My son is 20 months old,for 4 weeks he is not walking

Synovitis transitoria coxae or Transient synovitis is inflamation of hip joint wich occurs as the reaction on some infections, located in some other part of the body. Those infections are usualy cosed by viruses. Transient synovitis is self limited condition, and with bed rest and nonsteroid antiinflamatory drugs such as Ibuprofen, should subside in 2 to 4 weeks, without any long term sequelee. It is the most common cause of hip pain anmd lymping in shildren younger than 4 years. It is unusaly that symptoms persist for the period of more than 4 weeks, but it can happend in some cases. Hip ultrasound is the best diagnostic tool, and the best way to monitor the improvement of condition. If symtpoms persis, it is necessary to ruleout other posible causes such as Iuvenile idiopathic arthritis an Perthes desease in first place.