Hybrid corn. Hybrid beef. Hybrid hips? Hybrid means a mixture or combination of two things. A total hip replacement (THR) is made up of two main parts. There’s the socket, or cup, and the femoral stem. The stem fits down into the long thighbone (femur). The stem has a round head at the top that fits up into the cup.
A hybrid THR has a cemented femoral stem and a cementless cup. A hybrid THR can be used in patients with osteoarthritis from hip dysplasia. Hip dysplasia occurs when the natural socket is shallow and flat instead of deep and round. With hip dysplasia, the head of the femur doesn’t sit securely inside the socket. There is a greater risk of hip dislocation when dysplasia is present.
THR in the dysplastic hip can be a challenge. The shape of the bone on the cup side may not give enough bone for a cup implant to fit into. Sometimes a bone graft is used to build up the bone in the socket.
How well do the hybrid THRs hold up in the dysplastic hip? That’s the focus of this Japanese study. One hundred patients with hybrid THRs were followed for an average of 10 years. The authors found that only two patients needed a second operation to revise the implant. Almost half of the hips with bone graft to build up the bone had problems with the cup side of the implant. There was movement and rotation of the cup after it was placed inside the bone. The cup didn’t come loose, so the researchers think the changes were caused by bone loss in the graft.
The doctors in this study stopped using bone graft in hips with mild dysplasia. Instead, they changed the position and location of the cup as it is placed into the bone. This method also allows doctors to help the patient make up for a difference in leg length. Since no cement is used to hold the cup in place, revision (if needed) is easier. The authors conclude that a hybrid THR for patients with osteoarthritis from developmental hip dysplasia gives good results. It’s an acceptable choice for patients with dysplasia
who are 55 years old or older.