**4.3.3 Structural massive bone allograft**

Structural bone allograft offer**s** numerous advantages, including biocompatibility, bone stock restoration and potential for ligaments reattachment. Regarding their versatility it is possible to treat a wide range of bone deficiency allowing the surgeon to shape the allograft to fit the bone defect and avoid unnecessary removal of host bone. Finally allograft is relatively cost-effective if compared to the high cost of custom-made implants.

The goals of structural allograft reconstruction are to maximize the stability of the grafthost bone contact and provide a stable platform for fixation of the implant. The first step is to remove all the nonviable bone and soft tissue from in and around the defect, the presence of viable bone is absolutely necessary to maximize the likelihood of graft incorporation. Conversion of the oblique peripheral defects into rectangular space with vertical and horizontal surfaces has been demonstrate to improve stability for components fixation. The angular patterns have also a biological advantage since it allows improving the contact area of the host-graft construct maximizing the probability of graft incorporation. Regarding the choice of the graft it is important to shape the allograft similarly in order to fit the defect precisely. Graft fixation too is an important step to be taken in consideration: mainly used are partially or fully threaded cancellous screws.

In the literature there are various papers reporting about the use of allograft to restore bone defect during revision knee arthroplasty, especially for uncontained defects. In some cases with circumferential segmental bone defect of tibial plateau, have been demonstrated about 25% of allograft failure (De Long et al., 2007; Engh & Ammeen, 2007). Engh & Ammeen, whose have reviewed the results of 49 knees with severe tibial bone loss, found only four cases of failure for reasons not-directly related to collapse or resorption of the graft; most of patients had contained defect and ten presented an uncontained deficiency of which only four cases were restored with full segment allograft. Recently Backstein D, et al have reported 85.2% of success rate at an average follow-up of 5.4 years in a series of 68 revision that required a structural allograft for the treatment of uncontained defect (Backstein et al., 2006).

Even if a variability of result are present in the literature, due to the significant difference of the lesion treated, all authors agree on affirm that the use of a intramedullary stem with a sufficient length to engage diaphyseal bone is mandatory to decrease axial and shear loads to the structural allograft in accordance with previously data emerging from the laboratory (Mounasamy et al, 2006).

We have experienced reconstruction with massive structural allograft during primary total knee replacement for severe segmental medial post-traumatic tibial plateau defect in arthritic knee (Tigani et al., 2011); neither acute nor chronic complications were observed, and radiological examination referred no signs of prosthetic loosening or secondary resorption, with good grafting integration to host bone (Fig. 6).

Management of Bone Loss in Primary and Revision Knee Replacement Surgery 397

ingrowth (Bobyn et al., 1999). These unique material properties of porous trabecular metal allow it to achieve immediate structural support, together with early bony ingrowth and late

TM is available in many shapes and forms (Fig. 7): porous or solid, rectangular or wedge shaped, and can be attached with the use of cement or screws. It can be applied quickly, allow intraoperative custom fabrication, supply excellent biomechanical properties, and

require minimal bone resection as the augments attach on the residual bone.

Fig. 7. TM modular augments (courtesy of Zimmer, Warsaw, Ind, US).

Surgical advantages of metal augments with respect to bone graft are:

stress but necessitate removal of some intact host bone.

Possibility to customize the implant intraoperatively;

distal and posterior femoral condyles are used.

 Need not be incorporated into host bone; Do not carry a risk of nonunion or collapse.

mm of deep.

Preference between wedges and blocks should be accorded to the augmentation that most closely fills the defect (Fig. 8). The exception to this may be when a constrained insert is necessary; in this instance block may have some advantage because of its ability to directly transmit torsional loads as a result of geometric interlock. Even this, blocks avoid shear

On the tibial side, multiple sizes of metal wedges and blocks are available, up to full tibial block for defects of entire plateau, thus maintaining balanced flexion and extension spaces. Femoral defects can be reconstructed with metal blocks in increments of 5 mm; because bone loss in femur is most often on the posterior and distal surfaces, augments fixed to the

Despite the versatility and a wide geometry of augments, including hemi-wedges, full wedges, and symmetric spacers, these materials can manage only a limited defect, up to 20

In our practice we prefer to use cement and a step cut technique for Engh type 1 defects of less than 5 mm depth, and metal augmentation for type 2 defects of more than 5–10 mm.

restoration of bone stock.

Fig. 6. (a) Pre-operative plain radiographs showing post-traumatic severe depressed medial bone stock loss; (b) preparation of tibial plateau, in a way to convert oblique defect to rectangular stepped one; (c) Fitting the allograft into the defect; (d) last follow-up plain radiographs, 12 months after the surgery.

### **4.4 Modular components (metal augments)**

The use of metal augments for bone deficiencies has become quite popular since mid Eighties, after the work of Brooks et al which indicated that biomechanically the modular augments are equivalent to a custom implant (Brooks et al., 1984). In last decades a new biomaterial is largely used in knee prosthetic surgery: porous tantalum, in its trabecular form (trabecular metal, TM; Zimmer, Warsaw, Ind, US). TM show excellent mechanical characteristics compared to conventional implant materials (i.e. titanium and cobalt chromium): good biocompatibility, high porosity, low modulus of elasticity (Levine et al., 2007). Moreover biological advantages of TM include its negative charge and interconnective pores, which form a scaffolding and surface for osteoblast-mediated bone

Fig. 6. (a) Pre-operative plain radiographs showing post-traumatic severe depressed medial bone stock loss; (b) preparation of tibial plateau, in a way to convert oblique defect to rectangular stepped one; (c) Fitting the allograft into the defect; (d) last follow-up plain

The use of metal augments for bone deficiencies has become quite popular since mid Eighties, after the work of Brooks et al which indicated that biomechanically the modular augments are equivalent to a custom implant (Brooks et al., 1984). In last decades a new biomaterial is largely used in knee prosthetic surgery: porous tantalum, in its trabecular form (trabecular metal, TM; Zimmer, Warsaw, Ind, US). TM show excellent mechanical characteristics compared to conventional implant materials (i.e. titanium and cobalt chromium): good biocompatibility, high porosity, low modulus of elasticity (Levine et al., 2007). Moreover biological advantages of TM include its negative charge and interconnective pores, which form a scaffolding and surface for osteoblast-mediated bone

radiographs, 12 months after the surgery.

**4.4 Modular components (metal augments)** 

ingrowth (Bobyn et al., 1999). These unique material properties of porous trabecular metal allow it to achieve immediate structural support, together with early bony ingrowth and late restoration of bone stock.

TM is available in many shapes and forms (Fig. 7): porous or solid, rectangular or wedge shaped, and can be attached with the use of cement or screws. It can be applied quickly, allow intraoperative custom fabrication, supply excellent biomechanical properties, and require minimal bone resection as the augments attach on the residual bone.

Fig. 7. TM modular augments (courtesy of Zimmer, Warsaw, Ind, US).

Preference between wedges and blocks should be accorded to the augmentation that most closely fills the defect (Fig. 8). The exception to this may be when a constrained insert is necessary; in this instance block may have some advantage because of its ability to directly transmit torsional loads as a result of geometric interlock. Even this, blocks avoid shear stress but necessitate removal of some intact host bone.

On the tibial side, multiple sizes of metal wedges and blocks are available, up to full tibial block for defects of entire plateau, thus maintaining balanced flexion and extension spaces. Femoral defects can be reconstructed with metal blocks in increments of 5 mm; because bone loss in femur is most often on the posterior and distal surfaces, augments fixed to the distal and posterior femoral condyles are used.

Surgical advantages of metal augments with respect to bone graft are:


Despite the versatility and a wide geometry of augments, including hemi-wedges, full wedges, and symmetric spacers, these materials can manage only a limited defect, up to 20 mm of deep.

In our practice we prefer to use cement and a step cut technique for Engh type 1 defects of less than 5 mm depth, and metal augmentation for type 2 defects of more than 5–10 mm.

Management of Bone Loss in Primary and Revision Knee Replacement Surgery 399

Familiarity with the rationale and strategies for metaphyseal fixation in revision TKA is a valuable addition to the armamentarium of the revision surgeon. In the revision setting, reliance on metaphyseal area fixation is important to carry a portion of the axial load and protecting epiphyseal ingrowth (Haidukewych et al., 2011). Metaphyseal bone loss have historically required any one or numerous of the following: cement, impaction grafting with mesh containment, metal augmentation (TM cones or metaphyseal sleeves), structural

Porous tantalum structural cones (Fig. 9), which are a new modern extension among the family of metal augments, have been introduced in attempt to achieve a real structural and biomechanical reconstruction of such important metaphyseal bone defects. They are useful when there are significant bone defects, or if there is cortical deficiency or fracture. Tibial tantalum cones could be used with cemented or cementeless technique while femoral tantalum cones must be cemented to the bone in the United States and may be used with or

Tantalum cones along with offset stems, increase contact area between the implant, cone, and host bone, thus serving as a mechanical platform and as support for the revision implants with less stress shielding and disuse atrophy of the surrounding bone. In addition, tantalum's low modulus of elasticity is optimal to load transfer without stress shielding problems (Radnay & Scuderi, 2006). The modular nature of the cones allows to closely fill the defect addressing to both cancellous bone loss and cortical defects. Moreover the unique material properties of porous trabecular metal allow it to achieve rapid bony ingrowth with the potential for long-term biologic fixation and restoration of bone stock. During our experience with 12 femoral and tibial tantalum cones, we registered no cases of aseptic loosening or migration, with good osteointegration to surrounding bone, in both cemented and cementless cases. Therefore we think these implants may eliminate the need for extensive bone grafting that have historically been necessary in the presence of large defects. Recently modular porous coated press fit metaphyseal sleeves have been developed as modular prosthetic adjunctive (DePuy, Warsaw, Ind, US) to obtain fixation in the metaphyseal region. Sleeves have gained initial popularity because of possibility of acting as IM cutting guide. Moreover the interface between metaphyseal sleeves and the implant is created by a Morse tapered junction, while is cemented between TM cones and the implant. However theoretical failure of the junction between metaphyseal sleeves and articular component may occur during impaction or over time and unlike TM cones, sleeves cannot be customized with a burr and cannot be used in more severe uncontained defects (Haidukewych et al., 2011). Pagnotto et al. presented early results with porous-coated metaphyseal sleeves to fill Engh type 2 and 3 defects in revision total knee replacement (53 tibial and 32 femoral sleeves). After 2 years mean of follow-up he reported revision of five sleeves (three for infection and two for loosening); all 80 of the remaining 80 sleeves showed

We agree with other authors that although promising results of metaphyseal metal implants, concerns still exist regarding stress shielding and difficulty of their removal. Particularly literature is lacking of long-term follow-up studies to determine the durability of these constructs and studies are needed to compare TM cones or metaphyseal sleeves to

bulking grafts, custom-made or hinged/tumor-like prostheses.

radiographic evidence of ingrowth (Pagnotto et al., 2011).

alternative reconstructive techniques.

**4.5 Metaphyseal bone loss** 

without cement elsewhere.

Fig. 8. TM augments in tibia are available in a rectangular or wedge fashion

The success rates in the literature using these augments range from 84–98% good or excellent results (Lucey et al., 2000; Radnay & Scuderi, 2006; Rand, 1991). Nevertheless, we think like others, that metal augmentation should be reserved to elderly patients in reason of secondary implant failure and low resistance with the time.

### **4.5 Metaphyseal bone loss**

398 Recent Advances in Arthroplasty

Fig. 8. TM augments in tibia are available in a rectangular or wedge fashion

secondary implant failure and low resistance with the time.

The success rates in the literature using these augments range from 84–98% good or excellent results (Lucey et al., 2000; Radnay & Scuderi, 2006; Rand, 1991). Nevertheless, we think like others, that metal augmentation should be reserved to elderly patients in reason of Familiarity with the rationale and strategies for metaphyseal fixation in revision TKA is a valuable addition to the armamentarium of the revision surgeon. In the revision setting, reliance on metaphyseal area fixation is important to carry a portion of the axial load and protecting epiphyseal ingrowth (Haidukewych et al., 2011). Metaphyseal bone loss have historically required any one or numerous of the following: cement, impaction grafting with mesh containment, metal augmentation (TM cones or metaphyseal sleeves), structural bulking grafts, custom-made or hinged/tumor-like prostheses.

Porous tantalum structural cones (Fig. 9), which are a new modern extension among the family of metal augments, have been introduced in attempt to achieve a real structural and biomechanical reconstruction of such important metaphyseal bone defects. They are useful when there are significant bone defects, or if there is cortical deficiency or fracture. Tibial tantalum cones could be used with cemented or cementeless technique while femoral tantalum cones must be cemented to the bone in the United States and may be used with or without cement elsewhere.

Tantalum cones along with offset stems, increase contact area between the implant, cone, and host bone, thus serving as a mechanical platform and as support for the revision implants with less stress shielding and disuse atrophy of the surrounding bone. In addition, tantalum's low modulus of elasticity is optimal to load transfer without stress shielding problems (Radnay & Scuderi, 2006). The modular nature of the cones allows to closely fill the defect addressing to both cancellous bone loss and cortical defects. Moreover the unique material properties of porous trabecular metal allow it to achieve rapid bony ingrowth with the potential for long-term biologic fixation and restoration of bone stock. During our experience with 12 femoral and tibial tantalum cones, we registered no cases of aseptic loosening or migration, with good osteointegration to surrounding bone, in both cemented and cementless cases. Therefore we think these implants may eliminate the need for extensive bone grafting that have historically been necessary in the presence of large defects. Recently modular porous coated press fit metaphyseal sleeves have been developed as modular prosthetic adjunctive (DePuy, Warsaw, Ind, US) to obtain fixation in the metaphyseal region. Sleeves have gained initial popularity because of possibility of acting as IM cutting guide. Moreover the interface between metaphyseal sleeves and the implant is created by a Morse tapered junction, while is cemented between TM cones and the implant. However theoretical failure of the junction between metaphyseal sleeves and articular component may occur during impaction or over time and unlike TM cones, sleeves cannot be customized with a burr and cannot be used in more severe uncontained defects (Haidukewych et al., 2011). Pagnotto et al. presented early results with porous-coated metaphyseal sleeves to fill Engh type 2 and 3 defects in revision total knee replacement (53 tibial and 32 femoral sleeves). After 2 years mean of follow-up he reported revision of five sleeves (three for infection and two for loosening); all 80 of the remaining 80 sleeves showed radiographic evidence of ingrowth (Pagnotto et al., 2011).

We agree with other authors that although promising results of metaphyseal metal implants, concerns still exist regarding stress shielding and difficulty of their removal. Particularly literature is lacking of long-term follow-up studies to determine the durability of these constructs and studies are needed to compare TM cones or metaphyseal sleeves to alternative reconstructive techniques.

Management of Bone Loss in Primary and Revision Knee Replacement Surgery 401

Custom-made implants are currently being indicated for treatment of complex bone loss and for peripheral defects exceeding 15 mm in depth (Fig. 9). Use of custom implants have

Fig. 10. (a) Severe bone defect caused by septic mobilisation and treated with two-staged

Whatever classification used to determine best treatment and whatever any surgical option

Careful component removal is critical to preserve bone stock; the cancellous bone is much

We prefer the use of a small sagittal saw and flexible osteotomes to loosen the components and their fixation interfaces. After careful and successful exposure and component removal,

Tibia influences the flexion and extension spaces and establishes a platform for the subsequent arthroplasty. The surgeon must recognize severe proximal tibial bone loss, and recreate the appropriate height to allow for proper component placement and gap balancing. With contained defects, the goal is to obtain firm seating of the tibial tray on a rim of viable bone along with rigid press fixation of an intramedullary stem. Likewise, femoral condyle bone loss can influence femoral component's size and sagittal position. The joint line is an average of 25 mm from the lateral epicondyle and 30 mm from the medial epicondyle; the distance from the epicondyles to the posterior joint line is similar to the

Adjustments to ensure correct femoral component rotation usually require augmentation of the posterolateral condyle; additional modification to the position and size of the femoral component may be needed as the flexion and extension gaps are balanced. Once the gaps

revision. (b) Reconstruction was made with custom-made hinged prosthesis.

is available (Table 4), always have to be considered some rules.

the surgeon assesses the bone defects and begins the reconstruction.

are equal and stable, the tibial polyethylene is correctly sized.

distal joint line and is helpful in confirming the correct femoral component size.

weaker away from the native articular surface.

**5. Surgical management** 

been reduced with the advent of modular prosthesis.

Fig. 9. (a) Aseptic knee prosthesis failure in a 58 years old patient. (b) Intraoperatively a severe confined cavitary deficiency of the medial and lateral tibial plateau was found. (c) The defect was filled with TMT cone and cancellous allograft. (d) Postoperative radiological result.
