Abstract
Trauma & Orthopaedic Department, Bronglais Hospital & Hywel Dda University Health Board, Aberystwyth, UK
Auto-CAD study is done to observe the effects of head neck ratio (HNR) in joint replacements. Total hip replacement joints were reconstructed on CAD with increasing diameter of the head keeping neck diameter constant in 1997. Simulation was done and Range of Movement (ROM), impingement and stability of the hip joint was noted. A graph was plotted with HNR on X-axis and ROM on Y-axis. It was observed that as the HNR increases the ROM of the joint is increased, impingement is reduced and stability is also increased. It is also observed that diameter of the head and neck is more important than considering only head diameter of the hip joint. The graphical analysis confirms that different diameters of the head may have same HNR depending on the neck diameter. So even in smaller diameter head the HNR may be more due to smaller diameter neck and may be more advantages than larger diameter head with bigger neck having smaller HNR. We conclude that HNR is more important than the head diameter alone in hip replacements.
