Long-term Results of Spine Stapling for AIS to Skeletal Maturity and Beyond.

BACKGROUND: We looked at long-term follow-up of spine stapling with Nitinol Staples. This was a cohort of all adolescent idiopathic scoliosis (AIS) patients with curves at high risk to progress based on curve magnitude, premenarchal status in all females, failure of brace treatment, and skeletal immaturity. METHODS: This is a single surgeon retrospective review of consecutive AIS patients treated with Nitinol staples for progressive scoliosis. Fourteen patients, 16 curves from 2005 to 2008 were eligible. Minimum curve for stapling was 30 degrees. Standard preoperative, intraoperative, and postoperative data were collected. All patients were followed for a minimum of 36 months and to skeletal maturity. Three groups were: improved (group 1), correction of any amount; minimal progression (group 2), progression ≤10 degrees; and failure (group 3), ≥10 degrees of progression. RESULTS: A total of 13 thoracic curves and 2 compensatory lumbar curves met the inclusion criteria (94%). Average follow-up was 61 months. The mean preoperative main thoracic curve was 35 degrees. All but 1 patients progressed at least 9 degrees in a brace prior to stapling. Females were all premenarchal, 10 patients were Risser 0 and 3 Risser 1. The average number of vertebrae stapled per curve was 6. Group 1 included 6 curves (40%). Group 2, 5 curves (33%). Group 3, 4 curves (27%). Three patients went on to uncomplicated fusion. Final curve measurement at the end of follow-up or before fusion (P=0.0037), curve progression (P≤0.001), and percentage of coronal correction on first postoperative standing radiograph (P=0.042) were the significant differences between groups 1+2 (successful) versus group 3 (failures). In total, 73% of this group either progressed ≤10 degrees or improved. CONCLUSIONS: This is the first study that follows AIS patients treated with spine stapling to skeletal maturity. Staples likely changed natural history in some of our patients. Initial percentage of correction on first standing postoperative PA x-rays was the only predictor of success. Stapling was safe without any long-term complications. LEVEL OF EVIDENCE: Level III-retrospective study.

Spinopelvic Parameters: Lumbar Lordosis, Pelvic Incidence, Pelvic Tilt, and Sacral Slope: What Does a Spine Surgeon Need to Know to Plan a Lumbar Deformity Correction?

The pelvic incidence defines the amount of lordosis required in the lumbar spine, and a lumbar lordosis within 11° of the pelvic incidence defines alignment of the lumbo-pelvic region. Pelvic tilt is a compensatory mechanism that allows patients to achieve sagittal balance in the setting of decreased lumbar lordosis with the primary compensatory mechanisms being hip extension and knee flexion. Planning an adult lumbar deformity operation requires a comprehensive history and physical examination and thorough radiographic evaluation with the goal of restoring alignment between the pelvic incidence and lumbar lordosis and restoring a normal pelvic tilt.

Sagittal Alignment Two Years After Selective and Nonselective Thoracic Fusion for Lenke 1C Adolescent Idiopathic Scoliosis.

STUDY DESIGN/SETTING: Matched cohort. OBJECTIVE: To evaluate thoracic and thoracolumbar sagittal Cobb angles in patients undergoing either selective thoracic fusion (STF) or nonselective thoracic fusion (NSTF) for Lenke 1C adolescent idiopathic scoliosis (AIS). SUMMARY OF BACKGROUND DATA: The Lenke classification is used to guide fusion levels in AIS. For some curve types, including 1C, there is a disparity in practice regarding whether the thoracolumbar/lumbar curve should be included in the arthrodesis. The impact of performing an NSTF on sagittal parameters has not been adequately evaluated. METHODS: A multicenter database of AIS was queried for patients with right-sided 1C curves treated with posterior correction and fusion. A matched cohort for each group was created based on age, gender, preoperative Cobb angles, and Scoliosis Research Society-22R domain scores. Independent t tests for continuous variables and Fisher exact test for categorical variables were used to compare the STF and NSTF groups. RESULTS: Thirty-eight patients who underwent NSTF were matched to 38 patients in the STF. An average of 8.0 levels were fused in the STF group and 11.6 in the NSTF group (p < .001). Preoperative and radiographic variables were similar between the two groups. Postoperatively, there was a statistically significant difference between the STF and NSTF sagittal Cobb in the thoracic spine, 26.9° and 21.7° (p = .013). The greatest difference was in the thoracolumbar sagittal Cobb, which increased to 4.3° kyphosis in the STF group and decreased to 9° of lordosis in the NSTF group (p < .001). Residual thoracolumbar/lumbar scoliosis was 25.5° in the STF group and 14.5° in the NSTF group (p < .001). CONCLUSIONS: STF in 1C curves preserves lumbar motion segments but may be associated with an increase in thoracic and thoracolumbar kyphosis compared to NSTF. As expected, residual thoracolumbar/lumbar scoliosis was less in the NSTF group compared to the STF group. Although the long-term implications of these changes are unknown, consideration of sagittal balance is critical. Following these patients in the medium and long term will provide important information to guide fusion levels. LEVEL OF EVIDENCE: II.

Lumbar clinical adjacent segment pathology: predilection for proximal levels.

STUDY DESIGN: Retrospective case series. OBJECTIVE: To evaluate reoperations for lumbar adjacent segment pathology (ASP) during a 10-year period. SUMMARY OF BACKGROUND DATA: ASP after lumbar arthrodesis is an important clinical problem. There remains controversy, however, on the distribution of the most commonly affected levels. METHODS: Thirty-one patients undergoing revision operation for ASP in the lumbar spine were included in this study. Patients' charts were evaluated for demographic data including age at index and revision operations, time to revision operation, and index and revision levels fused. RESULTS: L4-L5 was the most commonly instrumented level in both single-level (n = 12), and multilevel (n = 13) index fusions. The mean length of time from the index operation to revision surgery was 81 months (range, 11-570 mo). Kaplan-Meier analysis predicted a disease-free survival rate of 32.3% at 5 years and of 12.9% at 10 years after the index operation. L3-L4 was the most commonly affected level by ASP with 75% (16/20) requiring reoperation. L2-L3 was the next most commonly affected level at 52% (14/27). The L5-S1 disk was relatively protected from ASP, with only 4/17 (24%) disks at risk developing ASP. A subgroup analysis of patients undergoing revision after a single-level L4-L5 arthrodesis revealed ASP at L3-L4 in 83% (10/12) of patients, compared with only 3/12 (25%) at L5-S1 (P < 0.05). Of all cases of ASP, the proximal segments were involved 90% of the time. CONCLUSION: ASP most commonly affects proximal levels in the lumbar spine. In this cohort of patients undergoing revision fusion for ASP, 90% of affected levels were rostral to the index level(s). In patients undergoing L4-L5 single-level arthrodesis, L3-L4 is at high risk, whereas L5-S1 is somewhat protected. Surgeons should pay particular attention to proximal levels when planning a lumbar arthrodesis, however, motion segments distal to fusion may not be as protected as previously thought. LEVEL OF EVIDENCE: 4.

Disappointing short-term results with the DePuy ASR XL metal-on-metal total hip arthroplasty.

Outcomes of ultralarge-diameter femoral heads used in metal-on-metal (MOM) total hip arthroplasty (THA) are relatively unknown. This study reports on early failures of the ASR XL (Depuy, Warsaw, Ind) and assesses whether a correlation with cup positioning exists. A retrospective review of 70 consecutive MOM THAs with ultralarge-diameter femoral head and monoblock acetabular component was conducted. Minimum follow-up was 24 months. Of 70 THAs, 12 (17.1%) required revision within 3 years for pain (7), loosening (3), and squeaking (2). Three additional THAs noted squeaking, 2 noted grinding, and 3 additional hips had persistent pain. In total, 20 (28.6%) of 70 demonstrated implant dysfunction. Acetabular components for all symptomatic hips were in acceptable range of cup abduction and anteversion. The failures noted with this design do not correlate to cup placement. The high rate of implant dysfunction at early follow-up suggests serious concerns with the concept of MOM THA with an ultralarge-diameter femoral head paired with a monoblock acetabular cup.

Minimally invasive approaches to the cervical spine.

Minimally invasive approaches and operative techniques are becoming increasingly popular for the treatment of cervical spine disorders. Minimally invasive spine surgery attempts to decrease iatrogenic muscle injury, decrease pain, and speed postoperative recovery with the use of smaller incisions and specialized instruments. This article explains in detail minimally invasive approaches to the posterior spine, the techniques for posterior cervical foraminotomy and arthrodesis via lateral mass screw placement, and anterior cervical foraminotomy. Complications are also discussed. Additionally, illustrated cases are presented detailing the use of minimally invasive surgical techniques.

Minimally invasive cervical spine foraminotomy and lateral mass screw placement.

STUDY DESIGN: This technique article describes accomplishing multilevel posterior cervical decompression and lateral mass screw placement through a tubular retraction system. OBJECTIVE: Multilevel foraminotomy and instrumented fusion using lateral mass screw fixation can be achieved through a minimally invasive technique using specialized retractors and intraoperative fluoroscopic imaging. SUMMARY OF BACKGROUND DATA: Minimally invasive surgical techniques have been adapted to the cervical spine with good results. These techniques have the theoretical advantages of reducing morbidity, blood loss, perioperative pain, and length of hospital stay associated with conventional open posterior spinal exposure. METHODS: Minimally invasive access to the posterior cervical spine was performed with exposure through a paramedian muscle-splitting approach. With the assistance of a specialized tubular retraction system with a deep soft tissue expansion mechanism, multilevel posterior cervical decompression and fusion can be accomplished. RESULTS: Minimized access to perform multilevel posterior cervical foraminotomy and fusion can be safely accomplished with tubular retraction systems. Complications associated with these techniques can include inadequate decompression, improper instrumentation placement, or neurologic injury due to poor access and visualization. CONCLUSION: Multilevel foraminotomy and instrumented fusion using lateral mass screw fixation can be safely achieved using these techniques. Complications associated with these strategies are typically due to inadequate visualization, incomplete decompression, or poor placement of instrumentation. As with all minimally invasive spine techniques, the surgeon must ensure that goals of the surgery, both technical and clinical outcomes, are comparable to those of a conventional open procedure.

A reversible molecular valve.

In everyday life, a macroscopic valve is a device with a movable control element that regulates the flow of gases or liquids by blocking and opening passageways. Construction of such a device on the nanoscale level requires (i) suitably proportioned movable control elements, (ii) a method for operating them on demand, and (iii) appropriately sized passageways. These three conditions can be fulfilled by attaching organic, mechanically interlocked, linear motor molecules that can be operated under chemical, electrical, or optical stimuli to stable inorganic porous frameworks (i.e., by self-assembling organic machinery on top of an inorganic chassis). In this article, we demonstrate a reversibly operating nanovalve that can be turned on and off by redox chemistry. It traps and releases molecules from a maze of nanoscopic passageways in silica by controlling the operation of redox-activated bistable [2]rotaxane molecules tethered to the openings of nanopores leading out of a nanoscale reservoir.

Redox-controllable amphiphilic [2]rotaxanes.

With the fabrication of molecular electronic devices (MEDs) and the construction of nanoelectromechanical systems (NEMSs) as incentives, two constitutionally isomeric, redox-controllable [2]rotaxanes have been synthesized and characterized in solution. Therein, they both behave as near-perfect molecular switches, that is, to all intents and purposes, these two rotaxanes can be switched precisely by applying appropriate redox stimuli between two distinct chemomechanical states. Their dumbbell-shaped components are composed of polyether chains interrupted along their lengths by i) two pi-electron rich recognition sites-a tetrathiafulvalene (TTF) unit and a 1,5-dioxynaphthalene (DNP) moiety-with ii) a rigid terphenylene spacer placed between the two recognition sites, and then terminated by iii) a hydrophobic tetraarylmethane stopper at one end and a hydrophilic dendritic stopper at the other end of the dumbbells, thus conferring amphiphilicity upon these molecules. A template-directed protocol produces a means to introduce the tetracationic cyclophane, cyclobis(paraquat-p-phenylene) (CBPQT(4+)), which contains two pi-electron accepting bipyridinium units, mechanically interlocked around the dumbbell-shaped components. Both the TTF unit and the DNP moiety are potential stations for CBPQT(4+), since they can establish charge-transfer and hydrogen bonding interactions with the bipyridinium units of the cyclophane, thereby introducing bistability into the [2]rotaxanes. In both constitutional isomers, (1)H NMR and absorption spectroscopies, together with electrochemical investigations, reveal that the CBPQT(4+) ring is predominantly located on the TTF unit, leading to the existence of a single translational isomer (co-conformation) in both cases. In addition, a model [2]rotaxane, incorporating hydrophobic tetraarylmethane stoppers at both ends of its dumbbell-shaped component, has also been synthesized as a point of reference. Molecular synthetic approaches were used to construct convergently the dumbbell-shaped compounds by assembling progressively smaller building blocks in the shape of the rigid spacer, the TTF unit and the DNP moiety, and the hydrophobic and hydrophilic stoppers. The two amphiphilic bistable [2]rotaxanes are constitutional isomers in the sense that, in one constitution, the TTF unit is adjacent to the hydrophobic stopper, whereas in the other, it is next to the hydrophilic stopper. All three bistable [2]rotaxanes have been isolated as green solids. Electrospray and fast atom bombardment mass spectra support the gross structural assignments given to all three of these mechanically interlocked compounds. Their photophysical and electrochemical properties have been investigated in acetonitrile. The results obtained from these investigations confirm that, in all three [2]rotaxanes, i) the CBPQT(4+) cyclophane encircles the TTF unit, ii) the CBPQT(4+) cyclophane shuttles between the TTF and DNP stations upon electrochemical or chemical oxidation/reduction of the TTF unit, and iii) folded conformations are present in which the CBPQT(4+) cyclophane, while encircling the TTF unit, interacts through its pi-accepting bipyridinium exteriors with other pi-donating components of the dumbbells, especially those located within the stoppers.

Dynamic chirality: keen selection in the face of stereochemical diversity in mechanically bonded compounds.

The template-directed syntheses, employing bisparaphenylene-[34]crown-10 (BPP34C10), 1,5-dinaphthoparaphenylene-[36]crown-10 (1/5NPPP36C10), and 1,5-dinaphtho-[38]crown-10 (1/5DNP38C10) as templates, of three [2]catenanes, whereby one of the two bipyridinium units in cyclobis(paraquat-p-phenylene) is replaced by a bipicolinium unit, are described. The crude reaction mixtures comprising the [2]catenanes all contain slightly more of the homologous [3]catenanes, wherein a "dimeric" octacationic cyclophane has the crown ether macrocycles encircling the alternating bipyridinium units with the bipicolinium units completely unfettered. X-ray crystallography, performed on all three [2]catenanes and two of the three [3]catenanes reveals co-conformational and stereochemical preferences that are stark and pronounced. Both the [3]catenanes crystallize as mixtures of diastereoisomers on account of the axial chirality associated with the picolinium units in the solid state. Dynamic (1)H NMR spectroscopy is employed to probe in solution the relative energy barriers for rotations by the phenylene and pyridinium rings in the tetracationic cyclophane component of the [2]catenanes. Where there are co-conformational changes that are stereochemically "allowed", crown ether circumrotation and rocking processes are also investigated for the relative rates of their occurrence. The outcome is one whereby the three [2]catenanes containing BPP34C10, 1/5NPPP36C10, and 1/5DNP38C10 exist as one major enantiomeric pair of diastereoisomers amongst two, four, and eight diastereoisomeric pairs of enantiomers, respectively. The diastereoisomerism is a consequence of the presence of axial chirality together with helical and/or planar chirality in the same interlocked molecule. These [2]catenanes constitute a rich reserve of new stereochemical types that might be tapped for their switching and mechanical properties.

Single-walled carbon nanotube based molecular switch tunnel junctions.

This article describes two-terminal molecular switch tunnel junctions (MSTJs) which incorporate a semiconducting, single-walled carbon nanotube (SWNT) as the bottom electrode. The nanotube interacts noncovalently with a monolayer of bistable, nondegenerate [2]catenane tetracations, self-organized by their supporting amphiphilic dimyristoylphosphatidyl anions which shield the mechanically switchable tetracations from a two-micrometer wide metallic top electrode. The resulting 0.002 micron 2 area tunnel junction addresses a nanometer wide row of approximately 2000 molecules. Active and remnant current-voltage measurements demonstrated that these devices can be reconfigurably switched and repeatedly cycled between high and low current states under ambient conditions. Control compounds, including a degenerate [2]catenane, were explored in support of the mechanical origin of the switching signature. These SWNT-based MSTJs operate like previously reported silicon-based MSTJs, but differently from similar devices incorporating bottom metal electrodes. The relevance of these results with respect to the choice of electrode materials for molecular electronics devices is discussed.