Penetration depth method--novel real-time strategy for evaluating femoroacetabular impingement

Acetabular labrum and cartilage contact mechanics during pivoting and walking tasks in individuals with cam femoroacetabular impingement syndrome

Femoroacetabular impingement syndrome (FAIS) is a motion-related pathology of the hip characterized by pain, morphological abnormalities of the proximal femur, and an elevated risk of joint deterioration and hip osteoarthritis. Activities that require deep flexion are understood to induce impingement in cam FAIS patients, however, less demanding activities such as walking and pivoting may induce pain as well as alterations in kinematics and joint stability. Still, the paucity of quantitative descriptions of cam FAIS has hindered understanding underlying hip joint mechanics during such activities. Previous in silico studies have employed generalized model geometry or kinematics to simulate impingement between the femur and acetabulum, which may not accurately capture the interplay between morphology and motion. In this study, we utilized models with participant-specific bone and articular soft tissue anatomy and kinematics measured by dual-fluoroscopy to compare hip contact mechanics of cam FAIS patients to controls during four activities of daily living (internal/external pivoting and level/incline walking). Averaged across the gait cycle during incline walking, patients displayed increased strain in the anterior joint (labrum strain: p-value = 0.038, patients: 11.7 ± 6.7 %, controls: 5.0 ± 3.6 %; cartilage strain: p-value = 0.029, patients: 9.1 ± 3.3 %, controls: 4.2 ± 2.3). Patients also exhibited increased average anterior cartilage strains during external pivoting (p-value = 0.039; patients: 13.0 ± 9.2 %, controls: 3.9 ± 3.2 %]). No significant differences between patient and control contact area and strain were found for level walking and internal pivoting. Our study provides new insights into the biomechanics of cam FAIS, including spatiotemporal hip joint contact mechanics during activities of daily living.

Interobserver and intraobserver reliability of a new radiological classification for femoroacetabular impingement syndrome

PURPOSE

Radiological evaluation of femoroacetabular impingement is based on single-plane parameters such as the alpha angle or the center edge angle, or complex software reconstruction. A new simple classification for cam and pincer morphologies, based on a two-plane radiological evaluation, is presented in this study. The determination of the intraobserver and interobserver reliability of this new classification is the purpose of this study.

METHODS

We retrospectively reviewed the three-view hip study in patient undergoing hip arthroscopy for FAI syndrome between October 2015 and April 2016. Any case having protrusio acetabuli, coxa profunda or which has undergone previous osteotomic surgery was excluded. Five observers used our proposed classification to identify three different stages for the cam and pincer morphologies. Inter- and intraobserver agreement of classification was determined using average pairwise Cohen's kappa coefficient.

RESULTS

The interobserver agreement for the pincer and cam morphologies was excellent. For the pincer morphology classification, the average Kappa agreement was 0.838 (range 0.764-0.944). For the cam morphology, the average pairwise Cohen's kappa coefficient was 0.846 (range 0.734-0.929). The intraobserver agreement was excellent as well. The average percent pairwise agreement was 0.870 and 0.845 for pincer and cam type, respectively.

CONCLUSIONS

The new classification system shows excellent levels of inter- and intraobserver agreement for both deformities. This classification is demonstrated to be a useful tool in planning hip arthroscopy. Further studies are needed to correlate the classification itself with specific intraoperative findings.

The Influence of Squat Kinematics and Cam Morphology on Acetabular Stress

PURPOSE

To evaluate the effect of varying degrees of simulated cam morphology on acetabular stress magnitude and location using a finite element model with 1 subject that incorporates population-specific hip/pelvis kinematics during a squat task.

METHODS

A reference model of the hip joint was created from magnetic resonance images obtained from 1 asymptomatic 28-year-old man without femoroacetabular impingement (FAI) morphology or hip dysplasia (alpha angle 41.9°, lateral center edge angle 34.0°, neck-shaft angle 137°, and no visible articular cartilage lesions or bone marrow edema on magnetic resonance). The femoral head/neck geometry was manipulated to mimic different cam morphology severities as reported in a previous study (minimum, moderate, and large). Peak hip and pelvis squat kinematics from healthy individuals (hip flexion 112.6°, abduction 10.5°, internal rotation 14.8°) and persons with FAI (hip flexion 106.3°, abduction 10.5°, internal rotation 8.9°) were applied to the control and cam models. Relative acetabular joint stress values and location of contact were the variables of interest.

RESULTS

Average von Mises stress values for control, minimum, moderate, and large cam models were 9.64, 9.27, 11.36, and 28.43 MPa, respectively. Contact in the control and minimum cam models occurred within the acetabular cup. In the moderate and large cam models, contact shifted anterosuperiorly within the acetabular cup and to anterosuperior acetabular rim, respectively.

CONCLUSIONS

Despite simulating lower degrees of hip flexion and internal rotation, increased stress and a shift in contact location were observed in the simulated models of FAI. This finding suggests that decreased hip internal rotation in this population during functional tasks may be the result of bony abutment.

CLINICAL RELEVANCE

Clinicians should be cautious about prescribing deep squats for persons with cam morphology. Performing squat exercises with neutral or external hip rotation may limit bony abutment at high hip flexion angles.

Radiographic Diagnosis of Pincer-Type Femoroacetabular Impingement: A Systematic Review

Background:

Femoroacetabular impingement (FAI) is a well-recognized condition that causes hip pain and can lead to early osteoarthritis if not managed properly. With the increasing awareness and efficacy of operative treatments for pincer-type FAI, there is a need for consensus on the standardized radiographic diagnosis.

Purpose:

To perform a systematic review of the evidence regarding imaging modalities and radiographic signs for diagnosing pincer-type FAI.

Study Design:

Systematic review; Level of evidence, 4.

Methods:

A literature review was performed in 2016 using the Cochrane, PubMed, and Embase search engines. All articles focusing on a radiographic diagnosis of pincer-type FAI were reviewed. Each of the included 44 articles was assigned the appropriate level of evidence, and the particular radiographic marker and/or type of imaging were also summarized.

Results:

There were 44 studies included in the final review. Most of the articles were level 4 evidence (26 articles), and there were 12 level 3 and 6 level 2 articles. The crossover sign was the most commonly used radiographic sign (27/44) followed by the lateral center-edge angle (22/44). Anteroposterior (AP) pelvis plain radiographs were the most commonly used imaging modality (33 studies). Poor-quality evidence exists in support of most currently used radiographic markers, including the crossover sign, lateral center-edge angle, posterior wall sign, ischial spine sign, coxa profunda, acetabular protrusion, and acetabular index. There is poor-quality conflicting evidence regarding the use of the herniation pit to diagnose pincer-type FAI. Some novel measurements, such as β-angle, acetabular roof ratio, and acetabular retroversion index, have been proposed, but they also lack support from the literature.

Conclusion:

No strong evidence exists to support a single best set of current radiographic markers for the diagnosis of pincer-type FAI, largely due to the lack of better quality trials (levels 1 and 2) that compare conventional radiographic findings with the gold standard, which is the intraoperative findings. More sophisticated imaging modalities such as computed tomography and magnetic resonance arthrography are often needed to diagnose pincer-type FAI, and these investigations are relatively accurate in assessing labral pathology or cartilage damage.

Hip Joint Stresses Due to Cam-Type Femoroacetabular Impingement: A Systematic Review of Finite Element Simulations

Background

The cam deformity causes the anterosuperior femoral head to obstruct with the acetabulum, resulting in femoroacetabular impingement (FAI) and elevated risks of early osteoarthritis. Several finite element models have simulated adverse loading conditions due to cam FAI, to better understand the relationship between mechanical stresses and cartilage degeneration. Our purpose was to conduct a systematic review and examine the previous finite element models and simulations that examined hip joint stresses due to cam FAI.

Methods

The systematic review was conducted to identify those finite element studies of cam-type FAI. The review conformed to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and studies that reported hip joint contact pressures or stresses were included in the quantitative synthesis.

Results

Nine articles studied FAI morphologies using finite element methods and were included in the qualitative synthesis. Four articles specifically examined contact pressures and stresses due to cam FAI and were included in the quantitative synthesis. The studies demonstrated that cam FAI resulted in substantially elevated contact pressures (median = 10.4 MPa, range = 8.5–12.2 MPa) and von Mises stresses (median 15.5 MPa, range = 15.0–16.0 MPa) at the acetabular cartilage; and elevated maximum-shear stress on the bone (median = 15.2 MPa, range = 14.3–16.0 MPa), in comparison with control hips, during large amplitudes of hip motions. Many studies implemented or adapted idealized, ball-and-cup, parametric models to predict stresses, along with homogeneous bone material properties and in vivo instrumented prostheses loading data.

Conclusion

The formulation of a robust subject-specific FE model, to delineate the pathomechanisms of FAI, remains an ongoing challenge. The available literature provides clear insight into the estimated stresses due to the cam deformity and provides an assessment of its risks leading to early joint degeneration.

Sagittal plane pelvis motion influences transverse plane motion of the femur: Kinematic coupling at the hip joint

Previous studies have suggested that internal femur rotation can influence sagittal pelvis motion. This indicates that there may be kinematic "coupling" of these two segments. The purpose of the current study was to determine whether there is a consistent and predictable kinematic relationship between the pelvis and the femur. Sixteen healthy subjects (nine females, seven males) performed three trials of maximum anterior and posterior pelvis tilt at four different hip flexion angles (0°, 30°, 60°, and 90°). Ordinary least squares regressions were used to calculate the ratio of transverse femur motion to sagittal pelvis motion using the mean kinematic curves during maximum anterior and posterior pelvis tilting. R(2) values were used to assess the strength of the kinematic relationship between these segments at each hip flexion angle. The ratios of transverse femur motion to sagittal pelvis motion were consistent across all hip flexion angles during anterior and posterior pelvis tilting (range 0.23-0.32; R(2) values greater than 0.97). On average, for every 5° of anterior pelvis tilt there was 1.2-1.6° of internal femur rotation and the converse was true for posterior pelvis tilt and external femur rotation. Our findings suggest that altered pelvis movement in the sagittal plane may influence transverse femur motion. The observed coupling behavior between the pelvis and femur may have implications for musculoskeletal conditions in which excessive internal femur rotation has been deemed contributory to symptoms (i.e. femoroacetabular impingement).

Combining femoral and acetabular parameters in femoroacetabular impingement: the omega surface

The concept of femoroacetabular impingement (FAI) proposes the development of hip osteoarthritis through motion-induced damage to the acetabular cartilage and labrum. Thus, dynamic interaction of the proximal femur and acetabulum is the crux of FAI. Several types of FAI can be distinguished, but FAI classification is mostly done with separate parameters for acetabular and femoral morphology on planar images, without direct representation of the femoroacetabular interaction. Five main parameters influence impingement between the proximal femur and the acetabular rim: alpha and center edge angles, acetabular and femoral version, and neck-shaft angle. We attempted to integrate these five parameters in order to reflect their interaction and derive a signal comprehensive parameter, the omega surface, to characterize the severity of FAI. The omega surface is a CT-based delineation of the femoral head surface that represents the area for impingement-free motion. The omega surface is determined with dedicated software (Articulis™) and can be determined for various positions of the hip joint. We determined the omega surface in a pilot study for five different hip morphotypes and found the omega surface was smaller in FAI morphotypes than in a normal hip. Furthermore, the omega surface was smaller in symptomatic versus control subjects with FAI morphotypes. The omega surface may therefore help in improved differentiation between symptomatic and asymptomatic FAI hips.

Can combining femoral and acetabular morphology parameters improve the characterization of femoroacetabular impingement?

BACKGROUND

Femoroacetabular impingement (FAI) presupposes a dynamic interaction of the proximal femur and acetabulum producing clinical symptoms and chondrolabral damage. Currently, FAI classification is based on alpha angle and center-edge angle measurements in a single plane. However, acetabular and femoral version and neck-shaft angle also influence FAI. Furthermore, each of these parameters has a reciprocal interaction with the others; for example, a shallow acetabulum delays impingement of the femoral head with the acetabular rim.

QUESTIONS/PURPOSES

We introduce the new parameter "omega zone," which combines five parameters into one: the alpha and center-edge angles, acetabular and femoral version, and neck-shaft angle. We sought to determine whether the omega zone could differentiate patients with FAI from (1) normal control subjects (alpha < 55°), but also from (2) control subjects with elevated alpha angles (≥ 55°).

METHODS

We evaluated CT data of 20 hips of male patients with symptomatic cam-type FAI and of 35 male hips extracted from 110 anonymized CT scans for vascular diagnosis. We excluded hips with osteoarthritis, developmental dysplasia, or coxa profunda (center-edge angle 20°-45° on AP pelvic view or corresponding coronal CT views). With dedicated software, femoral and pelvic orientation was standardized; we tested the omega zone in four hip positions in three distinct groups: patients with cam-type FAI (alpha > 60°) and control subjects with normal (< 55°) and high alpha angles (≥ 55°).

RESULTS

The omega zone was smaller in patients with cam-type FAI than normal control subjects (alpha angle < 55°) at 60° and 90° of flexion (mean, 12%; 95% confidence interval [CI], 7-17; p = 0.008; Cohen's d = 9%; 95% CI, 4-13; p = 0.003). Furthermore, the omega zone was smaller in all positions in patients with cam-type FAI than control subjects with high alpha angles (0° p = 0.017, 30° p = 0.004, 60° p = 0.004, 90° p = 0.007). In contrast, the omega zone did not differ between control subjects with normal or high alpha angles. In all hips, the omega zone decreased with flexion, corresponding to a decrease in remaining impingement-free motion with flexion.

CONCLUSIONS

The omega zone visualizes and quantifies the interaction of the proximal femur and acetabulum. The omega zone differed between patients with cam-type FAI and control subjects with high alpha angles (≥ 55°), who could not be distinguished based on alpha angle alone. For hip-preserving surgery, it can help surgeons decide whether to address the femur, the acetabulum, or both.

Hip preservation surgery: surgical care for femoroacetabular impingement and the possibility of preventing hip osteoarthritis

Despite its widespread usage, the hip preservation surgery can be most accurately described as a hypothesis that surgery can preserve a hip and prevent the need for arthroplasty. This premise has not been fully investigated to date, and there exist few summaries of the underlying evidence in regard to the basis of this terminology. This study seeks to define the hip preservation surgery, and then examines this premise critically in the context of treatment for its most commonly treated condition—femoroacetabular impingement. Finally, we report the current level of preservation of the hip that can be expected with current techniques.

A pre-operative approach of range of motion simulation and verification for femoroacetabular impingement

BACKGROUND

Femoroacetabular impingement (FAI) is increasingly recognized as a potential cause of hip osteoarthritis. A system capable of pre-operatively simulating hip range of motion (ROM) by given surface models from either healthy or FAI diseased bone is desirable.

METHODS

An impingement detection system using bounding sphere hierarchies was first developed. Both precision and accuracy of the impingement detection system were verified by a custom-designed phantom to imitate ball-and-socket hip movement. The impingement detection system was then implemented into the hip ROM simulation system to simulate the ROM of (1) healthy pelvis and femur, and (2) healthy pelvis and pathologic femur. The ROM simulation system was also verified by manipulating sawbones under the navigation of an optical tracking system.

RESULTS

The impingement detection system achieved a distance error of 0.53 ± 0.06 mm and an angular error of 0.28 ± 0.03°. The impingement detection accuracies were 100%, 100%, and 96% in three different phantom orientations, respectively. The mean errors between simulated and verified ROM were 0.10 ± 1.39° for the 'healthy pelvis and femur' group, and - 2.38 ± 3.49° for the 'healthy pelvis and pathologic femur' group.

CONCLUSION

The present study demonstrates a pre-operative approach to virtually simulate and predict the functional hip ROM based on the given bone models. The impingement detection and ROM simulation systems developed may also be used for other orthopedic applications.

A method for three-dimensional evaluation and computer aided treatment of femoroacetabular impingement

Several theoretical models have shown that the range of motion of the hip joint is impaired in patients with femoroacetabular impingement, and that the acetabular cartilage is at risk of being damaged as a result of abnormal shear stresses, even during normal everyday activities. Computer aided technologies might add to the early diagnosis and adequate treatment of such lesions. This paper describes the technique, theories and algorithms we have developed for patient-specific detection, analysis and computer aided surgery of femoroacetabular impingement. Currently available models applicable to femoroacetabular impingement offer modeling based on collision analysis of a constrained hip joint. Such an approach implies that neither the femur nor the acetabulum can be analyzed completely separately for the presence of structural lesions responsible for the impingement problem. Moreover, a constrained model does not allow for comprehensive prediction of the possible locations and extent of secondary cartilage lesions (so-called contre-coup lesions) of the posterior acetabulum opposite the anterior impingement site. We report a new technique for the subject-specific morphological analysis of the proximal femur, acetabulum and hip joint. The technique offers a number of advantages compared to currently used techniques for the diagnosis and evaluation of hip impingement, and has direct orthopaedic applications as it allows computer aided planning and minimally invasive surgery for patients with femoroacetabular impingement.