Subject-specific patterns of femur-labrum contact are complex and vary in asymptomatic hips and hips with femoroacetabular impingement

Abstract

Background: Femoroacetabular impingement (FAI) may constrain hip articulation and cause chondrolabral damage, but to our knowledge, in vivo articulation and femur-labrum contact patterns have not been quantified.

Purpose: In this exploratory study, we describe the use of high-speed dual-fluoroscopy and model-based tracking to dynamically measure in vivo hip articulation and estimate the location of femur-labrum contact in six asymptomatic hips and three hips with FAI during the impingement examination. We asked: (1) Does femur-labrum contact occur at the terminal position of impingement? (2) Could range of motion (ROM) during the impingement examination appear decreased in hips with FAI? (3) Does the location of femur-labrum contact coincide with that of minimum bone-to-bone distance? (4) In the patients with FAI, does the location of femur-labrum contact qualitatively correspond to the location of damage observed intraoperatively?

Methods: High-speed dual-fluoroscopy images were acquired continuously as the impingement examination was performed. CT arthrogram images of all subjects were segmented to generate three-dimensional (3-D) surfaces for the pelvis, femur, and labrum. Model-based tracking of the fluoroscopy images enabled dynamic kinematic observation of the 3-D surfaces. At the terminal position of the examination, the region of minimal bone-to-bone distance was compared with the estimated location of femur-labrum contact. Each patient with FAI underwent hip arthroscopy; the location of femur-labrum contact was compared qualitatively with damage found during surgery. As an exploratory study, statistics were not performed.

Results: Femur-labrum contact was observed in both groups, but patterns of contact were subject-specific. At the terminal position of the impingement examination, internal rotation and adduction angles for each of the patients with FAI were less than the 95% confidence intervals (CIs) for the asymptomatic control subjects. The location of minimum bone-to-bone distance agreed with the region of femur-labrum contact in two of nine hips. The locations of chondrolabral damage identified during surgery qualitatively coincided with the region of femur-labrum contact.

Conclusions: Dual-fluoroscopy and model-based tracking provided the ability to assess hip kinematics in vivo during the entire impingement examination. The high variability in observed labrum-femur contact patterns at the terminal position of the examination provides evidence that subtle anatomic features could dictate underlying hip biomechanics. Although femur-labrum contact occurs in asymptomatic and symptomatic hips at the terminal position of the impingement examination, contact may occur at reduced adduction and internal rotation in patients with FAI. Use of minimum bone-to-bone distance may not appropriately identify the region of femur-labrum contact. Additional research, using a larger cohort and appropriate statistical tests, is required to confirm the findings of this exploratory study.

Fig. 1A–F

(A) The AP radiograph for Patient 1 shows a mildly shallow acetabulum and (B) the frog-leg lateral radiograph shows decreased femoral head-neck offset. (C) The AP radiograph for Patient 2 shows protrusio and (D) the frog-leg lateral radiograph shows the pincer groove and femoral neck prominence. (E) The AP radiograph for Patient 3 shows acetabular overcoverage, and (F) the frog-leg lateral radiograph shows the pincer groove.

Fig. 2A–I

The locations of minimum bone-to-bone distance and labral contact at the terminal position of the impingement examination (maximum internal rotation in flexion) on the femur are shown for: (A) a 22-year-old asymptomatic man; (B) a 23-year-old asymptomatic man; (C) a 22-year-old asymptomatic man; (D) a 28-year-old asymptomatic man; (E) a 31-year-old asymptomatic woman; (F) a 27-year-old asymptomatic woman; (G) Patient 1, a 25-year-old man; (H) Patient 2, a 23-year-old woman; and (I) Patient 3, a 26-year-old woman. The region of minimum bone-to-bone distance is the region of the anterosuperior femoral head and neck closest to the acetabular rim. The region of labrum contact was defined as the region of overlap between the anterosuperior femoral head and neck and rigid labrum surface. (E) No contact between the labrum and anterosuperior femoral head and neck was detected for this asymptomatic control subject. (C and H) Regions of minimum bone-to-bone distance and femur-labrum contact overlapped by more than 25%.

Fig. 3A–I

The locations of minimum bone-to-bone distance and labral contact at the terminal position of the impingement examination (maximum internal rotation in flexion), on the pelvis and labrum are shown for: (A) a 22-year old asymptomatic man; (B) a 23-year-old asymptomatic man; (C) a 22-year old asymptomatic man; (D) a 28-year-old asymptomatic man; (E) a 31-year-old asymptomatic woman; (F) a 27-year-old asymptomatic woman; (G) Patient 1, a 25-year-old man; (H) Patient 2, a 23-year-old woman; and (I) Patient 3, a 26-year-old woman. The region of minimum bone-to-bone distance is the region of the acetabular rim closest to the anterosuperior femoral head and neck. The region of labrum contact was defined as the region of overlap between the anterosuperior femoral head and neck and rigid labrum surface. (C) For this asymptomatic control subject, the location of labral contact was directly above the region of minimum bone-to-bone distance. (E) No contact between the labrum and anterosuperior femoral head and neck was detected for this asymptomatic control subject. (C and H) The regions of minimum bone-to-bone distance and femur-labrum contact overlapped by more than 25%.

Fig. 4A–D

(A) Flexion, (B) adduction, and (C) internal rotation angles of the asymptomatic control subjects and patients with FAI during the impingement examination are shown. The angles are presented as mean ± 95% CIs for the asymptomatic control subjects. (D) Anterior views are shown for a subject with a normal hip at points of interest corresponding to x-axis tick marks on the joint angle plots: T₁ = neutral/start of the examination; T₂ = approximate midpoint of flexion; T₃ = maximum flexion; T₄ = maximum internal rotation in flexion/terminal position.

Fig. 5A–F

Positions of the pelvis, femur, and labrum for the patients at the terminal position of the impingement examination, maximum internal rotation in flexion, are shown. The black box highlights the enlarged region (shown to the right) to show the location of femur-labrum contact (*). (A) The position of Patient 1 in the terminal position is shown. (B) For Patient 1, contact between the femur and labrum occurs on the cam lesion. (C) The position of Patient 2 in the terminal position is shown. (D) The labrum contacts the bony prominence on the femur for Patient 2. (E) The position of Patient 3 in the terminal position is shown. (F) For Patient 3, the pincer groove on the femur contacts the labrum.

Fig. 6A–C

Arthroscopic images were obtained through an anterolateral portal (70° scope). (A) A labral tear and bruising (*) are seen at the anterosuperior chondrolabral junction in Patient 1. (B) Cartilage delamination (*) is observed at the anterosuperior chondrolabral junction in Patient 2. (C) Mechanical wear (*) is present at the location of the pincer groove on the anterolateral femoral neck in Patient 3. F = Femoral head, L = Labrum.