Corrections in alpha angle following two different operative approaches for CAM-type femoral acetabular impingement - Ganz surgical hip dislocation vs anterior mini-open

ARTICLE HIGHLIGHTS

Research background

Femoroacetabular impingement (FAI) is a predisposing factor for secondary osteoarthritis of the hip joint. The two extensively described impingement mechanisms of FAI are CAM and Pincer-type deformities. Regardless of predisposing etiology, this abnormal impingement type mechanism leads functional decrease of the patient and to secondary osteoarthritis of the hip joint. Early detection and removal of the asphericity alleviates this mechanical mismatch and oftentimes significantly improves the patient’s symptomatology. Various techniques (i.e., arthroscopic procedures ranging to more extensive open methods) have been well described in today’s literature and are broadly accepted. This study is significant since it shows statistically significant decreases in alpha angle were noted for both surgical techniques, the Ganz surgical hip dislocation vs anterior mini-open with larger decreases seen in the anterior mini-open group

Research motivation

Ultimately abnormal impingement type mechanisms can lead to symptomatic patients and to secondary osteoarthritis of the hip joint. Early detection and removal of the asphericity alleviates this mechanical mismatch. FAI and successful treatment has become a main focus of todays research focus. There are many surgical approaches to treat FAI. Finding effective surgical management to correct this deformity radiographically and improving functional outcome of the patient remains a challenge and requires further investigation.

Research objectives

The main objectives remains to find a successful way to address deformities of the acetabulum and proximal femur that lead to FAI. For this study the objectives were to evaluate the change from the baseline in the alpha angle on cross-table lateral radiograph after surgery and to compare radiographic corrections between the Ganz surgical hip dislocation and the anterior mini-open approach.

Research methods

This is a retrospective study assessing seventy-nine patients identified in a 5-year period. These patients had preoperative radiographic evidence of FAI and underwent surgery by a single surgeon at our institution, a tertiary care center. Patients with missing radiographic documentation, radiographs with insufficient quality which then precluded accurate measurement of the angle α, a diagnosed congenital condition, isolated Pincer deformity, and history of prior surgery were excluded from the study. Either the Ganz surgical hip dislocation or the anterior mini open approach was used. Postoperative radiographic evaluation of the alpha angle between the two surgical methods was done and corrected for age and gender using two-sample t-tests and chi-square analyses.

Research results

Statistically significant decreases in alpha angle were noted for both surgical techniques, with larger decreases seen in the anterior mini-open group. It is not fully understood if surgical intervention will ultimately prevent progression of osteoarthritis of the hip joint, however, it is believed that early detection and treatment should mitigate the presumed destructive forces. This study therefore shows that both surgical approaches provide a valid option for correcting the alpha angle which is implicated in FAI.

Research conclusions

Statistically significant decreases in alpha angle were noted for both surgical techniques, with larger decreases seen in the anterior mini-open group. While we do not know whether there is a difference in functional outcome of the patient, both surgical approaches provide a valid treatment option successfully decrease the alpha angle in patients with FAI.

Research perspectives

It remains difficult to design studies around surgical treatment options and radiographic findings do not necessarily correlate with clinical and functional outcome emphasizing the importance of investigating functional outcome of the patient. Future research should focus on arthroscopic vs open alpha angle reduction for FAI as well as functional outcome and future development of secondary osteoarthritis. Ideally, randomized controlled trials comparing functional outcome and radiographic changes pre vs post surgery between arthroscopic vs open treatment vs no treatment would be ideal. However, this study design my not be feasible in the US.