Minimally Invasive Periacetabular Osteotomy and Stress fractures

For a few years now my preference has been to use a minimally invasive approach for PAOs. This has allowed patients to mobilise more quickly and initially we were happy for patients to start to weight bear  to a greater extent. We then became aware that we were seeing quite a few stress fractures in the pelvis. A stress fracture is a crack that can develop in another part of the pelvis at some stage during rehabilitation, often at about 8 weeks and even up to 5 months. The reason for this is that immediately after the PAO the stresses in the pelvic ring tend to be concentrated where the bone is thinnest. This tends to be the lower pubic bone (inferior pubic ramus). As the osteotomy heals, so the stresses spread more evenly through the pelvic bone and this decreases the likelihood of a stress fracture developing. In 2015 we published a study analyzing stress fractures and seeing what the risk factors were and how common they were (The Bone and Joint Journal 2015;97-B: 24-8). Fortunately most stress fractures heal uneventfully but can be painful and often mean a longer period of time on crutches.

One of the factors we thought that could contribute to the stress fractures was the accelerated rehabilitation. We therefore reduced slightly the weightbearing status of patients after surgery to 20 Kgs for the first six weeks. We also often use some synthetic bone graft around the osteotomy, in particular the pubic osteotomy, to promote union as rapidly as possible and to try and speed up the union of the pubic bone which tends to be the slowest to unite. We have recently completed a follow-up study to see what influence these changes have made to the incidence of stress fractures. The good news is that we have been able to halve the incidence of stress fractures (to 9%), and these have tended to heal uneventfully often with patients not aware that they had one, with the only sign being rather subtle changes on a follow-up X-ray.

This clearly illustrates the importance of sticking to the restricted weight bearing protocol after surgery to give the pelvis time to adapt to the stresses going through it. I think we have to accept that biological processes take a certain length of time to complete and work within those limitations.