Sacral Insufficiency Fracture

Sacral insufficiency fractures are a relatively common fracture in elderly women that is notoriously difficult to diagnose due to nonspecific symptoms an insensitivity of plain films.
== Epidemiology ==
This condition classical affects osteoporotic elderly women. The mean age is 70-75, with almost all patients older than 55.
Other risk factors include prior pelvic radiation (prevalence 21-89%), prolonged glucocorticoid use, rheumatoid arthritis, multiple myeloma, Paget disease, renal osteodystrophy, and hyperparathyroidism. 
== Anatomy ==
The sacrum is a triangular bone and when talking about the broad group of traumatic sacral fractures, the sacrum is viewed as having three zones:
* Zone 1: The sacral ala lateral to the foraminae. The vast majority of sacral insufficiency fractures occur in this zone.
* Zone 2: the area involving the neural foraminae
* Zone 3: medial the the neural foraminae, containing the sacral bodies.
== Pathology ==
Insufficiency fractures are a subtype of stress fracture where normal stress is applied to bone with reduced elastic resistance. This is usually due to osteoporosis, which is usually primary. Other causes of insufficiency fractures are metastatic disease and bone marrow infiltration processes.
They most commonly affect the sacral ala, in a sagittal line lateral to the sacral foraminae and medial to the sacral iliac joints, called zone 1. There is an equal prevalence of unilateral versus bilateral fractures. In some cases there is a fracture line component in the axial plane.
The reason that the sacral ala are affected is because in osteoporosis there isn't uniform bone loss. There is relatively increased loss of bony trabeculae in the sacral alae compared to the vertebra bodies.
There are concomitant pubic rami fractures in 78% of affected individuals. There can also be additional fractures in the superior acetabulum and iliac wing. It is thought that the sacral ala fractures happen first, about 3-4 months prior to the pubic rami fractures. It is thought that the sacral ala fractures results in a cascade of abnormal biomechanics with disrupted in one area leading to increased stress elsewhere. The follow on pubic rami fractures more commonly have a prolonged course of healing.
== Clinical Features ==
=== History ===
In two thirds of patients there is no trauma, and when there is trauma it is usually minor. Patients will commonly have diffuse low back pain with radiation to the buttock, hip, or groin. The pain is usually exacerbated by weight bearing. 45% of patients have a history of malignancy.
=== Examination ===
Gait is usually antalgic. There may be lumbosacral spine tenderness and pain over the lateral aspect of the sacrum. There is pubic rami tenderness in the presence of associated pubic rami fractures. Sacroiliac provocation tests are often positive. There is usually no neurological deficit, however rarely patients can manifest with a sacral radiculopathy or even cauda equina syndrome.
== Investigations ==
=== Blood Tests ===
ALP may be slightly raised and can be useful if plain films are normal and high tech imaging can't be easily accepted. After diagnosis on imaging secondary causes of osteoporosis may need to be tested for: TSH, PTH, calcium, phosphorus, albumin, vitamin D, urinary calcium, creatinine, FBC, LFTs, CRP, ESR, and SPE.
=== Plan Films ===
Plain films are not very sensitive at picking up sacral insufficiency fractures, with them only being detected in 20-38% of cases.. Part of this is because dedicated sacral views are often not taken. The correct views are AP and lateral views of the pelvis plus/minus inlet and outlet views. When visible there is a vertical sclerotic band in zone 1 in 57% of cases, with a fracture line in 12% of cases.
=== High Tech Imaging ===
MRI has a sensitivity of close to 100%. It is very important that coronal oblique views of the sacrum are included. The fracture may be missed if "lumbar spine MRI" is requested. In New Zealand lumbar spine MRI and pelvis MRI are two separate scans for funding and insurance purposes.
CT has a sensitivity of 60-75%, however it can be helpful for surgical planning as well as differentiating between metastatic disease and fracture.
=== DEXA ===
Almost all patients will have severe osteopenia on DEXA imaging which is the gold standard for measuring bone mineral density.
== Management ==
=== Conservative care ===
Prolonged bedrest was traditionally recommended (for 3 to 6 months) however this has been questioned because of the potential for increased morbidity and increased bone resorption. For example DVTs occur in 29-61% of cases, and PE in 2-12%. Other complications of bedrest in elderly include sarcopenia, infection, and a multitude of other potential problems. Early mobilisation within the limits of pain may actually improve outcomes which makes sense from a biomechanical perspective as loading encourages bone growth. 
With the traditional approach recovery varies between 6 to 15 months. However 50% do not return to their premorbid state, and mortality is 14.3%. With early mobilisation most patients improve after 1-2 weeks and there is a significant pain reduction and increase in mobility after 6 months.
Conservative management therefore involves early mobilisation, walking aids such as walking frames, hydrotherapy, and traditional weightbearing exercises.
=== Medication ===
Prescribed analgesia may be required. There is caution with NSAIDs due to the demographics of the typical patient and theoretical concern for impairment in bone healing.
It is vital to manage the underlying osteoporosis. Usually antiresorptive medication (bisphosphanates are first line) and vitamin D are prescribed for preventative care. One case controlled study found that teriparatide improves pain, reduces analgesic use, and speeds fracture healing from 7.4 weeks to 13.6 weeks compared to control by 3 months.
=== Inverventions ===
Some surgeons have been exploring sacroplasty and balloon sascroplasty as surgical management options.
==Resources==
== References ==
Category:Fractures
Category:Pelvis, Hip and Thigh Conditions