Lower Limb Anatomy and Biomechanics

• The lower limb region consists of the pelvis, hip joint, knee joint, and ankle & foot.
• The region's biomechanics involve joint motions (kinematics), muscle control and loading (kinetics), and aspects of walking, centre of gravity, etc.

Hip Joint

• A ball-and-socket joint.
• Head of Femur articulates with Acetabulum (Pelvis).
• Ligamentum teres is located in the centre.
• The Acetabular Labrum surrounds the edge.
• The associated ligaments include Iliofemoral (anterior), Pubofemoral (anterior), and Ischiofemoral (posterior).
• The Labrum forms an important rim.
• Ligaments provide anterior and posterior stability to prevent dislocation.
• Ligaments are tightest in combined extension and medial rotation, and loosest in flexion and external rotation..
• Hip Dislocation occurs in car accidents, pushing the hip joint (90deg F & ER) in a posterior direction, which is termed a posterior dislocation.
• Trabeculae are arranged in different directions to bear loads including bending and compression forces.
• Important bony landmarks exist in the head of the femur
• There is high Congruence of the Head of Femur with the Acetabulum
• Osteoarthritis causes roughening of the surface, leading to articular cartilage being worn out.
• The Ligamentous Teres connects the head of the femur to the acetabulum.
• The ligament contains blood vessels supplying the head of the femur.
• If torn, necrosis can occur in the head of the femur.
• If Stretched/lax, this is deemed "ligamentous teres deficiency", resulting in painful clicking, “catching” sensation, pain on deep squat.
• The head of the femur is subject to bending moment and compression forces

Angle of Femoral head

• Femoral Head Angle Affects internal and external rotation of the head and shaft of the femur.
• A torsion angle between 10-20° is considered normal.
• Anteversion involves a pathological increase in the angle of torsion (>15°), externally rotating the hip (toe out). Hip is internally rotated with Retroversion
• Excessive angles can affect the contact between the head of the femur and the acetabulum.
• The Neck of Femur is the most common site of fracture in older adults.
• The normal angle of the neck of the femur is 125°.
• Coxa Vara is a decreased inclination (<125°) and is associated with a shorter leg length..
• Coxa Valgus is increased inclination (>125°) and associated with a longer leg length.
• Coxa Vara and Valgus can affect bending moment at the neck, muscle work (pulling effect), and weight bearing of LL.
• Coxa vara and Valgus affect congruence of the hip joint surface and may lead to degenerative changes.

Biomechanical Loading

• Involves lines of forces that move the limbs
• HAT: Weight-bearing line of Head, Arms and Trunk onto Head of Femur
• Ground Reaction Force (GRF) goes straight up along the shaft of the femur.
• Angle - bending moment at the neck of the femur
• Muscles exhibit moment arms at different points where they insert.
• All structures on sides of femur endure compressive loading and compressive torque

Leg Length Discrepancy

• Can be in-born with compensatory angulations developing in either hip, knee or ankle regions
• Can be caused by traumatic injuries
• Can affect the contact between the femoral head and acetabulum
• There may also be an issue with angulations > normal range (ante/retroversion, coxa vara/valga).
• Long-term discrepancies may causes of muscle imbalance, and uneven loading in joints
• The issue can result in the need to have joint replacement due to early or excessive degenerative changes
• There may be an Abnormal gait pattern, leading the subject to walk on their toes on the shorter side, or bent knee on longer side

Muscles and Pelvic Tilt

• Key muscles in the pelvis, hip and thigh region are responsible for biomechanical movements
• Muscle actions are considered with the hip starting from the anatomical position.
• Muscle actions can change if the hip movement begins from a different position.
• Adbuctors have a very important role in stabilizing the pelvis
• With Trendelenberg Gait, the pelvis drops on the opposite side
• Swing phase in Gait - left hip abductors, right hip hikes, to allow right leg to swing forward
• If left hip abductors are weak - the right pelvis will drop as the right foot attempts to clear the ground in swing phase
• Subject can compensate by:
  • going up on tiptoe on the left side, (compensate by left foot going up on tiptoe)
  • leaning the trunk towards the left side to compensate for the dropping down of the right pelvis
  • raising the right knee more to clear the right foot during swing phase
• Pelvic Tilt can either move Anterior and posterior directions
• Tilt Is affected by hip muscles and back muscles
• Erector spinae - back extensors - tight - also pull pelvis into anterior tilt
• Iliopsaos - pull the pelvis into anterior tilt
• Good standing posture - neutral amount of pelvic tilt Anterior pelvic tilt - associated with weak abdominal muscles, tight erector spinae and tight hip flexors
• Posterior pelvic tilt - an exercise to correct anterior pelvic tilt
• Habitual Posterior pelvic tilt may lead to a slouching posture of the whole spine

The Knee

• The lower limb region, involving The Knee Region, comprises;
  • the Tibio-femoral Joint,
  • the Patello-femoral Joint
  • the Superior Tib-Fib joint
• The patella connects the quadriceps muscle to the patellar tendon.
• The patellar tendon inserts into tibial tuberosity
• Normal "Q angle” falls in the range of 8-10 degrees.
• The Q angle has a mechanical advantage for the quadriceps femoris muscle group.
• The Q angle is calculated by the relationship
• The Patella has five facets or articulating surfaces:
  • Superior;
  • Inferior;
  • Medial;
  • Lateral;
  • Odd facets
• At different ranges of knee flexion: At 90° flexion, contact is on the lateral and medial sides of the femoral trochlea.
• Contact is split into distinct areas in high flexion.
• As the knee flexes or expands, different parts of the surface of the patella will contact the inside of the femoral groove.
• Medial and lateral facets of patella engage in flexion and extension.
• The highest contact area occurs at 90° F
• Compression forces are created
• Retropatellar pain can occur
• Chondromalacia Patellae can also occur in the kneecap
• The PFJ can degenerate over time
• The combined, resultant forces determine the movement of the patellar tracking mechanism
• Retropatellar pain exists due to excessive lateral gliding of patella
• Treatment involves gliding patella medially, or applying taping to patella to medial direction with Exercise for VMO to prevent excessive lateral glide.
• Deep and partial squats exert Quadriceps activation, depth affects compression force in the patellofemoral joint.
• PCL is twice as thick as ACL, and less easily damaged
• The AMB is moderately lax at the extended knee and tight at flexion
• The PLB is tight at the extended knee and lax at flexion.

Muscles of the leg

• Muscles and Ligaments that stabilize the knee:Limit tibial and/or femoral translation
• Muscles and Ligaments that stabilize the knee: limit varus/valgus movement of the tibia:
• Limits varus/valgus moment
• Medial and lateral structures have different functions in stabilizing rotation.
• The contribution of muscles and capsuloligamentous structures depends on the position of the knee and contiguous joints.
• Findings vary among investigators, given the testing conditions.
• Medial meniscus and lateral structures have different functions in tibial rotation.
• Can develop tear (partial) in the rim, and research shows some potential for regeneration
• The "Unhappy Triad” is a common sport injury.
• If injury occurs due to jumping/turning, landing with knee in flexion, valgus stress, femur IR, tibia ER
• This is likely to occur when the foot has external force planted on ground
• Injury to all 3 structures is deemed- “triad” - ACL, MCL, and medial meniscus
• Quadriceps contraction - is a key component in knee function.
• Important measure in clinic

###The Ankle

• Comprises The Ankle and bones of the foot:
• Ankle: Talocrural Joint, Subtalar Joint, Mid-tarsal joints
• Foot: Hind, mid, fore foot
• Calcaneum structure, key to biomechanics
• The three functional segments and movements of the feet are
  • Rearfoot
  • Midfoot -Forefoot.
• Protect ankle against excessive Inversion /eversion
• With Inversion sprain - Combined Inversion and Plantarflexion will stretch the Ant Talofibular Ligament
• Deltoid Ligament (MCL) is much stronger, less easily damaged
• the arch is a curved beam.
• Arch has interconnecting joints as well as supporting plantar ligaments.
• Tensile forces (t) are concentrated on the inferior beam surface as compressive forces (c) are generated at the superior surface.
• The arch of the foot is
  • Longitudinal
  • Transverse.
• It allows the foot the plantarflex and dorsiflex and move inverted and everted.
• The functions of the muscles are key.
• The lower leg muscles split into 3 compartments

Questions cover the anatomy of the lower limb, including conditions like coxa vara and coxa valga, and the function of ligaments like the ACL. It also covers the biomechanics and movements of the hip and knee joints.