May 2022

Slipper-Related Injuries of the Lower Extremity Treated at United States Emergency Departments

By Mathias B. Forrester, BS

Background: Footwear can affect balance and the risk of slips, trips, and falls. Various studies have reported that slippers are associated with increased risk of falls when compared to other footwear. The objective of this study was to characterize slipper-related injuries of the lower extremity treated at United States (US) hospital emergency departments (EDs).

Methods: An analysis was performed of slipper-related injuries of the lower extremity using data from the National Electronic Injury Surveillance System (NEISS) of the US Consumer Product Safety Commission (CPSC) during 2000-2020.

Results: A total of 1,709 slipper-related injuries of the lower extremity treated at a sample of US hospital EDs were identified, resulting in a national estimate of 70,707 such injuries. Of the estimated injuries, 8.3% occurred during 2000-2002, increasing to 22.3% during 2018-2020. Patients age 60 years or older accounted for 42.4% of the patients; 69.7% were female. The most common injuries were fracture (24.3%) and strain or sprain (22.1%). The most frequently affected body parts were the foot (39.1%), knee (17.3%), and ankle (17.1%). The patient was treated or evaluated and released from the ED in 87.7% of the estimated injuries.

Conclusions: Slipper-related injuries of the lower extremity increased during the 21-year study period. Patients with injuries tended to be older, and the majority were female. Their injuries were most frequently a fracture and affected the foot. The majority of patients were treated or evaluated at an ED and then released.

Falls are a public health problem, potentially resulting in serious injury and death. Risk of falling increases with age and is of particular concern among persons age 65 years and older.1,2 According to the 2014 Behavioral Risk Factor Surveillance System (BRFSS) survey, of respondents age 65 years or older, 28.7% reported falling at least once in the preceding 12 months.3 Of falls among older adults that were treated at United States (US) emergency departments (EDs), approximately 15% involved injuries of the lower extremity.4,5

Footwear can affect balance and the risk of slips, trips, and falls. Various studies have reported that slippers are associated with increased risk of falls when compared to other footwear.6-10 The objective of this study was to characterize slipper-related injuries of the lower extremity treated at US hospital EDs.

Methods

The source of data for this retrospective epidemiologic study was the National Electronic Injury Surveillance System (NEISS) website (https://www.cpsc.gov/cgibin/NEISSQuery/home.aspx). Operated by the US Consumer Product Safety Commission (CPSC), the NEISS collects data on consumer product-related injuries from the EDs of a stratified random sample of 100 hospitals from the more than 5,000 hospitals in the US. The random sample is stratified by hospital size, geographic location, and hospital type (general and pediatric hospitals). Professional NEISS coders view the medical charts at participating hospitals and, for patients with injuries that meet NEISS inclusion criteria, collect and code information such as treatment date; patient age, sex, and race; injury diagnosis and body part injured; discharge disposition; consumer product(s) involved in the injury; location where the incident occurred; and a brief narrative describing the incident.11,12 Data are publicly available and de-identified; thus, the study is exempt from institutional review board approval.

Cases were slipper-related injuries of the lower extremity reported to the NEISS database during 2000-2020. The publicly available NEISS database contains three numeric fields for coding the product involved in the injury (Product_1, Product_2, Product_3). The NEISS Coding Manual indicates that slipper-related injuries are assigned Product code 1615 (Footwear).12 However, Product code 1615 is used for other footwear in addition to slippers, such as sneakers and boots. In addition, Product code 1615 may not have been assigned to all slipper-related injury records. The NEISS database contains a text field (field name Narrative) that provides a brief summary of the circumstances of the injury. The NEISS database was searched for all records that included the letter groups “slipper” or “sliper” in the Narrative field. The Narrative fields of the resulting records were individually examined, and any records that involved an injury related to slippers were included in the study. Footwear designated as sock-slippers were included in the study while ballet slippers were excluded. That the injury involved a lower extremity was based on either the Body_Part or Body_Part_2 numeric fields containing codes for a lower extremity (upper leg, knee, lower leg, ankle, foot, toe).

The variables examined were treatment year (grouped into three-year periods); patient age and sex; circumstances of the injury, location where the incident occurred; disposition; injury diagnosis; and body part affected. The diagnosis was based on information coded in the Diagnosis and Diagnosis_2 numeric fields. In order to identify the circumstances of the injury, the Narrative field for each record was reviewed and the record was assigned to one of the following three groups with respect to whether the slippers appeared to be worn at the time the injury occurred:

1) Slippers worn

2) Slippers likely not worn – includes putting on slippers, taking off slippers, reaching for slippers, hit by slippers, etc.

3) Uncertain if slippers worn – includes tripped or slipped on or over slippers

Note also was made whether the Narrative field specifically included the term “fall” or “fell” and whether a foreign body was involved by puncture through the slipper or being inside the slipper. The NEISS Coding Manual indicates that the Diagnosis_2 and Body_Part_2 fields were added in 2018,12 although these fields do not appear to have been used until 2019.

Analyses were performed using Office Professional 2007 Access and Excel (Microsoft Corporation, Redmond, Washington, US). The distribution of cases and national injury estimates were determined for the variables. National injury estimates were calculated by summing the values in the Weight numeric field in the publicly available NEISS database, and 95% confidence intervals (CIs) were calculated for the estimates. The CPSC considers an estimate unstable and potentially unreliable when the number of records used is <20 or the estimate is <1,200.11 For those variable subgroups where the estimate was <1,200, 95% CIs were not calculated.

Results

During 2000-2020, 1,709 slipper-related injuries of the lower extremity treated at a sample of US hospital EDs were identified, resulting in a national estimate of 70,707 (95% CI, 57,813-83,601) such injuries (31.7% of the 222,737 total estimated injuries to any body part). Both the number of injuries and the mean age of the patients increased over the 21-year study period (Table 1). Table 2 shows the distribution of slipper-related injuries of the lower extremity by patient demographics. The proportion of patients with slipper-related injuries of the lower extremity increased with patient age through age group 40-49 years then remained relatively stable through the older age groups. Patients age 60 years or older accounted for 656 (38.4%) of the cases and 30,004 (42.4%) of the estimated injuries. The majority of patients were female.

Table 3 presents the distribution of slipper-related injuries of the lower extremity by the circumstances of the injury and patient disposition. Most of the injuries occurred when the slippers were being worn. Falls were specifically documented in almost 40% of the injuries, and a foreign body was involved by puncture through the slipper or being inside the slipper in approximately 20% of the injuries. Most of the injuries occurred at home. The majority of patients were treated or examined at the ED and released.

Table 4 shows the distribution of slipper-related injuries of the lower extremity by diagnosis and affected body part. The most commonly reported injuries were fracture, strain or sprain, contusion or abrasion, and puncture. The most frequently affected body part was the foot followed by the knee and ankle.

Discussion

This study describes slipper-related injuries of the lower extremity treated at US hospital EDs. Slippers are associated with increased risk of falls when compared to other footwear.6-10 Approximately 15% of falls among older adults treated at US hospital EDs involved injuries to the lower extremity.4,5

Slipper-related injuries of the lower extremity increased during the 21-year study period. This increase may be due to an increasing number of people wearing slippers or an increasing number of people wearing slippers experiencing injuries that required treatment at hospital EDs. The increase in the number of injuries also may be due to the aging of the US population. The mean patient age increased from 46.5 years during 2000-2002 to 53.1 years during 2018-2020. Alternately, it may be that the hospital staff increasingly mentioned slippers when documenting the injury in the NEISS Narrative field.

Although slipper-related injuries of the lower extremity were reported among all age groups, the number of injuries increased with patient age before stabilizing among patients age 40 years and older. Approximately 40% of the patients were age 60 years and older. This finding is consistent with the Baltimore Longitudinal Study on Aging (a descriptive study where participants completed a fall history questionnaire), which found that the reporting of falls increased with age from 18% in young to 21% in middle-aged and 35% in older adults.2

Almost 70% of the patients were female. Previous studies of falls among persons age 65 years and older also reported a higher proportion of falls among females. 2-5,13,14

While the majority of injuries occurred while the patient was wearing the slippers, a portion occurred when the slippers were not worn, such as when the patient was putting on, taking off, or reaching for the slippers, or tripping or slipping on or over the slippers. Almost 40% of the injuries were documented to have involved a fall. This is likely an underestimate because a portion of the other 60% of the injuries possibly involved falls that were not documented as such in the records’ Narrative fields. In addition, a foreign body was involved by puncture through the slipper or being inside the slipper in approximately 20% of the injuries. This suggests that, while education activities to prevent slipper-related injuries might focus on preventing falls while wearing slippers, such activities might include mention that slipper-related injuries also occur when the slippers are not being worn and that injuries other than falls might occur. For instance, people should be careful where they leave their slippers so that they do not become a tripping hazard. Also, people should be careful where they walk while wearing slippers to avoid stepping on an object that could penetrate their slippers, such as nails and broken glass or even grandchildren’s toys.

Over 70% of the injuries occurred at home. This might be expected since slippers generally are not intended to be worn outside.

While most of the patients were treated or examined in the ED and released, 10% were hospitalized, suggesting that a portion of slipper-related injuries of the lower extremity are serious. The most frequently reported injuries were fracture, strain or sprain, contusion or abrasion, and puncture. This is consistent with a previous study of falls among patients age 65 years and older treated at hospital EDs that reported the most common diagnoses to be fracture, contusion or abrasion, laceration, and strain or sprain.5

This study is subject to limitations. Cases were initially identified by searching for all records that included the letter groups “slipper” or “sliper” in the Narrative field. Slipper-related injuries where these letter groups were not documented in the Narrative field would not have been included in this study. Furthermore, with the possible exception of ballet slippers, it was not possible to distinguish between bedroom/house slippers and other types of slipper. In addition, the selection of records to be included in the study was performed by a single person and used the Narrative field, which contains a limited amount of information. Errors in the selection and classification of records may have resulted in records being included or excluded erroneously or misclassified. Furthermore, the NEISS database only includes injuries treated at an ED. Studies that include information on injuries not evaluated at hospital EDs would provide a more complete view of slipper-related injuries.

In conclusion, an estimated 71,000 slipper-related injuries of the lower extremity were treated at US hospital EDs during 2000-2020. Patients tended to be older, and the majority were female. Most of the injuries occurred while the patient was wearing the slippers, and the majority occurred at home. Most patients were treated or evaluated at the ED and released.

Mathias B. Forrester, BS, is an independent researcher in Austin, Texas. Now retired, he previously performed public health research for various university and government programs for 34 years.

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