Hip capsule dimensions in patients with femoroacetabular impingement: a pilot study

Abstract

Background: Joint-preserving hip surgery, either arthroscopic or open, increasingly is used for the treatment of symptomatic femoroacetabular impingement (FAI). As a consequence of surgery, thickening of the joint capsule and intraarticular adhesions between the labrum and joint capsule and between the femoral neck and the joint capsule have been observed. These alterations are believed to cause persistent pain and reduced range of motion. Because the diagnosis is made with MR arthrography, knowledge of the normal capsular anatomy and thickness on MRI in patients is important. To date there is no such information available.

Questions/purposes: The purpose of this study was to establish thickness, length of the hip capsule, and the size of the perilabral recess in patients with FAI.

Methods: We reviewed the preoperative MR arthrography of 30 patients (15 men) with clinical symptoms of FAI. We measured capsular thickness and made observations on the perilabral recess.

Results: The joint capsule was thickest (6 mm) anterosuperiorly between 1 and 2 o'clock. The average length from the femoral head-neck junction to the femoral insertion of the capsule ranged from 19 to 33 mm. A perilabral recess was present circumferentially, even across the acetabular notch, where the labrum is supported by the transverse acetabular ligament. The shortest recess occurred superiorly.

Conclusions: Knowledge of the capsular anatomy in patients with FAI before surgery is important to judge the postoperative changes and to plan potential further therapy including arthroscopic treatment of intraarticular adhesions.

Fig. 1

This figure shows the principle measurements that were obtained on a radial slice along the femoral neck: anterior capsule thickness on this slice is a = 5.84 mm, posterior thickness p = 1.97 mm. Distance of the anterior capsular insertion from the femoral head-neck junction is A = 21.02 mm; the posterior distance is P = 23.26 mm.

Fig. 2

MR arthrography through the 12 and 6 o‘clock positions. (1) Perilabral recess superiorly, the joint capsule is attached to the labrum. (2) Zona orbicularis. (3) Femoral insertion of the joint capsule at the superior base of the neck. (4) Inferior perilabral recess. (5) Labrum, supported by the transverse acetabular ligament. (6) Inferior femoral insertion of joint capsule. (7) Teardrop.

Fig. 3

This diagram shows the average capsular thickness along the circumference of the femoral neck.

Fig. 4

On this diagram, the average length of the joint capsule is shown. The length was measured from the head-neck junction to the distal insertion at the femoral neck.

Fig. 5

This diagram shows the depth of the perilabral recess relative to the adjacent labrum.

Fig. 6

Schematic showing the influence of joint distention. The fixed origin and insertion of the capsule remain unchanged independent of the amount of applied intraarticular fluid. The length of the perilabral recess remains unchanged.