Polyethylene Patellar Components Research Articles

A Crossed Screw Patellar Reconstruction Technique for the Treatment of the Severely Deficient Scaphoid Shaped Patella in Total Knee Arthroplasty

One of the contraindications to patella resurfacing in total knee arthroplasty is a thin and severely eroded ‘deficient’ patella. However, such patients often present with severe patellofemoral joint arthritis, patellar lateral subluxation, and patella maltracking, which can only be treated effectively with resurfacing. While various treatments have been proposed, options remain limited.Here we introduce a method of patella reconstruction using four 2.7-mm titanium cortical screws crossing each other into the inner shell of the patella. This provides a scaffold onto which bone cement and any standard polyethylene patellar component can be fixed. Postoperatively, the patient had no anterior knee pain, no patella maltracking, and no component loosening.Advantages of this technique include minimization of extensor disruption, low costs, easy accessibility, reproducibility, and improved mechanical strength.

Impingement of the patellar component against the tibial post after posterior stabilized and constrained TKA: a pilot study.

Patella-post impingement (PPI), contact of the patellar component with the tibial post, occurs during deep knee flexion after posterior stabilized total knee arthroplasty (TKA). PPI can cause anterior knee pain, increased patellar pressure, wear of the polyethylene patellar component and tibial post, and poor range of motion. There have been no reports on the relationship between PPI and tibial post design. The aim of this study was to compare different tibial post designs with regard to PPI incidence. Five posterior stabilized total knee prostheses were implanted in full-length models of the femur and tibia (Sawbones) using a navigation system. The thickness of the tibial component was 10mm in all prostheses. The patella was set on a transparent polypropylene sheet, which was fixed to the tibial tubercle. The distance between the lower edge of the patellar component and the cut surface of the tibia was defined as the tibial-patellar clearance (TPC), which represents the length of the patellar tendon. The TPC was varied from 18 to 40mm and the knee was moved from full extension to deep flexion while the knee angle at which PPI occurred (PPI angle) was recorded. The PPI angle differed between tibial post designs (p < 0.05). Shorter TPCs resulted in smaller PPI angles and longer TPCs resulted in larger PPI angles (p < 0.05). This is the first study to analyze the relationship between PPI and the design of tibial post. Our results clearly show that tibial post design and TPC affect PPI. To avoid patellar component and tibial post impingement in deep flexion, appropriate TPC must be achieved during surgery. Improvements in tibial post design, especially in constrained prostheses, are also desirable. This study highlights the potential risk of PPI during deep flexion after TKA.

Dislocation of the polyethylene in a patellofemoral replacement with a movable patella

Patellofemoral arthroplasty is an infrequently used surgical technique because of its controversial results. In an attempt to improve the results, a design with a mobile-bearing polyethylene patellar component has been developed. We describe a clinical case with an unusual complication: the dislocation of polyethylene from the metal backing; and accordingly, we carried out a literature review of this complication.

Acute Posttraumatic Catastrophic Failure of a Second-generation, Highly Cross-linked Ultra-high-molecular-weight Polyethylene Patellar Component

A 74-year-old man underwent total knee arthroplasty in 1996 and subsequent revision total knee arthroplasty for aseptic loosening in 2005. During revision, an all-polyethylene, 7-mm, second-generation, highly cross-linked ultra-high-molecular-weight polyethylene patellar component (Durasul; Zimmer, Warsaw, Indiana) was used. The patient recovered well, but he presented with severe acute pain after a popping feeling was detected during a game of golf in postoperative year 4. Radiographs demonstrated a fracture of the patellar component. At re-revision surgery, polyethylene fragments were encountered without visual evidence of wear. Appropriate rotational and axial alignment of the components was confirmed. Patellar revision was performed. To the authors' knowledge, this is the first report of an acute posttraumatic catastrophic fracture of a second-generation, highly cross-linked ultra-high-molecular-weight polyethylene patellar component. Although no malposition of the components was noted, abnormal tensile forces across the patellar component can be transmitted by altered patellofemoral kinematics. This combination could lead to a small surface crack that propagates deeper into the component with continued impaction and an eventual acute fracture of the entire component. The patellar component failed in a piecemeal fashion following acute trauma. Although many advantages exist to the enhancement of polyethylene patellar components, including the potential for improved wear characteristics, cross-linking has reduced resistance to crack initiation and propagation. Therefore, fracture risk should be considered when using second-generation, highly cross-linked ultra-high-molecular-weight polyethylene.

Patellar resurfacing in total knee replacement

A series of 100 consecutive osteoarthritic patients was randomised to undergo total knee replacement using a Miller-Galante II prosthesis, with or without a cemented polyethylene patellar component. Knee function was evaluated using the American Knee Society score, Western Ontario and McMaster University Osteoarthritis index, specific patellofemoral-related questions and radiographic evaluation until the fourth post-operative year, then via questionnaire until ten years post-operatively. A ten-point difference in the American Knee Society score between the two groups was considered a significant change in knee performance, with alpha and beta levels of 0.05. The mean age of the patients in the resurfaced group was 71 years (53 to 88) and in the non-resurfaced group was 73 years (54 to 86). After ten years 22 patients had died, seven were suffering from dementia, three declined further participation and ten were lost to follow-up. Two patients in the non-resurfaced group subsequently had their patellae resurfaced. In the resurfaced group one patient had an arthroscopic lateral release. There was no significant difference between the two treatment groups: both had a similar deterioration of scores with time, and no further patellofemoral complications were observed in either group. We are unable to recommend routine patellar resurfacing in osteoarthritic patients undergoing total knee replacement on the basis of our findings.

Patellar polyethylene peg fracture: a case report and review of the literature

The patellar component of a total knee replacement (TKR) is the most frequent source of non-septic complications after total knee arthroplasty. Fracture of patellar pegs in all polyethylene patellar components is a very rare occurrence. We report such a case of a patellar polyethylene fracture in a 72-year-old female patient 10 years after TKR. Due to patellar malalignment and high level of activity, the patellar components failed in this patient. This was treated arthroscopically by removing the components that failed and leaving the patella unresurfaced. We followed up the patient postoperatively and her symptoms were substantially resolved.

The Effects of Patellar Thickness on Patellofemoral Forces After Resurfacing

The purpose of this study was to determine the effect of patellar bone and patellar implant thickness on patellofemoral forces after resurfacing in total knee arthroplasty. Seven cadaver knees were tested using an Oxford Knee Testing Rig. This model gave the specimens 6 degrees freedom while dynamic data were collected. Each knee was tested from full extension to 95 degrees knee flexion. Knees were implanted with Press Fit Condylar femoral, tibial, and patellar implants. The effect of varying patellar thickness on patellofemoral forces was determined by using custom modular oval-domed polyethylene patellar components with progressive thickness increments of 2 mm. Patellofemoral forces were measured by a custom-designed uniaxial patellar load cell. Statistically significant increases in patellofemoral compression forces were found from 70 degrees to 95 degrees flexion with increased patellar bone and patellar implant thickness.

The influence of the position of the patellar component on tracking in total knee arthroplasty.

The position of the patellar component and patellofemoral symptoms were assessed in a series of 72 cemented polyethylene patellar components in total condylar arthroplasties. A small (25 mm) component was used. The minimum follow up was 2 years and maximum 3 years. A lateral retinacular release was carried out in 22 knees. Clinical results were assessed by questionnaire and 86% had no patellofemoral symptoms. The mean postoperative patellar height was not changed compared to the preoperative height. Lateral placement of the patellar component was associated with both increased medial tilt and lateral subluxation. The component should be inserted so that its centre is slightly medial to the centre of the bone.

Evaluation of the Effect of the Femoral Articular Surface Material on the Wear of a Metal-Backed Patellar Component

Wear characteristics of metal-backed, polyethylene patellar components were tested using cobalt-chromium, titanium alloy (Ti), and ion-implanted titanium alloy (IITi) articular surfaces. Patellar components were cycled in a bovine serum bath at 3 Hz for 1 million cycles, under a compressive load that varied from 343 N at 0 degree flexion to 2255 N at 120 degrees flexion. After testing, the polyethylene articular surfaces of the patellar components were evaluated for wear and graded using a subjective numbering system. Overall wear damage to the polyethylene surface was much worse with both Ti and IITi than with cobalt-chromium. Differences in mean wear scores were statistically significant when cobalt-chromium was compared with either Ti or IITi, but there were no statistically significant differences between Ti and IITi. Polyethylene surfaces that articulated against Ti femoral surfaces had more severe scratching. The IITi test group had areas of delamination not observed in the other test groups. Subjective evaluation of the metal surfaces showed evidence of wear damage as well. The metal articular surface of IITi resisted scratching as long as the treated surface was intact. In the high-stress areas, however, such as the edges of the intercondylar notch, the ion-implanted surface quickly wore away, exposing the untreated titanium alloy. The cobalt-chromium femoral articular surface had the least amount of scratching and no evidence of loss of metal.