Popliteal angle of low birth weight infants during the first year of life.

The aim of this study is to clarify the evolutional changes of the popliteal angle in low birth weight infants during the first year of life. The popliteal angle was measured at 1, 4, 8, and 12 months of corrected age on routine physical examination of 204 appropriate-for-date infants who had achieved normal psychomotor development. The popliteal angle was visually determined and categorized into two groups; tight, when it was 120 degrees or less, and wide, when it was more than 120 degrees. The infants were divided into five groups according to their birth weights; Group E, birth weight <or=999 gm; Group V, 1000-1499 gm; Group L1, 1500-1999 gm; Group L2, 2000-2499 gm; and Group N, >or=2500 gm. At 4 months of corrected age, the rate of a tight popliteal angle was significantly higher in Groups E + V + L1 than in Groups L2 + N. A tight popliteal angle was rare in all groups at 8 or 12 months of age. The results of this study indicate that the physiologic muscle tone of lower extremities is higher in infants with birth weights of <2000 gm at 4 months of corrected age. One should carefully interpret a tight popliteal angle in low birth weight infants during early infancy. Serial assessment of the popliteal angle is necessary before judging that a low birth weight infant has spastic cerebral palsy.