Category: Basic Sciences/Biologics Introduction/Purpose: Various biomechanical studies have examined pressure changes across the foot and ankle joints. However, most of these studies disrupted the capsuloligamentous complex surrounding the joint to insert pressure sensors, compromising the integrity of the natural joint structure and the accuracy of biomechanical assessments. This is the first noninvasive study to report measurement of natural joint reaction forces (JRF) across the foot and ankle while preserving all soft tissue structures. Since articular surfaces experience equal and opposing compression forces, we aimed to evaluate the distraction force needed to overcome these compression forces. Methods: Ten fresh-frozen cadavers of the lower extremity were obtained that were disarticulated at the knee joint. Steinmann pins were percutaneously placed across the distal tibia, and the center of the talus, navicular, cuboid, and calcaneus while preserving all surrounding soft tissues. A custom fixation device was utilized in conjunction with a tensile testing machine to allow distraction in line with the axis of the tibiotalar, subtalar, talonavicular (TN), and calcaneocuboid (CC) joints. Displacement was measured as distance between Steinmann pins on either side of the joint examined. Under progressive axial distraction, displacement and force were measured. Best-fit polynomials were calculated to fit the force-displacement curves. The inflection point, representing the joint reaction force (JRF) where distraction forces across the joint equal the compression forces, was calculated for each curve. Results: All force-displacement curves demonstrated an inflection point. Prior to the inflection point, relatively large increases in distraction force resulted in minimal displacement. Once the inflection point was reached, relatively small increases in distraction force resulted in large increases in displacement. Each cadaver was measured three times with high reproducibility. The mean JRF were tibiotalar 33.8 N [standard deviation (SD) 10], subtalar 18.2 N (SD 12), TN 13.3 N (SD 4), and CC 14.7 N (5.8). Conclusion: We present the first application of a reliable and noninvasive method of measuring JRF of the foot and ankle joints. In the medium or small joints, dissection of the capsule and surrounding ligaments can significantly alter joint stability and biomechanics. By preserving all the periarticular soft tissues, this experimental model will allow future investigation of biomechanical changes of pathologic states and efficacy of surgical intervention under conditions that most accurately reflect the in vivo state.
Animais silvestres mantidos sob cuidados humanos podem não estar aptos à soltura, mesmo após intensa união de esforços de uma equipe multidisciplinar composta por Biólogos, Tratadores e Veterinários. O presente relato tem por objetivo apresentar procedimento de orquiectomia em Ouriço-cacheiro (Coendou spinosus), macho, adulto, mantido no Zoológico Municipal de Canoas, na região Sul do Brasil. O procedimento foi realizado devido ao fato de o corpo técnico da instituição não ter interesse na reprodução da espécie, além de estar classificado como em estado de “preocupação mínima” pela IUCN (International Union for Conservation of Nature) em sua lista vermelha de espécies ameaçadas. Após sedação e anestesia geral, o paciente foi submetido ao procedimento por meio da técnica modificada fechada, ao qual foi atribuído êxito, com boa recuperação do animal no pós-cirúrgico.
Objectives:Joint reaction forces (JRF) and contact pressures are classically measured using destructive techniques which require dissection and interposition of materials into the joint, fundamentally altering the normal joint mechanics. Without an alternate method available, modern hip JRF biomechanical studies involve this stripping of periarticular tissues, potentially sacrificing accurate measurements. As hip arthroscopy is increasingly employed for minimally invasive treatment of hip pathology, there may be a need for minimally invasive biomechanical measurement techniques that reflect JRF more accurately. This study’s objectives were to demonstrate that a non-invasive, non-destructive technique for measuring JRF was feasible in the hip and to validate this concept using simultaneous radiographic imaging.Methods:Twenty fresh frozen male human cadaver hemipelves were instrumented with a custom-made retrograde intramedullary nail-plate construct in the femur and an iliac-crest locking plate. These otherwise fully-intact specimens were rigidly mounted for tensile testing (Instron Model 1122). With the hip in the neutral position, the joint was distracted 5mm along the axis of the femoral shaft at a rate of 0.4mm/s, while simultaneously measuring the force required for distraction. Force-displacement curves generated allowed the best-fit polynomial to be found with resulting revelation of the native state JRF. Next, the joint capsule was vented under fluoroscopic control using an 18 gauge spinal needle and distraction was repeated from the native state with fluoroscopic images captured at 0.5mm increments. All testing was repeated three times, and two specimens were excluded for severe osteoarthritis (<2mm joint-space).Results:Force-displacement curves demonstrated an initially steep but decreasing (concave-down) slope, followed by an inflection point, a linear region and then a relatively non-linear increasing (concave-up) slope with further distraction. High reproducibility between repeated measurements was found within specimens and the average native resting JRF was 115.1 N (n=18). Capsular venting decreased JRF by 16.3 N (mean post-venting=98.8 N). Under fluoroscopy, air arthrograms confirmed cartilage relaxation consistently at the measured force-distraction infection point.Conclusion:This study describes and validates a reproducible method of measuring hip JRF that preserves all periarticular stabilizing soft tissue structures. This is the first study in any joint to correlate force-distraction data with fluoroscopic images, confirming the method’s central premise: That JRF is equal to the measured force-distraction curve inflection point. This may be ideally suited for application in biomechanical studies of minimally invasive arthroscopic hip surgery.
Category: Ankle. Introduction/Purpose: Increasing evidence has suggested that alterations in joint mechanics results in articular pathology. Previous studies demonstrated noninvasive measurements of joint reactive forces (JRF) can be performed reliably without destruction of the peri-articular soft tissue in medium and small size joints of the upper extremity. This study presents a novel, noninvasive measurement of the JRF to investigate the normal and the effects of a syndesmotic injury. The JRF of the tibiotalar joint was also evaluated following anatomic reduction with fixation and malreduction of the syndesmosis. Methods: Eight fresh-frozen human cadaveric lower extremity limbs were obtained disarticulated above the knee. A distraction force was applied across the tibio-talar joint to determine the baseline (normal) ankle force displacement curve. Next, a syndesmotic injury was created by releasing the interosseous syndesmotic ligaments, the transverse tibiofibular ligament and the anterior and posterior tibiofibular ligaments. Prior to sectioning, two drill holes were placed across the joint and tapped to ensure anatomic reduction. JRF were measured using a quadricortical technique with a single or double screw configuration. The syndesmosis was malreduced by anteriorly displacing the fibula 5 mm. After each step, the resultant JRFs were determined using a distraction force across the tibiotalar joint. Results: Force displacement curves obtained from multiple measurements from each specimen with a mean ankle JRF of 31.4 + 2.6 N. Syndesmotic injury resulted in a 35% decrease in tibiotalar JRF (20.3 + 3.0 N, p=0.002). Fixation of the injury using one syndesmotic screw resulted in significant increase in JRF compared to injury JRF (28.7 + 1.4 N, p=0.02). Syndesmotic fixation with 2 screws also demonstrated a trend towards restoration of tibiotalar JRF (28.3 + 2.2 N, p=0.06). There was no statistical difference between fixation of one versus two syndesmotic screws. The JRF for the malreduced syndesmosis was 31.5 + 1.8 N (p=0.03,) resulting in increased forces approaching the baseline JRF. Conclusion: This study demonstrates a non-destructive model by which to measure joint reactive forces (JRF) across the tibiotalar joint and that these forces are diminished as a result of a syndesmotic injury, suggesting joint instability. Surgical stabilization with either 1 or 2 screws creates JRF that are similar to the normal JRF. Even with a malreduced syndesmosis, there appeared to be a JRF similar to baseline tibiotalar joint forces. However malreduction of the syndesmosis may alter the joint dynamics of the ankle in ways that were not measured in this study.
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