Large-scale retrieval studies have shown backside wear in tibial inserts is dependent on the surface roughness of the tibial tray. Manufacturers acknowledge this design factor and have responded with the marketing of mirror-finished trays, which are clinically proven to have lower wear rates in comparison to historically “rough” (e.g. grit blasted) trays. While the relationship between wear and surface roughness has been explored in other polymer applications, the quantitative dependence of backside wear rate on quantitative surface finish has not yet been established for modern devices. The present study evaluates small-excursion polyethylene wear on pucks of a variety of surface roughnesses. The objective of this study is to determine where inflection points exist in the relationship between surface roughness and wear rate. An AMTI Orthopod, 6-station pin on disk tribotest was designed to mimic worst-case in vivo backside wear conditions based on published retrieval analyses. Titanium (Ti6Al4V) pucks with six different surface roughness preparations (Sa ranges from 0.06 um to 1.06 um) were characterized with white light profilometry. Never implanted polyethylene tibial inserts (never irradiated, EtO sterilized) were machined into 6 mm diameter cylindrical pins. Fretting-type motion was conducted in a 2mm square pattern at 2Hz under 100 N constant force in 25% bovine serum lubricant for 1.35 million cycles in triplicate. Mass measurements were taken every 225 thousand cycles.Introduction
Materials and Methods
To determine whether neurophysiological electrical pedicle testing (EPT) is a useful aid in the detection of malpostioned pedicle screw tracts EPT data from 246 screws in 32 spinal operations on 32 patients over a 5 year period (2009–2014) were recorded and analysed. In addition to physical palpation, a ball-tipped electrode delivered stimuli and the output was recorded by evoked electromyogram (EMG). When breach threshold values were recorded, the surgeon rechecked the tract for breaches and responded appropriately. In addition, standard motor evoked potential (MEP) and sensory evoked potential(SEP) spinal cord monitoring was performed. There were 24(9.8%) pedicle breaches by tract testing and 8(3.3%) by screw testing. In 11 instances in 7 patients where the tract testing showed a breach, the tract was redirected and subsequent screw testing showed adequate integrity of the pedicle. The total time for tract and screw testing was 25 seconds. There were no associated changes in MEP or SEP monitoring with any of the recorded pedicle breaches and none of the patients had any post-operative neurological deficit. EPT for the pedicle screw and tract is a safe, simple, practical and reliable technique which improves the accuracy of screw placement. Further studies would be required to confirm (and possibly revise) the threshold levels and to demonstrate whether EPT reduces the risk of misplaced screws or post-operative neurological deficit.
An analysis of significant neuromonitoring changes (NMCs) and evaluation of the efficacy of multimodality neuromonitoring in spinal deformity surgery. A retrospective review of prospectively collected data in 320 consecutive paediatric and adult spinal deformity operations. Patients were sub-grouped according to demographics (age, gender), diagnosis, radiographic findings (Cobb angles, MR abnormalities) and operative features (surgical approach, duration, levels of fixation). Post-operative neurological deficit was documented and defined as either spinal cord or nerve root deficit.Aim:
Method:
To establish the current practice of spinal cord monitoring in units carrying out scoliosis surgery in the UK. To illustrate the benefit of routinely monitoring motor evoked potentials (MEPs). Questionaire: Nationwide survey of spinal monitoring modalities used by spinal units carrying out deformity surgery. 10 out of 27 units routinely measure motor evoked potentials (MEPs), the remainder use only sensory potentials (SEPs). There is significant variability in use of monitoring around the UK and we have compared this to the practice elsewhere in the world. We report the case of a thirteen year old girl who underwent posterior instrumentation for correction of an idiopathic scoliosis. Intra-operatively there was a significant reduction in the amplitude of the MEPs without any corresponding change in the SEPs. These changes reversed when the correction was released. The surgery was abandoned and was carried out as a staged procedure, initially anteriorly then posteriorly. There was no loss of motor potentials during either operation and no post operative neurological abnormalities. We propose that the changes noted initially were due to transient ischaemia of the cord which would not have been detected without MEPs and may have led to long term sequelae. This highlights the safety benefit of routinely using MEPs in scoliosis surgery. Nationally there is wide variation in the monitoring of spinal cord function during scoliosis surgery. We feel that monitoring of motor potentials is a vital component in ensuring scoliosis surgery is as safe as possible.
