P.-H. Hsieh

Biomechanical comparison of lumbar spine instability between laminectomy and bilateral laminotomy for spinal stenosis syndrome - an experimental study in porcine model.

BackgroundThe association of lumbar spine instability between laminectomy and laminotomy has been clinically studied, but the corresponding in vitro biomechanical studies have not been reported. We investigated the hypothesis that the integrity of the posterior complex (spinous process-interspinous ligament-spinous process) plays an important role on the postoperative spinal stability in decompressive surgery.MethodsEight porcine lumbar spine specimens were studied. Each specimen was tested intact and after two decompression procedures. All posterior components were preserved in Group A (Intact). In Group B (Bilateral laminotomy), the inferior margin of L4 lamina and superior margin of L5 lamina were removed, but the L4–L5 supraspinous ligament was preserved. Fenestrations were made on both sides. In Group C (Laminectomy) the lamina and spinous processes of lower L4 and upper L5 were removed. Ligamentum flavum and supraspinous ligament of L4–L5 were removed. A hydraulic testing machine was used to generate an increasing moment up to 8400 N-mm in flexion and extension. Intervertebral displacement at decompressive level L4–L5 was measured by extensometerResultsThe results indicated that, under extension motion, intervertebral displacement between the specimen in intact form and at two different decompression levels did not significantly differ (P > 0.05). However, under flexion motion, intervertebral displacement of the laminectomy specimens at decompression level L4–L5 was statistically greater than in intact or bilateral laminotomy specimens (P = 0.0000963 and P = 0.000418, respectively). No difference was found between intact and bilateral laminotomy groups. (P > 0.05).ConclusionWe concluded that a lumbar spine with posterior complex integrity is less likely to develop segment instability than a lumbar spine with a destroyed anchoring point for supraspinous ligament.

Biomechanical comparison of a new stand-alone anterior lumbar interbody fusion cage with established fixation techniques - a three-dimensional finite element analysis.

BackgroundInitial promise of a stand-alone interbody fusion cage to treat chronic back pain and restore disc height has not been realized. In some instances, a posterior spinal fixation has been used to enhance stability and increase fusion rate. In this manuscript, a new stand-alone cage is compared with conventional fixation methods based on the finite element analysis, with a focus on investigating cage-bone interface mechanics and stress distribution on the adjacent tissues.MethodsThree trapezoid 8° interbody fusion cage models (dual paralleled cages, a single large cage, or a two-part cage consisting of a trapezoid box and threaded cylinder) were created with or without pedicle screws fixation to investigate the relative importance of the screws on the spinal segmental response. The contact stress on the facet joint, slip displacement of the cage on the endplate, and rotational angle of the upper vertebra were measured under different loading conditions.ResultsSimulation results demonstrated less facet stress and slip displacement with the maximal contact on the cage-bone interface. A stand-alone two-part cage had good slip behavior under compression, flexion, extension, lateral bending and torsion, as compared with the other two interbody cages, even with the additional posterior fixation. However, the two-part cage had the lowest rotational angles under flexion and torsion, but had no differences under extension and lateral bending.ConclusionThe biomechanical benefit of a stand-alone two-part fusion cage can be justified. This device provided the stability required for interbody fusion, which supports clinical trials of the cage as an alternative to circumferential fixations.

Elevated intraosseous pressure in the intertrochanteric region is associated with poorer results in osteonecrosis of the femoral head treated by multiple drilling

Multiple drilling is reported to be an effective treatment for osteonecrosis of the head of femur, but its effect on intra-osseous pressure has not been described. We undertook multiple drilling and recorded the intra-osseous pressure in 75 osteonecrotic hips in 60 patients with a mean age of 42 years (19 to 67). At a mean follow-up of 37.1 months (24 to 60), 42 hips (56%) had a clinically successful outcome. The procedure was effective in reducing the mean intra-osseous pressure from 57 mmHg (SD 22) to 16 mmHg (SD 9). Hips with a successful outcome had a mean pressure of 26 mmHg (SD 19). It was less effective in preventing progression of osteonecrosis in hips with considerable involvement and in those with a high intra-osseous pressure in the intertrochanteric region (mean 45 mmHg (SD 25)). This study is not able to answer whether a return of the intra-osseous pressure to normal levels is required for satisfactory healing.

Liquid antibiotics in bone cement: an effective way to improve the efficiency of antibiotic release in antibiotic loaded bone cement.

Objectives The objective of this study was to compare the elution characteristics, antimicrobial activity and mechanical properties of antibiotic-loaded bone cement (ALBC) loaded with powdered antibiotic, powdered antibiotic with inert filler (xylitol), or liquid antibiotic, particularly focusing on vancomycin and amphotericin B. Methods Cement specimens loaded with 2 g of vancomycin or amphotericin B powder (powder group), 2 g of antibiotic powder and 2 g of xylitol (xylitol group) or 12 ml of antibiotic solution containing 2 g of antibiotic (liquid group) were tested. Results Vancomycin elution was enhanced by 234% in the liquid group and by 12% in the xylitol group compared with the powder group. Amphotericin B elution was enhanced by 265% in the liquid group and by 65% in the xylitol group compared with the powder group. Based on the disk-diffusion assay, the eluate samples of vancomycin-loaded ALBC of the liquid group exhibited a significantly larger inhibitory zone than samples of the powder or the xylitol group. Regarding the ALBCs loaded with amphotericin B, only the eluate samples of the liquid group exhibited a clear inhibitory zone, which was not observed in either the xylitol or the powder groups. The ultimate compressive strength was significantly reduced in specimens containing liquid antibiotics. Conclusions Adding vancomycin or amphotericin B antibiotic powder in distilled water before mixing with bone cement can significantly improve the efficiency of antibiotic release than can loading ALBC with the same dose of antibiotic powder. This simple and effective method for preparation of ALBCs can significantly improve the efficiency of antibiotic release in ALBCs. Cite this article: Bone Joint Res 2014;3:246–51.

The concentration of antibiotic in fresh-frozen bone graft

We investigated the antibiotic concentration in fresh-frozen femoral head allografts harvested from two groups of living donors. Ten samples were collected from patients with osteoarthritis of the hip and ten from those with a fracture of the neck of the femur scheduled for primary arthroplasty. Cefazolin (1 g) was administered as a pre-operative prophylactic antibiotic. After storage at -80 degrees C for two weeks the pattern of release of cefazolin from morsellised femoral heads was evaluated by an in vitro broth elution assay using high-performance liquid chromatography. The bioactivity of the bone was further determined with an agar disc diffusion and standardised tube dilution bioassay. The results indicated that the fresh-frozen femoral heads contained cefazolin. The morsellised bone released cefazolin for up to four days. The concentration of cefazolin was significantly higher in the heads from patients with osteoarthritis of the hip than in those with a fracture.Also, in bioassays the bone showed inhibitory effects against bacteria.We concluded that allografts of morsellised bone from the femoral head harvested from patients undergoing arthroplasty of the hip contained cefazolin, which had been administered pre-operatively and they exhibited inhibitory effects against bacteria in vitro.

A positive bacterial culture from allograft bone at implantation does not correlate with subsequent surgical site infection

Fresh-frozen allograft bone is frequently used in orthopaedic surgery. We investigated the incidence of allograft-related infection and analysed the outcomes of recipients of bacterial culture-positive allografts from our single-institute bone bank during bone transplantation. The fresh-frozen allografts were harvested in a strict sterile environment during total joint arthroplasty surgery and immediately stored in a freezer at -78º to -68º C after packing. Between January 2007 and December 2012, 2024 patients received 2083 allografts with a minimum of 12 months of follow-up. The overall allograft-associated infection rate was 1.2% (24/2024). Swab cultures of 2083 allografts taken before implantation revealed 21 (1.0%) positive findings. The 21 recipients were given various antibiotics at the individual orthopaedic surgeons discretion. At the latest follow-up, none of these 21 recipients displayed clinical signs of infection following treatment. Based on these findings, we conclude that an incidental positive culture finding for allografts does not correlate with subsequent surgical site infection. Additional prolonged post-operative antibiotic therapy may not be necessary for recipients of fresh-frozen bone allograft with positive culture findings.

THE INFLUENCE OF SURFACE ROUGHNESS AND CEMENTING TECHNIQUE ON THE MICROSTRUCTURE AND MECHANICAL STRENGTH AT THE CEMENT-PROSTHESIS INTERFACE

It was generally considered that a femoral stem with a rough surface was not suitable for cemented fixation in total hip arthroplasty. The long-term follow-up studies on the cemented rough stems clearly revealed a significantly higher loosening and revision rate than those of polished stems. However, from a biomechanics point of view, a rough surface might result in stronger cement-prosthesis bonding because of micro-interlocking between the bone cement and the stem. This contradiction between biomechanical standpoint and clinical observation remains as a problem to be resolved. Thus, this study was designed to evaluate the effect of stem surface roughness and the cement pre-coating process on the bonding strength of the prosthesis-cement interface. A total of 48 Co-Cr rods with three different levels of surface roughness (polished, plasma-treated and bead-coated, 16 in each group) were enrolled in the study. All specimens were cylindrical in shape with lengths of 120 mm and 12 mm diameters. Sixteen specimens in each group were then treated with non-precoated or precoated cement fixation (8 in each group). After fixing the Co-Cr rod, the pushout test was carried out using a MTS testing machine, and the shear strength for each group was compared. An additional microscopic observation of the metal/cement interface was also performed. The results of the pushout test indicated that the shear strength increased with increasing implant surface roughness, regardless of whether or not the stem was treated with the cement precoating process. However, stem precoating did not statistically improve the bonding strength at each level of surface roughness. Microscopic observation of the stem-cement interfaces revealed that the bone cement significantly infiltrated the rough surface in both the precoated and non-precoated groups with stems with various levels of surface roughness. Surface roughness of the femoral stem significantly affected the stem/cement interface, improving shear strength significantly. Stem precoating did not statistically improve the shear strength using the present cementing technique with retrograde high-pressure injection. Although a high surface roughness of the femoral stem appears to be an effective choice to improve implant fixation in cemented THA, the longevity of the prostheses implanted with such a stem can only be determined from long-term clinical trials.