a biomechanical study of torque and accuracy of halo pin insertional devices* by michael d. smith,...

A Biomechanical Study of Torque and Accuracy of Halo Pin Insertional Devices*

by MICHAEL D. SMITH, LINDA J. JOHNSON, JOSEPH H. PERRA, and BERNARD A. RAWLINS

J Bone Joint Surg AmVolume 78(2):231-8

February 1, 1996

©1996 by The Journal of Bone and Joint Surgery, Inc.

Devices A (PMT, Chanhassen, Minnesota), B (Ace Medical, Los Angeles, California), and C (Bremer Medical, Jacksonville, Florida) were single-use, shear-off devices that were designed to

measure 0.90 newton-meter (eight inch-pounds) of torque.

MICHAEL D. SMITH et al. J Bone Joint Surg Am 1996;78:231-8

©1996 by The Journal of Bone and Joint Surgery, Inc.

Devices D (Jerome Medical, Mount Laurel, New Jersey), E (PMT), and F (Bremer Medical) were fully adjustable devices that were tested at both 0.68 and 0.90 newton-meter (six and eight inch-

pounds) of torque.

MICHAEL D. SMITH et al. J Bone Joint Surg Am 1996;78:231-8

©1996 by The Journal of Bone and Joint Surgery, Inc.

Devices G (Levtech, Dallas, Texas) and H (Jerome Medical) were fixed spring-loaded devices that were designed to measure 0.68 newton-meter (six inch-pounds) of torque.

MICHAEL D. SMITH et al. J Bone Joint Surg Am 1996;78:231-8

©1996 by The Journal of Bone and Joint Surgery, Inc.

Devices I (Bremer Medical) and J-new (Ace Medical) were partially adjustable spring-loaded devices.

MICHAEL D. SMITH et al. J Bone Joint Surg Am 1996;78:231-8

©1996 by The Journal of Bone and Joint Surgery, Inc.

Box plots of the distributions of achieved torque across all trials in which the target torque was 0.68 newton-meter (six inch-pounds) compared with that across all trials in which the target

torque was 0.90 newton-meter (eight inch-pounds).

MICHAEL D. SMITH et al. J Bone Joint Surg Am 1996;78:231-8

©1996 by The Journal of Bone and Joint Surgery, Inc.

Graph showing the proportion of accurate trials and mean percentage deviation from the target torque for all devices tested.

MICHAEL D. SMITH et al. J Bone Joint Surg Am 1996;78:231-8

©1996 by The Journal of Bone and Joint Surgery, Inc.

Figs. 7-A and 7-B: One cause of error for the spring-loaded and fully adjustable devices was inaccurate placement of the calibration marks that guide the application of torque.

MICHAEL D. SMITH et al. J Bone Joint Surg Am 1996;78:231-8

©1996 by The Journal of Bone and Joint Surgery, Inc.

To obtain 0.90 newton-meter (eight inch-pounds) of achieved torque, the calibration dot was placed far beyond the correct marking.

MICHAEL D. SMITH et al. J Bone Joint Surg Am 1996;78:231-8

©1996 by The Journal of Bone and Joint Surgery, Inc.