Evaluation of a modification of the McKinnon technique to correct urine pooling in mares.
Authors: Prado T M, Schumacher J, Kelly G M, Henry R W
Journal: The Veterinary record
Summary
# Editorial Summary: Modified McKinnon Technique for Urine Pooling in Mares Urine pooling represents a significant reproductive and urinary health issue in mares, yet surgical correction techniques are prone to post-operative complications including tissue defects. Prado and colleagues evaluated a modification of the established McKinnon procedure in 30 mares, splitting the urethral fold transversely to create dorsal and ventral shelves, then using the dorsal shelf to reinforce and cover the cranial portion of the newly formed urethral extension; 20 of these mares also received an additional relaxing vaginal incision to allow greater caudal retraction of the dorsal shelf. Critically, no defects developed in the portions covered by the dorsal shelf, with only 8 of 30 mares (26.6%) developing grossly visible defects and a further 2 mares (6.7%) showing only dye-detectable defects—importantly, mares receiving the relief incision fared slightly worse (6 of 20 with defects) than those without it (4 of 10 with defects). This modification substantially improves tissue integrity in the cranial extension by providing autologous coverage and reinforcement, though the counterintuitive finding that the relief incision did not reduce complication rates suggests the reinforcement strategy itself, rather than extensibility, drives improved outcomes and warrants further investigation into optimal surgical technique.
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Practical Takeaways
- •The modified McKinnon technique effectively protects the cranial extension from defect formation by using the dorsal urethral fold as a biological cover
- •A vaginal relief incision may allow better positioning of the dorsal shelf but does not eliminate defect risk in the uncovered caudal extension
- •Consider this modification when performing urethral extension procedures in mares with urine pooling, though defect rates remain clinically significant and warrant post-operative monitoring
Key Findings
- •Modified McKinnon technique (transverse urethral fold splitting with dorsal shelf retraction) prevented defects in the cranial portion of the urethral extension in all 30 mares
- •Overall defect rate was 33.3% (10/30 mares), but only 26.6% (8/30) developed grossly visible and palpable defects
- •Adding a vaginal relief incision allowed further caudal retraction of the dorsal shelf and resulted in defect formation in 6/20 (30%) mares versus 4/10 (40%) without the incision
- •No defects developed in any portion of the extension covered by the dorsal shelf of the urethral fold