Page 143 - Journal of Special Operations Medicine - Winter 2014

Back Pain Metatarsalgia
Back injuries can pose a significant problem during load Metatarsalgia is a descriptive term for nonspecific foot
carriage. In Study 1 (Table 1), 23% of injuries involved pain under the metatarsals. Pain is generally localized
the back and 50% of the Soldiers who were unable to under the second, third, and fourth metatarsal heads.
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complete the march reported problems associated with During locomotion, the foot rotates around the distal
their backs. Symptoms involving the back were less of ends of the metatarsal bones. While the exact mecha-
a problem in Study 2, suggesting that there is a wide nism for load-carriage-related metatarsalgia has not
variation in the incidence of this problem in different been defined, it is reasonable to assume that the cyclic,
situations. Clinical experience suggests that 82% to focal pressures and mechanical stresses caused by the
97% of back pain involves muscle strains, disc injuries load can induce inflammation and trauma in the meta-
(herniations, tears, and degeneration), facet degenera- tarsal heads. The nature of the trauma is difficult to
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tion, and spinal stenosis, with few cases involving more identify but may be associated with bone stress injuries
serious pathologies. Systematic reviews and national (e.g., stress fractures or stress reactions) and/or strains
6,7
medical societies provide evidence-based guidelines for to the foot muscles, and may be aggregated by condi-
the assessment of back pain. 8,9 tions such as neuromas and arthritis. No prevention
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techniques have been developed for metatarsalgia, but it
When an individual walks with a backpack load, there is reasonable to assume that reductions in loads may re-
are cyclic stresses on the vertebrae, intervertebral discs, duce symptoms. In one study, guided placement of poly-
muscles, and other spinal structures. Backpack load car- urethane pads under the metatarsals reduced subjective
riage results in an increase in the forward inclination of pain scores and pressure under the metatarsal heads. 22
the trunk and an increase in the curve of the spine. Stresses
on the spine during load carriage include compressive Knee Pain
forces, shear forces, and torques that increase as the load
increases. 10–12 Shearing forces are lower than compressive The knee is another anatomic location in which pain is
forces, but the spinal structures that protect against shear often reported in association with load carriage. Clinical
forces appear to be weaker and may be more susceptible experience suggests that diagnosis of knee pain should
to injury with large loads or repeated loading cycles. 12,13 proceed from interview (history) to physical examina-
Individuals with more lordotic spines tend to increase the tion, to possible referral for imaging and diagnostic
spinal curvature more under load than individuals with tests. Interviews should characterize the nature of the
smaller lordotic curves and will likely experience greater pain, mechanical characteristics (locking, popping, knee
shear forces on the spine, making them more suscepti- giving way), mechanism of injury, and previous knee
14
ble to back injuries. In addition to stresses on the spine, problems. Physical examination should include visual
15
load carriage increases active contraction of the abdomi- evaluation (symmetry, erythema, swelling, bruising) fol-
nal and spinal muscles, and contraction forces increase as lowed by evaluation of the patella, ligaments, and me-
either load or speed increases. The combined stresses on nisci with specific tests (e.g., Lachman test, McMurry
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vertebrae, discs, muscles, and other spinal structures are test). Potential diagnoses are extensive, but the most
likely associated with back pain and injuries experienced common overuse injuries include patellofemoral pain
in susceptible individuals. syndrome (chrondromalacia patellae), medial plica
syndrome, bursitis (pes anserine), and tendonitis (ilio-
As loads increase, so does the risk of back injuries. 17,18 tibial band and popliteus). More common traumatic
This could be because as the load increases, there are injuries include ligamentous strains (anterior/posterior
greater changes in trunk angle (forward lean), compres- cruciate, medial/lateral collateral), meniscal tears, and
sive and shearing forces, and active muscle contraction. fractures. 23,24
A double pack (load equally distributed on the front
and back of the trunk) may help reduce the incidence of Carrying heavy loads on the trunk increases the knee
back problems, because it results in less forward trunk range of motion and increases forces experienced at the
flexion and likely reduces shearing forces from cyclic knee joint. As loads increase, the knee joint angle in-
bending of the trunk. However, a double pack is not creases, presumably as a protective mechanism to assist
feasible for military operations because it can induce re- in absorbing impact forces and lowering the body cen-
spiratory problems and reduce the ability to dissipate ter of mass so greater stability can be achieved. Also,
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heat. Nonetheless, it may be possible to move some as loads increase, forces experienced at the knees in-
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of the load to the front of the body through the use of crease. 25,26 The greater range of knee joint motion com-
vests or other equipment. The goal is to distribute the bined with the greater forces at the knee joint induced
load more evenly around the trunk so that the forward by the load may be associated with knee pain experi-
flexion of the trunk is reduced. enced during load carriage.

Foot Marching Injuries 133