Impact of Periacetabular Osteotomy on Cartilage Enhancement in Crowe Group I Hip Dysplasia: A Short-Term Analysis

Introduction

Developmental dysplasia of the hip (DDH) is characterized by abnormal development of the acetabulum and femoral head, along with laxity of surrounding ligaments [1]. These anatomical aberrations predispose individuals to hip instability, progressive joint degeneration, and an elevated risk of premature osteoarthritis, with epidemiological studies revealing marked racial disparities in incidence rates ranging from 0.06 to 76.1 per 1000 live births across populations [2–4]. Left untreated, DDH leads to structural sequelae, including acetabular cartilage erosion, femoral head subluxation, and eventual osteonecrosis, culminating in chronic pain, functional impairment, and premature requirement for total hip arthroplasty [5].

Early detection through clinical assessment and imaging modalities (ultrasound for neonates, weight-bearing radiography for older children) informs therapeutic decision-making. While total hip arthroplasty remains the endpoint solution for end-stage osteoarthritis, periacetabular osteotomy (PAO) – first described by Ganz et al in 1988 [6] – has emerged as the criterion standard for young patients with DDH. This precision surgery involves tri-planar pelvic osteotomies, enabling acetabular reorientation, and thereby restoring biomechanical congruence through 3 key mechanisms: optimizing femoral head coverage, redistributing joint loading forces, and realigning the weight-bearing acetabular zone [7]. Internal fixation with titanium screws stabilizes the repositioned acetabulum, achieving 87.4% 15-year survivorship by delaying osteoarthritis progression in appropriately selected cases [8].

Current evidence delineates strict indications: PAO demonstrates optimal outcomes in adolescents (≥13 years) with preserved acetabular cartilage integrity, whereas its efficacy diminishes in patients exhibiting advanced osteoarthritis. Clohisy et al [9] validate its utility for severe acetabular dysplasia correction, while Steppacher et al [10] caution against application in moderate/late-stage disease. Nevertheless, critical knowledge gaps persist regarding PAO’s immediate effects on acetabular cartilage morphology, particularly in the weight-bearing regions of Crowe group I hips – an area warranting focused investigation, given the mechanical restoration capacity of the procedure versus its biological impact on articular tissues.

As PAO can correct the anatomical abnormality of the hip joint and evenly distribute the stresses on the acetabular cartilage, thereby delaying or preventing acetabular cartilage injury, we speculated that the condition of the acetabular cartilage can improve after PAO. The aim of this study was to determine the short-term clinical outcomes and changes in the cartilage in the acetabular weight-bearing area after PAO in patients with mild DDH.

Several classification systems for DDH are currently in use for guiding surgical treatment choices, such as Salter osteotomy or Pemberton osteotomy in children and Bernese PAO in adolescents and adults, with each showing good therapeutic effects [11,12]. The Crowe classification of developmental DDH is based on the degree of femoral head subluxation relative to the acetabulum. In this system, Crowe group I involves less than 50% subluxation, group II involves 50%–75% subluxation, group III involves 75%–100%, and group IV involves more than 100% subluxation [13,14]. We recruited patients with Crowe group I DDH who underwent PAO between 2015 and 2019 and analyzed their hip radiographs (standard and false-profile), pelvic computed tomography (CT) scans, and hip magnetic resonance imaging (MRI) scans. We compared the patients’ clinical manifestations and imaging parameters before PAO and at the time of the last follow-up. Specifically, we analyzed the correlation between the length of the acetabular sourcil and the width of the cartilage in the acetabular weight-bearing area. We also analyzed the changes in the area and length of the cartilage in the acetabular weight-bearing area on MRI, as well as the length of the acetabular sourcil, to explore the outcomes of the acetabular cartilage in the weight-bearing area after PAO. By addressing these gaps, this study aims to contribute to a more comprehensive understanding of the short-term effects of PAO on acetabular cartilage and to provide robust evidence for optimizing the management of patients with Crowe group I DDH.

Material and Methods

PATIENT SELECTION AND ETHICS APPROVAL:

The study protocol was approved by the ethics committee of the institution, and the written informed consent was obtained from all participants or their legal guardians, as applicable. We retrospectively enrolled all patients with Crowe group I DDH who underwent PAO between 2015 and 2019. All operations were performed by the same surgeon, who had over 20 years of experience in hip surgery.

The inclusion criteria were expanded to include detailed diagnostic and imaging criteria: patients with a clinical diagnosis of DDH exhibiting typical symptoms, such as hip pain, limping, or reduced range of motion, and possessing complete preoperative imaging data. Radiographic findings confirmed that the femoral head was centrally located, with a center-edge angle less than 20° [15], based on standard anterior-posterior pelvic radiographs. The leg was internally rotated to compensate for femoral anteversion, the film-focus distance was set at 120 cm, and the central X-ray beam was directed to the midpoint between the pubic symphysis and the line connecting the left and right anterior superior iliac spines. Radiographic classification was Crowe group I DDH, and osteoarthritis was graded as Tönnis II or lower, based on X-ray imaging [16].

Patients were excluded if they did not meet the diagnostic criteria for DDH, had osteoarthritis exceeding Tönnis grade II with significant hip-joint mobility limitations, exhibited poor acetabular and femoral head congruence, had a Crowe classification greater than group I, had incomplete preoperative imaging data, or were lost to follow-up.

IMAGING STUDIES:

All patients underwent pre- and postoperative imaging consisting of 256-slice helical computed tomography (CT; Philips Brilliance iCT, Philips Healthcare, Cleveland, OH, USA), digital X-ray examination (DXR-Evolution, Philips, Eindhoven, Netherlands), and 3.0-T MRI (3T Achieva, Philips Medical Systems, Best, Netherlands). Hip joint X-ray, pelvic CT, hip joint MRI, and hip false-profile view were obtained and observed at the original processing station, and then, the data were recorded in the digital imaging and communications in medicine (DICOM) file format. The imaging data were processed and evaluated using the image-processing software 3D Slicer and Mimics 16.0 software (Materialise, Leuven, Belgium), and assessed by an attending physician and a radiologist who did not participate in the treatment process.

SURGICAL METHOD:

All patients underwent general anesthesia. The procedure began with the patient positioned in the lateral decubitus position for ischial osteotomy. A longitudinal incision, approximately 10 cm in length, was made along the lateral side of the left thigh, extending from just above the greater trochanter to the distal end along the greater trochanter. The incision was carefully deepened in layers to expose the ischium. A plate hook was used to retract the sciatic nerve posteriorly for protection. The osteotome was used to remove the anterior half of the ischium along the inferior acetabular groove (Figure 1A). Once the ischial osteotomy was complete, the patient was repositioned to the supine position for the subsequent steps.

A 20-cm-long anterolateral S-P incision was made on the left hip, and the tissues were dissected layer by layer to expose and separate the iliac crest’s outer plate from the surrounding muscles. Approximately 2×1 cm of the anterior superior iliac spine was excised using a bone knife and chainsaw, while preserving the sartorius muscle and the attachment of the inguinal ligament. Subperiosteal dissection of the iliac spine was performed, and the superior pubic ramus, extending toward the iliopubic tuberosity, was exposed and separated. Pubic double-tip bone chip osteotomy was then performed. The osteotomy was directed slightly upward on the outside and downward on the inside until completed. The quadrilateral body was exposed, and the iliac and periacetabular osteotomies were performed, connecting with the ischial osteotomy. The posterior column of the pelvis was preserved. Any excess bone from the anterior inferior iliac spine was excised and cut into strips for later use. The acetabulum was repositioned to its correct angle. The osteotomy site was initially fixed using Kirschner wires, and fluoroscopic imaging confirmed satisfactory correction of the acetabular deformity. Appropriate length cannulated screws were then used to replace the Kirschner wires for stable fixation. The iliac bone block was inserted into the osteotomy gap. The anterior superior iliac spine was reduced and fixed with cortical bone screws (Figure 1B, 1C).

POSTOPERATIVE CARE:

Postoperative care included pain management, physical therapy, and regular follow-up visits to monitor healing and hip function. Weight-bearing exercises were gradually introduced 8 weeks after surgery, allowing for gradual rehabilitation while ensuring that the hip joint function was restored without overloading the newly positioned acetabulum.

CLINICAL EVALUATION AND IMAGING MEASUREMENTS:

The Harris hip score and visual analog scale (VAS) pain score were calculated before and after the operation. Radiological parameters, including the vertical-center-anterior (VCA) angle [17], center-edge angle [15], acetabular index [18], Sharp angle [18], Shenton line [18], and acetabular sourcil length [18], were assessed by 2 radiologists with substantial experience in hip imaging, possessing 10 and 15 years of experience, respectively (Figure 2). CT images were used to measure the horizontal acetabular-sector angle (HASA), posterior acetabular-sector angle (PASA), and anterior acetabular-sector angle (AASA) [19]. The length of the cartilage in the weight-bearing area of the acetabulum was measured on MRI, while the area of the acetabular cartilage in this region was measured on 3D MRI reconstruction.

EVALUATION OF THE CARTILAGE IN THE ACETABULAR WEIGHT-BEARING AREA:

The acetabular sourcil, characterized by a sclerotic zone within the weight-bearing surface of the acetabulum, serves as a crucial indicator for assessing alterations in the weight-bearing area of the hip joint pre- and postoperatively. We conducted a thorough analysis to determine the correlation between the acetabular sourcil length observed on anterior-posterior X-ray radiographs and the acetabular cartilage length within the weight-bearing area as measured on mid-coronal MRI scans. Considering that in children, the acetabulum and femoral head undergo changes with age, we additionally compared the pre- and postoperative alterations in acetabular cartilage relative to the femoral head size, using a ratio for comparison.

MRI MEASUREMENT AND 3D RECONSTRUCTION OF ACETABULAR CARTILAGE:

The acetabular sourcil length and cartilage dimensions in the acetabular weight-bearing region were evaluated using MRI scans with a slice thickness of 3 mm. The mid-coronal MRI slice was selected because it aligns with the central weight-bearing region of the acetabulum. Additional adjacent slices were included to capture potential variability across the acetabular surface. Cartilage length measurements were performed at 4 points: anterior, middle, and posterior regions, with the average value recorded for analysis. Three-dimensional (3D) reconstructions of the cartilage were then performed using Mimics software, to obtain precise measurements of cartilage area within the acetabular weight-bearing region. The cartilage dimensions measured pre- and postoperatively were compared statistically.

STATISTICAL ANALYSIS:

Data were analyzed using SPSS version 21.0 (IBM, Armonk, NY, USA). Continuous variables are presented as mean±standard deviation (SD). To compare preoperative and postoperative values, paired t tests were used for normally distributed data, while Wilcoxon signed-rank tests were applied for non-normally distributed data. Pearson correlation analysis was performed to assess the relationship between acetabular sourcil length and cartilage length in the weight-bearing region. A 2-tailed P value <0.05 was considered statistically significant.

To evaluate clinical and radiological outcomes, the Harris hip score and VAS pain score were recorded before surgery and at the last follow-up. Radiological parameters, including center-edge angle, VCA angle, acetabular index, Sharp angle, Shenton line continuity, and acetabular sourcil length, were measured on standard hip-joint X-rays. CT-based measurements, such as HASA, PASA, and AASA, were derived from pelvic CT images. Cartilage length and area in the acetabular weight-bearing region were quantified using mid-coronal and reconstructed 3D MRI scans. Pearson correlation analysis was performed to assess the relationship between acetabular sourcil length (measured on X-rays) and cartilage width (measured on MRI) in the acetabular weight-bearing area. Assumptions of linearity and homoscedasticity were evaluated prior to conducting the correlation analysis. To address potential confounding variables, including age, sex, and baseline osteoarthritis severity, adjusted analyses were conducted where appropriate to ensure that these factors did not bias the results.

Sensitivity analyses were performed to validate key findings, particularly for critical correlations and outcome measures. Results were summarized using descriptive statistics, and confidence intervals (CI) were reported to enhance interpretability. These additional steps aimed to strengthen the robustness and reliability of the statistical analyses.

Results

CLINICAL OUTCOMES:

Functional improvement was observed in all patients, as indicated by the significant improvement in the Harris hip score and VAS pain score after the surgery (Table 1). Harris hip scores significantly improved from 71.65±5.23 preoperatively to 87.12±3.14 postoperatively (P<0.05). VAS pain scores decreased from 7.2±1.3 to 3.1±1.2 (P<0.05).

RADIOGRAPHIC OUTCOMES:

The X-ray findings (acetabular index and center-edge, Sharp, and VCA angles) showed significant improvements at the last follow-up, compared with the preoperative findings (Table 1). The center-edge angle improved from 20.4±3.2° to 29.8±4.1° (P<0.05), the Sharp angle improved from 40.5±5.0° to 35.2±4.4° (P<0.05), the VCA angle improved from 22.3±3.6° to 16.2±3.2° (P<0.05), and the acetabular index improved from 12.2±2.5° to 7.8±2.0° (P<0.05). Additionally, the Shenton line returned to the normal anatomical state in 23 hips, indicating adequate acetabular realignment. Typical imaging changes are shown in Figures 2 and 3.

CT IMAGING RESULTS:

CT parameters, such as HASA, PASA, and AASA, were significantly improved at the last follow-up (P<0.05). The HASA angle improved from 30.1±4.8° to 20.4±3.7° (P<0.05), the PASA improved from 45.3±5.2° to 35.2±4.4° (P<0.05), and the AASA improved from 60.5±6.1° to 50.3±4.5° (P<0.05). CT examination showed increased acetabular inclusion of the femoral head, improved acetabular sourcil length, and widening of the sclerotic band after surgery.

MRI FINDINGS:

The length and area of the cartilage in the weight-bearing region of the acetabulum both significantly increased after surgery. The length of the acetabular cartilage increased from 25.32±8.11 mm before surgery to 29.81±8.14 mm at the last follow-up (Z=2.978, P=0.003; Figure 4). The area of the acetabular cartilage increased from 613.73±119.37 mm2 before surgery to 710.02±117.17 mm2 at the last follow-up (t=4.308, P<0.01; Figure 5, Table 2).

Pearson correlation analysis showed a significant positive correlation between the length of the acetabular sourcil on X-ray examination and the length of the cartilage in the acetabular weight-bearing region on MRI (r=0.676, P<0.01; Table 3).

Discussion

This study unequivocally demonstrated that PAO yielded substantial short-term clinical and radiographic improvements in adolescents and young adults with Crowe group I DDH. Postoperative clinical parameters, such as Harris hip scores and VAS pain scores, showed significant improvements. Additionally, radiographic and CT-based acetabular coverage parameters, including center-edge angle, VCA angle, acetabular index, Sharp angle, HASA, PASA, and AASA, showed significant improvements, with normalization of the Shenton line. These findings are consistent with those reported by Clohisy et al [7], Steppacher et al [10], Okoroafor et al [20], and Dienst et al [21], further validating the efficacy of PAO in enhancing femoral head coverage and hip joint function (Table 4). Furthermore, this study underscores the importance of preoperative 3D CT assessment for evaluating acetabular coverage, aligning with prior recommendations [22,23].

Numerous studies have demonstrated the efficacy of PAO in significantly improving hip function and acetabular coverage parameters, affirming its role in preventing or delaying secondary osteoarthritis changes in patients with DDH [24–27]. Notably, this is the first study to use MRI to directly quantify significant increases in cartilage length and surface area within the acetabular weight-bearing region postoperatively, providing compelling evidence of adaptive cartilage remodeling following PAO. Moreover, a significant correlation was identified between the postoperative increase in acetabular sourcil length (representing the bony weight-bearing area on radiographs) and cartilage length measured via MRI. This correlation indicates that the structural reconstruction achieved through PAO effectively optimizes the biomechanical environment of the acetabular weight-bearing area. While previous studies have predominantly focused on clinical outcomes and radiographic structural improvements, our MRI findings reveal morphological changes in acetabular cartilage, potentially reflecting the beneficial effects of stress redistribution after surgery.

Previous research on cartilage changes following PAO has yielded inconsistent results. Shon et al [28], Okoroafor et al [20], and Dienst et al [21] reported significant improvements in hip function postoperatively, whereas Mechlenburg et al [29,30], in their mid- to long-term follow-ups, observed no significant change in acetabular cartilage thickness, suggesting that short-term functional improvements may not necessarily translate into long-term cartilage preservation. While our findings are consistent with previous studies regarding clinical and radiographic improvements, this study uniquely identifies actual increases in cartilage area and length within the acetabular weight-bearing region, addressing a critical gap in the existing literature. Previous studies have documented cartilage abnormalities in patients with DDH, including acetabular cartilage hypertrophy and labral tears, predominantly localized in the anterosuperior weight-bearing region [31–35]. Wyler et al [36] and McCarthy et al [18] further documented significant abnormalities in acetabular cartilage thickness and structure among DDH patients, while Tsukagoshi et al [37] suggested cartilage remodeling associated with changes in femoral head morphology. In our study, 3D MRI reconstructions revealed a significant increase in cartilage area, from an average of 613.73±119.37 mm2 preoperatively to 710.02±117.17 mm2 postoperatively (P<0.01), clearly demonstrating positive adaptive changes in hip joint structure following PAO. These findings underscore the necessity for future investigations using advanced MRI techniques, such as T2 mapping or dGEMRIC, to further explore cartilage metabolic changes and long-term stability [38–41].

Our study further highlights the significance of acetabular sourcil length as a potential indicator of cartilage changes within the acetabular weight-bearing region. While previous studies often treated acetabular sourcil length solely as a radiographic parameter [42,43], we demonstrate its significant correlation with cartilage expansion observed via MRI. This novel finding suggests that changes in acetabular sourcil length after PAO could serve as a convenient radiographic marker for evaluating cartilage improvements, particularly in settings where advanced MRI technology is unavailable. Although we used detailed 3D MRI reconstruction in our study, the 3-mm slice thickness might limit the detection of subtle cartilage changes. Therefore, future studies should use higher-resolution imaging techniques to address this limitation.

This study has several limitations. First, the sample size is relatively small, and the study’s retrospective nature could introduce selection bias and limit statistical power. Second, the follow-up period of 4.5 years may not be sufficient to evaluate the long-term stability of cartilage changes and their influence on osteoarthritis progression. Third, the MRI slice thickness of 3 mm could limit the accurate detection of subtle cartilage morphology changes. Moreover, untreated DDH patients face a significantly increased risk of developing osteoarthritis, eventually requiring total hip arthroplasty or even revision surgery [44–46], underscoring the importance of early diagnosis and intervention. Future prospective studies should include larger sample sizes, extended follow-up durations (5–10 years), and higher-resolution MRI imaging techniques, such as T2 mapping or dGEMRIC, to better assess long-term cartilage adaptation and clinical outcomes, thus providing more definitive evidence for early DDH intervention strategies.

Conclusions

Our study demonstrated that PAO significantly improved short-term clinical outcomes in adolescents and adults with Crowe group I DDH. Postoperative assessments revealed notable improvements in clinical indices, radiographic parameters, and acetabular cartilage coverage within the weight-bearing region. Specifically, increased acetabular sourcil length and MRI-confirmed enlargement of acetabular cartilage indicated improved biomechanical conditions and femoral head coverage. These findings suggest that PAO effectively redistributes joint stress, potentially mitigating cartilage degeneration and delaying the progression of osteoarthritis. However, further research with long-term follow-up and detailed imaging data is required to confirm sustained cartilage health and clinical benefits.