Is a positive femoroacetabular impingement test a common finding in healthy young adults?

Abstract

Background: Femoroacetabular impingement (FAI) is an incompletely understood clinical concept that implies pathomechanical changes in the hip as a cause for hip-related pain in young adults. While a positive anterior impingement test is suggestive of FAI, its association with clinical and radiographic findings remain unconfirmed in healthy young adults.

Questions/purposes: We determined the prevalence of a positive test in 1170 young adults and examined its possible associations with (1) self-reported hip discomfort for the past 3 months; (2) weekly physical exercise; (3) hip ROM; and (4) radiographic findings associated with femoroacetabular impingement.

Methods: We invited 2344 healthy 19-year-olds to a population-based hip study between 2008 and 2009; 1170 patients (50%) consented. The study included questionnaires on medical and functional status, a clinical hip examination including the impingement test and hip ROM, and two pelvic radiographs (AP and frog-leg views).

Results: Based on at least one affected hip, 35 of 480 (7.3%) men and 32 of 672 (4.8%) women had positive impingement tests. Eighteen of the 1170 patients were excluded owing to suboptimal or missing radiographs. Self-reported hip discomfort in the women and increased physical exercise in the men were strongly associated with the positive impingement tests. Decreased abduction and internal rotation in the men, decreased flexion in both genders, and radiographic cam type findings in the men also were associated with positive tests.

Conclusion: A positive test for anterior impingement is not uncommon in healthy young adults, especially in males. We believe it always should be performed along with pelvic radiographs in young, active patients presenting with hip pain.

Level of evidence: Level II, diagnostic study. See the Guidelines for Authors for a complete description of level of evidence.

Figures

Fig. 1

A pain-provocation test for anterior impingement was performed with the patient supine and scored as 0 (no pain provoked) or 1 (definite pain provoked when asked). A combined maneuver, consisting of 90° passive flexion of the hip, followed by forced adduction and internal rotation, was used.

Fig. 2A–C

(A) Normal anatomy of the hip (left) allows sufficient space for the caput to rotate properly in the acetabulum (right). In cam-type and pincer-type impingements, abnormal contact between the proximal femur and the acetabular rim disturbs adequate movement. (B) In cam-type impingement, during forceful motion, the aspheric portion of the head abuts and subsequently damages the acetabular rim, further damaging the cartilage and labrum. (C) In pincer-type impingement, an increase in either the coverage of the femoral head or the relative depth of the acetabulum causes an injured acetabular rim, followed by hypertrophy and degenerative changes in the labrum.

Fig. 3

The flow chart shows the inclusion and exclusion criteria for our study (n = 1170) at followups. Babies with birth weight less than 1500 g, who died within the first month, or whose mother resided outside the catchment area of the hospital were not included in the 1989 Bergen Birth Cohort. FOI = obturator foramen index.

Fig. 4A–B

(A) The alpha angle is the angle between a line running through the head center and the long axis of the femoral neck, and a line originating from the head center and to the point where the bone of the head neck junction crosses outside the radius curvature of the head. The higher the alpha angle, the greater the cam defect will be. (B) The triangular index is based on the equation R ≥ r + 2, where “r” is the head radius, and “R” is the pathologically increased radius. Half of the head radius distance measured along the neck axis is found, and a perpendicular line H is drawn up to the crossing point of the bony cam curvature. “R” then is found. If R ≥ r + 2, a head-neck asphericity indicating a cam type is confirmed.

Fig. 5A–C

(A) A pistol-grip deformity is flattening of the normal concavity of the femoral head-neck junction. (B) A focal prominence is a prominence or bump to the femoral neck. (C) Flattening of the lateral aspect of the femoral head is shown in this drawing.

Fig. 6A–C

(A) The posterior wall sign is scored positive when the posterior wall lies medial to the center of the femoral head. (B) The crossover-sign is scored positive when the upper part of the anterior acetabular wall lies more laterally than the posterior wall and crosses medially. (C) Excessive acetabular coverage leading to a deep acetabular socket is seen as a bony extension of the upper acetabular roof, quantified by an increased center-edge angle.