Anterior metaphyseal angle; much less individual variation in determining the posterior slope of the tibia.

Background: The question of how to specify the posterior tilt of the tibia during arthroplasty operations remains unclear. The most current opinion is that a design whereby incisions are made in parallel with the individual pre-arthritic posterior tilt will yield better post-operational results. However, the wide range of inter-individual variations of posterior tilt of the tibia and the difficult task of identifying the shaft axis of the tibia through standard lateral radiographs are the main obstacles to this particular method. Therefore, there is a need for another reference line that can be measured with plain radiography and yields less inter-individual variation. The hypothesis of this study was that the angle formed between the anterior metaphyseal line of the proximal tibia and the tibial plateau would prove to be less variable across individuals.

Methods: Long-shot radiographs of non-rotating lateral tibias of 85 patients aged between 18 and 38 years were analysed. The angle forming between the anterior metaphyseal line of the proximal tibia and the slope of the tibial plateau, and the posterior slope angle was measured by 2 separate observers using the classical method.

Results: From the measurements of the posterior slope angle taken with the classical method, 38% (33/85) of the patients were within the ±2-degree range of the mean, and the anterior metaphyseal angle was within ±2 degrees of the mean in 75% (64/85) of the total patients. 44.23% variation (CoV) in posterior slop degrees, 2.73% (CoV) variation in the anterior metaphyseal angle measured by the same researchers. The difference between the percentages of variation was also found to be statistically significant. (z = 15.36, p = 0.000).

Conclusion: The anterior metaphyseal angle can be utilized to predict the individual posterior slope. Nevertheless, further large-scale, multicentre studies are needed to establish a mean value for the population.