EP278 Kinematics of the Pre-Operative Dysplastic Hip Measured Using Dynamic Biplane Radiography

Evaluation of Bernese periacetabular osteotomy

Objectives:Hip muscle function is affected by surgical intervention and is of particular concern when considering post-operative rehabilitation of the joint1. However, little is known about the dynamic, in vivo function of the hip muscles during activities of daily living. Marker-based motion capture studies have associated dysplastic hip anatomy with shorter abductor moment arm lengths during walking2, but these measurements are complicated by soft tissue artifact3. Biplane radiography is a highly accurate technique for measuring in vivo bone motion of the hip4 and has recently been utilized to estimate dynamic muscle moment arms, which are important factors influencing force and torque capabilities. Previous research studies utilizing biplane radiography have identified shorter muscle lengths and moment arms in the implanted hip compared to the contralateral hip of individuals with total hip arthroplasty during the double support phase of gait2, but normative in vivo moment arms of the hip musculature in asymptomatic individuals have yet to be established. Further, it remains unknown how moment arms change between activities of daily living, particularly during deep flexion activities that challenge hip stability. Developing a normative dataset of dynamic in vivo moment arm lengths would provide a valuable reference for clinicians and physical therapists developing rehabilitation protocols to strengthen the hip musculature and increase stability. The objective of this study was to determine in vivo moment arms of the hip abductors, adductors, and external rotators during gait and squatting in a cohort of asymptomatic adults. We hypothesized that the maximum moment arm length during squatting would be longer than during walking and static standing.Methods:Young adults with no history of hip surgery, chronic hip pathology, or severe lower extremity musculoskeletal injury were recruited to participate in this IRB-approved study. Participants performed bodyweight squats and treadmill walking within a biplane radiography system while ground reaction forces were collected at 1000 Hz from a dual-belt instrumented treadmill. The support phase of gait was defined by vertical ground reaction forces over 50 N. Synchronized biplane radiographs were collected at 50 images per second to image three trials of each hip for each activity. Subject-specific bone models of the pelvis and proximal femur were created from computed tomography (CT) scans (average 0.37x0.3 mm in-plane resolution, 0.625mm slice thickness). Coordinate systems5 and muscle origin and insertion points for the gluteus medius (hip abductor), gluteus minimus (hip abductor), pectineus (hip adductor), and grouped external rotators1 were identified based upon bony landmarks on the 3D bone models (Figure 1). In-vivo bone motion during each activity was determined by matching digitally reconstructed radiographs, created from the CT-based bone models, to the biplane radiographs using a registration process with a validated accuracy4 of 0.3mm. The line of action for each muscle segment was determined for each frame of the biplane radiographs as the vector from the muscle origin to the insertion. Moment arm length (MAL) was calculated for each frame of the dynamic biplane radiographs as the perpendicular distance between the hip joint center (acetabulum center) and the line of action of each muscle1 and interpolated to gait cycle for walking or percent maximum hip flexion during squatting. Differences between the maximum MAL during static standing, walking, and squatting were assessed within each muscle group using ANOVA with post-hoc pairwise comparisons performed as necessary.Results:Data from 186 trials of 43 hips from 22 individuals were included in the analysis (9M, 13F; mean age 22.0±2.2years; BMI 21.3±5.2kg/m2). Average walking velocity was 1.0±0.2m/s and the average maximum hip flexion during squatting was 101.6±16.1°. Average static standing MAL was greatest in the gluteus medius and smallest in the pectineus (Table 1). Maximum MAL was significantly different between all activities for all muscle groups (all p<0.001) (Table 1, Figure 2). Contrary to our hypothesis, moment arms of the abductors were smaller during squatting compared to other motions.Conclusions:This study demonstrates the in vivo torque generating capabilities of muscles surrounding the hip (reflected by their moment arm) change considerably from the standing position to positions encountered during active functional motions. Muscles involved in hip abduction and stabilization have less mechanical advantage at greater hip flexion, highlighting the importance of strengthening these muscle groups during rehabilitation. Specifically, moment arms of the hip abductors and external rotators are shorter during walking and squatting compared to standing, while moment arms of the adductors are shorter during walking and greater during squatting and standing. Knowledge of these postural changes in mechanical advantage can be useful when designing targeted rehabilitation protocols to strengthen the hip musculature and improve stability. Further research into relationships between dynamic in vivo hip muscle moment arms and lengths will yield additional insight into force and torque generating capacity of muscles during activities of daily living. These results are limited to treadmill walking and bodyweight squatting in asymptomatic young adults.

Residual developmental dysplasia of hip (RDDH) is a factor of early osteoarthritis of the hip. The main problems are pain and instability of the hip joint due to inadequate coverage of the femoral head by the acetabulum. The purpose of this study was to radiologically evaluate RDDH after Bernese periacetabular osteotomy (PAO) and to compare RDDH to healthy hips. The radiological parameters of RDDH treated by PAO were retrospectively evaluated. Digital AP pelvic radiographs were taken, including parameters of central edge angle and femoral head coverage, medialization, distalization, and ilio-ischial angle. Clinical assessment is based on the VAS scale. The study group consisted of patients with RDDH, and the control group consisted of patients without RDDH. After PAO radiological parameters decreased: medialization by 2.68mm, distalization by 3.65mm, and ilio-ischial angle by 2.62°. However, there was an increase in the parameters: CEA by 17.61° and FHC by 16.46%. There was a mean 3 point decrease in pain on the VAS scale. There was also a statistically significant radiological difference in the structure of dysplastic hip joints before surgery and healthy hip joints of the control group. Radiological studies confirmed the effectiveness of the PAO method in the treatment of RDDH. Based on all radiological parameters, differences between healthy and dysplastic hip joints were demonstrated. We believe that a thorough understanding of the values of radiological parameters used to describe dysplastic hip joints will allow us to improve the imaging diagnosis of this condition.

The purpose of this study was to use computational modeling to determine if surgical correction of hip dysplasia restores hip contact mechanics to those of asymptomatic, radiographically normal hips. Discrete element analysis (DEA) was used to compute joint contact stresses during the stance phase of normal walking gait for 10 individuals with radiographically normal, asymptomatic hips and 10 age- and weight-matched patients with acetabular dysplasia who underwent periacetabular osteotomy (PAO). Mean and peak contact stresses were higher (p < 0.001 and p = 0.036, respectively) in the dysplastic hips than in the matched normal hips. PAO normalised standard radiographic measurements and medialised the location of computed contact stress within the joint. Mean contact stress computed in dysplastic hips throughout the stance phase of gait (median 5.5 MPa, [IQR 3.9-6.1 MPa]) did not significantly decrease after PAO (3.7 MPa, [IQR 3.2-4.8]; p = 0.109) and remained significantly (p < 0.001) elevated compared to radiographically normal hips (2.4 MPa, [IQR 2.2-2.8 MPa]). Peak contact stress demonstrated a similar trend. Joint contact area during the stance phase of gait in the dysplastic hips increased significantly (p = 0.036) after PAO from 395 mm2 (IQR 378-496 mm2) to 595 mm2 (IQR 474-660 mm2), but remained significantly smaller (p = 0.001) than that for radiographically normal hips (median 1120 mm2, IQR 853-1444 mm2). While contact mechanics in dysplastic hips more closely resembled those of normal hips after PAO, the elevated contact stresses and smaller contact areas remaining after PAO indicate ongoing mechanical abnormalities should be expected even after radiographically successful surgical correction.

Hip dysplasia is a three-dimensional pathomechanical condition that is often more complex than the standard method of measuring lateral center edge angle (CEA) can quantify. Yet there is a paucity of literature examining the differences in version seen between dysplastic and non-dysplastic femoroacetabular impingement (FAI) hips, the relationship of acetabular and femoral version (FV) within dysplastic hips and the contribution of each of these factors to symptoms and outcomes of dysplasia treatment. We sought to describe the acetabular version (AcetV) and FV in dysplastic hips and quantify how these measurements compared with non-dysplastic FAI hips. We also sought to analyze the association of these factors with patient-reported outcomes (PROs) after periacetabular osteotomy (PAO) and determine the need for subsequent femoral derotational osteotomy after PAO. A total of 113 dysplastic patients who underwent PAO (92% female, mean age 24) were compared with 1332 (45% female, mean age 25) non-dysplastic FAI (CEA > 25°) patients. We found that dysplastic hips had a statistically higher AcetV and FV than non-dysplastic FAI hips. There was a very weak correlation between AcetV and FV in dysplastic hips, suggesting that patients with higher AcetV did not necessarily have higher FV. There was no association with AcetV or FV and patient outcomes in our very limited analysis of PROs after PAO, and only 5% of patients with excessive FV (>20°) required subsequent femoral derotational osteotomy, suggesting that in a majority of patients with hip dysplasia, FV may not impact the post-operative clinical course.

Dynamic hip kinematics before and after periacetabular osteotomy in patients with dysplasia

Residual acetabular dysplasia is seen in combination with femoral pathomorphologies including an aspherical femoral head and valgus neck-shaft angle with high antetorsion. It is unclear how these femoral pathomorphologies affect range of motion (ROM) and impingement zones after periacetabular osteotomy. (1) Does periacetabular osteotomy (PAO) restore the typically excessive ROM in dysplastic hips compared with normal hips; (2) how do impingement locations differ in dysplastic hips before and after PAO compared with normal hips; (3) does a concomitant cam-type morphology adversely affect internal rotation; and (4) does a concomitant varus-derotation intertrochanteric osteotomy (IO) affect external rotation? Between January 1999 and March 2002, we performed 200 PAOs for dysplasia; of those, 27 hips (14%) met prespecified study inclusion criteria, including availability of a pre- and postoperative CT scan that included the hip and the distal femur. In general, we obtained those scans to evaluate the pre- and postoperative acetabular and femoral morphology, the degree of acetabular reorientation, and healing of the osteotomies. Three-dimensional surface models based on CT scans of 27 hips before and after PAO and 19 normal hips were created. Normal hips were obtained from a population of CT-based computer-assisted THAs using the contralateral hip after exclusion of symptomatic hips or hips with abnormal radiographic anatomy. Using validated and computerized methods, we then determined ROM (flexion/extension, internal- [IR]/external rotation [ER], adduction/abduction) and two motion patterns including the anterior (IR in flexion) and posterior (ER in extension) impingement tests. The computed impingement locations were assigned to anatomical locations of the pelvis and the femur. ROM was calculated separately for hips with (n = 13) and without (n = 14) a cam-type morphology and PAOs with (n = 9) and without (n = 18) a concomitant IO. A post hoc power analysis based on the primary research question with an alpha of 0.05 and a beta error of 0.20 revealed a minimal detectable difference of 4.6° of flexion. After PAO, flexion, IR, and adduction/abduction did not differ from the nondysplastic control hips with the numbers available (p ranging from 0.061 to 0.867). Extension was decreased (19° ± 15°; range, -18° to 30° versus 28° ± 3°; range, 19°-30°; p = 0.017) and ER in 0° flexion was increased (25° ± 18°; range, -10° to 41° versus 38° ± 7°; range, 17°-41°; p = 0.002). Dysplastic hips had a higher prevalence of extraarticular impingement at the anteroinferior iliac spine compared with normal hips (48% [13 of 27 hips] versus 5% [one of 19 hips], p = 0.002). A PAO increased the prevalence of impingement for the femoral head from 30% (eight of 27 hips) preoperatively to 59% (16 of 27 hips) postoperatively (p = 0.027). IR in flexion was decreased in hips with a cam-type deformity compared with those with a spherical femoral head (p values from 0.002 to 0.047 for 95°-120° of flexion). A concomitant IO led to a normalization of ER in extension (eg, 37° ± 7° [range, 21°-41°] of ER in 0° of flexion in hips with concomitant IO compared with 38° ± 7° [range, 17°-41°] in nondysplastic control hips; p = 0.777). Using computer simulation of hip ROM, we could show that the PAO has the potential to restore the typically excessive ROM in dysplastic hips. However, a PAO can increase the prevalence of secondary intraarticular impingement of the aspherical femoral head and extraarticular impingement of the anteroinferior iliac spines in flexion and internal rotation. A cam-type morphology can result in anterior impingement with restriction of IR. Additionally, a valgus hip with high antetorsion can result in posterior impingement with decreased ER in extension, which can be normalized with a varus derotation IO of the femur. However, indication of an additional IO needs to be weighed against its inherent morbidity and possible complications. The results are based on a limited number of hips with a pre- and postoperative CT scan after PAO. Future prospective studies are needed to verify the current results based on computer simulation and to test their clinical importance.

Pain and quality of life are impaired in adults with hip dysplasia undergoing periacetabular osteotomy: a systematic review and meta-analysis

ABSTRACTThis study investigated the relationship between three‐dimensional (3D) acetabular coverage and contact mechanics in dysplastic and ostensibly normal hips. Fifty asymptomatic hips previously imaged with CT scans/angiograms were matched on a 2:1 basis to 25 dysplastic hips with previous CT imaging, based on age, gender, weight, and BMI. CT imaging was used to create 3D patient‐specific hip models from which the 3D coverage metrics of subchondral arc angle (i.e., acetabular weight‐bearing morphology) and hip joint coverage angle (i.e., femoral head coverage), and the congruity metrics of acetabular sphericity index SI (i.e., sphericity of the acetabulum) and joint congruity index CI were assessed globally and in five octants spanning the weight‐bearing acetabulum. Discrete element analysis was used to calculate hip contact mechanics, with results assessed globally and subdivided into the same five octants. Increasing superior‐anterior subchondral arc angle was associated with increasing superior‐anterior mean chronic contact stress‐time exposure in dysplastic hips, which was significantly (p < 0.001) different from asymptomatic hips where increasing superior‐anterior subchondral arc angle was associated with decreasing superior‐anterior mean chronic contact stress‐time exposure. Similarly, increasing joint congruity CI anteriorly was associated with increasing anterior mean chronic contact stress‐time exposure in dysplastic hips, which was significantly (p = 0.003) different from the trend of decreasing anterior mean exposure with increasing anterior CI in asymptomatic hips. These results indicate fundamental differences in how contact mechanics in asymptomatic and dysplastic hips respond to differences in acetabular coverage and joint congruity, suggesting that asymptomatic hips follow the expected geometry‐based trend, while dysplastic hips do not.

Hip dysplasia is characterized by an excessively oblique and shallow acetabulum with insufficient coverage of the femoral head. It is a known cause of pain and the development of early osteoarthritis in young adults. The periacetabular osteotomy is the joint-preserving treatment of choice in young adults with symptomatic hip dysplasia. The surgical aim of this extensive procedure is to reorient the acetabulum to improve coverage and eliminate the pathological hip joint mechanics. Intraoperative assessment of the achieved acetabular reorientation is therefore crucial. The "classic" surgical approaches for the periacetabular osteotomy inflict extensive trauma to the tissues and some involve detachment of muscles. The type of surgical approach may affect the occurrence of complications, duration of surgery, intraoperative blood loss, transfusion requirements, and length of hospital stay. The aims of the PhD thesis were I) to assess the outcome of a new, minimally invasive transsartorial approach for periacetabular osteotomy; II) to compare the minimally invasive approach with the previously used "classic" ilioinguinal approach; and III) to assess the reliability of a novel device for intraoperative assessment of the achieved acetabular reorientation. Three studies underly this PhD thesis. In studies I and II, the experience with the minimally invasive and ilioinguinal approaches was retrospectively assessed by database inquiry and evaluation of radiographic material. Data regarding patient demographics, patient history, intraoperative measures and complications was recorded in a validated database. Center-edge and acetabular index angles were measured in preoperative and postoperative pelvic radiographs to assess preoperative dysplasia and the achieved acetabular reorientation. The well-defined study groups consisted of 94 and 263 periacetabular osteotomies in studies I and II, respectively. In study III, intraoperative angle measurements were carried out prospectively in 35 periacetabular osteotomies. The obtained measures (center-edge and acetabular index angles) were compared with those of postoperative pelvic radiographs. Furthermore, a cadaver study was conducted to evaluate intra- and interobserver variability of the device and to assess whether pelvic positioning influenced the variability of measurements. The applied methodology was critically reviewed. Study I--The minimally invasive approach had the following outcome. The mean duration of surgery was 73 min and the median intraoperative blood loss was 250 ml. Blood transfusion was required following 3% of the procedures. There were no cases of moderate or severe technical and neurovascular complications, and the achieved center-edge and acetabular index angles suggest that optimal reorientation can be achieved. Hip joint survival with total hip arthroplasty as the end point was 98% at 4.3 years. Study II--When compared with the outcome of the ilioinguinal approach, the procedures performed by using the minimally invasive approach had a statistically significant shorter duration of surgery, less intraoperative blood loss and hemoglobin reduction, and fewer transfusion requirements. The achieved reorientation was comparable between groups. There were no cases of moderate or severe complications in the minimally invasive group and three cases (3%) of arterial thrombosis in the ilioinguinal group. At follow-up 4.9 years after hip joint surgery, survival rates were 97% in the minimally invasive group and 93% in the ilioinguinal group. Study III--Intraoperatively obtained angle measures differed less than +/- 5 degrees from measurements on postoperative pelvic radiographs, and the intra- and interobserver variability of the device was confined well within +/-5 degrees. Positioning did not influence the variation of angle measurements beyond intraobserver variability of the device. The new minimally invasive transsartorial approach appears to be a safe technique, allowing optimal acetabular reorientation, and seems to minimize tissue trauma. In addition, short-term hip joint survival rate is encouraging. The outcome compares favorably with that of the ilioinguinal approach, and the results support continued use of the minimally invasive approach for periacetabular osteotomy. Optimal reorientation of the acetabulum is crucial in periacetabular osteotomy. The novel measuring device is a potentially helpful tool for intraoperative assessment of center-edge and acetabular index angels. It is simple to use and facilitates repeated reliable angle measurements during acetabular reorientation, making intraoperative radiographs unnecessary. The new, minimally invasive approach and the novel measuring device represent important surgical advances in contemporary periacetabular osteotomy.

Objectives: Developmental dysplasia of the hip (DDH) is a condition in which the hypoplastic acetabulum provides inadequate coverage of the femoral head. This abnormal coverage, while pathological, may be advantageous in some sporting and recreational activities needing significant hip range of motion (ROM), including dance, ballet, and performing arts. Although DDH allows patients to perform activities requiring supraphysiologic hip motion, subluxation of the hip joint generates excessive articular stresses, leading ultimately to pain, osteoarthritis (OA), and total joint arthroplasty. In some DDH patients, this degenerative pathway can be interrupted by performing a periacetabular osteotomy (PAO) to reorient the acetabular fragment, which increases femoral head coverage and reduces intra-articular stresses. This improved coverage is believed to come at the sacrifice of range of motion, particularly noticed while performing high-demand activities requiring supraphysiologic end-range motion. This study addresses the questions: 1. Does a PAO reduce the range of motion of the hip enough to reduce a patient’s ability to perform daily living, recreational and sporting activities? 2. If so, what activities are most impacted by these changes? Methods: We created an inventory of daily living, recreational and sporting activities commonly performed by patients with hip dysplasia. A systematic review of the literature provided the maximum hip range of motion required (required ROM) to perform eight activities of daily living (ADL) and thirteen sporting movements. The concurrent peak value for each anatomic component of hip motion, (i.e flexion/extension; adduction/abduction; internal/external rotation) was classified for every activity in terms of physiologic demand relative to the average ROM of the adult hip. Based on these values, we created a 7-level ordinal scale according to the peak kinematic demand required to perform each activity (Table 1), ranging from low to extreme difficulty. To examine the impact of a PAO on the limits of hip motion, we selected, with IRB approval, a cohort of 24 dysplastic hips (12 left and 12 right). Patient-specific 3D models of each pelvis and hip joint were created from preoperative CT scans, and each activity in our hip inventory was simulated using a custom Matlab hip simulation routine. For each activity, the ROM of the hip was recorded as the point at which either bony impingement was detected, or the specified movement was successfully completed. The percentage of the required motion successfully completed (percent function) was then calculated (100*measured ROM/required ROM) for each movement. This procedure was repeated on the same hips after completion of a computer-simulated PAO according to the technique described by Ganz and colleagues in which the LCEA was increased to 35° and reoriented anteriorly to appropriately restore head coverage. Wilcoxon Signed Rank tests were performed to compare preoperative and postoperative percent function for each movement. Results: When all activities were combined, there was no significant difference (p &gt; 0.05) between preoperative function (99.2 ± 0.6%) and postoperative function (98.0 ± 1.1%). The flexion portions of the right and left grand écart latéral, commonly used ballet movements, were the only activities where percent function was significantly decreased after PAO. Before surgery, the left hips performed 96.8 ± 1.8% of the motion required for the left grand écart latéral whereas after surgery hip function decreased to 82.5 ± 7.6% (p &lt; 0.05). Preoperatively, the right hips performed the right grand écart latéral at 96.7 ± 3.3% compared to 77.4 ± 8.3% postoperatively (p &lt; 0.05). There were no significant differences between preoperative and postoperative function for any other activities within the hip inventory. Conclusions: After testing a broad range of movements found in both daily life and sporting and recreational activities, just two of the twenty-one activities were significantly impaired after a computer-simulated PAO. A lack of significant change in percent function for most movements between preoperative and postoperative hips indicates that even high performing patients who undergo a PAO can expect little to no change in their ability to perform many of the activities they enjoyed before surgery. A significant change, however, was seen in the ballet positions right and left grand écart latéral and patients requiring performance of these activities after PAO should be counseled preoperatively regarding the demands of their sporting and recreational activities and their postoperative expectations. [Figure: see text]

Objectives: The management of borderline hip dysplasia (BHD) remains an area of interest in the field of hip preservation. The purpose of this study was to (1) evaluate mean 2-year outcomes for patients with BHD treated with staged hip arthroscopy and periacetabular osteotomy (PAO) to those who underwent hip arthroscopy alone, and (2) evaluate rates of complications, hardware removal, reoperations, conversions to total hip arthroplasty (THA), along with conversions to PAO. Methods: Hips with a lateral center-edge angle (LCEA) values 18° ≤ LCEA &lt; 25° that underwent a hip arthroscopy for femoroacetabular impingement syndrome (FAIS) between January 2018 and June 2022 were reviewed. Patients who underwent staged periacetabular osteotomy and hip arthroscopy were identified. Staged hips were propensity-matched 1:4 to other borderline dysplastic hips that underwent hip arthroscopy alone. Matching was performed based on age, sex, and body-mass index (BMI). Patient-reported outcomes (PROs) were collected, including Hip Outcome Score – Activities of Daily Living (HOS-ADL), HOS-Sports Specific (HOS-SS) subscale, 12-item International Hip Outcome Tool (iHOT-12) questionnaire, Patient-Reported Outcomes Measurement Information System-Pain Interference (PROMIS-PI) subscale, and PROMIS-Physical Function (PROMIS-PF) subscale. Cohort-specific minimal clinically important difference (MCID) and Patient Acceptable Symptom State (PASS) thresholds were calculated. Postoperative PROs, rates of MCID/PASS achievement, and rates of reoperation and conversion to THA were compared. Results: Twenty-four patients who underwent staged hip arthroscopy and PAO were successfully matched to 96 patients who underwent hip arthroscopy alone. Both groups were similar in terms of age, sex, and BMI. The patients who underwent a PAO had smaller LCEAs and larger Tönnis angles (21.0° vs. 23° and 11.6° vs. 9.1°, respectively). Both groups demonstrated significant improvement in PROs at minimum 1-year postoperatively (p &lt; 0.001, for all). There were no significant differences in postoperative PRO scores between the groups (p ≥ 0.223, for all). There were no significant differences in MCID/PASS achievement (p ≥ 0.224. for all). There were no reoperations or conversion to THA in the staged hip arthroscopy and PAO group. In the hip arthroscopy alone cohort, reoperation rates were 5.2% and conversion to THA occurred in 1% of the patients. There were no significant differences in secondary surgery rates between the groups (p = 1.000). Three patients in the hip arthroscopy alone group ultimately underwent PAO, 1 underwent a proximal femoral osteotomy (PFO), and one underwent a revision hip arthroscopy. These female patients were young and athletic with an LCEA &lt; 20°. Conclusions: Patients undergoing staged PAO and hip arthroplasty and isolated hip arthroplasty for treatment of BHD demonstrate similar clinical improvement. Rates of revision surgery and conversion to THA were similarly low. A small subset of patients who were initially treated arthroscopically ultimately received a PAO. This group was entirely made up of young, athletic female patients. This is encouraging early data and more long-term data is needed to evaluate the differences in survivorship. [Figure: see text]

Any abnormal structures that contribute to the narrowing of the ischiofemoral space could induce ischiofemoral impingement. Bernese periacetabular osteotomy (PAO) medializes the hip center and, therefore, decreases contact stress on the cartilage in developmental dysplasia of the hip (DDH). However, medialization of the hip center might also narrow the ischiofemoral space, which may increase the risk of postoperative ischiofemoral impingement in patients with acetabular dysplasia who are undergoing PAO. Furthermore, the dysplastic hip has less ischiofemoral space and less space for the quadratus femoris. A few studies have focused on the amount of medialization of the hip center, but the proportion of postoperative ischiofemoral impingement after PAO has not been investigated. (1) What proportion of patients develop ischiofemoral impingement after undergoing unilateral PAO for DDH? (2) What radiographic factors are associated with postoperative ischiofemoral impingement in patients who underwent PAO for DDH? (3) How much hip center medialization is safe so as to avoid postoperative ischiofemoral impingement during PAO? Between 2014 and 2016, we treated 265 adult patients who had symptomatic residual acetabular dysplasia (lateral center-edge angle less than 20°) using PAO. During that time, we generally offered PAO to patients with acetabular dysplasia when the patients had no advanced osteoarthritis (Tönnis grade < 2). Of those, we considered only patients who underwent primary PAO without femoral osteotomy as potentially eligible. Based on that, 65% (173 of 265) were eligible; a further 9% (24 of 265) were excluded due to leg length discrepancy, spine disorders, or joint replacement in the contralateral side, and another 6% (17 of 265) of patients were lost before the minimum study follow-up of 2 years or had incomplete datasets, leaving 50% (132 of 265) for analysis in this retrospective study at a mean of 2.70 ± 0.71 years. The diagnosis of ischiofemoral impingement was defined by symptoms, MRI, and diagnostic ischiofemoral injection. We ascertained the percentage of patients with this diagnosis to answer the first research question. To answer the second question, we divided the patients into two groups: PAO patients with ischiofemoral impingement and PAO patients without ischiofemoral impingement. The demographic data and preoperative imaging parameters of patients in both groups were compared. There were statistical differences in acetabular version, ischial angle, neck-shaft angle, the presence of positive coxa profunda sign, McKibbin index, ischiofemoral space, quadratus femoris space, anterior acetabular section angle, and the net amount of hip center medialization. To investigate potential factors associated with postoperative ischiofemoral impingement in patients who underwent PAO, these factors underwent binary logistic regression analysis. To answer the third question, the cutoff value of the net amount of hip center medialization was evaluated using receiver operator characteristic curve and the Youden index method. We found that 26% (35 of 132) of PAO dysplastic hips had postoperative ischiofemoral impingement. After controlling for confounding variables such as acetabular version, ischial angle, femoral neck version, McKibbin index, and ischiofemoral space, we found that an increasing neck-shaft angle (odds ratio 1.14 [95% confidence interval 1.01 to 1.29]; p = 0.03), a positive coxa profunda sign (OR 0.13 [95% CI 0.03 to 0.58]; p < 0.01), and an increasing net amount of hip center medialization (OR 2.76 [95% CI 1.70 to 4.47]; p < 0.01) were associated with postoperative ischiofemoral impingement in patients with DDH who underwent PAO (R 2 = 0.73). The cutoff values of neck-shaft angle was 138.4°. The cutoff values of the net amount of hip center medialization was 1.9 mm. Postoperative ischiofemoral impingement could occur in patients with acetabular dysplasia who have undergone PAO after hip center medialization. An increasing neck-shaft angle, a positive coxa profunda sign on preoperative imaging, and excessive medialization of the hip center are factors associated with ischiofemoral impingement development in these patients. Therefore, we suggest that physicians measure the ischiofemoral space on a preoperative CT when patients with DDH have an increasing neck-shaft angle (> 138.4°) or a positive coxa profunda sign on radiological imaging. During PAO, the amount of hip center medialization should be carefully controlled to keep these patients from developing postoperative ischiofemoral impingement. Level III, therapeutic study.

Several available compositional MRIs seem to detect early osteoarthritis before radiographic appearance. Delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) has been most frequently used in clinical studies and reportedly predicts premature joint failure in patients undergoing Bernese periacetabular osteotomies (PAOs). We asked, given regional variations in biochemical composition in dysplastic hips, whether the dGEMRIC index of the anterior joint would better predict premature joint failure after PAOs than the coronal dGEMRIC index as previously reported. We retrospectively reviewed 43 hips in 41 patients who underwent Bernese PAO for hip dysplasia. Thirty-seven hips had preserved joints after PAOs and six were deemed premature failures based on pain, joint space narrowing, or subsequent THA. We used dGEMRIC to determine regional variations in biochemical composition. Preoperative demographic and clinical outcome score, radiographic measures of osteoarthritis and severity of dysplasia, and dGEMRIC indexes from different hip regions were analyzed in a multivariable regression analysis to determine the best predictor of premature joint failure. Minimum followup was 24 months (mean, 32 months; range, 24-46 months). The two cohorts were similar in age and sex distribution. Severity of dysplasia was similar as measured by lateral center-edge, anterior center-edge, and Tönnis angles. Preoperative pain, joint space width, Tönnis grade, and coronal and sagittal dGEMRIC indexes differed between groups. The dGEMRIC index in the anterior weightbearing region of the hip was lower in the prematurely failed group and was the best predictor. Success of PAO depends on the amount of preoperative osteoarthritis. These degenerative changes are seen most commonly in the anterior joint. The dGEMRIC index of the anterior joint may better predict premature joint failure than radiographic measures of hip osteoarthritis and coronal dGEMRIC index. Level II, prognostic study. See Instructions for Authors for a complete description of levels of evidence.

Radiographic evaluation plays an important role in detecting and grading hip dysplasia. Acetabular sector angles (ASAs) measure the degree of femoral head coverage provided by the acetabulum on computed tomographic (CT) scans. In this study, we aimed to determine ASA values at different axial levels in a control cohort with asymptomatic, high-functioning hips without underlying hip pathology and a study group with symptomatic, dysplastic hips that underwent periacetabular osteotomy (PAO), thereby defining the ASA thresholds for hip dysplasia. This was a cross-sectional study evaluating a control group of 51 patients (102 hips) and a study group of 66 patients (72 hips). The control group was high-functioning and asymptomatic, with an Oxford Hip Score of >43, did not have osteoarthritis (Tönnis grade ≤1), underwent a pelvic CT scan, had a mean age (and standard deviation) of 52.1 ± 5.5 years, and was 52.9% female. The study group had symptomatic hip dysplasia treated with PAO, had a mean age of 29.5 ± 7.3 years, and 83.3% was female. Anterior ASA (AASA) and posterior ASA (PASA) were measured at 3 axial CT levels to determine equatorial, intermediate, and proximal ASA. The thresholds for dysplasia were determined using receiver operating characteristic (ROC) curve analysis, including the area under the curve (AUC). Patients with dysplasia had significantly smaller ASAs compared with the control group; the differences were most pronounced for proximal AASAs and proximal and intermediate PASAs. The control group had a mean proximal PASA of 162° ± 17°, yielding a threshold for dysplasia of 137° (AUC, 0.908). The mean intermediate PASA for the control group was 117° ± 11°, yielding a threshold of 107° (AUC, 0.904). The threshold for anterior dysplasia was 133° for proximal AASA (AUC, 0.859) and 57° for equatorial AASA (AUC, 0.868). The threshold for posterior dysplasia was 102° for intermediate PASA (AUC, 0.933). Measurement of ASA is a reliable tool to identify focal acetabular deficiency with high accuracy, aiding diagnosis and management. A proximal PASA of <137° or an intermediate PASA of <107° should alert clinicians to the presence of dysplasia. Diagnostic Level III . See Instructions for Authors for a complete description of levels of evidence.