When surgery is required for a broken bone, its important for patients to realize that the bone still needs time to heal after surgery . The purpose of surgery for treating a broken bone is to re-align the bone so that it heals in the correct position...however, the bone still needs 6 weeks or longer (depending on the location of the break) to fully heal. Basically surgery does not cause the bone to immediately fuse back together, it just holds the bone together so that over time, it fuses in the correct position.
If a broken bone does not require surgery, it usually means that the break didn't cause the bone to move out of position, and therefore the bone just needs time to heal. However, most orthopedic surgeons dont allow people to walk on a broken leg bone immediately because they dont want something to happen that causes the bone to move out of normal alignment. Therefore, if a tibia (leg bone) is broken and not going to get surgery, its usually placed in a long leg cast for a few weeks.
One advantage of surgery, is that people dont have to wait up to 22 weeks for the broken leg to heal before they can start walking again. If an "intramedullary nail" is used to fix the broken tibia (this is the most common type of surgery for a broken leg), people can typically walk on the leg immediately after surgery without a risk of the bone moving out of position or failing to heal properly.
You would think that walking on a broken bone would prevent it from healing...but in reality, the pressure on the bone stimulates growth factors and the bone cells (osteoblasts) to start healing. There have been a number of studies to suggest immediate weight bearing after fixing a broken tibia with an intramedullary nail (tibial IMN) is safe and effective.
Its also been shown in other bones, like the femur, that immediate weight bearing is ok.
1. Coles CP, Gross M. Closed tibial shaft fractures: management and treatment complications. A review of the prospective literature. Can J Surg. 2000;43:256–262. full article.
2. Can Tibial Shaft Fractures Bear Weight After Intramedullary Nailing A RandomizedControlled Trial. Gross SC et al. J Orthop Trauma. 2016 Jul;30(7):370-5. see paper. no difference in full weight bear and nonweight bearing on overall healing (still takes about 22 weeks to achieve union).
3. Sarmiento A, Latta LL. Fractures of the middle third of the tibia treated with a functional brace. Clin Orthop Relat Res. 2008;466:3108–3115. see paper.
4. Brumback RJ, Toal TR Jr, Murphy-Zane MS, et al. Immediate weight-bearing after treatment of a comminuted fracture of the femoral shaft with a statically locked intramedullary nail. J Bone Joint Surg Am. 1999;81:1538–1544. full article.
5. Arazi M, Ogun TC, Oktar MN, et al. Early weight-bearing after statically locked reamed intramedullary nailing of comminuted femoral fractures: is it a safe procedure? J Trauma. 2001;50:711–716. see full article.
6. McKibbin B. The biology of fracture healing in long bones. J Bone Joint Surg Br. 1978;60-B:150–162. weight bearing is good for stimulating bone healing. full article.
7. Bone LB, Johnson KD. Treatment of tibial fractures by reaming and intramedullary nailing. J Bone Joint Surg Am. 1986;68:877–887