We conducted a retrospective cohort study using the HealthCore Integrated Research Database (HIRD^SM), including individuals from 12 Anthem-affiliated plans (California, Connecticut, Georgia, Indiana, Kentucky, Maine, Missouri (excluding 30 counties in the Kansas City area), Nevada, New Hampshire, New York, Ohio, Virginia (excluding the northern suburbs of Washington, DC). Data include all fully-adjudicated claims submitted from providers, facilities, and outpatient pharmacies linked to health plan enrollment information. Fully insured women with enrollment in a fee-for-service plan with medical coverage of hospital and physician services were eligible for inclusion in the study. We excluded women coded for end-stage renal disease, organ transplant, or HIV positive status due to unique risk factors for infection. Medical claims were restricted to paid claims.

The database contained up to 5 International Classification of Diseases, 9^th Revision, Clinical Modification (ICD-9-CM) diagnosis codes per claim from 2004–2008 and up to 12 diagnosis codes per claim from 2009–2011. Inpatient hospitals included up to 5 ICD-9-CM procedure codes per claim (8 in 2009–2011), while provider and ambulatory facility claims used CPT-4 (Current Procedural Terminology, 4^th edition) codes.

To obtain hospital-level information, we matched the operative facility to the American Hospital Association Annual Survey of Hospitals (Health Forum, LLC, Chicago, IL) using National Provider Identifier codes, where available. Otherwise, matching to the AHA data was performed using facility name and address fields.

We identified mastectomy operations among women aged 18–64 years from 1/1/2004–12/31/2011 using ICD-9-CM and/or CPT-4 procedure codes from inpatient and outpatient facilities and provider claims (see Appendix). We classified the mastectomy as unilateral or bilateral based on the ICD-9-CM procedure and CPT-4 codes, billed units, and CPT-4 modifier codes assigned by the provider and facility.¹² Operations in members whose enrollment ended on the day of mastectomy were excluded since no follow-up was available. When CPT-4 or ICD-9-CM procedures codes for breast conserving surgery (BCS) were present during the same hospital admission or within +/− 3 days of mastectomy, we used an algorithm to determine whether BCS or mastectomy was more likely, as described previously.¹² We excluded procedures that were more consistent with BCS, since concurrent BCS and mastectomy is unlikely and the incidence of SSI after BCS is lower than after mastectomy.^12,13 We defined immediate reconstruction (IR) as the presence of CPT-4 and/or ICD-9-CM procedure codes for tissue expander/breast implant and/or flap reconstruction within +/− 7 days of the mastectomy (see Appendix), with prioritization of the provider classification of the type of flap when there was a discrepancy. Delayed reconstruction procedures were excluded since our focus was on NIWCs associated with mastectomy.

NIWCs first coded from 2–180 days (1–180 days for hematoma) after surgery were identified using ICD-9-CM diagnosis codes from inpatient and outpatient facilities and provider claims. NIWCs included fat necrosis (ICD-9-CM diagnosis codes 567.82, 611.3), dehiscence (875.0, 875.1, 879.0, 879.1, 998.3, 998.32), hematoma (998.12), and necrosis (998.83). We excluded claims with laboratory or patient’s home locations and provider claims with laboratory CPT-4 codes (88104–88399), since these diagnosis codes may have indicated diagnostic workup and not post-surgical complications. For women with autologous flap reconstruction, the site of NIWC (donor vs. flap) could not be determined, since ICD-9-CM diagnosis codes do not distinguish the site of complication.

The date of onset of NIWCs was defined according to the timing and location of diagnosis. For NIWCs coded by an inpatient facility during the original operative admission, we assigned the date of NIWCs to the discharge date if the difference between the discharge and admission date was greater than or equal to 2 days. For NIWCs diagnosed during a subsequent inpatient admission, the date of NIWCs onset was assumed to be the date of hospital readmission. For NIWCs diagnosed initially by a provider or in an outpatient setting, the onset date was defined as the first service date coded for the NIWC.

The observation period for NIWCs was through 180 days after surgery, with earlier censoring for the end of insurance enrollment, a subsequent mastectomy, implant, flap, or nipple reconstruction. We censored one day after the subsequent surgery since we assumed that an NIWC coded on the day of or one day after a surgical procedure was preexisting and could be attributed to the previous surgery. Non-breast specific NIWC codes (e.g., 998.12, 998.3, 998.32, 998.83) were not classified as an NIWC if they were first coded after a subsequent non-breast operation, defined using the National Healthcare Safety Network procedure list.⁶

We defined early implant loss as a breast implant removal, with or without an implant exchange, within 60 days of a mastectomy with implant IR. We used the CPT-4 and ICD-9-CM procedure codes described in the previous section. Codes for SSI or NIWCs in the 14 days prior to removal were considered the indication for implant removal. To compare outpatient utilization, we identified distinct dates with CPT-4 codes for physician office visits (99201–99215) and emergency department encounters (99281–99285).

The rates of NIWCs overall and by type of complication within 180 days after surgery for mastectomy with and without IR were compared using a Chi-square test, as were other categorical variable comparisons. For the comparisons of wound complication rates by type of procedure, the alpha was adjusted for multiple testing using the Bonferroni method.¹⁴ We used the Kruskal-Wallis test to compare continuous variables. All data management and statistical analyses were performed using SAS v9.3 (SAS Institute Inc., Cary, NC). This study was approved by the Washington University Human Research Protection Office.

The final analysis sample included 18,696 mastectomy procedures among 18,085 women. The median age of women was 51 years (interquartile range 45–57 years). The indication for mastectomy was cancer in 17,861 (95.5%), and prophylactic or benign conditions in 835 (4.5%). Forty-two percent of the operations were mastectomy-only, 44.0% mastectomy plus implant IR, 10.4% mastectomy plus flap IR, and 3.6% were categorized as mastectomy plus flap and implant IR (Table 1). As reported previously, 39% of procedures were bilateral and 81% were performed on during an inpatient admission.¹² Among procedures performed during an inpatient hospital stay that we could link to the AHA survey (n=11,756; 63%), 50% were performed at a hospital with a residency training program and 58% at a hospital with a medical school affiliation. Thirty-nine percent of procedures were performed at a hospital with <300 beds, 33% at a hospital with 300–499 beds, and 28% at a hospital with ≥ 500 beds. Most procedures were performed at an urban hospital (94%), and the procedures were distributed across the U.S. (18% Northeast, 34% South, 26% Midwest, and 21% West).

The overall NIWC rate following mastectomy with and without IR was 9.2% (1,714/18,696); 56% of the NIWCs required a surgical wound care procedure. The rates of NIWCs were 5.8% after mastectomy-only, 10.3% after mastectomy with implant, 17.4% after mastectomy with flap, and 11.7% after mastectomy with flap and implant (p<0.001, Chi-square test; Table 1). The risk of an NIWC was almost 2-fold higher after mastectomy plus implant and 3-fold higher after mastectomy plus flap compared with mastectomy-only. The rates of NIWCs requiring surgical wound care ranged from 3.0% after mastectomy-only to 8.3% for mastectomy with flap reconstruction (Table 1). The proportion of NIWC diagnosed during a hospitalization (index or readmission) varied from 28% after mastectomy plus implant to 39% after mastectomy plus flap.

Among mastectomies with IR, the NIWC rate was significantly higher after bilateral compared with unilateral procedures (12.7% (703/5,529) vs. 10.5% (556/5,307) respectively, p<0.001, Chi-square test). Similarly, among mastectomies without IR, the NIWC rate was significantly higher after bilateral compared with unilateral procedures (8.1% (141/1,739) vs. 5.1% (314/6,121), p<0.001, Chi-square test).

The rates of NIWCs were similar for women with cancer versus prophylaxis or benign conditions (9.2% vs. 8.9%, p=0.75, Chi-square test). NIWC after mastectomy-only occurred in 5.7% (439/7,639) of women with breast cancer (in situ or invasive) and 7.2% (16/221) of women undergoing mastectomy for prophylaxis or benign conditions (p=0.35, Chi-square test). Among mastectomy + IR, 11.7% (1,201/10,222) of procedures were complicated by NIWC in women with cancer versus 9.4% (58/614) of procedures performed for prophylaxis or benign conditions (p=0.08, Chi-square test).

Of 1,714 mastectomy procedures complicated by an NIWC, 29% were also coded for an SSI within 180 days after surgery. Among procedures with both an NIWC and SSI, the most common NIWCs were dehiscence (60.9%) and necrosis (35.3%). Among those procedures with both an SSI and an NIWC, 36% were coded for both complications at the same time, while the NIWC preceded SSI by more than one day in 36% of procedures (Table 2). The most common timing of wound complications after mastectomy-only and mastectomy with flap was coding of NIWC before SSI, while SSI and NIWC after mastectomy with implant IR most commonly was coded simultaneously (Table 2). For this and subsequent analyses, mastectomy with immediate flap included flap with or without concurrent implant because of the small number of immediate flap plus implant procedures.

Among mastectomy with immediate implant reconstruction, 216 (2.6%) had implant removal within 30 days and 506 (6.2%) had implant removal within 60 days after mastectomy, with or without implant exchange. Sixty-six percent of women with an early implant removal within 60 days were coded for an SSI or NIWC in the 14 days before implant removal. Fourteen percent of the procedures with early implant removal were coded for both SSI and NIWC (n = 73), 43.1% (n = 218) were coded for SSI only, and 8.5% (n= 43) were coded for NIWC only. The remaining 34.0% (n = 172) of procedures with early implant removal were not coded for either an infectious or noninfectious wound complication in the two weeks before implant removal. Of these early implant removals without wound complication per our definition, 59.3% (n = 102) were coded for another complication (e.g., malfunction or complication of prosthetic device, deformity/disproportion of reconstructed breast, breast pain, seroma). In addition, women with NIWCs had significantly more physician visits within 180 days after operation compared to women without a wound complication (median 8 vs. 7 visits on distinct dates, p<0.001, Kruskal-Wallis test) and more emergency department (ED) encounters (median 0 for both, mean 0.4 vs. 0.2 ED encounters, p<0.001, Kruskal-Wallis test).

The median time to diagnosis of NIWCs was significantly shorter following mastectomy-only compared with mastectomy plus implant or mastectomy plus flap (median 17 vs. 24 and 29 days respectively; p<0.001, Kruskal-Wallis test). NIWCs were first coded within 30 days after mastectomy-only in 65.7% of procedures, with 17.1% diagnosed between 31–60 days. Among mastectomy with IR, NIWCs were first coded within 30 days in 58.2% of procedures and 20.7% were diagnosed between 31–60 days (Figure 1).

Individual complication rates ranged from 0.5% for fat necrosis after mastectomy-only to 7.2% for dehiscence after mastectomy with flap reconstruction (Table 3). The fat necrosis, dehiscence, and necrosis NIWC rates were all significantly higher after mastectomy plus implant and mastectomy plus flap compared with the individual NIWC rates after mastectomy-only. The proportion of operations complicated by hematoma was significantly higher after mastectomy plus flap, but not mastectomy plus implant compared to mastectomy-only. Among mastectomy with reconstruction, the rates of all NIWC categories were significantly higher after flap versus implant reconstruction. Overall the median time to NIWC diagnosis ranged from 7 days for hematoma to 35 days for fat necrosis (Table 3).