CHAPTER 24

Aseptic Wolfgang Fitz and Richard D. Scott

septic effusions are occasionally seen after total knee particulate cement debris, or hypersensitivity allergic Aarthroplasty, but their source is not well understood. reactions. Effusions immediately following total knee fluid cell analysis is based on without (TKA) gradually disappear several weeks or a few months implants, based on the guidelines published by the Amer- after , and even though frequent, they raise no ican College of Rheumatology8–10 (Table 24.1). It is con- significant clinical concern. A new onset of an effusion sidered to be normal with a white blood cell count (WBC) beyond the postoperative period of 1 year or more is of less than 200/mL, and less than 25% polymorphonu- infrequent and raises clinical concern. clear leukoctyes (PML).11 Osteoarthritic patients (nonin- Some minimal effusions occur gradually, most of the flammatory, group I) may have a WBC of <2000/ml with time without other symptoms, and may not even be <25% PML to be considered as normal, whereas inflam- noticed by the patient. The time between surgery and the matory (group II), such as rheumatoid, gouty, or onset of an effusion varies, and problems related to poly- pseudogouty arthritis, can have WBC ranging between ethylene wear increase with time. Several technical issues 2000 and 50000/mL with >50% PML, whereas the crite- that require consideration may play a role in accelerated ria for septic synovial fluid would be WBC >50000/ml polyethylene wear: the quality of polyethylene; the steril- with >75% of PML. The amount of WBC in inflamma- ization method;1–4 its shelf-life;5 the use of extruded versus tory arthritis is not associated with accelerated press-molded polyethylene;6 its thickness; third body degradation in normal joints.12 It has been shown that wear; mechanical problems that may lead to increased these guidelines apply for failed aseptic TKA, too.11 wear, such as backside wear; and designs that are too con- The most important differential diagnosis of an effu- forming, among others. Misalignment of components sion is , which must be ruled out in every case. and tissue balancing play important roles and have to be Aspiration of these joints provides easy access for further considered as contributors to excessive wear. Therefore, diagnostic studies and should be combined with basic the joint aspirate should be examined in addition to the blood workup and other diagnostic workups. The most normal work-up with polarized light microscopy for important differential diagnoses include and polyethylene wear debris.7 pseudogout. A significant challenge in TKA is the diag- However, catastrophic failures due to poor poly- nosis of a low-grade infection, in which aspirates remain ethylene quality, poor implant designs, or poor surgical aseptic. techniques usually represent no diagnostic but rather a surgical challenge. Some effusions have an acute onset with or without a LOW-GRADE INFECTION history of trauma. Some are accompanied by pain and some by a change in stability or alignment. The combi- The combination of pain and aseptic effusion should raise nation of effusion with pain and a change in alignment suspicion of an infection, which is sometimes difficult to is related to the loosening of the implant and is easy to diagnose. Whereas the diagnosis of an acute infection is diagnose. So far, no specific markers have been described relatively easy, based on the acute onset of effusion, for specific diagnosis, such as inflammation, metallosis, redness, swelling, systemic infectious symptoms (see

258 Chapter 24: Aseptic Synovitis 259

TABLE 24.1. Standard Workup for Aseptic Synovitis In addition to aspirate analyses, the serum level of Includes Serum Tests, Analysis of , and WBC, the determination of C-reactive protein levels, and Radiography. bone scans, among other analyses, may not significantly 11 Blood test improve the sensitivity of a suspected infected TKR. Erythrocyte sedimentation rates However, the combination of all these measures have not White blood cell counts been studied yet. C-reactive protein levels A low-grade infection may be present with an aseptic Synovial fluid analysis Aerobic and anaerobic cultures effusion. Microbial colonies produce a carbohydrate-rich Fungus cultures biofilm that encases the bacteria on the surface of the bio- Gram’s staining material, dispersing over the surface and between the Leukocyte counting implant-bone interface. The infectious process with clin- Glucose and protein level ical symptoms and positive aspirates does not start before Crystals Polarized light microscopy for polyethylene wear debris the bacteria leave the surface of the biomaterial and Radiographic analysis invade surrounding tissue, specifically bone tissue, Radiography thereby provoking local osteomyelitis. Sooner or later the Scintigraphy bacteria come into contact with the synovial fluid; the Gallium aspirate may become positive at this point. However, it Indium Technetium may take months or even years before the infection becomes manifest. During this phase, the synovial fluid may remain free of bacteria and testing may produce Chapter 16 for discussion) a low-grade infection may not false-negative test results. present with classical symptoms but rather with aseptic The contamination of the culture media, also may effusion and different levels of pain. Laboratory studies, lead to a false-positive diagnosis. Culture of both tissue including complete blood cell count, sedimentation rate, and synovial fluid may help reduce false-positive results. and C-reactive protein are useful in evaluating a suspected Repetitive aspirations every 2 to 4 weeks without the infected total .13,14 Synovial fluid cul- administration of antibiotics are recommended, but it tures and white blood cell counts, including its differ- remains unclear when arthroscopic or open-tissue ential are commonly performed. The literature has sampling should be performed. demonstrated reliable specificity (80%–100%), but a vari- able sensitivity of 0% to 90% for aspirations in total hip arthroplasty.15–19 The use of white blood cell counts and GOUTY SYNOVITIS its differential was found to be helpful in a series of 79 failed TKR [11]. Only eight knees showed a white blood One of the most important differential diagnoses of an cell count >2000. The authors concluded that patients acute infected TKA is gouty or pseudogouty synovitis, with a primary diagnosis of and a WBC since its treatment for this diagnosis may result in the <2000/mL and a differential of <50% PMLs of the syn- unnecessary removal of the implants. Its presentation ovial fluid had a greater than 98% negative predictive may be undistinguishable from an acute infected TKR value for excluding infection.11 with erythema, pain, redness, effusion, elevated erythro- The standard test for the detection of bacteria is cyte sedimentation rate (ESR), and fever. The crystals, , followed by a Gram’s stain testing and which are either intracellular or extracellular, are usually culture, which actually fail to detect infection in 15% or visible with light microscopy under polarized light. His- even up to 50% of such cases. The percentage of false- tological examination of synovial tissue may be necessary negative test results from standard microbiologic assays to confirm the correct diagnosis under polarized light may be reduced significantly by the use of the polymerase [22]. Both conditions reveal a high WBC count ranging chain reaction (PCR).20 PCR testing results of 32 pre- from 50000 to 100000/mL in septic synovitis and from operative aspirates were all positive, whereas standard 20000 to 80000/mL in gouty arthritis.10 In the differen- microbiologic culturing assays performed preoperative tial WBC count for septic synovitis, the percentage of and intraoperative were positive in only 15 samples. PCR polymorphonuclear (PML) cells ranges from 75% to testing yielded no false-positive results in 21 negative 100% and is usually greater that 90%,10 whereas the per- control specimens obtained from aseptic joints. PCR may centage in gouty synovitis is usually slightly lower: 60% help to identify bacteria even under antibiotic in to 90%. A careful clinical evaluation, including a medical the detection of both live and dead bacteria as recently history of previous gouty episodes, serum levels of uric shown,21 but its clinical use is still very limited. acid, assessment of the total WBC count and the PML cell 260 Revision Total Knee Arthroplasty

count, and the presence or absence of monosodium urate synovial membrane consists of two types of synovio- crystals under light microscopy may provide the correct cytes.31 Synovial macrophages (type A) remove cellular diagnosis. and particulate debris from the synovial fluid, whereas The clinical presentation of pseudogouty synovitis synovial fibroblasts (type B) repair the damage of the syn- after TKA has been described as similar to that of septic ovial membrane. The activated synovial macrophages synovitis. In a series of 50 patients with a pseudogout produce a variety of inflammatory cytokines, such as attack, 14 patients were initially suspected or misdiag- interleukin (IL-1b, IL-6), tumor necrosis factor (TNF), 23 nosed as having . Only 1 of the 50 patients interferon, and prostaglandin (PGE2). IL-1b has been showed no calcium pyrophosphate dihydrate crystals shown to increase osteoclastic activity. In a study com- (CPPD) in the synovial fluid, and arthroscopic biopsy paring 7 severely osteoarthritic knees with 20 failed total helped establish the diagnosis. Clinically, the 2 most knee replacements, the levels of IL-1b and tartrate- important clues in the differentiation to septic arthritis resistant acid phosphatase were elevated in the latter are the presence of intracellular CPPD crystals in synovial group, suggesting that wear particulates caused significant aspirates and the involvement of more than one joint.23 elevations in these cytokines.32 The absence of crystals does not exclude gouty and Various amounts and sizes of wear particles, mostly pseudogouty synovitis and septic arthritis. Gout or polyethylene particles, are generated during the normal pseudogout can occur simultaneously with septic function of a total knee replacement. The amount of par- synovitis. ticles generated increases with malalignement and exces- sive activity and is influenced by the quality of the polyethylene2,4 and implant-specific design issues. It is POLYETHYLENE WEAR unclear if the shape, size, or relative number of wear particles influence the amount of osteolysis. One study The initial clinical symptom of failure of a total knee reported a mean particle size of polyethylene debris in replacement due to wear is a painless effusion. The occur- failed total knee replacement between 200 and 300nm rence of additional pain was considered to be the crite- and observed the volume fraction differed by a factor of rion for operative intervention24 and may suggest a 2 in osteolytic and nonosteolytic cases.30 Wolfarth et al. loosening of any of the components. reported submicron-sized debris in failed total knee Failure of the patellofemoral compartment may result replacement either in the synovial fluid or in tissue in patellofemoral pain with crepitus, caused by a nonre- samples surrounding TKA with osteolysis. Others exam- placed patella, wear failure, or loosening or fracture of the ined the synovial fluid for particles larger than 5mm in patella (or a combination of each). Clinically, a flexion diameter and found three fractions in failed total knee contracture with an associated weakness of the vastus replacement: 94% consisted of globular particles with a medialis muscle should raise attention to the mean diameter of 10mm, 4% of long fibrous particles patellofemoral compartment. The combination of a tight with a mean surface area of 1164mm, and large rhom- lateral retinaculum, a malpositioned femoral (internal boidal particles with a mean surface area of 557mm rotation, too much valgus, medial positioning), malposi- regardless of the wear pattern.33 No submicron particles tioned tibial (internal rotation and medial positioning), were analyzed. Larger polyethylene particles were found and/or a patellar component malpositioning (lateral) may in failed TKR with gross polyethylene wear,29 supporting lead to an increased lateral force vector on the patella. the recommendation to analyze the joint fluid aspirate This may in combination lead to early failure of the for polyethylene wear particles.7 patellofemoral compartment. Some studies show an The clinical triad of effusion, pain, and progressive advantage of a conforming patellofemoral groove and a change in the coronal alignment of the knee is character- 3-peg oval patellar component design.25–27 A single-peg istic of accelerated polyethylene wear34 and presents no patellar design caused a high prevalence of patellar diagnostic problem for the orthopedic surgeon. The diag- fracture in one series.27 nosis is made with regular radiographs comparing imme- At least 3 components of synovial fluid can contribute diate postoperative with recent films for the detection of to periprosthetic bone resorption and aseptic loosening: component changes. A septic workup with bone scan and wear particles, soluble factors, and the physical effect of knee aspiration for WBC count, differential, and cultures synovial fluid pressure.28 Wear particles are released into is recommended and provides the diagnosis of a failed the joint fluid and are dispersed throughout the joint total knee arthroplasty. space. They cause a cellular response in the synovial The combination of effusion with or without pain is tissue, resulting in release of inflammatory enzymes and much more problematic, since the incidence of a painful in inflammatory synovitis.29,30 The single cell layer of the total knee replacement is actually higher than we assume. Chapter 24: Aseptic Synovitis 261

In a prospective study for the evaluation of pain before and after total knee replacement, after the exclusion of patients with chronic pain, the pain decreased 50% every 3 months postoperatively. At 12 months a surprisingly high 10% of patients reported significant pain.35 There- fore, a careful and thoughtful assessment of a painful effusion is recommended. Early failure of polyethylene in total knee replacement is rare today, but care should be taken in regard of third- body wear. With new interest in mobile-bearing designs, the mechanism of abrasive wear should be reconsidered to improve surgical techniques, since the bearing surfaces are enlarged. Abrasive wear is caused through third-body wear from fretting, bone chips, loose grafts, and loose or broken pieces of bone cement. Therefore, the elimination FIGURE 24-2. Arthroscopic removal of residual bone cement in of these particles during surgery is important to improve the posterolateral corner with complete pain relief postoperative long-term results in younger and more active patients. In and subsidence of the . 13 consecutive patients despite a careful implantation and a meticulous cementing technique, the removal of a large amount of debris required intense irrigation with at least replacement with a small effusion and a radiopaque body several liters of fluid.36 in the posterolateral corner 2 years postoperatively. After Some mobile-bearing TKRs have less constrained arthroscopic removal of the cement, the patient had com- motion at the tibial counterface, which may lead to plete pain relief and a subsidence of the knee effusion further increase of wear.37 Scratching and surface rough- (Figure 24-2). Figure 24-3 shows a maltracking patella ening through bone cement may lead to accelerated wear. with painful effusion 18 months after surgery. Accelerated Figure 24-1 shows a moderately painful total knee early polyethylene wear is also seen with malalignment: Too much posterior slope in the sagittal plane led to early wear (Figure 24-4) in a posterior stabilized total knee replacement through impingement of the tibial post in FIGURE 24-1. Residual bone cement in the posterolateral corner the femoral box (Figure 24-5), causing villous hyper- of a posterior stabilized modular TKR with mild effusion and con- trophic synovitis (Figure 24-6). tinuous pain postoperatively. Adhesive wear can occur rapidly with thin or altered polyethylene. Thicker polyethylene inserts and improved sterilization processes in ETO and neutral gases have

FIGURE 24-3. Patella maltracking with painful effusion 18 months after surgery. 262 Revision Total Knee Arthroplasty

FIGURE 24-6. Villous hypertrophy secondary to early wear of post-cam impingement in a posterior stabilized TKR 2 years postoperatively.

More conforming tibial inserts may lead to increased micromotion between the insert and the tibial compo- FIGURE 24-4. Posterior slope of 12 degrees in a posterior stabi- nent of modular design, causing significant backside lized TKR with post-cam impingement. wear, and we may see more wear-related problems in these patients. We also have to be aware of the fact that certain production years of polyethylene may play an important 1,2,5 improved adhesive wear. More recent studies demon- factor. We observe currently more wear-related problems strate reduced radiolucent lines and less revisions with a in total knee replacements implanted after 1996. The con- compression-molded monoblock versus ram-extruded modular tibia in TKR with intermediate to long-term follow-up.6 Figures 24-7 and 24-8 show a nonconforming FIGURE 24-7. Radiograph 7 years postoperative with mild posterior cruciate retaining total knee replacement 7 years medial wear and extensive osteolysis (arrows). postoperative in an active 55-year-old patient with periprosthetic osteolyis.

FIGURE 24-5. Impingement of the tibial post in the femoral box (arrow) 2 years postoperative with mild effusion. Chapter 24: Aseptic Synovitis 263

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