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Biomedical subjects

D B Thordarson

Publications and source records attributed to D B Thordarson.

At least 37 records · Page 2Linked to original sources
PubMed1999

Superior compressive strength of a calcaneal fracture construct augmented with remodelable cancellous bone cement.

Twenty-six paired, fresh-frozen cadaveric feet were disarticulated at the ankle joint, and the dome of the talus was potted. Stress-risers were placed along the medial, lateral, and posterior aspects of the calcaneus, and the specimen was loaded rapidly to failure in a testing machine to produce a type-IIB displaced intra-articular fracture according to the classification system of Sanders et al. One specimen of each pair was treated with standard internal fixation with bone-grafting (the control group), and the other was treated with similar fixation but with SRS (Skeletal Repair System) calcium phosphate bone cement placed in any osseous defect. All of the specimens were cured for twenty-four hours in a bath of saline solution at 37 degrees Celsius. The specimens were tested cyclically for ten cycles from zero to 100 newtons at one hertz and for 1010 cycles from zero to 350 newtons at one hertz. The deformation per cycle (millimeters per cycle), first-cycle deformation (millimeters), number of cycles to failure, and number of specimens withstanding the cyclical testing were calculated. The specimens were examined radiographically before and after fracture and after reconstruction and testing. A large difference in the results of the cyclical testing was noted. The specimens that had been augmented with the SRS bone cement had an average deformation of 0.00195 millimeter per cycle compared with 1.013 millimeters per cycle in the control group (p < 0.005). A similar magnitude of difference was noted when the results were stratified for good and poor-quality bone. Visual examination and radiographs demonstrated that a type-IIB displaced intra-articular fracture had been created reproducibly, and computed tomographic scans showed that nearly anatomical reconstruction had been achieved in all of the specimens. The computerized tomographic scans revealed good filling of the osseous voids and no evidence of failure of the cement after cyclical loading.

Bone Cements↗
PubMed1998

Effect of calcaneal osteotomy and plantar fasciotomy on arch configuration in a flatfoot model.

Seven fresh-frozen cadaver specimens had a calcaneal osteotomy performed obliquely through the posterior portion of the calcaneus. Angular relationships between the first metatarsal and talus were recorded with the use of a motion-analysis system in the transverse, sagittal, and coronal planes. The specimen was mounted in a testing machine and loaded via an intramedullary rod to 150, 350, and 550 N. A flatfoot model was created, and repeat measurements were obtained. The calcaneal osteotomy was then displaced 1 cm medially, and repeat measurements were made at each of the three load levels. The calcaneal osteotomy was then returned to its original position, the plantar fascia was divided, and the new angular measurements were obtained. The calcaneal osteotomy was again displaced 1 cm, and repeat angular measurements were obtained. A mild consistent flatfoot deformity was created in all three axes before the plantar fascia was cut. A statistically significant increase in deformity was noted after cutting the plantar fascia. A correction of the flatfoot deformity in all three planes occurred with the medial displacement of the calcaneal osteotomy, which was greater at the lower load levels. We noted that a medial displacement calcaneal osteotomy partially corrected a flatfoot deformity in all three planes. The correction occurred with or without an intact plantar fascia and, therefore, is independent of the structure. We also noted an increased deformity after dividing the plantar fascia. This study provides some biomechanical insight as to the corrective effect of a medial displacement calcaneal osteotomy in correcting a flatfoot deformity.

Cadaver↗
PubMed1997

Running biomechanics.

With the interest of the general population in aerobic exercise, it is essential for physicians who treat sports injuries to understand the mechanism behind these problems. This article provided the reader with an introduction to the biomechanics of both walking and running to facilitate an understanding of the cause of these running injuries. It is hoped that with an improved understanding of the mechanics of walking and running, the reader will have an improved ability to diagnose these problems and improve the treatment of the injury.

Biomechanical Phenomena↗
PubMed1997

Effect of partial versus complete plantar fasciotomy on the windlass mechanism.

Eight adult below-knee cadaver specimens were placed in a testing machine and loaded to 350 newtons according to a strict protocol. Arch height and length measurements were obtained in each specimen with the toes resting on the foot plate, dorsiflexed to 30 degrees, and maximally dorsiflexed manually. The plantar fascia was then divided from medial to lateral in one-quarter increments, and the effect on arch height and length measurements was assessed using the same loading protocol. A consistent decrease in the arch-supporting function on sequential sectioning of the plantar fascia was encountered. A less consistent decrease in the arch-supporting function was reflected by the increase in the height of the arch with sequential sectioning of the plantar fascia. The study demonstrates that partial plantar fasciotomy decreases the arch-supporting function of the plantar fascia in addition to weakening the structure. Strict surgical indications for this type of procedure should be maintained.

Adult↗
PubMed1997

Salvage of the septic ankle with concomitant tibial osteomyelitis.

Five patients with concomitant distal tibia osteomyelitis and ankle sepsis with an open, draining wound were treated. All of the patients were men with an average age of 54.8 years. All of the bone infections were polymicrobial and had open draining wounds. A standardized protocol of radical soft tissue and bone debridement, soft tissue transfer, intravenous antibiotics, and delayed ankle fusion was employed. All five fusions were successful on first attempt, with an average time to fusion of 3.5 months. All patients were free of infection at an average follow-up of 27 months. We believe our aggressive treatment protocol can salvage these extremities and preclude amputation in properly selected cases.

Adult↗
PubMed1997

Intermittent pneumatic pedal compression and edema resolution after acute ankle fracture: a prospective, randomized study.

Thirty patients with an acute Weber B or C ankle fracture were enrolled after signing an informed consent. Fifteen patients were randomized to a control group where they received a posterior splint, ice, and elevation before surgery. Fifteen patients were randomized to a pneumatic pedal compression group where they received the same treatment plus a pneumatic pedal compression device which was used full-time before surgery. Baseline volumetric measurements of the injured foot were obtained, followed by measurements at 24-hour increments until surgery. On average, the patients in the pneumatic pedal compression group had an 88 mL decrease in volume in the first 24 hours versus a 33 mL increase in the control group (P < 0.03) and a 31 mL decrease in the first 48 hours of treatment versus a 32 mL increase for the control group (P < 0.05). The pneumatic pedal compression was well tolerated by the majority of patients (only one did not tolerate its use because of pain) and, we believe, serves as a useful adjunct in preoperative edema resolution after ankle fracture.

Ankle Injuries↗
PubMed1997

Biomechanical evaluation of polylactide absorbable screws used for syndesmosis injury repair.

Simulated syndesmosis injuries were created in 12 fresh-frozen, below-knee cadaver specimens. Six specimens were repaired with a 4.5 mm stainless steel screw, and six were repaired with a 4.5 mm polylactide screw. Three specimens of each group were tested in load to failure by axially loading with 1400 N and externally rotating to 90 degrees. Three specimens in each group underwent fatigue testing by axially loading with 700 N and applying 2.5 N-m of torque for 57,700 cycles. Radiographs and computed tomography scans were evaluated. None of the screws broke or failed. Similar load to failure was noted in polylactide and control groups. Fatigue testing revealed no significant change in stiffness. No significant screw damage was evident on radiographic or computed tomography evaluation. The data suggest that a polylactide screw has sufficient fatigue and failure strength to allow for healing of this injury in a clinical situation.

Biomechanical Phenomena↗
PubMed1997

The effect of fibular malreduction on contact pressures in an ankle fracture malunion model.

Nine fresh-frozen cadaveric specimens were disarticulated through the knee, and the soft tissues, except for the interosseous ligaments and interosseous membrane, were removed to the level of the ankle. The subtalar joint was secured with screws in neutral position (approximately 5 degrees of valgus). Contact pressures in the tibiotalar joint were measured with use of low-grade pressure-sensitive film, which was placed through an anterior capsulotomy. For each measurement, 700 newtons of load was applied to the specimen for one minute. The film imprints were scanned, and the contact pressures were quantitated in nine equal quadrants over the talar dome. A fracture-displacement device was secured to the distal end of the fibula; the device allowed for individual or combined displacements consisting of shortening, lateral shift, and external rotation of the fibula. The ankle was maintained in neutral flexion. The ligamentous injury associated with a pronation-lateral rotation fracture of the ankle was simulated by dividing the deep fibers of the deltoid ligament, the anterior-inferior tibiofibular ligament, and the interosseous membrane to a point that was an average of fifty-three millimeters proximal to the ankle joint. Baseline contact area and contact pressure in the joint were determined, followed by measurements after two, four, and six millimeters of shortening of the fibula; after two, four, and six millimeters of lateral shift of the fibula; and after 5, 10, and 15 degrees of external rotation of the fibula. The three types of displacement were tested individually as well as in combination. The simulated deformities were found to cause a shift of the contact pressure to the mid-lateral and posterolateral quadrants of the talar dome, with pressures as high as 4.1 megapascals. A corresponding decrease in the contact pressures was noted in the medial quadrants of the talar dome. The highest pressures were recorded for maximum shortening of the fibula, the combination of maximum shortening and lateral shift, the combination of maximum shortening and external rotation, and the combination of maximum shortening, lateral shift, and external rotation. In general, increases in each displacement variable corresponded to increasing contact pressures.

Aged↗
PubMed1996

Operative vs. nonoperative treatment of intra-articular fractures of the calcaneus: a prospective randomized trial.

Thirty patients with displaced, intra-articular calcaneus fractures were randomized to operative or nonoperative treatment. All patients had two or three major articular fragments of the posterior facet (Sanders type II or III). Nonoperative treatment included early mobilization and delayed weightbearing. Operative treatment involved open reduction and rigid internal fixation with a plate and screws through an extensile, L-shaped lateral approach followed by early mobilization and delayed weightbearing. Fifteen operative patients were evaluated at an average of 17 months follow-up and 11 nonoperative patients were seen at 14 months average follow-up. In the operative group, there were 7 excellent results, 5 good results, 2 fair results, and 1 poor result, and in the nonoperative group there was 1 excellent result, 3 good results, 1 fair result, and 6 poor results (difference significant as P < 0.01). A functional scoring system of 0-100 points was developed based upon the responses to an outcome assessment questionnaire. The average functional score for the operative group was far superior at 86.7, compared with 55.0 for the nonoperative group (P < 0.0001). Subtalar range of motion averaged 20 degrees for the operative group and 17 degrees for the nonoperative group with pain on extremes of motion of 25% of the operative patients compared with 100% of the nonoperative patients. This study is the first prospective, randomized trial to demonstrate the superior results of current operative treatment with early mobilization compared with nonoperative treatment.

Adult↗
PubMed1996

Magnetic resonance imaging to detect avascular necrosis after open reduction and internal fixation of talar neck fractures.

Twenty-one consecutive patients with displaced talar neck fractures (12 Hawkins type II, 9 Hawkins type III) were prospectively evaluated with magnetic resonance (MR) scans performed between 3 days and 12 months after surgery. All patients underwent open reduction and internal fixation with titanium screws, except two who underwent fixation with stainless steel implants that were subsequently removed. All patients had plain radiographs. We classified the scans as follows: type A, no abnormal signal changes in the body of the talus; type B, signal changes in less than 25% of the body; type C, signal changes in 25% to 50% of the body; and type D, signal changes in greater than 50% of the body. Plain anteroposterior radiographs correlated well with MR scans in patients with type D scans, but an inconsistent correlation was noted with lesser degrees of signal changes (types A-C), with the MR scans being more accurate in displaying the volume of avascular bone. Scans obtained less than 3 weeks after injury were not helpful in assessing for avascular necrosis. We found that high-quality MR images of the talus were consistently obtained in the presence of titanium screws in contrast to images obtained with stainless steel implants. We use titanium screws in all talar neck fracture repairs, because they permit high-quality MR images. We believe that further study of patients with Hawkins type III fractures and Hawkins type II fractures with equivocal radiographic evidence of avascular necrosis is warranted to try to identify those patients at risk for collapse and perhaps to guide weightbearing recommendations.

Adult↗
PubMed1996

Spontaneous fusion of the midfoot following reflex sympathetic dystrophy. A case report and review of the literature.

Reflex sympathetic dystrophy syndrome (RSDS) is a well-defined entity, caused by many clinical conditions, leading to pain, stiffness, and vasomotor changes in the affected region. In this case, a 49-year-old man presented with a history of right foot pain secondary to a fall. Plain radiographs did not reveal any fractures or bony fusions. Upon follow-up, a history consistent with that found in RSDS was given. Radiographs at 7 and 11 weeks revealed increasing osteopenia, lytic lesions, and absent joint spaces in the first through third metatarsocuneiform articulations suggesting ankylosis. Other possible causes of ankylosis, including infection, inflammatory and metabolic conditions, were excluded.

Ankle Injuries↗
PubMed1995

Subtotal calcanectomy for osteomyelitis of the os calcis: a reasonable alternative to free tissue transfer.

Composite wounds of the heel with secondary secondary osteomyelitis of the calcaneus remain a reconstructive challenge. A paucity of regional flaps has often necessitated microvascular transplantation in order to obtain wound healing. Subtotal calcanectomy, traditionally a technique of the orthopedic surgeon, can, in selected cases, eradicate infection and achieve wound closure and limb preservation. A review was undertaken of one hospital's experience with this procedure over a 4-year period. Five patients with osteomyelitis of the os calcis were identified who were successfully managed with subtotal calcanectomy.

Adult↗