Prevention of overuse injuries of the foot by improved shoe shock attenuation. A randomized prospective study.

In a randomized prospective study among 390 recruits, the hypothesis that improved shoe shock attenuation could lessen the incidence of overuse injuries was tested. During the 14 weeks of training, 90% of the recruits sustained overuse injuries. Recruits training in a modified basketball shoe had a statistically significant lower incidence of metatarsal stress fractures and foot overuse injuries, compared with standard infantry boots, but their overall incidence of overuse injuries was not reduced. The effect of improved shoe shock attenuation was limited to those overuse injuries resulting from vertical impact loads.

Risk factors for stress fractures among Israeli infantry recruits.

In order to answer the question of why the stress fracture morbidity rates among Israeli infantry recruits are so high, we prospectively evaluated 392 infantry recruits for risk factors for stress fractures. Prior to training, each recruit underwent a detailed evaluation. Using multivariate analysis, five risk factors for tibial fractures were identified: shorter tibial length (p less than 0.0001); relatively greater valgus knee alignment (p less than 0.002); right leg dominance (p less than 0.02); external rotation of the hip greater than 65 degrees (p less than 0.02); and training in specific subunits (p less than 0.0002., 0.03). No risk factors for femoral stress fracture were found by multivariate analysis.

Risk factors for lateral ankle sprain: a prospective study among military recruits.

In a prospective study of risk factors for lateral ankle sprain among 390 male Israeli infantry recruits, a 18% incidence of lateral ankle sprains was found in basic training. There was no statistically significant difference in the incidence of lateral ankle sprains between recruits who trained in modified basketball shoes or standard lightweight infantry boots. By multivariate stepwise logistic regression a statistically significant relationship was found between body weight x height (a magnitude which is proportional to the mass moment of inertia of the body around a horizontal axis through the ankle), a previous history of ankle sprain, and the incidence of lateral ankle sprains. Recruits who were taller and heavier and thus had larger mass moments of inertia (P = 0.004), and those with a prior history of ankle sprain (P = 0.01) had higher lateral ankle sprain morbidity in basic training.

Cyclic impacts on heel strike: a possible biomechanical factor in the etiology of degenerative disease of the human locomotor system.

The cyclic impacts induced by heel strike when walking were studied using both a high-resonance-frequency force plate and a low-mass skin-mounted accelerometer. The data were computer analyzed. The results showed that during normal human walking, the locomotor system is subjected to repetitive impact loads at heel strike, lasting about 5 ms and consisting of frequency spectra up to and above 100 Hz. The natural shock-absorbing structures in the musculoskeletal system have viscoelastic time-dependent mechanical behavior, which is relatively ineffective in withstanding sudden impulsive loads. Degenerative joint diseases may thus be seen as a late clinical result of fatigue failure of the natural shock absorbers, submitted to deleterious impacts over a period of time.

Low back pain: conservative treatment with artificial shock absorbers.

A new method of conservative treatment for low back pain (LBP) was studied by follow-up investigation of 382 patients during the last five years. The attempt to reduce repetitive impulsive intervertebral impact in the troublesome S1-L5-4 area by significant improvement of the foot's attenuational capacity through artificial viscoelastic shock absorbing was prompted by the authors' work on decreased capability of LBP spines to attenuate axially propagated walking stresses. Viscoelastic shoe inserts were used in addition to light flexible shoes as artificial shock absorbing devices. Maximal amplitudes of bone oscillation during walking were reduced by about 40% by the viscoelastic inserts. Rapid and surprisingly significant improvement of pain syndrome and patient mobility occurred in about 80% of the patients. The accelerographic patterns recorded on a sacrum of patient with LBP were unusual for a healthy subject; they usually disappeared after treatment in LBP cases. Results suggested that poor walking impact attenuation was a true cause for prolonging intervertebral structures overstrain and consequent degeneration. It seemed logical that as spine damage could be explained primarily by prolonged impulsive overstrain, treatment must include viscoelastic inserts which increase foot shock absorbing capacity and help cushion the spine.

Fracture fixation by using vibration absorbers.

During recent years, increasing attention has been focused on the importance of cyclic stresses or bone microstructure and bone/implant interaction. Use of rigid fixation often leads to loosening and reduction of the bone cortex strength under the rigid plate. This presentation discusses a new approach to the design of shock-absorbing bone fixation devices along with the supporting clinical experience. Even though this discussion concerns only preliminary results, it should stimulate orthopaedic researchers to think about alternative approaches for developing internal fixation devices.

Shock absorption of meniscectomized and painful knees: a comparative in vivo study.

The principles of a noninvasive measurement of the shock absorbing capacity of the knee are presented. Accelerometry, which has been proven to be a useful tool for noninvasive measurements in biomechanical investigation, was employed for quantitative evaluation of the knee's shock absorbing capacity by registration of bone vibrations resulting from the gait. Results of the experiments show that both patients with painful knee and patients after meniscectomy suffer from insufficient shock absorbing capacity of the knee. It was found that the shock absorbing capacity of a normal knee is about 20% higher than that of a pathological one. The results indicate that while meniscectomy may reduce pain, instability, swelling, etc. in an injured knee, it cannot improve its reduced shock absorbing capacity, which eventually will lead to development of degenerative osteoarthritis. It seems that the pain syndrome is a biological reaction to severe repetitive overloading of the knee. Noninvasive in vivo determination of the knee's shock absorbing properties may be useful as an additional clinical technique to reveal a knee's pathology. It may lead to early discovery of knee insufficiency, so that preventive steps can be taken to delay or reverse the process of degeneration.

An in vivo study of low back pain and shock absorption in the human locomotor system.

In this second of three papers, the principles of a non-invasive in vivo method to quantitatively evaluate the shock absorbing capacity of the human musculoskeletal system and the correlation of this shock absorbing capacity with low back pain (LPB) symptoms are presented. The experiments involved patients suffering from low back pain (as well as other degenerative joint diseases) and healthy patients. The obtained results reveal that low back pain correlates with the reduced capacity of the human musculoskeletal system between the femoral condyle and the forehead to attenuate incoming shock waves. Examination of the absolute values of the amplitude of the propagated waves leads to the conclusion that the human locomotor system, which possesses reduced attenuation capacity, tries to prevent overloading of the head from insufficiently attenuated shock waves. Results of the present investigation support the idea that the repetitive loading resulting from gait generates intermittent waves that propagate through the entire human musculoskeletal system from the heel up to the head. These waves are gradually attenuated along this course by the natural shock absorbers (bone and soft tissues). Contemporary methods for examination of the human musculoskeletal system may by improved by using the proposed non-invasive in vivo technique for quantitative characterization of the locomotor system's shock absorbing capacity.

Influence of artificial shock absorbers on human gait.

The effect of artificial shock absorbers on the human gait and the technique for its quantitative evaluation have been studied. The results obtained have shown that viscoelastic inserts reduced the amplitude of the incoming shock waves bearing upon the musculoskeletal system as a result of the heel strike, by 42 percent (mean value). Conservative treatment, using such inserts for patients with different clinical symptoms of degenerative joint diseases, has shown excellent results. Seventy-eight percent of the clinical symptoms disappeared, while satisfactory improvement was reported in 17 percent of the subjects.

Force wave transmission through the human locomotor system.

A method to measure the capability of the human shock absorber system to attenuate input dynamic loading during the gait is presented. The experiments were carried out with two groups: healthy subjects and subjects with various pathological conditions. The results of the experiments show a considerable difference in the capability of each group's shock absorbers to attenuate force transmitted through the locomotor system. Comparison shows that healthy subjects definitely possess a more efficient shock-absorbing capacity than do those subjects with joint disorders. Presented results show that degenerative changes in joints reduce their shock absorbing capacity, which leads to overloading of the next shock absorber in the locomotor system. So, the development of osteoarthritis may be expected to result from overloading of a shock absorber's functional capacity.