Total Knee Arthroplasty Implants Research Articles

Mobile-bearing Total Knee Arthroplasty

Premature polyethylene wear is a major cause of total knee arthroplasty (TKA) failure. It has been attributed to numerous factors including poor surgical technique, reduced polyethylene thickness, poor locking mechanisms of modular fixed bearing tibial components, gamma irradiation sterilization techniques in the presence of oxygen, and low conformity implant designs. The incidence of implantation of TKA into younger patients who have increased activity requirements and longevity expectations is increasing. This requires continued analysis of design features lessening polyethylene wear. The purpose of this manuscript is to review clinical and basic scientific studies of factors influencing polyethylene wear, focusing on the potential benefits of mobile bearing TKA which potentially reduce long-term polyethylene wear by providing increased implant conformity and reduced polyethylene contact stresses. In vivo kinematic studies have shown self-alignment of the polyethylene bearing with the femoral component typically occurs in rotating platform TKA designs which should hypothetically lessen polyethylene surface stresses, minimize stabilizing post impingement, and increase the potential for enhanced polyethylene longevity.

Early results of high-flex total knee arthroplasty: comparison study at 1 year after surgery

We compared clinical [including maximal flexion and range of motion (ROM)] and radiographical outcomes of high-flex versus conventional implants for total knee arthroplasty (TKA) after 1 year. We also analyzed the factors affecting postoperative ROM in high-flex implants. The high-flex group (n=90) had an average maximal flexion of 129.8 degrees (standard deviation (SD), 5.2 degrees ) significantly higher than the 124.3 degrees (SD, 9.2 degrees ) of the conventional group (n=90), especially for patients with less than 90 degrees of knee flexion (P<0.05). There was no significant difference in hospital for special surgery (HSS) score between the two groups. No knee developed osteolysis, aseptic loosening, or other complications. We found that, for high-flex implants, preoperative ROM had a significant effect on postoperative ROM.

Biomechanical aspects of revision components for knee arthroplasty

Total knee arthroplasty (TKA) is one of the most frequent orthopaedic surgical procedures. Despite continuous improvements in the endoprostheses, instruments, and operative techniques, revision TKA has a rate of about 10% of overall TKA. In addition to the restoration of the periprosthetic bone stock and a precise alignment, the choice of an adequate implant, which meets the patient's specific requirements, has high impact on the outcome. The most significant differences between implants involve the degree of reconstructed joint area (uni-, bi-, tri-compartimental) and the order of the constraining forces between the femoral and tibial component. Implants for revision TKA commonly range from un- or semiconstrained resurfacing implants to fully constrained hinged endoprostheses. In case of severe osseous, ligamentous, and/or muscular defects, special tumor endoprostheses or implants for arthrodesis might be an alternative option.

THE CHITRANJAN RANAWAT AWARD: In Vivo Knee Forces after Total Knee Arthroplasty

Tibial forces were measured in vivo during the first year after total knee arthroplasty in a 66 kg, 80-year-old man. Forces were measured during activities of daily living, rehabilitation, and exercise. Peak tibial forces recorded during walking increased up to 12 months postoperatively (2.8 times body weight). Tibial forces correlated with increasing speed during treadmill walking. Rising from a chair generated peak forces of 2.6 times body weight. Stair descent generated higher peak forces than stair ascent (3.3 versus 2.9 times body weight, respectively). Exercising on a stair-climbing machine generated forces close to two times body weight whereas stationary bicycling generated even lower forces, near one times body weight. In general, the tibial forces recorded during walking and stair climbing were lower than most predicted values. These measurements can be used to validate in vitro and mathematical models of the knee. This should lead to refined surgical techniques and to enhanced prosthetic designs that will improve patient function, patient quality of life, and longevity of total knee arthroplasty implants.

Consistency of Implantation of a Total Knee Arthroplasty with a Non–Image-Based Navigation System: A Case-Control Study of 235 Cases Compared With 235 Conventionally Implanted Prostheses

The aim of the study was to assess the consistency of the non–image-based navigation system OrthoPilot®, Aesculap, Tuttlingen, Germany, in total knee arthroplasty (TKA) implantation in 5 European centers. Two hundred thirty-five TKAs implanted with this navigation system were matched (according to severity of the preoperative coronal deformation and body mass index) to a historical control group of 235 TKAs implanted with a conventional technique. Consistency of implantation was studied on a 3-month postoperative radiological control with coronal long-leg and sagittal standard x-rays. The use of the OrthoPilot® navigation system allowed a statistically significant improvement in the consistent placement of both tibial and femoral components. In accordance with current literature, survival of the navigated implanted prostheses is expected to be longer.

Cemented Total Knee Arthroplasty in Patients with Juvenile Rheumatoid Arthritis

The optimal techniques and implants for total knee arthroplasty in patients with juvenile rheumatoid arthritis are controversial. We report the functional outcomes and complications of a series of 17 cemented total knee arthroplasties done by one surgeon during a 10-year period in which off-the-shelf implants were used, the posterior cruciate ligament was excised, and a lateral retinacular release was done. Preoperatively, all knees had severe loss of normal joint space and osteopenia on 3-foot, standing AP radiographs, lateral radiographs, and patellofemoral views. The patients were evaluated after a mean followup of 74 months (range, 36-116 months). The Knee Society scores improved from a mean of 38.9 +/- 23.9 points (range, 10-81 points) preoperatively to 81.9 +/- 16.6 points (range, 39-99 points) postoperatively. Range of motion showed significant improvement in all patients at the most recent followup. Ambulation scores improved significantly; nine of 10 patients (15 knees) were ambulatory after surgery. Complications included two transient regional pain syndromes and one patellofemoral subluxation requiring realignment. Cemented total knee arthroplasty with off-the-shelf implants, excision of the posterior cruciate ligament, and lateral retinacular release in patients with juvenile rheumatoid arthritis can provide substantial improvement in pain, deformity, ambulation, and function. Therapeutic study, Level IV (case series--no, or historical control group). See the Guidelines for Authors for a complete description of levels of evidence.

Modular Uncemented Tricompartmental Total Knee Arthroplasty

The incidence of posttraumatic osteoarthrosis, especially in younger patients, increases. In different studies total knee arthroplasty (TKA) is only indicated in 0–12% of cases of posttraumatic osteoarthrosis, because most authors feel that the indication for TKA in younger patients should be narrowly restricted. The most common indications for TKA include primary idiopathic osteoarthrosis and rheumatoid arthritis predominantly in patients > 60 years. In this prospective study a total of 188 patients with 197 TKAs were compared. 92 patients (93 TKAs) had a posttraumatic osteoarthrosis, 96 patients (104 TKAs) a nontraumatic osteoarthrosis. All patients received the same modular tricompartmental TKA in uncemented technique regarding femoral and tibial component. The patella was always cemented. All operations were performed by a group of six surgeons in a standardized operating technique. The evaluation of the study parameters included three components: patient questionnaire (pain, patient satisfaction, ability to walk, range of motion, workplace situation), clinical evaluation (Knee Society Clinical Rating Score), conventional X-ray, and CT evaluation (axial alignment, radiolucent lines, bone defects). In light of the results obtained in this study, TKA implantation appears to be a valid primary treatment option in young patients with posttraumatic arthrosis. Even though the results for nearly all parameters were poorer in the posttraumatic osteoarthrosis group, the condition of these patients still improved significantly following TKA.

Quadriceps function after TKA––an in vitro study in a knee kinematic simulator

Objective. The purpose of this in vitro study was to investigate the amount of quadriceps force required to extend the knee during an isokinetic extension cycle before and after total knee arthroplasty. Design. The magnitude of the extension torque used in simulating a constant moment extension exercise was derived from tests made using a dynamometer on patients who had received a total knee arthroplasty. Quadriceps force needed to extend the knee was measured. Methods. Human knee specimens ( n=8, mean age=65 SD 7 years, all male) were tested in a kinematic knee simulating machine untreated and after implantation of two different knee prosthesis. During simulation, a hydraulic cylinder applied sufficient force to the quadriceps tendon to produce an extension moment of 31 Nm about the knee. Results. The quadriceps forces needed to extend the knee during the physiologic simulation reached levels as high as 1238.9 N (SD 46.6). After implantation the Interax ®-prosthesis, quadriceps force increased up to 13.9% ( P=0.003), in conjunction with resurfacing of the patella 11.9% ( P=0.01). With the LCS ®-prosthesis implanted, quadriceps force showed a somewhat smaller increase of up to 6.6% ( P=0.007). Relevance The following study helps to clarify postoperative problems related to the extensor mechanisms of the knee after implantation of total knee arthroplasty.

The prevalence of corporate funding in adult lower extremity research and its correlation with reported results

The author reviewed 603 consecutive articles and scientific presentations pertaining to adult lower extremity orthopedic research from 2 major American orthopedic journals and 2 major American orthopedic meetings. The prevalence of commercial funding in these studies was 50%. Clinical studies of total hip arthroplasty implants by American investigators were commercially sponsored in 75% of studies. Commercially funded hip research reported positive outcomes in 93% of studies, whereas independently funded researchers reported good results in only 37%. Funded clinical studies of total knee arthroplasty implants yielded good results in 75%; this is in contrast to the findings of independently funded investigators, who reported positive conclusions in only 20% of studies. Investigators receiving royalties reported no negative outcomes related to the respective devices. The source of research funding was strongly correlated with reported outcomes.

Implant selection in revision total knee arthroplasty.

Revision total knee arthroplasty implants have evolved from fully constrained (fixed-hinge) to semiconstrained to contemporary constrained designs. The latter category includes nonlinked constrained (total condylar-III) designs ( Fig. 1) and rotating-hinge designs ( Figs. 2-A and 2-B). Fig. 1: Postoperative anteroposterior radiograph illustrating a nonlinked constrained knee design that was used to revise a failed primary total knee arthroplasty in a patient with rheumatoid arthritis. Figs. 2-A and 2-B: Preoperative (Fig. 2-A) and postoperative (Fig. 2-B) radiographs of the knee of a low-demand seventy-nine-year-old woman who was managed with a rotating-hinge knee prosthesis because of a comminuted periprosthetic supracondylar fracture of the femur. Additionally, the advent of limb-salvage procedures following tumor resection and other instances in which there is massive segmental bone loss, such as that seen after multiple failed arthroplasties (particularly following failed reimplantation for infection), has stimulated the development of modular or custom segmental replacement and the use of allograft-prosthesis composites. Segmental modular megaprostheses are rotating-hinge components with modular stems of varying lengths that are used to replace segmental femoral or tibial diaphyseal bone loss ( Fig. 3). Fig. 3: Lateral radiograph illustrating reconstruction of segmental bone defects of the distal part of the femur and proximal part of the tibia. On the femoral side a custom segmental distal femoral rotating-hinge prosthesis was used, and on the tibial side an allograft-prosthesis composite was used. Use of the proximal tibial allograft facilitated reattachment of the extensor mechanism. An allograft-prosthesis composite consists of a structural allograft, usually the distal part of a donor femur or the proximal part of a donor tibia, into which a stemmed prosthesis is cemented. The composite structure is attached to the remaining host bone with use of matching step-cuts at the junction of the allograft and the host bone. The construct is stabilized with an intramedullary stem ( Figs. 4-A …

Accuracy of implantation of a unicompartmental total knee arthroplasty with 2 different instrumentations: A case-controlled comparative study

The accuracy of implantation is an accepted prognostic factor for the long-term survival of unicompartmental total knee arthroplasties (UKAs). We adapted the conventional instruments for tricompartmental total knee arthroplasty implantation, with intramedullary femoral and extramedullary tibial guiding rods, to a UKA implantation. A total of 52 patients in whom a UKA was implanted with this instrumentation were matched (using age, sex, body mass index, preoperative coronal mechanical femorotibial angle, and severity of preoperative degenerative changes according to Ahlback) with 52 patients operated with the alternative instruments. Accuracy of implant placement measured by radiography was improved significantly by the new instrumentation, but there was no difference in the survival rate or the clinical outcome after 5 years in both groups. No complication related to the new instrumentation occurred. Longer follow-up is required to determine the advantages and disadvantages of both techniques. Copyright 2002, Elsevier Science (USA). All rights reserved.

Changes in bone mineral density following total knee arthroplasty: a 1-year follow-up study by dual energy X-ray absorptiometry

The assessment of bone density by means of dual energy Xray absorptiometry is a valid option for monitoring bone changes. In this study, time-related bone changes after total knee arthroplasty implantation were assessed in eight postmenopausal women (aged 62–72 years) up to one year from surgery. The pattern of bone changes followed a well-known design: an initial phase of accelerated bone loss and a subsequent phase of partial bone recovery. The greatest bone loss was observed at 2 months after surgery: 5.0% for the whole periprosthetic bone in the AP projection and 11.5% for the bone in the LL projection. In the following ten months the bone loss in the AP projection was completely recovered while the periprosthetic bone evaluated in the LL projection showed a residual bone loss of 9.0%. At 12 months from surgery, the distal femur in LL projection showed the greatest bone loss: 20.0% for the anterior region of interest and 17.0% for the posterior one. A significant correlation was found between the maximum postoperative bone loss and the residual bone loss at 12 months. These results suggest that pharmacological and rehabilitative strategies may be useful for the conservation of bone stock.

Supracondylar femoral fractures in knee endoprostheses. Stabilizing with retrograde interlocking nail

The treatment of supracondylar fractures of the femur in total knee arthroplasty is still challenging, and a variety of methods has been recommended. In a retrospective analysis, we reviewed six patients (average age: 70.5 years) with this type of fracture that had been stabilized with a retrograde intramedullary locking nail [Green-Seligson-Henry (GSH) nail]. The fracture had occurred 34.5 months after implantation of total knee arthroplasty. The average time of the operation was 97.16 min. There were no intra- or postoperative complications. All patients could be followed up at 17.3 months on average. Fracture healing was uneventful in all six cases. The postoperative range of motion was similar to the prefracture level in five patients. One patient demonstrated a loss of extension (10 degrees) associated with a valgus malalignment of 10 degrees. According to our experience, retrograde intramedullary nailing of supracondylar fractures in total knee arthroplasty is a promising alternative, which allows closed reduction and preservation of the soft tissue envelope. Immediate mobilization with partial weight bearing is possible, and the rate of complications is low.

Tibial post wear in posterior stabilized total knee arthroplasty. An unrecognized source of polyethylene debris.

With extensive use of posterior stabilized total knee arthroplasty implants, it is increasingly important to assess the mechanical performance of this design alternative. The purpose of this study was to examine the wear patterns at the femoral cam-tibial post interface in a series of posterior stabilized prostheses retrieved at revision arthroplasty. Qualitative and quantitative wear analysis was performed over the surface of the stabilizing posts from twenty-three retrieved total knee components that had been implanted for a mean of 35.6 months (range, 2.3 to 107.2 months). The implants were designs from four different manufacturers. Digital images of the anterior, posterior, medial, and lateral surfaces of the tibial post were made for quantitative analysis and determination of a post wear score. Wear was characterized with a grading system that isolates adhesive, abrasive, and fatigue wear, inferring a weighted score from an estimation of generated polyethylene debris. Evidence of wear or damage was observed on all twenty-three of the stabilizing posts, including those revised because of infection. On the average, 39.9% (range, 18.5% to 60%) of the post surface demonstrated some form of deformation, with adhesive wear, or burnishing, being the predominant wear mechanism. Seven posts (30%) exhibited severe damage with gross loss of polyethylene. The wear caused premature failure and early revision of two components: one of these failures was related to isolated post wear and the other, to severe post wear and subsequent fracture. Overall, wear was primarily posterior, but wear over the anterior, medial, and lateral surfaces was also notable. The cam-post articulation in posterior stabilized implants can be an additional source of polyethylene wear debris. The variability in wear patterns observed among designs may be due to differences in cam-post mechanics, post location, and post geometry. The surgeon should be aware that the cam-post interface is not an innocuous articulation, and manufacturers should be motivated to produce implants that maintain the function of the post while limiting wear and surface damage.

Factors influencing choice of implants in total hip arthroplasty and total knee arthroplasty: Perspectives of surgeons and patients

To determine the factors influencing surgeons' choice of implants for total hip arthroplasty (THA) and total knee arthroplasty (TKA), 650 surveys were mailed to all active members of the American Association of Hip and Knee Surgeons practicing in the United States; 364 surveys (56%) were completed and returned. Analysis revealed that the average number of total hip and total knee replacements performed by the respondents in 1997 was 81 and 97; there was substantial regional variation. The average number of hip implant and knee implant brands used by these surgeons in 1997 was 2.4 and 1.8. Anticipated improvement in clinical results and cost of components were the most frequently listed reasons for changing brands. Surgeons were also queried about cost reduction programs at their particular institution. The most frequently listed strategies for cost reduction of implants included surgeon cost-awareness programs and volume discounting. More than half of the respondents (53.5%) anticipate manufacturers to decrease the cost of implants in the next 2 years. Most of the respondents (93.7%) currently have the ability to choose a particular implant. About half (46.7%) anticipate losing some or all control of this decision in the next 3 years. These respondents foresee their hospitals requiring the use of a discounted implant in the future. An additional survey was completed by 102 consecutive patients scheduled either for primary THA (64) or primary TKA (38) at our institution. When asked about implant selection, 93.1% responded that their orthopaedic surgeon should choose the prosthesis; 5.9% responded that their physician in consultation with the patient should choose the prosthesis. When asked what should be the primary determinant of implant choice, cost or quality, the overwhelming majority (97.1%) chose quality. A small percentage (2.9%) chose cost and quality. No patient chose cost alone. A large number of patients (84.8%) responded that they would pay additional costs if their insurance companies or health maintenance organizations refused to pay for a better but more expensive implant. Most patients realized how expensive components are, and 51% of the respondents correctly estimated the cost of an implant. Orthopaedic surgeons perceive that they are losing control of implant choice in THA and TKA. Cost of implants is one of the most significant factors influencing which implant is chosen. Patients (the true payors), however, overwhelmingly want their surgeons to choose the implant used at surgery, and they want quality, not cost, to be the primary determinant of this decision.

Medial reconstruction during total knee arthroplasty for severe valgus deformity.

A painful arthritic knee with severe valgus deformity may be treated successfully with total knee arthroplasty using several techniques: constrained implant with lateral release, nonconstrained implant with lateral release and a thick tibial insert, or nonconstrained implant with lateral release and medial reconstruction. Eight patients with Type II valgus deformity were treated with nonconstrained total knee arthroplasty implants, lateral ITB release at the level of the tibial osteotomy, and proximal medial collateral ligament advancement with bone plug recession. The reconstruction led to predictably successful outcomes in all patients at 4- to 9-years followup. All patients were satisfied with the operation. All knees were stable with a functional range of motion at the time of last followup.