Femoroacetabular Joint (Hip Joint)

Authors
Affiliations

Doctor of Physical Therapy

B.S. in Kinesiology

Doctor of Physical Therapy

B.A. in Neuroscience

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).

Acetabulum

Acetabulum forms the socket aspect of hip, and its name originates from latin meaning “vinegar cup”. The acetabulum forms a partial circle with an inferior opening of 60-70° wide.

Note

This circle is completed by the transverse acetabular ligament.

Contact

The femoral head generally contacts the acetabulum along the articular cartilage lined lunate surface.

Gait

During gait the hip experiences forces ranging from 13%BW in midswing to >300% BW at midstance.

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 activation.

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 joint.

Note

This widening of the acetabulum decreases pressure (forcearea) and can potentially decrease peak force but does not change total force experienced at the joint

Angle of Inclination

Normal

  • Adult: ~125°
  • INFANT: 140-150°

Coxa vara

  • <120°
  • ↑ hip abd moment arm
  • ↑ joint stability
  • ↑ bending moment arm and shear force at femoral neck
  • ↓ hip abd functional length

Coxa Valga

  • >140°
  • ↓ hip abd moment arm
  • ↓ hip joint stability
  • ↓ bending moment arm and shear forces at femoral neck
  • ↑ hip abd functional length

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):

Stabilization

  • Active stabilization
  • Passive stabilization
  • Mechanical seal resists first 1-2mm of joint distraction

Mechanical seal

The “mechanical seal” or “suction seal” refers to the intra-articular pressure within the synovial capsule of the femoroacetabular joint.

Formed by:

  1. Acetabular labrum

This mechanical seal resists the first 1-2 mm of joint distraction

Center Edge Angle

Center edge angle refers to the extent to which acetabulum covers femoral head.

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 joint. Decreased contact surfaces will increase the amount of pressure the contact surfaces experience for the same amount of force.

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

  1. IR
  2. Flexion
  3. Abduction

Ligaments & Capsule

  • Iliofemoral:
    • Strongest
    • Limits Ext and ER
  • Pubofemoral lig.
    • Limits abd and ext, less er
  • Ischiofemoral lig.
    • Limits IR and Ext
  • Zona orbicularis (Anular ligament)

Joint Capsule

The joint capsule is weakest in the gaps between joint ligaments.

Fig 31.92

Fig 31.9

There is a gap between the iliofemoral lig. and pubofemoral lig. on the anterior aspect of the hip.

There is a second gap between the Iliofemoral lig. and the Ischiofemoral lig. on the posterior aspect of the hip.

Acetabular labrum

The acetabular labrum refers to the ring of fibrocartilage projecting from the acetabular rim.

The labrum improves joint stability by helping to form the mechanical seal of the hip joint.

The labrum maintains the environment for a healthy joint by creating a fluid seal for the synovial fluid.

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.

References

1.
Neumann DA, Kelly ER, Kiefer CL, Martens K, Grosz CM. Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation. 3rd ed. Elsevier; 2017.
2.
Gilroy AM, MacPherson BR, Wikenheiser JC, Voll MM, Wesker K, Schünke M, eds. Atlas of Anatomy. 4th ed. Thieme; 2020.

Citation

For attribution, please cite this work as:
Yomogida N, Kerstein C. Femoroacetabular Joint (Hip Joint). https://yomokerst.com/The Archive/Anatomy/Joints/LE Joints/femoroacetabular_joint.html