Introduction. Acetabular component positioning, offset, combined anteversion, leg length, and soft tissue envelope around the hip plays an important role in hip function and durability. In this paper we will focus on acetabular positioning of the cup. Technique. The axis of the pelvis is identified intra-operatively as a line drawn from the highest point of the iliac crest to the middle of the greater trochanter. Prior to reaming the acetabulum, an undersized trial acetabular component is placed parallel and inside the transverse ligament, inside the anterior column and projecting posterior to the axis of the pelvis. This direction is marked and the subsequent reaming and final component placement is performed in the same direction. The lateral opening is judged based on the 45-degree angle from the tear drop to the lateral margin of the acetabulum on anteroposterior pelvic radiographs. The final anteversion of the cup is adjusted based on increased or decreased lumbar lordosis and combined anteversion. Methods. Anteroposterior pelvic radiographs of 100 consecutive patients undergoing posterior THR between September 2010 and March 2011 with this method were evaluated for cup inclination angle and anteversion using EBRA software. Results. There were no malalignments or dislocations. The mean cup inclination angle and anteversion were 41 ± 5.1 degrees (range 37.1 – 48.4) and 22.1 ± 4.8 degrees (range 16.6 – 29.3), respectively. Conclusion. This is a reproducible method of cup positioning and with proper femoral component position and restoring leg length, offset, combined anteversion, and balance soft tissue around the hip. These factors affect the incidence of dislocation, infection, reduced wear, and durability

Introduction: Acetabular component positioning, offset, combined anteversion, leg length, and soft tissue envelope around the hip plays an important role in hip function and durability. In this paper we will focus on acetabular positioning of the cup. Technique: The axis of the pelvis is identified intra-operatively as a line drawn from the highest point of the iliac crest to the middle of the greater trochanter. Prior to reaming the acetabulum, an undersized trial acetabular component is placed parallel and inside the transverse ligament, inside the anterior column and projecting posterior to the axis of the pelvis. This direction is marked and the subsequent reaming and final component placement is performed in the same direction. The lateral opening is judged based on 45-degree angle from the tear drop to the lateral margin of the acetabulum on anteroposterior pelvic radiographs. The final anteversion of the cup is adjusted based on increase or decrease of lumbar lordosis and combined anteversion. Methods: Anteroposterior pelvic radiographs of 100 consecutive patients undergoing posterior THR between September 2010 and March 2011 with this method were evaluated for cup inclination angle and anteversion using EBRA software. Results: There were no malalignment or dislocation. The mean cup inclination angle and anteversion were 41 ± 5.1 degrees (range 37.1 – 48.4) and 22.1 ± 4.8 degrees (range 16.6 – 29.3), respectively. Conclusion: This is a reproducible method of cup positioning and with proper femoral component position, restores leg length, offset, combined anteversion, and balances soft tissue around the hip. These factors affect the incidence of dislocation, infection, reduced wear, and durability

Introduction. The limited field of view with less-invasive hip approaches for total hip arthroplasty can make a reliable cup positioning more challenging. The aim of this study was to evaluate the accuracy of cup placement between the traditional transgluteal approach and the anterior approach in a routine setting. Objectives. We asked if the (1) accuracy, (2) precision, and (3) number of outliers of the prosthetic cup orientation differed between three study groups: the anterior approach in supine position, the anterior approach in lateral decubitus position, and the transgluteal approach in lateral decubitus position. Methods. In a retrospective comparative study we compared the inclination and anteversion of the cup after total hip arthroplasty (THA) in a consecutive series of 325 patients (350 hips). The transgluteal approach group consisted of 67 hips operated in lateral decubitus position; the anterior approach in supine position consisted of 127 operated and the anterior approach in lateral decubitus position consisted of 156 hips. The aim of the cup orientation was Lewinnek's safe zone defined by an inclination of 40±10° and an anteversion of 15°±10°. The postoperative cup orientation was determined using a validated computer-assisted method based on statistical shape modeling. This method allows the virtual creation of an accurate three-dimensional pelvic model for each individual patient based on the two-dimensional anteroposterior pelvic radiograph. The inclination and anteversion was then calculated relative to the anterior pelvic plane – a natural reference plane for the calculation of inclination and anteversion. Accuracy was defined as the difference from the cup orientation to Lewinnek's target value. Precision was defined as the standard deviation of the two angles. Outliers were characterized by an anteversion or inclination angle outside of Lewinnek's safe zone. Results. (1) The accuracy of the anterior approach in supine position did not differ compared to the transgluteal approach, but differed to the anterior approach in supine position for inclination (p=0.882; p<0.001) (Figure 1) and anteversion (p = 0.014; p<0.001) (Figure 2). (2) The precision of the anterior approach in supine position was significantly higher compared to the transgluteal approach (p<0.001) and the anterior approach in lateral decubitus position for anteversion (p<0.001 for both groups) and inclination (p<0.001 for both groups) (Figure 3). (3) There was a significantly reduced number of outliers for the anterior approach in supine position compared to the anterior approach in lateral position (p=0.001) but not in comparison to the transgluteal approach (p=0.999) (Figure 2). Conclusions. The anterior approach in supine position results in a more precise placement of the prosthetic cup both for inclination and anteversion. Cup placement with less-invasive approaches does not lead to a higher variability of cup placement despite the more limited surgical field of view. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

Introduction. Navigation in total hip arthroplasty (THA) has the goal to improve accuracy of cup orientation. Measurement of cup orientation on conventional pelvic radiographs is susceptible to error due to pelvic malpositioning during acquisition. A recently developed and validated software using a postoperative radiograph in combination with statistical shape modelling allows calculation of exact 3-dimensional cup orientation independent of pelvic malpositioning. Objectives. We asked (1) what is the accuracy of computer-navigated cup orientation (inclination and anteversion) and (2) what is the percentage of outliers (>10° difference to aimed inclination and anteversion) using postoperative measurement of 3-dimensional cup orientation. Methods. We performed a retrospective comparative study including a single surgeon series with 114 THAs (109 patients). Surgery was performed through the anterolateral approach with the patient in supine position. An image-free navigation system (PiGalileo, Smith & Nephew) with a passive digital reference base for the pelvic wing and one for the distal femur was used. The anterior pelvic plane (APP) was registered manually using a pointer and used as anatomical reference. After implantation of the press-fit cup (EP-Fit plus, Smith & Nephew) the final cup orientation (inclination and anteversion) was registered with the navigation system. Postoperative orientation was calculated using validated software to calculate 3-dimensional cup orientation. The postoperative anteroposterior pelvic radiograph in combination with a statistical model of the pelvis allowed calculation of inclination and anteversion referenced to the APP. The software was previously validated using CT measurements and revealed a mean accuracy of 0.4° for inclination 0.6° for anteversion with a maximum error of 3.3° and 3.6°, respectively. The mean postoperative inclination in the current series was 46° ± 4° (range, 35° – 60°) and the mean anteversion was 23° ± 6° (range, 11° – 37°). Accuracy was calculated as the absolute difference of the intraoperative registered cup orientation and the postoperative calculated orientation. An outlier was defined if cup orientation was outside a range of ±10° of inclination and/or anteversion. Results. (1) The mean accuracy for inclination was 3 ± 3° (0 – 17°) and 6 ± 5° (0 – 22°) for anteversion. (2) Three out of 114 cups (3%) were outliers for inclination. An increased percentage of outliers was found for anteversion with 23 out of 114 cups (20%; p<0.001). In total, 25 cups (22%) were outliers (See Figure 1). Conclusions. Previous studies evaluating accuracy of cup orientation were limited in numbers of hips due to the use of CT or used measurements on conventional postoperative radiographs which are prone to error due to pelvic malpositioning. Novel and validated software allows accurate and anatomically referenced measurement of postoperative cup orientation. This study is the single largest case series with 3-dimensional measurement of cup orientation for validation of navigated THA. Computer-assisted image-free navigation of cup orientation showed a high accuracy of cup orientation with 78% within a narrow range of ±10° of inclination and anteversion. Accuracy of cup inclination was increased compared to cup anteversion. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

Introduction. Many authors have described component position and leg length discrepancy (LLD) after total hip arthroplasty (THA) as the most important factors for good postoperative outcomes. However, regarding the relationships between component position and different approaches for THA, the optimal approach for component position and LLD remains unknown. The aims of this study were to compare these factors among the direct anterior, posterolateral, and direct lateral approaches on postoperative radiographs retrospectively, and determine which approach leads to good orientation in THA. Methods. We retrospectively evaluated 150 patients who underwent unilateral primary THA in our department between January 2009 and December 2014, with the direct anterior, posterolateral, or direct lateral approach used in 50 patients each. Patients with significant hip dysplasia (Crowe 3 or 4), advanced erosive arthritis, prevented osteotomy of the contralateral hip, and body mass index (BMI) of more than 30 were excluded. The mean age, sex, and preoperative diagnosis of the affected hip were equally distributed in patients who underwent THA with the different approaches. The mean BMI did not differ significantly among the groups. The radiographic measurements included cup inclination angle, dispersion of cup inclination from 40°, and LLD on an anteroposterior pelvic radiograph, and cup anteversion angle and dispersion of cup anteversion from 20° on a cross-table lateral radiograph postoperatively. We also measured the ratios of patients with both cup inclination of 30–50° and cup anteversion of 10–30° (target zone in our department), femoral stem varus/valgus, and LLD of 10 mm or less. Statistical analyses used an unpaired t-test and Fisher's exact test, with significance set at p<0.05. Results. The mean cup inclination was 36.9±5.1° for direct anterior approach, 40.8±7.5° for posterolateral approach, and 38.5±7.5° for direct lateral approach. Dispersion of cup inclination from 40° was almost identical in the three groups, with no significant differences. The mean cup anteversion was 23.4±5.5° for direct anterior approach, 25.9±9.2° for posterolateral approach, and 24.3±8.6° for direct lateral approach. Dispersion of cup anteversion from 20° differed between direct anterior approach and posterolateral or direct lateral approach (P<0.05 for each). The mean LLD was 1.3±6.6mm for direct anterior approach, 3.0±8.6mm for posterolateral approach, and 2.6±7.4mm for direct lateral approach. The mean LLD did not differ significantly among the three groups. The ratio of patients with both cup inclination of 30–50° and cup anteversion of 10–30° was significantly better for direct anterior approach than for posterolateral or direct lateral approach (78% vs. 52% and 52%, respectively; p<0.05). The ratios of femoral stem varus/valgus and LLD of 10 mm or less did not differ among the groups. Conclusions. The direct anterior approach in THA appeared to have small dispersion of cup anteversion angle and high ratio of cup component position in our target zone compared with the posterolateral and direct lateral approaches. However, the LLD and femoral stem varus/valgus after THA did not differ significantly among the three approaches postoperatively

Pre-existing hip pathology such as femoroacetabular impingement is believed by some, to have a direct causal relationship with osteoarthritis of the hip. The strength of this relationship remains unknown. We investigate the prevalence of abnormal bone morphology in the symptomatic hip on the pre-operative anteroposterior pelvic radiograph of consecutive patients undergoing hip resurfacing. Rotated radiographs were excluded. One hundred patients, of mean age 53.5 years were included (range 33.4–71.4 years, 32% female). We examined the films for evidence of a cam-type impingement lesion (alpha angle >50.5°, a pistol grip, Pitt's pits, a medial hook, an os acetabuli and rim ossification), signs of acetabular retroversion or a pincer-type impingement lesion (crossover sign, posterior wall sign, ischial sign, coxa profunda, protrusio, coxa vara, Tonnis angle < 5°), and hip dysplasia (a Tonnis acetabular angle >14° and a lateral centre-edge angle of Wiberg <20°). Pre-existing radiographic signs of pathology were present in a large proportion of hips with low grade (Tonnis grade 1–2) arthritis. There is a group of patients who presented with more advanced osteoarthritis in which we suspect abnormal bone morphology to be a causative factor but, for example, neck osteophytes obscure the diagnosis of a primary cam lesion. Our findings corroborate those of Harris and Ganz. Impingement is radiographically detectable in a large proportion of patients who present with early arthritis of the hip, and therefore we agree that it is a likely pre-cursor for osteoarthritis. Treatments directed at reducing hip impingement may stifle the progression of osteoarthritis

Surgeons often target the Lewinnek zone (40°±10° of inclination; 15°±10° of anteversion) for acetabular orientation during total hip arthroplasty (THA). However, matching native anteversion (20°-25°) may achieve optimal stability. The purpose of this study was to (1) determine incidence of early dislocation with increased target acetabular anteversion, and (2) report the accuracy of imageless navigation for achieving target acetabular position in a large, single-surgeon cohort. A posterolateral approach with soft tissue repair was performed in the 553 THA meeting the inclusion criteria. The same imageless navigation system was used for acetabular component placement in all THA. Target acetabular orientation was 40° ± 10° of inclination and 25° ± 10° of anteversion. Computer software was used to measure acetabular positioning on 6-week postoperative anteroposterior pelvic radiographs. Incidence of dislocation within 6 months of surgery was determined. Repeated measures multiple regression using the Generalised Estimating Equations approach was used to identify baseline patient characteristics (age, gender, BMI, primary diagnosis, and laterality) associated with component positioning outside of the targeted ranges for inclination and anteversion. Fisher exact tests were used to examine the relationship between dislocation and component placement in either the Lewinnek safe zone or the targeted zone. All tests were two-sided with a significance level of 0.05. Mean inclination was 42.2° ± 4.9°, and mean anteversion was 23.9° ± 6.5°. 82.3% of cups were placed within the target zone. Variation in anteversion accounted for 67.3% of outliers. Only body mass index was associated with inclination outside the target range (p = 0.017), and only female gender was associated with anteversion outside the target range (p = 0.030). Six THA (1.1%) experienced early dislocation, and 3 THA (0.54%) were revised for multiple dislocations. There was no relationship between dislocation and component placement in either the Lewinnek zone (p = 0.224) or the target zone (p = 0.287). This study demonstrates that increasing target acetabular anteversion using the posterolateral approach does not increase the incidence of early THA dislocation. However, the long-term effects on bearing surface wear and stability must be elucidated. The occurrence of instability even in patients within our target zone emphasises the importance of developing patient-specific targets for THA component alignment

INTRODUCTION. Acetabular cup orientation is an important element of Total Hip arthroplasty (THA). The purpose of this retrospective case-control study was to compare variability of acetabular cup placement between THA performed via Direct Anterior Approach (DAA) with fluoroscopy in supine position and posterior approach (PA) in lateral position without use of fluoroscopy. METHODS. Radiographic and clinical records of THAs performed by a single, high volume arthroplasty surgeon at one institution were reviewed. Patients with similar design of uncemented acetabular cup, femoral component and bearing surface were included to form two groups. PA group consisted of 300 THAs performed from May 2006 to June 2009. DAA group consisted of 300 THAs performed from Oct 2009 to Oct 2011 excluding first 100 cases to eliminate the influence of learning curve. Radiographic analysis was done by two independent blinded observers to determine cup inclination and anteversion (Liaw et al) on standardized, 6 week postoperative, standing anteroposterior pelvic radiographs using Picture Archiving and Communication System software (PACS). RESULTS. Both groups were comparable in terms of age, sex and BMI. Mean inclination in both groups was similar; PA (41.2 degrees; range, 23 to 63) and DAA (40.36 degrees; range, 29 to 51). Mean anteversion was lower in DAA group (13.29 degrees; range, 6.2 to 32) as compared to PA group (24 degrees; range, 2.3 to 48.8). Variances for cup inclination (49.7 PA vs 19.1 DAA) and anteversion (75.1 PA vs 16.1 DAA) were significantly lower in the DAA group as compared to the PA group as per the F- test for equality of variances (p = 0.001). DISCUSSION. Acetabular cup placement in PA relies predominantly on internal landmarks. Utilization of fluoroscopy with supine position during DAA THA helps in intraoperative assessment of cup orientation and making adjustments for pelvic tilt, thus resulting in decreased variability

Obesity is a risk factor for acetabular malposition when total hip arthroplasty (THA) is performed with manual orientation techniques. However, conflicting evidence exists regarding the usefulness of computer-assisted surgery for performing THA in obese patients. The purpose of this study was to compare the precision and accuracy of imageless navigation for acetabular component placement in obese versus non-obese patients. After institutional review board approval, 459 THA performed for primary hip osteoarthritis were reviewed retrospectively. The same imageless navigation system was used for acetabular component placement in all THA. During surgery the supine anterior pelvic plane was referenced superficially. THA was performed via posterolateral approach in the lateral position. A hemispherical acetabular component was used, with target inclination of 40° and target anteversion of 25°. Computer software was used to determine acetabular orientation on postoperative anteroposterior pelvic radiographs. Obese patients (BMI ≥ 30 kg/m2) were compared to non-obese patients. A 5° difference in mean orientation angles was considered clinically significant. Orientation error (accuracy) was defined as the absolute difference between the target orientation and the measured orientation. Student's t test was used to compare means. Hartley's test compared variances of the mean differences (precision). Fisher exact tests examined the relationship between obesity and component placement in the target zone (target ± 10°) for inclination and version. All statistical tests were two-sided with a significance level of 0.05. Differences in mean inclination and anteversion between obese and non-obese groups were 1.1° (p=0.02 and p=0.08, respectively), and not clinically significant. Inclination accuracy trended toward improvement for non-obese patients (p=0.06). Inclination precision was better for non-obese patients (p=0.006). Accuracy and precision for anteversion were equal between the two groups (p=0.19 and p=0.95, respectively). There was no relationship between obesity and placement of the acetabulum outside of the target ranges for inclination (p=0.13), anteversion (p=0.39) or both (p=0.99), with a trend toward more inclination outliers in obese patients versus non-obese patients (7.3% versus 3.9%). The observed differences in mean acetabular orientation angles were not clinically significant (< 5°), although inclination orientation was less accurate and precise for obese patients. In contrast to existing literature, we found no difference in the accuracy and precision with regard to anteversion in obese and non-obese patients. We propose that accurate superficial registration of landmarks in obese patients is achievable, and the use of imageless navigation likely improves acetabular positioning in obese and non-obese patients

Method. The anteroposterior pelvic radiographs of 84 children (87 hips with developmental dysplasia) seen between 1995 and 2004 were reviewed retrospectively. Each radiograph was photographed digitally and converted to the negative using Microsoft Photo Editor. Arthrograms were also assessed at the time of femoral head reduction. The acetabular index (AI) and femoral head deformity were assessed. Acetabular response was measured using the AI at 6 and 12 months post-reduction. Results. Mean age at presentation was 11 months for the closed reduction group, versus 19 months for those with an arthrographic soft tissue obstruction requiring open reduction. Additionally, the average age of the children that underwent open reduction who later required a Salter osteotomy was 27 ± 3 months compared to an average of 14 ± 1.5 months for those who did not. The acetabular response was maximal during the first 6 months following treatment. Closed reduction (24 hips) gave comparable results to open reduction (63 hips), although the initial AI was greater in those requiring open reduction (39.5 ± 6.3° versus 36.1 ± 4.6°). Using two separate Bonferroni pairwise comparisons revealed no statistical difference in response between closed and open reduction. Arthrography revealed that hips requiring open reduction were more deformed, with spherical femoral heads in 29% as opposed to 68% in the closed reduction group. The AI was also slightly less (36.6 ± 3.2°) when the femoral head was spherical in comparison to those hips with an aspherical femoral head (38.0 ± 6.6°). Conclusion. Age at presentation and femoral head deformity therefore influence the outcome of reduction, but the acetabular index improves to a similar degree whether closed or open reduction is required

Over the last few years low dose digital radiography (DR) has all but replaced traditional chemical image processing. This appears to have created a paradigm shift in the suitability of intraoperative radiographic guidance for total hip arthroplasty. It is the purpose of this publication to describe our preferred technique and assess its reliability in achieving the desired parameters of a successful total hip arthroplasty. A consecutive prospective evaluation of 150 primary total hip arthroplasties employing intraoperative digital radiography was carried out. An anteroposterior pelvic radiograph with the patient in the lateral decubitus position was obtained for all hips. The orientation of the intraoperative film was matched to that of the preoperative pelvic radiograph. The image was taken after placement of the acetabular component and best estimate of femoral trial size, position, and head and neck length. The DR system produced an image within 6 seconds of exposure. This trial radiograph was then used to make adjustments. Given that the cassette does not have to be moved for image processing, a precise anteroposterior film was obtained by simply adjusting the operating table. Two to three minutes were allotted for each radiograph. Corrections to stem size, cup position, screw length and position, limb length, and offset were made based on this intraoperative radiograph. The final intraoperative image was then compared to a postoperative standard radiograph in supine position at 2 weeks after total hip arthroplasty to verify the accuracy of intraoperative digital radiography. Abduction angle, limb length, offset, and canal fit and fill were assessed for confirmation of the validity of the intraoperative imaging technique. Acetabular abduction angle was determined with a mean of 43 degrees (range, 35 to 48 degrees). The intraoperative measurement was within 3 degrees of the postoperative measurement in all cases. Adjustment of acetabular cup orientation was performed 10% of the time based on the intraoperative radiograph. Apposition was within 2 mm 100% of the time. Re-seating of the cup was carried out in one hip only. Femoral component was neutral in 92% and between 3 and 5 degrees of varus in 8%. Femoral component was upsized 55% of the time. Intraoperatively measured limb length discrepancy and offset were within 3 mm of the postoperative measurement in all hips. Intraoperative digital imaging is a reliable tool for achieving the desired radiographic results in THA. The technique is efficient and affordable. The high rate of success in this series suggests that this technology should contribute to a paradigm shift in the standard of care in total hip arthroplasty

The success of total hip replacement (THR) is closely linked to the positioning of the acetabular component. Malalignment increases rates of dislocation, impingement, acetabular migration, pelvic osteolysis, leg length discrepancy and polyethylene wear. Many surgeons orientate the cup in the same anteversion and inclination as the inherent anatomy of the acetabulum. The transverse acetabular ligament and acetabular rim can be used as a reference points for orientating the cup this way. Low rates of dislocation have been reported using this technique. Detailed understanding of the anatomy and orientation of the acetabulum in arthritic hips is therefore very important. The aim of this study was to describe the anteversion and inclination of the inherent acetabulum in arthritic hips and to identify the number that fall out with the ‘safe zone’ of acetabular position described by Lewinnek et al. (anteversion 15°±10°; inclination 40°±10°). A series of 65 hips, all with symptomatic osteoarthritis undergoing THR were investigated. Patients with developmental dysplastia of hip (DDH) were excluded. All patients had a navigated THR as part of their normal clinical treatment. A posterior approach to the hip was used. A commercially available non image based computer navigation system (Orthopilot BBraun Aesculap, Tuttlingen, Germany) was used. Rigid bodies (using active trackers) were attached to pelvis and femur. Anterior pelvic plane was registered using the two anterior superior iliac spines and pubic symphysis. The femoral head dislocated and removed and the labrum and soft tissue were excised to clear floor and rim of the acetabulum. Inner size of the empty acetabulum was sized with cup trials and appropriately size trial fixed with a computer tracker was then aligned in the orientation of the natural acetabulum as defined by the acetabular rim ignoring any osteophytes. The inclination and anteversion were calculated by the software. Surgery then proceeded with guidance of the computer navigation system. The computer software defines the anatomical values of orientation, to allow comparison with radiographs these were converted to radiological values as described by Murray et al. The acetabular inclination in all hips was also measured on pre-operative anteroposterior pelvic radiographs. This was done using digital radiographs analysed with the PACS system (Kodak, Carestream PACS Client, version 10.0). Acetabular inclination was measured using as the angle between a line passing through the superior and inferior rim of the acetabulum and a line parallel to the pelvis as identified by the tear drops, using the method described by Atkinson et al. All patients were Caucasian and had primary osteoarthritis. There were 29 males and 36 females. The average age was 68 years (SD 8). Mean anteversion was 9.3° (SD 10.3°). Anteversion for males was significantly lower than females with a mean difference of −5.5° (95%CI −10.5°,−0.5°) p = 0.033 but there was no significant difference in the number falling outside the “safe zone”. Mean inclination was 50.4° (SD 7.4°). There was no significant difference between males and females with respect to inclination angle or the number that fell outside the “safe zone”. Overall 69% of patients had a combined inclination and anteversion of the native acetabulum that fell outside the “safe zone” of Lewinnek. Mean acetabular inclination falls out with the ‘safe zone’. This trend has been seen in a recent study of arthritic hips using CT scans which found that the average angle of inclination in both males and females was greater than the upper limit of the safe zone. This study using CT also demonstrated a statistically significant 5.5° difference between males and females in terms of anteversion. This is the same as the figure we have found in our work. Inherent acetabular orientation in arthritic hips falls out with the safe zone defined by Lewinnek in 69% of cases. When using the natural acetabular orientation as a guide for positioning implants it should therefore not be assumed this will fall with in the safe zone although the validity of safe zones itself is questionable. Variation between patients must be taken into account and the difference between males and females, particularly in terms of anteversion, should also be considered

Magnification of anteroposterior radiographs of the pelvis is variable. To improve the accuracy of templating, reliable and radiographer-friendly methods of scaling are necessary. We assessed two methods of scaling digital radiographs of the pelvis: placing a coin of known diameter in the plane of interest between the patient’s thighs, and using a caliper to measure the bony width of the pelvis. A total of 39 patients who had recently undergone hemiarthroplasty of the hip or total hip replacement were enrolled in the study. The accuracy of the methods was assessed by comparing the actual diameter of the head of the prosthesis with the measured on-screen value. The coin method was within a mean of 1.12% (0% to 2.38%) of the actual measurement, the caliper group within 6.99% (0% to 16.67%). The coin method was significantly more accurate (p < 0.001). It was also reliable and radiographer friendly. We recommend it as the method of choice for scaling radiographs of the pelvis before hip surgery.