Mixed Reality has the potential to improve accuracy and reduce required dissection for the performance of peri-acetabular osteotomy. The current work assesses initial proof of concept of MR guidance for PAO. A PAO planning module, based on preoperative computed tomography (CT) imaging, allows for the planning of PAO cut planes and repositioning of the acetabular fragment. 3D files (holograms) of the cut planes and native and planned acetabulum positions are exported with the associated spatial information. The files are then displayed on mixed reality head mounted device (HoloLens2, Microsoft) following intraoperative registration using an FDA-cleared mixed reality application designed primary for hip arthroplasty (HipInsight). PAO was performed on both sides of a bone model (Pacific Research). The osteotomies and acetabular reposition were performed in accordance with the displayed holograms. Post-op CT imaging was performed for analysis. Cutting plane-accuracy was evaluated using a best-fit plane and 2D angles (°) between the planned and achieved supra (SA)- and retroacetabular (RA) osteotomy and retroacetabular and ischial osteotomies (IO) were measured. To evaluate the accuracy of acetabular reorientation, we digitized the acetabular rim and calculated the acetabular opening plane. Absolute errors of planned and achieved operative inclination and anteversion (°) of the acetabular fragment, as well as 3D lateral-center-edge (LCE) angles were calculated. The mean absolute difference between the planned and performed osteotomy angles was 3 ± 3°. The mean absolute error between planned and achieved operative anteversion and inclination was 1 ± 0° and 0 ± 0° respectively. Mean absolute error between planned and achieved 3D LCE angle was 0.5 ± 0.7°. Mixed-reality guidance for the performance of pelvic osteotomies and acetabular fragment reorientation was feasible and highly accurate. This solution may improve the current standard of care by enabling reliable and precise reproduction of the desired acetabular realignment.
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? 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 Aims
Methods
Hyaline cartilage has a low capacity for regeneration. Untreated osteochondral lesions of the femoral head can lead to progressive and symptomatic osteoarthritis of the hip. The purpose of this study is to analyze the clinical and radiological long-term outcome of patients treated with osteochondral autograft transfer. To our knowledge, this study represents a series of osteochondral autograft transfer of the hip with the longest follow-up. We retrospectively evaluated 11 hips in 11 patients who underwent osteochondral autograft transfer in our institution between 1996 and 2012. The mean age at the time of surgery was 28.6 years (8 to 45). Outcome measurement included standardized scores and conventional radiographs. Kaplan-Meier survival curve was used to determine the failure of the procedures, with conversion to total hip arthroplasty (THA) defined as the endpoint.Aims
Methods
To investigate whether anterior pelvic plane-pelvic tilt (APP-PT) is associated with distinct hip pathomorphologies, we asked: (1) Is there a difference in APP-PT between symptomatic young patients eligible for joint preservation surgery and an asymptomatic control group? (2) Does APP-PT vary between distinct acetabular and femoral pathomorphologies? (3) Does APP-PT differ in symptomatic hips based on demographic factors? IRB-approved, single-center, retrospective, case-control, comparative study in 388 symptomatic hips (357) patients (mean age 26 ± 2 years [range 23 to 29], 50% females) that presented to our tertiary center for joint preservation over a five year-period. Patients were allocated to 12 different morphologic subgroups. The overall study group was compared to a control group of 20 asymptomatic hips (20 patients). APP-PT was assessed in all patients based on AP pelvis X-rays using the validated HipRecon software. Values between overall and control group 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. Minimal clinically important difference (MCID) of APP-PT was defined as >1 standard deviation. No significant differences in APP-PT between the control group and overall group (1.1 ± 3.0° [−4.9 to 5.9] vs 1.8 ± 3.4° [−6.9 to 13.2], p = 0.323) were observed. Acetabular retroversion and overcoverage groups showed higher APP-PT compared to the control group (both p < 0.05) and were the only diagnoses with significant influence on APP-PT in the stepwise multiple regression analysis. However, all observed differences were below the MCID. Demographic factors age, gender, height, weight and BMI showed no influence on APP-PT. APP-PT across different hip pathomorphologies showed no clinically significant variation. It does not appear to be a relevant contributing factor in the evaluation of young patients eligible for hip preservation surgery.
Femoroacetabular impingement (FAI) patients report exacerbation of hip pain in deep flexion. However, the exact impingement location in deep flexion is unknown. The aim was to investigate impingement-free maximal flexion, impingement location, and if cam deformity causes hip impingement in flexion in FAI patients. A retrospective study involving 24 patients (37 hips) with FAI and femoral retroversion (femoral version (FV) < 5° per Murphy method) was performed. All patients were symptomatic (mean age 28 years (SD 9)) and had anterior hip/groin pain and a positive anterior impingement test. Cam- and pincer-type subgroups were analyzed. Patients were compared to an asymptomatic control group (26 hips). All patients underwent pelvic CT scans to generate personalized CT-based 3D models and validated software for patient-specific impingement simulation (equidistant method).Aims
Methods
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. Outcome of hip-preserving head reduction osteotomy combined with periacetabular osteotomy was good in one and moderate in the other up to three years after surgery; based on the pronounced hip destruction, the third received initially a total hip arthroplasty.Aims
Methods
The frequency of severe femoral retroversion is unclear in patients with femoroacetabular impingement (FAI). This study aimed to investigate mean femoral version (FV), the frequency of absolute femoral retroversion, and the combination of decreased FV and acetabular retroversion (AR) in symptomatic patients with FAI subtypes. A retrospective institutional review board-approved observational study was performed with 333 symptomatic patients (384 hips) with hip pain due to FAI evaluated for hip preservation surgery. Overall, 142 patients (165 hips) had cam-type FAI, while 118 patients (137 hips) had mixed-type FAI. The allocation to each subgroup was based on reference values calculated on anteroposterior radiographs. CT/MRI-based measurement of FV (Murphy method) and AV were retrospectively compared among five FAI subgroups. Frequency of decreased FV < 10°, severely decreased FV < 5°, and absolute femoral retroversion (FV < 0°) was analyzed.Aims
Methods
Femoral head necrosis in the context of high impact gymnastics of young adolescents is rare but seems a more serious complication compared to a Perthes like necrosis. Between 2017 and 2019, three young females aged from12 to 14 years were referred due incapacitating hip pain and severe collapsing femoral head necrosis. The indication of hip preserving surgery was based on the extent of the necrosis, presence of a vital lateral pillar and joint subluxation. In one of our 3 cases total head involvement made THR necessary, which was performed elsewhere. In the remaining 2 cases, head reduction osteotomy plus periacetabular osteotomy led to a good and a fair result. Repetitive impact between the main supplying vessels on the posterolateral femoral neck and the posterior acetabular wall in hyperextension/ external rotation could be the cause of severe femoral head necrosis in three adolescent female gymnasts we are reporting on. Supra-selective angiography or sonography may be helpful to improve indication. Targeted adaptation of training methods should be discussed. Due to the severe vascular insult, results have to be considered moderate.
The effect of pelvic tilt (PT) and sagittal balance in hips with pincer-type femoroacetabular impingement (FAI) with acetabular retroversion (AR) is controversial. It is unclear if patients with AR have a rotational abnormality of the iliac wing. Therefore, we asked: are parameters for sagittal balance, and is rotation of the iliac wing, different in patients with AR compared to a control group?; and is there a correlation between iliac rotation and acetabular version? A retrospective, review board-approved, controlled study was performed including 120 hips in 86 consecutive patients with symptomatic FAI or hip dysplasia. Pelvic CT scans were reviewed to calculate parameters for sagittal balance (pelvic incidence (PI), PT, and sacral slope), anterior pelvic plane angle, pelvic inclination, and external rotation of the iliac wing and were compared to a control group (48 hips). The 120 hips were allocated to the following groups: AR (41 hips), hip dysplasia (47 hips) and cam FAI with normal acetabular morphology (32 hips). Subgroups of total AR (15 hips) and high acetabular anteversion (20 hips) were analyzed. Statistical analysis was performed using analysis of variance with Bonferroni correction.Aims
Methods
Posterior extraarticular ischiofemoral hip impingement can be caused by high femoral torsion and is typically located between the ischium and the lesser trochanter. We asked if patients undergoing derotational femoral osteotomies for posterior FAI have (1) decreased hip pain and improved function and evaluated (2) subsequent surgeries and complications? Thirty-three hips undergoing derotational femoral osteotomies between 2005 and 2016 were evaluated retrospectively. Of them 15 hips underwent derotational femoral osteotomies and 18 hips underwent derotational femoral osteotomies combined with varisation (neck-shaft angle >139°). Indication for derotational osteotomies was a positive posterior impingement test in extension and external rotation, high femoral torsion (48° ± 9) on CT scans and limited external rotation. Offset improvement was performed to avoid intraarticular impingement in hips with a cam-type FAI. All patients were female and mean followup was 3 ± 2 (1 – 11) years. At latest followup the positive posterior and anterior impingement test decreased from preoperatively 100% to 5% (p< 0.001) and from preoperatively 85% to 30% (p< 0.001). The mean Merle d'Aubigné Postel score increased from 14 ± 1 (11 – 16) to 16 ± 1 (13 – 17) at latest followup (p< 0.001). At followup 32/33 hips had been preserved and one hip had been converted to a total hip arthroplasty (THA). In two hips (6%) revision osteosynthesis was performed for delayed healing of the femoral osteotomy. Derotational femoral osteotomies for the treatment of posterior extraarticular ischiofemoral impingement caused by high femoral torsion result in decreased hip pain and improved function at midterm followup but had 6% delayed healing rate requiring revision surgery.
To validate a small, easy to use and cost-effective augmented marker-based hybrid navigation system for peri-acetabular osteotomy [PAO] surgery. A cadaver study including 3 pelvises (6 hip joints) undergoing navigated PAO was performed. Inclination and anteversion of two navigation systems for PAO were compared during acetabular reorientation. The hybrid system consists of a tracking unit which is placed on the patient's pelvis and an augmented marker which is attached to the patient's acetabular fragment. The tracking unit sends a video stream of the augmented marker to the host computer. Simultaneously, the augmented marker sends orientation output from an integrated inertial measurement unit (IMU) to the host computer. The host computer then computes the pose of the augmented marker and uses it (if visible) to compute acetabular orientation. If the marker is not visible, the output from the IMU is used to update the orientation. The second system served as ground truth and is a previously developed and validated optical tracking-based navigation system.Purpose
Methods
Acetabular retroversion is an accepted cause of Pincer-type femoroacetabular impingement. There is increasing evidence that acetabular retroversion is rather a rotational abnormality of the pelvis than an overgrowth of the acetabular wall or even a dysplasia of the posterior wall. Initially, patients with a retroverted acetabulum were treated with an open rim trimming through a surgical hip dislocation (SHD) based on the early understanding of the pathomorphology. Theoretically, the reduction of the anterior wall can decrease the already small joint contact area in retroverted hips to a critical size. Based on the most recent literature, anteverting periacetabular osteotomy (PAO) seems to be the more appropriate surgical treatment. With this technique, the anterior impingement conflict can be treated efficiently without compromising the joint contact area. However, it is unknown whether this theoretical advantage in turn results in better mid term results of treatment. We asked if anteverting PAO results in better clinical and radiographical mid term results compared to rim trimming through a surgical hip dislocation.Introduction
Objectives
Torsional deformities are increasingly recognized as an additional factor in young patients with hip pain resulting from pincer- and cam-deformities. For example decreased femoral torsion can worsen an anterior Femoroacetabular impingement (FAI) conflict while an increased torsion can be beneficial with the same configuration. It is unknown how often torsional deformities are present in young patients presenting with hip pain that are eligible for joint preserving surgery. We questioned (1) what is the prevalence of a pathological femoral torsion in hips with FAI or hip dysplasia? (2) which hip disorders are associated with an abnormal torsion? An IRB-approved retrospective study of 463 consecutive symptomatic FAI patients (538 hips) and a MRI or CT scan on which femoral torsion could be measured was performed (‘study group'). Out of 915 MRI we excluded 377 hips. The study group was divided into 11 groups: Dysplasia (< 22° LCE), retroversion, anteverted hips, overcoverage (LCE angle 36–39°), severe overcoverage (LCE>39°), cam (>50° alpha angle), mixed FAI, varus- (<125° CCD angle), valgus- (>139° CCD), Perthes-hips and hips with no obvious pathology. The ‘control group' of normal hips consisted of 35 patients (35 hips) without radiographic signs of osteoarthritis or hip pain wich was used for a previous study. Femoral antetorsion was measured according to Tönnis et al. as the angle between the axis of the femoral neck and the posterior axis of the femoral condyles. Normal femoral torsion was defined by Tönnis et al. as angles 10–25° while decreased resp. increased torsion was defined as <5° and >25°. Statistical analysis was performed using analysis of variances (ANOVA).Introduction
Methods
Hips following in-situ pinning for slipped capital femoral epiphysis (SCFE) have an altered morphology of the proximal femur with cam type deformity. This deformity can result in femoroacetabular impingement and early joint degeneration. The modified Dunn procedure allows to reorientate the slipped epiphysis to restore hip morphology and function. To evaluate (1) hip pain and function, (2) 10-year survival rate and (3) subsequent surgeries and complications in hips undergoing modified Dunn procedure for SCFE.Introduction
Objectives
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. 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.Introduction
Objectives
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. 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.Introduction
Objectives
Delayed gadolinium enhanced MRI of cartilage (dGEMRIC) is a novel MRI-based technique with intravenous contrast agent that allows an objective quantification of biochemical cartilage properties. It enables a ‘monitoring' of the loss of cartilage glycosaminoglycan content which ultimately leads to osteoarthritis. Data regarding the longitudinal change of cartilage property after joint preserving hip surgery is sparse. We asked (1) if and how the dGEMRIC-index changes in patients undergoing open/arthroscopic treatment of femoroacetabular impingement (FAI) one year postoperatively compared to a control group of patients with non-operative treatment; (2) and if a change correlates with the clinical short term outcome. IRB-approved prospective comparative longitudinal study of two groups involving a total of 61 hips in 55 symptomatic patients with FAI. The ‘operative' group consisted of patients that underwent open/arthroscopic treatment of their pathomorphology. The ‘non-operative' group consisted of conservatively treated patients. Groups were comparable for preoperative radiographic arthritis (Tönnis score), preoperative HOOS- and WOMAC-scores and baseline dGEMRIC indices. All patients eligible for evaluation had preoperative radiographs and dGEMRIC scans at baseline and repeated dGEMRIC scans using the same scanner and protocol. (1) dGEMRIC indices of femoral and acetabular cartilage were assessed separately on the initial and follow-up dGEMRIC scans. Radial images were reformatted from a 3D T1 map for measurements. Regions of interest were placed manually peripherally and centrally within the cartilage based on anatomical landmarks at the 12 ‘hour' position of the clcok-face with the help of radial high-resolution PD-weighted MR images. (2) Patient-reported outcome was evaluated at baseline and at 1 year follow-up: Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and Hip disability and Osteoarthritis Outcome Score (HOOS). Statistical analysis included Student's t-Tests, Mann-Whitney U-tests and Wilcoxon signed-rank tests (p<0.05).Objectives
Methods
Since its first description in We determined the (1) cumulative 30-year survivorship of symptomatic patients treated with this procedure, determined the (2) clinical and (3) radiographic outcomes of the surviving hips, and (4) identified factors predicting the need for total hip arthroplasty (THA).Introduction
Objectives
Magnetic resonance imaging with intraarticular contrast (arthro-MRI) and radial cuts is the gold standard to quantify labral and chondral lesions in the setting of femoroacetabular impingement. To date, no study exists that has evaluated these findings as potential predictors of outcome for the long term follow-up after surgical treatment of FAI. The purpose of this study was to detect potential predictors for failure after surgical hip dislocation for FAI based on specific preoperative arthro-MRI of the hip at a minimum follow-up of 10 years.Introduction
Objectives
Labral refixation has established as a standard in open or arthroscopic treatment for femoroacetabular impingement (FAI). The rationale for this refixation is to maintain the important suction seal in the hip. To date, only few short-term results are available which indicate a superior result in FAI hips with labral refixation compared to labral resection. Scientific evidence of a beneficial effect of labral refixation in the long-term follow-up is lacking. Aim of this study was to evaluate if labral refixation can improve the cumulative 10-year survivorship in hips undergoing surgical hip dislocation for FAI compared to labral resection. We performed a retrospective comparative study of 59 patients treated with surgical hip dislocation for symptomatic FAI between December 1998 and January 2003. We analyzed two matched groups: The ‘resection’ group consisted of 25 hips that were treated consistently by excision of the damaged labrum. The ‘refixation’ group consisted of 34 hips that were treated with labral reattachment. Correction of the osseous deformity (rim trimming/femoral osteochondroplasty) did not differ between the two groups. We then evaluated the clinical (Merle d'Aubigné score) and radiographical results (according to Tönnis) at a follow-up of ten years. We calculated a cumulative Kaplan-Meier survivorship curve with the following factors as endpoints: conversion to total hip arthroplasty (THA), radiographic evidence of osteoarthritis progression, or a poor clinical result (defined as Merle d'Aubigné score of less than 15). The two curves were compared using the Log-rank test.Introduction & Objective
Methods
Torsional deformities of the femur have been recognized as a cause of femoroacetabular impingement (FAI) and hip pain. High femoral antetorsion can result in decreased external rotation and a posterior FAI, which is typically located extraarticular between the ischium and trochanter minor. Femoral osteotomies allow to correct torsional deformities to eliminate FAI. So far the mid-term clinical and radiographic results in patients undergoing femoral osteotomies for correction of torsional deformities have not been investigated. Therefore, we asked if patients undergoing femoral osteotomies for torsional deformities of the femur have (1) decreased hip pain and improved function and (2) subsequent surgeries and complications?Introduction
Objectives
Young patients have been reported to have a higher risk of revision following total hip arthroplasty than older cohorts. This was attributed to the higher activity level which led to increased wear, osteolysis, and component fracture. We prospectively assessed the clinical results, wear and osteolysis, the incidence of squeaking, and the survivorship of ceramic on ceramic THA in patients younger than 50 years (mean age of 42 [18–50] years). The series included 425 THAs in 370 patients with 368 hips followed for a minimum of 2 years (mean 7.1 years, range 2–14 years). All patients received uncemented acetabular components with flush-mounted acetabular liners using an 18 degree taper. No osteolysis was observed in any uncemented construct. There was osteolysis around one loose cemented femoral component. The survivorship for reoperation for implant revision was 96.7%. There were only two acetabular liner fractures (0.47%) and one femoral head fracture (0.24%). Two of the three fractures involved a fall from a significant height. There were no hip dislocations. Five patients (1.17%) noted rare or occasional squeaking. None had reproducible squeaking. In summary, the current study shows that ceramic-on-ceramic THAs in the young patient population are extremely reliable with a very low revision rate and an absence of wear-induced osteolysis. In addition, it shows that both bearing fracture in this young patient population typically occurs with polytrauma and squeaking issues that have been raised relative to ceramic bearings occur very rarely with the flush-mounted ceramic liner design used in this study.
Traumatic hip dislocation is a rare injury in orthopaedic practice and typically occures in high energy trauma. The goal of this study was to analyze hip morphology in patients with low energy traumatic hip dislocations and to compare it with a control group. We performed a retrospective comparative study. The study group included 45 patients with 45 traumatic posterior hip dislocation. Inclusion criteria were traumatic hip dislocation with simple acetabular rim or Pipkin I or II fracture. Traumatic dislocations combined with other acetabular or femoral fractures were excluded. The control group consisted of 90 patients (180 hips) that underwent radiographic examination for urogenital indication and had no history of hip pain. Hip morphology was assessed on antero-posterior and axial views. The study group showed significantly increased incidence (p<0.001) of positive cross-over sign (82% vs. 27%) with a increased retroversion index (26 ± 17 [0–56] vs. 6 ± 12 [0–53]), positive ischial spine sign (70% vs. 34%), and positive posterior wall sign (79% vs. 21). Hips that underwent an low energy posterior traumatic hip dislocation show significanly more radiographic signs for acetabular retroversion compared to a control group. Therefore, acetabular retroversion seems to be a contributing factor for posterior traumatic hip dislocation.
The Bernese Periacetabular Osteotomy (PAO) has become the established method for treating developmental dysplasia of the hip. In the 1990s, the surgical technique was modified to avoid postoperative cam impingement due to uncorrected head neck offset or pincer impingement due to acetabular retroversion after reorientation. The goal of the study was to compare the survivorship of two series of PAOs with and without the modifications of the surgical technique and to calculate predictive factors for a poor outcome. A retrospective, comparative study of two consecutive series of PAOs with a minimum follow-up of 10 years was carried out. Series A included 75 PAOs performed between 1984 and 1987 and represent the first cases of PAO. Series B included 90 hips that underwent PAO between 1997 and 2000. In this series, emphasis was put on an optimal acetabular version next to the correction of the lateral coverage. Additionally, a concomitant arthrotomy was performed in every hip to check impingement-free range of motion after reorientation and in 50 hips (56%) an additional offset correction was performed. Survivorship analyses according to Kaplan and Meier were carried out and the endpoint was defined as conversion to a total hip arthroplasty, progression of osteoarthritis, or a Merle d'Aubign score 14. Predictive factors for poor outcome were calculated using the Cox-regression analysis. The cumulative 10-year survivorship of Series A was significantly decreased (77%; 95%-confidence interval [CI] 72–82%) compared to Series B (86%; 95%-CI 82–89%, p=0.005). Hips with an aspherical head showed a significantly increased survivorship if a concomitant offset correction was performed intraoperatively (90% [95%-CI 86–94%] versus 77% [95%-CI 71–82%], p=0.003). Preoperative factors predicting poor outcome included a high age at surgery, a Merle d'Aubign score 14, a positive impingement test, a positive Trendelenburg sign, limp, an increased grade of osteoarthritis according to Tönnis, and (sub-) luxation of the femoral head (Severin > 3). In addition, predictive factors related to the three dimensional orientation of the acetabular fragment were identified. These included total, anterior, and posterior acetabular over-coverage or under-coverage, acetabular retroversion or excessive anteversion, a lateral center edge angle < 22 °, an acetabular index > 14 °, and no offset correction in aspherical femoral heads. A good long term result after PAO mainly depends on optimal three-dimensional orientation of the acetabulum and impingement-free range of motion with correction of an aspherical head neck junction if necessary.
Femoroacetabular impingement (FAI) is a pathologic condition of the hip that leads to osteoarthrosis. The goal of the surgical hip dislocation is to correct the bony malformations to prevent the progression of osteoarthrosis. We investigated the topographical cartilage thickness variation in patients with FAI and early stage osteoarthrosis using an ultrasonic probe during surgical hip dislocation. We performed a prospective case-series of 38 patients (41 hips) that underwent surgical hip dislocation. The mean age at operation was 30.6 (range, 18–48) years. Indication for surgery was symptomatic FAI with 4 hips (10%) with pincer-type, 7 hips (17%) with cam-type, and 20 hips (73%) with mixed-type of FAI. Cartilage thickness was measured intraoperatively using an A-mode 22 MHz ultrasonic probe at 8 locations on the acetabular cartilage. The thickest acetabular cartilage was found in the weight bearing zone (range 2.8–3.5mm), whereas the thinnest cartilage was in the posterior acetabular horn (1.0–2.2 mm). In all hips, cartilage was thicker in the periphery area compared to the central area. In the anterior and posterior acetabular horn, the anterior area, and the superior area (central parts) a significantly decreased cartilage thickness in pincer-type compared to cam-type of FAI was found (p<0.05). Cartilage thickness shows topographical differences in all types of FAI with pincer-type of FAI having generally thinner cartilage than cam-type FAI. This is the first study measuring in vivo cartilage thickness in the human hip.
The use of less invasive techniques for total hip arthroplasty (THA) has remained controversial with some studies showing a higher incidence of complications. The technique of performing total hip arthroplasty through a superior capsulotomy was developed to maximally preserve the soft tissue envelope surrounding the hip. The current study assesses the recovery and complications of hips replaced using conventional and tissue preserving techniques. 206 hips in 191 patients with a mean follow-up of 4.3 ± 1.0 (range, 3.2 – 5.9) years underwent total hip arthroplasty using the superior capsulotomy technique. The mean age at operation was 55.7 ± 12.9 (19 – 85) years and the operation was performed for 106 hips (51%) in men. The surgical technique involves exposing the superior hip joint capsule posterior to the medius and minimus, and anterior to the short external rotators. The femur is prepared with the femoral head in place and then the femoral head is excised without dislocation. These 206 hips were compared to a cohort of 279 hips replaced using the transgluteal exposure (control group). These 2 series were controlled for complexity and demographic factors. Recovery was evaluated using the Merle d'Aubigné score at 6 and 12 weeks postoperatively.Introduction
Methods
Total hip arthroplasty (THA) in patients with developmental dysplasia of the hip (DDH) has been associated with increased rates of complications and revision. Hip instability and wear-induced osteolysis are among the more common and serious of these problems. The current investigation prospectively assessed the survivorship and clinical results of patients with DDH treated by alumina ceramic-ceramic THA. We investigated 161 consecutive hips in 145 patients with DDH classified as Crowe type I (131 hips, 81%), II (26 hips, 16%), III (2 hips, 1%), and IV (2 hips, 1%). All patients had an uncemented titanium acetabular component with a flush mounted alumina ceramic-ceramic bearing. The mean age at operation was 48.0 ± 12.2 years (range, 18 – 79 years). The preoperative Merle d'Aubigné score was 11.4 ± 1.7 (6 – 15). 27 hips (17%) had at least one previous surgical procedure. 92 hips (57%) were replaced with the use of surgical navigation for acetabular component positioning. The mean cup diameter was 49.9 ± 3.4 mm (46 – 60 mm). 88 (55%) bearings were 28mm and 73 (45%) bearings were 32mm. At a mean follow-up of 6.1 ± 2.5 years (2 – 11.3 years), the mean Merle d'Aubigné score was 17.4 ± 0.9 (14 – 18). There were no cases of osteolysis or dislocation. There was one reoperation of an early displaced cup. In addition, there was one calcar crack that was cerclaged, one intraoperative trochanteric fracture also repaired at surgery. No patient complained of squeaking. 94 patients with 100 hips (61%) completed a questionnaire specifically asking for squeaking. None of these patients reported squeaking. The 10-year Kaplan Meier survivorship of the implants (revision of any component for any reason) was 99.4% (95% confidence interval 98.2-100%). Results of ceramic-ceramic THA in young patients with low to middle graded DDH after two to eleven years follow-up are promising with no radiographic signs of osteolysis or dislocation.
Patients who are less than 50 years old at the time of total hip arthroplasty (THA) have been known to have higher failure rates than patients who are older. Wearinduced osteolysis and associated component loosening is the most common mode of failure reported. The current investigation prospectively assessed the survivorship and clinical results of alumina ceramic-ceramic THA in patients younger than 50 years. 238 consecutive hips in 201 patients treated by alumina ceramic-ceramic THA were studied. The mean age at operation was 41.4 ± 7.5 years (range, 18 – 50 years). The preoperative Merle d’Aubigné score was 11.1 ± 1.6 (6 – 15). The preoperative diagnosis included primary osteoarthritis or impingement (105 hips, 44%), developmental dysplasia of the hip (90 hips, 38%), osteonecrosis of the femoral head (17 hips, 7%), post-traumatic osteoarthrosis (16 hips, 7%), and rheumatoid arthritis (6 hip, 3%). 144 hips (61%) were replaced with the use of surgical navigation for acetabular component positioning. The mean cup diameter was 51.8 ± 3.7 (range, 46 – 60 mm). 73 (31%) bearings were 28 mm and 165 (69%) bearings were 32 mm. At mean follow-up of 5.6 ± 2.3 years (2 – 11 years), the mean Merle d’Aubigné score was 17.4 ± 0.9 (14 – 18). There were no radiographic signs of osteolysis. There were two revisions (0.8%): one for acute cup displacement and one for a ceramic liner fracture. In addition, one hip was treated by I&
D for acute infection and another with I&
D but without evidence of infection. Other complications included one greater trochanter fracture and one calcar fracture, both repaired at surgery, and one transient peroneal nerve palsy. The 10-year Kaplan Meier survivorship of the implants (revision of any component for any reason) was 98.7% (95% confidence interval 96.3–100%). There were no hip dislocations. Results of THA in patients less than 50 years using alumina ceramic-ceramic bearings at two to eleven years follow-up are promising with no case of osteolysis or dislocation.
Acetabular component malpositioning increases the risk of impingement, dislocation, and wear. The goal of computer-assisted techniques is to improve the accuracy of component positioning, in particular optimizing the orientation of the acetabular cup. The goal of the current study was to measure accuracy of cup placement in a large clinical series of hips that underwent CT-based computer-assisted THA. 146 hips in 140 patients underwent CT-based computer-assisted THA between 2006 and 2008. In all cases cup orientation was planned according to the individual preoperative CT and the anterior pelvic plane with an inclination of 41° and anteversion of 30°. For the procedure, all patients were placed in the lateral position and the cup was implanted using angled instruments. Intra-operatively all cases were navigated using an optoelec-tronic camera and tracked instruments (Vector Vision prototype, BrainLab, Germany). Post-operatively, cup orientation was measured using a previously validated technique of 2D/3D-matching using the preoperative CT and post-operative radiographs. This technique allows for accurate measurement of cup position from plain radiographs corrected for individual pelvic orientation. The mean accuracy for inclination was −2.5° ± 4.0° (−12° – 10°) and for anteversion it was 0.7° ± 5.3° (−11° – 15°). In 2 hips (1.4%) a deviation of more then 10° in inclination and in 4 hips (2.7%) a deviation of more then 10° in anteversion were found. The current study demonstrates that the acetabular component can routinely be implanted with the assistance of CT-based navigation with reasonable agreement between the navigation measurements of component orientation at the time of surgery. Nonetheless, outliers still occasionally occur. These might be due to unrecognized loosening of the pelvic reference base, inaccurate registration or the use of the ipsilateral surface-based registration algorithms which rely heavily on points near the center of rotation of the hip.
Femoroacetabular impingement (FAI) is a pathologic condition of the hip joint that leads to hip pain and osteoarthrosis (OA), especially in the young and active patient population. It is characterized by an early pathologic contact during hip motion between osseous malformation of the femoral neck and acetabular rim. The goal of the surgical dislocation of the hip is to prevent the development of OA by correcting these malformations. We investigated the clinical and radiographic outcome, the survivorship, and factors predicting poor outcome at 5-year followup. We retrospectively evaluated 101 hips in 78 patients that underwent surgical hip dislocation at a mean age of 32 ± 8.4 (range, 15 – 52) years. The mean followup was 5.7 ± 1.0 (0.9 – 7.1) years. The series included pincer type impingement in 5 hips (5%), cam type in 9 hips (9%), and mixed type of FAI in 87 hips (87%). Pre-operatively, the patients presented with a mean Merle d’Aubigné score of 14.3 ± 3.3 (8 – 17) and a mean osteoarthrosis score according to Tönnis of 0.13 ± 0.34 (0 – 1). At followup, the clinical results were graded using the Merle d’Aubigné score and the radiographic results using the Tönnis score. Failure was defined as a conversion to a total hip arthroplasty (THA), a Merle d’Aubigné score of less than 15 or a progression of osteoarthrosis with a Tönnis score ≥2 at last followup. Demographic, clinical, radiographic, and surgical factors were tested for predictive factors for poor outcome using the Cox regression. At followup the mean Merle d’Aubigné score was 17.2 ± 1.2 (12 – 18) and the mean Tönnis score was 0.19 ± 0.47 (0 – 2). Failures (13 hips, 13%) included 6 hips (6%) with a progression of osteoarthrosis, 5 hips (5%) hips that converted to a THA, and 2 (2%) hips presenting with a Merle d’Aubigné score of less than 15. This resulted in a cumulative survivor ship at 5 years of 97.0 ± 3.3 % (95%-confidence interval, 93.6 – 100%). Factors predicting poor outcome were a preoperative Tönnis score of 1, a cartilage tear in the Arthro-MRI, and increased age or BMI at operation. Surgical hip dislocation has the potential to prevent the progression of osteoarthrosis and to decrease hip pain in patients with FAI. The optimal patient is young, with a decreased BMI and no sign of degeneration in the conventional radiograph or Arthro-MRI.
The ultimate goal of surgery for acetabular fractures is hip joint preservation for the rest of the patient’s life. However, besides Letournel’s series, long term survi-vorship in this predominantly young patient group has never been published in a very large series. The aim of this study was to determine the cumulative 20-year sur-vivorship of the hip after fixation of acetabular fractures and to identify factors predicting the need for total hip arthroplasty. A Kaplan-Meier survivorship analysis of 1218 consecutive surgically treated acetabular fractures was carried out. 816 fractures were available for analysis with a mean follow up of 10.3 years (range 2–29 years). All the surgeries were performed by a single surgeon in accordance to an established treatment protocol based on Letournel’s principles. Inclusion criteria were a minimum follow-up of two years or failure at any time. Failure was defined as conversion to total hip arthroplasty of hip arthrodesis. A Cox-regression analysis identified significant risk factors predicting the need for total hip arthroplasty. Analyzed parameters comprised data on patient history, preoperative clinical examination, associated injuries, fracture pattern, radiographic and intra-operative features, and the accuracy of reduction. The cumulative 20-years survivorship was 79% (95% CI, 76–81%). Statistically significant factors influencing the need for artificial hip replacement/arthrodesis were: age over 40 years (Hazard ratio [HR] 2.4), femoral head damage (HR 2.6), acetabular impaction (HR 1.5), postoperative incongruence of the acetabular roof (2.9), involvement of the posterior wall (HR 1.6), anterior dislocation (5.9), initial displacement >
20mm (HR 1.6), and a malreduction with residual displacement >
1mm (HR 3.0). There was a significantly different survivorship of the individual fracture types. The worst survivorship occurred in anterior wall fractures (34% at 20 years) and the best survivorship in both column fractures (87% at 20 years). The accuracy of reduction improved significantly over time. In summary, the hip joint can be successfully preserved and prosthetic replacement avoided in 79% of displaced acetabular fractures at 20 years. Many of the factors influencing the long term prognosis are already determined at the time of injury. The factors that can be influenced by the surgeon are anatomic reduction, achievement of congruency of the acetabular roof and correction of marginal impaction. The presented unique results even exceed Letournel’s series in size and follow up. Therefore, they provide benchmark data for any type of comparative evaluation studies dealing with surgical treatment of acetabular fractures in future.
The iliocapsularis muscle is a little known muscle that originates in part from the inferior border of the anterior-inferior iliac spine, but the main origin arises from an elongated attachment of the anteromedial hip capsule and inserts just distal to the lesser trochanter. Nevertheless, this muscle is an important landmark for exposure of the anteromedial hip capsule and psoas tendon interval during performance of the Bernese periacetabular osteotomy. Speculations about the function of this muscle as a tightener of the hip capsule and femoral head stabilisator have grown when an apparent hypertrophy of this muscle was encountered in patients with dysplasia of the hip. The aim of this study was to compare the morphology of the iliocapsularis muscle between patients with decreased (developmental dysplasia of the hip) and increased acetabular coverage (pincer-type of femoroac-etabular impingement) using Arthro-MRIs. Dysplasia of the hip (Group I) was defined as an LCE angle of less than 25° with a minimal acetabular index of 14° and pincer type of FAI (Group II) was defined as and LCE angle exceeding 39° on conventional radiographs. This resulted in 37 hips in Group I and 45 hips in Group II. The morphology of the iliocapsularis muscle was measured on axial slices of Arthro-MRIs. The parameters were muscle thickness, width and cross section at 4cm distal of the spina iliaca anterior inferior and also distal of the femoral head. Additionally, the volume of the muscle from its origins to the cross section distal of the femoral head was computed. All parameters were significantly increased in Group I compared to Group II (p<
0.05). In Group I the mean thickness was 20 ± 4.5 (range, 12 – 29) mm, width 25 ± 5.2 (range, 17 – 37), and cross section 281 ± 10.7 (range, 139 – 591) mm2 compared to Group II with a mean thickness of 17 ± 4.4 (range, 10 – 27) mm, width 22 ± 5.0 (range, 11 – 31), and cross section 235 ± 10.3 (range, 90 – 535) mm2. The muscle volume in Group I was 6.8 ± 2.9 (range, 2.2 – 13.0) cm3 compared to Group II with 8.7 ± 3.7 (range, 3.4 – 18.1) cm3. The results differed more when corrected for gender with the largest differences found for women. In hip dysplasia the anterior acetabular coverage is decreased. Because of the iliocapsularis muscle’s origination on the hip capsule, contrition of the muscle theoretically can tighten the anterior hip capsule, thus helping to stabilized the femoral head within the dysplastic acetabular. Although the true function of the iliocapsularis muscle remains unknown, constant use of this muscle in attempting to stabilize the femoral head in hip dysplasia theoretically would explain the apparent hypertrophy of this muscle.
Pelvic tilt is a characteristic feature of the individual patients’ posture. Large differences in pelvic tilt are well known among individuals, over time or related to activity. To our knowledge, it is unknown how patients with developmental dysplasia of the hip (DDH) behave in terms of pelvic tilt. One can assume that patients with a dysplastic acetabulum might compensate for their acetabular under coverage by functionally increasing pelvic tilt. Theoretically, this effect should be reversible when an acetabular redirection osteotomy is performed. We therefore hypothesized that pelvic tilt decreases after periacetabular osteotomy. Sixty-three consecutive patients (67 hips) with documented PAO at our institution were analyzed. 39 patients (40 hips) were excluded because of indications than other DDH (e.g. acetabular retroversion), incomplete radiographic documentation or insufficient follow-up leaving us 24 patients (27 hips) for evaluation. Preoperative, intraoperative (under general anesthesia), and at least 1 year postoperative anteroposterior radiographs were analysed. All x-rays were done in a standardized manner. Two distances were measured: the vertical/horizontal distance between the mid point of the sacrococcygeal joint and the symphysis. The change of these distances allows exact determination of the pelvic tilt. A significant decrease for pelvic tilt was found between the preoperative x-ray and the one after at least one year. Pelvic tilt did not change significantly between the pre- and the intraoperative x-ray, and between the intra- and follow-up x-ray. Our findings support the hypothesis that patients with DDH try to compensate for their insufficient acetabular coverage by increasing the tilt of their pelvis. After PAO, i.e. after iatrogenically increasing acetabular coverage, the patients’ pelvis significantly turns back in to less lordosis.
Since 1984, more than 1000 Bernese periacetabular osteotomies (PAO) have been performed for the treatment of developmental dysplasia of the hip (DDH) in adolescents and adults at the institution where this technique was developed. We present a concise 20-year follow-up of the first 75 PAOs whose initial and 10-year results had been published previously. A retrospective study of the first 75 consecutive hips (63 patients) treated with PAO for DDH between April 1984 and December 1987 was performed. The mean patient age at surgery was 29.3 years ± 11.4 (13 – 56) and in 31% of all hips a previous surgical attempt to achieve sufficient coverage had been performed. Preoperatively, 58% of all hips presented with osteoarthritis and 49% with dysplasia Class 4 or higher according to Severin. Four patients (5 hips) were lost-to-follow-up and 1 patient (2 hips) died unrelated to surgery. The remaining 58 patients (68 hips) were followed for a mean of 20.4 years ± 1.1 (18.8 – 22.9) and 41 hips (60%) were preserved at last follow-up. Regarding the surviving hips with preoperatively no or slight osteoarthritis (52 hips), the survivor ship rate was 75%. Twenty-seven hips were converted to a THA (26 hips) or hip arthrodesis (1 hip) which were defined as endpoints. The cumulative Kaplan-Meier survivorship at 20 years was 61%. The Cox regression analysis was performed to detect predictive factors for poor outcome and to calculate the corresponding hazard ratios. Six predictive factors for poor outcome were found: age over 30, a preoperative Merle d’Aubigné score less than 15, a positive preoperative anterior impingement test and limp, preoperative OA grade of more than 1, and a postoperative extrusion index of more than 20%. Despite the fact that this series represented the learning curve of a technically demanding intervention of a very inhomogeneous patient group with various previous surgical attempts to achieve sufficient coverage and several concomitant intertrochanteric osteotomies, the 20-year results on the first 75 hips are promising. Increased survivorship rates are expected for more recent series after identification of relative contraindications based on or analysis. PAO is an effective and successful surgical technique for correction of DDH.
The software is based on a spline-based multi-resolution 2D-3D image registration algorithm and a Markov random field theory based on similarity measurement. Based on a cone projection (imitating the path of the x-rays), the software is able to match the three-dimensional CT-based data set with the contours of the projected pelvis on the AP pelvic radiograph. This gives the possibility to correct the measured cup orientation (inclination and anteversion) by measuring it according to an anatomical defined coordinate system (anterior pelvic plane). The validation of the software consisted of accuracy, reproducibility and observer reliability measurements using cadaver and clinical data. For the cadaver validation 10 human pelves (20 hips) were used. From each pelvis 2 CT scans, one with and one without an inserted cup were acquired. The CT scan with the cup was used as the ground truth. With the cup inserted 4 AP pelvic radiographs with the pelvis in an unknown arbitrary position during acquisition were performed resulting in 80 measurements for accuracy. These measurements were performed by 2 observers at 2 different occasions resulting in a total of 320 measurements for reproducibility and observer reliability. The intraclass correlation coefficient (ICC) was used for quantification of reproducibility and observer reliability and the Bland-Altman analysis was used to detect systemic errors. The clinical validation included 33 patients with a pre- and a postoperative CT and 49 patients with only a postoperative CT in addition to the postoperative radiographs. In the cases with only a postoperative CT, for the 2D-3D matching the postoperative CT after manual excision of the cup from the CT slice sticks was used. In all cases the postoperative CT was used as the ground truth. For each patient all the available postoperative radiographs were used resulting in 236 measurements of accuracy. In the cadaver validation the cup orientation ranged from 34° – 57° for the inclination and from 1° – 24° for the anteversion measured on the CT. The accuracy showed a mean difference for the inclination of 0.9° ± 1.6° (−3.2° – 4.0°) and of 1.2 ± 2.4° (−5.3° – 5.6°) for the anteversion. The ICC for the reproducibility ranged from 0.96 to 0.99 and for the interobserver reliability from 0.95 to 0.98. No relevant systematic error was detected. In the clinical validation the cup orientation measured on the postoperative CT ranged for the inclination from 22° – 57° and for the anteversion from 7° – 35°. In the clinical setup the accuracy showed a mean difference for inclination of 1.8° ± 1.6° (−4.0° – 5.3°) and of −1.1° ± 2.9° (−5.9° – 5.7°) for the anteversion. The 2D-3D matching technique showed a good accuracy and a very good reproducibility and observer reliability. This technique allows to measure the exact cup orientation out of an AP pelvic radiograph with the help of a preoperative CT and to correct the parameters for the individual pelvic position. Therefore this software is a powerful tool to measure accuracy of CT-based computer-assisted cup placement in a large clinical series.
Traditional total hip arthroplasty (THA) using metal-on-polyethylene bearings has been established as a reliable procedure but wear and wear debris-associated osteolysis are among the most frequent reasons for revision. Ceramic-ceramic bearings represent an alternative for THA with improved wear characteristics and low biological reactivity of wear particles. We investigated the clinical outcome of alumina ceramic-ceramic THA in a series of more than 400 THAs. A total 418 alumina ceramic-ceramic THAs performed in 360 patients treated between 1997 and 2007 were studied prospectively. All patients had an uncemented titanium acetabular component with a flush mounted alumina ceramic-ceramic bearing (Wright Medical Technology, Inc. and Ceramtec AG). The mean age at operation was 51.7 ± 12.3 years (range, 18 – 79 years). 47 cases (11%) had previous hip surgery. The indication for surgery included primary osteoarthritis or impingement (58%), developmental dysplasia of the hip (32%), osteonecrosis of the femoral head (5%), post-traumatic osteoarthrosis (2%), and other indications (3%). In 202 (48%) a minimally invasive approach, the superior capsulotomy, was used with the help of the surgical navigation for acetabular component placement. There were no cases of osteolysis or wear. We found 7 (1.1%) implant revisions: 1 acute cup displacement, 1 acetabular liner fracture, 1 case with failure of osseointegration of the cup, and 4 trochanteric wafer nonunions. A dislocation of the hip was found in 2 (0.5%) cases. The 10-year Kaplan Meier survivorship of the implants (revision of any component for any reason) was 98.4% (95% confidence interval 97.1–100%). The results of alumina ceramic-ceramic THA after one to ten years are promising, especially considering the young age and high incidence of previous surgery in this patient population. The data are especially encouraging since no hip has demonstrated osteolysis. In particular, we are not aware of any other bearing that has shown an absence of lysis and 10 years follow-up. Since many of these patients are quite young, we await further assessment at 15 and 20 years.
An ample number of radiographic hip parameters on anteroposterior (AP) pelvic radiographs vary significantly with individual pelvic tilt and rotation. We developed specific computer software Hip2Norm to perform 3D analysis of the individual hip joint morphology using 2D AP pelvic radiographs. Twenty-five parameters can be calculated for a neutral orientation. The aim of the study was to evaluate the validity of this method for tilt and rotation correction of the acetabular rim and associated radiographic parameters. The validation comprised three steps:
External and internal validation; and intra-/interobserver analysis. A series of x-rays of 30 cadaver pelves were available for step 1 and 2. External validation comprised the comparison of radiographical parameters of the cadaver hips when determined with Hip2Norm in comparison with CT-based measurements or actual radiographs in a neutral pelvic orientation. Internal validation evaluated the consistency of the parameters when each single pelvis was calculated back from different random orientations to the same neutral pelvic position. The intra-/interob-server analysis investigated the reliability/reproducibility of all parameters with the help of 100 randomised, blinded radiographs of a consecutive patient series.
All but two parameters (acetabular index, ACE angle) showed a good to very correlation with the CT-measurements. Internal validity was good to very good for all parameters. There was a good to very good reliability and reproducibility of all parameters except five parameters. The software could be shown to be an accurate, reliable and reproducible method for correction of AP pelvic radiographs. This computer-assisted method allows standardised evaluation of all relevant radiographic parameters for detection of anatomic morphologic differences. It will be used to study the influence of pelvic malorientation on the radiographic appearance of each individual parameter and the clinical significance of standardising pelvic parameters.
We developed fast and easy-to-use computer software to perform three-dimensional (3D) analysis of the individual hip joint morphology using two-dimensional (2D) AP pelvic radiographs. Landmarks extracted from the radiograph were combined with a cone beam x-ray projection model and a strong lateral pelvic radiograph to reconstruct 3D hip joints. Twenty-five parameters including quantification of femoral head coverage can be calculated for a neutral orientation. The aim of the study was to evaluate the validity of this method for tilt and rotation correction of the acetabular rim and associated radiographic parameters.
External validation; internal validation; and intra-/interobserver analysis. A series of x-rays of 30 cadaver pelves mounted on a flexible holding device were available for step 1 and 2. External validation comprised the comparison of radiographical parameters of the cadaver hips when determined with our software in comparison with CT-based measurements or actual radiographs in a neutral pelvic orientation as gold standard. Internal validation evaluated the consistency of the parameters when each single pelvis was calculated back from different random orientations to the same neutral pelvic position. The intra-/interobserver analysis investigated the reliability and reproducibility of all parameters with the help of 100 randomized, blinded AP pelvic radiographs of a consecutive patient series.
All but one parameter (acetabular index) showed a substantial to almost perfect correlation with the CT-measurements. Internal validity was substantial to almost perfect for all parameters. There was a substantial to almost perfect reliability and reproducibility of all parameters except the acetabular index.