Arthroscopic assessment of patello-femoral tracking and related clinical data

Purpose of the study The dynamic study of the patello-femoral joint is of outstanding interest i n unexplained anterior knee pain syndrome. Accuracy of information provided by video-arthroscopy is of concern due to its technical conditions. Serum inflow favors the natural patellar tendency to shift. laterally (mean value , 7 degrees). Absence of active quadriceps muscle contraction under anesthe sia and use of a tourniquet act conversely. The aim of this study conducted in less than 40 year-old patients, was to correlate retrospectively arthro scopic evaluation of patello-femoral tracking and trochlear centralization measured during conventional "inflow" procedure, with patella related pain syndrome and its outcome. Material and Methods The study group included 116 knees in 66 male and 49 female patients (I bil ateral). Mean age at arthroscopy was 26 years (range, 12 to 40 years). Acco rding to pre-arthroscopic clinical data, knees were broken down into 3 stud y groups: Gr-T (Test, painless patella), 50 knees with meniscal and/or liga ment injury: Gr-PRP (Patella Related Pain but no dislocation), 55 knees: Gr -DLC (patella DisLoCation), 11 knees. Arthroscopic technique was the follow ing: general anesthesia, high-proximal pneumatic tourniquet(40mmHg), single antero-lateral portal and serum inflow by simple gravity (2m). The minimum flexion angle that was necessary to obtain de visu a perfect centralizatio n of the patella dome into the trochlear groove was systematically measured before any arthroscopic procedure was performed. Results Average value of the Flexion Angle providing perfect Centralization (FAC) i n the "serum inflow" arthroscopic situation was 39 degrees in Gr-T and 52 d egrees in Gr-PRP; this difference was highly significant (p <.0001). Patell a centralization could not be achieved despite maximum possible flexion in 5 of the 55 PRP-knees and in 9 of the 11 DLC-knees. FAC value > 65 degrees correlated significantly (chi2, p = 0.0001) with patella related clinical s ymptoms (pain and instability, groups PRP + DLC) and indicated patellar mal tracking. In the PRP-group, an "FAC value > 65 degrees" showed a low sensit ivity (0.34), but high specificity and positive predictive value of 0.98 an d 0.95, respectively. Discussion and Conclusion Arthroscopic examination for patello-femoral tracking can provide measurabl e information on the FAC angle, that is reproducible under precise technica l conditions. Its diagnostic value in unexplained anterior knee pain versus information provided by conventional imaging, and their respective effecti veness-risk and -cost relations could be the purpose of future prospective studies.