Pathologic supracondylar fracture due to osteolytic pseudotumor of knee following cementless total knee replacement

Large Soft-tissue Mass Formation After Revision Total Knee Arthroplasty: An Unusual Case of Adverse Reaction to Metal Debris and Review of the Literature

We report about the rare case of a patient who developed large soft-tissue mass formations related with revision total knee arthroplasty which was implanted 4 years prior. Owing to suspected periprosthetic joint infection, the prosthesis was removed and the lesions were resected, resulting in severe soft-tissue loss and temporary arthrodesis using a poly(methyl methacrylate) spacer. Histological analysis revealed a type VI periprosthetic membrane. The situation was further complicated by wound infection requiring multiple revision surgeries. After discussion and evaluation of the available treatment options, the decision for an above-the-knee amputation was made. The tissue reaction resulting in these soft-tissue lesions is referred to as an “adverse local tissue reaction.” Wear-induced lesions after total knee arthroplasty, especially of this magnitude, are very rare and difficult to treat.

Two Cases of Polyethylene Granuloma After Distal Femoral Endoprosthesis With All-Polyethylene Tibia

Limited literature exists on complications specific to the all-polyethylene tibial component in distal femoral replacement (DFR). Unlike in primary arthroplasty with polyethylene components, polyethylene granuloma has not been reported in DFR with an all-polyethylene tibia. Here, we report 2 cases of polyethylene granuloma in patients with primary bone sarcoma who underwent DFR with an all-polyethylene tibia. Radiologically, evidence of intraosseous granuloma formation and periprosthetic osteolysis was observed at the anterior tibial metaphysis. Both patients underwent an operative debridement of polyethylene granuloma and necrotic tissues, followed by a revision to a long-stem, cemented metal-backed tibia with impacted allograft to fill the defect. Polyethylene granuloma should be considered a differential diagnosis in the presence of a periprosthetic lytic lesion after DFR with an all-polyethylene tibial component.

Vitamin E-infused highly cross-linked polyethylene did not reduce the number of in vivo wear particles in total knee arthroplasty

AIMS

Vitamin E-infused highly cross-linked polyethylene (E1) has recently been introduced in total knee arthroplasty (TKA). An in vitro wear simulator study showed that E1 reduced polyethylene wear. However there is no published information regarding in vivo wear. Previous reports suggest that newly introduced materials which reduce in vitro polyethylene wear do not necessarily reduce in vivo polyethylene wear. To assist in the evaluation of the newly introduced material before widespread use, we established an in vivo polyethylene wear particle analysis for TKA. The aim of this study was to compare in vivo polyethylene wear particle generation between E1 and conventional polyethylene (ArCom) in TKA.

METHODS

A total of 34 knees undergoing TKA (17 each with ArCom or E1) were investigated. Except for the polyethylene insert material, the prostheses used for both groups were identical. Synovial fluid was obtained at a mean of 3.4 years (SD 1.3) postoperatively. The in vivo polyethylene wear particles were isolated from the synovial fluid using a previously validated method and examined by scanning electron microscopy.

RESULTS

The total number of polyethylene wear particles obtained from the knees with E1 (mean 6.9, SD 4.0 × 10⁷ counts/knee) was greater than that obtained from those with ArCom (mean 2.2, SD 2.6 × 10⁷ counts/knee) (p = 0.001). The particle size (equivalent circle of diameter) from the knees with E1 was smaller (mean 0.5 μm, SD 0.1) than that of knees with ArCom (mean 1.5, SD 0.3 μm) (p = 0.001). The aspect ratio of particles from the knees with E1 (mean 1.3, SD 0.1) was smaller than that with ArCom (mean 1.4, SD 0.1) (p < 0.001 ).

CONCLUSION

This is the first report of in vivo wear particle analysis of E1. E1 polyethylene did not reduce the number of in vivo polyethylene wear particles compared with ArCom in early clinical stage. Further careful follow-up of newly introduced E1 for TKA should be carried out. Cite this article: Bone Joint J 2020;102-B(11):1527-1534.

Massive osteolysis due to galvanic corrosion after total knee arthroplasty: a rare cause for early revision?

A 66-year-old male underwent a total knee arthroplasty for osteoarthritis after previous anterior cruciate ligament (ACL) reconstruction. Seven years postoperatively, a symptomatic large lytic lesion was present surrounding the tibial stem. A titanium interference screw, which was used prior to fixate the Anterior Cruciate Ligament (ACL) graft, was in direct contact with the tibial component. Galvanic corrosion may have attributed to the development of the lytic lesion. It is advised to remove any metal hardware in the vicinity of joint prosthesis in order to prevent a possible galvanic corrosive reaction.

Popliteal Skin Lesion due to Wear Disease in Total Knee Arthroplasty: A Case Report

CASE

An 87-year-old woman presented with a popliteal skin lesion due to polyethylene wear 13 years following a left total knee arthroplasty. Excisional biopsy through a posterior approach was performed. Histology showed inflammation with granulomas and birefringent foreign body particles in the skin. Cultures remained negative, and revision knee arthroplasty was performed.

CONCLUSIONS

A popliteal skin lesion due to polyethylene wear disease in total knee arthroplasty has not previously been described. Patients with an atypical inflammation of the skin with an underlying joint implant should be referred to an orthopaedic surgeon, and dermal biopsies should be checked for birefringent material.

LEVEL OF EVIDENCE

Level V.

Sequentially annealed highly cross-linked polyethylene reduced in vivo wear particle generation in total knee arthroplasty

INTRODUCTION

Sequentially annealed highly cross-linked polyethylene (HXLPE) was recently introduced to reduce the wear in total knee arthroplasty (TKA). However, an in vivo advantage of sequentially annealed HXLPE on wear particle generation is still controversial. The purpose of this study is to compare the characteristics of in vivo wear particles between sequentially annealed HXLPE and conventional polyethylene after TKA.

MATERIALS AND METHODS

Synovial fluid was obtained from the eight knees with sequentially annealed HXLPE and from eight knees with conventional polyethylene 12 months after the operation. Polyethylene particles were isolated and examined using a scanning electron microscope and image analyzer.

RESULTS

Total number of wear particles in each knee was 2.1 ± 1.0 × 10⁷ with sequentially annealed HXLPE (mean ± standard deviation) and 4.9 ± 3.6 × 10⁷ with conventional polyethylene ( p = 0.036). Particle size (equivalent circle diameter) was 1.01 ± 0.26 μm with sequentially annealed HXLPE and 1.02 ± 0.20 μm with conventional polyethylene ( p = 0.674). Aspect ratio was 1.33 ± 0.04 with sequentially annealed HXLPE and 1.39 ± 0.10 with conventional polyethylene ( p = 0.462).

CONCLUSIONS

The sequentially annealed HXLPE reduced the in vivo polyethylene wear particles by 58% compared with conventional polyethylene without the significant change of particle size and shape.

Proposed ICDRG Classification of the Clinical Presentation of Contact Allergy

The International Contact Dermatitis Research Group proposes a classification for the clinical presentation of contact allergy. The classification is based primarily on the mode of clinical presentation. The categories are direct exposure/contact dermatitis, mimicking or exacerbation of preexisting eczema, multifactorial dermatitis including allergic contact dermatitis, by proxy, mimicking angioedema, airborne contact dermatitis, photo-induced contact dermatitis, systemic contact dermatitis, noneczematous contact dermatitis, contact urticaria, protein contact dermatitis, respiratory/mucosal symptoms, oral contact dermatitis, erythroderma/exfoliative dermatitis, minor forms of presentation, and extracutaneous manifestations.

Comparison of in vivo polyethylene wear particles between mobile- and fixed-bearing TKA in the same patients

PURPOSE

Polyethylene wear particle generation is one of the most important factors that affects the mid- to long-term results of total knee arthroplasties (TKA). Mobile-bearing total knee prostheses were developed to reduce polyethylene wear generation. However, whether mobile-bearing prostheses actually generate fewer polyethylene wear particles than fixed-bearing prostheses remains controversial. The aim of this study was to compare, within individual patients, the in vivo polyethylene wear particles created by a newly introduced mobile-bearing prosthesis in one knee and a conventional fixed-bearing prosthesis in other knee.

METHODS

Eighteen patients receiving bilateral TKAs to treat osteoarthritis were included. The synovial fluid was obtained from 36 knees at an average of 3.5 years after the operation. The in vivo polyethylene wear particles were isolated from the synovial fluid using a previously validated method and examined using a scanning electron microscope and an image analyser.

RESULTS

The size and shape of the polyethylene wear particles from the mobile-bearing prostheses were similar to those from the conventional fixed-bearing prostheses. Although the number of wear particles from the mobile-bearing prosthesis (1.63 × 10⁷ counts/knee) appeared smaller than that from the fixed-bearing prosthesis (2.16 × 10⁷ counts/knee), the difference was not statistically significant.

CONCLUSIONS

The current in vivo study shows that no statistically significant differences were found between the polyethylene wear particles generated by a newly introduced mobile-bearing PS prosthesis and a conventional fixed-bearing PS prosthesis during the early clinical stage after implantation.

LEVEL OF EVIDENCE

Therapeutic study, Level III.

Periprosthetic fractures of the distal femur after total knee arthroplasty : Plate versus nail fixation

The incidence of periprosthetic fractures about a TKA is increasing. Traditionally, these fractures are classified by their location and prosthesis integrity. In the setting of a supracondyar fracture about a well-fixed prosthesis, both plate and nail fixation of the fracture present themselves as options, each with unique benefits and pitfalls. Through review and discussion of the literature, we aim to describe some of the patient, fracture, and implant related factors that should be considered when planning fixation of periprosthetic fractures about a TKA. Additionally, we present several technical pearls that may be useful in the successful treatment of these difficult injuries.

LEVEL OF EVIDENCE

4.

Metal wear-induced pseudotumour following an endoprosthetic knee replacement for Ewing sarcoma

Pseudotumours are well recognised as a complication of metal-on-metal hip arthroplasties and are thought to develop on the basis of an innate and adaptive immune response to cobalt-chrome (Co-Cr) wear particles. We report a case of a large pseudotumour that developed following a knee endoprosthetic replacement (EPR) undertaken for Ewing sarcoma. The lesion contained necrotic and degenerate connective tissue in which there were numerous scattered metal wear-containing macrophages, eosinophil polymorphs, lymphocytes, plasma cells and aseptic lymphocyte-dominated vascular-associated lesion-like lymphoid aggregates. Metal ion levels were elevated. No evidence of infection or tumour was noted and it was concluded that the lesion was most likely an inflammatory pseudotumour developing on the basis of an innate and adaptive immune response to components of Co-Cr metal wear derived from the knee EPR.

A rare case of pseudotumor formation associated with methyl methacrylate hypersensitivity in a patient following cemented total knee arthroplasty

Hypersensitivity to orthopedic implant materials has been well documented with potential catastrophic consequences if not addressed pre-operatively. The spectrum of reactions is wide, from mild non-specific pain with localized erythema to severe periprosthetic inflammatory destruction and pseudotumor formation. It is therefore essential to identify patients who have or are at risk for implant-associated hypersensitivity. Although metal sensitivity is commonly cited as the cause of these reactions, methyl methacrylate (MMA) has rarely been implicated. To the best of our knowledge, methyl methacrylate-associated pseudotumor formation has not yet been described. The following is a case report of a 68-year-old female who, after undergoing a routine cemented right total knee arthroplasty, developed a painless, enlarging mass during a 13-year period. This mass was found to be a pseudotumor in association with methyl methacrylate hypersensitivity. A review of pseudotumor pathogenesis, methyl methacrylate hypersensitivity, and preoperative preventative care is discussed.

Analysis of friction between articular cartilage and polyvinyl alcohol hydrogel artificial cartilage

Many biomaterials are being used to repair damaged articular cartilage. In particular, poly vinyl alcohol hydrogel has similar mechanical properties to natural cartilage under compressive and shearing loading. Here, three-factor and two-level friction experiments and long-term tests were conducted to better evaluate its tribological properties. The friction coefficient between articular cartilage and the poly vinyl alcohol hydrogel depended primarily on the three factors of load, speed, and lubrication. When the speed increased from 10 to 20 mm/s under a load of 10 N, the friction coefficient increased from 0.12 to 0.147. When the lubricant was changed from Ringer's solution to a hyaluronic acid solution, the friction coefficient decreased to 0.084 with loads as high as 22 N. The poly vinyl alcohol hydrogel was severely damaged and lost its top surface layers, which were transferred to the articular cartilage surface. Wear was observed in the surface morphologies, which indicated the occurrence of surface adhesion of bovine cartilage. Surface fatigue and adhesive wear was the dominant wear mechanism.

No difference in in vivo polyethylene wear particles between oxidized zirconium and cobalt-chromium femoral component in total knee arthroplasty

PURPOSE

Polyethylene wear particle generation is one of the most important factors affecting mid- to long-term results of total knee arthroplasties. Oxidized zirconium was introduced as a material for femoral components to reduce polyethylene wear generation. However, an in vivo advantage of oxidized zirconium on polyethylene wear particle generation is still controversial. The purpose of this study was to compare in vivo polyethylene wear particles between oxidized zirconium total knee prosthesis and conventional cobalt-chromium (Co-Cr) total knee prosthesis.

METHODS

Synovial fluid was obtained from the knees of 6 patients with oxidized zirconium total knee prosthesis and from 6 patients with conventional cobalt-chromium (Co-Cr) total knee prosthesis 12 months after the operation. Polyethylene particles were isolated and examined using a scanning electron microscope and image analyser.

RESULTS

Total number of particles in each knee was 3.3 ± 1.3 × 10(7) in the case of oxidized zirconium (mean ± SD) and 3.4 ± 1.2 × 10(7) in that of Co-Cr (n.s.). The particle size (equivalent circle diameter) was 0.8 ± 0.3 μm in the case of oxidized zirconium and 0.6 ± 0.1 μm in that of Co-Cr (n.s.). The particle shape (aspect ratio) was 1.4 ± 0.0 in the case of oxidized zirconium and 1.4 ± 0.0 in that of metal Co-Cr (n.s).

CONCLUSIONS

Although newly introduced oxidized zirconium femoral component did not reduce the in vivo polyethylene wear particles in early clinical stage, there was no adverse effect of newly introduced material. At this moment, there is no need to abandon oxidized zirconium femoral component. However, further follow-up of polyethylene wear particle generation should be performed to confirm the advantage of the oxidized zirconium femoral component.

LEVEL OF EVIDENCE

Therapeutic study, Level III.

Treatment for Wear and Osteolysis in Well-Fixed Uncemented TKR

Background. Traditionally, osteolysis around total knee replacements (TKRs) is treated with complete revision. In certain subsets, polyethylene insert exchange and bone grafting may be applicable. This study reports the clinical outcomes for selective bone grafting in patients with osteolysis without complete revision of the TKR. Methods. This retrospective study analyzes 10 TKRs (9 patients, 66.5 ± 6.1 years old) presenting with osteolysis and revised after 8.7 ± 1.9 years of in vivo function. At index TKR, all patients were implanted with uncemented prosthesis and modular polyethylene insert with anteroposterior articular constraint (Ultracongruent, Natural Knee II, Sulzer Medica). The surgical technique for treating the osteolysis included removal of necrotic bone tissue using curettage, filling of the defect with bone graft materials, and polyethylene insert exchange. Results. Patients have not exhibited any further complications associated with osteolysis after 5.1 ± 2.4 years of followup. Routine radiographic exams show total incorporation of the graft material into the previously lytic regions in all patients. Conclusion. In some TKRs with osteolysis and firmly fixed components, the removal of lytic tissue and subsequent defect filling with bone graft materials can be a viable solution. This case series shows complete resolution of osteolysis in all patients with no complications.

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.

Cutaneous and systemic hypersensitivity reactions to metallic implants

Cutaneous reactions to metal implants, orthopedic or otherwise, are well documented in the literature. The first case of a dermatitis reaction over a stainless steel fracture plate was described in 1966. Most skin reactions are eczematous and allergic in nature, although urticarial, bullous, and vasculitic eruptions may occur. Also, more complex immune reactions may develop around the implants, resulting in pain, inflammation, and loosening. Nickel, cobalt, and chromium are the three most common metals that elicit both cutaneous and extracutaneous allergic reactions from chronic internal exposure. However, other metal ions as well as bone cement components can cause such hypersensitivity reactions. To complicate things, patients may also develop delayed-type hypersensitivity reactions to metals (ie, in-stent restenosis, prosthesis loosening, inflammation, pain, or allergic contact dermatitis) following the insertion of intravascular stents, dental implants, cardiac pacemakers, or implanted gynecologic devices. Despite repeated attempts by researchers and clinicians to further understand this difficult area of medicine, the association between metal sensitivity and cutaneous allergic reactions remains to be fully understood. This review provides an update of the current knowledge in this field and should be valuable to health care providers who manage patients with conditions related to this field.

The risk of peri-prosthetic fracture after primary and revision total hip and knee replacement

Peri-prosthetic fracture after joint replacement in the lower limb is associated with significant morbidity. The primary aim of this study was to investigate the incidence of peri-prosthetic fracture after total hip replacement (THR) and total knee replacement (TKR) over a ten-year period using a population-based linked dataset.

Between 1 April 1997 and 31 March 2008, 52 136 primary THRs, 8726 revision THRs, 44 511 primary TKRs, and 3222 revision TKRs were performed. Five years post-operatively, the rate of fracture was 0.9% after primary THR, 4.2% after revision THR, 0.6% after primary TKR and 1.7% after revision TKR. Comparison of survival analysis for all primary and revision arthroplasties showed peri-prosthetic fractures were more likely in females, patients aged > 70 and after revision arthroplasty.

Female patients aged > 70 should be warned of a significantly increased risk of peri-prosthetic fracture after hip or knee replacement. The use of adjuvant medical treatment to reduce the effect of peri-prosthetic osteoporosis may be a direction of research for these patients.

Total hip replacement pseudotumoral osteolysis

We report three cases of pseudotumoral lesion secondary to total hip replacement using metal on polyethylene bearings, presenting two distinct macroscopic aspects: (a) classic inflammatory granuloma and, in one case, (b) onset of hematoma associated with gluteal vessel lesions, probably affected by the pseudotumoral process. Diagnosis was radiographic, with CT-scan serving to confirm and, more importantly, to reveal extension and analyze surrounding tissue. Arteriography is needed when the lesion is liquid, and biopsy may be envisaged depending upon the clinical situation. In all three cases, histology was typically that of granulomatous lesions related to wear debris. Once diagnosis could be established, treatment was similar in both presentations, with surgical revision, which should be as early as possible in case of cortical bone involvement, to prevent pathologic fracture.

Influence of dynamic load on friction behavior of human articular cartilage, stainless steel and polyvinyl alcohol hydrogel as artificial cartilage

Many biomaterials are being developed to be used for cartilage substitution and hemiarthroplasty implants. The lubrication property is a key feature of the artificial cartilage. The frictional behavior of human articular cartilage, stainless steel and polyvinyl alcohol (PVA) hydrogel were investigated under cartilage-on-PVA hydrogel contact, cartilage-on-cartilage contact and cartilage-on-stainless steel contact using pin-on-plate method. Tests under static load, cyclic load and 1 min load change were used to evaluate friction variations in reciprocating motion. The results showed that the lubrication property of cartilage-on-PVA hydrogel contact and cartilage-on-stainless steel contact were restored in both 1 min load change and cyclic load tests. The friction coefficient of PVA hydrogel decreased from 0.178 to 0.076 in 60 min, which was almost one-third of the value under static load in continuous sliding tests. In each test, the friction coefficient of cartilage-on-cartilage contact maintained far lower value than other contacts. It is indicated that a key feature of artificial cartilage is the biphasic lubrication properties.

Wear debris pseudotumor following total knee arthroplasty: a case report

INTRODUCTION

In patients who have undergone a total joint replacement, any mass occurring in or adjacent to the joint needs thorough investigation and a wear debris-induced cyst should be suspected.

CASE PRESENTATION

An 81-year-old man presented with a painful and enlarging mass at the popliteal fossa and calf of his right knee. He had had a total right knee replacement seven years previously. Plain radiographs showed narrowing of the medial compartment. Magnetic resonance imaging showed a cystic lesion at the postero-medial aspect of the knee joint mimicking popliteal cyst or soft tissue sarcoma. Fine needle aspiration was non-diagnostic. A core-needle biopsy showed metallosis. Intraoperative findings revealed massive metallosis related to extensive polyethylene wear, delamination and deformation. Revision knee and patella arthroplasty was carried out after a thorough debridement of the knee joint.

CONCLUSION

Long-term follow-up is critical for patients with total joint replacement for early detection of occult polyethylene wear and prosthesis loosening. In these cases, revision arthroplasty may provide a satisfactory knee function.

In vivo comparison of wear particles between highly crosslinked polyethylene and conventional polyethylene in the same design of total knee arthroplasties

Reduction of wear with highly crosslinked polyethylene (HXLPE) has been reported in in vitro and in vivo studies of total hip prostheses. However, use of HXLPE in total knee prostheses is still controversial. The aim of this study was to compare in vivo polyethylene wear particle generation of HXLPE with that of conventional polyethylene in total knee prostheses of the same design. Synovial fluid was obtained from four knees with HXLPE inserts and three knees with conventional polyethylene inserts at 1 year after operation. Polyethylene particles were isolated and examined using a scanning electron microscope and image analyzer. The total number of particles in each knee was 0.28 +/- 0.12 x 10(6) in HXPLE group (mean +/- standard error) and 6.87 +/- 2.85 x 10(6) in conventional polyethylene group (p = 0.040). Particle size (equivalent circle diameter) was 0.64 +/- 0.07 microm in HXPLE group and 1.21 +/- 0.21 microm in conventional polyethylene group (p = 0.030). Particle shape (aspect ratio) was 1.33 +/- 0.10 in HXLPE and 1.88 +/- 0.19 in conventional polyethylene (p = 0.035). Thepercentage of particles of submicron size was greater than 90% in HXLPE group and 55% in conventional polyethylene group. Except for the material of the polyethylene insert, the design and material of prostheses were completely the same in both groups. The HXLPE insert generated fewer, smaller, and rounder polyethylene wear particles than the conventional polyethylene insert in the early stage after surgery.

Periprosthetic knee fractures

Fractures of the distal femur, proximal tibia, and patella that occur adjacent to a total knee replacement may be very difficult to treat. Fixation options are compromised because of the short articular segment, frequent comminution, pre-existing osteoporosis, previous surgical incisions, and the presence of the knee implant itself. This review article summarizes current concepts regarding the incidence, classification, treatment options, and outcomes for periprosthetic fractures of the knee.

Distal leg wear debris mass from a rotating hinged knee prosthesis

An 18-year-old woman presented with a gradually increasing distal leg mass 8 years after wide resection for an osteosarcoma and reconstruction of the proximal left tibia with a rotating hinged knee megaprosthesis. Open biopsy of the distal leg mass showed necrobiotic tissue, metallosis, fibroblasts, osteoblasts, histiocytes, and multinucleated giant cells. The patient underwent debridement of the distal leg mass, metallosis, and wear debris surrounding the tibial component, followed by revision of the destructed polyethylene-bearing components. At the latest follow-up, 4 years after the revision surgery, the patient is alive and tumor-free, asymptomatic, and has no clinical or imaging evidence of wear and metallosis.

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.

Periprosthetic fractures after total knee arthroplasties

The management of periprosthetic fracture around the knee remains a challenging problem. The objective of this article was to review the general concepts, treatment algorithms, and the overall treatment outcomes of femoral and tibial periprosthetic fractures after total knee arthroplasty. This article aimed to highlight the deficiencies of the current classification systems that fail to provide a guideline for selection of appropriate treatment options. We proposed a new classification system for periprosthetic femoral fractures that takes into account the status of the prosthesis, the quality of distal bone stock, and the reducibility of the fracture. Type I fractures are those occurring in patients with good bone stock with the prosthesis being fixed and well positioned. Type IA fractures are either nondisplaced or easily reducible and can be treated conservatively. Type IB fractures are irreducible and require reduction and internal fixation. Type II fractures are defined as those occurring also in patients with good bone stock and being reducible, but either the components are loose or malpositioned. These fractures are treated by revision arthroplasty. Type III fractures are reducible or irreducible fractures that occur in patients with poor bone stock and in the vicinity of loose or malpositioned components. These fractures are treated by distal femoral replacement.

LEVEL OF EVIDENCE

Therapeutic study, level V (expert opinion). See Guidelines for Authors for a complete description of levels of evidence.

Polyethylene wear particle generation in vivo in an alumina medial pivot total knee prosthesis

Polyethylene wear particle generation is one of the most important factors affecting mid- to long-term results of total knee arthroplasties. It has been reported that the medial pivot total knee prosthesis (MP) design and alumina ceramic femoral component reduce polyethylene wear. The aim of this study is to evaluate in vivo polyethylene wear particle generation in the newly introduced alumina MP, in comparison with a metal MP. Synovial fluid was obtained from 11 knees with alumina MP and 15 knees with metal MP at nine months after the operation. Polyethylene particles were isolated, and examined using scanning electron microscope and image analyzer. Total number of particles in each knee was 7.10+/-2.86x10(6) in alumina (mean+/-standard error), and 5.70+/-2.82x10(7) in metal MP (p=0.048). Particle size (equivalent circle diameter) was 0.78+/-0.04 microm in alumina, and 0.66+/-0.06 microm in metal MP (p=0.120). Particle shape (aspect ratio) was 1.52+/-0.05 in alumina, and 1.88+/-0.11 in metal MP (p=0.014). Apart from the femoral component, the material and manufacturing method of polyethylene insert differed between the two groups, although the sterilization method was the same. Alumina MP generated fewer and rounder polyethylene wear particles than metal MP in early clinical stage, and could potentially reduce prevalence of osteolysis and aseptic loosening.

Characteristics of polyethylene wear particles isolated from synovial fluid after mobile-bearing and posterior-stabilized total knee arthroplasties

The size, shape, and number of polyethylene wear particles found in synovial fluids of patients 1 year after implantation of 22 well-functioning total knee prostheses (11 contemporary mobile-bearing type, 11 posterior-stabilized type) were determined. Polyethylene wear particles were isolated from synovial fluids and examined by scanning electron microscopy. Particle size (equivalent circle diameter) was 0.81 +/- 0.12 microm (mean +/- standard error) in mobile-bearing types and 0.78 +/- 0.08 microm in posterior-stabilized types. Particle shape (aspect ratio) was 1.94 +/- 0.13 in mobile-bearing types and 2.30 +/- 0.22 in posterior-stabilized types. Total numbers of particles were (1.75 +/- 1.02) x 10(8) in mobile-bearing and (1.16 +/- 0.57) x 10(8) in posterior-stabilized types. The differences in these parameters between the two groups were not statistically significant. In the early stages after surgery, contemporary mobile-bearing types were comparable to posterior-stabilized types in terms of polyethylene wear-particle generation. The present results do not support the proposition that has been put forward in the literature; namely, that the contemporary mobile-bearing design has an advantage, in terms of the polyethylene wear rate. These data suggest that the advantage of complete conformity in the femoro-tibial articulating surface of contemporary mobile-bearing design may be offset by wear of the mobile undersurface and slot, apart from the articulating surface.

Wear debris-induced pseudotumour in a cemented total knee replacement

We present a case of wear debris-induced osteolysis around the tibial component of a cemented total knee replacement associated with an expansile pseudotumour in the head of the fibula.