Individuals with genu valgum have larger than normal Q-angles causing the weight-bearing line to fall lateral to the centre of the knee causing overstretching of the MCL and stressing the lateral meniscus and cartilages.The cause of pain and dysfunction often results from either abnormal forces (e.g. increased pull of the lateral quadriceps retinaculum with acute or chronic lateral PF subluxation/dislocation) or prolonged repetitive compressive or shearing forces (running or jumping) on the PF joint. The result is synovial irritation and inflammation and subchondral bony changes in the distal femur or patella known as "bone bruises". Secondary causes of PF Syndrome are fractures, internal knee derangement, osteoarthritis of the knee and bony tumors in or around the knee. Diagnosis
Examination
People can be observed standing and walking to determine patellar alignment. The Q-angle, lateral hypermobility, and J-sign are commonly used determined to determine patellar maltracking. The patellofemoral glide, tilt, and grind tests (Clarkes sign), when performed, can provide strong evidence for PFPS. Lastly, lateral instability can be assessed via the patellar apprehension test, which is deemed positive when there is pain or discomfort associated with lateral translation of the patella. Various clinical tests have been investigated for diagnostic accuracy. The Active Instability Test, knee pain during stair climbing, Clarkes test, pain with prolonged sitting, patellar inferior pole tilt, and pain during squatting have demonstrated the best accuracy. However, careful consideration is still needed when using these tests to make a differential diagnosis of PFPS.
Dysmelia (from the Greek dys (δυσ-), "bad" + mélos (μέλος), "limb" + English suffix -ia) is a congenital disorder of a limb resulting from a disturbance in embryonic development. Types
Dysmelia can refer to
missing (aplasia) limbs: amelia, oligodactyly, congenital amputation e.g. tibial or radial aplasia
malformation of limbs: shortening (micromelia, rhizomelia or mesomelia), ectrodactyly, phocomelia, meromelia, syndactyly, brachydactyly, club foot
too many limbs: polymelia, polydactyly, polysyndactyly
others: tetraamelia, hemimelia, symbrachydactyly

Occurrence rate
Birth defects involving limbs occur in 1 per 1000. Causes
Dysmelia can be caused by
Inheritance of abnormal genes, e.g. polydactyly, ectrodactyly or brachydactyly, symptoms of deformed limbs then often occur in combination with other symptoms (syndromes)
external causes during pregnancy (thus not inherited), e.g. via amniotic band syndrome
teratogenic drugs (e.g. thalidomide, which causes phocomelia) or environmental chemicals
ionizing radiation (nuclear weapons, radioiodine, radiation therapy)
infections
metabolic imbalance

Syndromes with dysmelia
References
External links
DysNet: An organisation for people affected by Dysmelia (congenital limb difference)
Reach: Association for Children with Upper Limb Deficiency)