Development of Y II Cementless Total Hip System Using a Socket with Three Spikes

The advantage of a surgical procedure using the design of the Y II cementless total hip system using a socket with three spikes (Y II THA), which is applied in our department, is reported. The Y II THA has been developed based on the results of the computer simulation using the rigid body spring model (RBSM), animal experiments, and previous clinical experience. The Y II socket consists of a hemispherical metal socket made of titanium alloy and artificial cartilage made of polyethylene, which is screwed into the metal socket, called a metal back system. The thickness of the artificial cartilage is 9mm. The metal socket has three spikes. One of them has a notched surface and the length is 35 mm. The surface of the remaining two spikes is smooth and 23 mm in length. This socket is inserted at a 35° open angle by using an angle finder without removing the residual cartilage or subchondral bone. The Y II stem is made of titanium alloy and has a collar at the neck. The femoral neck angle is 35° and the length is 178 mm. Several longitudinal grooves are engraved on the smooth surface, called a fluted type. There are three sizes: small, standard, and large. The femoral head, made of cobalt-chromium alloy, is 23 mm in diameter. This is called a modular type. The femoral neck is excised at a 35° angle to the horizontal line with 8 mm of calcar left from the base of the lesser trochanter. Then, the femoral medullary canal is reamed to the minimal necessary extent using a rasp whose size was preoperatively determined by a template. Forty-one joints of 41 patients underwent total hip arthroplasty using the Y II THA and were followed up for more than 3 years. All patients achieved excellent clinical results and stable mechanical durability according to radiographic findings.