[Arthroscopic assessment and clinical correlation of femoro-patellar tracking. Apropos of 116 knees in 115 patients under 40].

PURPOSE OF THE STUDY

The dynamic study of the patello-femoral joint is of outstanding interest in 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 anesthesia and use of a tourniquet act conversely. The aim of this study conducted in less than 40 year-old patients, was to correlate retrospectively arthroscopic 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 (1 bilateral). Mean age at arthroscopy was 26 years (range, 12 to 40 years). According to pre-arthroscopic clinical data, knees were broken down into 3 study groups: Gr-T (Test, painless patella), 50 knees with meniscal and/or ligament injury: Gr-PRP (Patella Related Pain but no dislocation), 55 knees: Gr-DLC (patella DisLoCation), 11 knees. Arthroscopic technique was the following: 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 centralization 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) in the "serum inflow" arthroscopic situation was 39 degrees in Gr-T and 52 degrees in Gr-PRP; this difference was highly significant (p <.0001). Patella 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 symptoms (pain and instability, groups PRP + DLC) and indicated patellar maltracking. In the PRP-group, an "FAC value > 65 degrees" showed a low sensitivity (0.34), but high specificity and positive predictive value of 0.98 and 0.95, respectively.

DISCUSSION AND CONCLUSION

Arthroscopic examination for patello-femoral tracking can provide measurable information on the FAC angle, that is reproducible under precise technical conditions. Its diagnostic value in unexplained anterior knee pain versus information provided by conventional imaging, and their respective effectiveness-risk and -cost relations could be the purpose of future prospective studies.