An analysis of injury claims from low-seam coal mines

Sean Gallagher ⁎,

⁎ Corresponding author.

E-mail address: sfg9@cdc.gov (S. Gallagher).

Susan Moore, Patrick G. Dempsey

National Institute for Occupational Safety and Health, Mining Injury Prevention Branch, PO Box 18070, Pittsburgh, PA 15236-0070, USA

abstract

Introduction: The restricted workspace present in low-seam coal mines forces workers to adopt awkward

working postures (kneeling and stooping), which place high physical demands on the knee and lower back.

Method: This article provides an analysis of injury claims for eight mining companies operating low-seam

coal mines during calendar years 1996-2008. All cost data were normalized using data on the cost of medical

care (MPI) as provided by the U.S. Bureau of Labor Statistics. Results: Results of the analysis indicate that the

knee was the body part that led in terms of claim cost ($4.2 million), followed by injuries to the lower back

($2.7 million). While the average cost per injury for these body parts was $13,100 and $14,400, respectively

(close to the average cost of an injury overall), the high frequency of these injuries resulted in their preeminence in terms of cost. Analysis of data from individual mining companies suggest that knee and lower

back injuries were a consistent problem across companies, as these injuries were each among the top five

most costly part of body for seven out of eight companies studied. Application/Impact: Results of this

investigation suggest that efforts to reduce the frequency of knee and low back injuries in low-seam mines

have the potential to create substantial cost savings.

1. Introduction

Low-seam coal mines (mines having a coal seam of 1.2 m or less)

compel workers to adopt postures that impose significant physical

loading on the musculoskeletal system (Gallagher, 2005). The limited

vertical space in these mines prohibits upright standing, and workers

must spend the entirety of their work shift in kneeling or stooping

postures. Not surprisingly, frequent kneeling has been associated with

an increased risk of knee disorders, including knee-joint inflammation,

bursitis, and osteoarthritis (Sharrard,1963; Myllymaki, Tikkakoski, Typpo,

Kivimaki, & Suramo, 1993; Manninen, Heliovarra, Riihimaki, & Suomalainen, 2002). The stooping posture has similarly been associated with an

increased risk of low back disorders. Such postures have been associated

with up to an 8-fold increase in low back disorders among autoworkers

(Punnett, Fine, Keyserling, Herrin, & Chaffin, 1991), and also have been

associated with degenerative changes in the lumbar spines of underground mine workers (Lawrence, 1955; Brinckmann, Forbin, Biggemann,

Tillotson, & Burton, 1998). Given these relationships, it is important to develop an awareness of the societal burden associated with these injuries.

One approach to better understanding the relative importance

of different types of occupational injuries and illnesses with respect

to incidence and severity is to analyze administrative databases. An

example is workers compensation (WC) records, which have been

analyzed for several research purposes. Examples include analysis by

antecedent event to prioritize a research agenda (Murphy, Sorock,

Courtney, Webster, & Leamon, 1996), analysis within claims attributed

to certain occupational exposures to better understand research and

practice needs for that exposure (Dempsey & Hashemi, 1999), and

analysis of a specific body part and nature of injury combination to

understand jurisdictional variations in cost (Webster & Snook, 1994).

One important source of accident/injury data in mining is the Mine

Safety and Health Administration (MSHA) database. Stobbe, Bobick,

and Plummer (1986) used these data to estimate the burden of MSDs

in underground coal and metal/nonmetal mines. In both industry segments, the back accounted for over 50% of reported strains/sprains,

and was usually attributed to materials handling activities. For coal,

knees had the highest mean days lost per strain/sprain with a mean of

30.8 days lost in 1984 compared to 21.1 days lost for the back. More

recently, Moore, Bauer, and Steiner (2008) used the MSHA database to

examine trends in the incidence of musculoskeletal disorders (MSDs)

by comparing 1983-1984 data with 2003-2004 data. During that time

period, low-back MSDs decreased from 41% to 31% of the reported

injuries/illnesses while knee MSDs increased from 9% to 17%.

One drawback of the MSHA database is that it does not contain

information regarding the financial costs associated with specific accidents or injuries. As a current research initiative at the National Institute for Occupational Safety and Health (NIOSH) Pittsburgh Research

Laboratory is targeted toward reducing knee disorders in underground coal mines, researchers were interested in obtaining WC costs

of knee injuries in low-seam coal mines, and comparing these costs to

injuries involving other parts of the body. Appreciation of the financial
costs associated with these injuries may help motivate intervention

strategies to reduce injury risk in low-seam coal mines.

2. Methods

Injury claims from eight coal mining companies operating lowseam mines were obtained from a cooperating insurer. These claims

were comprehensive in that they represented the totality of claims

submitted to the insurance company by the various mining companies

over a particular time frame. Researchers were unaware of the company names or locations as the data were provided in a format where

mine operators were identified by different letters of the alphabet.

Data from these mining companies were provided for differing time

frames, ranging from a low of 4.75 years to a high of 12.0 years, dependent on the length of time for which the companies were insured

with the cooperating insurance company. All data provided for this

analysis were collected during the years ranging from 1996-2008 inclusive. The average length of time for which data were provided by a

given company was 7.8 years± 2.4 SD. Unfortunately, the staggered

starting and ending times of coverage for the various companies made

it impossible to assess overall injury trends. Thus, researchers focused

on analyzing the data with respect to the cost of injuries to various

parts of the body.

Costs for medical claims for each mining company were indexed

for inflation by using data on the cost of medical care (MPI) as provided by the U.S. Bureau of Labor Statistics (www.bls.gov). Since the

time frames for company data often spanned two calendar years, the

inflation adjustment was performed using the monthly MPI data. For

example, if cost data were provided for a company for the time period

May 1, 2004 through May 1, 2005 the monthly MPI data were obtained

from the BLS and the average of the MPI for the 12 months from May

2004 through April 2005 was calculated. This value was used to adjust

the cost of the claims for inflation.

Table 1

Summary of costs by body part over all low-seam coal operating companies (May 2008

dollars).

Body Part Frequency Cost % Total Cost Average Cost/

Injury

Knee 318 $4,172,600 17.39 $13,100

Lower back 187 $2,688,600 11.20 $14,400

Multiple body parts 52 $1,947,200 8.11 $37,400

Whole Body 10 $1,706,100 7.11 $170,600

Shoulders 84 $1,324,200 5.52 $15,800

Finger(s) 175 $1,209,000 5.04 $6,900

Soft Tissue 33 $1,143,200 4.76 $34,600

Disc (Lumbar) 2 $848,200 3.53 $424,100

Multiple body systems 7 $801,300 3.34 $114,500

Multiple trunk 5 $746,900 3.11 $149,400

Chest 27 $730,300 3.04 $27,000

Lung 22 $652,200 2.72 $29,600

Upper arm 22 $564,200 2.35 $25,600

Pelvis 11 $527,600 2.20 $48,000

Foot 53 $501,100 2.09 $9,500

Lower leg 23 $483,600 2.02 $21,000

Thigh / upper leg 17 $430,200 1.79 $25,300

Hand 106 $426,300 1.78 $4,000

Hip 6 $362,500 1.51 $60,400

Eye(s) 91 $317,700 1.32 $3,500

Ankle 26 $290,200 1.21 $11,200

Elbow 36 $251,300 1.05 $7,000

Abdomen (including groin) 45 $243,900 1.02 $5,400

Multiple upper extremity 8 $213,400 0.89 $26,700

Toe(s) 7 $190,600 0.79 $27,200

Vertebrae 1 $179,700 0.75 $179,700

Wrist 45 $163,500 0.68 $3,600

Great toe 1 $110,700 0.46 $110,700

Ear(s) 20 $99,400 0.41 $5,000

Thumb 29 $96,500 0.40 $3,300

Other facial soft tissue 49 $92,400 0.39 $1,900

Buttocks 2 $92,000 0.38 $46,000

Lower arm 34 $79,000 0.33 $2,300

Upper back 41 $76,000 0.32 $1,900

Wrist(s) and Hand(s) 8 $40,900 0.17 $5,100

Facial bones 3 $32,500 0.14 $10,800

Nose 14 $31,200 0.13 $2,200

Internal Organs 8 $29,400 0.12 $3,700

Multiple lower extremities 6 $25,500 0.11 $4,300

Multiple neck injury 3 $22,500 0.09 $7,500

Teeth 12 $11,600 0.05 $1,000

Disc (Cervical) 1 $11,600 0.05 $11,600

Skull 7 $10,900 0.05 $1,600

Mouth 9 $5,600 0.02 $600

Sacrum and coccyx 3 $5,400 0.02 $1,800

Multiple head injury 6 $5,000 0.02 $800

Artificial appliance 2 $1,600 0.01 $800

Brain 1 $1,200 0.00 $1,200

No physical injury 1 $500 0.00 $500

Total 1678 $23,997,000 100.00 $14,300

Table 2

Injury frequency, total costs, and average cost per injury for individual mining

companies.

Mining

Company

Time Frame Injury

Frequency

Total Cost Average Cost/

injury

C 9/1/1996 - 9/1/2005 168 $ 2,225,800 $ 132,500

B 5/1/2001 - 5/1/2008 136 $ 3,351,600 $ 24,600

I 6/1/1996 – 7/1/2005 277 $ 5,259,700 $ 19,000

D 8/1/1996 - 8/1/2003 60 $ 1,014,600 $ 16,900

J 5/1/1996 – 5/1/2008 347 $ 5,326,600 $ 15,400

H 8/1/2003 – 5/1/2008 534 $ 5,669,800 $ 10,600

F 11/1/1999 - 5/1/2008 126 $ 974,900 $ 7,700

G 2/15/2000 - 2/1/2005 31 $ 174,100 $ 5,600

The time frame represents the period during which claim data was available for each

individual company.

3. Results

For ease of presentation, all cost data in this article have been

rounded to the nearest hundred dollars. Table 1 provides a summary

of costs by the part of body injured for all of the low-seam coal mines

studied in order of descending total cost. As can be seen in this table,

several of the leading body parts affected by injury are associated with

the musculoskeletal system. In particular, injuries to the knee and

lower back are the two leading body parts in terms of injury cost and

together are responsible for 28.6% of the total costs incurred by the

eight mining companies studied. These two body parts also lead in

terms of injury frequency in these data. In fact, the average cost of an

individual injury to the knee or back ($13-14K) ranks very close to the

mean cost for all injuries; however, the high frequency with which

these injuries occur leads to their pre-eminence in terms of cost.

Shoulders ranked as the fifth most costly part of body injured (and had

the fifth highest injury frequency), and accounted for an additional

5.5% of the total injury cost.

In discussing the costs associated with musculoskeletal injuries,

it may also be noted that injuries to lumbar (low back) spinal discs

ranked eighth in terms of total cost with a frequency of only two

injuries. The cost of these two injuries ($848,200) was driven by a

single case that was over $750,000 by itself, and made lumbar disc

injuries by far the leader in terms of average cost per injury. If one

considers injuries to the lumbar discs as a type of lower back injury,

the combined cost of these injuries increases to over $3.5 million.

Besides the injuries to body parts discussed above, the top 10 most

costly include several categories that involve injury to multiple body

parts or systems. Four such categories appear in the top 10 most costly

injuries, including: multiple body parts (3rd), whole body (4th),

multiple body systems (9th), and multiple trunk (10th). These injuries

tend to have a relatively low frequency of injury (i.e., a frequency of 10

or less for three of these four categories) but a relatively high average

cost. Unfortunately, it is difficult to interpret the nature of these types

of injuries since it is unclear specifically what body parts or systems
were injured. However, it must be considered likely that a different

combination of parts or systems were injured for each instance thus

classified, making generalizations regarding these categories even

more difficult.

Rounding out the top 10 most costly body parts are fingers and

soft tissue injuries. Fingers had the third highest injury frequency

(175 cases), but had the lowest average injury cost of body parts

appearing in the top 10 ($6,900). Soft tissue injuries ranked 7th overall with just 33 instances and an above average cost of $34,600 per

injury. Overall the top 10 body parts injured accounted for 69% of the

total injury cost, with 40 other categories accounting for the balance.

Table 2 provides information regarding the injury frequencies and

cost for the individual companies operating low seam mines and

provides information regarding the time frame for which injury data

were available for each mine. Unfortunately, the authors did not have

specific denominator data for these mines, so the injury frequency and

cost data may simply reflect differences in the size of the workforce

at these different mining companies. There is wide variability of the

mining companies in terms of the average injury cost, which very well

may be influenced by one or a few claims in each case. Raw data were

not available to calculate median costs, which tend to exhibit less

variability. The lowest average injury cost of these companies is that of

company G ($5,600 per injury), which is more than four times lower

than that of mine B, which had the highest average cost of $24,600.

Table 3 provides information on a mine by mine basis on the top

five leading body parts injured in terms of cost incurred over the time

for which claim data were available from each company. As can be

seen from this table, each mine exhibits a unique combination of body

parts representing its top five most costly. However, as noted in Table 4,

certain body parts appear more frequently in the top five most costly

injuries across the eight companies studied. Specifically, the knee and

the lower back each appear in the top five most costly for seven out of

the eight companies operating in low-seam conditions. The shoulder

is the next most frequent body part, and appears in four of the eight

top five most costly injury lists. Multiple body parts, multiple body

systems, and abdomen (including groin) appear in the top five most

costly two times each, and the balance (comprising 16 body part categories) appear only one time each.

Table 3

Top five leading part of body injured in terms of percentage of total cost (May 2008 dollars) for individual mining companies (B-J).

B C D F G H I

1st Whole

Body

(50.3%)

Chest

(25.1%)

Soft

Tissue

(45.2%)

Finger

(59.7%)

Lower

back

(34.1%)

Lower

back

(23.0%)

Multiple

body parts

(24.6%)

Knee

(44.7%)

2nd Multiple

body

systems

(10.2%)

Lung

(19.1%)

Knee

(40.9%)

Great toe

(11.0%)

Ear

(21.3%)

Multiple

trunk

(11.2%)

Disc

(Lumbar)

(15.8%)

Pelvis

(9.4%)

3rd Knee

(9.5%)

Knee

(18.3%)

Lower

back

(3.1%)

Knee

(7.3%)

Shoulder

(17.1%)

Knee

(10.3%)

Shoulder

(13.1%)

Upper

arm

(6.3%)

4th Lower

back

(8.0%)

Lower

back

(12.2%)

Shoulder

(3.0%)

Ankle

(7.2%)

Abdomen

(including

groin)

(7.6%)

Multiple

body

systems

(8.6%)

Lower

back

(8.9%)

Hip

(6.1%)

5th Hand

(7.8%)

Shoulder

(3.5%)

Wrist

(1.4%)

Abdomen

(including

groin)

(3.8%)

Knee

(6.5%)

Multiple

body

parts

(6.4%)

Lower

leg (8.7%)

Lower

back

(6.1%)

Numbers in parentheses represent the percentage of total costs accounted for by the specified part of body.

J

Table 4

Frequency with which specific body parts appeared in the top 5 most expensive injuries

across the eight companies.

Number of times in top

5 across eight companies

Body Parts

7 Knee, Lower Back

4 Shoulders

2 Multiple Body Parts, Multiple body systems,

Abdomen (including groin)

1 Whole Body, Hand, Chest, Lung, Soft Tissue, Wrist,

Fingers, Great Toe, Ankle, Ear, Multiple Trunk, Disc,

Lower leg, Pelvis, Upper Arm, Hip

4. Discussion

The restricted workspace present in low-seam coal mines forces

workers to adopt awkward working postures (kneeling and stooping),

which place high physical demands on specific joints of the body. The

present analysis makes clear that both the knee and the lower back

have very high frequencies of injury in this environment, and the data

illustrate that knee injuries and lower back injuries are a consistent

problem across all of the mining companies studied. As a result of the

high frequency of injury to these two body parts, the costs associated

with knee and lower back injuries lead in terms of the injury burden

experienced in low-seam coal mines.

The findings of this analysis of injury claims are congruent with

other studies that have examined the effects of working in restricted

postures. With respect to the effects on the lower extremity, Sharrard

(1963) reported on the results of examinations on 579 coal miners in a

study examining the etiology of “beat knee.” Forty percent of the

miners reportedly were symptomatic or had previously experienced

symptoms, characterized as acute or simple chronic bursitis. Incidence

rates were found to be higher in seam heights lower than four feet and

in workers required to kneel for prolonged periods at the mine face.

The incidence of “beat knee” was found to be higher in younger mineworkers; however, this finding was thought to be due to a “healthy

worker” effect. Specifically, it was thought that older workers with

“beat knee” might have already left the mining profession.

Studies examining other occupations where frequent kneeling is

necessary have also found higher rates of knee problems than comparison occupational groups (Tanaka, Smith, Halperin, & Jensen, 1982;

Myllymaki et al., 1993; Coggon et al., 2000; Jensen, Mikkelsen, Loft,

& Eenberg, 2000; Sandmark, Hogstedt, & Vingard, 2000; Nahit,

Macfarlane, Pritchard, Cherry, & Silman, 2001; Manninen et al.,

2002). Tanaka et al. (1982) found that occupational morbidity ratios

for workers compensation claims involving knee-joint inflammation for carpet layers was over 13 times greater than that of carpenters,

sheet metal workers, and tinsmiths. Knee inflammation among tile

setters and floor layers were over six times greater than the same

comparison groups. Workers in these occupations have been shown

more likely to exhibit fluid accumulation in the superficial infrapatellar
bursa, subcutaneous thickening of this bursa, and increased thickness

in the prepatellar region (Myllymaki et al., 1993). The much higher

incidence associated with carpet layers is probably also related to their

use of a knee-kicker, a device used to stretch carpet during its installation. Knee impact forces during the use of this device have been shown

to be as high as four times body weight (Bhattacharya, Mueller, & PutzAnderson, 1985).

In terms of lower back injuries, an early study by Lawrence (1955)

examined British coal miners to identify factors related to degenerative disk changes, and found that injury, duration of heavy lifting,

duration of stooping, and exposure to wet mine conditions were the

factors most associated with spinal changes. Another study investigating spinal changes in miners was reported by MacDonald, Porter,

Hibbert, and Hart (1984). These investigators used ultrasound to

measure the spinal canal diameter of 204 coal miners and found that

those with the greatest morbidity had significantly narrower spinal

canals. The study by Lawrence (1955) suggests that the seam height of

the mine has a marked influence on the incidence of low back disorders. The finding of increased low back claims in conditions where

stooping is common is similar to other evidence relating non-neutral

trunk postures to low back disorders. For example, a case-control

study by Punnett et al. (1991) examined the relationship between

non-neutral trunk postures and risk of low back disorders. After

adjusting for covariates such as age, gender, length of employment,

and medical history, time spent in non-neutral trunk postures (mild

or severe flexion and bending) was strongly associated with back

disorders (OR 8.0, 95% CI 1.4-44). Although it was difficult in their

study to find subjects that were not exposed to non-neutral postures,

the strong increase in risk observed with both intensity and duration

of exposure were notable.

There is also evidence that the kneeling posture not only impacts

the frequency of knee injuries, but may affect low back pain rates, as

well. A study of 1773 randomly selected construction workers also

examined the effects of awkward working postures on the prevalence

rates of low back pain (Holmstrom, Lindell, & Moritz, 1992). This study

found that prevalence rate ratios for low back pain were increased for

both stooping (pb0.01) and kneeling (pb0.05) when the duration of

work in these postures were reported to be at least one hour per day.

Furthermore, a dose-response relationship was observed whereby

longer durations of stooping and kneeling were associated with increased prevalence rate ratios for severe low back pain.

Several limitations associated with our analysis must be noted.

Because individual claims costs were not available, means rather than

medians were reported. Medians are commonly used in analysis of

workers compensation claims to minimize the influence of outliers,

and the data provided to the authors did not allow for their use.

Additionally, claims cost overall was adjusted using medical inflation

because the component medical, indemnity, and other costs were not

available for individual claims. Since medical costs are often a reasonably high percentage of workers compensation claims for musculoskeletal disorders, the authors feel that this limitation would have only

a modest influence on the conclusions drawn.

5. Conclusions

Results of the current analysis of injury claims from low-seam coal

mines allow several conclusions to be drawn. One conclusion is that

musculoskeletal disorders as a whole represent a significant portion of

the total injury burden experienced by low-seam coal mines. Injuries

to three joints of the body (knee, lower back, and shoulder) represent

approximately one-third of the total costs of injuries experienced by

these mines. This finding is fairly consistent across the mining companies studied. Furthermore, it is apparent that the restricted vertical

space present in these mines, which obligates mine workers to adopt a

kneeling posture for the majority of the workday, exacts a significant

toll on the knee joint, making it the most frequent injury and most

costly body part in terms of injury claims. Although knee pads are

often used in these environments, these data suggest that kneepads

are not a sufficient means to control these injuries and that additional

measures need to be taken. Additional research is necessary to further

investigate the nature and severity of knee claims so that potential

preventive measures can be postulated and more effective safety and

health approaches developed.

Acknowledgements

The authors gratefully acknowledge the assistance of Rockwood

Casualty Insurance Company, who supplied the claims information

reported in this paper, and who provided valuable assistance and

guidance in this effort. The authors also gratefully acknowledge the

contributions of Diana Schwerha, PhD, Lisa Steiner, MS, and William J.

Wiehagen, MS in the development of this manuscript. Disclaimers:

Mention of any company or product does not constitute endorsement

by NIOSH. The findings and conclusions in this report are those of the

authors and do not necessarily represent the views of the National

Institute for Occupational Safety and Health.

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