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 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. 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

Abstract. Objectives. Accurate orientation of the acetabular component during a total hip replacement is critical for optimising patient function, increasing the longevity of components, and reducing the risk of complications. This study aimed to determine the validity of a novel VR platform (AescularVR) in assessing acetabular component orientation in a simulated model used in surgical training. Methods. The AescularVR platform was developed using the HTC Vive® VR system hardware, including wireless trackers attached to the surgical instruments and pelvic sawbone. Following calibration, data on the relative position of both trackers are used to determine the acetabular cup orientation (version and inclination). The acetabular cup was manually implanted across a range of orientations representative of those expected intra-operatively. Simultaneous readings from the Vicon® optical motion capture system were used as the ‘gold standard’ for comparison. Correlation and agreement between these two methods was determined using Bland-Altman plots, Pearson's correlation co-efficient, and linear regression modelling. Results. A total of 55 separate orientation readings were obtained. The mean average difference in acetabular cup version and inclination between the Vicon and VR systems was 3.4° (95% CI: −3–9.9°), and −0.005° (95% CI: −4.5–4.5°) respectively. Strong positive correlations were demonstrated between the Vicon and VR systems in both acetabular cup version (Pearson's R = 0.92, 99% CI: 0.84–0.96, p<0.001), and inclination (Pearson's R = 0.94, 99% CI: 0.88–0.97, p<0.001). Using linear regression modelling, the adjusted R. 2. for acetabular version was 0.84, and 0.88 for acetabular inclination. Conclusion. The results of this study indicate that the AescularVR platform is highly accurate and reliable in determining acetabular component orientation in a simulated environment. The AescularVR platform is an adaptable tracking system, which may be modified for use in a range of simulated surgical training and educational purposes, particularly in orthopaedic surgery. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Introduction. Acetabular component orientation is an important determinant of outcome following total hip arthroplasty (THA). Although surgeons aim to achieve optimal cup orientation, many studies demonstrate their inability to consistently achieve this. Factors that contribute are pelvic orientation and the surgeon's ability to correctly orient the cup at implantation. The goal of this study was to determine the accuracy with which surgeons can achieve cup orientation angles. Methods. In this in vitro study using a calibrated left and right sawbone hemipelvis model, participants (n=10) were asked to place a cup mounted on its introducer giving different targets. Measurements of cup orientation were made using a stereophotogrammetry protocol to measure radiographic inclination and operative anteversion (OA). A digital inclinometer was used to measure the intra-operative inclination (IOI) which is the angle of the cup introducer relative to the floor. First, the participant stated his or her preferred IOI and OA and positioned the cup accordingly. Second, the participant had to position the cup parallel to the anteversion of the transverse acetabular ligament (TAL). Third, the participant had to position the cup at IOI angles of 35°, 40° and 45°. Fourth, the participant used the mechanical alignment guide (45° of IOI and 30° of OA) to orient the cup. Each task was analysed separately and subgroup analysis included left versus right side and hip surgeons versus non-hip surgeons. Results. For the first task, hip surgeons preferred smaller IOI and larger OA than non-hip surgeons, but there was no significant difference in accuracy between both groups. When aiming for TAL, both surgeon groups performed similar, but accuracy on the non-dominant side was significantly better compared with the dominant side (mean deviation 0.6° SD 2.4 versus −2.6° SD 2.3) (p=0.004). When aiming for a specific IOI target of 35°, 40° or 45°, non-hip surgeons outperformed hip surgeons (mean deviation form target IOI 1.9° SD 2.7 versus −3.1° SD 3.8) (p<0.0001) with less variance (p=0.03). Contrary to version, accuracy on the dominant side was significantly better compared with the non-dominant side (mean deviation −0.4° SD 3.4 versus −2.1° SD 4.8). When using a mechanical guide, surgeons performed similar (0.6° SD 1.2 versus −0.4° SD 2.1 for inclination p=0.11 and −0.5° SD 2.6 versus −1.8° SD 3.3 for version p=0.22) and these values did not differ significantly from the actual IOI and OA of the mechanical guide. When using a mechanical guide, there was no difference in accuracy between the dominant and non-dominant side. Conclusion. There was no difference in accuracy between hip surgeons and non-hip surgeons when they aimed for their preferred IOI and OA or used a mechanical guide. When aiming for a specific IOI target, non-hip surgeons outperformed hip surgeons. Hip surgeons overestimate IOI and underestimate OA, presumably because this helps to achieve the desired radiographic cup orientation. Regarding accuracy, the non-dominant side was better for version and the dominant side for inclination. When aiming for a specific IOI and OA target, using a mechanical guide is significantly better than freehand cup orientation

There is great variability in acetabular component orientation following hip replacement. The aims of this study were to compare the component orientation at impaction with the orientation measured on post-operative radiographs and identify factors that influence the difference between the two. A total of 67 hip replacements (52 total hip replacements and 15 hip resurfacings) were prospectively studied. Intra-operatively, the orientation of the acetabular component after impaction relative to the operating table was measured using a validated stereo-photogrammetry protocol. Post-operatively, the radiographic orientation was measured; the mean inclination/anteversion was 43° (. sd. 6°)/ 19° (. sd. 7°). A simulated radiographic orientation was calculated based on how the orientation would have appeared had an on-table radiograph been taken intra-operatively. The mean difference between radiographic and intra-operative inclination/anteversion was 5° (. sd . 5°)/ -8° (. sd.  8°). The mean difference between simulated radiographic and intra-operative inclination/anteversion, which quantifies the effect of the different way acetabular orientation is measured, was 3°/-6° (. sd.  2°). The mean difference between radiographic and simulated radiographic orientation inclination/anteversion, which is a manifestation of the change in pelvic position between component impaction and radiograph, was 1°/-2° (. sd . 7°). This study demonstrated that in order to achieve a specific radiographic orientation target, surgeons should implant the acetabular component 5° less inclined and 8° more anteverted than their target. Great variability (2 . sd. about ± 15°) in the post-operative radiographic cup orientation was seen. The two equally contributing causes for this are variability in the orientation at which the cup is implanted, and the change in pelvic position between impaction and post-operative radiograph. Cite this article: Bone Joint J 2014;96-B:1290–7

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

Aim: A radiological review to assess component orientation in a consecutive series of primary total hip replacements performed by a high volume hip surgeon through either a standard or reduced size incision. Background: Using a posterior approach and standard instrumentation the senior author has reduced his incision size in selected patients over the last 2 years. There is no fixed definition of incision size in this series, incision sizes fall between 10 and 15cm in most cases. The implication is that deliberate efforts were made to limit the incision length compared to a routine exposure at the start of surgery. Method: From the operative records kept for the senior author a series of 48 patients was identified, with equal numbers having reduced or standard incisions. A radiological review was performed looking at the cementation, leg length and component orientation in both the AP and lateral planes. Results: In the AP plane there was no significant difference in the alignment of the components. In the reduced incision group an increased number of stems were directed from anterior to posterior on the lateral x-rays. The quality of the femoral cement mantles was significantly better in the standard incision group (75% Barrack A vs. 50% Barrack A). On the acetabular side the components were better positioned and orientated in the small incision group but cementation was again improved in the standard incision group. Conclusions: Reducing incision size does have an influence on cementation and the positioning of components during hip arthroplasty. The orientation and cementation of components in both study groups would be considered acceptable in the majority of cases. The authors recommend small audit studies of this nature as a way of providing ongoing feedback on the quality of their surgery thereby allowing improvements to be made to their surgical technique

Many factors can negatively impact acetabular component positioning including poor visualization, increased patient size, inaccuracies of mechanical guides, and inconsistent precision of conventional instruments and techniques, and changes in patient positioning. Improper orientation contributes to increased dislocation rates, leg length discrepancies, altered hip biomechanics, component impingement, acetabular component migration, bearing surface wear, and pelvic osteolysis thus affecting revision rates and long-term survivorship. Despite the established definitions of acetabular safe zones, recent analysis of U.S. Medicare THA data found dislocation rates during the first six months to be 3.9% for primary surgeries and 14.4% for revision surgeries. Accurate and precise acetabular component orientation during initial THA is an increasingly important factor in decreasing revision THA; a recent report cites instability and dislocation as the primary cause of revision accounting for 22.5% of cases. Larger femoral heads and alternative bearing couples are less tolerant of variation in acetabular orientation and thus are poor substitutes for proper acetabular component placement. Variability in acetabular orientation has been reported to have both an inter-surgeon and an intra-surgeon component; pre-surgical templating combined with intraop-erative measurements is subject to inconsistencies and errors. Current methods for determining acetabular orientation include preoperative imaging such as CT scans, intraoperative imaging such as plain radiographs and fluoroscopy, and intraoperative anatomical tests. Combining the concepts of patient-specific morphology (PSM) and quantitative technologies (QuanTech) such as computer-assisted navigation (CAN) has the potential to maximise range of motion and to further improve acetabular component orientation through improved accuracy and precision. PSM refers to the practice of allowing the form and structure of the patient’s hip joint to guide surgical reconstruction and component placement thus creating an individualised and more accurate “target zone”; unlike “safe zones,” PSM does not rely on averages. Although gross anatomic changes may make it difficult to use PSM, certain structures may be used as guide-posts for orientation, alignment, and stability in most patients. At present, there are three options when considering anatomic landmarks as guides for acetabular component placement: bony landmarks, soft tissue landmarks, or a combination. QuanTech has been shown to increase the precision of component placement by reducing intra-surgeon deviation. Some pitfalls of current CAN techniques result from maintaining camera line of sight during surgery, registration process, and pin placement. Performing THA using smaller incisions can impose additional complications as well as risks for errors in component positioning; QuanTech has the potential to provide greater visualization and precision, thus decreasing the impact of those constraints. THA has become one of the most common and successful orthopaedic procedures; its efficacy at relieving pain and its ability to help patients have improved quality of life is without dispute yet results continue to vary with inter-surgeon and intra-surgeon differences. As the population needing THA increases, the prevalence of complications and problems will increase, even if the percentage of complications decreases. Coupling PSM with QuanTech such as CAN may allow the surgeon to decrease variability and more consistently implant THA components based on each patient’s individualized requirements. The goal of combining PSM and CAN is to further reduce inter-and intra-surgeon variation, thereby decreasing outliers, complications, and revision rates, and possibly narrowing the gap between specialist and generalist. More accurate and precise acetabular component orientation correlates with better hip biomechanics, translating into better function, fewer dislocations, fewer impingements, maximized safe range of motion, less wear, and therefore less aseptic loosening and improvements in survivorship of primary THA. Decreasing revision rates, combined with the benefits listed above, could translate into increased THA survivorship, improved patient satisfaction, and decreased economic burden on the entire healthcare system

Orientation of the native acetabular plane as defined by the transverse acetabular ligament (TAL) and the posterior labrum was measured intra-operatively using computer-assisted navigation in 39 hips. In order to assess the influence of alignment on impingement, the range of movement was calculated for that defined by the TAL and the posterior labrum and compared with a standard acetabular component position (abduction 45°/anteversion 15°). With respect to the registration of the plane defined by the TAL and the posterior labrum, there was moderate interobserver agreement (r = 0.64, p < 0.001) and intra-observer reproducibility (r = 0.73, p < 0.001). The mean acetabular component orientation achieved was abduction of 41° (32° to 51°) and anteversion of 18° (−1° to 36°). With respect to the Lewinnek safe zone (abduction 40° ±10°, anteversion 15° ±10°), 35 of the 39 acetabular components were within this zone. However, there was no improvement in the range of movement (p = 0.94) and no significant difference in impingement (p = 0.085). Alignment of the acetabular component with the TAL and the posterior labrum might reduce the variability of acetabular component placement in total hip replacement. However, there is only a moderate interobserver agreement and intra-observer reliability in the alignment of the acetabular component using the TAL and the posterior labrum. No reduction in impingement was found when the acetabular component was aligned with the TAL and the posterior labrum, compared with a standard acetabular component position

Summary. Computer assisted surgery (CAS) during total knee arthroplasty (TKA) is known to improve prosthetic alignment in coronal and sagittal plane. In this systematic review, no evidence is found that CAS also improves axial component orientation when used during TKA. Introduction. Primary total knee arthroplasty (TKA) is a safe and cost-effective treatment for end-stage knee osteoarthritis. Correct prosthesis alignment is essential, since malpositioning of the prosthesis leads to worse functional outcome and increased wear, which compromises survival of the prosthesis. Computer assisted surgery (CAS) has been developed to enhance prosthesis alignment during TKA. CAS significantly improves postoperative coronal and sagittal alignment compared to conventional TKA. However, the influence of CAS on rotational alignment is a matter of debate. Therefore purpose of this review is to assess published evidence on the influence of CAS during TKA on postoperative rotational alignment. Patients and Methods. This review was performed according to the PRISMA Statement. An electronic literature search was performed in Pubmed, Medline and Embase on studies published between 1991 and April 2013. Studies were included when rotational alignment following imageless CAS-TKA was compared to rotational alignment following conventional TKA. At least one of the following outcome measures had to be assessed: 1) rotational alignment of the femoral component, 2) rotational alignment of the tibial component, 3) tibiofemoral mismatch, 4) the amount of rotational outliers of the femoral component, 5) the amount of rotational outliers of the tibial component. Study selection was performed in two stages and data extraction and methodological quality assessment was conducted independently by two reviewers. Standardized mean difference (SMD) with 95% confidence interval (95% CI) was calculated for continuous variables. The SMDs were interpreted according to Cohen: an SMD of 0.2–0.4 was considered a small effect; 0.5–0.7 was considered moderate; and ≥ 0.8 was considered a large effect. For the comparison of the amount of outliers for femoral and tibial component rotation, the Odds ratio (OR) and 95% CI was calculated. The OR represents the odds of outliers occurring in the CAS group compared with the conventional group. An OR of < 1 favors the CAS group. The OR is considered statistically significant when the 95% CI does not include the value of 1. Results. Seventeen studies met the inclusion criteria. One study was considered of high, 15 studies of medium and one study of low methodological quality. SMD for rotation of the femoral component was −0.07 (−0.19–0.04). For rotation of the tibial component, the SMD was 0.11 (−0.01–0.24). Regarding tibiofemoral mismatch, the SMD was −0.27 (−0.57–0.02). For femoral outliers, the OR was 1.05 (0.78–1.43) and for tibial outliers the OR was 1.12 (0.86–1.47). Discussion / Conclusion. Results of this review show no evidence that CAS-TKA leads to better rotational alignment of the femoral or tibial component or tibiofemoral mismatch. Also no evidence was found that CAS results in a decrease of the amount of outliers regarding femoral or tibial component orientation. However, these conclusions have to be interpreted with caution. The number of included studies was low and strong heterogeneity existed between the studies. Of the 17 included studies, only one study was considered of high methodological quality. Moreover, different methods for assessing tibial component rotation have been used in the studies included

INTRODUCTION. The introduction of hard-on-hard bearings and the consequences of increased wear due to edge-loading have renewed interest in the importance of acetabular component orientation for implant survival and functional outcome following hip arthroplasty. Some studies have shown increased dislocation risk when the cup is mal-oriented which has led to the identification of a safe-zone1. The aims of this prospective, multi-centered study of primary total hip arthroplasty (THA) were to: 1. Identify factors that influence cup orientation and 2. Describe the effect of cup orientation on clinical outcome. METHODS. In a prospective study involving seven UK centers, patients undergoing primary THA between January 1999 and January 2002 were recruited. All patients underwent detailed assessment pre-operatively as well as post-op. Assessment included data on patient demographics, clinical outcome, complications and further surgery/revision. 681 primary THAs had adequate radiographs for inclusion. 590 hips received cemented cups. The primary functional outcome measure of the study was the change between pre-operative and at latest follow up OHS (OHS). Secondary outcome measures included dislocation rate and revision surgery. EBRA was used to determine acetabular inclination and version. The influence of patient's gender, BMI, surgeon's grade and approach on cup orientation was examined. Four different zones tested as possibly ± (Lewinnek Zone, Callanan's described zone and zones ± 5 and ±10 about the study's mean inclination and anteversion) for a reduced dislocation risk and an optimal functional outcome. RESULTS. There were 21 dislocations (3.1%) and 8 (1.2%) patients required revision at a mean follow up of 7 years. Experienced surgeons (2=0.047) and those operating with the patient in the lateral decubitus position (p=0.04) were more likely to achieve a cup orientation within any of the tested zones. Surgical approach (2=0.14) and patient's BMI (2=0.93) had no influence on whether a cup was within or outside any zone. There was no difference in dislocation rate between the posterior and anterio-lateral approaches (2=0.88). None of the zones tested had a significantly reduced dislocation risk (2=0.13), nor revision risk (2=0.55). OHS was not different for patients with cups within or outside any of the zones tested (p=0.523). DISCUSSION. There was a wide variation in cup orientation. Despite the wide scatter in cup orientation, no safe zone could be identified that would reduce dislocation and revision rate, nor improve patient reported outcome (OHS). Hence, these data suggest that acetabular component orientation should not be considered predictive of patients' early/mid-term complication/revision rate and outcome following THA

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

Optimum component orientation in hip arthroplasty is vital in an effort to avoid dislocation and excessive wear. Computer navigation in hip arthroplasty surgery has the potential to improve accuracy in component placement. However, it has been slow to gain widespread acceptance. One of the major concerns surgeons have is the difficulty in registering pelvic landmarks. We used a retrospective series of 200 pelvic CT scans to validate a new methodology to construct the anterior pelvic plane, using anatomical landmarks that are easily palpated with the patient positioned and draped in the lateral decubitus position. Analysis of the scans was also made in an effort to stimulate the inaccuracies of obtaining the anterior pelvic plane through soft tissue. When comparing the new registration methodology to the anterior pelvic plane, the error in acetabular component inclination was 0.69° (SD 2.96) and anteversion was 1.17° (SD 3.53). This compares favourably to the error in acetabular component inclination of −0.92° (SD 0.26) and anteversion of −5.24° (SD 2.09) when the anterior pelvic plane is registered through soft tissue. The data also shows that using the new registration method in more than 99.6% of cases the acetabular placement is within the safe zone as described by Lewinnek. This study appears to show that through the identification of anatomical constants we are able to construct the anterior pelvic plane from anatomical landmarks that are easily palpable in the lateral decubitus position during hip arthroplasty. These landmarks also appear to be more accurate in obese patients than registering the anterior pelvic plane

Aims

The mobile bearing Oxford unicompartmental knee arthroplasty (OUKA) is recommended to be performed with the leg in the hanging leg (HL) position, and the thigh placed in a stirrup. This comparative cadaveric study assesses implant positioning and intraoperative kinematics of OUKA implanted either in the HL position or in the supine leg (SL) position.

Introduction. Pelvic posterior tilt change (PPTC) after THA is caused by release of joint contracture and degenerative lumbar kyphosis. PPTC increases cup anteversion and inclination and results in a risk of prosthesis impingement (PI) and edge loading (EL). There was reportedly no component orientation of fixed bearing which can avoid PI and EL against 20°PPTC. However, dual mobility bearing (DM) has been reported to have a large oscillation angle and potential to withstand EL without increasing polyethylene (PE) wear against high cup inclination such as 60∼65°. Objective. The purpose of this study was to investigate the optimal orientation of DM-THA for avoiding PI and EL against postoperative 20°PPTC. Methods. Our study was performed with computer tomography -based three-dimensional simulation software (ZedHip. LEXI co. Japan). The CT data of hip was derived from asian typical woman with normal hips. Used prosthesises were 50mm cup and 42mm outer head of modular dual mobility system and Accolade II 127°(stryker). Femoral coordinate system was retrocondylar plane with z-axis from trochanteric fossa to intercondylar notch. Cup orientation was described as anatomical definition. The safe zone was calculated by the required hip range of motion which was defined as 130°flexion, 40°extension, 30°external rotation, and 50°internal rotation with 90°flexion and the maximum inclination of DM cup which was 60°in consideration of withstanding EL. Cup orientations withstanding 20°PPTC were defined as the primary cup orientation which changes consistently within the safe zone with the match of 20°PPTC. And among them cup orientation with lowest inclination was defined as the optimal cup orientation. result. The optimal orientations could be identified only within stem anteversion from 15°to 40°. The relationship between the optimal cup orientation and stem anteversion could be automatically identified. The correlation between stem anteversion and cup anteversion was linearly distributed and could be expressed as an approximated line of the formula that (stem anteversion)+(cup anteversion)=36.8. And likewise the relationship between stem anteversion and cup inclination was curved-linerly distributed and could be expressed as an approximated curved line of the formula that (cup inclination)=0.04(stem anteversion). 2. 2.18(stem anteversion)+74.8. Cup orientation calculated by the Widmer's combined anteversion theory is easily deviated from the safe zone by PPTC. The optimal cup orientation calculated in this study could be set more inclination and retroversion than it calculated by the Widmer's theory in contribution of large oscillation angle and admissibility of high inclination cup setting of DM. Therefore it could be possible to withstand 20°PPTC. Conclusion. Performing THA with considering postoperative PPTC is necessary for good long term outcome without dislocation and PE wear. The solution for 20°PPTC after THA is to apply dual mobility bearing and the formula of combined orientation theory calculated in this study

Aims

The aim of this study was to determine whether there is a difference in the rate of wear between acetabular components positioned within and outside the ‘safe zones’ of anteversion and inclination angle.

Introduction

For nearly 58% of total knee arthroplasty (TKA) revisions, the reason for revision is exacerbated by component malalignment. Proper TKA component alignment is critical to functional outcomes/device longevity. Several methods exist for orthopedic surgeons to validate their cuts, however, each has its limitations. This study developed/validated an accurate, low-cost, easy to implement first-principles method for calculating 2D (sagittal/frontal plane) tibial tray orientation using a triaxial gyroscope rigidly affixed to the tibial plateau of a simulated leg jig and validated 2D tibial tray orientation in a human cadaveric model.