What went wrong? My grandson had surgery about six months ago for a chronically dislocating knee cap. They kept the same knee cap but took a piece of his hamstring tendon to replace the ligament that usually holds the knee cap in place. Everything seemed to go well and then the knee cap popped off again. We are wondering what went wrong? Can they get this problem fixed?

The use of graft tendon to replace the torn medial patellofemoral ligament (MPFL) is a fairly new procedure. Most of the results reported so far come from small studies. Reports of postoperative complications like this one are few and far between. But a recent study from Cincinnati Children’s Hospital may have some helpful information.

This large case series (179 knees) is the first report of its kind. And although it offers level four evidence (low level), it is still significant in the information offered. One surgeon performed all of the procedures using a single medial-sided patellar tunnel screw fixation. The tissue graft used to replace the MPFL came from the hamstring tendon.

Statistically, 16 per cent of the group had complications. Most of those were major problems (i.e., requiring further treatment, most often another surgery). The list of both major and minor complications included patellar fracture, hematoma, patellar instability (subluxation or dislocation), poor wound healing, scar formation, pain, reaction to the sutures, blood clots, and complex regional pain syndrome.

Almost half of all complications (47 per cent) for all 179 knees were the result of surgical technical factors. Placement of the tunnel drilled through the bone for the graft and graft tension were the most common technical problems. The surgeon considered these complications to be the result of improper technique and therefore preventable.

Patients who had both knees (MPFL ligament) reconstructed at the same time were at the greatest risk for complications. One other risk factor that was considered statistically significant included gender (females at greater risk than males). Most likely anatomic differences in the shape of the patella contribute to the gender difference.

Exactly what went wrong in the case of your grandson isn’t clear from your description. Experts agree that recurrent patellar dislocation following reconstruction surgery is probably multifactorial (i.e., many factors are present contributing to the problem). Getting the proper placement of the graft and tension on the graft tissue are very important. This depends on the experience and skill of the surgeon.

Patient compliance (following postoperative instructions) is also a key factor. Too much load too soon on the healing tissue can disrupt the surgical site leading to recurrent patellar dislocation. The surgeon is the most likely one to be able to explain (if it is even clearly known) what went wrong. Follow-up arthroscopic examination, X-rays, and/or MRIs can help identify potential causes but in some cases, it’s simply unclear where the problem lies.