1 Introduction

Large bone defects in femur and tibia are common after removal of the prosthesis and debridement of the bony surfaces in revision Total Knee Arthroplasty (TKA). The outcome in such cases often depends on the management of this bone deficiency. Filling up of large osseous defects remains a difficult and challenging problem not only for orthopaedic surgeons but also an additional financial burden for patients.¹ There are a variety of options available to fill these defects which include natural (autologous or allogenous bone graft) and artificial (bone graft substitutes, Polymethylmethacrylate Cement and metal augments).^2–4 Recently Trabecular Metal™ implant has been used to fill bony defects. These are biologically inert and highly porous 3D structure similar to that of trabecular bone.⁵ These augments are available in different sizes and shapes and get perfectly incorporated into the host bone. However, disadvantages of these augments include their cost and limited availability in low resource settings. Harvesting autologous bone graft for large defects requires additional surgery, blood loss and related complications which increases morbidity. Allograft bone is a good option to fill large bony defects because of its perfect shape and size.⁶ A structural allograft can provide a stable and durable reconstruction of bone deficiency.⁷ Herein we describe a technique in which a structural allograft from distal tibia has been used to reconstruct a proximal tibial bone defect encountered at the time of the revision TKA.

2 Case history

A 43-year-old female patient was operated for fracture of left distal femur with plating 9 years back which not only failed to unite at one year, but also developed osteoarthritis of knee. Total Knee Arthroplasty was done with megaprosthesis (Adler’s knee prosthesis) after removal of the plate (Fig. 1A & B). She remained asymptomatic till 9 years then after when she presented to our institute with complaints of pain, swelling and inability to bear weight on left lower limb for 4 months. On examination, the knee joint was diffusely swollen and tender with normal temperature. Anteroposterior radiograph of left knee showed a loose prosthesis. On investigation, the ESR was raised (55 mm in first hour), C reactive protein (CRP) level was within normal limit (1.8 mg/L). Magnetic resonance imaging could not be performed because of metal prosthesis in-situ. A clinical diagnosis of infection was suspected and aspiration of joint fluid was performed. However, the aspirated fluid did not reveal any bacteria and culture was sterile on microbiological evaluation. The patient was planned for revision surgery. In view of anticipated massive bone defect and yet possibility of low grade infection, the patient was counselled and taken for two stage revision surgery.

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Fig. 1 X-ray of left knee in Anteroposterior view [A] and Lateral view [B] showing the failed megaprosthesis in situ. Intraoperative picture [C] of the same knee showing severe metallosis around the knee joint. The capsule was thickened with hypertrophied synovium densely tinged with black metallic particles.

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Operative procedure stage 1: The knee was approached through one of the previous incision and arthrotomy done via medial para-patellar incision. Intraoperatively, dense black tissue was seen all around the joint with synovial proliferation (Fig. 1C). The implant was found to be loose. On examination, link of the prosthesis was worn-out and we suspect the same to be the source of metallosis. Prosthetic components were extracted and the bone ends and surfaces were debrided. The intramedullary debris was removed by curette and reamers. Care was taken to preserve as much bone as possible. The wound was thoroughly washed with pulsatile lavage. A static cement spacer over a K-nail was bridged across the distal end of femur and proximal end of tibia (Fig. 2). Patient was kept under follow-up. Histological evaluation of specimens retrieved at revision surgery demonstrated metallosis. The extracted implant was sent for sonication and did not grow any organism.

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Fig. 2 X-ray of the knee following first stage debridement. Note the cement spacer nail in situ. The proximal end of the nail had cut out of the distal end of femur which was seen before the second stage surgery.

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Operative procedure stage 2: After 6 months of the first stage surgery, the patient was planned for stage 2 revision. The knee was approached through previous incision and the K nail with cement spacer was removed. The bones were prepared for femoral and tibial components with stem. Large defects were seen in the distal femur as well as the proximal tibia (Fig. 3). There was a large segment defect in the distal femur which we had anticipated preoperatively. In addition, there was a large contained defect in tibia surrounding the keel of the prosthesis classified as type 3 According to Anderson Orthopaedic Research Institute classification. As the collaterals were absent, we planned to reconstruct the knee with following:a)Structural distal femoral allograft [Fig. 4

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Fig. 4 Distal femoral allograft [A]. Tibial allograft [B] from which the distal metaphyseal allograft [C] of the size matching the defect in proximal tibia was taken out and prepared.

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Fig. 3 Intraoperative picture showing trial implants in situ. Arrows showing the bone defect in the distal femur and well as proximal tibia.

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Both distal femoral and distal tibial allografts were taken from our institutional bone bank. These allografts were pre-irradiated and cryopreserved at −70 °C. After selecting appropriate size, the distal femoral allograft was prepared on the back table by an assistant. The distal tibial was cut and prepared. Both the malleoli were cut to give proper shape of metaphyseal cone. The tibial allograft was made akin to trabecular metal tibial cone augment shape to fill the tibial defect (Fig. 5). The prepared distal metaphyseal tibial allograft was placed in the proximal tibial defect with bone with in bone technique to create stable tibial platform. The stability of the allograft was ensured. The distal femoral allograft prosthesis composite was inserted and trial performed. Care was taken during cementing to avoid getting cement on the interface between the graft and the host bone. At the latest follow up of one year, patient is pain-free and walking independently. The range of motion is 0 to 90°. At the latest follow up of two years, the allograft-and host bone interfaces showed no radiolucent zones or gaps indicating incorporation of allograft into the host bone (Fig. 6).

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Fig. 5 Intraoperative picture showing the distal femoral allograft as well as the distal tibial metaphyseal cone allograft (inset).

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Fig. 6 One year follow-up X-ray showing incorporated metaphyseal cone allograft in the proximal tibia in Anteroposterior [A] and Lateral [B] views.

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3 Discussion

The large bone defects are encountered in primary or revision knee arthroplasty and can affect implant alignment and the bone-implant interface.⁸ These bony defects are secondary to osteolysis due to polyethylene wear, after aggressive debridement, infection, mechanical motion generated from a loose implant, implant migration, bone loss after multiple revision and iatrogenic loss at the time of prosthesis removal.⁸,⁹ These bony defects must be filled up to restore the joint line, ensure proper implant alignment and to provide structural support for the new prosthesis. The management of bone defects in revision TKA depends on its location (femur or tibia), type (Anderson Orthopaedic Research Institute Grading) and size of the defect.¹⁰

A detailed preoperative planning is required to choose best possible method to deal with such large bone defects. Treatment approaches for large bone defects include cancellous or structural bone graft (both autologous and allogenic) or metal augments and cones.¹¹,¹² Recently porous tantalum metal metaphyseal cones are found to be suitable for filling large, centrally based tibial defects. These cones are easy to implant and provide stable metaphyseal foundation for the revision construct.¹³ However, in developing countries where the patients have to purchase the implants by themselves, these are expensive and not readily available too. They are not cost-effective as well. The use of allograft for filling up large bone defects in revision setting has been described in many studies. Allograft can be used if the defect is too large to be managed with prosthetic augments or impaction grafting. The use of distal femoral and proximal tibial allograft is a routine procedure at our institute for the management of massive skeletal allograft in relatively younger patients. An innovative case of using dual massive allograft (distal femur and proximal tibia) in the management of large skeletal defects have already been described by the senior author (RM).¹⁴ However, the use of distal metaphyseal tibial allograft to fill the contained defect in the proximal tibia was first of its kind to the team. We used the distal tibia to make a cone for proximal tibial defect. The advantage of using distal tibia as a graft for filling centrally located proximal metaphyseal defects was that it was anatomical similar and fitting to the defect. The allograft bone from the distal tibia after removal of distal end and malleoli can be fitted exactly into the central metaphyseal defects as in our case. The distal tibial allograft provides cortical bone for structural support to the metaphysis, and their medullary canal can be used to pass prosthetic stem through it; which is important for stable bone-implant interface and alignment. The use of structural allograft has additional advantages of biocompatibility, matched size, an option of customization of shape according to the defect created after removal of implant, biologic union with host bone, restoration of anatomy and cost-effectiveness.¹⁵ Hence, the use of distal tibial metaphyseal allograft is an cost effective and reliable option for the management of large contained bone defect in the proximal tibia.

4 Conclusion

Allograft is a reliable option in case of large bone defect after prosthesis removal. The allograft is a biological and cost-effective option especially in developing countries where availability of Trabecular Metal™ implant is limited and not easily afforded by patients.