Abstract
Purpose: Aseptic loosening is one of the leading causes of failure in total elbow arthroplasty. It is logical to postulate that incorrect implant positioning and alignment may lead to excessive loading and wear which can induce the loosening cascade. However, the effect of implant malalignment on wear inducing loads in the elbow is not yet known. This in-vitro study determined the effect of anterior malpositioning, and varus-valgus (VV) and internal-external (IE) malrotations on humeral stem loading in total elbow arthroplasty.
Method: The humeral, ulnar, and radial components of a linked total elbow arthroplasty were optimally positioned using computer navigation in eight cadaveric elbows, mounted in a load/motion control elbow simulator (age 75yrs, range 42–93; 5 male). A modular, humeral component was employed to generate implant malpositioning errors of ±6° VV, ±8° IE, and 5mm anterior. The implant was instrumented with strain gauges to quantify VV and IE bending loads during elbow flexion with the forearm in supination. Load output was combined using a sum-of-squares technique. Passive flexion was performed with the arm in the varus and valgus orientations; passive and active flexion were performed with the arm in the vertical orientation.
Results: With the arm (humerus) in the vertical orientation, bending loads increased between 418Nmm and 1618Nmm for all malaligned implant positions (p< 0.05). Passive flexion (1354±859Nmm) produced higher resultant loads for the optimally positioned implant than active (819±891Nmm) flexion (p< 0.05). Although it varied during flexion, loading with the arm in varus (2928±1273Nmm) or valgus (2494±743Nmm) orientations resulted in up to a three-fold increase in loading when compared to the vertical orientation (p< 0.01).
Conclusion: These data demonstrate that humeral component malpositioning increases loading in the implant, however further studies are required to determine the long term effect on polyethylene wear and component loosening. Prosthesis designs that replicate the native flexion-extension axis and make use of sophisticated instrumentation or computer assistance to achieve precise positioning during implantation should lead to improved arthroplasty durability. Also, loading was higher with the arm in varus or valgus orientations, suggesting that patients should avoid activities post-operatively that require their elbow to be positioned in this way.
Correspondence should be addressed to Meghan Corbeil, Meetings Coordinator Email: meghan@canorth.org
