Pediatric Tree House–Related Injuries Treated in Emergency Departments in the United States: 1990–2006

Abstract

Objectives:  The objective was to describe the epidemiology of tree house–related injuries in the United States among children and adolescents.

Methods:  The authors conducted a retrospective analysis using data from the National Electronic Injury Surveillance System for patients ≤19 years who were treated in an emergency department (ED) for a tree house–related injury from 1990 through 2006.

Results:  An estimated 47,351 patients ≤19 years of age were treated in EDs for tree house–related injuries over the 17-year study period. Fractures were the most common diagnosis (36.6%), and the upper extremities were the most commonly injured body part (38.8%). The odds of sustaining a head injury were increased for children aged <5 years. Falls were the most common injury mechanism (78.6%) and increased the odds of sustaining a fracture. Falls or jumps from a height ≥10 feet occurred in 29.3% of cases for which height of the fall/jump was recorded. Boys had significantly higher odds of falling or jumping from a height of ≥10 ft than girls, and children 10 to 19 years old also had significantly higher odds of falling or jumping from a height of ≥10 feet, compared to those 9 years old and younger. The odds of hospitalization were tripled if the patient fell or jumped from ≥10 feet and nearly tripled if the patient sustained a fracture.

Conclusions:  This study examined tree house–related injuries on a national level. Tree house safety deserves special attention because of the potential for serious injury or death due to falls from great heights, as well as the absence of national or regional safety standards. The authors provide safety and prevention recommendations based on the successful standards developed for playground equipment.

Building and playing in tree houses is widely considered a rite of passage for young children. Unfortunately, the very nature of tree houses, which involves their placement in trees, often at significant heights, creates the potential for catastrophic and life-threatening injuries.

Falls are the leading cause of unintentional injury in children¹ and the second leading cause of death from unintentional injury after motor vehicle crashes.² In 2002, falls resulted in more than 2.3 million visits to U.S. emergency departments (EDs) for children 14 years of age and younger, and the cost of these injuries can be high.^1,3–5 Deaths resulting from falls numbered 20,426 in 2005, with 211 deaths among children ≤20 years of age (approximately 1% of all fall-related fatalities), including 87 deaths among children ≤15 years of age.⁶ These fatalities in children are often the result of falls from heights greater than two stories (22 feet).²

Injuries from falls are preventable, and therefore, identifying modifiable risk factors can lead to interventions that reduce or eliminate these injuries.⁷ In 2000, falls resulted in the greatest total lifetime costs (more than $10 billion) among children and adolescents ages 5 to 14 years of age.⁸ In a July 1993 study of 93 children who fell from heights (windows, balconies, etc.), the average cost of hospitalization per child was estimated to be $5,000–$8,000.⁵ Falls from playground equipment are the second most common type of fall-related injury among children⁷ and have been shown to be the most common type of fall injury among 5- to 12-year-olds.⁹ It is estimated that from 1996 through 2005, there were more than 2 million playground equipment–related injuries to children ≤18 years old treated in hospital EDs in the United States. The leading mechanism of injury was falls (75%).¹⁰ Falls from playground equipment result in more severe injuries than most other common childhood injury mechanisms.¹¹ Nearly 200 studies on fall injuries from playground equipment have been published.

However, to our knowledge, no previous research has addressed tree house–related injuries despite many of the same risks, injury types, and injury mechanisms as playground injuries and other falls from heights. The objective of this study was to describe national patterns of tree house–related injuries treated in U.S. EDs to fill an important gap in the literature. More specifically, we wanted to characterize the associations between injury diagnosis, mechanism of injury, injured body part, and injury disposition. We tested the following hypotheses: 1) among tree house–related injuries, fractures are the most common injury diagnosis and are most likely to occur to the arm (defined as upper and lower arm including elbow, wrist, hand, and finger); 2) injuries resulting from falls account for the majority of tree house–related injuries; and 3) the height of falls is a significant predictor of injury severity.

Methods

Study Design and Population

This was a retrospective analysis of data from the National Electronic Injury Surveillance System (NEISS) for patients ≤19 years who were treated in an ED for a tree house–related injury from 1990 through 2006. The institutional review board of the Research Institute at Nationwide Children’s Hospital approved this study.

Study Protocol

Data were obtained from the NEISS of the U.S. Consumer Product Safety Commission (CPSC). The NEISS is a stratified probability sample of approximately 100 U.S. hospital EDs, including seven children’s hospitals, representing 6,100 hospitals with more than six beds and a 24-hour ED.¹² The NEISS provides data on consumer product–related and sports activity–related injuries treated in the sampled EDs.¹² Dedicated NEISS coders at each hospital abstract information from patient medical charts and record data on several variables, including patient’s age, sex, race, injury diagnosis, and body part injured, as well as the product or activity involved, disposition of the case, and a brief narrative describing the incident.¹² An example of a narrative, quoted from the NEISS used in this study, is “PATIENT FELL 8 FT OUT OF TREEHOUSE AT HOME, LANDED ON SHOULDER; SHOULDER/HUMERUS FX.” The national estimates generated in this study were based on weighted data for 1,360 patients ≤19 years of age treated for tree house–related injuries in U.S. EDs from January 1, 1990, to December 31, 2006.

Case-selection Criteria.  All cases identified by the NEISS consumer product code 1234 for “tree houses or playhouses” were selected for the 17-year period. After a preliminary review of case narratives by one author (CR), criteria for inclusion and exclusion were developed and additional variables were created. A random subset of 100 cases was then reviewed by two authors (US, LBM) to verify consistency of the inclusion and exclusion criteria and the coding of new variables. Any discrepancies were resolved by discussion, with ambiguous cases eliminated from the study and ambiguous variables coded as missing. Tree houses were defined as structures, most likely used for play and/or recreation, built and/or installed in or around a tree and elevated from the ground. Cases were included if the injury was caused by something intrinsic to the tree house, specifically, direct interaction with its parts and/or features (e.g., building/installing, playing in, or falling/jumping from a tree house). Cases involving “playhouses,”“clubhouses,”“forts,” and “dollhouses” were excluded because many were described as small, indoor, and/or plastic and most likely resulted in injury mechanisms that were distinct from tree house–related injuries. Cases were excluded if the tree house did not contribute to the incident or tree house play/building was not the primary activity. For example, if a child fell off of a bicycle and hit part of a tree house, if a patient tripped “near a tree house,” or if a child was punched in a tree house, the case was excluded. All cases of patients ≥20 years were excluded.

Variables.  Data regarding each patient’s age, body part(s) injured, locale where injury occurred, and case disposition were coded into categorical variables. Age was categorized into 5-year increments (<5 years, 5 to 9 years, 10 to 14 years, and 15 to 19 years). Body parts were categorized into the following body regions: head and/or face, upper trunk (including shoulders and neck), arm (upper and lower arm including elbow, wrist, hand, and finger), leg (upper and lower leg including knee, ankle, foot, and toe), lower trunk, and other (pubic region, 25% to 50% of body, and all parts of body). Injury diagnoses were categorized as follows: fracture, contusion/abrasion, laceration, strain/sprain, internal organ injury (including concussion), and other (including puncture, dislocation, foreign body, hematoma, dermatitis/conjunctivitis, hemorrhage, avulsion, dental injury, and other, but excluding cases in which diagnosis was unknown or not stated). The locale or place where an injury occurred was categorized as home or other (which included “recreational facility,”“school,”“street/highway,” and “other public property”). Case disposition was categorized as hospitalized (which included “treated and transferred to another hospital,”“treated and transferred for hospitalization,”“treated and admitted for hospitalization,” or “held for observation”) and not hospitalized (which included “treated and released” or “examined and released without treatment”). Cases were coded as missing for patients who left without being seen, left against medical advice, or were not documented.

Case narratives were used to generate several new variables. Injury mechanism was categorized as a fall, jump, or other (including object fell on patient, patient hit into object, nonfalling object hit patient, injured while building, interaction with dangerous materials, structural failure, and extra devices). The distance in feet that a patient fell before landing on the ground was recorded as height of fall, and these heights were then used to create several new categorical height variables. Element of the tree house that contributed to injury included ladder, rope/swing/chain, and dangerous materials such as exposed nails and broken glass.

Data Analysis

Data were analyzed using SPSS Version 14.0 (SPSS Inc., Chicago, IL) and Stata SE version 10.0 (StataCorp., College Station, TX). Summary statistics (means, standard deviations [SDs], and proportions) were calculated to describe the characteristics of the sample. Sample weights assigned to each case were based on the inverse probability of selection. Statistical analyses accounted for the complex survey sample design of NEISS and consisted of univariate logistic regression to produce odds ratios (ORs) along with associated 95% confidence intervals (CIs). Means are reported with associated SDs, and proportions are reported along with 95% CIs. Linear regression was used to analyze trend data for the number of tree house–related injuries over time. All data reported in this article are national estimates, unless otherwise specified as actual unweighted cases.

Results

Demographics and Overall Injury Trends

From 1990 through 2006, there were an estimated 47,351 (95% CI = 40,257 to 54,445) visits to EDs in the United States for tree house–related injuries among children ≤19 years, yielding an annual average of 2,785 visits per year. Males represented 32,873 cases (69.5%; 95% CI = 66.6% to 72.3%). Patients ranged in age from 12 months to 18 years, with a mean age of 8.1 years (SD ± 3.41) and a median age of 8 years (Figure 1). Table 1 contains the actual unweighted counts, as well as national estimates and frequency of tree house–related injuries for the variables in this study. The number of injuries sustained was highest for 5- to 9-year-olds (52.8%; 95% CI = 49.9% to 55.7%). Patients were hospitalized in 3,135 cases (6.6%; 95% CI = 5.0% to 8.8%). Among the 33,102 cases for which locale was recorded, 31,448, or 95.0% of cases (95% CI = 91.9% to 97.0%), occurred at home. Tree house–related injuries were most common in the summer (36.7%), with the highest single monthly injury incidence occurring in August (13.9%). Yearly frequencies and injury trends are shown in Figure 2. There was a significant yearly decrease based on linear regression of estimated yearly injuries (p < 0.05).

Figure 1.  Estimated number of tree house–related injuries by child’s age and sex from January 1, 1990, through December 31, 2006.

Table 1.   Characteristics of Tree House–Related Injuries to Children ≤19 Years Old Treated in U.S. EDs, 1990–2006

Characteristic	Actual cases (n)	National estimates (N)*	Percent†	95% CI
CI = confidence interval; CPSC = Consumer Product Safety Commission; NEISS = National Electronic Injury Surveillance System. *National estimates were calculated by applying statistical weights provided by the CPSC/NEISS to observed counts; estimates of <1,200 or observations <20 should be viewed as potentially unstable. †Percentages may not add to 100.0 due to rounding. ‡Including puncture, dislocation, foreign body, hematoma, dermatitis/conjunctivitis, hemorrhage, avulsion, dental injury, and other, but excluding cases in which diagnosis is unknown or not stated. §Upper and lower arm, including elbow, wrist, hand, and finger. ||Upper and lower leg, including knee, ankle, foot, and toe. ¶Upper trunk, shoulders, and neck. **Pubic region, 25%–50% of the body, and all parts of body. ††Includes patients who were “treated and transferred to another hospital,”“treated and transferred for hospitalization,”“treated and admitted for hospitalization,” or “held for >24 hours observation.” ‡‡Patients who were “treated and released or examined and released without treatment.” §§Includes school, recreational facility, street/highway, and other public property. ||||Includes patient hit object, injured while building, interaction with dangerous materials, object fell on patient, nonfalling object hit patient, structural failure, and extra devices (e.g., electrical).
Age (years)	1,360	47,350	100.0
<5	203	6,669	14.1	11.5, 17.2
5–9	742	25,020	52.8	49.9, 55.7
10–14	380	14,010	29.6	26.2, 33.3
15–19	35	1,651	3.5	2.4, 5.1
Gender	1,359	47,284	100.0
Male	953	32,873	69.5	66.6, 72.3
Female	406	14,411	30.5	27.7, 33.4
Diagnosis	1,318	46,154	100.0
Fracture	524	16,871	36.6	32.6, 40.7
Contusion/abrasion	246	9,296	20.1	17.4, 23.1
Laceration	232	9,116	19.8	17.4,22.3
Strain/sprain	123	4,963	10.8	8.6, 13.3
Internal organ injury (including concussions)	125	3,157	6.84	5.11, 9.09
Other‡	68	2,750	5.96	4.32, 8.16
Body region injured	1,350	47,073	99.9
Arm§	562	18,286	38.8	35.6, 42.2
Head/face	334	11,361	24.1	21.3, 27.2
Leg||	245	9,968	21.2	17.9, 24.9
Upper trunk¶	118	4,277	9.1	7.5, 11.0
Lower trunk	76	2,565	5.4	4.0, 7.4
Other**	15	616	1.3	0.6, 2.8
Disposition	1,354	47,239	100.0
Hospitalized††	102	3,135	6.6	5.0, 8.8
Not hospitalized‡‡	1,252	44,104	93.4	91.2, 95.0
Location of event	932	33,102	100.0
Home	887	31,448	95.0	91.9, 97.0
Other§§	45	1,654	5.0	3.0, 8.1
Injury mechanism	1,359	47,280	100.0
Fall	1,116	37,167	78.6	75.1, 81.7
Jump	83	3,410	7.2	5.6, 9.2
Other||||	160	6,703	14.2	11.9, 16.8
Height of fall/jump (feet)	334	12,646	100.0
<5	59	2,668	21.1	15.8, 27.6
5–9.9	181	6,276	49.6	43.3, 56.0
10–14.9	69	2,905	23.0	16.8, 30.6
≥15	25	797	6.3	3.5, 11.1

Figure 2.  Number of estimated tree house–related injuries by year. Estimates are represented by the solid line, and upper and lower bounds of the corresponding 95% CI are represented by dashed lines.

Injury Diagnoses and Body Region Injured

Fractures were the most common injury type (36.6%; 95% CI = 32.6% to 40.7%), followed by contusions and abrasions (20.1%; 95% CI = 17.4% to 23.1%) and lacerations (19.8%; 95% CI = 17.4% to 22.3%). However, for children <5 years of age, contusions and abrasions were the leading diagnosis (26.2%), while lacerations were the second leading injury diagnosis for boys (21.1%). The odds of hospitalization were 2.71 (95% CI = 1.70 to 4.30) times greater for fractures than for other diagnoses.

The arm was the most common body area injured (38.8%; 95% CI = 35.6% to 42.2%), followed by the head and/or face (24.1%; 95% CI = 21.3% to 27.2%). Fractures were the most common injury type for arms (73.3%) and for legs (55.0%; Figure 3). The odds of sustaining a fracture were 11.50 times greater (95% CI = 8.10 to 16.34) when injuring an arm compared with another body part and 14.52 times greater (95% CI = 9.77 to 21.59) when injuring an arm specifically from a fall. The most common injury for the head and/or face was a laceration (42.1%), and the odds of sustaining a laceration (compared with another diagnosis) were 5.25 times greater (95% CI = 3.23 to 8.61) for the head and/or face when compared to other body parts. The most common injury for the upper and lower trunk was a contusion or abrasion (47.3%), and the odds of sustaining a contusion or abrasion (compared with another diagnosis) were 4.91 times greater (95% CI = 3.20 to 7.54) for the upper and lower trunk when compared to other body parts. The odds of a head injury (compared with another diagnosis) were 3.69 times greater (95% CI = 2.31 to 5.90) for children <5 years (compared with all older children) and 5.58 times greater (95% CI = 3.23 to 8.61) for children <5 years when looking only at falls.

Figure 3.  Percentage of injury diagnoses by body region for children ≤19 years treated in U.S. emergency departments (EDs) for tree house–related injuries.

Injury Mechanism and Height of Falls

Falls were the most common injury mechanism overall (78.6%; 95% CI = 75.1% to 81.7%), while jumps accounted for 7.2% of injuries (95% CI = 5.6% to 9.2%; Table 1). Fall-related injuries resulted in hospitalization 7.8% of the time, whereas injuries from jumps resulted in hospitalization 3.4% of the time.

The odds of sustaining a fracture were 3.92 times greater (95% CI = 2.46 to 6.25) for falls than for other mechanisms. Injuries from falls were most often sustained to the arm (43.2%) and injuries from jumps were most often sustained to the leg (67.6%), specifically the foot and ankle (53.0%). The odds of injuring the arms or trunk (upper and lower) were 3.55 times greater (95% CI = 2.47 to 5.11) for falls than for other mechanisms. Strains and sprains accounted for 23.8% of injuries from jumps, compared to 11.0% of injuries from falls.

Ladders were involved in an estimated 3,401 cases (7.2%); swings, ropes, or chains in 1,272 cases (2.7%); and dangerous materials such as exposed nails or broken glass in 2,717 cases (5.7%). Among the cases in which the height of a fall or jump was recorded (estimated 12,646 cases), the mean height was 7.7 feet (SD ± 3.66 feet), and the range was <1 to 25 feet. A total of 29.3% of injuries from falls and jumps occurred from a height of ≥10 feet and 6.3% occurred from a height ≥15 feet. The percentage of fall/jump injuries that resulted in hospitalization increased with height (Figure 4), and the odds of being hospitalized were 3.00 times greater (95% CI = 1.14 to 7.88) for falls or jumps from ≥10 feet (compared to <10 feet). Finally, the height of a fall or jump was related to both age and gender. Boys had significantly higher odds of falling or jumping from a height of ≥10 feet (vs. <10 feet) than girls (OR = 3.45; 95% CI = 1.57 to 7.58). Likewise, children 10- to 19-years-old had significantly higher odds of falling or jumping from a height of ≥10 feet (vs. <10 feet) compared to those 9 years old and younger (OR = 3.96; 95% CI = 2.06 to 7.64). For cases that reported the height of falls and jumps, the odds of injury from a height ≥10 feet (vs. an injury from <10 feet) were 3.96 times greater (95% CI = 2.06 to 7.64) for 10- to 19-year-olds compared to children <10 years and 3.45 times greater (95% CI = 1.57 to 7.58) for boys compared to girls.

Figure 4.  Percentage of injuries due to a jump or fall that resulted in either hospitalization or release, categorized by the height of the fall/jump. The odds of hospitalization (versus release) were three times greater for falls/jumps from a height of 10 feet or greater compared to a height of less than 10 feet.

Discussion

To our knowledge, this is the first published study to examine tree house–related injuries treated in U.S. EDs. We used nationally representative data spanning a 17-year period to examine patterns and trends of tree house–related injuries among children ≤19 years. Falls were the most common injury mechanism (more than three-quarters of all injuries), a pattern similar to playground injuries.^10,13 In addition, many of the falls in our study were from significant heights—approximately 30% from ≥10 feet and more than 6% from ≥15 feet. Some cases reported falls from as high as 20 to 25 feet. Furthermore, a fall from ≥10 feet tripled the odds of hospitalization. Fractures were the most common injury diagnosis, and the arm was the body part most commonly injured. Greater than one in four tree house–related injuries were diagnosed as a fracture to the arm.

Consistent with our findings, previous studies on falls and playground injuries have shown that fractures (often to the upper limbs) are the most common type of injury,^{2–5,9,10,13–30} that injury severity increases with height of fall,^{1–4,16,17,20,21,23,26–28,31–33} and that boys are injured more often than girls.^{2–5,11,15–18,23,26,29,30,34–39} Risk-taking behavior has been found to be more common in males than in females and in older children compared with younger children.¹¹ This may explain why we found that boys had a higher frequency of injuries and why the odds of falling from ≥10 feet were greater for boys compared to girls and for 10- to 19-year-olds compared to children <10 years. We also found that among falls, children <5 years of age had about five times greater odds of a head injury. This may be the result of younger children having larger heads and a higher center of gravity, which predisposes them to fall head first.^{9,15,27,40,41}

When comparing falls and jumps, several trends are apparent. Jumps typically resulted in leg injuries, whereas falls typically resulted in arm injuries, possibly because of attempts to break a fall with an outstretched arm. A greater percentage of fall injuries required hospitalization than jump injuries, perhaps due to the relative control and balance associated with jumps versus falls. In addition, the percentage of sprains and strains was higher for jumps than falls, reflecting the high incidence of ankle sprains.

After a landmark paper by Illingworth and colleagues¹⁸ on the dangers of playground equipment in 1975, safety standards regarding height and surface type were soon adopted for playgrounds in Europe, Australia, and the United States²⁴ and are now commonplace. However, tree houses and homemade playgrounds have not had the same regulation or oversight. Standards for construction are minimal and vary by location. For example, at the location of this study (Columbus, OH), there are no regulations for tree houses unless the structure is >169 feet² (personal communication, Columbus Building Services Division, Columbus, OH, 2008). This lack of centralized regulation may explain why the 2001 CPSC report on playgrounds found that almost 80% of public playgrounds had protective surfacing on the ground, whereas only 9% of home equipment did, and of the 128 child deaths on playgrounds that were reported between 1990 and 2000, 70% occurred at home.¹³

The two most prevalent risk factors for serious injury in the literature on fall and playground injuries are increased height,^{1–4,16,17,20,21,23,26,28,31–33} and hard, non–impact-absorbing surfaces.^{1,2,5,23,31,34,42–45} Therefore, our recommendations for tree house safety are modeled after standards developed by the CPSC and the American Society for Testing and Materials (ASTM) for playground safety and address height, surfacing, construction, and age of children using the tree house. Stricter safety standards already exist for playgrounds designed for 2- to 5-year-olds compared to those for 5- to 12-year-olds.⁴⁶ Supervision is recommended, and children ≤5 years of age should never play in tree houses unless accompanied by an adult. For playgrounds, a minimum of 9 inches of compressed wood mulch is recommended for ground surface beneath platforms ≤10 feet high.⁴⁷ Organic surfacing has not been found to have adequate shock absorbing properties to prevent life-threatening head injuries in falls greater than 10 feet.⁴⁷ Tree houses should be built low to the ground and never >10 feet high. Additionally, a minimum of 9 inches of protective surfacing such as wood mulch should be used in a 72-inch zone around the structure. (Note that wood chips, sand, and gravel may not provide sufficient safety protection for structures >5–6 feet high.) Barriers, not guardrails, should be used for all platforms >4 feet, with a minimum barrier height of 38 inches. Ropes or similar devices such as chains should be avoided because of strangulation hazards. Climbing ropes should be secured at both ends and not be long enough to create a loop with a 5-inch or greater perimeter. To prevent entrapment, any completely bound openings in the structure should be <3.5 or >9 inches in diameter. Ensure structural integrity by choosing a strong and sturdy tree and quality building materials. Examine the tree roots and do not build in a tree with disease such as fungus or damaged bark at the base. Branches that extend at a 90° angle are strongest; do not use branches that are ≤8 inches thick.⁴⁷ Keep the structure free of dangerous materials such as exposed nails or broken glass.

Limitations

Neither national statistics nor estimates are available regarding the existing number of tree houses or the demographics related to tree house builders or users. NEISS data only include cases that present to U.S. EDs and therefore exclude injuries that present to urgent care facilities, pediatricians, and family physicians. In addition, fatalities are not well sampled by NEISS, and thus we have no information regarding the number of fatalities resulting from tree house–related injuries. Some of our analysis relied on data from case narratives, which may have been incomplete or inconsistent. The majority of narratives lacked details about the height of falls, the type of ground surface, and the type of activity leading up to the injury. In addition, injuries are only coded as a single main diagnosis, thereby potentially missing different types of injuries incurred by one patient. The NEISS only reports one main diagnosis and one main body part, unless the injury involves multiple body parts, in which case there is a category for 25% to 50% of body, or 100% of body.

Conclusions

Tree houses deserve special attention because of the potential for dangerous falls from great heights and the absence of centralized safety standards. Considering this unique status of tree houses, the lack of research on injuries associated with them, the analogous dangers to playground equipment, and the evident worldwide interest in playground-related injuries, this study fills an important gap in the literature on pediatric injuries. To reduce the number and severity of tree house–related injuries, we provide safety and prevention recommendations based on successful current standards for playground equipment.