Metal hypersensitivity in total joint arthroplasties

Preliminary Study on Immediate Postoperative CT Images and Values of the Modular Polyetheretherketone Based Total Knee Arthroplasty: An Observational First-in-Human Trial

Background

Total knee arthroplasty (TKA) is now frequently performed and is highly successful. However, patient satisfaction after TKA is often difficult to achieve. Because of the presence of metallic prosthetic knee joints, there is a lack of imaging tools that can accurately assess the patient's postoperative prosthetic position, soft tissue impingement, and periprosthetic bone density after TKA. We conducted a clinical trial of the world's first totally modular polyetheretherketone (PEEK) TKA and determined the bone density values in the stress concentration area around the prosthesis based on postoperative computed tomography data to reconstruct a three-dimensional model of the PEEK prosthetic knee joint after implantation. Based on the model, the overhang of the prosthesis was measured at various locations on the prosthesis.

Methods

All patients who underwent PEEK-based TKA were postoperatively assessed with radiography and computed tomography (CT). Hounsfield units (HUs) for the different components of the quantitative CT assessment were measured separately.

Results

Ten patients (nine female and one male) aged 59–74 (mean 66.9, median 67) years were included. The HU values were as follows: PEEK prosthesis mean 182.95, standard deviation (SD) 4.90, coefficient of variation (CV) 2.68; polyethylene mean −89.41, SD 4.14, CV −4.63; lateral femoral osteochondral mean 192.19, SD 55.05, CV 28.64; lateral tibial osteochondral mean 122.94, SD 62.14, CV 42.86; medial femoral osteophyte mean 180.76, SD 43.48, CV 24.05; and medial tibial osteophyte mean 282.59, SD 69.28, CV 24.52. Analysis of the data at 1, 3, and 6 months showed that the mean PE (p = 0.598) and PEEK (p = 0.916) measurements did not change with the time of measurement. There was a decrease in bone mineral density in the lateral tibia at 3 months (p = 0.044). Otherwise, there was no significant change in bone density in other regions (p = 0.124–0.803). There was no overhang in all femoral prostheses, whereas there were two cases of overhang in tibial prostheses. Overhang measurements do not differ significantly across time points. The overhang measurements were not significantly different at all time points (p = 0.186–0.967).

Conclusion

PEEK knee joint prosthesis has excellent CT compatibility. The change in periprosthetic bone volume during the follow-up period can be determined using the HU value after CT scan, while the prosthesis position can be assessed. This assessment may potentially guide future improvements in knee prosthesis alignment techniques and artificial knee prosthesis designs.

The role of metal patch testing in evaluating patients for metallic prosthetic joint failure

BACKGROUND

Metal allergy may be an uncommon cause of prosthetic joint failure. There exist little data on patch testing to metals in this context and its impact on outcomes of joint revision in these patients.

OBJECTIVE

To explore the use and indications for metal patch testing in the evaluation of patients suspected of having metal allergy as a cause of failed joint replacements and to clarify the outcomes of patients revised with alternative metallic joints because of positive patch testing result.

METHODS

A retrospective analysis from January 2016 to April 2020 was completed on a patient cohort referred for evaluation of metal hypersensitivity. Charts were reviewed for age, biological sex, referring specialty, patch testing results, joint, revision status, and outcome measures. Biostatistical analysis and descriptive statistics were performed to determine patch testing performance and functional outcome trends among this patient cohort.

RESULTS

The sensitivity and specificity of patch testing, in general, are limited when evaluating patients with metallic joint replacements. However, the predictive value of testing seemed to improve with strongly positive patch testing results. Functional outcomes in patients when positive results were used to guide revision prosthesis revealed clinical improvement.

CONCLUSION

The attribution of metal allergy or hypersensitivity as a cause of failure in metal prosthetic joint replacement remains unproven. Some patients with positive histories and patch testing results that were used to modify the implanted prosthesis had improved functional outcomes. These results suggest that patch testing may be useful in patients with history of metal sensitivity and prosthetic failure.