Tibial bone loss in revision TKA: Options for management without sleeves and cones –a schematic review

1. Introduction

The aim of revision total knee arthroplasty is to produce a stable, painless knee with restoration of near normal biomechanics. One of the major challenges encountered in revision total knee arthroplasty is management of large bone defects The etiology for bone loss in the revision setting includes osteolysis, disuse osteoporosis, infection, mechanical bone loss due to a loose implant, and iatrogenic loss during implant removal.1, 2, 3, 4 Osseous defects encountered during revision TKA demands additional strategies to reconstruct these bony defects to ensure implant stability and survival. It has been reported that one of the major reasons for TKA failure is loosening of the tibial component with bone loss found in up to 30% of revision TKRs.⁵ The defects vary greatly in types (contained or non contained), location and magnitude. Management of the defects encompasses a wide variety of techniques like bone cement, bone cement with screw reinforcement, bone grafts (autografts or allografts) and metal augmentations (metal wedges, blocks, cones,sleeves) depending on the location and size of the defects.6, 7, 8, 9 Smaller defects are usually treated with bone cement, cement plus screws, or impaction auto/allograft bone. Large defects require structural allografts or metal augments/stems/cones/sleeves/megaprostheses.

Despite the multitude of treatment methods available, the best reconstructive technique for tibial bone defects during revision knee arthroplasty has not been clearly determined. With the rising numbers of revision cases, a technically simple, durable and cost-effective approach is the need of the hour. We reviewed the use of methods other than cones and sleeves for tibial bone defect management in revision TKA.

1.1. Stems

Stems in revision TKA are used to bypass the deficient metaphyseal bone and fix the stem within the tibial diaphysis. It acts as a load sharing construct reducing the stress on the tibial base plate. Implant options include cemented, non-cemented, and hybrid stems. The optimal method of stem fixation is still a debatable topic.

Cemented stems are implanted with a cement restrictor following good preparation of the host cancellous bone ensuring adequate interdigitation of the cement. Cemented stems provide immediate fixation stability. They may increase stress shielding of the metaphyseal bone and can be challenging to remove. They are indicated in osteoporotic bones with wide canals. Lachiewicz et al. reported no tibial component loosening at a mean 5-year follow-up of 58 revision TKAs with 30-mm cemented stems.¹⁰

Hybrid stem fixation depends on the placement of cement at the metaphyseal implant-bone interface. These stems must have an interference fit of atleast 1–2 cm in the diaphysis for construct stability.¹¹ Noncemented stems are usually offset stems. Offset stems can assist with implant alignment when the metaphyseal portion of the bone may not be directly centered over the diaphysis. Offset stems can prevent mediolateral or anteroposterior protrusion of the tibial component. They rely on the stem fixation within the diaphysis until biologic fixation is achieved. They are indicated in cases with relatively good bone stock.

Greene et al. reported no complications associated with aseptic loosening in a study of 119 revision TKAs with hybrid stem fixations at a mean follow-up of 62 months.¹² The fixation strength with short cemented stems has been found to be equivalent to that of long press-fit stems.¹³ Gross et al. reported a 10-year survival of 96% in a retrospective study of 23 patients who underwent revision TKA with long porous-coated stems.¹⁴ Metaanalysis by Wang et al. on fixation of cemented versus noncemented stems in revision TKA found no substantial differences between the stems with regard to failure, aseptic loosening, revision and infection rates.¹⁵

1.2. Bone cement

Cement is highly versatile and conforms readily to the size and shape of the tibial bone defect. It is recommended for repairing small contained defects, typically Anderson Orthopaedic Research Institute (AORI) type-1 or cystic defects. Bone cement is the best suited to fill the bone defects less than 5 mm in width and depth, for peripheral deficiency up to 10% of the condylar area, for small central defects, for cystic defects and contained bone defects.¹⁶

Cement has been used for bone defect repair in tumor surgery with satisfactory biomechanical and clinical outcomes.¹⁷ Cement is not a biological scaffold and hence not ideally recommended for filling large bony defects. Bone cement is known to produce thermal necrosis of the surrounding bone which may be the cause for debonding and long term loosening of the prosthesis. The degree of thermal necrosis is directly proportional to the amount of cement used. Cement may lose up to 2% of its volume during its polymerization, leading to a decreased mechanical stability and loosening. Sclerotic defects need adequate preparation of the defect to get an acceptable long term clinical outcome. Sloping surfaces are converted to step-shaped surfaces to minimize the amount of shear forces acting on the cement, as cement is known to be much more biomechanically stable and supportive in compression. Proper cementing techniques, such as removal of the fibrous tissue and drilling the sclerotic bone to expose the cancellous bone bed, washing with pulsatile lavage, and injecting the cement under pressure promotes better cement penetration and minimises radiolucent lines. Radiolucent lines at the bone defect interface are not a problem unless they are progressive or >2 mm.

Dorr et al. reported outcomes of treating the osseous defects with cement filling in 54 patients with AORI type-1 defect with follow up for 7 years. All had good outcomes, except for one who had loosening.¹⁸ Lotke et al. reported 59 knees with a defect of 10–20 mm (n = 33) or >20 mm (n = 23) in height treated with cement.¹⁹ At 7.1 years of follow up, the overall mean knee score was 78 and the radiographic score was 85. Although non-progressive radiolucent lines were noted in 43 knees, only one case failed. There was no correlation between radiolucent lines and symptoms. They concluded that long-term results of cement filling are good when the bone defects are <20 mm height and affects <50% of either tibial plateau.

1.3. Cement with screw

Cement in combination with screws is recommended for management of contained or uncontained bony defects between 5 mm and 10 mm in proximal tibia.²⁰ This treatment option can be considered for both AORI type 1 and AORI type 2 A bone defects involving less than 50% of condylar width and up to 10 mm in depth. Screws, acting as pillars, are used to distribute the load away from the joint line and cement bone interface.²¹ This type of fixation results in 30% less loosening of the prosthesis than cement alone in tibial defects reconstruction. It is advisable to use titanium cancellous screw with titanium implants to avoid issues of galvanic corrosion. Screws should be sunk deep into the cement to avoid contact between their heads and the tibial tray.¹⁶It is a reliable, reproducible and inexpensive technique.

Different authors have shown good clinical outcome in mid to long term follow up. Ritter et al. reported a study with 57 patients with medial tibial defects. At 3 years follow-up, 25% had non-progressive radiolucency at the bone cement interface.²² After 7 years, there was no progression of radiolucency lines either at the bone-cement or at the cement-prosthesis interface and none of the components failed. Berend et al. showed that screws with cement in conjunction with a revision specific prosthesis repairs large tibial defects (>20 mm and >50% plateau involvement) with long term survival probalility of more than 0.985 at 15 yrs follow-up.²³ They suggested cement reinforced with screws as a suitable and economical alternative of restoring the biomechanics of the knee in revision scenario without compromising the longevity of implants. They propounded the use of cement with screws technique is bone preserving, time saving, economical, technically simpler and limiting open wound exposure.

Application of cement and screw technique in large uncontained bone defects is not highly recommended.²⁴ It carries the risk of thermal necrosis and radiolucency in the bone cement interface. The radiolucency seen in these cases could be attributed to the poor penetration of the cement into sclerotic bones at the time of primary surgery.²⁵

1.4. Modular metal augments

Uncontained, 5–20 mm deep tibial defects, with breach of cortical rim, may be ideally managed with modular metal augments that selectively fill bone deficiencies. They are recommended when >40% of the bone-implant interface is unsupported by host bone, resulting in instability of the trial implant, or when the periphery of the defect involves >25% of the adjacent cortex.²⁶ Metal augments in various shapes and sizes are readily available for bridging the tibial defects in revision TKA.²⁷ These augments are shaped either as wedges (including hemiwedges and full wedges) or rectangular blocks. They come in different thicknesses and angles to replace the bone defects of varying severity. Contrarily to cement, which fills the gap, augments require a reshaping of the defects with some bone sacrifice, especially if blocks are used. The additional resection required for tibial hemiplateau augments must be made in the correct external rotation for proper placement of the final construct. Wedge augments, allow for more bone preservation, being on the other side subject to shear stress because of their oblique nature and more susceptible to mechanical failure.²⁸ Symmetric blocks help in restoring the joint line while asymmetric augments contribute in filling the defect. Augments are assembled to fit the tibial components with screws or bone cement and then cemented as a single unit. They provide stable support and transfer loading forces to the bone. In tibia, they allow use of larger tibial base plate covering the bone defects.

Biomechanical studies have shown that prostheses with a built-up metal wedge are mechanically superior to cement alone or cement with screws in terms of resisting deflections when loaded.²⁹ Tensile strain within the cement-bone interface is less with block augments than with wedge augments as the cement gets loaded in compression in the former. The maximum strain differential between the blocks and wedges is negligible. Thus, it is advisable to use the augment that best fills the bone defect.³⁰

Non-progressive radiolucent lines around the augments were observed in 102 revisions TKA patients with AORI type 2 defects at a mean follow-up of 7 years.³¹ Failure with metal augments commonly happens in situations of severe bone loss with impairment of cancellous bone support leading to compromised device-host bone interface.¹⁶ The potential drawbacks with metal augments are the risk of fretting and corrosion.³² The difference in the elasticity of the metal and bone may cause stress shielding and lead to potential bone loss in long run.³¹ Use of metal augments usually demands resection of host bone to accommodate the augments, so using them may be viewed as a bone sacrificing option rather than a preserving one.This technique is ideally suitable for AORI type 2a & 2 b defects in elderly low demand patients.³³

1.5. Impaction bone grafting

Impaction bone grafting enables restoration of the native bone stock in revision TKAs. So this is an appealing technique in young patients in whom further revision sugeries are anticipated. They are commonly used for contained tibial defects. Contained bone defects can be treated immediately, whereas uncontained defects require wire mesh augmentation. Use of wire mesh prevents escape of the bone particles during impaction when used for uncontained defects.³⁴ Moderate sized bone particles (3–5 mm) are ideal to provide adequate stability during impaction and to promote host bone ingrowth due to better vascularisation.³⁵ Adequate impaction force makes the grafts strong enough to carry the load while excessive impaction reduces host bone ingrowth.³⁶ Loose impaction results in fast resorption of the graft, increasing the risk for subsidence of the prosthesis. Use of a supportive stem, stiffer instruments, solid support of the graft-host bone interface, moderately sized particles and removing fat are important strategies to improve the outcome of impaction grafting.³⁷ Impaction grafting is unique in its osteoconductive ability allowing a more rapid revascularization with progressive incorporation and remodelling of the bone graft compared to structural allografts.³⁸

Graft incorporation duration differs on whether its allo- or autograft. Autograft is restricted by the donor site morbidity but takes lesser time for incorporation. The allografts used in impaction bone grafting are non-vascularized. The incorporation of allograft involves two overlapping processes: the union of the graft-host bone interface and the remodelling of the graft by creeping substitution, which is a relatively slow process.³⁹ Bone allograft processing, sterilization and preservation can alter its physical and chemical features as well as the immune response towards it. In terms of biological efficacy, cryopreserved cancellous grafts are superior to freeze-dried cancellous grafts and demineralized cortical grafts.⁴⁰ Although mineralized cancellous grafts have greater osteoconductive features, they are weaker than the demineralized cortical grafts in providing stability.

Toms et al. compared the stability provided by three methods of graft containment (cement, mesh and a novel bag technique) for segmental medial tibial defects (45% or 65%) in a laboratory based biomechanical study.⁴¹ Cyclical and permanent tray displacements recorded during cyclical mechanical loading showed satisfactory stability with cement and mesh technique of impaction grafting. The novel bag technique failed to provide adequate stability. Biomechanical studies showed that rim support, stem type, and graft impaction affected early stability of the tibial tray.⁴² Trays with short and long stems in varying diameters with or without rim support were implanted and studied. It was found that long stems that bypassed the impacted graft with rim support gave the maximum stability. Hanna et al. reported a prosthesis survivorship of 98% at 10 years with use of cementless TKA prosthesis and loosely packed morselized cancellous allograft mixed with autograft for revision knee arthroplasty.⁴³

Impaction bone grafting is usually indicated for contained tibial defects. Long-term graft incorporation depends on achieving initial stability during revision TKA. Inadequate initial stability leads to failure of revision TKA before the eventual incorporation of the graft. The cortical rim plays an important role to provide initial stability to the tibial tray. Hence impaction grafting is not recommended for repairing uncontained cortical defects.¹⁶ Lack of cortical rim support increased permanent movement by a factor of 2.6 and cyclical movement by a factor of 1.7 when compared to intact cortical rim support; this highlights poor support strongly decreased stability of the tibial tray.⁴² A case report with histologic analysis of uncontained tibial defect repaired by impaction bone grafting with a short-stemmed tibial tray showed failure of graft incorporation with necrotic central area after four years. This highlights the importance of stability provided by the tibial cortical rim.⁴⁴

Midterm results are available for impaction allograft reconstruction of bone loss in revision TKA. 48 patients treated with impaction bone grafting in revision TKA reported good radiographic incorporation and no mechanical failure after 3.8 years of follow up.⁴⁵ Benjamin et al. reported good radiographic incorporation at 2 years follow-up using impaction bone grafting for tibial and femoral defects in revision TKA.⁴⁶ There were no clinical failures or reoperations in patients with morselised impaction bone grafting. Lonner et al. reviewed the results of 17 revision total knee arthroplasties in 14 patients in whom large uncontained defects were treated with impaction allografting and molded wire mesh for containment.⁴⁷ Knee Society clinical scores increased from an average of 47 points to 95 points and function scores increased from 48 points to 73 points. They suggested that the use of impaction grafting with wire mesh is an effective method to treat massive uncontained tibial bone loss in revision TKA. There are not many studies for impaction bone grafting with wire mesh technique with good long-term outcomes.

While several studies supported the versatility and durability of impaction grafting in revision TKA, Hilgen et al. highlighted the potential limitation of impaction grafting for more severe defects and re-revision cases.⁴⁸ They reported a survival rate of 50% at 10 years of follow up in revision of rotational and hinged TKAs with AORI type 2 and 3 defects. Failures were related to mechanical breakdown and aseptic loosening of the components showing a lack of graft incorporation in all failed cases.

1.6. Structural allograft

Structural allografts provide a durable and biological reconstruction of large and segmental tibial bone defects. Femoral heads or upper tibial segments are the commonly used options available. These allografts incorporate into the host bone and provide stress protection to the tibial implant.⁴⁹

The defect must be cleared of all soft tissues, osteolytic membranes and residual cement. At this point the graft is prepared removing with a burr or a female reamer the sclerotic peripheral bone at the interface with the host to fit into the defect. If a femoral head allograft is used, the diameter of the male reamer to prepare the host bone should be 2 mm narrower to obtain a primary press-fit fixation.⁵⁰ We need to use stemmed components, either cemented or pressfit, to bypass the defect and to reduce stresses on the allograft, host bone and fixation interface.⁵¹ Additional plates and screws may help to achieve primary stability, especially in the larger uncontained defects.

Dorr et al. reported outcome of structural bone grafting for tibial defects in revision TKA. Of the 24 treated knees, 22 achieved bony union and revascularization of grafts with no clinical collapse at 3–6 years followup, whereas remaining 2 cases showed nonunion of the graft. Structural bone grafts are recommended for tibial defects involving >50% of either tibial plateau.⁵² No graft collapse or aseptic loosening was found after a mean of 7.9 years in 46 knees with AORI type-3 tibial bone defects treated with structural allografts.⁵³ Majority of the tibial defects were contained ones and treated with femoral head allograft. Femoral head allografts were used for cavitary defects, whereas size-matched allografts were used for segmental or combination defects in revision TKA patients. Wang et al. reported no graft failure in a study of 28 patients (30 Knees) treated with revision TKA at an average follow-up of 76 months.⁵⁴ On average, each reconstruction required 1.7 femoral head allografts per revision. Malhotra et al. reported use of distal tibial allograft for reconstruction of proximal tibial bone loss in revision TKA with two-year followup.⁵⁵

The results of structural allografts are not consistently uniform. Bauman et al. showed greater than 20% rate of complications and failures with use of structural allografts in revision TKA.⁵⁶ The 5-and 10-year survival rates were 80.7% and 75.9% respectively. Clatworthy et al. reported 8-year follow-up of 50 patients with 52 revision TKAs using allografts with a survival rate of 72% at 10 years.⁵⁷ Ghazavi et al. reported found failures in seven of the 30 knees with massive bone loss treated with revision TKA using allografts.⁵⁸ These reports support the use of bulk allograft for severe tibial or femoral bone defects in revision knee arthroplasty, but also highlight the need for a more durable reconstruction method for the long-term success and to avoid the complications inherent with allografts, such as graft nonunion and resorption.

It is difficult to compare the results of various published series using structural allografts because they differ in type of bone loss, graft fixation, length and type of stem fixation, constraint of the prosthesis and follow-up. The failure of allograft was influenced by the type of allograft. Smaller allografts in the form of femoral heads failed secondary to allograft resorption resulting in component loosening. Conversely, the large bulk allografts failed secondary to infection or nonunion in the majority. There are multiple issues associated with allografts. Availability of allografts, risk of bacterial and viral disease transmission, graft resorption, fatigue fracture, immune response leading to delayed incorporation. The allograft sterilization process may also compromise the tissue biology and biomechanics.⁵⁹

Structural allografts are indicated for revision TKAs in relatively younger patients or patients with life expectancy longer than 10 years in an effort to restore the bone stock. Megaprostheses were favored in older patients with large structural bony defects for early mobilization. The use of structural allografts could be limited in septic revision since a higher risk of periprosthetic infection has been reported when using allografts.⁵⁷ In cases with a history of infection, it is safer to use metal bone augments with antibiotic bone cements.

1.7. Megaprosthesis

Megaprosthesis are used to replace the entire proximal tibia. These prostheses are used to treat patients with severe proxima tibial bone loss following chronic infection or multiple surgeries. However, few studies have evaluated the outcomes of megaprostheses in the setting of revision TKA. Kostuj et al. compared the clinical outcomes of these implants used in patients who underwent revision TKA or resection of a malignant tumor.⁶⁰ They found that the outcomes in both groups were comparable. However, in the revision group, the reported rate of infection was 29.5% compared with 9.1% in the malignant tumor group.

2. Discussion

Tibial bone defects are commonly encountered during revision TKA. Although classifications are useful to quantify the defects and to plan the operation, the final evaluation made intra-operatively after removal of the components gives the true picture of the tibial defect. “Fill and fix” is the cornerstone concept to pursue during revision TKAs. Literature does not provide any evidence-based approach. Available systematic review and meta-analysis are usually of low quality mainly because examined studies are case series without control groups. The options include filling the defects with bone cement, cement with screw augmentation, stems, metal augments and structural bone grafts (both auto and allografts) depending upon the size and location of the tibial defects, bone quality, surgeons expertise and experience with their use and availability and affordability of the patient.⁷(Fig. 1) Estimation of tibial bone loss begins by evaluating the integrity of the tibial tuberosity. Bone loss at this location may result in a nonfunctional extensor mechanism, that requires use of a high-constraint implant (eg, rotating hinge implant, megaprosthesis).¹¹ (Fig. 3) The fibular head (typically 15 mm distal to the joint line) can be used as a reference to assess the depth of bone loss.⁶¹ In cases with total loss of the upper tibia, megaprostheses and modular implants needs to be used(Fig. 2).

Fig. 1.

Review of tibial defect intervention techniques.

Fig. 3.

Protocol for tibial defect management (excluding sleeves/cones).

Fig. 2.

Algorithm for management of proximal tibial bone loss.

Cement is routinely used for AORI type 1 defects of <5 mm. If defects are 5–10 mm and >50% of the tibial plateau is available, cement with reinforcing screws provides better biomechanical stability. Use of this technique in defects of >10 mm is not well established. The resistance of cement to shear stress is low. Thermal bone necrosis occurs when used in large quantities. In addition, 2% shrinkage occurs during polymerization and lamination. All these leads to frequent immediate and secondary radiolucent lines which are especially visible in tibia. Good preparation of the sclerotic defect is mandatory for a good outcome with cement filling. Cement is only indicated in shallow, limited bone defects especially in elderly patients.⁶² For type 2 defects, metal augments and/or structural bone grafts are preferred depending upon the size, location and bone quality. The metal augments are indicated to fill bone loss not larger than 10–20 mm in elderly patients. The limitation of metal augment option is fixation with cement in mediocre bone.⁶¹ The downside is fretting and stress shielding issues with metal augments. Failure with metal augments leads to creation of even larger defects in re-revision when compared to bone graft failure. As long as one third of the peripheral rim and a good part of the metaphyseal cortex is intact, morselized or structural allografts can be used for reconstruction. Graft reconstruction is easier, and the contact surface with the graft is larger in the tibia. For contained defects of >10 mm, structural allografts or impaction bone grafts are preferred as they can replenish host bone stock for the next possible revision in younger patients.¹¹ (Fig 2) It, however, requires a relatively a large amount of bone graft, is time consuming, expensive and technically challenging procedure. Impaction bone grafting is not an ideal treatment in uncontained defects due to the lack of an intact cortical rim. Structural allografts can be used to repair the large cortical defects and to replenish the host bone stock. Initial stability of allografts may be insufficient due to absorption and fatigue fractures and needs support with use of intramedullary stems. When the epiphysis is nearly inexistent, the choice is between a massive allograft in young patients and a megaprosthesis in elderly patients.

Durability of the any of the above-mentioned reconstruction technique depends highly in following essential principles of TKA: proper alignment and ligament balance, constraint of the prosthesis and stem fixation. Cautious removal of implants is critical to avoid further iatrogenic bone loss. The wide array of intra-operative scenarios and the experience of the surgeon in one technique rather than another make difficult to conduct a controlled trial comparing different options.

3. Conclusion

A systematic approach that includes a proper assessment of tibial bone loss, careful implant selection, and a thorough understanding of the available reconstruction options allows the surgeon to adequately manage the defects and achieve reproducible outcomes. Methods such as using autograft and allograft bone should be considered in younger patients due to the potential for biologic incorporation and bone stock restoration for future reconstructive procedures. Smaller contained defects may be addressed with bone grafting, bone cement or metal augments. Larger defects may require metaphyseal sleeves, trabecular metal cones or bulk allografts. Intramedullary stems should be used in large defects involving the condyles or in those with questionable bone stock. Further long-term studies are desirable to draw firm conclusions on management of tibial defects in revision TKA.

Conflicts of interest

None declared.