Lower Limb Biomechanics Revision Flashcards
Define varus
Inward angulation of the distal segment of a bone or joint towards the midline
Define Varus Stress
Force being applied away from the midline, forcing the distal limb segment towards the midline
Define Valgus
Outward angulation of the distal segment of bone or joint away from the midline
Define Valgus Stress
Force being applied towards the midline, resulting in the distal limb segment being forced away from the midline
What is coxa vara?
- When the angle between the femoral neck and femoral shaft is less than 120degrees
- It can result in leg length being shortened
- Adductors strength > abductor strength
- Commonly caused by injury (#) or soft bone causing bending
- smaller angle therefore leg angled TOWARD midline
- RESULTANT FORCE is LESS than normal
What is Coxa Valga?
- When the angle between the neck and shaft of femur is >135degrees
- There is generally a wider hip range and a wider squat angle
- Adductor strength
What gives the hip joint stability?
- bone congruence
- acetabular labrum (continuous, transverse ligament over the acetabular notch)
▶️ mainly avascular
▶️ presence of nociceptors
▶️ deepens acetabulum by 21% increases acetabular contact by 28% and limits extreme ROM
▶️ distributes impact of load and maintains negative pressure - very strong capsule
- ligaments
What are the ligaments that increase stability in the hip?
- Iliofemoral ligament
- strongest, taught in extension & relaxed in flexion
- prevents pelvis tilting posteriorly in stance, limits extension, external rotation and Adduction in extended lower limb - Pubofemoral ligament
- probably the weakest, strengthens anteroinferior part of capsule - Ischiofemoral ligaments
- supports the capsule posteriorly - Ligamentum teres
- triangular in shape and flattened, implanted by apex into anterosuperior part of fovea capitis femoris and base either side of acetabular notch
- has LITTLE role in STABILITY and little influence as a ligament past childhood
- ligament tensed when thigh semi-flexed and externally rotated - Zona orbicularis (annular ligament)
- little role in stability
- anteriorly blend with deep surface of iliofemoral ligament and gain attachment to the anterior inferior iliac spine
Where are the two weak points in the ligaments of the hip?
- Between ilio and pubofemoral ligaments
2. Between ilio and ischiofemoral ligaments
Which hip muscles take part in the hips rotator cuff?
- Piriformis - External Rotation
- Gemellus superior & inferior - external rotation
- Obturator internus - abduction and external rotation
- Obturator externus - Adduction and external rotation
- Quadratus femoris - Adduction and external rotation
- Gluteus Minimus - abduction and internal rotation
Which muscles flex the hip?
Iliopsoas Rectus femoris TFL Sartorius Adductors
Which muscles extend the hip?
Inferior part of gluteus max
Gluteus medius
Gluteus minimus
Hamstrings
Which muscles addict the leg at the hip?
Adductor brevis, Magnus, longus
Pectineus
Gracilis
Which muscles abduct the leg at the hip?
Gluteus medius Upper portion of gluteus max Gluteus minimus Piriformis TFL
Which muscles control internal rotation at the hip?
Gluteus minimus
Piriformis
Anterior gluteus medius
TFL
Which muscles control external rotation at the hip?
Deep external rotators
Piriformis
Posterior gluteus medius
Gluteus max
What is the joint reaction force in the hip?
The compressive force experienced at the femeroacetabular articulation and it is the result of the need to balance the moment arms of the body weight with the pull of the hip abductors at the greater trochanter to maintain a level pelvis
How can you decrease the joint reaction force at the hip?
Increase abductor strength
Using a cane in the opposite hand (lengthens lever arm and provides a force which counteracts the body load at he end of e lever arm)
How do you work out joint reaction force at the hip?
Joint Reaction Force = Body Weight + Abductor Force
JRF is always higher than body weight
What are the determinants of joint reaction force?
Body weight
Body weight moment arm
Abductor force (muscles)
Abductor force moment arm
What are the keystones in the arches of the foot?
Medial longitudinal arch = talus
Lateral longitudinal arch = cuboid
Transverse arch = middle cuneiform
What class of lever is the hip?
Class 1/First order lever
What class of lever is the foot and ankle?
Second order/class 2
What is the function of the foot and ankle?
Lever/propulsion
Shock absorption
Support
Which part of the foot is loaded during the gait cycle?
Heel strike - lateral heel
Propulsion - lateral foot
Toe off - lateral ➡️ medial
How is propulsion achieved in the foot?
Achieved at the foot by a combination of inertia and muscle activation (in particular the activation of Gastroc, soleus and tibialis posterior)
What is the Windlass mechanism?
Describes the influence of the passive structures of the foot (mainly plantar fascia) to create supination with the foot.
Dorsi flexion of the hallux, leads to tension of the plantar fascia and locking of the metatarsal joint ready for propulsion
Why is pronation important during the gait cycle?
It is critical to attenuate load
What provides stability in the knee?
- Bony shape and meniscal attachment
- lateral meniscus smaller and more U shaped
- medial meniscus larger and more C shaped - Strong ligamentous structures
- cruciate ligaments - Tendons acting as active ligaments
Describe the knee during gait
- TIBIA EXTERNALLY rotates during terminal extension PRIOR to HEEL STRIKE
- results in INVERSION of the foot at the subtalar joint
- knee FLEXION during LOADING phase allows TIBIAL INTERNAL rotation and thus foot PRONATION ➡️ shock absorption
- during TERMINAL STANCE, EXTENSION again occurs resulting in tibial EXTERNAL ROTATION and resultant subtalar joint INVERSION creating a rigid lever for PROPULSION
Describe 3 features of the hip joint
- it’s a ball and socket joint
- surrounded by powerful and well-balanced muscles
- high level of mobility vs remarkable stability
