Date

2-2-2017

Document Type

Article

Disciplines

Orthopedics

Abstract

PURPOSE: Intra-operative imaging plays a key role in screw placement for slipped capital femoral epiphysis (SCFE). Complications have been associated with inadequate screw position. The purpose of this study was to evaluate computed tomography (CT) (3D fluoroscopy) and standard fluoroscopy (C-arm) images as compared with direct anatomic measurement to determine final screw position in a cadaveric SCFE model.

METHODS: Osteotomy with pinning was performed at the physeal scar in ten cadaveric hips. A standardised approach-withdrawal technique was performed with C-arm images taken at 15 degrees increments. We also obtained a CT (3D fluoroscopy) scan of each hip. The screw tip-subchondral bone (STSB) distance was measured on digital imaging software and also with a digital calliper directly when the femoral head was cut in plane to expose the STSB distance anatomically. Statistical analysis included t-tests and Fisher's exact test.

RESULTS: Moderate SCFE osteotomies were achieved with a mean Southwick angle (39.5 degrees +/- 7 degrees ). The 60 degrees fluoroscopic image was found to be the most representative image (41% of the time) compared with both anteroposterior (AP) and lateral images (8% and 21%). Both fluoroscopy (2.7 +/- 0.8 mm, p < 0.001) and CT (1.6 +/- 0.7 mm, p = 0.03) overestimated the STSB distance compared with direct measurement (0.94 +/- 0.51 mm). Two-thirds (67%) of CT measurements were within 1 mm of the cadaveric measurement, while only 20% of C-arm measurements fulfilled this criterion (p = 0.04).

CONCLUSIONS: Both standard fluoroscopy and CT overestimated the STSB distance when compared with direct measurement in a cadaveric model of SCFE. Surgeons should be aware of the limitations of intra-operative imaging to determine the STSB distance. We suggest that using the known pitch of a screw (2.9 mm in a 7.3-mm cannulated screw) as an intra-operative tool to help guide screw placement.

Rights and Permissions

Copyright © 2017, The British Editorial Society of Bone and Joint Surgery. Citation: J Child Orthop. 2017;11(1):36-41. doi: 10.1302/1863-2548-11-160174. Link to article on publisher's site

DOI of Published Version

10.1302/1863-2548-11-160174

Related Resources

Link to Article in PubMed

Keywords

cadaver model, computed tomography (CT), fluoroscopy, pinning, slipped capital femoral epiphysis

Journal Title

Journal of children's orthopaedics

PubMed ID

28439307

Creative Commons License

Creative Commons Attribution-Noncommercial 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial 4.0 License

Included in

Orthopedics Commons

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