Participants were enrolled prospectively in the Veterans Affairs (VA) TBI Model Systems National Database-- a multicenter, longitudinal study of TBI outcomes. Currently, there are 5 sites across the country enrolling subjects in the database, which has been in existence since 2010. All TBIMS enrollees are age 18 or older, and were transferred to comprehensive rehabilitation program at a Polytrauma Rehabilitation Center in VHA. All participants provided informed consent directly or by legal proxy, depending on their capacity to consent for research at the time of study enrolment. Within the VHA TBIMS sites, patient inclusion criteria are 1) medically documented or clinician-confirmed TBI at any severity level (including disorders of consciousness); 2) age 18 or older at time of TBI; and 3) presentation to a VHA Polytrauma Rehabilitation Center for comprehensive inpatient TBI rehabilitation. Because the VHA TBIMS project does not require rehabilitation admission within a specified period of time after the TBI and includes mild TBI cases, some Veterans may have sought care months or years post-injury. Exclusion criteria include presenting for care related to another neurological condition and already being enrolled in either the VHA TBIMS or NIDILRR TBIMS study at another site. See Lamberty et al. (2013) for VHA TBIMS inclusion and exclusion criteria.⁷ This analysis was conducted with a subset of participants who were 1) enrolled into the VHA TBIMS and discharged from rehabilitation between 2010 and June 2015, 2) within one-year of index TBI at time of enrollment and 3) eligible for and completed a one-year post-injury follow-up. Individuals were excluded if deceased, refused interview, or withdrew from the study at the time of one-year post-injury follow-up. Individuals with missing rehospitalization data were also excluded from analyses.

The VHA TBIMS was approved by locally designated Institutional Review Boards (IRB) at each VA study site. IRB approval from the Department of Defense was sought at study sites where DOD personnel were involved in the conduct of the TBIMS study. Following IRB-approved protocols, participants or their caregivers provided written informed consent following admission to inpatient rehabilitation at a VHA Polytrauma Rehabilitation Center. Trained VA TBIMS research assistants collected information regarding injury severity (GCS, time to follow commands [TFC]) from hospital and emergency medical service records. Demographic information such as date of birth, education, and premorbid functioning were collected in interview with the participants or family/significant others. Duration of unconsciousness (TFC) was defined as the time from injury to the occurrence of 2 consecutive days of command following as documented in medical record review.

Participants are contacted at fixed intervals post-injury (1, 2, 5 years post-injury and every 5 years thereafter) to collect psychosocial, vocational, economic, and rehabilitation outcomes paralleling the civilian TBI Model System database. This study analyzed participant and family responses at one year post-injury to document rehospitalization status. One-year follow-up measures are collected within a two-month window before or after the anniversary date of injury.

Data were analyzed using statistical software R v3.2.2 (R Foundation for Statistical Computing, Vienna, Austria). Descriptive statistics were expressed as 1^st quartile; median; 3^rd quartile for continuous variables and percentage (count) for categorical variables. Comparisons were made between those with no rehospitalization (Rehospitalization No) to those with one or more rehospitalizations (Rehospitalization Yes). Next, group comparisons were made between those with no rehospitalization, a single rehospitalization, and two or more rehospitalizations. The distributions of continuous variables were compared between two groups using the Mann-Whitney U tests, and between three groups using the Kruskal-Wallis H tests. The proportions of categorical variables were compared using the chi-square tests. P-values ≤ 0.05 were considered to indicate statistical significance.

A total of 712 participants were enrolled in the Veterans TBIMS database at the time of analyses. Individuals were ineligible for study analyses if enrolled after one year post-injury (N=164), ineligible for (N=18) or actively in the one-year post injury follow-up window (N30), or expired by time of analysis (N=4) resulting in an eligible sample of N=496. A total of 51 participants were lost to follow-up, withdrew, or refused interview, and an additional N=44 were missing the primary outcome (rehospitalization) resulting in a final sample size of N=401 participants. Figure 1 shows a consort diagram describing how the sample was derived from the VA TBI Model System dataset.

Among 401 individuals, N=164 (41%) of them had at least one rehospitalization at one year follow-up. Among N=164 individuals with at least one rehospitalization, N=115 had only one rehospitalization, N=28 had two rehospitalizations, N=8 had three rehospitalizations, N=1 had four rehospitalizations, and N=12 had five or more rehospitalizations. The number of hospitalizations variable was truncated at a maximum of 5. Therefore for the purpose of this analysis, all participants with 5 or more were recorded as a value of 5. This resulted in a total sum of 295 rehospitalizations from N=164 individuals. The overall summary of reasons for all rehospitalizations in descending order is shown in Table 2a with inpatient rehabilitation as the leading cause. Frequency of each type of rehospitalization is shown in Table 2b with inpatient rehabilitation as the most frequent reason for rehospitalization. Sub-analyses revealed that N=42 of the N=85 rehabilitation readmissions were due to participation in the Inpatient Polytrauma Transitional Rehabilitation Program (PTRP)⁸ to facilitate higher level rehabilitation goals (i.e., community reintegration).

The demographic and clinical data were summarized for all individuals (N=401), rehospitalization No (N=237), rehospitalization Yes (N=164), one rehospitalization (N=115) and two or more rehospitalizations (N=49) (Table 3). Individuals with at least one rehospitalization had significantly longer PTA duration and time to follow commands compared to those without any rehospitalization (PTA duration: 28 days vs. 19 days, p=0.016; time to follow commands: 9 days vs. 2 days, p<0.001). Significantly more individuals with at least one rehospitalization were on active duty at the time of their index TBI compared to those without any rehospitalization (67% vs. 56%, p=0.041).

Individuals with two or more rehospitalizations were more likely to have more than a high school education and sustain their TBI during deployment compared to those with one rehospitalization and to those without any rehospitalization (more than high school education: 65% vs. 45% vs. 44%, p=0.023; injury during deployment: 47% vs. 30% vs. 27%, p=0.018). Individuals with two or more rehospitalizations had longer time to follow commands compared to those with one rehospitalization and to those without any rehospitalization (14 days vs. 6 days vs. 2 days, p<0.001). Individuals with two or more rehospitalizations had longer rehabilitation length of stay compared to those with one rehospitalization and to those without any rehospitalization (66 days vs. 42 days vs. 44 days, p=0.039).

As suggested above, the ability to further delineate the sources of relatively unspecified hospitalizations in this sample would strengthen the ability of the finding to inform future strategies to enhance the successful recovery of TBI patients. An additional limitation of this study is the nature of the setting as relevant only to Polytrauma Centers within the Veterans Health Administration system; however, these findings may be highly relevant to adapting the VA system of care to better serve its population. Like previous civilian studies, the data were derived from patient interviews. Future work that includes medical record based data will provide an important avenue to better address the trajectory of recovery in the TBI patient.

The strengths of this study include a prospective evaluation of a large, consecutive sample of patients with TBI who were followed longitudinally for at least one year yielding a representative picture of the nature of rehospitalization at 1-year post injury. This sample is representative of Veterans and active duty Service Members followed at the regional Polytrauma Rehabilitation Centers and the sample consisted of a range of TBI etiology and severity using consistent outcome measures. The limitations of this study are important to recognize. Of the 712 patients enrolled in the VHA TBIMS, 496 were eligible for study analyses with a 10% (N=51) lost to follow-up, withdrew, or refused data collection. An additional N=44 (9%) were missing the primary outcome (rehospitalization) leaving a sample of 401 or 81% of the eligible sample. Participants were lost due to missing data, timing ineligibility, withdrawal from study, refusal to participate, or death. In addition, it is uncertain if these readmissions were elective or unplanned due to medical necessity. The data reflect family/participant self-report rather than review of medical records. Finally, many of the inpatient rehospitalizations involved a continuation of the rehabilitation process in the journey to final disposition that may be unique to the VA system of care. Thus the generalizability of the findings in this study to the non-VA population is somewhat limited though informative of the VA and DOD healthcare systems.

Approximately 41% (164/401) of had at least one hospitalization within one year of acute PRC discharge, of which, 30% (49/164) had two or more hospitalizations. The most common reason was for hospitalization for Veterans and Service Members was readmission for inpatient rehabilitation followed by other surgical, medical and psychiatric hospital admissions. These data suggest that the need for longitudinal follow-up and patient management is paramount to understand the long-term outcomes in this unique patient population. Future research should evaluate preventable cause of rehospitalizations and provide targeted therapeutic interventions to improve health outcomes and mitigate rehospitalization.