Abstract
Aims
Metaphyseal cones and sleeves are components used in revision knee arthroplasty to ensure load transfer, encourage bone on-growth and prevent stress shielding. Additive manufacturing of titanium alloy implants is a novel technique with limited clinical outcome reports in the literature. The aim of this study was to determine radiographic evidence of osseointegration and early results of a single manufacturer porous titanium metaphyseal components in the proximal tibia.
Methods
We retrospectively reviewed the prospectively collected database of two institutions. Patients who underwent revision knee arthroplasty using porous titanium components by a single manufacturer were identified. Immediate post-operative and latest follow-up radiographs were independently analysed by 2 reviewers to determine metaphyseal bone contact and level of osseointegration in relevant Knee Society Radiographic Evaluation and Scoring System zones.
Results
22 patients (15 males; 7 females) with a mean age of 71 (49–92) years were included. The mean follow-up period was 14 months (2–44 months). Cones were used in 16 patients and sleeves in 6. Interobserver reliability assessment showed substantial agreement (weighted Kappa 0.71, (95% CI: 0.60, 0.81). There was significant correlation between the bone contact in the immediate postop radiograph and osseointegration at final follow-up (kendall’s tau-b: 0.698, p < 0.001). Infection free prosthetic joint survival was 20/22 at final follow-up.
Conclusion
Porous titanium metaphyseal components produced with additive manufacturing provided excellent osseointegration and no early clinical failures. Partial or complete contact of the cone with native bone in the immediate postoperative radiograph resulted in osseointegration in all cases.
Keywords: Revision knee arthroplasty, Metaphyseal cones, Metaphyseal sleeves, Additive manufacturing, Titanium, Osseointegration
1. Introduction
The outcome of revision total knee arthroplasty (TKA) is influenced by several factors including the cause of primary implant failure, degree of bone loss, presence of infection, ligament stability, and the condition of the soft tissue envelope.1,2 Metaphyseal bone deficiency may arise secondary to osteolysis or damage during extraction of the primary implant and presents as a common challenge during revision TKA.3 Bone defect classification systems commonly used in revision TKA, recommend augmenting the metaphyseal bone and using stems when the metaphysis is deficient.4, 5, 6 Metaphyseal fixation with porous metal implants has been used to reconstruct bone defects and improve base plate stability at the time of revision arthroplasty with good clinical results.3,7, 8, 9 Bone ingrowth has been documented and quantified in retrieved well fixed porous tantalum hip and knee implants.10
Additive manufacturing of titanium alloy implants is a novel technique that allows for complex 3-dimensional (3D) structures to be generated as a uniform implant. Implant components are designed using a porous trabecular-like structure; similar to that of cancellous bone. The titanium alloy is biologically inert, ductile, and corrosion resistant. Its durability makes it a suitable choice for in vivo use as a modular augment in arthroplasty procedures. An electrochemically deposited calcium phosphate coating is uniformly applied to the porous exterior to encourage postoperative capillary and bone ingrowth.11 This manufacturing technique is gaining popularity with several manufacturers now offering 3D printed implants.12,13 Despite the large number of products available on the market, there is limited reports on the clinical outcomes when these components were used.
The purpose of this study was to determine radiographic evidence of osseointegration and early results of a single manufacturer porous titanium metaphyseal components in the proximal tibia.
2. Materials & methods
2.1. Patient selection
The prospectively collected databases of two institutions were retrospectively reviewed. All patients who underwent revision procedures around the knee using EPORE® titanium metaphyseal components or cones (implantcast GmbH, Buxtehude, Germany) between 2015 and 2020 were included. Four surgeons in Birmingham, UK, and one in Perth, Western Australia performed all procedures. All surgeons practice in orthopaedic oncology as well as arthroplasty. 22 patients were identified (16 treated with tibial cones, 6 with metaphyseal components). Demographic data including patient age, number of prior knee procedures and indication for the revision procedure were collected. Postoperative progress notes were assessed for the following parameters; weight bearing capacity (unaided, aided, non-ambulatory), loosening of implant, infection, amputation, mortality.
2.2. Implant and operative details
All implants assessed in this series were implantcast EPORE® metaphyseal components and implantcast EPORE® tibial cones. These components are made from TiAl6V4 alloy and additive manufacturing achieving 60% porosity, 330 to 390 μm rod thickness and a 3 GPa modulus of elasticity.11 Tibial cones came in one of four sizes and were implanted intraoperatively using a ‘press-fit’ technique without cement, Fig. 1a. These components are not linked to the stem or tibial baseplate. Following satisfactory contact of the cone to the host bone, the tibial prosthesis was inserted using antibiotic impregnated cement. The selection of stem length was a surgeon-specific choice at the time of the operation. The metaphyseal components, often described as sleeves, are linked to the implant with solid fixation, Fig. 1b. The metaphyseal bone (including central defect) is prepared with broaches and the implant is implanted as monoblock after assembly on the side table.
Fig. 1.
(a) Implantcast metaphyseal EPORE® tibial (cone) implant (b) Implantcast metaphyseal EPORE® tibial (sleeve) component.
2.3. Radiographic assessment
Two independent reviewers (TE, JP) assessed the immediate postoperative radiograph and the most recent follow-up radiograph (Fig. 2, Fig. 3). The medial (3 M), lateral (3 L), anterior (3A), and posterior (3P) aspect of the metaphyseal cone or component was assessed using radiographic zones as described in the Knee Society Radiographic Evaluation and Scoring System (KSRESS).14 Radiographic appearances of the implant-bone interface in the central/keel zone immediately following the operation were described as: complete contact, partial contact, or no contact. Zones of the most recent follow-up radiograph were assessed as: complete osseous integration, partial integration, stable radiolucent line, or progressive radiolucent line.
Fig. 2.
Metaphyseal cone implant (a) immediate postoperative AP view; (b) immediate postoperative lateral view; (c) one-year follow up AP view; (d) one-year follow up lateral view.
Fig. 3.
Metaphyseal component (sleeve) implant (a) immediate postoperative AP view; (b) immediate postoperative lateral view; (c) eight months follow up AP view; (d) eight months follow up lateral view.
2.4. Statistical analysis
Descriptive statistics were used for data presentation. Interobserver agreement was assessed using weighted Kappa (linear weighting). Correlation of the bone contact grades in the immediate postoperative radiograph to the integration in the final postoperative radiograph was done using Kendall’s tau-beta. Analysis was done using IBM SPSS Statistics for Macintosh, Version 25.0. Armonk, NY: IBM Corp.
3. Results
3.1. Clinical outcomes
22 patients were included in the analysis with a mean age of 71 (49–92) years. The mean follow-up period was 14 months (2–44 months). The mean number of procedures performed on the knee of each subject prior to metaphyseal cone insertion was 1 (range: 1–5). The most common indication for revision with the use of a metaphyseal cone was periprosthetic infection (50%).
During the follow-up period no patient was required to undergo a re-revision procedure for aseptic loosening of the tibial reconstruction. Two patients underwent revision surgery: One for infection and one for aseptic loosening of the femoral component. During the revision procedure, the tibial component was well fixed and was not revised. At the most recent follow-up appointment 10 patients (45.5%) were able to mobilise unaided, 11 (50.0%) required a mobility aid such as crutches, and 1 patient (4.5%) remained non-ambulatory.
Postoperative infection occurred in 9.1% of cases (2/22). One patient required revision knee arthroplasty for infection of a distal femoral replacement; unsuccessful conservative management of the chronic infected endoprosthesis resulted in amputation. One patient with a postoperative infection was managed non-operatively and passed away within 1 year of the revision procedure. At the time of submission, one patient awaits re-revision for a suspected low grade periprosthetic joint infection despite negative inflammatory serum markers.
3.2. Radiographic assessment
Immediate post-operative metaphyseal bone contact and final follow-up osseointegration scores can be seen in Table 1. There was a significant correlation of the immediate postoperative bone contact grade and the final follow-up osseointegration score (kendall’s tau-b: 0.698, p < 0.001).
Table 1.
Metaphyseal Cones & Sleeves Displaying Radiographic Contact on Immediate Postoperative and Osseointegration at Latest Follow up. KSRESS - Knee Society Radiographic Evaluation & Scoring System; 3 M – zone 3 medial aspect; 3 L – zone 3 lateral aspect; 3A - zone 3 anterior aspect; 3P - zone 3 posterior aspect. n = 22.
| KSRESS Zone |
|||||
|---|---|---|---|---|---|
| 3 M | 3 L | 3A | 3P | ||
| Immediate Post-Op | Complete Contact | 11 (50.0%) | 13 (59.1%) | 16 (72.7%) | 17 (77.3%) |
| Partial Contact | 11 (50.0%) | 8 (36.4%) | 5 (22.7%) | 5 (22.7%) | |
| None | 0 (0.0%) | 1 (4.5%) | 1 (4.5%) | 0 (0.0%) | |
| Latest Follow Up | Full Ingrowth | 14 (63.6%) | 16 (72.7%) | 15 (68.2%) | 18 (59.9%) |
| Partial Ingrowth | 8 (36.4%) | 5 (22.7%) | 7 (31.8%) | 4 (18.2%) | |
| Stable Radiolucency | 0 (0.0%) | 1 (4.5%) | 0 (0.0%) | 0 (0.0%) | |
Patients treated with sleeves in our series had Anderson Orthopaedic Research Institute (AORI) type 1 defects hence all components had complete bone contact at the immediate postoperative radiograph. At the final follow-up radiograph, all of those components were seen to be fully integrated with no radiolucent lines. We therefore proceeded with a further analysis of the cases managed with a tibial cone (n = 16). These cases had AORI type 2 defects and only partial bone contact was possible in the immediate postoperative radiograph in a large proportion of the KSRESS zones analysed. The radiographic results of the cone components can be seen in Table 2. When these cases were analysed independently, the immediate postoperative bone contact grade was again significantly associated with the final follow-up osseointegration score (kendall’s tau-b: 0.649, p < 0.001), Table 2.
Table 2.
Metaphyseal Cones Displaying Radiographic Contact on Immediate Postoperative and Osseointegration at Latest Follow up. KSRESS - Knee Society Radiographic Evaluation & Scoring System; 3 M – zone 3 medial aspect; 3 L – zone 3 lateral aspect; 3A - zone 3 anterior aspect; 3P - zone 3 posterior aspect. n = 16.
| KSRESS Zone |
|||||
|---|---|---|---|---|---|
| 3 M | 3 L | 3A | 3P | ||
| Immediate Post-Op | Complete Contact | 5 (31.3%) | 7 (43.8%) | 10 (62.5%) | 11 (68.8%) |
| Partial Contact | 11 (68.8%) | 8 (50.0%) | 5 (31.3%) | 5 (31.3%) | |
| None | 0 (0.0%) | 1 (6.3%) | 1 (6.3%) | 0 (0.0%) | |
| Latest Follow Up | Full Ingrowth | 8 (50.0%) | 10 (62.5%) | 9 (56.3%) | 12 (75.0%) |
| Partial Ingrowth | 8 (50.0%) | 5 (31.3%) | 7 (43.8%) | 4 (25.0%) | |
| Stable Radiolucency | 0 (0.0%) | 1 (6.3%) | 0 (0.0%) | 0 (0.0%) | |
4. Discussion
The use of porous titanium metaphyseal components in our series was associated with early osseointegration and favourable clinical results at short term follow-up. Bone contact of the porous titanium component, either complete or partial, with the host bone at the immediate postoperative radiograph was associated with integration at the final radiographic follow-up. We had no cases of subsidence or early fixation failures. In one case, a postoperative radiolucency was identified in both the tibial baseplate and femoral components and the patient is awaiting revision surgery for a working diagnosis of periprosthetic joint infection. The sleeve remains fully osseointegrated with no radiolucent lines.
The success of metaphyseal cone implantation and stability relies on the degree of osseointegration.15 Osteocyte migration from trabecular bone to the porous implant is influenced by mechanical stress. Mechanical stress is proposed to stimulate a biochemical response which results in cellular movement into the nascent porous metallic surface.16 The porous external surface, with its high coefficient of friction, aids in initial short-term stability and facilitates osseointegration for improved long-term outcomes.5 Failure of the implanted metaphyseal cone can occur in the acute postoperative setting when no osteoblast migration occurs across the bone-implant interface. Furthermore, the osseointegration of the prosthesis may fail in the long term if early bone formation does not undergo remodelling to create trabeculation and marrow inclusions.16 In our series 100% of implants displayed radiographic features of host bone ingrowth in all KSRESS zones where bone contact was achieved intraoperatively.
These early findings are consistent with series of metaphyseal fixation in revision TKA using porous metal (tantalum) components. A systematic review analysing the results of 927 metaphyseal cones and 1801 sleeves found that tantalum implants provided satisfactory radiographic and clinical outcomes at a minimum of one-year follow up.5 Metaphyseal components reviewed were associated with an aseptic survivorship of 97.3% and 97.8% for cones and sleeves, respectively.5 Kamath et al. reported >95% survival of the tibial cone fixation in their knee reconstruction series at intermediate follow up (five to nine years).9 Brown et al. report a re-revision rate of 12% at a mean follow-up of 21 months (2–79 months) in their series of 83 complex primary and revision TKAs using metaphyseal tantalum cones.17 Of the 73 non-revised knees, 72 (99%) displayed radiographic evidence of osseointegration after a minimum of 2 years follow up.17 Lachiewicz et al. retrospectively reviewed 27 patients (33 tantalum metaphyseal cones) after a minimum 2-year follow up. Radiographic osseointegration was noted in 94% of metaphyseal cones at most recent follow up.18 In their series, two cases required re-revision for infection and aseptic loosening. Our findings are similar to the high rate of stable fixation for tantalum components reported to be 94–100% after at least 24 months of follow up.5,18,19
Additive manufacturing of has emerged as promising technique allowing complex structure manufacturing including custom made implants. Two series of porous titanium cones have had promising results. Denehy et al. evaluated 62 revision TKAs for a minimum 2-year follow up and found revision free survival of tibial cones to be 90.2%.13 Ohlmeier et al. analysed 52 revision TKAs using titanium tibial cones, they showed that radiographic evidence of integration was present in 89.3% of cases at 18 months.12 These results are in keeping with the early results in our series.
There are several limitations to this study. The relatively short follow up of our study means that further surveillance of these cases is recommended to identify any failures at mid or long term. All cases in our study were followed up until definitive radiographic evidence of osseointegration was present. Our cohort is small in number and therefore our study is at risk of a type II error. Further studies with larger sample size and longer follow up are required to support these porous titanium implants. We have not included patient reported outcome measures in this study as the focus was on osseointegration. The complex surgical history of the cases included would have a significant effect on any functional outcome measures. Furthermore, a large number of cases included had a revision of a tumour endoprosthesis making arthroplasty outcome measures less applicable.
5. Conclusions
Our study has found that titanium metaphyseal cones are an appealing alternative to tantalum cones. They are associated with reliable osseointegration and satisfactory short-term clinical outcomes. In order to evaluate the long-term durability of titanium cones future investigation should focus on cone-survivorship after a longer postoperative time period.
Funding
No financial disclosures. No funding to declare.
Declaration of competing interest
One of the authors declares a paid consultancy with Implantcast GmbH, not related to this study.
Acknowledgements
None.
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