PRESSURES APPLIED TO ANATOMICAL LANDMARKS OF THE KNEE WHILE IN KNEELING 

POSTURES 

Moore, Susan M.; Porter, William L.; Mayton, Alan G. 

National Institute for Occupational Safety and Health (NIOSH), Pittsburgh, PA, USA 

Email: SMMoore@cdc.gov, Web: http://www.cdc.gov/NIOSH/Mining/ 
	

INTRODUCTION 

According to the Mine Safety and Health 

Administration (MSHA) injury database, 

227 knee injuries were reported in 

underground coal m ining in 2007 [ 1]. Lowseam coal mines are those with extremely 

low working heights (<42”). Gallagher et. al 

[2] found that the average cost per knee 

injury in low-seam coal operations was 

$13,121.29. Thus, it can be estimated that 

the financial burden of knee injuries was 

nearly three million dollars in 2007. 

Pressure applied to the knee while kneeling 

and crawling is likely a risk factor. 

Typically, mine workers utilize kneepads to 

better distribute the pressures at the knee; 

however, their ability to reduce the stresses 

at the knee is unknown. The objective of this 

study was to determine the pressure applied 

to the knee during static postures used in 

low-seam mining while not wearing 

kneepads and while wearing two kneepads 

commonly used in the industry (one 

articulated and one non-articulated). 

METHODS 

Ten subjects (7 male, 3 female) with an 

average age of 34±17 ye ars (19 to 60 years) 

and an average weight and height of 683±98 

N and 168.7±8.0 cm, respectively, 

participated. The subjects simulated postures 

utilized in low-seam mines: kneeling in full 

flexion; kneeling at 90° of knee flexion; and 

kneeling on one knee. These postures were 

simulated with working heights of 38” and 

48” except for kneeling at 90°. This posture 

was performed only in 48”, since it is nearly 

impossible for adults at 38”. These postures 

were simulated for three kneepad states: no 

kneepads, non-articulated kneepads, and 

articulated kneepads. Testing order was 

randomized. 

A custom -made capacitive pressure sensor 1 

1

 Included 196 individual sensing units; Pressure 

Profile Systems, CA TactArray 

was used that was pre-shaped to the knee 

when it was at 90° of flexion. With the 

sensor affixed to the knee, a researcher 

palpated around the patella, patellar tendon 

(PT), and tibial tubercle (TT) identifying the 

sensing units associated with each structure. 

The sensor was zeroed in non-weight 

bearing conditions with the subject’s knee in 

90° of knee flexion (for kneeling on one 

knee and kneeling at 90° of knee flexion) or 

when they were in a squat (for kneeling in 

full flexion). This ensured that the pressure 

measurements taken while the subject was in 

the assigned posture we ere only a result of 

the pressure applied directly to the knee by 

the floor and not due to pressure being 

applied to the sensor by the knee itself. 

The subject assumed each of the five 

different postures and data were collected 

for 10 seconds. During analysis, the PT and 

TT data we reccombined due to their small 

individual size (~2 in. 2

). The ratio of the 

pressure applied to the patella and the 

combined PT and TT was then determined 

for each point in time and the average of 

these ratios was taken to obtain a mean 

pressure ratio. For the patella and combined 

PT and TT, the maximum pressure at each 

point in time was then calculated and the 

average of these values taken to obtain the 

mean of the maximum pressure on each 

structure. 
A priori orthogonal contrasts were 

developed. Contrasts for kneepad states 

included comparisons of no kneepad state to 

wearing kneepads and comparing the nonarticulated to articulated kneepads. All 

contrasts were tested using a T statistic 

using an alpha = 0.05 

RESULTS 

The majority (>60%) of the pressure was on 

the com bined PT and TT for all postures 

(Figure 1). 

Figure 1. Mean pressure ratio at the combined PT
	

and TT. *p<0.05 

No difference was detected 

between the no kneepad and kneepad states , 

but a difference was detected between the 

articulated and non-articulated states. The 

presence of kneepads significantly reduced 

the mean of the maximum pressure applied 

to the combined PT and TT (Figure 2). 

Figure 2. Mean of the maximum pressure at 

combined PT and TT. *p<0.05 

 The 

mean maximum pressure on the patella was 

much lower and ranged from 1.3 ± 1.1 psi to 

27.1± 17.2 psi between postures. The 

pressure on the patella was sometimes 

higher with kneepads compared to the no 

kneepad state. 

DISCUSSION 

The pressure applied to the patella and 

combined PT and TT was determined for 

postures as sociated with low-seam m ining. 

The majority of the pressure was transmitted 

to the knee via the combined PT and TT. 

While the kneepads did decrease the

maximum pressure experienced at the 

combined PT and TT, pressures of greater 

than 25 psi were still experienced. At this 

time, it is unknown how this external 

pressure affects the internal stabilizing 

structures of the knee. The kneepads 

performed similarly despite significant 

differences in their m aterial make-up. Some 

new kneepad designs in the industry have 

focused on elim inating the pressure at the 

patella. These data suggest that future 

kneepad designs should focus on 

redistributing the pressure at the combined 

PT and TT to other areas such as the shin. 

REFERENCES 

1. Mine Safety and Health Administration, 

Injury and Illness Database. 2007. 

2. Gallagher, S., S. Moore, and P. Dem psey, 

An Analysis of Injury Claims in LowSeam Coal Mines. Journal of Safety 

Research (submitted), 2008. 

ACKNOWLEDGEMENTS 

This work was funded by the National 

Institute for Occupational Safety and Health. 

DISLCAIMER 

The findings and conclusions in this study 

are those of the authors and do not represent 

the views of the National Institute for 

Occupational Safety and Health.