Information for Patients

The operation

6 THE OPERATIONS

 

Primary total hip replacement - Pinnacle socket/Corail stem

 

The Pinnacle cup - this is a hemi-spherical cup that is placed into the pelvis. The surface that interfaces with the bone is called porocoat. It is three layers of beads burnt onto the metal shell leaving spaces into which the bone will grow. This technique has been used for over 25 years with considerable success and I can be certain that this bone growth will occur assuming good primary fixation of the cup is made. Usually this can be achieved with a simple press-fit but there are holes in the cup to allow it to be screwed into the pelvis for good fixation. Once the shell has been introduced and has got good fixation a liner can be used. This may be made of the newer hard wearing polyethylene or metal or ceramic.

 

Corail

On the femoral side a Corail stem is used. This is made of titanium but it is covered in a material called hydroxyapatite. this is a substance with the same mineral structure as bone.  The host bone believes it is coming into contact with more bone and will join onto it as if healing a fracture. There is therefore a bonding of the host bone onto the hydroxyapatite to give good fixation. This implant has been in use primarily in France for a period of 22 years. I have used it since 2001.

 

The bearing surface, whether it be modern polyethylene liner with metal ball, metal liner with metal ball, ceramic liner with ceramic ball or metal liner with ceramic ball, can be chosen according to the particular patient.

 

My choice is to use a ball, whether this be metal or ceramic, of at least 36 mm diameter. This is regarded as a large head in a total hip replacement although still considerably smaller than a natural head. The advantages of such large heads is that it brings stability to the joint. The larger the head, the more stable is the joint. In the past the criticism of this was that the wear rate would also be greater with an increased size in the head. Using the hard on hard bearings of metal or ceramic this is of less significance.

 

The Operation:

 

hip replacement

During the operation the socket is prepared by making it into a hemi-spherical shape. Into this would be placed the metal cup. A press-fit is obtained by slightly under-reaming the shape created in the pelvis so that when the metal cup is placed into it, there would be good primary fixation. Subsequently bone will grow into the surface of the metal shell to secure it in place.

 

On the femoral side the arthritic femoral head will have been removed and a hole reamed along the shaft of the femur to accept the stem of the prosthesis. An appropriate size prosthesis is placed into the stem, again depending on a press-fit for its initial fixation. Bone then grows in to the hydroxy-apatite surface. A liner is then placed into the cup and a femoral head placed on the end of the stem. The length of the head can be altered to achieve an appropriate leg length.