We know that being in space has negative effects on bones. If you had a broken bone is space would it heal ok? Has there ever been a broken bone healed in space? Other then Spaceflight osteopenia would there be any concerns like the bone not knowing how to grow because of the lack of gravity?
Studies, simulations and observations reported in the National Space Biomedical Research Institute's document Fracture healing in spaceflight and in a ground-based hypogravity analog conclude that
Fibular fracture healing in a chronically unloaded condition is impaired when compared to the healing response in a weight weight-bearing condition.
Where the unloaded condition represents zero or a low gravity environment. The conclusions were based on the observations on test rats, finding that in low gravity:
- healing rate was more variable
- the rate and extent of callus size was diminished to 20-30%
- Non union incidence (meaning, union of both sides of the fracture) was 46%.
Further, in the article Effects of Long-Duration Spaceflight, Microgravity, and Radiation on the Neuromuscular, Sensorimotor, and Skeletal Systems (Carpenter et al. 2010), it is reported that in simulated tests using rats, bone fracture repair was delayed significantly.
So, no, unless you had some means to simulate the mechanical loading (Carpenter et al. 2010) necessary for the healing process, in a microgravity environment, the healing process would be delayed and not complete (according to the simulations studied).
You are right. Bones would "not know how to grow". Fracture healing would likely be delayed or abnormal in microgravity.
Bones are piezoelectric. This means they generate electric potential when mechanically stressed. This electric field is aligned with the direction of stress. This is how bone tissue “knows” the direction and magnitude of stresses imposed on it.
Many people consider bones inert since they persist after death when the soft tissues have long decomposed. However, during life bone is constantly being re-absorbed and replaced. In cancelous (“spongey”) bone, this remodeling aligns with the piezoelectric electric fields. This cross section of the hip section of the thigh bone shows the radiating lines of bone corresponding to force distribution in the bone.
Bone healing benefits from piezoelectric effects. This is likely why bone mass is impaired in non-weight bearing mice. https://www.nature.com/articles/s41598-019-47695-3
Bone healing in microgravity may benefit from electrical stimulation https://pubmed.ncbi.nlm.nih.gov/2208859