Question juridique clé
Whether the surgical incident of 21 February 2006 qualified as an accident under Art. 4 ATSG, especially regarding an unusual external factor.
Solution extraite
The lower court applied the accident concept too narrowly; the defective, repeatedly malfunctioning drill during the operation could constitute an unusual external factor. Further causation findings were still required.
Motifs extraits
In medical treatment, unusualness concerns the external factor itself, not its effect. Operating with an insufficient drill that repeatedly malfunctioned and could only be kept running temporarily departed significantly from ordinary medical practice and entailed substantial risk.