Biomechanics - Lower Limb Flashcards
3 segments of the lower limb?
3 main joints of the lower limb?
Thigh, leg and foot
Hip, knee and ankle - these are synovial joints
Bony anatomy and of the hip joint?
What does this allow?
Connective tissue anatomy?
Ball and socket joint - where the ball-shaped head of femur fits into the cup-shaped depression of the acetabulum.
This allows movement in 3 axes: flexion/extension; abduction/adduction; internal/external rotation. It also allows circumduction
The surfaces of the hip joint are covered in articular cartilage , and the joints are enclosed in a sleeve of tough fibrous tissue, the joint capsule, which forms the synovial cavity. This is filled with synovial fluid, which lubricates the joint and provides nutrients to the articular cartilage. It is produced by the synovial membrane, which lines the inner surface of the capsule
How is the hip joint intrinsically stable?
It is surrounded by a very strong articular joint capsule and several ligaments. These, in turn, are surrounded by several large, very strong muscles. This, along with the ball and socket shape, makes the hip joint intrinsically stable
ROM of hip joint?
Flexion: 140 degrees
Extension: 20 degrees
Abduction: 30 degrees
Adduction: 25 degrees
Internal Rot: 70 degrees
External: 90 degrees
(this is with the hip flexed - less rotation is possible when extended due to restrictions of soft tissues)
What are the planes of movement and what movements occur in each plane?
Sagittal: flexion/extension
Coronal: abduction/adduction
Transverse/axial: internal/external rotation
What functional ROM is required of the hip for ADL’s such as ascending/descending stairs, sitting/standing and stooping to pick up objects?
120 degrees flex/ext
20 degrees abd/add
20 degrees rotation
What ROM of hip is needed for walking?
30 degrees flexion
15 degrees extension
12 degrees in other 2 planes
In bilateral stance, what external forces are acting on the pelvis?
Weight of upper body
Reaction forces at each hip joint
What forces act on the lower limb during unilateral stance?
Weight of lower limb
Abductor muscle force
Joint force at the hip
Ground reaction force
Why is the hip joint force 0.5x upper body weight in bilateral stance but 4.5x upper body weight during unilateral stance?
Partly because of the fact that the whole upper body weight is being transmitted through one hip instead of 2
Mostly due to the action of abductor muscle forces, which effectively draw the 2 sides of the hip together, greatly increasing force
Articulations in the knee joint?
Which one actually moves the knee?
Tibiofemoral - moves knee
Patellofemoral
What are menisci?
Two crescent-shaped pieces of fibrocartilage attached to the proximal end of the tibia by short, tough ligaments. The menisci make the flat top of the tibia concave, which aids in stability
Describe structure of distal femur?
2 circular-shaped femoral condyles, which are covered by articular cartilage. The smooth anterior depression between them is called the trochlea, which develops into the posterior depression between the the condyles called the intercondylar notch. The cruciate ligaments, which help bind the femur to the tibia, are lodged in the intercondylar notch
What type of bone is the patella?
Structure?
Sesamoid - this means it is found within the quadriceps femoris tendon
Posterior surface has 2 smooth articular surfaces either side of a slight central ridge, each of which articulate with a femoral condyle
The ridge guides the patella along the groove between the femoral condyles as the knee joint flexes and extends
Is the fibula part of the knee joint?
No, however it does act as an anchor for the biceps femoris muscle
How does the knee joint get its stability? (4)
From the ligaments - the anterior and posterior cruciate ligaments cross centrally and limit forward and backward sliding of the femur on the tibia, and limit hyperextension
It is surrounded by a tough fibrous joint capsule, which is thickened around the posterior medial and lateral sides
Outside of the joint capsule lie the medial and lateral collateral ligaments, which prevent abduction and adduction
the quadriceps muscle also aids in stability, as do the menisci, esp in rotation
Why can the knee not be described as a true hinge joint?
A hinge joint always rotates around the same axis, but the knee doesn’t. If the sagittal plane is considered the centre of rotation, the joint moves in an approximate semicircle.
This is because the femoral condyles are not perfectly circular, and due to restrictions imposed by the knee ligaments.
It actually has a screw-home mechanism, following a spiral motion. As the knee flexes, the tibia rotates internally slightly, and as it extends it externally rotates slightly
ROM of knee?
Sagittal plane: 140 degrees flexion and a few degrees extension
Frontal plane: a few degrees abd/add-cution when at 30 degree flex
Transverse plane: maximum rotation at 90 degrees flexion
- 45 degrees internal rotation
- 30 degrees external rotation
Functional ROM of knee required for ADL’s?
115 degrees flexion - full extension, and about 10 degrees rotation in transverse plane
Function of the patella?
How does it work?
Increase the lever arm of the quadriceps femoris muscle by displacing the quadriceps tendon
At full extension, the quadriceps tendon is displaced anteriorly, lengthening the effort arm considerably. As the knee flexes, the patella sinks into the intercondylar notch, decreasing its contribution to the effort arm. At full flexion, the patella is fully in the intercondylar notch
What happens if the patella is severely fractured and a patellectomy must be performed?
The lever arm is reduced, and the quadriceps muscle must produce 30% more force to compensate for this
Function of the menisci?
Absorb shock and distribute force across the whole tibial plateau, decreasing focal stress
Can the menisci heal if they are damaged?
They have no capacity to heal because there is only blood supply to the outer edges.
Tears can obstruct motion of the knee and cause it to jam. However, meniscectomy will increase likelihood of joint damage and OA, therefore they are preserved if possible
What type of joint is the ankle?
What are the articulations?
Essentially a hinged synovial joint, with motion primarily in the sagittal plane
Tibiotalar
Fibulotalar
Distal tibiofibular
3 important ligaments in the ankle joint?
Anterior inferior talofibular ligament
Medial ligament
Lateral ligament
ROM of ankle joint?
Varies widely, but usually 45 degrees:
- 10-20 degrees dorsiflexion
- 25-35 degrees plantarflexion
What is a sprained ankle?
The most common ankle injury - it is a partial tear of the anterior inferior talofibular ligament, resulting from sudden adduction of the foot when the ankle is plantar flexed
How many bones and joints are in the foot?
Divisions of the foot and what bones are in each?
26 bones and 57 synovial joints
Hindfoot - talus and calcaneus
Midfoot - cuboid, navivular and medial, intermediate and lateral cuneiforms
Forefoot - metatarsal and phalanges
What is the subtalar joint?
Position?
Joint between talus and calcaneus
It has an oblique axis, positioned at 42 degrees to the plantar surface and 16 degrees medial to the midline of the foot
Function of the subtalar joint?
ROM?
Allows inversion and eversion of foot
Inversion - 20 degrees
Eversion - 5 degrees
Structure of foot?
Has a 2-way arched structure formed by bones and held in place by strong ligaments
There are 5 longitudinal arches that extend from calcaneus along the 5 sets of tarsals and metatarsals
The transverse arch runs across the foot
What is the plantar fascia?
What happens to it when loaded?
Function?
A heavy ligamentous structure which extends from the calcaneus to the planter aspect of the proximal phalanges.
It may only be elongated slightly when loaded.
It acts as a shock absorber, and supports the longitudinal arches, preventing the vertical downward force at the ankle from collapsing them
What happens to the plantar fascia when toes are dorsiflexed?
It is put under tension, and the two ends of the foot are drawn together, raising the longitudinal arches. The bones of the foot are thus held tightly together and function as a single unit rather than separate bones
What is the name for normal walking?
What is the name of the gait when using crutches?
Reciprocal gait
Swing through gait
What may gait analysis be used for? (4)
Determine if surgical intervention is required to improve gait
Quantify severity of a disorder
Determine outcome of an operation e.g. joint replacement
Ensure best alignment of an artificial leg to ensure comfort and energy efficiency
How to analyse gait?
Experienced practitioner may do so by eye in person by watching a video recording
Gait laboratories equipped with motion analysis systems, force plates and EMG equipment are not used to give accurate, in-depth, quantitative data
What is a motion analysis system?
What are they used with?
A system which uses cameras to pick up retro-reflective placed at certain landmarks over the body. Provided the markers are picked up by 2 or more cameras, the system is able to calculate the position of the marker in 3D, enabling the examiner to view the marker from any angle they wish
These are commonly integrated with force plates and EMG equipment
What is the definition of a gait cycle?
One stride, which is equivalent to two steps. It starts with the initial contact of one foot on the ground, termed heel contact, and ends with the next heel contact of the same foot
In reciprocal gait:
- what is the stance phase?
- what is the swing phase?
- what is double support?
Stance is the part when each foot is in contact with the ground (when left is in contact it is the left stance phase)
Swing is when each foot is not on the ground (when left is not in contact with ground it is the left swing phase, which will occur during the right stance phase)
Double support is the period when both feet are on the ground. As speed of gait increases, double support decreases until there is none - this becomes running
What are the 6 landmark events which happen during the gait cycle of a single foot?
Heel contact Foot flat Mid stance Heel off Toe off Mid swing (then heel contact again)
When might the order of landmark events be changer or some events be missing in gait cycle?
If someone has a gait disorder, e.g. has had a stroke or has weak dorsiflexors and suffers from foot drop
ROM during reciprocal gait of:
- hip?
- knee?
- ankle?
30 degrees flexion to 15 degrees extension. Peak flexion occurs shortly after midswing and peak extension before toe off
70 degrees flexion to a few degrees extension. Peak flexion during the swing phase.
10 degrees dorsiflexion to 15 degrees plantarflexion. There are 2 peaks of plantarflexion: at foot flat and before toe off. Peak dorsiflexion at heel off
What do force plates measure?
Ground reaction forces - the equal and opposite force to that imposed on the force plate by the person walking
Describe a typical graph displaying vertical force on a force plate during gait?
Initial small peak at heel contact
Followed by a larger double hump, with both peaks greater than body weight. The first peak is due to deceleration of body mass as weight is transferred onto that foot. The second is due to the foot pushing off the ground
What can be calculated using the data collected from gait analysis?
Joint forces and moments
Why do the hamstrings contract at heel contact?
To prevent over-extension of the knee
