Primary Total Knee Replacement: Results

Donald T. Reilly, MD. PhD


Introduction
At the recent State of the Art Update in Orthopaedics 2000 in Whistler, British Columbia, James A. D'Antonio, MD, moderated a group of presentations on results of various designs in total knee arthroplasty (TKA).


Results of Porous Coated Total Knee Replacement
Lester S. Borden, MD,[1] acknowledged that cemented TKA is the "gold standard." Early designs of uncemented components were developed in an attempt to eliminate the need for cement and to prevent "cement disease." Surgeons wanted more stable bony ingrowth. Eventually "cement disease" was recognized as particle disease (mostly from polyethylene wear into crevices).
The original and most successful TKA, the porous coated anatomical (PCA) artificial total knee joints, were introduced in the early 1980s. These joints were designed for bony ingrowth and to provide for normal knee kinematics. The design also introduced modularity of the tibial components. To allow for more normal kinematics, the lack of constraint dictated a "flat-on-flat" design. This resulted in a very high rate of polyethylene wear and a revision rate of 10% per year. This design, however, contributed to the development of instrumentation for alignment of components.


Thin polyethylene, when subjected to high stresses, tends to wear excessively. This has been a major contributing factor to wear in all designs. Bartel and colleagues[2] examined polyethylene stresses in patellar components with convex-shaped articulating surfaces that contacted convex metallic surfaces. For patellar models, the von Mises stress was at or near the polyethylene yield stress in most of the contact area, which is consistent with the permanent deformation observed in many retrieved components. As such, deformation may continue, even when the component's surface has deformed and been worn into a concave shape.
Fehring and colleagues[3] evaluated 20 patients referred for pain and disability after TKA with fluoroscopy-guided radiographs. Fourteen of the 20 patients had radiolucent lines in their prostheses during this evaluation. All loose components as determined by fluoroscopy were confirmed on revision.
Fluoroscopy-guided radiographs can be helpful in evaluating the patient with a painful TKA and normal-appearing office radiographs. Newer uncemented total knee designs have improved anatomical shapes and contact areas and use screws for additional fixation. These enhancements have led to improved results with uncemented knee designs.


Results with an Hydroxyapatite-Coated Total Knee Design
Jean-Alain Epinette, MD,[4] opened by reviewing the prospective randomized analysis of Nilsson and colleagues[5] in which fixation of hydroxyapatite (HA)-coated designs in 29 knees were compared with cemented tibial components in 28 knees in the Tricon II TKA. Radiostereometric analysis revealed continuous migration of cemented components compared with slight unprogressive migration of HA-coated components. In the 40 patients (19 HA-coated, 21 cemented) remaining after 5 years, the HA-coated implants had most of their migration occurring within the initial 3 months but then stabilized, whereas the cemented implants showed an initially lower -- but over time continuously increasing -- migration.


Epinette's experience with 309 knees follow after a mean of 5 years (range 0 to 9 years) showed no mechanical failure in the femoral or tibial component. Eight of these knees required a repeated procedure for patella problems. Epinette found that HA filled in radiolucent gaps in follow-up radiographs.
Results With an All-Polyethylene Tibial Component


Evolution in TKA tibial component design has centered around metal tibial trays with improved stress transfer to the proximal tibia[6] and better fixation with pegs and cement. Benefits of metal tibial trays include durable fixation and modularity. With longer follow-up, however, polyethylene "backside" wear and osteolysis are increased.
The best data on polyethylene wear and osteolysis has been reported in the all polyethylene total condylar prosthesis,[7,8] the one piece molded metal backed IB-1 prosthesis[9] and the compression molded one piece metal backed ACG prosthesis.[10] Currently on e the AGC total knee system is being manufactured.


Chitranjan S. Ranawat, MD,[11] described his 20-year follow-up study of 220 all polyethylene total condylar prostheses. At 20-years, 20 had been revised--4 for infection, 3 for fracture, and 13 for loosening. There were no cases of osteolysis. This study presents a good case for the all-polyethylene tibial component.
Ranawat[11] also reported on a prospectively randomized 180 press-fit condylar modular versus all-polyethylene tibial components performed between 1992 and 1994. At a mean follow-up of 6 years, 5 cases in the metal-backed group underwent revision for osteolysis compared with 0 cases in the all polyethylene group (P<.05). In all cases of revision for osteolysis, there was failure of the locking mechanism and "backside" wear.


In Ranawat's opinion, improvement in the locking mechanism between the tibial polyethylene insert and the metal tibial tray is imperative to reducing the incidence of osteolysis in cemented TKA. In the meantime, he considers preferable the components of molded or newer wear-resistance polyethylene (all poly) or molded, newer polyethylene components mechanically locked during manufacture to the metal tibial tray.


Results With an Epicondylar Axis Knee
Lawrence G. Morawa, MD[12] described a retrospective analysis of 50 consecutive posterior, stabilized, demented, tricompartmental total knee replacements with a minimum follow-up of 2 years. After surgery, the average range of motion was increased from 86° to 118° flexion. All patients had improved postoperative SF-36 scores. Pain and stair climbing function improved dramatically, and there were no revisions or infections. Nonprogressive radiolucent lines were present at the cement interface of the medial tibial bone in 10% of the tibial radiographs because of sclerotic subcondyle bone. After 2 years, overall Knee Society scores were excellent in 83% and good in 17% of patients, with a mean total score of 96 points.



References
1. Borden. Results of Porous coated total knee replacement. State of the Art Update in Orthopedics 2000. Whistler, BC: February 12-16, 2000.
2. Elbert K, Bartel D, Wright T. The effect of conformity on stresses in dome-shaped polyethylene patellar components. Clin Orthop. 1995; 317:71-75.
3. Fehring TK, McAvoy G. Fluoroscopic evaluation of the painful total knee arthroplasty. Clin Orthop. 1996;331:226-233.
4. Epinette JA. Results with an HA coated total knee. State of the Art Update in Orthopedics 2000. Whistler, BC: February 12-16, 2000.
5. Nilsson KG, Karrholm J, Carlsson L, Dalen T. Hydroxyapatite coating versus cemented fixation of the tibial component in total knee arthroplasty: prospective randomized comparison of hydroxyapatite-coated and cemented tibial components with 5-year follow-up using radiostereometry. J Arthroplasty. 1999;14:9-20.
6. Bartel DL, Burstein AH, Santavicco EA, Insall JN. Performance of the tibial component in total knee replacement. J Bone Joint Surg. 1982;64A:1026-1033.
7. Ranawat CS, Boachie-Adjei O Survivorship analysis and results of total condylar knee arthroplasty. Eight- to 11-year follow-up period. Clin Orthop 1988 Jan;(226):6-13.
8. Ranawat CS, Flynn WF Jr, Deshmukh RG Impact of modern technique on long-term results of total condylar knee arthroplasty. Clin Orthop 1994 Dec;(309):131-5
9. Font-Rodriguez DE, Scuderi GR, Insall JN: Survivorship of cemented total arthroplasty. Clin Orthop, 345:79-86, 1997.
10. Ritter MA, Worland R, Saliski J. Flat-on-flat, nonconstrained compression molded polyethylene total knee replacement. Clin Orthop 321:79-85, 1995.
11. Ranawat CS. Results with an all-poly tibial component. State of the Art Update in Orthopedics 2000. Whistler, BC: February 12-16, 2000.
12. Morawa LG. Results with an epicondylar axis knee. State of the Art Update in Orthopedics 2000. Whistler, BC: February 12-16, 2000.