Relationship of acetabular dysplasia and femoroacetabular impingement to hip osteoarthritis: a focused review

Abstract

Hip osteoarthritis (OA) leads to significant functional limitations and economic burden. If modifiable risk factors for hip OA are identified, it may be possible to implement preventative measures. Bony abnormalities associated with acetabular dysplasia (AD) and femoroacetabular impingement have been recently implicated as risk factors for hip OA. The purpose of this focused review is to summarize the available evidence describing the relationship between bony abnormalities and hip OA. A librarian-assisted database search with PubMed, Embase, and CENTRAL was performed. Relevant articles were identified and assessed for inclusion criteria. The authors reviewed cohort and case-control studies that reported on the association between abnormal hip morphology and hip OA. The available literature suggests that an association exists between bony abnormalities found in AD and femoroacetabular impingement and hip OA, and preliminary evidence suggests that AD is a risk factor for OA; however, these conclusions are based on limited evidence. Prospective, longitudinal studies are needed to confirm the causal relationship between abnormal hip morphology and the future development of hip OA.

Figure 1

Figure 1a. Acetabulum without dysplasia. One measurement to represent acetabular dysplasia is lateral center edge angle of Wiberg (CEA). The CEA is formed by (A) line perpendicular to the transverse axis of the pelvis drawn from femoral head center and (B) line from the femoral head center to the superolateral point of acetabulum. A range of CEA values are reported to define acetabular dysplasia including ≥ 20°, ≥ 25°≥ 30°. A range of CEA values is also reported to define pincer impingement including ≥ 40°, ≥ 45°. Figure 1b. Acetabular dysplasia represented by a small lateral center edge angle of Wiberg (CEA).

Figure 1

Figure 1a. Acetabulum without dysplasia. One measurement to represent acetabular dysplasia is lateral center edge angle of Wiberg (CEA). The CEA is formed by (A) line perpendicular to the transverse axis of the pelvis drawn from femoral head center and (B) line from the femoral head center to the superolateral point of acetabulum. A range of CEA values are reported to define acetabular dysplasia including ≥ 20°, ≥ 25°≥ 30°. A range of CEA values is also reported to define pincer impingement including ≥ 40°, ≥ 45°. Figure 1b. Acetabular dysplasia represented by a small lateral center edge angle of Wiberg (CEA).

Figure 2

Figure 2a. Acetabular depth index (ADI). The ADI is the length of line A. Line (B) is drawn from the edge of the articular surface of the acetabulum and the upper corner of the ipsilateral symphysis pubis. Line A is the distance from the deepest part of the acetabular margin to line B. Acetabular dysplasia is often defined an ADI as < 9 mm. Figure 2b. Acetabular depth ratio (ADR). The ADR is calculated by dividing (A) perpendicular line from line B to the medial corner of the acetabular weight-bearing surface by (B) acetabular width and multipliing by 1000 (A/B × 1000). Acetabular dysplasia is often defined an ADR≤ 250.

Figure 2

Figure 2a. Acetabular depth index (ADI). The ADI is the length of line A. Line (B) is drawn from the edge of the articular surface of the acetabulum and the upper corner of the ipsilateral symphysis pubis. Line A is the distance from the deepest part of the acetabular margin to line B. Acetabular dysplasia is often defined an ADI as < 9 mm. Figure 2b. Acetabular depth ratio (ADR). The ADR is calculated by dividing (A) perpendicular line from line B to the medial corner of the acetabular weight-bearing surface by (B) acetabular width and multipliing by 1000 (A/B × 1000). Acetabular dysplasia is often defined an ADR≤ 250.

Figure 3. Femoral head extrusion index (FHEI)

Percentage calculated by dividing (A) the amount of the femoral head lateral to the acetabulum by (B) the total width of the head and multiplying by 100. A/B × 100. Acetabular dysplasia is often defined as FHEI ≥25%

Figure 4

Figure 4a. Hip joint without femoroacetabular impingement Figure 4b. Cam femoroacetabular impingement. Shaded area denotes the loss of concavity of the head-neck junction in cam impingement. Figure 4c. Pincer femoroacetabular impingement. Shaded area denotes the acetabular overcoverage of the femur.

Figure 4

Figure 4a. Hip joint without femoroacetabular impingement Figure 4b. Cam femoroacetabular impingement. Shaded area denotes the loss of concavity of the head-neck junction in cam impingement. Figure 4c. Pincer femoroacetabular impingement. Shaded area denotes the acetabular overcoverage of the femur.

Figure 4

Figure 4a. Hip joint without femoroacetabular impingement Figure 4b. Cam femoroacetabular impingement. Shaded area denotes the loss of concavity of the head-neck junction in cam impingement. Figure 4c. Pincer femoroacetabular impingement. Shaded area denotes the acetabular overcoverage of the femur.

Figure 5. Crossover sign

The broken line represents the posterior acetabular wall and the solid line represents the anterior acetabular wall. Crossover sign noted on the right hip where the anterior wall crosses the line of the posterior wall before reaching the lateral edge of the sourcil.

Figure 6. Global acetabular retroversion

Axial image of the pelvis. Angle formed by (A) line perpendicular to the coronal axis of the pelvis (B) line connecting the anterior and posterior acetabular rims. Pincer impingement was defined as angle ≤14°.

Figure 7. Alpha angle

Angle is formed by (A) line from the femoral head center to the point on the anterolateral head-neck junction where the radius of the femoral neck first becomes greater than the radius of the femoral head and (B) line drawn from the femoral head center through the center of the femoral neck. Cam impingement was defined as an alpha angle >50°.