Noelle Klocke

A risk calculator for short-term morbidity and mortality after hip fracture surgery

Objective: Hip fractures are a common source of morbidity and mortality among the elderly. Although multiple prior studies have identified risk factors for poor outcomes, few studies have presented a validated risk stratification calculator. Methods: The American College of Surgeons National Surgical Quality Improvement Program database was used to identify 4331 patients undergoing surgery for hip fracture between 2005 and 2010. Patient demographics, comorbidities, laboratory values, and operative characteristics were compared in a univariate analysis, and a multivariate logistic regression analysis was then used to identify independent predictors of 30-day morbidity and mortality. Weighted values were assigned to each independent risk factor and used to create predictive models of 30-day morbidity, minor complication risk, major complication risk, and total complication risk. The models were internally validated with randomly partitioned 80%/20% cohort groups. Results: Thirty-day mortality was 5.9% and morbidity was 30.0%. Patient age, especially age greater than 80 years [mortality: odds ratio (OR): 2.41, 95% confidence interval (CI): 1.17–4.99); morbidity: OR: 1.43, 95% CI: 1.05–1.94], and male gender (mortality: OR: 2.28, 95% CI: 1.61–3.22; morbidity: OR: 1.26, 95% CI: 1.03–1.54) were associated with both increased mortality and morbidity. An increased American Society of Anesthesia class had the highest negative impact on total complication incidence in the scoring models. Additionally, complete functional dependence, active malignancy, patient race, cardiopulmonary disease, laboratory derangements, prolonged operating time, and open versus percutaneous surgery independently influenced outcomes. Risk scores, based on weighted models, which included the aforementioned variables, predicted mortality (P < 0.001, C index: 0.702) and morbidity (P < 0.001, C index: 0.670) after hip fracture surgery. Conclusions: In this study, we have developed an internally validated method for risk stratifying patients undergoing hip fracture surgery, and this model is predictive of both 30-day morbidity and mortality. Our model could be useful for identifying high-risk individuals, for obtaining informed consent, and for risk-adjusted comparisons of outcomes between institutions. Level of Evidence: Prognostic Level II. See Instructions for Authors for a complete description of levels of evidence.

Volar/dorsal compressive mechanical behavior of the transverse carpal ligament.

Mechanical insult to the median nerve caused by contact with the digital flexor tendons and/or carpal tunnel boundaries may contribute to the development of carpal tunnel syndrome. Since the transverse carpal ligament (TCL) comprises the volar boundary of the carpal tunnel, its mechanics in part govern the potential insult to the median nerve. Using unconfined compression testing in combination with a finite element-based optimization process, nominal stiffness measurements and first-order Ogden hyperelastic material coefficients (μ and α ) were determined to describe the volar/dorsal compressive behavior of the TCL. Five different locations on the TCL were tested, three of which were deep to the origins of the thenar and hypothenar muscles. The average (± standard deviation) low-strain and high-strain TCL stiffness values in compression sites outside the muscle attachment region were 3.6 N/mm (±2.7) and 28.0 N/mm (±20.2), respectively. The average stiffness values at compression sites with muscle attachments were notably lower, with low-strain and high-strain stiffness values of 1.2 N/mm (±0.5) and 9.7 N/mm (±4.8), respectively. The average Ogden coefficients for the muscle attachment region were 51.6 kPa (±16.5) for μ and 16.5 (±2.0) for α, while coefficients for the non-muscle attachment region were 117.8 kPa (±86.8) for μ and 17.2 (±1.6) for α. These TCL compressive mechanical properties can help inprove computational models, which can be used to provide insight into the mechanisms of median nerve injury leading to the onset of carpal tunnel syndrome symptoms.

Stabilization of the craniocervical junction after an internal dislocation injury: an in vitro study.

BACKGROUND CONTEXT Reconstructive surgeries at the occipitocervical (OC) junction have been studied in treating degenerative conditions. There is a paucity of data for optimal fixation for a traumatically unstable OC joint. In clinical OC dislocations, segmental fixation may be impossible because of vertebral artery injury or fracture. Segmental fixation of the occiput, C1, and C2 demonstrated maximum biomechanical stability in fixation of an unstable craniocervical dislocation. A biomechanical study comparing various points of cervical posterior screw fixation after recreating traumatic injury would illuminate relative advantages between the various techniques. PURPOSE To determine the rigidity lost, if any, of segmental C0-C2 posterior screw fixation versus fixation skipping C1 at the OC junction, with or without a cross-connector. STUDY DESIGN This study is a cadaveric biomechanical investigation. METHODS Intervertebral motions and translations were recorded in seven specimens under conditions in the following order: intact, OC dislocation model with complete disruption of the cruciate ligaments, alar ligaments, and occipitoatlantal/atlantoaxial capsules (injury), segmental posterior fixation (SPF) with posterior instrumentation (ELLIPSE; Globus Medical, Inc., Audubon, PA, USA) at occiput, C1, and C2 levels, endpoint fixation (EPF) with posterior instrumentation at occiput and C1 level skipping C1, and endpoint fixation with a cross-connector (EPFC). Motion was applied through a custom spine simulator with a pure moment load of 2.5 Nm and measured with motion capture markers attached to occiput (C0), anterior C1 ring, and C2. Flexion-extension (FE), lateral bending (LB), axial rotation (AR), and cranial-caudal (CC) motions were recorded in terms of C0-C2. Results were reported as a percentage of injured motion (injury=100%), unless otherwise stated. RESULTS The injury significantly increased the motion to 165%, 263%, and 130%, during FE, LB, and AR, respectively, of intact. The CC translations increased to 164%, 254%, and 121% during FE, LB, AR, respectively, of intact. Segmental posterior fixation significantly reduced motion to 7%, 8%, and 1%, during FE, LB, and AR, respectively, of injury. Endpoint fixation significantly increased motion in FE, resulting in 12%, 6%, and 4% during FE, LB, and AR, respectively, of injury when compared with SPF. The EPFC construct decreased the motion compared with its counterpart to 8.6%, 5.7%, and 3.2% during FE, LB, and AR, respectively. CONCLUSIONS All fixation constructs significantly reduced motion in all loading modes and CC translations, compared with intact and injury. The construct with the greatest stability against craniocervical dislocation included SPF with instrumentation at the occiput, C1, and C2. By skipping C1 using the EPF, FE and cephalad-caudal translations significantly increased compared with posterior fixation at every level. The addition of a cross-connector increased the stability but was not statistically significant.

Additional sagittal correction can be obtained when using an expandable titanium interbody device in lumbar Smith-Peterson osteotomies: a biomechanical study

BACKGROUND CONTEXT Insertion of intervertebral fusion devices between consecutive Smith-Peterson osteotomies (SPOs) provides an anterior fulcrum during compression, which has been documented to improve achievable Cobb angle correction. Extension of these principles to an expandable device would theoretically provide greater surgical adjustment for flatback and scoliotic cases than a static cage. PURPOSE To investigate whether an expandable titanium interbody device would produce greater sagittal correction than a static spacer when used during SPO procedures. STUDY DESIGN/SETTING Cadaveric research was performed. PATIENT SAMPLE Seven T10-S1 human specimens were used. OUTCOME MEASURES Cobb angle changes and range of motion are the physiological measures. No self-report/functional measures were applicable. METHODS Bilateral pedicle screws were placed (T11-L5) before Smith-Petersen osteotomy creation from L2 to L4. A transforaminal lumbar interbody fusion titanium expandable implant was placed in each disc space from L2-L3 to L4-L5, which is currently an off-label use of this implant. Initial placement simulated a static spacer, and then incremental device expansion was performed to obtain an intermediate and final height. Lateral fluoroscopic images were taken for Cobb angle evaluation between L2 and L5, and range of motion as observed during application of pure bending moments was captured using a six degree-of-freedom spine simulator. A one-way analysis of variance with Tukey post hoc analysis was performed to determine significant differences (p<.05) between surgical constructs (intact, SPO only, contracted, semiexpanded, and expanded). Study costs were allocated within the research budget of a medical device company, where some authors are salaried employees; another author has been a paid consultant elsewhere. These financial associations were not believed to bias the results. RESULTS Change in Cobb angle from L2 to L5 was significantly greater with the interbody spacer compared with SPO alone. Despite an obvious increase in lordosis with expansion height, there were no significant differences between implant expansion states for the L2-L5 Cobb angle. All instrumented constructs were statistically equivalent in every mode of motion once rigid instrumentation was implemented, regardless of expansion state. CONCLUSIONS The expandable interbody did have a slight effect on lordotic correction; each additional millimeter in height expansion yielded approximately 1° in correction across the three SPO levels. Even without significant differences between the states, an expandable device may allow the surgeon more control of lordotic correction within the operating room than a static spacer alone.

Does Lumbopelvic Fixation Add Stability? A Cadaveric Biomechanical Analysis of an Unstable Pelvic Fracture Model

Objective: We sought to determine the role of lumbopelvic fixation (LPF) in the treatment of zone II sacral fractures with varying levels of sacral comminution combined with anterior pelvic ring (PR) instability. We also sought to determine the proximal extent of LPF necessary for adequate stabilization and the role of LPF in complex sacral fractures when only 1 transiliac–transsacral (TI–TS) screw is feasible. Materials and Methods: Fifteen L4 to pelvis fresh-frozen cadaveric specimens were tested intact in flexion-extension (FE) and axial rotation (AR) in a bilateral stance gliding hip model. Two comminution severities were simulated through the sacral foramen using an oscillating saw, with either a single vertical fracture (small gap, 1 mm) or 2 vertical fractures 10 mm apart with the intermediary bone removed (large gap). We assessed sacral fracture zone (SZ), PR, and total lumbopelvic (TL) stability during FE and AR. The following variables were tested: (1) presence of transverse cross-connector, (2) presence of anterior plate, (3) extent of LPF (L4 vs. L5), (4) fracture gap size (small vs. large), (5) number of TI–TS screws (1 vs. 2). Results: The transverse cross-connector and anterior plate significantly increased PR stability during AR (P = 0.02 and P = 0.01, respectively). Increased sacral comminution significantly affected SZ stability during FE (P = 0.01). Two versus 1 TI–TS screw in a large-gap model significantly affected TL stability (P = 0.04) and trended toward increased SZ stabilization during FE (P = 0.08). Addition of LPF (L4 and L5) significantly improved SZ and TL stability during AR and FE (P < 0.05). LPF in combination with TI–TS screws resulted in the least amount of motion across all 3 zones (SZ, PR, and TL) compared with all other constructs in both small-gap and large-gap models. Conclusions: The role of LPF in the treatment of complex sacral fractures is supported, especially in the setting of sacral comminution. LPF with proximal fixation at L4 in a hybrid approach might be needed in highly comminuted cases and when only 1 TI–TS screw is feasible to obtain maximum biomechanical support across the fracture zone.

Does pedicle screw fixation of the subaxial cervical spine provide adequate stabilization in a multilevel vertebral body fracture model? An in vitro biomechanical study.

Background Cervical vertebral body fractures generally are treated through an anterior‐posterior approach. Cervical pedicle screws offer an alternative to circumferential fixation. This biomechanical study quantifies whether cervical pedicle screws alone can restore the stability of a three‐column vertebral body fracture, making standard 360° reconstruction unnecessary. Methods Range of motion (2.0 Nm) in flexion‐extension, lateral bending, and axial rotation was tested on 10 cadaveric specimens (five/group) at C2–T1 with a spine kinematics simulator. Specimens were tested for flexibility of intact when a fatigue protocol with instrumentation was used to evaluate construct longevity. For a C4–6 fracture, spines were instrumented with 360° reconstruction (corpectomy spacer + plate + lateral mass screws) (Group 1) or cervical pedicle screw reconstruction (C3 and C7 only) (Group 2). Findings Results are expressed as percentage of intact (100%). In Group 1, 360° reconstruction resulted in decreased motion during flexion‐extension, lateral bending, and axial rotation, to 21.5%, 14.1%, and 48.6%, respectively, following 18,000 cycles of flexion‐extension testing. In Group 2, cervical pedicle screw reconstruction led to reduced motion after cyclic flexion‐extension testing, to 38.4%, 12.3%, and 51.1% during flexion‐extension, lateral bending, and axial rotation, respectively. Interpretation The 360° stabilization procedure provided the greatest initial stability. Cervical pedicle screw reconstruction resulted in less change in motion following cyclic loading with less variation from specimen to specimen, possibly caused by loosening of the shorter lateral mass screws. Cervical pedicle screw stabilization may be a viable alternative to 360° reconstruction for restoring multilevel vertebral body fracture. HighlightsCervical fracture is corrected by 360° fusion using lateral mass screws with corpectomy spacer/plate360° fusion may be unnecessary as navigational techniques lower complication rates associated with cervical pedicle screwsBiomechanical comparisons between 360° fusion (C3 to C7) and pedicle screw reconstruction (C3 and C7 only) are madeSurgical constructs significantly reduced intact; no significant differences were observed between constructs

Biomechanical Assessment of Stabilization of Simulated Type II Odontoid Fracture with Case Study

Study Design Researchers created a proper type II dens fracture (DF) and quantified a novel current posterior fixation technique with spacers at C1–C2. A clinical case study supplements this biomechanical analysis. Purpose Researchers explored their hypothesis that spacers combined with posterior instrumentation (PI) reduce range of motion significantly, possibly leading to better fusion outcomes. Overview of Literature Literature shows that the atlantoaxial joint is unique in allowing segmental rotary motion, enabling head turning. With no intervertebral discs at these joints, multiple ligaments bind the axis to the skull base and to the atlas; an intact odontoid (dens) enhances stability. The most common traumatic injury at these strong ligaments is a type II odontoid fracture. Methods Each of seven specimens (C0–C3) was tested on a custom-built six-degrees-of-freedom spine simulator with constructs of intact state, type II DF, C1–C2 PI, PI with joint capsulotomy (PIJC), PI with spacers (PIS) at C1–C2, and spacers alone (SA). A bending moment of 2.0 Nm (1.5°/sec) was applied in flexion-extension (FE), lateral bending (LB), and axial rotation (AR). One-way analysis of variance with repeated measures was performed. Results DF increased motion to 320%, 429%, and 120% versus intact (FE, LB, and AR, respectively). PI significantly reduced motion to 41%, 21%, and 8%. PIJC showed negligible changes from PI. PIS reduced motion to 16%, 14%, and 3%. SA decreased motion to 64%, 24%, and 54%. Reduced motion facilitated solid fusion in an 89-year-old female patient within 1 year. Conclusions Type II odontoid fractures can lead to acute or chronic instability. Current fixation techniques use C1–C2 PI or an anterior dens screw. Addition of spacers alongside PI led to increased biomechanical rigidity over intact motion and may offer an alternative to established surgical fixation techniques.

415 EFFECTS OF SPIN-LOCK TIME SELECTION IN T1RHO RELAXOMETRY

acquisition in the steady state; flip angle 55°; repetition time 58ms; echo time 12ms; 512x512 matrix with 0.31x0.31mm resolution; 60 partitions at 1.5mm thickness). Image segmentation was performed semi-automatically using custom software written in MATLAB, and measures of mean signal intensity for different regions of cartilage were obtained. Urinary levels of C-terminal crosslinking telopeptide of type II collagen (U-CTX-II) were measured. Cartilage defects were scored using a 5-point scale. Multivariable linear regression was used to test associations. Results: Cartilage signal intensity varied by site (mean (SD) for femur: 120.1 (8.4); medial tibia: 94.5 (9.8); lateral tibia: 95.9 (11.6); patella: 123.4 (10.7)). After adjustment for confounders, BMI was negatively associated with mean signal intensity of cartilage in the medial femoral (b = −0.82 per kg/m, p = 0.005), lateral femoral (b = −0.69 per kg/m, p = 0.020), whole femoral (b = −0.60 per kg/m, p = 0.034) and lateral tibial (b = −0.80 per kg/m, p = 0.027) sites. Cartilage defects were associated with sameregion mean intensity in the lateral tibia (b = −10.22 per grade, p = 0.017), and patella (b = −6.06 per grade, p = 0.002). After excluding cases with cartilage defects, CTX-II was negatively associated with mean signal intensity in the medial femoral (b = −2.46 per pg/ml, p = 0.010), lateral femoral (b = −2.13 per pg/ml, p = 0.036), whole femoral (b = −2.44 per pg/ml, p = 0.010) and patellar (b = −2.77 per pg/ml, p = 0.031) sites. Conclusions: Reduced cartilage signal intensity on MRI is associated with early osteoarthritic changes and thus may be used as a marker of early osteoarthritis.