Abstract
Background: There is little information in the literature regarding the outcome of total knee arthroplasty following distal femoral varus osteotomy. The purpose of the present study was to evaluate the intermediate-term results of total knee arthroplasty following distal femoral varus osteotomy.
Methods: The study group consisted of nine consecutive patients (eleven knees) who had had a total knee arthroplasty following varus osteotomy of the distal part of the femur. The average age of the patients was forty-four years (range, fifteen to seventy years) at the time of the arthroplasty. The results were evaluated with use of the Knee Society score preoperatively and after a mean duration of follow-up of 5.1 years. Radiographs made preoperatively and at the time of follow-up were evaluated for alignment in the coronal plane.
Results: The mean Knee Society knee score was 35 points before the arthroplasty and 84 points after the arthroplasty. The mean Knee Society function score was 49 points before the arthroplasty and 68 points after the arthroplasty. The mean interval between the femoral osteotomy and the total knee replacement was fourteen years (range, two to thirty-two years). A constrained prosthesis was required in five of the eleven knees. Two knees had an excellent result, five had a good result, and four had a fair result. The mean arc of motion improved from 81.8° to 105.9°. The mean radiographic alignment was 3.6° of valgus (range, 7° of varus to 18° of valgus) before the arthroplasty and 3.3° of valgus (range, 1° of valgus to 6° of valgus) at the time of the latest follow-up. There were no infections or wound complications.
Conclusion: Total knee arthroplasty following distal femoral varus osteotomy decreases pain and improves knee function, but the procedure is technically demanding and is associated with inferior results when compared with those of primary arthroplasty performed in a patient without a prior femoral osteotomy. In the present series, the use of an intramedullary femoral alignment guide increased the tendency to place the femoral component in relative varus angulation (that is, in <5° of valgus). We recommend checking the alignment of the femoral component with an extramedullary guide in knees that have had a previous distal femoral varus osteotomy.
Level of Evidence: Therapeutic study, Level IV (case series [no, or historical, control group]). See Instructions to Authors for a complete description of levels of evidence.
Many surgeons advocate distal femoral varus osteotomy as a joint-preserving alternative for patients with genu valgum, associated lateral compartment arthritis, and pain that is unresponsive to nonoperative therapy. The ideal patient has unicompartmental disease, satisfactory ligamentous stability, a good range of motion, and an age or activity level that makes total knee arthroplasty less desirable.
Previous reports have described the potentially compromising effect of a proximal tibial osteotomy on the results of total knee arthroplasty
1,2 . Although we are aware of only two published studies on the results of total knee arthroplasty following distal femoral varus osteotomy
3,4 , there have been no studies, to our knowledge, that have quantified the clinical outcome with use of a scoring system and investigated the technical aspects of this procedure. Understanding how a previous distal femoral varus osteotomy affects the results of total knee arthroplasty is critical to surgical decision-making. Therefore, the goal of the present study was to evaluate the results of total knee arthroplasty in the setting of a previous distal femoral varus osteotomy.
We identified nine consecutive patients (eleven knees) who had undergone a previous distal femoral varus osteotomy and who eventually had had a total knee replacement between 1980 and 1997. The average duration of follow-up after the total knee arthroplasty was 5.1 years (range, 2.5 to eighteen years). The study group included two men and seven women who had a mean age of forty-four years (range, fifteen to seventy years) at the time of the arthroplasty. Seven right knees and four left knees were involved. The total knee replacements were performed at an average of fourteen years (range, two to thirty-two years) after the osteotomies. Before the arthroplasty, six of the eleven knees had a flexion contracture of 5° to 15° (average contracture for all eleven knees, 4.5°). Tibiofemoral alignment was measured on standing (35 × 43 cm) anteroposterior radiographs made before the arthroplasty. Six of the eleven knees had a varus deformity (range, 7° of varus to 3° of valgus), two had neutral alignment (5° or 6° of valgus), and one had valgus alignment (18° of valgus). Preoperative radiographs were not available for one patient (two knees) who had died of unrelated causes after her forty-two-month follow-up visit.
Four of the osteotomy sites had been internally fixed with a medial blade-plate, five had been fixed with a lateral blade-plate, and two had been fixed with a combination of internal fixation (screws) and plaster. Two patients (three knees) had undergone a previous proximal tibial osteotomy of the ipsilateral lower extremity. In all patients, pain was the primary complaint that had led to the arthroplasty.
Surgical Considerations
A midline incision with a medial arthrotomy was performed in nine knees, with incorporation of a portion of the previous scar whenever possible, and a lateral arthrotomy was performed in two knees. Hardware removal and total knee arthroplasty were performed simultaneously in six knees. One knee had total knee arthroplasty without hardware removal. The remaining knees had hardware removal before total knee arthroplasty. An intramedullary femoral alignment guide was used during ten total knee arthroplasty procedures, and extramedullary alignment was used during one. The operative notes did not indicate any modification of the starting hole in knees in which an intramedullary guide was used for alignment.
Five knees that had good collateral ligamentous stability and balance received a posterior stabilized prosthesis; these devices included one Insall-Burstein prosthesis (Zimmer, Warsaw, Indiana), two Insall-Burstein II prostheses (Zimmer), and two PFC PS prostheses (DePuy, Johnson and Johnson, Warsaw, Indiana). Five knees that had ligamentous instability received a constrained condylar knee CCK prosthesis (Hospital for Special Surgery, New York, New York [four knees] or Zimmer [one knee]). One knee received a rotating-hinge prosthesis (FINN; Biomet, Warsaw, Indiana). When hardware removal and total knee arthroplasty were performed in a single stage, screw-holes were bypassed with use of a stemmed femoral component. A stemmed femoral component was used in seven of the eleven knees.
Functional evaluations were performed preoperatively and postoperatively (at the time of follow-up) with use of the 200-point system of the Knee Society
5 . Demographic data (age, gender, comorbidities, and complications) were obtained retrospectively by means of a chart review. The two components of this scale, the 100-point knee score and the 100-point function score, were extracted before and after the arthroplasty by means of a chart review performed after an average of 5.1 years of follow-up. The Knee Society instrument is divided into three subsections: (1) the knee score (pain, stability, and range of motion), (2) the function score (walking ability and stair-climbing), and (3) the patient category (medical comorbidities that potentially can affect the surgical outcome). The 100-point knee score is classified as excellent (85 to 100 points), good (70 to 84 points), fair (60 to 69 points), or poor (<60 points)
6 .
One patient (two knees) died of unrelated causes after the 3.5-year follow-up visit. Standing anteroposterior and lateral radiographs were assessed for alignment preoperatively and after a mean duration of follow-up of five years for nine knees; preoperative radiographs were unavailable for the remaining two knees.
None of the patients had poor wound-healing or prolonged drainage that lasted for more than seven days. There were no infections. The mean arc of motion improved from 81.8° (range, 40° to 120°) to 105.9° (range, 90° to 125°) (Appendix). The overall mean increase in the arc of active motion was 24°. Preoperatively, six knees had a flexion contracture of 5° to 15°; postoperatively, one knee had a flexion contracture of 10°. One patient had persistent medial and lateral instability upon examination but had no subjective complaints. Radiolucent lines were noted in all patients; however, the radiolucent lines were incomplete and were located primarily between the tibial baseplate and the tibial plateau.
The mean Knee Society knee score increased from 35 points (range, 13 to 58 points) before the arthroplasty to 84 points (range, 71 to 93 points) after the arthroplasty. The mean Knee Society function score increased from 49 points (range, 30 to 65 points) preoperatively to 68 points (range, 50 to 90 points) postoperatively. The mean overall Knee Society score increased from 84 points (range, 52 to 103 points) preoperatively to 152 points (range, 134 to 169 points) postoperatively. Two knees had an excellent result, five had a good result, and four had a fair result. The reasons for the fair results included pain and malalignment in three knees and pain and instability in one knee.
An intramedullary alignment guide had been used for placement of ten of the eleven femoral components. The mean radiographic alignment was 3.6° of valgus (range, 7° of varus to 18° of valgus) before the total knee arthroplasty and 3.3° of valgus (range, 1° of valgus to 6° of valgus) at the time of the most recent follow-up. Only two patients (three knees) had anatomical valgus alignment (that is, radiographic alignment in =5° of valgus at the time of the last follow-up). In the six knees in which the anatomic axis was in <5° of valgus, the relative varus angulation was on the femoral side rather than the tibial side. Sagittal plane deformities were not encountered before or after total knee arthroplasty.
One patient (one knee) had an intraoperative complication. This patient sustained a nondisplaced femoral fracture during femoral preparation. The fracture was bypassed with a stemmed component. One patient (one knee) had a reoperation. This patient underwent arthroscopic excision of suprapatellar scar tissue because of patellar clunk four years after total knee arthroplasty.
One patient (two knees) died after the forty-two month follow-up; the cause of death was unrelated to the total knee arthroplasty procedures.
Knee osteoarthritis may be related to an alteration in the mechanical axis of the lower extremity. A deviation into varus alignment will lead to greater load transmission to the medial compartment, and valgus deviation will lead to greater loading of the lateral compartment. This change in load transfer is thought to precipitate the progression of arthritis
2 .
Varus distal femoral osteotomy is indicated for some patients with isolated lateral compartment gonarthrosis with associated valgus deformity of the knee. The ideal patient has isolated lateral compartment arthritis with a moderate valgus deformity, is physiologically young, has an occupation or activity level that makes arthroplasty less appropriate, and has a normal body-mass index and satisfactory range of motion and stability of the knee. Often, there is a treatment dilemma regarding whether varus distal femoral osteotomy, total knee arthroplasty, or unicompartmental arthroplasty is most appropriate for such patients. Insight regarding the outcome of varus distal femoral osteotomy and the consequences with regard to the outcome of subsequent reconstructive or salvage procedures is helpful for making an informed decision in the management of many of these patients.
Several studies have investigated the effects of proximal tibial osteotomy on the results of subsequent total knee arthroplasty
1,2,7,8 . Most of those studies have demonstrated increased difficulty and higher complication rates when the results of conversion of a previously osteotomized knee to a total knee arthroplasty are compared with those of primary total knee arthroplasty. Specific difficulties have included more difficult exposure secondary to patella infera and wound-healing difficulties, leading to increased risks of patellar tendon avulsion and infection, respectively.
Only a few studies have evaluated the effects of varus distal femoral osteotomy on the results of subsequent total knee arthroplasty
3,4 . Varus distal femoral osteotomy is an entirely different procedure from proximal tibial osteotomy. Rigid internal fixation is nearly always employed during varus distal femoral osteotomy, and patella infera has not been reported as a consequence of the procedure. The resulting deformity is extra-articular; therefore, intra-articular correction during total knee arthroplasty may lead to ligamentous instability that in some cases is not correctable with ligament releases.
The extra-articular varus deformity of the femur following varus distal femoral osteotomy often results in a situation in which the femoral anatomical axis intersects the lateral femoral condyle rather than the intercondylar notch. Therefore, when intramedullary alignment is used, the starting hole should be placed where the femoral anatomic axis intersects the distal part of the femur at the knee. In our series, the femoral component was placed in less than the desired amount of valgus angulation in seven of the nine knees for which radiographs were available.
We believe that careful preoperative templating and determination of the appropriate location of the starting hole with the use of an intramedullary guide is important for obtaining optimal femoral alignment in these cases. The other option is to use extramedullary femoral alignment. Whether intramedullary or extramedullary alignment guides are utilized for positioning of the cutting blocks, we recommend an extramedullary check of alignment with localization of the femoral head prior to distal femoral resection in an effort to obtain optimal coronal alignment.
The extra-articular deformity that results from distal femoral osteotomy presents additional problems
9-11 . In order to create a neutral mechanical axis (an axis through the center of the hip, knee, and ankle joints in the coronal plane) in a patient who has a varus extra-articular deformity, resection of relatively more bone from the distal aspect of the lateral femoral condyle than from the distal aspect of the medial femoral condyle is often necessary, which is the opposite of the typical surgical preparation
12 . As a consequence, lateral ligamentous instability that is not correctable with use of standard medial releases may result, as demonstrated by our frequent need to use constrained condylar knee prostheses in the present series.
Despite the technical difficulties encountered during total knee arthroplasty following varus distal femoral osteotomy, the result was good or excellent for seven of the eleven knees in the present study. The four patients (four knees) who had a fair result had only mild pain but had additional problems due either to malalignment or instability.
On the basis of previous studies that have demonstrated higher infection rates following total knee arthroplasty performed for the treatment of posttraumatic arthritis
13 , we currently recommend that all patients who are managed with distal femoral varus osteotomy have preoperative joint aspiration as well as intraoperative gram-staining and frozen-section analysis. Joint aspiration should be done to rule out infection before revision surgery is considered
14 . The results on culture of joint aspirate are not 100% positive when a latent infection is present. Nevertheless, in many cases the aspirate will yield a positive result
3 . Also, we recommend the adjuvant use of antibiotic-impregnated cement for all patients undergoing total knee arthroplasty following varus distal femoral osteotomy.
We acknowledge that the sample size of the present study is small, which limits the number of potential conclusions that can be derived
15 . On the basis of our results, we conclude that total knee arthroplasty decreases pain and improves knee function in patients who have had a previous distal femoral varus osteotomy with subsequent development of instability and/or end-stage posttraumatic arthritis. However, these results must be interpreted carefully. The malposition rate was relatively high, and the results were not as good as the 92.5% rate of good-to-excellent results reported by Insall et al.
6 in their review of 139 total condylar knee prostheses used for the treatment of osteoarthritis nor as good as those reported by Windsor et al.
2 in their review of knee arthroplasty after proximal tibial osteotomy.
A table showing specific demographic and preoperative data on all eleven knees is available with the electronic versions of this article, on our web site at www.jbjs.org (go to the article citation and click on "Supplementary Material") and on our quarterly CD-ROM (call our subscription department, at 781-449-9780, to order the CD-ROM).
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