Ingrid Ekenman

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

Twenty-three patients with stress fractures of the fem oral 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 con servatively. Seven patients (30%) developed complica tions 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 subjec tive rating was observed between the surgically and conservatively treated group either preinjury or postin jury. The most important factor influencing the compli cation rate seems to be the type of fracture. The high incidence of displaced fractures (Type 3) could specu latively 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.

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.

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.

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.

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.

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 role of biomechanical shoe orthoses in tibial stress fracture prevention.

Background Biomechanical orthoses have been shown to lower stress fracture incidence in infantry recruits. However, these results may not be applicable to running athletes. Hypothesis Training in either running shoes or military boots with custom biomechanical shoe orthoses lessens tibial bone strains and strain rates during walking and running. Study Design Randomized controlled laboratory study. Methods In vivo strain measurements were made in nine subjects to determine whether the use of biomechanical orthoses lowers tibial strains during both walking and running and whether such lowering depends on the type of shoe worn. Measurements were made during treadmill walking at 5 km/hr and then during serial 2-km treadmill runs at 13 km/hr with running shoes, with and without the orthoses, and during serial 1-km runs with army boots, with and without the orthoses. Results When soft or semirigid biomechanical orthoses were worn with boots, the tibial peak-to-peak strains were significantly lowered. Soft orthoses also significantly lowered the tension and compression strain rates when worn with boots. During running, semirigid orthoses significantly increased the compression and tension strain rates when worn with boots. Conclusions The use of biomechanical orthoses may be warranted for tibial stress fracture prevention during training in which boots are worn and that mostly involves walking, but they are not warranted for activities that primarily involve running or are performed in running shoes.

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.

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.

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.