Patellar Component Research Articles

6- to 10-year experience using countersunk metal-backed patellas

Three hundred two consecutive cementless total knee arthroplasties (Natural Knee, Intermedics Orthopedics, Inc., Austin, TX) were performed using a metal-backed, porous-coated patellar component. Fifty-nine patients died and 31 were lost to follow-up evaluation, resulting in 212 knees available for evaluation at 6 to 10 years. The mean follow-up period was 91 months. The mean modified Hospital for Special Surgery total knee score improved from 58 before surgery to 98 at the most recent follow-up visit. Mean patellar translation and tilt were 2.75 mm and 3.5°, respectively. There were no patellar lucencies nor loosening. Eleven patients (5%) underwent revision of the patellar component. Overall patellar survivorship was 96%. Comparatively good results can be achieved with the use of a metal-backed patellar component if component design, surgical technique, and patellar alignment are properly addressed.

Patellar component medialization in total knee arthroplasty

Intraoperative correction of patellar maltracking has traditionally involved the use of a lateral retinacular release. Problems, however, related to lateral retinacular release include increased postoperative pain and wound healing complications, compromised patellar blood flow, and longer rehabilitation. The purpose of this study was to assess the effect of patellar medialization in total knee arthroplasty. One hundred forty patients underwent total knee arthroplasty using the same components. Two groups of 70 patients each made up the study. Group 1 included patients whose patellar components were centralized on the patella, and group 2 consisted of patients in whom the patellar component was medialized to reproduce the patient's anatomic high point (ie, sagittal ridge). Lateral retinacular release was required in 45.5% of the patients in group 1 compared with 17% in group 2. The technique of patellar medialization is described.

Late complications and survivorship of dome shaped metal backed patellar components

Late complications and survivorship of dome shaped metal backed patellar components

当科における変形性膝関節症に対するセメントレスＴＫＡの術後成績 ＭＧ ＩとＭＧ ＩＩの比較検討

We clinically evaluated the result of 41 knees in 28 OA patients treated by MG I with MG II total knee systems. MG I were used in 11 knees (MG I group) and MG II were used in 30 knees (MG II group). The mean post-operative JOA score was 80.9 points for MG I and 80.8 points for MG II. There were two cases with patella component failure in MG I group. We found tibial component subsidence in 9.0% of MG I group and in 3.3% of MG II group. Femoral and tibial component placement in the two groups was good. Patella component placement of MG II group was good but that of MG I group was not good according to measurement of the tilting angle and lateral shift. Patella ligament-tibial shaft angle (a) of MG I group was significantly greater than that of the MG II group. It was supposed that PF joint pressure of MG I group was higher than that of MG II group by calculating sin 1/2(a+knee flexion angle).The reasons of patella component malalignment and PF joint high pressure were due to designs of femoral and patella components.

Effect of Femoral Component Rotation and Patellar Design on Patellar Forces

A force transducer attached to the patella was used to measure patellar contact forces after total knee arthroplasty for neutral femoral component position and for 10 degrees internal and external femoral component rotations. Knees were cycled continuously under load from 10 degrees to 110 degrees flexion. Two designs of knee replacement with differing degrees of intrinsic tibiofemoral constraint were studied. Additionally, contact forces for a dome shaped patella and a modified dome shaped patella (a patellar component with a central projection surrounded by a peripheral flat region) were compared. When using the design with relatively high intrinsic tibiofemoral constraint, there were no significant changes in patellar contact forces after axial rotation of the femoral component. When using the design with relatively low intrinsic tibiofemoral constraint and averaging over the range of flexion angles tested, the mediolateral component of the patellar contact force increased approximately 17% after 10 degrees internal rotation compared with neutral rotation, and the normal component of the patellar contact force decreased approximately 8% after a 10 degrees external rotation compared with 10 degrees internal rotation of the femoral component. The inferosuperior component of the patellar shear force, when using the modified dome shaped patellar component, was significantly lower than for the dome shaped patella.

Results of total knee arthroplasty with a metal-backed patellar component: A 6-year follow-up study

This study reviews the clinical outcome of knee artroplasty (Microloc, Johnson & Johnson Orthopedics, Norderstedt, Germany) with a resurfacing metal-backed patellar component. Thirty patients were available for clinical and radiographic reexamination with follow-up periods of 36 and 72 months. There were 21 women and 9 men, with an average age of 71.1 years. At the follow-up examination, seven patients demonstrated a metallic friction noise, and three had only mild crepitation at the patellofemoral joint level. In the group complaining of knee pain, the average knee score dropped from 76.9 ± 9.9 at 36 months to 44.7 ± 15.3 ( P < .05) prior to revision surgery on average at 66 months. The function score dropped during the same time from 72.0 ± 19.7 to 53.5 ± 14.9. In contrast, the pain-free group did not demonstrate any significant changes in either knee or function score. Radiographic evaluation showed a patellar tilt of 8.1° ± 4.0° in the group complaining of pain, compared with 2.5° ± 2.3° in the pain-free patient collective. All 10 patients complaining of pain and increasing disability underwent revision surgery. At the time of surgery, an obvious polyethylene particle-induced synovitis was found, and in 7 patients it was associated with a metallosis. One of the main reasons for failure of metal-backed polyethylene components is thought to be the undue high stresses forced onto the insert. High loading of only a small fraction of the surface will lead to increased polyethylene creep and particle formation, resulting in synovitis and finally metallosis. Early revision seems to be the best solution to prevent progressive destruction of the entire joint. Previously reported results on metal-backed patellar components show a failure rate of 8.4% after 12 to 24 months. In this study, this rate had already increased to 33.3% after 6 years. One might therefore speculate that at 10 years, revision surgery might become necessary in more than 50% of the surviving patients with this type of implant.

Follow up on uncemented total knee arthroplasty.

Follow up data on 42 uncemented total knee arthroplasty patients were examined at an average follow-up period of 5 to 7 years. The prosthetic components were examined clinically using the modified Hospital for Special Surgery knee rating system and radiographically using fluoroscopically guided radiographs. When compared to the preliminary report, the knee rating score dropped from an average of 94 to 78, with most of the poor results due to patellar failure requiring revision. As in our preliminary study, complications centered on the metal-backed patellar component. Revision of the patellar component was required in 19 of 42 knees (45%). Three of 42 (7%) tibial components required revision, and 2 of 42 (5%) femoral components were revised. Interface lucencies were examined and changes were documented. Other complications included osteolysis in 4 of 42 (10%), bent patellar component in 3 of 42 (7%), and loose titanium mesh (5%).

Anatomic alignment of the patellar groove.

The variability in alignment of the natural patellar groove was determined about various anatomic axes of the femur, using 3 plane radiographs and electronic digitization. After the patellar groove was identified and marked on 15 anatomic specimen femurs, radiographs were taken in the coronal, sagittal, and transverse planes so that principal anatomic axes could be outlined. Through electronic digitization, a 3-dimensional representation of the patellar groove was constructed about the distal anatomic axis, mechanical axis, transepicondylar axes, and transcondylar axes. Regarding these 4 principal anatomic axes, the variability in orientation of the patellar groove was profound in both coronal and transverse planes, typically involving a range of 11 degrees to 16 degrees about the mean. The average orientation most closely approximated the perpendicular to the transepicondylar axis in the coronal plane; however, the range varied extensively. None of the anatomic axes tested proved reliable as a reference axis for proper position of the patellar groove, and this study shows that the orientation of the natural patellar groove is more variable than previously suspected. The failure of femoral components to accommodate this variability may explain many complications associated with the patellar component in total knee arthroplasty.

Safety and efficacy of ethylene oxide sterilized polyethylene in total knee arthroplasty.

Eleven unassembled metal backed patellar interfaces were inoculated with 0.1 ml of Sportol (Bacillus subtilis variety niger spore) and then assembled. Ten of the 11 implants were exposed to 1/2 of a standard ethylene oxide sterilization cycle. The remaining implant was left unsterilized as a control. All the implants were separately incubated in soybean casein digest broth for 7 days at 30 degrees to 35 degrees C and tested for positive growth of Bacillus subtilis. To measure residual ethylene oxide content, 4 ultrahigh molecular weight polyethylene tibial inserts were exposed to a full ethylene oxide sterilization cycle. The implants were removed from the sterilization chamber and tested for residual ethylene oxide at 3, 5, 8, and 9 days after sterilization using an exhaustive extraction headspace technique. Residual ethylene oxide was measured in 3 additional implants 26 days after sterilization. No growth of Bacillus subtilis occurred on any of the 10 inoculated and ethylene oxide sterilized metal backed patellar components, whereas positive growth occurred on the inoculated, unsterilized control implant. Residual ethylene oxide measured in the tibial inserts at 3, 5, 8, and 9 days after sterilization was 23, 15, 12, and 9 ppm, respectively. Twenty-six days after sterilization, residual ethylene oxide was below the minimum detectable level of the measurement technique (5 ppm).

Titanemia from total knee arthroplasty: A case resulting from a failed patellar component

The subject of this case report is a patient with elevated serum levels of titanium (77 parts/billion [ppb]; normal, 3.3 ppb) and vanadium (0.38 ppb; normal, 0.17 ppb) resulting from excessive wear of a metal-backed patellar component in a total knee arthroplasty. The patellar component was worn through both its polyethylene and metal backing as a result of abnormal contact between the patellar and femoral components. Scanning electron microscopic examination of the ingrowth surface of the patellar component indicated that particle debonding occurred as a result of overloading of the sintered neck regions at the particle-substrate interface, suggesting a possible damage during initial insertion of the device, which may have predisposed it to loosening and abnormal contact with the femoral component. Wear particles resulted in staining of the tissues within the knee and an inflammatory and immune response in the synovium consisting of giant cells and T lymphocytes. The serum metal levels were reduced 22 weeks after replacing the patellar component: however, the titanium level was still slightly elevated (8 ppb).

Bone hardness testing in the trabecular bone of the human patella

Bone hardness of 10 human patellas in 15 regions and at three depths was measured through in situ indentation tests. Indentation tests were performed perpendicular to the three articular surfaces (lateral and medial facets, and central ridge area) and, thus, parallel to the trabeculae. Multiple regression analysis demonstrated a significant reduction of bone hardness with depth. In addition, the lateral facet had a higher bone hardness than the medial facet, and the proximal and central regions demonstrated higher bone hardness than the distal region. Overall, the proximolateral region of the patella exhibited the highest hardness compared with other regions. As bone hardness is indicative of load bearing, these results may have important consequences for patellar resurfacing and patellar component design.

The prosthesis-bone interface adjacent to tibial components inserted without cement. Clinical and radiographic follow-up at nine to twelve years.

We evaluated the radiographic and functional status of a one-piece composite tibial component, designed to be inserted without cement, that was developed and used only at our institution. Thirty-six patients (thirty-seven knees) were managed with the component between November 1981 and September 1983, and none were lost to follow-up. When they were last seen, thirty-four (92 per cent) of the thirty-seven knees had a well-fixed tibial component, both clinically and radiographically. Eight patients (eight knees; 22 per cent) died. Eleven patients (eleven knees; 30 per cent) had a revision at an average of sixty-five months (range, four to ninety-five months) postoperatively. The reason for the revision was failure of a metal-backed patellar component in three knees, excessive wear of the polyethylene of the tibial component in one, a hematogenous infection in four, aseptic loosening of the tibial component in two, and chronic synovitis in one. The remaining seventeen patients (eighteen knees; 49 per cent) were seen for clinical and radiographic follow-up at an average of eleven years (range, nine to twelve years) after the operation. With removal of the implant as the end point, the cumulative rate of survival was 83 per cent at fifty-six months and 67 per cent at 108 months. Some of the failures were secondary to features of the prosthetic design that currently are considered to be inadequate, including a metal-backed patellar component and carbon-fiber-reinforced polyethylene. In the twenty-six knees in which the prosthesis had been retained, the implant was stable and the prosthesis-bone interface was unchanged as seen radiographically at the time of the most recent follow-up examination. This finding demonstrates that a porous ingrowth surface is capable of providing a secure interface for biological fixation over the long term.

Paper #31 Patellar component medialization in total knee arthroplasty

Paper #31 Patellar component medialization in total knee arthroplasty

The porous-coated anatomic total knee experience: Special emphasis on complications and wear

One hundred sixty knees in 141 patients with the Primary Porous-Coated Anatomic prosthesis (Howmedica, Rutherford, NJ) were evaluated after a follow-up period of 5.6 years (range, 1–10 years). One hundred six knees were in the latest follow-up evaluation, including clinical examination and a defined standing radiograph with a follow-up period of 6.3 years (range, 3–10 years). Survivorship analysis regarding the cumulative revision rate (including completion with a patellar component) was 0.88 at the 8-year and 0.84 at the 10-year follow-up examination. The clinical result was satisfying/good, with a mean Hospital for Special Surgery score of 83 (range, 39–97). Five percent had thinning greater than 30% of the tibial component. The wear was calculated to be 1.0 mm (range, 0–9 mm), including three revised tibial components with heavy wear. Excluding the revised cases, the wear was 0.7 mm.

ＭＧＩ型人工膝関節の大腿膝蓋関節障害の検討 再置換３例を中心として

From May 1987 to November 1990, We performed 28 Miller-Galante Total Knee Arthroplasties in patents with osteoarthritis or rheumatoid arthritis, wear of patellar component was seen in 3 knees and revision surgery was performed in these three cases. We evaluated 22 knees including revision cases with femorotibial angle, percent of patellar cutting, tilting angle and lateral shift. We considered that wear of the patella component was caused by a low percentage of patellar cutting and a tendency for lateral shift. The Harris Osteotomy Blade and Metal Cutting Blade are very useful for removing components of Miller-Galante Total Knee Arthroplasty.

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.

ＴＫＡ術後の膝蓋大腿関節障害の検討

We reviewed the patellofemoral problems of patients who received Mark 3 type total knee arthroplasty (TKA). There were 99 knee joints including 39 osteoarthrosis (OA) and 60 rheumatoid arthritis (RA) patients. Radiograms of all knees were reviewed. In 45 knee joints, clinical examination and radiological measurement were done and JOA scores before and after surgery were compared. The lateral shift ratio was calculated and the thickness of the patella was measured from the skyline view.There were two patella fractures. One fracture might be attributed to strenuous work as a farmer, and the other might be due to severe osteoporosis with ankylosis in the contralateral knee. Neither patella dislocation nor broken patella component were seen these 99 knees.Anterior knee pain appeared in only two out of 45 knees. Mean JOA score improved after TKA both in OA (preop. 44, post op. 71) and in RA knees (preop. 33, post op. 72). All 45 knees showed lateral shift of the patella. However, this did not indicate a poor result.There was no correlation between JOA score and the lateral shift ratio nor between JOA score and thickness of the patella.

Tibial Wedge Augmentation for Bone Deficiency in Total Knee Arthroplasty

This report constitutes a followup of a previous study of 28 knees in 25 patients with metal wedge augmentation for tibial bone deficiency. Those patients were reviewed 2.3 years after surgery; 79% had excellent results, and 21% had good results. Twenty-four knees in 21 patients with a metal wedge augmentation for tibial bone deficiency were reviewed 5.6 years clinically and 4.8 years radiographically after surgery. Clinical results were excellent in 67%, good in 29%, and poor in 4%. The only poor result was in 1 knee that required 2 revision procedures: the first for failure of a metal-backed patellar component and the second for aseptic loosening of the femoral component. Radiolucent lines at the cement bone interface beneath the metal wedge were present in 13 knees. Eleven of those radiolucencies were < 1 mm in width, and 2 were 1 to 3 mm in width. None of those lucent lines were progressive. Metal wedge augmentation for tibial bone deficiency is a useful option. No deterioration of the wedge-prosthesis or wedge-cement-bone interface was seen at midterm followup.

Lateral patellar burnishing in total knee arthroplasty following medialization of the patellar button

This case report describes a total knee revision necessitated by painful contact between the exposed lateral facet of the patella and the femoral component. Pain was resolved following repositioning and enlarging the patellar component. The clinical significance of this report is that the contemporary practice of medializing the patellar component to improve patellar tracking should be performed in moderation to avoid overexposure of the lateral patella. In the setting of persistent anterior knee pain following total knee arthroplasty, the etiology of the pain may be identified as contact between the patellar and femoral component on the sunrise radiograph.

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.