Many navigation (Image Guided Surgery or IGS) systems are keyed to safely and accurately placing implants into complex anatomy. In spine surgery such as disc arthroplasty and fusion surgery this can be extremely helpful. Likewise, in joint arthroplasty the accurate placement with respect to the operative plan is widely recognized to be of benefit to long term results.

However, where realignment of anatomy is desired following implant placement, such as in high tibial osteotomy, spinal fusion with correction of deformity, and spinal disc arthroplasty, navigation systems can tell you where you are, but not where you would like to be.

We have developed specific software modification technology, applicable to all current navigation systems that addresses this need for assistance in surgical correction of anatomy to a desired alignment without the requirement for further imaging or irradiation. The benefits of our software allow image free re-referencing of image guided surgery, accommodation of intra-operative changes in anatomy, and intra-operative accountability and adjustment to allow errors of image guidance to be identifiable and correctible, at any stage of image guided surgery.

This software allows accurate pre-operative planning, intra-operative verification and assessment of the operative plan, and actual outcomes of the surgery to be assessed as the surgery is performed. It allows the surgeon to subsequently verify if the operative planning has been adequately achieved, and if not can verify if continued surgery has then achieved the planning goals. This verification and image guidance does not require further imaging during surgery, relying upon the original data set and software enhancements.

Image guided surgery (IGS), or “Navigation,” is now widely used in many areas of surgery including arthroplasty. However, the options for establishing, in real time, the veracity of the navigation information are limited. Manufacturers recommend registering with a “prominent anatomical feature” to confirm accurate navigation is being presented. In their fine print, they warrant the accuracy proximate to the navigation array attached to the body. In multi-level spine surgery where it is most sorely needed, this limits the warrants to the vertebra of reference array attachment. In arthroplasty surgery, the accuracy of the system can be erroneous through technical errors and a delay may occur prior to verification of such innacuracy.

In response to this situation surgeons have taken to using K-wires, FaxMax screws and a variety of other “Fiducial Markers”, but these were not specifically designed for this purpose and in many ways are inadequate for the task of verification of navigation accuracy.

We have developed a fiducial marker that is designed to address these unmet needs. The Precision Screw is clearly visible on imaging modalities and the central registration point is identifiable at any angle of viewing, with accuracy of fractions of a millimeter. It does not interfere with surgery, being low profile and securely fixed to bone. Finally, in use, it is secure in capturing the navigation probe so that the surgeon does not need to focus on keeping the probe located while reviewing the navigation data.

We believe these features make this a useful and worthwhile addition to IGS.

Purpose: There is very little evidence to guide treatment of patients with spinal surgical site infection (SSI) who require irrigation and debridement (I& D) with respect to need for single or multiple I& D’s. The purpose of this study is to build a predictive model which stratifies patients with spinal SSI to determine which patients will go on to need single versus multiple I& D.

Method: A consecutive series of 128 patients from a tertiary spine center (collected from 1999–2005) who required I& D for spinal SSI, were studied based on data from a prospectively collected outcomes database. Over 30 variables were identified by extensive literature review as possible risk factors for SSI, and tested as possible predictors of risk for multiple I& D. Logistic regression was conducted to assess each variable’s predictability by a “bootstrap” statistical method. Logistic regression was applied using outcome of I& D – single or multiple as the “response”.

Results: 24/128 patients required multiple I& D. Primary spine diagnosis was approximately represented by ¼ trauma, ¼ deformity, ¼ degenerative and ¼ oncology/inflammatory/other. Six predictors: spine location, medical comorbidities, microbiology of the SSI, presence of distant site infection (ie. UTI or bacteremia), presence of instrumentation and bone graft type, proved to be the most reliable predictors of need for multiple I& D. Internal validation of the predictive model yielded area under the curve (AUC) of .84

Conclusion: Infection factors played an important role in need for multiple I& D. Patients with +MRSA culture or those with distant site infection such as bacteremia with or without UTI or pneumonia, were strong predictors of need for multiple I& D. Presence of instrumentation, location of surgery in the posterior lumbar spine and use of non-autograft bone predicted multiple I& D. Diabetes also proved to be the most significant medical comorbidity for multiple I& D.

Purpose: Upper cervical spine stabilization in children can be challenging due to anatomic abnormalities such as incomplete posterior elements, vertebral artery variability and small patient size. Several techniques have been described for stabilization of the upper cervical spine, each with its own advantages and disadvantages. Since the introduction of the technique by Harms, many authors have shown C1 lateral mass screws to be safe and effective in the stabilization of the upper cervical spine in adults. No large series of paediatric C1 lateral mass screw fixation has been reported in the literature. The purpose of this study was to describe the indications, technique, and outcomes of C1 lateral mass screw fixation in a consecutive series of 11 paediatric patients.

Method: A database generated retrospective review of all patients who underwent C1 lateral mass screw fixation as part of an upper cervical spine stabilization construct was performed. In all patients the C2 dorsal root ganglion was sacrificed. Patient demographics and clinical outcomes were obtained through chart review. Radiographs immediately post-operatively, at six-weeks, three-months, and final follow-up were reviewed.

Results: Eleven consecutive paediatric patients underwent bilateral C1 lateral mass screw fixation for a variety of conditions including C1-C2 instability, deformity, congenital malformation, trauma, as well as revision surgery. The average age was 10 years (range 4 to 16 years) with a mean follow-up of 11 months (range 6 – 18 months). There were no iatrogenic vertebral artery, hypoglossal nerve or spinal cord injuries. All 11 patients had solid fusion clinically and radiographically, with no loss of fixation. The C2 dorsal root ganglion was sacrificed in all patients with resulting minor occipital parasthaesia that progressively diminished in severity.

Conclusion: This is the largest series of consecutive patients reported in the literature to date showing that the technique is safe and effective, with acceptable morbidity when applied to the paediatric population. We believe that C1 lateral mass screws offer significant advantages over traditional fixation techniques when the C1 vertebra is to be included in an upper cervical instrumented construct.

Purpose: There is scant literature with respect to reproducibility in radiological measurements of vertebral morphology. The purpose was to determine the reliability of measurement of various parameters of vertebral morphology in idiopathic scoliosis.

Method: Ten patients with AIS were investigated with standardised low dose multi-slice helical CT. Axial reconstructions in the plane of the T8 (apical) vertebra were performed prone, as per Jamieson et al (2008). Antero-posterior (AP) canal diameter, left and right pedicle width, canal width, left and right mid-point to medial pedicle length, left and right pedicle length, and cord length, left and right transverse angles, and left and right canal area were measured by our spine surgeons and spine surgery fellow. Statistical analysis for intra-class coefficients (ICC) for intra and inter observer reliability was then performed.

Results: Intra-observer reliability was excellent, with a mean ICC score of 0.930 (range 0.608–0.996), across all fourteen variables. Inter-observer reliability was very good with a mean ICC score of 0.890 (range 0.360–0.987), across all variables. There was poor inter-observer reliability for measurement of the transverse pedicle angles (0.360 – 0.446). The intra-observer reliability for transverse pedicle angles, whilst good (0.608–0.861), was worse than any of the other intra-observer reliabilities.

Conclusion: We demonstrate excellent intra, and inter observer reliability for measurement of apical vertebrae morphology in AIS. This tool can be utilized in the further study of pedicle dysplasia. Measurement of transverse pedicle angle was less reliable than any of the other measurement variables. A standardised measurement of the morphology of vertebral canal, pedicles and vertebral body morphology is reliable both within individual observers, and across a group of observers. A standardised measure for further investigation has been validated which will enable study of the evolution of pedicle dysplasia over time. This will lead to a better understanding of the etiology of pedicle dysplasia in scoliosis.