[Effect of arthroscopic fluid inflow on the femoro-patellar tracking. Comparative study of the dry and fluid filled knee].

INTRODUCTION

The dynamic study of the patello-femoral joint is of outstanding interest in unexplained anterior knee pain syndrome. Nevertheless, the accuracy of information regarding this particular point by means of video-arthroscopy is of concern, due to the surgical conditions of the procedure. The aim of this study was to appreciate the effect of serum inflow on the visual evaluation of the patello-femoral tracking during conventional knee arthroscopy.

MATERIAL AND METHODS

The study group included 100 knees in 68 male and 32 female patients. Mean age at surgery was 36 years (range, 13 to 69 years). Indication for knee arthroscopy was: meniscal and/or ligament injury in 77 knees (group I), patello-femoral pain in 13 knees (group II), tibial tuberosity screw removal in 7 knees (group III) and "mysterious" painful knee in 3 patients (group IV). Arthroscopic technique was conventional; general anaesthesia, pneumatic tourniquet, single antero-lateral portal and serum inflow by simple gravity. We measured the minimum flexion angle that was necessary to obtain de visu a perfect centralization of the patella dome into the trochlear groove in two situations: before inflating the knee ("dry" angle) and after serum inflow ("serum" angle).

RESULTS

The average value of the flexion angle providing perfect centralization (FAC) in the "dry" situation and in the "serum" situation was 31 degrees (range, 10 to 75 degrees) and 38 degrees (range, 20 to 85 degrees), respectively. Of the 100 studied knees, the average difference between the "serum" and the "dry" FAC was about 7 degrees (6 degrees 45', standard deviation: 3 degrees 56') and was superior to 10 degrees in only one occasion; this difference is significative (T-test; p < 0.0001). Conversely, there was no significant difference between the average differential FAC figure noted in each group of patients (ANOVA; p = 0.28).

DISCUSSION

The role, if any, of the tourniquet inflated around the proximal thigh is more or less constrictive, thus restricting the natural patellar tendency to shift laterally. Moreover, the absence of active quadriceps muscle contraction under general anaesthesia acts also in the same way.

CONCLUSION

By comparison with the more natural "dry" situation, in nearly all occasions serum inflow by simple gravity induced less than 10 degrees of knee flexion overcourse until the obtention of a perfect patello-trochlear centralization. This data must be taken to consideration during arthroscopic examination of the patello-femoral tracking in the diagnosis of anterior knee pain that would remain unexplained after conventional imaging procedures.