The tip of the greater trochanter is the attachment site for the abductor muscles of the hip joint. Its preservation in robotic and conventional THR is important for normal gait. The effect of different stem designs and robotic cutterpaths on the preservation of the trochanter tip is examined.
One anatomical stem, one straight stem, and one stem specifically designed for robotic THR were implanted virtually in CT scans of osteoarthrotic hip joints using the Torch preoperative planning unit (URS-ortho). In transverse sections of the trochanter tip, dimensions of the trochanter area removed by the milling tool were recorded for each stem design and different cutterpaths (3-axis versus 5-axis milling).
Five-axis milling showed significantly better results than 3-axis milling. For straight stems, more bone was removed than for anatomic stems. The most favorable results were achieved with 5-axis milling and a curved stem specifically designed for robotic THR.
The introduction of 5-axis milling in robotic THR is an improvement of the technique and makes preservation of the abductor mechanism at the tip of the greater trochanter easier for the surgeon.