anesthetic, Surgical approach for primary total hip arthroplasty: indications or preferences for direct anterior, anterolateral, posterior, less invasive exposures, Acetabular fixation, Tips for optimising acetabular component orientation, Femoral fixation: Indications for cemented and uncemented implants and Role of hip resurfacing, Preferred femoral head size, Choice of bearing surface, Tips for optimising intra-operative hip stability, Tips for optimising leg length, Post-operative venous thromboembolism prophylaxis, Heterotopic bone prophylaxis, Post-operative pain management, rehabilitation protocol, activity restrictions and antibiotic prophylaxis