Daniel C. Fitzpatrick, MD
General Orthopedics & Trauma Specialist
13 years of experience

Accepting new patients
Slocum Center for Orthopedics & Sports Medicine
55 Coburg Rd.
Eugene, OR 97401
(541) 485-8111
Locations and availability (1)

Education ?

Medical School Score Rankings
University of Iowa (1997)
  • Currently 4 of 4 apples
Top 25%
Residency
University Of Iowa Hospital & Clinic (2001) *
* This information was reported to Vitals by the doctor or doctor's office.

Affiliations ?

Dr. Fitzpatrick is affiliated with 3 hospitals.

Hospital Affilations

Score

Rankings

  • McKenzie - Willamette Medical Center
    Orthopaedic Surgery
    1460 G St, Springfield, OR 97477
    • Currently 4 of 4 crosses
    Top 25%
  • Sacred Heart Medical Center
    Orthopaedic Surgery
    1255 Hilyard St, Eugene, OR 97401
    • Currently 4 of 4 crosses
    Top 25%
  • Sacred Heart Medical Center At Riverbend
    3333 Riverbend Dr, Springfield, OR 97477
  • Publications & Research

    Dr. Fitzpatrick has contributed to 29 publications.
    Title Stabilization of Distal Femur Fractures with Intramedullary Nails and Locking Plates: Differences in Callus Formation.
    Date February 2011
    Journal The Iowa Orthopaedic Journal
    Excerpt

    This study compared callus formation in distal femur fractures stabilized with locking plates and intramedullary nails to test the hypothesis that locking plates induce less fracture callus than IM nails.

    Title Effects of Construct Stiffness on Healing of Fractures Stabilized with Locking Plates.
    Date December 2010
    Journal The Journal of Bone and Joint Surgery. American Volume
    Title Effects of Hybrid Plating with Locked and Nonlocked Screws on the Strength of Locked Plating Constructs in the Osteoporotic Diaphysis.
    Date September 2010
    Journal The Journal of Trauma
    Excerpt

    Hybrid plating (HP) may improve fixation strength of locked plating (LP) constructs by combining the use of locked and nonlocked screws within a bone segment. This biomechanical study evaluated whether a hybrid bridge plating construct provides greater fixation strength than an all-locked construct in the osteoporotic diaphysis.

    Title Far Cortical Locking Can Improve Healing of Fractures Stabilized with Locking Plates.
    Date July 2010
    Journal The Journal of Bone and Joint Surgery. American Volume
    Excerpt

    Locked bridge plating relies on secondary bone healing, which requires interfragmentary motion for callus formation. This study evaluated healing of fractures stabilized with a locked plating construct and a far cortical locking construct, which is a modified locked plating approach that promotes interfragmentary motion. The study tested whether far cortical locking constructs can improve fracture-healing compared with standard locked plating constructs.

    Title A Computational Technique to Measure Fracture Callus in Radiographs.
    Date May 2010
    Journal Journal of Biomechanics
    Excerpt

    Callus formation occurs in the presence of secondary bone healing and has relevance to the fracture's mechanical environment. An objective image processing algorithm was developed to standardize the quantitative measurement of periosteal callus area in plain radiographs of long bone fractures. Algorithm accuracy and sensitivity were evaluated using surrogate models. For algorithm validation, callus formation on clinical radiographs was measured manually by orthopaedic surgeons and compared to non-clinicians using the algorithm. The algorithm measured the projected area of surrogate calluses with less than 5% error. However, error will increase when analyzing very small areas of callus and when using radiographs with low image resolution (i.e. 100 pixels per inch). The callus size extracted by the algorithm correlated well to the callus size outlined by the surgeons (R2=0.94, p<0.001). Furthermore, compared to clinician results, the algorithm yielded results with five times less inter-observer variance. This computational technique provides a reliable and efficient method to quantify secondary bone healing response.

    Title Locked Plating of Distal Femur Fractures Leads to Inconsistent and Asymmetric Callus Formation.
    Date May 2010
    Journal Journal of Orthopaedic Trauma
    Excerpt

    Locked plating constructs may be too stiff to reliably promote secondary bone healing. This study used a novel imaging technique to quantify periosteal callus formation of distal femur fractures stabilized with locking plates. It investigated the effects of cortex-to-plate distance, bridging span, and implant material on periosteal callus formation.

    Title Processing Temporal Modulations in Binaural and Monaural Auditory Stimuli by Neurons in the Inferior Colliculus and Auditory Cortex.
    Date February 2010
    Journal Journal of the Association for Research in Otolaryngology : Jaro
    Excerpt

    Processing dynamic changes in the stimulus stream is a major task for sensory systems. In the auditory system, an increase in the temporal integration window between the inferior colliculus (IC) and auditory cortex is well known for monaural signals such as amplitude modulation, but a similar increase with binaural signals has not been demonstrated. To examine the limits of binaural temporal processing at these brain levels, we used the binaural beat stimulus, which causes a fluctuating interaural phase difference, while recording from neurons in the unanesthetized rabbit. We found that the cutoff frequency for neural synchronization to the binaural beat frequency (BBF) decreased between the IC and auditory cortex, and that this decrease was associated with an increase in the group delay. These features indicate that there is an increased temporal integration window in the cortex compared to the IC, complementing that seen with monaural signals. Comparable measurements of responses to amplitude modulation showed that the monaural and binaural temporal integration windows at the cortical level were quantitatively as well as qualitatively similar, suggesting that intrinsic membrane properties and afferent synapses to the cortical neurons govern the dynamic processing. The upper limits of synchronization to the BBF and the band-pass tuning characteristics of cortical neurons are a close match to human psychophysics.

    Title Far Cortical Locking Can Reduce Stiffness of Locked Plating Constructs While Retaining Construct Strength.
    Date August 2009
    Journal The Journal of Bone and Joint Surgery. American Volume
    Excerpt

    Several strategies to reduce construct stiffness have been proposed to promote secondary bone healing following fracture fixation with locked bridge plating constructs. However, stiffness reduction is typically gained at the cost of construct strength. In the present study, we tested whether a novel strategy for stiffness reduction, termed far cortical locking, can significantly reduce the stiffness of a locked plating construct while retaining its strength.

    Title A Nonlocking End Screw Can Decrease Fracture Risk Caused by Locked Plating in the Osteoporotic Diaphysis.
    Date April 2009
    Journal The Journal of Bone and Joint Surgery. American Volume
    Excerpt

    Locking plates transmit load through fixed-angle locking screws instead of relying on plate-to-bone compression. Therefore, locking screws may induce higher stress at the screw-bone interface than that seen with conventional nonlocked plating. This study investigated whether locked plating in osteoporotic diaphyseal bone causes a greater periprosthetic fracture risk than conventional plating because of stress concentrations at the plate end. It further investigated the effect of replacing the locked end screw with a conventional screw on the strength of the fixation construct.

    Title Relative Stability of Conventional and Locked Plating Fixation in a Model of the Osteoporotic Femoral Diaphysis.
    Date April 2009
    Journal Clinical Biomechanics (bristol, Avon)
    Excerpt

    This study investigated the stiffness and strength of bridge plating with uni-cortical and bi-cortical locking plate constructs relative to a conventional, non-locked construct in the osteoporotic femoral diaphysis.

    Title Does Locked Plating of Periprosthetic Supracondylar Femur Fractures Promote Bone Healing by Callus Formation? Two Cases with Opposite Outcomes.
    Date April 2009
    Journal The Iowa Orthopaedic Journal
    Excerpt

    Contemporary locking plates promote biological fixation through indirect reduction techniques and by elevating the plate from the bone. They have improved fixation strength in osteoporotic bone. Periarticular locking plates are rapidly being adopted for bridge plating of periprosthetic femur fractures. When these plates are used for indirect reduction and bridge plating osteosynthesis, fracture union occurs by secondary bone healing with callus formation which is stimulated by interfragmentary motion. In two patients with similar periprosthetic femur fractures treated with periarticular locking plates one fracture healed by ample callus formation while the other resulted in a non-union and had no callus formation six months post-operatively. The case, which progressed to secondary bone healing with callus formation, exhibited varus migration as a result of loss of fixation. The non-union case retained stable fixation. The difference in outcome may indicate that callus formation was promoted by interfragmentary motion secondary to loss of fixation. Conversely, in absence of fixation failure, callus formation was suppressed by stable fixation with a stiff locking plate construct which reduced interfragmentary motion. These observations suggest that locked plating constructs should be sufficiently flexible when applied for bridge plating of comminuted fractures to promote callus formation.

    Title Auditory Response Properties of Neurons in the Tectal Longitudinal Column of the Rat.
    Date December 2008
    Journal Hearing Research
    Excerpt

    The newly-discovered tectal longitudinal column (TLC) spans the paramedian region of the mammalian tectum. It has connections with several nuclei of the auditory system. In this report, we provide the first detailed description of the responses of TLC neurons to auditory stimuli, including monaural and binaural tones and amplitude modulated tones. For comparison, responses in the inferior colliculus (IC) were also recorded. Neurons in the TLC were sensitive to similar ranges of frequency as IC neurons, could have comparably low thresholds, and showed primarily excitatory responses to stimulation of the contralateral ear with either phasic or sustained response patterns. Differences of TLC compared to IC neurons included broader frequency tuning, higher average threshold, longer response latencies, little synchronization or rate tuning to amplitude modulation frequency and a smaller degree of inhibition evoked by stimulation of the ipsilateral ear. These features of TLC neurons suggest a role for the TLC in descending auditory pathways.

    Title Behavioral Sensitivity to Interaural Time Differences in the Rabbit.
    Date March 2008
    Journal Hearing Research
    Excerpt

    An important cue for sound localization and separation of signals from noise is the interaural time difference (ITD). Humans are able to localize sounds within 1-2 degrees and can detect very small changes in the ITD (10-20micros). In contrast, many animals localize sounds with less precision than humans. Rabbits, for example, have sound localization thresholds of approximately 22 degrees . There is only limited information about behavioral ITD discrimination in animals with poor sound localization acuity that are typically used for the neural recordings. For this study, we measured behavioral discrimination of ITDs in the rabbit for a range of reference ITDs from 0 to +/-300micros. The behavioral task was conditioned avoidance and the stimulus was band-limited noise (500-1500Hz). Across animals, the average discrimination threshold was 50-60micros for reference ITDs of 0 to +/-200micros. There was no trend in the thresholds across this range of reference ITDs. For a reference ITD of +/-300micros, which is near the limit of the physiological window defined by the head width in this species, the discrimination threshold increased to approximately 100micros. The ITD discrimination in rabbits less acute than in cats, which have a similar head size. This result supports the suggestion that ITD discrimination, like sound localization [see Heffner, 1997. Acta Otolaryngol. 532 (Suppl.), 46-53] is determined by factors other than head size.

    Title A Surrogate Long-bone Model with Osteoporotic Material Properties for Biomechanical Testing of Fracture Implants.
    Date January 2008
    Journal Journal of Biomechanics
    Excerpt

    In vitro comparative testing of fracture fixation implants is limited by the highly variable material properties of cadaveric bone. Bone surrogate specimens are often employed to avoid this confounding variable. Although validated surrogate models of normal bone (NB) exist, no validated bone model simulating weak, osteoporotic bone (OPB) is available. This study presents an osteoporotic long-bone model designed to match the lower cumulative range of mechanical properties found in large series of cadaveric femora reported in the literature. Five key structural properties were identified from the literature: torsional rigidity and strength, bending rigidity and strength, and screw pull-out strength. An OPB surrogate was designed to meet the low range for each of these parameters, and was mechanically tested. For comparison, the same parameters were determined for surrogates of NB. The OPB surrogate had a torsional rigidity and torsional strength within the lower 2% and 16%, respectively, of the literature based cumulative range reported for cadaveric femurs. Its bending rigidity and bending strength was within the lower 11% and 8% of the literature-based range, respectively. Its pull-out strength was within the lower 2% to 16% of the literature based range. With all five structural properties being within the lower 16% of the cumulative range reported for native femurs, the OPB surrogate reflected the diminished structural properties seen in osteoporotic femora. In comparison, surrogates of NB demonstrated structural properties within 23-118% of the literature-based range. These results support the need and utility of the OPB surrogate for comparative testing of implants for fixation of femoral shaft fractures in OPB.

    Title Neural and Behavioral Sensitivity to Interaural Time Differences Using Amplitude Modulated Tones with Mismatched Carrier Frequencies.
    Date October 2007
    Journal Journal of the Association for Research in Otolaryngology : Jaro
    Excerpt

    Bilateral cochlear implantation is intended to provide the advantages of binaural hearing, including sound localization and better speech recognition in noise. In most modern implants, temporal information is carried by the envelope of pulsatile stimulation, and thresholds to interaural time differences (ITDs) are generally high compared to those obtained in normal hearing observers. One factor thought to influence ITD sensitivity is the overlap of neural populations stimulated on each side. The present study investigated the effects of acoustically stimulating bilaterally mismatched neural populations in two related paradigms: rabbit neural recordings and human psychophysical testing. The neural coding of interaural envelope timing information was measured in recordings from neurons in the inferior colliculus of the unanesthetized rabbit. Binaural beat stimuli with a 1-Hz difference in modulation frequency were presented at the best modulation frequency and intensity as the carrier frequencies at each ear were varied. Some neurons encoded envelope ITDs with carrier frequency mismatches as great as several octaves. The synchronization strength was typically nonmonotonically related to intensity. Psychophysical data showed that human listeners could also make use of binaural envelope cues for carrier mismatches of up to 2-3 octaves. Thus, the physiological and psychophysical data were broadly consistent, and suggest that bilateral cochlear implants should provide information sufficient to detect envelope ITDs even in the face of bilateral mismatch in the neural populations responding to stimulation. However, the strongly nonmonotonic synchronization to envelope ITDs suggests that the limited dynamic range with electrical stimulation may be an important consideration for ITD encoding.

    Title Detection of Interaural Correlation by Neurons in the Superior Olivary Complex, Inferior Colliculus and Auditory Cortex of the Unanesthetized Rabbit.
    Date February 2007
    Journal Hearing Research
    Excerpt

    A critical binaural cue important for sound localization and detection of signals in noise is the interaural time difference (ITD), or difference in the time of arrival of sounds at each ear. The ITD can be determined by cross-correlating the sounds at the two ears and finding the ITD where the correlation is maximal. The amount of interaural correlation is affected by properties of spaces and can therefore be used to assess spatial attributes. To examine the neural basis for sensitivity to the overall level of the interaural correlation, we identified subcollicular neurons and neurons in the inferior colliculus (IC) and auditory cortex of unanesthetized rabbits that were sensitive to ITDs and examined their responses as the interaural correlation was varied. Neurons at each brain level could show linear or non-linear responses to changes in interaural correlation. The direction of the non-linearities in most neurons was to increase the slope of the response change for correlations near 1.0. The proportion of neurons with non-linear responses was similar in subcollicular and IC neurons but increased in the auditory cortex. Non-linear response functions to interaural correlation were not related to the type of response as determined by the tuning to ITDs across frequencies. The responses to interaural correlation were also not related to the frequency tuning of the neuron, unlike the responses to ITD, which broadens for neurons tuned to lower frequencies. The neural discriminibility of the ITD using frozen noise in the best neurons was similar to the behavioral acuity in humans at a reference correlation of 1.0. However, for other reference ITDs the neural discriminibility was more linear and generally better than the human discriminibility of the interaural correlation, suggesting that stimulus rather than neural variability is the basis for the decline in human performance at lower levels of interaural correlation.

    Title Connections of Functional Areas in the Mustached Bat's Auditory Cortex with the Auditory Thalamus.
    Date January 2007
    Journal The Journal of Comparative Neurology
    Excerpt

    The auditory thalamus is the major target of the inferior colliculus and connects in turn with the auditory cortex. In the mustached bat, biosonar information is represented according to frequency in the central nucleus of the inferior colliculus (ICc) but according to response type in the cortex. In addition, the cortex has multiple areas with neurons of similar response type compared to the single tonotopic representation in the ICc. To investigate whether these transformations occur at the level of the thalamus, we injected anatomical tracers into physiologically defined locations in the mustached bat's auditory cortex. Injections in areas used for target ranging labeled contiguous regions of the auditory thalamus rather than separate patches corresponding to regions that respond to the different harmonic frequencies used for ranging. Injections in the two largest ranging areas produced labeling in separate locations. These results indicate that the thalamus is organized according to response type rather than frequency and that multiple mappings of response types exist. Injections in areas used for target detection labeled thalamic regions that were largely separate from those that interconnect with ranging areas. However, injections in an area used for determining target velocity overlapped with the areas connected to ranging areas and areas involved in target detection. Thus, separation by functional type and multiplication of areas with similar response type occurs by the thalamic level, but connections with the cortex segregate the functional types more completely than occurs in the thalamus.

    Title Knee Stability After Articulated External Fixation.
    Date January 2006
    Journal The American Journal of Sports Medicine
    Excerpt

    BACKGROUND: Articulated external fixation has been proposed as a method to protect ligament reconstructions while allowing aggressive and early postoperative rehabilitation after knee dislocation. However, the ability of these fixators to protect and stabilize the knee joint has not been clearly determined. HYPOTHESIS: Articulated external fixation can reduce anteroposterior translation in the cruciate-deficient knee and reduce cruciate ligament strain in cases of intact or reconstructed ligaments. STUDY DESIGN: Controlled laboratory study. METHODS: Knee stability was assessed by 3 standard clinical stability tests (Lachman, anterior drawer, and posterior drawer) on 7 human cadaveric lower extremities. Instrumented forces of 100 N were applied to the tibia to measure cruciate ligament forces and tibiofemoral displacement in intact and cruciate-deficient specimens with and without articulated external fixation to determine the degree to which a fixator can protect cruciate ligaments and stabilize the knee. Articulated external fixation was applied using monolateral and bilateral fixators to comparatively analyze the effectiveness of each construct. Statistical analysis was performed using 2-tailed, paired Student t tests. RESULTS: Application of the monolateral articulated external fixator to specimens with intact ligaments significantly reduced cruciate ligament forces by 1.0 N (P = .011), 1.7 N (P = .046), and 1.4 N (P = .009) for Lachman, anterior drawer, and posterior drawer tests, respectively. In the cruciate ligament-deficient knees, the application of a monolateral fixator significantly reduced tibiofemoral translation by 49%, 70%, and 46% for Lachman, anterior drawer, and posterior drawer tests, respectively. No significant differences between the monolateral and bilateral fixator frames, in terms of ligament protection and joint stabilization, were observed.Conclusion and CLINICAL RELEVANCE: Articulated external fixation of the knee can reduce stress in the cruciate ligaments after multiligament reconstructions and can decrease anteroposterior translation in the cruciate-deficient knee.

    Title Lag Screws for Hip Fracture Fixation: Evaluation of Migration Resistance Under Simulated Walking.
    Date December 2005
    Journal Journal of Orthopaedic Research : Official Publication of the Orthopaedic Research Society
    Excerpt

    Previous mechanical studies concerning cut-out of lag screws for pertrochanteric hip fractures have relied on static or dynamic uniaxial loading regimens to induce construct failure by varus collapse and superior cut-out. However, the hip is loaded in a multiplanar, dynamic manner during normal gait. We designed a hip implant performance simulator (HIPS) system to evaluate lag screw cut-out under multiplanar loading representative of normal gait. Five surrogate pertrochanteric fracture specimens with lag screw fixation were loaded up to 20,000 cycles using a biaxial rocking motion (BRM) gait simulation protocol. Another five specimens were loaded using a standard uniaxial loading protocol. The BRM loading group exhibited combined varus collapse (5.4+/-2.9 degrees ) and backward rotation (7.2+/-2.8 degrees ). The uniaxial loading group exhibited four times less varus collapse (1.4+/-1.1 degrees ) as compared to the BRM group, and only negligible rotation. For correlation of lag screw migration in surrogate specimens to that in native bone, six human cadaveric specimens were subjected to BRM loading. The degree of varus collapse (8.5+/-7.7 degrees ) and rotation (7.2+/-6.4 degrees ) in cadaveric specimens were comparable to that in surrogate specimens, with the surrogate specimens showing significantly less variability. The results demonstrate that accounting for clinically realistic multiplanar loading vectors significantly affects implant migration, and therefore should be considered when evaluating the fixation strength of hip screw implants.

    Title Kinematic and Contact Stress Analysis of Posterior Malleolus Fractures of the Ankle.
    Date September 2004
    Journal Journal of Orthopaedic Trauma
    Excerpt

    OBJECTIVE: To determine if there are measurable dynamic contact stress aberrations and kinematic abnormalities (instability) that have not been observed in conventional static loading studies of posterior malleolar ankle fractures. DESIGN: Cadaveric fracture model. SETTING: Biomechanics laboratory. INTERVENTION: Seven fresh cadaveric specimens were fixed in an unconstrained testing apparatus and loaded to one body weight. The ankle was moved from 25 degrees of plantarflexion to 15 degrees of dorsiflexion. The model included the intact ankle and four fracture simulations (50% fracture without internal fixation, 2 mm gap and step malreductions, and anatomically fixed). MAIN OUTCOME MEASURE: Motion at the ankle was monitored with an electromagnetic tracking device, and intra-articular contact stresses were measured using a real-time stress sensor. RESULTS: There were no kinematic abnormalities suggestive of tibiotalar subluxation in any of the fracture simulations. There was no increase in peak contact stress in any of the fracture models compared with the unfractured model. However, there was a shift in the location of the contact stresses to a more anterior and medial location following the fracture. When summed over the range of motion, these areas of cartilage bore significantly higher cumulative contact stresses relative to the nonfracture situation. CONCLUSIONS: We found no talar subluxation and no increase in contact stresses near the articular incongruity, making it unlikely that these factors explain the increased incidence of arthrosis after trimalleolar fractures (OTA/AO classification 44 B3 fractures). Rather, we found that the joint remaining bears increased stress and that the center of stress shifts anteriorly, loading cartilage that normally sees little load.

    Title Hinged External Fixation of the Knee: Intrinsic Factors Influencing Passive Joint Motion.
    Date May 2004
    Journal Journal of Orthopaedic Trauma
    Excerpt

    OBJECTIVE: To measure changes in knee kinematics after the application of articulated external fixators along a previously described knee flexion/extension axis and 16 specific "off-axis" fixator hinge configurations. DESIGN: Cadaver, biomechanical study. SETTING: Biomechanics laboratory. PARTICIPANTS: Nine fresh cadaver knee specimens. INTERVENTION: Each specimen was mounted on a custom-built frame that constrained the knee to move about a fixed flexion/extension axis. Passive knee motion was induced, and the resulting flexion moment was measured. Data were collected for the on-axis fixator position and 16 distinct rotational and translational off-axis positions. In addition, effects of tibial translation and rotation were investigated. MAIN OUTCOME: Range of motion (ROM) attainable within a moment envelope of +/-1 N-m and average energy required to impart movement. RESULTS: The average ROM for unconstrained knees was 122 degree. Constraining the knee to rotation around an on-axis aligned hinge significantly reduced the ROM by 35% to 79 degree. The 5-mm posterior translated hinge was the only alignment to show on average a slightly larger ROM (86 degree) than the on-axis hinge. All other hinge alignments showed decreased average ROM compared with the on-axis position. Tibiofemoral alignments significantly affected the obtainable ROM for the on-axis aligned hinge. CONCLUSION: It was not possible to replicate precisely the complex kinematics of the knee using a single axis fixator over the entire ROM. Using the axis of rotation previously defined in the literature, however, it was possible to obtain a limited ROM of the knee without placing excessive forces on the periarticular structures.

    Title Sources of the Scalp-recorded Amplitude-modulation Following Response.
    Date November 2002
    Journal Journal of the American Academy of Audiology
    Excerpt

    The scalp-recorded amplitude-modulation following response (AMFR) is gaining recognition as an objective audiometric tool, but little is known about the neural sources that underlie this potential. We hypothesized, based on our human studies and single-unit recordings in animals, that the scalp-recorded AMFR reflects the interaction of multiple sources. We tested this hypothesis using an animal model, the unanesthetized rabbit. We compared AMFRs recorded from the surface of the brain at different locations and before and after the administration of agents likely to enhance or suppress neural generators. We also recorded AMFRs locally at several stations along the auditory neuraxis. We conclude that the surface-recorded AMFR is indeed a composite response from multiple brain generators. Although the response at any modulation frequency can reflect the activity of more than one generator, the AMFRs to low and high modulation frequencies appear to reflect a strong contribution from cortical and subcortical sources, respectively.

    Title Responses of Neurons to Click-pairs As Simulated Echoes: Auditory Nerve to Auditory Cortex.
    Date February 2000
    Journal The Journal of the Acoustical Society of America
    Excerpt

    When two identical sounds are presented from different locations with a short interval between them, the perception is of a single sound source at the location of the leading sound. This "precedence effect" is an important behavioral phenomenon whose neural basis is being increasingly studied. For this report, neural responses were recorded to paired clicks with varying interstimulus intervals, from several structures of the ascending auditory system in unanesthetized animals. The structures tested were the auditory nerve, anteroventral cochlear nucleus, superior olivary complex, inferior colliculus, and primary auditory cortex. The main finding is a progressive increase in the duration of the suppressive effect of the leading sound (the conditioner) on the response to the lagging sound (the probe). The first major increase occurred between the lower brainstem and inferior colliculus, and the second between the inferior colliculus and auditory cortex. In neurons from the auditory nerve, cochlear nucleus, and superior olivary complex, 50% recovery of the response to the probe occurred, on average, for conditioner and probe intervals of approximately 2 ms. In the inferior colliculus, 50% recovery occurred at an average separation of approximately 7 ms, and in the auditory cortex at approximately 20 ms. Despite these increases in average recovery times, some neurons in every structure showed large responses to the probe within the time window for precedence (approximately 1-4 ms for clicks). This indicates that during the period of the precedence effect, some information about echoes is retained. At the other extreme, for some cortical neurons the conditioner suppressed the probe response for intervals of up to 300 ms. This is in accord with behavioral results that show dominance of the leading sound for an extended period beyond that of the precedence effect. Other transformations as information ascended included an increased variety in the shapes of the recovery functions in structures subsequent to the nerve, and neurons "tuned" to particular conditioner-probe intervals in the auditory cortex. These latter are reminiscent of neurons tuned to echo delay in bats, and may contribute to the perception of the size of the acoustic space.

    Title Upper Extremity Musculoskeletal Manifestations of Dialysis-associated Amyloidosis.
    Date June 1997
    Journal The Iowa Orthopaedic Journal
    Title An Articulated Ankle External Fixation System That Can Be Aligned with the Ankle Axis.
    Date September 1995
    Journal The Iowa Orthopaedic Journal
    Excerpt

    Aligning an articulated ankle external fixator with the ankle axis located using a mechanical axis finder has been shown to preserve normal ankle joint kinematics while the fixed hinge device is attached. However, several problems exist preventing the clinical application of this finding for fractures of the tibial plafond. We initiated a series of studies to resolve these issues. First, the accuracy of the mechanical axis finder in biological systems was quantified by comparing it to that of a computationally derived helical axis. Second, a prototype fixator design was developed in the biomechanics lab to increase the versatility of intraoperative fixator placement. Finally, a radiographic method of locating the ankle axis was developed which is based on talar morphology independent of the fractured tibia. The prototype fixator has been accurately aligned along the ankle axis in cadaveric specimens using this method. Open reduction and internal fixation (ORIF) is the accepted method of treatment for tibial plafond fractures. It holds the advantage of sufficient fracture fixation to permit early joint motion. Good results have been reported using this method, but some authors have reported complication rates up to 50%. The wide surgical approaches required, in conjunction with preexisting soft tissue injury, are thought to significantly increase the risk of soft tissue complications. In response to these problems, many investigators are beginning to utilize external fixation as an alternate treatment modality. One external fixation system which has shown particularly good results is a monolateral cross-ankle articulated fixator (Orthofix SRL., Verona, Italy) which allows motion at the ankle joint as the plafond fracture is healing (Figure 1).(ABSTRACT TRUNCATED AT 250 WORDS)

    Title Articulated External Fixation of Pilon Fractures: the Effects on Ankle Joint Kinematics.
    Date May 1995
    Journal Journal of Orthopaedic Trauma
    Excerpt

    The effect of the Orthofix articulated ankle external fixator on ankle and subtalar joint kinematics and fracture fragment motion was investigated in fresh cadaver specimens using biplanar radiographic analysis. The kinematic testing was performed for the normal ankle (i.e., no fixation) and for three alternate fixator hinge orientations. The fixator applications simulated a horizontal ankle axis (the current clinically preferred orientation), an axis coincident with a previously defined approximate ankle axis, and an axis located using a mechanical axis finder. The horizontal fixator application significantly disturbed normal ankle kinematics. Aligning the fixator hinge with an approximate ankle axis caused significant distortion of motion about only two of six possible rotational axes. Aligning the fixator hinge with the (specimen-specific) ankle axis determined by the axis finder most closely matched the motion of the normal ankle. For pilon fractures simulated by a transverse osteotomy, there appeared to be no physiologically significant fracture fragment motions, regardless of fracture stability or fixator orientation.

    Title Combination-sensitive Neurons in the Primary Auditory Cortex of the Mustached Bat.
    Date March 1993
    Journal The Journal of Neuroscience : the Official Journal of the Society for Neuroscience
    Excerpt

    In the mustached bat, Pteronotus parnellii, neurons in the primary auditory cortex (AI) have been thought to respond primarily to single frequencies, as in other mammals. However, neurons in the Doppler-shifted constant-frequency (DSCF) area, a part of the mustached bat's AI that contains an overrepresentation of the prominent CF2 component of the biosonar signal, were found to show facilitative responses to combinations of different frequencies in the pulse and echo. The essential components for facilitation were the pulse FM1 and the echo CF2. The FM1-CF2 facilitation was sensitive to echo delays, indicating that DSCF neurons respond better to targets within particular ranges. On average, the longest discriminable echo delay, based on increased impulse counts due to facilitation, corresponded to a target range of 4.3 m, and the most discriminable delay corresponded to a target 3.6 m distant. Since mustached bats first show a behavioral response to a target at a distance of 3-4 m, DSCF neurons are suited to signal the presence of an insect within this behaviorally important range. DSCF neurons were broadly tuned to echo delay, with the average minimum discriminable echo delay corresponding to a target range of 1.9 m, and the delay tuning of the neurons followed (tracked) changes in pulse duration, indicating that facilitation occurs during much of the approach phase of insect pursuit when target characterization is presumably occurring. These results show that AI neurons in the mustached bat are specialized to respond to complex, behaviorally relevant stimuli during the search and approach phases of insect pursuit.

    Title Interaural Time Discrimination of Envelopes Carried on High-frequency Tones As a Function of Level and Interaural Carrier Mismatch.
    Date
    Journal Ear and Hearing
    Excerpt

    OBJECTIVES: The present study investigated interaural time discrimination for binaurally mismatched carrier frequencies in listeners with normal hearing. One goal of the investigation was to gain insights into binaural hearing in patients with bilateral cochlear implants, where the coding of interaural time differences (ITDs) may be limited by mismatches in the neural populations receiving stimulation on each side. DESIGN: Temporal envelopes were manipulated to present low frequency timing cues to high-frequency auditory channels. Carrier frequencies near 4 kHz were amplitude modulated at 128 Hz via multiplication with a half-wave rectified sinusoid, and that modulation was either in-phase across ears or delayed to one ear. Detection thresholds for nonzero ITDs were measured for a range of stimulus levels and a range of carrier frequency mismatches. Data were also collected under conditions designed to limit cues based on stimulus spectral spread, including masking and truncation of sidebands associated with modulation. RESULTS: Listeners with normal hearing can detect ITDs in the face of substantial mismatches in carrier frequency across ears. CONCLUSIONS: The processing of ITDs in listeners with normal hearing is likely based on spread of excitation into binaurally matched auditory channels. Sensitivity to ITDs in listeners with cochlear implants may depend on spread of current that results in the stimulation of neural populations that share common tonotopic space bilaterally.

    Title Operative Stabilization of Flail Chest Injuries: Review of Literature and Fixation Options.
    Date
    Journal European Journal of Trauma and Emergency Surgery : Official Publication of the European Trauma Society
    Excerpt

    BACKGROUND: Flail chest injuries cause significant morbidity, especially in multiply injured patients. Standard treatment is typically focused on the underlying lung injury and involves pain control and positive pressure ventilation. Several studies suggest improved short- and long-term outcomes following operative stabilization of the flail segments. Despite these studies, flail chest fixation remains a largely underutilized procedure. METHODS: This article reviews the relevant literature concerning flail chest fixation and describes the different implants and techniques available for fixation. Additionally, an illustrative case example is provided for description of the surgical approach. RESULTS: Two prospective randomized studies, five comparative studies, and a number of case series documented benefits of operative treatment of flail chest injuries, including a decreased in ventilation duration, ICU stay, rates of pneumonia, mortality, residual chest wall deformity, and total cost of care. Historically, rib fractures have been stabilized with external plates or intramedullary implants. The use of contemporary, anatomically contoured rib plates reduced the need for intraoperative plate bending. Intramedullary rib splints allowed less-invasive fixation of posterior fractures where access for plating was limited. CONCLUSION: Operative treatment can provide substantial benefits to patients with flail chest injuries and respiratory compromise requiring mechanical ventilation. The use of anatomically contoured rib plates and intramedullary splints greatly simplifies the procedure of flail chest fixation.


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