Original Article
Acetabular Rim Reduction for the Treatment of Femoroacetabular Impingement Correlates With Preoperative and Postoperative Center-Edge Angle

https://doi.org/10.1016/j.arthro.2009.11.003Get rights and content

Purpose

The purpose of this study was to quantify the change in degrees in the center-edge (CE) angle for each millimeter of acetabular rim resected in hips undergoing arthroscopic acetabular rim trimming.

Methods

Preoperative and postoperative CE angle and millimeters of rim reduction were prospectively collected in 58 hips that underwent arthroscopic rim reduction. There were 35 women and 23 men. The mean age was 32 years. The inclusion criterion was hip arthroscopy for femoroacetabular impingement in patients without dysplastic hips. Two orthopaedic surgeons made independent measurements of the CE angle on preoperative and postoperative anteroposterior pelvis radiographs. To determine the amount of rim reduction intraoperatively, the lunate surface was measured with an arthroscopic ruler at the 12-o'clock position before and after rim trimming. The rim trimming was performed by a single surgeon using a 5.5-mm motorized bur.

Results

For the 58 hips included in this study, the mean rim reduction performed was 3.2 mm (range, 1 to 9 mm). The mean change in CE angle was 3.9° (range, 0° to 17°). All numbers were normally distributed. By use of a regression model, the change in the CE angle could be determined by the following formula: Change in CE angle = 1.8 + (0.64 × rim reduction in millimeters). The interobserver intraclass correlation coefficient for radiographic measurement of the CE angle was 0.92 (95% confidence interval, 0.87 to 0.95), indicating excellent interobserver reliability.

Conclusions

The amount of change in the CE angle can be estimated by the amount of bony resection performed at the 12-o'clock position on the lunate surface in the arthroscopic treatment of femoroacetabular impingement. We found that 1 mm of bony resection equals 2.4° of change in the CE angle and 5 mm of bony resection equals 5° of change in the CE angle.

Level of Evidence

Level II, diagnostic study.

Section snippets

Methods

Between August 2007 and April 2008, 58 patients were prospectively enrolled in this institutional review board–approved study. Patients presented for the treatment of debilitating hip pain. The mean age at the time of arthroscopy was 32 years (range, 18 to 61 years). There were 23 men and 35 women. There were 22 left hips and 36 right hips. The mean body mass index was 23 (range, 18 to 32).

Inclusion criteria were hip arthroscopy for the treatment of FAI and rim reduction at the time of hip

Results

The mean preoperative CE angle was 36.4° (range, 25° to 51°) for observer 1. For observer 2, the mean preoperative CE angle was 36.7° (range, 22° to 51°). The mean postoperative CE angle was 32.3° (range, 23° to 49°) for observer 1. For observer 2, the mean postoperative CE angle was 33.1° (range, 22° to 44°). The interobserver intraclass correlation coefficient for radiographic measurement of the CE angle was 0.92 (95% confidence interval, 0.87 to 0.95), indicating excellent interobserver

Discussion

This study showed that the change in CE angle could be estimated from millimeters of acetabular bony resection. Furthermore, this study showed that the CE angle is a reliable measurement with excellent inter-rater reliability as a radiographic diagnostic tool for the measurement of acetabular coverage.

Although CE angle is not a perfect means of assessing acetabular coverage, there is certainly a range below which the hip is at a higher risk of developing osteoarthritis, labral tears, and even

Conclusions

The findings of this study showed that the amount of change in the CE angle can be estimated by the amount of bony resection performed at the 12-o'clock position on the lunate surface in the arthroscopic treatment of femoroacetabular pincer impingement. We found that 1 mm of bony resection equals 2.4° of change in the CE angle and 5 mm of bony resection equals 5° of change in the CE angle. The following formula can be used: Change in CE angle = 1.8 + (0.64 × rim reduction in millimeters).

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    Recipient of the 2009 Arthroscopy Association of North America Fellows Essay Award.

    Supported by Smith & Nephew, Andover, MA.

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