Fracture of the femoral component associated with polyethylene wear and osteolysis after total knee arthroplasty

Femoral Component Fracture in a Total Knee Arthroplasty Patient With a Persistent Flexion Contracture

This article reports a rare case of a total knee arthroplasty femoral component fracture. Fractures of early knee systems were attributed to design flaws. Modern design failures have been attributed to poor surgical technique or underlying osteolysis. Here, we report a fracture in the Vanguard prosthesis (Zimmer Biomet, Warsaw, IN) 12 years after implantation in a patient with a persistent flexion contracture. The fracture likely occurred due to fatigue failure of the anterior flange secondary to increased stress from a high riding patella. Although femoral component fractures are rare, they should be considered as a potential complication, especially in patients with special load considerations. For these patients, it is essential that the prosthesis be properly supported with clean cuts and an adequate cement mantle.

Early Tibial Baseplate Fracture After Medial Unicondylar Knee Arthroplasty: A Report of 2 Cases

CASE

Implant failure after unicondylar knee arthroplasty (UKA) is a rare but well-described complication in the arthroplasty literature. However, there is a paucity of literature regarding rapid catastrophic failure of modern implant designs. This is a case report of 2 patients with early catastrophic failure of the tibial baseplate after UKA with a Stryker Restoris MultiCompartmental Knee System implant using Mako robotic assistance, both requiring revision to total knee arthroplasty.

CONCLUSION

Improved awareness and understanding of early UKA tibial baseplate failure may help identify both patient and surgical risk factors that could help prevent further instances in the future.

Atraumatic Fracture of the Femoral Component of a Cemented Total Knee Arthroplasty: A Case Report

CASE

An 81-year-old man presented with severe atraumatic knee pain. Sixteen years before, he had undergone a primary cemented total knee arthroplasty (TKA). A radiological study showed osteolysis and loosening of the femoral component. Intraoperatively, a medial femoral condyle fracture was found. A rotating-hinge revision TKA with cemented stems was implanted.

CONCLUSION

Femoral component fracture is extremely rare. Surgeons should remain vigilant with younger and heavier patients with severe unexplained pain. Early revision TKA using cemented, stemmed, and more constrained implants is usually necessary. Full and stable metal-to-bone contact through perfect cuts and a careful cementing technique avoiding debonded areas are recommended to prevent this complication.

The Evolution, Current Indications and Outcomes of Cementless Total Knee Arthroplasty

Total knee arthroplasty (TKA) has been performed by orthopedic surgeons for decades, but the cementless TKA has only recently gained much interest in the world of arthroplasty. Initially, early designs had multiple complications, particularly with aseptic loosening due to osteolysis and micromotion. However, modifications have shown good outcomes and excellent survivorship. Over the last several decades, changes in implant designs as well as implant materials/coatings have helped with bone in growth and stability. Furthermore, surgeons have been performing TKA in younger and more obese patients as these populations have been increasing. Good results from the cementless TKA compared to cemented TKA may be a better option in these more challenging populations, as several studies have shown greater survivorship in patients that are younger and have a greater BMI. Additionally, a cementless TKA may be more cost effective, which remains a concern in today's healthcare environment. Overall, cemented and cementless TKA have great results in modern times and there is still a debate as to which implant is superior.

Fracture of the oxidized zirconium femoral component after total knee arthroplasty

BACKGROUND

Femoral component fracture is a rare complication of total knee arthroplasty (TKA).

CASE

We report a case of oxidized zirconium (Oxinium) femoral component fracture after total knee arthroplasty. The fracture site was the junction of the central and medial flanges. The patellar component and polyethylene insert had delamination at the contact point of the fracture line, and the tibial tray had loosening at the medial side. There was no cement adherence at the component fracture site, suggesting that debonding had occurred at the cement-implant interface in this area. Examination with a scanning electron microscope revealed beach marks, which are characteristic findings of metal fatigue.

CONCLUSION

We considered that the cause of femoral component fracture was a fatigue fracture due to poor fixation of the component to the bone caused by poor osteotomy technique or poor cementing technique. To our knowledge, this is the first case of Oxinium femoral component fracture.

Fatigue fracture of the femoral component in total knee replacement

BACKGROUND

Fracture of femoral component in total knee arthroplasty (TKA) has become a rare complication with improvements in metal alloy manufacturing technology.

METHODOLOGY

We report two cases of fracture of femoral components 9 and 10 years after primary TKA. The Buechel-Pappas (BP) knee system used in our two cases were designed by the same team who designed the LCS TKA implants. The femoral component is made of cobalt chromium alloy. The break in the femoral component noted in both the cases were at a similar site, at the distal medial flange just posterior to the peg of the femoral component.

RESULT

Both these cases underwent revision surgery using stemmed implants with good results. Implants retrieved were analysed with Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) to study the fracture pattern and material properties respectively. Fractography analysis of both our cases showed that the crack initiated laterally from the thin edge (1mm) around the sharp angulated corner of the medial femoral condyle and spread medially towards the thicker segment.

CONCLUSION

We feel two fractures of femoral component out of 9000 TKA in ten years is significant. We recommend a re-evaluation of the femoral component of the BP knee system to ensure that the edges, specifically the sharp corners, have adequate thickness to avoid a fatigue fracture.

Atraumatic Fracture of Cemented Vanguard Total Knee Arthroplasty Femoral Component

The authors report the case of an atraumatic femoral component fracture 10 years after primary total knee arthroplasty (TKA) with a modern cemented fixed bearing system. The patient, a 70-year-old man, had the complication without inciting trauma, and he subsequently had severe pain and disability. This rare mode of TKA failure occurred at the superolateral aspect of the femoral component's anterior flange. At the time of revision, no femoral osteolysis was seen and the backside of the prosthesis fracture fragment was found to be free of cement. To the authors' knowledge, this is the first case of femoral component fracture in a Vanguard TKA (Biomet, Warsaw, Indiana), and the first case of fracture in a modern cobalt-chrome alloy femoral component associated with aseptic cement debonding. Femoral component stress fracture is a rare but serious complication of TKA. Reports of femoral component fracture in early designs were attributed to geometric design flaws, whereas modern TKA designs appear to fail when ingrowth failure, aseptic debonding, or osteolysis result in inadequate bony support of the prosthesis. Careful attention to bone cuts in porous-coated uncemented TKA systems and proper cementing technique in cemented TKA systems may preclude this rare complication. In the case of severe osteolysis, early revision may prevent catastrophic implant failure. [Orthopedics. 2020;43(5):e476-e479.].

Bilateral Femoral Component Fractures After Primary Total Knee Arthroplasty With Cruciate-Retaining Femoral Component

A 69-year-old male presented with atraumatic bilateral femoral component fractures at different time intervals after simultaneous bilateral total knee arthroplasty using the cemented Biomet Ascent Knee System. The right and left knee implant fractures occurred 12 and 17 years after primary arthroplasty, respectively. This patient was notably tall (190.5 cm, 98th percentile) and maintained an active lifestyle before implant fractures. Sequential, bilateral knee implant fractures in a system with a previously acceptable track record suggest that biomechanics, patient characteristics, and surgical factors can significantly influence the risks for fracture of an implant.

Catastrophic Polyethylene Failure and Fractured Femoral Component in Modern Knee Arthroplasty Design: A Case Report

CASE

We report a 67-year-old gentleman who presented with a painful unstable knee. He had undergone a successful total knee arthroplasty 12 years earlier and was highly functional. He presented with a 10-month history of mild pain, instability, and gait alteration. During revision surgery, there was a loss of bony support, and a fractured femoral component was identified. He required constrained revision components for reconstruction and made an uneventful recovery.

CONCLUSIONS

Fractured femoral components are rare complications of modern primary total knee arthroplasty. Loss of bony support in critical areas of high loading will inevitably lead to catastrophic component failure.

Comparison of ISO 14243-1 to ASTM F3141 in terms of wearing of knee prostheses

BACKGROUND

The wear properties of knee implants need to be thoroughly evaluated prior to clinical use to ensure implant longevity. ISO 14243-1:2009 and ASTM F3141-17 are the two standards typically used for evaluating wear, with the ISO standard being more common; ASTM F3141-17 was first released in 2015. The aim of this study is to compare differences between these two standards in terms of wearing on a knee prosthesis.

METHODS

Using finite element analysis based on Archard's law, this study evaluated anterior-posterior and internal-external motion, contact area, contact force, contact stress, volumetric wear rate, wear depth, and wear distribution on the knee prosthesis.

FINDINGS

The results show that simulations performed according to ASTM F3141 produced knee kinematics that were more similar to human gait. The maximum wear depth occurred on the medial side of the tibia. However, the region of peak contact stress did not always correspond with the region of the maximum wear depth, indicating that considering the contact stress alone is not sufficient for evaluating wear as the sliding distance also plays an important role. The resulting wear region from the ASTM F3141 simulation was smaller but deeper than the wear region from the simulation per ISO 14243-1. However, the volumetric wear rates were very similar, with 13.48-55.26 mm³/million for ASTM F3141 and 13.64-54.9 mm³/million for ISO 14243-1.

INTERPRETATION

The resulting rate of wear is almost identical between ISO 14243-1 and ASTM F3141. However, there are differences in wear contours and wear depth.

Osteolysis Complicating Total Knee Arthroplasty

Osteolysis is a process mounted by the host immune system that relies on several variables, including patient-related factors, type of insert material, modes of wear, and implant design. Imaging techniques such as radiography, computed tomography (CT) scans, magnetic resonance imaging (MRI), and tomosynthesis aid in diagnosing osteolysis. Surgical options for the treatment of osteolysis include the insertion of bone grafts, bone cement, and prosthetic augmentation. Although no approved pharmacological therapies for the specific treatment of osteolysis exist, the use of bisphosphonates and statins decreases the risk of osteolysis.

The mechanical response of a polyetheretherketone femoral knee implant under a deep squatting loading condition

The current study was designed to investigate the mechanical response of a polyetheretherketone-on-polyethylene total knee replacement device during a deep squat. Application of this high-demand loading condition can identify weaknesses of the polyetheretherketone relative to cobalt-chromium. This study investigated whether the implant is strong enough for this type of loading, whether cement stresses are considerably changed and whether a polyetheretherketone femoral component is likely to lead to reduced periprosthetic bone loss as compared to a cobalt-chromium component. A finite element model of a total knee arthroplasty subjected to a deep squat loading condition, which was previously published, was adapted with an alternative total knee arthroplasty design made of either polyetheretherketone or cobalt-chromium. The maximum tensile and compressive stresses within the implant and cement mantle were analysed against their yield and fatigue stress levels. The amount of stress shielding within the bone was compared between the polyetheretherketone and cobalt-chromium cases. Relative to its material strength, tensile peak stresses were higher in the cobalt-chromium implant; compressive peak stresses were higher in the polyetheretherketone implant. The stress patterns differed substantially between polyetheretherketone and cobalt-chromium. The tensile stresses in the cement mantle supporting the polyetheretherketone implant were up to 33% lower than with the cobalt-chromium component, but twice as high for compression. Stress shielding was reduced to a median of 1% for the polyetheretherketone implant versus 56% for the cobalt-chromium implant. Both the polyetheretherketone implant and the underlying cement mantle should be able to cope with the stress levels present during a deep squat. Relative to the cobalt-chromium component, stress shielding of the periprosthetic femur was substantially less with a polyetheretherketone femoral component.

Computational study on the effect of malalignment of the tibial component on the biomechanics of total knee arthroplasty: A Finite Element Analysis

Objectives

Malalignment of the tibial component could influence the long-term survival of a total knee arthroplasty (TKA). The object of this study was to investigate the biomechanical effect of varus and valgus malalignment on the tibial component under stance-phase gait cycle loading conditions.

Methods

Validated finite element models for varus and valgus malalignment by 3° and 5° were developed to evaluate the effect of malalignment on the tibial component in TKA. Maximum contact stress and contact area on a polyethylene insert, maximum contact stress on patellar button and the collateral ligament force were investigated.

Results

There was greater total contact stress in the varus alignment than in the valgus, with more marked difference on the medial side. An increase in ligament force was clearly demonstrated, especially in the valgus alignment and force exerted on the medial collateral ligament also increased.

Conclusion

These results highlight the importance of accurate surgical reconstruction of the coronal tibial alignment of the knee joint. Varus and valgus alignments will influence wear and ligament stability, respectively in TKA.

Cite this article: D-S. Suh, K-T. Kang, J. Son, O-R. Kwon, C. Baek, Y-G. Koh. Computational study on the effect of malalignment of the tibial component on the biomechanics of total knee arthroplasty: A Finite Element Analysis. Bone Joint Res 2017;6:623–630. DOI: 10.1302/2046-3758.611.BJR-2016-0088.R2.

Fracture of the Tibial Baseplate 16 Years after Miller-Galante II Total Knee Arthroplasty

We report a rare case of tibial baseplate fracture of Miller-Galante II (MG II) prosthesis. We examine the factors that may cause such late fracture and review the literature on radiographic analysis and retrieval studies. A 76-year-old woman, who had undergone bilateral MG II total knee arthroplasty due to rheumatoid arthritis 16 years earlier, presented to our department with a 3-month history of left knee pain. Plain radiographs revealed severe distortion of the medial tibial component. During revision knee arthroplasty, we observed severe metallosis in the knee joint, polyethylene insert deformation, and posteromedial coronal baseplate fracture. After removal of the fractured tray, a bone deficit due to osteolysis was noted. The revision prosthesis (LCCK, Zimmer-Biomet) was implanted uneventfully. Four months after revision surgery, the patient was ambulating and had no complications. The implants on the right side had survived without complications for 17 years. We speculate that the primary causative factor of the fatigue fracture of the base plate due to loss of bony support most likely secondary to osteolysis was varus malalignment at primary implantation. This case highlights the importance of paying close attention to the correct alignment of each component at primary implantation.

Same-Level Fracture of the Tibial Metal Tray and Polyethylene Insert After Total Knee Arthroplasty

The authors report a case of failure fracture of the tibial metal tray and polyethylene insert at the same level in a 73-year-old woman 10 years after total knee arthroplasty using the AMK Total Knee System (DePuy, Warsaw, Indiana). Causes of this fracture are analyzed and discussed, with the focus on the importance of component design, position, and size. The overall aim of this case report is for orthopedic surgeons to avoid this complication in total knee arthroplasty by paying attention to these controllable factors. [Orthopedics. 2016; 39(4):e787-e789.].

Fracture of titanium nitride-coated femoral component after total knee arthroplasty

We report a case of fracture of a titanium nitride-coated femoral component 3 years after primary total knee arthroplasty (TKA). The fracture was at the medial condylar area just posterior to the medial peg of the femoral component. The backside of the broken medial condylar portion of the femoral component was devoid of cement. Debonding of the component is a possible cause of the stress fracture. To our knowledge, this is the first case report of the fracture of the femoral component manufactured from titanium alloy.

LEVEL OF EVIDENCE

IV.

Fracture of an Oxford femoral component: a case report

Component fracture is a rare complication after knee replacement, especially in contemporary designs. We report the first case of a fractured femoral component in a cemented Oxford unicondylar knee prosthesis, 9 years after its implantation. Factors leading to this rare kind of component failure are discussed. Revision should be warranted in cases of unicondylar femoral component loosening, eliminating the risk of component fracture, especially in obese patients.

Tibial baseplate fracture associated with polyethylene wear and osteolysis after total knee arthroplasty

INTRODUCTION

Fracture of the tibial baseplate following total knee arthroplasty is very rare given the developments in modern prosthesis design. Tibial baseplate fracture secondary to polyethylene wear, osteolysis and component malalignment in an elderly obese patient is reported in the present article.

PRESENTATION OF CASE

A 69-year-old woman had undergone total knee arthroplasty eleven years prior to presentation and reported nine months of chronic pain, which was caused by a neglected fracture of the baseplate.

DISCUSSION

We discuss the prevention of implant fracture after total knee arthroplasty and address the risk factors associated with this complication.

CONCLUSION

The present case emphasizes the importance of properly informing patients and encouraging them to report such complaints immediately to allow for early revision and prevention of component fracture, especially in patients with risk factors such as obesity and component, malalignment.

Imaging periprosthetic osteolysis around total knee arthroplasties using a human cadaver model

We examined the sensitivity and accuracy of measuring osteolysis around total knee arthroplasty (TKA) on radiographs, computed tomography (CT), and magnetic resonance imaging (MRI) in a cadaver model. Fifty-four simulated osteolytic defects ranging from 0.7 to 14 cm(3) were created in 6 cadaver knees implanted with either a cemented or an uncemented TKA. Three blinded investigators assessed the presence, location, and volume of defects on radiographs and CT and MRI scans with metal reduction protocols. Both CT and MRI had significantly higher sensitivities and specificities than did plain radiographs (P < .005). Overall, there was no difference in the accuracy of defect volume measurements between CT and MRI (P = .574). This study demonstrates the limitations of radiographs and the high sensitivity and specificity of both CT and MRI in assessing osteolysis around TKA.

Fracture at the stem-condylar junction of a modular femoral prosthesis in a varus-valgus constrained total knee arthroplasty

We present a rare case of fracture of the modular femoral component in a varus-valgus constrained total knee arthroplasty (TKA) prosthesis which occurred 2 years after implantation. Both femoral and tibial components underwent a second revision using a constrained hinged TKA. Laboratory analysis revealed insufficient metaphyseal bone stock in association with inadequate cement mantle incorporation which made implant fixation solely reliant on the intramedullary stem construct. It was therefore hypothesized that high repetitive stresses over the junction of the modular component led to the fracture.

LEVEL OF EVIDENCE

Case report, Level IV.

Bilateral fatigue fracture of the femoral components in a cruciate-retaining cementless total knee prosthesis

This article reports a case of bilateral fatigue fracture of the femoral components in a cruciate-retaining uncemented total knee arthroplasty (TKA). A 75-year-old woman (height, 158 cm; weight, 72 kg; body mass index, 29.2) had undergone one-stage bilateral TKA for osteoarthritis 11 years previously at the author's institution. Surgery was performed using an uncemented Flexible Nichidai Knee. Equal tension of the collateral ligaments and normal mechanical axis were achieved during the primary procedure. The patient was an ardent lover of the game of badminton and had higher activity levels with daily playing. At 8 years postoperatively, she started complaining of mild pain in both knees. The pain gradually increased, and at 11 years postoperatively, she had difficulty walking. Anteroposterior radiographs showed narrowing of the medial joint space, indicating wear of the polyethylene insert. Lateral radiographs showed signs of broken implants in both knees. There were no signs of gross implant loosening or osteolysis. One-stage revision surgery was performed, and the knees were converted to cemented posterior-stabilized TKAs. At revision, the bilateral femoral components were found to be fractured at the junction between the trochlear flange and the medial condyle, anteriorly to the medial peg. The polyethylene insert showed mild wear at the medial middle portion. In the majority of case reports, stress fractures of the femoral component have predominantly affected the medial condyle, following uncemented implantation of fixed-bearing knees. In this case, failure of bone ingrowth in uncemented components, higher body mass index, and a higher athletic activity led to fatigue fracture of the femoral components.

FRACTURE OF THE TIBIAL COMPONENT IN TOTAL KNEE ARTHROPLASTY: REPORT ON TWO CASES

The authors report the rare occurrence of two cases of fracture of the tibial component in total knee arthroplasty. They review the literature and discuss the main factors that can cause failure of the implants.

Fatigue fracture of the hinge pin in a semi-constrained total knee arthroplasty: a case report

Material failure is a rare complication in total knee arthroplasty (TKA). This case report shows a fatigue fracture of the hinge pin as a consequence of a postoperative persisting valgus deviation in a semi-constrained TKA.

Wear, delamination, and fatigue resistance of melt-annealed highly crosslinked UHMWPE cruciate-retaining knee inserts under activities of daily living

The wear, delamination, and fatigue resistance of artificially aged gamma irradiation-sterilized conventional polyethylene (CPE) and gas-plasma-sterilized melt-annealed highly crosslinked polyethylene tibial inserts (HXPE) were compared. Six CPE and 12 HXPE (six irradiated at 58 kGy and six at 72 kGy) left knee inserts were wear tested for 5.5 million cycles (Mc) under loads and motions that mimic activities of daily living, such as walking, chair rise, stair ascent, and deep squatting. Another six HXPE (72 kGy) and six CPE inserts were also tested under conditions that could produce severe delamination for 8 Mc. Ten other knees (five 72 kGy HXPE and five CPE) were subjected to posterior edge loading fatigue testing for 5 Mc. The HXPE inserts had an average wear rate reduction of about 80% relative to their CPE counterparts during all activities. All of the CPE inserts delaminated and fractured during high cycle deep squat (152 degrees flexion) motions, while all the HXPE remained intact. None of the HXPE inserts delaminated after 8 Mc, while all of the CPE inserts developed delamination damage within 1.5-5.8 Mc of delamination testing. All CPE inserts developed subsurface cracks and delamination within 2.8 Mc during posterior edge loading fatigue studies, while none of the HXPE inserts showed cracking or delamination after 5 Mc. These results show that aged HXPE has higher wear and fatigue resistance than aged CPE, and offers potential long-term advantages for young active patients with sustained activities of daily living.

Femoral component fracture due to osteolysis after cemented mobile-bearing total knee arthroplasty

A 58-year-old man with osteoarthritis in the left knee underwent a total knee arthroplasty with a New Jersey anterior-posterior gliding low contact stress mobile-bearing implant. All femoral, tibial, and patellar components were implanted with bone cement. Pain developed at 43 months postsurgery, and plain radiography revealed a vertical crack in the femoral component and osteolysis at the medial femoral condyle. The femoral and tibial components were revised, and the bone defect at the medial femoral condyle was reconstructed using an allogeneic strut bone graft. Microscope examination identified polyethylene particles with foreign body granulomatous reaction, and scanning electron microscopy revealed fatigue failure of the femoral component. Osteolysis due to polyethylene particles can lead to fracture of the femoral component after cemented anterior-posterior gliding low contact stress mobile-bearing total knee arthroplasty.

[Finite element analysis of a cemented ceramic femoral component for the assembly situation in total knee arthroplasty]

The femoral components of the total knee replacements are generally made of metal. In contrast, ceramic femoral components promise improved tribological and allergological properties. However, ceramic components present a risk of failure as a result of stress peaks. Stress peaks can be minimised through adequate implant design, proper material composition and optimum force transmission between bone and implant. Thus, the quality of the implant fixation is a crucial factor. The objective of the present study was to analyse the influence of the cement layer thickness on stress states in the ceramic femoral component and in the femur. Two- and three- dimensional finite element analyses of an artificial knee joint with cement layers of different thickness and with an unbalanced cement layer thickness between the ceramic femoral component and the femur were performed. Higher stress regions occurred in the area of force transmission and in the median plane. The maximum calculated stresses were below the accepted tensile strength. Stresses were found to be lower for cement layer thickness of <2.0 mm.

Osteolysis after total knee arthroplasty

Osteolysis ranks as the most significant cause of revision surgery in both total hip arthroplasty and total knee arthroplasty (TKA). The factors leading to osteolysis in TKA are unique and sometimes preventable. Changes in polyethylene manufacturing and implant design are striving to improve overall wear. In this review, we discuss osteolysis as it relates to TKAs. The etiology, diagnosis, contributing factors, and management are presented. The final section focuses on future improvements in TKA design, which may ultimately decrease the rate of osteolysis.

A rare cause for knee pain: fracture of the femoral component after TKR. A case report

We report the rare case of sudden knee pain due to fracture of the total knee replacement nine years after implantation. Fracture occurred because of subsequent osteolysis due to polyethylene wear.

Wear and osteolysis around total knee arthroplasty

Osteolysis induced by wear debris of ultra-high-molecular-weight polyethylene has emerged as a significant problem after total knee arthroplasty. The generation of polyethylene wear and the development of osteolysis around total knee arthroplasty are caused by a combination of patient, implant, and surgical factors. Activity level over time may be the most important patient factor affecting the loads placed on a total knee replacement, but it is the most difficult to manage. Multiple factors related to the manufacturing of the polyethylene implant influence the extent of wear, and surgeons should be cautious in considering enhanced polyethylenes pending results of further investigations. The optimal design of the articular bearing surface remains controversial but needs to be considered with respect to the stresses imparted on component-bone and modular tibial backside interfaces. Surgical factors, including restoration of alignment and ligament balance, are important for long-term durability of the implant. Methods of measuring the wear of total knee implants are still evolving. Thus, when confronted with a worn total knee implant and developing osteolysis, the surgeon should consider each of these factors in selecting the best management option to eliminate the source of debris and minimize the potential for wear and osteolysis following revision.

Fracture of femoral component in a resurfacing total knee arthroplasty

We present a case of an unusual complication after a resurfacing total knee arthroplasty. Fracture of the uncemented porous-coated femoral component occurred 4 years after its implantation. The mechanical axis was restored and collateral ligament balance was achieved at the primary procedure. At revision, the femoral component was found fractured at the junction of the trochlea with the medial condyle, anteriorly to the medial peg. A thin layer of fibrous tissue was interposed between bone and metal under the fracture area. Metallurgical analysis of the fractured component revealed fatigue failure but no structural defect. Lack of bony support and excessive cyclic loading led to fracture of the implant.

Long-term results of low contact stress mobile-bearing total knee replacements

Five hundred ninety-eight consecutive primary low contact stress total knee replacements were done in 502 patients between 1985 and 1990. Clinical review was available for 495 knees (406 patients), 228 knees with meniscal-bearing prostheses and 267 knees with rotating-platform prostheses. The average followup was 12 years (range, 10-15 years). The average postoperative knee and functional scores were 87 points and 75 points, respectively. The average postoperative range of motion was 110 degrees. Fifty-six knees (11%) required revision for excessive wear of the tibial insert (41), dislocation (10), patellar polyethylene breakage (one), component loosening (one patellar, one tibial), and infection (two). During revision, osteolysis (20 knees), patellar polyethylene failure (33), and femoral component fracture (one) were seen. The overall survivorship was 88.1% at 15 years using Kaplan-Meier analysis. The survival rate was 83% for the meniscal-bearing prostheses and 92.1% for the rotating-platform prostheses. The Low Contact Stress mobile-bearing knee prosthesis has no superiority over that of fixed-bearing knees, especially for the meniscal-bearing design in prevention of polyethylene failure or revision. Based on the results of this study, the use of the LCS meniscal-bearing prosthesis does not appear to be justified.

Optical analysis of surface changes on early retrievals of highly cross-linked and conventional polyethylene tibial inserts

Retrieved tibial liners of highly cross-linked and conventional polyethylene were examined for articular and backside surface damage. Surfaces were graded for pitting, machine-mark loss, scratching, abrasion, delamination, and embedded debris. Whereas no difference existed in the damage score for the 2 groups, the highly crosslinked group showed significantly less elimination of machine marks. Wear, surface plastic deformation, or a combination, could account for the damage on these components. Only 1 of the highly crosslinked polyethylene inserts was available for destructive testing. That insert was melted to activate the shape memory, and thus differentiate, between wear versus plastic deformation. Nearly all changes on the articular and backside surfaces disappeared upon melting, and original machining marks reappeared, suggesting that the surface changes for that component were primarily the result of plastic deformation and not material removal.

Polyethylene wear particles in synovial fluid after total knee arthroplasty

The aims of the current study were to examine polyethylene particles in synovial fluid at an early stage, and to compare a newly introduced medial pivot total knee prosthesis with an established posterior-stabilized total knee prosthesis. Synovial fluid was obtained 1 year after knee arthroplasty from 17 patients with well-functioning prostheses (22 knees, 11 posterior-stabilized prostheses and 11 medial pivot prostheses) under complete sterile conditions. Polyethylene particles were isolated and analyzed by scanning electron microscopy. Particle size (equivalent circle diameter) was 0.78 +/- 0.08 microm (mean +/- standard error) in posterior-stabilized prostheses and 0.67 +/- 0.06 microm in medial pivot prostheses. Particle shape (aspect ratio) was 2.30 +/- 0.22 in posterior-stabilized prostheses and 1.90 +/- 0.16 in medial pivot prostheses. The total numbers of particles were 1.16 +/- 0.57 x 10(8) in posterior-stabilized prostheses and 9.01 +/- 2.95 x 10(6) in medial pivot prostheses. Particles were smaller and rounder in medial pivot prostheses than in posterior-stabilized prostheses, but the differences were not significant. The difference in the common logarithm of particle number was significant. The medial pivot prosthesis generated less wear particles than the posteriorstabilized prosthesis, and these findings may have an impact on the incidence of osteolysis and aseptic loosening.

The incidence of revision of the metal component of total knee arthroplasties in different tibial-insert designs

Seventy-one revisions of knee arthroplasty due to wear of modular tibial polyethylene inserts undertaken from May 1990 to May 1999 were reviewed. In 38 cases (53.5%), severe damage was noted that necessitated replacement of the metal components. This proportion was less than in a previous study (88.7%). All the cases were further divided into two groups based on the design of the tibial component, one group having mobile bearings and the other fixed. In only 17.7% of the mobile group was there a need to replace metal parts at revision, whereas 83.8% of the fixed group required such replacement, which is much more comparable to the previous study. Therefore, the incidence of revision of the metallic component of a total knee arthroplasty depends greatly on the design of the tibial components.

In vitro kinematic patterns are similar for a fixed platform and a mobile bearing prosthesis

In vitro dynamic simulation of knee flexion was performed to quantify knee kinematics for a mobile bearing prosthesis that allows the tibial insert to translate and rotate with respect to the baseplate. Six cadaver knees were tested in the intact state, after implanting a fixed platform prosthesis, and after implanting a mobile bearing prosthesis. The mobile bearing prosthesis significantly increased the tibial internal rotation and medial shift compared with the intact knee, near 90 degrees of flexion. Both prostheses increased the patellar medial shift near 90 degrees of flexion. The patellar flexion was significantly larger for the mobile bearing prosthesis than for the fixed platform prosthesis for most of flexion. Motion of the insert with respect to the baseplate may have contributed to the variations in tibiofemoral kinematics, whereas tibiofemoral kinematic changes influenced the patellofemoral kinematics. Although the kinematics were similar for the 2 types of prosthesis, the possibility of complications related to increased patellar flexion and backside wear of the tibial insert should be considered.

The effect of malalignment on stresses in polyethylene component of total knee prostheses--a finite element analysis

OBJECTIVE

To investigate the effects of malalignment on stresses in tibial polyethylene component of total knee prostheses.

DESIGN

A three-dimensional finite element analysis was used to calculate the contact stress and von Mises stress in the tibial polyethylene component subjected to a compressive load, and the malalignment situations were simulated.

BACKGROUND

Many biomechanical studies to investigate the stresses in tibial polyethylene component were assumed at the ideal contact alignment. The effect of malalignment on stresses in tibial polyethylene component was not investigated extensively.

METHODS

Three-dimensional finite element models of the tibiofemoral joint of knee prostheses for three different designs were constructed. Three malalignment conditions including the medial translation (0.25, 0.5 and 1.0 mm), internal rotation (1 degree, 3 degree and 5 degree), and varus tilt (1 degree, 3 degree and 5 degree) of the femoral component relative to the tibial component were simulated. A compression load of 3000 N was applied to the tibiofemoral joint at 0 degree of flexion. The maximum contact stress and von Mises stress in the tibial component were compared to investigate the effects of malalignment.

RESULTS

In comparing with the neutral position, the greatest increase of maximum contact stress were 67.6%, 14.3% and 145.9% and the greatest increase of maximum von Mises stress were 92.5%, 22.7% and 120.6% in maltranslation, internal rotation and varus tilt simulations, respectively.

CONCLUSION

The greatest increase of contact stress and von Mises stress was occurred in the high conformity flat-on-flat design of knee prosthesis under the severest malalignment condition. The high conformity curve-on-curve design of knee prosthesis has the minimal risk of polyethylene wear under the malalignment conditions.

RELEVANCE

This study revealed the importance of malalignment effect on stresses in tibial polyethylene component. Polyethylene wear in surface replacement total knees will be minimal when a high conformity curve-on-curve knee design is used and the rotational line between the femoral and tibial components has the least effect on polyethylene wear but varus/valgus malalignment, even with the best designed prosthesis will still accelerate wear.

Fractured Whiteside Ortholoc II knee components

A comprehensive failure analysis was performed on 6 femoral components and 1 tibial component that fractured in service. All were Whiteside Ortholoc II total knee arthroplasty components, manufactured from cast cobalt-chromium-molybdenum alloy and porous coated. Fracture surface analysis revealed fatigue-induced failure in all cases. Most fractures occurred at regions of high stress concentration, such as sharp corners, sintered beads, and thin sections. Metallurgical examination showed significant variation in grain size, interdendritic carbides, and hardness between samples. In some cases, continuous carbide networks and voids were prominent at the bead-substrate interface. Patient weight and surgical placement were identified as contributory factors in component failure. Limitations of cast cobalt-chromium-molybdenum alloy in weight-bearing applications must be emphasized, particularly when important determinants, such as design, metallurgy, and specific clinical factors, are less than optimal.