Knee motion in a long leg cast.

Five principles to reestablish static ligamentous stability are introduced, including secure, temporary, tibiofemoral fixation to protect against early postoperative stretch or disruption. The necessity for emphasizing this point is demonstrated by a cadaver study. Knee motion in and out of long leg plaster casts was carefully studied in necropsy specimens. Casts applied over minimal or no padding allowed significant varus-valgus, anterior, posterior, and rotatory motion at the knee when manipulated manually. Medial opening to valgus stress ranged from 64 to 100% after casting as compared to the amount of instability present prior to casting. Legs with normally contoured thighs were not protected against anterior instability after casting, and an average of 48% of precasting rotational instability remained after casting. We believe that these results are relevant to much knee ligament surgery. Current means for solving the problems posed by cast immobilization alone, including case examples, are discussed.