I find that hard to believe. In fact I would like to know which hospital's emergency room(s) this study is referring to.
Arch Surg 1988 Jun;123(6):733-7
Marijuana and alcohol use among 1023 trauma patients. A prospective study.
Soderstrom CA, Trifillis AL, Shankar BS, Clark WE, Cowley RA.
Department of Surgery/Traumatology, Maryland Institute for Emergency Medical Services Systems, Baltimore 21201-1595.
Marijuana use prior to injury was determined prospectively in 1023 patients injured as the result of vehicular (67.6%) and nonvehicular (32.4%) trauma. Most were men (72.8%); most were 30 years of age or younger (58.4%). All were admitted directly from the scene of injury. Serum delta-9-tetrahydrocannabinol activity was ascertained using a radioimmunoassay. Activity of 2 ng/mL or more was detected in 34.7% of subjects. Blood alcohol determinations were made in 1006 patients; 33.5% were positive. Marijuana use among vehicular and nonvehicular trauma victims was not significantly different. Marijuana use was higher among those 30 years of age or younger and among men. Vehicular crash victims consumed alcohol more frequently. Use of marijuana and alcohol in combination (16.5%) was highly significant compared with marijuana alone (18.3%), alcohol alone (16.1%), or neither drug (49.1%).
Note that this doesn't say that marijuana was involved in the trauma, rather, it says that 34% of trauma vicims have used marijuana. Since Marijuana is detectable in the blood and urine much longer than other drugs and alcohol (THC is fat soluble) and given that this article earlier said that studies show that 34% of Americans have used marijuana, isn't this what you would expect?