Spin-Orbit Coupling and Spin Textures in Optical Superlattices.

We propose and demonstrate a new approach for realizing spin-orbit coupling with ultracold atoms. We use orbital levels in a double-well potential as pseudospin states. Two-photon Raman transitions between left and right wells induce spin-orbit coupling. This scheme does not require near resonant light, features adjustable interactions by shaping the double-well potential, and does not depend on special properties of the atoms. A pseudospinor Bose-Einstein condensate spontaneously acquires an antiferromagnetic pseudospin texture, which breaks the lattice symmetry similar to a supersolid.

Correlations and pair formation in a repulsively interacting Fermi gas.

A degenerate Fermi gas is rapidly quenched into the regime of strong effective repulsion near a Feshbach resonance. The spin fluctuations are monitored using speckle imaging and, contrary to several theoretical predictions, the samples remain in the paramagnetic phase for an arbitrarily large scattering length. Over a wide range of interaction strengths a rapid decay into bound pairs is observed over times on the order of 10ℏ/E(F), preventing the study of equilibrium phases of strongly repulsive fermions. Our work suggests that a Fermi gas with strong short-range repulsive interactions does not undergo a ferromagnetic phase transition.

Speckle imaging of spin fluctuations in a strongly interacting Fermi gas.

Spin fluctuations and density fluctuations are studied for a two-component gas of strongly interacting fermions along the Bose-Einstein condensate-BCS crossover. This is done by in situ imaging of dispersive speckle patterns. Compressibility and magnetic susceptibility are determined from the measured fluctuations. This new sensitive method easily resolves a tenfold suppression of spin fluctuations below shot noise due to pairing, and can be applied to novel magnetic phases in optical lattices.

Suppression of density fluctuations in a quantum degenerate Fermi gas.

We study density profiles of an ideal Fermi gas and observe Pauli suppression of density fluctuations (atom shot noise) for cold clouds deep in the quantum degenerate regime. Strong suppression is observed for probe volumes containing more than 10 000 atoms. Measuring the level of suppression provides sensitive thermometry at low temperatures. After this method of sensitive noise measurements has been validated with an ideal Fermi gas, it can now be applied to characterize phase transitions in strongly correlated many-body systems.

Demonstration of an area-enclosing guided-atom interferometer for rotation sensing.

We demonstrate area-enclosing atom interferometry based on a moving guide. Light pulses along the free-propagation direction of a magnetic guide are applied to split and recombine the confined atomic matter-wave, while the atoms are translated back and forth along a second direction in 50 ms. The interferometer is estimated to resolve 10 times the earth rotation rate per interferometry cycle. We demonstrate a "folded figure 8" interfering configuration for creating a compact, large-area atom gyroscope with multiple-turn interfering paths.

Semiconstrained knee arthroplasty in the setting of a chronic knee dislocation: a case report.

We present the case of a 27-month chronic knee dislocation treated with a semiconstrained, stemmed total knee arthroplasty. The patient was neurovascularly intact preoperatively but had severe functional limitations caused by pain, stiffness, and instability. At 2-year follow-up, the patient remains pain-free with functional range of motion and the ability to ambulate without complication. This case report represents the longest-cited chronic knee dislocation treated with a reconstructive procedure.

Orthopedic surgical management of hip and knee involvement in patients with juvenile rheumatoid arthritis.

Juvenile rheumatoid arthritis is the most common arthritic disease of childhood and a leading cause of childhood disability, affecting an estimated 300,000 US children and adolescents aged < or =16 years. Approximately 10% to 30% of patients experience functional deficits resulting from both the articular and systemic manifestations of their disease, including leg length inequality and deformity, that are often more crippling than joint destruction. Surgical intervention to treat bone and soft-tissue deformity, leg length inequality, and joint destruction is indicated when medical therapy has failed. Synovectomy, soft-tissue release, osteotomy, and epiphysiodesis are used to treat deformity and early joint destruction. Arthroplasty remains the primary therapy for joint destruction, although it is fraught with complications specific to this young patient population.

A proposed classification of supracondylar femur fractures above total knee arthroplasties.

A new classification system is proposed for supracondylar femur fractures above total knee arthroplasties based on fracture location relative to the femoral component. Radiographs of 28 cases were evaluated and classified according to the proposed system by 12 physicians: 3 trauma specialists, 3 adult reconstruction specialists, 3 musculoskeletal radiologists, and 3 orthopaedic residents. The same 12 physicians reevaluated the same 28 cases 3 months later. The mean reliability coefficient for all observers was 0.74 (substantial agreement). The coefficient for reproducibility after 3 months was 0.85 (almost perfect). The power of the study was 80%. The proposed classification system is easy to use and has good interobserver reliability among orthopaedic residents, orthopaedic attendings--trauma and reconstruction--and radiologists. Intraobserver reliability was also excellent at 3 months.

Efficacy of abduction bracing in the management of total hip arthroplasty dislocation.

A retrospective review of total hip arthroplasty (THA) dislocations was performed to determine the effectiveness of abduction bracing following closed reduction. Patients were grouped as a first-time dislocation (n = 91) or recurrent dislocation (n = 58) and whether or not they received an abduction brace; re-dislocation defined failure of treatment. The mean follow-up was 4.0 years in the first-time group and 3.7 years in the recurrent group. Among patients treated for first-time dislocations, 61% re-dislocated with a brace and 64% of nonbraced patients re-dislocated. In the recurrent group, 55% re-dislocated with a brace, whereas 56% re-dislocated without a brace. Chi-square analysis revealed that observed differences were not significant. There was no significant difference among groups with regards to age, sex, operative side, or significant surgical parameters. Abduction bracing following closed reduction of THA dislocation is ineffective in preventing re-dislocation.

Treatment of complex tibial plateau fractures using the less invasive stabilization system plate: clinical experience and a laboratory comparison with double plating.

BACKGROUND: Bicondylar tibial plateau fractures are complex injuries, historically associated with high complication rates. The purpose of this study was: 1) to evaluate the clinical use L.I.S.S plating system for stabilization of bicondylar tibial plateau fractures. 2) To compare the biomechanics of this plating system with a double plate construct. METHODS AND MATERIALS: Thirty-eight patients who sustained a complex tibial plateau fracture (OTA type 41C) at one of three level-one trauma centers were stabilized using the Less Invasive Stabilization System (L.I.S.S.). The cohort of patients was evaluated clinically and radiographically for outcomes at a mean 15 months. In phase 2 of this study a model of a bicondylar tibial plateau fractures was made in six matched pairs of embalmed, human tibia and randomized to fixation with either a L.I.S.S plate or a standard double plate construct. The tibias were then subjected to an axial cyclic load of 500N for 10 cycles (3Hz) to approximate 2 months in vivo and displacements measured. RESULTS: Thirty-six of /38 (95%) patients united at 4 months after surgery with no loss of fixation nor infection. Two patients underwent prophylactic autogenous bone grafting for bone loss and united by 3 months postgrafting. Significant loss of knee range of motion (<90) was seen in five patients.Biomechanically, no differences in permanent inferior displacement of the medial fragment were found in initial axial loading and after 10 cycles between the two plate constructs. However, when loaded to 500N the L.I.S.S plate construct demonstrated almost twice the displacement of the medial fragment compared with the dual plate construct. No specimen lost fixation during cycling. CONCLUSION: The L.I.S.S plating system provides stable fixation of complex bicondylar tibial plateau fractures allowing early range of knee motion with favorable clinical results.

Periprosthetic femoral fractures above total knee replacements.

Periprosthetic femoral fractures above total knee replacements can be managed by a variety of methods, including casting, open reduction and internal fixation, external fixation, or revision arthroplasty. Because no single method has emerged as the optimal choice for all such fractures, it is important to understand which options are appropriate for each fracture pattern. Early classification systems focused on displacement as a major indication for either surgical or nonsurgical management. However, recent techniques and current implants have made surgical management preferable for most periprosthetic fractures. Classification based on fracture location can help guide such treatment. Generally, intramedullary nails are best for proximal fractures, fixed-angle devices for fractures originating at the component, and revision arthroplasty for very distal fractures or those with implant loosening.

The effect of an attachable lateral support plate on the stability of intertrochanteric fracture fixation with a sliding hip screw.

BACKGROUND: Use of a sliding hip screw (SHS) alone for some unstable intertrochanteric femur fractures can allow excessive medial shaft displacement during impaction. This study evaluated the effect of an attachable lateral support plate on these fractures after loading. METHODS: Unstable, three-part intertrochanteric fractures were created in 10 matched pairs of embalmed femurs that were instrumented with 135-degree SHSs with or without an attachable lateral support plate. Under physiologic loading, inferior and lateral head displacements and lag screw sliding distances were measured. RESULTS: After 10,000 cycles at 750 N, all measurements for femurs with the lateral support plate were significantly less than for the femurs with the SHS alone: mean lateral difference was 1.7 mm (34%) (p < 0.05), mean inferior difference was 3.0 mm (38%) (p < 0.05), and mean lag screw sliding difference was 4.5 mm (58%) (p < 0.05). CONCLUSION: The addition of an attachable lateral support plate to an SHS significantly decreased displacement of the femoral head after cyclic loading.

Instability following total hip arthroplasty.

Dislocation is the second most common complication of total hip arthroplasty. Most dislocations occur early in the postoperative period and are caused by patient factors, surgical factors, or a combination of both. Patient factors that predispose to postoperative dislocation include previous surgery and neurologic impairment. Surgical factors include surgical approach, component orientation, and prosthetic and/or bony impingement. Evaluation of patients undergoing total hip arthroplasty requires a thorough history and physical examination, as well as a detailed radiographic assessment. Closed treatment of instability is successful in two thirds of cases; the remainder require surgical management. Surgical techniques used to treat or minimize risk of further dislocation include revision arthroplasty, trochanteric advancement, use of elevated rim liners, and use of constrained liners.

Use of structural bone graft with cementless acetabular cups in total hip arthroplasty.

We retrospectively studied 15 primary and 13 revision total hip arthroplasties in which structural acetabular bone grafts were used in conjunction with cementless acetabular cups (for 11 type I segmental acetabular defects and 17 type III combined segmental/cavitary acetabular defects). Mean follow-up was 7.7 years in the primary and 6.8 years in the revision group. Radiographic analysis was performed to assess graft incorporation, component migration, bone-implant radiolucencies, and polyethylene wear. Two acetabular components (7.1%) were radiographically loose and demonstrated component migration. One of the two patients with these components also showed evidence of eccentric polyethylene wear. Three patients (10.7%) exhibited eccentric polyethylene wear. All grafts were well-incorporated radiographically without evidence of resorption. Modified Harris hip scores for all patients improved postoperatively.

Comparison of the LISS and a retrograde-inserted supracondylar intramedullary nail for fixation of a periprosthetic distal femur fracture proximal to a total knee arthroplasty.

Simulated supracondylar fractures were created proximal to posterior cruciate ligament-retaining total knee arthroplasty components in paired human cadaver femora and stabilized with either a retrograde-inserted locked supracondylar nail or the Less Invasive Stabilization System (LISS; Synthes USA, Paoli, PA). Loads were applied to create bending and torsional moments on the simulated fracture stabilized with either no gap or a 10-mm gap. The LISS exhibited less torsional stability with anterior (P<.001) and posterior loads (P<.01). When varus loads were applied to 10-mm-gap specimens, the specimens stabilized with a retrograde nail had an 83% reduction in fracture displacement (P<.001) and 80% less medial translation of the distal fragment (P<.001). The samples stabilized with the LISS had a 93% reduction in fracture gap displacement when a valgus load was applied with a 10-mm gap (P<.001). Overall, these results suggest that the retrograde-inserted nail may provide greater stability for the management of periprosthetic supracondylar femur fractures in patients with a posterior cruciate ligament-retaining femoral total knee arthroplasty component.