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13 questions
Q1What is the facet orientation in each region of the spine?▸
Cervical: coronal 0, sagittal 45
Thoracic: coronal 20, sagittal 60
Lumbar: coronal 45, sagittal 90
Q2How does vertebral body shape differ between cervical, thoracic and lumbar vertebrae?▸
Cervical: superior concave, inferior convex
Thoracic: heart shape, with inferior/superior costal (demi) facets
Lumbar: kidney shape
Q3Describe the spinous processes and transverse processes by region.▸
Cervical: short bifid SP; TP has anterior and posterior tubercle + transverse foramen
Thoracic: long slender SP pointing down; TP has transverse costal facet
Lumbar: broad and tall SP
C7: SP not bifid, no prominent tubercle
T12: no inferior demifacet / transverse costal facet
Q4What is the joint of Luschka and why is it surgically important?▸
Formed by the uncinate process in the cervical spine
It is the lateral margin of dissection
Damage risks the sympathetic trunk / vertebral artery
Q5Describe pedicle dimensions and orientation by region.▸
Cervical: mostly <3.5mm
Thoracic: medial wall 2x thicker than lateral; smallest diameter at T4; convergence decreases caudally to T12 (20 deg at T1 to 0 deg at T12); 15 deg cephalad tilt
Lumbar: diameter increases from L1; convergence increases caudally to S1; neural CC tilt
mamillary process (mammillary process) = junction of ossification centres
Q6What are the free-hand entry points for thoracic and lumbar pedicle screws?▸
Thoracic: intersection of lateral margin of facet joint and midline of transverse process; entry more cephalad proximally
Lumbar: midline of TP + SAP lateral border
Lumbar: pars border + midline of TP
Lumbar: mamillary process + midline of TP
Q7What is the design of a dual core diameter, dual pitch pedicle screw?▸
Cylindrical large core + low broad threads - strength in the dense cortical bone of the pedicle
Short smooth transition zone to decrease stress concentration
Cylindrical small core + high thin threads - purchase in the cancellous bone of the vertebral body; increases area for load sharing
Q8What are the overall advantages of this screw design?▸
Increase pull-out resistance
Length adjustment by backing out without abandoning safe anchorage
Q9Why is the old conical core design less favourable?▸
Decreases pull-out strength once backed out
A loosened screw cannot be relied on for safe anchorage
Q10What are the head options and their advantages?▸
Low profile, threaded for the set screw
Polyaxial: increases contact area between rod and locking mechanism (locking strength)
Monoaxial: allows reduction and lordolisation (now overcome by new polyaxial reduction systems)
Q11What are the features of the screw tip and the double lead?▸
Tip: Self tap and self centering (self-tapping and self-centering)
+/- round tip for bicortical purchase
Double lead - faster insertion without compromising purchase
Q12What is the principle of interspinous distraction devices (IDDs)?▸
Create local flexion to stretch the posterior structures and increase space for the nerve roots
Rationale: flexion makes back pain better
Q13What is the evidence for IDDs in lumbar spinal stenosis?▸
Borg 2021 (Neurosurgery): IDD cannot replace laminectomy
Not as cost effective as laminectomy in lumbar spinal stenosis
Fact check
Cervical spine pedicles are mostly <3.5mm in diameter — imprecise/misleading — Mean outer cervical pedicle width is about 4.8-6.6mm from C3 to C7; a 3.5mm screw generally needs an outer width >=4.5mm, which the narrowest upper subaxial pedicles (C3/C4) may not provide — (medium confidence) — source