Cam type femoro-acetabular impingement: quantifying the diagnosis using three dimensional head-neck ratios

Evaluation of Cam Deformity on 3-Dimensional Computed Tomography With the Best-Fit Sphere Technique and the Alpha Angle Marking Method

BACKGROUND

Three-dimensional computed tomography (3D-CT) is commonly used for the evaluation of cam deformity; however, it does not display the cam border directly.

PURPOSE

To compare the efficacy of the best-fit sphere (BFS) method and the alpha angle marking (AAM) method in 3D-CT evaluation for the cam border.

STUDY DESIGN

Cohort study (Diagnosis); Level of evidence, 3.

METHODS

Twenty-six cases of cam deformity, confirmed during hip arthroscopy, were included in this study. All patients underwent a CT scan before surgery. Using multiplanar reconstruction, we obtained reformatted CT images of oblique axial, oblique coronal, and radial views. The alpha angle and femoral head-neck offset ratio (hnoR) were measured on the reformatted CT images. The cam area on 3D-CT was displayed in 4 different ways: by importing the markers from the reformatted CT images of the oblique axial view (cam-oa), the oblique coronal view (cam-oc), or the radial view (cam-r) using the AAM method, or by using the BFS method (cam-bfs). The sizes and locations of the displayed cams were compared.

RESULTS

All hips in this study had an alpha angle greater than 60° and an hnoR smaller than 0.17. The radial view measured a larger alpha angle and smaller hnoR than the oblique axial and coronal views (P < .05). The areas of cam-oa, cam-oc, cam-r, and cam-bfs were 161.47 ± 27.96, 89.78 ± 19.23, 241.73 ± 34.55, and 329.75 ± 42.73 mm², respectively, and their medial-to-lateral ranges along the acetabulum (clockface referents) were 12:30 to 03:00, 11:30 to 01:30, 11:30 to 03:00, and 11:00 to 03:30, respectively. Among the 4 displays, cam-bfs had the largest area and medial-to-lateral range (P < .05), and cam-r had the second largest area and range (P < .05). No significant difference in the mean distances from the acetabular rim to the superior border was detected among the 4 displays (P > .05).

CONCLUSION

The cam area displayed by the BFS method on 3D-CT was larger than those evaluated by the AAM method. In the reformatted CT, the sizes and locations of cam deformity differed among the oblique axial, oblique coronal, and radial views, with the radial view showing the greatest area.

Prevalence of femoroacetabular impingement morphology in asymptomatic youth soccer players: magnetic resonance imaging study with clinical correlation

OBJECTIVE

To determine the prevalence of femoroacetabular impingement morphology (FAIM), cam- or pincer-type, by magnetic resonance imaging (MRI) in asymptomatic adolescent soccer players, and to evaluate the possible correlation between alterations on MRI and clinical examination findings.

METHODS

A cross-sectional study was conducted to determine the prevalence of FAIM in asymptomatic youth soccer players aged 13-18 years. A total of 112 hips in 56 players (mean age 15.3 years) were evaluated by MRI. Images were examined by two musculoskeletal radiologists for signs of FAIM. Cam-type (impingement) deformity was diagnosed by alpha angle ≥55° or head-neck offset <7 mm. Pincer-type (impingement) deformity was diagnosed by center-edge angle (CEA) ≥35° or acetabular index ≤0°. Other MRI changes, characteristic of FAIM, were observed. Clinical examination was performed to determine the range of motion (ROM) of the hips. In addition, specific tests for anterolateral and posteroinferior impingement were performed.

RESULTS

The prevalence of MRI findings consistent with FAIM among this young population was 84.8% (95/112). The alpha angle was ≥55° in 77.7% (87/112) of hips, while the CEA was altered in 10.7% (12/112) of hips. Qualitative MRI findings consistent with FAIM were highly prevalent, and included loss of sphericity of the femoral head (77%), osseous bump (44%), femoral neck edema (21%), and acetabular osteitis (9%). The anterior impingement test was positive in 15% of the hips evaluated.

CONCLUSION

Youth soccer players have a high prevalence of FAIM as diagnosed by MRI. There is no correlation between physical examination findings and MRI evidence of FAIM in this population.

Sex Differences in Patients With CAM Deformities With Femoroacetabular Impingement: 3-Dimensional Computed Tomographic Quantification

PURPOSE

To determine if significant differences exist between male and female CAM deformities using quantitative 3-dimensional (3D) volume and location analysis.

METHODS

Retrospective analysis of preoperative computed tomographic (CT) scans for 138 femurs (69 from male patients and 69 from female patients) diagnosed with impingement from November 2009 to November 2011 was completed. Those patients who presented with hip complaints and had a history, physical examination (limited range of motion, positive impingement signs), plain radiographs (anteroposterior pelvis, 90° Dunn view, false profile view), and magnetic resonance images consistent with femoroacetabular impingement (FAI) and in whom a minimum of 6 months of conservative therapy (oral anti-inflammatory agents, physical therapy, and activity modification) had failed were indicated for arthroscopic surgery and had a preoperative CT scan. Scans were segmented, converted to point cloud data, and analyzed with a custom-written computer program. Analysis included mean CAM height and volume, head radius, and femoral version. Differences were analyzed using an unpaired t test with significance set at P < .05.

RESULTS

Female patients had greater femoral anteversion compared with male patients (female patients, 15.5° ± 8.3°; male patients, 11.3° ± 9.0°; P = .06). Male femoral head radii were significantly larger than female femoral heads (female patients, 22.0 ± 1.3 mm; male patients, 25.4 ± 1.3 mm; P < .001). Male CAM height was significantly larger than that in female patients (female patients, 0.66 ± 0.61 mm; male patients, 1.51 ± 0.75 mm; P < .001). Male CAM volume was significantly larger as well (male patients, 433 ± 471 mm(3); female patients, 89 ± 124 mm(3); P < .001). These differences persisted after normalizing height (P < .001) and volume (P < .001) to femoral head radius. Average clock face distribution was from the 1:09 o'clock position ± the 2:51 o'clock position to the 3:28 o'clock position ± the 1:59 o'clock position, with an average span from the 3:06 o'clock position ± the 1:29 o'clock position (male patients, the 11:23 o'clock position ± the 0:46 o'clock position to the 3:05 o'clock position ± the 1:20 o'clock position; female patients, the 11:33 o'clock position ± the 0:37 o'clock position to the 2:27 o'clock position ± the 0:45 o'clock position). There were no differences in the posterior (P = .60) or anterior (P = .14) extent of CAM deformities. However, the span on the clock face of the CAM deformities varied when comparing men with women (male patients, the 3:43 o'clock position ± the 1:29 o'clock position; female patients, the 2:54 o'clock position ± the 1:09 o'clock position; P = .02).

CONCLUSIONS

Our data show that female CAM deformities are shallower and of smaller volume than male lesions. Further studies will allow further characterization of the 3D geometry of the proximal femur and provide more precise guidance for femoral osteochondroplasty for the treatment of CAM deformities.

CLINICAL RELEVANCE

Female CAM deformities may not be detectable using current 2D nonquantitative methods. These findings should raise the clinician's index of suspicion when diagnosing a symptomatic CAM lesion in female patients.

Cam-type deformities: Concepts, criteria, and multidetector CT features

Interpreting imaging studies of a painful hip requires detailed knowledge of the regional anatomy. Some variants of the proximal femur, such as cam-type deformities, can course asymptomatically or cause femoroacetabular impingement. The principal numerical criterion for defining cam-type deformities, the alpha angle, has some limitations. In this article, we review the anatomic variants of the anterior aspect of the proximal femur, focusing on cam-type deformities. Using diagrams and multidetector CT images, we describe the parameters that are useful for characterizing these deformities in different imaging techniques. We also discuss the potential correspondence of imaging findings of cam-type deformities with the terms coined by anatomists and anthropologists to describe these phenomena.

Does cam osteochondroplasty compromise proximal femur strength?

Little is known about the effect on load bearing ability of cam-type femurs following osteochondroplasty. The aim of this study was to compare the change in deformation undergone by cam-type femoral acetabular impingement femur models after resection of different volumes. Dry-bone replicas (N = 10) of two cam-type femurs (cam A and B) underwent resections of increasing volume (Surgery I, II and III) representing conservative, adequate and radical resections. Deformation under cyclic loading of 700 N for five cycles after each surgery was compared. The 360° alpha angle and the change in head to neck ratio at four equidistant points along the femoral neck were used as measures of surgical efficacy and volume resected. Intact cam A and B replicas had a maximum alpha angle of 88° and 90°, respectively, which were reduced to 55° and 54° post Surgery I. Cam A replicas showed a significant reduction (p < 0.01) in mean axial displacement after Surgery I (up to 10% reduction in neck volume) and an increase after Surgery III (~20%-40% reduction in neck volume) compared to unresected controls (p < 0.01). Surgery II (~10%-15% reduction in neck volume) produced no significant change in mean displacement (p > 0.05). Cam B models exhibited lower mean displacement after Surgery I, II and III (p < 0.01) compared to unresected controls. Conservative surgery appears to improve the axial load bearing ability of dry-bone models. Radical resections may significantly decrease the fracture-resistant properties of bone following osteochondroplasty which should be noted when planning such a procedure.

The three-dimensional relationship between acetabular rim morphology and the severity of femoral cam lesions

We examined the relationship between the size of the femoral cam in femoroacetabular impingement (FAI) and acetabular pathomorphology to establish if pincer impingement exists in patients with a femoral cam.

CT scans of 37 symptomatic impinging hips with a femoral cam were analysed in a three-dimensional study and were compared with 34 normal hips. The inclination and version of the acetabulum as well as the acetabular rim angle and the bony acetabular coverage were calculated. These measurements were correlated with the size and shape of the femoral cams.

While the size of the femoral cam varied characteristically, the acetabular morphology of the two groups was similar in terms of version (normal mean 23° (sd 7°); cam mean 22° (sd 9°)), inclination (normal mean 57° (sd 5°); cam mean 56° (sd 5°)), acetabular coverage (normal mean 41% (sd 5%); cam mean 42% (sd 4%)) and the mean acetabular rim angle (normal mean 82° (sd 5°); cam mean 83° (sd 4°)).

We found no correlation between acetabular morphology and the severity of cam lesion and no evidence of either global or focal over-coverage to support the diagnosis of ‘mixed’ FAI. The femoral cam may provoke edge loading but removal of any acetabular bearing surface when treating cam FAI might induce accelerated wear.

Cite this article: Bone Joint J 2013;95-B:314–19.

Emerging ideas: Novel 3-D quantification and classification of cam lesions in patients with femoroacetabular impingement

BACKGROUND

Femoroacetabular impingement (FAI) can lead to labral injury, osseous changes, and even osteoarthritis. The literature contains inconsistent definitions of the alpha angle and other nonthree-dimensional (3-D) radiographic measures. We present a novel approach to quantifying cam lesions in 3-D terms. Our method also can be used to develop a classification system that describes the exact location and size of cam lesions.

QUESTIONS/HYPOTHESES

We asked whether automated quantification of CAM lesions based on CT data is a reasonable way to detect CAM lesions and whether they may be classified based on location.

METHOD OF STUDY

We developed a method to quantify femoral head cam lesions using 3-D modeling of CT scans. By segmenting raw DICOM data, we can determine the distance from the cam lesion's surface points to the centroid of the femoral head to quantify the mean bump height, volume, and location. The resulting 3-D femoral and acetabular models will be analyzed with custom software. We then will quantify the cam lesion with 3-D parameters using a modified zoning method. The mean bump height, volume, and location on the clock face, and relative zoning will be calculated. Zonal differences will be statistically analyzed. To assess the ability of this method to predict arthroscopic findings, we will obtain preoperative CT scans for 25 patients who undergo hip arthroscopy for FAI. We will compare measurements with the method with our measurements from arthroscopy. The clinical implications of our method's measurements then will be reviewed and refined for future prospective studies.

SIGNIFICANCE

We present a novel approach that can quantify a cam lesion's location and size. This method will be used to provide guidelines for the exact amount of bony resection needed from a specific location of the proximal femur. There is also potential to develop software for ease of use so this method can be more widely applied.

Mathematical representation of the normal proximal human femur: Application in planning of cam hip surgery

Precise modelling of the proximal femur can be used for detecting and planning corrective surgery for subjects with deformed femurs using robotic technology or navigation systems. In this study, the proximal femoral geometry has been modelled mathematically. It is hypothesised that it is possible to fit a quadratic surface or combinations of them onto different bone surfaces with a relatively good fit. Forty-six computed tomography datasets of normal proximal femora were segmented. A least-squares fitting algorithm was used to fit a quadratic surface on the femoral head and neck such that the sum of distances between a set of points on the femoral neck and the quadratic surface was minimised. Furthermore, the position of the head–neck articular margin was also measured. The femoral neck was found to be represented as a good fit to a hyperboloid with an average root mean-squared error of 1.0 ± 0.13 mm while the shape of the femoral articular margin was a reproducible sinusoidal wave form with two peaks. The mathematical description in this study can be used for planning corrective surgery for subjects with cam-type femoroacetabular impingement.