Exercise-induced strain and strain rate in the distal radius.

Strains applied to bone can stimulate its development and adaptation. High strains and rates of strain are thought to be osteogenic, but the specific dose response relationship is not known. In vivo human strain measurements have been performed in the tibia to try to identify optimal bone strengthening exercises for this bone, but no measurements have been performed in the distal radial metaphysis, the most frequent site of osteoporotic fractures. Using a strain gauged bone staple, in vivo dorsal metaphyseal radial strains and rates of strain were measured in ten female patients during activities of daily living, standard exercises and falls on extended hands. Push-ups and falling resulted in the largest compression strains (median 1345 to 3146 microepsilon, equivalent to a 0.1345% to 0.3146% length change) and falling exercises in the largest strain rates (18582 to 45954 microepsilon/s). On the basis of their high strain and/or strain rates these or variations of these exercises may be appropriate for distal radial metaphyseal bone strengthening.

A comparison of external plantar loading and in vivo local metatarsal deformation wearing two different military boots.

The introduction of the M90 boot with a more flexible outer sole to military recruits in Sweden was accompanied by an increase in second metatarsal stress fractures. This study compared the new boot with the previous, stiffer model. A combination of external plantar pressure measurement (two subjects) and an in vivo measurement of dorsal metatarsal strain (six subjects) using strain gauge instrumented staples was implemented. Walking in both boot models resulted in increased plantar pressure under the heads of the lesser metatarsals and generally decreased loading under the remainder of the foot. Dorsal metatarsal tension increased for subjects wearing the new boot throughout a walking protocol.

Are overground or treadmill runners more likely to sustain tibial stress fracture?

BACKGROUND: Repetitive high bone strain and/or strain rates, such as those that occur during running, contribute to stress fractures as well as promoting maintenance of or increase in bone mass. Kinematic differences are known to exist between overground and treadmill running and these may be reflected in different bone strains and strain rates during the two running techniques. AIM: To measure in vivo strains and strain rates in human tibia during treadmill and overground running and determine if there are significant differences in strain and strain rate levels between the two running techniques. METHODS: A strain gauged bone staple was mounted percutaneously along the axial direction in the mid diaphysis of the medial tibia in three subjects, and in vivo tibial strains were measured during treadmill and overground running at 11 km/h. RESULTS: Axial compression strains (p<0.0001), tension strains (p<0.001), compression strain rates (p<0.0001), and tension strain rates (p<0.0001) were 48-285% higher during overground running than during treadmill running. CONCLUSIONS: On the basis of lower in vivo strains and strain rates, treadmill runners are at lower risk of developing tibial stress fractures, but less likely to achieve tibial bone strengthening, than overground runners.

Metatarsal strains are sufficient to cause fatigue fracture during cyclic overloading.

Human in vivo tibial strains during vigorous walking have not been found to exceed 1200 microstrains. These values are below those found in ex vivo studies (>3000 microstrains) to cause cortical bone fatigue failure, suggesting that an intermediate bone remodeling response may be associated with tibial stress fractures. Metatarsal stress fractures, however, often develop before there is time for such a response to occur. Simultaneous in vivo axial strains were measured at the mid diaphysis of the second metatarsal and the tibia in two subjects. Peak axial metatarsal compression strains and strain rates were significantly higher than those of the tibia during treadmill walking and jogging both barefoot and with running shoes and during simple calisthenics. During barefoot treadmill walking metatarsal compression strains were greater than 2500 microstrains. During one- and two-leg vertical jumps and broad jumping, both metatarsal compression and tension strains were >3000 microstrains. Compression and tension strains in the metatarsus unlike those of the tibia may be sufficiently high even during moderate exertional activities to cause fatigue failure of bone secondary to the number of loading cycles without an intermediate bone remodeling response.

Effects of fatigue and load variation on metatarsal deformation measured in vivo during barefoot walking.

This in vivo study presents information to assist in the understanding of metatarsal stress fracture etiology. The aims were (a) to provide a fundamental description of loading patterns of the second metatarsal (MTII) during barefoot walking, and (b) to investigate the hypothesis that MTII dorsal strain increases with fatigue and external carrying load. Dorsal MTII strain was measured in vivo under local anaesthetic with an instrumented staple in eight subjects. Experimental conditions were external loading with a 20 kg backpack and pre- and post-fatigue. M. flexor digitorum longus electromyography tentatively indicated fatigue after an extended walking treatment. A reproducible, cyclic temporal pattern of dorsal MTII surface deformation was described. Mean peak compression and tension strains in unloaded barefoot walking were -1534 +/- 636 and 363 +/- 359 muepsilon, respectively. Mean peak compression strain rate (SR) was -4165 +/- 1233 muepsilon/s. Compression strain increased significantly (alpha=0.05) both with the addition of the backpack and post-fatigue while maximum tension decreased significantly post-fatigue. SR increased significantly with the addition of the backpack. The highest plantar force time integrals were recorded underneath the heads of metatarsals II-V for all conditions (1561Ns pre-fatigue, without backpack; 2123Ns post, with). EMG and plantar pressure data presented a comprehensive description of biomechanical parameters influencing dorsal MTII deformation and alterations in strain following two experimental conditions were suggested as contributing factors in the pathogenesis of metatarsal stress fractures.

The effect of shoe sole composition on in vivo tibial strains during walking.

To test the hypothesis that shoe sole composition can affect the level of bone strain and strain rates that contribute to the development of stress fractures, in vivo tibial strain measurements were made during treadmill walking while wearing four shoes which differed only in their sole composition. Soles of 65 Shore A polyurethane with an embedded heel air cell had significantly lower compression and shear strains and shear strain rates than soles of 65, 75 and a composite of 40/65 Shore A polyurethane with no embedded air cells. A sole composed of 65 Shore A polyurethane with an embedded air cell can potentially be protective against stress fracture in a walking shoe.

A home exercise program for tibial bone strengthening based on in vivo strain measurements.

OBJECTIVE: To compare the strain and strain rates generated during lower limb calisthenics with walking, an exercise that has been found to have only minimal effect on bone mass. Strengthening of bone, while it still has adaptive ability, can be achieved by exercise. Mechanical loading during physical activity produces strains and strain rates within the bones. It is thought that strain and strain rates higher than the usual provide the stimulus for the bones' adaptation. DESIGN: Three strain-gauged bone staples were inserted percutaneously in a 30 degrees rosette pattern in the medial aspect of the midtibial diaphysis of two volunteers. The principal compression, tension, shear strains, and strain rates were measured during various lower limb calisthenics and compared with those of jogging and walking. RESULTS: Zig-zag hopping was in the grouping of exercises with the highest principal compression, tension, and shear strains and compression strain rates, whereas walking was in the lowest or next-to-the-lowest grouping for all principal strain or strain rates. CONCLUSION: Zig-zag hopping, based on the high strain and strain rates that it produces, may be an optimal tibial bone-strengthening exercise.

Stress fractures of the tibia: can personality traits help us detect the injury-prone athlete?

One of the few serious drawbacks associated with running is overuse injuries such as stress fractures of the tibia, which cause local pain and swelling, often resulting in a temporary cessation of training. Whereas some runners rarely become injured, others experience recurrent injuries even during fairly short periods of time. The aim of the present study was to compare selected personality traits in a group of runners who had sustained a previous tibial stress fracture (n=17), with a matched group of runners (n=17) who had never experienced stress fractures. The results indicated that the injured runners, especially the women, scored higher than the non-injured runners did on inventories measuring both the Type A behavior pattern and exercise dependency. Since motivation, ambitiousness, and competitiveness are integral parts of these inventories, high scoring individuals might be part of a high-risk population for running injuries, the more so if the individual also feels dependent on regular running for managing stress related mood states, which was the case particularly for the injured women in the present study. However, the somewhat limited number of runners who had had a confirmatory scintigram, which was a criterion for inclusion in the study, warrants a cautious interpretation of the results. The findings nevertheless suggest that in order to prevent recurrent injuries, health education professionals and clinicians ought to focus on conveying the importance of detecting precursors of injury, and the subsequent steps which should be taken to avoid developing a serious injury.

Do high impact exercises produce higher tibial strains than running?

BACKGROUND: Bone must have sufficient strength to withstand both instantaneous forces and lower repetitive forces. Repetitive loading, especially when bone strain and/or strain rates are high, can create microdamage and result in stress fracture AIM: To measure in vivo strains and strain rates in human tibia during high impact and moderate impact exercises. METHODS: Three strain gauged bone staples were mounted percutaneously in a rosette pattern in the mid diaphysis of the medial tibia in six normal subjects, and in vivo tibial strains were measured during running at 17 km/h and drop jumping from heights of 26, 39, and 52 cm. RESULTS: Complete data for all three drop jumps were obtained for four of the six subjects. No statistically significant differences were found in compression, tension, or shear strains with increasing drop jump height, but, at the 52 cm height, shear strain rate was reduced by one third (p = 0.03). No relation was found between peak compression strain and calculated drop jump energy, indicating that subjects were able to dissipate part of the potential energy of successively higher drop jumps by increasing the range of motion of their knee and ankle joints and not transmitting the energy to their tibia. No statistically significant differences were found between the principal strains during running and drop jumping from 52 cm, but compression (p = 0.01) and tension (p = 0.004) strain rates were significantly higher during running. CONCLUSIONS: High impact exercises, as represented by drop jumping in this experiment, do not cause higher tibial strains and strain rates than running and therefore are unlikely to place an athlete who is accustomed to fast running at higher risk for bone fatigue.

In-vivo strain measurements to evaluate the strengthening potential of exercises on the tibial bone.

Mechanical loading during physical activity produces strains within bones. It is thought that these forces provide the stimulus for the adaptation of bone. Tibial strains and rates of strain were measured in vivo in six subjects during running, stationary bicycling, leg presses and stepping and were compared with those of walking, an activity which has been found to have only a minimal effect on bone mass. Running had a statistically significant higher principal tension, compression and shear strain and strain rates than walking. Stationary bicycling had significantly lower tension and shear strains than walking. If bone strains and/or strain rates higher than walking are needed for tibial bone strengthening, then running is an effective strengthening exercise for tibial bone.

An in vitro comparison of bone deformation measured with surface and staple mounted strain gauges.

Chicken tibiae were chosen as a model for human second metatarsals. Local surface bone deformation in a 4-point bending configuration was measured in vitro by both strain gauge instrumented staples and strain gauges bonded to the bone's cortical surface. A series of staple bridge dimensions (0.5, 0.6, 0.8 and 1.0 mm) was compared to test for staple influence on bone characteristics and greatest measurement validity and reliability. Thicker staple inhibition of bone deformation was the greatest but differences to thinner staples were not statistically significant (p > 0.05). All staples except 0.5 mm had maximum deviations from linearity less than 1%. The 1.0 mm staple had an R2 value of 0.992 +/- 0.006 plotted against the 4-point bending input force and 0.994 +/- 0.002 plotted against the surface strain gauge signal. The mean intraclass correlation coefficients (ICC) calculated with four input forces (30, 60, 90 and 120 N) and for loading and unloading conditions for the 0.5, 0.6, 0.8 and 1.0 mm staples were 0.75, 0.83, 0.87 and 0.92, respectively. Finally, the differences in slope of the staple strain gauge signal plotted against surface strain gauge signal between input force loading and unloading conditions (0.32), and between input compression and tension conditions (0.79) was least for the 1.0 mm staple which also resulted in the lowest standard deviations. These results suggested the appropriateness of the 1.0 mm staple for in vivo application.

Local bone deformation at two predominant sites for stress fractures of the tibia: an in vivo study.

Local bone deformation was registered at two predominant injury sites for tibial stress fractures in a healthy female volunteer. Two instrumented strain gauge staples were inserted under local anesthesia to the anterior middiaphysis (AM) and to the posteromedial part of the distal tibia (PD). Calibration and reliability of the instrumented staple system have previously been demonstrated in vitro. Concomitant ground reaction forces were registered with a Kistler force plate. Studying peak values, it was shown that during a voluntary 30-cm forward jump, PD deformation was greater during forefoot landing (2700-4200 microstrain) than during a heel strike landing (1200-1900 microstrain) and also compared with the concomitant AM deformation under both above testing conditions (1300-1900 microstrain). The stance phase during walking resulted in PD deformation of 950 microstrain, whereas the concomitant AM deformation was 334 microstrain. The greatest AM deformation (mean, 2128 microstrain) was registered during ground contact after a voluntary vertical drop from a height of 45 cm, concomitant with a PD deformation of 436 microstrain. These data are the first to show different local deformations at various sites of the tibia in vivo. The PD deformation was larger than previously noted from other parts of the tibia, whereas the middiaphysis data are consistent with other reports. The results may support the clinical assumption of different etiologies for stress fractures at these predominant sites.

The reliability and validity of an instrumented staple system for in vivo measurement of local bone deformation. An in vitro study.

We recently presented a pilot study using an instrumented staple system for measuring in vivo local deformation on tibia. Methodological development has now proceeded in vitro. Consecutively, we performed 1. a sheep bone micrometer study, 2. a sheep bone four-point bending test and 3. a pig bone four-point and three-point bending test. This was done in order to secure a standardized application of the staple, to analyze the interaction of the bone and the staple and to secure calibration and the reliability of the system to be used in vivo. With reference to the above studies: 1. There was a linear relationship (r = 0.998) between the applied deformation of the bone and the measured deformation of the staple. ICC values ranged from 0.866 to 0.997. 2. An excellent intra-test reliability as well as linearity between staple measures and surface strain on the bone was observed (r = 0.998). 3. The slope of regression lines (k) was min 7.2 and max 9.4. The results from this test are used for calibration of the instrumented staple. Great variations were found between tension and compression measurements. However, within each test the SD was negligible. We suggest that the instrumented staple system may be calibrated in vitro and validly used for in vivo measurement of local bone deformation.

The anterior stress fracture of the tibia: an atrophic pseudoarthosis?

Histopathological examination of biopsies from the fracture site in two cases of anterior stress fractures of the tibia demonstrated no bone remodelling activity, absence of inflammatory cells, extensive fibrotic infiltration and local avascular bone necrosis. The biopsies were taken peroperatively from two elite soccer players who earlier had to stop training due to severe exertional pain. When non-operative treatment failed to heal the fractures within 1 year and 6 months, respectively, surgery was performed in order to stabilize the fractures. Both subjects were relieved from exertional pain within 6 months of surgery. Consecutive radiographs showed the pattern of direct healing and 8 months postoperatively confirmed complete healing without callus formation. Both elite soccer players returned to pre-injury activity level. We suggest that the excessive fibrotic tissue ingrowth and hypovascularity under repetitive stress causes the delayed healing and histopathological signs similar to an atrophic pseudoarthosis. Treatment should consequently consider the pseudoarthrotic character of the anterior stress fracture of the tibia.

An experimental in vivo method for analysis of local deformation on tibia, with simultaneous measures of ground reaction forces, lower extremity muscle activity and joint motion.

This paper presents the pilot procedures of a new in vivo experimental method for measures of local bone deformation on tibia. The tibia transducer consists of a strain gauge mounted on a surgical staple, and was designed to measure local bone deformation. Pilot measurements were undertaken during two standardized conditions of forefoot and heel landing in seven healthy volunteers. Implantation of two tibia force transducers on tibia were performed under local anaesthesia. The local peak tibia deformation occurred at 20-42 ms (median) after ground contact, and was up to eight times higher during stance phase loading compared with standing still on one leg. Ground reaction forces, muscle activation patterns and kinematics were registered simultaneously, and were used to validate that the observed local deformation on tibia occurred under controlled and clinically relevant conditions. The new method may be used for investigating local deformation within various bone structures of the lower extremity. There are further methodological issues to address before major clinical interpretations may be concluded. In order to verify that the strain gauge transducer system was valid, a controlled displacement of the staple shanks was performed with a micrometer, and showed a linear relationship between applied deformation and strain gauge response (r = 0.97-0.99). In addition, a linear relationship was found between externally applied static forces and strain gauge response in a four-point bending cadaver system (r = 0.96-0.98).

Dislocation of the tibialis posterior tendon: diagnosis and treatment.

Traumatic dislocation of the tibialis tendon occurred from minor ankle sprains in a 37-year-old male and a 53-year-old female. Both complained of local pain at the medial malleolus, and both walked with a limp. The diagnosis was suspected by clinical examination, in one case with 2 months' delay, and verified by ultrasound, computed tomography, and magnetic resonance imaging. The male patient was initially treated for an "uncomplicated ankle sprain." For various reasons surgery was delayed 4 months. During this interval the male patient complained of pain and severe dysfunction, requiring analgesic treatment. A medial Achilles tendon flap was used to support the repositioned tendon. The female patient was operated on within 1 week from injury, by resuturing of the retinaculum over the tendon. Postoperatively, both patients were immobilized with below-knee casts for 6 weeks, allowing full weightbearing, followed by strength and stretching exercises. They were free of symptoms 2 and 3 months, respectively, after surgery. At follow-up 1 year postoperatively, both were asymptomatic and participated in activities like those before their injuries.

A study of intrinsic factors in patients with stress fractures of the tibia.

We aimed to study intrinsic factors in 29 consecutive patients with well-documented unilateral stress fractures of the tibia. Anthropometry, range of motion, isokinetic plantar flexor muscle performance, and gait pattern were analyzed. The uninjured leg served as the control. A reference group of 30 uninjured subjects was compared regarding gait pattern. Anterior stress fractures of the tibia (N = 10) were localized in the push-off/ landing leg in 9/10 athletes, but were similarly distributed between legs in posteromedial injuries (N = 19). Ten (30%) of the stress fracture subjects had bilateral high foot arches, similar to those found in the reference group. There were no other systematic differences in anthropometry, range of motion, gait pattern, or isokinetic plantar flexor muscle peak torque and endurance between injured and uninjured legs. No other differences were found between anterior and posteromedial stress fractures. We conclude that anterior stress fractures of the tibia occur mainly in the push-off/landing leg in athletes. Within the limitations of our protocol, no registered intrinsic factor was found to be directly associated with the occurrence of a stress fracture of the tibia.

The plantar flexor muscle attachments on the tibia. A cadaver study.

Thirty-six tibiae from 11 female and 7 male cadavers were dissected. Anatomical and histological examinations of the plantar flexor muscle origins at the posteromedial border of the tibia were performed. Many individual variations in the type and size of muscle origin were observed. Muscle fibers and/or connective tissue in different proportions attached the muscle to the periosteum or directly to the cortical bone. The length of the attachments varied greatly and there was a considerable overlap of the muscles in some individuals. The attachments of the flexor digitorum longus overlapped the tibialis posterior and the flexor digitorum longus muscle was overlapped by the soleus muscle. In two cases the soleus muscle did not attach to the tibia at all. Our findings may shed some light on the question as to why some athletes sustain posteromedial tibial stress fractures and others develop shin splits or other posteromedial injuries from similar precipitating activity.

Bone density in medieval skeletons.

We studied the most complete skeletons found in an excavation from the 14th and 15th century in central Stockholm. One hundred eighty-seven were from men and 156 from women: 241 individuals were estimated to be between 20 and 39 and 102 between 40 and 59 years old at death. We examined the bones radiographically and by dual photon absorptiometry. The bone mineral density (BMD) was similar to the finding in North America and Northern Europe today as was the relationship between men and women. However, there appeared to be a higher diaphyseal bone density in the lower extremities, especially in men. The femur score was higher and the BMD of the femoral and tibial shafts was higher than today. In the upper extremities the diaphyseal bone density was lower. Meema's index, as well as the metacarpal score, was smaller than in individuals in this century and the BMD of the humeral shaft was also lower than seen today. Overall, the metaphyseal bone density was similar to what we now consider normal; i.e., the mean BMD of the femoral neck was 0.96 g/cm2 in men and 0.90 g/cm2 in women and of the distal radius 0.43 and 0.32 g/cm2, respectively. The low diaphyseal density and in the upper extremities may be related to the nutritional status, whereas the greater need for walking and standing in the 14th and 15th century might have led to the high diaphyseal density in the lower extremities. There was no evidence of bone loss after 40 years of age in either sex in our study. The average expected lifespan for an adult individual was less than 50 years and we suggest that the relatively high bone density in the older age group may be due to selection of the most physically fit. The activity pattern, therefore, may be considered the most important determinant for the differences.

Stress fractures of the femoral neck in athletes. The consequence of a delay in diagnosis.

Twenty-three patients with stress fractures of the femoral neck were followed up at an average of 6.5 years after the injury. There were 16 recreational athletes and seven elite athletes. Most injuries (N = 15) occurred during running. The diagnosis was confirmed within 3 to 104 weeks (mean, 14 weeks) after the initial onset of symptoms. Sixteen of the patients were treated with internal fixation, the remaining seven were treated conservatively. Seven patients (30%) developed complications requiring major surgery. Five of these patients had Type 3 fractures (displaced) and four had been treated with internal fixation initially. The remaining two patients had Type 1 fractures (endosteal or periosteal callus without an overt fracture line); one was treated operatively and the other conservatively. Three patients developed avascular necrosis and two were treated by hip replacement. The third patient was treated with arthrodesis. Three refractures and one pseudarthrosis were treated by osteotomy. At followup, all elite athletes stated that they had to end their career as a result of the injury. Results were rated by the ability of the athlete to return to sports. There were 9 bad or fair results, 13 good, and 1 excellent result. No difference in activity level or subjective rating was observed between the surgically and conservatively treated group either preinjury or postinjury. The most important factor influencing the complication rate seems to be the type of fracture. The high incidence of displaced fractures (Type 3) could speculatively be caused by undiagnosed tension side stress fractures. If so, the delay in correct diagnosis may be disastrous. However, we could only objectively observe this in one of our cases.