Summary

The COS indicative of acetabular retroversion does not influence the acetabuloplasty rate as it does in hips with normal or high lateral coverage, where the acetabuloplasty rates increase significantly.

Abstract

Background

The radiographic crossover sign (COS) is an indicator of acetabular retroversion, classically representing relative anterosuperior overcoverage often treated with rim trimming (i.e., acetabuloplasty) which could exacerbate acetabular hypovolemia in dysplasia. No prior study has investigated the prevalence of acetabular retroversion in patients with dysplasia undergoing hip arthroscopy or if the COS increases acetabuloplasty rates in dysplasia.

Purpose

To report the prevalence of acetabular retroversion, posterior wall insufficiency, and influence of the COS on acetabuloplasty rates in dysplasia compared with control groups of normal and high lateral acetabular coverage. Hypothesis: The arthroscopic management of the COS varies in patients as a function of lateral acetabular coverage. Acetabuloplasty rates significantly increase in the presence of the COS in patients with normal and high LCEA groups but not those with low LCEA (Dysplasia).

Study design: Level of evidence 3, retrospective comparative observational cohort study

Methods

A retrospective observational cohort study was performed from a prospectively collected multi-center database. Patients undergoing isolated hip arthroscopic surgery were assigned to either dysplasia (lateral center-edge angle (LCEA) = 25°, normal (LCEA 26-38°), or pincer femoroacetabular impingement (FAI) groups (LCEA = 39°). The prevalence of radiographic crossover sign (COS), posterior wall sign (PWS), and acetabuloplasty rates between and within study and control groups were obtained.

Results

Of 1729 total patients undergoing hip arthroscopy, 277 (16%) patients comprised the dysplasia group, 1170 (68%) normal group, and 282 (16%) pincer group. Mean LCEAs were 22.3°, 31.9°, and 43.4°, respectively (p<0.001). Prevalence of COS were similar at 31%, 35%, and 40%, respectively (p=0.120). Prevalence of PWS in hips with COS were similar at 31%, 23%, and 23%, respectively (p=0.354). Acetabuloplasty was less commonly performed in the dysplasia group than in the normal group or pincer group (p<0.001). The presence of a COS did not significantly influence the acetabuloplasty rate in dysplasia, whereas it significantly increased the acetabuloplasty rates in the control groups (p<0.001).

Conclusions

Acetabular retroversion occurs with similar prevalence in dysplasia compared with normal and high lateral acetabular coverage hips undergoing hip arthroscopy but with lower acetabuloplasty rates which are not influenced by the COS.

Clinical relevance: To the open or arthroscopic hip preservation surgeons: acetabuloplasty to “treat” the “pathologic” COS may cause iatrogenic worsening of an already hypovolemic socket. In the setting of dysplasia with acetabular retroversion, the COS may represent physiologic anterosuperior coverage of the femoral head.
To PAO surgeons: classic retroverting PAO will cause iatrogenic pincer femoroacetabular impingement. Direct coronal plane repositioning or even anteverting PAO may be indicated in this setting.
To hip arthroplasty surgeons: iatrogenic worsening via either aforementioned error can also adversely impact patients that eventually proceed to total hip arthroplasty.
Key terms: Dysplasia, retroversion, hip arthroscopy, acetabuloplasty, center-edge angle, crossover sign.

What this study adds to existing knowledge: Acetabular retroversion occurs in 31% of hips undergoing arthroscopy with borderline dysplasia. The retroversion is caused by relative posterior insufficiency in 31% of those hips rather than relative anterior overcoverage. A low LCEA may trump the COS in the surgical decision-making; high-volume hip arthroscopy surgeons recognize that acetabular retroversion in dysplasia should be treated with relatively infrequent focal rim trimming and the COS does not influence the acetabuloplasty rate as it does in hips with normal or high lateral coverage, where the acetabuloplasty rates increase significantly.