Improved outcomes in patients with positive metal sensitivity following revision total knee arthroplasty

Abstract

Background: Metal sensitivity as a cause for painful joint replacement has become increasingly prevalent; however, there is a lack of reported clinical outcome data from total knee arthroplasty patients with metal allergies. The purpose of this study was to determine whether patients presenting with a painful total knee arthroplasty with a positive metal sensitivity have improved outcomes following revision to a hypoallergenic implant.

Methods: A retrospective review was conducted for patients that underwent a revision total knee arthroplasty after metal sensitivity testing over a 3-year period from January 1, 2015, to December 31, 2017. Based on the results of sensitivity testing, patients underwent revision total knee arthroplasty to a hypoallergenic component or a standard component. Following revision, patients returned to the clinic at an interval of 6 weeks, 5 months, and 12 months for functional, pain, and satisfaction assessment. Outcomes were compared within and between sensitivity groups.

Results: Of the included patients, 78.3% (39/46) were positive for metal sensitivity. The most common metal sensitivity was to nickel (79.5%, 32/39). Both non-reactive and reactive patients significantly improved in range of motion after revision arthroplasty. The reactive group saw a 37.8% decrease in pain at 6 weeks post-revision (p < 0.001) Whereas, the non-reactive group only saw a moderate, non-significant improvement in pain reduction at 6 weeks post-revision (27.0%; p = 0.29). Frequency of pain experienced did not vary significantly between groups. Maximum metal lymphocyte transformation test (LTT) sensitivity score did not correlate with pain level at the time of revision (R² = 0.02, p = 0.38) or percent improvement after revision (R² = 0.001, p = 0.81). Overall, all patients reported being very satisfied after revision total knee arthroplasty; there was no difference between positive and negative sensitivity groups (W = 62, p = 0.89).

Conclusions: Patients presenting with a painful knee arthroplasty and positive metal LTT have improved pain scores, walking function, and range of motion following revision to a hypoallergenic component. This study also provides a treatment algorithm for patients presenting with a painful knee replacement, in order to provide effective and timely diagnosis and management.

Keywords: Arthroplasty; Hip; Knee; LTT; Lymphocyte transformation test; Metal allergy; Metal sensitivity; Orthopedics.

Fig. 1

Metal-LTT sensitivity percentage. Percent of all included patients who tested positive for each metal. Metals are subdivided by concentration

Fig. 2

Mean metal-LTT sensitivity score grouped by magnitude of sensitivity. Error bars denote standard deviation and solid horizontal bar denotes a significant (p < 0.05) difference in mean compared to the negative sensitivity group

Fig. 3

Range of motion in reactive and non-reactive metal-LTT groups. Mean knee flexion/extension range of motion prior to revision and post-revision. There were insufficient non-reactive patients at post-revision 2 and 3 to generate statistical comparisons. Error bars denote standard deviation and solid horizontal bar denotes a significant (p < 0.05) difference in mean range of motion between visits

Fig. 4

Pain scores in reactive and non-reactive metal-LTT groups. Mean pain score prior to revision and post-revision. There were insufficient non-reactive patients at post-revision 2 and 3 to generate statistical comparisons. Solid horizontal bar denotes a significant (p < 0.05) difference in pain score between visits

Fig. 5

Pain and metal-LTT sensitivity correlation. a Correlation between pain level at the time of revision and LTT sensitivity score. b Correlation between percent change in pain from pre-revision to post-revision and LTT sensitivity score