William R. Ledoux

Triangular osteosynthesis and iliosacral screw fixation for unstable sacral fractures: a cadaveric and biomechanical evaluation under cyclic loads.

Objective To conduct a biomechanical comparison of a new triangular osteosynthesis and the standard iliosacral screw osteosynthesis for unstable transforaminal sacral fractures in the immediate postoperative situation as well as in the early postoperative weight-bearing period. Design Twelve preserved human cadaveric lumbopelvic specimens were cyclicly tested in a single-limb-stance model. A transforaminal sacral fracture combined with ipsilateral superior and inferior pubic rami fractures were created and stabilized. Loads simulating muscle forces and body weight were applied. Fracture site displacement in three dimensions was evaluated using an electromagnetic motion sensor system. Intervention Specimens were randomly assigned to either an iliosacral and superior pubic ramus screw fixation or to a triangular osteosynthesis consisting of lumbopelvic stabilization (between L5 pedicle and posterior ilium) combined with iliosacral and superior pubic ramus screw fixation. Main Outcome Measures Peak loaded displacement at the fracture site was measured for assessment of initial stability. Macroscopic fracture behavior through 10,000 cycles of loading, simulating the early postoperative weight-bearing period, was classified into type 1 with minimal motion at the fracture site, type 2 with complete displacement of the inferior pubic ramus, or type 3 with catastrophic failure. Results The triangular osteosynthesis had a statistically significantly smaller displacement under initial peak loads (mean ± standard deviation [SD], 0.163 ± 0.073 cm) and therefore greater initial stability than specimens with the standard iliosacral screw fixation (mean ± SD, 0.611 ± 0.453 cm) (p = 0.0104), independent of specimen age or sex. All specimens with the triangular osteosynthesis demonstrated type 1 fracture behavior, whereas iliosacral screw fixation resulted in one type 1, two type 2, and three type 3 fracture behaviors before or at 10,000 cycles of loading. Conclusion Triangular osteosynthesis for unstable transforaminal sacral fractures provides significantly greater stability than iliosacral screw fixation under in vitro cyclic loading conditions. In vitro cyclic loading, as a limited simulation of early stages of patient mobilization in the postoperative period, allows for a time-dependent evaluation of any fracture fixation system.

The distributed plantar vertical force of neutrally aligned and pes planus feet

The distributed vertical ground reaction forces were determined for a normative population and contrasted with data from subjects with flat feet. Nineteen asymptomatic subjects, 11 with a neutrally aligned foot type (normal arch) and 8 with a pes planus foot type (low arch), were studied as they walked barefoot across a pressure plate. The pressure plate data were converted to force values at seven locations (subhallucal, five submetatarsal and subcalcaneal) on the plantar aspect of the foot. The distributed loading pattern of the plantar soft tissue throughout the stance phase of gait was determined. Pes planus feet had significantly more force at the subhallucal area with no difference seen under the other areas. These data are indicative of aberrant first ray mechanics in pes planus feet.

The midtarsal joint locking mechanism

Background: The midtarsal joint, consisting of the talonavicular and the calcaneocuboid joints, is presumed to be responsible for the foot being both flexible and rigid during different parts of the stance phase of gait. However, this mechanism has never been well quantified. This study explores the midtarsal joint locking mechanism by comparing the effect of hindfoot inversion and eversion on midfoot and forefoot mobility. Methods: Motion of the tibia, talus, calcaneus, navicular, cuboid and the first, second, and fifth metatarsals were measured in nine cadaver feet using Polhemus Fastrak® electromagnetic sensors (EST GmbH & Co. KG, Kaiserslautern, Germany). The talus was fixed to the tibia, and then the forefoot was maximally dorsiflexed, plantarflexed, inverted, and everted, with the hindfoot in maximal eversion and inversion, for a total of eight test positions. The range of motion of the individual bones between maximal forefoot dorsiflexion and plantarflexion and between maximal forefoot inversion and eversion was calculated for the hindfoot in maximal eversion and inversion. Results: For the range of motion from maximal dorsiflexion to maximal plantarflexion there was significantly increased movement of the first, second, and fifth metatarsals in the sagittal plane (p-value = 0.003, 0.007, and 0.002, respectively) when the calcaneus was maximally everted compared to when the calcaneus was maximally inverted. No significant differences were detected for the range of motion from forefoot inversion to eversion for the two hindfoot positions. Conclusions: This study demonstrated that motion in the forefoot is influenced by hindfoot position through the midtarsal joint. Specifically, the sagittal plane range of motion of the metatarsals is increased when the hindfoot is in valgus.

Biomechanical Differences Among Pes Cavus, Neutrally Aligned, and Pes Planus Feet in Subjects with Diabetes:

The purpose of this study was to quantify differences in joint range of motion, foot deformity, and foot morphology among pes cavus, neutrally aligned, pes planus rigid, and pes planus flexible feet. A cohort of 1047 veterans with diabetes (contributing 2047 feet) was enrolled in a prospective study of diabetic ulcer risk factors (the Seattle Diabetic Foot Study). Significant differences between foot types were found. Pes cavus feet had an increased percentage of prominent metatarsal heads, bony prominences, and hammer/claw toes (p <.0001), as well as significantly increased amounts of hallux dorsiflexion and decreased amounts of hallux plantarflexion (p <.0001) with a total range of motion equal to the other foot types (p =.3). Neutrally aligned feet had a lower percentage of intrinsic muscle atrophy, bony prominences, and hammer/claw toes (p <.0001). Pes planus feet had an increased lateral talometatarsal angle (p <.0001) and an increased second metatarsal length. These data demonstrate structural differences between foot types in a population with diabetes.

Iatrogenic Syndesmosis Malreduction via Clamp and Screw Placement

Objectives: The purpose of this study was to assess the impact of variations in angulation of clamp placement to hold syndesmotic reduction and how subsequent syndesmotic screw placement affects malreduction of the syndesmosis. We hypothesized that an anatomic syndesmosis reduction cannot be reliably achieved with a clamp alone; and, inaccurate placement of intraoperative clamps and trans-syndesmotic screws after reduction can malreduce the ankle syndesmosis. Methods: After computed tomography scanning of the intact limbs, 14 cadaver legs were dissected; the syndesmosis was completely disrupted in all. Using planned drill holes, clamps were first placed at 0°, 15°, and 30° angles from the fibula, then separate posterolateral, followed by lateral, screws were placed. After each intervention, the limb had a computed tomography scan so the fibular reduction could be evaluated precisely. Results: Clamps placed at 15° and 30° significantly displaced the fibula in external rotation and caused significant overcompression of the syndesmosis. Thirty-degree lateral screws caused significant anteromedial displacement, external rotation, and overcompression of the syndesmosis. The 15° posterolateral screws also caused significant external rotation and overcompression of the syndesmosis. Conclusions: Our study demonstrates that intraoperative clamping and fixation can cause statistically significant malreduction of the syndesmosis. This article should alert clinicians that clamp and screw placement can cause iatrogenic malreduction of the syndesmosis and make them aware that these dangers occur with specific clamp and screw angles in particular.

Relationship between foot type, foot deformity, and ulcer occurrence in the high-risk diabetic foot

We hypothesized an association between foot type, foot deformity, and foot ulceration and conducted an analysis of a well-characterized, high-risk diabetic population of 398 subjects. The average age was 62 years of age and 74% of the study population were males. Foot-type distributions were 19.5% pes cavus (high arch), 51.5% neutrally aligned (normal arch), and 29.0% pes planus (low arch). We quantified the presence of hallux valgus (23.9%), hammer/claw toes (46.7%), and hallux limitus (24.4%). A significant association was found between foot type and hallux valgus (p = 0.003); pes planus feet had the highest prevalence as compared with neutrally aligned feet (odds ratio [OR] = 2.43, p = 0.0006). Foot type was also significantly associated with fixed hammer/claw toes (p = 0.01); pes cavus feet had the highest prevalence as compared with neutrally aligned feet (OR = 3.89, p = 0.001). Foot type was also significantly associated with hallux limitus (p = 0.006) with pes planus feet having the highest prevalence as compared with neutrally aligned feet (OR = 2.19, p = 0.003). However, foot type was not significantly related to any ulcer outcome (p = 0.7). Fixed hammer/claw toes (OR = 3.91, p = 0.003) and hallux limitus (OR = 3.02, p = 0.006) were associated with increased risk of any ulcer occurrence. This study affirms that foot type and foot deformity are related and that foot deformities are associated with ulcer occurrence.

Comparative gait analysis of ankle arthrodesis and arthroplasty: initial findings of a prospective study.

Background: Little is known about functional outcomes of ankle arthroplasty compared with arthrodesis. This study compared pre-surgical and post-surgical gait measures in both patient groups. Methods Eighteen patients with end-stage ankle arthritis participated in an ongoing longitudinal study (pre-surgery, 12 months post-surgery) involving gait analysis, assessment of pain and physical function. Outcome measures included temporal-distance, kinematic and kinetic data, the Short Form 36 (SF-36) body pain score, and average daily step count. A mixed effects linear model was used to detect effects of surgical group (arthrodesis and arthroplasty, n = 9 each) with walking speed as a covariate (α = 0.05). Results Both groups were similar in demographics and anthropometrics. Followup time was the same for each group. There were no complications in either group. Pain decreased (p < 0.001) and gait function improved (gait velocity, p = 0.02; stride length, p = 0.035) in both groups. Neither group increased average daily step count. Joint range of motion (ROM) differences were observed between groups after surgery (increased hip ROM in arthrodesis, p = 0.001; increased ankle ROM in arthroplasty, p = 0.036). Peak plantar flexor moment increased in arthrodesis patients and decreased in arthroplasty patients (p = 0.042). Conclusion Initial findings of this ongoing clinical study indicate pain reduction and improved gait function 12 months after surgery for both treatments. Arthroplasty appears to regain more natural ankle joint function, with increased ROM. Long-term follow up should may reveal more clinically meaningful differences. Level of Evidence: II, Prospective Observational Study

The compressive mechanical properties of diabetic and non-diabetic plantar soft tissue

Diabetic subjects are at an increased risk of developing plantar ulcers. Knowledge of the physiologic compressive properties of the plantar soft tissue is critical to understanding the possible mechanisms of ulcer formation and improving treatment options. The purpose of this study was to determine the compressive mechanical properties of the plantar soft tissue in both diabetic and non-diabetic specimens from six relevant locations beneath the foot, namely the hallux (big toe), first, third, and fifth metatarsal heads, lateral midfoot, and calcaneus (heel). Cylindrical specimens (1.905 cm diameter) from these locations were excised and separated from the skin and bone from 4 diabetic and 4 non-diabetic age-matched, elderly, fresh-frozen cadaveric feet. Specimens were then subjected to biomechanically realistic strains of approximately 50% in compression using triangle wave tests conducted at five frequencies ranging from 1 to 10 Hz to determine tissue modulus, energy loss, and strain rate dependence. Diabetic vs. non-diabetic results across all specimens, locations, and testing frequencies demonstrated altered mechanical properties with significantly increased modulus (1146.7 vs. 593.0 kPa) but no change in energy loss (68.5 vs. 67.9%). All tissue demonstrated strain rate dependence and tissue beneath the calcaneus was found to have decreased modulus and energy loss compared to other areas. The results of this study could be used to generate material properties for all areas of the plantar soft tissue in diabetic or non-diabetic feet, with implications for foot computational modeling efforts and potentially for pressure alleviating footwear that could reduce plantar ulcer incidence.

Residual-limb skin temperature in transtibial sockets

The insulated environment of the lower-limb prosthesis can result in elevated residual-limb skin temperatures that may contribute to skin irritation, blistering, and a reduced quality of life. The design and materials of the prosthetic socket, suspension system, and liner can potentially alleviate these conditions, but the thermal load may vary with activity and location within the socket. To characterize the thermal environment at the skin-prosthesis interface, we made temperature measurements on five transtibial amputees at 14 locations on the residual limbs. After the participants donned their prosthesis and rested in the seated position for 15 min, the mean skin temperatures of their residual limbs increased by 0.8 degrees Celcius. Subsequent walking for 10 min resulted in a 1.7 degrees Celsius total increase in mean skin temperature. Thermal contour maps revealed the skin was coolest at the anterior proximal location and warmest across the posterior section, correlating with areas of low and high perfusion. From the results, we determined that residual-limb skin temperature depends on activity and locality. This information may aid in understanding where and why skin problems develop on lower-limb residual limbs and may provide design requirements for new prosthetic socket systems intended to alleviate temperature-related discomfort.

A shear and plantar pressure sensor based on fiber-optic bend loss.

Lower-limb complications associated with diabetes include the development of plantar ulcers that can lead to infection and subsequent amputation. While we know from force-plate analyses that medial/lateral and anterior/posterior shear components of ground-reaction forces exist, little is known about the actual distribution of these stresses during daily activities or about the role that shear stresses play in causing plantar ulceration. Furthermore, one critical reason why these data have not been obtained previously is the lack of a validated, widely used, commercially available shear sensor, partly because of the various technical issues associated with measuring shear. In this study, we present a novel means of transducing plantar pressure and shear stress with a fiber-optic sensor. The pressure/shear sensor consists of an array of optical fibers lying in perpendicular rows and columns separated by elastomeric pads. We constructed a map of normal and shear stresses based on observed macrobending through the intensity attenuation from the physical deformation of two adjacent perpendicular fibers. Initial results show that this sensor exhibits low noise and responds to applied normal and shear loads with good repeatability.