A computed tomography–based feasibility study of translaminar screw placement in the pediatric thoracic spine

Laboratory investigation

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Object

Translaminar screws (TLSs) were originally described as a safer alternative to pedicle and transarticular screw placement at C-2 in adult patients. More recently, TLSs have been used in both the cervical and thoracic spine of pediatric patients as a primary fixation technique and as a bailout procedure when dysplastic pedicle morphology prohibits safe pedicle screw placement. Although authors have reported the anatomical characteristics of the cervical and thoracic lamina in adults as well as those of the cervical lamina in pediatric patients, no such data exist to guide safe TLS placement in the thoracic spine of the pediatric population. The goal of this study was to report the anatomical feasibility of TLS placement in the thoracic spine of pediatric patients.

Methods

Fifty-two patients (26 males and 26 females), with an average age of 9.5 ± 4.8 years, were selected by retrospective review of a trauma registry database after institutional review board approval. Study inclusion criteria were an age from 2 to 16 years, standardized axial bone-window CT images of the thoracic spine, and the absence of spinal trauma. For each thoracic lamina the following anatomical features were measured using eFilm Lite software: laminar width (outer cortical and cancellous), laminar height (LH), maximal screw length, and optimal screw trajectory. Patients were stratified by age (an age < 8 versus ≥ 8 years) and sex.

Results

Collected data demonstrate the following general trends as one descends the thoracic spine from T-1 to T-12: 1) increasing laminar width to T-4 followed by a steady decrease to T-12, 2) increasing LH, 3) decreasing maximal screw length, and 4) increasing ideal screw trajectory angle. When stratified by age and sex, male patients older than 8 years of age had significantly larger laminae in terms of both width and height and allowed significantly longer screw placement at all thoracic levels compared with their female counterparts. Importantly, it was found that 78% of individual thoracic laminae, regardless of age or sex, could accept a 4.0-mm screw with 1.0 mm of clearance. As expected, when stratifying by age and sex, it was found that older male patients had the highest acceptance rates.

Conclusions

Data in the present study provide information regarding optimal TLS length, diameter, and trajectory for each thoracic spinal level in pediatric patients. Importantly, the data collected demonstrate no anatomical limitations within the pediatric thoracic spine to TLS instrumentation, although acceptance rates are lower for younger (< 8 years old) and/or female patients. Lastly, given the anatomical variation found in this study, CT scanning can be useful in the preoperative setting when planning TLS use in the thoracic spine of pediatric patients.

Abbreviations used in this paper: BLW = bicortical laminar width; CLW = cancellous laminar width; LH = laminar height; PS = pedicle screw; TLS = translaminar screw.

Article Information

Address correspondence to: Camilo Molina, B.A., CRB-II 264, 1550 Orleans Street, Baltimore, Maryland 21205. email: cmolina2@jhmi.edu.

Please include this information when citing this paper: DOI: 10.3171/2011.10.PEDS11121.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    Left: Axial CT scan obtained at T-2, showing the optimal TLS length, outer cortical diameter, cancellous diameter, and trajectory. Right: Axial CT scan obtained at T-2, showing determination of the insertion medialization angle in relation to the midline.

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    Graph showing the mean BLW and mean CLW against the thoracic spine level, with stratification based on age, that is, < 8 versus ≥ 8 years.

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    Graph showing the mean LH against the thoracic spine level, with stratification based on age, that is, < 8 versus ≥ 8 years.

  • View in gallery

    Graph demonstrating the mean maximal TLS length against the thoracic spine level, with stratification based on age, that is, < 8 versus ≥ 8 years.

  • View in gallery

    Graph demonstrating the mean ideal screw trajectory angle against the thoracic spine level, with stratification based on age, that is, < 8 versus ≥ 8 years.

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