Impingement after total knee arthroplasty caused by cement extrusion and proximal tibiofibular instability

A 57-year-old patient with rheumatoid arthritis showed posterolateral impingement after total knee arthroplasty. The radiographs showed bone cement extrusion posterolateral to the tibial tray. Arthrotomy through a posterolateral approach revealed that the impingement was caused not only by cement extrusion against the fibular head but also by proximal tibiofibular joint instability. It was speculated that rheumatoid arthritis had caused proximal tibiofibular instability, active knee motion had caused fibular head shift by tension of biceps femoris and the fibular head had been impinged on the extruded cement. In cementing the tibial tray, especially in a rheumatoid patient, it is of paramount importance to take caution against posterolateral cement extrusion in order to minimize the risk of fibular head impingement during total knee arthroplasty.     

Renal expression of parathyroid hormone-related protein (PTHrP) and PTH/PTHrP receptor in a rat model of tubulointerstitial damage

The effect of a meniscal bearing on knee laxity in anterior cruciate ligament-sacrificing total knee arthroplasty was evaluated in 7 cadaver knees using a knee testing device that measured knee flexion angle as well as laxity to medial-lateral, anterior-posterior [AP], and rotational loads. A standard fixed tibial component and mobile tibial components (AP sliding, rotationally sliding, and AP and rotationally sliding) were used to evaluate AP, rotational, and varus-valgus stability and maximal flexion and extension with the neutrally positioned and malrotated tibial tray. The AP movable components increased AP laxity, and the fixed component decreased rotational laxity significantly when compared with the normal knees. The rotationally movable components did not change knee laxities significantly even when the tibial tray was malrotated. No significant difference among the components was detected when the maximal flexion and extension angles were compared in the neutrally positioned tibial tray. Malrotation of the tibial tray decreased the maximal extension angle in the fixed component. This study showed that the rotationally movable component can achieve near-normal laxity regardless of tibial tray rotation, but AP mobility of the bearing produces AP laxity that could lead to implant failure.     

Uncemented total shoulder arthroplasty. A review

Clinicians have had much experience with uncemented humeral components. A press-fitted humeral component will usually remain stable in the absence of a glenoid component. From the information available, surgeons should not continue to use press-fitted humeral components for total shoulder arthroplasty. Tissue ingrowth humeral components offer promise; however, the reports to date have short or intermediate length followup, and radiographic results do not equal those of cemented components. Early clinical results with tissue ingrowth glenoid components are excellent; radiographically evident changes occur much less frequently than they do following cement fixation. However, their disadvantage is the possibility of accelerated polyethylene wear and subsequent metal-induced synovitis. As such, there are no clear cut indications for cement fixation versus tissue ingrowth fixation for the glenoid component other than those intuitively based on bone quality and quantity in the glenoid fossa. Accruing experience will help to define the indications better, but given the similarity of clinical outcomes to date, distinction between the options may be difficult.     

Treatment of major defects of bone with bulk allografts and stemmed components during total knee arthroplasty

We reviewed the results an average of fifty months (range, twenty-four to 120 months) after the use of thirty-five allografts in thirty patients during primary or revision total knee replacement. Twenty-nine femoral-head allografts, five distal femoral allografts, and one proximal tibial allograft were used in conjunction with a long-stemmed implant to reconstruct large osseous defects. The patients were evaluated clinically, radiographically, and subjectively (with use of a questionnaire). Twenty-six (87 per cent) of the thirty patients had a good or excellent clinical result, and no revisions were necessary. As none of the patients had collapse of the graft, subsidence of the implant, or revision, we believe that the outcome of treatment with a femoral-head allograft, particularly in association with a component inserted with cement, is excellent. Four non-porous-coated components were placed without cement on structural allografts. Radiographically, three of those components subsided, but none of the three needed revision and two were associated with a good clinical result. Our current practice is to cement components in all arthroplasties involving grafting. Our findings suggest that the use of a stemmed component reduces the stress on the allograft, host bone, and fixation interface. In addition, such a component contributes to the longevity of a total knee replacement associated with a bone graft. Additional studies with long-term follow-up are necessary to confirm this outcome.     

Revision of failed prosthetic anterior cruciate ligament reconstruction

Revision of failed prosthetic anterior cruciate ligament reconstructions will continue to be necessary as previously placed prosthetic devices fail with time. These patients often present with recurrent instability, pain, swelling, or effusions. Graft rupture and the generation of particulate debris are common causes of these symptoms. To effectively treat these patients requires careful preoperative evaluation and planning. Operative treatment includes removing the prosthesis and metal fixation devices, evaluating femoral and tibial bone stock, and determining adequacy of previous tunnel position. Staging of the operation may be a necessity if significant bone loss or poor tunnel position on either the femoral or tibial side requires bone grafting. The use of an autogenous bone-patellar tendon-bone graft is suggested and has proven to be effective in restoring knee stability in these revision cases. The ultimate outcome following revision of failed prosthetic ligaments may be limited by associated intraarticular pathology often seen in this patient population.     

A quantitative pharmacological study of the cholinergic depolarization of hippocampal pyramidal cells in rat brain slices

Twenty-eight unicompartmental knee arthroplasties performed as an alternative to high tibial osteotomy or tricompartmental knee arthroplasty in patients under 60 years of age were reviewed after 2 to 6 years of follow-up. The patient's age at the time of operation averaged 52 years. Using the Knee Society Score, 90% were rated good or excellent results in terms of function and pain relief. The average flexion angle obtained was 124 degrees, and the average postoperative alignment was 4 degrees of anatomic valgus for varus deformities and 8 degrees for valgus deformities. The average activity level according to the Tegner and Lysholm score slightly improved (preoperative, 2.3; follow-up, 2.7 points). Of the 28 knees, 9 (32%) presented radiolucent lines about the tibial component and two had incomplete radiolucent lines at the bone-cement interface on the femoral side. There was no correlation between activity level and tibial radiolucent lines. Two revisions were performed because of loosening of the femoral component at the prosthesis-cement interface. One was converted to another unicompartmental arthroplasty and the other to a tricompartmental arthroplasty. One tibial component exhibited an asymptomatic slowly progressive radiolucency. Unicompartmental knee arthroplasty in middle-aged patients yields 2- to 6-year results competitive with osteotomy but inferior to tricompartmental arthroplasty in terms of revision. The specific prosthetic design used in this series appeared to be vulnerable to femoral component loosening possibly because of constrained tibial topography and smooth tapered femoral fixation lugs.     

The effect of hydroxyapatite on the micromotion of total knee prostheses. A prospective, randomized, double-blind study

A prospective, randomized, double-blind study was performed to evaluate three different means of fixing tibial components during total knee arthroplasty. Eleven components fixed with cement, ten hydroxyapatite-coated components fixed without cement, and ten noncoated components fixed without cement were studied. A posterior cruciate ligament-retaining total condylar implant was used. Micromotion of the components was assessed with roentgen stereophotogrammetric analysis during the two-year follow-up period. There were no significant differences among the patients with regard to age (mean [and standard deviation], 68 +/- 11.6 years), body-mass index (mean, 23 +/- 2.8 kilograms per square meter), or stage of osteoarthrosis (mean, 4 +/- 2.4 according to the classification system of Ahlback and 5 +/- 0.6 according to that of Larsen et al.). The diagnosis was osteoarthrosis in five knees, and it was rheumatoid arthritis in twenty-six. The clinical scores were similar among the study groups. According to the system of the Knee Society, the mean preoperative functional score was 10 +/- 2.9 points and the mean preoperative knee score was 24 +/- 3.2 points. At the two-year follow-up evaluation, these scores were 41 +/- 8.3 and 79 +/- 3.2 points, respectively. A significant difference with regard to micromotion was found between the noncoated components fixed without cement and the hydroxyapatite-coated components fixed without cement as well as between the noncoated components fixed without cement and the components fixed with cement (p < 0.001, analysis of variance). The hydroxyapatite-coated components fixed without cement and the components fixed with cement both had far less micromotion along the longitudinal axis (subsidence) throughout the follow-up period than did the noncoated components fixed without cement. At the two-year follow-up evaluation, the subsidence of the noncoated components was -0.73 +/- 0.924 millimeter, the subsidence of the cemented components was -0.05 +/- 0.109 millimeter, and the subsidence of the hydroxyapatite-coated components was -0.06 +/- 0.169 millimeter. The cemented components as well as the hydroxyapatite-coated components also had less translation along the transverse axis (p < 0.001, analysis of variance) and the sagittal axis (p < 0.001, analysis of variance) compared with the noncoated components. In conclusion, micromotion of hydroxyapatite-coated tibial components fixed without cement was similar to that of tibial components fixed with cement. Therefore, hydroxyapatite, a biological mediator, may be necessary for the adequate fixation of tibial components when cement is not used.     

Intracellular distribution of phospholipase C gamma 1 in cell lines with different levels of transformation

PURPOSE OF THE STUDY: To assess after 83 months of follow-up, the results of 19 femoral revisions carried out according to an original method combining a cemented stem and bone reconstruction by means of impacted-morcelized bone allograft protected by a titanium mesh. MATERIALS: Twenty hips (18 patients mean aged 58 at surgery) were included between 1986 and 1991. Five hips had a least one previous prosthetic revision, one hip was revised because of septic loosening. No patient was lost for follow-up, but two had died during the follow-up period: one patient died one month after surgery was excluded, one other died 7 years after the index procedure and was included with his last hip rating. Loss of femoral bone stock was severe according to the SOFCOT four stage rating system: 2 femurs were grade II, 14 grade III, and 3 grade IV. Femoral stem migration was assessed with landmarks recommended by Walker. All the measurements were performed with a digitizer (OrthoGraphics). METHODS: All the procedures were carried out through a posterolateral approach, augmented by 4 trochanteric osteotomies and 5 distal femoral windows. After prosthesis and cement removal, a bone plug was placed into the medullary canal. Then, cancelous bone morcelized allografts were impacted in the femoral defects through the medullary canal. A titanium mesh cylinder was placed into the femur to separate the graft from the cement introduced later to obtain fixation of the revision stem. The stem was extended about 5 centimeters over the distal edge of the grafts in order to bridge the femoral defects. The mesh was extended only in front of the grafts and was used to protect them from excessive cement penetration. RESULTS: Functional improvement was noticeable since the Merle d'Aubigné Hip score improved from 9.8 to 16.3 at follow-up. The pain score improved from 2.1 to 5.5 and walking score from 2.3 to 5. Adverse effects occurred during the first cases and were related to cement removal: 3 greater trochanter fractures, 5 distal femoral perforations and 2 non displaced femoral shaft fractures. The septic revision had recurrence of infection associated with radiolucent lines > 2 millimeters and the only one graft resorption. One trochanteric non-union was observed but no prosthetic dislocation. Only one femoral stem migration (4.4 millimeters) was detected without any other radiographic features of loosening after 9 years of follow-up. This stem was considered as loosed, but was not revised because of few clinical symptoms. Only 2 radiolucent lines less than 2 millimeters at the bone cement interface in Gruen's zones 3 to 5. Likewise, no radiographic feature of stress-shielding was observed. On follow-up X-rays, 3 hips had corticalisation of the grafts, and 12 hips demonstrated normal cancelous trabeculations in the grafts. CONCLUSION: Satisfactory functional and radiographic results were obtained with this method after 5 to 10 years of follow-up instead of severe preoperative femoral bone stock impairement. Likewise, we observed only one recurrence of loosening diagnosed with the help of digitized X-ray examination. Only one significant (> 3.5 mm) femoral stem migration was detected. Radiographic features of femoral reconstruction were observed but without histologic proof of graft integration. This method uses a longer stem than the "Exeter", but avoids a high rate of femoral stem migration and appears compatible with femoral bone reconstruction.     

Stability of proximal femoral grafts in canine hip arthroplasty

In a canine model, the fixation stability of a prosthesis and proximal bone graft composite were measured relative to the distal femur. One group had the prosthesis graft composite cemented into the distal femur. The second group had the prosthesis graft composite press fit into the distal femur for biologic ingrowth. Displacements of the proximal femoral grafts relative to the host bone in each group were measured after ex vivo (acute with graft) implantation and 4 months after implantation. A third group with no osteotomy (acute intact) simulated perfect graft to host bone union. Relative displacements representing 6 degrees freedom (translation and rotation) were calculated from the displacement values measured by 9 eddy current transducers. Measurements of displacement were used to test the hypothesis that distal press fit fixation equals distal cement fixation at 4 months after implantation. In all cases the measured translations and rotations of the graft to implant construct were small and of a magnitude that should encourage bone ingrowth (< 0.05 mm and < 0.1 degree, respectively). The stability of the press fit group at 4 months was not significantly different from the cemented group in axial and transverse displacement during axial and transverse loading, respectively. There was no difference in stabilities at 4 months between distal press fit and cemented fixation in hip replacements requiring a proximal femoral graft.     

Duo-condylar knee arthroplasty: hospital for special surgery design

This is a report of 94 knees in 88 patients with the duo-condylar type of knee arthroplasty. The follow-up period of time was between 2 to 4 years with an average of 3 years. The rheumatoid to osteoarthritic patient ratio was 3 to 1. The overall results were excellent in 37.5 per cent, good in 37.5 per cent, fair in 16 per cent, and poor in 9 per cent. The main causes of failure and poor results were: (1) under or over correction of deformity leading to subluxation and/or instability of the knee; (2) loosening of the tibial component, and (3) symptoms arising from the patellofemoral joint. The revision rate is 5.5 per cent. The progressive radiolucency at the cement bone bond is 26 per cent of which 16 per cent is up to 1 mm and 10 per cent is between 1.5 to 3 mm. To further improve the results of arthroplasty, one should take into consideration (1) replacement of the patellofemoral joint, (2) insertion of the prosthesis in the proper anatomical location under correct tension of the ligaments and capsule with the help of proper instrumentation and (3) improvement in fixation of the tibial component.     

Characteristics of impaired awareness after traumatic brain injury

The condylar constrained total knee arthroplasty was performed on 29 patients undergoing 33 procedures and were reviewed clinically and radiographically at an average follow-up of 5 years (range, 2-10 years). There were 21 women and 8 men. The average age at the time of surgery was 70 years (range, 32-84). Of the 16 knees that were revision total knee arthroplasties, 8 had a previous infected total knee arthroplasty, and 17 knees had severe deformities requiring the use of the condylar constrained prosthesis. The patients were rated according to the Knee Society clinical and radiological evaluation protocol. Measurements of femoral and tibial component position were obtained as well as femoral tibial angle, patella position, and cement bone radiolucencies. All clinical measurements were made by an independent physical therapist. Clinical results revealed an improvement from an average preoperative knee score of 38 points to an average postoperative score of 86 points. The clinical results for 19 (58%) knees were excellent, 8 (24%) had a good result, 1 (3%) was fair, 2 (6%) were poor, and 3 (9%) were failures. The patients' average functional levels increased from 24 to 58. The final average flexion was 96 degrees. Three knees have been revised (9%). One was revised for recurrent infection, one for periprosthetic fracture, and one for mechanical loosening of the tibial component. There were no other knees with evidence of radiologic loosening. We conclude that the condylar constrained total knee prosthesis provides an acceptable solution for revision and complex primary total knee replacements at an intermediate follow-up term of 5 years.     

Patellar component resection in revision and reimplantation total knee arthroplasty

Between 1979 and 1995, 34 knees in 31 patients had a revision or reimplantation total knee arthroplasty in which the patellar component could not be reinserted. The patellar bone stock in each of those cases was compromised markedly and precluded adequate prosthetic fixation. The mean followup after the revision operation was 3.5 years (range, 2-14 years). The Knee Society knee score improved from a mean of 59 points preoperatively to a mean of 75 points postoperatively. The function score improved from a mean of 46 points preoperatively to a mean of 69 points postoperatively. Complications occurred in five patients: one patient sustained a patellar fracture that required no additional treatment; one experienced intermittent episodes of patellar subluxation; one had a recurvatum deformity develop and was treated with a brace; one had persistent knee stiffness and had four manipulations; and one patient had an extensor lag of 30 degrees develop. Twenty-six patients were satisfied with the results of their revision operations and five were dissatisfied. Ten patients had persistent knee symptoms referable to the patellofemoral articulation: mild pain in three; moderate pain in six; and severe pain in one. This study suggests that resection of the patellar component during revision or reimplantation total knee arthroplasty may be a reasonable approach for patients with markedly compromised patellar bone stock; however, mild or moderate anterior knee pain can be expected to persist in as much as 1/3 of these patients.     

Effect of flexibility of the femoral stem on bone-remodeling and fixation of the stem in a canine total hip arthroplasty model without cement

The purpose of this study was to compare, with regard to fixation of the implant and femoral bone resorption, two fully porous-coated stems of different stiffnesses in a canine total hip arthroplasty model. A bilateral arthroplasty was carried out with insertion of a titanium-alloy stem (which had stiffness properties comparable with those of the canine femur) on one side and with insertion of a composite stem (which was three to fivefold more flexible than the canine femur) on the contralateral side. Eight femora were evaluated at six months and eight, at eighteen months after the operation, to determine the extent of bone ingrowth, periprosthetic cortical area, intracortical porosity, and bone-remodeling. Despite the markedly greater flexibility of the composite stems, no significant difference could be detected (with the numbers available), with regard to the overall degree of femoral stress-shielding, cortical area, or cortical porosity, between these stems and the stiffer, titanium-alloy stems at either time-period. However, the composite stems had less bone ingrowth and more formation of radiopaque lines than did the titanium-alloy stems. At eighteen months, the values for bone ingrowth were 9.7 +/- 5.38 percent (mean and standard deviation) for the composite stems compared with 28.1 +/- 5.31 percent for the titanium-alloy stems (p = 0.003). Furthermore, the histological sections from the femora containing a composite stem showed radiopaque lines indicative of fibrous ingrowth approximately threefold more often than did those from the femora containing a titanium-alloy stem (p = 0.02).     

Patellar tracking after total knee arthroplasty. The effect of tibial tray malrotation and articular surface configuration

The effect of total knee arthroplasty (TKA) with neutrally aligned and malrotated tibial trays was studied in five fresh anatomic specimen knees. Patellar shift, tilt, and rotation, and the rotational position of the tibia were measured in normal knees and after TKA with the Ortholoc Modular knee system. Both semiconstrained and unconstrained articular surfaces were assessed in the neutral position and at anatomic, 15 degrees internal, and 15 degrees external rotation of the tibial tray. After TKA, the patellae shifted slightly medially in the early phase of knee flexion because the anterior lateral flange of the femoral component was longer than the lateral trochlea of the femur and because the tibia rotated internally. The raised lateral flange on the femoral component tilted the patella medially at full extension after TKA. The semiconstrained tray allowed minimal tibial rotation because of its articular configuration. As much as 15 degrees malrotation of the unconstrained tibial tray did not affect patellar tracking. The semiconstrained tibial tray in the neutral position had almost the same patellar tracking as the unconstrained tray, but at 15 degrees external rotation, the semiconstrained tray internally rotated the tibia, leading to medial shift of the patella. Although 15 degrees internal rotation caused external rotation of the tibia, the patella did not shift as much laterally, despite the increase in the Q angle.     

A histomorphometric and histologic analysis of the implant interface in five successful, autopsy-retrieved, noncemented porous-coated knee arthroplasties

Five clinically successful, primary uncemented porous-coated anatomic knee implants were retrieved postmortem, 13-56 months after implantation, and were sectioned and evaluated histologically and histomorphometrically for bone ingrowth. The prosthesis-bone interface was divided into the following four zones: (1) the tissue prosthetic surface interface; (2) the beaded area; (3) the immediate beadless area; and (4) the marrow space. Although fibroosseous ingrowth was present in all cases, it varied quantitatively with each case and component. Average component bone ingrowth for the prosthesis interface (Zones 1 and 2) of patellae was 29%; tibias, 6%; and femora, 8%. In Zone 3, the percentage of bone apposed to the prosthesis for the patellae was 53%; tibias 36%; and femora, 32%. Zone 4, the marrow space, was not quantitated. The fibrous tissue filling nonbone-ingrown porous space in Zone 2 appeared "ligamentoid," connecting bone to beads within Zone 2 and between Zones 2 and 3. Zone 3 exhibited a bony plate formation parallel to the prostheses. No significant inflammation was noted. Overall there was more bone ingrowth into Zone 3 than Zones 1 and 2 with greater bone ingrowth found in the patellar components. The implant interface in clinically successful noncemented porous-coated prostheses of this design is characterized histologically by a noninflammatory fibroosseous ingrowth of varying degrees, and the fibrous component of this composite structure exhibits a highly organized pattern.     

From the RSNA refresher courses. Total hip arthroplasty: radiographic evaluation

Expected appearances of total hip arthroplasty vary according to type of implant, its method of fixation (cemented, porous coating for bone ingrowth, press fit), and whether it is a revision. Cemented arthroplastic components normally may show 1-2-mm-wide radiolucent zones at cement interfaces. Definite loosening is diagnosed when progressive widening of the radiolucent zone, migration of a cemented component, or change in alignment is seen. In cementless arthroplasty, normal findings include calcar resorption, radiolucent zones up to 2 mm in width, cortical thickening, periosteal reaction, endosteal sclerosis, and even subsidence of the femoral component that stabilizes at less than 1 cm. The most reliable radiographic signs of loosening in cementless arthroplasty are progressive subsidence, migration, or tilt of the component. Because subsidence or change in alignment may be very subtle, serial radiography and measurement are often required for diagnosis. Other signs that indicate loosening include bead shedding (in porous-coated prostheses), extensive cortical hypertrophy, endosteal bone bridging at the stem tip, endosteal scalloping, and a radiolucent zone wider than 2 mm. In revision arthroplasty, wide radiolucent zones and subsidence are common. The diagnosis of revision failure is based on progressive widening of the radiolucent zones and change in component position after 12 months.     

Development of bioactive bone cement and its clinical applications

This paper is a summary of already published papers on the bioactive bone cement (BA cement) which consists of CaO-SiO2-P2O5-MgO-CaF2 (AW glass-ceramic) powder and bisphenol-a-glycidyl methacrylate (Bis-GMA) resin. Two types of BA cement, dough and injection type, were prepared by changing their chemical compositions slightly. They harden in a few minutes exhibiting much lower curing temperature than PMMA cement. They have significantly higher compressive, bending, and tensile strengths than PMMA cement and have a character of bonding directly with bone in 4-8 weeks in vivo. Intercalary prosthetic replacement of the femur and total prosthetic replacement of the hip were performed in dogs using either PMMA cement or BA cement. Mechanical tests demonstrated that fixation strengths of these prostheses with BA cement increased with time and were significantly greater than those with PMMA cement tested at any time. Results of histological examinations showed direct bonding between BA cement and bone, and that the bone trabeculae around BA cement mantle grew with time, while with PMMA cement an intervening soft tissue layer was always observed at the cement-bone interface. BA cement was used in a few aged patients to install a hip prosthesis either in cases of revision or femoral neck fracture. The longest follow-up period of the patient is 4 yrs. The patients have been doing well with no adverse effect of the cement to date.     

Roentgen criteria and radiologic results of the Hofer-Imhof (H-I) threaded acetabulum cup in first time implantation

The Hofer-Imhof cup consists of a parabola-shaped titanium acetabular component with flat threads. These flat threads are designed to be self-cutting and allow accurate insertion without incarceration, even in sclerotic bone. In a prospective study conducted from May 1988 to July 1989, 143 Hofer-Imhof cups were implanted. Radiographic assessment included initial bone contact, cup position, fixation on osteophytes, presence of any radiolucencies or sclerosis, cup migration and bone ingrowth. Initial prosthesis fit was evaluated with a 20 degrees caudally angled anteroposterior X-ray for accurate demonstration of the threads. 119 of the Hofer-Imhof cups (83.2%) were available for radiographic follow-up at a mean of 65 months (min. 37 mo., max. 95 mo.). One cup required revision after 23 months due to infection. The cups had an average inclination of 47 degrees, and complete bone contact was evident in 86.6% on the postoperative X-ray. In 8.4% of the cups, some threads were not in contact with bone at the edge of the acetabulum. At final follow-up, 82.4% had complete bone ingrowth without any evidence of radiolucency (type I), 15.1% had near-complete bone ingrowth with minimal radiolucencies (type II), and 2.5% had predominantly fibrous fixation (type III). One cup (0.8%) showed excessive migration. The technique of anchorage using a flat thread, minimal bone resection as a result of the parabolic shape and the sandblasted titanium surface are the characteristic features of the Hofer-Imhof threaded cup and produce good medium-term results in primary hip arthroplasty.     

Algorithm for the surgical treatment of malignant lesions of the proximal tibia

Complications are common among patients treated for malignant lesions of the proximal tibia and can be difficult to manage. This investigation was a retrospective review of 40 patients treated with total knee replacements after proximal tibial resections. Various reconstructive methods were used to fix the prosthetic stems, reestablish the extensor mechanism, and provide soft tissue coverage. Thirty-one patients had adequate followup to allow for review of prosthetic outcome (means, 78 months; range, 25-193 months). Seven patients died with less than 2 years followup, and two patients had postoperative acute infections treated by early amputation to allow chemotherapy to resume promptly. The overall 5-, 8-, and 12-year event free prostheses survival rates were 62%, 33%, and 16%, respectively. Prognostic factors for prosthetic survival were analyzed (age, gender, type of excision, type of prosthesis, type of fixation, and percent of bone resected). None were statistically significant. Patients with less than 40% of the tibia resected had better prosthetic survival at 5 years. The durability of uncemented stem fixation exceeded that of cemented stems. Expected survival of prostheses after revision was 52% at 8 years. The major cause of limb loss was infection. Failure to reconstruct soft tissues satisfactorily caused most failures. Aggressive multistage management of infection is needed. Prosthetic knee replacement is most suitable for patients with cancers that require chemotherapy and for those patients who have short potential survival.     

Hemangiopericytoma: a 20-year single-institution experience

In this overview, which is based on selected books and reviews, the microscopic appearances of prosthesis-bone interfaces resulting from clinically relevant implantation techniques are highlighted. The following techniques are distinguished to insert and attach prostheses in the recipient bone: impaction into bone, primary mechanical interlocking, cement fixation, bone ongrowth and secondary mechanical interlocking with bioinert materials, and enhanced bone ongrowth and bone bonding to bioactive materials. The resulting typical histomorphologies of orthopedic and dental prostheses-bone interfaces are described and illustrated from the author's studies employing light, fluorescence, and backscattered electron microscopy, and corresponding microradiographs of undecalcified ground sections of bone and implants. Special emphasis is given to the mineralization-demineralization kinetics of the interfacial bone matrix interacting with specific surface reactions of some implant materials. Consequently, the distinction between bioinert and bioactive prosthetic materials is critically analyzed.