Subject-specific Patterns of Femur-labrum Contact are Complex and Vary in Asymptomatic Hips and Hips With Femoroacetabular Impingement

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.

Electronic supplementary material

The online version of this article (doi:10.1007/s11999-014-3919-9) contains supplementary material, which is available to authorized users.     

Development of a Valid Simplified Chinese Version of the Oxford Hip Score in Patients With Hip Osteoarthritis

Background

Although the Oxford Hip Score has been translated and validated in several languages, there is currently no Chinese version of the outcomes measurement. Our study aims to crossculturally adapt and validate the Oxford Hip Score into a simplified Chinese version.

Questions/purposes

We tested the (1) reliability; (2) validity; and (3) responsiveness of the Chinese version of the Oxford Hip Score.

Methods

First we translated the Oxford Hip Score into simplified Chinese, then back into English, then held a consensus meeting to achieve the final simplified Chinese version. Then we evaluated the psychometric properties of Chinese version of the Oxford Hip Score in patients undergoing total hip arthroplasty (THA). All patients undergoing THA between July and December 2012 were invited to participate in this study; a total of 108 (79% of 136 invited) did so. To assess the test-retest validity, all participants completed the Chinese version of the Oxford Hip Score again with a 2-week interval. Pearson correlation coefficient was used to evaluate the construct validity between the Chinese version of the Oxford Hip Score and visual analog scale (VAS), Harris hip score, and eight individual domains of the SF-36. Responsiveness was demonstrated by comparing the pre- and postoperative scores of the Chinese version of the Oxford Hip Score.

Results

The test-retest reliability with intraclass correlation coefficient (0.937) and internal consistency with Cronbach’s alpha (0.91) were excellent. The Chinese version of the Oxford Hip Score correlated with the Harris hip score (0.89, p < 0.01), VAS (−0.79, p < 0.01), and Physical Functioning (0.79, p < 0.01) and Bodily Pain (0.70, p < 0.01) domains of SF-36, which suggested construct validity. No floor or ceiling effects were found. The effect size and standardized response mean values were 3.52 and 3.31, respectively, indicating good responsiveness.

Conclusions

The Chinese version of the Oxford Hip Score showed good reliability, validity, and responsiveness in evaluating standard Chinese-speaking patients with hip osteoarthritis undergoing THA. It can be used by clinical surgeons as a complement to the traditional outcome measures.