Patellar Component Research Articles

Patello-femoral joint replacement

It is well known that the knee can suffer from a unicompartmental osteoarthritis which leaves the rest of the joint relatively normal, It is surgically attractive to conserve normal tissues, especially in younger patients, and consequently there have, over the years, been a number of prostheses developed with the aim of treating the single worn compartment, whether it be medial, lateral or patello-femoral. Although good results have been reported, particularly for medial compartment osteoarthritis, these have mostly been by enthusiastic innovators and have not to date achieved widespread acclaim. Isolated replacement of the patello-femoral joint has in particular met with scepticism. There are several reasons for this: 5. 1. The excellent long-term survival rates for conventional total knee replacement. 2. When problems do occur following a total knee replacement, the patello-femoral mechanism is the commonest site. This naturally raises doubt in the surgeon's mind about the wisdom of isolated patello-femoral replacements. 3. Concern over the extent to which a patellofemoral replacement will interfere mechanically with the tibio-femoral articulation. What, for example, will happen in flexion beyond 90 ° when the patellar component 'runs onto' the intercondylar margins of the femoral condyles? Polyethylene bearing against articular cartilage has not got a good reputation, c.f. 'soft-top' Monk hemiarthroplasty of the hip. ~ 6. 4. Since patello-femoral osteoarthritis is primarily

Metal Release and Excretion From Cementless Titanium Alloy Total Knee Replacements

Concentrations of titanium, aluminum, and vanadium were measured in the serum and urine of patients with titanium alloy cementless primary total knee arthroplasty components. Patients were categorized in one of five groups. In Group 1, the patellar and tibial articulating surfaces were made of carbon fiber reinforced ultrahigh molecular weight polyethylene. In Group 2, the patellar and tibial surfaces were made of ultrahigh molecular weight polyethylene. In Group 3, the femoral titanium alloy articulating surface was nitrogen ion implanted with ultrahigh molecular weight polyethylene patellar and tibial articulating surfaces. Patients in Group 4 had failed patellar components, and Group 5 was comprised of age and gender matched control subjects without implants. Serum concentrations of titanium were approximately 50 times greater in patients with failed patellar components (Group 4) and approximately 10 times greater in patients with carbon fiber reinforced polyethylene bearing surfaces (Group 1) when compared with Groups 2 and 3 and the control subjects (Group 5). For aluminum and vanadium, no detectable differences were observed among any of the groups. In addition, analysis of 24-hour urine samples showed no significant differences in titanium, aluminum, or vanadium concentrations among any of the groups. Elevated serum titanium levels may serve as a marker of patellar component failure or accelerated femoral component wear in total knee replacements with titanium alloy bearings. The toxicologic ramifications of these findings are unknown.

Total Knee Anthroplasty: Patella Resurfacing Versus Nonresurfacing

The results of total knee arthroplasty (TKA) with or without patellar resurfacing were restropectively evaluated in 164 knees of 128 patients. All of the patients recived primary total knee arthroplasty using a Miller-Galante I (MGI) prosthesis. Hybrid fixation including non-cemented femoral component with cemented tibial and patellar components was used in this series. The patella was resurfaced with cemented metal-backed patellar component when there was either gross destruction or eburnation of the articular surface. Hospital for Special Surgery (HSS) knee score, radiographic examination and muscle strength using isokinetic assessment were used to evaluate the functional status of knees. One hundred TKAs with patellar resurfacing and 64 TKAs without patellar resurfacing were evaluated. The average duration of follow-up was 4.8 years. The demographic data were similar between groups. The resurfacing group had worse preoperative HSS knee scores than the nonresurfacing group (p < 0.05). Yet, the final HSS knee scores were similar between two groups (p > 0.05). The resurfacing group had better muscle torque balance (Hamstring/Quadriceps ratio) than the nonresurfacing group (p < 0.05). There were more postoperative complications in the resurfacing group (21%) than the nonresurfacing group (4.7%). Seventeen patellar polyethylene wear in the resurfacing group caused chronic pain or click and required the revision surgery (17%). Although MGI TKAs with patellar resurfacing acquired similarly good knee's functional recovery as in those without resurfacing, yet, it had high patellar complications. Therefore, selective patellar resurfacing might be considered in primary TKA. The metal-backed patella components should be avoided and all-polyethylene designed component be used when patellar was resurfaced. Unlike most marketed knee system, all patients having a Miller-Galante 1 patella replacement were at future risk if they had not already failed.

Patellar Component Resection in Revision and Reimplantation Total Knee Arthroplasty

Between 1979 and 1995, 34 knees in 31 patients had a revision or reimplantation total knee arthroplasty in which the patellar component could not be reinserted. The patellar bone stock in each of those cases was compromised markedly and precluded adequate prosthetic fixation. The mean followup after the revision operation was 3.5 years (range, 2-14 years). The Knee Society knee score improved from a mean of 59 points preoperatively to a mean of 75 points postoperatively. The function score improved from a mean of 46 points preoperatively to a mean of 69 points postoperatively. Complications occurred in five patients: one patient sustained a patellar fracture that required no additional treatment; one experienced intermittent episodes of patellar subluxation; one had a recurvatum deformity develop and was treated with a brace; one had persistent knee stiffness and had four manipulations; and one patient had an extensor lag of 30 degrees develop. Twenty-six patients were satisfied with the results of their revision operations and five were dissatisfied. Ten patients had persistent knee symptoms referable to the patellofemoral articulation: mild pain in three; moderate pain in six; and severe pain in one. This study suggests that resection of the patellar component during revision or reimplantation total knee arthroplasty may be a reasonable approach for patients with markedly compromised patellar bone stock; however, mild or moderate anterior knee pain can be expected to persist in as much as 1/3 of these patients.

Patellofemoral complications in symmetrical total knee arthroplasty

A review of 356 Kinemax (Howmedica, Inc, Rutherford, NJ) cemented posterior cruciate ligament-retaining condylar total knee arthroplasties employing a symmetrical femoral component articulating with a medially offset symmetrical dome patella component was carried out to examine the results and determine the incidence and nature of the patellofemoral complications. Follow-up was from 3 to 8 years, with a mean of 5.1 years. A review of patellofemoral complications in previously reported homogeneous series of symmetrical and asymmetrical implants is presented. Mean postoperative Knee Society scores improved to 91, function scores to 86, and Hospital of Special Surgery scores to 90 yielding 95% good and excellent results. Mean postoperative range of motion was −1.5° extension to 113° flexion. There were five patellofemoral complications (1.4%), including two symptomatic subluxations, two distal pole avulsion fractures, and one lateral facet fracture. There were two reoperations necessary for patellofemoral problems (0.56%), one to correct subluxation and one for excision of the fractured lateral facet. These rates are lower than those previously reported for asymmetrical implants as well as current and phased-out symmetrical designs of total knee arthroplasty in the intermediate term. This review suggests that cemented total knee arthroplasty with symmetrical patellofemoral resurfacing with an offset patella dome and posterior cruciate ligament retention yields low patellofemoral complications and reoperations. The symmetrical femoral component appears to be a satisfactory compromise of “normal” femoral anatomy, which decreases inventory and cost without adversely affecting patellofemoral function and complications.

Effect of patellar meniscus on patellofemoral contact stress in total knee arthroplasty

The effect of a meniscus of fibrous tissue (patellar meniscus), on patellofemoral contact area and stresses was evaluated. Two knees with total knee arthroplasty and dome-shaped patellar components were retrieved at autopsy. Both had substantial fibrous menisci surrounding the dome of the patellar component. Contact area and contact stresses were measured with a digital electronic sensor, first with the patellar meniscus intact, then again after the patellar meniscus was removed. No dramatic difference was detected in patellofemoral contact area and contact stresses between the patellas with an intact or removed patellar meniscus, and there was no detectable load under the patellar meniscus. The results of this case study suggest that fibrous tissue surrounding the dome-shaped patellar component does not share compressive loads with the patellar component.

Contact areas and pressures between native patellas and prosthetic femoral components

Contact areas and pressures between native patellas and a prosthetic condylar design femoral component were measured at flexion angles of 30°, 60°, and 90°. These were compared to measurements obtained with a domed all-polyethylene patellar component. Mean native patellar contact areas were found to be fourfold greater than seen with the prosthetic patellar component. Contact stresses in the native patellas were below the yield strength of articular cartilage in 80% of the contact area. By contrast, stresses measured in the prosthetic patella exceeded the yield strength of ultrahigh molecular weight polyethylene in 64% of the measured contact area. Contact areas and stresses were not significantly effected by flexion angle. Although contact areas and stresses reflect only a part of the dynamics of the patellofemoral articulation this information would support the selective retention of the native patella in total knee arthroplasty.

Can a total knee replacement prosthesis be made entirely of polymers?

We have prospectively studied 63 total knee replacements (TKR) in which the femoral component was polyacetal, and 138 TKRs in which the femoral component was conventional cobalt chrome. The tibial and patellar components were of ultrahigh molecular weight polyethylene (UHMWPE). Patients were followed-up for at least 10 years. In the polyacetal group, a number of patients have died or have been revised, for reasons unrelated to the presence of polyacetal. There were no instances of femoral component fracture, nor failure by wear. One postmortem specimen, retrieved at 9 years after surgery, showed no measurable polyacetal wear and negligible HDP wear. The histology of tissue in contact with polyacetal was indistinguishable from that adjacent to polymethyl methacrylate and UHMWPE in the same knee. We believe that polyacetal could be used for the femoral component of a IKR and that a further trial should be undertaken.

Misconceptions about patellofemoral resurfacing in total knee replacement

mation is minimized and more uniform load transmission occurs. Metal backing provides a surface for secure and durable biological fixation. The metal-backed patella consist of a cancellous structured t i tanium porous sintered to a t i tanium base. The metal backing should support the polyethylene circumferentially. The addition of three smooth pegs ensures initial stability without stress shielding and allows for easy, bone-sparing revisions. We feel that application of a bone slurry of autogenous cancellous bone to the cut surface of the bone is an integral step in achieving cementless fixation [3]. We have shown that the bone slurry increases the initial contact of the metal backing to the cut bone surface, recreating a new subchondral plate. Through osteoinduction and osteoconduction, bone slurry application promotes and reliably achieves durable bony ingrowth and ongrowth over the porous coating. A microradiographic analysis of postmortem retrievals of patellas indicated that 84 ± 12% of the porous coating was in direct contact with bone [4]. Backscattered electron image analysis showed the bone ingrowth measured 13 ± 10%, which confirmed that reproducible bone ongrowth and ingrowth can be achieved in clinically functioning porous-coated metal-backed patellar components. Allpolyethylene patellas are standard for the fully cemented knee. A recent 6to 10-year retrospective review of 302 consecutive cementless TKAs, using the modified domeshaped metal-backed patella, indicated a 96% patellar survivorship [5]. There was no lucency or loosening. These results contrast strongly with those of earlier metal-backed designs, and compare favorably with cemented all-polyethylene patellae. Our results are also better than the reported results of unresurfaced patellas. This is accomplished with the dome-shaped patella that articulates with a deep-dished trochlear grooved asymmetrical femoral component. Patellofemoral forces are further minimized by medializing the patellar component such that it matches the patient's anatomic high point, maintaining limb alignment at 6 ° of valgus and optimizing patellar tracking. In summary, improvements in implant design, instrumentation, and surgical technique allow reproducible and excellent results with patellar resurfacing performed with or without cement.

Drs. Hofmann and Van Gorp's response to Dr. Jacobs

ture. Another feature of the overdesign of patella components includes the generation of patella components that are either asymmetric or designed with a central peak and sloping sides that thin out the patella components along the edges. These designs clearly evolved from in vitro studies on knee simulators in which contact stresses were measured directly. The validity of these measurements in the in vitro setting is not to be questioned. The problem is in the execution of the surgical technique. Despite the quality of the in vitro research, these data are not in any way applicable if, in vivo, the patella is cut at various biases such that the perfect setting used in vitro cannot be recreated. The patellar angle recently described by Evanich and colleagues [ 1 ] proves that the in vivo environment can create a patella in which the in vitro data would not apply. In these situations, the contact stresses would be accentuated because of failure to align the congruent surfaces in the non-domed-shaped patella. When a metal backing is applied, this leads to a somewhat precarious situation in that there may be only a few millimeters of plastic between the metal base and the patella. The failure to cut perfectly and track the patella will lead to premature failure of many of these components. Common sense dictates that component design must take into account the realities of inconsistent cuts and the patella tilt angle as the practical result. Common sense should be in the ascendency in the treatment of the patellofemoral joint. This means the recognition that each patient is unique and patellofemoral tracking is an art that cannot be dismissed by simply using a newer jig. The goal of patellofemoral instrumentation should be to avoid blindly overcutting the patella, which can have serious results. The femoral side of the joint must be taken into consideration and an acceptable patellofemoral complex recreated. Similarly, we must take into account the inconsistency of our surgical technique when designing the components themselves. It is likely that the careful study of each patient, which was necessitated by the relative newness of the procedure and the limitations of the available instrumentation, can probably explain why some of the original tricompartmental designs of the 1970s have such remarkable long-term durability.

Particulate debris presenting as radiographic dense masses following total knee arthroplasty

Two cases of failed total knee arthroplasty associated with significant titanium debris that created massive radiographic densities are reported. The similarities of the failed total knee arthroplasties are that both involve titanium femoral components with failed metal-backed patellar components. At the time of surgical intervention, patellar polyethylene dissociation from metal-backed patellar components was noted with excessive burnishing and wear of the remaining metal-backed patellar component and of the titanium femoral component. Wear of the tibial polyethylene was noted in both cases. The titanium-on-titanium wear couple produced significant debris, resulting in large mass formation about the total knee arthroplasty. Additionally, there were loculated, fluid-filled sacks of titanium debris. Histologic sections performed for both cases revealed significant deposits of titanium in combination with polyethylene. In both cases, radiographs revealed the presence of large, radiodense masses. These cases illustrate that when considering etiologies for radiodense masses about total joint arthroplasty, particulate titanium debris resulting in mass formation must be added to the differential diagnosis.

Porous-coated metal-backed patellar components in total knee replacement. A postmortem retrieval analysis.

The use of porous-coated metal-backed patellar components to achieve consistent fixation by bone ingrowth and to provide relief of pain warrants serious scrutiny. We conducted a quantitative postmortem investigation of eleven consecutively retrieved components with use of high-resolution contact radiographs, electron microscopy, and histological analysis. The implants had been in situ for a mean (and standard deviation) of 45+/-36 months (range, one to eighty-four months). Analysis of the high-resolution contact radiographs revealed that a mean of 86+/-12 per cent (range, 61 to 100 per cent) of the porous coating was in contact with the host bone. Backscattered electron imaging showed that the mean volume fraction of bone ingrowth was 13+/-9 per cent (range, 0 to 30 per cent). No significant difference was detected, with the numbers available, between the volume fraction of the bone ingrowth measured in the porous coating and that of the host cancellous bone in the patellae.

4??? to 10-Year Results With The Anatomic Modular Total Knee

The outcome of 186 consecutive total knee arthroplasties performed with the Anatomic Modular Knee is reported. One hundred forty-two knees had followup of 4 to 10 years (mean, 6.9 years). Two knees required revision of all components, one because of infection and the other for instability. Seven patients underwent exchange of the modular tibial polyethylene insert at an average of 84 months postoperatively. The mean age of these seven patients at primary arthroplasty was 54 years. No implant showed clinical or radiographic evidence of loosening and there were no complications related to patellofemoral articulation. The revision rate of the femoral, tibial, and patellar components was two of 142 or 1.4%. The revision rate including exchange of the polyethylene insert was nine of 142 or 6.3%. This minimally constrained posterior cruciate retaining modular design performed well at intermediate followup. The absence of patellofemoral complications and aseptic loosening was notable. Wear related phenomena were the most common indications for reoperation and these occurred in younger, active individuals with relatively thin polyethylene bearings. The relative value of modular tibial inserts and the outcome of isolated polyethylene exchanges warrant additional study.

Extensor mechanism problems in patellar surface replaced total knee arthroplasty patients

In this study we recorded the complications of extensor mechanism in 534 patients whose 584 knees were operated and patellar reconstruction was done between May 1988 and June 1997. Mean follow-up time is 51.5 months. Patellofemoral complications were occured in 7% of patients. There was patellar subluxation in 18 patients, patella infera in 12 patients, heterotopic ossification localised in extensor mechanism in 6 patients, fracture of patella in 2 patients and loosening, synovial construction and rupture of patellar tendon in one patient. Lateral retinacular release and medial capsular plication was the preferred method in 8 patients who had sympthomatic subluxation where as reconstruction was done in a patient whose patellar tendon was ruptured. There wasn't any reconstructions applied, depending on the patellar component complications. As a result we agreed that if technical pecularities like patello-femoral tracking and prevention of patellar blood supply are taken into consideration the complications can be minimized.

ＲＡに対するセメントレスＴＫＡ（ＭＧ Ｉ型）の中期成績

23 primary uncemeneted total knee arthroplasties (MG I) were performed in 16 patients with rheumatoid arthritis. Average age at the time of surgery was 60.3 years. Average duration of the disease was 10.4 years. The follow up period averaged 7.3 years (range, 5 to 10 years). Clinical evaluation based on the Japanese Orthopedic Association (JOA) score indicated significant improvement in pain from preoperative to the most recent follow-up examination. One knee required revision surgery due to metalosis of the patellar component after 7 years. There was no evidence of roentogenographic failure in femoral and tibial components. These medium term results suggest that uncemented TKA may be successful in rheumatoid knees. However, longer follow-up periods will be necessary for problems of patellar component in MG I TKAs, because 4 knee had progressive lateral shift of the patella.

Patellofemoral joint after total knee arthroplasty: Effect on contact area and contact stress

Compressive contact stress between the patella and the anterior femur and between the quadriceps tendon and anterior femur was measured before and after total knee arthroplasty in 5 cadaver knee specimens using a digital electronic sensor. Contact stresses were measured in the normal knee and after total knee arthroplasty with an unresurfaced patella, a dome-shaped patella, and a conforming patella. Patellofemoral contact stresses did not change significantly after total knee arthroplasty when the patella was not resurfaced, but they increased significantly after the patella was resurfaced with both the dome-shaped and the conforming components. The conforming patella had the highest contact stresses because it tilted at flexion angles greater than 90° and applied load to a small area on the superior portion of the patellar component. The conforming patella markedly decreased tendofemoral contact force because the thicker superior pole of the patella tented the quadriceps tendon at flexion angles greater than 120°. This further increased patellofemoral contact force in deep knee flexion.

Patellofemoral joint kinematics and contact pressures in total knee arthroplasty.

Patellofemoral joint kinematics, contact areas, and contact pressures were measured concomitantly before and after total knee arthroplasty in 10 fresh frozen human cadaver knees using an Instron machine, a custom patellofemoral joint testing jig, axial bone markers, a continuous video digitizing system, and Fuji pressure sensitive film. The implant used in this study was the Kirschner Performance Knee System with an all polyethylene, domed patellar component. For all tests, the patella was aligned in its anatomically neutral position. Patellofemoral joint contact areas decreased as much as 19-fold after total knee arthroplasty. Mean patellofemoral joint contact pressures increased as much as 32-fold, and peak patellofemoral joint contact pressures increased as much as 22-fold after total knee arthroplasty. No statistically significant differences between preoperative and postoperative specimens were observed with respect to the patellofemoral, patellotibial, or patellar tilt angles from 30 degrees to 120 degrees knee flexion. Thus, the elevated patellofemoral joint contact pressures observed after total knee arthroplasty in vitro are not a primary consequence of iatrogenically altered patellofemoral kinematics.

A fully mobile patellar prosthesis: design, biomechanics and laboratory evaluation

The patello-femoral joint is a highly loaded component of a total knee arthroplasty, but its design has often received scant attention. Plotting the patellofemoral congruity of five commonly used, loaded patellar prostheses at different angles of flexion, provides evidence of extremely high contact stresses in all the current designs. Finite element stress analysis shows how poor design leads to excessive stresses within the polyethylene of the patellar component during flexion of the knee. A patellar prosthesis has been developed that is more congruent with the femoral component than the other designs tested. In addition, it allows side-to-side movement of the patella relative to the femur and rotation, in the coronal plane, during active loaded flexion of the knee.

Total knee replacement in young, active patients. Long-term follow-up and functional outcome.

We reviewed our experience with total knee arthroplasties performed between 1977 and 1992 in patients who were fifty-five years old or less to determine the appropriate management for younger patients who have severe osteoarthrosis. One hundred and fourteen knee replacements were performed in eighty-eight patients who were an average of fifty-one years old (range, twenty-two to fifty-five years old). All of the operations were performed by one of the two senior ones of us (J. N. I. or W. N. S.) with the use of cementing techniques. A posterior stabilized, posterior cruciate-substituting design was used for all but one replacement, for which a semiconstrained total condylar prosthesis was used. Six knees (four patients) were lost to follow-up. Follow-up data for the remaining 108 knees (eighty-four patients) were used to perform the survivorship analysis. One hundred and three unrevised knees (eighty patients) were available for clinical evaluation with the scoring systems of The Hospital for Special Surgery and the Knee Society at an average of eight years (range, three to eighteen years) postoperatively; thirty-six knees were followed for more than ten years. In addition, the activity levels of the patients were assessed with the activity score of Tegner and Lysholm. Radiographs were examined for evidence of loosening of the component. At the latest follow-up examination, the average knee score according to the system of The Hospital for Special Surgery had improved from 55 points preoperatively to 92 points. According to the system of the Knee Society, the average knee score was 94 points and the average functional score was 89 points. The result for all 103 knees was good or excellent according to the knee scores of The Hospital for Special Surgery and the Knee Society. Ninety-seven knees (94 per cent) had good or excellent function according to the functional score of the Knee Society. The average activity score of Tegner and, Lysholm improved from 1.3 points (range, 0 to 4 points) preoperatively to 3.5 points (range, 1 to 6 points) at the latest follow-up examination. All but two patients had improvement in the activity score postoperatively, and nineteen (24 per cent) of the eighty patients had an activity score of at least 5 points, indicating regular participation in activities such as tennis, skiing, bicycling, or strenuous farm or construction work. Nine (9 per cent) of the 103 knees had non-progressive tibial radiolucent lines. Two patients had a revision because of late infection, and one patient had revision of a well fixed tibial component because of wear of the polyethylene. In addition, three patellar components were revised for loosening, and one spacer was exchanged to treat instability. With failure defined as revision of either the femoral or the tibial component, the over-all rate of survival was 94 per cent at eighteen years. When the three patellar revisions were included in the failures, the survival rate was 90 per cent at eighteen years. When the exchange of the spacer was also included in the failures, the survival rate was 87 per cent at eighteen years. We consider arthroplasty with cementing of a posterior stabilized total knee prosthesis to be effective operative treatment with durable results for osteoarthrosis in younger patients when other, less invasive measures have failed. Within the average eight-year follow-up interval of this study, polyethylene wear, osteolysis, and loosening of the conforming posterior cruciate-substituting prosthesis were not major problems for these younger, active patients, although it is possible that this observation could change with an even longer duration of follow-up.

Medialization of the patella in total knee arthroplasty

Patellar complications of total knee arthroplasty remain the most common cause of pain and reoperation. Laboratory studies have suggested that medialization of the patella will improve tracking of the patella on the trochlea of the femoral component. The purpose of this study was to determine if clinical medialization of the patellar component on the patellar bone would improve tracking of the patella as demonstrated radiographically. Sixty-two knees were randomized so that 31 knees had a centrally placed patellar component and 31 had the patellar component placed on the medial two thirds of the patellar bone. There was no difference between the two groups with respect to either clinical or radiographic results in the first year after surgery. There was no improvement compared with previous reports in the incidence of tilt and displacement. The one improvement was a reduction in the incidence of lateral release. Thus, consequences of lateral release such as postoperative morbidity, avascular necrosis of the patella, and stress fracture of the patella can be avoided. It is recommended that the patellar component be placed on the medial two thirds of the patella to reduce the occurrence of lateral release. Tracking of the patella during surgery can be assessed using a single suture placed at the superior pole of the patella, and this technique in combination with the no-thumbs test provides an additional means of evaluation for patellar tracking.