Between December 1986 and February 1988, we performed 204 total knee arthroplasties. Both cruciate ligaments were retained in 163 (80 percent) of the knees. The anterior cruciate ligament was preserved when, at the beginning of the operation, it appeared functional as demonstrated by a normal anterior drawer sign. There were thirty-four men and ninety-six women, and the average age at the time of the index arthroplasty was 67 ± 8.6 years (range, forty-two to eighty-four years). The primary diagnosis was osteoarthritis in 122 knees (75 percent) and rheumatoid arthritis in forty-one knees (25 percent). Twenty-six knees (16 percent) had a preoperative valgus deformity of 11 to 20 degrees, 109 (67 percent) had a varus deformity of 1 to 30 degrees, and twenty-eight (17 percent) had a normal alignment of 5 to 10 degrees of valgus. The average preoperative flexion was 104 degrees (range, 10 to 130 degrees). Sixteen knees (10 percent) had a preoperative flexion contracture of 25 to 65 degrees.
The femoral component of the prosthesis that was used was a titanium total condylar replacement with a so-called anatomical articular surface geometry and a deep trochlear groove. The tibial component consisted of two symmetrical polyethylene inserts with a flat articular surface on a single-piece metal retainer, which allowed preservation of the tibial spines. The retainer had two symmetrical, round, fifteen-millimeter fixation pegs (Fig. 1). The dome-shaped articular surface of the polyethylene patellar implant had a metal retainer with two eight-millimeter fixation pegs. In all knees, both components were fixed with cement. The femoral component was implanted in 3 to 5 degrees of external rotation. The anterior and posterior femoral osteotomies were performed at 90 degrees to the long axis of the tibia with the knee at 90 degrees of flexion. The collateral capsuloligamentous structures were adequately balanced and were under physiological tension accomplished with use of a joint distractor4.
At the time of the operation, the anterior cruciate ligament was without notable degeneration or other abnormality in ninety-six knees (59 percent). The ligament was partially deteriorated (or degenerated) and had evidence of rupture of many fibers but was functional, as demonstrated by a normal anterior drawer sign, in sixty-seven knees (41 percent).
The knees were assessed preoperatively and at yearly intervals postoperatively with use of the rating system of the Knee Society15. The survival rate was determined with the Kaplan-Meier method25, and the end point for all of the knees in this series was revision for any reason.
The radiographic evaluation performed at the time of the clinical examination consisted of standard anteroposterior and lateral radiographs of the knee, made with the patient standing, and a tangential radiograph of the patella with the knee in 30 degrees of flexion. Fluoroscopy was not routinely used to position the knee for radiographs9.
The average preoperative knee score was 33 points (range, 0 to 40 points), and the average functional score was 44 points (range, 0 to 62 points).
Clinical Results
After an average duration of follow-up of ten years (range, nine to eleven years), thirty-three patients (25 percent) had died, two patients (2 percent) had been lost to follow-up, and seven knees (4 percent) in six patients had been revised. The assessment was therefore performed on 107 knees in eighty-nine patients. Eighteen patients had a bilateral arthroplasty. However, all of the complications and revisions after the 163 total knee arthroplasties are included in this report. There were twenty-four men and sixty-five women, and the average age at the time of this assessment was 77.3 ± 8.6 years (range, fifty-two to ninety-five years).
Seventy-two knees (67 percent) were not painful, twenty-six knees (24 percent) had limited and intermittent pain, and nine knees (8 percent) had moderate-to-severe pain. The average active range of flexion was 107 ± 12.6 degrees (range, 65 to 135 degrees). Four knees (4 percent) had less than 90 degrees of flexion. Ninety-nine knees (93 percent) had a flexion contracture of 0 to 5 degrees, and eight knees (7 percent) had a flexion contracture of 6 to 25 degrees. Three of the eight knees had a good result.
The anteroposterior stability was normal (less than five millimeters of movement in this plane) in ninety-five knees (89 percent). There was a positive anterior drawer sign (five to ten millimeters) in twelve knees (11 percent).
In ninety-six knees (90 percent) mediolateral laxity was normal (less than 5 degrees), and in eleven (10 percent) mediolateral laxity was 5 to 9 degrees.
Seventy-three knees (68 percent) were in patients who were able to walk an unlimited distance. Six knees (6 percent) were in patients who could walk more than ten blocks, fourteen (13 percent) were in patients who could walk five to ten blocks, seven (7 percent) were in patients who could walk less than five blocks, and seven were in patients who could walk indoors only. Fifty-five knees (51 percent) were in patients who could ascend and descend stairs normally, forty-seven (44 percent) were in patients who could ascend and descend stairs with the use of a ramp, and five (5 percent) were in patients who could not use stairs. The average knee score was 91 ± 8.4 points (range, 59 to 100 points), and the average functional score was 82 ± 21 points (range, 59 to 100 points). The result was good or excellent for 104 knees (97 percent). The survival rate, with revision as the end point, was 95 ± 2.0 percent at an average of ten years (Fig. 2).
Radiographic Results
Anteroposterior and lateral radiographs, with the patient standing, and a tangential radiograph of the patella were made for all 107 knees at the time of the latest follow-up visit (nine to eleven years after the index arthroplasty). The anteroposterior axial alignment was 5 to 10 degrees of valgus in ninety-four knees (88 percent). The alignment was 1 to 4 degrees of valgus in four knees (4 percent) and 11 to 25 degrees of valgus in two knees (2 percent). There was a residual varus deformity of 5 to 8 degrees in seven knees (7 percent). The average score for all seven knees with a varus deformity was 81 points (range, 70 to 100 points).
In the sagittal plane, the femoral component was at an angle of 90 degrees to the long axis of the femur in sixty-five limbs; it was flexed from 1 to 8 degrees with respect to the long axis in forty-one limbs, and it was in extension in one limb. In the frontal plane, the femoral component was in 5 to 10 degrees of valgus alignment in 100 limbs, in 11 to 20 degrees of valgus in five limbs, and in 5 degrees of varus alignment in two limbs.
In the sagittal plane, the tibial component was at an angle of 90 degrees to the long axis of the tibia (that is, no posterior slope) in forty-seven limbs, at an angle of 80 to 85 degrees (5 to 10 degrees of posterior slope) in fifty-eight limbs, and at an angle of 75 degrees (25 degrees of posterior slope) in two limbs. In the frontal plane, the tibial component was at an angle of 90 degrees to the long axis of the tibia in 101 limbs, at an angle of 85 degrees (5 degrees of varus) in three limbs, and at an angle of 95 to 100 degrees (valgus) in three limbs.
There were no radiolucent lines adjacent to ninety-seven femoral components (91 percent). There was a one-millimeter-thick radiolucent line in zone 1 in seven knees (7 percent) and a two-millimeter-thick radiolucent line in zone 1, 2, or 3 in three knees (3 percent). There were no radiolucent lines adjacent to eighty-eight (82 percent) of the tibial components. There was a one-millimeter-thick radiolucent line in zone 1, 2, or 3 in seven knees (7 percent) and a two-millimeter-thick radiolucent line in zone 1, 2, or 3 in twelve knees (11 percent). None of the components were considered to be radiographically loose.
Complications
Although a tourniquet and suction drainage were routinely used, hemarthrosis in one knee necessitated operative drainage. In one knee, the medial collateral ligament ruptured after a fall immediately postoperatively and needed operative repair. Fracture of the patella without loosening of the patellar button occurred in two knees and was successfully treated without an operation. A traumatic fracture of the medial tibial plateau occurred in one knee in the sixth postoperative year and was also treated successfully without an operation.
Seven (4 percent) of the 163 knees in the present study were revised. The complications and revisions in the patients who had died or had been lost to follow-up were included in this analysis. Three knees were revised because of a deep infection, and one was revised because of instability after rupture of the cruciate ligaments. The ruptures occurred in a patient who had rheumatoid arthritis, and at the time of the revision the anterior and posterior cruciate ligaments were found to be totally nonfunctional. In another knee, a loose femoral component was revised fifteen months after the index arthroplasty. There was no evidence of infection in that knee. Two knees in the same patient were revised five and eight years postoperatively because of severe wear of the central portion of the polyethylene component. There were no revisions for aseptic loosening of a tibial component or for complications involving the patella.
In recent years, many authors have reported posteromedial wear of the tibial component8,10,18,35,36 caused by so-called edge-loading brought about by progressive anterior subluxation of the tibia in the absence of the anterior cruciate ligament. The lack of this complication (posteromedial wear leading to failure) in the present series (with the exception of one knee with rupture of both cruciate ligaments in a patient who had rheumatoid arthritis) is probably related to the retention of the anterior cruciate ligament in those knees. The posterior cruciate ligament alone cannot provide adequate stability when a relatively flat, nonconstrained tibial plateau is used10. To solve this problem, many current knee systems use a cup-shaped tibial plateau. Such a design might limit the posterior femoral rollback in flexion and consequently be incompatible with the normal function of the posterior cruciate ligament17.
In the present series, an anterior cruciate ligament that we considered to be of an acceptable quality was present and was retained in 163 (80 percent) of the 204 arthroplasties. A comparison of the results in the two groups, one with a grossly normal anterior cruciate ligament and the other with partial degeneration, showed no statistical difference, with the numbers available, with regard to relief of pain (p = 0.753), anteroposterior (p = 0.954) or mediolateral (p = 0.555) stability, axial alignment (p = 0.433), or the knee score (p = 0.517). The results show that both cruciate ligaments (with the exception of those in one rheumatoid knee described earlier) remained clinically functional at an average of ten years. In other words, even the sixty-seven knees that showed partial degeneration of the anterior cruciate ligament at the time of the operation had good anterior tibial stability at an average of ten years. No knee was revised because of posteromedial wear of the tibial component. In two of the knees that were revised in this series, the wear was at the center of the medial tibial plateau and evidently was not related to anterior subluxation of the tibia.
Recent in vivo studies by Dennis et al.7 showed that relatively normal kinematics of the knee is not achieved by retention of the posterior cruciate ligament alone because the so-called posterior femoral rollback in flexion did not occur in the knees studied or, if it did, it was erratic. It is probable that the anterior cruciate ligament must be present to achieve close-to-normal kinematics of the knee in total knee replacement16. In gait studies by Andriacchi et al.1,2, the knees in which both cruciate ligaments were retained were the only ones that had normal flexion when the patient ascended and descended stairs. In many contemporary knee-replacement designs with preservation of the posterior cruciate ligament alone, the flat tibial component in the sagittal plane in these prostheses does not substitute for the very important stabilizing function of the anterior cruciate ligament20,28,30,32,34,37.
The prevalence of revision in the present series was 4 percent (seven knees). In a previous study5 by the senior one of us (J.-M. C.), the prevalence of revision when the posterior cruciate ligament alone was preserved (25 percent; six of twenty-four knees) was significantly higher (p < 0.0022) than the prevalence when both cruciate ligaments were preserved (4 percent; one of twenty-eight knees). Although the femorotibial contact area was relatively small with the Hermes prosthesis (Ceraver Osteal, Paris, France), the cruciate ligaments adequately prevented anterior subluxation of the tibia and so-called edge-loading. Retention of the anterior cruciate ligament, together with the deep trochlear groove of the femoral component of the Hermes prosthesis and the placement of the prosthesis in external rotation, are probably responsible for the absence of patellofemoral complications in the present series.
Despite a nonprogressive radiolucent line distal to the tibial component in nineteen limbs (18 percent), there were no revisions for aseptic loosening of the component. Two fifteen-millimeter pegs appear to be adequate fixation for the cemented tibial component when the cruciate ligaments are present and the tibial plateau is minimally constrained. Therefore, there appears to be no need to excise the anterior cruciate ligament, as has been suggested by many, to simplify the operative technique of knee replacement11.
Tibial osteotomies in which the tibial spines are preserved are relatively easy to perform. A distractor, to expose the knee and to maintain the balanced ligaments under physiological tension in order to create precise flexion and extension gaps, was very useful in achieving optimum tension in the cruciate ligament4.
The allowance of knee rotation guided exclusively by the ligaments and the rolling and sliding movements during flexion, without revision for wear of the posterior tibial plateau, are compelling reasons to preserve both cruciate ligaments, when possible, in total knee replacement.
In the current series, the anterior cruciate ligament was present and functional in 163 knees (80 percent) in which a total knee replacement had been performed. The indication to preserve the anterior cruciate ligament appears to be similar to the indication to preserve the posterior cruciate ligament alone. The advantage of preserving the anterior cruciate ligament is that it provides anterior stability and contributes to normal kinematics of the knee with a minimally constrained prosthesis. When the anterior cruciate ligament is preserved (and also when the posterior cruciate ligament is preserved), a precise femorotibial gap must be created both in flexion and in extension to achieve so-called physiological tension in the cruciate ligament4.