The effect of cane ambulation on hip biomechanics has been well studied, but its effect on tibial strains and strain rates is not known. To test the hypothesis that cane use may lower tibial strain and strain rates during walking, percutaneous axial extensometers were mounted on the right medial cortex of the midtibial diaphysis in seven male volunteers. In vivo peak-to-peak axial tibial strains and strain rates were measured for ipsilateral and contralateral cane usage and compared with a no cane control. Cane-assisted ambulation was not found to significantly lower strain magnitudes; however, tibial strain rates were significantly lowered by both ipsilateral and contralateral cane usage. We conclude that either ipsilateral or contralateral cane usage may be beneficial when lowering tibial strain rate is desired, such as in the treatment of tibia stress fracture or osteoarthrosis of the knee.

Adult↗

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Effect of fatiguing exercise on longitudinal bone strain as related to stress fracture in humans.

Muscular fatigue in the training athlete or military recruit has been hypothesized to cause increased bone strain that may contribute to the development of a stress fracture. Under normal circumstances, muscles exert a protective effect by contracting to reduce bending strains on cortical bone surfaces. In vivo strain studies in dogs show that muscle fatigue following strenuous exercise elevates bone strain and changes strain distribution. However, a similar experiment has yet to be performed in humans. The purpose of this work was to test the hypothesis in humans that strenuous fatiguing exercise causes an elevation in bone strain. It was also hypothesized that this elevation is greater in younger people than in older people due to the decline in muscle strength and endurance that normally occurs with age. To test these hypotheses, strain in the tibiae of seven human volunteers was measured during walking before and after a period of fatiguing exercise. Neither hypothesis was sustained. Post-hoc analysis of the strain data suggests that strain rate increases after fatigue with a greater increase in younger as opposed to older persons. Although not conclusive, this suggests that it is strain rate, rather than strain magnitude, that may be causal for stress fracture.

Adult↗

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Breaking strength of fluoride-treated dentin.

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Dental Stress Analysis↗

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The effect of protein malnutrition and nutritional support on the mechanical properties of fracture healing in the injured rat.

We investigated the effect of different nutritional regimens on fracture healing in the injured rat model. Four groups, each consisting of 12 male rats (307 +/- 16 g), were subjected to anesthesia, laparotomy (injury), and tibial osteotomy with internal fixation. Group I received 23% protein, group II received 23% protein and high caloric feed, group III received 5% protein, and group IV received 38% protein. After 8 weeks, calluses were x-rayed and the tibia was removed, fixed in a special block of methyl-metacrylate, and tested at tension up to failure in a mechanical testing apparatus. The distraction force at failure was measured, and callus stiffness and energy absorbed to failure were calculated. The low protein diet resulted in significantly lower tensile strength and stiffness of calluses compared to the other three dietary regimens, this despite adequate caloric intake. In addition, the low protein diet resulted in a callus with "rubbery" mechanical properties compared to the "rigid" calluses of the other three groups. The high protein diet did not result in any significant improvement in fracture healing. These results gain clinical significance in the face of a high incidence of protein calorie malnutrition in injured orthopedic surgery patients.

Analysis of Variance↗

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Using bone's adaptation ability to lower the incidence of stress fractures.

In three prospective epidemiologic studies of the effect of pre-military-induction sport activities on the incidence of lower extremity stress fractures during infantry basic training, recruits who played ball sports (principally basketball) regularly for at least 2 years before basic training had a significantly lower incidence of stress fractures (13.2%, 16.7%, and 3.6% in the three studies, respectively) than recruits who did not play ball sports (28.9%, 27%, and 18.8%, respectively). Preinduction running was not related to the incidence of stress fracture. To assess the tibial strain environment during these sport activities, we made in vivo strain measurements on three male volunteers from the research team. Peak tibial compression and tension strain and strain rates during basketball reached levels 2 to 5.5 times higher than during walking and about 10% to 50% higher than during running. The high bone strain and strain rates that occurred in recruits while playing basketball in the years before military induction may have increased their bone stiffness, according to Wolff's Law. The stiffer bone could tolerate higher stresses better, resulting in lower strains for a given activity and a lower incidence of stress fractures during basic training.

Adaptation, Physiological↗

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Stress fractures. Identifiable risk factors.

To answer the question why such large differences in stress fracture morbidity rates (2% to 64%) exist in different countries, we prospectively evaluated 312 recruits for possible risk factors for stress fractures. Prior to training, each recruit underwent an evaluation including the following: orthopaedic examination, foot and tibial radiographs, measurements of tibial bone width, bone mineral content, bone density, aerobic physical fitness and leg power, assessments of somatotype and smoking habits, and evaluation of sociological and psychological factors. Using a multivariate analysis, two risk factors were identified: recruits with stress fractures had significantly narrower tibiae (P less than 0.001), and a higher degree of external rotation of the hip (P = 0.016). These two variables were independent and cumulative. Stress fracture morbidity was 17%, 29%, and 45% when neither, one, or both risk factors were present, respectively (P less than 0.001). Identification of these risk factors might explain the susceptibility of some people to stress fractures.

Adult↗

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