chondral modelling phenomenon

chondral modelling phenomenon

the rate of bone formation from hyaline cartilage (i.e. articular cartilage, epiphyseal plates, tendon and ligament insertions, apophyseal plates, endplates within symphyses and sesamoids) is directly proportional to exerted and imposed load (see Table 1)
Table 1: Bone modelling
Type of modellingComment
Chondral modelling during bone growthRate of ossification of cartilaginous precursor of bone/articular cartilage/epiphyseal plates depends on imposed load during development
Joint incongruence within normal range: load inequality across articular cartilage causes remodelling and restoration of maximal congruence, via negative-feedback loop
Joint incongruence beyond normal range: load inequality across articular cartilage causes remodelling adapting to abnormal load, and loss of maximal congruence, via positive-feedback loop
Metaphyses and epiphysesWhere abduction and adduction forces about a joint (e.g. knee) are equal, resultant transverse force across the joint is of zero magnitude
Where adductor force > abductor force:
• Soft-tissue anomaly causes soft-tissue positional genu valgum and increases force on lateral articular surface/epiphyseal areas
• Rate of bone growth at lateral areas increases; that of medial areas remains normal
• Joint congruence is restored, and the horizontal force is restored to zero magnitude, but soft-tissue genu valgum deformity persists as bone deformity
Articular surfacesMinor incongruence between articular surfaces within a synovial joint causes large changes in forces acting at different parts of articular surface, e.g.
• Absent subtalar joint inversion/eversion causes trochlear talus to undergo reactive twist within ankle mortise, and compression at articular areas remaining in contact
• Excess loading at these sites reduces local bone growth; unloaded areas continue to grow at normal rate
• Shape of articular surface gradually changes, adapting to abnormal loading pattern, and maximum congruence is achieved, but trochlea becomes rounded (rather than pulley-shaped) and ankle joint forms ball-and-socket, rather than hinge, joint