Self-expanding intestinal expansion sleeves (IES) for short gut syndrome.

PURPOSE: Many disease processes (necrotizing enterocolitis, caustic esophageal injury, malrotation with volvulus), can result in short-gut syndrome (SGS), where remnant intestinal segments may dilate axially, but rarely elongate longitudinally. Here we mechanically characterize a novel model of a self-expanding mesh prototype intestinal expanding sleeve (IES) for use in SGS. METHODS: Gut lengthening was achieved using a proprietary cylindrical layered polyethylene terephthalate IES device with helicoid trusses with isometric ends. The IES is pre-contracted by diametric expansion, deployed into the gut and anchored with bioabsorbable sutures. IES expansion to its equilibrium dimension maintained longitudinal gut tension, which may permit remodeling, increased absorptive surface area while preserving vascular and nervous supplies. We performed mechanical testing to obtain the effective force-displacement characterization achieved on these prototypes and evaluated minimal numbers of sutures needed for its anchoring. Furthermore, we deployed these devices in small and large intestines of New Zealand White rabbits, measured IES length-tension relationships and measured post-implant gut expansion ex vivo. Histology of the gut before and after implantation was also evaluated. RESULTS: Longitudinal tension using IES did not result in suture failure. Maximum IES suture mechanical loading was tested using 4-6 sutures; we found similar failure loads of 2.95 ± 0.64, 4 ± 1.9 and 3.16 ± 0.24 Newtons for 4, 6 and 8 sutures, respectively (n = 3, n.s). Pre-contracted IES tubes were deployed at 67 ± 4% of initial length (i.l.); in the large bowel these expanded significantly to 81.5 ± 3.7% of i.l. (p = 0.014, n = 4). In the small bowel, pre-contracted IES were 61 ± 3.8% of i.l.; these expanded significantly to 82.7 ± 7.4% of i.l. (p = 0.0009, n = 6). This resulted in an immediate 24 ± 7.8% and 36.2 ± 11% increase in gut length when deployed in large and small bowels, respectively, with maintained longitudinal tension. Maintained IES induced tension produced gut wall thinning; gut histopathological evaluation is currently under evaluation. CONCLUSION: IES is a versatile platform for gaining length in SGS, which may be simply deployed via feeding tubes. Our results need further validation for biocompatibility and mechanical characterization to optimize use in gut expansion.

No effect of femoral offset on bone implant micromotion in an experimental model.

BACKGROUND: In total hip replacement (THR), the femoral offset (FO) is assessed preoperatively, and the surgeon must determine whether to restore, increase, or decrease the FO based on experience and the patient's clinical history. The FO is known to influence the abductor muscle strength, range of motion (ROM), gait, and hip pain after THR; however, the true effect of FO on bone implant micromotion is unclear. Therefore, we investigated to assess: (1) the muscle loading response during gait, (2) whether FO affects bone implant micromotion during gait. HYPOTHESIS: A variation of ±10mm from the anatomical FO affects the muscle loading forces. MATERIALS AND METHODS: We modified a personalized musculoskeletal model of the lower extremity to determine the 3-dimensional contact forces at the hip joint in the presence of a stem with varying offsets during a gait cycle. A detailed finite element (FE) model was then constructed for increased, restored, and decreased FOs. The maximum load obtained during normal walking gait from the musculoskeletal model was applied to the respective FE models, and the resultant stem-bone micromotion and stress distribution were computed. RESULTS: Increasing the FO to +10mm decreased the peak force generated by the abductor muscles during the cycle by 15.0% and decreasing the FO to -10mm increased the von Mises stress distribution at the distal bone by 77.5% (P<0.05). A variation of the offset within 10mm of the anatomical offset showed no significant differences in micromotion (P>0.05) and peak stresses (P>0.05). DISCUSSION: Coupling the musculoskeletal model of the gait cycle with FE analysis provides a realistic model to understand how FO affects bone implant micromotion. We found that there was no effect of FO on bone implant micromotion; thus, a surgeon does not need to evaluate the implications of FO on micromotion and can determine a FO that best decreases the work load of abductor muscles, increases ROM, and reduces hip pain. LEVEL OF EVIDENCE: IV, biomechanical study.

Finite elements/Taguchi method based procedure for the identification of the geometrical parameters significantly affecting the biomechanical behavior of a lumbar disc.

The aim of this work is to show a quick and simple procedure able to identify the geometrical parameters of the intervertebral disc that strongly affect the behavior of the FEM model. First, we allocated a selection criterion for the minimum number of geometrical parameters that describe, with a good degree of approximation, a healthy human vertebra. Next, we carried out a sensitivity analysis using the 'Taguchi orthogonal array' to arrive at a quick identification of the parameters that strongly affect the behavior of the Fem model.

Primary cup stability in THA with augmentation of acetabular defect. A comparison of healthy and osteoporotic bone.

BACKGROUND CONTEXT: Reconstruction of acetabular defect has been advocated as standard procedure in total hip arthroplasty. The presence of bony defects at the acetabulum is viewed as a cause of instability and acetabular wall augmentation is often used without proper consideration of surrounding bone density. The initial cup-bone stability is, however, a challenge and a number of studies supported by clinical follow-ups of patients suggested that if the structural graft needs supporting more than 50% of the acetabular component, a reconstruction cage device spanning ilium to ischium should be preferred to protect the graft and provide structural stability. This study aims to (1) investigate the relationship between cup motion and bone density and (2) quantify the re-distribution of stress at the defect site after augmentation. HYPHOTESIS: Paprosky type I or II, acetabular defects, when reconstructed with bone screws supported by bioabsorbable calcified triglyceride bone cement are significantly less effective for osteoporotic bone than healthy bone. MATERIALS AND METHODS: Acetabular wall defects were reconstructed on six cadaveric subjects with bioabsorbable calcified triglyceride bone cement using a re-bar technique. Data of the specimen with higher bone density was used to validate a Finite Element Model. Values of bone apparent density ranging from healthy to osteoporotic were simulated to evaluate (1) the cup motion, through both displacement and rotation, (2) and the von Mises stress distribution. RESULTS: Defect reconstruction with bone screws and bioabsorbable calcified triglyceride bone cement results in a re-distribution of stress at the defect site. For a reduction of 65% in bone density, the cup displacement was similar to a healthy bone for loads not exceeding 300 N, as load progressed up to 1500 N, the reconstructed defect showed increase of 99 µm (128%) in displacement and of 0.08° in rotation angle. CONCLUSIONS: Based on the results, we suggest that an alternative solution to wall defect augmentation with bone screws supported by bioabsorbable calcified triglyceride bone cement, be used for osteoporotic bone. LEVEL OF EVIDENCE: Level IV, experimental and cadaveric study.