Genetic architecture for hole-board behaviors across substantial time intervals in young, middle-aged and old mice.

A quantitative trait locus (QTL) analysis of behaviors across the life span was conducted in F(2) mice from a C57BL/6J x DBA/2J cross and 22 BXD recombinant inbred (RI) strains. Mice of three age groups were tested in a hole-board apparatus for 3 min on three occasions approximately 1 month apart (average age at test 150, 450 and 750 days, approximately 400 mice per group, divided equally by sex). Quantitative trait loci with small effect size were found on 11 chromosomes for hole-board activity (Hbact) and hole-board rearing (Hbrear). Analysis of 22 RI strains tested at 150 and 450 days of age found only suggestive linkage, with four QTL for Hbact overlapping with those from the F(2) analysis. There was a significant phenotypic correlation between Hbact and Hbrear (approximately 0.55-0.69) and substantial commonality among QTL for the two behaviors. QTL analyses of head-pokes (HP) and fecal boli (FB) only identified QTL at the suggestive level of significance. Age accounted for approximately 15% of the phenotypic variance (sex approximately 3%), and there were genotype by age interactions at approximately 25% of the Hbact and Hbrear QTL. Quantitative trait loci for Hbrear were relatively stable across the three measurement occasions (those for Hbact somewhat less so), although mean levels of each index declined markedly comparing the first to subsequent trials. Considered as a whole, the polygenic system influencing exploratory behaviors accounts for approximately the same amount of phenotypic variance as age (within the range studied), is stable across substantial periods of time, and acts, for the most part, independently of age and sex.

Evidence of isometric function of the flexor hallucis longus muscle in normal gait.

Studying mechanics of the muscles spanning multiple joints provides insights into intersegmental dynamics and movement coordination. Multiarticular muscles are thought to function at "near-isometric" lengths to transfer mechanical energy between the adjacent body segments. Flexor hallucis longus (FHL) is a multiarticular flexor of the great toe; however, its potential isometric function has received little attention. We used a robotic loading apparatus to investigate FHL mechanics during simulated walking in cadaver feet, and hypothesized that physiological force transmission across the foot can occur with isometric FHL function. The extrinsic foot tendons, stripped of the muscle fibers, were connected to computer-controlled linear actuators. The FHL activity was controlled using force-feedback (FC) based upon electromyographic data from healthy subjects, and subsequently, isometric positional feedback (PC), maintaining the FHL myotendinous junction stationary during simulated walking. Tendon forces and excursions were recorded, as were the strains within the first metatarsal. Forces in the metatarsal and metatarsophalangeal joint were derived from these strains. The FHL tendon excursion under FC was 6.57+/-3.13mm. The forces generated in the FHL tendon, metatarsal and metatarsophalangeal joint with the FHL under isometric PC were not significantly different in pattern from FC. These observations provide evidence that physiological forces could be generated along the great toe with isometric FHL function. A length servo mechanism such as the stretch reflex could likely control the isometric FHL function during in vivo locomotion; this could have interesting implications regarding the conditions of impaired stretch reflex such as spastic paresis and peripheral neuropathies.

Strontium administration in young chickens improves bone volume and architecture but does not enhance bone structural and material strength.

Genetic selection for rapid body growth in broiler chickens has resulted in adverse effects on the skeletal system exemplified by a higher rate of cortical fractures in leg bones. Strontium (Sr) has been reported to have beneficial effects on bone formation and strength. We supplemented the diet of 300-day-old chicks with increasing dosages of Sr (0%, 0.12%, or 0.24%) to study the capacity of the element to improve bone quality and mechanical integrity. Treatment with Sr increased cortical bone volume and reduced bone porosity as measured by micro-computed tomography. The higher level of Sr significantly reduced bone Ca content (34.7%) relative to controls (37.2%), suggesting that Sr replaced some of the Ca in bone. Material properties determined by the three-point bending test showed that bone in the Sr-treated groups withstood greater deformation prior to fracture. Load to failure and ultimate stress were similar across groups. Our results indicate that Sr treatment in rapidly growing chickens induced positive effects on bone volume but did not improve the breaking strength of long bones.

Changes in muscle moment arms following split tendon transfer of tibialis anterior and tibialis posterior.

Moment arms of tibialis anterior (TA) and tibialis posterior (TP) about the subtalar and talocrural joint axes were measured in anatomic specimens both before and after split tendon transfers. These procedures are commonly performed to correct hindfoot varus, a gait deformity that is often seen in patients with cerebral palsy, stroke, and brain injury. Split tendon transfer significantly reduced the inversion moment arms of tibialis anterior and tibialis posterior at all subtalar joint angles except for the most everted position in the case of TA. Changes in subtalar joint moment arms produced by split tendon transfer, especially those seen in TA, were variable, suggesting that the procedure may be susceptible to technical errors, especially related to balancing tensions in the medial and lateral tendon halves. Talocrural joint moment arms of both muscles were preserved following split tendon transfer. This study presents the first measurements of the moment arms of split transferred muscles. These characterizations of the mechanics of split tendon transfer will aid in the planning and assessment of these procedures.

Effect of rearfoot orthotics on postural sway after lateral ankle sprain.

OBJECTIVE: To investigate the effects of different rearfoot orthotics on postural sway during unilateral stance after lateral ankle sprain. DESIGN: Repeated-measures 3-factor analysis of variance on postural sway length and velocity in the frontal and sagittal planes with factors being stance leg (injured, uninjured), session (within 3 d, 2 wk, 4 wk postinjury), and condition (6 orthotic conditions). SETTING: University biomechanics laboratory. PATIENTS: Fifteen collegiate athletes with acute, unilateral first- or second-degree lateral ankle sprain. INTERVENTIONS: Balance testing was performed under 6 conditions: (1) shoe only, (2) molded Aquaplast orthotic, (3) lateral heel wedge, (4) 7 degrees medially posted orthotic, (5) 4 degrees laterally posted orthotic, and (6) neutral orthotic. MAIN OUTCOME MEASURES: Postural sway length and postural sway velocity in the frontal and sagittal planes. RESULTS: Significant main effects were found for side and session, but not orthotic condition, for all 4 dependent variables. Postural sway length and velocity were greater on the injured limbs as compared with the uninjured limbs during the first 2 sessions but not during the third session. None of the orthotics significantly reduced postural sway compared with the shoe-only condition after lateral ankle sprain. CONCLUSIONS: Rearfoot orthotics, irrespective of design or posting, were ineffective at improving postural sway after lateral ankle sprain.

In vitro modeling of human tibial strains during exercise in micro-gravity.

Prolonged exposure to micro-gravity causes substantial bone loss (Leblanc et al., Journal of Bone Mineral Research 11 (1996) S323) and treadmill exercise under gravity replacement loads (GRLs) has been advocated as a countermeasure. To date, the magnitudes of GRLs employed for locomotion in space have been substantially less than the loads imposed in the earthbound 1G environment, which may account for the poor performance of locomotion as an intervention. The success of future treadmill interventions will likely require GRLs of greater magnitude. It is widely held that mechanical tissue strain is an important intermediary signal in the transduction pathway linking the external loading environment to bone maintenance and functional adaptation; yet, to our knowledge, no data exist linking alterations in external skeletal loading to alterations in bone strain. In this preliminary study, we used unique cadaver simulations of micro-gravity locomotion to determine relationships between localized tibial bone strains and external loading as a means to better predict the efficacy of future exercise interventions proposed for bone maintenance on orbit. Bone strain magnitudes in the distal tibia were found to be linearly related to ground reaction force magnitude (R(2)>0.7). Strain distributions indicated that the primary mode of tibial loading was in bending, with little variation in the neutral axis over the stance phase of gait. The greatest strains, as well as the greatest strain sensitivity to altered external loading, occurred within the anterior crest and posterior aspect of the tibia, the sites furthest removed from the neutral axis of bending. We established a technique for estimating local strain magnitudes from external loads, and equations for predicting strain during simulated micro-gravity walking are presented.

Contributions of active and passive toe flexion to forefoot loading.

Toe flexion during terminal stance has an active component contributed by the muscles that flex the toes and a passive component contributed by the plantar fascia. This study examined the relative importance of these two mechanisms in maintaining proper force sharing between the toes and forefoot. Thirteen nonpaired cadaver feet were tested in a dynamic gait stimulator, which reproduces the kinematics and kinetics of the foot, ankle, and tibia by applying physiologic muscle forces and proximal tibial kinematics. The distribution of plantar pressure beneath the foot was measured at the terminal stance phase of gait under normal extrinsic muscle activity with an intact plantar fascia, in the absence of extrinsic toe flexor activity (no flexor hallucis longus or flexor digitorum longus) with an intact plantar fascia, and after complete fasciotomy with normal extrinsic toe flexor activity. In the absence of the toe flexor muscles or after plantar fasciotomy the contact area decreased beneath the toes and contact force shifted from the toes to the metatarsal heads. In addition, pressure distribution beneath the metatarsal heads after fasciotomy shifted laterally and posteriorly, indicating that the plantar fascia enables more efficient force transmission through the high gear axis during locomotion. The plantar fascia enables the toes to provide plantar-directed force and bear high loads during push-off.

Bone strain and microcracks at stress fracture sites in human metatarsals.

Microcracks in bone have been implicated in the development of stress fractures. The goal of this study was to evaluate bone strain and microcracks at locations where stress fractures are common (second metatarsal diaphysis) and rare (fifth metatarsal diaphysis) in an attempt to increase our understanding of the pathogenesis of stress fractures. A dynamic gait simulator was used to simulate normal walking with cadaver feet. The feet were loaded over the entire stance phase of gait and diaphyseal strains were recorded in second and fifth metatarsals. Microcrack density (Cr.Dn) and surface density (Cr.S.Dn) were determined in metatarsal cross sections from the contralateral feet. Bone strain was significantly higher in second metatarsals (-1897 +/- 613 microstrain) than in fifth metatarsals (-908 +/- 503 microstrain). However, second metatarsal Cr.Dn (0.23 +/- 0.15 #/mm(2)) was not significantly different from fifth metatarsal Cr.Dn (0.35 +/- 0.19 #/mm(2)). There was also no significant difference between Cr.S.Dn in second (17.64 +/- 10.99 microm/mm(2)) and fifth (26.70 +/- 15.53 microm/mm(2)) metatarsals. There were no significant relationships between the microcrack parameters and peak strain in either metatarsal. Cracks that occurred in trabecular struts (92 +/- 33 microm) were significantly longer than those found ending at cement lines (71 +/- 15 microm) and within osteons (57 +/- 16 microm). There were no significant relationships between the microcrack parameters and age in either metatarsal. Peak strain was more than twofold greater in second metatarsals than in fifth metatarsals for simulations of normal walking; however, microcrack parameters were unable to explain the greater incidence of second metatarsal stress fractures.

The role of exercise in the prevention and treatment of osteoporosis and osteoarthritis.

Osteoporosis and osteoarthritis are two distinctly different rheumatic conditions that target elderly, primarily female, populations. This article examines the scientific evidence supporting the use of exercise as a specific therapeutic modality, the general physiologic and psychological benefits of exercise, and the exercise programs currently recommended to combat these prevalent musculoskeletal disorders. Exercise is a valuable adjunct to treatment programs aimed at alleviating the risks and symptoms of osteoporosis and osteoarthritis. In addition to its potential impact on the disease processes themselves, exercise improves general health and well being, enhances quality of life, and preserves physical independence.

Strains in the metatarsals during the stance phase of gait: implications for stress fractures.

BACKGROUND: Stress fractures of the metatarsals are common overuse injuries in athletes and military cadets, yet their etiology remains unclear. In vitro, high bone strains have been associated with the accumulation of microdamage and shortened fatigue life. It is therefore postulated that stress fractures in vivo are caused by elevated strains, which lead to the accumulation of excessive damage. We used a cadaver model to test the hypothesis that strains in the metatarsals increase with simulated muscle fatigue and plantar fasciotomy. METHODS: A dynamic gait simulator was used to load fifteen cadaveric feet during the entire stance phase of gait under conditions simulating normal walking, walking with fatigue of the auxiliary plantar flexors, and walking after a plantar fasciotomy. Strains were measured, with use of axial strain-gauges, in the dorsal, medial, and lateral aspects of the diaphysis of the second and fifth metatarsals as well as in the proximal metaphysis of the fifth metatarsal. RESULTS: When the feet were loaded under normal walking conditions, the mean peak strain in the dorsal aspect of the second metatarsal (-1897 microstrain) was more than twice that in the medial aspect of the fifth metatarsal (-908 microstrain). Simulated muscle fatigue significantly increased peak strain in the second metatarsal and decreased peak strain in the fifth metatarsal. Release of the plantar fascia caused significant alterations in strain in both metatarsal bones; these alterations were greater than those caused by muscle fatigue. After the plantar fasciotomy, the mean peak strain in the dorsal aspect of the second metatarsal (-3797 microstrain) was twice that under normal walking conditions. CONCLUSIONS: The peak axial strain in the diaphysis of the second metatarsal is significantly (p < 0.0001) higher than that in the diaphysis of the fifth metatarsal during normal gait. The plantar fascia and the auxiliary plantar flexors are important for maintaining normal strains in the metatarsals during gait.

Unilateral elbow arthrodesis: the preferred position.

Twenty-five volunteers had unilateral elbow immobilization for 24 hours in each of two positions of flexion, 45 degrees and 90 degrees . Twenty-two of the 25 volunteers preferred a position of 90 degrees of flexion. Standard functional testing revealed significant limitations in each position of immobilization, confirming that there is no single optimal position of elbow arthrodesis. This study suggests that, for most individuals, 90 degrees is the preferred position of elbow arthrodesis for activities of daily living. However, factors such as age, sex, occupation, and dominance of the extremity should be considered when choosing a position of arthrodesis.

Biomechanical evaluation of impaction fractures of the femoral head.

OBJECTIVES: To measure the effect of an impaction fracture of the femoral head on load transmission in the hip joint. DESIGN: We measured the contact areas and pressure between the acetabulum and femoral head of cadaveric pelves in four different conditions: intact, with an operatively created one-square-centimeter defect in the superior femoral head, with a two-square-centimeter defect, and with a four-square-centimeter defect. All defects were uniformly three millimeters deep. SETTING: Hips were loaded in a simulated single-limb stance. Pressure and area measurements were made with Fuji pressure-sensitive film. SPECIMENS: Seven hip joints in seven whole pelves were tested. MAIN OUTCOME MEASUREMENTS: Contact area, load, and mean and maximum pressures were measured. RESULTS: Peripheral loading was seen in the intact acetabulum. This was not disrupted after impaction fractures of any size. A significant increase in mean maximum pressures in the superior acetabulum was seen with two-square-centimeter and four-square-centimeter defects. CONCLUSIONS: In contrast to prior biomechanical studies of acetabular fractures, our investigation revealed that disruption of the peripheral distribution of load does not occur with impaction fractures of the femoral head. Clinical series indicate that impaction injuries to the femoral head are associated with a poor prognosis. Previous biomechanical data on acetabular fracture patterns associated with a poor prognosis have shown increases in mean and peak pressures in the superior acetabulum. This was seen with two-square-centimeter and four-square-centimeter impaction injuries. Other factors, such as wear of the articular cartilage during joint motion or associated microscopic damage to the remainder of the joint surface at the time of injury, may also contribute to the rapid joint deterioration seen in these injuries. Further study is indicated.

Forearm interosseous ligament isometry.

Biomechanical testing was performed to determine isometric interosseous ligament graft placement as a preliminary step for reconstruction after an axial forearm disruption. Twenty-five combinations of potential ligament graft placement were studied on 7 fresh-frozen cadavers. Suture was used to simulate these potential ligament reconstructions, and suture excursion was used as an index of isometry. Ligament orientation was defined by the angle formed between the ulna and the suture (surrogate graft). Ligament position was defined by its insertion on the ulna as a percentage of ulna length. Suture-ulna angles from 9 degrees to 38 degrees produced significantly less suture excursion than angles of > or = 39 degrees. Minimal suture excursion was noted at angles of < or = 20 degrees, which we feel represents the optimal range for reconstruction. The optimal location on the ulna for isometric interosseous ligament reconstruction was at 25% to 30% of total ulna length, as measured proximally from the distal ulna articular surface. The radius isometric location is optimally located by a vector starting from the ulna isometric point and directed toward the proximal radius at an angle of < or = 20 degrees relative to the long axis of the ulna. Interosseous ligament reconstruction may prove beneficial in the long-term outcome of reconstruction after axial forearm disruption.

Biomechanical consequences of plantar fascial release or rupture during gait. Part II: alterations in forefoot loading.

With a model using feet from cadavers, we tested the hypothesis that plantar fascial release or rupture alters the loading environment of the forefoot during the latter half of the stance phase of gait. The model simulated the position and loading environment of the foot at two instants: early in terminal stance immediately after heel-off and late in terminal stance just preceding contralateral heel strike. Eight feet were loaded at both positions by simulated plantar flexor contraction, and the distribution of plantar pressure was measured before and after progressive release of the plantar fascia. Strain in the diaphysis of the second metatarsal was also measured, from which the bending moments and axial force imposed on the metatarsal were calculated. Cutting the medial half of the central plantar fascial band significantly increased peak pressure under the metatarsal heads but had little effect on pressures in other regions of the forefoot or on second metatarsal strain and loading. Dividing the entire central band or completely releasing the plantar fascia from the calcaneus had a much greater effect and caused significant shifts in plantar pressure and force from the toes to beneath the metatarsal heads. These shifts were accompanied by significantly increased strain and bending in the second metatarsal. Complete fasciotomy increased the magnitude of strain in the dorsal aspect of the second metatarsal by more than 80%, suggesting that plantar fascial release or rupture accelerates the accumulation of fatigue damage in these bones. Altered forefoot loading may be a potential complication of plantar fasciotomy.

Characteristics of pedicle screw loading. Effect of surgical technique on intravertebral and intrapedicular bending moments.

STUDY DESIGN: A static nondestructive bending analysis of pedicle screws inserted into vertebral analogues was conducted. Pedicle screw load was studied as a function of variables in insertion technique. OBJECTIVES: To determine how the sagittal bending moment in pedicle screws is affected by changes in pedicle screw length, insertional depth, and sagittal placement. BACKGROUND DATA: An unexpectedly high rate of clinical failure has been observed in pedicle screws used in short-segment instrumentation for unstable burst fractures. The majority of screws fail in sagittal bending within the pedicle. Little is known of the insertion technical factors that affect in situ loads incurred by pedicle screws. METHODS: Synthetic vertebral analogues were fabricated. Pedicle screws internally instrumented with strain gauges were used as load transducers to determine screw bending moments within the pedicle and body of the analogue. Analogues were loaded in compression to simulate loading of an unstable burst fracture. RESULTS: Screw bending moments within the pedicle increased 33% and 52% when screws were left 3 mm and 5 mm short of full insertion. Intrapedicular moments increased 20% to 29% in screws inserted superiorly or inferiorly within the pedicle. Thirty-five-millimeter screws developed intrapedicular moments 16% higher than 40-mm and 45-mm screws. CONCLUSIONS: In situ pedicle screw loads increased significantly as a direct result of variations in surgical technique. Screws left short of full insertion, placed off center in the sagittal plane of the pedicle, or less than 40 mm long developed increased intrapedicular bending moments.

Biomechanical consequences of anterior column fracture of the acetabulum.

OBJECTIVES: To measure biomechanical consequences of a high anterior column acetabular fracture. DESIGN: A benchtop biomechanical model using quasi-static loading of the hip joint in a simulated single-leg stance. Pressure-sensitive prescale (Fuji) film was used to determine hip joint loading parameters. PARTICIPANTS: Six cadaveric hemipelvi with one hip tested in each specimen. Three right and three left hips were tested. INTERVENTION: Creation of an anterior column fracture with anatomic reduction and fixation, followed by gap malreduction/fixation, and subsequently step malreduction/fixation. MAIN OUTCOME MEASUREMENTS: Contact pressure, contact area, and load distribution throughout the hip joint in each experimental condition. RESULTS: There were significant increases in load (p<0.01) and peak pressures (p<0.01) in the superior acetabular region after gap malreduction and in peak contact pressures after step malreduction (p<0.01) as compared with the intact acetabulum. Anatomic reduction was not associated with increased mean or peak contact pressures (in any region). CONCLUSIONS: Both step and gap malreductions of a high anterior column fracture resulted in significantly increased peak contact pressures in the superior acetabular region. These biomechanical data cannot be directly extrapolated to clinical applications, but these data suggest that anatomic reduction of anterior column fracture affords the best opportunity to restore contact pressures, contact area, and load distribution within the hip to levels similar to those seen in the intact acetabulum.

Pathomechanics of closed rupture of the flexor tendon pulleys in rock climbers.

We performed a study on twenty-one cadaveric fingers (seven non-paired forearms) to determine the pathomechanics of closed traumatic rupture of the flexor tendon pulleys in rock climbers. The ages of the individuals at the time of death ranged from sixty-one to eighty-four years (mean, seventy-four years). The forearm was placed in a custom-made loading apparatus, and individual fingers were tested separately under simulated in vivo loading conditions. The flexor digitorum superficialis and profundus tendons of each digit were attached to computer-controlled linear stepper motors that were equipped with force transducers, and the force in the tendons was simultaneously increased until avulsion of the tendons or osseous failure occurred. The force in the tendons, the excursion of the tendons, and the force at the fingertip were measured. Damage to the pulleys and bowstringing of the tendons were visualized with a fiberoptic camera. Two fingers fractured before complete rupture of the pulleys. Seventeen of the remaining nineteen fingers sustained an isolated rupture of either the A2 or the A4 pulley as the initial failure event; the A4 pulley ruptured first in fourteen digits (p < 0.001). The A3 and A4 pulleys ruptured simultaneously in one finger, and the A2, A3, and A4 pulleys ruptured simultaneously in another. Subtle bowstringing of the flexor digitorum profundus tendon occurred only after two consecutive pulleys had ruptured (either the A2 and A3 pulleys or the A3 and A4 pulleys). Rupture of all three pulleys was required to produce obvious bowstringing. Isolated rupture of the A2 or A4 pulley did not result in detectable bowstringing of the flexor digitorum profundus tendon. The A1 pulley always remained intact.

Biomechanical evaluation of a low anterior wall fracture: correlation with the CT subchondral arc.

OBJECTIVE: To measure the effect of a simulated low anterior wall fracture of the acetabulum on load transmission in the hip joint. DESIGN: We measured the contact areas and pressure between the acetabulum and the femoral head of cadaveric pelves in three different conditions: intact, with an operatively created fracture of the anterior wall, and after anatomic reduction and internal fixation of the fracture. SETTING: Hips were loaded in simulated single-limb stance. Pressure and area measurements were made with Fuji pressure-sensitive film. SPECIMENS: Seven hip joints in seven whole pelves were tested. INTERVENTION: Anterior wall fractures were anatomically reduced and fixed. MAIN OUTCOME MEASUREMENTS: Contact area, load, and mean and maximum pressures were measured. RESULTS: Anterior wall fractures in our specimens entered the hip joint an average of 9.7 millimeters from the vertex of the acetabulum, corresponding to a 45-degree roof arc measurement. Peripheral loading seen in the intact acetabulum was disrupted after fracture. The loading pattern was not restored to preinjury levels with anatomic reduction and fixation. There was no significant change in the contact area (p = 0.43), force (p = 0.06), or mean (p = 0.57) or maximum (p = 0.20) pressures in the superior aspect of the acetabulum after creation of the anterior wall fracture. CONCLUSIONS: These results differ from those of previous studies with posterior wall acetabulum fractures, where significant increases in force and mean and maximum pressures were noted in the superior acetabulum after fracture. The lack of significant increases in superior acetabular pressures is discussed in relation to the mean computed tomographic subchondral arc of approximately ten millimeters in our specimens.

Consequences of transverse acetabular fracture malreduction on load transmission across the hip joint.

OBJECTIVE: To evaluate the biomechanical behavior of gap and step malreductions in a model of transverse acetabular fracture. DESIGN: Cadaver pelvis loading in simulated single-leg stance with intact acetabulum, after transverse acetabular fracture anatomically reduced, and after step and gap malreduction. Five transtectal transverse fractures; five juxtatectal transverse fractures. SETTING: Quasi-static loading of the hip with simulated abductor mechanism to physiologic loads with pressure-sensitive film interposed in the joint to determine contact area and contact pressure within the hip joint. MAIN OUTCOME MEASUREMENT: Hip joint contact parameters: contact area, peak and mean contact pressure, and load distribution. RESULTS: Step malreduction of the transtectal transverse fracture resulted in significantly increased peak contact pressures (20.5 megapascals) in the superior acetabular articular surface as opposed to the intact acetabulum (9.1 megapascals). Gap malreduction of transtectal transverse fracture and step and gap malreduction of juxtatectal fracture did not result in significantly increased contact pressures in the hip. CONCLUSION: Step malreduction of a transverse acetabular fracture in the superior articular surface results in abnormally high contact forces and may predispose to the development of posttraumatic arthritis.

Biomechanical consequences of plantar fascial release or rupture during gait: part I--disruptions in longitudinal arch conformation.

To examine whether conformational changes induced by plantar fascial division may progress during gait, we loaded the feet of seven cadavers using an apparatus that simulates the actions of the extrinsic plantarflexors. We measured the effects of plantar fasciotomy at two instants in the terminal-stance phase of gait. Radiographic measurements of height of the arch, base length of the arch, and talo first-metatarsal angle were used to assess contributions to arch support made by the plantar fascia, tibialis posterior, peroneus longus and brevis, and digital flexor muscles. Complete fasciotomy caused significant collapse of the arch in the sagittal plane. Early in terminal stance, at the instant after heel-off, mean height of the arch decreased from 47 to 45 mm. Late in terminal stance, at the instant preceding contralateral heel strike, mean height of the arch decreased from 46 to 43. Effects of division of the central band, though significant, were mild. Medial base length of the arch increased from 163 to 167 mm in the absence of tibialis posterior contraction at late terminal stance. Arch-supporting abilities of the other extrinsic muscles were insignificant.