Stability Of Set Research Articles

Prospective Evaluation of Glenoid Bone Loss After First-time and Recurrent Anterior Glenohumeral Instability Events

Background: Determining the amount of glenoid bone loss in patients after anterior glenohumeral instability events is critical to guiding appropriate treatment. One of the challenges in treating the shoulder instability of young athletes is the absence of clear data showing the effect of each event. Purpose: To prospectively determine the amount of bone loss associated with a single instability event in the setting of first-time and recurrent instability. Study Design: Cohort study; Level of evidence, 2. Methods: The authors conducted a prospective cohort study of 714 athletes surveilled for 4 years. Baseline assessment included a subjective history of shoulder instability. Bilateral noncontrast shoulder magnetic resonance imaging (MRI) was obtained for all participants with and without a history of previous shoulder instability. The cohort was prospectively followed during the study period, and those who sustained an anterior glenohumeral instability event were identified. Postinjury MRI with contrast was obtained and compared with the screening MRI. Glenoid width was measured for each patient’s pre- and postinjury MRI. The projected total glenoid bone loss was calculated and compared for patients with a history of shoulder instability. Results: Of the 714 athletes (1428 shoulders) who were prospectively followed during the 4-year period, 22 athletes (23 shoulders) sustained a first-time anterior instability event (5 dislocations, 18 subluxations), and 6 athletes (6 shoulders) with a history of instability sustained a recurrent anterior instability event (1 dislocation, 5 subluxations). On average, there was statistically significant glenoid bone loss (1.84 ± 1.47 mm) after a single instability event (P < .001), equivalent to 6.8% (95% CI, 4.46%-9.04%; range, 0.71%-17.6%) of the glenoid width. After a first-time instability event, 12 shoulders (52%) demonstrated glenoid bone loss ≥5% and 4 shoulders, ≥13.5%; no shoulders had ≥20% glenoid bone loss. Preexisting glenoid bone loss among patients with a history of instability was 10.2% (95% CI, 1.96%-18.35%; range, 0.6%-21.0%). This bone loss increased to 22.8% (95% CI, 20.53%-25.15%; range, 21.2%-26.0%) after additional instability (P = .0117). All 6 shoulders with recurrent instability had ≥20% glenoid bone loss. Conclusion: Glenoid bone loss of 6.8% was observed after a first-time anterior instability event. In the setting of recurrent instability, the total calculated glenoid bone loss was 22.8%, with a high prevalence of bony Bankart lesions (5 of 6). The findings of this study support early stabilization of young active patients after a first-time anterior glenohumeral instability event.

Glenohumeral Dislocation Arthropathy: Etiology, Diagnosis, and Management.

Dislocation arthropathy describes the development of progressive degenerative changes of the glenohumeral joint in the setting of instability. Although the specific etiology remains unclear, the trauma of a single dislocation, repetitive injury associated with recurrent dislocations, changes in shoulder biomechanics, and complications associated with instability surgery have all been implicated in its development. Pain and restricted range of motion are the most common patient complaints. Conservative management, consisting of pain control, activity modification, and physical therapy, is the first-line treatment after the development of arthropathy. If conservative management fails, multiple surgical options exist. Arthroscopic débridement can be attempted in young, active patients and in those patients with mild-to-moderate arthropathy. Open subscapularis lengthening and capsular release can be done in patients with prior instability repairs that are overly tight. In young patients with minimal bone loss and glenoid wear, surface replacement arthroplasty and hemiarthroplasty are surgical options. In older patients with moderate-to-severe arthropathy, total shoulder or reverse shoulder arthroplasty is the preferred treatment option. Further study is needed to better predict which patients will develop dislocation arthropathy and will thus benefit from early surgical intervention.

Is Long-Segment Fixation a Rule in Fractures Associated With Ankylosing Spondylitis?

Technical report. We describe the outcomes of percutaneous vertebroplasty in 3-columnar thoraco-lumbar fracture secondary to hyper-extension injury in 3 patients with ankylosing spondylitis (AS). Thoraco-lumbar hyperextension injuries in AS are generally unstable as they involve all 3 spinal columns and traditionally require long-segment posterior instrumented stabilization. Three cases of AS with severe medical comorbidities underwent percutaneous vertebroplasty for hyper-extension injury involving all 3 columns. Visual analog scale (VAS) and Oswestry Disability Index (ODI) scores were documented preoperatively, postoperatively, and at the last follow-up. Excellent improvements in VAS and ODI scores were achieved. The patients have no complaints and are independent and mobile at 2 years follow-up. Vertebroplasty is an excellent option in such medically unfit patients with similar diagnosis and should be performed as early as possible before profound instability or neurological insult sets in, which would necessitate bigger and morbid surgeries.

Mechanism for the Structural Transformation to the Modulated Superconducting Phase of Compressed Hydrogen Sulfide

A comprehensive description of crystal and electronic structures, structural transformations, and pressure-dependent superconducting temperature (Tc) of hydrogen sulfide (H2S) compressed from low pressure is presented through the analysis of the results from metadynamics simulations. It is shown that local minimum metastable crystal structures obtained are dependent on the choice of pressure-temperature thermodynamic paths. The origin of the recently proposed ‘high-Tc’ superconducting phase with a modulated structure and a diffraction pattern reproducing two independent experiments was the low pressure Pmc21 structure. This Pmc21 structure is found to transform to a Pc structure at 80 K and 80 GPa which becomes metallic and superconductive above 100 GPa. This structure becomes dynamically unstable above 140 GPa beyond which phonon instability sets in at about a quarter in the Γ to Y segment. This explains the transformation to a 1:3 modulation structure at high pressures proposed previously. The pressure trend of the calculated Tc for the Pc structure is consistent with the experimentally measured ‘low-Tc phase’. Fermi surface analysis hints that pressurized hydrogen sulfide may be a multi-band superconductor. The theoretical results reproduced many experimental characteristics, suggesting that the dissociation of H2S is unrequired to explain the superconductivity of compressed H2S at any pressure.

The Glenojet Procedure: A Bone Preserving Alternative

Bone loss in the setting of shoulder instability increases the likelihood of recurrent instability and increases the failure rate of arthroscopic interventions. Bone loss of the anteroinferior glenoid can be addressed via autograft (coracoid transfer or iliac crest bone graft) or allograft (iliac crest or osteochondral). We describe a technique for managing glenoid bone loss with a preshaped allograft. The Glenojet (Arthrosurface Inc.) is an allograft cortical bone augment for the glenoid. It is placed with a standard deltopectoral approach. The graft is predrilled and has a disposable targeting guide that fits 2 3.5 mm cortical screws. It offers an easy solution for addressing anteroinferior glenoid bone loss that preserves normal patient anatomy. It is particularly appealing for revision procedures of failed coracoid transfers.

The use of static external fixation for chronic instability of the elbow

Chronic elbow instability after trauma is a challenging problem. Clinical results of external elbow fixation in this setting are limited, with most studies focusing on hinged external fixation. A static fixator is an alternative for maintaining joint reduction. Advantages of a static frame include ease of application, decreased need for special instrumentation, and more secure maintenance of a concentrically reduced joint in the setting of bone or soft tissue instability. The primary limitation of static fixation is the potential for stiffness. This retrospective review represents the largest reported cohort evaluating the use of static elbow external fixation for the treatment of chronic elbow instability. Twenty-seven cases treated by a single surgeon between 2004 and 2015 were identified. Twenty patients were available for a clinical evaluation, including radiographs and a physical examination at a mean follow-up of 5.8 years (range, 1.4-12.4 years). Of note, 19 of 20 were clinically obese or overweight. At final evaluation, range of motion averaged from 20° ± 13° of extension to 134° ± 9° of flexion. All patients had stable elbows, except 1 patient who had valgus and varus laxity on stress examination. Radiographs of this patient showed an incongruous joint. Eight patients required an additional operation after external fixator removal, 3 for infection and 5 for stiffness. At almost 6 years of follow-up, static elbow external fixator resulted in a congruous joint with adequate functional and clinical outcomes in 95% of patients.

CURRENT PRACTICE TRENDS IN THE SURGICAL MANAGEMENT OF PATELLOFEMORAL INSTABILITY; A SURVEY OF THE PEDIATRIC RESEARCH IN SPORTS MEDICINE (PRiSM) SOCIETY

Background: Patellofemoral instability in young athletes presents both diagnostic and management dilemmas for which consensus often does not exist. Surgical options and treatments are heterogeneous among orthopaedic surgeons. The purpose of this study is to survey members of the Pediatric Research in Sports Medicine (PRiSM) Society regarding their practice and treatment for patellofemoral instability and to identify trends in management of patellofemoral instability in children and adolescents nationwide. Methods: A 27-question multiple choice online survey was distributed to the members of the PRiSM Society. The survey was sent via email 3 times over a six week time span after which time the survey was closed. Members were asked about clinical and imaging evaluation, methods of conservative treatment, surgical indications, and surgical techniques when treating patellofemoral instability. Results: 65/70 (93%) of respondents reported performing surgery for patella instability more than 5 times in the past year. Of these 65, 56 respondents completed the questionnaire in its entirety. While some trends regarding treatment emerged, the respondent data demonstrated the large discrepancies in practice patterns that exist nationwide. 48% (27/56) of respondents obtained an MRI for patients with a 1+ knee effusion or greater on exam within one week after a first-time traumatic patellar dislocation while 20% (11/56) obtain an MRI in all patients presenting with a patella dislocation. To assess skeletal maturity, 75% (42/56) of respondents obtained knee x-rays to evaluate the physes around the knee, whereas 53% (30/56) obtained a hand x-ray to assess bone age. 41% (23/56) of respondents reported that surgical intervention for fragment refixation or loose body removal is indicated anytime there is evidence of a loose body or osteochondral fragment regardless of fragment size. 11% (6/56) reported only performing osteochondral fracture repair when the fragment was large enough to repair. If surgery is performed for an osteochondral loose body, 38% (21/56) of respondents performed an MPFL reconstruction. 59% (33/56) reported performing the MPFL reconstruction in children and adolescent athletes with hamstring allograft, while 30% (17/56) prefer autograft (hamstring, quadriceps). MRI was strongly preferred over CT when considering a tibial tubercle anteromedialization. TT-TG distance is the diagnostic measurement of choice with no respondents selecting TT-PCL as their preferred diagnostic measurement. The indication for surgical correction of angular deformity in the setting of patellar instability had mixed responses. 18% (10/56) would indicate surgery when the mechanical axis is lateral to the center of the lateral femoral condyle, while others considered this angular correction only when the patient is skeletally immature or when the mechanical axis is lateral to the lateral tibial spine. For surgical recommendations in a patient with significant trochlear dysplasia, 46% (26/56) reported no surgical management of trochlear dysplasia in first-time surgery while 41% (23/56) reported no surgical management of trochlear dysplasia in first-time or revision surgery. Conclusion: There was significant heterogeneity among respondents that highlights a lack of consensus regarding optimal diagnostic and treatment algorithms. Understanding management trends nationwide may help practicing surgeons gain insights and develop evidence based treatment algorithms to best serve patients with this condition.

Cooperative effects of strain and electron correlation in epitaxial VO2 and NbO2

We investigate the electronic structure of epitaxial VO2 films in the rutile phase using density functional theory combined with the slave-spin method (DFT + SS). In DFT + SS, multi-orbital Hubbard interactions are added to a DFT-fit tight-binding model, and slave spins are used to treat electron correlations. We find that while stretching the system along the rutile c-axis results in a band structure favoring anisotropic orbital fillings, electron correlations favor equal filling of the t2g orbitals. These two distinct effects cooperatively induce an orbital-dependent redistribution of the electron occupations and spectral weights, driving strained VO2 toward an orbital selective Mott transition (OSMT). The simulated single-particle spectral functions are directly compared to V L-edge resonant X-ray photoemission spectroscopy of epitaxial 10 nm VO2/TiO2 (001) and (100) strain orientations. Excellent agreement is observed between the simulations and experimental data regarding the strain-induced evolution of the lower Hubbard band. Simulations of rutile NbO2 under similar strain conditions are performed, and we predict that an OSMT will not occur in rutile NbO2. Our prediction is supported by the high-temperature hard x-ray photoelectron spectroscopy measurement on relaxed NbO2 (110) thin films with no trace of the lower Hubbard band. Our results indicate that electron correlations in VO2 are important and can be modulated even in the rutile phase before the Peierls instability sets in.

Improved Range of Motion and Patient-Reported Outcome Scores With Fixed-Bearing Revision Total Knee Arthroplasty for Suboptimal Axial Implant Rotation

BackgroundSuboptimal implant rotation has consequences with respect to knee kinematics and clinical outcomes. We evaluated the functional outcomes of revision total knee arthroplasty (TKA) for poor axial implant rotation. MethodsWe retrospectively reviewed 42 TKAs undergoing aseptic revision for poor axial implant rotation. We assessed improvements in Knee Society Score (KSS) and final range of motion (ROM). Subgroup analyses were performed for preoperative instability and stiffness, as well as the number of components revised and level of implant constraint used. ResultsRevision for poor axial rotation in isolation improved KSS from 52 ± 22 to 84 ± 25 (P < .001), and flexion increased from 105 ± 21° to 115 ± 13° (P = .001). Revision in the setting of instability significantly improved the KSS (P < .001) but did not affect ROM (P = .172). Revision in the setting of stiffness significantly improved both KSS (P < .001) and ROM (P = .002). There was no statistically significant difference between the postoperative KSS (P = .889) and final knee flexion (P = .629) with single- or both-component revision TKA for isolated poor axial rotation or between the postoperative KSS (P = .956) and final knee flexion (P = .541) with or without the use of higher constraint during revision TKA for isolated poor axial rotation. ConclusionRevision TKA for poor axial alignment improves clinical outcomes scores and functional ROM.

Thermal Instability of a Micropolar Fluid Layer with Temperature-Dependent Viscosity

In this paper, the effect of temperature-dependent viscosity on the onset of thermal convection in a micropolar fluid layer heated from below for each combination of rigid (the surfaces with non-slip condition) and dynamically free (the surfaces with stress-free condition) boundaries is investigated. It is shown here analytically that the principle of exchange of stabilities is valid for the problem, which means that instability sets in as stationary convection. The expressions for Rayleigh numbers for each combination of rigid and dynamically free boundary conditions are derived using Galerkin method. The effects of micropolar parameters and viscosity variation parameter on critical wave numbers and consequently on the critical Rayleigh numbers are computed numerically.

Assessment of Bone Loss in the Shoulder

The accurate identification and quantification of both glenoid bone loss and the presence of a Hill-Sachs lesion is essential in the setting of anterior shoulder instability as it directly dictates patient outcomes. The ability to diagnose and address these potential osseous defects of the glenohumeral joint based on patient history, physical exam, and the findings of various imaging modalities in a clinical setting is fundamental to the overall success of a surgeon's treatment algorithm. Multiple methods exist to quantify bone loss based on diagnostic imaging or arthroscopy, and the surgeon should be mindful of the respective pearls and pitfalls of each imaging modality and their ability to accurately diagnose shoulder bone loss. Pertinent findings in a patient's history such as age, level of activity, enlistment status, and events of recurrent anterior glenohumeral instability can help one not only predict the presence of bone loss, but the location and size of the defect as well. Furthermore, symptoms and signs of chronic instability along with accurate quantification of glenoid bone loss are essential in the algorithm of selecting the correct surgical procedure to provide optimal stabilization and maximize clinical outcomes.

Регуляризация интегральных операторов в сингулярно возмущенных задачах с помощью нормальных форм

The main difficulty encountered in generalizing S.А. Lomov’s regularization method for integral and integro-differential singularly perturbed problems lies in bringing integral operators to a regular kind. If there are no integral operators, that is, if there is only a differential operator, the corresponding singularly perturbed problem is usually regularized by the spectrum of the limit operator using the well-known formula of complex differentiation. For integral operators, there is no an analog of the complex differentiation formula; therefore, it is not possible to directly construct an extension of the integral operator. In one of the authors' works that was addressed to generalization of S.A. Lomov’s ideas, a regularization method for differential systems with the use of normal forms was developed. With such regularization, additional (regularizing) variables are not entered directly from the limit operator spectrum, but are indirectly calculated using some normal differential form, the solution of which is written in quadratures. In the case of nonzero points of the limit operator’s simple spectrum, such regularization coincides with the regularization along the spectrum developed by S.А. Lomov. However, if there are eigenvalues of the limit operator that vanish in at least one point of the considered time interval, S.А. Lomov’s classical regularization does not make it possible to construct an extension of an integral operator and carry out its full regularization. This difficulty has been fully eliminated by applying regularization with the use of normal forms. The basic ideas of the method of normal forms have been demonstrated taking as an example the simplest integro-differential problem with spectrum instability on a continual set, and the statement using which integral operators are regularized is given. The main term of the problem solution asymptotics is written, after studying of which a conclusion is drawn about the presence of two layers in the solution: the boundary layer in the neighborhood of the initial point of the considered time interval and the inner transition layer (a contrast structure) in the neighborhood of the instability set end point.

Role of Allergic Inflammatory Cells in Coronary Artery Disease.

Inflammation is an important player both for the initiation and progression of coronary artery disease and for coronary plaque instability. Moreover, inflammation contributes to stent thrombosis and in-stent restenosis after percutaneous coronary intervention. In the past several decades, most studies evaluated the involvement of cellular effectors of classic inflammatory responses, such as monocytes/macrophages, neutrophils, and T cells. Yet, besides classic inflammation, mounting evidence derived from both experimental and clinical studies suggests an important, often unrecognized, role for effector cells of allergic inflammation in both the pathogenesis of coronary artery disease and adverse events following stent implantation. In this review, we discuss the role of effector cells of allergic inflammation in the setting of coronary artery disease progression and instability, and in the occurrence of adverse events following stent implantation, as well. Moreover, we discuss possible therapeutic approaches targeting different specific pathways of allergic inflammatory activation.

The Unstable Spine: A Surgeon's Perspective

Instability of the spine is a complex clinical entity that exists on a wide spectrum encompassing many aspects of spinal pathology including traumatic, neoplastic, infectious, and degenerative processes. The importance of determining stability is paramount in the decision-making process regarding the need for operative or nonoperative care. Defining clinical instability can be a challenging and requires careful attention to the pathology involved, findings of necessary imaging, and a thorough clinical exam. Several classification systems have been developed to aid in surgical decision making, but certain limitations exist. Various imaging modalities play a crucial role in the evaluation of suspected instability. Computed tomography is the initial imaging modality of choice in the traumatic setting. Magnetic resonance imaging is an important adjunct in the setting of suspected ligamentous injury and the modality of choice in suspected infectious and neoplastic processes. Upright radiographs can be particularly useful in the setting of acute or subacute instability to glean information about how the spine responds to gravity and weightbearing. The clinical exam is also of critical importance in the determination of stability. The presence of a neurologic deficit is highly suggestive of a potentially unstable spine and appropriate spinal precautions should be maintained until instability and injury has been ruled out. Certain clinical entities, such as ankylosing spondylitis and diffuse idiopathic skeletal hyperostosis, are at high risk for instability particularly in the traumatic setting. In these situations, the spine should be considered unstable until proven otherwise. Ultimately, the determination of spinal stability, and subsequent need for surgical treatment, should be based on the individual case. Combining information from the clinical exam and imaging findings, including upright radiographs when appropriate, allows for the appropriated determination of spinal stability.

A matrix-based approach to verifying stability and synthesizing optimal stabilizing controllers for finite-state automata

In this paper, we develop a matrix-based methodology to investigate the problems of stability and stabilizability for a deterministic finite automaton (DFA) in the framework of the semi-tensor product (STP) of matrices. First, we discuss the equilibrium point stability (resp., set stability) of a DFA, i.e., verifying whether or not all state trajectories starting from a subset of states converge to a specified equilibrium point (resp., subset of states). The necessary and sufficient conditions for verifying both stabilities are given, respectively. Second, equilibrium point stabilizability (resp., set stabilizability) of a DFA is investigated as verifying the issue of whether or not a DFA can be globally or locally stabilized to a specified equilibrium point (resp., subset of states) by a permissible state-feedback controller. Based on the pre-reachability set and invariant-subset defined in this paper, the matrix-based criteria for verifying equilibrium point stabilizability and set stabilizability are derived, respectively. Furthermore, for each type of stabilizability, all permissible state-feedback controllers for the case of minimal length state trajectories, called optimal state-feedback controllers, are characterized by using the proposed polynomial algorithms. Finally, two examples are presented to illustrate the effectiveness of the theoretical results.

Set of electromagnetic instabilities observed in Mercier stable plasmas of the L-2M stellarator

Electromagnetic instabilities that have been experimentally observed at the L-2M zero net current stellarator and their theoretical analysis are discussed in this paper. We report the structure of the magnetic surfaces and the numerical calculation results. Under experimental conditions, the ideal internal MHD (magnetohydrodynamic) modes are stable. However, the external ideal peeling modes, which start to increase only if the plasma pressure gradient exceeds some particular threshold value, are unstable. If the peeling mode is stable, an electromagnetic mode, which starts to increase only if the plasma density and pressure exceed some particular threshold values, is observable. The characteristic frequency of the unstable modes was in the range of 70–90 kHz, and the direction of its rotation coincides with the direction of the ion diamagnetic drift. An instability was observed at n(0) > 1.5 × 1013 cm−3 and at 〈β〉 > 0.14%, where n(0) is the plasma density averaged over the central chord and 〈β〉 is the volume-averaged ratio of the gas kinetic pressure to the magnetic pressure. This phenomenon cannot be described within the framework of the theory of resistive interchange MHD modes. Analytical estimates have been performed within the framework of two fluid magnetohydrodynamics, and the calculations and experimental data are in reasonable agreement.

Rifle bullet deflection through a soft tissue simulant

Trajectory deflections of 5.56 NATO and 7.62×39mm rifle bullets, fired through 7.5, 15 and 22.5cm of gelatine, were studied. The magnitude of the deflections from the bullets’ original trajectories after perforation are related to the length and the profile of the (wound) channels through gelatine. After 7.5cm of penetration depth, deflection was less than 1°. With the longer channel lengths, bullet instability set in and subsequently, deflection was much larger. Deflection was highest with fragmented 5.56 NATO bullets after perforating 22.5cm of gelatine. The data from this study can be used to assess the degree of bullet deflection in trajectory reconstructions after incidents where human bodies were perforated with rifle bullets of the respective calibres and cartridge types.

Prospective Evaluation of Glenoid Bone Loss After First-Time and Recurrent Anterior Glenohumeral Instability Events

Objectives:Determining the amount of glenoid bone loss in patients following anterior glenohumeral instability events is critical to guiding appropriate treatment. One of the challenges in managing shoulder instability in young athletes is the absence of clear data showing the impact of each event. The purpose of this study was to prospectively determine the amount of bone loss associated with a single instability event, in the setting of both first-time and recurrent instability.Methods:We conducted a prospective cohort study of 714 athletes followed for four years. Baseline assessment included a subjective history of shoulder instability. Bilateral shoulder MRIs were obtained in all participants with and without a history of previous shoulder instability. The cohort was prospectively followed during the study period and those who sustained an anterior glenohumeral instability event were identified. A post-injury MRI was obtained and compared to the screening MRI. Glenoid width was measured for each patient’s pre- and post-injury MRI. The projected total glenoid bone loss was calculated and compared for patients with a prior history of shoulder instability.Results:Of the 714 athletes that were prospectively followed during the four-year period, 23 shoulders in 22 subjects sustained a first-time anterior instability event (5 dislocations, 18 subluxations), and six subjects with a previous history of instability sustained a recurrent anterior instability event (1 dislocation, 5 subluxations). On average, there was statistically significant glenoid bone loss (1.84 ± 1.47 mm) following a single instability event (p<0.001), equivalent to 6.8% (95% CI: 4.46%, 9.04%, range 0.71%-17.6%) of the glenoid width. Twelve shoulders (52%) demonstrated glenoid bone loss ≥ 5%, 4 shoulders demonstrated glenoid bone loss ≥13.5% and no shoulders had ≥20% glenoid bone loss after a first-time instability event. Pre-existing glenoid bone loss in subjects with a history of instability was 10.2% (95% CI: 1.96%, 18.35%, range 0.6% - 21.0%). This bone loss increased to 22.8% (95% CI: 20.53%, 25.15%, range 21.2% to 26.0%) following an additional instability event (P=0.0117). All six shoulders with recurrent instability had >20% glenoid bone loss.Conclusion:Glenoid bone loss of 6.8% was observed after a first-time anterior instability event. In the setting of recurrent instability, the total calculated glenoid bone loss was 22.8% with a high prevalence of bony Bankart lesions (5/6). The findings of this study support early stabilization of young, active subjects following a first-time anterior glenohumeral instability event.Figure 2.Clinical demonstration of a sagital en face MRI obtained prior to any instability event (A) and following a single subluxatiion event (B) with 14% bone loss and a bony Bankart.Table 2:Glenoid Bone Loss in First-time and Recurrent Instability CohortsInstability TypeNo. ShouldersΔ Glenoid Width (mm)ΔGlenoid Width (%)Total Glenoid Bone Loss* (%)P valueFirst-time231.85 ± 1.496.8%6.8%< .0001Recurrent63.75± 2.3713.6%22.8%.0117

Direction of Capsular Strain Implies Surgical Repair Following Recurrent Anterior Shoulder Dislocation

Objectives:Capsular plication is often performed in addition to arthroscopic Bankart repair. However, little is known regarding the direction of capsular injury making the direction of plication fairly arbitrary. This study aimed to determine the optimal direction for capsular plication within four sub-regions of the inferior glenohumeral capsule following multiple dislocations.Methods:Seven fresh-frozen cadaveric shoulders (age range 48-66 yrs) were dissected free of all soft tissue except the glenohumeral capsule. A grid of strain markers was affixed to the anterior and posterior band (A/PB) of the inferior glenohumeral ligament (IGHL), and the axillary pouch. The position of the markers while the capsule was inflated with minimal pressure served as the reference state. The humerus and scapula were then mounted in a 6 degree-of-freedom robotic testing system. At 60 degrees of abduction and 60 degrees of external rotation of the glenohumeral joint, an anterior load was applied to reach an anterior translation of one half the maximum AP width of the glenoid plus 10 mm. This definition of dislocation resulted in non-recoverable strain and a reproducible Bankart lesion. Following 1, 2, 3, 4, 5 and 10 dislocations, the positions of the strain markers were again recorded with the capsule inflated. The difference in these positions compared to the reference state defined the non-recoverable strain. The strain map was split into four sub-regions, the anterior band of IGHL (AB), anterior axillary pouch (AA), posterior axillary pouch (PA), and the posterior band of IGHL (PB) (Fig. 1). The angle of deviation between each of the maximum principle strain vectors and the AB-IGHL or PB-IGHL for the anterior and posterior regions of the capsule were determined using ImageJ. Circular statistics were employed to calculate mean direction of each sub-region and a Watson-Williams test was performed to compare mean direction among each dislocation with significance set at p < 0.05. The mean direction of all strain vectors in each sub-region was categorized as parallel or perpendicular to the AB-IGHL or PB-IGHL serving as the clinical reference. Direction ranging from 0 to 45 or 135 to 180 degrees was categorized as parallel. Direction ranging between 45 and 135 degrees was categorized as perpendicular.Results:The direction of 81.8% of the AB sub-regions was categorized as parallel and 18.2% categorized as perpendicular to the AB-IGHL. Direction of 61.3% of the AA sub-region was categorized as parallel (Table 1) and 38.7% categorized as perpendicular to AB-IGHL. The direction of 33.3% of the PA sub-region was categorized as parallel and 66.7% categorized as perpendicular to the PB-IGHL. The direction of 21.4% of PB sub-region was categorized as parallel and 78.6% categorized as perpendicular to PB-IGHL. A Watson-Williams test demonstrated that the direction of 81.3% of the sub-regions were not significantly different (p > 0.05) among dislocations for each specimen (Table 1).Conclusion:The non-recoverable strain in most of the AB and AP sub-regions were categorized as parallel to the AB-IGHL while for the PA and PB sub-regions mostly perpendicular to the PB-IGHL. These findings imply that it may be more optimal to plicate the anteroinferior capsule parallel to the AB-IGHL while posteroinferior capsular plication, which is often not classically considered for plication in the setting of anterior instability, may also be necessary and best performed perpendicular to the PB-IGHL.Figure 1.Fringe plot of non-recoverable strain for anterior half of inferior capsule in a typical shoulder following 5th dislocation. The borderline of AA and posterior axillary pouch sub-regions was the column of markers placed at the 6 o'clock position of the glenoid. AB-IGHL, anterior band of inferior glenohumeral ligament; AA, anterior axillary pouch sub-region; AB, anterior band of IGHL sub-region.Table 1.Direction of non-recoverable strain in the anterior axillary pouch sub-region following 1st to 10th dislocations for a typical shoulder (mean ± SD)Anterior Axillary Pouch sub-regionDirection of non-recoverable strainCategorizationDislocation 1168±5Parallel to AB-IGHLDislocation 2168±8Parallel to AB-IGHLDislocation 3166±5Parallel to AB-IGHLDislocation 4165±5Parallel to AB-IGHLDislocation 5175±13Parallel to AB-IGHLDislocation 10158±20Parallel to AB-IGHLWatson-Williams test showed directions were not significantly different among dislocation (p=0.33). Direction through 6 dislocation states were categorized as parallel (between 135 to 180 degrees) to anterior-band (AB) of IGHL

Automated 3D MRI Allows for Accurate Evaluation of Glenoid Bone Loss as Compared to 3D CT

Objectives:Glenoid bone loss is frequently present in the setting of recurrent shoulder instability. The magnitude of bone loss is an important determinant of the optimal surgical treatment. The current gold-standard for measurement of glenoid bone loss is three-dimensional (3D) reconstruction of a computed tomography (CT) scan. CT scans, however, carry an inherent risk of radiation and increased cost for a second modality. Magnetic resonance imaging (MRI) offers excellent soft tissue contrast and may allow resolution of bony structures to generate 3D reconstructions without a risk of ionizing radiation. We hypothesized that automated 3D MRI reconstruction would offer similar measurements of glenoid bone loss as recorded from a 3D CT scan in a clinical setting.Methods:A retrospective review was performed for fourteen patients who had both pre-operative MRI scan and CT scan of the shoulder. All MR scans were performed on a 1.5 T scanner (Siemens) utilizing a Dixon chemical shift separation sequence and the out-of-phase images with 0.90 mm slice thickness. Reconstructions of the glenoid were performed from axial images (Figure 1A) using an open-platform image processing system (3D Slicer; slicer.org). A single point on the glenoid was selected and a standard threshold was used to build a 3D model (Figure 1B). High-resolution CT scans underwent 3D reconstruction in Slicer based on Houndsfield Unit thresholding. Glenoid bone loss on both scans was measured with the Pico method by defining a circle of best fit using the inferior 2/3 of the glenoid and determining the percent area missing from this circle. Pearson’s correlation coefficient was utilized to determine the similarity between MR and CT based measurements. Statistical significance was defined as p<0.05.Results:The correlation between 3D MR and CT-based measurements of glenoid bone loss was excellent (r = 0.95, p<0.0001). The mean bone loss as measured by the 3D MR was 13.2 +- 7.2% and was 12.5 +- 8.6% for the 3D CT reconstruction (p=0.32). Bone loss in this cohort ranged from 3.7-25.4% on 3D MR and 1.4-26.0% on 3D CT. The root-mean-square difference between measurements was 2.7%.Conclusion:There was excellent agreement between automated 3D MR and 3D CT measurements of glenoid bone loss and minimal differences between these measurements. This reconstruction method requires minimal post-processing, no manual segmentation, and is obtained with widely-available MR sequences. This method has the potential to decrease the utilization for CT scans in determining glenoid bone loss.Figure 1.(A) An axial T1-weighted Dixon subtraction MR image of the glenoid is used to develop a three-dimensional reconstruction of the glenoid. The three-dimensional reconstruction is shown for one patient for both MR scan (B) and CT scan (C), both produced in 3D Slicer with a single click on the glenoid and a threshold-based reconstruction method.