Aims. Leg length discrepancy (LLD) is a common pre- and postoperative issue in total hip arthroplasty (THA) patients. The conventional technique for measuring LLD has historically been on a non-weightbearing anteroposterior pelvic radiograph; however, this does not capture many potential sources of LLD. The aim of this study was to determine if long-limb EOS radiology can provide a more reproducible and holistic measurement of LLD. Methods. In all, 93 patients who underwent a THA received a standardized preoperative EOS scan, anteroposterior (AP) radiograph, and clinical LLD assessment. Overall, 13 measurements were taken along both anatomical and functional axes and measured twice by an orthopaedic fellow and surgical planning engineer to calculate intraoperator reproducibility and correlations between measurements. Results. Strong correlations were observed for all EOS measurements (r. s. > 0.9). The strongest correlation with AP radiograph (inter-teardrop line) was observed for functional-ASIS-to-floor (functional) (r. s. = 0.57), much weaker than the correlations between EOS measurements. ASIS-to-ankle measurements exhibited a high correlation to other linear measurements and the highest ICC (r. s. = 0.97). Using anterior superior iliac spine (ASIS)-to-ankle, 33% of patients had an absolute LLD of greater than 10 mm, which was statistically different from the inter-teardrop LLD measurement (p < 0.005). Discussion. We found that the conventional measurement of LLD on AP pelvic radiograph does not correlate well with long leg measurements and may not provide a true appreciation of LLD. ASIS-to-ankle demonstrated improved detection of potential LLD than other EOS and radiograph measurements. Full length, functional imaging methods may become the new gold standard to measure LLD. Cite this article: Bone Jt Open 2022;3(12):960–968

Aims. The aim of this study was to investigate whether anterior pelvic plane-pelvic tilt (APP-PT) is associated with distinct hip pathomorphologies. We asked: is there a difference in APP-PT between young symptomatic patients being evaluated for joint preservation surgery and an asymptomatic control group? Does APP-PT vary among distinct acetabular and femoral pathomorphologies? And does APP-PT differ in symptomatic hips based on demographic factors?. Methods. This was an institutional review board-approved, single-centre, retrospective, case-control, comparative study, which included 388 symptomatic hips in 357 patients who presented to our tertiary centre for joint preservation between January 2011 and December 2015. Their mean age was 26 years (SD 2; 23 to 29) and 50% were female. They were allocated to 12 different morphological subgroups. The study group was compared with a control group of 20 asymptomatic hips in 20 patients. APP-PT was assessed in all patients based on supine anteroposterior pelvic radiographs using validated HipRecon software. Values in the two groups were compared using an independent-samples t-test. Multiple regression analysis was performed to examine the influences of diagnoses and demographic factors on APP-PT. The minimal clinically important difference (MCID) for APP-PT was defined as > 1 SD. Results. There were no significant differences in APP-PT between the control group and the overall group (1.1° (SD 3.0°; -4.9° to 5.9°) vs 1.8° (SD 3.4°; -6.9° to 13.2°); p = 0.323). Acetabular retroversion and overcoverage groups showed higher mean APP-PTs compared with the control group (p = 0.001 and p = 0.014) and were the only diagnoses with a significant influence on APP-PT in the stepwise multiple regression analysis. All differences were below the MCID. The age, sex, height, weight, and BMI showed no influence on APP-PT. Conclusion. APP-PT showed no radiologically significant variation across different pathomorphologies of the hip in patients being assessed for joint-preserving surgery. Cite this article: Bone Joint J 2024;106-B(5 Supple B):3–10

This retrospective study was to investigate radiographic and clinical outcomes in treatment of hip instability in children and young adults undergoing periacetabular osteotomy (PAO) with or without femoral osteotomy. 19 patients (21 hips) with CP were treated with PAO with or without femoral osteotomy The mean age was 16.2 years old (7 to 28 years). Five patients (5 hips) received PAO, Six patients (7 hips) PAO with femoral derotation osteotomy, Eight patients (9 hips) PAO with varus derotational osteotomy (VDRO). Anteroposterior pelvic radiographs and CT were taken to assess the migration percentage (MP), lateral center-edge angle (LCEA), Sharp angle, femoral neck anteversion, neck-shaft angle. Gross Motor Function Classification System (GMFCS) was assessed pre- and post-surgery. Complications were recorded. The mean follow-up time was 41.2 months (range, 24 to 86 months). All hips but one were pain free at final visit. The GMFCS improved by one level in 10 of 19 patients. MP improved from a mean of 76.6% to 18.6% at the final follow-up(p<0.001). The mean pre-operative LCEA and Sharp angle were −33.5 ? and 35 ? respectively, improved to 21.5 ? and 11.8 ? at the final follow-up (p < 0.001). There were six patients (7 hips) had re-subluxation at latest follow-up. Nervus cutaneus femoris lateralis was impaired in four patients after surgery. There was no re-dislocation, AVN, or infections in this group. Satisfactory clinical and radiologic results can be obtained by PAO with or without femoral osteotomy minor complications

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. In total hip arthroplasty, a high radiographic inclination angle (RI) of the acetabular component has been linked to short- and long-term complications. There are several factors that lead to RI outliers including cup version, pelvic orientation and angle of the cup introducer relative to the floor. The primary aim of this study was to analyse what increases the risk of having a cup with an RI outside the target zone when controlling cup orientation with a digital inclinometer. Methods. In this prospective study, we included 200 consecutive patients undergoing uncemented primary THA in the lateral decubitus position using a posterior approach. Preoperatively, the surgeon determined the target intraoperative inclination (IOI. target. ). The intra-operative inclination of the cup (IOI. cup. ) was measured with the aid of a digital inclinometer after seating of the acetabular component. Anteroposterior pelvic radiographs were made to measure the RI of the acetabular component. The target zones were defined as 30°-45° and 35°-45° of RI. The operative inclination relative to the sagittal plane of the pelvis (OI. math. ) was calculated based on the radiographic inclination and anteversion angle. The difference between two outcome measures was expressed as Δ. Results. The mean RI was 37.9° SD 4.7, there were 12 cases with RI outside the 30°– 45° zone (6%) and 53 outliers (26.5%) with RI outside the 35°-45° zone. The mean absolute ΔIOI. cup. -IOI. target. was 1.2° SD 1.0. The absolute ΔIOI. cup. -IOI. target. was less than 1° in 108 patients (54%), less than 2° in 160 patients (80%), less than 3° in 186 patients (93%), and in 14 patients (7%) the difference was 3°-5°. The mean pelvic motion (ΔOI. math. -IOI. cup. ) was 8.8° SD 3.9 (95% CI 8.2° to 9.3°). The absolute deviation from the mean ΔOI. math. -IOI. cup. , which corresponds with the amount of pelvic motion, was significantly higher in RI outliers compared with non-outliers for both the 30°-45° and 35°-45° inclination zone (7.4° SD 3.3 vs 2.8° SD 2.1 and 4.7° SD 2.8 vs 2.5° SD 2.0 respectively) (p<0.0001). A linear regression analysis demonstrated a strong correlation between ΔOI. math. -IOI. cup. and the RI of the cup (r. 2. =0.70; P<0.0001). A multiple regression was run to predict ΔOI. math. -IOI. cup. from gender, BMI, side and hip circumference. These variables statistically significantly predicted ΔOI. math. -OIa. cup. , F(4, 195) = 19,435, p<0.0001, R2 = 0.285, but only side (p=0.04) and hip circumference (p<0.0001) added statistically significantly to the prediction. Discussion and Conclusion. When using a digital inclinometer 94% of cups had a RI within a 30°-45° zone and 73.5% of cups within a 35°-45° zone using a predefined IOI. target. based on the patient's hip circumference. The difference between the IOI. target. and the IOI. cup. of the acetabular component was less than 3° in 93% and less than 5° in all patients signifying that the surgeons were able to implant the cup close to their chosen intra-operative orientation. Deviation from the mean ΔOI. math. -IOI. cup. was significantly bigger in the RI outliers indicating that RI outliers were caused by more or less than deviation of the sagittal plane of the pelvis at time of cup impaction

Aims

The aim of this study was to assess the clinical and radiological results of patients who were revised using a custom-made triflange acetabular component (CTAC) for component loosening and pelvic discontinuity (PD) after previous total hip arthroplasty (THA).

The orientation of the acetabular component is influenced by the orientation at which the surgeon implants the component and the orientation of the pelvis at the time of implantation. When operating with the patient in the lateral decubitus position, pelvic orientation can be highly variable. The goal of this study was to examine the effect of two different pelvic supports on cup orientation. In this prospective study, 200 consecutive patients undergoing uncemented primary THA in the lateral decubitus position were included. In the control group a single support over the pubic symphysis (PS) was used. In the study group, a single support over the ipsilateral anterior superior iliac spine (ASIS) was used. In every patient, the cup was inserted and the angle of the cup introducer relative to the floor (apparent operative inclination; OIa) was measured with the aid of a digital inclinometer. The radiographic inclination (RI) was measured on anteroposterior pelvic radiographs at 6 weeks postoperatively. The target zone for cup inclination was 35–45°. In both cohorts the cups were implanted close to the target OIa with an absolute difference with the OIa of 0.86° SD 0.82 in the PS cohort and 1.03° SD 0.99 in the ASIS cohort (p=0.18). The difference between the RI and OIa was higher in the PS cohort 12.2° SD 4.1 compared with 7.5° SD 3.7 in the ASIS cohort (p<0.0001) with also a bigger variance (p=0.04) in the PS cohort. The mean RI was 38.5° SD 4.4 compared with 39.2° SD 4.1 (p=0.26) respectively. There were more cups outside the RI target zone in the PS cohort compared with the ASIS cohort (respectively 26 versus 15; p<0.05). In this study the mean difference between the RI and OIa (the angle of the cup introducer during surgery) was significantly less when using a support over the ASIS compared with a support over the pubic symphysis. Apparently using a support over the ASIS causes less pelvic motion during surgery compared with a support over the pubic symphysis. This resulted in less variance and inclination outliers when using a tight target zone of 35–45°

Aims

Avascular femoral head necrosis in the context of gymnastics is a rare but serious complication, appearing similar to Perthes’ disease but occurring later during adolescence. Based on 3D CT animations, we propose repetitive impact between the main supplying vessels on the posterolateral femoral neck and the posterior acetabular wall in hyperextension and external rotation as a possible cause of direct vascular damage, and subsequent femoral head necrosis in three adolescent female gymnasts we are reporting on.

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).

Aims

Limited implant survival due to aseptic cup loosening is most commonly responsible for revision total hip arthroplasty (THA). Advances in implant designs and materials have been crucial in addressing those challenges. Vitamin E-infused highly cross-linked polyethylene (VEPE) promises strong wear resistance, high oxidative stability, and superior mechanical strength. Although VEPE monoblock cups have shown good mid-term performance and excellent wear patterns, long-term results remain unclear. This study evaluated migration and wear patterns and clinical and radiological outcomes at a minimum of ten years’ follow-up.

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

Introduction. In total hip arthroplasty (THA), a high radiographic inclination angle (RI) of the acetabular component has been linked to an increased dislocation rate, liner fracture, and increased wear. In contrast to version, we have more proven boundaries when it comes to a safe zone for angles of RI. Although intuitively it seems easier to achieve a target RI, most studies demonstrate a lack of accuracy and the trend towards a high RI with all surgical approaches when using a freehand technique or a mechanical guide. This is due to pelvic motion during surgery, which can be highly variable. The current study had two primary aims, each with a different primary outcome. The first aim was to determine how accurate a surgeon could obtain the target operative inclination (OI) during THA when using a cementless cup using a digital protractor. The second aim was to determine how accurate a surgeon can estimate the target OI to obtain a RI of 40° based on the patient's hip circumference as demonstrated in a previous study. Methods. In this prospective study, we included 200 consecutive patients undergoing uncemented primary THA in the lateral decubitus position using a posterior approach. Preoperatively, the surgeon determined the target OI based on the patient's hip circumference (22.5°, 25°, 27.5° or 30°). Intraoperatively, the effective OI was measured with the aid of a digital inclinometer after seating of the acetabular component. Six weeks postoperatively anteroposterior pelvic radiographs were made and two evaluators, blinded to the effective OI, measured the RI of the acetabular component. The safe zone for inclination was defined as 30°-45° of inclination. Results. The mean difference between the target OI and the effective OI of the acetabular component was −0.7° SD 1.4 (95% CI −0.9° to −0.5°). The difference between the target and effective OI was less than 1° in 108 patients (54%), less than 2° in 160 patients (80%) and less than 3° in 186 patients (93%). In 14 patients (7%) the difference was 3°-5°. The mean RI was 37.9° SD 4.7 (95% CI 37.2° to 38.5°). The mean difference between the RI and effective OI was 11.5° SD 4.7 (95% CI 10.8° to 12.1°). Overall, 188 cups (94%) were within the inclination safe zone. When analysing the RI outliers, 1 could have be avoided if a better target OI was chosen and 2 could have been avoided if the difference between the target and effective OI would have been smaller. For the remaining 9 outliers (75%) the difference between the RI and effective OI was in the upper and lower 7. th. percentile, indicating more or less than average motion of the pelvis in these patients. Discussion and Conclusions. When using a digital protractor, the mean difference between the target OI and the effective OI of the acetabular component was less than 3° in 93% and less than 5° in all patients. The use of a digital protractor allows surgeons to accurately implant the acetabular component in the desired OI in a cheap and easy way. By adjusting the target OI based on the patient's hip circumference, 94% of the acetabular components were placed within an inclination safe zone of 30°-45°. Most outliers were caused by more of less than average intraoperative pelvic motion

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

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

Native anatomy of the arthritic hip is an important consideration in hip replacement surgery and implant design. Acetabular component orientation in total hip replacement (THR) is the single greatest factor that influences dislocation rate. Detailed knowledge regarding orientation of the native acetabulum is therefore essential. Native acetabular orientation in healthy hips is well documented but we could not find any papers detailing native acetabular orientation in the arthritic hip. A commercially available computer navigation system (Orthopilot BBraun Aesculap, Tuttlingen, Germany) was used to assess acetabular inclination and anteversion in 65 hips with symptomatic arthritis requiring THR. Acetabular inclination in all hips was also measured on pre op anteroposterior pelvic radiographs. Patients with DDH were excluded. All patients were Caucasian and had primary osteoarthritis, 29 males and 35 females. Average age 68(SD 8). Mean values as recorded by computer navigation were: inclination 51.4°(SD 7.1); anteversion 11.7°(SD 10.7). As recorded from radiographs mean acetabular inclination was 58.8°(SD 5.7). There was a difference between males and females. Mean navigated inclination: male 50.5°(SD 7.8); female 52.1°(SD 6.7). Mean navigated anteversion: male 8.3°(SD 8.7); female 14.39°(SD 11.6) Mean radiographic inclination: male 57.4°(SD 5.1) and female 59.8°(SD 6). Natural acetabular orientation in arthritic hips falls out with the safe zones defined by Lewinnek. When compared with healthy hips, as described in current literature, the arthritic hip appears to have a smaller angle of inclination and anteversion, by approximately 5° and 10° respectively, in both males and females. This is useful when positioning the cup during surgery. The difference between males and females, particularly in terms of anteversion, should also be considered