Metal Conserve Plus, Hip Resurfacing & Potential Complications

DURABILITY OF METAL-METAL CONSERVE PLUS HYBRID HIP RESURFACING AND POTENTIAL COMPLICATIONS

A Personal Experience of >10 years with over 1000 closely followed hips

H.C.Amstutz

01-15-08

There has been a dramatic reduction of post operative complications and improved durability due to operative technical improvements and added versatility of the system with new components and instruments.

Durability of Components:

The durability of the Conserve Plus sockets implanted at the Joint Replacement Institute has been excellent. There have been no cases with a loss of fixation or loosening. In fact, there have been no socket loosenings since I began using this porous bead technology for fixation with other systems in 1983.

The incidence of femoral loosening in patients with primary osteoarthritis and good bone quality has been rare even from the beginning of implantations in 1996. Overall femoral loosening occurred in 2% of my patients over 10 years. In the vast majority of cases the failures were associated with a hip that had risk factors (i.e. large cystic degeneration and/or a small surface area) and who were operated on in our early experience during which time the instrumentation and early technique was being developed. Fifty per cent of our problem cases occurred in the first 110 patients. After carefully studying retrievals, we deemed that the major reason for failure was inadequate fixation at the time of surgery. Because the surface area for femoral fixation is small compared to conventional stem-type devices, meticulous attention to preparation of the bone surfaces is critical and that optimizing fixation can likely mean years of increased durability. As a result of instituting numerous technique changes there has been a dramatic decrease in the incidence of loosening and the signs of loosening

We have not identified a single patient who has had a loosening or has signs of potential loosening in over five years, and there have been no patients revised due to loosening in over six years with the Conserve Plus device. The improvement is such that long-term durability is now anticipated with our technique. My efforts to improve fixation have continued each operating day reaching the point that even patients with risk factors such as cystic degeneration can be successfully resurfaced. We continue to recommend, however, that other surgeons begin their surgical experience with resurfacing with patients with good bone quality.

While high impact activities have not been associated with failure when the bone quality was ideal, there have been two patients during the period of our early technique with very high activity levels who have had femoral loosening when there were deficiencies in bone stock. Thus far the durability of the resurfacing patients with risk factors who have been operated with the revised techniques and who have continued their high impact activities has been excellent.

Neck Fractures:

The worldwide incidence of femoral neck fracture after hip resurfacing is greater than 1.25 per cent. This is from a study combining all of the reports in the literature in approximately 7,500 cases with 3,500 of those being from the Australian Hip Registry. It is likely that the number of fractures has been under reported with a wide range of reports up to 10 per cent. The cause of a neck fracture is often multifactorial, and seems to vary with prosthetic design. From our critical analysis technique is the most important factor with patient selection next depending on prosthetic type. The incidence of neck fractures in my early period patients was < 0.75% with several technical and bone stock issues being identified. By eliminating those issues, there have been no fractures occurring in the last 5 years using a 1 mm cement mantle. These results using this fixation technique with the Conserve Plus validates our philosophy. Unfortunately as we see it some of the other resurfacing prostheses such as the BHR and Corin are designed for no or minimal mantle thus increasing the risk for facture.

One of the most desirable features of the Conserve Plus system relates to the easy conversion should a revision be necessary. Those patients who required conversion to a THR were all successfully converted to a THR with a big femoral head without changing the socket. In effect the operation is much like a primary THR with comparable results and the patients have maintained normal range of motion with the same stability as the resurfaced hip.

Range of Motion and Dislocation

The low profile socket of the Conserve Plus is less than a hemisphere (170 degrees). By increasing the normal anteversion of the socket and with appropriate bone sculpting, maximum range of motion is possible without impingement. The dislocation incidence has been low (<0.5%) in early cases, and was associated with socket component malposition. The inserter was redesigned for more optimal viewing of the component during insertion, and when combined with the thin acetabular shell introduced in December of 2003, facilitates resurfacing with an increased femoral size. Dislocation has been virtually eliminated with no dislocations in the past 350 hips. Dislocation had occurred in four hips in patients who had severe trauma. All were reduced without reoccurrence or a problem with fixation.

Wear and Ion Concerns

The wear of this metal-metal bearing is extremely low. The bearing will not wear through in a patient’s lifetime. The volumetric wear is insufficient to cause osteolysis except in rare situations. However, some of the particles from the bearing surface will come off during the activities of daily living or sports, and have been traceable in the blood as ions. These ions can be measured and are elevated in all patients to a varying degree. The majority of these ions are excreted by the kidneys. It is unknown at this time as to whether there are any adverse consequences. We have measured ion elevations in some patients who had metal-metal implanted over 30 years ago without any known adverse consequences. Although there is a concern that these ions may cause cancer, at the present time, there is no cause and effect relationship known. A relatively small number of these prostheses were implanted in the late 60's and early 70's with some patients having had successful implants lasting 40 or more years. However there have not been enough patients with long term metal-metal implants that have been studied over the long time to be absolutely certain that there is no risk. More than 350, 000 metal-metal implants have been implanted since the reintroduction of metal-metal bearings in 1988 and with each passing year these numbers become more significant. We believe that if there were a risk it must be extremely low.

For more than five years metal ion concentrations in the blood of more than 100 patients who have had metal-metal implants have been studied serially at the Joint Replacement Institute with no adverse effects noted.

Most importantly the wear and ions can be potentially reduced up to 50% by using the newly introduced hardened metal femoral component.

Metal-metal Hypersensitivity

Metal-metal hypersensitivity due to the implantation of metal-metal bearings does occur, but is extremely rare. It is thought by one of our collaborators in Germany that the incidence could be 1 in 10,000, although several series in England suggest that the incidence could be ~ 1% using the BHR prosthesis. At the present time there is no known definitive methodology for identifying someone who is likely to develop this rare, delayed-type of hypersensitivity.

The methods of studying this rare complication are under investigation in our laboratory in collaboration with Rush St. Luke's, Chicago, as well as in labs in England and Germany. We have studied 5 cases that have been sent to us from Europe and Australia, all of which required an exchange of bearing surfaces. Fortunately to date we have not identified any in our Conserve®Plus series .

Sepsis:

Immediate postoperative sepsis (infections) has not been demonstrated in any of our over 1140 resurfaced hips. Six patients have developed sepsis which emanated from elsewhere in the body and was hematogenously spread to the hip joint. Four of these patients were successfully treated by debridement (removal of the infected tissue in a reoperation) in combination with antibiotic treatment. In one patient a surface arthroplasty was converted to a total hip in a one-stage procedure. This patient had a delay of treatment for one month as it was believed not possible to anticipate a successful recovery by simple debridement alone. One other patient has had a two-stage reimplantation. Following surgery we advise patients to have antibiotic prophylaxis for dental cleaning for one year. After that, the recommendations from the ADA and AAOS (dental and orthopaedic societies) are that no prophylaxis is required for just cleaning of the teeth. However, if a root canal or other procedures that might be a greater risk for infection are done, then prophylaxis is recommended. Bacterial infections which occur anywhere in the body must be promptly treated to avert their spread to the site of an implant.

Heterotopic Ossification:

The incidence of heterotopic ossification (bone which forms in the soft tissues after arthroplasty) in male patients who have had hip surgery without any prophylaxis is greater than 40 percent, but it is rare in women. The amount of bone that forms in the vast majority of the hips is inconsequential. Only the most severe amounts cause any loss of range of motion. In my first 400 patients the incidence in male patients was 12 per cent of Grade 3 and 4 with a few patients (~1%) having a slight reduction in their range of motion. All of our patients were treated with indomethacin prophylaxis. More recently with new measures instituted, including more irrigation, protection of tissues from bone debris, and improved technique at surgery, we have decreased this figure to about 2 percent with no recent serious case of bone causing a reduction of range of motion. Male patients, who undergo bilateral surgery, in addition to receiving indomethacin have one dose of x-ray therapy of 700 rads preoperatively which is 1/10 of the dose used in the treatment of cancer. This treatment improves the effectiveness of prophylaxis in patients who are undergoing bilateral surgery.

Nerve Damage:

In order to perform hip resurfacing the surgeon must work around the hip joint in order to get at the socket and implant the replacement in an optimal position. This requires some additional stretching as compared to THR. The risk of injury to the femoral nerve has been above 1 per cent in our early patients, but with alterations in technique that complication has not now occurred in the last 200 patients. Fortunately all of those patients who encountered nerve damage (palsy) of the femoral nerve, which operates the quadriceps (knee extension), have recovered without residual after effects. It is possible to injury the sciatic nerve much in the same way as this potential complication can occur with a THR, but it has been rare in my patients with the posterior approach (1 in greater than 1000).

Thromboembolic phenomenon:

All patients are at risk for blood clots following hip or knee surgery. Therefore, we recommend utilizing Coumadin (warfarin) for prophylaxis starting the night of surgery and continuing for three weeks. This will be monitored by internal medicine physicians. Following that regimen we recommend aspirin for three weeks. In our opinion Coumadin is the safest and most efficacious of all the chemical prophylactic measures, but its use does require monitoring. The results in our patient population have been excellent. We have had only five cases of phlebitis in 1140 hips, no pulmonary embolus or death. There have been two postoperative bleeding episodes; therefore, it is important to be followed carefully to make sure the level of protection is safe and efficacious. Patients have been able to fly across the U.S. safely with this method of prophylaxis as early as three-four days after surgery.

Postoperative Recovery:

The hospital stay for patients with one hip is generally two or three days. Patients who are traveling distances greater than three or more hours by plane generally stay an additional overnight at a local hotel or other facility. Sutures are generally removed at approximately 10 days. A program of relatively simple exercises is generally given with the more intense therapy initiated after an x-ray is sent to the Joint Replacement Institute for review at one month. Subsequent x-ray and follow up is obtained at 3-1/2 months. If this cannot be done at the Joint Replacement Institute or at one of my traveling clinics, then it is preferable to have a local orthopaedist send the results to us. During the first year it is anticipated that the patient will be seen by Dr. Amstutz at the Joint Replacement Institute or one of his clinics held in other U.S. cities. Additional follow up will be carried out on an annual basis through the first three years, and at less frequent intervals thereafter. Long-term follow up is essential to optimize the results for you the patient and future patients as well as to inform you of any impending problems.

Study group:

Between November 1996 and September 2006, 1000 hips in 838 patients received a hybrid metal-on-metal resurfacing (Conserve Plus) implanted by the author at our institution. The average age of the patients was 49.9 years and 73% of the study group was male.

A summary of the overall demographics of the study group is presented in the following table.

	Average	Range
Age at surgery (Years)	50.0	14 to 78
Height Males (cm)	179.1	155 to 203
Height Females (cm)	164.9	140 to 183
Weight Males (kg)	88.8	57 to 164
Weight Females (kg)	67.1	42 to 119
BMI Males	27.7	18.4 to 46.4
BMI Females	24.6	17.5 to 42.3


Gender (n = 838 patients)	Count	%
Males	626	74.7
Females	212	25.3

Charnley Class (n = 838 patients)	Count	%
A-Unilateral -	511	61.0
B-Bilateral	280	33.4
C-Other skeletal abnormality	47	5.6

Etiology (n = 1000 hips)	Count	%
Idiopathic OA	696	69.6
ON	83	8.3
DDH	103	10.3
Epiphyseal Dysplasia	4	0.4
Post Traumatic OA	43	4.3
Inflammatory OA	11	1.1
SCFE	17	1.7
LCP	21	2.1
Rheumatoid	12	1.2
Ankylosing Spondylitis	5	0.5
Pigmented Villonodular S ynovitis	2	0.2
Melorheostosis	1	0.1
Arthrokatadysis	1	0.1
Osteopetrosis	1	0.1

Femoral defect size (n = 1000 hips)	Count	%
no defect	361	36.1
<1cm	292	29.2
1-2 cm	247	24.7
>2cm	100	10.0

Previous surgeries (n = 1000 hips)	Count	%
Hemi-Resurfacing	2	0.2
Osteotomy	13	1.3
Coring	12	1.2
Pinning	17	1.7
Judet Graft	1	0.1
Acetabular Reconstruction	2	0.2
ORIF	3	0.3
Free Vascularized Fibular Graft	2	0.2
Other	1	0.1
Total	53	5.3