J Korean Neurosurg Soc.  2018 Mar;61(2):258-266. 10.3340/jkns.2017.0188.

Sacral Insufficiency Fractures: How to Classify?

  • 1Hannover Region Public Health Department, Hannover Region, Hannover, Germany. gesabakker@gmx.de
  • 2Department for Radiology and Neuroradiology, KRH Nordstadt, Hannover, Germany.
  • 3Institute for Medical Statistics, Computer Science and Epidemiology IMSIE, University of Cologne, Cologne, Germany.
  • 4Department of Traumatology and Orthopedics, KRH Nordstadt, Hannover, Germany.


The diagnosis of insufficiency fractures of the sacrum in an elder population increases annually. Fractures show very different morphology. We aimed to classify sacral insufficiency fractures according to the position of cortical break and possible need for intervention.
Between January 1, 2008 and December 31, 2014, all patients with a proven fracture of the sacrum following a low-energy or an even unnoticed trauma were prospectively registered : 117 females and 13 males. All patients had a computer tomography of the pelvic ring, two patients had a magnetic resonance imaging additionally : localization and involvement of the fracture lines into the sacroiliac joint, neural foramina or the spinal canal were identified.
Patients were aged between 46 and 98 years (mean, 79.8 years). Seventy-seven patients had an unilateral fracture of the sacral ala, 41 bilateral ala fractures and 12 patients showed a fracture of the sacral corpus : a total of 171 fractures were analyzed. The first group A included fractures of the sacral ala which were assessed to have no or less mechanical importance (n=53) : fractures with no cortical disruption ("bone bruise") (A1; n=2), cortical deformation of the anterior cortical bone (A2; n=4), and fracture of the anterolateral rim of ala (A3; n=47). Complete fractures of the sacral ala (B; n=106) : parallel to the sacroiliac joint (B1; n=63), into the sacroiliac joint (B2; n=19), and involvement of the sacral foramina respectively the spinal canal (B3; n=24). Central fractures involving the sacral corpus (C; n=12) : fracture limited to the corpus or finishing into one ala (C1; n=3), unidirectional including the neural foramina or the spinal canal or both (C2; n=2), and horizontal fractures of the corpus with bilateral sagittal completion (C3; n=8). Sixty-eight fractures proceeded into the sacroiliac joint, 34 fractures showed an injury of foramina or canal.
The new classification allowes the differentiation of fractures of less mechanical importance and a risk assessment for possible polymethyl methacrylate leaks during sacroplasty in the direction of the neurological structures. In addition, identification of instable fractures in need for laminectomy and surgical stabilization is possible.


Insufficiency fractures; Sacrum; Classification; Cementoplasty

MeSH Terms

Fractures, Stress*
Magnetic Resonance Imaging
Polymethyl Methacrylate
Prospective Studies
Risk Assessment
Sacroiliac Joint
Spinal Canal
Polymethyl Methacrylate


  • Fig. 1 A : Type A-fractures of the sacral ala : A1 with bone bruise (MRI) without a visible fracture line in the CT-scan; A2 deformation of the anterior cortical bone without a cortical disruption; and A3 anterolateral rim fracture of the ala with up to 1 cm distance in the direction of the medial sacroiliac joint. B : A1 with bone bruise in MRI; A2 plasticity of the cortical bone; A3 anterolateral fracture of the ala with up to 1 cm distance in the direction of the medial sacroiliac joint (rim fracture). A1 arrow shows bone bruise; A2 arrow shows plastic deformation of the anterior cortex; A3 arrow shows compression fracture of the anteolateral rim of ala.

  • Fig. 2 A : Type B fractures of the sacral ala : B1 fracture parallel to the sacroiliac joint; B2 fracture involving the sacroiliac joint; and B3 fracture with an involvement of the neural foramina or the spinal canal. B : B1 fracture parallel to the sacroiliac joint; B2 fracture involving the sacroiliac joint; B3 fracture with a participation of two neural foramina. B1 arrows show fracture following the sacroiliac joint; B2 arrows show the fracture process in the ala; B3 arrows show the involvement of two neural foramina.

  • Fig. 3 A : Type C- or corpus-fractures : C1 fracture moves from anterior cortex dorsally or into the sacroiliac joint; C2 fracture with an unilateral involvement of the neural foramina or the spinal canal; and C3 is unstable and represents bilaterally sagittal fractures combined with a transverse leasion. B : C1 fracture of the corpus with an extension in the anterior direction; C2 and C3 bilateral fracture of the corpus with an involvement of the neural foramina which are connected by a transverse fracture. C1 arrows show the fracture development from anterior to the dorsal cortex; C2 and C3 arrows show the bilateral fracture of the corpus, the arrow in the middle shows the fracture connection by a transverse component.

  • Fig. 4 Sagittal dislocation of type C3 fracture in magnetic resonance imaging. Arrow shows the horizontal dislocation by the transverse corpus fracture.

  • Fig. 5 Patient number in the distribution of age groups containing 117 females (average age, 79.8 years) and 13 males (average age, 76.9 years); average age of all of 79.5 years (range, 46 to 98 years).

  • Fig. 6 Age range of 117 females (average age, 79.8 years) and 13 males (average age, 76.9 years) an average of all of 79.5 years (range, 46 to 99).

  • Fig. 7 Patient number and distribution of unilateral (unilat.) and bilateral (bilat.) ala fractures (types A and B) as well as of corpus fractures (type C).

  • Fig. 8 The most frequent fracture was the fracture of the ala parallel to the sacroiliac joint (type B1) followed by the anterolateral ala rim fracture (type A3). There was an involvement of the spinal canal or the neural foramina in 34 cases (B3, C2, and C3). A corpus fracture was seen in 12 cases, thereof eight patients with a combination of transverse and bilateral sagittal fractures (type C3).

  • Fig. 9 A : Insertion of PMMA-cement near neurological structures does normally not cause a leakage through the cortical bone. B : In rare cases an uninjured dura seems to stop the leakage. Temporary neurological sensations had been reported. C : If fractures reached the ventral border, a ventral passover was possible. Arrow in (A) shows PMMA-cement position inside the ala. Arrow in (B and C) show PMMA-leakage. PMMA : polymethyl methacrylate.



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