Biomedical subjects
Publications and source records attributed to H U Cameron.
A Moore prosthesis that had been in place for 28 years was revised. Apparent metallosis resulted from contact between the collar and the calcar. A supra-acetabular cyst was found packed with black stained debris. Metallurgical examination failed to reveal any metallic debris in the cyst material. This case indicates that all black staining in and of itself is not necessarily indicative of metallosis.
A review of 50 cases of a proximally modular noncemented stem has been carried out. The primary method of fixation was a proximal threaded sleeve which was screwed into bone. Mean follow-up was 5.2 years. Six cases were revised, two for stem loosening. The remaining cases rate 69% excellent, 14.3% good, 11.9% fair and 4.8% poor. Two cases showed distal lucency due to polyethylene debris which leaked through the taper lock because of two vertical grooves. The results were felt to be adequate, but the threaded sleeve is too difficult to insert which lead to an alternative method of sleeve fixation. The longitudinal grooves, which were obviously a fault in design, have been removed.
Delayed union and nonunion are uncommon complications of femoral supracondylar osteotomy, and repair attempts usually involve reopening the medial side and readjusting the compression plate. However, the author suggests that better results can be obtained in these cases if the medial hardware is left intact and a T-plate is applied to the lateral side with compression and bone grafting. In lateral compartment arthritis of the knee, a femoral supracondylar osteotomy will return the mechanical axis of the knee to normal if the medial side is in good condition, and will usually produce long-term pain relief. The results are generally good, because 60% to 80% of the load on the knee is normally concentrated on the medial side.
A 7-year review of 30 cases of cemented ceramic acetabular components has shown that all components rapidly become surrounded by a lucent zone between the cement and bone that appears to be nonprogressive. Although these prostheses have functioned well, some separation inferiorly between the ceramic cup and the cement suggests that "creep" of the cup within the cement occurs and that the cup should be modified to provide greater "pull out" resistance from the cement. This study has failed to substantiate some of the theoretical advantages of ceramic cups.
A titanium-head Thomson endoprosthesis was revised 2.5 years after insertion. Metallosis with burnishing of the head and acetabular erosion were noted. The stem and the cement mantle were in perfect condition. Because this is not an isolated case, the author recommends that a titanium-stem endoprosthesis have a cobalt-chrome or ceramic bearing surface.
In revising knee replacements 3 wear patterns have been noted; severe single facet wear which only occurs when the patella is dislocated or severely tilted, mild single facet wear from contact with the trochlear groove, and double facet wear. Double facet wear can occur when the knee flexes to more than 105-110 degrees, the edges of the patellar component then making contact with the edges of the femoral condyles across the cruciate gap. This double facet wear is potentially serious and may result in the patellar component wearing through.
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Of 101 patients who underwent knee replacement with the Tricon P prosthesis and were followed up for 2 or more years, 68 had patellar resurfacing with a recessed press-fit plastic button and 43 patients had patelloplasty (shaving of the patella and removal of osteophytes). All patients were followed up for more than 2 years. Three percent of the patients who had patellar resurfacing, later had patellar fractures; 4.6% of the patients who had patelloplasty initially, subsequently required patellar replacement. There were no instances of loosening of the patellar replacement. Patellofemoral aching was experienced by 7.6% of the patients who had patellar resurfacing and by 17.6% of those who did not. Of the patients who had patellar resurfacing, 61.5% could climb stairs without aids using the replaced side as the lead leg compared with 37.2% of the patients who had patelloplasty. Overall ratings of the surgical results were similar for the two groups. The author concludes that patellar resurfacing improves the quality of the result and that there are few drawbacks to the use of an inset patellar button.
Revision of a total knee replacement because of medial tibial plateau insufficiency revealed the base plate of a noncemented plastic-peg tibial component to have sheared off the plastic pegs which were still tightly embedded in bone. The fact that these plastic pegs remained tight indicates that even in extremely adverse situations the pegs are capable of providing fixation.
A fracture of the anterior flange of a femoral component in a unicompartmental knee has been seen. This was thought to be due to lack of bony support leading to cantilever bend. The solution would seem to be to add a metal web to strengthen that area of the femoral component.
Long-stem noncemented revision implants allow the creation of large windows for removal of cement distal to a primary stem tip. If the window is cut so that it can be wired back in place, the femur is proximally and distally protected with cerclage wires, and a long noncemented revision stem is used to bypass the defect, the window can heal rapidly and without complication.
The results of total knee replacement with a semiconstrained prosthesis after patellectomy are poor because the stabilizing effect of the patella is lost. A series of bicompartmental unicompartmental knee replacements (five patients) carried out for this condition was compared with a series of Insall-Burstein posterior stabilized knee prostheses (six patients). If both cruciate ligaments are present the results are not notably different, but those with an Insall-Burstein prosthesis generally fared better at stair-climbing using the replaced side as the lead leg. Since the Insall-Burstein knee is technically easier to implant there seems little to recommend the bicompartmental unicompartmental prosthesis in this condition.
In using bipolar prostheses for selected acetabular revision two groups were identified, those with an intact ring with thin flexible walls and those requiring massive allografting. In the intact ring group (15 cases), the largest possible bipolar head was used with minimal grafting. These have uniformly been trouble-free with acetabular reconstitution with minimal to no migration. In the massive allograft group (22 cases), the results have not been so spectacular, with only 55% good or excellent results. This is not necessarily a function of the acetabulum, since many of the femurs in this group also required allografting. No major migration has occurred, but the follow-up period is less than three years, and some migration is probably to be anticipated. It is concluded that, in these two situations, use of a bipolar prosthesis is a simple technique for dealing, at least in the short term, with a very difficult problem.
Twenty-seven hinged (Guepar II) knee replacements were performed on 26 patients with a follow-up of 1 to 7 years (mean 3 years). Indications for the procedure were bone loss (nine cases) nonunion of tibial or femoral fractures (four), anteroposterior instability (five), mediolateral instability (eight) and recurvatum instability (one). Results were good or excellent in 66.6%. Two patients required revision and there were three other implant-related complications. All press-fit stems were radiolucent to some extent and some radiolucency was present close to the knee in all revisions of stem components. No radiolucency was present in revisions of non-stem cemented components. Although the introduction of variable stem length, semi-constrained knees has reduced the need for implants such as the Guepar II prosthesis, the results, especially in terms of radiolucency, are surprisingly good. The authors conclude that a hinged knee remains of value in desperate situations.
Artificial joint prostheses can be expected to fail eventually. The author describes the case of a woman whose cemented knee-joint hinge prosthesis failed and required revision. This prosthesis was designed so that the stem became thinner as it approached the bearing surfaces. As a result the implant could not be removed from the cement and the cement could not be removed without severe destruction of surrounding bone. Although this prosthesis is no longer being used, there may be patients having this implant who will require revision in the future. This paper warns surgeons that its removal will be extremely difficult and appropriate plans should be made preoperatively. The author concludes that no stemmed implant should be cemented in place if it cannot readily be removed from the cement.
Since the introduction of metals into orthopaedic surgery over a hundred years ago, patients often present with a wide variety of hardware in their bones. Normally this is of little significance, but if the hardware is in the proximal femur and the hip is arthritic, then the metal must be removed before hip replacement can commence. This paper presents a series of guidelines to be used in such cases.
Preoperative factors that may lead to poor results in bipolar prostheses were examined in 34 patients with aseptic failures of their prostheses. Nineteen cases were revised for acetabular pain, seven for failure of the bearing insert, seven for a loose stem, and one for dislocation. The single significant factor that predicted a poor outcome was the angle of the sourcil of the acetabular roof. The group with acetabular pain had an average sourcil angle of 15.6 degrees compared with 5 degrees in those that failed for other reasons.
Due to rapid bone turnover in Paget's disease, loosening of artificial joints might be expected to be a problem, especially if they are of the tissue ingrowth type. Two patients with Paget's disease, who had had knee replacement with this type of prosthesis and have been followed for two years, have both done well to date. It appears that ingrowth-type implants can be used in the presence of Paget's disease. Paget's disease, which was first described in 1877, is characterized by a rapid turnover of bone. The cause of Paget's disease has yet to be determined. The common sites attacked, at least in a Canadian population, are the pelvis (45.4%), vertebrae (22%), femur (10%), tibiae (3.6%), and patellae (0.2%). Paget's occasionally gives rise to arthritic changes in a joint adjacent to the lesion, although the precise mechanism is uncertain. Disturbance of the subchondral bone due to hyperemia and overload due to increasing deformity have been cited as possible reasons. There was and is concern that joint replacement with cemented components would result in rapid loosening due to increased bone turnover. However, it has yet to prove a major problem. So far no reports have appeared in the literature on the effects of Paget's disease on knee replacement, specifically the effects of the porous tissue ingrowth type components that are now in common use. Two patients with Paget's disease around the knee who had had a knee replacement of this type are presented, with over two years of follow-up.