Purpose. Cementless cup with structural allograft is one of option for acetabular revision in the cases which has severe bone loss. This study was performed to verify that the structural allograft with cementless cup could be one of good options for revision of acetabular cup with severe bone defect and to verify that the allograft resorption affect the stability of cementless acetabular cup. Materials and Methods. We reviewed 25 cases of 25 patients who underwent acetabular cup rvision using cementless porous coated hemispherical cup with structural allograft from May 1992 to July 2011 July 2011. There were nine males and sixteen females with an average age of 50.0 years. The average follow-up period was 76.7(28∼212) months. The clinical evaluation was performed using Harris Hip Score(HHS) and UCLA activity score. Radiologically, the degree of resorption of grafted bone, incorporation of allograft bone with normal bone, osteolysis and cup loosening were evaluated. Results. Clinically, the average Harris hip score was improved from 54 preoperatively to 93.4 at the last follow-up. The average UCLA activity score was also improved from 4.3 preoperatively to 6.4 at the last follow-up. Radiologically, the incorporation of allograft was accomplished in 11.4 months and the resorption of grafted bone was noted in 3 cases(12%), but the allograft resorption had not progressed to moderate degree even in long term follow-up. There was no cup loosening and average survivor rate was 100% in 6 years. There was no infection, allograft nonunion, osteolysis. Conclusion. Cementless cup with structural allograft in acetabular cup reconstruction can provide excellent mi-term results in both clinical and radiological aspects. Structural allograft can provide strong mechanical support for the bone ingrowth of cementless cup. The clinical result of this study auggest that cementless cup with structural allograft can be a good option for acetabular cup revision with severe bone defect. Resorption of structural allograft rarely occurred, and the resorption of structural allograft does not affect stablility of cup even in long term follow-up

INTRODUCTION. Allograft reconstruction after resection of primary bone sarcomas has a non-union rate of approximately 20%. Achieving a wide surface area of contact between host and allograft bone is one of the most important factors to help reduce the non-union rate. We developed a novel technique of haptic robot-assisted surgery to reconstruct bone defects left after primary bone sarcoma resection with structural allograft. METHODS. Using a sawbone distal femur joint-sparing hemimetaphyseal resection/reconstruction model, an identical bone defect was created in six sawbone distal femur specimens. A tumor-fellowship trained orthopedic surgeon reconstructed the defect using a simulated sawbone allograft femur. First, a standard, ‘all-manual’ technique was used to cut and prepare the allograft to best fit the defect. Then, using an identical sawbone copy of the allograft, the novel haptic-robot technique was used to prepare the allograft to best fit the defect. All specimens were scanned via CT. Using a separately validated technique, the surface area of contact between host and allograft was measured for both (1) the all-manual reconstruction and (2) the robot-assisted reconstruction. All contact surface areas were normalized by dividing absolute contact area by the available surface area on the exposed cut surface of host bone. RESULTS. The mean area of contact between host and allograft bone was 24% (of the available host surface area) for the all-manual group and 76% for the haptic robot-assisted group (p=0.004). CONCLUSIONS. This is the first report to our knowledge of using haptic robot technology to assist in structural bone allograft reconstruction of defects left after primary bone tumor resection. The findings strongly indicate that this technology has the potential to be of substantial clinical benefit. Further studies are warranted

Massive bone loss on both the femur and tibia during revision total knee arthroplasty (TKA) remains a challenging problem. Multiple solutions have been proposed for small osseous defects, including morselised cancellous bone grafting, small-fragment structural allograft, thicker polyethylene inserts, and the use of modular augments attached to revision prosthetic designs. Large osseous defects can be treated with structural allografts, impaction bone-grafting with or without mesh augmentation, custom prosthetic components, and specialised hinged knee components. The metaphyseal area of the distal femur and proximal tibia is a particularly attractive option during revision TKA given that it is usually undamaged and well-vascularised. While multiple reconstructive options have been recommended, porous tantalum metaphyseal cones have the advantage of improved biologic fixation because of their high porosity (75–80%), interconnected pore space, and low modulus of elasticity (3 MPa) similar to that of cancellous bone. Such features allow tantalum cones to fill bone defects while tolerating physiological loads. Indications for porous tantalum metaphyseal cones include patients with Anderson Orthopaedic Research Institute Type 2B or greater defects. The surgical technique is simpler than structural allograft reconstructions with decreased preparation time, resulting in a possible decrease in infection rates. The modularity of porous tantalum metaphyseal cones also allows the surgeon to choose a size and position that best fits the individual defect encountered. Moreover, tantalum cones can be used with several revision systems. Short-term clinical follow up indicates that porous tantalum metaphyseal cones effectively provide structural support with the potential for long-term biologic fixation and durable reconstructions

The management of bone loss in revision total knee replacement (TKA) remains a challenge. To accomplish the goals of revision TKA, the surgeon needs to choose the appropriate implant design to “fix the problem,” achieve proper component placement and alignment, and obtain robust short- and long-term fixation. Proper identification and classification of the extent of bone loss and deformity will aid in preoperative planning. Extensive bone loss may be due to progressive osteolysis (a mechanism of failure), or as a result of intraoperative component removal. The Anderson Orthopaedic Research Institute (AORI) is a useful classification system that individually describes femoral and tibial defects by the appearance, severity, and location of bone defects. This system provides a guideline to treatment and enables preoperative planning on radiographs. In Type 1 defects, femoral and tibial defects are characterised by minor contained deficiencies at the bone-implant interface. Metaphyseal bone is intact and the integrity of the joint line is not compromised. In this scenario, the best reconstruction option is to increase the thickness of bone resection and to fill the defect with cancellous bone graft or cement. Type 2 defects are characterised by deficient metaphyseal bone involving one or more femoral condyle(s) or tibial plateau(s). The peripheral rim of cortical bone may be intact or partially compromised, and the joint line is abnormal. Reconstruction options for a Type 2A defect include impaction bone grafting, cement, or more commonly, prosthetic augmentation (e.g. sleeves, augments or wedges). In Type 2B defects, metaphyseal bone of both femoral condyles or both tibial plateaus is deficient. The peripheral rim of cortical bone may be intact or partially compromised, and the joint line is abnormal. Options for a Type 2B defect include impaction grafting, bulk structural allograft, prosthetic augmentation, metaphyseal sleeves (in some cases), or metaphyseal cones. Finally, in the presence of a Type 3 deficiency, both metaphyseal and cortical bone is deficient and there is partial or complete disruption of the collateral ligament attachments. In this case, the most commonly used reconstruction options include hinged implants or megaprostheses with or without bulk structural allograft, prosthetic augmentation, and/or metaphyseal/diaphyseal sleeves or cones. Today, we are fortunate to have a wide variety of options available to aid in reconstruction of a revision TKA with massive bone loss. Historically, use of cement, bone grafting, or use of a tumor-type or hinged implant were considered the main options for reconstruction. The development and adoption of highly porous sleeves and cones has given the surgeon a new and potentially more durable option for reconstruction of previously difficult to treat defects. Using radiographs and computed tomography, surgeons are able to preoperatively classify bone loss and anticipate a reconstruction plan based upon the classification; however, it is always important to have several back-up options on hand during revision surgery in the event bone loss is worse than expected

The moderator will lead a structured panel discussion that explores how to manage challenges commonly found in the multiply revised knee. Topics covered will include: (1) Exposure in the multiply operated knee (when to use quad snip, tibial tubercle osteotomy, other techniques); (2) Implant removal: Tips for removing stemmed implants; (3) Management of bone loss in multiply operated knees (metal cones/sleeves vs. structural allograft vs. particulate graft); (4) Level of constraint (when to use posterior stabilised, constrained condylar, and hinge) and management of instability in multiply operated knees; (3) Management of bone loss in multiply operated knees (metal cones/sleeves vs. structural allograft vs. particulate graft); (5) Preferred management of infection in the multiply operated knee; (6) The extensor mechanism: Preferred deficient patellar bone management; Preferred extensor mechanism deficiency management; (7) When is it time to convert to a salvage procedure (i.e. fusion, resection arthroplasty, amputation)?; (8) Post-operative management: wound management; knee range of motion

Metaphyseal bone loss, due to loosening, osteolysis or infection, is common with revision total knee arthroplasty (TKA). Small defects can be treated with screws and cement, bone graft, and non-porous metal wedges or blocks. Large defects can be treated with bulk structural allograft, impaction grafting, or highly porous metal cones. The AORI classification of bone loss in revision TKA is very helpful with pre-operative planning. Type 1 defects do not require augments or graft—use revision components with stems. Type 2A defects should be treated with non-porous metal wedges or blocks. Type 2B and 3 defects require a bulk structural allograft or porous metal cone. Highly-porous metal metaphyseal cones are a unique solution for large bone defects. Both femoral (full or partial) and tibial (full, stepped, or cone+plate) cones are available. These cones substitute for bone loss, improve metaphyseal fixation, help correct malalignment, restore joint line, and permit use of a short cemented stem. The technique for these cones involve preparing the remaining bone with a high speed burr and rasp, followed by press-fit of the cone into the remaining metaphysis. The interface is sealed with bone graft and putty. The fixation and osteoconductive properties of the outer surface allow ingrowth and biologic fixation. The revision knee component is then implanted, with antibiotic-cement, into the porous cone inner surface, which provides superior fixation compared to cementing into deficient metaphyseal bone. There are several manufacturers that provide porous cones for knee revision, but the tantalum-“trabecular metal” cones have the largest and longest clinical follow-up. The advantages of the trabecular metal cone compared to allograft include: technically easier; biologic fixation; no resorption; and lower risk of infection. The disadvantages include: difficult extraction and intermediate-term follow-up. The author has reported the results of 33 trabecular metal cones (9 femoral, 24 tibial) implanted in 27 revision cases at 2–5.7 years follow-up. One knee (2 cones) was removed for infection. All but one cone showed osseointegration. Multiple other studies have confirmed these results. Trabecular metal cones are now the author's preferred method for the reconstruction of large bone defects in revision TKA

The goals of revision arthroplasty of the hip are to restore the anatomy and achieve stable fixation for new acetabular and femoral components. It is important to restore bone stock, thereby creating an environment for stable fixation for the new components. The bone defects encountered in revision arthroplasty of the hip can be classified either as contained (cavitary) or uncontained (segmental). Contained defects on both the acetabular and femoral sides can be addressed by morselised bone graft that is compacted into the defect. Severe uncontained defects are more of a problem particularly on the acetabular side where bypass fixation such as distal fixation on the femoral side is not really an alternative. Most authors agree that the use of morselised allograft bone for contained defects is the treatment of choice as long as stable fixation of the acetabular component can be achieved and there is a reasonable amount of contact with bleeding host bone for eventual ingrowth and stabilisation of the cup. On the femoral side, contained defects can be addressed with impaction grafting for very young patients or bypass fixation in the diaphysis of the femur using more extensively coated femoral components or taper devices. Segmental defects on the acetabular side have been addressed with structural allografts for the past 15 to 20 years. These are indicated in younger individuals with Type 3A defects. Structural grafts are unsuccessful in Type 3B defects. Alternatives to the structural allografts are now being utilised with shorter but encouraging results in most multiply operated hips with bone loss. New porous metals such as trabecular metal (tantalum), which has a high porosity similar to trabecular bone and also has a high coefficient of friction, provide excellent initial stability. The porosity provides a very favorable environment for bone ingrowth and bone graft remodeling. Porous metal acetabular components are now more commonly used when there is limited contact with bleeding host bone. Porous metal augments of all sizes are being used instead of structural allografts in most situations. On the femoral side, metaphyseal bone loss, whether contained or uncontained, is most often addressed by diaphyseal fixation with long porous or tapered implants, modular if necessary. Distal fixation requires at least 4 centimeters of diaphyseal bone and in Type IV femurs, a choice must be made between a mega prosthesis or a proximal femoral allograft. The proximal femoral allograft can restore bone stock for future surgery in younger patients. The mega prosthesis which is more appropriate in the older population may require total femoral replacement if there is not enough diaphyseal bone for distal fixation with cement. Cortical struts are used for circumferential diaphyseal bone defects to stabilise proximal femoral allografts, to bypass stress risers and to serve as a biological plate for stabilising peri-prosthetic fractures

Femoral components in total hip replacements fail in well-known ways. There is vertical sink, posterior rotation and pivot, either distal or mid-stem. In order to sink, the stem moves into valgus and then slides down the inside of the calcar. It does not cut through the calcar. To prevent sink and pivot, a canal filling stem is required. Canal fill prevents the stem from moving into valgus and, therefore, it will not sink. Two centimeters with complete canal fill is adequate in a primary stem. A long stem will give longer canal fill in a revision. Sharp distal flutes will prevent rotation. The distal end of the stem should be polished. One is looking for a distal stability, not distal fixation. If the isthmus is intact, a primary stem can be used. If the isthmus is damaged, a long stem is necessary. If the calcar is intact, a primary neck is adequate. If the calcar is missing down to the level of the lesser trochanter, a calcar replacement neck is required. If there is more than 70 millimeters of completely missing proximal femur, a structural allograft is required. If the proximal femur is damaged, the ability to place a sleeve or collar to seek the best bone available independently of the stem version is very helpful. No matter how poor the proximal bone quality is, it can be supplemented by cerclage wires. The implant will sink only if the cerclage wires break. The advantage of proximal fixation is that loading the proximal femur speeds recovery. The huge disadvantage of distal fixation is removal of the implant should it become necessary. My long term results for the S-ROM stem used in revision are now out over 20 years. There were 119 primary stems with a minimum follow up of 5 years with no revisions for aseptic loosening. There were 262 long stems used. Nine (3.7%) underwent aseptic loosening. Most of these were due to technical errors due to my inexperience in the learning process of revision surgery. Four were dependent on strut-grafts and should have been treated with structural allografts. There were seven cases with structural allografts. Three were revised. Again, these were largely from problems arising from inexperience. I believe proximal modularity with distal stability allows the vast majority of revision cases to be treated with proximal fixation

Impaction grafting is an excellent option for acetabular revision. It is technique specific and very popular in England and the Netherlands and to some degree in other European centers. The long term published results are excellent. It is, however, technique dependent and the best results are for contained cavitary defects. If the defect is segmental and can be contained by a single mesh and impaction grafting, the results are still quite good. If, however, there is a larger segmental defect of greater than 50% of the acetabulum or a pelvic discontinuity, other options should be considered. Segmental defects of 25–50% can be managed by minor column (shelf) or figure of 7 structural allografts with good long term results. Porous metal augments are now a good option with promising early to mid-term results. Segmental defects of greater than 50% require a structural graft or porous augment usually protected by a cage. If there is an associated pelvic discontinuity then a cup cage is a better solution. An important question is does impaction grafting facilitate rerevision surgery? There is no evidence to support this but some histological studies of impacted allograft would suggest that it may. On the other hand there are papers that show that structural allografts do restore bone stock for further revision surgery. Also the results of impaction grafting are best in the hands of surgeons comfortable with using cement on the acetabular side, and one of the reasons why this technique is not as popular in North America

Metaphyseal bone loss, due to loosening, osteolysis or infection, is common with revision total knee arthroplasty (TKA). Small defects can be treated with screws and cement, bone graft, and non-porous metal wedges or blocks. Large defects can be treated with bulk structural allograft, impaction grafting, or highly porous metal cones. The AORI classification of bone loss in revision TKA is very helpful with preoperative planning. Type 1 defects do not require augments or graft—use revision components with stems. Type 2A defects should be treated with non-porous metal wedges or blocks. Type 2B and 3 defects require a bulk structural allograft or porous metal cone. Trabecular metal (TM) metaphyseal cones are a unique solution for large bone defects. Both femoral (full or partial) and tibial (full, stepped, or cone+plate) TM cones are available. These cones substitute for bone loss, improve metaphyseal fixation, help correct malalignment, restore joint line, and permit use of a short cemented stem. The technique for these cones involve preparing the remaining bone with a high speed burr and rasp, followed by press-fit of the cone into the remaining metaphysis. The interface is sealed with bone graft and putty. The fixation and osteoconductive properties of the outer surface allow ingrowth and biologic fixation. The revision knee component is then cemented into the porous cone inner surface, which provides superior fixation compared to cementing into deficient metaphyseal bone. The advantages of the TM cone compared to allograft include: technically easier; biologic fixation; no resorption; and lower risk of infection. The disadvantages include: difficult extraction and intermediate-term follow-up. The author has reported the results of 33 TM cones (9 femoral, 24 tibial) implanted in 27 revision cases at 2–5.7 years follow-up. One knee (2 cones) was removed for infection. All but one cone showed osseointegration. TM cones are now the preferred method for the reconstruction of large bone defects in revision TKA

In North America, and for the most part globally, a cementless acetabular component with adjuvant screw fixation is the preferred technique for revision total hip arthroplasty. However, there are situations that involve massive pelvic bone loss that preclude the use of a cementless cup alone. Options include: . i). Enhanced fixation components and augments. ii). Specialised constructs (cup/cage). iii). Structural allografts. iv). Bone graft substitutes. Complex acetabular revisions present the arthroplasty surgeon with challenges that require an approach with more than one solution for all scenarios. While structural allografts have recently fallen out of favour with the increasing use of enhanced fixation components, there would still appear to be a role in the case in which bone stock restoration is a primary goal. The role of bone graft substitutes remains unclear, with supportive basic science data, but limited clinical experience to date. An algorithm will be discussed to assist in prioritising the multiple goals of acetabular reconstruction and one stock restoration

Restoration of bone loss is a major challenge of revision TKA surgery. It is critical to achieve of a stable construct to support implants and achieve successful results. Major bone defects of the femoral and/or tibia (AORI type IIB/III) have been reconstructed using impaction grafting, structural allografts or tumor prostheses. The major concerns with structural allograft are graft resorption, mechanical failure, tissue availability, disease transmission, considerable surgical skill required and prolonged operative time. Porous tantalum metaphyseal cones, are becoming the established method of choice to correct large bone defects with several recent studies demonstrating promising results. The high coefficient of friction of these implants provides structural support for femoral and tibial components. The high degree of porosity has excellent potential for bone ingrowth and long-term biologic fixation. Several published series, although with relatively small cohorts of patients, have reported good short-term results with trabecular metal cones for major femoral and tibial bony defects in revision TKA. In a recent study, 16 femoral and 17 tibial cones were reviewed at an average follow up of 33 months (range, 13 to 73 months) the mean Knee Society Score improved from 42 pre-operatively to 83 at last follow up with an improvement of the functional score from an average of 34 to 66 (p<0.0001). Radiological follow up revealed no evidence of loosening or migration of the constructs. No evidence of complications were noted in correlation with the use of trabecular metal cones

Segmental defects of the acetabulum are often encountered in revision surgery. Many times these can be handled with hemispherical cups. However when larger defects are encountered particularly involving the dome and/or posterior wall structural support for the cup is often needed. In the past structural allograft was used but for the last 12 years at our institution trabecular metal augments have been used in the place of structural allograft in all cases. This talk will focus on technique and mid-term results using augments in association with an uncemented revision shell. The technique can be broken down into 6 steps outlined below: 1. Exposure, 2. Reaming, 3. Trialing, 4. Augment Inserted, 5. Cup Insertion/Stabilization, 6. Trial Reduction/Liner Cementation. A recent study was undertaken to assess the mid-term results of this technique. We prospectively followed the first 56 patients in whom these augments were utilised in combination with a trabecular metal acetabular component in our unit. Details of this study will be presented. The median follow up of the surviving patients was 110 months (range 88–128 months). Survivorship of the augments at 10 years was 92.2% (95% CI: 97.0–80.5%). In one case the augment was revised for infection and in 3 for loosening. In 1 of the revised cases there was a pre-operative pelvic discontinuity, the other 2 discontinuities in the series were not revised and remain asymptomatic. Conclusions. The results of the acetabular trabecular metal augments continue to be encouraging in the medium to long term with low rates of revision or loosening in this complex group of patients

The S-ROM stem is distally circular canal filling with thin sharp flutes which engage the endosteal cortex. The rotational stability produced by this is 37 Nm, which exceeds the service loads on the hip of 22 Nm. The distal canal fill prevents varus and valgus displacement. The porous-coated proximal sleeve provides resistance to vertical sink and also excludes the distal stem from the effective joint space. The primary stem is straight and the long stem is bowed with a 15 degrees anteversion twist proximally. The neck comes in lengths from 30 to 46mm with varying offset. The sleeves come in variable size and geometry. The stem choice in revision surgery is based on the Scoot Diamond Classification. Type 1 (this is going to be easy) is a primary stem. Type 2 (this is going to be difficult) implies diaphyseal bone loss and will require a long stem. Type 3 (Oh My God), implies more than 70mm of completely missing proximal femur and will require a structural allograft cemented to the sleeve. Results. The follow-up is from 2 to 22 years. There were 119 primary stems. Revisions for aseptic loosening were zero. One stem was removed for late sepsis at nine years. There were 262 long stem cases. Stem revision for aseptic loosening occurred in nine cases (3.7%). Four became loose because of inappropriate and obsolete techniques of allografting, one for non-union of a subtrochanteric osteotomy and four for failure of ingrowth into the sleeve. Four were revised for late sepsis. Structural allografts comprised seven cases. Three were revised at years 7, 11 and 16. Conclusion. The revision rate for aseptic loosening in hip revision cases is acceptably low. Other issues such as late polyethylene wear and dislocation continue to decrease

Metaphyseal bone loss is common with revision total knee arthroplasty (TKA). The causes of bone loss include: osteolysis, loosening, infection, iatrogenic or a combination. Small defects can be treated with screws and cement, bone graft, and non-porous metal wedges or blocks. Large defects can be treated with bulk structural allograft, impaction grafting, or highly porous metal cones or augments. The AORI classification of bone loss in revision TKA is very helpful with preoperative planning. Type 1 defects do not require augments or graft—use revision components with stems. Type 2 defects should be treated with non-porous metal augments—wedges or blocks. Type 3 defects require a bulk structural allograft or large highly porous metal cone. Trabecular metal (TM) metaphyseal cones are a unique solution for large bone defects. There are both femoral (full or partial) and tibial (full or stepped) TM cones available. These cones substitute for bone loss, improve metaphyseal fixation, help correct malalignment, restore joint line, and perhaps, permit use of a shorter stem. The technique for these cones involve sculpturing of the remaining bone with a high speed burr and rasp, followed by press-fit of the cone into the remaining metaphyseal bone. The interface is sealed with bone graft and putty. The fixation and osteoconductive properties of the outer surface allow ingrowth and hopefully long term biologic fixation. The revision knee component is then cemented into the porous cone inner surface, which provides superior fixation compared to deficient metaphyseal bone. The advantages of the TM cone compared to allograft include: technically easier; biologic fixation; no resorption; and (?) lower risk of infection. The disadvantages include: difficult extraction and relatively short-term follow-up. The author has reported the results of 33 TM cones (9 femoral, 24 tibial) implanted in 27 revision cases at 2–5.7 years follow-up. One knee (2 cones) was removed for infection. All but one cone showed osseointegration. TM cones are a promising method for the reconstruction of large bone defects in revision TKA

Background. Despite promising results have shown by osteogenic cell-based demineralized bone matrix composites, they need to be optimized for grafts that act as structural frameworks in load-bearing defects. The purpose of this experiment is to determine the effect of bone marrow mesenchymal stem cells seeding on partially demineralized laser-perforated structural allografts that have been implanted in critical femoral defects. Materials and Methods. Thirty-two wistar rats were divided into four groups according to the type of structural bone allograft; the first: partially demineralized only (Donly), the second: partially demineralized stem cell seeded (DST), the third: partially demineralized laser-perforated (DLP), and the fourth: partially demineralized laser-perforated and stem cell seeded (DLPST). Trans-cortical holes were achieved in four rows of three holes approximated cylindrical holes 0.5 mm in diameter, with centres 2.5 mm apart. P3 MSCs were used for graft seeding. Histologic and histomorphometric analysis were performed at 12 weeks. Results. DLP grafts had the highest woven bone formation, where most parts of laser pores were completely healed by woven bone. DST and DLPST grafts surfaces had extra vessel-ingrowth-like porosities. Furthermore, in the DLPST grafts, a distinct bone formation at the interfaces was noted. Conclusion. This study indicated that surface changes induced by laser perforation, accelerated angiogenesis induction by MSCs, which resulted in endochondral bone formation at the interface. Despite non-optimal results, stem cells showed a tendency to improve osteochondrogenesis, and the process might have improved, if they could have been supplemented with the proper stipulations

The moderator will lead a structured panel discussion that explores how to manage challenges commonly found in the multiply revised knee. Topics covered will include: (1) Exposure in the multiply operated knee (when to use quad snip, tibial tubercle osteotomy, other techniques); (2) Implant removal: Tips for removing stemmed implants; (3) Management of bone loss in multiply operated knees (metal cones/sleeves vs. structural allograft vs. particulate graft); (4) Level of constraint (when to use posterior stabilised, constrained condylar, and hinge) and management of instability in multiply operated knees; (5) Preferred management of infection in the multiply operated knee; (6) The extensor mechanism: Preferred deficient patellar bone management; Preferred extensor mechanism deficiency management; (7) When is it time to convert to a salvage procedure (i.e. fusion, resection arthroplasty, amputation)?; (8) Post-operative management: wound management; knee range of motion

Introduction. Acetabular revision surgery is challenging due to severe bone defects. Burch-Schneider anti-protrusion cages (BS cage: Zimmer-Biomet) is one of the options for acetabular revision, however higher dislocation rate was reported. A computed tomography (CT)-based navigation system indicates us the planned direction for implantation of a cemented acetabular cup during surgery. A large diameter femoral head is also expected to reduce the dislocation rate. The purpose of this study is to investigate short-term results of BS cage in acetabular revision surgery combined with the CT-based navigation system and the use of large diameter femoral head. Methods. Sixteen hips of fifteen patients who underwent revision THA using allografts and BS cage between September 2013 and December 2017 were included in this study with the follow-up of 2.7 (0.1–5.0) years. There were 12 women and three men with a mean age of 78.6 years (range, 59–61 years). The cause of acetabular revision was aseptic loosening in all hips. The failed acetabular cup was carefully removed, and acetabular bone defect was graded using the Paprosky classification. Structural allografts were morselized and packed for all medial or contained defects. In some cases, solid allograft was implanted for segmental defects. BS cage was molded to optimize stability and congruity to the acetabulum and fixed with 6.5 mm titanium screws to the iliac bone. The inferior flange was slotted into the ischium. The upside-down trial cup was attached to a straight handle cup positioner with instrumental tracker (Figure 1) and placed on the rim of the BS cage to confirm the direction of the target angle for cement cup implantation under the CT-based navigation system (Stryker). After removing the cement spacer around the X3 RimFit cup (Stryker) onto the BS cage for available maximum large femoral head, the cement cup was implanted with confirming the direction of targeting angle. Japanese Orthopedic Association score (JOA score) of the hip was used for clinical assessment. Implant position, loosening, and consolidation of allograft were assessed using anterior and lateral radiographies of the pelvis. Results. Fifteen hips had a Paprosky IIIB defect, and one hip had a pelvic discontinuity. JOA score significantly improved postoperatively. No radiolucent lines and no displacement of BS cage could be found in 9 of 15 hips. Consolidation of allografts above the protrusion cage was observed in these patients. Displacement of BS cage (>5mm) was observed in 6 hips and displacement was stopped with allograft consolidation in 5 of 6 hips. The other patient showed lateral displacement of BS cage and underwent revision surgery. Average cup inclination and anteversion angles were 37.7±5.0 degree and 24.6±7.2 degree, respectively. 12 of 16 patients were included in Lewinnek's safe zone. One patient with 32 mm diameter of the femoral head had dislocation at 17 days postoperatively. All patients who received ≥36mm diameter of femoral head showed no dislocation. Conclusions. CT-based navigation system and the use of large femoral head may influence the prevention of dislocation in the acetabular revision surgery with BS cage for severe acetabular bone defects

The treatment of extensive bone loss and massive acetabular defects is a challenging procedure, especially in cases with concomitant pelvic discontinuity (PD). Pelvic discontinuity describes the separation of the ilium proximally from the ischio-pubic region distally. The appropriate treatment strategy is to restore a stable continuity between the ischium and the ilium to reconstruct the anatomical hip center. Several treatment options such as antiprotrusio cages, metal augments, reconstruction cages with screw fixation, structural allograft with plating, jumbo cups, oblong cups and custom-made triflange acetabular components have been described as possible treatment options. Cage and/or ring constructs or acetabular allograft are commonly used techniques with unsatisfactory results and high failure rates. More favorable results have been presented with custom triflange acetabular components (CTAC), although the results are still unsatisfactory. Three-dimensional printing technology (3DP) has already become part of the surgical practice. In this context, preliminary clinical and radiological results using a 3D-printed custom acetabular component in the management of extensive acetabular defects are presented. The overall complication rate was 33.3 %. In one out of 15 patients (6.6 %), implant-associated complication occurred revealing an overall implant-associated survival rate of 93.3%. The 3D-printed custom acetabular component suggests a promising future, although the manufacturing process has high costs and the complication rate is still high

The treatment of extensive bone loss and massive acetabular defects is a challenging procedure, especially the concomitant pelvic discontinuity (PD) can be compounded by several challenges and pitfalls. The appropriate treatment strategy is to restore a stable continuity between the ischium and the ilium and to reconstruct the anatomical hip center. Antiprotrusio cages, metal augments, reconstruction cages with screw fixation, structural allograft with plating, jumbo cups, oblong cups and custom-made triflange acetabular components have been reported as possible treatment options. Nevertheless, the survivorship following acetabular revision with extensive bone loss is still unsatisfactory. The innovation of three-dimensional printing (3DP) has become already revolutionary in engineering and product design. Nowadays, the technology is becoming part of surgical practice and suitable for the production of precise and bespoke implants. The technique of a 3D-printed custom acetabular component in the management of extensive acetabular defect is presented