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© 2002 The Journal of Bone and Joint Surgery, Inc.
What's New in Adult Reconstructive Knee Surgery
Michael J. Archibeck, MD The purpose of this update on adult reconstructive knee surgery is to discuss, in summary fashion, topics presented at selected orthopaedic meetings and published in related orthopaedic journals between January and December 2001. The sources for this review are articles published in The Journal of Bone and Joint Surgery (American edition) and The Journal of Arthroplasty . The podium presentations mentioned in this article include those given at the annual meeting of the American Academy of Orthopaedic Surgeons (held in San Francisco, California, on February 28 through March 4, 2001), on Specialty Day at the meeting of The Knee Society (held in San Francisco, California, on March 3, 2001), and at the meeting of The American Association of Hip and Knee Surgeons (held in Dallas, Texas, on November 9 through 11, 2001). The Interim Meeting of the Knee Society was cancelled as a result of the events of September 11, 2001. Surgical Treatment of Osteoarthritis Without Arthroplasty While total knee replacement has been very successful for alleviating pain and improving function in patients of all ages, surgical treatments other than arthroplasty remain an option for some patients. Mosely et al., in a randomized, double-blind, placebo-controlled trial of arthroscopic treatment of osteoarthritis of the knee in 180 patients with two years of follow-up, found equal improvement in the three treatment groups (débridement, lavage, and placebo arthroscopy), suggesting that the improvement was secondary to a placebo effect. However, Fond et al. reported that 69% (twenty-five) of thirty-six patients who underwent arthroscopic notchplasty and débridement for osteoarthritis of the knee had a good or excellent result at five years. Mandelbaum, in a four-year, multicenter study of more than 1300 patients who underwent autologous chondrocyte implantation in the knee, reported clinical improvement in 70% of patients, with the best results occurring in patients with femoral lesions (85% of whom had improvement). Very little was published or presented on the use of osteotomy for the treatment of knee osteoarthritis. Marti et al. reported on the use of proximal tibial varus (opening-wedge) osteotomy for the treatment of valgus gonarthrosis in a study of thirty-six patients with proximal tibial deformity and found a good or excellent result in 88% (thirty) of thirty-four patients after a mean duration of follow-up of eleven years 1 . Kaper et al. found that 54% (twenty-five) of forty-six patients who had undergone high tibial osteotomy had development of patella baja (>10% lowering of patellar height as measured with use of the Insall-Salvati ratio) and 61% (twenty-eight) had a loss of posterior tibial slope of >5°. Unicompartmental Knee Replacement Unicompartmental knee replacement has become increasingly popular because of improved rates of survivorship and the development of less invasive techniques. As the indications for unicompartmental knee replacement expand, the results in younger, heavier, and more active patients remain largely unknown. Price et al. found that the ten-year survivorship of the Oxford medial unicompartmental knee replacement was 92% in patients who were less than sixty years old compared with 96% in patients who were more than sixty years old (p = 0.6). The same group found that the rate of recovery (as determined by the time needed to achieve straight-leg raising, 70° of flexion, and independent stair-climbing) after unicompartmental knee replacement performed through a short incision and without eversion of the patella was two times faster than that after open unicompartmental knee replacement and three times faster than that after total knee replacement, without a compromise in the radiographic appearance 2 . Ohdera et al., in a report on eighteen unicompartmental knee replacements performed for lateral gonarthrosis, found one loose femoral component and only slight deterioration of the medial compartment in five knees after a minimum of five years of follow-up. Emerson et al. compared fifty-eight mobile-bearing unicompartmental implants with fifty-one fixed-bearing unicompartmental implants and found nearly equal ten-year survivorship rates (90% and 87%); however, polyethylene wear was more common in the fixed-bearing group (p < 0.04) and progression of arthritis was more problematic in the mobile-bearing group (p < 0.15). Hyldahl et al., in a prospective, randomized study, compared twenty-two all-polyethylene tibial components with twenty-three metal-backed tibial components of the same unicompartmental design and found no clinical or radiographic differences at two years. Engh et al. demonstrated that polyethylene that had been sterilized by gamma irradiation in air and exposed to a prolonged shelf life led to catastrophic failure of 47% (thirty-four) of seventy-three unicompartmental knee replacements at a mean of eighteen months after implantation, placing the onus on the surgeon to know the method of sterilization and the shelf life of the implants that he or she uses. McAuley, in a report on thirty-nine revision procedures performed because of the failure of a unicompartmental knee replacement, found polyethylene wear to be the most common cause of failure, followed by loosening. Primary femoral components were used for all revisions. Fourteen revisions required the use of a stemmed tibial component, and eight required the use of tibial augments. Alignment in Primary Total Knee Replacement Surgical technique remains a crucial factor in the success and longevity of total knee replacement. Errors in soft-tissue balancing and component alignment are relatively common. Novotny et al. demonstrated potential errors in femoral component alignment that can occur in association with the use of intramedullary instrumentation and recommended the use of a 9-in (255-mm) by 9-mm rod introduced through a reproducible entry hole and aligned rotationally with the epicondylar axis. Katz et al. compared the use of the transepicondylar axis, the anteroposterior axis, the posterior condylar line, and the balanced flexion gap technique for determining femoral component rotational alignment and found the anteroposterior axis and the balanced flexion gap technique to be more accurate for defining the flexion-extension axis of the knee 3 . Berger et al., in a study of eleven cadaveric knees, found that aligning the femoral component parallel to the epicondylar axis resulted in optimum patellofemoral tracking and minimized tibiofemoral instability. Scuderi et al. found that femoral components that were aligned parallel to the transepicondylar axis had a lower prevalence of femoral condylar lift-off, which may result in reduced wear. While there remains some controversy with regard to the most accurate technique, relying on one landmark for femoral rotational alignment may be inadequate. Techniques in Primary Total Knee Replacement Three reports discussed cementing techniques and the design of cemented components. Wall et al., in a study of 300 tibial components that were inserted with a "hybrid" cementing technique (insertion of the tray with cement and the tibial keel without cement), reported a 0.1% rate of failure after a mean duration of follow-up of seventy-five months. In contrast, Sekundiak reviewed a similar series of 110 tibial components and found a 3.6% rate of failure in their "hybrid" group (insertion of the tibial tray with cement and the tibial stem without cement) and no failures in the group treated with cemented tray and stem. Vertullo et al. found that a peripheral lip on a cemented tibial component resulted in significantly greater peripheral cement penetration (p < 0.05). Soft-tissue balancing is of paramount importance in the achievement of a successful result after total knee replacement. Peters et al. compared two sequences of lateral release and quantified the effect on flexion and extension gaps in paired cadaveric knees, with the sequence consisting of release of the posterior cruciate ligament, the posterolateral capsule, the iliotibial band, the popliteus tendon, and the lateral collateral ligament producing more symmetric flexion-extension gaps 4 . Lateral collateral ligament release, independent of the sequence, produced marked gap asymmetry. Whiteside et al. performed a similar cadaveric study and found that lateral tightness in extension is well treated with iliotibial band and posterior capsule release and that tightness in flexion is corrected with lateral collateral ligament and popliteus tendon release. In another cadaveric study, Whiteside et al. demonstrated that the posterior cruciate ligament provides medial stability to the knee following medial collateral ligament release, especially in flexion. Leopold et al. reported on sixteen cases of intraoperative medial collateral ligament disruption that occurred during primary total knee replacement and that were treated successfully with direct repair, primary unconstrained knee components, and six weeks of bracing 5 . The indications for simultaneous bilateral total knee replacement remain controversial. Lombardi et al., in a series of 1090 simultaneous bilateral and 958 unilateral total knee procedures, found greater blood loss and higher rates of transfusion, postoperative ileus, pulmonary complications, cardiac complications, and neurologic complications in patients who were more than eighty years old and underwent simultaneous bilateral total knee replacement (p < 0.05 for all comparisons). Adili et al., in a study in which eighty-two patients who were more than seventy-five years old and who underwent simultaneous bilateral total knee replacement were compared with eighty-two matched patients who underwent unilateral total knee replacement, found that the rate of postoperative cardiovascular complications was significantly higher in the bilateral group (p = 0.003). Benjamin et al. found that obesity (defined as a body-mass index of >30) did not result in a higher prevalence of wound complications or systemic complications when patients undergoing bilateral total knee replacement were compared with similar obese patients undergoing unilateral total knee replacement. There were, however, higher complication rates in the obese patients when compared with rates in "thin" patients. Minimizing blood loss during total knee replacement was investigated in several studies. Wang et al. reported that patients who had been treated with a fibrin sealant that was sprayed into the wound prior to tourniquet deflation had reduced drainage (185 compared with 408 mL) (p = 0.002) and higher hemoglobin levels (as indicated by a 28.9% smaller decrease in hemoglobin) (p = 0.005) in comparison with a control group. Tetro et al. found greater total blood loss (1792 compared with 1499 mL) in patients undergoing total knee replacement when a tourniquet was used (p = 0.02). Postoperative pain control was the topic of five reports. Tanaka et al., in a study of sixty-nine patients, found that the use of intra-articular morphine and bupivacaine following total knee replacement improved pain scores and reduced the need for systemic analgesics, with a greater effect in patients with rheumatoid arthritis. Browne et al., in a double-blind, randomized, prospective study of thirty-seven patients who were treated with or without intra-articular bupivacaine, found lower pain scores and lower narcotic requirements in the bupivacaine group. Chelly et al., in a series of ninety-two patients, found that continuous femoral nerve blocks reduced postoperative morphine requirements by 74% (p < 0.05) and provided better recovery than did patient-controlled analgesia machines or epidural blocks. Luber et al. used a combination of lumbar plexus blocks and sciatic nerve blocks in eighty-seven patients, 78% of whom achieved an adequate block for surgery and 22% of whom required conversion to a general anesthetic. The overall postoperative patient satisfaction rate with the blocks was 92%. Cheville et al., in a randomized trial of scheduled controlled-release oxycodone following total knee replacement in fifty-nine patients, found less pain, faster rehabilitation, and earlier discharge (p < 0.05) in the group that was treated with controlled-release oxycodone. Clinical Results of Primary Total Knee Replacement The debate regarding the superiority of posterior cruciate ligament-retaining or posterior cruciate ligament-substituting total knee replacements continues. Title et al. compared seventy-four matched pairs of posterior cruciate ligament-sacrificing and posterior cruciate ligament-substituting knee replacements and found that the cruciate-substituting design was associated with better results in terms of range of motion, stair function, anterior knee pain, and walking ability. Guoan et al. compared the kinematics of cruciate-retaining and cruciate-substituting total knee replacements with a robotic in vitro model and found that both types of replacement only partially restored the kinematics of the normal knee in flexion while posterior cruciate ligament-deficient knees failed to do so. Swanik et al., in a randomized, prospective study, compared proprioception, balance, and quadriceps activity in patients with posterior cruciate ligament-retaining and posterior cruciate ligament-substituting total knee replacements and found an improved sense of joint position in the posterior stabilized group, with no difference in the other parameters. Clark et al., in a multicenter, randomized comparison of posterior cruciate-sacrificing total knee replacements (seventy-two knees) and posterior cruciate-retaining total knee replacements (eighty knees), found no difference in Knee Society scores, range of motion, WOMAC scores, or SF-12 scores at two years 6 . Several clinical reports on posterior cruciate-retaining knee replacements were presented. Chen et al., in a review of 110 cruciate-retaining total knee replacements (Genesis I; Smith and Nephew, Memphis, Tennessee), reported a 97% survivorship at ten years and a 97% rate of good and excellent results. Gill and Joshi, in a study of 282 consecutive cruciate-retaining total knee replacements that were followed for a minimum of fifteen years, reported a survivorship of 97.9%, 96.2%, and 82.5% at seventeen, nineteen, and twenty-two years, respectively 7 . Gill, in a study of 115 all-polyethylene tibial components and 252 metal-backed tibial components with a cruciate-retaining design that were followed for a minimum of ten years, found no difference in revision rates or knee scores. Survivorship was slightly improved in the all-polyethylene group (p = 0.013). Archibeck et al., in a study of seventy-two cruciate-retaining total knee replacements in patients with rheumatoid arthritis who were followed for a minimum of eight years, reported a 95% rate of good or excellent results, a 93% survivorship at ten years (with femoral or tibial revision as the end point), and only a 2.8% rate of late posterior instability 8 . Gill et al. also compared cruciate-retaining knee replacements in patients with rheumatoid arthritis and in patients with osteoarthritis and found equivalent pain and knee scores in the two groups. The twenty-year survivorship for patients with rheumatoid arthritis and osteoarthritis was 87.7% and 85.1%, respectively. Rasquinha et al. reviewed the mean ten-year results associated with a cruciate-retaining total knee prosthesis (Press-Fit Condylar; Johnson and Johnson, Raynham, Massachusetts) and reported a 90% rate of good and excellent results and a 94% survivorship at twelve years. The wear mechanisms of posterior stabilized total knee replacements were reviewed in two studies. Mikulak et al. found a 2.9% rate of revision for loosening and osteolysis in a study of 557 posterior-cruciate-substituting total knee replacements after a mean duration of follow-up of fifty-six months 9 . All failures were associated with polyethylene post damage and backside wear. Puloski et al. examined the wear patterns on twenty-three retrieved cruciate-substituting tibial inserts and found wear of the post in all twenty-three, with seven (30%) demonstrating "severe" wear 10 . The optimal fixation technique for total knee replacement remains controversial. Schroder et al., in a study of 114 consecutive ACG 2000 (Biomet, Warsaw, Indiana) cementless total knee replacements, reported one case of tibial osteolysis and two cases of aseptic loosening of the tibial component. The ten-year survivorship was 97%. Berger et al. reported on 129 cementless total knee replacements (Miller-Galante I; Zimmer, Warsaw, Indiana) after a mean duration of follow-up of twelve years and found excellent femoral component fixation, a 34% rate of revision of the metal-backed patellar component, a 5% rate of aseptic loosening of the tibial component, and a 10% rate of tibial osteolysis 11 . Khaw et al. conducted a prospective, randomized trial of 224 cementless and 277 cemented total knee replacements (Press-Fit Condylar; Johnson and Johnson), with no significant difference in ten-year survivorship between the groups (96.6% and 96.5%, respectively). Two studies on the etiology of failure of total knee replacements provided insight into the improvements that are required to enhance longevity. Fehring et al. reviewed 281 total knee replacements that were revised within five years after implantation and found that the causes of revision included infection (37%), instability (26%), failure of bone growth into cementless components (13%), patellofemoral problems (8%), and wear or osteolysis (7%) 12 . Sharkey et al. reviewed 215 revision total knee replacements and found that the causes of failure included instability (27%), loosening (25%), polyethylene wear (22%), infection (17%), arthrofibrosis (13%), patellar complications (7%), a deficient extensor mechanism (6%), pain from an unknown source (6%), malalignment (5%), and other factors (6%). Mobile-Bearing Total Knee Replacements With issues related to articular surface and back-side polyethylene wear limiting the longevity of total knee replacements in younger, more active patients, mobile-bearing knees have been proposed as a potential solution. Hartford et al., in a report on 139 mobile-bearing knee replacements that were followed for a mean of 7.8 years, found a 93% rate of survivorship and a significantly higher rate of aseptic loosening in association with uncemented components (p = 0.0051) 13 . Buechel et al., in a review of their minimum ten-year experience with 309 cementless mobile-bearing total knee replacements, found similar ten-year survivorship rates for rotating-platform knee replacements (98.9%) and meniscal-bearing knee replacements (97.4%) and noted excellent results in association with the cementless rotating-bearing patellar component. Dennis et al. found no significant difference between mobile-bearing and fixed-bearing posterior stabilized total knee replacements with regard to passive flexion or maximum flexion during weight-bearing (p > 0.05). Dennis also reported on the fluoroscopic evaluation of a fixed-bearing posterior stabilized total knee and a mobile-bearing cruciate-sacrificing prosthesis and found that the fixed-bearing implant demonstrated more normal and reproducible knee kinematics during deep-knee bending whereas the mobile-bearing total knee replacement showed more normal kinematics during gait. Kim et al. performed a randomized, prospective comparison of a fixed-bearing knee replacement (AMK; DePuy, Warsaw, Indiana) and a mobile-bearing knee replacement (LCS; DePuy) in a series of 116 patients undergoing bilateral procedures and found no significant difference in range of motion or knee scores after a mean duration of follow-up of 6.4 years. However, they found a slightly higher prevalence of medial tibial radiolucencies in the fixed-bearing group. Hartford et al. evaluated eighty-one Low Contact Stress (DePuy) meniscal-bearing total knee replacements and found that 48% had paradoxical anterior motion of both bearings with flexion, 20% had posterior motion of both bearings, 12% had reciprocal motion of the two bearings, 11% had motion of only one bearing, and 9% had no motion of either bearing. Knees with anterior sliding of the condyles had significantly less flexion (p = 0.03) and lower Knee Society scores. Banks et al. found that cruciate-substituting knee replacements had greater rollback (13 mm) than did cruciate-retaining (6.3 mm) and mobile-bearing knee replacements (2.5 mm) (p < 0.001). In their Coventry Award-winning study, Brown et al. used a servohydraulic machine and a finite-element model to demonstrate that the amount of torque required to initiate rotation in a mobile-bearing total knee replacement was greater than the amount required to sustain rotation, perhaps explaining why a percentage of these mobile-bearing joints do not move under routine functional loads. The Difficult Primary Total Knee Arthroplasty Total joint replacements in patients with the human immunodeficiency virus (HIV) have been reported to be associated with increased risks, such as infection. Dungy et al. reported on sixty arthroplasties in thirty-two HIV-positive patients (mean CD4 count, 386 cells/mm 3 ) after a mean duration of follow-up of eight years and noted only one infection and four revisions for polyethylene wear. Unger et al., in a review of forty-eight total knee replacements that had been performed in twenty-nine male patients with advanced hemophilic arthropathy (twenty-one of whom were HIV-positive), reported that three knees were revised for aseptic loosening (at a mean of 12.3 years) and that no patient had an infection. Norian et al., in a review of fifty total knee replacements that had been performed in thirty-five patients with hemophilic arthropathy (twenty-six of whom were HIV-positive), reported a ten-year survivorship of 84% and a twenty-year survivorship of 71%. The most common cause of failure was infection; however, this finding was not correlated with HIV status. In contrast, Sullivan et al. found an alarmingly high rate of complications in their review of twenty total joint replacements in fifteen HIV-positive patients, with thirteen reoperations performed at an average of 3.5 years (including six performed because of infection). Lehman et al. evaluated twenty-nine total knee replacements in patients with HIV and/or a history of intravenous drug use and found a 14% rate of infection in the HIV group and a 40% rate of infection among the intravenous drug users who had HIV 14 . Prior fractures about the knee complicate total knee replacement. Saleh et al., in a review of fifteen total knee replacements performed after internal fixation of a tibial plateau fracture, reported an 80% rate of good or excellent clinical results but a high rate of complications, including three infections, two patellar-tendon disruptions, and three manipulations 15 . Parvizi et al. reported on forty-eight total knee replacements performed after a previous distal femoral fracture and also found good clinical results but a high rate of complications, including two instances of aseptic loosening and three infections. Yoshino et al., in a review of three primary total knee arthroplasties that were performed because of acute distal femoral fractures in osteoarthritic knees, reported that all three fractures united and all three knees had a good functional result. Henkel et al., in a report on seven total knee replacements that were performed following knee fusion, noted six complications (three open releases of adhesions, two free-flaps for skin necrosis, one painful peroneal nerve paresis), with two knees requiring revision fusion because of infection or instability. Turner et al. reported on nine patients who had a total knee replacement following a previous ipsilateral peripheral artery reconstruction. Two of the replacements (including one performed with and one performed without a tourniquet) were complicated by acute arterial occlusion, emphasizing the importance of diligent postoperative vascular monitoring in patients with peripheral vascular disease. Parvizi et al., in a study of thirty total knee replacements in patients with ankylosing spondylitis, reported a 20% prevalence of heterotopic bone, a 10% manipulation rate, and one revision for patellar loosening after a mean duration of follow-up of 11.2 years. Giori and Lewallen, in a review of sixteen knee replacements performed in fifteen patients with poliomyelitis, noted improved pain relief and improved knee scores in patients with at least antigravity (grade-3) quadriceps strength 16 . In patients with less-than-antigravity quadriceps function, there was an increased risk of poor pain relief, recurrence of laxity, and poor long-term function. Infection at the Site of Total Knee Replacement The diagnosis of infection at the site of a total knee replacement can often be difficult. Mason et al., in a report on the use of knee aspiration, found that a white blood-cell count of >2500 cells/mm 3 (2.5 10 9 /L), with at least 60% polymorphonuclear cells, had a 98% sensitivity and a 95% specificity for the diagnosis of infection 17 . Joseph et al. reported that the use of combined indium-111 leukocyte and technetium-99m sulfur colloid scans had a 100% specificity but only a 46% sensitivity for the diagnosis of infection. Inclusion of blood-pooling and flow-phase data improved the sensitivity to only 66%, and those authors therefore concluded that the routine use of these studies was not supported by their data. Peersman et al., in their Insall Award-winning report on 6439 total knee replacements performed with vertical laminar airflow and body-exhaust suits, noted a 0.43% rate of deep infection. One-third of the infections occurred within the first three months after surgery. Prior open knee procedures, immunosuppressive therapy, poor nutrition, hypokalemia, diabetes mellitus, obesity, and smoking were comorbidities that significantly increased the risk of infection (p < 0.05). Revisions and procedures that took longer than 2.5 hours were associated with an increased risk as well (p < 0.001). The treatment of infection at the site of a total knee replacement was reviewed in four studies. Rah et al. compared the effectiveness of two, three, and four-stage treatment approaches and reported cure rates of 70%, 76%, and 83%, respectively. Nazarian et al. reviewed the use of a monolithic antibiotic spacer for the treatment of 124 infections that occurred at the site of a total knee replacement and found a 90% cure rate and a 66% rate of good or excellent results after an average duration of follow-up of 4.5 years. Emerson et al. compared static spacer blocks (twenty-six knees) with articulating spacers (twenty-two knees) and found an improved postoperative range of motion in the articulating-spacer group (108° compared with 94°) and no significant difference in the reinfection rate (9% compared with 7.6%). Kilgus et al. observed that the success rate following the treatment of deep total knee infections due to resistant organisms (18%) was much lower than that following the treatment of deep infections due to antibiotic-sensitive bacteria (88%). The Patellofemoral Joint Patellar resurfacing during total knee replacement remains controversial. Barrack et al., in a prospective, randomized, double-blind study of 118 knees that were treated with or without patellar resurfacing during total knee replacement, found no significant difference between the resurfaced and nonresurfaced groups with regard to the overall Knee Society score or the pain or function subscores after five to seven years of follow-up 18 . However, 12% of the knees in the nonresurfaced group were subsequently resurfaced because of anterior knee pain. Boldt et al., in a report on 1777 knees that were treated with the Low Contact Stress mobile-bearing total knee replacement (DePuy) without patellar resurfacing, found a 95% rate of good or excellent results after two to fifteen years of follow-up. Nineteen patients (1.1%) had a reoperation because of patella-related anterior knee pain, but only nine of those patients had improvement. Thompson et al., in a review of thirty-three total knee replacements that were performed without patellar resurfacing for the treatment of isolated patellofemoral arthritis, reported that twenty-one knees were pain-free and that no reoperations had been performed after twenty months of follow-up. Parvizi et al., in a study of thirty-one total knee replacements that were performed because of isolated patellofemoral syndrome, reported Knee Society pain and function scores of 89 and 90 points, respectively, after a mean duration of follow-up of 5.2 years. They performed a lateral release in twenty-one knees (68%), performed one subsequent patellar realignment procedure, and noted one case of aseptic loosening of the patellar component. Hartford et al., in a review of 109 knees that were treated with a press-fit, metal-backed, rotating patellar component, reported that two patellar revisions were performed (one because of a polyethylene fracture and one because of dislocation) after a mean of nine years of follow-up. Ezzet et al., in a cadaveric study, found that patellar components with an inset design demonstrated greater lateral tilt and shift than those with an onset design. Keating et al., in a review of 4583 total knee replacements, identified 177 patellar fractures. Both of the fractures that were treated with internal fixation went on to nonunion, and four of the eight patients who were treated with excision of the patellar button had an infection. Those authors concluded that most patellar fractures are best treated nonoperatively. Polyethylene Wear in Total Knee Replacement Wear between the tibial baseplate and the modular polyethylene insert, also known as backside wear, has been identified in several studies. Engh et al. measured the anteroposterior and mediolateral motion between the polyethylene insert and the tibial tray of a variety of modular tibial components and found a mean insert-motion index of 64 m in the group of unimplanted implants, 341 m in the group of implants that were obtained from patients undergoing revision arthroplasty, and 380 m in the group of implants that were obtained at the time of an autopsy, indicating that backside wear may account for the increasing prevalence of osteolysis that has been observed since modular components have become widely used 19 . The same group of authors evaluated thirty-eight modular tibial trays and found that the micromotion index deteriorated with time in vivo (p < 0.001). Wasielewski studied the backside articulation under cyclic axial physiologic loads and found that all inserts moved 20 to 25 m relative to the metal backing, with the variations in magnitude and direction depending on the locking mechanism. Conditt et al. evaluated sixteen posterior stabilized total knee replacements (retrieved one to 106 months after implantation) with stereomicroscopic analysis of the back side of the polyethylene as well as with a knee simulator. They found medial-lateral sliding to be the predominant motion with simulated gait and noted no increase in sliding with prolonged time in situ. Pagnano et al. reported a case of marked tibial osteolysis in association with a cemented, posterior stabilized total knee replacement in which the nonarticular surface of the tibial polyethylene insert appeared to be the source of wear debris. Fehring et al., in a prospective, multicenter review of 2149 primary Press-Fit Condylar total knee replacements (Johnson and Johnson), reported a 1.9% rate of revision for wear and osteolysis. The authors were unable to determine if this phenomenon was related to the quality of the polyethylene (which was compression-molded and machined), the sterilization methods (which changed during the study), or the use of modular tibial components. While these studies point to the problems with modularity, Scott et al. reviewed the prevalence of isolated polyethylene exchanges after 2000 consecutive posterior cruciate-retaining total knee arthroplasties and found modularity to be advantageous in 2.1% of the revision cases (wear in eighteen, instability in six, "incidental" exchanges in thirteen, and isolated femoral revision in one) after eight years of follow-up. While this number is small, it represents 55% of the reoperations in this series. Surgical technique and alignment have been shown to have an effect on polyethylene wear as well. D'Lima et al., with use of a finite element model, demonstrated that increasing articular conformity significantly reduced stresses when the knee was well aligned. In the presence of rotational malalignment, increased conformity appeared to be detrimental. The same group of authors compared wear in association with "low intensity" loading, "high intensity" loading, and simulated malalignment (3° varus) and found that the most wear occurred in the malalignment group (as indicated by wear values of 3.1, 7.4, and 9.2 mg/million cycles for the three groups, respectively) (p < 0.01). Bergandi et al., in an animal model involving New Zealand rabbits, evaluated the time to onset of osteolysis in association with cemented and cementless implants. By twenty-two weeks, osteolysis was noted in association with 96.6% of the cementless implants compared with 22.9% of the cemented implants (p < 0.001). Lavernia et al. assessed the relationship between activity level, length of implantation, and wear in a study of twenty-eight retrieved total knee replacements. The most important predictor of volumetric wear was the weight of the patient (p = 0.01), and the most important predictor of creep or deformation was the activity level (as determined with use of the UCLA score) (p = 0.039). Revision Total Knee Replacement Several papers focused on techniques of revision total knee replacement. Jazrawi et al., in a study of twelve cadaveric knees, evaluated the effect of stem length, diameter, and mode of fixation on the motion and stress transfer of a cemented tibial tray. They found that a press-fit stem can achieve tray stability similar to that obtained with a shorter cemented stem and can avoid the potential problems that are associated with cement. Barrack et al., in a study of 112 revision total knee replacements performed with cemented components with press-fit stems, found a 9% rate of reoperation and a 2.2% rate of aseptic loosening (defined as revision or radiographic evidence of loosening) after four to eight years of follow-up. Bugbee et al., in a review of 139 revision total knee replacements, compared implants that were designed for primary total knee replacement with those that were designed for revisions. They found that the revision implants exhibited superior durability and performance (as indicated by a revision rate of 6% compared with a revision rate of 29% at a mean of seven years; p < 0.05), despite their use in more difficult reconstructions. Clatworthy et al. reported on fifty-two revision total knee replacements in which structural allograft was used for uncontained defects. The mean duration of follow-up was ninety-seven months. The authors reported a 23% rerevision rate by seventy months and a ten-year survivorship of 72% following the treatment of these very difficult cases involving massive bone loss. Hanssen described a novel technique of bone-grafting for severe patellar bone loss during revision total knee replacement and found that the mean patellar thickness improved from 8 mm to 22 mm postoperatively, with satisfactory short and intermediate-term clinical results. Two reports on exposure were presented. Sharkey et al., in a study of 215 revision total knee replacements, found that the use of extensor mechanism tenolysis for exposure obviates the need for more extensive release of the extensor mechanism and is associated with a low rate of complications (as indicated by a 0.47% prevalence of patellar tendon rupture and a 0.47% prevalence of extensor lag). Ahluwalia et al., in a review of twenty-two revision total knee replacements in which a tibial tubercle osteotomy was performed, reported a 100% rate of union by three months, no extensor lag, no wound-healing difficulties, no infections, and no fractures. The fate of eighty-eight unrevised all-polyethylene patellar components in patients who had had a revision total knee replacement was reviewed by Lonner et al. after forty-two months of follow-up. The authors reported anterior knee pain in only four patients (two of whom had aseptic loosening of the patellar component). Babis et al., in a review of the Mayo Clinic's experience with isolated tibial insert exchange and arthrolysis for the management of stiffness following total knee replacement, reported poor improvement in Knee Society pain and function scores 20 . Two of the seven knees in the study were rerevised (one for infection and one for loosening), and the remaining five were painful and stiff at the time of the latest follow-up, with a mean postoperative arc of motion of 58°. It is generally agreed that the minimal amount of constraint that is required should be used during revision total knee replacement. Determining the amount of constraint that is needed can be difficult. Maheshwer et al., in a report on the clinical and radiographic outcome of twenty-nine revision total knee arthroplasties performed with the Constrained Condylar Knee prosthesis (Zimmer), noted only two reoperations (one for fracture and one for patellar realignment) and no instances of aseptic loosening after a mean duration of follow-up of fifty-four months. Beckenbaugh et al., in a report on the fifteen-year results of twenty revision procedures performed with use of a cemented Total Condylar III replacement (Johnson and Johnson), noted that four of the replacements had failed (two because of aseptic loosening and two because of infection) and that the remaining sixteen were radiographically stable. There were two reports on the use of hinged components for revision total knee replacement. Hanssen reported on the results of sixty-nine total knee replacements that were performed with use of the Kinematic Rotating Hinge prosthesis (Howmedica, Rutherford, New Jersey) for the treatment of severe bone loss and collateral ligament instability (seventeen knees), failure of a prior hinge (fifteen), nonunion of a periprosthetic fracture (twelve), acute periprosthetic fracture (ten), infection (seven), severe instability (six), and congenital dislocation of the knee (two). After a mean duration of follow-up of six years, the reoperation rate was 29%. Jones et al. reported on sixteen procedures (fifteen revisions and one primary replacement) in which the S-ROM hinged prosthesis was used for the treatment of severe instability and bone loss. After a minimum duration of follow-up of two years, there was significant improvement in Knee Society scores (p < 0.001) and no loosening.
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