Casting on Shabbos
In a previous article, we discussed whether one is permitted to violate Shabbos due to the danger of losing a limb. (See Sakanas Haguf Sakanas Eiver) It was established that one may not break a Torah Prohibition for losing a limb, as it was not considered life-threatening at the time of the Gemara. Therefore, it seems that a doctor may not help a patient with a broken limb on Shabbos. One may not create a cast as one prohibits several of the 39 categories of labor, such as Lash (kneading due to mixing water with gypsum powder, hence forming a paste), Sochet (squeezing the excess water out of the cast), Memareach (smoothing over the cast), Boneh (building and shaping the cast to a specific structure), and Makeh B’patish (the action of completing a structure, in this case giving the final design and shape to the cast). (Shmerias Shabbos Kehilchasa 16:13)
Although it seems that one should not break Shabbos for a broken limb, if it is Pikuach Nefesh (mortal danger), then one should violate Shabbos. For example, if the patient has an open fracture or a long bone fracture where the ends are not aligned. Additionally, suppose the doctors feel that the patient will worsen. In that case, it is permissible to apply a cast on Shabbos (Shemiras Shabbos Kehilchasa 35:5). In general, though, as discussed previously, one should ask a non-jew or a fellow doctor to apply the cast on Shabbos in a case where the patient is not in mortal danger, but the limb itself is in danger.
To conclude, many hospitals in Israel use a new cast called MAGICAST. MAGICAST employs a method where a soft fabric sleeve is wrapped over the affected limb, followed by a second adhesive sleeve, which is immersed in warm water and wrapped around the limb, hardening within seconds. Rav Asher Weiss permitted the application of MAGICAST because a person applying the cast does not directly violate any of the 39 Malachos.
Adapted from medicalhalacha.org