A prospective study on outcome of patient-specific cones in revision knee arthroplasty

Utilizing 3d-printed patient-specific porous titanium cones in complex primary and revision total knee arthroplasty

INTRODUCTION

Effective management of bone defects is crucial in revision total knee arthroplasty (rTKA) to ensure implant stability in low-density bone environments, especially following prosthesis removal. While various reinforcement techniques exist, such as allografts, augments, metal cones, sleeves, or combinations thereof, metal cones are increasingly favored for their ability to reconstruct significant bone defects. A prominent challenge with off-the-shelf (OTS) cones is their unsuitability for Asian and specifically Iranian anatomies due to mismatched sizes and smaller medullary canals. This study explores the application of customized 3D-printed porous titanium cones, tailored to individual patient anatomy, for bone defect reconstruction in complex primary or revision total knee arthroplasty (TKA).

MATERIALS AND METHODS

Utilizing CT scans for 3D preoperative planning, porous cones were individually designed to fit each patient's anatomy. A novel aspect of these cones is their dual functionality: promoting bone ingrowth while preventing cement infiltration. The cones were fabricated using selective laser melting with medical-grade Ti6Al4V alloy. To aid in surgical preparation, single-use polyamide trials were also 3D-printed.

RESULTS

A total of nineteen cones/half cones (four diaphyseal, twelve metaphyseal, and three meta-diaphyseal) for femoral and tibial applications were successfully designed and implanted across ten cases. There was a perfect alignment between preoperative planning and intraoperative outcomes, with precise defect reconstruction achieved in all cases. Early follow-ups indicated no loosening or implant migration.

CONCLUSIONS

Customized patient-specific porous cones offer not only the long-term benefits of OTS options, such as osseointegration and biological fixation but also accurately address a wide range of complex metaphyseal and diaphyseal defects. This approach preserves residual bone stock and streamlines the surgical process, presenting a promising advancement in bone defect management in rTKA.

Unbalanced metaphyseal fixation is associated with an increased aseptic loosening of revision total knee arthroplasty at mean 4-year follow-up

INTRODUCTION

The total number of total knee arthroplasty performed is rising, and the number of revisions is rising accordingly. Periprosthetic joint infection emerged in recent years as a leading cause of total knee revisions. Bone loss is a real challenge when facing septic knee revisions since radical debridement is crucial to overcome infection. Many devices have already demonstrated to reliably address bone loss and guarantee enhanced fixation. However, the role of balancing metaphyseal fixation and its interplay with the level of constraint has not been elucidated yet.

MATERIAL AND METHODS

An institutional arthroplasty registry was retrospectively reviewed looking for patients who underwent two-stage revision of the knee and metaphyseal cones implantation. Patients were divided into two groups based on the presence of cones only on one side (femoral or tibial, Group U) or both femoral and tibial side (Group B). Failure, aseptic loosening, and revision rates were compared between groups, as were values of patient-reported outcome measure. Kaplan-Meier analysis was used to assess survival of implants.

RESULTS

A total of 65 patients were included in the analysis and were evaluated at a mean final follow-up of 4 years (range, 2-7). Mean age was 67 (range, 43-81) years. Mean BMI was 27.4 (range, 20-37) kg/m2. The overall mean KSS, OKS, ROM significantly increased from baseline values to last follow-up (p < 0.001). Kaplan-Meier analysis demonstrated that patients included in Group U had a significantly lower rate of implant survival compared to those included in Group B.

CONCLUSIONS

Patients undergoing revision total knee arthroplasty for periprosthetic infection present considerable rates of complication and failure. Management of bone loss represents a concern for the surgeon, who must achieve a stable fixation. Our study demonstrated that implants characterized by an unbalanced metaphyseal fixation are at higher risk of aseptic loosening and consequent revision, especially when coupled with hinged inserts.

Biomechanical study of using patient-specific diaphyseal femoral cone in revision total knee arthroplasty (rTKA)

Background

The primary objective of revision total knee surgery is to achieve solid bone fixation. Generally, this could be accomplished using sleeves and long stems, which require substantial remaining bone stock and may increase the risk of stem tip pain. An alternative approach involves the use of customized diaphyseal cones, which can preserve the integrity of the bone canal. This study evaluates the impact of employing femoral diaphyseal cones with various stem lengths on stress distribution and relative motion.

Methods

CT scan data from five patients were used to generate the 3D model of the femur, cement, customized stems, and cones, along with assigning patient-specific material for each candidate's femur. Three different stem lengths, both with and without the customized cone, were assessed under three gait loading conditions to compare the resulting Von Mises stress distribution and relative motion.

Results

Analysis indicated that the use of customized femoral cones moderately increases stress distribution values up to 30 % while significantly reducing relative motion at the femoral canal-cone interface by nearly 60 %. The presence of the cone did not significantly alter relative motion with varying stem lengths, although stem length variation without a cone substantially affected these values.

Conclusion

Incorporating cones alongside stems enhances metaphyseal fixation, reduces stress shielding, potentially allowing for the use of shorter stems. Furthermore, cones promote osseointegration by minimizing relative motion, ultimately improving prosthetic stability.

Revision Distal Femoral Replacement Using Custom-made Stem and Cone to Augment Proximal Fixation

Achieving bone fixation during megaprosthesis revision presents a formidable challenge in view of the substantial bone loss. We report treatment of a failed revision distal femoral replacement in an active 36-year-old male mechanic remotely treated for osteosarcoma. A custom stem and cone were manufactured to augment fixation and preserve bone stock within a short segment of the remaining proximal femur. The patient returned to regular function without the need for assistive devices. Follow-up imaging demonstrated stable implant fixation at 1-year follow-up. While cones and sleeves have vastly improved fixation in revision knee arthroplasty, a custom-made cone for the proximal femur was used to augment fixation of a revision megaprosthesis and obviate the use of a total femoral replacement.

An overview of 3D printed metal implants in orthopedic applications: Present and future perspectives

With the ability to produce components with complex and precise structures, additive manufacturing or 3D printing techniques are now widely applied in both industry and consumer markets. The emergence of tissue engineering has facilitated the application of 3D printing in the field of biomedical implants. 3D printed implants with proper structural design can not only eliminate the stress shielding effect but also improve in vivo biocompatibility and functionality. By combining medical images derived from technologies such as X-ray scanning, CT, MRI, or ultrasonic scanning, 3D printing can be used to create patient-specific implants with almost the same anatomical structures as the injured tissues. Numerous clinical trials have already been conducted with customized implants. However, the limited availability of raw materials for printing and a lack of guidance from related regulations or laws may impede the development of 3D printing in medical implants. This review provides information on the current state of 3D printing techniques in orthopedic implant applications. The current challenges and future perspectives are also included.

Short-Term Survivorship of 3D-Printed Titanium Metaphyseal Cones in Revision Total Knee Arthroplasty: A Systematic Review

BACKGROUND

Several studies have evaluated the outcomes of tantalum cones in revision knee arthroplasty with moderate-to-severe metaphyseal bone defects. However, recent innovations have led to the development of 3-D printed titanium cones to better adapt to host bone, there remains no consensus on their overall performance.

OBJECTIVE

We therefore performed a systematic review of the literature to examine short-term survivorship and complication rates of their usage in revision TKAs.

METHODS

A systematic review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. A comprehensive search of PubMed, MEDLINE, EMBASE, and the Cochrane Database of Systematic Reviews was conducted for English articles using various combinations of keywords.

RESULTS

In all, 7 articles met the inclusion criteria. A total of 687 cones were implanted in 557 revision TKAs. The all-cause revision-free survivorship of the implants was 95.3% (26 revisions), and of the cones was 95.5% (31 cones revised) at mean 24 months follow-up. The cones revision-free survivorship from aseptic loosening was 99.7%. The overall complication rate was 19.7% with infection as the most common complications observed and the most frequent reason for revision with an incidence of 10.4% and 4.1%, respectively. Overall, functional outcomes improved as documented by postoperative knee scores.

CONCLUSION

3-D printed metal cones represent a reliable option in metaphyseal bone defects reconstruction that provides high fixation, good short-term survivorship, and complications rates in line with similar devices. In addition, they are associated with lower intraoperative complications, and higher survivorship from aseptic loosening.

Effect of Pore Size of Porous-Structured Titanium Implants on Tendon Ingrowth

Purpose

The reconstruction of a tendon insertion on metal prostheses is a challenge in orthopedics. Of the available metal prostheses, porous metal prostheses have been shown to have better biocompatibility for tissue integration. Therefore, this study is aimed at identifying an appropriate porous structure for the reconstruction of a tendon insertion on metal prostheses.

Methods

Ti6Al4V specimens with a diamond-like porous structure with triply periodic minimal surface pore sizes of 300, 500, and 700 μm and a porosity of 58% (designated Ti300, Ti500, and Ti700, respectively) were manufactured by selective laser melting and were characterized with micro-CT and scanning electron microscopy for their porosity, pore size, and surface topography. The porous specimens were implanted into the patellar tendon of rabbits. Tendon integration was evaluated after implantation into the tendon at 4, 8, and 12 weeks by histology, and the fixation strength was evaluated with a pull-out test at week 12.

Results

The average pore sizes of the Ti300, Ti500, and Ti700 implants were 261, 480, and 668 μm, respectively. The Ti500 and Ti700 implants demonstrated better tissue growth than the Ti300 implant at weeks 4, 8, and 12. At week 12, the histological score of the Ti500 implant was 13.67 ± 0.58, and it had an area percentage of type I collagen of 63.90% ± 3.41%; both of these results were significantly higher than those for the Ti300 and Ti700 implants. The pull-out load at week 12 was also the highest in the Ti500 group.

Conclusion

Ti6Al4V implants with a diamond-like porous structure with triply periodic minimal surface pore size of 500 μm are suitable for tendon integration.

[Bone defect management in revision knee arthroplasty]

BACKGROUND

In 2019, 124,677 primary total knee arthroplasties and 14,462 revision TKA were performed in Germany. This corresponds to a percentage of 11.6%. According to the EPRD, the probability of further revision surgery after the first exchange operation is around 15%.

REASONS

The most common reason for revision surgery is still aseptic loosening with 23.9%. One possible cause could be the difficult fixation of revision total knee arthroplasty. If the bone quality is insufficient, cement-free or cemented diaphyseal anchoring of the prosthesis is often not sufficient to ensure adequate fixation. As a rule, defect management and fixation of the implant are based on the defect situation and the quality of the bone. Therefore, revision total knee arthroplasties based on the fixation principle of Jones et al. should be sufficiently fixed in at least 2 zones.

TECHNIQUES

There are various techniques for stable anchoring of revision implants. In addition to cemented or cementless stem anchoring, bone allografts, wedges and blocks and, in recent years, cones and sleeves have become increasingly popular. In the present work, the various options for a stable anchoring of revision implants are presented and evaluated. In addition, the clinical and radiological outcome of cones vs. sleeves in bone defect management in revision knee arthroplasty will be compared.