Biomechanical effects of transverse partial sacrectomy on the sacroiliac joints: an in vitro human cadaveric investigation of the borderline of sacroiliac joint instability.
METHODS
In vitro laboratory study.


OBJECTIVE
To measure the effects of transverse partial sacrectomies on the compressive and torsional stiffness of the sacroiliac joints.


BACKGROUND
Surgical treatment for sacral tumor of different location and nature includes partial or complete sacrectomy. Though the biomechanical investigations about the local destructive force of residual sacrum after partial sacrectomy have been reported, biomechanical properties of the residual sacroiliac joints after different transverse partial sacrectomies remain unknown.


METHODS
Seven fresh human cadaveric L5-pelves with normal bone mineral density were used in this study. Each specimen was tested in intact condition first, followed by a series of segmental transverse partial sacrectomies: under S2 partial sacrectomy (U-S2); U-(1/2)S2; U-S1; U-(1/2)S1; and right side sacroiliac joint resection (one-side). A material testing machine was used to apply 800 N compression and 7 Nm torsion loads through the L5/S1 joint. The resected dimensional area of sacroiliac joints and structural stiffness of the residual sacroiliac joints were analyzed.


RESULTS
Average percentages of the resected area of sacroiliac joints were 8.4% in U-S2, 15.1% in U-(1/2)S2, 24.8% in U-S1, and 72.3% in U-(1/2)S1, respectively. In compression U-S2 approximately one-side preserved 98.7%, 97.1%, 94.4%, 82.9%, and 55.2% of the initial stiffness of the sacroiliac joint, respectively. No significant differences were detected among intact, U-S2, U-(1/2)S2, and U-S1 (P > 0.05). However, compressive stiffness of U-(1/2)S1 and one-side was markedly less than that of intact, U-S2, and U-(1/2)S2 (P < 0.05). In Torsion U-S2 approximately one-side preserved 90.7%, 88.5%, 81.9%, 71.9%, and 44.5% of the initial sacroiliac joint stiffness, respectively. No significant differences were demonstrated among intact, U-S2, and U-(1/2)S2 (P > 0.05); However, U-S1, U-(1/2)S1 and one-side exhibited significantly less torsional stiffness than intact and U-S2 (P < 0.05).


CONCLUSIONS
In surgical treatment of distal sacral tumor, transverse partial sacrectomy involving S1 could result in rotational instability, and the resection level beyond (1/2)S1 further led to compressive instability. When the sacrectomy was at or above the S1/2 level, local reconstruction should be considered.
Yu
Binsheng
B
Department of Spine Surgery, First Affiliated Hospital of Sun Yat-sen University, Guangzhou, China. hpyubinsheng@hotmail.com
Zheng
Zhaomin
Z
Zhuang
Xinming
X
Chen
Hui
H
Xie
Denghui
D
Luk
K D K
KD
Lu
W W
WW
D000328:Adult; D001696:Biomechanical Phenomena; D002102:Cadaver; D019245:Compressive Strength; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology / Q000601:surgery*; D008023:Ligaments, Articular / Q000601:surgery; D008297:Male; D008875:Middle Aged; D010027:Osteotomy / Q000379:methods*; D012446:Sacroiliac Joint / Q000503:physiopathology / Q000601:surgery*; D012447:Sacrum / Q000601:surgery*; D054159:Torsion, Mechanical; D016474:Weight-Bearing