Applied Anatomy of Bones and Joints of Lower Limb
Week 25
NOTE: Craig said not to worry about the foot this year – it is for second year, but I have still
answered the LOs
13. The mechanism of locking and unlocking in the normal knee , in comparison to the
‘locking’ which may occur after injury
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flexion and extension are the main knee movements, some rotation occurs when the
knee is flexed
when the knee is fully extended with the leg and foot on the ground, the knee ‘locks’
because of medial rotation of the femur on the tibia
the position makes the leg a stable column and more adapted for weight bearing
when the knee is ‘locked’ the thigh and leg muscles can relax briefly without making
the knee joint too unstable
to ‘unlock’ the knee, the popliteus contracts, rotating the femur laterally so that
flexion of the knee can occur
Injury - A torn meniscus can displace into the knee joint causing a mechanical block
to extension and resulting in pain and muscle spasm. The classic type of meniscal
tear producing a locked knee is the "Bucket Handle" tear. The torn meniscus remains
attached front and back allowing the central torn portion to flip into the knee joint
like the handle of a bucket. As the pain and spasm reduce the displaced meniscus
can drop back allowing the knee to move freely again. This mechanical "locking" of
the knee can be an intermittent feature with symptomless periods of in-between
episodes.
14. The mechanism and effect of dislocation of the patella (including the factors tending to
provoke and prevent recurrence)
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usually occurs laterally sue to action of quadriceps pulling along the line of the femur
which is at an angle to the tibia
happens more often in women due to the wider angle and relatively smaller patella
the lateral dislocation is counterbalanced by the medial, more horizontal pull of the
powerful vastus medialis
also, the lateral femoral condyle has a more anterior projection and a deeper slope
for the larger lateral patellar facet – hence a mechanical deterrent to lateral
dislocation exists
the stretch that occurs in the ligaments makes recurrence easier
15. The site, mechanism and diagnosis of ankle sprains
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ankle sprains are tearing of fibers of the ankle ligaments
nearly always an inversion injury on the weightbearing foot, the person steps on an
uneven surface and the foot is forcibly inverted
lateral ligament sprains occur in sports that involve running and jumping
the lateral ligament is weaker than the medial and is thus more commonly injured
this is due to the fact that the lateral ligament is 3 small complexes while the medial
ligament is one large dand (deltoid)
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many fibers of the anterior talofibular ligament (part of the lateral ligament) are torn
during ankle sprains, either partially or totally, resulting in ankle instability
the calcaneofibular ligament may also be torn
in severe sprains, the lateral malleolus of the fibula may be fractured
16. Contrasting the medial ligament with the lateral, noting why the latter is more commonly
injured
- ligaments tend to tear at their weakest point
- the weakest points are at or near their attachments rather than in between them
- a ligament that is arranged in discrete parts, rather than a continuous band, allows more
joint mobility but is weaker and is therefore more vulnerable e.g. the lateral ligament of
the ankle joint
- lateral ligament is 3 small ligaments; the anterior talofibular, calcaneofibular and
posterior talofibular while the medial ligament is a broad deltoid ligament
17. The site, mechanism and effects of ‘flat foot’ (Pes Planus)
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results from ‘fallen arches’, usually the medial parts of the longitudinal arches
when a person is standing, the plantar ligaments and plantar aponeurosis stretch under
the body weight
if these ligaments become abnormally stretched during long periods of standing, the
plantar calcaneonavicular ligament can no longer support the head of the talus
the talar head displaces inferomedially and becomes prominent
result – some flattening of the medial part of the longitudinal arch occurs along with
lateral deviation of the forefoot
18. The mechanism and effects of hallux valgus
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Hallux valus is a foot deformity characterized by lateral deviation of the great toe (the L
in valgus indicates lateral deviation)
in some people the great toe overlaps the second, these people cannot move their 1st
digit away from the 2nd because the sesamoids under the head of the 1st metatarsal are
usually displaced and lie in the space between the heads of the 1st and 2nd metatarsals
the 1st metatarsal bone shifts laterally and the sesamoid bones shift medially
often the surrounding tissues swell and and the resultant pressure and friction against
the shoe cause a bursa to form
when tender and inflamed, the bursa is called a bunion
19. The mechanism and effect of ‘anterior compartment syndrome’ (of the leg)
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the septa forming the boundaries of the leg are strong, therefore trauma to muscles in
compartments may cause haemorrage, oedema and inflammation of the muscles
with arterial bleeding, the pressure may reach levels high enough to compress structures
in the compartments concerned
structures distal to the compressed area may become iscaemic, and permanently injured
– i.e. loss of motor function on muscles whose blood supply and/or innervation is
affected
loss of dital pulses is an abvious sign of arterial compression as is lowering of the
temperature of tissues distal to the compression
a fasciotomy (incision of a fascial septum) may be performed to relieve the pressure in
the compartment concerned