Combination of Anterior Acetabular Coverage and Femoral Head Shape Predicts Femoroacetabular Impingement After Periacetabular Osteotomy

Published:October 26, 2021DOI:https://doi.org/10.1016/j.arth.2021.10.012

      Highlights

      • The combined anterior center-edge (CE) and alpha angle is a predictive factor for postoperative femoroacetabular impingement.
      • Osteochondroplasty of the femoral head is recommended in patients with preoperative combined anterior center-edge (CE) and alpha angles >90°.
      • Postoperative combined anterior center-edge (CE) and alpha angles >108° may cause femoroacetabular impingement.

      Abstract

      Background

      Femoroacetabular impingement (FAI) after periacetabular osteotomy (PAO) may be affected by both anterior acetabular coverage and femoral head shape. This study aimed to radiographically evaluate the relationship of the combination of acetabular coverage and femoral head shape with the occurrence of FAI after curved PAO.

      Methods

      In this study, 76 hip joints from patients with symptomatic developmental dysplasia of the hip underwent curved PAO. The relationship between the combined postoperative anterior center-edge and alpha angles (ie, the combination angle) and the occurrence of postoperative FAI was evaluated. Clinical factors and the preoperative and postoperative 3-dimensional center-edge angles, acetabular versions, femoral versions, radiographic alpha angles of the femoral head, and the combination angle were measured and compared to clinical outcomes.

      Results

      The modified Harris Hip Scores, University of California, Los Angeles activity scores, and acetabular coverage angles were significantly improved following curved PAO. Receiver operator characteristic curve analysis demonstrated that the combination angle over 108° may be a predictive factor for the occurrence of FAI after curved PAO. Multivariate analysis demonstrated that an age <40 years (odds ratio 6.6, 95% confidence interval 1.2-36.4, P = .037) and a combination angle <108° (odds ratio 9.2, 95% confidence interval 1.7-50.0, P = .010) were significantly associated with modified Harris Hip Scores ≧90 points.

      Conclusion

      A combination angle >108° may be a predictive factor for the occurrence of FAI after curved PAO and impaired clinical outcomes. To avoid postoperative FAI, we propose that osteochondroplasty of the femoral head should be performed for patients with preoperative combination angles >90°.

      Keywords

      Hip dysplasia is one of the most common causes of osteoarthritis (OA) in the Japanese young adult population. More than 70% of hip OA cases in this population are caused by developmental dysplasia of the hip (DDH) [
      • Nakamura S.
      • Ninomiya S.
      • Nakamura T.
      Primary osteoarthritis of the hip joint in Japan.
      ]. The abnormal characteristics in this disorder, including a shallow acetabulum, acetabular malorientation, and high anteversion of the femoral neck, cause hip OA due to instability and increased joint contact pressure, resulting in hip pain [
      • Klaue K.
      • Durnin C.W.
      • Ganz R.
      The acetabular rim syndrome. A clinical presentation of dysplasia of the hip.
      ,
      • Murphy S.B.
      • Ganz R.
      • Muller M.E.
      The prognosis in untreated dysplasia of the hip. A study of radiographic factors that predict the outcome.
      ,
      • Dandachli W.
      • Kannan V.
      • Richards R.
      • Shah Z.
      • Hall-Craggs M.
      • Witt J.
      Analysis of cover of the femoral head in normal and dysplastic hips: new CT-based technique.
      ]. Therefore, several types of acetabular redirection osteotomies, such as dial osteotomy [
      • Eppright R.H.
      Dial osteotomy of acetabulum in treatment of dysplasia of hip.
      ], Bernese (Ganz) periacetabular osteotomy (PAO) [
      • Ganz R.
      • Klaue K.
      • Vinh T.S.
      • Mast J.W.
      A new periacetabular osteotomy for the treatment of hip dysplasias - technique and Preliminary-results.
      ], and rotational acetabular osteotomy (RAO) [
      • Ninomiya S.
      • Tagawa H.
      Rotational acetabular osteotomy for the dysplastic hip.
      ], have been developed for DDH cases with mild degenerative changes in the cartilage. Curved PAO (curved PAO) [
      • Naito M.
      • Shiramizu K.
      • Akiyoshi Y.
      • Ezoe M.
      • Nakamura Y.
      Curved periacetabular osteotomy for treatment of dysplastic hip.
      ] was developed as an acetabular redirection osteotomy and was considered a modification of the Bernese (Ganz) PAO [
      • Ganz R.
      • Klaue K.
      • Vinh T.S.
      • Mast J.W.
      A new periacetabular osteotomy for the treatment of hip dysplasias - technique and Preliminary-results.
      ]. The periacetabular exposure is similar to that performed in the Bernese (Ganz) PAO, but the osteotomy line is similar to that used in RAO [
      • Ninomiya S.
      • Tagawa H.
      Rotational acetabular osteotomy for the dysplastic hip.
      ].
      Previous reports demonstrated good survival rates of acetabular redirection osteotomies [
      • Wells J.
      • Schoenecker P.
      • Duncan S.
      • Goss C.W.
      • Thomason K.
      • Clohisy J.C.
      Intermediate-term hip survivorship and patient-reported outcomes of periacetabular osteotomy: the Washington University Experience.
      ,
      • Lerch T.D.
      • Steppacher S.D.
      • Liechti E.F.
      • Tannast M.
      • Siebenrock K.A.
      One-third of hips after periacetabular osteotomy survive 30 Years with good clinical results, No progression of arthritis, or conversion to THA.
      ,
      • Yasunaga Y.
      • Ochi M.
      • Yamasaki T.
      • Shoji T.
      • Izumi S.
      Rotational acetabular osteotomy for pre- and early osteoarthritis secondary to dysplasia provides durable results at 20 Years.
      ]; the survival rate of conversion to total hip arthroplasty (THA) was 92% at 15 years [
      • Wells J.
      • Schoenecker P.
      • Duncan S.
      • Goss C.W.
      • Thomason K.
      • Clohisy J.C.
      Intermediate-term hip survivorship and patient-reported outcomes of periacetabular osteotomy: the Washington University Experience.
      ] and 61% at 20 years after Bernese (Ganz) PAO [
      • Lerch T.D.
      • Steppacher S.D.
      • Liechti E.F.
      • Tannast M.
      • Siebenrock K.A.
      One-third of hips after periacetabular osteotomy survive 30 Years with good clinical results, No progression of arthritis, or conversion to THA.
      ], while the survival rate of radiographic OA progression was 78% at 20 years after RAO [
      • Yasunaga Y.
      • Ochi M.
      • Yamasaki T.
      • Shoji T.
      • Izumi S.
      Rotational acetabular osteotomy for pre- and early osteoarthritis secondary to dysplasia provides durable results at 20 Years.
      ]. Hip pain may prevent participation in recreational and sporting activities and directly impact the quality of life of DDH patients. Previous studies have shown that acetabular redirection osteotomies relieved pain and improved hip function [
      • Klaue K.
      • Durnin C.W.
      • Ganz R.
      The acetabular rim syndrome. A clinical presentation of dysplasia of the hip.
      ,
      • Naito M.
      • Shiramizu K.
      • Akiyoshi Y.
      • Ezoe M.
      • Nakamura Y.
      Curved periacetabular osteotomy for treatment of dysplastic hip.
      ,
      • Novais E.N.
      • Heyworth B.
      • Murray K.
      • Johnson V.M.
      • Kim Y.J.
      • Millis M.B.
      Physical activity level improves after periacetabular osteotomy for the treatment of symptomatic hip dysplasia.
      ]. Several predictive factors of failure and poor outcomes were reported: advanced age, advanced preoperative arthrosis, poor joint congruency, large preoperative alpha angles, postoperative impingement, and postoperative excessive acetabular coverage [
      • Wells J.
      • Schoenecker P.
      • Duncan S.
      • Goss C.W.
      • Thomason K.
      • Clohisy J.C.
      Intermediate-term hip survivorship and patient-reported outcomes of periacetabular osteotomy: the Washington University Experience.
      ,
      • Matheney T.
      • Kim Y.J.
      • Zurakowski D.
      • Matero C.
      • Millis M.
      Intermediate to long-term results following the Bernese periacetabular osteotomy and predictors of clinical outcome.
      ,
      • Steppacher S.D.
      • Tannast M.
      • Ganz R.
      • Siebenrock K.A.
      Mean 20-year followup of Bernese periacetabular osteotomy.
      ,
      • Troelsen A.
      • Elmengaard B.
      • Soballe K.
      Medium-term outcome of periacetabular osteotomy and predictors of conversion to total hip replacement.
      ,
      • Amano T.
      • Hasegawa Y.
      • Seki T.
      • Takegami Y.
      • Murotani K.
      • Ishiguro N.
      Preoperative prognosis score is a useful tool regarding eccentric rotational acetabular osteotomy in patients with acetabular dysplasia.
      ]. DDH patients expect complete pain relief and excellent hip function after acetabular redirection osteotomies. However, predictive factors for excellent clinical outcomes after acetabular redirection osteotomies are not well documented.
      Femoroacetabular impingement (FAI) after PAO causes hip pain leading to impaired clinical outcomes and early OA progression [
      • Albers C.E.
      • Steppacher S.D.
      • Ganz R.
      • Tannast M.
      • Siebenrock K.A.
      Impingement adversely affects 10-year survivorship after periacetabular osteotomy for DDH.
      ,
      • Ziebarth K.
      • Balakumar J.
      • Domayer S.
      • Kim Y.J.
      • Millis M.B.
      Bernese periacetabular osteotomy in males: is there an increased risk of femoroacetabular impingement (FAI) after Bernese periacetabular osteotomy?.
      ,
      • Clohisy J.C.
      • Nepple J.J.
      • Ross J.R.
      • Pashos G.
      • Schoenecker P.L.
      Does surgical hip dislocation and periacetabular osteotomy improve pain in patients with Perthes-like deformities and acetabular dysplasia?.
      ]. Albers et al [
      • Albers C.E.
      • Steppacher S.D.
      • Ganz R.
      • Tannast M.
      • Siebenrock K.A.
      Impingement adversely affects 10-year survivorship after periacetabular osteotomy for DDH.
      ] demonstrated that proper reorientation and a spherical femoral head improved long-term function and decreased OA progression. Clohisy et al [
      • Clohisy J.C.
      • Nepple J.J.
      • Ross J.R.
      • Pashos G.
      • Schoenecker P.L.
      Does surgical hip dislocation and periacetabular osteotomy improve pain in patients with Perthes-like deformities and acetabular dysplasia?.
      ] demonstrated that surgical hip dislocation combined with PAO corrected major deformities and provided good patient-reported outcomes in Perthes-like hip deformities associated with DDH. Therefore, the combination of a curved PAO and an endoscopic osteochondroplasty is chosen when patients present with femoral head alpha angles >55°. However, some impingement signs after curved PAO may still be present, even in patients with spherical femoral heads. We recently discovered that the postoperative range of motion (ROM) for flexion and internal rotation was significantly associated with the postoperative 3D-anterior center-edge (CE) angles and concluded that excessive anterior acetabular coverage caused a decrease in the ROM for flexion and internal rotation leading to FAI after curved PAO [
      • Hayashi S.
      • Hashimoto S.
      • Matsumoto T.
      • Takayama K.
      • Kamenaga T.
      • Niikura T.
      • et al.
      Overcorrection of the acetabular roof angle or anterior center-edge angle may cause decrease of range of motion after curved periacetabular osteotomy.
      ,
      • Hayashi S.
      • Hashimoto S.
      • Matsumoto T.
      • Takayama K.
      • Shibanuma N.
      • Ishida K.
      • et al.
      Postoperative excessive anterior acetabular coverage is associated with decrease in range of motion after periacetabular osteotomy.
      ]. However, we hypothesized that the occurrence of FAI may be affected by elements of both anterior acetabular coverage and femoral head shape.
      Therefore, this study aimed to answer the following questions:
      • 1.
        Does the radiographical factor of the combination of acetabular coverage and femoral head shape affect the occurrence of FAI after curved PAO?
      • 2.
        Does postoperative anterior CE and alpha angles (the combination angle) influence clinical outcomes after curved PAO?

      Materials and Methods

       Patients and Surgery

      In this retrospective cohort study, consecutive patients who underwent curved PAO for DDH by 2 senior surgeons at our institution between January 2015 and May 2019 were selected. This study included 72 patients (9 men, 63 women; 82 hip joints). After exclusion of 6 joints due to additional procedures, including endoscopic osteochondroplasty for cam lesions of the femoral head, 76 joints were analyzed. No patients were lost to follow-up in this study.
      Endoscopic osteochondroplasty was performed for patients with femoral head alpha angles >55°. DDH patients who presented aspherical femoral heads (eg, Perthes-like hip deformities) were excluded from this study because Chiari osteotomies are usually preferred for such patients in our institution [
      • Chiari K.
      Medial displacement osteotomy of the pelvis.
      ]. The curved PAO was developed as an acetabular redirection osteotomy and considered a modification of the Bernese (Ganz) PAO [
      • Ganz R.
      • Klaue K.
      • Vinh T.S.
      • Mast J.W.
      A new periacetabular osteotomy for the treatment of hip dysplasias - technique and Preliminary-results.
      ]. The periacetabular exposure was similar to that achieved in the Bernese (Ganz) PAO, while the osteotomy line was spherical, similar to that in RAO [
      • Ninomiya S.
      • Tagawa H.
      Rotational acetabular osteotomy for the dysplastic hip.
      ]. All patients were classified as having grade 0 or 1 OA according to the Tönnis classification system [
      • Tonnis D.
      • Heinecke A.
      Acetabular and femoral anteversion: relationship with osteoarthritis of the hip.
      ]. The mean age at surgery was 33.3 years (range 16-54).
      All patients underwent preoperative 3D planning with a 100-mm radius sphere using a navigation software (OrthoMap 3D Navigation System; Stryker Orthopedics, Mahwah, NJ). Curved PAO was performed as previously reported [
      • Hayashi S.
      • Hashimoto S.
      • Matsumoto T.
      • Takayama K.
      • Shibanuma N.
      • Ishida K.
      • et al.
      Computer-assisted surgery prevents complications during peri-acetabular osteotomy.
      ]. Briefly, a direct anterior approach with an approximately 9-cm skin incision was used for surgical exposure. A flexion chisel was introduced into the space between the distal joint capsule and psoas tendon. The direction of the chisel toward the infracotyloid groove was confirmed with fluoroscopy, and osteotomy was performed. A pubic osteotomy was performed just medial to the iliopubic eminence. A C-shaped osteotomy line was marked with a power drill from the anterior inferior iliac spine to the distal part of the quadrilateral surface along the spherical position and direction with navigation guidance. After performing a spherical osteotomy, the acetabular fragments were rotated laterally to the position and direction determined by fluoroscopy during the preoperative planning and then fixed temporarily using a Kirschner wire. Two or 3 poly-l-lactic acid screws or metal cancellous screws were used to finally fix the reoriented acetabular fragment.
      Figure 1 demonstrates a representative case of X-ray before and 1 year after curved PAO.
      Figure thumbnail gr1
      Fig. 1Anteroposterior view of plain radiograph for curved PAO: (A) preoperative X-ray and (B) X-ray at 1 year postoperatively. PAO, periacetabular osteotomy.

       Clinical Evaluation

      Hip function was evaluated using the modified Harris Hip Scores (mHHSs) and University of California, Los Angeles (UCLA) activity scores [
      • Zahiri C.A.
      • Schmalzried T.P.
      • Szuszczewicz E.S.
      • Amstutz H.C.
      Assessing activity in joint replacement patients.
      ,
      • Ashby E.
      • Grocott M.P.
      • Haddad F.S.
      Outcome measures for orthopaedic interventions on the hip.
      ]. The initial mHHSs (91 points) were normalized to 100 by multiplying the raw scores by 1.1. Scores ≧90 were defined as excellent mHHSs [
      • Sariali E.
      • Gaujac N.
      • Grimal Q.
      • Klouche S.
      Pre-operative bone mineral density is a predictive factor for excellent early patient-reported outcome measures in cementless total hip arthroplasty using a proximally fixed anatomic stem. A prospective study at two year minimum follow-up.
      ]. The UCLA activity scores were based on 10 descriptive activity levels [
      • Zahiri C.A.
      • Schmalzried T.P.
      • Szuszczewicz E.S.
      • Amstutz H.C.
      Assessing activity in joint replacement patients.
      ], and high levels of activity were defined as those having a UCLA activity score ≧8 (ie, participation in either very active events or high-impact sports) [
      • Novais E.N.
      • Heyworth B.
      • Murray K.
      • Johnson V.M.
      • Kim Y.J.
      • Millis M.B.
      Physical activity level improves after periacetabular osteotomy for the treatment of symptomatic hip dysplasia.
      ]. Patients were classified as postoperative FAI when symptoms were predominantly caused by FAI (hip pain occurred due to daily activities of sitting and hip flexion) and results of physical examination showed a positive anterior impingement sign (hip pain was caused by flexion, adduction, and internal rotation) according to a previous report [
      • Ganz R.
      • Parvizi J.
      • Beck M.
      • Leunig M.
      • Notzli H.
      • Siebenrock K.A.
      Femoroacetabular impingement: a cause for osteoarthritis of the hip.
      ]. The mHHSs and UCLA activity scores were evaluated preoperatively; the mHHSs, UCLA activity scores, and symptoms of postoperative FAI were evaluated at the 1-year follow-up.

       Imaging Evaluation

      All patients were positioned on the computerized tomography (CT) table in the supine position. Scans were performed preoperatively and 3 weeks postoperatively from the pelvis to the knee joint using a 64-row multislice CT system; the obtained image datasets were transferred to 3D template software (ZedHip; LEXI Co, Tokyo, Japan). The lateral and anterior CE angles were measured from the coronal and sagittal views through the femoral head center to quantitatively evaluate acetabular coverage in multiple directions. Acetabular anterior CE was measured in the sagittal view through the center of the femoral head according to the functional pelvic plane on the 3D template (Fig. 2, left upper panel). We created an approximate sphere of the femoral head according to the femoral head center on the sagittal view and drew 2 lines: first line, the horizontal line through the femoral head center; second line, the line through acetabular anterior edge and the femoral head center, and the anterior CE angle was measured as the angle between 2 lines (Fig. 2).
      Figure thumbnail gr2
      Fig. 2Image of the 3D template software measuring postoperative lateral (32.5°, left lower panel) and anterior (60.7°, left upper panel) center-edge angles.
      Femoral anteversion was defined according to a previous report [
      • Hayashi S.
      • Hashimoto S.
      • Matsumoto T.
      • Takayama K.
      • Kamenaga T.
      • Niikura T.
      • et al.
      Preoperative anterior coverage of the medial acetabulum can predict postoperative anterior coverage and range of motion after periacetabular osteotomy: a cohort study.
      ]. Briefly, the femoral neck axis was calculated as the best-fit line connecting slices drawn through a central segment of the neck. The original canal anteversion was defined as the angle between the axis of the neck and the line connected to the epicondylar line. Total anteversion was defined as a combination of the 3D anterior CE and the original canal anteversion. A recent report showed a comparison of magnetic resonance imaging, CT, Dunn 45°, and Dunn 90° alpha angle measurements and concluded that the Dunn 45° alpha angle is the most sensitive evaluation for cam deformity [
      • Smith K.M.
      • Gerrie B.J.
      • McCulloch P.C.
      • Lintner D.M.
      • Harris J.D.
      Comparison of MRI, CT, Dunn 45 degrees and Dunn 90 degrees alpha angle measurements in femoroacetabular impingement.
      ]. Therefore, the alpha angle was determined by Dunn 45° view of the X-ray according to previous reports [
      • Smith K.M.
      • Gerrie B.J.
      • McCulloch P.C.
      • Lintner D.M.
      • Harris J.D.
      Comparison of MRI, CT, Dunn 45 degrees and Dunn 90 degrees alpha angle measurements in femoroacetabular impingement.
      ]. Briefly, the alpha angle is the angle between the line from the center of the femoral head through the middle of the femoral neck and the line through a point where the contour of the femoral head-neck junction exceeded the radius of the femoral head (Fig. 3A). All measurements of images were performed by 2 blind observers. Plain radiographs were taken at each follow-up visit, and we confirmed that the acetabular fragment following osteotomy did not move during the follow-up.
      Figure thumbnail gr3
      Fig. 3(A) Dunn 45° view of plain radiograph for alpha angle measurement. (B) A schema for the explanation of the combination angle. The combination angle was the sum of CT-anterior CE angle and the alpha angle of Dunn 45° view plain radiograph. CE, center edge; CT, computerized tomography.

       Statistical Analysis

      All data are expressed as means ± standard deviations, unless otherwise indicated. The clinical and radiographical results were analyzed using the paired t-test, comparing preoperative values with values 1 year after surgery. Thresholds of combination with anterior CE and alpha angle (Fig. 3B) and their accuracy were measured using receiver operator characteristic (ROC) curve. The ROC allows for a graphical representation of a binary model and provides the ability to determine a discriminatory threshold. This methodology has been previously utilized in the literature for determining the Patient Acceptable Symptomatic State—a threshold that approximates patient satisfaction as a binary response [
      • Okoroha K.R.
      • Beck E.C.
      • Nwachukwu B.U.
      • Kunze K.N.
      • Nho S.J.
      Defining Minimal clinically important difference and patient Acceptable symptom state after Isolated endoscopic Gluteus Medius Repair.
      ]. The area under the curve (AUC) measured the accuracy of classifying the outcome based on the model. AUCs of 0.50, between 0.7 and 0.8, >0.80, and 1.0 were equated with random assignment, acceptable discrimination, excellent discrimination, and perfect assignment, respectively [
      • Copay A.G.
      • Subach B.R.
      • Glassman S.D.
      • Polly Jr., D.W.
      • Schuler T.C.
      Understanding the minimum clinically important difference: a review of concepts and methods.
      ]. The threshold was found through the specificity and sensitivity approach: the Youden index, the point on the curve that achieves the highest sensitivity and specificity, was used to set the optimal threshold value [
      • Copay A.G.
      • Subach B.R.
      • Glassman S.D.
      • Polly Jr., D.W.
      • Schuler T.C.
      Understanding the minimum clinically important difference: a review of concepts and methods.
      ]. To identify predictive factors, mHHS ≧90 points and UCLA activity scores ≧8 points were compared using Fisher’s exact test for nominal variables and unpaired t-test for continuous variables. Additionally, we performed a multivariate analysis to test the association between age and the combination angle with excellent mHHS. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated using the Fisher’s exact test and multivariate analysis, and the Wilcoxon signed-rank test was used for ordinal variables. The database was analyzed using SPSS version 16.0 (IBM Corp, Armonk, NY), and P-values <.05 were considered statistically significant.

       Ethics

      The study protocol was approved by the Institutional Review Boards of the authors’ affiliated institution, and informed consent for participation in the study was obtained from all participants.

      Results

       Clinical and Radiographical Outcomes

      The clinical and radiographical outcomes are shown in Table 1. The follow-up visit had a mean of 4.1 years (range 2.0-6.3). The mean preoperative mHHS and UCLA activity scores were 72.1 ± 12.1 and 6.9 ± 1.3 points, respectively. The mean postoperative mHHS and UCLA activity scores significantly improved to 95.4 ± 7.4 (P = .044) and 8.2 ± 1.2 (P < .001) points, respectively. The mean values of the preoperative and postoperative lateral CE angles changed from 12.2° ± 8.9° to 29.8° ± 8.8° (P < .001), and those of the anterior CE angles changed from 43.2° ± 15.3° to 62.3° ± 13.4° (P < .001). The CE angles, acetabular anteversion, and combination of acetabular and femoral anteversion showed significant changes (P < .001 for all). The preoperative mean femoral anteversion was 30.0° (range 4.4°-60.5°), and the mean femoral head alpha angle was 40.2° (range 20°-54°).
      Table 1Clinical and Radiographic Results.
      PreoperativePostoperativeP-Value
      mHHS score72.1 ± 12.195.4 ± 7.4.044
      UCLA score6.9 ± 1.38.2 ± 1.2<.001
      Lateral CE angle12.2 ± 8.929.8 ± 8.8<.001
      Anterior CE angle43.2 ± 15.362.3 ± 13.4<.001
      Tönnis grade0.5 ± 0.60.5 ± 0.8.065
      Acetabular version21.4 ± 7.411.1 ± 14.6<.001
      Total anteversion47.2 ± 14.841.3 ± 20.0<.001
      Alpha angle40.2 ± 8.5
      CE, center edge; mHHS, modified Harris Hip Score; UCLA, University of California, Los Angeles.

       The Combination of Anterior Center-Edge and Alpha Angles Predicted Postoperative Femoroacetabular Impingement

      Postoperative FAI was observed in 17 patients (22.4%). We evaluated the relationship between the combined anterior CE and alpha angles (combination angle) and the occurrence of anterior FAI after PAO. The ROC curve for combination with anterior CE and alpha angle demonstrated excellent discrimination between patients who developed postoperative FAI and those who did not, with an AUC of 0.88 (Fig. 4). Using the Youden index, a threshold of the combination angle 108° (sensitivity 0.81; specificity, 0.86) was determined for the occurrence of postoperative FAI.
      Figure thumbnail gr4
      Fig. 4The ROC curve for combination with anterior CE and alpha angle. CE, center edge; ROC, receiver operator characteristic.

       Age and Combination Angle Are Predictive Factors for Excellent Clinical Outcomes After Periacetabular Osteotomy

      We evaluated the effects of different factors on mHHS. Age, Tönnis OA grade, and combination angles were significantly associated with mHHS ≧90 (P = .044, P = .017, and P = .016, respectively) (Table 2). Since predictive factors may depend on multiple confounders, these 3 significant predictive factors were used as covariates for the multivariate analysis. We demonstrated that age <40 years (OR 6.6, 95% CI 1.2-36.4, P = .037) and combined angle <108° (OR 9.2, 95% CI 1.7-50.0, P = .010) were significantly associated with mHHS ≧90 (Table 3).
      Table 2Characteristic of High mHHS Patients After PAO.
      mHHS ≧ 90 PointsYes (n = 64)No (n = 12)P-ValueHedge’s g95% CI (Lower, Upper)
      Age (y)32.3 ± 12.439.1 ± 10.7.044−0.56−1.18−0.06
      BMI (kg/m2)23.3 ± 2.923.0 ± 2.3.8210.11−0.510.72
      Preoperative UCLA score (points)6.9 ± 1.37.0 ± 0.9.888−0.08−0.700.54
      Postoperative UCLA score (points)8.4 ± 1.17.8 ± 0.9.0660.55−0.071.18
      Preoperative frequency of Tönnis grade 068.8% (44/64)33.3% (4/12).017
      Postoperative lateral CE angle28.9 ± 8.731.5 ± 9.8.374−0.29−0.910.32
      Postoperative anterior CE angle61.1 ± 13.668.0 ± 13.5.132−0.50−1.130.12
      Postoperative acetabular version11.5 ± 15.012.1 ± 11.1.884−0.07−0.690.55
      Postoperative total anteversion43.8 ± 19.638.6 ± 19.7.2750.26−0.350.88
      Alpha angle39.9 ± 8.640.2 ± 6.8.951−0.04−0.650.58
      Combination with anterior CE angle and alpha angle99.7 ± 14.5112.0 ± 11.2.016−0.87−1.50−0.24
      BMI, body mass index; CE, center edge; CI, confidence interval; mHHS, modified Harris Hip Score; PAO, periacetabular osteotomy; UCLA, University of California, Los Angeles.
      Table 3Results of the Multivariate Analysis for Predictive Factors of High mHHS Patients After PAO.
      Predictive FactorOdds Ratio (95% CI)P-Value
      Age under 40 y6.6 (1.2-36.4).037
      Combination with anterior CE and alpha angle <108°9.2 (1.7-50.0).010
      CE, center edge; CI, confidence interval; mHHS, modified Harris Hip Score; PAO, periacetabular osteotomy.

       Preoperative UCLA activity score was a predictive factor for high-activity patients after PAO

      We evaluated the effect of different factors on the UCLA activity score. Preoperative UCLA activity scores were significantly associated with postoperative UCLA activity scores ≧8 (P = .001) (Table 4). However, other factors, including age, body mass index, and radiographic factors, were not associated with postoperative UCLA activity scores (Table 4).
      Table 4Characteristic of High-Activity Patients After PAO.
      UCLA Score ≧8 PointsYes (n = 60)No (n = 16)P-ValueHedge’s g95% CI (Lower, Upper)
      Age (y)32.6 ± 12.435.7 ± 10.6.351−0.25−0.810.30
      BMI (kg/m2)23.0 ± 4.023.5 ± 3.9.540−0.12−0.680.43
      Preoperative UCLA score (points)7.3 ± 1.16.1 ± 1.3.0011.040.471.62
      Postoperative UCLA score (points)8.7 ± 0.96.4 ± 0.82.591.913.29
      Preoperative frequency of Tönnis grade 060.0% (36/60)75.0% (12/16).604
      Postoperative lateral CE angle32.0 ± 10.428.5 ± 8.4.2060.35−0.210.90
      Postoperative anterior CE angle63.0 ± 15.062.1 ± 13.3.7580.06−0.490.61
      Postoperative acetabular version14.1 ± 18.510.4 ± 13.3.4090.21−0.340.76
      Postoperative total anteversion35.8 ± 21.341.2 ± 19.1.438−0.27−0.830.28
      Alpha angle42.4 ± 10.539.1 ± 8.3.2980.32−0.230.88
      Combination with anterior CE angle and alpha angle107.2 ± 15.4101.2 ± 14.4.2140.33−0.220.88
      BMI, body mass index; CE, center edge; CI, confidence interval; mHHS, modified Harris Hip Score; PAO, periacetabular osteotomy; UCLA, University of California, Los Angeles.

       Complications

      No perioperative complication, such as pulmonary embolism, deep infection, peroneal nerve dysesthesia, and vascular injuries, was observed in this study group. The complications in this study included nonunion of the superior ramus of the pubis in 3 patients, an intra-articular osteotomy in 1 patient, and a posterior column fracture in 1 patient.

      Discussion

      In this study, we demonstrated that the combined anterior CE and alpha angles may be a predictive factor for the occurrence of FAI after curved PAO. Multivariate analysis demonstrated that an age <40 years or a combination angle <108° was significantly associated with excellent clinical results.
      Hamada et al [
      • Hamada H.
      • Takao M.
      • Nakahara I.
      • Sakai T.
      • Nishii T.
      • Sugano N.
      Hip range-of-motion (ROM) is less than normal after rotational acetabular osteotomy for developmental dysplasia of the hip: a simulated ROM analysis.
      ] demonstrated in a simulation study that a lateral CE of 30° and an anterior CE of 55° measured using CT images produced a coverage similar to that of normal hips, and only the lateral rotation of the acetabulum to achieve a lateral CE of 30° resulted in a larger anterior coverage than that for an anterior CE of 55°, with a decrease in flexion and internal rotation at 90° flexion in a comparison of pre-RAO and post-RAO values. These results were similar to our findings. In our study, the mean value of postoperative anterior CE was 62.3° although only the lateral rotation of the acetabulum to achieve a lateral CE of 30°.
      Higher alpha angles have been associated with cam-type FAI; cam-type FAI, as measured by an increased offset angle alpha, was correlated with increased chondral damage, labral injury, and decreased ROM [
      • Beaule P.E.
      • Hynes K.
      • Parker G.
      • Kemp K.A.
      Can the alpha angle assessment of cam impingement predict acetabular cartilage delamination?.
      ,
      • Johnston T.L.
      • Schenker M.L.
      • Briggs K.K.
      • Philippon M.J.
      Relationship between offset angle alpha and hip chondral injury in femoroacetabular impingement.
      ]. Notzli et al [
      • Notzli H.P.
      • Wyss T.F.
      • Stoecklin C.H.
      • Schmid M.R.
      • Treiber K.
      • Hodler J.
      The contour of the femoral head-neck junction as a predictor for the risk of anterior impingement.
      ] reported that the mean alpha angles of normal and symptomatic FAI were 42° and 74°, respectively. Neumann et al [
      • Neumann M.
      • Cui Q.
      • Siebenrock K.A.
      • Beck M.
      Impingement-free hip motion: the ‘normal’ angle alpha after osteochondroplasty.
      ] identified impingement-free ROM at a mean angle of 43° (range 34°-60°). They concluded that the value of their measurements could be considered as a normal limit, which, consequently, was lower than the currently accepted range of 50°-55°. However, more than 80% of patients presenting with FAI are reported to have a combination of acetabular overcorrection and aspherical femoral head shape [
      • Beck M.
      • Kalhor M.
      • Leunig M.
      • Ganz R.
      Hip morphology influences the pattern of damage to the acetabular cartilage: femoroacetabular impingement as a cause of early osteoarthritis of the hip.
      ]. When we focused on the relationship between the alpha angle and FAI after PAO, the typical aspherical femoral heads in DDH increased the risk of secondary cam-type FAI that is reportedly symptomatic in 48% of all cases after reorientation [
      • Ziebarth K.
      • Balakumar J.
      • Domayer S.
      • Kim Y.J.
      • Millis M.B.
      Bernese periacetabular osteotomy in males: is there an increased risk of femoroacetabular impingement (FAI) after Bernese periacetabular osteotomy?.
      ]. Beaule et al [
      • Beaule P.E.
      • Dowding C.
      • Parker G.
      • Ryu J.J.
      What factors predict improvements in outcomes scores and reoperations after the Bernese periacetabular osteotomy?.
      ] reported that higher alpha angles were associated with poorer patient-reported outcomes. We demonstrated that the mean preoperative alpha angle was 40.2°, which is less than the currently accepted normal limit of 50°-55°. However, the acetabular anterior CE angle was increased by 19.1°, from 43.2° to 62.3°, increasing the combination angle by the same amount. Furthermore, we showed that a threshold postoperative combination angle of 108° was the most accurate predictive factor for the occurrence of FAI. The occurrence of FAI was affected by both the anterior acetabular coverage and femoral head shape. Therefore, to avoid postoperative FAI, we proposed that osteochondroplasty of the femoral head should be performed for patients with preoperative combination angles >90° or preoperative alpha angle >46°.
      Previous studies demonstrated that preoperative age was a critical factor for postoperative clinical outcomes and survival for conversion to THA [
      • Lerch T.D.
      • Steppacher S.D.
      • Liechti E.F.
      • Tannast M.
      • Siebenrock K.A.
      One-third of hips after periacetabular osteotomy survive 30 Years with good clinical results, No progression of arthritis, or conversion to THA.
      ,
      • Wells J.
      • Millis M.
      • Kim Y.J.
      • Bulat E.
      • Miller P.
      • Matheney T.
      Survivorship of the Bernese periacetabular osteotomy: what factors are associated with long-term failure?.
      ]. Radiographic progression of OA and Merle d’Aubigné-Postel scores <15 were associated with preoperative ages over 40 years [
      • Lerch T.D.
      • Steppacher S.D.
      • Liechti E.F.
      • Tannast M.
      • Siebenrock K.A.
      One-third of hips after periacetabular osteotomy survive 30 Years with good clinical results, No progression of arthritis, or conversion to THA.
      ]. The patients with preoperative ages over 25 years were significantly symptomatic compared with patients with preoperative ages less than 25 years [
      • Wells J.
      • Millis M.
      • Kim Y.J.
      • Bulat E.
      • Miller P.
      • Matheney T.
      Survivorship of the Bernese periacetabular osteotomy: what factors are associated with long-term failure?.
      ]. Age over 40 [
      • Amano T.
      • Hasegawa Y.
      • Seki T.
      • Takegami Y.
      • Murotani K.
      • Ishiguro N.
      Preoperative prognosis score is a useful tool regarding eccentric rotational acetabular osteotomy in patients with acetabular dysplasia.
      ] or 45 [
      • Troelsen A.
      • Elmengaard B.
      • Soballe K.
      Medium-term outcome of periacetabular osteotomy and predictors of conversion to total hip replacement.
      ] years was identified as a factor predicting conversion to THA [
      • Amano T.
      • Hasegawa Y.
      • Seki T.
      • Takegami Y.
      • Murotani K.
      • Ishiguro N.
      Preoperative prognosis score is a useful tool regarding eccentric rotational acetabular osteotomy in patients with acetabular dysplasia.
      ]. The results of these reports are in line with our finding that age <40 years was significantly associated with excellent clinical results.
      Moreover, we demonstrated that the combination angle was associated with postoperative clinical outcomes. Beaule et al [
      • Beaule P.E.
      • Dowding C.
      • Parker G.
      • Ryu J.J.
      What factors predict improvements in outcomes scores and reoperations after the Bernese periacetabular osteotomy?.
      ] reported that the presence of a cam deformity was associated with severe cartilage damage, leading to poor outcomes with PAO. There may be effects on the postoperative clinical outcomes in addition to hip pain with FAI.
      Previous studies demonstrated that activity levels improved after PAO [
      • Wells J.
      • Schoenecker P.
      • Duncan S.
      • Goss C.W.
      • Thomason K.
      • Clohisy J.C.
      Intermediate-term hip survivorship and patient-reported outcomes of periacetabular osteotomy: the Washington University Experience.
      ,
      • Novais E.N.
      • Heyworth B.
      • Murray K.
      • Johnson V.M.
      • Kim Y.J.
      • Millis M.B.
      Physical activity level improves after periacetabular osteotomy for the treatment of symptomatic hip dysplasia.
      ,
      • Petrie J.R.
      • Novais E.N.
      • An T.W.
      • Group A.S.
      • Clohisy J.
      What is the impact of periacetabular osteotomy surgery on patient function and activity levels?.
      ].
      We demonstrated that postoperative activity levels improved and were associated with preoperative activity levels. Novais et al [
      • Novais E.N.
      • Heyworth B.
      • Murray K.
      • Johnson V.M.
      • Kim Y.J.
      • Millis M.B.
      Physical activity level improves after periacetabular osteotomy for the treatment of symptomatic hip dysplasia.
      ] reported that patients with lower ages, higher preoperative activity levels, and lower postoperative pain levels had improved physical activity levels after PAO. The results of these studies aligned with our results.
      This study had some limitations. First, our study is a retrospective cohort study with no controls. Second, this is a short-term follow-up study and did not provide any information regarding medium to long-term results. Further insight into predictors of the functional outcomes for longer times is needed. Third, the number of patients included in the study was very small to completely analyze all parameters.

      Conclusion

      The combined anterior CE and alpha angle >108° may be a predictive factor for the occurrence of FAI after curved PAO and impairment of clinical outcomes. To avoid postoperative FAI, we propose that osteochondroplasty of the femoral head should be performed for patients with preoperative combination angles >90° or preoperative alpha angle >46°.

      Appendix A. Supplementary Data

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