One Patient, Two Knees, No Difference: Magnesium Sulfate Fails to Improve Total Knee Arthroplasty Outcomes

Whether the addition of magnesium sulfate (MgSO₄) to intra-articular analgesic cocktails improves early pain after total knee arthroplasty (TKA) remains uncertain.

This prospective, double-blind, within-patient randomized controlled trial enrolled 72 adults undergoing simultaneous bilateral primary TKA. For each patient, one knee received an intra-articular cocktail with MgSO₄, and the contralateral knee received the identical cocktail without MgSO₄. The first-operated knee (left or right) was independently randomized to balance order effects. Baseline pain and function were assessed preoperatively in both knees. Primary outcomes were numeric rating scale (0 to 10) scores for pain at rest (six, 12, 24, 48, and 72 hours) and during motion (12, 24, 48, and 72 hours). The secondary outcomes were range of motion and active straight-leg raise (24 to 72 hours). Paired analyses of between-knee differences are reported as mean paired differences with 95% confidence intervals (CIs).

At 24 hours, the mean paired difference in numeric rating scale was +0.35 at rest and +0.21 during motion (95% CI: -0.10 to 0.80 and -0.13 to 0.55, respectively). From six to 72 h (rest) and 12 to 72 hours (motion), absolute differences were small (less than 0.35), and all 95% CI included zero. Range of motion and active straight-leg raise did not differ between knees at 24, 48, or 72 hours. No treatment-related adverse events were observed within 72 hours.

In this paired, within-patient randomized study, MgSO₄ in an intra-articular cocktail after simultaneous bilateral TKA conferred little to no additional analgesic benefit and did not improve early function.