Impact of posttraumatic steps on the intra-articular pressure of the lateral tibial plateau after fracture reconstruction: A biomechanical human cadaver study

AIMS AND OBJECTIVES: The aim of reconstructing a tibial head fracture is the anatomical reconstruction. Which deviations from the anatomical position are tolerable and which misalignments could be treated conservatively, is currently not investigated. It is known that after tibial plateau fractures up to 7.3% of even treated patients develop a posttraumatic osteoarthritis requiring a prosthesis after 10 years. A rate of osteoarthritis after 5 1/2 years up to 40% is known after tibial head fractures. The aim of this study is to investigate the effects of the reduction on the intra-articular pressure distribution within the lateral tibial plateau in various degrees of flexion. MATERIALS AND METHODS: In a human lateral tibial plateau fracture model (AO 41 B1, n = 8), the intra-articular pressure distribution was measured depending on misalignment after reposition (0-8 mm step in 1.0 mm steps) in various angles of flexion (0°, 15, 30°, 60°, 90°). Preserving the relevant ligamental structures, the soft tissues was removed and the knees wer embedded in PMMA cement (Technovit 3400, Heraeus). A standardized osteotomy, dividing the lateral articular surface in the middle of the primary-load zone has been performed. The lateral fragment was fixed by a self-constructed sled with an angular-stable plate (LCP TomoFix, Fa. Synthes) and moved in 1 mm steps from the anatomical position distal. The intra-articular pressure distribution was measured by pressure sensors (S2015 Double kneepad sensor, Fa. Novel) under axial compression on a servo-hydraulic testing machine (Instron 8874, Fa. Instron). Taking the mean of the averaged pressure distribution in the medial and lateral plateau, data was measured for 20 sec with a reading rate of 10 frames per second. RESULTS: Increasing the misalignment-step, there is an increasing mean pressure in both plateaus in every angle of flexion. For example at 90° of flexion relative growth in pressure (means) in 1 mm increments steps: In the lateral plateau -5.6%; -2.1%; + 9.3%; + 11.8%; + 13.3%; + 15.9%; + 20.6%; + 23%. In the medial plateau, the pressure change is as follows: + 4.8%; + 8.0%; + 8.3%; + 8.8%; + 9.0%; + 9.3%; + 9.4%; + 9.5%. The data is similar in the other investigated degrees of flexion. The turning point of the pressure increase is lateral always at the 1-2 mm step. CONCLUSION: Small steps of only 2 mm lead to a significant increase in pressure - initially in the intact and later also in the fractured plateau. Referring to these findings, the indication for primary operative or conservative care and revision operations should be made. Intraoperative reposition should be performed as precise as possible - preferably controlled f.e. arthroscopically. The influence of the menisci on the pressure distribution is seen in the lateral plateau as it compensates the loss of area in smaller joint-steps. This mechanism will be content of further studies.