Assessment of Hip Translation In Vivo in Patients With Femoracetabular Impingement Syndrome Using 3-Dimensional Computed Tomography

Abstract

Purpose: To determine the 3-dimensional (3D) in vivo hip translation in patients with symptomatic femoroacetabular impingement syndrome (FAIS) using 3D computed tomography (CT) models with the hip in neutral and FABER (flexion, abduction, and the external rotation) positions and to identify patient predictors associated with the degree of hip translation. Methods: Seventy-eight patients with FAIS and cam lesions underwent CT scans in neutral and FABER positions. Demographics including age, sex, and body mass index (BMI) were recorded for each patient. The cam deformity was characterized both in plain x-ray film and 3D. Translation between both positions was calculated using a validated high-precision 3D-3D registration technique. Univariate and multivariate regression analyses sought factors correlated with translation. Results: The mean age of the patients included in the analysis was 36.3 AE 9.2 years, with 51% of the study group being female. The mean 3D femoral head center translation was 0.84 AE 0.37 mm, decomposed into vectors on standard anatomical directions as 0.13 AE 0.58 mm medial, 0.10 AE 0.54 mm posterior, and 0.08 AE 0.46 mm inferior. Multivariate analysis demonstrated that total translation was associated with larger alpha angles (b ¼ 0.014; 95% confidence interval [CI] 0.003-0.024; P ¼ .013), and greater BMI (b ¼ 0.033; 95% CI 0.001-0.065; P ¼ .042). Furthermore, posterioreinferior translation was associated with BMI (b ¼ 0.032; 95% CI 0.003-0.061; P ¼ .031), whereas medialelateral translation is associated with the female sex (b ¼ 0.388; 95% CI 0.124-0.634; P ¼ .002), and smaller head radius (b ¼ e0.068; 95% CI e0.128 to e0.007; P ¼ .029). Conclusions: As a provocative maneuver, FABER positioning in patients with FAIS resulted in an average measurable translation of the femoral head center in the posterior, medial, and inferior direction. Factors including sex, BMI, and alpha angle predicted the degree of translation. Clinical Relevance: The current study demonstrates that there is measurable hip translation between the neutral and FABER positions in patients with symptomatic FAIS, which may cause hip microinstability. Furthermore, the study found an association between hip translation and both modifiable and nonmodifiable factors. This may indicate the need for more comprehensive preoperative surgical planning, intraoperative dynamic examination of the hip, and consideration of capsular plication in certain patients.

Patients with cam‐type femoroacetabular impingement demonstrate increased change in bone‐to‐bone distance during walking: A dual fluoroscopy study

“…These tools traditionally use a fixed center of rotation 28 . As demonstrated here and by Cvetanovich et al, 19 it is unlikely that femurs with cam morphology maintain a single point of rotation within the acetabulum. Further, studies have also shown that regions of minimum bone‐to‐bone distance do not necessarily correlate with the regions of femur‐labrum contact 28,29 .…”

“…One prior study using CT evaluated the translation of the femoral head between neutral and combined hip flexion, abduction, and external rotation (FABER) in individuals with FAI syndrome. 19 In their evaluation of two static positions, 29% of patients had total translations greater than 1 mm, with the average translation of all patients being 0.84 mm. While joint translations are not equivalent to bone-to-bone distances, we noted larger changes during dynamic activities.…”

“…Our study is the first to quantify changes in bone‐to‐bone distance in individuals with FAI syndrome during functional tasks. One prior study using CT evaluated the translation of the femoral head between neutral and combined hip flexion, abduction, and external rotation (FABER) in individuals with FAI syndrome 19 . In their evaluation of two static positions, 29% of patients had total translations greater than 1 mm, with the average translation of all patients being 0.84 mm.…”

EURO-MUSCULUS/USPRM Dynamic Ultrasound Protocols for (Adult) Hip

“…Different types of femoroacetabular impingement can be confirmed by the evidence of abnormal mechanical contact/motion between the acetabular/labral side and the femoral head/neck during real-time imaging (with hip flexion and internal rotation; Video 6, http://links.lww.com/PHM/B711, Video 7, http://links.lww.com/PHM/B712, Video 8, http://links.lww.com/PHM/B713). 9,10 To assess femoral head instability, the hip joint is stressed using the “apprehension position.” To achieve stress on the anterior structures, the patient holds the contralateral knee to maintain the contralateral hip flexion in the supine position. Meanwhile, the ipsilateral hip is being extended, the knee is flexed, and the shin hangs over the bed.…”

Hip microinstability: fact or fiction?

“…It has been previously established that the hip does not simply rotate in its socket but also exhibits translational movements as well [1,2,6,13,16,22]. Recently, biomechanical models have shown that capsular laxity increases femoral head rotation and translation [8][9][10].…”