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© 1996 The Journal of Bone and Joint Surgery, Inc. Varus Osteotomy of the Distal Part of the Femur. A Survivorship Analysis* , TORONTO, ONTARIO, CANADAInvestigation performed at the Division of Orthopedic Surgery, University of Toronto, Mt. Sinai Hospital, Toronto
Varus osteotomy of the distal part of the femur is often the procedure of choice for the treatment of osteoarthrosis of the lateral compartment associated with genu valgum. We followed twenty-one knees (twenty patients) long term or until failure. At the most recent evaluation (average, 133 months; range, ninety-seven to 240 months), thirteen osteotomies were still successful, seven had failed, and one patient (in whom the knee had remained functional) had died. Of the seven failures, three occurred early (at twelve or twenty-four months) and four occurred late (between seventy-two and ninety-eight months). The probability of survival at ten years was 64 per cent (95 per cent confidence interval, 48 to 80 per cent), as determined with use of the Kaplan-Meier method. We concluded that, with proper selection of patients, this procedure is effective for the treatment of gonarthrosis of the lateral compartment associated with valgus deformity.
Osteotomy about the knee is an accepted operative procedure for the treatment of unicompartmental gonarthrosis2. Primary involvement of the lateral compartment associated with valgus deformity is much less common than primary involvement of the medial compartment associated with varus deformity. If an osteotomy is to be performed on a knee with a valgus deformity, varus osteotomy of the distal part of the femur is the procedure of choice, as the clinical results appear to last longer than those achieved with osteotomy of the proximal part of the tibia10. Osteotomy of the proximal part of the tibia also fails to correct the superolateral tilt of the joint line3. We previously reported the results after varus osteotomy of the distal part of the femur in patients who had osteoarthrosis of the knee associated with valgus deformity9. At an average of four years, twenty-two (92 per cent) of twenty-four knees had a good or excellent result9. Good results have also been reported by other authors5,6; however, we are not aware of any long-term study that has determined whether these results deteriorate over time. The purpose of the current study was to review the long-term results after varus osteotomy of the distal part of the femur, to compare them with the results that we reported earlier, and to determine the longevity of the results of this procedure with use of survivorship analysis.
Patients: Between 1972 and 1985, twenty-four varus osteotomies of the distal part of the femur were performed in twenty-three patients for the treatment of osteoarthrosis at our institution. Of these twenty-four knees, twenty-one (twenty patients) were available for follow-up. Fifteen osteotomies were performed in women (one of whom had a bilateral procedure) and six, in men. The average age at the time of the operation was fifty-six years (range, twenty-seven to seventy-seven years). Clinical evaluation: A detailed protocol that included subjective and objective scoring was completed for each patient9. Points were allocated for pain, distance that the patient could walk, instability, ability to climb stairs, use of walking aids, range of motion, and fixed flexion deformity. Anteroposterior radiographs of the lower extremity, made with the patient standing, were used to determine the tibiofemoral angle (the anatomical angle created by the intersection of lines drawn down the long axes of the femur and the tibia) both preoperatively and at the follow-up evaluations. Standard radiographs of the knee were also made in order to monitor the status of the osteoarthrosis. The criterion for a successful result was an increase in the postoperative score, as compared with the preoperative score, of at least 10 points or a total score of more than 70 points. A procedure was considered to have failed when this criterion was no longer met or when a revision operation was needed. The time to failure was recorded (Table I).
Operative technique: The operative technique has been described previously9. The osteotomy is performed from the medial side. A medially based wedge of bone is removed. The 90-degree-offset dynamic-compression blade-plate is inserted parallel to the articular surface. The osteotomy site is closed, and the plate is brought into contact with the medial femoral cortex. The medial cortex and the femoral transcondylar line are then at 90 degrees to each other. This results in a tibiofemoral angle of approximately 0 degrees, which is the desired correction. Postoperative regimen: The postoperative regimen included prophylaxis against deep venous thrombosis with warfarin, with the first dose given on the evening before the operation. The limb was immobilized in a cylinder cast for two weeks, and range-of-motion exercises were then allowed. Non-weight-bearing for six weeks was prescribed. When the radiographs revealed that the osteotomy site was uniting, a program of graduated weight-bearing was started. Statistical analysis: Survivorship analysis was performed with the Kaplan-Meier method. The technique of Greenwood was used to calculate 95 per cent confidence limits4. The knee scores that were determined preoperatively, at the short-term follow-up evaluation (at an average of four years), and at the most recent follow-up evaluation were compared with use of a paired t test and multiple regression analysis.
Clinical results: At the time of the latest follow-up evaluation, thirteen of the twenty-one osteotomies were still considered successful, seven had failed, and one patient (Case 19) had died at eighty-four months with a functioning knee (Table I). The average duration of follow-up for the thirteen successful osteotomies was 133 months (range, ninety-seven to 240 months). The average increase in the score at the most recent follow-up evaluation, compared with the preoperative score, in the thirteen knees with a successful result was 30 points (range, 16 to 55 points) (p < 0.0001). The component of the score that showed the greatest improvement was relief of pain. Three knees had some loss of the correction of the alignment of the tibiofemoral axis accompanied by radiographic progression of the osteoarthrosis of the lateral compartment. The over-all anatomical alignment, however, remained no more than 2 degrees of valgus (Figs. 1-A, 1-B and 1-C).
Failed osteotomies: Seven osteotomies failed, and all of the patients who had a failure subsequently had a total knee arthroplasty. Three failures occurred early: two (Cases 1 and 9), at twelve months, and one (Case 6R), at twenty-four months. The former two patients, both of whom had had tricompartmental disease at the time of the osteotomy, had no decrease in pain despite an adequate correction. The latter patient was also considered to have had a complication of the operation as the femur fractured proximal to the plate, necessitating conversion to a total knee arthroplasty with a long-stem femoral component. The four late failures occurred seventy-two to ninety-eight months after the operation and were characterized by an increase in pain and radiographic evidence of progressive osteoarthrosis. The alignment of the tibiofemoral axis also returned to a few degrees of valgus because of the deterioration in the lateral compartment. At the time of the earlier follow-up, the probability of survival (the osteotomy remaining successful) was 83 per cent (95 per cent confidence interval, 65 to 98 per cent); this decreased at ten years to 64 per cent (95 per cent confidence interval, 48 to 80 per cent) (Fig. 2).
Complications: Five complications occurred in four patients. One patient (Case 2) had stiffness, which necessitated a manipulation with the patient under anesthesia at six months postoperatively. Another patient (Case 5) had a superficial wound infection in the knee, which resolved after intravenous administration of antibiotics. The third patient (Case 8) had a pulmonary embolus, which was treated successfully with anticoagulants. The final patient (Case 6) had failure of the fixation at five months when the blade cut out of the right femur, resulting in a progressive varus deformity. This patient had revised fixation and bone-grafting. She did well initially; however, two years after the index operation she sustained a fracture just proximal to the plate, necessitating revision to a total knee arthroplasty with a long-stem femoral component, as already described.
To our knowledge, the current study had the longest duration of follow-up of the results of varus osteotomy of the distal part of the femur. A shortcoming of the study was that three of the original twenty-three patients (three of twenty-four knees) were lost to follow-up. The small number of patients reflects the infrequency with which this procedure is performed. The three early failures can be attributed to poor selection of patients (two patients) and failure of the fixation (one patient). The former two patients (Cases 1 and 9) both had pre-existing radiographic and clinical evidence of disease of the medial compartment and placed relatively high demands on the knee. The failures in these two patients were not surprising and are in agreement with the findings of Edgerton et al., who reported less satisfactory results after varus osteotomy of the distal part of the femur in patients who had more advanced disease in the medial and patellofemoral compartments. The third patient (Case 6) had two complications: failure of the fixation at five months and a fracture proximal to the plate at twenty-four months. She ultimately had a revision to a total knee arthroplasty with a long-stem femoral component. The remaining four patients who had a failure were able to function for seventy-two to ninety-eight months before they needed a conversion to a total knee arthroplasty. These late failures were due to an increase in pain with radiographic evidence of progression of the osteoarthrosis, primarily in the lateral and patellofemoral compartments. Motion was preserved, and there was some loss of the corrected varus alignment; however, the mechanical, or weight-bearing, tibiofemoral axis remained in varus. This finding differs from those in patients who had an osteotomy of the proximal part of the tibia for varus deformity7. In those patients, the loss of alignment was more pronounced and the initially corrected valgus weight-bearing axis often drifted back into varus alignment. Although the nature of the failure differs, survivorship analysis showed that the ten-year results of varus osteotomy of the distal part of the femur were similar to those of valgus osteotomy of the proximal part of the tibia performed for disease of the medial compartment11. In the seven knees that were revised to a total knee arthroplasty, there was little scarring and no difficulty with exposure because of the use of a medial parapatellar arthrotomy at the time of the arthroplasty. The arthrotomy was performed with use of a preserved operative plane as a medial subvastus approach had been used at the time of the osteotomy9. Similarly, there was no difficulty in obtaining correct alignment of the femoral component. Our technique allows correct rotation of the distal fragment to be obtained at the time of the osteotomy9. The use of a stemmed femoral component was necessary in only two of the seven patients who had a revision to a total knee arthroplasty. One patient needed such a component so that the screw-holes could be bypassed when the blade-plate was removed during the total joint arthroplasty. A long-stem femoral component was also needed in the patient who had a fracture proximal to the plate. We routinely stage the procedures and remove the blade-plate three to six months before the anticipated total joint arthroplasty, thus avoiding the use of a stemmed component. Beyer et al. reported increased technical difficulty when total joint arthroplasty was performed after varus osteotomy of the distal part of the femur. Those authors noted difficulty with exposure due to extensive scarring in six of seventeen knees that had previously had a varus osteotomy of the distal part of the femur; however, the ultimate clinical result, at an average of seventy-five months after the procedure, was not compromised1. In our experience, the clinical results of revision to a total knee arthroplasty have similarly not been compromised. We believe that, in some patients in whom there is difficulty with soft-tissue balancing and patellar tracking because of a severe valgus deformity, a varus osteotomy of the distal part of the femur can make a future total knee replacement technically easier. We concluded that, with proper selection of patients (those in whom the disease is limited to the lateral compartment), adequate correction of the alignment of the tibiofemoral axis, and stable fixation, varus osteotomy of the distal part of the femur is an effective technique for the treatment of gonarthrosis of the lateral compartment associated with valgus deformity. This procedure may allow the postponement of joint replacement in patients who place high demands on the knee. We have not found that a previous varus osteotomy of the distal part of the femur makes a subsequent total knee arthroplasty more technically demanding or adversely affects its clinical results.
*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.
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