Search PubMed⌕ Search

Biomedical subjects

D B Thordarson

Publications and source records attributed to D B Thordarson.

46 records · Page 3Linked to original sources
PubMed1995

Reconstruction with tenodesis in an adult flatfoot model. A biomechanical evaluation of four methods.

Six fresh-frozen adult cadaveric specimens were mounted in an Instron materials testing machine with use of a cemented intramedullary rod. Angular relationships between the first metatarsal and the talus were recorded with a sonic digitizer. A flatfoot deformity was created by dividing the talonavicular joint capsule (superiorly, medially, and inferiorly), the spring ligament, the anteromedial aspect of the subtalar joint capsule, and the plantar fascia. Angular displacement in the sagittal and transverse planes was recorded at no load and at 100, 350, and 700-newton plantar loads. Each specimen was subjected to four different reconstructions with tenodesis, and the angular relationship between the first metatarsal and the talus was measured at the four levels of load. A reconstruction with use of the peroneus longus tendon was performed by preserving its insertion into the first metatarsal, rerouting the tendon and passing it from medial to lateral through a calcaneal bone tunnel, and anchoring it to the lateral aspect of the calcaneus. A reconstruction with the tibialis tendon was performed by passing the medial third of the tendon from dorsal to plantar through the navicular and from medial to lateral through the calcaneal bone tunnel and securing it to the lateral aspect of the calcaneus. The reconstruction with the tibialis anterior tendon was repeated with the tendon graft routed along the medial aspect of the navicular, directly through the calcaneal bone tunnel. The fourth reconstruction was done with use of an Achilles tendon allograft.(ABSTRACT TRUNCATED AT 250 WORDS)

Achilles Tendon↗
PubMed1995

Dynamic support of the human longitudinal arch. A biomechanical evaluation.

This study was designed to evaluate the dynamic support provided to the human longitudinal arch by the leg muscles active in the stance phase of gait and by the plantar aponeurosis. Ten fresh adult cadaveric specimens were mounted in a materials testing machine. The tendons of the posterior tibialis, flexor digitorum longus, flexor hallucis longus, peroneus longus, peroneus brevis, and Achilles tendon were attached to force transducers. Plantar loads of 0, 350 and 700 N were applied, and the tendons were tensioned individually. The Achilles tendon was tensioned an amount equal to the plantar load; the posterior tibialis, flexor digitorum longus, flexor hallucis longus, peroneus longus, and peroneus brevis were tensioned a fractional amount (depending on the proportion of the cross-sectional area to the gastrocsoleus complex). The angular relationships between the first metatarsal, navicular, and talus were recorded using a 3-dimensional movement analysis system. An additional series of measurements was obtained by positioning the ankle plantarflexed 10 degrees under a plantar load of 350 N. Dorsiflexing the toes with the ankle in a neutral position and loading the foot to 350 N and 700 N permitted an evaluation of the effect of the plantar aponeurosis. The plantar aponeurosis, via dorsiflexion of the toes, contributed the most significant arch support in the sagittal plane with a 3.6 degrees increase between the first metatarsal and talus at 350 N and a 2.3 degrees increase at 700 N. The posterior tibialis tendon consistently provided arch support at plantar loads of 350 N and 700 N. The peroneus longus consistently abducted the forefoot in the transverse plane at 350-N and 700-N load levels. The study provides further insight into the dynamic supporting and deforming forces of the longitudinal arch.

Biomechanical Phenomena↗
PubMed1994

A disposable fiberoptic arthroscope: a cadaver study.

Nine fresh cadaver ankle joints underwent arthroscopy to determine effectiveness of a small diameter, disposable, fiberoptic arthroscope. A sequential examination of the joint was performed through routine anteromedial and anterolateral portals. The anterior aspect of the joint with all anatomical structures was well visualized via the two anterior portals. The posterior aspect of the joint was also well visualized via anterior portals without distraction due to the flexibility of the scope and its small diameter. The quality of the visualization of the posterior joint from the anterior portals alone was comparable to that from the posterior approach. The results of this study indicate that diagnostic arthroscopy of the ankle joint with this disposable 1.6-mm arthroscope is comparable to the standard 2.7-mm to 5-mm arthroscopes. The size, flexibility, and 30 degrees viewing angle of this scope allow excellent and thorough joint visualization by routine anterior portals and minimize the need for joint distractors and posterior portals during routine diagnostic ankle arthroscopy.

Ankle Joint↗
PubMed1994

External fixation in arthrodesis of the ankle. A biomechanical study comparing a unilateral frame with a modified transfixion frame.

Arthrodesis of the ankle was performed on eight fresh-frozen human specimens, and four external fixator configurations were applied: a unilateral external fixator, a Calandruccio clamp alone, a Calandruccio clamp with two anterior struts, and a Calandruccio clamp with four struts (two anterior and two posterior). Each specimen was subjected to 4.0 newton-meters of internal-external tibial torque and 4.0 newton-meters of plantar flexion-dorsiflexion bending moment. The unilateral frame permitted the least tibiotalar motion during plantar flexion-dorsiflexion testing. The Calandruccio clamp allowed more than twice the motion allowed by the unilateral fixator in this testing mode, but the rigidity of the fixation with the Calandruccio clamp was improved with the addition of two interlocking struts, which connected fixator pins proximal and distal to the site of the arthrodesis. The addition of two more struts, to make a four-strut construct, resulted in a small (0.8-degree) additional decrease in the mean tibiotalar motion. There were no detectable differences in the mean tibiotalar motion due to torsional loading between the four fixation configurations.

Aged↗
PubMed1993

Midtarsal fracture-subluxation. Case report and review of the literature.

Avulsion of the navicular tuberosity in association with fracture at the calcanecuboid joint is a characteristic pattern of injury resulting from an acute valgus and dorsiflexion stress. Only 22 cases of this unusual injury pattern have been reported, and confusion exists regarding treatment. Recommendations for management focus primarily on the calcaneocuboid disruption. Only two of these reports specifically addressed the posterior tibial tendon avulsion. Each component of this injury pattern should be considered separately. Calcaneocuboid fractures should be treated conservatively or operatively, depending on the extent of articular involvement. Conversely, the navicular tuberosity avulsion should be considered as the acute phase of a syndrome potentially leading to a chronic, posterior tibial tendon-deficient foot. Depending on the degree of displacement of the navicular avulsion fracture, prompt surgical intervention may be justified. A 73-year-old woman illustrates the rationale and treatment of a typical case.

Aged↗
PubMed1992

Stability of an ankle arthrodesis fixed by cancellous-bone screws compared with that fixed by an external fixator. A biomechanical study.

Twenty-three fresh-frozen human specimens were subjected to ankle arthrodesis and fixation with two cancellous-bone screws. The specimens were then subjected to four newton-meters of manually applied tibial torque, plantar flexion-dorsiflexion moment, and medial-lateral bending moment; relative rotation between the tibia and the talus was recorded for each mode of testing. A Calandruccio triangular compression device was then applied to threaded pins penetrating the tibia and talus, the screws were removed, and the test sequence was repeated. Tibiotalar motions recorded with both systems of fixation were markedly affected by the quality of the bone. When less than 2 degrees of total tibiotalar rotation was recorded in response to four newton-meters of manually applied internal-external tibial torque, all specimens demonstrated less torsional rotation with the screw fixation than with the external fixator. The mean rotations produced by medial-lateral bending moment were equivalent for both systems of fixation. When torsional rotations with the use of screw fixation were greater than 2 degrees, all specimens demonstrated more torsional rotation with the screws than with the external fixator, and all but one specimen had more medial-lateral rotation with the screws than with the fixator. For applied plantar flexion-dorsiflexion moment, twenty-two of the twenty-three specimens demonstrated more rotation with the Calandruccio fixator than with the screws; this was due in part to motion permitted at the hinge points of the frame itself.

Aged↗
PubMed1990

Arthrodesis of the ankle with cancellous-bone screws and fibular strut graft. Biomechanical analysis.

The stability of an arthrodesis with two cancellous-bone screws across the ankle joint was evaluated in eighteen ankles from fresh-frozen cadavera. Tibiotalar motion was recorded in response to the following loading modes: medial-lateral moment, plantar flexion-dorsiflexion moment, and internal-external tibial torque. The series of loading tests was performed with two cancellous-bone screws through the tibia into the talus and a lateral fibular strut graft fixed with a proximal and a distal screw. The tests were repeated after the strut graft was removed, and again after it had been reapplied. The amount of motion at the site of the arthrodesis was greatest with tibial torque and was least with medial-lateral bending; this was true for specimens with or without a fibular strut graft. Removal of the strut graft allowed increased tibiotalar motion for all modes of loading; increases in motion were far greater for specimens of poor bone quality.

Aged↗
PubMedDate not supplied

Hallux valgus correction with proximal metatarsal osteotomy: two-year follow-up.

We evaluated the results of 33 feet in 23 patients who underwent a basilar crescentic osteotomy with a modified McBride procedure with a minimum 24-month follow-up. The average hallux valgus improved from 37.5 degrees to 13.8 degrees and the intermetatarsal 1-2 angle from 14.9 degrees to 4.7 degrees. The angle of declination of the first metatarsal was found to have dorsiflexed an average of 6.2 degrees. Unfortunately, osteotomies secured with staples dorsiflexed to a greater degree. Bilateral foot surgery produced results similar to those with unilateral procedures. Four of our patients developed a hallux varus (range 2-8 degrees); however, none were dissatisfied at the time of evaluation. Although this bunion procedure resulted in more prolonged swelling and pain than a distal osteotomy, it should be considered for more complex deformities to avoid the failure that a distal metatarsal osteotomy might produce given a high 1-2 intermetatarsal angle or a high hallux valgus angle.

Adult↗
PubMedDate not supplied

Complications after treatment of tibial pilon fractures: prevention and management strategies.

Complications after treatment of tibial pilon fractures can occur intraoperatively or in the early or late postoperative period. Perioperative complications include malreduction, inadequate fixation, and intra-articular penetration of hardware, all of which may be minimized by preoperative planning and meticulous operative technique. Wound complications can lead to deep infection, with potentially catastrophic consequences. The incidence of wound complications may be lessened by delaying surgery 5 to 14 days, until the posttraumatic swelling has subsided. Temporary fixation with a medial spanning external fixator is recommended if definitive internal fixation is delayed. Fracture blisters should be left undisturbed until the time of surgery. Incisions through blood-filled blisters should be avoided whenever possible. Limited incisions to achieve reduction and fixation should be made directly over fracture sites, to minimize soft-tissue stripping. An indirect reduction technique involving the use of ligamentotaxis and low-profile small-fragment implants that minimize tension on the incision should be used. Late complications, such as stiffness and posttraumatic arthritis, correlate with the severity of the initial injury and the accuracy of reduction. Loss of ankle motion can be minimized by early range-of-motion exercise after stable fixation has been achieved. Posttraumatic ankle arthrosis should be initially treated with anti-inflammatory medication, activity modification, and walking aids. Symptomatic patients often require an ankle arthrodesis.

Arthritis↗