Multiacquisition Variable-Resonance Image Combination Magnetic Resonance Imaging Used to Study Detailed Bone Apposition and Fixation of an Additively Manufactured Cementless Acetabular Shell

Femoral Component Debonding Frequently Missed on Advanced Imaging Prior to Revision of a Recalled Total Knee Arthroplasty

BACKGROUND

Identification of femoral component debonding in the work-up of painful total knee arthroplasty (TKA) often poses a diagnostic challenge. The purpose of this study was to compare the sensitivity and specificity of radiographs, computed tomography (CT), and magnetic resonance imaging (MRI) for identifying femoral component loosening with debonding at the time of revision of a primary TKA with a recalled polyethylene insert.

METHODS

Using an institutional database, we identified all cases of revision TKA performed for this specific implant recall following a primary TKA between 2014 and 2022. Patients who had a preoperative radiograph, CT, and MRI were included (n = 77). Sensitivity, specificity, and positive and negative likelihood ratio (LR) for predicting loosening were compared among the imaging modalities, using the intraoperative evidence of implant loosening as the gold standard.

RESULTS

At the time of revision surgery, the femoral component was noted to have aseptic loosening with debonding in 46 of the 77 (60%) of the TKAs. There were no significant differences in demographics in the cohort with femoral debonding compared to those with well-fixed implants. The CT demonstrated a sensitivity of 28% and a specificity of 97%, while the MRI demonstrated a sensitivity of 37% and a specificity of 94% for detecting femoral loosening due to debonding. Both CT and MRI demonstrated poor negative LRs for femoral loosening (LR 0.7).

CONCLUSIONS

In this series of revision TKAs for a specific recalled component, neither CT nor MRI accurately diagnosed femoral component debonding. For patients who have this implant, it is imperative to interrogate the implant-cement interface intraoperatively and prepare for full revision surgery as well as marked bone loss secondary to osteolysis.

Patient-reported and radiographic outcomes of a porous-coated acetabular cup in robotic assisted total hip arthroplasty at 2-year follow up

Introduction

Several implant manufacturers have developed ultra-porous metal substrate acetabular components recently. Despite this, data on clinical and radiographic outcomes remain limited. Our study evaluated postoperative patient-reported outcome measures (PROMs) and radiographic analyses in patients fitted with a novel acetabular porous-coated component.

Methods

A total of 152 consecutive patients underwent a total hip arthroplasty by a single orthopaedic surgeon. All patients underwent surgery utilizing the same CT-scan based robotic-assisted device with the same porous cementless acetabular shell. They received standardized postoperative physical therapy, rehabilitation, and pain protocols. Preoperatively, first postoperative visit, 6-months, 1-year, and 2-years, patients were evaluated based on Western Ontario and McMaster Universities Arthritis Index (WOMAC) pain, physical function, and total scores; 2) Patient-Reported Outcomes Measurement Information System (PROMIS)-10 physical and mental scores; 3) Hip Disability and Osteoarthritis Outcome Score (HOOS)-Jr scores; as well as 4) acetabular component positions and 5) evidence of acetabular component loosening.

Results

Significant improvements were observed by 6 months in WOMAC pain, physical function, and total scores (p < 0.05), maintained at 1 and 2 years. PROMIS-10 physical scores also improved significantly from preoperative to 6 months postoperative and remained so at 1 and 2 years postoperative (p < 0.05). No significant changes were found in PROMIS-10 mental scores. HOOS-Jr scores significantly improved from preoperative to 6 months postoperative and remained so through 2 years (p < 0.05). At 6 months, slight changes were noted in abduction angle and horizontal and vertical offset. Radiolucencies, initially found in 3 shells, reduced to 1 shell with 2 new radiolucencies by 6 months, and remained stable with no subsequent operative interventions. At 1 year and 2 years, no radiographic abnormalities were noted, including complete resolution of prior radiolucencies as well as stable components.

Conclusion

This porous cementless acetabular shell, implanted with CT-scan-based robotic-assisted techniques, demonstrated excellent postoperative PROMs at 2 years. Stable radiolucencies suggest good component stability. The early stable clinical and radiographic results suggest promising long-term outcomes with this device.

Level of evidence

III (retrospective cohort study).

Low cycle fretting and fretting corrosion properties of low carbon CoCrMo and additively manufactured CoCrMoW alloys for dental and orthopedic applications

Additive manufacturing (AM) of CoCrMo metallic implants is growing in the orthopedic and dental fields. This is due to the traditional alloy's excellent corrosion resistance and mechanical properties. AM processes like selective laser melting (SLM) require less time, materials, and waste than casting or subtractive manufacturing complex-geometry structures (bridges, partial dentures, etc.). The objective of this work was to investigate the low cycle tribological and tribocorrosion characteristics of AM CoCrMoW alloys compared to wrought LC CoCrMo (ASTM F-1537) to assess this AM alloy's performance. Fretting and tribocorrosion testing was performed in air (wear only), PBS (wear + corrosion), and PBS with 10 mM H₂ O₂ (wear + corrosion + inflammation) by a single diamond asperity. No variation between alloys in volume of material removed (p = .12), volume of plastic deformation (p = .13), and scratch depth (p = .84) showed that AM was substantially similar in wear resistance to LC in air and PBS. AM exhibited significantly higher fretting currents (p < .01) at loads up to 100 mN ( I AM PBS $$ {I}_{\mathrm{AM}}^{\mathrm{PBS}} $$  = 57 nA and I AM H 2 O 2 $$ {I}_{\mathrm{AM}}^{H_2{O}_2} $$  = 49 nA) than LC CoCrMo ( I LC PBS $$ {I}_{\mathrm{LC}}^{\mathrm{PBS}} $$  = 30 nA) and ( I LC H 2 O 2 $$ {I}_{\mathrm{LC}}^{H_2{O}_2} $$  = 29 nA). In PBS, wear track depth linearly correlates to fretting current, averaged over 100 cycles. Additionally, fretting currents of both alloys were significantly lower in simulated inflammatory conditions compared to PBS alone. AM alloy has generally similar wear and tribocorrosion resistance to wrought LC CoCrMo and would be ideal for patient specific dentistry or orthopedics where precise, complex geometries are required.

Failure of Screw/Shell Interface in the Trident II Acetabular System in Total Hip Arthroplasty

We report a case series of 2 patients with screw/shell interface failure in the Stryker Trident II Acetabular System. Both failures consisted of screw penetration through the Trident II acetabular shell. One failure was observed postoperatively after a revision from a cephalomedullary nail to a total hip arthroplasty while the other was observed intraoperatively during a primary total hip arthroplasty. Both component failures were managed conservatively with weight-bearing as tolerated and radiographic monitoring. These are the first reported cup/screw failures of the Stryker Trident II system and should raise awareness of the potential complication and implant design flaw. When placing acetabular screws, we recommend obtaining intraoperative orthogonal screw radiographs that are tangential to the shell surface to assess for screw/shell failure.

Effective magnetic susceptibility of 3D-printed porous metal scaffolds

PURPOSE

3D-printed porous metal scaffolds are a promising emerging technology in orthopedic implant design. Compared to solid metal implants, porous metal implants have lower magnetic susceptibility values, which have a direct impact on imaging time and image quality. The purpose of this study is to determine the relationship between porosity and effective susceptibility through quantitative estimates informed by comparing coregistered scanned and simulated field maps.

METHODS

Five porous scaffold cylinders were designed and 3D-printed in titanium alloy (Ti-6Al-4V) with nominal porosities ranging from 60% to 90% using a cellular sheet-based gyroid design. The effective susceptibility of each cylinder was estimated by comparing acquired B₀ field maps against simulations of a solid cylinder of varying assigned magnetic susceptibility, where the orientation and volume of interest of the simulations was informed by a custom alignment phantom.

RESULTS

Magnitude images and field maps showed obvious decreases in artifact size and field inhomogeneity with increasing porosity. The effective susceptibility was found to be linearly correlated with porosity (R²  = 0.9993). The extrapolated 100% porous (no metal) magnetic susceptibility was -9.9 ppm, closely matching the expected value of pure water (-9 ppm), indicating a reliable estimation of susceptibility.

CONCLUSION

Effective susceptibility of porous metal scaffolds is linearly correlated with porosity. Highly porous implants have sufficiently low effective susceptibilities to be more amenable to routine imaging with MRI.

Off-the-shelf 3D printed titanium cups in primary total hip arthroplasty

Three-dimensional (3D)-printed titanium cups used in primary total hip arthroplasty (THA) were developed to combine the benefits of a low elastic modulus with a highly porous surface. The aim was to improve local vascularization and bony ingrowth, and at the same time to reduce periprosthetic stress shielding. Additive manufacturing, starting with a titanium alloy powder, allows serial production of devices with large interconnected pores (trabecular titanium), overcoming the drawbacks of tantalum and conventional manufacturing techniques. To date, 3D-printed cups have achieved dependable clinical and radiological outcomes with results not inferior to conventional sockets and with good rates of osseointegration. No mechanical failures and no abnormal ion release and biocompatibility warnings have been reported. In this review, we focused on the manufacturing technique, cup features, clinical outcomes, open questions and future developments of off-the-shelf 3D-printed titanium shells in THA.