Orthopedics

Feature Article 

Short-term Outcomes of 3D-Printed Titanium Metaphyseal Cones in Revision Total Knee Arthroplasty

Ethan A. Remily, DO; Iciar M. Dávila Castrodad, MD; Nequesha S. Mohamed, MD; Wayne A. Wilkie, DO; Margaret N. Kelemen; Ronald E. Delanois, MD

Abstract

Recently, 3-dimensional (3D) printing technology has been used in the development of titanium metaphyseal cones to manage severe bone loss in revision total knee arthroplasty (rTKA). This study assessed (1) radiographs; (2) functional outcomes; (3) complications; and (4) 2-year implant survivorship in patients receiving 3D-printed titanium metaphyseal cones for moderate-to-severe tibial and femoral bone loss in rTKA. A single institution, retrospective chart review was performed for patients with large bone defects treated with a 3D-printed femoral or tibial titanium metaphyseal cone between 2015 and 2017 during rTKA (N=54). Paired sample t tests analyzed Knee Society Scores (KSS). Kaplan–Meier analyses determined implant survivorship when the endpoint was cone revision for aseptic loosening, cone revision for any reason, and reoperation for any reason. The authors found that 51 (98.1%) of 52 available radiographs demonstrated well-fixed components without any evidence of loosening or migration. Mean postoperative KSS scores were significantly higher when compared with preoperative scores (80.4 vs 52.0; P>.001). One patient experienced aseptic loosening of their cone. Seven additional cones were explanted as a consequence of reinfection, 1 of which was removed prior to arthrodesis. Cone survivorship was 98.5% when the endpoint was cone revision due to aseptic loosening, 88.2% when cone revision was due to any reason, and 77.9% for any reoperation. Metaphyseal cones appear to be well-suited for large bone defects during rTKA and the authors' findings suggest that cones may be a viable option for metaphyseal fixation during rTKA. Future studies should focus on their durability during a longer time period. [Orthopedics. 2021;44(1):43–47.]

Abstract

Recently, 3-dimensional (3D) printing technology has been used in the development of titanium metaphyseal cones to manage severe bone loss in revision total knee arthroplasty (rTKA). This study assessed (1) radiographs; (2) functional outcomes; (3) complications; and (4) 2-year implant survivorship in patients receiving 3D-printed titanium metaphyseal cones for moderate-to-severe tibial and femoral bone loss in rTKA. A single institution, retrospective chart review was performed for patients with large bone defects treated with a 3D-printed femoral or tibial titanium metaphyseal cone between 2015 and 2017 during rTKA (N=54). Paired sample t tests analyzed Knee Society Scores (KSS). Kaplan–Meier analyses determined implant survivorship when the endpoint was cone revision for aseptic loosening, cone revision for any reason, and reoperation for any reason. The authors found that 51 (98.1%) of 52 available radiographs demonstrated well-fixed components without any evidence of loosening or migration. Mean postoperative KSS scores were significantly higher when compared with preoperative scores (80.4 vs 52.0; P>.001). One patient experienced aseptic loosening of their cone. Seven additional cones were explanted as a consequence of reinfection, 1 of which was removed prior to arthrodesis. Cone survivorship was 98.5% when the endpoint was cone revision due to aseptic loosening, 88.2% when cone revision was due to any reason, and 77.9% for any reoperation. Metaphyseal cones appear to be well-suited for large bone defects during rTKA and the authors' findings suggest that cones may be a viable option for metaphyseal fixation during rTKA. Future studies should focus on their durability during a longer time period. [Orthopedics. 2021;44(1):43–47.]

Metaphyseal bone loss in the setting of revision total knee arthroplasty (rTKA) remains an ongoing issue. Several options, such as allografts, impaction bone grafting with mesh augmentation, and metaphyseal cones, exist for the management of larger Anderson Orthopaedic Research Institute (AORI) type 2 and 3 bone defects.1 Metaphyseal cones in particular are suitable for these defects because they act as osteoconductive scaffolds and facilitate biologic fixation of implants to existing bone.2–4 The porous tantalum-based cone is most commonly used because studies have demonstrated low complication rates and successful osseointegration.5,6 Despite the known advantages, tantalum cones do not conform to the defect of the patient without the removal of bone prior to implantation.4,7 Furthermore, they also have demonstrated higher fracture rates.8 For these reasons, the use of titanium as the metallurgical construct for cones has been increasing in recent years.

Titanium-based cones have been gaining favor due to their ability to be constructed through 3-dimensional (3D) printing. Cones developed using this method maintain their porosity similar to tantalum metaphyseal cones, yet facilitate a customized fit into the metaphyseal space, resulting in less bone loss and greater stability.4 These proposed advantages of 3D-printed porous titanium cones represent an attempt to address the shortcoming of porous tantalum cones: their long-term stability.

Early reports in the literature have demonstrated favorable outcomes. In a study measuring the stability of titanium cones vs tantalum cones, titanium cones in both the femur and tibia exhibited less micromotion than tantalum cones when put under stress, making them a potentially superior option.4 Because favorable short-term outcomes are being reported, titanium cones appear to be a promising alternative to standard cones made of tantalum.

Despite the promising early outlook for 3D-printed titanium cones, increased research pertaining to the stability of titanium cones in patients with moderate-to-severe metaphyseal bone loss who underwent rTKA is needed. Therefore, this study aimed to investigate the short-term postoperative outcomes of patients implanted with 3D-printed titanium cones during rTKA. Specifically, the authors assessed (1) radiographic outcomes; (2) functional outcomes; (3) complications; and (4) 2-year implant survivorship in patients receiving 3D-printed titanium metaphyseal cones for tibial and femoral bone loss in rTKA.

Materials and Methods

Patient Selection

A single-institution, retrospective chart review was performed for patients who underwent rTKA from 2015 to 2017. Patients were included if they had an AORI type 2 or 3 bone defect, were treated with a 3D-printed femoral or tibial porous titanium metaphyseal cone, and had a minimum of 2-year follow-up. After stratification, a total of 54 patients were included. Institutional review board approval was obtained prior to the initiation of this study.

Patient Variables

Patient demographics collected were indication for revision, sex, race, mean age, mean follow-up, mean body mass index (BMI), health status, mean number of previous procedures, number and location of cones implanted, and AORI classification of bone defect. Patient health status was graded preoperatively according to American Society of Anesthesiologists (ASA) scores, mean Charlson Comorbidity Index (CCI), smoking status, alcohol status, and drug status. Reports of adequate radiographic osseointegration were extracted from the radiographic impression dictated by the provider from the latest postoperative follow-up visit. Pre- and postoperative Knee Society Scores (KSS) were collected to determine short-term functional outcomes. Postoperative complications, such as infection, prosthesis loosening, and additional surgeries, were collected.

Patient Demographics

The most common indication for revision surgery requiring cone implantation was infection (55.5%), followed by loosening (20.4%) and instability (11.1%). Sex was evenly distributed, with 27 (50.0%) women and 27 (50%) men. Twenty-eight (51.8%) patients were White and 26 (48.2%) were Black. Mean age was 65 years (range, 45.2–91.8 years). Mean follow-up was 29.9 months (range, 24.0–42.0 months). Mean BMI was 36.8 kg/m2 (range, 20.5–69.0 kg/m2). Mean ASA score was 2.9 (range, 2–4), whereas mean CCI was 3.5 (range, 0–9). Eight (14.8%) patients had a history of smoking, 5 (9.2%) had a history of alcohol abuse, and 6 (11.1%) had a history of drug abuse (Table 1).

Demographics of Patients Implanted With Metaphyseal Cones for Bone Loss During Revision Total Knee Arthroplasty (N=54)Demographics of Patients Implanted With Metaphyseal Cones for Bone Loss During Revision Total Knee Arthroplasty (N=54)

Table 1:

Demographics of Patients Implanted With Metaphyseal Cones for Bone Loss During Revision Total Knee Arthroplasty (N=54)

Patients previously underwent a mean of 4.2 procedures (range, 1–14). Mean length of stay (LOS) was 6.8 days, with a median LOS duration of 4.0 days. A total of 68 cones consisting of 53 (77.9%) tibial cones and 15 (22.1%) femoral cones were implanted. Twelve (17.6%) bone defects were classified as AORI type 2A, 32 (47.1%) as AORI type 2B, and 24 (35.3%) as AORI type 3 (Table 1). Both femoral and tibial cones were implanted in 14 patients during their initial implantation surgery.

Statistical Analysis

Continuous and categorical variables were assessed using descriptive statistical analysis. Paired samples t tests were used to compare KSS. Kaplan–Meier analyses were used to determine cone survivorship when the endpoint was cone revision for aseptic loosening, cone revision for any reason, and reoperation for any reason. A P value of .05 was set as the threshold for statistical significance. All statistical analysis was performed using SPSS, version 25, software (IBM Corporation).

Results

Radiographic and Functional Outcomes

Subsequent radiographic imaging was available for 52 (96.2%) of 54 patients. Radiographic assessment revealed 51 (98.1%) of the 52 cones were well-fixed without any evidence of loosening or migration. Mean postoperative KSS were significantly higher when compared with preoperative KSS (80.4 vs 52.0; P>.001; Table 2).

Radiographic and Functional Outcomes for Patients Implanted With Metaphyseal Cones for Bone Loss During Revision Total Knee Arthroplasty

Table 2:

Radiographic and Functional Outcomes for Patients Implanted With Metaphyseal Cones for Bone Loss During Revision Total Knee Arthroplasty

Complications Involving Cone Revision

Seven surgeries were performed involving the explantation of 8 cones (Table 3; Figure 1). One patient initially receiving a femoral and tibial cone subsequently experienced aseptic loosening of the femoral cone, requiring revision involving explantation and reimplantation of only the femoral cone. Another patient who also received a femoral and tibial cone developed a prosthetic joint infection and had both cones explanted during 2-stage revision. Furthermore, 5 other patients had their cone explanted during a 2-stage revision for prosthetic joint infections.

Metaphyseal Cone Complications and Survivorship

Table 3:

Metaphyseal Cone Complications and Survivorship

Anteroposterior radiograph showing a femoral cone demonstrating radiographic loosening along the medial metaphyseal region of the femur. The yellow arrows represent a radiolucency suggestive of osteolysis around the femoral implant.

Figure 1:

Anteroposterior radiograph showing a femoral cone demonstrating radiographic loosening along the medial metaphyseal region of the femur. The yellow arrows represent a radiolucency suggestive of osteolysis around the femoral implant.

Complications Not Involving Cone Revision

Eleven additional knee surgeries not involving the cone were performed (Table 3). One patient initially receiving only a tibial cone subsequently underwent revision for a loosened femoral component, leaving the well-fixed tibial cone in place. Five patients experienced infection and required extensive irrigation with polyethylene exchange only. Three patients underwent irrigation and debridement without any revision of their previously implanted components. One patient experienced a periprosthetic femur fracture postimplantation requiring total femur replacement, although the tibial cone was deemed structurally sound and not revised at that time. Finally, 1 patient experiencing continued stiffness required knee arthroscopy for lysis of adhesions.

Cone Survivorship

Survivorship was 98.5% when the endpoint was cone revision due to aseptic loosening (n=1; Figure 2). When the endpoint was considered cone revision for any reason, survivorship was 88.2% (n=8). Cone survivorship was 77.9% for any reoperation of the knee (n=15; Table 3).

Kaplan–Meier analysis assessing cone survivorship after revision total knee arthroplasty.

Figure 2:

Kaplan–Meier analysis assessing cone survivorship after revision total knee arthroplasty.

Discussion

Among the various options available for managing moderate-to-severe femoral and tibial bone loss in rTKA, metaphyseal cones have been increasingly used. Efforts to further improve these implants have led to the development of titanium porous cones by 3D-printing technology. Although in vitro analysis demonstrates adequate mechanical stability in 3D-printed titanium cones, literature has been lacking in examining in vivo outcomes. Therefore, the current study reports the short-term clinical outcomes for AORI type 2A, 2B, and 3 bone defects in patients treated with titanium cones during rTKA. These findings demonstrated well-fixed components via radiographic assessment with similar or better implant survivorship compared with the reported rates of tantalum cones.

This study was not without limitations. The strict inclusion criteria prohibited the authors from involving a large group of patients. In effect, patients must have undergone revision surgery, lost a great deal of bone stock, and been managed with a specific metaphyseal cone recently released to the market, which substantially limited the study population. Due to the novelty of this implant and the recent emergence of 3D printing in the field of medicine, these findings were restricted to the short-term. Despite the novelty, the current study provides preliminary insight on implant performance in the mid- to long-term setting. In addition, this cohort was somewhat limited by the inability to obtain radiographic documentation for 2 patients. Although this information was lacking, the proportion was small and the other endpoints pertinent to the study were available and did not affect the results.

The examined patients in this study demonstrated a higher degree of bone loss than those in studies reported in the literature. Brown et al9 retrospectively reviewed 83 patients who received tantalum cones during rTKA, whereas Bohl et al10 retrospectively analyzed 49 patients receiving tantalum cones in rTKA. In both studies, most patients possessed AORI type 1, 2A, or 2B bone defects, with 10% or less of patients having type 3 defects. This is a distinct contrast from the current study because 35.2% of the defects received an AORI type 3 classification. Despite the increased proportion of severe bone defects observed in the current study, KSS and radiographic follow-up were similar to those of both the Brown et al9 and the Bohl et al10 studies. Compared with the current study, Brown et al9 demonstrated similar rates of reoperation and revision. Furthermore, the current reoperation rates were lower than those reported in the study by Bohl et al.10 Therefore, titanium cones may perform similarly to or better than tantalum cones in terms of patient satisfaction and outcomes in patients with larger metaphyseal bone defects.

The current study found that most patients had well-fixed components and improved KSS postoperatively. Other studies reporting on trabecular tantalum cones have also demonstrated successful osseointegration and improved functional outcomes. Girerd et al11 performed a retrospective study of 51 patients undergoing rTKA and found that all cones were well integrated at final follow-up. They also noted that mean KSS improved significantly from 45±13 to 70±15 (P=.007).11

In the previously mentioned study by Bohl et al,10 the authors reported that all cones were well-fixed and that KSS increased by 28.4±17.8 at final follow-up (51.4±14.7 preoperative KSS vs 79.8±15.7 postoperative KSS). From a radiographic and functional standpoint, 3D-printed titanium cones appear to perform similarly to titanium cones in the short-term.

Regarding survivorship, the current study found similar survivorship to porous tantalum cones. Potter et al6 retrospectively examined mid-term outcomes of patients undergoing rTKA treated with femoral cones. The authors reported a 5-year survivorship of 96% when the endpoint was revision of the cone for aseptic loosening, 84% when the endpoint was revision of the cone for any reason, and 70% when it was for any reoperation.6 Although their follow-up was longer, the current survivorship findings demonstrate improved preliminary results for these newer implants.

In addition, Burastero et al12 performed a retrospective study involving 60 patients receiving tantalum cones during septic knee revisions. The authors assessed mid-term survivorship (mean follow-up, 43.5±17.4 months) and found a 90% survival rate when the endpoint was revision for any reason and a 100% survival rate when the endpoint was revision due to aseptic loosening.12 The current findings demonstrate similar survivorship, and it appears that 3D-printed titanium cones perform similarly to tantalum cones in the setting of septic knee revision. Although the entire cohort did not consist of revisions due to infection, parallels can be made between the performances of the 2 cone types.

Conclusion

Revision total knee arthroplasty frequently results in some magnitude of bone loss. In instances of large amounts of metaphyseal bone loss, cones appear to be well-suited for the management of large bone defects. Ongoing improvements regarding the precise fixation of metaphyseal cones have continued and led to the development of 3D-printed titanium cones. The rates of survivorship in this study suggest 3D-printed titanium cones are a promising option for metaphyseal fixation during rTKA. Future studies should shed light on how these cones fare over time.

References

  1. Panegrossi G, Ceretti M, Papalia M, Casella F, Favetti F, Falez F. Bone loss management in total knee revision surgery. Int Orthop. 2014;38(2):419–427. doi:10.1007/s00264-013-2262-1 [CrossRef] PMID:24407821
  2. Barnett SL, Mayer RR, Gondusky JS, Choi L, Patel JJ, Gorab RS. Use of stepped porous titanium metaphyseal sleeves for tibial defects in revision total knee arthroplasty: short term results. J Arthroplasty. 2014;29(6):1219–1224. doi:10.1016/j.arth.2013.12.026 [CrossRef] PMID:24444570
  3. Kamath AF, Lewallen DG, Hanssen AD. Porous tantalum metaphyseal cones for severe tibial bone loss in revision knee arthroplasty: a five to nine-year follow-up. J Bone Joint Surg Am. 2015;97(3):216–223. doi:10.2106/JBJS.N.00540 [CrossRef] PMID:25653322
  4. Faizan A, Bhowmik-Stoker M, Alipit V, et al. Development and verification of novel porous titanium metaphyseal cones for revision total knee arthroplasty. J Arthroplasty. 2017;32(6):1946–1953. doi:10.1016/j.arth.2017.01.013 [CrossRef] PMID:28196619
  5. 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(5):478–484. doi:10.2106/JBJS.I.01322 [CrossRef] PMID:21368080
  6. Potter GD III, Abdel MP, Lewallen DG, Hanssen AD. Midterm results of porous tantalum femoral cones in revision total knee arthroplasty. J Bone Joint Surg Am. 2016;98(15):1286–1291. doi:10.2106/JBJS.15.00874 [CrossRef] PMID:27489319
  7. Ponzio DY, Austin MS. Metaphyseal bone loss in revision knee arthroplasty. Curr Rev Musculoskelet Med. 2015;8(4):361–367. doi:10.1007/s12178-015-9291-x [CrossRef] PMID:26362647
  8. Villanueva-Martínez M, De la Torre-Escudero B, Rojo-Manaute JM, Ríos-Luna A, Chana-Rodriguez F. Tantalum cones in revision total knee arthroplasty: a promising short-term result with 29 cones in 21 patients. J Arthroplasty. 2013;28(6):988–993. doi:10.1016/j.arth.2012.09.003 [CrossRef] PMID:23414934
  9. Brown NM, Bell JA, Jung EK, Sporer SM, Paprosky WG, Levine BR. The use of trabecular metal cones in complex primary and revision total knee arthroplasty. J Arthroplasty. 2015;30(9)(suppl):90–93. doi:10.1016/j.arth.2015.02.048 [CrossRef] PMID:26100475
  10. Bohl DD, Brown NM, McDowell MA, et al. Do porous tantalum metaphyseal cones improve outcomes in revision total knee arthroplasty?J Arthroplasty. 2018;33(1):171–177. doi:10.1016/j.arth.2017.07.033 [CrossRef] PMID:28844630
  11. Girerd D, Parratte S, Lunebourg A, et al. Total knee arthroplasty revision with trabecular tantalum cones: preliminary retrospective study of 51 patients from two centres with a minimal 2-year follow-up. Orthop Traumatol Surg Res. 2016;102(4):429–433. doi:10.1016/j.otsr.2016.02.010 [CrossRef] PMID:27052939
  12. Burastero G, Cavagnaro L, Chiarlone F, Alessio-Mazzola M, Carrega G, Felli L. The use of tantalum metaphyseal cones for the management of severe bone defects in septic knee revision. J Arthroplasty. 2018;33(12):3739–3745. doi:10.1016/j.arth.2018.08.026 [CrossRef] PMID:30266325

Demographics of Patients Implanted With Metaphyseal Cones for Bone Loss During Revision Total Knee Arthroplasty (N=54)

ParameterValue
Indication for revision (cone implantation), No.
  Instability6 (11.1%)
  Loosening11 (20.4%)
  Infection30 (55.5%)
  Fracture5 (9.2%)
  Stiffness1 (1.9%)
  Dislocation1 (1.9%)
Sex, No.
  Female27 (50.0%)
  Male27 (50.0%)
Race, No.
  White28 (51.8%)
  Black26 (48.2%)
Age, mean (range), y65 (45.2–91.8)
Follow-up, mean (range), mo29.9 (24.0–42.0)
BMI, mean (range), kg/m236.8 (20.5–69.0)
ASA score, mean (range)2.9 (2–4)
CCI, mean (range)3.5 (0–9)
Tobacco abuse, No.8 (14.8%)
Alcohol abuse, No.5 (9.2%)
Drug abuse, No.6 (11.1%)
Prior procedures, mean (range), No.4.2 (1–14)
Length of stay, d
  Mean6.8
  Range1–64
  Median4.0
Cones implanted, No.68
Type of cone, No.
  Tibial53 (77.9%)
  Femoral15 (22.1%)
AORI classification, No.
  Type 2A12 (17.6%)
  Type 2B32 (47.1%)
  Type 324 (35.3%)

Radiographic and Functional Outcomes for Patients Implanted With Metaphyseal Cones for Bone Loss During Revision Total Knee Arthroplasty

OutcomeValueP
Radiographic follow-up, No.
  Patients with radiographic follow-up52 (96.2%)
  Patients without radiographic follow-up2 (3.8%)
  Normal postoperative radiograph findings51 (98.1%)
  Component loosening1 (1.9%)
Functional outcome, mean>.001
  Preoperative KSS52.0
  Postoperative KSS80.4

Metaphyseal Cone Complications and Survivorship

ParameterValueIndication
Surgeries involving explantation of cone
  Two-stage revision, No. of cones7Infection
  One-stage revision, No. of cones1Aseptic loosening
  Surgeries involving explantation of cone, Total no.7
  Cones explanted, Total no.8
Additional surgeries not involving cone explantation, No.
  Revisions not involving cone explantation6
  Irrigation and debridement3
  Total femur arthroplasty1
  Arthroscopy1
Surgeries not involving cone explantation, Total no.11
Surgeries, Total no.19
Cone survivorship
  Cone revision due to aseptic loosening (n=1)98.5%
  Cone revision for any reason (n=8)88.2%
  Reoperation for any reason (n=15)77.9%
Authors

The authors are from the Rubin Institute for Advanced Orthopedics, Center for Joint Preservation and Replacement, Sinai Hospital of Baltimore, Baltimore, Maryland.

Dr Remily, Dr Dávila Castrodad, Dr Mohamed, Dr Wilkie, and Ms Kelemen have no relevant financial relationships to disclose. Dr Delanois has received research support from Orthofix, Inc, Stryker, and Unity Orthopedics.

Correspondence should be addressed to: Ronald E. Delanois, MD, Rubin Institute for Advanced Orthopedics, Center for Joint Preservation and Replacement, Sinai Hospital of Baltimore, 2401 W Belvedere Ave, Baltimore, MD 21215 ( delanois@me.com).

Received: August 16, 2019
Accepted: November 07, 2019
Posted Online: December 07, 2020

10.3928/01477447-20201202-04

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