Abstract
A polyethylene liner can be cemented into a well-fixed and well-oriented acetabular component with success. This technique has been used by us for over 5 years. In the last year, we have used this technique in patients that are considered to be unlimited community ambulators and who participate in vigorous exercises as well as sports such as golf and skiing. These cemented inserts have therefore functioned in patients who have activity levels, which vary from a household ambulator to an unlimited community ambulator.
We have reviewed 17 patients with 18 hips that have follow-up beyond 2 years. Ten of these patients had the cemented insert performed because of dislocation and a constrained liner was inserted into the shell. Seven of these patients had a liner cemented at the time of revision because either the locking mechanism of the cup was not good enough to replace the liner or a new bearing surface was desired by the patient. Twelve of the liners that were cemented into the shells were constrained and five were standard polyethylene articulation surfaces (without constraint). Two of these were crosslinked polyethylene liners. At the time of revision eight hips also had stem revision and in nine hips only the modular femoral head and insert were exchanged.
There have been three revisions of these 18 hips. In the second hip replacement performed, the size of polyethylene used was too large and the ledge of the polyethylene rim was not abutted against the metal rim of the shell (the poly stood proud). This polyethylene disassembled within three months and a revision of this cup was done to a constrained cup and liner. The second revision was in a patient who had a cup changed with a standard polyethylene liner for dislocation. The dislocation persisted so that this patient was reoperated five months later and a constrained liner was cemented into the acetabular shell, which successfully stopped the dislocation. The third was a patient who had a constrained liner cemented into a cup, but continued to dislocate even with the constrained liner. There was no loosening of the cemented constrained insert. This patient had the entire cup revised to a ring support with a new constrained liner. In all three of these patients there was profound gluteus medius muscle absence of function.
Radiographic review of these acetabular reconstructions show that in those patients who had screw holes in the acetabulum there are no radiolucent lines apparent around the cement “puffs” which are visible in the acetabular bone. In those cups that did not have screw holes, the inner aspect of the acetabular cup was roughened with a Midas-Rex and there is no visible cement outside these cups. All of the acetabular plastic liners had the backside roughened with the Midas-Rex prior to being cemented into the metal shell.
Lever-out strengths of cemented polys into metal shells have shown that this is stronger than that provided by a regular locking mechanism.
The abstracts were prepared by Mrs Dorothy L. Granchi, Course Coordinator. Correspondence should be addressed to her at PMB 295, 8000 Plaza Boulevard, Mentor, Ohio 44060, USA.
