· separation of avascular fragment of bone and overlying cartilage
· type of osteochondrosis
· most common in knee
· more common in males
· M:F = 2:1
· occurs between age 10 and age 50
· mean age is 18
· bilateral in 25%
· most common cause of loose bodies in knee
· other causes are synovial chondromatosis, osteophytes, fractured articular surfaces and damaged menisci
· twisting injury
· instability
· patellar dislocation
· more important in children
· interruption of blood supply
· subsequent avascular necrosis
· more important in adults
· may be accessory centre of ossification
· eg. multiple epiphyseal dysplasia
· area of subchondral bone undergoes avascular necrosis
· overlying cartilage undergoes degenerative changes
· in young patients, segment often heals
· in adults, segment usually separates from underlying bone and cartilage
· becomes loose body
· leads to degenerative changes
· defect may fill with fibrocartilage
· occurs on medial condyle in 85%
· classical location is on lateral aspect near attachment of PCL
· may also occur in inferocentral location
· occurs on lateral condyle in 10%
· most common in inferocentral region
· may rarely be anterior
· occurs on patella in 5%
· history of trauma in 50%
· symptoms usually vague and poorly localised
· most commonly vague ache
· may be
· locking
· giving way
· recurrent effusions
· joint mouse
· features of internal derangement
· quadriceps atrophy
· effusion
· loss of terminal flexion
· may be localised tenderness of femoral condyle
· may be palpable loose body
· Wilson’s sign
· knee flexed to 90o, internally rotated and gradually extended
· causes pain
· relieved by external rotation
Plain x-ray
· most commonly seen on intercondylar view
· appearance is
· well-circumscribed area of subchondral bone
· separated from femoral condyle by crescent-shaped radiolucent line
· may be empty crater with loose body elsewhere in joint
Bone scan
· useful where diagnosis unclear
· shows localised increased uptake
MRI
· shows area of decreased intensity on T1 image
· surrounding bone also abnormal
· allows
· visualisation of lesion
· assessment of attachment
· may miss undetached lesions
1. soft cartilage but no separation
2. soft cartilage with early separation but no displacement
3. attached separation
4. loose body with crater in NWB area
5. loose body with crater in WB area
· small or large defect
· loose body has bone that fits OR no bone or won’t fit
· of loose bodies
· osteochondral fracture
· osteoarthritis with cartilage fragments or osteophytes
· synovial chondromatosis
· Charcot’s disease
Observation
· restriction of activities for 3 months
Immobilisation
· non-weight-bearing cast for 6 wks
Drilling
· with K-wires
· access may be
1. through overlying cartilage
· straightforward
· causes cartilage damage
2. through nonarticular adjacent femoral condyle
· no damage to overlying cartilage
· difficult
· requires image intensifier
· early resumption of activities postoperatively
· often good pain relief
· healing rate is 50%
Excision
· fragment excised or removed
· base curetted and drilled
· to encourage ingrowth of fibrocartilage
· postoperative
· if small defect, early resumption of activities allowed
· if large crater, wt bearing restricted for 6 wks
Fixation
· if fragment in situ, lesion drilled first
· if fragment displaced, base curetted and drilled
· fixation achieved with
· resorbable K-wires
· Herbert screws
· postop
· LLPOP applied fo 6 wks with NWB
· then PWB and ROM exercises
· wt bearing when x-ray shows healing
· arthroscopy performed
In situ lesion
· if cartilage intact
· observation for child
· immobilisation for adult
· if fragment unstable
· excise small lesion (< 5 mm)
· drill medium lesion (5-10 mm)
· fix large lesion (> 10 mm)
Displaced lesion
· if fragment fits back perfectly, fix lesion
· if fragment cannot be reattached, excise lesion