Radiographic Measures Predicting Failure of Arthroscopy in Borderline Hip Dysplasia: Letter to the Editor

Dear Editor:

We read with great interest the paper by McQuivey et al ⁴ who aimed to identify certain radiographic parameters that could help orthopaedic providers recognize a group of patients with hip dysplasia that would not be suitable for treatment with hip arthroscopy. We found the study to be well structured and we applaud the fact that treatment failure consisted of not only any reoperation, but also the inability to achieve a minimal clinically important difference in the modified Harris Hip Score following arthroscopic treatment. As the authors stated, this criterion is useful to determine the true clinical relevance of a surgery given that isolated evaluation of patient-related outcome measures is not always directly related with clinical improvement, despite reaching statistical significance. However, we do have some inquiries regarding the methodology.

The authors searched their database looking for hips with a lateral center-edge angle (LCEA) between 20° and 25° or a Tönnis angle of >10°, which they equally considered as “mildly dysplastic.” They additionally stated in their inclusion criteria that only those with a Tönnis angle >10° or a LCEA <25° and clinical signs of intra-articular hip pain were included. Using these criteria, a patient with a LCEA of 22° to 24° (ie, “borderline”) and a Tönnis angle of 30° (ie, not so “borderline”) would be classified as “mildly dysplastic.” The mean LCEA and Tönnis angle of the series were 30° ± 7.3° and 5.1° ± 4.4°, respectively. Taking into account the prior criteria used to define dysplasia, these mean values seem rather distant from the actual ones seen in dysplastic cohorts, which usually have lower LCEAs and higher Tönnis angles.

In a systematic review by Yeung et al, ⁸ no agreement was found on whether hip arthroscopy actually results in better outcomes in patients with “mild” dysplasia when compared to those with “more evident” hip dysplasia due to lack of consensus on the definition of borderline hip dysplasia. There is a dissimilar concept of what should be considered a normal LCEA range. ⁶ Additionally, femoral head under-coverage can exist even in the presence of a normal LCEA. ² Siebenrock et al ⁶ described the anterior (AWI) and posterior (PWI) wall indexes as a versatile method to assess the anterior and posterior wall coverage of the femoral head. These tools are particularly valuable in cases of so-called borderline dysplasia, in which sometimes there is an underdiagnosed deficient anterior and/or posterior wall coverage. The concept of “mild” dysplasia based purely on an almost normal LCEA sounds minimalistic, as these hips can likely exhibit deficient anterior or posterior wall coverage with normal lateral coverage.^2,3 Also, understanding that hip dysplasia is a structural (ie, 3-dimensional [3-D]) problem of the hip should make orthopaedic providers further characterize acetabular anatomy with 3-D computed axial tomography (CT) or 3-D magnetic resonance imaging (MRI) to help reach an accurate diagnosis. ⁷

Moreover, the authors used the anterior center-edge angle (ACEA) to assess anterior femoral head coverage. Nonetheless, it is not completely clear if the false profile view (and, therefore, the ACEA) is accurate enough to delineate the true anterior coverage of the femoral head, ⁵ while it better defines posterior wear and osteoarthritis progression in acetabular dysplasia. ¹ In this sense, cross-sectional imaging is of utmost importance.

We compliment the authors on their objectivity and look forward to their future advances in this field. We feel hip arthroscopy may play a role in the treatment of hip dysplasia with subtle lateral/anterior under-coverage. However, further advances should be made to better understand spinopelvic parameters that may affect the femoral head’s structural coverage.