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The motions of the tibia, talus, and calcaneus during walking were analyzed three-dimensionally using a dynamic cadaver model that recreates the stance phase of walking. Rigid marker clusters were attached to each of the three bones, and the rotations of the talus and calcaneus with respect to the tibia and the calcaneus with respect to the talus were analyzed for eight right cadaver feet. The talus rotated primarily in plantarflexion/dorsiflexion about the talocrural joint, with an average range of 18 degrees +/- 4.7 degrees. The calcaneus began in inversion and internal rotation with respect to the tibia, moved into the neutral position at 28% of the stance phase and rotated primarily in plantarflexion from that point onward. Rotation of the calcaneus with respect to the talus at the subtalar joint occurred about all three axes, with approximately 5 degrees of relative dorsiflexion and 7 degrees of relative internal rotation. After 25% of stance, the talus and calcaneus moved together as one body into plantarflexion, providing a rigid lever as toe-off was approached.

A closed intraarticular fracture is a complex injury that consists of a physical disruption of the subchondral bone and articular surface, and an impaction injury to the articular surface that occurs at the time of the fracture. Few experimental models have been able to incorporate the elements of displaced articular fractures and blunt impaction injury to the articular surface. This work details the initial stages of an attempt to develop such model. Using a model of a dorsal wall fracture of the acetabulum in a goat, we have developed a bench-top method for assessing articular contact stress. Additionally, preliminary in vivo survival data are presented.

Background: The plantar aponeurosis is known to be a major contributor to arch support, but its role in transferring Achilles tendon loads to the forefoot remains poorly understood. The goal of this study was to increase our understanding of the function of the plantar aponeurosis during gait. We specifically examined the plantar aponeurosis force pattern and its relationship to Achilles tendon forces during simulations of the stance phase of gait in a cadaver model., Methods: Walking simulations were performed with seven cadaver feet. The movements of the foot and the ground reaction forces during the stance phase were reproduced by prescribing the kinematics of the proximal part of the tibia and applying forces to the tendons of extrinsic foot muscles. A fiberoptic cable was passed through the plantar aponeurosis perpendicular to its loading axis, and raw fiberoptic transducer output, tendon forces applied by the experimental setup, and ground reaction forces were simultaneously recorded during each simulation. A post-experiment calibration related fiberoptic output to plantar aponeurosis force, and linear regression analysis was used to characterize the relationship between Achilles tendon force and plantar aponeurosis tension., Results: Plantar aponeurosis forces gradually increased during stance and peaked in late stance. Maximum tension averaged 96% +/- 36% of body weight. There was a good correlation between plantar aponeurosis tension and Achilles tendon force (r = 0.76)., Conclusions: The plantar aponeurosis transmits large forces between the hindfoot and forefoot during the stance phase of gait. The varying pattern of plantar aponeurosis force and its relationship to Achilles tendon force demonstrates the importance of analyzing the function of the plantar aponeurosis throughout the stance phase of the gait cycle rather than in a static standing position., Clinical Relevance: The plantar aponeurosis plays an important role in transmitting Achilles tendon forces to the forefoot in the latter part of the stance phase of walking. Surgical procedures that require the release of this structure may disturb this mechanism and thus compromise efficient propulsion.

Fiberoptic cables have previously been used for tendon force measurements in vivo. To measure forces in the Achilles tendon, a cable is passed mediolaterally through the skin and tendon, transverse to the loading axis. As the tendon is loaded, its fibers compress the cable and modulate the intensity of transmitted light, which can be related to tendon force by an in situ calibration. The relative movement between skin and tendon at the cable entry and exit sites may cause error by bending the cable and thus altering transducer output. Cadaver simulations of walking were conducted to compare fiberoptic measurements of Achilles tendon forces to known loads applied to the tendon by actuators attached in series. Force measurement errors, which were high when the skin was intact (RMS errors 24-81% peak forces), decreased considerably after skin removal (RMS errors 10-33% peak forces). The fiberoptic transducer is a useful tool for measurement of tendon forces in situ under natural loading conditions when skin can be removed, but caution should be exercised during in vivo use of this technique or under circumstances where skin is in contact with the fiberoptic cable at the insertion and exit sites.

Background: Previous studies involving axially loaded ankle cadaver specimens undergoing a passive range of motion after fracture have demonstrated rotatory instability patterns consisting of excessive external rotation during plantar flexion. The present study was designed to expand these studies by using a model in which ankle motion is controlled by physiologically accurate motor forces generated through phasic force-couples attached to the muscle-tendon units., Methods: Eight right unembalmed cadaver feet were tested in a dynamic gait simulator that reproduces the sagittal kinematics of the tibia while applying physiological muscle forces to the tendons of the major extrinsic muscles of the foot. Six-degrees-of-freedom kinematics of the tibia and talus were measured with use of a VICON motion-analysis system. The experimental conditions included all combinations of lateral and medial injury to reproduce the clinical classifications of ankle fracture. Statistical analysis was performed with repeated-measures analyses of variance., Results: The talus of the intact ankles demonstrated coupled external rotation and inversion relative to the tibia as the ankle plantar flexed. Osteotomy of the fibula, simulating a lateral ankle fracture, slightly but significantly increased external rotation and inversion of the talus (p < 0.001), whereas disruption of either the superficial or the deep deltoid ligament increased talar eversion (p < 0.003) and disruption of the deep deltoid ligament increased internal rotation (p < 0.0001). The aberrant motions were corrected by repair of the injured structure., Conclusions: The predominant coupled rotation of the talus is external rotation associated with plantar flexion. Following progressive ankle destabilization, talar external rotation and inversion increased., Clinical Relevance: The clinical decision-making process regarding the treatment of ankle fractures centers on determination of whether the injury is expected to result in abnormal motion, which is thought to predispose to the development of arthritis. The present study demonstrated a remarkable degree of ankle stability during stance phase even when there was severe disruption of medial and lateral structures. This finding suggests that a main determinant of clinical outcome after ankle fracture may be ankle motion during swing phase, when ankle stability is not augmented by the combination of axial loading and active motor control of motion. If swing-phase motion is abnormal, then the ankle may be in a vulnerable position at the point of heel-strike.

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.

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.

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.

We performed a biomechanical study of seventeen hip joints in the pelves of nine cadavera in order to assess the role that the acetabular labrum and the transverse acetabular ligament play in load transmission. The distribution of contact area and pressure between the acetabulum and the femoral head was measured with the hip in four different conditions: intact (seventeen hips), after removal of the transverse acetabular ligament (eight hips), after removal of the entire labrum (nine hips), and after removal of both the transverse acetabular ligament and the labrum (seventeen hips). The hip joint was loaded in simulated single-limb stance, and the measurements were made with use of pressure-sensitive film. A peripheral distribution of load was seen in the intact acetabula. This pattern was altered only minimally after removal of the transverse acetabular ligament or the labrum, or both. When both of these structures were removed, the only significant change was a decrease in the maximum pressure in the posterior aspect of the acetabulum (p = 0.02). No significant changes were detected with regard to the contact area, load, mean pressure, or maximum pressure in the anterior or superior aspect of the acetabulum under any testing condition.

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.

OBJECTIVE: This study was undertaken to evaluate the performance of a new dynamic laboratory model of the stance phase of gait. DESIGN: Five cadaver feet were repetitively tested in the apparatus. BACKGROUND: Typical biomechanical investigations of cadaver feet simply place a static load on the tibia. The present system was designed to better simulate the changing in-vivo loading environment of the foot and ankle during gait. METHODS: The device mimics the behavior of the tibia, foot, and ankle from heel-strike to toe-off by reproducing the physiologic actions of five extrinsic foot muscles and physiologic motion at the proximal tibia. To verify its utility, cadaver gait simulations were conducted while measuring applied muscle forces, ground reaction forces, and plantar pressures. RESULTS: Dynamic muscle forces were consistently delivered to within 10% of pre-programmed values. Dynamic measurements of ground reaction forces and plantar pressure were similar to those measured in healthy human subjects. Peak vertical (y), foreaft (x) and medio-lateral (z) forces were 110, 18, and 4% of body weight respectively. Compressive force in the tibial shaft reached 410% of body weight. RELEVANCE: Cadaver studies have greatly enhanced our understanding of normal and pathologic foot function, but are often limited by over-simplified loading conditions. The apparatus presented here accurately reproduces the in-vivo loading environment and provides a powerful investigational tool for the study of foot and ankle function. With this device, musculoskeletal structures can be examined in detail under biomechanical conditions similar to those they experience in life.

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.

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.

The hip is a common site of orthopaedic trauma and disease, and considerable research has been directed toward understanding the development of contact pressures within the joint. Virtually all experimental studies to date have employed proximal femurs compressed along the joint reaction force vector into acetabulae explanted from cadaver pelves. This approach presumes that deformations of the acetabulum are highly localized, and that the pelvis is functionally a rigid body. We have developed a methodology that uses intact pelves loaded through simulation of the abductor mechanism. A direct comparison of the two techniques revealed significantly different joint contact characteristics and periacetabular strains. Fuji film measurements of contact area and pressure were more widely distributed across the acetabulum for the intact pelvis, with significant pressure development in anterior and posterior regions. Contact patterns in the explanted acetabulae were concentrated in the superior portion of the joint. Principal strains from three rosette gages placed near the acetabular rim were also significantly different for the two testing techniques, but were not substantially altered by the presence of Fuji film within the joint. The results indicate that deformation of the entire pelvis and the manner in which loads are applied significantly affect development of contact pressures within the hip joint, and that Fuji film is a suitable technique for recording those patterns.

One hundred seventeen patients had indwelling arterial illness for hemodynamic monitoring and blood sampling. The duration of catheterization varied from 25 to 439 hours, during which time no components of the system were replaced. In contrast to other reports, our study showed no instance of contamination of transducer dome fluid when the continuous flush device was located just distal to the transducer. The sampling stopcock showed bacterial growth in 16.2% of patients. In the one case in which the arterial catheter tip, stopcock, and patient's blood showed the same organism, culture of the transducer fluid was negative. Our results suggest that elimination of a static inline fluid column and proper aseptic sampling technique limit risk to the patient of transmitted bacterial infection from the fluid in the system. Routine changes of components of the system are not indicated and a substantial cost saving can be achieved.

Internal intrapartum fetal monitoring has been implicated as a source of maternal and fetal sepsis. We report water-borne contamination of a component of the intrauterine pressure transducer and suggest that this may be a potential source of nosocomial infection.

Using the standard MA-1 breathing circuit, the Cascade Heated Humidifier and tubing become rapidly contaminated with patient organisms. The rapidity with which this occurs seems to depend on the quantity and quality of patient secretions and dumping infected water from lazy loops into the Humidifier. Following modifications to the ventilator circuit which included: (1) closed system humidifier filling, (2) the addition of a small copper trap and drainage system to the inspired side of the breathing circuit, and (3) alteration of the heater, no contamination of the humidifier contents occurred for periods as long as 28 days. This trap was manufactured in our hospital using standard plumbing fixtures; a commercial model is available. This system is applicable to any volume ventilator using a heated reservoir humidifier.