Acetabular retroversion is present when the acetabular opening is posterior rather than anterior in the sagittal plane. Some have understood acetabular retroversion to be a volumetrically sufficient acetabulum that is malrotated while others have postulated that it results from posterior insufficiency or anterior over-coverage. We find that retroversion can be associated with regional over and under-coverage in the same hip and yield symptoms ranging from instability to impingement or both. While the understanding of the pathomorphology of acetabular retroversion is still evolving, the appropriate treatment strategy of retroversion is in even a more primordial state, ranging from rim trimming to reorientation, with limited clinical data to direct one to either.
The clinical and radiographic results of acetabular reorientation for retroverted hips have been reported in a limited number of patients. Siebenrock et al. studied 29 hips with a crossover sign, 24 of which had a posterior wall sign.49
All underwent PAO with average follow up 30 months (range 24–49) with good to excellent result in 26. Reynolds et al. described “encouraging results” in 12 patients treated with PAO but provided no detailed analysis of the preoperative and postoperative parameters that characterize retroversion such as the crossover sign and posterior wall sign.11
Our results also indicate encouraging clinical outcomes with reliable elimination of the crossover sign and correction of the posterior wall sign in over 90% of patients utilizing our proposed surgical algorithm.
It has been shown that the posterior wall sign is a significant factor found to affect the progression of osteoarthritis in hips with cam impingement and therefore was included in our treatment algorithm.1
Our treatment algorithm for hips with FAI due to acetabular retroversion with a deficient posterior wall (a volumetrically deficient acetabulum) and “intact” acetabular articular cartilage is to perform acetabular reorientation with PAO. In our experience, these patients are typically younger, female, and have radiographic acetabular criteria that are also commonly associated with hip instability in addition to the acetabular retroversion. We have shown, as have others, that acetabular retroversion may constitute up to one third of hips with acetabular dysplasia.50
Conversely, we believe hips with acetabular retroversion and normal lateral and posterior coverage may be best treated with osteochondroplasty the anterior acetabular rim and femoral head-neck junction. These hips frequently have anterior acetabular articular cartilage lesions that need to be addressed.2
These patients are more likely to be older, male, and have radiographic criteria that reflect normal volumetric acetabula with adequate acetabular coverage in addition to acetabular retroversion.
This study found statistically significant differences in radiographic measures in the subpopulations of patients with acetabular retroversion as well as recognizable demographic/clinical characteristics. First, there were statistically more female patients amongst those treated with PAO and male patients treated with SDO. Ninety percent (27/30) of hips which underwent PAO had a positive posterior wall sign (the other 10% had deficient lateral coverage) but only 37 % (11/30) of hips which underwent SDO (these hips had either suspicion or preoperative evidence on advanced imaging of acetabular cartilage lesions).
There is evidence that pincer impingement due to acetabular retroversion is associated with labral injury.2,51
However, compared to cam impingement, pincer is thought to cause less damage to the underlying acetabular articular cartilage, most often leading to lesions limited to the outermost rim.5
Nevertheless, because most impingement deformities are combinations of cam and pincer components (reported as high as 72%)5,51
the constellation of labral and cartilage lesions will likely necessitate a combination of strategies to address chondrolabral pathology.5
Our data indicates that all but three of the patients treated with SDO had sufficient resection of anterior wall to eliminate the crossover sign. In general, we have used the extent of damaged articular cartilage to direct the amount of anterior acetabular osteochondroplasty rather than intra-operative imaging directed at producing a negative crossover sign. This approach with additional femoral debridement appears to provide sufficient anterior hip clearance with infrequent production of iatrogenic hip dysplasia.27,28,32
Clinically, patients in both treatment groups experienced statistically significant improvement in the HHS and at latest followup only one patient in each group required conversion to total hip arthroplasty. Two patients treated with SDO and anterior rim trimming for the retroversion and underlying hyaline cartilage subsequently required acetabular reorientation to improve coverage but both went on to excellent clinical results. Although the reported results for PAO in this study are specific to acetabular retroversion, the overall improvement in HHS and absolute magnitude of the post-operative HHS are similar to the larger population of patients treated with PAO at our institution.16
Similarly, the clinical improvement of patients treated with SDO due to acetabular retroversion are similar to what has been previously reported.20
We believe this demonstrates that the algorithm appropriately directed these patients with symptomatic acetabular retroversion to the correct surgery based upon the condition of their acetabular cartilage and adequacy of acetabular coverage.
The current work has several limitations, foremost of which is the fact that the treatment groups were not randomized and that the surgical decision making process evolved over the time of the study. Additionally, clinical and radiographic followup was not long-term and development of osteoarthritis commonly takes several years. Our study did not include arthroscopy in the treatment algorithm. However, arthroscopic osteochondroplasty could be used as an alternative to surgical dislocation while allowing the same principles to direct surgical decision-making.
In summary, the rationale of treating FAI due predominantly to acetabular retroversion in younger, more active patients with lateral and/or posterior wall insufficiency and intact articular cartilage with PAO, and patients with evidence of normal lateral and posterior acetabular coverage and compromised articular cartilage with SDO appears sound based on the clinical and radiologic results using our proposed surgical algorithm. Nevertheless, the decision regarding the best surgical management of the patient with FAI and associated acetabular retroversion remains difficult and depends on a thorough consideration of the hip 3D morphology and the degree of articular cartilage damage. ()