dynamic stability at hip + knee

Question 1

Hip joint stability - intrinsic

Answer 1

• Joint stability at the hip is enhanced by passive structures including: the bony architecture + congruency (e.g. deeper socket - acetabulum), acetabular labrum, articular cartilage, joint capsule ligaments + actively by surrounding muscles

Congruency of the hip
Increases:
- as you extend, abduct + medially rotate the femur
Decreases:
- as you flex, adduct + laterally? rotate the femur (surgical risk post total hip replacement – post. Approach)

Question 2

Stability at the tib/fem and pat/fem joints - intrinsic

Answer 2

Patellofemoral joint
- Sesamoid bone, contained in quads tendon, but can easily dislocate
- Shape of the undersurface of patella + corresponding groove in distal femur provides some guide to movt
- Medial + lateral patellar retinaculum
- Patellar tendon
- MPFL
Tibiofemoral joint
- Little bony stability
- Collateral + cruciate ligaments
- Medial + lateral menisci
- Surrounded + reinforced by muscles providing dynamic stability

Question 3

Local (stabilise) + global (mobilise) muscles

Answer 3

• Local muscles - important in joint stability by acting close to the joint axis (deeper), thereby providing predominantly joint compression rather than torque, + with attachments to key passive elements of the joint
• Global muscles are more superficial muscles that can generate greater torque at joints as a result of their larger physiological cross sectional area + greater moment arms

Question 4

Stability at the hip – gluteus maximus

Answer 4

• Movt role: major hip extensor + external rotator (+ then adductor/abductor),
• Stability role: plays an important role in sagittal plane stability
• In WB: Eccentric activation leads to anterior pelvic tilt + trunk control during hip flexion, then the concentric activation brings the trunk to upright standing;
• Fascial connections of the glut max to ITB (+ TFL) assists in knee ext via ITB + provides further stability to the lumbopelvic region

Question 5

Stability at the hip – gluteus medius + minimus

Answer 5

• The Gluteus Medius (+ Minimus) stabilise the hip particularly in the Coronal plane, controlling contralateral pelvic drop during gait + running, + other single leg stance activities.
• The Gluteus Medius abducts the hip joint + is very important for lateral hip stability
• The anterior gluteus medius fibres also contribute to hip flexion + hip internal rotation, + the posterior fibres to hip extension + hip external rotation

Question 6

Stability at the hip – gluteus minimus

Answer 6

• The deep location + alignment of gluteus minimus also reinforces its role as a hip stabiliser
• The muscle belly adheres directly to the superior joint capsule, + the fibres run close to parallel to the neck of the femur, thereby enabling this muscle to augment joint stability + protection

Question 7

Stability at the hip – hip external rotators

Answer 7

• Active hip stability is modulated by the deep local external rotator muscles posteriorly (quadratus femoris, inferior + superior gemelli, obturator internus + externus)
• These local stabilisers of the hip joint have been referred to by some authors as the ‘posterior rotator cuff’ of the hip

Question 8

Stability at the hip – anterior

Answer 8

• Pectineus/adductor brevis can provide a stabilising role (like an anterior rotator cuff of the hip), + the deep fibres of iliopsoas can also act as stabilisers of the hip anteriorly. Iliopsoas also may play a shunting role in providing dynamic hip stability when the hip is flexed + less congruent

Question 9

Dynamic stability of tibiofemoral joint (medial/lateral/rotational) stability

Answer 9

Medial and Lateral Stability:
- Quads via Med + lat retinacula
- Hamstrings
- Biceps fem: postlat
- Semimemb & semitend: postmed
- Pes anserinus (med)
- ITB (lat)
Rotational Stability:
- Pes anserine
- Popliteus
- Hamstrings

Question 10

Dynamic stability tibiofemoral joint - anterior

Answer 10

Anterior Translation Stability:
- Excessive anterior translation of the tibia is prevented by the hamstrings + possibly also gastro
- These muscles dynamically support the ACL

Question 11

Dynamic stability tibiofemoral joint - posterior

Answer 11

Posterior Translation Stability:
- Excessive posterior translation of the tibia is prevented by the quads (via the medial + lateral retinacula), w/ contribution from popliteus.
- These muscles dynamically support the PCL

Question 12

Trendelenburg

Answer 12

• Positive Trendelenburg sign - The pelvis falls on the unsupported side (leg off the ground) when the individual stands on the affected limb.

Gluteus Medius (& Minimus) actions:
- Non WB (OKC): Hip Abd, IR (when hip neutral), + ER (when hip flexed – G.medius only)
- WB (CKC): prevent Trendelenberg in Single Leg Stance (SLS)

• To maintain single leg stance, 70% of force is supplied by muscles inserting onto the greater trochanter (especially gluteus medius) + 30% from muscles tensioning the ITB (TFL, vastus lateralis + gluteus maximus)