| Dx1 | ICD9/ICD9M | Concussions by principal diagnosis,* n | Principal procedures, n (%) | Principal procedures with imaging,† n (%) |
| Total‡ | 755 | 143 (18.9) | 93 (12.3) | |
| 850.0 | Concussion with no loss of consciousness | 308 | 57 (18.5) | 38 (12.3) |
| 850.1 | Concussion with brief loss of consciousness (<1 hr) | 294 | 54 (18.4) | 32 (10.9) |
| 850.2 | Concussion with moderate loss of consciousness (1–24 hrs) | DS§ | DS§ | DS§ |
| 850.5 | Concussion with loss of consciousness of unspecified duration | 95 | 21 (22.1) | 17 (17.9) |
| 850.9 | Concussion, unspecified | 52 | DS§ | DS§ |
*Concussion was defined based on primary diagnosis of seven ICD-9-CM codes (see Methods). †Imaging included CT and MRI. ‡There was no concussion case with primary diagnosis codes of 850.3 or 850.4 in the data. §Discharge information suppressed because cell count was ⩽10 (The Nationwide Inpatient Sample data user agreement precludes us from publishing cell counts ⩽10).