GC226 Lumbar Spine Pathology: Part C
Lumbar spine pathology Part C encompasses conditions such as lumbar spinal stenosis, spondylolisthesis, and cauda equina syndrome that cause narrowing or structural displacement of the lower spinal canal, leading to neurological compromise.
Investigations for Lumbar Spine Pathology — GC 226 Part C
Big Idea: This lecture is entirely about how to investigate a patient with back pain — from blood tests to imaging, and crucially, how to interpret what you find. The overarching message is that investigations must always be correlated with clinical findings. Imaging alone can mislead you: many asymptomatic people have "abnormal" MRIs, and many patients with genuine pathology have normal X-rays early on. The lecture teaches a systematic approach to reading lumbar spine X-rays (the A–J mnemonic) and understanding when and why to order CT, CT myelogram, and MRI. [1]
Learning Objectives (derived from slides + related Ortho lecture):
- Know which blood investigations to order for back pain and why each matters [1] [2]
- Understand the role and limitations of plain X-rays in lumbar spine pathology [1]
- Apply the systematic A–J mnemonic for reading lumbar spine radiographs [1]
- Know when to escalate to CT, CT myelogram, and MRI [1]
- Interpret key MRI features of the lumbar spine [1]
- Understand the principle: treat symptoms, not images [1]
How this fits into clinical practice and exams: This is the "investigations" arm of the lumbar spine pathology series. In exams, you will be shown X-rays and MRI images and asked to identify pathology (spondylolisthesis, disc herniation, stenosis, tumour, infection). You will also be asked "what investigations would you order?" for a given clinical scenario — the blood tests and the rationale behind each are directly examinable. The 2023 Minicase Case 3 was literally this lecture in exam form. [3]
1. Blood Investigations
High Yield: The lecture explicitly lists the following blood tests for investigating back pain [1]:
| Test | What it Detects | Why it Matters / Mechanism |
|---|---|---|
| WCC (White Cell Count) | Infection, haematological malignancy | Elevated neutrophils suggest bacterial infection (e.g. discitis, epidural abscess). However, WCC can be normal in chronic/indolent infections (e.g. TB spondylitis). |
| ESR (Erythrocyte Sedimentation Rate) | Non-specific inflammation | The lecture notes: "High blood fibrinogen causes RBC to stick to each other" — this is the mechanism. In infection, malignancy, or inflammatory conditions, the liver produces acute-phase proteins including fibrinogen. Fibrinogen neutralises the negative charge on RBCs → RBCs aggregate (rouleaux formation) → sediment faster. ESR is slow to rise and slow to fall — it's a "trend" marker. Very high ESR ( > 100) → think malignancy (especially myeloma), severe infection, or autoimmune disease. [1] |
| CRP (C-Reactive Protein) | Acute-phase reactant | The lecture notes: "6–8 hours after onset of infection" — CRP rises faster than ESR and falls faster, making it more useful for monitoring acute infection. Produced by hepatocytes in response to IL-6. In back pain, elevated CRP + fever → infection until proven otherwise. [1] |
Why ESR and CRP Together?
ESR and CRP measure overlapping but different aspects of inflammation. ESR is influenced by fibrinogen, immunoglobulins, and anaemia (all raise it non-specifically). CRP is a more direct measure of acute inflammation. In clinical practice, you order both because:
- CRP rises and falls quickly → useful for acute monitoring
- ESR stays elevated longer → useful for chronic disease (e.g. myeloma, TB)
- A markedly raised ESR with normal CRP → think myeloma (paraproteins cause rouleaux but myeloma doesn't always trigger CRP)
| Test | Clinical Relevance |
|---|---|
| Alkaline Phosphatase (ALP) | Elevated in osteoblastic metastases (especially prostate cancer), Paget's disease, osteomalacia. ALP is produced by osteoblasts during bone formation — if bone is being destroyed and rebuilt (as in metastases), ALP rises. |
| Globulin level | Elevated globulins → think myeloma, chronic infection, autoimmune disease. The ratio of albumin:globulin is disrupted. In myeloma, the paraprotein (monoclonal immunoglobulin) inflates the globulin fraction. |
| Calcium and Phosphate (CaPO4) | Hypercalcaemia → metastatic bone disease, myeloma, hyperparathyroidism. The pattern matters: ↑Ca + ↓PO4 → primary hyperparathyroidism; ↑Ca + normal/↑PO4 → bony metastases (bone destruction releases both). |
| Serum Protein Electrophoresis (SPEP) | Detects monoclonal bands (M-protein) → myeloma, MGUS. This is the definitive screening test when myeloma is suspected. An elderly patient with back pain + anaemia + renal impairment + high globulin → SPEP is mandatory. |
| Tumour markers | PSA (prostate), CA 125 (ovarian), CEA (colorectal), AFP (hepatocellular) — used when you suspect metastatic disease to the spine. The primary cancer dictates which marker you order. |
Why These Specific Blood Tests?
The lecture is building a framework: when back pain has red flags (age > 50 or < 20, weight loss, night pain, fever, history of cancer), you need to exclude malignancy and infection. These blood tests are the first-line screen before you even get advanced imaging. A normal WCC/CRP/ESR in a well patient with mechanical back pain is reassuring. But any elevation demands further investigation.
2. Plain Radiographs (X-ray)
High Yield: The lecture lists four key considerations for X-ray [1]:
- Correlation with symptoms — An X-ray finding is only meaningful if it matches the clinical picture
- Positive history — X-ray is more useful when there is a specific clinical indication (trauma, red flags)
- Malignancy and infection — X-ray can show lytic/blastic lesions, vertebral collapse, endplate erosion
- False assurance? — A normal X-ray does NOT exclude serious pathology (e.g. early metastases need 30–50% bone loss before visible on X-ray; soft tissue pathology like disc herniation is invisible on X-ray)
The 'False Assurance' Trap
This is a classic exam concept. Students (and patients) often think "the X-ray is normal, so there's nothing wrong." But X-rays cannot show:
- Disc herniation (soft tissue)
- Early infection (discitis takes 2–4 weeks to show on X-ray)
- Small metastases ( < 1 cm, or < 30–50% bone destruction)
- Neural compression
- Spinal cord pathology
A "normal" X-ray in a patient with red flags requires further investigation (typically MRI). Never let a normal X-ray stop you from pursuing a sinister diagnosis.
High Yield: The lecture presents the A–J mnemonic for systematic X-ray reading [1]:
| Letter | Structure | What to Look For |
|---|---|---|
| A | Alignment | Trace the anterior vertebral line, posterior vertebral line, spinolaminar line, and spinous process line. Any step-off indicates spondylolisthesis (anterior translation) or retrolisthesis (posterior translation). |
| B | Bony structures | Look at each vertebral body for fractures, lytic lesions, sclerotic lesions, and abnormal morphology. |
| C | Collapse | Vertebral body height: compare anterior to posterior height. Wedge fracture = anterior height loss. Burst fracture = loss of both anterior and posterior height. Pathological collapse = consider metastases, osteoporosis, infection. |
| D | Disc space | Disc height should generally be: L4/5 > L5/S1 > L3/4 [4]. Narrowed disc space → disc degeneration. Complete loss of disc space → infection (discitis) or advanced degeneration. |
| E | End plates | End plates should be smooth and intact. Irregularity → Schmorl's nodes (disc herniating into vertebral body), infection, or tumour. End plate erosion is a hallmark of pyogenic spondylodiscitis. |
| F | Foramen | Neural foramina seen best on lateral view. Narrowed foramina → osteophyte encroachment or disc bulge → foraminal stenosis → nerve root compression. |
| G | Girdle (SIJ — Sacroiliac Joint) | Look at the SIJs on the AP view. Sacroiliitis (blurred/sclerotic joint margins) → ankylosing spondylitis, psoriatic arthritis, reactive arthritis. This is especially relevant in young patients with inflammatory back pain. |
| H | Height | Overall vertebral body height and disc height. Progressive loss of height suggests compression fractures (osteoporotic or pathological). |
| I | Iliopsoas | The psoas shadow is visible on AP X-ray. Psoas abscess (TB, pyogenic) → loss or enlargement of psoas shadow. This is a subtle but important sign. |
| J | Interarticularis (Pars interarticularis) | Best seen on oblique view ("Scotty dog"). A break in the pars → spondylolysis. Bilateral pars defects → spondylolisthesis (anterior slippage of vertebral body). The "collar" on the Scotty dog represents the pars defect. |
The lecture shows a case of lumbar spondylosis with [1]:
- Pedicle — identified on AP view
- SI joint — identified
- L3/4 retrolisthesis — posterior slippage of L3 on L4
- L4/5 spondylolisthesis — anterior slippage of L4 on L5
Why this matters: Spondylolisthesis and retrolisthesis can coexist at adjacent levels, creating a complex biomechanical picture. The direction of slippage matters because it determines which structures are compressed:
- Anterolisthesis (spondylolisthesis): narrows the central canal and foramina → can cause spinal stenosis and radiculopathy
- Retrolisthesis: less common, typically associated with disc degeneration, can narrow the foramen from behind
3. Advanced Imaging
High Yield from the lecture [1]:
- CT is best for: fracture configuration — bony detail is superior to MRI
- CT shows bone architecture in fine detail → critical for surgical planning (e.g. burst fractures, pedicle screw placement)
- CT cannot adequately assess soft tissues like discs and neural structures
Listed in the lecture as an imaging modality [1]:
- Involves intrathecal contrast injection + CT
- Used when MRI is contraindicated (e.g. pacemaker, severe claustrophobia) or when dynamic imaging is needed
- Shows the outline of the thecal sac and nerve roots → identifies compression
- Largely replaced by MRI in modern practice but still appears in exams
High Yield from the lecture — MRI is indicated for [1]:
- Nerve compression — the gold standard for visualising neural structures
- Sinister pathologies — tumours, infections, inflammatory conditions
- Confirmation of lesions — correlating clinical findings with structural pathology
MRI is a Confirmatory Test, Not a Screening Tool
The lecture explicitly states: "Imaging modalities should be confirmatory tests" [1]. This means:
- You should have a clinical hypothesis BEFORE ordering MRI
- You must explain to patients why you are ordering MRI (to avoid unnecessary anxiety)
- Incidental findings on MRI (disc bulges, minor degeneration) are extremely common in asymptomatic people — up to 60% of 40-year-olds have disc bulges on MRI with no symptoms
"Treat symptoms not images" is a direct quote from the lecture [1]. This is the most important principle — if the MRI shows a disc bulge but the patient's symptoms don't match, do NOT operate on the image.
The lecture identifies the following structures on axial and sagittal MRI [1]:
Sagittal MRI Features:
- Black disc — loss of T2 signal in the disc indicates disc degeneration (loss of water content in the nucleus pulposus). A healthy disc is bright (white) on T2 because of high water content.
- Vertebral body alignment
- Disc herniation — visible as material extending beyond the disc margin
Axial MRI Features:
| Structure | Location / Significance |
|---|---|
| Inferior Vena Cava | Anterior, right of midline |
| Aorta | Anterior, left of midline |
| Subcutaneous fat | Superficial, bright on T1 |
| Psoas muscle | Anterolateral to vertebral body |
| Superior articular facet | Part of the facet joint complex |
| Inferior articular facet | Articulates with superior facet |
| Facet joint with fluid | Fluid in facet joint → synovitis/degeneration (bright on T2) |
| Intervertebral disc | Central, between vertebral bodies |
| Disc herniation | Focal protrusion beyond the disc margin |
| Ligamentum flavum | Posterior, can hypertrophy → spinal stenosis |
| Spinous process | Most posterior midline structure |
| Lamina | Connects spinous process to pedicle |
| Transverse process | Lateral bony projection |
Additional MRI features from the lecture [1]:
- Pedicle — identified on axial images
- Fatty infiltration at paraspinal muscles — sign of chronic denervation or disuse atrophy; bright on T1
- Nerve roots — visualised within the thecal sac and foramina
- CSF — bright on T2, surrounds the nerve roots
- Dural sac — contains CSF and cauda equina
The "Mickey Mouse sign" on axial MRI at lumbar levels: the cross-section of the dural sac shows the cauda equina nerve roots clustered centrally (the "face") with the traversing nerve roots laterally (the "ears"). This is described in senior notes as a way to assess for adequate CSF space around nerves — loss of this sign suggests stenosis. [4]
High Yield — direct lecture quote [1]:
- "Treat symptoms not images"
- "Imaging modalities should be confirmatory tests"
- "Must explain to patients the reason for MRI"
Why this is emphasised:
- Overdiagnosis problem: Studies show that 30–60% of asymptomatic adults have disc bulges, and up to 90% of people over 60 have disc degeneration on MRI. If you treat the image, you will operate on people who don't need surgery.
- Patient anxiety: Telling a patient "you have a slipped disc" or "your spine is degenerating" without context causes unnecessary fear. The lecture insists you must explain why the MRI is being done and what the findings mean in context.
- Clinical correlation is king: The investigation that matters most is the one that confirms your clinical suspicion. If physical exam shows L5 radiculopathy and MRI shows L4/5 disc herniation compressing the L5 root — now you have a diagnosis. If MRI shows L3/4 bulge but the patient has L5 symptoms — the MRI finding is irrelevant.
Combining lecture content with related material, here is the decision pathway:
6. Clinical Approach Summary
| Clinical Feature | Investigation Triggered | Why |
|---|---|---|
| Age > 50 + new back pain | Blood tests + X-ray ± MRI | Increased risk of malignancy, osteoporotic fracture |
| History of cancer | Blood tests + MRI whole spine | Metastatic disease — MRI needed as 33% have multilevel involvement [5] |
| Fever + back pain | WCC, CRP, ESR + MRI urgently | Infection (discitis, epidural abscess) — X-ray is often normal early |
| Weight loss | SPEP, tumour markers + MRI | Myeloma, metastatic disease |
| Trauma | X-ray first, CT if fracture suspected | CT defines fracture configuration for surgical planning |
| Neurological deficit | MRI urgently | Cauda equina syndrome, cord compression — surgical emergency |
| Inflammatory pattern (young, morning stiffness > 30 min) | X-ray including SIJ + HLA-B27 + MRI SIJ | Ankylosing spondylitis — X-ray SIJ may be normal early → MRI SIJ shows bone marrow oedema [7] |
The 2023 Minicase Case 3 directly asked: "Name four red flag signs for back pain" [3]. Based on the lecture series:
- Age > 50 (or < 20 in some frameworks)
- History of malignancy
- Unexplained weight loss
- Fever / night sweats
- Night pain / pain at rest (unrelieved by lying down)
- Progressive neurological deficit
- Bladder / bowel dysfunction (cauda equina)
- Saddle anaesthesia
- History of IV drug use or immunosuppression
- Significant trauma (or minimal trauma in osteoporotic patient)
- Thoracic pain (more sinister than lumbar statistically)
- Duration > 6 weeks without improvement
7. Exam Intelligence
| Trap | Correct Understanding |
|---|---|
| "Normal X-ray means nothing is wrong" | X-ray has low sensitivity for early infection, small metastases, and all soft tissue pathology. MRI is needed when clinical suspicion is high. |
| Ordering MRI for all back pain | MRI is a confirmatory test. Most mechanical back pain resolves in 6 weeks without imaging. |
| Treating MRI findings without clinical correlation | "Treat symptoms not images." Disc bulges are common in asymptomatic people. |
| Confusing spondylolysis, spondylolisthesis, and spondylosis | Spondylolysis = pars interarticularis defect (stress fracture). Spondylolisthesis = anterior slip of one vertebra on another (often due to bilateral spondylolysis). Spondylosis = degenerative changes (osteophytes, disc narrowing). |
| Forgetting SPEP in elderly patient with back pain | Myeloma is a common cause of back pain in the elderly — must order SPEP and globulin level. |
| ESR vs CRP timing | ESR rises slowly (days), falls slowly. CRP rises within 6–8 hours, falls quickly. CRP is better for acute monitoring. |
| Modality | Best For | Not Useful For |
|---|---|---|
| X-ray | Alignment, fractures, degenerative changes, SIJ | Soft tissue, early infection, neural compression |
| CT | Fracture configuration, bony detail | Soft tissue, neural structures |
| CT Myelogram | Neural compression (when MRI contraindicated) | Intramedullary pathology |
| MRI | Disc herniation, neural compression, infection, tumour, cord pathology | Fine fracture lines (CT is better) |
Past Paper Questions
Stem: "A middle-aged obese man developed acute back pain, urinary incontinence, buttock numbness and bilateral lower limb weakness after lifting heavy objects at work. What is the MOST LIKELY diagnosis?"
- A. Aortic dissection
- B. Cauda equina syndrome ✓
- C. Psoas abscess
- D. Transverse myelitis
Rationale: The triad of urinary incontinence + saddle anaesthesia (buttock numbness) + bilateral lower limb weakness after heavy lifting = cauda equina syndrome from acute central disc herniation. This is a surgical emergency requiring urgent MRI and decompression. Aortic dissection causes tearing pain and would not give saddle anaesthesia. Psoas abscess presents more insidiously with fever. Transverse myelitis is usually subacute and would give UMN signs below the lesion.
Stem: "You are a resident working in the Department of Orthopaedics and Traumatology. Mr. Chan, a 75-year-old man presented to you with a history of lower back pain for a few weeks, started to have low-grade fever since last week. His body temperature was 38°C. Urinalysis was normal."
Q1: "Name four red flag signs for back pain." (8 marks)
Markscheme answer: Any four of: age > 50, fever, night pain, weight loss, history of malignancy, neurological deficit, bladder/bowel dysfunction, immunosuppression, thoracic pain, pain at rest, progressive symptoms
Q2: "Name three MOST LIKELY differential diagnoses for this patient." (6 marks)
Markscheme answer:
- Spinal infection (spondylodiscitis / epidural abscess)
- Spinal metastasis / vertebral tumour
- TB spondylitis (Pott's disease) (Key: elderly + back pain + fever → infection is top differential)
Q3: "Name three investigations you would like to offer to this patient." (6 marks)
Markscheme answer:
- Blood tests (WCC, CRP, ESR)
- Plain X-ray lumbar spine
- MRI lumbar spine (Directly from this lecture's content)
Stem (continued): "Clinical examination demonstrated the pain was localised to L2/3 and tender on percussion. There was no neurological deficit. Blood results showed elevated leukocyte counts and C-reactive protein. Imaging examinations were arranged."
(This section then shows imaging for interpretation — the investigations taught in this lecture are exactly what was tested.)
Stem: "A 56-year-old gentleman, was receiving chemotherapy for his metastatic lung cancer. He was admitted through the accident and emergency department for severe low back pain. His lower limb power was 3 out of 5. A magnetic resonance imaging of the spine noted a pathological collapse of the L1 vertebra with cord compression. What is the MOST APPROPRIATE initial management for this gentleman?"
- A. Arrange urgent staging FDG PET-CT scan
- B. Obtain an urgent bone scan to evaluate for other bony metastatic sites
- C. Start high-dose steroids and arrange urgent orthopaedic consultation for decompressive surgery ✓
- D. Stereotactic radiotherapy to L1
Rationale: This patient has metastatic spinal cord compression — a surgical/oncological emergency. The immediate management is high-dose dexamethasone (to reduce oedema around the cord) + urgent surgical consultation for decompression ± stabilisation. Staging and bone scans can wait. Radiotherapy alone is for stable spines or patients with poor prognosis. This integrates the lecture's teaching on MRI for confirmation of sinister pathology + the management principles from Part D/E of the lecture series.
Stem: "A 26-year-old man with a history of recurrent uveitis, alternating buttock pain, and bilateral plantar fasciitis has complained of lower back pain for 6 months. You suspect a diagnosis of ankylosing spondylitis."
(a) "Name four characteristics of back pain in this condition." (4 marks)
Markscheme: Insidious onset, age < 40, morning stiffness > 30 min, improves with exercise, does not improve with rest, nocturnal pain (wakes patient in second half of night)
(b) "Lumbosacral spine radiograph of the man was normal. Name two investigations that you would perform to make the diagnosis." (4 marks)
Markscheme: MRI sacroiliac joints (shows bone marrow oedema before structural damage), HLA-B27
Relevance to this lecture: This question tests the "G" in the A–J mnemonic (Girdle/SIJ) and the principle that normal X-ray does not exclude disease — MRI is needed as a confirmatory test. [1] [7]
Stem: "A 50-year-old business man presented to the Accident and Emergency Department with severe low back pain. He had noticed weight gain over the past few months. X-ray showed osteopenia and wedge fracture of the 3rd lumbar vertebra. Further questioning revealed that he had been receiving frequent injections for osteoarthritis of his knee for over 1 year. Which of the following is the MOST LIKELY cause of his osteoporosis?"
- A. Hyperparathyroidism
- B. Hypogonadism
- C. Hypothyroidism
- D. Iatrogenic due to exogenous steroid ✓
Rationale: Frequent joint injections = corticosteroid injections. Weight gain + osteoporosis + wedge fracture in a relatively young man = iatrogenic Cushing's/steroid-induced osteoporosis. The X-ray shows "C" (Collapse) from the A–J mnemonic. This tests the principle that the X-ray finding must be correlated with clinical history.
Stem: "A 70-year-old man has a history of chronic neck pain. This time, he sustains a fall on level ground, causing hyper-extension of his neck. Plain X-rays of his cervical spine show multiple osteophytes and narrowing of the spinal canal. Magnetic resonance imaging studies showed hyperintense signals on T2 sequence within the cervical spinal cord. What is MOST LIKELY to be present on clinical examination?"
- A. Clumsy hand movement ✓
- B. Foot drop
- C. Loss of proprioception in lower limbs
- D. Urinary retention
Rationale: T2 hyperintensity in the cord = cord oedema/myelopathy. Cervical myelopathy classically presents with "myelopathic hand" — clumsy, loss of dexterity (10-second test, finger escape sign). While loss of proprioception and urinary retention can occur, clumsy hand is the most likely early finding. This question tests MRI interpretation (T2 signal = pathology in the cord) which is the same principle taught in this lecture for lumbar imaging.
High Yield Summary
Core Principles from GC 226 Part C:
-
Blood tests for back pain: WCC, ESR (fibrinogen-mediated rouleaux → slow rise/fall), CRP (rises 6–8 hours, fast rise/fall), ALP, globulin, CaPO4, SPEP, tumour markers — ordered when red flags are present
-
X-ray: The A–J mnemonic — Alignment, Bony structures, Collapse, Disc space, End plates, Foramen, Girdle (SIJ), Height, Iliopsoas, Interarticularis (pars)
-
X-ray limitations: Cannot show soft tissue pathology; can give false assurance; needs 30–50% bone loss before lytic lesions visible; must correlate with symptoms
-
Advanced imaging: CT → fracture configuration; CT myelogram → when MRI contraindicated; MRI → nerve compression, sinister pathology, confirmatory
-
MRI anatomy: Black disc = degeneration; know the axial anatomy (IVC, aorta, psoas, facets, ligamentum flavum, disc, nerve roots, CSF, dural sac)
-
THE golden rule: "Treat symptoms not images" — imaging is confirmatory, not diagnostic in isolation
-
Must explain to patients why MRI is ordered — avoid unnecessary anxiety from incidental findings
Active Recall - Lumbar Spine Investigations
[1] Lecture slides: GC 226. Lumbar Spine Pathology_Part C.pdf (all pages) [2] Lecture slides: Ortho and Trauma - Spine.pdf (p2, p75) [3] Past papers: 2023 Fourth Summative Minicase.pdf (pp.17–24, Case 3) [4] Senior notes: Maksim Surgery Notes.pdf (p225) [5] Senior notes: Ryan Ho Neurology.pdf (p170) [6] Senior notes: Ryan Ho Fundamentals.pdf (p145, p148) [7] Past papers: 2020 Fourth Summative SAQ.pdf (p6, Q5) [8] Past papers: 2021 Fourth Summative Assessment MCQ.pdf (p25, Q70) [9] Past papers: 2025 Fourth Summative MCQ.pdf (p24, Q61; p40, Q88) [10] Past papers: 2024 Fourth Summative MCQ.pdf (p13, Q31) [11] AOS material: AOS - Radiology.pdf (p34–35)
GC226 Lumbar Spine Pathology: Part B
Lumbar spine pathology Part B encompasses conditions such as lumbar disc herniation, spinal stenosis, spondylolisthesis, and cauda equina syndrome that cause low back pain, radiculopathy, or neurological deficits due to structural or degenerative changes in the lumbar region.
GC226 Lumbar Spine Pathology: Part D
Lumbar spine pathology Part D encompasses advanced degenerative, infectious, neoplastic, and inflammatory conditions of the lumbar spine, including spinal stenosis, spondylolisthesis, discitis, and metastatic disease, with emphasis on diagnostic evaluation and management strategies.