Retropatellar forces after rupture of the PCL and patello-tibial transfixation: An in vitro study

Abstract

Compared to injuries of the other knee ligaments, a rupture of the posterior cruciate ligament (PCL) is relatively rare. Treatment may be conservative or operative. A rupture that has been operated on temporarily can be stabilised using a Grammont patello-tibial transfixation (olecranisation). Flexion and extension between 30° and 60° are allowed. The advantage of this method is that it avoids complete immobilisation of the joint and also the reduction of pull on the PCL. However, patients treated with this method show long-term osteoarthritis of the retropatellar joint area. Our study aimed to show the distribution of forces at the dorsal patellar surface in the following: (1) knee with intact ligament; (2) knee with PCL rupture; (3) knee with PCL rupture plus olecranisation. Fourteen fresh knee specimens were investigated in a Plitz/Wirth knee kinemator. The femur was fixed while the tibia was flexed between 5° and 120°. Pull was placed on the patella and on the dorsal side of the tibia with weights over the tendons of the quadriceps and the roots of the ischio-crural muscles. With the aid of a special measurement device in the patella, the medially laterally, proximally and distally acting forces in a movement cycle could be measured as well as the total retropatellar force in the above experimental setups. We found that, dependent on load and flexion angle in each preparation, (1) the total retropatellar force and some of the force components were greater when the PCL was ruptured than in the intact specimen. (2) with olecranisation the total force and the medial and lateral components were less than in the unrestricted patella with ruptured PCL, (3) the proximal area of the patella with olecranisation was less loaded than in the knee with either intact or defective PCL, and (4) the distal area of the patella with olecranisation was more loaded than in the knee joint with either intact or defective PCL.

Conclusions

To avoid destruction caused by overloading, especially in the distal area of the patella, the duration of patello-tibial transfixation should be carefully considered. Patients should be kept moving, at the same time being warned about excessive loading.