Inclusion of the Acetabular Labrum Reduces Simulated Range of Motion of the Hip Compared With Bone Contact Models

Abstract

Purpose: To determine whether inclusion of the acetabular labrum affects the maximum range of motion (ROM) during simulation of the flexioneadductioneinternal rotation impingement examination. Methods: Three-dimensional surface reconstructions of the femur, hemi-pelvis, and labrum from computed tomography arthrography images of 19 participants were used to simulate maximum ROM during the flexioneadductioneinternal rotation examination. Simulations were conducted for positions between 70 and 110 flexion and 0 and 20 adduction at 10 increments to measure maximum internal rotation and the position of contact between the femur and acetabular rim (bone-to-bone) or the femur and labrum (bone-to-labrum). Internal rotation angles and clock-face position values were compared between the 2 contact scenarios for each position. Results: The ROM in the bone-to-labrum contact model was significantly less than that of the bone-to-bone contact model for all evaluated positions (P .001, except at 110 flexion and 20 adduction, P ¼ .114). The inclusion of the labrum reduced internal rotation by a median [interquartile range] of 18 [15, 25] while altering the position of contact on the acetabular clock-face by e0:01 [e0:27, 0:16]. The variability in contact location for the bone-to-labrum contact scenario was nearly double that of the bone-to-bone contact scenario, as indicated by the interquartile range. Conclusions: Inclusion of the anatomy of the acetabular labrum in collision models used to simulate impingement examinations reduced the internal rotation ROM by approximately 20 and increased variability in the location of contact relative to the acetabular rim. Clinical Relevance: While standard bone-to-bone contact ROM simulations may be informative with respect to the relative change in ROM based on a surgical intervention (e.g., pre-and post-osteochondroplasty for cam-type femoroacetabular impingement), they may not accurately represent the clinical ROM of the joint or the kinematic position at which damage may occur due to shape mismatch between the femur and acetabulum.

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

“…In addition to contributing to the understanding of how cam morphology and pain alters hip joint mechanics, our study also emphasized the need for advancements in computerized surgical planning and impingement evaluation tools. 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.…”

“…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 . As such, incorporating dynamic joint translation and soft‐tissue structures into these models could substantially improve the validity and value of surgical planning and impingement evaluation tools.…”

Hip joint range of motion is restricted by pain rather than mechanical impingement in individuals with femoroacetabular impingement syndrome

“…On average, CT motion simulation yielded a ROM 16 degrees larger than 3D motion analysis. The simulated range of motion based on CT scans describe a theoretically possible ROM, allowed by the patient’s bone conformation, while for clinically assessed passive ROM, movement is affected by pain, discomfort, and possibly the labrum [ 22 ]. CT motion simulation may oversimplify hip contact mechanics, since these models include bone-to-bone contact but remove all soft tissue, including the cartilage and labrum [ 22 ].…”

“…The simulated range of motion based on CT scans describe a theoretically possible ROM, allowed by the patient’s bone conformation, while for clinically assessed passive ROM, movement is affected by pain, discomfort, and possibly the labrum [ 22 ]. CT motion simulation may oversimplify hip contact mechanics, since these models include bone-to-bone contact but remove all soft tissue, including the cartilage and labrum [ 22 ]. Findings of a recent study, examining the effect of inclusion of the acetabular labrum on maximum ROM during simulation of the flexion–adduction–internal rotation impingement, demonstrated reduced internal rotation ROM by close to 20° and increased variability in the location of contact relative to the acetabular rim [ 22 ].…”

“…CT motion simulation may oversimplify hip contact mechanics, since these models include bone-to-bone contact but remove all soft tissue, including the cartilage and labrum [ 22 ]. Findings of a recent study, examining the effect of inclusion of the acetabular labrum on maximum ROM during simulation of the flexion–adduction–internal rotation impingement, demonstrated reduced internal rotation ROM by close to 20° and increased variability in the location of contact relative to the acetabular rim [ 22 ]. Many patients with FAIS have concomitant hip and groin pain originating from other sources, i.e.…”