Abstract The subchondral pressure in the patella was dynamically quantified in relation to the transpositions of the tibial tuberosity and variations in the force exerted by the quadriceps tendon. In a pilot project, we tried to determine the transmission coefficient between the effective pressure in the subchondral layer. The pressure on the patella depends primarily upon the angle of flexion of the femoro-tibial joint, secondarily upon the tension of the quadriceps tendon (1400 N), the greatest pressure (up to 3.5 N/mm 2) was measured. The areas most affected by pressure on the patella are the proximal crista and both facets, the medical and lateral. Each of these areas showed a particular pattern, the facets were most exposed to the greatest forces at flexion angles of 40° to 60° and the proximal crista at angles of over 60° and 70° of flexion. With further flexion the pressure on these three areas was reduced to a very small amount due to the action of the quadriceps tendon in the groove. The contact zone and the pressure were maximal on both facets and the proximal crista at angles between 40° and 80°. 10 mm ventralisation of the tibial tubersity generally decreased the pressure by 30%. The relationship between ventralisation and reduction of pressure was nonlinear. A combination of 10 mm ventralisation and 6 mm distalisation reduced the pressure by 40% on average. For 160 cases of anterior knee pain the average results at 4.75 years after ventralisation were excellent to good in 80% of cases, reasonable in 15.6% and insufficient in 4.4%. The assessment after ventralisation and distalisation in cases of patella alta and femoro-patellar pain showed even better results. The transmission factor was difficult to determine. Our results yielded a pressure dependent factor. In lower pressures of up to 1.5 N/mm 2 values were between 0.6 and 0.8 and went up to 1.0 for pressures over 2.0 N/mm 2. These numbers are not definitive but provide a reference.