Kegel exercises should be recommended for patients recovering from severe leg, torso, or hip injuries because strengthening any part of the lower body will help heal their injuries. They simply must do the kegel exercises in moderation so they do not spur on more severe injuries in their already vulnerable state.
I think all types of exercise can be effective when patients are recovering from severe body injuries. I think learning to move and bend it again is going to make a big difference and finding out how to position those old injured body parts in new ways will help strengthen them.
Kegel exercises work by flexing and relaxing muscles surrounding the pelvis. Any strengthening of these muscles can only help people recovering from severe injuries below the waist. Kegel exercises are simple to do and require little movement. There are drawbacks, but Kegel movements in general support a strong uterus and bladder in addition to the pelvis.
Unless the injuries affect the pelvic floor muscles, or strengthening those muscles will help in recovering from severe leg, torso or hip injuries, kegel exercises would not be recommended. Kegel exercises are suggested for both men and women, but are usually used to help with recovery from childbirth, or urinary incontinence.
Kegel exercises are exercises meant to increase the strength of the pelvic floor muscles. As women age, they tend to have at least some lack of strength and minor incontinence, sometimes just through doing something like laughing or sneezing. I can't understand why the exercises would specifically be taught to people suffering from something like a broken leg or similar injury. It certainly wouldn't hurt to teach them just in general, but I'm not sure how it would help with leg, torso, and hip injuries.