A law student at the University of Texas, Michael T. Raupp, has written a note in the Texas Law Review (Issue 90, Volume 1) titled "The Multiplication of Indivisible Injury." The work is critical of the handling of the subject by the Restatement (Third) of Torts, which prompted a response by the Reporters.
This is a complicated area of the law, and Raupp does a good job gathering case law and describing the applicable public policy concerns.
As Raupp, explains, "the indivisible injury doctrine, [which operates] as an exception to the causation component of damages, rescues the plaintiff from the position of not being able to recover simply because he happened to encounter two negligent actors instead of one. Additionally, it prevents the tortfeasors from escaping liability for their negligent acts simply because the hapless plaintiff was injured a second time."