16 Femoroacetabular Impingement
I. Femoroacetabular impingement (FAI) refers to hip joint pathomorphology.
FAI does not necessarily imply symptoms of pain or dysfunction.
First defined by Professor Reinhold Ganz and colleagues as abnormal contact that may arise as a result of either of the following 1 :
Abnormal morphological features.
Subjecting the hip to excessive supraphysiological motion.
Definition expanded by (American Academy of Orthopaedic Surgeons (AAOS) 2 :
Abnormal morphology of femur and/or acetabulum.
Abnormal contact between femur and acetabulum.
Especially vigorous supraphysiological motion that results in such abnormal contact and collision.
Repetitive motion resulting in the continuous insult.
Presence of soft-tissue damage.
Presence of symptoms = FAI syndrome (Warwick Agreement):
Motion-related clinical disorder of the hip with a triad of:
Represents symptomatic premature contact between proximal femur and acetabulum.
No role for prophylactic surgery in asymptomatic FAI. 4
II. Two main types of FAI pathomorphology:
Proximal femoral asphericity:
Loss of head–neck junction offset.
Combined cam and pincer:
More common than either cam or pincer in isolation.
III. Prevalence of FAI morphology:
Common in asymptomatic individuals.
2.4 times more common in athletes than nonathletes. 6
Participation in competitive sports as young adult associated with increased prevalence of FAI pathomorphology (odds ratio 1.49). 7
Mixed cam and pincer.
IV. Common cause of labral injury:
Cam leads to primarily delamination articular surface chondrolabral junction injury.
Pincer leads to primarily labral pinching, crushing, tearing injury.
V. Common cause of osteoarthrosis:
Multiple large-scale, population-based, longitudinal or cross-sectional investigations have shown significant association of FAI and osteoarthrosis:
I. The “layer” concept of hip pain generators:
Layer I: osteochondral (femur, acetabulum/pelvis).
Layer II: static soft tissue (labrum, capsule).
Layer III: dynamic soft tissue (muscles, tendons).
Layer IV: neurokinetic, neuromechanical (nerves, vessels).
II. The hip is a multiaxial, diarthrodial synovial, deep, highly congruent joint:
III. Shape largely believed as spherical (“ball-and-socket”). This is not exactly true.
Actually, shape is elongated in neck axis, “egg-shaped,” or conchoidal: 20
Femoral head forms two-thirds of a sphere. 21
Acetabulum has slightly smaller diameter than the femoral head 22 :
Primarily a rotational joint, with minimal rolling or gliding (translation).
Greater degrees of incongruity (such as those observed in FAI) may increase the translational (shearing stress) motion of the joint, leading to articular cartilage injury, and eventual joint degeneration (osteoarthrosis).
IV. Extra-articular femoral and pelvic anatomy plays significant role in FAI syndrome:
Decreased (coxa vara): increases femoral offset (and abductor moment arm) and femoral head coverage.
Increased (coxa valga): decreases femoral offset (and abductor moment arm) and increases abductor force and joint contact forces.
Increased (excessive anteversion): decreases abductor lever arm and increases abductor force and joint contact forces.
Decreased (relative retroversion): increases impingement risk due to insufficient head–neck offset during flexion and rotation.
Normal sagittal balance: C7 plumb line from center of C7 to posterosuperior corner of S1 superior end plate:
i. Also known as sagittal vertical axis (SVA).
Negative sagittal balance: axis falls posterior to sacrum:
i. In patients with lumbar hyperlordosis.
Positive sagittal balance: axis falls anterior to sacrum:
i. In patients with hip flexion contracture or flat back.
Pelvic incidence (PI; fixed, position independent):
i. Sacral slope (SS; positional).
ii. Pelvic tilt (PT; positional).
iii. PI = SS + PT:
Mean normal PI is 53 ± 7 degrees in men and 49 ± 7 degrees in women. 25
In general, PI = lumbar lordosis + 9 degrees.
Normal sagittal balance aligns forces behind lumbar spine and femoral heads:
i. When standing, the pelvis tilts anteriorly, PT decreases, and SS increases, but PI remains constant.
ii. When supine, lumbar lordosis increases, PT decreases (more than standing), and SS increases (more than standing).
iii. When sitting, lumbar lordosis decreases, PT increases, and SS decreases.
iv. With hip flexion contracture, the body tilts forward, and lumbar lordosis must increase to maintain sagittal balance.
v. Increased PI associated with increased lumbar lordosis, forcing posterior PT to maintain sagittal balance: reduces anterior impingement.
vi. Decreased PI associated with decreased lumbar lordosis, forcing anterior PT to maintain sagittal balance: increases anterior impingement: 26
T1 pelvic angle (position independent):
i. The angle formed by the line formed from the femoral head axis to the centroid of T1 and the line from the femoral head axis to the middle of the S1 superior end plate. 29
ii. Sum of T1 spinopelvic inclination and PT.
iii. Does not change with PT.
History and Examination
A thorough history and physical examination, without any imaging, may diagnose an intra-articular hip problem (FAI syndrome, dysplasia, and arthritis) in majority of cases.
Warwick Agreement: primary symptom of FAI syndrome is motion- or position-related pain in the hip or groin. Pain may also be felt in the back, buttock, or thigh. Patients may also complain clicking, catching, locking, stiffness, restricted range of motion, or giving way. 3
Acute on chronic.
Typically deep groin, rather than superficial.
“C” sign ( Fig. 16.2a).
“Between the fingers” sign ( Fig. 16.2b).
Anterior most common location (groin), followed by lateral, posterolateral, and posterior.
May go undiagnosed for significant duration, frequently mistaken for other cause of groin pain (gastrointestinal, genitourinary, obstetric, gynecologic, pelvic floor disorder, neurovascular, extra-articular impingement, and other musculoskeletal pains).
Patients have a mean duration of symptoms 32.0 months prior to diagnosis of labral tear and FAI, see a mean of 4.0 health care providers, mean of 3.4 diagnostic imaging tests, attempted mean of 3.1 treatments prior to diagnosis, and mean amount spent prior to diagnosis of $2,456.97. 30
Deep flexion, rotational maneuvers.
Sports: six categories 31 :
Sitting typically affects patients more than standing.
Rest, activity modification, oral medications (nonsteroidal anti-inflammatory).
Low back or sacroiliac (SI) joint pain (“hip-spine syndrome”).
Coughing, sneezing (athletic pubalgia, core muscle injury, sports hernia).
Stiffness, loss of hip motion.
Deep, audible: usually iliopsoas.
Deep, palpable: iliopsoas, labral tear.
Superficial, lateral, visible: usually iliotibial band.
II. Physical examination:
No deformity, no cutaneous abnormalities.
Gait, single leg stance, single leg squat.
All bony and soft-tissue landmarks.
Typically no peritrochanteric, proximal hamstring, adductor, inguinal, pubis, rectus abdominis, deep gluteal space, SI tenderness.
Always remember to assess contralateral limb for symmetry.
Typically, a loss of motion: usually hip flexion, internal rotation in 90 degrees of flexion, total arc sum of rotational motion (internal and external).
Typically not limited, unless by pain.
FADIR (flexion, adduction, and internal rotation): most sensitive test for FAI syndrome, but poorly specific.
Impingement maneuvers: assure that an affirmative response to pain during the maneuver reproduces the patient’s symptoms prompting the evaluation:
Anterior: taking hip from flexed, abducted, and externally rotated position to a position of FADIR:
i. Note clockface arc perception and localization of pain (typically 12 o’clock to 3 o’clock position).
Subspine: straight hip flexion in sagittal plane.
Lateral: straight hip abduction in coronal plane, with permissive limb external rotation:
i. Once end of abduction is reached, internal rotation to a gentle stop indicates trochanteric–pelvic impingement.
Posterior: extension, external rotation causing pain:
i. Differentiate from apprehension, fear: indicative of anterior hip instability, microinstability.
FABER (flexion, abduction, and external rotation): assess for asymmetry in distance of lateral knee to table (vs. contralateral hip)—inquire with patient if pain is deep in the hip (anterior groin) versus SI joint.
III. The Doha agreement resolved the problem of heterogeneity in terminology and definitions in groin pain in athletes. 32
Defined clinical entities for groin pain ( Fig. 16.3 ):
Hip-related groin pain.
Other causes of groin pain in athletes.