Do puppies and kittens with physeal fractures always need surgery?

Fractures of the physes are always best managed surgically. The more common physeal fractures involve the growth plates of the distal and proximal (head) femur as well as the distal humerus (the lateral condylar fracture).  Because this latter fracture also involves the joint itself, it will be discussed under articular fractures.
The proximity of the physes to the joints, along with the tendency for less bulky musculature in the areas, tend to result in more significant displacement and poorer alignment of the joints affected by the fractured bone.  For this reason, the conservative approach to these fractures tend not to result in a very positive outcome.
Should the amount of displacement be minimal, then stabilizing the affected area with a splint can have a very good outcome.  Because these fractures occur (by definition) in immature patients, the healing time tends to be quite rapid (2-4 weeks).
A capital physeal fracture of the femur (femoral head) can also be managed with a Femoral Head Ostectomy (FHO).  The prognosis for a young patient with an FHO is excellent with good post-operative management.
In the hands of the trained surgeon, physeal fractures carry an excellent prognosis with minimal complications.  Clinically relevant angular limb deformities and shortened limbs, although possible, are not seen commonly at all.  Probably the more common complication is the backing out of the pins. These are usually quite easily managed and do not have any long term effects on the patient.  Therefore, please do not hesitate to encourage the owners of these young pets to spend the money and travel to where necessary to seek the appropriate care.