SECTION I SYMPOSIUM: The Papers Presented at the Knee Society Meeting 2002: Session I: Long-Term Results of Total Knee Replacement
The long-term followup success of primary total knee replacement surgery has been one of the great success stories of the last half of the twentieth century. Many studies have reported 85% and 94% survival at 10 to 15 years. 1,3,4,6–8,10,13,15,21 With the exception of Insall-Burstein II, AGC knee, and the LCS knee, most of these studies used prostheses that are no longer on the market. Many factors have been found to be associated with early failure of total knee replacement surgery including component malalignment and ligament imbalances. 1,16 Late failures have included excessive polyethylene stress and wear, failure of modular components, thin polyethylene, and polyethylene manufactured with calcium sterate and gamma sterilized in air. There has been considerable debate about the use of posterior cruciate-retaining and posterior cruciate-sacrificing prostheses with excellent reports of both at 10 years followup. 1,3,4,6–8,10–21 In 1983, the current authors began using a cemented flat-on-flat total knee replacement with nonmodular metal-backed tibia components, AGC (Biomet, Inc, Warsaw, IN), in patients having primary total knee replacement. This is a one-piece posterior cruciate-retaining design with the tibia component having a CoCr base plate and an articular surface direct compression molded to the base plate. 2 The femoral component used was universal and did not have left or right geometry. All tibial and patella components were cemented. A metal-backed patella was used in 296 knees and an all-polyethylene component was used in 4287 knees. Although the success and survival of these prostheses has been reported, 14 the current study was done to determine the mechanism and etiology of failure of the components that failed.
MATERIALS AND METHODS
A retrospective review of all patients who had primary total knee replacements with the AGC since 1983 at the authors’ institution was done. All surgery was done by one of the four authors using very similar techniques. Demographic data were collected as to age, gender, indication for surgery, complications, and clinical and radiographic failures. All failures also were evaluated by reviewing charts and radiographs to try to determine the etiology and cause of failure in each patient. Implant survival data also were determined for each component. Radiographs were taken at 6 months, 1 year, 3, 5, 7, 10, 12, 15, and 17 years postoperatively. Kaplan-Meier 9 survival analysis was used in the standard method in which patients lost to followup were excluded from the study and were considered to have a successful result at their last visit. Failure was defined as loosening, revision of any component, or a recommendation for revision of any component. Prostheses were considered loose if they had a complete radiolucent line, migrated, or had a change in alignment. Statistics were done with the Kaplan-Meier survival curves and log rank and Wilcoxon tests were done to determine factors associated with failures, p values less than 0.05 were used to determine significant significance.
Four thousand nine hundred thirteen AGC primary total knee replacements were done in 3328 patients between September 1983 and December 1996. Sixty-two knees in 62 patients were excluded because of infection for a rate of 1.3%. There were 58 revisions in 57 patients and 155 patients (210 knees) were lost to followup (4.2%). This left 4583 total knee replacements done on 3054 patients. In this series, 388 patients died (407 knees) during the followup period. The average age of the patients at the time of total knee replacement was 70.4 years (standard deviation, 8.9 years; range, 19–83 years). Sixty percent of the patients were women. The primary diagnosis was osteoarthritis (87% of patients). All patients had femoral, tibial, and patella components inserted. The first 296 patients had metal-backed patella components. The last 4287 had all-polyethylene components, all of which were cemented. During the followup period, six femoral components were considered loose and all were revised (0.18%). The mean time to failure of the femoral component was 4.6 years (range, .5–7.6 years) (Fig 1). All loose femoral components were observed to be loose by 5 years postoperatively. An indepth review was done to determine the cause of failure of the femoral components. One femoral component failed because the patient fell and sustained a supercondylar femur fracture. This patient was treated with Rush rods and the fracture eventually healed. After the fracture, the patient had loosening of the femoral component, which was revised at 7.6 years postoperatively. One patient who had loose tibial and femoral components, who probably had an infection, had revision surgery at 2 years, followed by rerevision and excisional arthroplasty 1.5 years later because of infection. Four femoral components failed. All components had radiolucencies on the first radiographs taken after surgery and had complete radiolucency and loosening by an average of 4.5 years.
There were 21 tibia components that were loose and 19 were revised (0.46%). The mean time to failure was 4.5 years (range, .6–10.9 years) (Fig 2). Of these tibia component revisions, 12 were done because of an osteonecrotic lesion in the medial tibia plateau, which first was observed between 6 months and 1 year postoperative. The lesions healed in many patients; however, in 12 patients the lesion did not heal. This resulted in breakage of the tibia base plate in two patients and revision for loosening in the other 10 patients (Fig 3). This is a lesion that the authors have not described before, which cannot be seen on the first radiograph taken after surgery, and eventually can be seen between 6 months and 1 year after surgery. This lesion was not associated with excess varus in the tibia component except in one patient in whom the tibial prosthesis was inserted in too much varus. However, in the remainder of the patients, the alignment was near perfect and was not associated with varus alignment of the tibia. In four tibias, the preoperative alignment was between 16° and 20° valgus. These patients had extensive ligament balancing and insertion of an AGC component with posterior cruciate retention. The prostheses were well-aligned in the initial postoperative radiographs; however, between 4 and 6 years postoperatively, these patients had subluxation of the lateral femur condyle on the lateral tibia plateau with posterior subluxation of the lateral femoral condyle, and anterior subluxation of the lateral tibial condyle. These patients all had revision surgery to a more constrained type of prosthesis and did fine. These patients probably all needed a more constrained type of prosthesis at the time of the original surgery. Four patients had tibial component revision for pain and for increased activity on the bone scan; their prostheses were not thought to be loose at the time of revision surgery. These patients did not have pain relief and so it is thought that these tibial components were not loose. As mentioned previously, there was one patient who also had revision of a femoral component. This patient had an infection that was not documented at the time of the initial revision surgery. However, on the secondary revision surgery, the patient had an infection. No knee component was revised for osteolysis or polyethylene wear.
Total knee replacements have become one of the more reliable and predictable procedures in orthopaedic surgery to relieve pain and restore function in patients with arthritis. 1,3,4,6–8,10–13,15–21 Total knee replacement with the nonmodular metal-backed component has been very predictable at the authors’ institution with a greater than 98% survival rate at 15 years. This has resulted in no knee component being revised for polyethylene wear or osteolysis at as many as 17 years. In another series reported from the authors’ institution with minimum 10-year followup in patients with 8-mm tibial trays with 4.4 mm of polyethylene, no failure was reported for polyethylene wear or osteolysis. 11 The problems with osteolysis, backside wear, and polyethylene wear as described by Engh et al 5 have largely been solved by this prosthesis. It is interesting to examine causes and time to failure. In the current series, the authors found that tibial and femoral component failures did so at an average of less than 5 years after implantation, and these failures were identifiable on the radiographs taken at 5 years. 14 If the radiographs were normal at 5 years, then there was 0% chance of failure at 15 years. This is in contrast to other authors who have continued to have failures. In 1993, Ranawat et al 13 reported on TCK replacements using an early cement technique. There was a 94.1% survival at 10 years and a 90.9% survival at 15 years. In some long-term series, the outcome leading to loosening and revision most likely was related to a varus position with a limb alignment of 4° varus or less. 15–17 Because of the low failure rate in the current series, this was not statistically significant; however, it would stand to reason that this would lead to failure, as has been reported in another series. 16 The majority of failures in the current series were either attributable to technique or to an osteonecrotic lesion in the medial tibial plateau that previously has not been well-described.
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Richard S. Laskin, MD—Guest Editor© 2002 Lippincott Williams & Wilkins, Inc.