Magnetic resonance imaging verification of anterior capsular impingement in the hip joint: A three-dimensional analysis

Background: This study aimed to clarify whether the anterior hip capsular ligament is impinged between the acetabulum and femur during hip flexion or adduction and to determine the difference in the distance between the femur and capsular ligament in healthy adults and those with hip pain.

Methods: Magnetic resonance imaging of the hip joint was conducted at the following hip positions: 0° of flexion, 60° of flexion, maximal flexion, and maximal flexion with adduction. A three-dimensional model of the capsular ligament and femur was constructed. The minimal distance between the femur and capsular ligament, termed the capsule-femur distance, was computed. Because a capsule-femur distance of 0 mm indicates contact between the femur and the capsular ligament, that is, capsular impingement, the distance in each position was compared for each group using a one-sample t-test. The capsule-femur distance in the various groups and for different positions was compared using a split-plot analysis of variance.

Findings: Fifteen healthy individuals and sixteen individuals experiencing hip pain were enrolled. The capsule-femur distance was significantly greater than 0 mm in all positions in both groups, and none of the groups had a capsule-femur distance of 0 mm. The capsule-femur distance was significantly longer in the other positions than in the 0° flexion position, and significantly longer in the hip pain group than in the healthy group.

Interpretation: Capsular impingement did not occur in either group, even during hip flexion or adduction. Furthermore, the capsule-femur distance was longer in the hip flexion and hip pain groups.