Acetabular dysplasia presenting in adolescence or young adulthood can result from unresolved or undiagnosed congenital/childhood developmental dysplasia of the hip (DDH) or it can occur in hips that were anatomically normal until adolescence. Normal acetabular development continues through adolescence, and late presenting acetabular dysplasia could be a result of deficient growth just prior to skeletal maturity.¹ This is postulated to be due to delayed ossification of the triradiate cartilage and insufficient development of the lateral secondary ossification centers at the acetabular rim that usually ossify between the ages of 12 and 18 years.² Acetabular dysplasia, characterized by a shallow and oblique acetabular weight-bearing zone, leads to unfavorable mechanics and increased cartilage contact stresses, which ultimately cause early cartilage degeneration and osteoarthritis. The incidence of hip dysplasia ranges from 1.7% to 20% in the general population, with females having an increased relative risk of hip dysplasia.³ A recent US-based study of 950 patients, undergoing periacetabular osteotomy (PAO) for symptomatic acetabular dysplasia, reported 83% of the patients being females and 87.2% patients being Caucasians, with most patients being symptomatic for 1 to 3 years.⁴

The commonest presenting complaint of patients seeking medical attention is activity-related pain around the hip.⁵ Patients commonly localize the pain to the groin or the greater trochanter or both. Some patients have been misdiagnosed as having primary trochanteric bursitis and have undergone prolonged prior intervention for the same, often in the form of steroid injections.

It is very uncommon for patients with dysplasia to have buttock pain unless they have associated femoroacetabular impingement (FAI). The pain associated with hip dysplasia is usually related to abnormal mechanical loading of the involved hip. In due course of time, it becomes more persistent and frequent. This pain typically improves with rest and by weight-bearing activities of the involved hip. Catching and/or popping are frequent nonspecific hip symptoms and are usually due to extra-articular causes—iliopsoas riding over the iliopectineal eminence or the iliotibial (IT) band over the trochanter. Patients often seek physical therapy regimens and/or injections in and around the hip for pain relief in the absence of a specific mechanical diagnosis.

A thorough general medical, surgical, and social history is important. The history taking should also screen for neuromuscular causes of dysplasia (e.g., myelomeningocele, Charcot-Marie-Tooth disease, hypertonia). Hip dysplasia may have a genetic component, so family history of hip dysplasia and/or of early total hip replacement (THR) in the family is also pertinent. We recommend collecting a validated hip-specific patient function instrument, such as Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) or International Hip Outcome Tool (iHOT). In addition to documenting the patient’s functional status, expectations should also be discussed during the patient interview.

Patients presenting with hip symptoms due to underlying hip dysplasia may benefit from joint preserving surgery. Undiagnosed acetabular dysplasia usually leads to osteoarthritis, which may require otherwise-avoidable hip replacement. Hence, prompt diagnosis of dysplasia is important. Appropriate imaging is needed to assess acetabular dysplasia and to plan out further treatment. Plain radiographs, advanced cross-sectional imaging (computed tomography [CT] scans and magnetic resonance imaging [MRI]), and dynamic ultrasound assessment are important tools and have specific roles in the diagnosis and treatment of acetabular dysplasia. In addition to getting the appropriate projections, it is also important to have strict criteria to assess the quality of the images.⁶

The radiograph remains the gold standard for assessing structural hip abnormalities, including hip dysplasia. The minimum radiographic data set that are generally
employed in assessing mature acetabular dysplasia include a well-centered anteroposterior (AP) radiograph of the entire pelvis (standing preferred in the United States; supine is preferred in Europe), faux profil views, and a modified Dunn lateral radiograph, taken in 45° of flexion, 30° of abduction, and neutral rotation, to show in profile that anterolateral neck area is the most common location of reduced offset. The AP radiograph is evaluated with measures of lateral and anterior coverage (lateral center-edge angle [LCEA], Figures 5.2, 5.3 and 5.4, Shenton line intact or broken). The faux profil view predominantly assesses anterior coverage, quantitated by the anterior CE angle (Figure 5.5). The modified Dunn lateral helps in identification of a proximal femur cam
deformity (Figure 5.6). All radiographs should be scrutinized for changes indicative of osteoarthritis, including cartilage space width and appearance of the subchondral bone. Table 5.3 presents the relevant measurements commonly made on these radiographs. For preoperative assessment of patients being considered for PAO, anticipated postoperative congruity is best confirmed by functional flexion, abduction, and internal rotation radiographs, simulating effect of the proposed redirection (Figure 5.7).

Additional imaging sometimes useful in assessing hip deformity and selecting treatment includes lowdose CT and MRI. CT in particular has improved our
three-dimensional understanding of acetabular deformity in dysplasia. Acetabular dysplasia presents with three patterns of undercoverage: anterior, posterior, and global.⁷,⁸ Recognition of the pattern of acetabular deficiency is critical in selecting the optimal acetabular reorientation. MRI allows evaluation of intra- and extra-articular soft-tissue structures of the hip affected by acetabular dysplasia. The acetabular labrum should be assessed for damage at the chondrolabral junction as well as global hypertrophy, both of which can remain symptomatic following PAO, if not addressed. In our institution, CT and MRI are also used to assess acetabular and femoral version. MR cartilage-specific sequences, such as delayed gadolinium-enhanced MRI (dGEMRIC), are invaluable in evaluating cartilage health (Figure 5.8) in hips with signs of early osteoarthritis. Preoperative dGEMRIC scores have been shown to have a predictive value in the survival of PAO⁹ (Figure 5.9).

Moving beyond static imaging, dynamic ultrasonography is being used at our center as a diagnostic tool in assessing both instability and impingement even in mature hips in which the mechanics are poorly understood.¹⁰

The only multicenter prospective cohort study looking at outcomes after PAO, by the ANCHOR (Academic Network of Conservational Hip Outcomes Research) group, reported improved patient-reported outcomes, with a minimum follow-up of 2 years (mean = 2.6, 2-5.4 years) in 391 hips and a 99.2% hip survival rate and 93% early satisfaction rate. They reported improvements in pain, function, quality of life, overall health, and activity level. Increasing age and a body mass index status of overweight or obesity were predictive of improved results for certain outcome metrics. Male sex and mild acetabular dysplasia were predictive of lesser improvements in certain outcome measures. Three (0.8%) of the hips underwent early conversion to total hip arthroplasty, 12 (3%) required reoperation, and 26 (7%) experienced a major complication.¹¹

Multiple retrospective studies report outcomes of PAO. The Bernese experience has the longest minimum follow-up of 30 years, noting conversion rate to total hip arthroplasty or arthrodesis of 12.4% at 10 years and 39.5% at 20 years. At 30-year follow-up, 30% of hips were asymptomatic without radiographic evidence of progression.¹²,¹³,¹⁴

Similar results from our center showed cumulative survival of 76% at 10-year follow-up and 74% at mean 18-year follow-up. At a mean of 18 years after PAO, 53% of patients were asymptomatic, and 26% were symptomatic based on WOMAC pain score greater than 10. In all, 21% of hips had been replaced, with a mean age of 9 years post-PAO.¹⁵,¹⁶

Troelsen et al described similar results from another high-volume PAO center, with 82% of hips surviving for a decade following surgery.¹⁷,¹⁸,¹⁹

Factors associated with poor outcome included older age, the severity of osteoarthritis, and evidence of labral pathology and poor acetabular index postoperatively.
Even though widely accepted, the use of conversion to THR as an end point is in some ways problematic. At the time of follow-up, more patients may have developed endstage hip joint osteoarthritis or functionally compromising pain. These hip joints may also require THR in the near future; thus, the true failure rate may be underestimated. There is no commonly accepted definition of which secondary end points to consider. While the overall results among most studies looking at mid- to long-term outcomes were consistent, the characteristics of failed PAOs were also highly similar. Older patients, patients with severe preoperative dysfunction, radiographic osteoarthritis, and poor joint congruency prior to surgery were strong predictors of PAO failure in a number of studies.