Total femoral spanning for distal femur "fragility" fractures utilising nail-plate fixation "short-term experience of a district general hospital".

PURPOSE: Our primary objective was to investigate the time to radiological union following linked nail-plate fixation of distal femur "fragility" fractures. Secondary objectives were to evaluate all-cause reoperations, 90-day mortality, rate of blood transfusion and the impact on quality of life. METHODS: In this retrospective study of all adults (≥ 65 years) with native or periprosthetic distal femur fragility fractures, underwent a linked nail-plate fixation, data were retrieved on fracture classifications, clinical frailty score, blood transfusion, length of hospital stay, 90-day mortality, time to radiological union, overall complication rates and EuroQoL-5D. RESULTS: In total, 18 out of 23 patients completed sequential follow-up. Radiological union was observed in 14 patients (median 143 days; range 42-414). Three patients underwent reoperations. There were no implant failures or a subsequent periprosthetic fractures. Ninety-day mortality was 17.4%. Eighteen patients required blood transfusion. The QoL was significantly lower after index surgery (0.875 vs. 0.684; p < 0.01). CONCLUSION: Based on our observation, with short-term follow-up, the linked nail-plate yields optimal stability to allow immediate weight bearing, in a cohort with moderate frailty. It is reproducible, with variable radiological union rates. The concept of "total femoral spanning" reduces the risk of subsequent periprosthetic fractures. The additional intervention has increased the rates of allogenic blood transfusion. There is significant impact on overall QoL, with almost 50% being more dependent in self-care.

Closed Internal Degloving of the Toes: A Case Report.

Closed degloving injuries are uncommon, high-energy injuries that separate the bony structures from the soft tissue and frequently result in amputation. Because the epidermis is often intact, it is difficult to visualize the extent of the soft tissue damage. Although there is no gold standard of treatment for closed degloving injuries at present, previous cases have reported that neurovascular presentation is a key predictor of amputation Herein, we report a closed degloving injury involving the second through fifth phalanges of the left foot following a crushing injury with a forklift. Despite adequate capillary refill upon initial presentation, the patient ultimately underwent transmetatarsal amputation.

The development and performance of a perforated plate burner to produce vitiated flow with negligible swirl under engine-relevant gas turbine conditions.

The development and performance of a perforated plate burner (PPB) operating using premixed natural gas and air at engine-relevant inlet temperatures and combustor pressures with thermal powers up to 1 MW is discussed. A significant benefit of using burners with simplified flow fields, such as the PPB, for experimental studies in the laboratory is the potential for decoupling the complex fluid dynamics in typical combustors from the chemical kinetics. The primary motivation for developing this burner was to use it as a source of vitiated flow with negligible swirl for reacting jet in vitiated crossflow experiments. The design methodology for the PPB is described, including plate geometry selection and flashback mitigation features. The stable operation of the PPB within a high-pressure test rig was validated: successful ignition, effective use of red-lines for flashback mitigation, and long duration steady-state operation in both piloted and nonpiloted modes were all observed. Exhaust gas emissions measured using a Fourier-transform infrared (FTIR) spectrometer showed very good performance of the PPB in terms of the combustion efficiency (based on measured CO and UHC), and a stability diagram of the PPB was developed as a function of the equivalence ratio and the PPB hole velocity. FTIR measurements also showed very low levels of NOX in nonpiloted operation that were generally within 3 ppm (reported dry and referenced to 15% O2). The capability for steady-state operation, high combustion efficiency, and low levels of NOX makes this PPB an excellent burner candidate for combustion experiments in the laboratory.

Early Sports Specialization in Elite Wrestlers.

BACKGROUND: Sports specialization is becoming an increasingly common training strategy in young athletes. Very little research currently exists examining the occurrence of serious injury (>3 months off sport or loss of season) in elite-level wrestlers who specialize early (before age 12 years). HYPOTHESIS: Wrestlers who specialize early will sustain more serious injuries than wrestlers who specialize at age 12 years or older. STUDY DESIGN: Descriptive epidemiological study. METHODS: We sent an anonymous online survey to a total of 312 elite-level wrestlers (National Collegiate Athletic Association Division I athletes and World/Olympic team members) containing questions documenting age of specialization and number of serious injuries sustained. The number of serious injuries both before and after starting college were compared between wrestlers specializing at <12 years old and ≥12 years old using an independent-samples t test. Respondents' opinions on the necessity of early specialization and their primary source of encouragement to specialize were also reported. RESULTS: A total of 143 wrestlers completed the survey, for a total response rate of 46%. Thirty-six (25%) wrestlers specialized at <12 years old. The early specialization group sustained significantly more serious injuries than the late specialization group (1.14 vs 0.60; P = 0.035). Sixty-two (43%) believed early specialization was necessary to achieve elite-level status. The decision to specialize was encouraged primarily by the athlete (78/143; 55%), parents (37/143; 26%), and coaches (22/143; 15%). CONCLUSION: Elite wrestlers who specialize prior to age 12 years sustain a greater number of serious injuries before starting college than those who specialize at or after the age of 12 years. CLINICAL RELEVANCE: Athletes, coaches, and parents should consider the risk of injury before adopting a wrestling-specialized training strategy at a young age.

Mindfulness in sustainability science, practice, and teaching.

This paper explores the current role of mindfulness in sustainability science, practice, and teaching. Based on a qualitative literature review that is complemented by an experimental learning lab, we sketch the patterns and core conceptual trajectories of the mindfulness-sustainability relationship. In addition, we assess this relationship within the field of climate change adaptation and risk reduction. The results highlight that notions such as 'sustainability from within', 'ecological mindfulness', 'organizational mindfulness', and 'contemplative practices' have been neglected in sustainability science and teaching. Whilst little sustainability research addresses mindfulness, there is scientific support for its positive influence on: (1) subjective well-being; (2) the activation of (intrinsic/ non-materialistic) core values; (3) consumption and sustainable behavior; (4) the human-nature connection; (5) equity issues; (6) social activism; and (7) deliberate, flexible, and adaptive responses to climate change. Most research relates to post-disaster risk reduction, although it is limited to the analysis of mindfulness-related interventions on psychological resilience. Broader analyses and foci are missing. In contrast, mindfulness is gaining widespread recognition in practice (e.g., by the United Nations, governmental and non-governmental organizations). It is concluded that mindfulness can contribute to understanding and facilitating sustainability, not only at the individual level, but sustainability at all scales, and should, thus, become a core concept in sustainability science, practice, and teaching. More research that acknowledges positive emotional connections, spirituality, and mindfulness in particular is called for, acknowledging that (1) the micro and macro are mirrored and interrelated, and (2) non-material causation is part of sustainability. This paper provides the first comprehensive framework for contemplative scientific inquiry, practice, and education in sustainability.

Dynamic foraminal dimensions during neck extension and rotation in fusion and artificial disc replacement: an observational study.

BACKGROUND: Changes in the dimensions of the cervical neural foramina (CNF) are considered to be a key factor in nerve root compression and development of cervical radiculopathy. However, to what extent foraminal geometry differs between patients who underwent anterior cervical discectomy and fusion (ACDF) and those who underwent total disc arthroplasty with an artificial disc (AD) during physiological motion is largely unknown. PURPOSE: The objective of this study is to compare CNF dimensions during physiological neck motion between ACDF and AD. STUDY DESIGN/SETTING: This is a retrospective comparative analysis of prospectively collected, consecutive, non-randomized series of patients at a single institution. PATIENT SAMPLE: A total of 16 single-level C5-C6 ACDF (4 males, 12 females; 28-71 years) and 7 single-level C5-C6 cervical arthroplasty patients (3 males, 4 females; 38-57 years), at least 12 months after surgery (23.6±6.8 months) were included. OUTCOME MEASURES: Patient demographics, preoperative magnetic resonance imaging (MRI)-based measurements of cervical spine degeneration, and 2-year postoperative measurements of dynamic foraminal geometry were the outcome measures. METHODS: Biplane X-ray images were acquired during axial neck rotation and neck extension. A computed tomography scan was also acquired from C3 to the first thoracic vertebrae. The subaxial cervical vertebrae (C3-C7) were reconstructed into three-dimensional (3D) bone models for use with model-based tracking. Foraminal height (FH) was calculated as the 3D distance between the superior point of the inferior pedicle and the inferior point of the superior pedicle using custom software. Foraminal width (FW) was similarly calculated as the 3D distance between the anterolateral aspect of the superior vertebral body inferior notch and the posterolateral aspect of the inferior vertebral body superior notch. Dynamic foraminal dimensions were quantified as the minimum (FH.Min, FW.Min), the range (FH.Range, FW.Range), and the median (FH.Med, FW.Med) of each trial and then averaged over trials. Mixed model analysis of variance framework was used to examine the differences between ACDF and AD groups. The initial severity of disc degeneration as determined from preoperative MRI images was introduced as covariates in the models. RESULTS: At the operated level (C5-C6), FH.Med and FH.Range were smaller in ACDF than in AD during axial rotation and neck extension (p<.003 to p<.05). At the superior adjacent level (C4-C5), no significant difference was found. At the inferior adjacent level (C6-C7), FW.Range was greater in ACDF than in AD during axial rotation and extension (p<.05). At the non-adjacent level (C3-C4), FW.Range was greater in ACDF than in AD during extension (p<.008). CONCLUSIONS: This study demonstrated decreases in foraminal dimensions and their range for ACDF compared with AD at the operated level. In contrast, it demonstrated increases in the range of foraminal dimensions during motion for ACDF compared with AD at the non-operated segments. Together, these data support the notion that increased mobility at the non-operated segments after ACDF may contribute to a greater risk for adjacent segment degeneration. Because of the significant presence of range variables in the findings, the current data also indicate that a dynamic evaluation is likely more appropriate for evaluation of the differences in foramina between ACDF and AD than a static evaluation.

Dynamic measurements of cervical neural foramina during neck movements in asymptomatic young volunteers.

PURPOSE: Neural foraminal dimensions are considered important in nerve root compression and development of cervical radiculopathy, but baseline data regarding their range during normal motion are not available. An in vivo study of cervical foraminal motion was conducted to characterize normal 3D dynamic foraminal dimensions during physiological neck motion and compare between different tasks and intervertebral segments. METHODS: Biplane X-ray imaging and computed tomography-based markerless tracking were used to measure foraminal height (FH) and width (FW) from five asymptomatic subjects during neck axial rotation and extension. FH and FW were quantified as the minimum (SI.Min and AP.Min), range (SI.Range and AP.Range), and median (SI.Med and AP.Med) of superoinferior (SI) and anteroposterior (AP) dimensions for each trial and as the coefficient of variation of these variables from three trials (SI.Med.CV and AP.Med.CV, SI.Range.CV and AP.Range.CV) at C3-4 through C6-7 levels for each subject. Differences were analyzed using mixed model ANOVA. RESULTS: AP.Range and AP.Med.CV were greater (P < 0.0001) while AP.Min and AP.Range.CV were smaller (P < 0.0006 and P < 0.0005) during neck extension than rotation. SI.Range and SI.Med.CV were greater for extension than rotation at C5-6 (P < 0.002 and P < 0.03), whereas SI.Med.CV was greater for rotation than extension at C3-4 (P < 0.03). AP.Range (P < 0.02), AP.Med.CV (P < 0.05), SI.Range (P < 0.0004), and SI.Med.CV (P < 0.02) were different between cervical levels, the latter two being during extension only. CONCLUSIONS: Patterns of FH and FW during normal motion are different between tasks and cervical levels. These findings are expected to provide a basis for future studies of spinal degeneration and surgical efficacy.

Molecule specific effects of PKA-mediated phosphorylation on rat isolated heart and cardiac myofibrillar function.

Increased cardiac myocyte contractility by the ß-adrenergic system is an important mechanism to elevate cardiac output to meet hemodynamic demands and this process is depressed in failing hearts. While increased contractility involves augmented myoplasmic calcium transients, the myofilaments also adapt to boost the transduction of the calcium signal. Accordingly, ventricular contractility was found to be tightly correlated with PKA-mediated phosphorylation of two myofibrillar proteins, cardiac myosin binding protein-C (cMyBP-C) and cardiac troponin I (cTnI), implicating these two proteins as important transducers of hemodynamics to the cardiac sarcomere. Consistent with this, we have previously found that phosphorylation of myofilament proteins by PKA (a downstream signaling molecule of the beta-adrenergic system) increased force, slowed force development rates, sped loaded shortening, and increased power output in rat skinned cardiac myocyte preparations. Here, we sought to define molecule-specific mechanisms by which PKA-mediated phosphorylation regulates these contractile properties. Regarding cTnI, the incorporation of thin filaments with unphosphorylated cTnI decreased isometric force production and these changes were reversed by PKA-mediated phosphorylation in skinned cardiac myocytes. Further, incorporation of unphosphorylated cTnI sped rates of force development, which suggests less cooperative thin filament activation and reduced recruitment of non-cycling cross-bridges into the pool of cycling cross-bridges, a process that would tend to depress both myocyte force and power. Regarding MyBP-C, PKA treatment of slow-twitch skeletal muscle fibers caused phosphorylation of MyBP-C (but not slow skeletal TnI (ssTnI)) and yielded faster loaded shortening velocity and ∼30% increase in power output. These results add novel insight into the molecular specificity by which the ß-adrenergic system regulates myofibrillar contractility and how attenuation of PKA-induced phosphorylation of cMyBP-C and cTnI may contribute to ventricular pump failure.

Retinotopic organization of extrastriate cortex in the owl monkey--dorsal and lateral areas.

Dense retinotopy data sets were obtained by microelectrode visual receptive field mapping in dorsal and lateral visual cortex of anesthetized owl monkeys. The cortex was then physically flatmounted and stained for myelin or cytochrome oxidase. Retinotopic mapping data were digitized, interpolated to a uniform grid, analyzed using the visual field sign technique-which locally distinguishes mirror image from nonmirror image visual field representations-and correlated with the myelin or cytochrome oxidase patterns. The region between V2 (nonmirror) and MT (nonmirror) contains three areas-DLp (mirror), DLi (nonmirror), and DLa/MTc (mirror). DM (mirror) was thin anteroposteriorly, and its reduced upper field bent somewhat anteriorly away from V2. DI (nonmirror) directly adjoined V2 (nonmirror) and contained only an upper field representation that also adjoined upper field DM (mirror). Retinotopy was used to define area VPP (nonmirror), which adjoins DM anteriorly, area FSTd (mirror), which adjoins MT ventrolaterally, and TP (mirror), which adjoins MT and DLa/MTc dorsoanteriorly. There was additional retinotopic and architectonic evidence for five more subdivisions of dorsal and lateral extrastriate cortex-TA (nonmirror), MSTd (mirror), MSTv (nonmirror), FSTv (nonmirror), and PP (mirror). Our data appear quite similar to data from marmosets, though our field sign-based areal subdivisions are slightly different. The region immediately anterior to the superiorly located central lower visual field V2 varied substantially between individuals, but always contained upper fields immediately touching lower visual field V2. This region appears to vary even more between species. Though we provide a summary diagram, given within- and between-species variation, it should be regarded as a guide to parsing complex retinotopy rather than a literal representation of any individual, or as the only way to agglomerate the complex mosaic of partial upper and lower field, mirror- and nonmirror-image patches into areas.

Three-dimensional motion analysis of the cervical spine for comparison of anterior cervical decompression and fusion versus artificial disc replacement in 17 patients: clinical article.

OBJECT: Cervical arthroplasty with an artificial disc (AD) has emerged as an alternative to anterior cervical discectomy and fusion (ACDF) for the management of cervical spondylosis. This study aims to provide 3D motion analysis data comparing patients after ACDF and AD replacement. METHODS: Ten patients who underwent C5-6 ACDF and 7 who underwent C5-6 AD replacement were enrolled. Using biplanar fluoroscopy and a model-based track technique (accurate up to 0.6 mm and 0.6°), motion analysis of axial rotation and flexion-extension of the neck was performed. Three nonoperative segments (C3-4, C4-5, and C6-7) were assessed for both intervertebral rotation (coronal, sagittal, and axial planes) and facet shear (anteroposterior and mediolateral). RESULTS: There was no difference in total neck motion comparing ACDF and AD replacement for neck extension (43.3° ± 10.2° vs 44.3° ± 12.6°, p = 0.866) and rotation (36.0° ± 6.5° vs 38.2° ± 9.3°, p = 0.576). For extension, when measured as a percentage of total neck motion, there was a greater amount of rotation at the nonoperated segments in the ACDF group than in the AD group (p = 0.003). When comparing specific motion segments, greater normalized rotation was seen in the ACDF group at C3-4 (33.2% ± 4.9% vs 26.8% ± 6.6%, p = 0.036) and C6-7 (28.5% ± 6.7% vs 20.5% ± 5.5%, p = 0.009) but not at C4-5 (33.5% ± 6.4% vs 31.8% ± 4.0%, p = 0.562). For neck rotation, greater rotation was observed at the nonoperative segments in the ACDF group than in the AD group (p = 0.024), but the differences between individual segments did not reach significance (p ≥ 0.146). Increased mediolateral facet shear was seen on neck extension with ACDF versus AD replacement (p = 0.008). Comparing each segment, C3-4 (0.9 ± 0.5 mm vs 0.4 ± 0.1 mm, p = 0.039) and C4-5 (1.0 ± 0.4 mm vs 0.5 ± 0.2 mm, p = 0.022) showed increased shear while C6-7 (1.0 ± 0.4 mm vs 1.0 ± 0.5 mm, p = 0.767) did not. CONCLUSIONS: This study illustrates increased motion at nonoperative segments in patients who have undergone ACDF compared with those who have undergone AD replacement. Further studies will be required to examine whether these changes contribute to adjacent-segment disease.

Development of an image-based technique to examine joint congruency at the elbow.

Identifying joint contact in articular joints is important for both the biomechanical investigation of joint mechanics and the study of osteoarthritis. The purpose of this study is to develop a proximity mapping technique to non-invasively determine joint congruency, as a surrogate of joint contact. To illustrate the capabilities of this algorithm, a cadaveric upper extremity was positioned at varying degrees of elbow flexion. This technique was validated using a gold standard experimental casting technique. The pattern of the cast showed an excellent agreement with the generated proximity map using the inter-bone distance algorithm. The results from this study agree with the results of previous studies examining joint contact at the elbow both in the location and in the tracking of the joint contact throughout elbow flexion. Ultimately, this technique will lead to an increased understanding of the effect of malalignment and instability of the joint on contact mechanics.

Kinematics and laxity of a linked total elbow arthroplasty following computer navigated implant positioning.

Aseptic loosening in total elbow arthroplasty (TEA) remains the most common cause of long-term failure. While several different mechanisms of implant loosening have been suggested, it is likely that one important underlying cause is implant malpositioning, resulting in changes in joint kinematics and loading. Although use of computer navigation has been shown to improve component positioning in other joints, no such system currently exists for the elbow. This study used real-time computer feedback for humeral, ulnar, and radial component positioning in 11 cadaveric extremities. An elbow motion simulator evaluated joint kinematics. Endosteal abutment of the stems of the humeral and ulnar components precluded optimal positioning in 5 and 6 specimens, respectively. Loss of the normal valgus angulation following elbow arthroplasty (p < 0.05) suggests that errors in humeral component positioning translate directly into changes in joint kinematics during active motion. These findings suggest that although computer navigation can reproduce normal joint kinematics, optimal implant positioning may require a TEA system which allows for some modularity to accommodate the normal variations in osseous morphology of the elbow.

Measuring dynamic in-vivo elbow kinematics: description of technique and estimation of accuracy.

BACKGROUND: The objectives of this study were to characterize the translational and rotational accuracy of a model-based tracking technique for quantifying elbow kinematics and to demonstrate its in vivo application. METHOD OF APPROACH: The accuracy of a model-based tracking technique for quantifying elbow kinematics was determined in an in vitro experiment. Biplane X-ray images of a cadaveric elbow were acquired as it was manually moved through flexion-extension. The 3D position and orientation of each bone was determined using model-based tracking. For comparison, the position and orientation of each bone was also determined by tracking the position of implanted beads with dynamic radiostereometric analysis. Translations and rotations were calculated for both the ulnohumeral and radiohumeral joints, and compared between measurement techniques. To demonstrate the in vivo application of this technique, biplane X-ray images were acquired as a human subject extended their elbow from full flexion to full extension. RESULTS: The in vitro validation demonstrated that the model-based tracking technique is capable of accurately measuring elbow motion, with reported errors averaging less than ±1.0 mm and ±1.0 deg. For the in vivo application, the carrying angle changed from an 8.3 ± 0.5 deg varus position in full flexion to an 8.4 ± 0.5 deg valgus position in full extension. CONCLUSIONS: Model-based tracking is an accurate technique for measuring in vivo, 3D, dynamic elbow motion. It is anticipated that this experimental approach will enhance our understanding of elbow motion under normal and pathologic conditions.

A morphological analysis of the humeral capitellum with an interest in prosthesis design.

INTRODUCTION: Although interest in capitellar arthroplasty is increasing, the morphology of the capitellum has not been fully characterized. Our purpose was to quantify the anthropometric features of the capitellum with an interest in arthroplasty design. We hypothesized that the shape is more complex than originally believed, and cannot be accurately modeled as a spherical structure. METHODS: Fifty cadaveric human elbows underwent helical computer tomography scans. After reconstruction and establishment of a coordinate system for the distal humerus, circle-fits were applied to each of the 1-mm-thick slices. Sagittal radii of curvature were calculated every 10° of flexion around each circle (0-130° of flexion). A single transverse radius was calculated at 60° of flexion. The surface of the capitellum was described by sagittal and transverse radii of curvature and the footprint by height and width. These pairs of parameters were correlated to determine their strength of association. RESULTS: The average height was 23.2 ± 2.9 mm (range, 18.3-29.5), while the average width was 13.9 ± 2.3 (range, 9-19). The sagittal radius of curvature was 11.6 ± 1.4 mm (range, 8.7-14.8), and the transverse radius was 14.0 ± 3.0 mm (range, 9.6-20.9). Correlations of height and width and sagittal and transverse radii were significant (R = .547, .705) (P < .01). Sagittal and transverse radii and height and width were significantly different (P < .001 for each pair). CONCLUSION: The capitellum does not have a spherical surface or a circular footprint. There is substantial variability in the relationship between the height and width, and between the surface radii, that may be difficult to replicate with an off-the-shelf implant.

Stem abutment affects alignment of the humeral component in computer-assisted elbow arthroplasty.

OBJECTIVES AND HYPOTHESIS: The humeral component in total elbow arthroplasty has limited geometric modularity, and the extent to which this affects accurate positioning is unknown. The objectives of this study were to (1) validate the accuracy of a computer-assisted implant alignment technique, and (2) identify variations in distal humeral morphology that affected computer-assisted implant alignment. This was achieved by implanting both an unmodified humeral component and an implant with a reduced stem using computer assistance. We hypothesized that implantation of a humeral component with a reduced stem length would be more accurate than implantation of the standard length stem. In addition, we hypothesized that the variation in flexion-extension (FE) varus-valgus angulation would significantly affect computer-assisted implant alignment. MATERIALS AND METHODS: Computer-assisted alignment of the implant articulating axis with the humeral FE axis was performed on 13 cadaveric humeri for both the regular and modified humeral component. Navigation was based on alignment of the prosthesis with a preoperative plan and registration of this plan to the humerus. RESULTS: Implant alignment was significantly improved for the reduced stem. Alignment error of the reduced stem averaged 1.3 ± 0.5 mm in translation and 1.2° ± 0.4° in rotation, compared with 1.9 ± 1.1 mm and 3.6° ± 2.1° for the regular stem. Humeral varus-valgus angulation significantly affected alignment of the unmodified stem. DISCUSSION: A humeral component with a fixed valgus angulation cannot be accurately positioned in a consistent fashion without sacrificing alignment of the FE axis. Improved accuracy of implant placement can be achieved by introducing a family of humeral components, with 3 valgus angulations of 0°, 4° and 8°.

Osteochondral lesions of the capitellum do not affect elbow kinematics and stability with intact collateral ligaments: an in vitro biomechanical study.

PURPOSE: Osteochondritis dissecans (OCD) of the capitellum most commonly affects adolescent pitchers and gymnasts, who present with pain and mechanical symptoms. Patients with larger lesions have poorer outcomes, possibly related to increased contact pressures on the surrounding articular surface with or without instability. The purpose of this in vitro study was to determine whether displaced OCD lesions of the capitellum lead to altered kinematics and stability of the elbow. METHODS: We mounted 9 fresh-frozen cadaveric arms in an upper extremity joint testing system, with cables attaching the tendons of the major muscles to motors and pneumatic actuators. An electromagnetic receiver on the ulna enabled quantification of the kinematics of the radius and ulna with respect to the humerus. We used 3-dimensional computed tomography scans and computer-assisted techniques to navigate sequential osteochondral defects ranging in size from 12.5% to 100% of the capitellum. The arms were subjected to active and passive flexion in both the vertical and valgus positions with the forearm in both pronation and supination. RESULTS: We found no significant differences in valgus angulation or ulnar rotation between any of the OCD lesions and the intact elbow during flexion, regardless of arm position or forearm rotation. CONCLUSIONS: Osteochondritis dissecans lesions of the capitellum, both small and large, did not alter the ulnohumeral kinematics and stability with intact collateral ligaments. Therefore, excision of unfixable osteochondral fragments of the capitellum in the setting of intact collateral ligaments can be considered without the risk of creating instability.

Contribution of the olecranon to elbow stability: an in vitro biomechanical study.

BACKGROUND: The amount of the olecranon that can be removed without substantially affecting the kinematics and stability of the elbow is controversial. The purpose of this study was to determine the effect of serial resections of the olecranon on elbow kinematics and stability. METHODS: Eight fresh, previously frozen cadaver arms were mounted in an in vitro motion simulator, and kinematic data were obtained with use of an electromagnetic tracking system for active and passive motion. Flexion was studied in the varus, valgus, horizontal, and dependent positions. Custom-written three-dimensional computer navigation software was utilized to guide serial resection of the olecranon in 12.5% increments from 0% to 100%. A traditional triceps advancement repair was performed following each resection. Flexion angle, amount of olecranon resection, and active and passive motion measurements were compared. RESULTS: Serial resection of the olecranon resulted in a significant increase in varus-valgus angulation with the arm in the varus (p < 0.04) and valgus (p = 0.01) orientations. Ulnohumeral rotation significantly increased in the varus (p < 0.001) and valgus (p < 0.007) orientations. Angular (p = 0.02) and rotational (p < 0.001) kinematics were greater with passive compared with active motion. There was no difference in elbow kinematics following olecranon resection with the arm positioned in the horizontal and dependent positions. CONCLUSIONS: Valgus-varus angulation and ulnohumeral rotation progressively increase with sequential excision of up to 75% of the olecranon. Elbow stability is progressively lost with sequential excision, with gross instability noted at resection of > or = 87.5% of the olecranon.

Effect of coronal shear fractures of the distal humerus on elbow kinematics and stability.

BACKGROUND: Coronal shear fractures of the distal humerus can include some or all of the cartilaginous and bony surface. Fixation is preferred, but severe comminution, nonunion, and avascular necrosis may mandate excision. The amount of distal humerus that is safe to excise is unknown. This study examined the effect of excision of the capitellum and trochlea on elbow kinematics and stability with intact collateral ligaments. METHODS: Eight cadaveric arms were mounted in an upper extremity joint testing system. Electromagnetic receivers on the radius and ulna enabled quantification of ulnohumeral and radiocapitellar kinematics. The distal humeral articular surface was sequentially excised to replicate clinically relevant coronal shear fractures, leaving the collateral ligaments undisturbed. The arms underwent simulated active flexion in vertical and valgus-loaded positions, and passive forearm rotation in the vertical position. RESULTS: In the vertical position, sequential excision of the articular surface increased valgus angulation during active flexion (P < or = .04), and excision of the entire articular surface increased ulnar external rotation compared to the intact elbow (P < or = .02). In the valgus position, excisions involving the trochlea increased valgus angulation for active flexion (P < or = .04). The radial head moved distal, posterior, and medial on the capitellum with some or all of the trochlea excised (P < or = .02). DISCUSSION: While the capitellum alone does not contribute to elbow stability, the trochlea has an important role. Excision of the trochlea resulted in multiplanar instability of the ulnohumeral and radiocapitellar joints. Therefore, excision of an irreparable capitellum fracture may be considered if collateral ligaments are intact, while excision of some or all of the trochlea may not.

Three-dimensional dynamic in vivo motion of the cervical spine: assessment of measurement accuracy and preliminary findings.

BACKGROUND CONTEXT: Previous research has quantified cervical spine motion with conventional measurement techniques (eg, cadaveric studies, motion capture systems, and fluoroscopy), but these techniques were not designed to accurately measure three-dimensional (3D) dynamic cervical spine motion under in vivo conditions. PURPOSE: The purposes of this study were to characterize the accuracy of model-based tracking for measuring 3D dynamic cervical spine kinematics and to demonstrate its in vivo application. STUDY DESIGN: Through accuracy assessment and application of technique, in vivo cervical spine motion was measured. METHODS: The accuracy of model-based tracking for measuring cervical spine motion was determined in an in vitro experiment. Tantalum beads were implanted into the vertebrae of an ovine specimen, and biplane X-ray images were acquired as the specimen's neck was manually moved through neck extension and axial neck rotation. The 3D position and orientation of each cervical vertebra were determined from the biplane X-ray images using model-based tracking. For comparison, the position and orientation of each vertebra were also determined by tracking the position of the implanted beads with dynamic radiostereometric analysis. To demonstrate in vivo application of this technique, biplane X-ray images were acquired as a human subject performed two motion tasks: neck extension and axial neck rotation. The positions and orientations of each cervical vertebra were determined with model-based tracking. Cervical spine motion was reported with standard kinematic descriptions of translation and rotation. RESULTS: The in vitro validation demonstrated that model-based tracking is accurate to within +/-0.6 mm and +/-0.6 degrees for measuring cervical spine motion. For the in vivo application, there were significant rotations about all three anatomical axes for both the neck extension and axial neck rotation motion tasks. CONCLUSIONS: Model-based tracking is an accurate technique for measuring in vivo, 3D, dynamic cervical spine motion. Preliminary data acquired using this technique are in agreement with previous studies. It is anticipated that this experimental approach will enhance our understanding of cervical spine motion under normal and pathologic conditions.

Image-based navigation improves the positioning of the humeral component in total elbow arthroplasty.

HYPOTHESIS: Implant alignment in total elbow arthroplasty (TEA) is a challenging and error-prone process using conventional techniques. Identification of the flexion-extension (FE) axis is further complicated for situations of bone loss. This study evaluated the accuracy of humeral component alignment in TEA. We hypothesized that an image-based navigation system would improve humeral component positioning, with navigational errors less than or approaching 2.0 mm and 2.0 degrees . MATERIALS AND METHODS: Implantation of a modified commercial TEA humeral component was performed with and without navigation on 11 cadaveric distal humeri. Navigated alignment was based on positioning the humeral component with the aid of a computed tomography (CT)-based preoperative plan registered to landmarks on the distal humerus. Alignment was performed under 2 scenarios of bone quality: (1) an intact distal humerus, and (2) a distal humerus without articular landmarks. RESULTS: Navigation significantly improved implant alignment accuracy (P < .001). Navigated implant alignment was 1.2 +/- 0.3 mm in translation and 1.3 degrees +/- 0.3 degrees in rotation for the intact scenario. For the bone loss scenario, navigated alignment error was 1.1 +/- 0.5 mm and 2.0 degrees +/- 1.3 degrees . Non-navigated alignment was 3.1 +/- 1.3 mm and 5.0 degrees +/- 3.8 degrees for the intact scenario and 3.0 +/- 1.6 mm and 12.2 degrees +/- 3.3 degrees for the bone loss scenario. DISCUSSION: Image-based navigation improves the accuracy and reproducibility of humeral component placement in TEA. Implant alignment errors for the navigated alignments were below the target of 2.0 degrees and 2 mm that is considered standard for most navigation systems. Non-navigated implant alignment error was significantly greater for the bone loss scenario compared with the intact scenario. CONCLUSIONS: Implant malalignment may increase the likelihood of early implant wear, instability, and loosening. Improved implant positioning will likely lead to fewer complications and greater prosthesis longevity.