Meaning of plateau-patella angle for describing patellar height before and after total knee arthroplasity

Objective To study the accuracy, reproducibility, characteristics and defects of plateau-patella angle before and after total knee arthroplasity(TKA), and to discuss the factors that influence the patellar height. Methods All the samples’ resource were from the patients underwent total knee arthroplasty from Jan.2015 to Jan.2016, 100 case in department of orthopedic from China-Japan Union Hospital of Jilin University, and all patients are patients with osteoarthritis and rheumatoid arthritis. The plateau-patella angle was used to evaluate 100 patients’ radiographs before and after total knee arthroplasty. The preoperative and postoperative modified Black-burne-Peel ratio, modified Caton-Desehamps ratio and modified Insall-Salvati ratio of 54 patients on X ray were measured by two observers. Intraclass correlation coefficient was used to assess the reliability.The preoperative and postoperative data measured by these methods were analyzed by paired t test. Results According to ICC, the reproducibility of modified Insall-Salvati ratio and modified Black-burne-Peel ratio and modified Caton-Desehamps ratio increased in the postoperative measurements. The reproducibility was the highest for the mPPA (preop ICC=0.65; postop ICC=0.88) compared to the other methods.The results of these four methods showed significant differences in patellar height between pre-and post-operative data in modified Caton-Desehamps ratio (t =3.69, P<0.01), modified Black-burne-Peel ratio(t =3.50, P<0.01)and plateau-patella angle(t =7.55, P<0.01). Conclusion The plateau-patella angle is highly accurate, reproducible, intuitive simple and rapid; Using plateau-patella angle can effectively evaluate the changes of patella height in patients with TKA. Key words: Arthroplasty, replacement, knee; Patella; Anthropometry