Clinical Profile of Patients with a Loose Durom Cup
Information for Patients and Doctors
General Comments: These patients often come in and will say that they are not any better then they were before the operation. Most of them do have some improvement in pain relief at rest, but they cannot function doing the activities that they want to do and therefore they have not achieved their goals for their operation, and are unhappy with their result for that reason. That is why they express that they are not better.
Clinical Symptoms: The two recurring complaints are startup pain and stiffness which means they will hurt or limp badly for 10-20 steps when they first arise from a chair, or out of a car, or similar activities. This is usually similar to the preoperative situation. Patients with a good cup will have startup pain and stiffness for 2-3 steps for as long as three months. The difference in startup pain and stiffness is both in intensity and duration. Secondly, they limp. They do not have a smooth gait and they have a classic antalgic hip limp as they walk down the hall of the office. Sometimes they don't think they limp, but they do limp. A third symptom is that when they move from a bent position to an upright position they get a sharp pain in the groin that is transient, but it is so painful for them that they will avoid that activity because they do not want to experience it. The fourth symptom is difficultly in doing stairs, usually coming down stairs is difficult for them. The fifth symptom is that they can't walk with any endurance. They sometimes say that they can walk 100 yards, and that is all, before they have to stop. Lastly, many of them have to use a cane for their outdoor ambulation.
Some patients have what they consider just healing symptoms in the first few months that seem to nag on and on. Then their symptoms begin to get worse and worse. As their symptoms get worse their x-ray usually shows more prominent radiolucent lines. These patients get reoperated between 18 months and two years. Clearly their cups were held by the pressfit during the first few months and when that worked free there was no longer any fixation.
Radiographic symptoms: The reason that we initially had trouble identifying the fact that these cups were loose in 2006 was that the x-rays during the first six months can look normal. The position of the cup can be considered ideal and no radiolucent lines can be present. The patients can be having the clinical symptoms listed above. When these cups are operated they are loose even without radiographic findings.
For patients who have progressive symptoms there are almost always progressive radiolucent lines. One characteristic feature of the failure of these cups, that differs from the Sulzer Interop cup, is that there is no migration that we have seen to date. Of course the finding with no radiolucent lines is also a different radiographic finding. We think that the pressfit, which ironically keeps the cup from getting fixation, does also help prevent it from migrating which does save bone.
Revision: At the time of revision the cup can be hit on the inferior medial edge with a bone tamp and sometimes with 1 or 2 blows, and sometimes with 4 or 5 blows the cup will pop free. It can then be lifted out with a clamp. The acetabular bone is almost always in good condition with a very thin membrane behind the cup. The membrane is not thick as it was behind the Interop cup. The capsule also does not appear to be inflammatory. The revisions that we performed have all been done with trabecular metal cups and those have performed well in all of the patients to date. We would recommend that the trabecular metal cup be used for these revisions. We have not had to use screws with the trabecular cup because the bone is in such good condition that a good initial fixation can be achieved.