SPECT in spine

General

Technetium 99m-methyl diphosphonate (99mTc-MDP)

Common bone agent
MDP is not significantly metabolised and is renally excreted;
Within 2–3 hours non‑skeletal activity clears, so renal function and hydration materially affect image quality and patient dose.
A bisphosphonate that diffuses into the extracellular space and chemisorbs onto hydroxyapatite crystals and calcium salts, especially at osteoid and osteocyte lacunae (mineralisation fronts).

Uptake is minimal near osteoclast‑dominant resorption sites.

Biodistribution is strongly time‑dependent:

Very early images emphasise vascular structures.
Early “soft‑tissue” phase (minutes) shows hyperaemia and soft‑tissue uptake.
Late phase (hours) is dominated by skeletal and genitourinary activity, reflecting osteoblastic turnover

Degenerative diseases

Facetogenic pain

Facet joints are common axial pain generators, but clinical exam and CT/MRI often cannot reliably identify the symptomatic level or side.

SPECT/CT can show focal facet hotspots and is used to target injections, with series reporting clinically meaningful reductions in pain scores after SPECT/CT‑guided facet injections.

Facet joints, characterized as true synovial joints with cartilaginous articular surfaces, are crucial for
spinal motion, load transmission, and stability.

They can generate an inflammatory response and activate nociceptive nerve endings in response to cartilage compression, leading to facetogenic pain

It frequently alters target selection compared with morphology‑based choices alone, but diagnostic medial branch or intra‑articular blocks remain necessary before definitive treatment.

A 52-year-old woman had lumbar back pain. Anteroposterior (A) and lateral (B) spine radiographs show mild multilevel degenerative disc narrowing most notable at L4 to L5 (arrowhead). Posterior planar 99m-methyl diphosphonate bone scan image (C) shows focal increased osteoblastic activity within the left lateral aspect of L5 vertebra. Axial noncontrast computed tomography (CT) (D) and fused axial (E) and coronal (F) single photon emission CT with CT images demonstrate increased osteoblastic activity within the left L4 to L5 facet joint with associated subchondral cysts and joint space narrowing compatible with degenerative facet arthropathy

Discogenic and endplate pain

SPECT/CT can demonstrate increased uptake in anterior vertebral body and endplates that correlates with degenerative disc changes and Modic‑type signal changes on MRI.

Intervertebral disc pathology in the absence of nerve root compression or segmental instability.

In the degenerated disc, the presence of radial fissures upregulates inflammatory modulators and growth factors that increase the density of nociceptive nerve fibers in the area of the tear

Case series describe using focal disc/endplate uptake to justify short‑segment fusion in otherwise multilevel degenerative disease.

Not all painful discs are SPECT‑positive and some asymptomatic levels may show uptake, so SPECT/CT is best used alongside MRI, discography (where used), and clinical assessment; it may also help refine indications for endplate‑targeting procedures such as basivertebral nerve ablation.

A 70-year-old man had previously undergone L3 to L5 decompression for lumbar spinal stenosis with leg dominant radicular pain. After the decompression, the patient presented with a new complaint of axial flexion-dominant mid-lumbar pain in the absence of leg symptoms. Advanced imaging demonstrated no significant residual/recurrent stenosis on sagittal and axial T2-weighted MRI sequences (A, B, C) and appropriate decompression on sagittal and axial computed tomography images without evidence of pars interarticularis fracture or subtotal facetectomy (D, E, and F). Single photon emission computed tomography with computed tomography findings demonstrated increased radiotracer uptake in the L3 to L4 disc (G and H). The L3 to L4 disc was determined to be the dominant pain generator, resulting in a discogenic pain pattern. The patient was then referred for further physical therapy and physical medicine and rehabilitation.

Fractures

Osteoporotic and insufficiency fractures

In osteoporotic vertebral compression fractures, SPECT/CT can distinguish metabolically active (acute/subacute) from chronic fractures and reveal additional active levels beyond those obvious on radiographs.

Presence of vertebral uptake has been associated with a higher likelihood of pain relief after vertebral cement augmentation and helps choose which level(s) to treat.

A 76-year-old woman presented with acute-onset low back pain. Anteroposterior (A) and lateral (B) spine radiographs show mild height loss at the level of the L1 vertebral body (arrow). Anterior (C) and posterior (D) planar 99mTc-MDP bone scan images show focal increased osteoblastic activity at L1 and L3 vertebral levels (arrows). Sagittal fused single photon emission computed tomography with computed tomography (E) demonstrates increased activity at the L1 and L3 vertebral bodies. Noncontrast computed tomography images (F) demonstrate corresponding height loss (arrowhead) at the L1 vertebral body and inferior endplate irregularity and linear sclerotic changes (arrow) at the L3 vertebral body, compatible with healing vertebral compression fractures.

For sacral insufficiency fractures, SPECT/CT can depict the characteristic sacral uptake pattern and is particularly useful when MRI is unavailable, contraindicated, or limited by metal artefact after lumbosacral fusion.

71-year-old woman with low back, buttock, and bilateral leg pain. Lateral (A) spine radiograph shows L4 to L5 instrumentation with prior interspinous spacer and unilateral pedicle screws with interbody device (arrow) without evidence of complications. Lumbar spine T2 sagittal magnetic resonance image (B) shows no central canal stenosis, also seen on axial (not displayed) and metal artifact at L4 to L5 (arrow) related to instrumentation. Posterior planar 99mTc-MDP bone scan (C) and axial fused single photon emission computed tomography with computed tomography (D) images show H-shaped radiotracer uptake within the sacrum, with associated sclerotic changes on computed tomography (E), compatible with sacral insufficiency fracture.

Pars defects in adolescents and young adults

In young athletes with extension‑related low back pain, SPECT/CT can localize metabolically active pars interarticularis stress injuries more accurately and more quickly than planar bone scan alone, potentially reducing delay to bracing or activity modification.

It is diagnostic only when there is active bone turnover; established fibrous nonunions without activity will appear “cold” on SPECT and rely on CT morphology.

A 14-year-old male football player presenting with low back pain. Anteroposterior (A) and lateral (B) spine radiographs show subtle lucency on the lateral view within the L5 pars interarticularis (arrow). Posterior planar 99mTc-MDP bone scan image (C) was unremarkable. Axial noncontrast computed tomography (CT (D) and fused single photon emission CT with CT (E) images demonstrate bilateral pars defects, with asymmetric increased activity within the left pars defect,
respectively

Previously operated spine

Pseudarthrosis and hardware issues

Focal increased uptake along a fusion construct, at a motion segment, or around screws/cages suggests ongoing bone turnover compatible with nonunion or hardware loosening.

When plain films and CT are equivocal, SPECT/CT can increase confidence about whether a motion segment is truly active and symptomatic, but findings still need to be integrated with symptoms and examination.

Adjacent‑segment and alternative pain sources

SPECT/CT can highlight hyperactive adjacent facets, endplates, or sacroiliac joints in patients with prior fusion, helping explain new or shifted pain patterns.

This can support targeted injections or limited extension of fusion rather than broad multilevel revision based only on degenerative changes on CT/MRI.

Role in revision planning

In patients being considered for revision surgery, SPECT/CT can narrow the focus to one or two metabolically active levels, providing a biologic rationale for a limited revision strategy.

It remains an adjunct rather than a stand‑alone gatekeeper: indications for revision should still rest on the combination of clinical picture, standard imaging, and, where appropriate, confirmatory diagnostic blocks.

A 56-year-old woman presented with low back pain after prior L4 to S1 posterior instrumented fusion and subsequent standalone L3 to L4 anterior lumbar interbody fusion with anterior plate fixation. Lateral lumbar spine radiograph (A) shows fractured screw related to anterior instrumentation at the level of L4 (arrow). Sagittal T2 magnetic resonance imaging (B) shows no evidence of acute central canal stenosis and metal artifact (arrow) related to instrumentation. Sagittal noncontrast computed tomography (C) demonstrates fractured screw into the L4 vertebral body and sclerotic changes within the bone. Fused sagittal and coronal images demonstrate increased osteoblastic activity and radiotracer uptake within the L3 to L4 disc space concerning for hardware loosening and pseudoarthrosis

A 54-year-old man presented with persistent axial mechanical neck pain after previously undergoing C4-7 anterior cervical discectomy and fusion 2 years earlier. Anteroposterior (A) and lateral (B) plain films demonstrated all implants from the index surgery were appropriately positioned. Sagittal (C) and coronal computed tomography (CT) reconstructions did not demonstrate any bridging bone across the C4-5 disc space. No residual/recurrent central stenosis was seen on mid-sagittal T2-weighted magnetic resonance imaging (E). Sagittal (F) and coronal (G) single photon emission CT with CT images demonstrated increased radiotracer uptake at the C4-5 level, which suggested symptomatic pseudarthrosis. The patient subsequently underwent posterior cervical instrumented fusion with good result.

Predicting spinal fusion

The scan is used to find focal “hot” levels (facets, endplates, short segments) in patients who otherwise have multilevel degenerative change on MRI/CT and non‑specific clinical findings.

Fusion is then aimed at only these active levels, rather than performing extensive multilevel constructs based purely on morphology.

Focal SPECT/CT uptake in a limited number of segments can support the decision to perform short‑segment fusion for axial pain and may reduce the tendency toward unnecessarily extensive fusion.

Malignancy

Used

In spinal malignancy to better characterize suspected metastases

Clarifying whether a solitary spinal “hot spot” in an oncology patient is malignant, degenerative, or infectious, thereby guiding biopsy, radiotherapy, or systemic treatment decisions.

Distinguish them from degenerative change
Direct targeted treatment when there are multiple lesions or equivocal findings on planar bone scans or SPECT alone.

Diagnostic advantages in spinal metastases

Compared with planar bone scintigraphy or SPECT alone, SPECT/CT markedly reduces the number of indeterminate vertebral lesions by adding CT morphology to the functional “hot spot,” allowing separation of benign causes (degenerative endplates, facet arthropathy, infection) from true metastases.
In spine cancer patients with solitary or few equivocal lesions on planar bone scan, SPECT/CT substantially increases diagnostic sensitivity and overall accuracy while lowering the proportion of equivocal reports.
MRI remains the gold standard for spinal metastasis, but SPECT/CT generally outperforms planar scintigraphy and approaches MRI specificity; it is especially useful when MRI is unavailable or contraindicated, or when there are numerous similar‑appearing lesions and a dominant pain generator needs to be identified.

A 49-year-old man had a history of tonsillar squamous cell carcinoma and low back pain. Sagittal T1 (A) and STIR (B) magnetic resonance images show low T1 and high T2 signal changes within the L3 vertebral body (arrows). Posterior planar 99mTc-MDP bone scan image (C) shows increased osteoblastic activity at L3 vertebral body. Coronal fused single photon emission computed tomography with computed tomography image (D) demonstrates an osteoblastic lesion within the right L3 vertebral body with associated sclerotic changes on computed tomography (E) compatible with metastatic bone lesion.

Pyogenic infection of spin

Diagnostic role

Pyogenic spondylodiscitis often presents with nonspecific back pain and can be difficult to distinguish from Modic endplate changes on MRI, which contributes to diagnostic delay.
Bone and gallium SPECT/CT can show increased tracer uptake at the infected disc–endplate complex and adjacent vertebrae, and the CT component clarifies whether activity is centred in bone, disc, or surrounding soft tissues.
Across reported series, gallium–MDP SPECT/CT has shown high sensitivity and specificity compared with final clinical diagnosis and performs roughly comparably to MRI for detecting vertebral osteomyelitis, though PET/CT may be superior where available.
Indium‑labelled biotin SPECT (with or without CT) is another option that offers good sensitivity and specificity and better localisation than planar imaging, but its use is limited by tracer availability.

Practical use and limitations

SPECT/CT is most useful when MRI is contraindicated, unavailable, or equivocal, or when there is a need to separate bone from soft‑tissue involvement to guide biopsy or surgical planning.
It reduces equivocal nuclear medicine studies by fusing metabolic and anatomical data, but it does not replace MRI as the primary modality; instead it serves as a complementary problem‑solving tool in suspected pyogenic spinal infection.

Sacroiliac joint dysfunction

In peripartum or post‑traumatic sacroiliac joint incompetence, SPECT/CT can show focal sacroiliac tracer uptake that reflects chronic ligamentous microtrauma and calcium deposition.

Cohort data suggest high sensitivity and specificity for clinically defined sacroiliac joint dysfunction, with tracer burden correlating with symptom severity and likelihood of requiring more invasive treatment, although routine use is not yet incorporated into formal guidelines.