Epidemiological Analysis of Upper Extremity Amputations From Lawn Mower–Related Injuries

Introduction

Lawn mower–related injuries (LMIs) present a complex spectrum of pathology with significant variation in both demographics and anatomical locations affected.^{1 -3} Lawn mower–related injuries pose significant public health concerns, often imposing demanding financial, physical, and psychological tolls on victims as well as health care systems.^4,5 A better appreciation of the epidemiological patterns and risk factors associated with upper extremity amputations secondary to LMIs is paramount in the development of prevention, management, and medical intervention strategies.

Traumatic amputations represent a significant number of emergency department visitations annually, with estimations around 30 000 patients annually.^1,5 The National Electronic Injury Surveillance System (NEISS) is a public health resource that compiles data surrounding consumer product–related injuries in an effort to project nationwide estimates, which serve to benefit consumers and researchers alike. ⁶ The NEISS uses a nationally representative sample of approximately 100 hospitals as a probability sample of the greater than 5000 hospitals present in the United States. ⁶ From this surveillance data, which is perpetually redesigned and updated, NEISS sampling statisticians are able to extrapolate national injury incidences. ⁶ Previous studies have estimated power lawn mowers to be the third leading cause of traumatic amputation in the United States, behind doors and table saws. ⁵ Furthermore, when NEISS data was queried specifically for finger amputations, LMIs were also identified as the third leading cause overall, and even the second leading cause in patients of 40 to 60 years. ⁷

There is a scarcity of data elucidating the epidemiology of traumatic upper extremity amputations directly as a sequelae to LMIs.^5,7 The goal of the present study was to further delineate the epidemiological patterns of lawn mower upper extremity amputations to further educational, safety, and medical initiatives to mitigate the prospective catastrophic ramifications often associated with these injuries. The authors hypothesized that overall cases and incidence rates of lawn mower upper extremity amputations would significantly decrease in tandem with evolving legislative and technological safety initiatives.

Materials and Methods

The NEISS database was queried over the most recent 10-year period (2014-2023). Product codes for “Lawn Mowers, all types” under the product grouping of “Yard and Garden,” including codes 1439, 1402, 1401, 1446, 1422, 1448, and 1434, were factored into the query. Available ages were subdivided into 10-year age groups. The NEISS database was queried to include each body part coded under “Upper Extremity,” including Finger (92), Hand (82), Wrist (34), Lower Arm (33), Upper Arm (80), Elbow (32), and Shoulder (30). Finally, the diagnosis code of Amputation (50) was used.

Lawn mower–related amputation-associated demographic and epidemiological data were analyzed. Incidence rates were calculated per 100 000 individuals using US census data for yearly US populations. National case estimates, coefficient of variation (CV), and 95% confidence interval of estimate were compiled. As per the NEISS, unstable (and therefore unreliable) estimates were encountered where national estimates were below 1200, case number was less than 20, or if the CV exceeded 33%. ⁸ In addition, annual case records from participating NEISS hospitals were assessed and further analyzed by age, sex, body part involved, and further stratified by specific injury characteristics. Specific injury characteristics of note included the number of fingers amputated in each recorded representative case, as well as which fingers were most frequently amputated.

Regression analyses were performed to identify and quantify trends in yearly case numbers as well as incidence rates from the years 2014 to 2023. Analysis of variance testing was conducted to analyze the finger-specific epidemiological data recorded from the NEISS database.

Results

An estimated 17 509 total upper extremity amputations occurred from 2014 to 2023 in the United States secondary to LMI. These diagnoses made up a substantial portion of all estimated lawn mower–related upper injuries over this interval, with other common injury sequelae including “Laceration” (80 213), “Fracture” (36 266), “Sprain” (24 512), and “Burns” (9178). The estimated number of cases each year remained relatively consistent, although 2023 marked the lowest year in the 10-year span at 1413 amputation cases (Table 1). There was an overall negative trend in case estimates over the 10-year period although this was not significant (Coefficient = −8.67; P = .76) (Figure 1). Actual case numbers, CV, and 95% confidence intervals were also recorded (Table 1). Incidence rates of upper extremity amputation secondary to LMI mirrored the annual case estimates, with an overall negative trend, albeit not statistically significant (Coefficient = −0.005; P = .54) (Table 1). Incidence rate peaked in the year 2020 (0.603) and reached a nadir in 2023 (0.416) (Figure 1). When grouping national estimates by 10-year age cohorts over the 10-year study period, most injuries were estimated to occur in 50- to 59-year-old patients (3533 cases), followed by 40- to 49-year-old patients (3268 cases). Case estimates for the age cohorts of 0 to 9, 10 to 19, 70 to 79, and 80 years and older were deemed unstable per NEISS estimation criteria due to their relative infrequency (Figure 1).

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Table 1.

Ten-Year Data Leveraging NEISS Database.

Year	2014	2015	2016	2017	2018	2019	2020	2021	2022	2023	P
Variable
National estimate	1831	1507	1660	1863	1877	1975	1986	1738	1659	1413	.762
Number of cases	49	38	46	51	48	50	60	49	38	40
Coefficient of variation (CV)	0.21	0.23	0.20	0.24	0.19	0.17	0.19	0.17	0.25	0.21
95% confidence interval	1063-2600	826-2188	1014-2305	991-2735	1150-2604	1313-2638	1227-2745	1153-2322	827-2491	808-2018
Incidence rate	0.575	0.470	0.514	0.573	0.574	0.602	0.603	0.523	0.500	0.416	.539

Note. There were no significant changes in neither national estimates nor national incidence rates from 2014 to 2023 in the present study. NEISS = National Electronic Injury Surveillance System.

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Figure 1.

Ten-year National Electronic Injury Surveillance System data on lawn mower–associated upper extremity amputations in the United States from 2014 to 2023.

Case record review from pooled participating NEISS hospitals yielded 469 cases of upper extremity amputation directly associated with LMI. The median age of this patient cohort was 47 (Minimum 3, maximum 96; first quartile 33, third quartile 60). These cases demonstrated a relatively stable trend in median ages of injury across the 10-year study period (Figure 2). There was a significant male predominance in the cases recorded across the 10-year period (91%), which was relatively stable from year to year (Figure 2).

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Figure 2.

Demographic data acquired from recorded cases from National Electronic Injury Surveillance System–participating hospital systems on lawn mower upper extremity amputations from 2014 to 2023.

Of the 469 cases pooled from 2014 to 2023, 474 product codes were recorded (factoring individual cases receiving up to 2 codes and body parts following 2019). Of these cases, 97% were associated with amputation of a finger (body part 92). Amputations of hands, lower arms, wrists, and upper arms were far less frequent (2.1%, 0.4%, 0.2%, and 0.2% of cases, respectively) (Figure 3).

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Figure 3.

Injury-specific epidemiological data from participating National Electronic Injury Surveillance System hospital cases. (a) Most amputations (97%) involved the finger (92), whereas hands (82), wrists (34), lower arms (33), and upper arms (80) were less common. (b) Most amputations led to injury of a single digit (64%), and (c) the third digit was most involved (41.6%).

There were significant differences that existed when examining both the fingers which were amputated (P = .002) in these pooled cases as well as the number of fingers amputated (P = .002). In total, 109 records of the 469 total cases included the specific finger amputated, which amounted to 447 fingers recorded in total. The most amputated finger over the 10-year study period was the third (41.6%), followed by the fourth (29.5%), second (17.4%), fifth (6.3), and thumb (5.1%) (Table 2, Figure 3). Three hundred sixty-seven of the 469 cases recorded the number of digits involved in the amputation event. Most commonly, only one finger was involved (64% of cases), although a sizable portion of patients suffered a traumatic multi-finger amputation event (Table 2, Figure 3).

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Table 2.

Case-Specific Data Acquired From Recorded Cases From NEISS-Participating Hospital Systems.

Case-specific data	Percentage of total	P value
Numbers of fingers amputated (N = 367)
1	64.0	.002
2	25.9
3	8.4
4	1.4
5	0.3
Finger amputated (N = 447)
1	5.1	.002
2	17.4
3	41.6
4	29.5
5	6.3

Note. There were significant differences that existed between the number of fingers amputated and which digit was involved. NEISS = National Electronic Injury Surveillance System.

Statistical significance for bold values was set at p<0.05.

Discussion

The findings of this study provide valuable insights into the epidemiological and injury patterns associated with LMI upper extremity amputations by leveraging the NEISS database. Despite advances in product safety and consumer education, over the past 10 years, the estimated frequency and incidence rate of upper extremity amputations secondary to lawn mowers has remained largely unchanged. When these events did occur, 50- to 59-year-old men were most often involved, most commonly leading to amputation of the third finger in isolation. These findings further bolster and augment previous investigations.

This study demonstrated a small, but not significant, decrease in both cases and incidence rates of upper extremity lawn mower amputations over the past 10 years. These data mirror previous investigations ³ and reflect the complexity of addressing these injuries both through technological and educational initiatives.^3,4 Both the mechanism and body region of LMIs are highly variable, which may underlie this societal hurdle. ⁴ Lawn mowers have demonstrated the capacity to incur amputations secondary to moving blades, burn injuries from engine components, as well as ejected projectiles, which strike both operators and bystanders.^{2 -4,9 -11} Furthermore, pediatric run-over events represent an additional source of polytrauma with enormous psychological, emotional, physical, and economic burdens to patients, families, and the health system at large. Considering lawn mowers have been shown to rank third among consumer products in amputations (behind doors and power saws), this at-risk population offers a significant opportunity to enact meaningful change to this preventable morbidity.^{3 -5,12 -14}

Prior US Consumer Product Safety Commission (CPSC) efforts have shown demonstrable success at curbing other product causes of upper extremity amputation. ¹⁵ Vosbikian et al ¹⁵ found that regulatory changes surrounding the use of power saws led to an annual decrease in upper extremity injuries (5.8%) from 2006 to 2015. The CPSC has issued federal standards for power mowers since 1982, while instituting continuous revisions and iterations since its inception. This governing body, along with the American National Standards Institute (ANSI), provides legislation, specifications, and education aimed toward curbing product hazards and improving customer safety. Despite current, exhaustive CPSC guidelines and requirements, additional codes and standards may serve to augment the current slow decline in cases and incidence rate observed in the present study. One prospective area for regulatory improvement and user education lies in the realm of stored energy. Lawn mower engines can store energy like a spring when jammed and despite being shut off, blade revolutions can occur following debris removal. Explicit user education on this phenomenon and technological innovations to inhibit its occurrence may both contribute to decrease the rates of upper extremity amputation when using this technology.

Between 2014 and 2023, most cases of LMI upper extremity amputation occurred in men, between the ages of 40 and 60 years. Among the pooled cases of NEISS-participating hospitals, median age was 47 years. These data are consistent with previous investigations, which indirectly addressed similar injuries.^5,7,10 Although this age likely reflects the population who use the equipment with the most regularity, other cohorts may have been underestimated in the present study. Notably, considering that NEISS only allowed for single one diagnosis, one body part coding prior to 2019, pediatric amputation events may be underrepresented here as prior investigations have demonstrated the propensity for this age group to suffer disproportionately morbid sequelae with multiple concomitant injuries.^4,13,14,16 As LMIs have been found to be the third leading cause of pediatric amputation in the United States, ¹³ and decreasing age having an inverse relationship with mean injury severity scores and odds of intensive care unit admission, ⁴ the methodical limitations of the present study may have missed some cases in this age cohort.

From 2014 to 2023, LMIs leading to upper extremity amputations most commonly involved the fingers (97% of all cases), which corroborates previous investigations.^5,7,10 Previous pediatric-focused LMI investigations have found hands and fingers to be the most commonly injured body part (14.7%-34.6%), followed by lower extremity and finally feet or toes.^10,11,17 In a previous NEISS-based investigation, Renfro et al ⁷ found lawn mowers to be the third most common cause of traumatic fingertip amputation–related consumer products behind table saws and doors. Traumatic finger amputations are a source of significant economic and physical strain, imposing demands on patients and health systems alike.^{18 -21} Furthermore, LMI-associated traumatic digit amputations are often complicated wound contamination, the inability to salvage the severed digit, and associated fractures and injuries. A better appreciation of the burden and epidemiology of these traumatic lawn mower amputations may serve to improve awareness and initiatives targeting their reduction. Given that inadequate management of these injuries can lead to stiffness, persistent neurovascular compromise, deformity, and pain, ¹ this represents an important public safety opportunity.

In the present study, among the pooled cases of NEISS-participating hospitals, most patients suffered an isolated finger amputation (64% of patients), most commonly of the third digit (41.6% of all amputated digits). Interestingly, trends in relative amputated-finger frequency appeared to mirror finger length with the third, fourth, and second digits being most involved (in descending order). Although anecdotal and unable to be standardized, a common chief complaint associated with the NEISS-collected LMI amputation cases involved reaching under the lawn mower to clear debris from the blades, which mechanistically makes intuitive sense when interpreting epidemiological upper extremity amputation data. Thirty-six percent of cases collected from 2014 to 2023 involved multiple digits, which has significant ramifications regarding management as a classically accepted indication for replantation includes multiple digit amputation.^1,22,23 In addition, considering the frequency of middle, index, and ring finger amputations (involved in more than 88% of NEISS cases), reconstructive principles that anticipate eventual patterns of hand use (ie, pinching tasks) are uniquely pertinent in LMI upper extremity amputations. ²²

This study is not without limitations. Prior to 2019, NEISS only allowed for the coding of a single diagnosis, and a single body part, which may have led to incomplete estimations in the present study. This is uniquely applicable regarding lawn mower–associated injuries in light of their propensity toward causing polytraumatized patient presentations. Due to NEISS parameters of instability regarding population-based estimations, multiple age-specific cohort estimations were unable to be collected (Figure 1). Furthermore, as alluded to in previous NEISS studies, the referenced database relies on patients who present to emergency departments, as well as the accuracy of the data recorded, ⁷ which limits both potential sensitivity and specificity in the present study. Finally, the epidemiological data collected per the NEISS database is incomplete regarding medical comorbidities and comprehensive demographic variables, among additional modifiable risk factors such as lawn mower model, time of year, and prior individual lawn mower expertise. Additional research, which incorporates complimentary sources of data, may help provide a broader understanding of the epidemiology and mechanisms of these injuries.

This investigation illuminates the complex public health obstacles inherent to lawn mower upper extremity amputations and provides key epidemiological data that may prove useful in curbing patient-specific and injury-specific risk factors associated with these injuries. These data offer the opportunity to develop targeted prevention strategies and policies on the end of the product manufacturers and regulators, as well as the prospective treatment interventions on the part of prospective managing physicians. Moving forward, additional research into the causes and factors surrounding these injuries may help promote safer practice and lead to a significant decline in the incidence of these preventable, catastrophic injuries.