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1.  Three-dimensional mechanical evaluation of joint contact pressure in 12 periacetabular osteotomy patients with 10-year follow-up 
Acta Orthopaedica  2009;80(2):155-161.
Background and purpose Because of the varying structure of dysplastic hips, the optimal realignment of the joint during periacetabular osteotomy (PAO) may differ between patients. Three-dimensional (3D) mechanical and radiological analysis possibly accounts better for patient-specific morphology, and may improve and automate optimal joint realignment.
Patients and methods We evaluated the 10-year outcomes of 12 patients following PAO. We compared 3D mechanical analysis results to both radiological and clinical measurements. A 3D discrete-element analysis algorithm was used to calculate the pre- and postoperative contact pressure profile within the hip. Radiological angles describing the coverage of the joint were measured using a computerized approach at actual and theoretical orientations of the acetabular cup. Quantitative results were compared using postoperative clinical evaluation scores (Harris score), and patient-completed outcome surveys (q-score) done at 2 and 10 years.
Results The 3D mechanical analysis indicated that peak joint contact pressure was reduced by an average factor of 1.7 subsequent to PAO. Lateral coverage of the femoral head increased in all patients; however, it did not proportionally reduce the maximum contact pressure and, in 1 case, the pressure increased. This patient had the lowest 10-year q-score (70 out of 100) of the cohort. Another hip was converted to hip arthroplasty after 3 years because of increasing osteoarthritis.
Interpretation The 3D analysis showed that a reduction in contact pressure was theoretically possible for all patients in this cohort, but this could not be achieved in every case during surgery. While intraoperative factors may affect the actual surgical outcome, the results show that 3D contact pressure analysis is consistent with traditional PAO planning techniques (more so than 2D analysis) and may be a valuable addition to preoperative planning and intraoperative assessment of joint realignment.
PMCID: PMC2689368  PMID: 19404795
2.  Outcome of periacetabular osteotomy 
Acta orthopaedica  2005;76(3):303-313.
Due to wide variations in acetabular structure of individuals with hip dysplasia, the measurement of the acetabular orientation may not be sufficient to predict the joint loading and pressure distribution across the joint. Addition of mechanical analysis to preoperative planning, therefore, has the potential to improve the clinical outcome.
We analyzed the effect of periacetabular osteotomy on hip dysplasia using computer-aided simulation of joint contact pressure on regular AP radiographs. The results were compared with the results of surgery based on realignment of acetabular angles to the normal hip.
Patients and methods
We studied 12 consecutive periacetabular osteotomies with no femoral head deformity. The median age of patients, all females, was 35 (20−50) years. The median follow-up was 2 years (1.3−2.2). Patient outcome was measured with the total score of a self-administered questionnaire (q-score) and with the Harris hip score. The pre- and postoperative orientation of the acetabulum was defined using reconstructed 3D CT-slices to measure angles in the three anatomical planes. Peak contact pressure, weight-bearing area, and the centroid of the contact pressure distribution (CP-ratio) were calculated.
While 9 of 12 cases showed decreased peak pressure after surgery, the mean changes in weight-bearing area and peak contact pressure were not statistically significant. However, CP-ratio changed (p < 0.001, paired t-test) with surgery. For the optimal range of CP-ratio (within its mid-range 40−60%), the mechanical outcome improved significantly.
Verifying the correlation between the optimal CP-ratio and the outcome of the surgery requires additional studies on more patients. Moreover, the anatomically measured angles were not correlated with the ranges of CP-ratio, suggesting that they do not always associate with objective mechanical goals of realignment osteotomy. Mechanical analysis, therefore, can be a valuable tool in assessing two-dimensional radiographs in hip dysplasia.
PMCID: PMC2745131  PMID: 16156455
3.  Mid-term results of Bernese periacetabular osteotomy for developmental dysplasia of hip in middle aged patients 
International Orthopaedics  2013;37(4):589-594.
To address the question, compared to having hip replacement with latent revision, does Bernese periacetabular osteotomy (PAO) before primary hip replacement occupy a preferable treatment strategy for middle aged (aged 35–54 years) hip dysplasia patients? We assessed the mid-term functional outcome and survivorship of PAO in those patients.
Forty-one hips in 36 patients at middle age at the time of surgery (mean age, 39.5 years; range, 35–47 years) were retrospectively identified out of a total PAO cohort of 315 patients. Eleven of the 41 PAO hips also underwent osteochondroplasty at the femoral head-neck junction. Radiographic parameters of lateral centre edge angle, anterior centre edge angle and hip joint medialisation were investigated using the Harris Hip Score (HHS).
The average follow-up was 5.1 years (range, two to ten years). Radiographic parameters postoperatively improved into the normal range, whereas no progression was found from preoperative Tonnis osteoarthritis score. Forty hips survived at the last follow-up, with HHS Score improved from 63.7 to 88.4. Compared to the sole PAO group, both postoperative alpha angle and range of joint motion improved in the PAO combined with osteochondroplasty group. However, no difference in HHS score was found.
Good survivorship and improved joint function were identified in middle-aged Chinese patients following PAO with or without osteochondroplasty. We prudently suggest PAO as an alternative strategy for treating DDH in those patients.
PMCID: PMC3609987  PMID: 23381611
4.  Biomechanical Factors in Planning of Periacetabular Osteotomy 
Objective: This study addresses the effects of cartilage thickness distribution and compressive properties in the context of optimal alignment planning for periacetabular osteotomy (PAO).
Background: The Biomechanical Guidance System (BGS) is a computer-assisted surgical suite assisting surgeon’s in determining the most beneficial new alignment of a patient’s acetabulum. The BGS uses biomechanical analysis of the hip to find this optimal alignment. Articular cartilage is an essential component of this analysis and its physical properties can affect contact pressure outcomes.
Methods: Patient-specific hip joint models created from CT scans of a cohort of 29 dysplastic subjects were tested with four different cartilage thickness profiles (one uniform and three non-uniform) and two sets of compressive characteristics. For each combination of thickness distribution and compressive properties, the optimal alignment of the acetabulum was found; the resultant geometric and biomechanical characterization of the hip were compared among the optimal alignments.
Results: There was an average decrease of 49.2 ± 22.27% in peak contact pressure from the preoperative to the optimal alignment over all patients. We observed an average increase of 19 ± 7.7° in center-edge angle and an average decrease of 19.5 ± 8.4° in acetabular index angle from the preoperative case to the optimized plan. The optimal alignment increased the lateral coverage of the femoral head and decreased the obliqueness of the acetabular roof in all patients. These anatomical observations were independent of the choice for either cartilage thickness profile, or compressive properties.
Conclusion: While patient-specific acetabular morphology is essential for surgeons in planning PAO, the predicted optimal alignment of the acetabulum was not significantly sensitive to the choice of cartilage thickness distribution over the acetabulum. However, in all groups the biomechanically predicted optimal alignment resulted in decreased joint contact pressure and improved acetabular coverage.
PMCID: PMC4126379  PMID: 25152876
periacetabular osteotomy; preoperative planning; articular cartilage thickness; cartilage compressibility; biomechanical analysis
5.  Combined Periacetabular and Femoral Osteotomies for Severe Hip Deformities 
Periacetabular osteotomy (PAO) is an effective acetabular reorientation technique for treatment of symptomatic acetabular dysplasia. In hips with severe deformities, an adjunctive femoral osteotomy (PFO) may optimize correction, joint stability, and congruency. We analyzed the clinical and radiographic results of combined PAO/PFO in treating severe hip deformities. Second, we compared the clinical results of patients treated with PAO/PFO with patients treated with isolated PAO for lesser deformities. Twenty-five patients (28 hips) treated with PAO/PFO were reviewed and followed a minimum of 16 months (mean, 44 months). The matched PAO cohort included 25 patients (28 hips). For the PAO/PFO group, the average Harris hip score improved from 60.9 to 86.3. Eighty-nine percent of the patients demonstrated at least a 10-point improvement in the hip score and 75% had a Harris hip score over 80 points. Radiographic evaluation demonstrated consistent deformity correction. The PAO/PFO group had a lower average Harris hip score preoperatively, yet hip function after surgery was comparable between groups. These data indicate combined PAO/PFO is associated with improved hip function in most patients. These clinical results are comparable to those obtained with isolated PAO for lesser hip deformities.
Level of Evidence: Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
PMCID: PMC2866920  PMID: 19333669
6.  Anterior Delayed Gadolinium-enhanced MRI of Cartilage Values Predict Joint Failure After Periacetabular Osteotomy 
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 of Evidence
Level II, prognostic study. See Instructions for Authors for a complete description of levels of evidence.
PMCID: PMC3492640  PMID: 22907475
7.  What Factors Predict Failure 4 to 12 Years After Periacetabular Osteotomy? 
The goal of periacetabular osteotomy (PAO) is to delay or prevent osteoarthritic development in dysplastic hips. However, it is unclear whether the surgical goals are achieved and if so in which patients. This information is essential to select appropriate patients for a durable PAO that achieves its goals.
We therefore (1) determined hip survival rates; (2) determined how many preserved hips were functionally unsuccessful after PAO; and (3) identified demographic, clinical, and radiographic factors predicting failure after PAO.
We retrospectively reviewed 316 patients (401 hips) who had PAO between December 1998 and May 2007. We evaluated radiographic parameters of dysplasia and osteoarthritis and obtained WOMAC scores. Through inquiry to the National Registry of Patients, we identified conversions to THA. Risk factors for conversion to THA were assessed. Minimum followup was 4 years (mean, 8 years; range, 4–12 years).
The overall Kaplan-Meier hip survival rate was 74.8% at 12.4 years. A WOMAC pain score of 10 or more, suggesting clinical failure, was observed in 13% of preserved hips at last followup. Higher age, preoperative Tönnis grade of 2, incongruent hip, postoperative joint space width of 3 mm or less, and postoperative center-edge angle of less than 30° or more than 40° predicted conversion to THA.
PAO preserved three of four hips with most functioning well at 4- to 12-year followup. When planning surgery, surgeons should attempt to achieve hip congruence and a center-edge angle of between 30° to 40° to improve the durability of PAO.
Level of Evidence
Level II, prognostic study. See Instructions for Authors for a complete description of levels of evidence.
PMCID: PMC3462869  PMID: 22576934
8.  Prevalence and Treatment of Intraarticular Pathology Recognized at the Time of Periacetabular Osteotomy for the Dysplastic Hip 
The indication for hip arthrotomy accompanied by intraarticular work during periacetabular osteotomy (PAO) has not been precisely defined. To validate a role for routine hip arthrotomy accompanied by intraarticular work, frequent intraarticular pathology must exist, and the adjunct procedures must not be associated with inferior relief of pain, reduced function, radiographic osteoarthritis progression, or conversion to THA.
(1) What is the prevalence of intraarticular pathology at the time of PAO? (2) Does concomitant hip arthrotomy with associated intraarticular work negatively affect PAO as reflected by differences in Harris hip scores (HHS), Tönnis grade, and failure rates?
We retrospectively reviewed the intraarticular findings in all 151 patients who underwent PAO accompanied by routine hip arthrotomy and intraarticular work from 2002 to 2009. Using multivariate regression models, we compared the HHS and Tönnis grades of patients receiving arthrotomy with a cohort of 39 patients who received PAO alone.
The overall prevalence of intraarticular pathology identified during PAO was 89%. Eight (5.3%) failures were identified within the arthrotomy cohort with mean postoperative HHS, postoperative Tönnis grade, postoperative change in HHS, and postoperative change in Tönnis grade of 87.5, 0.7, 29.8, and 0.3, respectively. By contrast, seven (17.9%) failures were identified in the nonarthrotomy cohort. The mean postoperative HHS, postoperative Tönnis grade, postoperative change in HHS, and postoperative change in Tönnis grade for the nonarthrotomy cohort were 83.1, 1.3, 19.0, and 0.3, respectively.
We believe the high prevalence of intraarticular pathology is sufficient to warrant routine joint inspection at the time of PAO. Hip arthrotomy accompanied by intraarticular work at the time of PAO is safe and does not impose additional patient morbidity.
Level of Evidence
Level III, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.
PMCID: PMC3549169  PMID: 23054510
9.  Medial Translation of the Hip Joint Center Associated with the Bernese Periacetabular Osteotomy 
This study assessed medial translation of the hip joint achieved by the Bernese periacetabular osteotomy (PAO) in correcting residual acetabular dysplasia deformities. 86 hips in 75 patients with an average age of 25 years (range, 12-50) were treated for symptomatic acetabular dysplasia with a periacetabular osteotomy. Radiographic analysis was performed to assess correction of the acetabular deformity with specific attention to the horizontal position of the hip joint center. All hips were followed until bony union of the iliac osteotomy and the average follow-up was 28 months. The lateral center edge angle improved an average 31.6° (-0.4° preoperative, 31.2° at follow-up). Anterior center edge angle improved 39.3° (-4.5° to 34.8°). The acetabular roof obliquity improved an average 21.8° (25.1° to 3.3°). Preoperatively, the average distance from the medial aspect of the femoral head to the ilioischial line was 17.6 mm. This distance was decreased to an average 7.8 mm postoperatively. This change resulted in an average medial translation of the hip joint center of 9.8 mm, (range -6 to 31mm). Overall, some degree of medial translation of the hip joint center was obtained in 79 (92%) of the hips. 4 (5%) were maintained in the same horizontal position, and 3 (3%) had slight lateral repositioning. For the hips translated medially, the average change was 10.0 mm, and 72% of all hips had an optimal correction with the distance between the medial aspect of the femoral head and the ilioischial line being between 0 and 10 mm. This study demonstrates that in addition to optimizing femoral head coverage, a major and distinct advantage of the periacetabular osteotomy is reproducible and consistent medial translation of the hip joint center.
PMCID: PMC1888407  PMID: 15296205
Adult hip dysplasia (AHD) is a common etiology of hip pain in the young adult. Patients with adult hip dysplasia may present with hip pain and early degenerative changes resulting from elevated cumulative hip-contact stress. While there are numerous studies using radiographic parameters coupled with general and disease-specific health status measures to demonstrate that periacetabular osteotomy improves the orientation of the acetabulum, decreases pain and improves function, to our knowledge there is only one study that utilized gait analysis to demonstrate an objective functional alteration. The purpose of the present study was to prospectively evaluate the walking pattern and assess the activity level of patients undergoing periacetabular osteotomy for symptomatic adult hip dysplasia.
Institutional review board approval was obtained for collection and review of data on 55 patients who underwent periacetabular osteotomy at one institution by the senior author (TM) between the years 2007-2009. Walking pattern characteristics were assessed including velocity, cadence, stride
length of the affected side, and percent of single-limb support on the affected limb using GaitRite® walking pattern analysis. Activity was assessed as average steps/day over a consecutive seven-day period. As a secondary analysis, the disease-specific and generalized health status outcome measures of all patients who underwent periacetabular osteotomy were reviewed.
At an average of 11.5 months post periacetabu-lar osteotomy the walking patterns of 27 patients were available for review. Several trends were observed, including an approximate 5% increase in walking velocity (118 cm/sec to 125 cm/sec), and a 4.5 % increase in stride length (132 cm to 138 cm, p=0.01). At a mean 9.5 months following surgery, 26 patients reported an 8.75% decrease in average steps taken daily (4598 steps/day to 4196 steps/day). A significant improvement in SF-36 PC scores (p<0.01), the WOMAC hip pain and function scores (p<0.01) and the HHS (p<0.01) was noted during the same period.
At an average of 11.5 months following periacetabular osteotomy for the treatment of symptomatic hip dysplasia, a trend toward increased walking velocity and a significant increase in stride length was noted. A significant improvement in pain relief as well as improved physical function was observed in the short term. Subgroup analysis of patients without pre-existing osteoarthritis (as compared to those with pre-existing osteoarthrosis) revealed increased walking velocity, stride length of the affected limb, and percent of gait cycle in single support on the affected limb following periacetabular osteotomy. Further prospective studies are needed to fully clarify the long-term impact of the periacetabular osteotomy on patients with symptomatic hip dysplasia.
PMCID: PMC3215120  PMID: 22096426
11.  Evaluation of a computerized measurement technique for joint alignment before and during periacetabular osteotomy 
Periacetabular osteotomy (PAO) is intended to treat a painful dysplastic hip. Manual radiological angle measurements are used to diagnose dysplasia and to define regions of insufficient femoral head coverage for planning PAO. No method has yet been described that recalculates radiological angles as the acetabular bone fragment is reoriented. In this study, we propose a technique for computationally measuring the radiological angles from a joint contact surface model segmented from CT-scan data. Using oblique image slices, we selected the lateral and medial edge of the acetabulum lunate to form a closed, continuous, 3D curve. The joint surface is generated by interpolating the curve and the radiological angles are measured directly using the 3D surface. This technique was evaluated using CT data for both normal and dysplastic hips. Manual measurements made by three independent observers showed minor discrepancies between the manual observations and the computerized technique. Inter-observer error (mean difference±standard deviation) was 0.04±3.53° Observer 1; −0.46±3.13° for Observer 2; and 0.42±2.73° for Observer 3. The measurement error for the proposed computer method was −1.30±3.30°. The computerized technique demonstrates sufficient accuracy compared to manual techniques, making it suitable for planning and intraoperative evaluation of radiological metrics for periacetabular osteotomy.
PMCID: PMC2716292  PMID: 17786597
Periacetabular osteotomy; inter-observer error; radiographic angles; preoperative planning; acetabular coverage; cartilage segmentation
12.  Treatment of Adolescents with a Periacetabular Osteotomy After Previous Pelvic Surgery 
Although the success of the Bernese periacetabular osteotomy (PAO) has been reported for primary dysplasia, there is no study analyzing the radiographic, functional, and gait results of the PAO to correct residual hip dysplasia after previous pelvic surgery.
We assessed (1) radiographic and (2) functional and gait outcomes of patients treated with a PAO after previous pelvic surgery (PPSx) and compared their results with results of patients with no previous surgery (NPSx) to determine whether the PAO was equally effective in patients with revision pelvic surgery.
Twenty-nine dysplastic hips in 26 patients (average age, 16.3 years) were included: 13 in the PPSx group and 13 in the NPSx group. Radiographic parameters included the lateral center-edge angle, acetabular index, and femoral head extrusion index measured preoperatively and at 6 months and 1 year. We assessed preoperative and postoperative function using the Harris hip score (HHS). Preoperative and postoperative gait analysis included the hip abductor impulse.
Improvements in groups were seen from preoperatively to 1 year postoperatively for the lateral center-edge angle, acetabular index, and femoral head extrusion index without differences between groups. The modified HHSs improved at 6 months and were maintained at 1 year for patients in both groups without differences between groups. The hip abductor impulse returned to preoperative values at 6 months in the NPSx group but not until 1 year in the PPSx group.
The Bernese PAO is effective in providing similar final radiographic and functional results, however, a trend toward decreased hip flexion and abduction power at 1 year was seen with previous pelvic surgery.
Level of Evidence
Level II, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
PMCID: PMC3830103  PMID: 22456947
13.  Periacetabular Osteotomy for Acetabular Dysplasia in Patients Older than 40 Years: A Preliminary Study 
The functional outcomes of periacetabular osteotomy (PAO) and factors predicting outcome in the older patient with acetabular dysplasia are not well understood. We therefore retrospectively determined the functional outcome of 70 patients (87 hips) over age 40 treated with PAO in three institutions; we also determined whether preoperative factors, particularly the presence of osteoarthritis, influenced the survival of the hip or time to total hip arthroplasty after PAO. The average age at surgery was 43.6 years. The minimum followup was 2 years (mean, 4.9 years; range, 2–13 years). Twenty-one hips (24%) had undergone total hip arthroplasty (THA), at a mean of 5.2 years after PAO (range, 1.9–7.6 years). Surviving hips had a mean improvement in Harris hip score from 60.7 to 90.3 and in total WOMAC pain score from 8.7 to 3. We observed no differences in preoperative or postoperative radiographic measurements or preoperative clinical function scores (HHS, WOMAC) in hips surviving and hips having THA. The risk of THA at 5 years after PAO was 12% in hips with preoperative Tönnis Grade 0 or 1 and 27% for Tönnis Grade 2. Our preliminary study suggests that PAO will give satisfactory functional and pain scores in patients over age 40 having dysplastic hips with mild or no arthrosis.
Level of Evidence: Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
PMCID: PMC2866943  PMID: 19421831
14.  Algorithm for Femoral and Periacetabular Osteotomies in Complex Hip Deformities 
Residual acetabular dysplasia of the hip in most patients can be corrected by periacetabular osteotomy. However, some patients have intraarticular abnormalities causing insufficient coverage, containment or congruency after periacetabular osteotomy, or extraarticular abnormalities that limit either acetabular correction or hip motion. For these patients, we believe an additional proximal femoral osteotomy can improve coverage, containment, congruency and/or motion.
We provide algorithms for (1) identifying patients we believe will benefit from proximal femoral osteotomy, (2) selecting the appropriate osteotomy, and (3) choosing the sequence of these osteotomies.
Anteroposterior, false-profile and functional radiographs and MR can identify most patients we believe will benefit from periacetabular and femoral osteotomies. Recently described techniques, including relative femoral neck lengthening, femoral neck osteotomy and femoral head osteotomy have expanded indications for a combined procedure. Historically performed first, periacetabular osteotomy is now frequently performed following femoral osteotomy.
The rate of intertrochanteric osteotomy performed with periacetabular osteotomy has decreased from approximately 10% in the first 500 surgeries to about 2% currently. Among 151 relative neck lengthenings (23 with PAO), 53 femoral neck osteotomies (4 with PAO) and 14 femoral head osteotomies (11 with PAO), eleven complications occurred including osteonecrosis in two and delayed unions in eight. No complication occurred following a combined procedure.
Although isolated periacetabular osteotomy can provide sufficient coverage, containment and congruency for most patients with residual hip dysplasia, some may benefit from an additional proximal femoral osteotomy. Knowing the appropriate indications, selection, and sequencing of these osteotomies is critical for enhancing patient outcomes.
Level of Evidence
Level V, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
PMCID: PMC2974895  PMID: 20700675
15.  Patient Selection Criteria for Periacetabular Osteotomy or Rotational Acetabular Osteotomy 
Hip dysplasia is the most common cause of secondary osteoarthritis (OA). Periacetabular osteotomy (PAO) or rotational acetabular osteotomy (RAO) has been used as a joint-preserving procedure. However, the patient selection criteria are not clearly defined.
Based on a systematic review, we identified reported patient selection criteria for PAO or RAO.
We performed a systematic review of RAO and 18 studies met our inclusion criteria. For the PAO, the systemic review performed by Clohisy et al. was used.
Where Are We Now?
For patients with symptomatic hip dysplasia, lateral center-edge angle less than 10° to 30°, radiographic pre- or early OA, mean age at the time of surgery of 18 to 45 years, and improvement in joint congruency on AP radiograph with hip abduction, radiographic deformity correction consistently improved hip function in all studies. Radiographic OA progression was noted in 5% to 33% at 3.2 to 20 years postoperatively. Clinical score and prevention of radiographic OA progression of patients 50 years or older or with advanced stage were worse in younger patients or those with early stage.
Where Do We Need to Go?
The key challenges are (1) preoperative evaluation of articular cartilage; (2) indication for older patients; (3) prevention of secondary femoroacetabular impingement; and (4) intraarticular treatment combined with PAO or RAO.
How Do We Get There?
Future prospective, longitudinal cohort studies need to determine optimal patient selection criteria, risk factors for clinical failure, optimal deformity correction parameters, and the role of adjunctive surgical procedures.
PMCID: PMC3492602  PMID: 22895690
16.  What Are the Factors Associated With Acetabular Correction in Perthes-like Hip Deformities? 
Perthes-like hip deformities encompass variable proximal femoral abnormalities and associated acetabular dysplasia that can be reconstructed with contemporary hip preservation procedures. Nevertheless, the necessity and indications for surgical correction of associated acetabular dysplasia have not been established.
We determined whether patient-specific factors (sex, age, BMI, previous surgery, hip pain and function) and/or structural deformity characteristics (radiographic parameters of acetabular morphology) were associated with our indications for acetabular reorientation in surgical reconstruction of Perthes-like hip deformities.
We compared patient-specific characteristics and radiographic parameters of acetabular morphology in 94 patients (97 hips) with residual Perthes deformities who underwent joint preservation surgery without or with a periacetabular osteotomy (PAO) as part of the reconstruction.
Patient sex, BMI, preoperative Harris hip score, and previous hip surgery were not associated with our indications for a combined femoral and PAO procedure. Radiographic parameters associated with the indication for a PAO included the lateral center-edge angle, anterior center-edge angle, acetabular inclination, and acetabulum-head index. No or mild secondary osteoarthritis and joint congruency were associated with the indication for a PAO as part of the reconstruction.
Contemporary hip preservation surgery for residual Perthes deformities covers a wide spectrum of procedures. We believe a PAO should be considered in the surgical treatment plan for symptomatic patients having radiographic parameters indicating acetabular dysplasia, no or mild secondary osteoarthritis, and adequate joint congruity.
Level of Evidence
Level III, prognostic study. See Instructions for Authors for a complete description of levels of evidence.
PMCID: PMC3492615  PMID: 22895688
17.  Does Previous Reconstructive Surgery Influence Functional Improvement and Deformity Correction After Periacetabular Osteotomy? 
The Bernese periacetabular osteotomy (PAO) is commonly used to surgically treat residual acetabular dysplasia. However, the degree to which function and radiographic deformity are corrected in patients with more severe deformities that have undergone previous reconstructive pelvic or femoral osteotomies is unclear.
We evaluated hip pain and function, radiographic deformity correction, complications, reoperations, and early failures (conversion to THA) associated with PAO in hips treated with previous reconstructive hip surgery.
We retrospectively reviewed 63 patients who had undergone 67 PAOs after a previous reconstructive hip procedure. We compared preoperative hip scores and radiographic parameters with postoperative values at most recent followup. We recorded complications, need for nonarthroplasty revision surgery, and failures. Minimum followup was 2 years.
Five of the 67 hips (8%) were converted to THA between 24 and 118 months. The average followup for the remaining 62 hips was 60 months (range, 24–147 months). The average Harris hip score improved 11 points, and postoperatively, 83% of the hips had pain component scores of greater than 30 (none, slight, or mild pain). Radiographically, there were improvements in lateral center-edge angle (25°), anterior center-edge angle (23°), Tönnis angle (17°), and medialization of the hip center (8 mm). Complications occurred in 13 hips (19%). Seven hips (10%) underwent a subsequent surgical procedure to address residual pain or deformity.
PAO performed after previous reconstructive hip surgery improves hip function and corrects residual dysplasia deformities. These procedures are inherently more complex than primary PAO and are associated with a considerable risk of perioperative complications, reoperations, and early treatment failures.
Level of Evidence
Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
PMCID: PMC3254768  PMID: 22042717
18.  Caution Should be Taken in Performing Surgical Hip Dislocation for the Treatment of Femoroacetabular Impingement in Patients Over the Age of 40 
HSS Journal  2012;8(3):230-234.
Open and arthroscopic procedures are treatment options for patients with femoroacetabular impingement (FAI). Age has been found to be a predictive factor in the outcome of patients undergoing periacetabular osteotomy (PAO) for hip dysplasia. It is unclear if older age contraindicates joint preservation through a surgical hip dislocation (SHD).
The purpose of this retrospective case series was to evaluate the short-term outcomes of patients over 40 years of age without radiographic evidence of end-stage arthritis who underwent SHD for the treatment of FAI and to determine whether older age should be a contraindication for joint-preserving procedures in these patients. Our specific aims included (1) documenting the intraoperative findings and procedures, (2) assessing pain relief provided, and (3) assessing treatment failures and postoperative complications, noting the number of patients that ultimately required total hip arthroplasty (THA).
Patients and Methods
All patients at age 40 and older who had SHD for the treatment of FAI were identified from a series of patients treated with SHD. Clinical notes, radiographs, and operative reports were reviewed to determine clinical results, complications, and the need for additional procedures. The minimum follow-up was 1 year (mean 3.9 years; range 1–8 years).
At final follow-up, 11/22 (50%) of hips had pain relief, while 11/22 (50%) either continued having significant symptoms or required THA. Five (23%) reported nontrochanteric pain symptoms that were the same or worse than before surgery, and six hips (27%) underwent subsequent THA). The average time between SHD and THA was 1.9 years (0.9–6.2). The average age of patients who went on to require THA was 45 (42–50) years.
Surgical hip dislocation can be used for the treatment of FAI in patients over age 40, but strict selection criteria should be adhered to, as only half of the patients experienced significant improvement in their hip pain. THA was required in one-third of hips for continued pain and radiographic progression of arthritis. SHD for treatment of pathology that is not amenable to hip arthroscopy should remain a surgical option in older patients with FAI only if joint degeneration is not present.
PMCID: PMC3470673  PMID: 24082865
hip offset; femoracetabular impingement; joint preservation; surgical hip dislocation
19.  A Modification of Periacetabular Osteotomy Using a Two-Incision Approach 
In residual hip dysplasia periacetabular osteotomy (PAO) can improve insufficient coverage of the femoral head. It requires a broad dissection of the pelvic bones and detachment of muscle insertions, however. We have developed a modification of the Bernese periacetabular osteotomy with reduced soft tissue exposure. It uses two small skin incisions and offers therefore the perspective of nicer scars but also increases the risk of technical complications due to impaired vision. To be able to draft these risks, the clinical and radiographic results of 23 patients with PAO through the modified Smith-Petersen approach of Ganz (group A) and 24 patients with our two-incision modification (group B) have been reviewed retrospectively with an average follow-up of 19 (group A) and 12 (group B) months postoperatively.
Functional improvement (Harris Hip Score) and center-edge-angle normalization did not differ significantly in both groups. Scars of patients in group B were significantly shorter. However, the overall patient satisfaction (as measured with a visual analogous scale) was the same in both groups. 4 patients in group A and one patient in group B developed superficial or deep wound infections.
In conclusion, the experience with our cohort study showed that approach-related morbidity can be reduced without increasing the risk for the individual patient. This observation clearly holds a promise for further minimal invasive approaches as well as for further morbidity reduction of PAO.
Level of Evidence: Retrospective comparative study (Level III).
PMCID: PMC2684705  PMID: 19461904
20.  Impingement Adversely Affects 10-year Survivorship After Periacetabular Osteotomy for DDH 
Although periacetabular osteotomy (PAO) for developmental dysplasia of the hip (DDH) provides conceptual advantages compared with other osteotomies and reportedly is associated with joint survivorship of 60% at 20 years, the beneficial effect of proper acetabular reorientation with concomitant arthrotomy and creation of femoral head-neck offset on 10-year hip survivorship remains unclear.
We asked the following questions: (1) Does the 10-year survivorship of the hip after PAO improve with proper acetabular reorientation and a spherical femoral head; (2) does the Merle d’Aubigné-Postel score improve; (3) can the progression of osteoarthritis (OA) be slowed; and (4) what factors predict conversion to THA, progression of OA, or a Merle d’Aubigné-Postel score less than 15 points?
We retrospectively reviewed 147 patients who underwent 165 PAOs for DDH with two matched groups: Group I (proper reorientation and spherical femoral head) and Group II (improper reorientation and aspherical femoral head). We compared the Kaplan-Meier survivorship, Merle d’Aubigné-Postel scores, and progression of OA in both groups. A Cox regression analysis (end points: THA, OA progression, or Merle d’Aubigné-Postel score less than 15) was performed to detect factors predicting failure. The minimum followup was 10 years (median, 11 years; range, 10–14 years).
An increased survivorship was found in Group I. The Merle d’Aubigné-Postel score did not differ. Progression of OA in Group I was slower than in Group II. Factors predicting failure included greater age, lower preoperative Merle d’Aubigné-Postel score, and the presence of a Trendelenburg sign, aspherical head, OA, subluxation, postoperative acetabular retroversion, excessive acetabular anteversion, and undercoverage.
Proper acetabular reorientation and the creation of a spherical femoral head improve long-term survivorship and decelerate OA progression in patients with DDH.
Level of Evidence
Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
PMCID: PMC3613512  PMID: 23354462
21.  Joint kinematics and kinetics during walking and running in 32 patients with hip dysplasia 1 year after periacetabular osteotomy 
Acta Orthopaedica  2014;85(6):592-599.
Background and purpose —
Hip dysplasia can be treated with periacetabular osteotomy (PAO). We compared joint angles and joint moments during walking and running in young adults with hip dysplasia prior to and 6 and 12 months after PAO with those in healthy controls.
Patients and methods —
Joint kinematics and kinetics were recorded using a 3-D motion capture system. The pre- and postoperative gait characteristics quantified as the peak hip extension angle and the peak joint moment of hip flexion were compared in 23 patients with hip dysplasia (18–53 years old). Similarly, the gait patterns of the patients were compared with those of 32 controls (18–54 years old).
Results —
During walking, the peak hip extension angle and the peak hip flexion moment were significantly smaller at baseline in the patients than in the healthy controls. The peak hip flexion moment increased 6 and 12 months after PAO relative to baseline during walking, and 6 months after PAO relative to baseline during running. For running, the improvement did not reach statistical significance at 12 months. In addition, the peak hip extension angle during walking increased 12 months after PAO, though not statistically significantly. There were no statistically significant differences in peak hip extension angle and peak hip flexion moment between the patients and the healthy controls after 12 months.
Interpretation —
Walking and running characteristics improved after PAO in patients with symptomatic hip dysplasia, although gait modifications were still present 12 months postoperatively.
PMCID: PMC4259030  PMID: 25191933
22.  Intracapsular pressure and interleukin-1β cytokine in hips with acetabular dysplasia 
Acta Orthopaedica  2010;81(2):189-192.
Background and purpose Several studies have demonstrated an increased intracapsular pressure in several hip disorders such as septic arthritis, synovitis, and trauma. We therefore measured the intracapsular pressure in different positions in early dysplasic hips and its relation to the concentration of interleukin-1β (IL-1β), the volume of joint fluid, and the clinical and radiographic findings before a periacetabular osteotomy.
Methods 12 female patients (12 hips, mean age 35 (18–52)) with hip dysplasia were investigated. The intracapsular pressure was recorded and we investigated possible correlations with the Harris hip score, the Tönnis scale, radiographic findings, the volume of joint fluid, and the concentration of IL-1β.
Results An increased intracapsular pressure was noted, especially in flexion or extension with internal rotation. We found positive correlations between the intracapsular pressure and both the volume of joint fluid and the concentration of IL-1β.
Interpretation Increased intracapsular pressure varied with different positions, indicating the presence of synovitis resulting from early osteoarthritis in dysplastic hips. Positive correlations between the pressure and both the concentration of IL-1β and the volume of joint fluid suggest that the inflammatory cytokines produced by the synovial membrane as a consequence of mechanical instability of the hip joint may be of importance for the initiation and/or development of osteoarthritis in dysplastic hips.
PMCID: PMC2852155  PMID: 20367415
23.  Factors predicting the failure of Bernese periacetabular osteotomy: a meta-regression analysis 
International Orthopaedics  2008;33(6):1483-1488.
There is no clear evidence regarding the outcome of Bernese periacetabular osteotomy (PAO) in different patient populations. We performed systematic meta-regression analysis of 23 eligible studies. There were 1,113 patients of which 61 patients had total hip arthroplasty (THA) (endpoint) as a result of failed Bernese PAO. Univariate analysis revealed significant correlation between THA and presence of grade 2/grade 3 arthritis, Merle de’Aubigne score (MDS), Harris hip score and Tonnis angle, change in lateral centre edge (LCE) angle, late proximal femoral osteotomies, and heterotrophic ossification (HO) resection. Multivariate analysis showed that the odds of having THA increases with grade 2/grade 3 osteoarthritis (3.36 times), joint penetration (3.12 times), low preoperative MDS (1.59 times), late PFO (1.59 times), presence of preoperative subluxation (1.22 times), previous hip operations (1.14 times), and concomitant PFO (1.09 times). In the absence of randomised controlled studies, the findings of this analysis can help the surgeon to make treatment decisions.
PMCID: PMC2899154  PMID: 18719916
24.  Bernese Periacetabular Osteotomy in Males: Is There an Increased Risk of Femoroacetabular Impingement (FAI) After Bernese Periacetabular Osteotomy? 
The Bernese periacetabular osteotomy (PAO) is a popular option for treating symptomatic acetabular dysplasia. We noted symptomatic impingement after PAO in several male patients.
We therefore determined (1) the incidence of clinical signs of FAI after PAO in the male population; and (2) whether any factors were associated with the positive impingement signs after PAO in males.
Patients and Methods
We retrospectively reviewed 38 males who underwent 46 periacetabular osteotomies (PAO) between 2000 and 2007. Clinical and radiographic data were analyzed with the focus on pre- and postoperative incidence of femoroacetabular impingement. Minimum followup was 12 months (average, 43 months; range, 12–90 months).
We found a positive impingement sign in 19 of the 46 hips during the preoperative examination compared to 22 (47.8%) hips postoperatively. The ROM (flexion and internal rotation) decreased postoperatively compared to preoperatively. Radiographic parameters of coverage LCE-, ACE- and Tönnis angle improved into the normal range. Twenty hips had postoperative heterotopic ossification to varying degrees, mostly minor. WOMAC scores improved in the function and pain domains postoperatively.
Despite normalization of coverage we found a high postoperative rate of clinical signs of FAI after PAO in males.
Level of Evidence
Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
PMCID: PMC3018207  PMID: 20848246
25.  Curved Periacetabular Osteotomy for the Treatment of Dysplastic Hips 
Clinics in Orthopedic Surgery  2014;6(2):127-137.
Curved periacetabular osteotomy (CPO) was developed for the treatment of dysplastic hips in 1995. In CPO, the exposure of osteotomy sites and osteotomy of the ischium are made in the same manner as Bernese periacetabular osteotomy, and iliac and pubic osteotomies are performed in the same manner as rotational acetabular osteotomy. We studied the dynamic instabilities of 25 dysplastic hips before and after CPO using triaxial accelerometry. Overall magnitude of acceleration was significantly decreased from 2.30 ± 0.57 m/sec2 preoperatively to 1.55 ± 0.31 m/sec2 postoperatively. Pain relief and improvement of acetabular coverage resulting from acetabular reorientation seem to be related with reduction of dynamic instabilities of dysplastic hips. Isokinetic muscle strengths of 24 hips in 22 patients were measured preoperatively and after CPO. At 12 months postoperatively, the mean muscle strength exceeded the preoperative values. These results seem to be obtained due to no dissection of abductor muscles in CPO. The preoperative presence of acetabular cysts did not influence the results of CPO. An adequate rotation of the acetabular fragment induced cyst remodeling. Satisfactory results were obtained clinically and radiographically after CPO in patients aged 50 years or older. CPO alone for the treatment of severe dysplastic hips classified as subluxated hips of Severin group IV-b with preoperative CE angles of up to -20° could restore the acetabular coverage, weight-bearing area and medialization of the hip joint. CPO without any other combined procedure, as a treatment for 17 hips in 16 patients with Perthes-like deformities, produced good mid-term clinical and radiographic results. We have been performing CPO in conjunction with osteochondroplasty for the treatment of acatabular dysplasia associated with femoroacetabular impingement since 2006. The combined procedure has been providing effective correction of both acetabular dysplasia and associated femoral head-neck deformities without any increased complication rate. We have encountered an obturator artery injury in one case and two intraoperative comminuted fractures. Although serious complications such as motor nerve palsy, deep infection, necrosis of the femoral head or acetabulum, and delayed union or nonunion of the ilium were reported, such complications have never occurred in our 700 cases so far.
PMCID: PMC4040371  PMID: 24900892
Dysplastic hip; Curved periacetabular osteotomy; Dynamic instability; Abductor muscle; Retroversion

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