Determination of posterior tibia slope and slope deterioration with osteoarthritis: A radiological study in an African population
AbstractBackground: The posterior inclination of the tibia plateaux relative to the longitudinal axis of the tibia is referred to as the Posterior Tibia Slope (PTS). Fore knowledge of the mean PTS in a given population is important in order to keep it as close to the normal range as possible during knee replacement. In various studies among the Caucasians, Asiatic or racial mixtures and using diverse methods the slope has been found to range in adults from 0 to 18 degrees. There is paucity of information regarding PTS
in the indigenous African population.
Objective: This study was performed partly to determine the mean posterior slope in the African population and partly to study slope behaviour in arthritic degeneration.
Design: Investigational, case control study.
Methods: Two hundred twenty four X-ray films from 152 patients were used for the purpose of this study. Orthogonal radiographs for the full-limb including the knee were obtained using a standardized technique. The posterior tibia slope was obtained through measuring the angle between the tangent to the tibial plateau and the perpendicular direction to Tibial Shaft Anatomical Axis (TSAA).
Results: There were a total of 152 cases by the end of the study, 79 had non-arthritic knees (group 1) while 73 knees were osteoarthritic (group 2). Group 1 had a mean age of 48 years (95% CI 44.9 - 49.1 (2.1) and consisted of 37 males (47%) and 42 females (53%). Group 2 had a mean age of 53 years (95% CI 45.8- 50.2 (2.2) and consisted of 33 males (47%) and 40 females (53%). Control group had a mean slope angle of 6.8 compared to the arthritic group mean of 6.1 (95% confidence level P < 0.05) which was significant.
Conclusion: Our findings are that the mean posterior tibia slope among the African population is about 7o. We also conclude that the slope decreases with osteoarthritic degeneration. This would also suggest cruciate insufficiency that would result in either anterior or posterior tibia instability.