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Mullins et al: Accuracy of pin placement in the canine thoracolumbar spine using a free-hand probing technique versus 3D-printed patient-specific drill guides: An ex-vivo study
Veterinary Surgery 5, 2023

🔍 Key Findings

  • Both free-hand probing (FHP) and 3D-printed guides (3DPG) enabled accurate spinal pin placement, with 87.5% vs 96.4% of pins graded as optimal (Grade I).
  • 3DPGs had fewer intraoperative deviations (0/56 pins) compared to 6/56 with the FHP technique.
  • No pins using either method fully breached the medial vertebral canal (Grade IIb) — a critical safety outcome.
  • Pins placed using 3DPGs required less time overall (mean 2.6 min) than FHP (mean 4.5 min).
  • FHP required specific experience and has a learning curve, whereas 3DPG use requires CAD software and 3D printing access.
  • FHP had more lateral canal violations (Grade IIIa: 4/56 vs 0/56 for 3DPG), suggesting slightly less precision.
  • Both techniques were safe, and all deviations were recognized and corrected intraoperatively.
  • 3DPGs may offer practical advantages in clinical settings lacking surgical expertise, while FHP allows immediate intervention without 3D printing delay.

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← Articles

Mullins et al: Accuracy of pin placement in the canine thoracolumbar spine using a free-hand probing technique versus 3D-printed patient-specific drill guides: An ex-vivo study
Veterinary Surgery 5, 2023

🔍 Key Findings

  • Both free-hand probing (FHP) and 3D-printed guides (3DPG) enabled accurate spinal pin placement, with 87.5% vs 96.4% of pins graded as optimal (Grade I).
  • 3DPGs had fewer intraoperative deviations (0/56 pins) compared to 6/56 with the FHP technique.
  • No pins using either method fully breached the medial vertebral canal (Grade IIb) — a critical safety outcome.
  • Pins placed using 3DPGs required less time overall (mean 2.6 min) than FHP (mean 4.5 min).
  • FHP required specific experience and has a learning curve, whereas 3DPG use requires CAD software and 3D printing access.
  • FHP had more lateral canal violations (Grade IIIa: 4/56 vs 0/56 for 3DPG), suggesting slightly less precision.
  • Both techniques were safe, and all deviations were recognized and corrected intraoperatively.
  • 3DPGs may offer practical advantages in clinical settings lacking surgical expertise, while FHP allows immediate intervention without 3D printing delay.

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Multiple Choice Questions on this study

In Mullins 2023 et al., on thoracolumbar pin placement, which technique had zero intraoperative technique deviations?

A. Free-hand probing (FHP)
B. 3D-printed drill guides (3DPG)
C. Fluoroscopy-guided pin placement
D. Image-guided screw insertion
E. Manual pin tapping

Answer: 3D-printed drill guides (3DPG)

Explanation: 3DPGs had no intraoperative technique deviations, whereas 6 deviations occurred using the FHP technique.
In Mullins 2023 et al., on thoracolumbar pin placement, which of the following best explains the design advantage of 3DPGs?

A. Flexible probe redirection
B. Real-time feedback from impedance device
C. Custom fit based on CT-derived anatomy
D. Compatible with fluoroscopy and ultrasound
E. Manual placement using goniometer

Answer: Custom fit based on CT-derived anatomy

Explanation: 3DPGs were created from CT data and designed for anatomic conformity, enhancing accuracy.
In Mullins 2023 et al., on thoracolumbar pin placement, what was the **mean duration** for pin placement using the 3DPG technique?

A. 2.6 minutes
B. 4.5 minutes
C. 3.8 minutes
D. 1.9 minutes
E. 2.0 minutes

Answer: 2.6 minutes

Explanation: Pin placement with 3DPGs took significantly less time, averaging 2.6 minutes compared to 4.5 with FHP.
In Mullins 2023 et al., on thoracolumbar pin placement, which grading outcome was **not** observed with either technique?

A. Grade I (optimal placement)
B. Grade IIa (partial medial violation)
C. Grade IIb (full medial violation)
D. Grade IIIa (partial lateral violation)
E. Grade IIIb (full lateral violation)

Answer: Grade IIb (full medial violation)

Explanation: Neither technique resulted in Grade IIb canal violations, indicating high safety for both methods.
In Mullins 2023 et al., on thoracolumbar pin placement, what was a key **limitation** of the FHP technique noted in the study?

A. Required fluoroscopic guidance
B. Unreliable in thoracic pedicles
C. Limited to cervical spine
D. Steep learning curve and operator experience dependency
E. Only usable in small breed dogs

Answer: Steep learning curve and operator experience dependency

Explanation: FHP required training and anatomical familiarity, which impacted intraoperative deviation rates.

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