Search Results
A new theory of foot function based on the spatial location of the subtalar joint axis in relation to the weightbearing structures of the plantar foot is proposed. The theory relies on the concept of subtalar joint rotational equilibrium to explain how externally generated forces, such as ground reaction force, and internally generated forces, such as ligamentous and tendon tensile forces and joint compression forces, affect the mechanical behavior of the foot and lower extremity. The biomechanical effect of variations among individuals in the spatial location of the subtalar joint axis are explored, along with their clinical consequences, to offer an additional theory of foot function, which may improve on existing podiatric biomechanics theory. (J Am Podiatr Med Assoc 91(9): 465-487, 2001)
Background: The biomechanics of the foot and leg are responsible for shock absorption during human gait. Lack of shock absorption is known to be a key component of knee pain. This study compares a new model of shoe sole with a built-in modification intended to absorb shock with a traditional sole shoe to examine whether shoe design modifications can help alleviate knee pain.
Methods: A double-blind randomized controlled study was performed. Fifty-two adults with overuse symptoms of knee pain, either unilateral or bilateral, were enrolled and randomly assigned to use the intervention sole or the traditional sole shoes. For 5 weeks, participants wore either the shoe with the intervention sole or the shoe with the traditional sole, rating their knee pain on a 10-point visual analog scale at study onset, midway, and study completion.
Results: After 5 weeks, participants using the intervention sole shoe reported an average reduction in knee pain of 85%, significantly better than participants using the traditional sole shoe (P < .001), whose average pain scores increased. Positive effects on back and foot pain were also observed in those with the intervention sole shoe compared with the traditional sole shoe.
Conclusions: The intervention shock-absorbing sole represents an approach to midsole and outsole construction that can potentially increase shock absorption and decrease knee pain during prolonged standing and walking.
Background
Screw fixation of syndesmotic injuries facilitates ligament healing and restoration of ankle stability, but failure of the screw might threaten the success of the treatment. Screw design parameters, such as outer diameter, inner diameter, thread pitch, leading edge radius, trailing edge radius, leading edge angle, and trailing edge angle, might have effects on the stresses that occur in the screws. This is the first study, to our knowledge, to investigate which geometric screw parameters play key roles in stresses that occur in screws used for syndesmotic fixation.
Methods
A three-dimensional finite element model of an ankle was reconstructed. Four different types of titanium screws—4.5-mm malleolar, 4-mm cancellous, 4-mm machine, and 3.5-mm cortical—were placed on this model. Physiologic load was applied to evaluate the stress in the screw. Then the contribution of each design factor to stress in the screws was analyzed systematically by Taguchi's robust design method.
Results
The maximum equivalent ductile failure (von Mises equivalent stress) value was found in the 4-mm cancellous screw (402 MPa). Taguchi's analysis showed that the descending order of contribution of the design factors to stress emerging on the screw is inner diameter, leading edge angle, thread pitch, outer diameter, and trailing edge angle.
Conclusions
Stress that occurs in syndesmotic screws is closely related to their geometry and dimensions. According to the results, a 3.5-mm cortical screw with the ideal screw design regarding optimal parameters to resist against stresses in the syndesmosis seems more reasonable to choose in syndesmotic fixation.
In this study of people with diabetes mellitus and peripheral neuropathy, it was found that the feet of patients with a history of hallux ulceration were more pronated and less able to complete a single-leg heel rise compared with the feet of patients with a history of ulceration elsewhere on the foot. The range of active first metatarsophalangeal joint dorsiflexion was found to be significantly lower in the affected foot. Ankle dorsiflexion, subtalar joint range of motion, and angle of gait differed from normal values but were similar to those found in other studies involving diabetic subjects and were not important factors in the occurrence of hallux ulceration. These data indicate that a more pronated foot type is associated with hallux ulceration in diabetic feet. Further studies are required to evaluate the efficacy of footwear and orthoses in altering foot posture to manage hallux ulceration. (J Am Podiatr Med Assoc 96(3): 189–197, 2006)
Background:
Rocker shoes are commonly prescribed to healthy and pathologic populations to decrease stress on the lower limbs. An optimal rocker shoe design must consider both toe and heel rockers. Heel rockers are as effective as toe rockers in relieving foot plantar pressures. However, most studies have focused on the position of toe rockers. The aim of this study was to assess the effect of different heel rocker apex placements on lower-limb kinetics and kinematics.
Methods:
Eighteen healthy females participated in this study. Three pairs of rocker shoes with rocker apex positions anterior to the medial malleolus (shoe A), at the medial malleolus (shoe B), and posterior to the medial malleolus (shoe C) were fabricated and then compared with a flat shoe (shoe D). Kinetic and kinematic data were collected, and lower-extremity joint ranges of motion and moments were calculated.
Results:
Ankle range of motion was increased by shoe C (P = .04) during initial contact and by shoe A (P = .02) during single-limb support. Peak knee moment was significantly larger for shoes A and B (P < .05) during single-limb support.
Conclusions:
Results showed that forward and backward shifting of the heel rocker apex could change the knee moment and ankle joint range of motion in the stance phase of gait. Therefore, placement of the heel rocker in a rocker-bottom shoe can be manipulated to promote the desired lower-limb motion, at least in healthy individuals.
The presence of synovial folds in various joints of the foot has been previously documented. The function and clinical significance of these structures within the joint have not been established. Histologically they are considered anatomically different from a meniscus primarily owing to their makeup of loose connective tissue with nerve fibrils and several synovial cell layers. We hypothesize that the function of these folds is similar to that of the menisci: to increase joint congruity and stability. We further hypothesize that these folds will be present in joints of the foot that require greater stability. To demonstrate this, 41 fixated cadaveric feet were sectioned in the sagittal plane and the incidence and locations of the synovial folds were documented. Three fixated cadaveric feet were evaluated using a materials testing machine. The first metatarsophalangeal joint was incised, and the presence of the synovial fold was documented. The joint was then taken through its range of motion with and without the synovial fold while data on the force and displacement were collected. The steps were then repeated for the ankle joint. The results showed statistically stiffer ankle and first metatarsophalangeal joints with the synovial fold present, as determined by the stress-strain curve. On the basis of the presence and location of these synovial folds, we demonstrated arthroscopic surgical approaches to many of the documented joints that contain these folds. Because the folds contain synovial cells and vascular tissue, damage to them can result in considerable pain. In such cases, arthroscopic surgery would be of benefit. Further research may indicate whether they need to be salvaged during joint procedures to facilitate normal joint function or should be removed to reduce postoperative complications. (J Am Podiatr Med Assoc 94(6): 519–527, 2004)
Background: Muscle disorders may cause a change in plantar pressures by the misalignment on the foot during gait phases. Therefore, corns or calluses develop at the plantar regions, and diabetic foot ulcers follow for severe cases, although it can be prevented and even treated by podiatric approaches with patient-specific therapeutic insoles and footwear. Although the importance of a threshold value of 200 kPa in peak plantar pressure reduction has been highlighted as a standard to prevent reulceration in the diabetic foot, it may not be possible to ensure this pressure reduction for each patient.
Methods: In this study, three types of ethylene-vinyl acetate have been used to optimize the off-loading performance for predetermined early-stage diabetic foot ulcer scenarios by means of baropodometric plantar pressure analyses and finite element method for each gait phase.
Results: The total cost of the manufacturing for this study was reduced to $10.26 and it was performed in 24.6 minutes. In addition, the off-loaded pressure was increased by 2.3 times and the volume of the off-loading geometry was increased 8.12 times based on the foam polymer used.
Conclusions: Consequently, improved off-loading was obtained and a standard was proposed for the first time to calculate the off-loading performance before manufacturing of the therapeutic insole model to ensure a better recovery period.
Background: We investigated the relationship between functional and static foot posture and medial tibial stress syndrome in distance runners.
Methods: Twenty-eight runners with a clinical diagnosis of medial tibial stress syndrome and 12 asymptomatic runners were assessed with the Foot Posture Index to measure static overpronation. Range of motion was measured at the talocrural joint, with the knee extended and flexed as was range of motion at the first metatarsophalangeal joint and the angular difference between the neutral and relaxed calcaneal stance positions. Each participant was then videotaped while running on a treadmill shod and unshod. This videotape was analyzed using freeze frame to identify abnormal or mistimed pronation at each phase of gait. The results were analyzed using logistic regression to give the probability that a runner is likely to experience medial tibial stress syndrome, predicted from the static measurements and dynamic observations.
Results: Variables identified as being significant predictors of medial tibial stress syndrome were the difference between the neutral and relaxed calcaneal stance positions, range of motion of the talocrural joint with the knee extended, early heel lift and abductory twist during gait, and apropulsive gait.
Conclusion: Runners with suspected symptoms of medial tibial stress syndrome should be assessed dynamically and statically for abnormal or mistimed pronation. (J Am Podiatr Med Assoc 98(6): 436–444, 2008)