Ans. is 'd' i.e., All the above Genu recurvatum (hyperextension of the knee)a) Congenital recurvatum* This may be due to abnormal intra-uterine posture; it usually recovers spontaneously. Rarely, gross hyperextension is the precursor of true congenital dislocation of the knee.b) Lax ligaments* Normal people with generalized joint laxity tend to stand with their knees backset. Prolonged traction, especially on a frame, or holding the knee hyperextended in plaster, may overstretch ligaments, leading to permanent hyperextension deformity. Ligaments may also become overstretched following chronic or recurrent synovitis (especially in rheumatoid arthritis), the hypotonia of rickets, the flailness of poliomyelitis or the insensitivity of Charcot's disease.* In paralytic conditions such as poliomyelitis, recurvatum is often seen in association with fixed equinus of the ankle: in order to set the foot flat on the ground, the knee is forced into hyperextension. In moderate degrees, this may actually be helpful (e.g. in stabilizing a knee with weak extensors). However, if excessive and prolonged, it may give rise to a permanent deformity. If bony correction is undertaken, the knee should be left with some hyperextension to preserve the stabilizing mechanism. If quadriceps power is poor, the patient may need a caliper. Severe paralytic hyperextension can be treated by fixing the patella into the tibial plateau, where it acts as a bone block.c) Miscellaneous* Other causes of recurvatum are growth plate injuries and malunited fractures. These can be safely corrected by osteotomy.