Biomedical subjects
Publications and source records attributed to H U Cameron.
Nonunion after high tibial osteotomy is an uncommon complication. Ten cases have been treated with a single plate; failure occurred twice in five. Double plates, bolted together, healed in all five attempts. Although the healed osteotomies had only "fair" functional results, none have as yet required total knee arthroplasty (TKA).
The various causes of effusions in artificial knees can be divided into four groups: implant related, technique related, interface problems, and infection. Diagnosis can be made from the patient's history and a clinical examination. Treatment is usually surgical revision.
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.
It is possible to use a noncemented porous metal-backed acetabular component with an outer diameter as small as 39mm with safety. A two to three year follow-up of the first 40 cases in which this type of acetabular component was used has revealed no particular problems. These small acetabular components have considerably reduced the necessity for acetabular bone grafting in patients with hip dysplasia.
A prospective, nonrandomized study was conducted in an attempt to determine if the addition of a stem to the tibial component in noncemented total knee replacement reduces the incidence of sinkage. A stemmed tibial component was used in 125 cases and an identical artificial knee without a stem was used in 307 cases. Follow-up was two to six years. Sinkage occurred in 0.8% of the cases with stemmed tibial components and in 3.5% of the nonstemmed tibial components, among which two (0.8%) required revision. The clinical results for both groups were similar. A small group of 34 patients who had a stemmed tibial component on one side and a nonstemmed component on the other also were examined. Fifty percent of these patients preferred the stemmed component knee. The results of these studies suggest that the addition of a stem to the tibial component in noncemented total knee replacement is of value in preventing tibial sinkage.
A clinical trial is reported that was conducted in an attempt to establish a timeframe for replacement of tricalcium phosphate by bone. In 20 cases, an 8.5mm by 3mm disc of tricalcium phosphate was implanted into the cut surface of the tibia at the time of total knee replacement. When followed radiographically, the disc of tricalcium phosphate generally could not be identified at six months. At two years, no untoward effects have occurred and no vestigial shadows remain, indicating that the block has fully incorporated and largely been absorbed and replaced by host bone. The experience in this series of cases indicates that tricalcium phosphate is a useful resorbable bone filler material.
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.
Revision of some Moore stems with a straight lateral shoulder where the stem has subsided distally and laterally may be difficult and can result in fracture of the greater trochanter. A trochanteric osteotomy that extends a long way down the lateral cortex of the femur facilitates this type of revision. A similar approach simplifies revision of proximally-fixed noncemented stems.
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.