Total Knee Arthroplasty (TKA) patients may present with effusion, pain, stiffness and functional impairment. A positive metal hypersensitivity (positive LTT) may be an indication for a revision surgery with a custom-made implant devoid of any hypersensitivity-related metal or an implant with the least possible ion content of the metal hypersensitivity, if no custom-made is available. The purpose of the current study is to assess the prevalence of metal hypersensitivity in subjects requiring a primary TKA and assess their early functional outcomes.

We are recruiting 660 subjects admitted for TKA. Subjects are randomly assigned to 2 groups: oxidized zirconium implant group or cobalt-chrome implant group. Functional outcomes and quality of life (QoL) are measured pre operatively, 3, 6 and 12 months post operatively with WHOQOL-BREF (domain1-Physical Health, domain 2- Psychological, domain 3- Social relationships, domain 4-Environment), KSS, KOOS and pain Visual Analog Scale (VAS). LTT and metal ions are evaluated pre operatively and 12 months post-surgery.

One hundred-sixty patients, 98 women, were enrolled in the study. Mean age was 65.6±8.9. Mean follow up (FU) was 7.1±3.8 months. Eighty-one (50.6%) were randomised in the cobalt-chrome group. Infection rate was 1.9%, one patient required debridement. Three patients (1.9%) presented with contracture at three months FU. At 12 months, WHOQOL-BREF domain 1, 2 and 4 improved significantly (p0,05).

Overall, all 160 patients improved their functional outcomes and QoL. At 12 months, VAS scores decreased from 7±2.06 at baseline to 1.95±2.79. Furthermore, the high prevalence of positive LTT (27/65) do not seem to affect early functional outcomes and QoL on patients that may have received a potential implant with hypersensitivity (18/27).

Total joint arthroplasty has proven to be efficient to relieve pain and regain mobility. In fact, most patients undergoing a total knee arthroplasty (TKA) are satisfied with their surgery (80 to 90%), yet 4 to 7% still complain of unexplainable pain and stiffness. Several authors have proposed that reactivity to the implant could explain this phenomenon. Still, no strong evidence supports this theory as of today. We aimed to determine the prevalence of metal and cement hypersensitivity in a cohort of patients with unexplained pain and stiffness after TKA.

We retrieved data for a group of patients presenting unexplained pain and stiffness. We excluded all other potential known causes of pain. All patients were tested with a Lymphocyte Transformation Test from whole blood taps. We analysed data of hypersensitivity to metals (alloy particles of titanium and cobalt, aluminum, cobalt, nickel, zirconium, vanadium, molybdenum, cobalt, chromium and iron) and PMMA cement (bone cement monomer and particles).

Fifty-three patients underwent a LTT for unexplained pain and stiffness after total knee arthroplasty between May 2012 and May 2015. The cohort consisted of 26 men and 27 women with a mean age of 66.3(±8.0) years. Six patients had no hypersensitivity (11.3%), leaving 88.7% of the cohort with hypersensitivity to metal and/or cement. Almost half the cohort of patients tested for PMMA was hypersensitive to cement (44.0%). The most common metal hypersensitivity was nickel (69.8%). Twelve patients presented sensitivity to only one metal (22.6%), whereas 35 patients were hypersensitive to more than one metal (66.0%). Eleven patients had revision surgery with a hypoallergenic prosthesis. Patients reported a significant diminution of pain as well as better knee function compared to preoperative status as early as 6 weeks postop, although some reported residual stiffness.

The results of this study suggest that metal and/or cement hypersensitivity could play a role in cases of total knee arthroplasty with unexplained pain and stiffness. Randomised controlled clinical trials on the subject will be initiated by our team to further investigate this phenomenon.