Femoroacetabular Joint (Hip Joint)
Anatomy
The femoroacetabular joint AKA the “hip joint” is a “classic” ball-and-socket joint where the “ball” is the femoral head which sits in the acetabulum (socket)1.
Acetabulum
Acetabulum forms the socket aspect of hip, and its name originates from latin meaning “vinegar cup”1. The acetabulum forms a partial circle with an inferior opening of 60-70° wide1.
This circle is completed by the transverse acetabular ligament1.
Contact
The femoral head generally contacts the acetabulum along the articular cartilage lined lunate surface1.
Gait
During gait the hip experiences forces ranging from 13%BW in midswing to >300% BW at midstance1.
Force absorption
Force absorption at the hip joint occur through a combination of passive structures including the articular cartilage and cancellous bone of the proximal femur in conjunction with active shock absorption through eccentric muscle activation1.
When experiencing high amounts of force, such as midstance in gait, the acetabulum can deform and widen to increase contact area and decrease pressure on the joint1.
This widening of the acetabulum decreases pressure (
Angle of Inclination
Angle of Torsion
The angle of torsion refers to the angle in the Transverse plane of the twist from the head and neck of femur to the femoral shaft
Normal
- Infant: 40°
- Adult: 8-15°
Anteversion
- />15°
- Common w CP
- Can lead to hip dislocation
- Can lead to OA In toe to improve alignment so that there is greater moment arm of abductors and stability, but this lengthens hip ERs , and shortens IRs
Excessive anteversion
- MR>LR
- Compensations: lateral tibial torsion
- Tibiofemoral ER
- Tends to W sit (stable position)
- Butterfly uncomfy
Retroversion
- <8°
- Toe out
Excessive Retroversion
- Femoral LR
- HIP prom LR>MR
- Compensations: medial tibial torsion, tibiofemoral MR
Examination
Femoral Torsion can be measured using the following test(s):
- Craig’s Test
- Functional squat (neutral, IR, ER)
Stabilization
- Active stabilization
- Passive stabilization
- Mechanical seal resists first 1-2mm of joint distraction1
Mechanical seal
The “mechanical seal” or “suction seal” refers to the intra-articular pressure within the synovial capsule of the femoroacetabular joint1.
Formed by:
This mechanical seal resists the first 1-2 mm of joint distraction1
Center Edge Angle
Center edge angle refers to the extent to which acetabulum covers femoral head1.
Normal values:
- Adults: 35-40°
- If larger: more likely to develop hip impingement
A low (25-35°) CE angle indicates that there is reduced acetabular coverage of the femoral head which places the individual at greater risk of dislocation and decreases contact surfaces within the joint1. Decreased contact surfaces will increase the amount of pressure the contact surfaces experience for the same amount of force1.
Pincer Impingement
- inc center edge angle, too much coverage of acetabulum, labrum can be crushed
CAM impingement
- Thickened bone at intersection of head/neck
- Can cause impingement of labrum
- If smaller: more likely to dislocate
Acetabular anteversion
- Extent to which acetabulum surrounds femoral head
- Normal: 20
- />20 = dislocation
- <20 = inc stability
Capsular pattern
- IR
- Flexion
- Abduction
Ligaments & Capsule
Joint Capsule
The joint capsule is weakest in the gaps between joint ligaments2.
There is a gap between the iliofemoral lig. and pubofemoral lig. on the anterior aspect of the hip2.
There is a second gap between the Iliofemoral lig. and the Ischiofemoral lig. on the posterior aspect of the hip2.
Acetabular labrum
The acetabular labrum refers to the ring of fibrocartilage projecting from the acetabular rim1.
The labrum improves joint stability by helping to form the mechanical seal of the hip joint1.
The labrum maintains the environment for a healthy joint by creating a fluid seal for the synovial fluid1.
Synovium
Fluid seal
The fluid seal is supported by the:
Closed & Open Pack
Closed Pack
- Full ext
- Slight IR
- Slight ABD
Open Pack
15° flexion, abd, lateral rotation
Congruency
- 90° Flexion
- Moderate abd
- External rotation
Arthrology
Osteokinematics
Flexion
- ROM 120°
- OKC: Posterior/inferior glide and some spin
- CKC: Pelvis ant pelvic tilt 30 deg available
Extension
- ROM: 10-20°
- OKC: Ant slide/spin
- CKC: Pelvic post pelvic tilt 15 deg available
Abduction
- ROM: 40°
- OKC: Superior roll, inf/medial slide
- CKC: If abd oppo leg OKC, pelvis on stance leg CKC will abd
Adduction
- ROM: 25°
- OKC: Inferior roll, superior/lateral glide
- CKC: Closed chain hip drop – ADD of pelvis
Internal rotation
- ROM 35°
- OKC: Ant roll, posterior slide
- CKC: Clockwise pelvic rotation
External Rotation
- ROM: 35-45°
- OKC: Posterior roll, anterior slide
- CKC: Counter clockwise pelvic rotation
Osteoarthritis
- Assess for where the bony spurs are formed
- If the bony spurs are still creating issues even at a “correctly” aligned lower extremity, your options are to either get surgical management for the spurs or find a different compensatory pattern that avoids these spurs.
- Recruit deep hip stabilizers
Total hip arthroplasty
When getting a total hip replacement, the rod that is inserted through the femur can worsen fractures. The difference in materials between the rod and bone can result in the bone shattering or splintering completely if a fracture were to occur. Without a total hip surgery, that same person could potentially have a less severe fracture.