Abstract: This prospective study analyzed the data from 100 primary total knee arthroplasties performed on 79 patients using the Duracon total knee arthroplasty system. Thirty-two males representing 46 knees, and forty-seven females representing 54 knees had a mean age of 68 years (range 42-87 years) and were evaluated at a mean follow-up period of 3.4 years (range 2 - 5 years). Thirty knees were followed for a minimum of five years. In thirty-nine procedures (39%) cemented femoral and tibial components were used. Fifty-eight procedures (58%) used cementless femoral and cemented tibial components (hybrid technique), and three procedures (3%) used cementless femoral and tibial components. The patellar component was cemented in all cases.
The preoperative mean Hospital for Special Surgery (HSS) knee score was 55 (range 37-69) and at most recent follow-up had improved to 94 (range 83-100). Ninety-seven knees rated as excellent, 3 knees rated as good, and no knees were rated as fair or poor. The mean preoperative range of motion (ROM) was 97 degrees (range 65-120) which improved to 113 degrees (range 90-130) at the most recent follow-up examination. There were no gender differences noted in either HSS score or ROM. The group of patients followed a minimum of five years had a mean HSS knee score of 94 (range 87-97) and a mean ROM of 113 (range 92-125). There appeared to be no deterioration of result with time.
Lateral releases were required in 16 knees and postoperatively mild lateral patellar subluxation was seen in only one knee. The average preoperative alignment was 2 degrees of varus (range 24 degrees varus to 19 degrees valgus) and improved to 6 degrees of valgus postoperatively (range 3 degrees varus to 10 degrees valgus). Only 2 knees remained in varus postoperatively. Radiolucencies were infrequent and when seen were non-progressive. Two patients underwent revision, one for a loose femoral component and one for a patellar revision associated with ectopic bone formation.
In summary, the Duracon system provides reliable instrumentation, excellent patellofemoral tracking, and promising early clinical results.
The Duracon total knee system is anatomic in design, and through enhanced articular conformity and balanced patellofemoral tracking, should minimize polyethylene wear and reduce patellofemoral complications. By increasing the conformity and contact between the tibiofemoral and patellofemoral articulating surfaces, point contact stresses generally associated with accelerated wear are reduced and patellofemoral tracking should be improved. This study represents the first reported follow-up results for this total knee system.
MATERIALS & METHODS
Between May 1992 and May 1995, 113 primary Duracon total knee arthroplasties (TKA) were performed by a single surgeon in 90 patients. All surgeries were performed at institutions with an orthopaedic residency training program. A total of 11 patients representing 13 knees were lost to follow-up. Four patients had expired, with one death occurring in the immediate post-operative period secondary to a myocardial infarction. The other three deaths were from causes unrelated to the surgical procedure occurring 14 - 47 months postoperatively. The remaining 7 patients representing 8 knees had either left the Figure 3. Bilateral TKR utilizing tibial components. geographic area or had switched insurance carriers and were unable to allow for adequate follow-up data. None of these 13 knees have been revised. This left 100 knees in 79 patients for inclusion in this study. The mean follow-up period was 3.4 years (range 2-5 years). There were 47 women representing 54 knees (54%) and 32 men representing 46 knees (46%) in the study group. The primary diagnosis was osteoarthritis in 91 knees (91%), rheumatoid arthritis in 6 knees (6%), and posttraumatic arthritis in 3 knees (3%).
The knee utilized in this study was a posterior cruciate ligament retaining Duracon total knee which is a system with a conforming articular surface. The femoral component and tibial base plate are cobalt chrome and patellas are an all polyethylene patellar button with an eccentrically placed dome. Cemented femoral and tibial components were used in 39 knees (39%), a cementless femoral component and cemented tibial component (hybrid technique) were used in 58 knees (58%) (fig. 1), and cementless tibial and femoral components were used in 3 knees.
Figure 1. Hybrid Duracon TKR with cemented tibial base plate.
Figure 2. All polyethylene patellar component illustrating its tracking within the femoral groove.
Figure 3. Bilateral TKR utilizing all-polyethylene using tibial components.
Figure 4. Bilateral uncemented TKR using modular porous baseplates.
A patellar resurfacing was performed in all cases and a cemented all polyethylene patellar component was utilized (fig. 2). In 6 knees (6%) all polyethylene tibial components were utilized (fig. 3), with the remainder being modular metal-backed tibial components. In cemented metal-backed tibial components a cruciate stemmed tibial base plate was utilized. In uncemented tibial cases a modular porous baseplate was used with supplemental screw fixation (fig. 4).
A midline incision with a medial parapatellar arthrotomy under tourniquet control was used in all cases. All femoral cuts were made in 6 degrees of valgus and all tibial cuts were made perpendicular to the axis of the shaft of the tibia. During each case the tourniquet was released prior to closure to assure proper patellofemoral tracking and to achieve hemostasis prior to closure. A lateral release was performed when the patella did not track properly in the femoral groove. In 53 knees no lateral release was carried out, and in 31 knees a release of only the patellofemoral ligament was performed. A formal lateral release was utilized in 16 knees (16%) and was associated with a prior lateral arthrotomy in four cases.
Postoperatively, no continuous passive motion was utilized. Weight bearing as tolerated was allowed for the patients with all cemented components and was initiated on the first postoperative day. Patients with hybrid or uncemented components were allowed partial weight bearing. Deep vein thrombosis prophylaxis consisted of pneumatic cuffs. Doppler ultrasound was performed only when the patient's clinical exam was suspicious for deep vein thrombosis. Manipulation under general anesthesia was performed if the patients lacked 90 degrees of flexion at six weeks following surgery.
CLINICAL & RADIOGRAPHIC EVALUATIONN
All patients underwent a clinical evaluation both preoperatively and post-operatively consisting of a Hospital for Special Surgery (HSS) knee score. A radiographic evaluation consisting of a weight bearing AP, lateral and sunrise view of the knee was also done preoperatively and postoperatively. HSS knee scores of 85 to 100 were rated as excellent, 70 to 84 rated good, 60 to 69 fair, and less than 60 was considered a poor result. Radiographs were assessed for component position, alignment and patellar tracking. Radiolucencies were measured, recorded and followed using the zones described by the Knee Society .
The mean preoperative HSS knee score for all patients was 55 (range 37-69), increasing to 94 (range 83-100) at the most recent followup examination. The mean preoperative HSS knee score for men was 55 (range 41-69), increasing to 95 (range 84-97) at the most recent follow-up examination. The mean preoperative HSS knee score for women was 55 (range 37-69), increasing to 94 (range 83-100) at the most recent follow-up exam (Table 1). Mean preoperative range of motion for all patients was 97 degrees (range 65-120), increasing to 113 degrees (range 90-130) at the most recent follow-up exam. Mean preoperative range of motion for women was 96 degrees (range 70-110), increasing to 113 degrees (range 90-130) at the most recent follow-up exam.
HSS Knee Score
| || Pre-operative || Most recent F/U |
|Men || 55 (41-69) || 95 (84-97) |
|Women || 55 (37-69) || 94 (83-100) |
|Total || 55 (37-69) || 94 (83-100) |
Table 1. Summary of Hospital for Special Surgery knee scores for patients preoperatively and at their most recent follow-up examination.
Mean preoperative range of motion for men was 98 degrees (range 65-120), increasing to 114 degrees (range 100-130) at the most recent follow-up exam (Table 2). Ninety-seven knees (97%) were rated as excellent and three knees (3%) were rated as good results. There were no fair or poor results.
Range of Motion
| || Pre-operative || Most recent F/U |
|Men || 98(65-120) || 114(100-130) |
|Women || 96(70-110) || 113 (90-130) |
|Total || 97(65-120) || 113 (90-130) |
Table 2. Range of motion measured both preoperatively and at the most recent visit.
Thirty knees were followed for a minimum of 5 years. This group of patients had a mean HSS knee score of 94 (range 87-97) and a mean ROM of 113 (range 92-125). There was no deterioration of result with time.
There was no statistical difference in clinical results or range of motion measurements between the hybrid (cemented tibia and uncemented femur), uncemented and all cemented groups.
The average hospital stay was 6.7 days (range 4 - 11 days). In those patients who underwent a unilateral TKA or staged bilateral TKA, the patient was discharged to home in 51 cases (73%) and to a rehabilitation unit or extended care facility in 19 cases (27%). In those patients who underwent bilateral simultaneous TKA, 7 were discharged to home and 8 were discharged to rehab.
Preoperatively, all patients as a group had a mean angular deformity of 2 degrees of varus, (range, 24 degrees of varus to 19 degrees of valgus). This was corrected to a mean 6 degrees of valgus (range, 3 degrees of varus to 10 degrees of valgus) as measured at the most recent follow-up exam. The mean preoperative alignment for men was 5 degrees of varus (range, 24 degrees of varus to 19 degrees of valgus). The mean alignment for men was 5 degrees of valgus (range, 3 degrees of varus to 8 degrees of valgus) at the most recent follow-up exam. The mean preoperative alignment for women was I degree of valgus (range, 15 degrees varus to 19 degrees of valgus). The average alignment for women was 6 degrees of valgus (range, 2 degrees of valgus to 10 degrees of valgus) at the most recent follow-up exam, (Table 3). Only 2 knees were left in persistent varus position after surgery. One of these knees had a 24 degree varus deformity preoperatively, and corrected to 3 degrees of varus postoperatively.
| || Pre-operative || Most recent F/U |
|Men || 5°varus |
| 5° valgus |
|Women || 1° valgus |
| 6°valgus |
|Total || 2°varus |
| 6°valgus |
Table 3. Radiographic alignment based on a weight-bearing AP radiograph preoperatively and at the most recent follow-up visit.
Radiolucencies were infrequent and nonprogressive in all cases. There were no patellar radiolucencies seen, either initially or at most recent follow-up(fig. 5).
Figure 5. Patellar radiolucencies seen immediately after surgery, and at the most recent follow-up evaluation (in parentheses).
There were 7 radiolucencies under the tibial component, all of which were nonprogressive (fig. 6).
Figure 6. Tibial radiolucencies seen immediately after surgery, and at the most recent follow-up evaluation (in parentheses).
There were 17 initial femoral radiolucencies seen (fig. 7), none of which where progressive and 6 of which resolved in uncemented femoral components (fig. 8). No knee had more than 2 radiolucent zones present on any of their implants. Patellar subluxation was also evaluated and only one patient showed a mild degree of persistent lateral tracking.
Figure 8. Femoral radiolucencies seen immediately after surgery, and at the most recent follow-up evaluation (in parentheses).
Complications occurred in 10 patients in the study. One patient with known coronary artery disease underwent bilateral TKA and suffered a fatal myocardial infarction in the immediate postoperative period. There were no pulmonary emboli or acute postoperative infections. Five patients developed a deep vein thromboses which were treated with intravenous heparin followed by oral warfarin for 3 months . One patient developed a neuroma of the infrapatellar tendon branch of the saphenous nerve requiring an injection of local anesthetic and a corticosteroid.
Five patients representing 6 knees had diabetes mellitus. There were no complications in this group and they had a mean HSS knee score of 94 (range 87-98). The were 5 patients representing 7 knees who were steroid dependent. They had no complications and had a mean HSS knee score of 91 (range 83-96).
Two patients required manipulation. One patient was able to maintain 95 degrees of flexion following the manipulation, and the other patient improved to 115 degrees.
Four patients in the group underwent repeat operations. One patient developed discomfort in the peroneal nerve distribution six weeks following surgery. Her pain resolved after decompression of the peroneal nerve. One patient developed a delayed acute infection 10 months after the index operation. This was successfully managed by an acute debridement and irrigation with retention of components. He has been symptom free for 4 years.
Two components have been revised. One patient developed persistent pain in the anterior aspect of the knee. Radiographs revealed ectopic bone laterally about the patella (fig. 9). She was reoperated on one year after her original surgery and a lateral release was carried out along with debridement of fibrous adhesions and ectopic bone.
Figure 9. Ectopic bone at lateral margin of patella.
A revision of her patellar button to a smaller component was carried out at that time. At last follow-up she had an HSS knee score of 93 and flexion to 125 degrees.
One of the patients who had a DVT had a fall in the initial post-operative period and developed persistent pain in the anterior aspect of the knee. At two years following surgery she continued to have pain and radiographs revealed bead shedding about the femoral component (fig. 10).
Figure 10. Bead sheeding at two year follow-up indicating loosening of the femoral component.
She was re-operated on two years postoperatively and she was found to have only a fibrous interface securing the femoral component. A revision of her femoral component to a cemented one was carried out, and she currently has a range of motion from 0 to 110 degrees and a knee score of 87.
Unlike other reported series [2-5], patellar complications were rare. Patellar alignment has been consistently reproducible with excellent clinical and radiographic results. There were no patellar fractures or dislocations, and only one patella showed a mild tendency to track laterally on radiographic follow-up.
The ability to obtain postoperative limb alignment in 5-9 degrees of valgus has consistently been shown to give superior results [6,7]. In this series, the Duracon instrumentation allowed for accurate alignment in all but two cases which were associated with severe preoperative deformities.
In summary, the Duracon total knee system has shown to be effective in providing excellent clinical and radiographic results following total knee arthroplasty. While we realize this series represents an early experience with follow-up only to 5 years, the clinical results appear to be promising with no fair or poor results in our series. These results are equal to or superior to other reported studies using various knee systems [8-181. When comparing the 30 knees with a minimum of 5 year follow-up to the group as a whole, there is no clinical or radiographic deterioration of results with time. Revisions have been carried out in 2 of the 100 knees and were not specific to the implant design.
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