The best treatment method for massive bone defects during revision knee arthroplasty remains uncertain. Options have included the use of impaction bone-grafting [22, 25, 38, 40, 44], structural bulk allografts [7, 11, 14, 16, 17, 28, 31, 39], and tumor-type megaprostheses [2]. Studies with structural allografts and tumor megaprostheses during revision knee arthroplasty have reported encouraging mid-term results, but the high number of complications is a concern. Complications with these techniques include infection, graft resorption, nonunion, failure of graft incorporation, concerns regarding disease transmission, aseptic loosening, and periprosthetic fracture [1, 7, 14, 17, 33]. Although the short-term results with tantalum cones have been promising [9, 18, 21, 23, 24, 26, 34–36, 42], to our knowledge, there have been no studies reporting mid-term outcomes with their use. We therefore sought to determine the mid-term results evaluating (1) reoperation rates for septic and aseptic causes, (2) radiologic findings of osseointegration, and (3) clinical outcomes based on the Knee Society score in patients who underwent revision knee arthroplasty with tantalum cones for significant bone loss.
This study has several limitations. First, as a retrospective series, it is reasonable to be concerned that some patients with severe defects might have been treated in other ways, or that patients with milder defects might have received cones. However, we carefully reviewed our institutional registry and found that this was not the case during the study period, therefore selection bias was unlikely to have influenced our findings. Second, there may be some selection bias against the use of press-fit stems in revision TKAs by the senior author (GG). Cemented stems were used sporadically during the study period by the senior author in selected patients with wide intramedullary canals and poor bone stock. Third, the patient cohort was relatively small but similar in size to cohorts in previous reports [9, 18, 21, 23, 24, 26, 34–36, 42]. Even so, with small series, it is impossible to detect uncommon complications and lower-frequency events that might be clinically important. Fourth, although mid-term at 5 years to 8 years, the followup was relatively short, and these patients therefore still need to be followed to make sure that fixation remains durable during longer service periods. Fifth, fluoroscopic positioning of the knee was not done and the presence of radiolucent lines between the cones and the adjacent tibial and femoral bone may be underestimated. We hoped to minimize this concern using a standardized protocol with experienced radiology technicians to ensure knee positioning, and by reviewing serial postoperative radiographs for reactive trabeculae formation at the cone-host bone interface. Sixth, this study was a combined analysis of femoral and tibial cones, resulting in small numbers of each. Larger numbers, longer followup, and perhaps multicenter trials will be needed to determine whether femoral and tibial cones are similarly durable.
In this cohort, two of 18 patients had a reoperation, both for recurrent infection. This compares favorably with the reoperation frequencies reported by Meneghini et al. [26] (27%), Howard et al. [18] (21%), and Lachiewicz et al. [23] (15%) for patients with AORI Types 2B and 3 defects. However, if we take into consideration only the reoperations for infection and aseptic loosening of the cone, our revision frequency was in line with the reoperation frequencies reported by Meneghini et al. [26] (two of 15) and Lachiewicz et al. [23] (two of 27), although it was higher than reported by Howard et al. [18] (0 of 24). Other studies reported reoperation rates similar to ours, between 5% and 14% [9, 21, 24, 34–36, 42]. However, in those cohorts cones also were used to reconstruct less-severe defects (AORI Type 2A).
The results of our patients may be compared with those of patients treated with structural bulk allografts during revision knee arthroplasty. Bauman et al. [1], Engh and Ammeen [11], and Chun et al. [6] reported reoperation rates of 23% (16 of 70), 19% (nine of 46), and 0% (0 of 27) in their series of 70, 46, and 27 knees respectively at minimum 5 years followup. Our revision frequency compares favorably with the reoperation frequencies reported by Bauman et al. [1] and Engh and Ammeen [11], but unfavorable with the rate reported by Chun et al. [6].
The proportion of patients who had infections in our study (two of 18) was comparable to that reported by Meneghini et al. [26] (13%) and Long and Scuderi [24] (13%), but was lower than reported in other studies [9, 18, 21, 23, 34–36, 42] (Table 1). Furthermore, in our cohort, 13 of the 18 revisions were second-stage reimplantations for deep infection and yet, at this longer followup, had an infection rate comparable to those in the other reports. Our data compare unfavorably with the infection frequencies reported in the bulk allografts studies [1, 6, 11]. Bauman et al. [1], Engh and Ammeen [11], and Chun et al. [6] reported infection rates of 7% (five of 70), 4% (two of 46), and 4% (one of 27) respectively in their series. However, only 9% to 11% of these reconstructions with bulk allografts were reimplantations for infection, whereas in our study 13 of the 18 revisions were second-stage reimplantations for deep infection. Our reinfection frequency (two of 13) compares favorably with those reported in the bulk allograft studies. Bauman et al. [1], Engh and Ammeen [11], and Chun et al. [6] reported reinfection rates of 33% (two of six), 17% (one of six), and 33% (one of three), respectively, in their series.
Table 1 Studies of tantalum cones in revision knee arthroplasty
In our cohort, all cones showed signs of radiographic osseointegration at the latest followup. Our results are in agreement with those of other studies [9, 18, 21, 23, 24, 26, 34–36, 42]. In these studies, with a total of 285 cones used during 242 knee revisions, there are only two knees with cones showing no bone ingrowth (0.7%). Our radiographic osseointegration rate (18 of 18) compares favorably with those reported in the bulk allografts studies. Bauman et al. [1] reported two knees with progressive radiolucencies and two knees with asymptomatic allograft-host nonunion among the 33 knees with adequate radiographs. Engh and Ammeen [11] reported osteolytic lesions in six of 33 knees, however the osteolysis did not involve the metaphyseal area repaired with the bulk allograft. Compared with tantalum cones, the use of bulk allografts is associated with some disadvantages including nonunion of the graft, late collapse of the graft, and fracture of the graft.
Knee Society knee scores for our patients improved on average 46 points from their preoperative state to the latest followup and their functional scores improved by a mean 43 points. The increase between mean pre- and postoperative Knee Society scores in our patients was similar to the mean reported in other studies of cones [9, 18, 23, 26, 35, 36] and bulk allografts [1, 11].
The use of tantalum cones in the treatment of severe bone loss encountered during revision TKA was found to be successful in our patients with a minimum 5-year followup. These devices are a viable option for surgeons when faced with patients with severe bone loss during total knee revisions. Given that each revision presents its own challenges, tantalum cones can aid in providing a stable construct for joint reconstruction that show excellent osseointegration and clinical outcomes at mid-term followup. Further studies with longer followups are needed to confirm the durability of these reconstructions.