Background/Purpose:

Total knee arthroplasty (TKA) is one of the most common elective
orthopedic procedures in the US.  However, up to 20% of patients have chronic
post-operative pain.  There is therefore an urgent need to identify modifiable
risk factors to improve patients’ outcomes. Inflammation is reversible, and has
been associated with pain in knee osteoarthritis (KOA). However, whether
inflammation is associated with chronic pain or other suboptimal outcomes after
TKR is unknown. Therefore, this study investigated the association between pre-operative
synovial inflammation and 2-year outcomes following TKA for KOA.

Methods:

We identified 33 KOA patients who underwent primary unilateral
TKA and had chronic pain (WOMAC ≤60; 100 =best) at 2 years. Patients were
matched 2:1 on surgeon and surgery date with TKA cases with little pain at 2
years, (WOMAC ≥70).   All patients provided demographic and pre-and
post-operative self-report data. Preoperative radiographs were graded by two blinded
evaluators for alignment and Kellgren and Lawrence score.  H+E slides of
intra-operative synovial tissue were reviewed and graded for inflammation
according to the validated Krenn Criteria. Prosthesis information, history of previous
surgery to the index knee, post-operative steroid injection and manipulations
were recorded from surgeons’ and inpatient charts.  Regression analyses were performed
to evaluate whether pre-operative inflammation was an independent predictor of
pain, function or stiffness 2 years after TKA.

Results:

Average age was 67 years, (±7.9), 65% were women and 91%
were Caucasian.  In a multivariate linear regression controlling for Krenn
Score, post-operative steroid injection, age, MCS, PCS, pre-operative WOMAC
pain and Euroqol, patients with greater inflammation (Krenn  ≥3) had more
pain at 2-years (WOMAC 65.01 vs. 76.14; p-value 0.03). Patients who had a
steroid injection soon after TKA (based on surgeon’s suspicion  of
tenosynovitis) were more likely to have worse 2 year WOMAC pain scores (60.3
vs. 80.9;  p-value = 0.0495).  Every 10 year increase in age was associated
with a 6.6 unit increase in 2-year WOMAC pain score,( i.e. less pain.). Separate
models showed a similar association between high Krenn score and worse 2-year
function, (WOMAC Function 70.2 vs. 81.1; p-value 0.01), but no association
between Krenn score and 2 year WOMAC stiffness. Neither radiographic findings nor
implant type were associated with 2-year outcomes.

Conclusion:

Increased synovial inflammation at the time of surgery
predicts worse WOMAC pain and function 2 years after TKA.  This is a
potentially modifiable risk factor which could be a target for future
interventional trials.