Bone loss in total knee arthroplasty (TKA) may be encountered in the primary or revision setting. It is more commonly seen in the latter, and may arise from osteolysis due to polyethylene wear, aseptic loosening, or aggressive debridement for the treatment of infection. It may be exacerbated by iatrogenic damage during surgery.
The workup for a patient who may undergo revision TKA starts with a careful history and physical examination. The patient’s age and functional status are assessed, as well as the presence of medical comorbidities. Any history of previous wound healing problems or night pain should arouse suspicion for the presence of infection.
The physical exam focuses on alignment, presence of contractures, range of movement, patellar tracking, competency of the extensor mechanism and the integrity of the ligamentous structures. Careful examinations of previous surgical incisions and the neurovascular status of the limb are mandatory. Laboratory studies are necessary to screen for the presence of infection with elevated inflammatory markers (erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP)) warranting aspiration of the joint for further investigation. Imaging studies include weight-bearing anteroposterior, lateral and sunrise views of the knee.
Classification of bone loss
The Anderson Orthopaedic Research Institute (AORI) classification system (Table I) is commonly employed to describe bone loss in revision TKA.1
Successful TKA revision surgery is dependent upon adequate pre-operative planning. Bone loss can have a detrimental effect on the success of revision knee surgery by adversely affecting the survivorship of the revision TKA, level of the joint line, the rotation of the tibial and femoral components, ligamentous balancing and stability throughout the knee’s range of movement, and patellar tracking. Pre-operative planning must take all of these into account. It is important to determine what implants may be required for the procedure and ensure their availability.
The standard surgical exposure is the medial parapatellar approach, which provides extensile access to the joint. The quadriceps snip, which has a minimal effect on post-operative rehabilitation, may be useful to improve exposure when the extensor mechanism is noncompliant.2 A thorough synovectomy further improves visualisation. Frozen section and/or tissue cultures are sent to check for the presence of occult infection. It is paramount to remove existing implants with care to minimise iatrogenic bone loss. The remaining bone is debrided to remove the soft-tissue membrane that would prevent proper cement interdigitation or osseointegration. Once the remaining bone stock is exposed, the bone defects are re-classified according to the AORI system.
Management of bone loss
Type I defects.
AORI Type I defects do not require any treatment beyond the use of polymethylmethacrylate (PMMA) cement or cancellous allograft, which adequately fill any contained defects that are < 5 mm in size.
Type IIa defects.
AORI Type IIa defects may also be filled with PMMA if they are contained. PMMA is inexpensive, readily available, and easily contoured to fill the deficit. Defects between 5 mm and 10 mm in size may be filled with PMMA, although reinforcement with screws is recommended.
Defects > 10 mm in size can be treated with morsellised allograft bone or standard metal augmentation. Morsellised allograft bone is economical, readily available, and has the theoretical advantage of restoring bone stock. Disadvantages include potential for graft resorption, the technically demanding nature of the procedure, and potential for disease transmission. Lotke et al3 reviewed 48 patients who underwent impaction allografting for bone defects, some of whom required wire mesh for uncontained defects. There were no mechanical failures at a mean follow-up of 3.8 years, although the authors did describe the technique as demanding and time-consuming. Not insignificantly, they also reported a complication rate of 14%.3 Impaction grafting may be considered in younger patients where subsequent revision surgery is likely and bone stock restoration is desirable.
Modular metal augments are another option for uncontained bony defects involving the femoral condyle or tibial plateau. The advantages of modular augments include favourable load transfer from metal to bone, allowing immediate weight-bearing by the patient. Disadvantages include size and shape limitations, unsuitability for larger bone defects, and the fact that they do not restore bone stock. They are recommended for use in moderately sized (< 15 mm), non-contained defects. Pagnano et al4 investigated the use of tibial wedge augments in primary TKA. They reported the results of 24 knees in 21 patients at a mean of 5.6 years after surgery, and found excellent clinical results in 67%, with only one knee requiring re-operation.4 Patel et al5 reported on the five- to ten-year results of AORI Type 2 bone defects in 79 knees treated with modular metal augments in revision knee surgery. The survival of the components at 11 years (95% confidence interval (CI) 10.3 to 11.2) was 92% (sd 0.03%).5
Type IIb/III defects.
AORI Type IIb and Type III defects involve bone loss of a major portion of the tibial plateau or a femoral condyle. There may be loss of integrity of supporting ligamentous structures or of their bony attachments. Structural allografts, porous metal cones or sleeves, or megaprostheses may be required.
Structural bone allograft may be contoured to fill larger osseous defects. The disadvantages are risk of disease transmission, non-union, malunion, or late collapse. Structural allografts should be bypassed by an intramedullary stem to reduce stress on the graft. Engh and Ammeen6 reported
46 revised knees in 44 patients who had allogeneic bone grafting with or without additional augments, at a mean of eight years post-operatively. Four knees failed and required re-operation. For the remaining knees, the mean Knee Society clinical score was 84 and the mean arc of motion was 104°. There was no instance of graft collapse or aseptic loosening associated with the structural allograft.6
Porous metal metaphyseal cones are very useful for filling large, centrally based defects. These devices have the advantage of providing a stable metaphyseal foundation for the revision construct, availability in a wide array of sizes, and relative ease of implantation. The disadvantages of these devices include the need to remove host bone, difficulty of removal once osseointegration occurs, potential for soft-tissue irritation, and the fact that they do not restore bone stock. Clinical studies with trabecular metal cones for bone loss in revision TKA have shown promising, excellent short-term outcomes. Long and Scuderi7 looked at 16 cases of revision TKA requiring trabecular metal cones at a mean follow-up of 31 months. Of these, 14 were deemed to have a successful outcome, with correction of the mechanical axis and restoration of the joint line, and signs of stable osseointegration of the cup. Two cases of recurrent sepsis necessitated removal of a well-fixed cone.7 Meneghini et al8 reported on 15 knees with AORI type IIb and III defects that were managed by revision TKA using tibial trabecular metal cones. The mean follow-up was 34 months. The mean Knee Society clinical scores improved from 52 pre-revision to 85 points at the time of final follow-up, and all cones showed radiological evidence of osseointegration.8 Tantalum cones have proved equally effective for managing severe femoral bone loss in revision TKA; femoral cones were clinically functioning well in all 24 patients who had undergone revision TKA at a mean 33 months follow-up in a series reported on by Howard et al.9 The 20 patients who had radiological data available at 35 months howed that they were all well-fixed with no complications related to the cones.9
Porous coated metaphyseal sleeves are very useful for filling large, centrally based defects. Similar to metaphyseal cones, these devices have the advantage of providing a stable metaphyseal foundation for the revision construct, are available in a wide array of sizes, and are relatively easy to implant secondary to a ream-broach-trial system. The disadvantages of these devices include the need to remove host bone, difficulty of removal once osseointegration occurs, potential for iatrogenic fracture during bone preparation, and the fact that they do not restore bone stock. Jones et al10 reported on 16 S-ROM mobile-bearing hinge total knee prostheses implanted with porous coated metaphyseal sleeves. The surgical indications were severe instability and bone loss, and the majority of cases were revision TKAs. There was no evidence of loosening, and complete bone apposition was seen in nearly all cases at a minimum two-year follow-up.10 In a combined series, 30 knees with porous metaphyseal sleeves were followed up for four years11; there were no mechanical failures, and all knees showed evidence of apposition and remodeling around the sleeves.
Severe bone defects, if accompanied by loss of supporting ligamentous structures, mandate use of a rotating hinge knee. Hinged knee constructs should not be used in a cavalier fashion, especially in younger, active patients. Although good outcomes are reported in low demand patients, there is a high risk of complications. Berend and Lombardi12 reported on 39 revision TKAs in 37 patients with (non-tumour related) massive bone loss and instability. Patients obtained very good clinical and functional outcomes, with average Knee Society scores improving from
39 pre-operatively to 87 at a minimum follow-up of two years. Eight patients died, and five patients required re-operation; three for infection, one to correct hyperextension deformity, and one for a peri-prosthetic fracture. The survivorship was 87% at 46 months.12
Pour et al13 reported the outcome in 43 patients who underwent 44 salvage revision knee arthroplasties for global instability or severe bone loss, using a modern generation modular rotating hinged total knee prosthesis. The mean follow-up was 4.2 years. Similarly, they reported substantial improvement in function and reduction in pain, but a relatively large number of complications. Four patients developed aseptic loosening, three had deep infection, and one was revised for peri-prosthetic fracture. The rate of survival of the prosthesis was only 68.2% at five years. The authors recommended the procedure should be reserved primarily for elderly, sedentary patients.13
Revision implants typically require the use of stems to help offload stress at the bone-implant interface. Attempts to use primary implants in ‘simple’ revisions typically lead to inferior results compared with the use of revision implants in ‘difficult’ revisions.1 Stems can be short, narrow and cemented into metaphyseal bone, or longer, cementless and diaphyseal engaging. Cementless stems are easy to use and facilitate component alignment. However, anatomic variation may require the use of offset stems, especially in the tibia. Published reports using cementless stems show a two- to five-year survivorship ranging from 81% to 94%.14 Cemented metaphyseal engaging stems and cementless diaphyseal engaging stems appear to have equivalent results at mid-term follow-up.15,16 However, it should be emphasised that cementless stems must engage the diaphysis. Shorter, so-called ‘dangle’ stems have higher reported failure rates.15
Patellar bone loss
If the patella was resurfaced at index arthroplasty, the polyethylene button should be retained if possible. Removal of a well-fixed patellar component can result in severe bone loss and compromise attempts at revision resurfacing. Options for management of the non-resurfaceable patella include patellectomy, patelloplasty, gull-wing osteotomy, bone grafting, or use of a porous tantalum implant. Patellectomy has historically been reported as showing a poor outcome, with inferior quadriceps strength, quadriceps fatigue and reduced active range of movement after the procedure.
Hanssen17 reported significant improvement in post-operative Knee Society pain and function scores in a series of nine patients who had bone grafting of a patellar shell performed at the time of revision. The technique involves creation of a retropatellar soft-tissue pouch that is filled with bone graft. Patellar thickness was largely maintained at final follow-up.17 Patelloplasty comprises shaving of the patella with removal of osteophytes. It has an inferior result to resurfacing in primary TKA,18 and while early results following revision surgery are satisfactory, Knee Society scores show deterioration with time.19 Tracking of the residual patella can be improved by performing a gull-wing osteotomy, which allows the patellar remnant to articulate better with the femoral trochlea. Klein20 reported on 12 patients after revision TKA with a gull-wing osteotomy of a deficient patellar remnant. One patient had a poor result that was attributed to a concomitant quadriceps snip; the remaining 11 patients had improved range of movement, no significant extension lag, and improvement in Knee Society pain and function scores at the mean three-year follow-up. Radiographs showed successful healing of all osteotomies, and central tracking of the patella.20
Porous tantalum-backed patellar components have also shown some success in improving the outcome of revision TKA where the patella is severely compromised. This device aims to restore patellar thickness, thus improving the quadriceps moment arm. These implants, however, add considerable cost to the procedure as compared with the other methods of patellar reconstruction. In one study, 11 patients had the tantalum-backed patella inserted and all showed evidence of incorporation at a mean follow-up of 32 months.21 Another study reported a successful outcome in 19 out of 23 components at minimum follow-up of five years. The indication for the tantalum-backed patella was revision surgery in which there was residual patellar thickness ≥ 10 mm. Failures were associated with avascular patellar bone and fixation of components directly to the soft tissues, thus emphasising the need to attach these components directly to viable bone.22,23
Bone loss in revision TKA presents a challenge for the surgeon. Often, such patients may have had multiple previous procedures, and it is essential to respect the integrity of the soft tissues and ligamentous structures. Pre-operative planning and careful surgical technique is paramount. One must be prepared to have instruments and implants available to address severe bone defects in order to successfully reconstruct the knee. Bone grafting is useful in younger patients who may require later revision. Salvage procedures should be reserved for elderly, low-demand patients.
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4. Pagnano MW, Trousdale RT, Rand JA. Tibial wedge augmentation for bone deficiency in total knee arthroplasty: a follow-up study. Clin Orthop Relat Res 1995;321:151-5.
5. Patel JV, Masonis JL, Guerin J, Bourne RB, Rorabeck CH. The fate of augments to treat type-2 bone defects in revision knee arthroplasty. J Bone Joint Surg [Br] 2004;86-B:195-9.
6. Engh GA, Ammeen DJ. Use of structural allograft in revision total knee arthroplasty in knees with severe tibial bone loss. J Bone Joint Surg [Am] 2007;89-A:2640-7.
7. Long WJ, Scuderi GR. Porous tantalum cones for large metaphyseal tibial defects in revision total knee arthroplasty: a minimum 2-year follow-up. J Arthroplasty 2009;24:1086-92.
8. Meneghini RM, Lewallen DG, Hanssen AD. Use of porous tantalum metaphyseal cones for severe tibial bone loss during revision total knee replacement. J Bone Joint Surg [Am] 2008;90:78-84.
9. Howard JL, Kudera J, Lewallen DG, Hanssen AD. Early results of the use of tantalum femoral cones for revision total knee arthroplasty. J Bone Joint Surg [Am] 2011;93:478-84.
10. Jones RE, Skedros JG, Chan AJ, Beauchamp DH, Harkins PC. Total knee arthroplasty using the S-ROM mobile-bearing hinge prosthesis. J Arthroplasty 2001;16:279-87.
11. Jones RE, Barrack RL, Skedros J. Modular, mobile-bearing hinge total knee arthroplasty. Clin Orthop Relat Res 2001;392:306-14.
12. Berend KR, Lombardi AV Jr. Distal femoral replacement in nontumor cases with severe bone loss and instability. Clin Orthop Relat Res 2009;467:485-92.
13. Pour AE, Parvizi J, Slenker N, Purtill JJ, Sharkey PF. Rotating hinged total knee replacement: use with caution. J Bone Joint Surg [Am] 2007;89:1735-41.
14. Sah AP, Shukla S, Della Valle CJ, Rosenberg AG, Paprosky WG. Modified hybrid stem fixation in revision TKA is durable at 2 to 10 years. Clin Orthop Relat Res 2011;469:839-46.
15. Fehring TK, Odum S, Olekson C, et al. Stem fixation in revision total knee arthroplasty: a comparative analysis. Clin Orthop Relat Res 2003;416:217-24.
16. Whaley AL, Trousdale RT, Rand JA, Hanssen AD. Cemented long-stem revision total knee arthroplasty. J Arthroplasty 2003;18:592-9.
17. Hanssen AD. Bone-grafting for severe patellar bone loss during revision knee arthroplasty. J Bone Joint Surg [Am] 2001;83-A:171-6.
18. Cameron HU. Comparison between patellar resurfacing with an inset plastic button and patelloplasty. Can J Surg 1991;34:49-52.
19. Parvizi J, Seel MJ, Hanssen AD, Berry DJ, Morrey BF. Patellar component resection arthroplasty for the severely compromised patella. Clin Orthop Relat Res 2002;397:356-61.
20. Klein GR, Levine HB, Ambrose JF, Lamothe HC, Hartzband MA. Gull-wing osteotomy for the treatment of the deficient patella in revision total knee arthroplasty. J Arthroplasty 2010;25:249-53.
21. Nasser S, Poggie RA. Revision and salvage patellar arthroplasty using a porous tantalum implant. J Arthroplasty 2004;19:562-72.
22. Kamath AF, Gee AO, Nelson CL, et al. Porous tantalum patellar components in revision total knee arthroplasty minimum 5-year follow-up. J Arthroplasty 2012;27:82-7.
23. Ries MD, Cabalo A, Bozic KJ, Anderson M. Porous tantalum patellar augmentation: the importance of residual bone stock. Clin Orthop Relat Res 2006;452:166-70.