Arthritis & Rheumatism

Transcription

1 ARTHRITIS & RHEUMATISM Vol. 39, No. 1, December 1996, pp , American College of Rheumatology Arthritis & Rheumatism ~~~~ ~ Official Journal of the American College of Rheumatology REVIEW REVISION TOTAL HIP ARTHROPLASTY Indications and Outcomes NIZAR MAHOMED and JEFFREY N. KATZ Introduction hip arthroplasty (THA) has become the standard treatment of choice for end-stage hip disease of all etiologies, including degenerative, inflammatory, and posttraumatic conditions. More than 9% of patients experience dramatic pain relief with THA. Aseptic loosening is the most common cause of failure for both cemented and uncemented primary THA. The longest followup data on contemporary THA techniques are those for the Charnley total hip. In a recent review in which all patients studied had been followed up for a minimum of years, the combined rates of radiographic loosening and clinical loosening were % for the acetabulum and 7% for the femoral component (1). Cementless THA was introduced more recently and hence does not have published -year followup data. However, studies with more than 1-year followup of the AML cementless system have shown a failure rate of <lo% (). It is reasonabie to presume that most welldesigned THA systems should yield 8% implant survivorship at years (3). Currently, more than 3, Supported by NIH grant AR-3638 and by an Arthritis Foundation Investigator Award (to Dr. Katz). Dr. Mahomed is the recipient of a Canadian Arthritis Society Research Fellowship (no ). Nizar Mahomed, MD, FRCSC, Jeffrey N. Katz. MD, MS: Robert Brigham Multipurpose Arthritis and Musculoskeletal Diseases Center, Brigham and Women s Hospital, Harvard Medical School, Boston, Massachusetts. Address reprint requests to Jeffrey N. Katz, MD, MS, Division of Rheumatology and Immunology, PBB-, Brigham and Women s Hospital, Boston, MA 115. Submitted for publication March,1996; accepted in revised form July 4, revision THAs are performed annually in the US. Given the finite lifespan of primary THA and the increasing use of primary THA in younger patients with a longer life expectancy (4), the rate of revision hip arthroplasty will continue to increase. Evaluation of the painful hip following THA History. A thorough history and physical examination are the most important elements of the assessment of a painful hip. Patient characteristics associated with increased risk for aseptic loosening include young age, active lifestyle, increased weight, male sex, and rheumatoid arthritis (5). The location, temporal sequence, and characteristics of pain can provide important insights into the possible etiology (Table 1). For example, lateral hip pain may suggest trochanteric bursitis. Deep buttock and groin pain can result from acetabular sources or capsular impingement. Thigh pain is often associated with loose femoral components. Pain that has been present since the original surgery can indicate acute sepsis, hematoma, heterotopic ossification, or stress thigh pain. Risk factors for heterotopic ossification include male sex, bilaterality, age >, revision surgery, and history of prior heterotopic ossification (6). Pain that develops after a period of symptom-free function suggests mechanical loosening. Pain that occurs at the start of activities (start-up pain), i.e., getting out of a chair, also indicates mechanical loosening of the prosthesis. Pain that worsens with activity may be due to mechanical loosening or stress-related thigh pain in a well-fixed (typically uncemented) prosthesis (7). Such pain commonly occurs after prolonged weight bearing 1939

2 194 MAHOMED AND KATZ Table 1. Differential diagnosis of the painful total hip replacement Non-hip sources Sciatica Spinal stenosis with or without neurogenic claudication Spondylosis Vascular claudication Hip sources Aseptic loosening Thigh pain from well-fixed uncemented femoral stem Deep infection Heterotopic ossification Impingement Subluxation/dislocation Fracture Bursitis: trochanteric, iliopsoas Malignancy and is described by the patient as a dull ache or a sensation of fatigue. Constant pain present with activity, at rest, and at night often indicates deep infection. This can be corroborated by a history of fever, chills, surgical wound site inflammation, or drainage. Known perioperative risk factors for deep sepsis include diabetes, failed fracture osteosynthesis, breakdown of sterile environment during surgery, postoperative urinary tract infection, and the presence of an unhealed wound at hospital discharge (6). Other causes of constant pain include malignancy and stress fracture (8-1). Pain that is brought on only by certain movements, such as hip adduction, suggests instability, impingement, or tendinitis (iliopsoas, iliopectineal band). Lumbar nerve root compression, particularly at upper lumbar levels, must also be considered in the differential diagnosis of post-tha hip pain. Radiation of pain below the knee and associated neurologic symptoms (paresthesia, dysesthesia, weakness) indicate disc herniation, lumbar facet arthropathy, or spinal stenosis (1 1). Questions specifically addressing symptoms in other major joints in the lower extremity should also be asked, to determine whether other sources of pain may be affecting the individual, and to what extent. Physical examination. The physical examination should include assessment of the lumbar spine and all major joints of the lower extremity, and a thorough detailed neurovascular examination. Pain upon hyperextension of the trunk suggests lumbar facet arthropathy or stenosis, rather than the hip being the source. Detailed neurologic assessment may suggest lumbar radiculopathy, lateral femoral cutaneous nerve compression, or generalized neuropathy, all of which enter the differential diagnosis. Careful attention to gait patterns will elucidate whether the patient has problems with leg length discrepancy and/or weak abductors in addition to an antalgic gait. Local examination of the hip should include assessment of the skin and soft tissue envelope. Evidence of wound drainage or irritation suggests the possibility of deep infection. Assessment of range of motion of the hip with particular emphasis on movements that reproduce the pain will help identify the etiology. For example, pain on abduction can indicate pain due to impingement of heterotopic ossification. Pain with adduction and internal rotation can indicate posterior instability. Groin pain upon moving the hip through an arc can indicate acetabular component loosening. In contrast, thigh pain upon hip range of motion examination may indicate femoral loosening. Fixed reduction in the range of motion help to quantify the extent of functional limitation. Leg length discrepancy must be assessed carefully (using fixed anatomic landmarks) since it may increase over time, indicating progressive collapse of the index arthroplasty. Radiography. Serial radiography provides valuable insight into the mechanism and etiology of the painful total hip. It is crucial that current films be compared with early postoperative films in order to discern prosthesis migration, osteolysis, loss of bone stock (the total volumetric amount of bone present in a particular area of the skeleton for structural support) due to stress shielding, endosteal erosions, and progression of radiolucent lines. Osteolysis, i.e., softening, absorption, and destruction of bone, is an inflammatory process initiated by particulate debris. It is demonstrated on radiographs by progressive radiolucent lines or cavitation at the cement-bone or prosthesis-bone interface (1). The early stages of osteolysis can be asymptomatic but warrant close followup. Lacy periosteal new bone formation about the femoral cortex, with or without evidence of loosening, is pathognomonic of a deep infection but is insensitive, occurring in only 1-% of individuals with an infected THA (13). All subjects with an artificial joint replacement require regular followups on an annual basis for the life of the joint implant. Individuals should be referred to an orthopedic surgeon if significant or progressive osteolysis is detected, in order to prevent further bone loss necessitating a more complicated revision later on. Various investigators have developed radiographic rating scales to determine if a given prosthesis is stable. Harris et a1 (14) proposed a scheme by which cemented femoral components are classified as definitely loose (migration of the component or cement), probably loose (a radiolucent line all around the implant

3 REVISION THA 1941 in one or two projections), or possibly loose (a radiolucent line around more than one-half of the prosthesis). Engh and colleagues (15) put forth a system in which uncemented femoral components are rated as having stable bone ingrowth, stable fibrous ingrowth, or as being unstable. A full discussion of these rating systems is beyond the scope of this article; suffice it to say that loosening can and should be documented with regularinterval radiographs. Finally, the patient's expectations of the revision surgery must be discussed. Generally, the results of revision surgery are inferior to those of primary THA. Although both provide significant pain relief, revision surgery yields poorer functional results and a higher failure rate. It is imperative that the patient be made aware that revisions generally have inferior results, since this will likely have a bearing on the level of satisfaction postoperatively. Evaluation for suspected infection One of 4 infected THAs can be diagnosed by history and physical examination alone, based on the presence of pain, fever, chills, wound drainage, and sinus tracts (13). Of the remainder, a diagnosis can be established in 5% with further investigation, and the remaining 5% elude diagnosis until surgery. These infections are classified on the basis of temporal sequence of onset of symptoms (13), as follows: stage 1 = acute postoperative infections (-6 months postsurgery); stage = delayed deep infection (6-4 months postsurgery); stage 3 = late hematogenous infection (developing beyond 4 months postsurgery). The majority of patients present with a painful hip and no obvious evidence of infection. In these individuals it is useful to determine the erythrocyte sedimentation rate and C-reactive protein level. These can be normal in up to 5% of individuals with a painful infected THA (13). Any unexplained elevated values (i.e., in patients who do not have a systemic rheumatic disease) indicate the need for further investigation. Hip aspiration and arthrography should be performed to help isolate the causative organism. Pocketing of the radiopaque medium in the pseudocapsule is suggestive of infection. The aspirate should be sent for aerobic and anaerobic cultures. In only two-thirds of cases do aspirates reveal the causative organisms (13). If the aspiration is unsuccessful, nuclear imaging studies should be considered. The traditional combination of differential technetium and gallium imaging has been replaced by indium-1 11-labeled autologous white blood cell scintig- raphy. In a recent study of 4 patients with suspected musculoskeletal infections, "'In-labeled white blood cell scintigraphy was 88% accurate in defining the presence or absence of infection. In contrast, combination imaging with technetium and gallium was accurate in only 6% of the cases (16). Technical considerations Infected THA. If infection has been established as the cause of failure, the treatment options include suppressive antibiotic therapy, debridement only with retention of the prosthesis, single-stage revision, and two-stage revision. Suppressive therapy is used for individuals in whom surgery would have a high risk due to comorbid medical conditions (17). Debridement with retention of the prosthesis is indicated for infections of acute onset in a previously asymptomatic, aseptic joint replacement. Buchholz et a1 (18) introduced single-stage exchange arthroplasty, which involves complete removal of all foreign materials including cement and surgical debridement of infected tissues, followed by reconstruction with an antibiotic-impregnated cemented arthroplasty. This technique is indicated for individuals with less virulent infections (such as methicillin-susceptible Staphylococcus epidermidis) with organisms that do not elaborate a glycocalyx and are sensitive to antibiotics that can be incorporated into cement. For the majority of cases, a two-stage reconstruction is considered the standard. The first stage involves careful removal of all foreign materials and surgical debridement of infected tissues. Frequently a temporary antibiotic-impregnated cement spacer is placed in the hip joint, to help prevent soft tissue contractures and provide localized high concentrations of antibiotic. This is followed by 4-6 weeks of parenteral antibiotics and then a subsequent interval of 1-5 weeks without antibiotic treatment prior to the reimplantation, depending on the virulence of the organism. At the second stage, the hip is usually reconstructed with an antibioticimpregnated cemented arthroplasty and bone grafts are used as necessary to restore deficient bone stock. Aseptic loosening. Implant removal. Revision surgery for aseptic loosening entails distinct procedures: implant removal and joint reconstruction. The surgical dissection often must be larger than that of the previous surgery to afford adequate exposure (and may include a trochanteric osteotomy). If the components are grossly loose, they can be removed without sacrificing bone stock. However, in many instances removal of a wellfixed cement mantle can be difficult and lead to further

4 194 MAHOMED AND KATZ loss of bone stock or perforation of the femoral cortex. A similar problem can be encountered when removing an extensively porous coated component. Removal of a broken femoral stem represents a difficult problem because often the distal fragment is well fixed. This may necessitate making a cortical window in the femur to facilitate removal. At times the surgeon is forced to remove a well-fixed component in order to replace a loose femoral stem or cup due to component mismatch, recurrent dislocation, focal osteolysis, or some types of infection. Once all of the components are removed, the surgeon must assess the remaining bone stock in order to decide which technique of reconstruction is required. Femoral reconstmction. The complexity of a femoral reconstruction depends on the number of previous arthroplasties and extent of loss of bone stock. The American Academy of Orthopaedic Surgeons proposed a classification system whereby femoral defects are categorized as segmental deficiencies (any loss of bone in the supporting cortical shell of the femur), cavitary defects (containing lesions representing an excavation of the cancellous or endosteal cortical bone without violation of the outer cortical shell), or combined segmental and cavitary defects (19). In most primary revisions, the femoral deficiency is cavitary and can be managed by replacing the original stem with a new prosthesis. The range of choices for managing deficient bone stock includes morselized impaction grafting, cortical strut grafts, proximal femoral allografts, and tumor prosthesis. Impaction grafting is used to restore significant intraluminal bone loss resulting from inflammatory reactions to particulate debris. Morselized (ground-up) allograft bone is tightly impacted into the femoral canal with special tamps in order to reconstruct the thinned cortical walls. A smooth, tapered femoral component is then cemented into this construct. Cortical strut grafts are used to restore bone stock and neutralize stresses from segmental defects or iatrogenic cortical windows (Figure 1). Long-stem uncemented femoral components spanning the region of cortical disruption are used in these reconstructions. Proximal femoral allografts have been recommended for cases of large proximal segmental or combined defects exceeding 5 cm (). The allograft prosthesis construct is used to essentially substitute for the deficient proximal femur (Figure ). The advantage of this technique over use of a tumor prosthesis is that it helps to restore bone stock for future revisions and allows the soft tissues to reattach to the allograft. Acetabular reconstruction. Acetabular deficiencies are classified by the American Academy of Orthopaedic A Figure 1. A, Proximal femur with a lateral cortical defect which has been spanned by a long-stem prosthesis. A strut allograft of appropriate size will be used to bridge this defect. B, The cortical strut allograft is secured in place by multiple circumferential cerclage wires. This allows the graft to unite with host bone, thus restoring deficient bone stock and neutralizing stress in the proximal femur due to the underlying cortical defect. (Reproduced, with permission, from ref..) Surgeons as cavitary, segmental, combined, pelvic discontinuity, or arthrodesis (1). Cavitary defects consist of focal, contained areas of bone loss where the walls and roof of the acetabulum remain intact. These can be reconstructed with impaction of morselized bone graft. Disruption of either the anterior or posterior column or roof of the acetabulum defines a segmental defect. Large defects may be reconstructed with either structural allograft or morselized graft. For massive combined segmental and cavitary defects or pelvic discontinuity, reconstruction often requires a combination of fixed structural and morselized allograft. In addition, an antiprotrusio acetabular ring or internal fixation device may be required to stabilize segmental and pelvic discontinuity problems. Another option involves special prosthetic components designed to accommodate bone defects. Once bone stock is restored by grafting, the B

5 REVISION THA 1943 acetabular component is inserted. The two basic options are cemented or uncemented cups. The use of cemented.. \ cups alone has declined due to reports of high failure rates. This option is generally reserved for elderly patients with low physical demands. Nevertheless, cemented cups have been used successfully in combination with acetabular antiprotrusio rings (Figure 3). They are the preferred choice when there is more than 5% allograft contact with the prosthesis, since fixation by biologic ingrowth would not be expected to occur in this region. In the majority of cases, however, large uncemented ingrowth acetabular components are preferred. These cups allow for reliable biologic fixation when 5% or more of the contact area is with viable bone. In addition, they permit the use of multiple pass-through screws to help secure the graft and span structural defects. Results of reported studies All of the North American and most European reports on the results of revision THA are case series I from tertiary referral centers, where the procedures are, I 1 performed by experts in the field. Although such studies contribute greatly to our understanding of these procedures, they do not reflect the effectiveness of revision i, : : I I!, I : i /-Ai Figure 3. Reconstruction of a contained cavitary defect in the acetabulum, with a polyethylene acetabular prosthesis cemented into an acetabular antiprotrusio ring futed with multiple large cancellous screws. The cavitary defect (hatched area) is filled with either cement or a combination of morselized bone graft and cement. A Figure. A, Prosthesis structural allograft construct. The allograft construct is prepared at the surgical table and then inserted into the deficient host femur. Note the step cut in the allograft and the complementary step cut in the host femur to allow for rotational stability of the overall reconstruction. B, The prosthesis allograft construct is placed into the host femur and the remaining fragments of host proximal femur are wrapped around the allograft. The greater trochanter, if present, is then reattached to the allograft proximal femur. (Reproduced, with permission, from ref..) B THA in community-based care settings, where many of these operations are performed. This is in contrast to reports from the Swedish national joint registry, where the results are a compilation of the experience from all centers in the country (-4). Quality-of-life issues are not assessed in most case series. When they are addressed, various instruments are used, and seldom is there any information on preoperative patient functional status. Similarly, radiographic results are reported using a variety of classification systems. This lack of standardization makes comparison of results difficult. Consequently, re-revision rates are used to compare the results of case series, since they provide a hard outcome measure. However, this is limited by the fact that some older, sicker individuals who have poor clinical results are not represented because they are not good candidates for further surgery. Additionally, some articles report all revisions (including those due to aseptic loosening, sepsis, and recurrent dislocation), while others focus only on those

6 1944 MAHOMED AND KATZ Table. Summary of the results of studies of cemented femoral revisions Reference Hunter et al (5) 1979 Callaghan et a1 (7) 1985 Kavanagh et a1 (8) 1985 Pellicci et a1 (6) 1985 Kavanagh et al (77) 1987 Stromberg et al () Rubash and Harris (9) Engelbrecht et a1 (48) 199 Marti et al (49) 199 Kershaw et al (3) 1991 Stromberg et a1 (3) 199 Raut et al (76) Stromberg et al (4) Izquierdo and Northmore-Ball (31) Estok and Harris (3) Ballard et al (75) Raut et al (35) Raut et al (34) Iorio et al (5) Katz et al (33) Garcia-Cimbrelo et al (74) * NA = data not available. Mean length % No. of hips Mean age, of followup, % radiographically Year studied years years re-revised loose NA* NA due to aseptic loosening. To date, there have not been analyses utilizing administrative databases to provide population-based estimates of the complications and mortality rates associated with revision THA. Cemented femoral revisions. The early rerevision rates for cemented revision arthroplasty, as reported by Hunter et a1 (5) and Pellicci et a1 (6), ranged from 19% to 3% (Table ). These early series reflected poor cementing techniques and the lack of other reconstruction options available today. Subsequent studies in the late 19SOs by Callaghan et a1 (7) and Kavanagh et a1 (8) showed improved results, with re-revision rates of 8.6% and 9.%, respectively (Table ). The results of cemented femoral revision arthroplasty improved with modifications in implant design and the introduction of second-generation cementing techniques. These include a PMMA femoral plug, a cement gun, pulsatile lavage irrigation, and cement pressurization. The results with the use of these techniques were reported by Rubash and Harris (9) as a % revision rate at 6. years (Table ). This cohort was reviewed again at 11.7 years by Estok and Harris (3), who reported a 1.5% re-revision rate. Reports by Izquierdo and Northmore-Ball (31), Kershaw et a1 (3), Katz et a1 (33), and Raut et a1 (34,35) have shown similar results, with re-revision rates ranging from 5% to 9.5% over mean followup periods of 6-11 years (Table ). Despite improved results with modern techniques, the difficulty associated with extraction of long-stem cemented components in case of subsequent revisions has limited the applicability of this technique. Reporting on a unique cumulative national experience from Sweden, Stromberg and colleagues () documented a 19% re-revision rate at 4 years in a cohort of younger patients (mean age 47 years) (Table ). In a subsequent longer followup study of this cohort, they reported a 43% re-revision rate at 1 years (4). In another study, the same group reported a 15% rerevision rate at 7 years in an older cohort (mean age 64 years) from the Swedish National Registry (3). In general, these population-based studies reflect poorer outcomes compared with those reported from tertiary referral centers. Additionally, it becomes evident that younger patients with high physical demands have higher failure rates compared with older, less active individuals. The authors conclude that these difficult procedures might best be performed at referral centers by surgeons with expertise in this area. Uncemented femoral revisions. With the poor early results of cemented revisions and concerns about cement disease in primary hip arthroplasty (which turned out to be unfounded), there was a trend toward the development of femoral revision techniques that did not entail the use of cement. Uncemented stems were

7 REVISION THA 1945 Table 3. Summary of the results of studies of cementless femoral revisions Reference Harris et al (36) Hedley et al (39) Gustilo and Pasternak (37) Engh et al (38) Pak et al (81) Lawrence et al (78) Head et al (46) Meding et al (79) Hussamy and Lachiewicz (4) Lawrence et al (43) Chandler et al (45) Onsten et al (8) Berry et al (4) Gross et al (47) Moreland and Bernstein (44) Peters et al (41) * NA = data not available. Mean length % No. of hips Mean age. of followup, % radiographically Year studied years years re-revised loose I NA* also promoted for revisions due to severe osteolysis, where there was concern of recurrence with the use of cement. Additionally, it was believed that if an uncemented stem became loose, it could be revised relatively easily compared with a cemented long-stem femoral component. There were two basic stem designs, one relying on metaphyseal fixation with proximal coatings and the other relying on distal medullary canal fixation. The early reports from Harris et a1 (36), Gustilo and Pasternak (37), Engh et al (38), and Hedley et a1 (39) showed re-revision rates of to 4% (Table 3). These were all short-term (<5 years) radiographic followup studies representing each author s early experience with these techniques. Subsequent studies helped to define which designs yielded sustained benefits at midterm (5-1-year) followup. Hussamy and Lachiewicz (4), Peters et a1 (41), and Berry et a1 (4), in studies with a mean followup of years, reported that 3-45% of patients with proximally porous-coated revision prostheses had radiographic loosening (Table 3). All 3 groups of authors expressed concern about these high failure rates and concluded that this design does not yield stable long-term fixation. In contrast, Lawrence et a1 (43) and Moreland and Bernstein (44) reported re-revision rates between 4% and 1% with the use of extensively porouscoated medullary locking femoral stems (Table 3). This design appears to have superior midterm results due to its ability to allow biologic ingrowth in the distal portion of the femoral component. Various innovative approaches have been de- scribed for the management of very complex revisions with significant bone loss. Chandler et a1 (45) reported a 5% re-revision rate at an average followup of 3 years in patients with a modular proximally coated prosthesis (Table 3). The modular design allowed the attainment of improved fixation in both the metaphyseal and diaphyseal regions. Head et a1 (46) used strut onlay allografts to restore segmental defects in conjunction with calcarreplacing long-stem components for their series of difficult revisions. They reported a 3.4% re-revision rate at 3 years, with 98% of the grafts uniting to host bone. In a population of individuals with multiple revisions requiring structural proximal femoral allografts, Gross et a1 (47) reported a re-revision rate of 1.1% at a mean followup of 4.8 years. Which of the various types of reconstruction is best indicated for which condition remains unclear as further mid- and long-term results are awaited. Nevertheless, it is evident that the general results of femoral revisions have improved over the course of the last decades and will likely continue to do so in the future. Cemented acetabular revisions. The early experience with acetabular revisions centered on the use of cemented polyethylene components. Similar to the findings with femoral revisions, there were high rates of mechanical loosening, ranging from 9% to % as documented by Pellicci et a1 (6), Kavanagh et a1 (8), and Callaghan et a1 (7) (Table 4). Engelbrecht et a1 (48) reported an alarming rate of radiographic loosening (39%) (Table 4). In a younger cohort (mean age 47 years), Stromberg and Herberts (4) reported a 41%

8 MAHOMED AND KATZ Table 4. Summary of the results of studies of cemented acetabular revisions Mean length of % No. of hips Mean age, followup, % radiographically Reference Year studied years years re-revised loose Callaghan et al (7) Kavanagh et a1 (8) Pellicci et al (6) Trancik et al (84) Fuchs et a1 (83) Stromberg et al () Jasty and Harris (5) Engelbrecht et a1 (48) Marti et al (49) Kershaw et al (3) Berry and Muller (53) Rosson and Schatzker (5) Stromberg et al (3) Zehntner and Ganz (54) Stromberg and Herherts (4) Raut et a1 (51) Iorio et a1 (5) Garcia-Cimbrelo et a1 (74) re-revision rate (Table 4); they related the high failure rates to the younger age and consequent higher physical demands of this cohort. From this early experience, improved techniques evolved, including second-generation cementing procedures, the use of bone grafts to restore large acetabular defects, and antiprotrusio rings to help reduce stresses on the reconstruction. Iorio et a1 (5) reported a 4% re-revision rate in a series of patients studied over a long period of time (study spanned decades, during which the surgical techniques evolved and incorporated all of those described above with the exception of acetabular rings) (Table 4). Raut et a1 (51) documented a 6.% re-revision rate in a similar study spanning decades of experience (Table 4). They concluded that the results of their study were profoundly affected by the quality of acetabular bone stock. Several studies have documented the outcomes of acetabular reconstructions utilizing anti-protrusio rings. Rosson and Schatzker (5) described a 7.5% re-revision rate in their experience using reinforcement rings (Table 4). Berry and Muller (53) used the Burch- Schneider anti-protrusio ring for massive bone deficiencies and documented a 4% re-revision rate at 5 years (Table 4). Half of the failures were attributed to infection and the other half to aseptic loosening. The high failure rate due to infection was related to the fact that, in a significant portion of the patients, the index revision was necessitated by infection. Zehntner and Ganz (54) reported no re-revision at an average of 7. years in a series of relatively difficult reconstructions (Table 4). They emphasized that the quality of the bone stock at the time of revision directly affects the end result. The overall results of reconstruction utilizing reinforcement rings are less favorable compared with the results in other recent series utilizing different techniques, due to the selection bias toward more complex cases. These patients usually have worse bone stock at the time of revision and hence tend to have poorer outcomes. Uncernented acetabular revisions. Given the alarming rates of early loosening in cemented revisions, some investigators focused their attention on using uncemented acetabular components, based on their success in primary hip arthroplasty. The two basic design philosophies were a conical screw-in cup with threads (designed to be inserted like a large screw into the acetabulum) or a press-fit hemispherical cup with the option for pass-through screws (intended for interference fit from rim contact with the acetabulum). Although initial results were encouraging, the midterm reports of outcomes with screw-in cups made it clear that they had a significantly high failure rate, and hence they have fallen out of favor (6,55-58). The early results with cementless hemispherical cups were also very favorable (36,59,) (Table 5). In contrast to the screw-in cup, this design continued to maintain encouraging results at midterm followup as documented by Silverton et a1 (61), who reported an 11% re-revision rate at 8.3 years (Table 5). The authors attributed the failures to infection or recurrent dislocation, and not to aseptic loosening. At a mean of 5 years after revision, Lachiewicz and Hussamy (6) found no

9 REVISION THA 1947 Table 5. Summary of the results of studies of cementless acetabular revisions Reference Harris et al (36) Convery et a1 (86) Tanzer et al (59) Padgett et al () Hooten et al (85) Lachiewicz and Hussamy (6) Paprosky et al (65) Paprosky and Magnus (64) Lawrence et al (43) Dorr and Wan (63) Silverton et al (61) Mean length % No. of hips Mean age, of followup, 7 radiographically Year studied years years re-revised loose so I re-revisions. Others, including Dorr and Wan (63), Lawrence et a1 (43), and Paprosky and colleagues (64,65), have echoed these findings, with midterm followup reports showing re-revision rates ranging from % to 7% (Table 5). Similar to femoral revisions, the outcomes of acetabular revisions have improved over time. However, longer followup studies are required to clearly define the indications for each of the various reconstruction techniques. Revision for infected THA. THA infection presents a very difficult reconstruction challenge. These patients often have poor bone stock and have a greater prevalence of comorbid medical conditions. Patients who are poor candidates for general anesthetics are usually treated with suppressive antibiotics. In a series of patients with THA infection reported by Goulet et a1 (17), 5% retained their prosthesis at 3 years with suppressive therapy. Surgical treatment for an infected THA includes a single-stage exchange procedure or a -stage reconstruction. Buchholz et a1 (18) advocated the former and reported a 77% success rate for eradication of infection (Table 6). These findings were supported by Wroblewski (66) and Raut et a1 (67), who reported success rates of 91% and 86%, respectively, using single-stage exchange arthroplasty (Table 6). Those authors went on to conclude that a draining sinus was not a contraindication for this procedure and that the results are influenced by the quality of debridement and fixation of components. Others, such as Morscher et a1 (68), have advocated single-stage exchange for select indications. After reviewing their experience of 1- and -stage reconstructions, those authors recommended using single-stage exchange in only those cases where the components were loose and the organism was of low virulence (Table 6). Additionally, they pointed out that the soft tissue envelope must be of satisfactory quality. McDonald et a1 (69) reported an 87% success rate with -stage reconstruction using cement (Table 6). Berry et a1 (7), in their review of -stage reconstruction with ailograft bone, reported an 11% rate of infection recurrence and concluded that it was relatively safe to use allograft bone to reconstruct bone defects in conjunction with a staged revision for infection (Table 6). Nestor and colleagues (71), using a -stage technique and uncernented components, concluded that cementless revisions offer no Table 6. Summary of the results of studies of revision due to infection Reference Year No. of hips studied Mean age, years Mean length of followup, years % in which infection recurred Type of revision Buchholz et a1 (18) Wroblewski (66) Sanzen et a1 (88) McDonald et al (69) Morscher et a1 (68) Berry et al (7) Nestor et al (71) Raut et al (67) Went et al (87) stage 1-stage I- and -stage -stage 1- and -stage -stage -stage I-stage 1- and -staae

10 1948 MAHOMED AND KATZ benefit over antibiotic-impregnated cemented revisions (Table 6). Additionally, they found that patients with rheumatoid arthritis were at a higher risk for recurrence. Limitations of the literature. None of the studies reviewed herein were randomized controlled trials. Clearly, experimental trials would provide valid, unbiased data about the technical merits of one reconstruction technique in comparison with another. This would allow treating physicians to select procedures based on sound scientific evidence about their efficacy. However, these trials are difficult to implement for a number of reasons, including the long length of followup required for assessing reconstruction technologies and hence the great cost of such a trial. Additionally, the findings of such a clinical trial may be outdated by the time meaningful results are obtained, given the rapid rate of change in orthopedic technologies. Nontechnical correlates of outcomes of revision THA Most analyses of factors associated with outcome have focused on prosthesis design, use of bone grafts, and the controversy over cement use. Less is known about nontechnical factors. Research is needed on the prognostic importance of patient expectations, comorbidity, and preoperative functional status. Also, the volume of procedures performed at specific institutions and by specific surgeons has been shown to correlate with mortality following a range of surgical procedures, including coronary artery bypass grafting, peripheral vascular surgery, and primary THA (7). Preliminary evidence from one state suggests that procedure volume may be associated with outcome of revision THA as well (73). Further research on the association between volume and outcome is necessary to develop rational responses to the policy question of whether revision THA should be restricted to select large institutions. Conclusions It is difficult to compare the results of different revision techniques, due to the heterogeneity of the patients and complexity of the revision involved. Furthermore, there is no accepted standardized method for assessing the clinical and radiographic results of these procedures. The only common end points that can be used to compare various series are the rates of rerevision or recurrence of infection. Nevertheless, we can justly state that the results of revision hip arthroplasty have generally improved over time. Second, given the aging population and increasing rate of primary hip arthroplasty, particularly in younger patients, the number of patients requiring revision hip arthroplasty will increase. Third, the results from revision surgery are directly related to the quality of bone stock available at the time of surgery. 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