Painful knee prosthesis: CT scan to assess patellar angle and implant malrotation.

BACKGROUND: According to literature, the incidence of pain in knee prostheses is on the increase. In the last decade Authors have focused attention on rotational alignment of the prosthetic components. The aim of this study is to evaluate the efficiency of a new angle, which we define as patellar angle, in order to achieve early diagnosis of malrotation.

METHODS: We set up a retrospective observational study recruiting 100 subjects who had undergone total knee prosthesis. 50 subjects suffered from knee anterior pain and 50 without any symptoms. Through CAT scan and VITREA software®, we were able to study the rotation of prosthetic components. We defined a new angle, which links the tibial component and the patella margins. The angles were measured by two different orthopaedic surgeons blinded to the study.

RESULTS: The patella angle ranged from 10 to 28°, with an average value of 23.2° in the control group; in the study group the angle ranged from 26 to 34°, with an average value of 29.9°.

CONCLUSION: Our data supported the reproducibility and efficacy of new angular value. It would represent a new method to detect tibial rotational malalignment.

LEVEL OF EVIDENCE: IV.