Normal range of fetal knee movements.

Fetal limb movement abnormalities have been described to date in the literature only in subjective terms. The aim of the present study was to define objectively the normal range of fetal knee motion. The study population consisted of 240 normal fetuses at gestational age 16-39 weeks. The range of active knee motion was determined on routine prenatal ultrasound scans by measuring the angles between the midtibia, midfemur, and midknee on maximum flexion and extension. From 16 to 32 weeks, average knee flexion was 129.4 degrees (range, 120-140 degrees) and average extension was 23.7 degrees (range, 15-40 degrees). From 33 to 39 weeks, there was a gradual decrease in knee extension owing to lack of space in uterus. Knowledge of the normal range of fetal knee motion will assist clinicians in the prenatal diagnosis of neuromusculoskeletal disease.