After obtaining approval from the Institutional Review Board, patient demographic data consisting of age, sex, and medical comorbidities were obtained from the patients’ medical records. Perioperative and postoperative data gathered included type of surgery, site of surgery, whether the procedure was a revision, date of discharge from initial hospital stay, date of readmission, length of hospital stay on readmission, type of infecting organism, and need for additional surgical procedure. We analyzed the parameters using a one-tailed t-test for continuous variables and Fisher’s exact test for categorical data. Microsoft Excel 2007 (Microsoft, Redmond, WA, USA) was used for all statistical analyses.
Readmissions for SSIs within 30 days from discharge occurred at a higher (p = 0.045) rate after spine surgery compared with TJA. Of the 46 patients who were readmitted after elective spine surgery, 37 (80.4%) were readmitted within 30 days of discharge whereas 28 of 45 patients (62.2%) after elective TJAs were readmitted within 30 days. There was no difference (p = 0.31) in readmission rates between cervical and lumbar procedures. However, there was a trend (p = 0.062) in the cohort that had TJAs toward a higher 30-day readmission rate after THA. Readmission occurred within 30 days in 13 of 16 (81.3%) patients in the subset of patients who had undergone THAs. In contrast, only 15 of 29 (51.7%) patients in the TKA subset were readmitted within 30 days. The mean time to readmission in the THA subset was 32 days as compared with 58 days among the TKA subset.
Payers, led by the federal government, are rapidly moving toward the episode-of-care payment model. In this model, all care rendered to a patient up to 30 days after discharge, including readmissions, will be the financial responsibility of the hospital. Several studies have addressed overall incidence of infection after elective spine and total joint procedures; however, few have examined the timing of those infections. Our study aimed to determine whether most patients with SSIs were readmitted within 30 days of discharge and whether the number of readmissions within 30 days differed according to the type of surgery performed. Additionally, we examined if the type of infecting organism influenced the presentation of readmissions.
We note some limitations. First, while our study includes all patients readmitted to our institution during a 4-year period, we had small numbers of patients in each group because our infection rate is 0.9% for total joint surgeries and 2% for spine surgeries. Therefore, although our institution is high volume with more than 2000 total joint replacements and 1300 spine surgeries per year, the total number of infections is small (approximately 50 per year). This resulted in a limited ability to determine differences in readmission rates between the total joint and spine cohorts. Second, we included only patients who were readmitted to hospitals in our health system, and it is likely there were patients readmitted to outside facilities. We know that no patients with Medicare were readmitted to other institutions for SSIs. Our infection rate mirrors what has been reported in the literature for spinal surgery and TJAs [1, 7, 10-17 ]. As such the number of patients readmitted to other hospitals would not likely be large enough to affect the findings of our study. Thirty percent of our patients receive Medicare and our readmission rate to other institutions for infections is zero in 1 year. Each year we have one to two patients who are evaluated and admitted to other institutions for infections, then transferred to us for definitive treatment, however these patients are captured in our analysis (this information can be extrapolated to patients not receiving Medicare patients as well but not with absolute certainty). Additionally our institution has a large urban tertiary orthopaedic referral center for the tri-state. Owing to the expertise of our center, patients with postoperative infections whose index procedure was done at another institution (it is unlikely a small community hospital would treat one of our patients with infections) are referred to us for treatment.
We found readmissions within 30 days of discharge for SSIs were more likely to occur after elective spine surgery. The majority of this difference came from the TKA subset with the TJA group. Whereas greater than 80% of spine readmissions occurred within 30 days of discharge, only 51.7% of readmissions after TKAs occurred within 30 days. Huotari et al. , in a review of SSIs after THAs, TKAs, and open reduction and internal fixation of the femur, reported a median time to presentation of SSIs, including superficial infections, at 11 days, and 25 days for deep infections alone. Pull ter Gunne et al. , in a retrospective review of SSIs after spinal surgery, found that 72.7% of the SSIs, including superficial and deep infections, were identified in the outpatient setting an average of 28.7 days after the procedure was performed. Chikawa et al. , in a retrospective review of early deep SSIs, defined as within 1 month from the initial surgery, reported an incidence of 1.1%; however, they did not address what percentage of all SSIs were early. Although Weinstein et al. , in a review of more than 2000 spinal procedures did not comment on the exact timing of readmission, 93% of their patients with postoperative infections presented with substantial wound drainage at an average of 15 days postoperatively. Our findings vary from those of Pulido et al. , who determined that only 27% of SSIs after TJAs occurred within the first 30 days postoperatively, and those of Peersman et al.  in which 29% of deep SSIs after TKA occurred within the first 3 months.
There was a trend for patients with SSIs after THAs to be admitted more frequently within 30 days of discharge compared with patients with SSIs after TKAs. This trend is consistent with the findings of Huotari et al. , who showed that a higher proportion of patients who had TKAs would present with SSIs after discharge from the hospital. The reason for the lower percentage of early readmissions in the TKA subset is unclear. One hypothesis for the disparity is that patients who have had TKAs may be treated more conservatively during the immediate postoperative setting. It is uncertain how many of these patients were treated on an outpatient basis with oral antibiotics before admission.
The infecting organism did not have an effect on the timing of readmission. Although Pulido et al.  reported 80% of their patients with acute infections after TJAs had staphylococcal isolates, they did not comment on the effect of the strain of bacteria on timing of the presentation of the SSI. Our microbiologic data are consistent with those from prior studies on SSIs after orthopaedic procedures [6, 12].
Whether 30 days is a sufficient time for the postoperative episode-of-care model remains uncertain. Although 80.4% of spinal infections and 81.3% of THA infections occurred within 30 days from discharge, only 51.7% of TKA infections were captured. If the episode-of-care model were to be extended to 60 days after discharge, 65.5% of patients with TKA infections requiring readmission would have presented, whereas greater than 93% of patients with SSIs after THAs and spinal procedures would have been readmitted. The results of extending the episode of care to 120 days would include 82.8% of readmissions for SSIs after TKAs.
We focused on the timing of readmissions after elective spine surgery and TJAs to highlight the financial risk when participating in episode-of-care agreements. The potential cost burden for healthcare providers created by readmissions for SSIs has the potential to be considerable if episode-of-care models were to be enacted. Whitehouse et al. , in a study on the effect of SSIs, reported an average of 14 days of additional hospital stay with readmission and more surgical procedures and rehospitalizations. In our study, 94.7% of the readmitted patients required at least one secondary procedure during the hospital stay. With infection rates of approximately 1% to 2% after elective spine and TJAs and higher rates for revision surgeries, there is potential for substantial unreimbursed expenditure by healthcare systems. Bozic and Ries  and Calderone et al.  reported the average cost of treating an infected TJA to be approximately $70,000 and $100,000 for the treatment of an infected spinal fusion, respectively. This potential implication must be considered when participating in a payment system based on the episode-of-care model.
1. Babkin, Y., Raveh, D., Lifschitz, M., Itzchaki, M., Wiener-Well, Y., Kopuit, P., Jerassy, Z. and Yinnon, AM. Incidence and risk factors for surgical infection after total knee replacement. Scand J Infect Dis.
2007; 39: 890-895. 10.1080/00365540701387056
2. Bozic, KJ. and Ries, MD. The impact of infection after total hip arthroplasty on hospital and surgeon resource utilization. J Bone Joint Surg Am.
2005; 87: 1746-1751. 10.2106/JBJS.D.02937
3. Calderone, RR., Garland, DE., Capen, DA. and Oster, H. Cost of medical care for postoperative spinal infections. Orthop Clin North Am.
1996; 27: 171-182.
4. Chikawa, T., Sakai, T., Bhatia, NN., Sairyo, K., Utunomiya, R., Nakamura, M., Nakano, S., Shimakawa, T. and Minato, A. Retrospective study of deep surgical site infections following spinal surgery and the effectiveness of continuous irrigation. Br J Neurosurg.
2011; 25: 621-624. 10.3109/02688697.2010.546902
5. Enquist, M., Bosco, JA, 3rd, Pazand, L., Habibi, KA., Donoghue, RJ. and Zuckerman, JD. Managing episodes of care: strategies for orthopaedic surgeons in the era of reform. J Bone Joint Surg Am.
2011; 93: e55. 10.2106/JBJS.J.01703
6. Huotari, K. Hospital Infection Surveillance TeamImpact of postdischarge surveillance on the rate of surgical site infection after orthopaedic surgery. Infect Control Hosp Epidemiol.
2006; 27: 1324-1329. 10.1086/509840
7. Koutsoumbelis, S., Hughes, AP., Girardi, FP., Cammisa, FP, Jr, Finerty, EA., Nguyen, JT., Gausden, E. and Sama, AA. Risk factors for postoperative infection following posterior lumbar instrumented arthrodesis. J Bone Joint Surg Am.
2011; 93: 1627-1633. 10.2106/JBJS.J.00039
8. McCormack RA, Hunter T, Ramos N, Michels R, Hutzler L, Bosco JA. An analysis of causes of readmission after spine surgery. Spine (Phila Pa 1976)
9. Harrop, JS., Styliaras, JC., Ooi, YC., Radcliff, KE., Vaccaro, AR. and Wu, C. Contributing factors to surgical site infections. J Am Acad Orthop Surg.
2012; 20: 94-101. 10.5435/JAAOS-20-02-094
10. Olsen, MA., Nepple, JJ., Riew, KD., Lenke, LG., Bridwell, KH., Mayfield, J. and Fraser, VJ. Risk factors for surgical site infection following orthopaedic spinal operations. J Bone Joint Surg Am.
2008; 90: 62-69. 10.2106/JBJS.F.01515
11. Peersman, G., Laskin, R., Davis, J. and Peterson, M. Infection in total knee replacement: a retrospective review of 6489 total knee replacements. Clin Orthop Relat Res.
2001; 392: 15-23. 10.1097/00003086-200111000-00003
12. Pulido, L., Ghanem, E., Joshi, A., Purtill, JJ. and Parvizi, J. Periprosthetic joint infection: the incidence, timing, and predisposing factors. Clin Orthop Relat Res.
2008; 466: 1710-1715. 10.1007/s11999-008-0209-4
13. Pull ter Gunne AF, Cohen DB. Incidence, prevalence, and analysis of risk factors for surgical site infection following adult spinal surgery. Spine (Phila Pa 1976)
14. Pull ter Gunne, AF., Mohamed, AS., Skolasky, RL., Laarhoven, CJ. and Cohen, DB. The presentation, incidence, etiology, and treatment of surgical site infections after spinal surgery. Spine
2010; 35: 1323-1328.
15. Pull ter Gunne AF, van Laarhoven CJ, Cohen DB. Incidence of surgical site infection following adult spinal deformity surgery: an analysis of patient risk. Eur Spine J
16. Urquhart, DM., Hanna, FS., Brennan, SL., Wluka, AE., Leder, K., Cameron, PA., Graves, SE. and Cicuttini, FM. Incidence and risk factors for deep surgical site infection after primary total hip arthroplasty: a systematic review. J Arthroplasty
2010; 25: 1216-3.
17. Weinstein, MA., McCabe, JP. and Cammisa, FP, Jr, Postoperative spinal wound infection: a review of 2,391 consecutive index procedures. J Spinal Disord.
2000; 13: 422-426. 10.1097/00002517-200010000-00009
18. Whitehouse, JD., Friedman, ND., Kirkland, KB., Richardson, WJ. and Sexton, DJ. The impact of surgical-site infections following orthopedic surgery at a community hospital and a university hospital: adverse quality of life, excess length of stay, and extra cost. Infect Control Hosp Epidemiol.
2002; 23: 183-189. 10.1086/502033