High Yield Overview

Pyogenic Spondylodiscitis

Ininfection of the Intervertebral Disc and Adjacent Vertebral Bodies

S. aureusMost Common Organism

LumbarMost Common Region

50%Have Fever (Unreliable)

90%Back Pain Sensitivity

Classification (Routes of Spread)

Hematogenous

PatternMost common. Arterial (Skin/UTI/Resp) or Venous (Batson's Plexus).

TreatmentSystemic Abx

Direct Inoculation

PatternPost-operative or Lumbar Puncture.

TreatmentSource Control

Contiguous Spread

PatternFrom adjacent abscess or aorta.

TreatmentTreat Primary

Critical Must-Knows

Back pain + CRP elevation = Discitis until proven otherwise.
MRI with Gadolinium is the Gold Standard for diagnosis.
Do NOT start antibiotics before biopsy unless the patient is septic or has neurological compromise.
Biopsy yield is only ~50-70%. Negative biopsy may require open biopsy.
Treatment duration is typically 6 weeks minimum.

Examiner's Pearls

"
Batson's Venous Plexus is valveless - allows retrograde spread from pelvis/UTI.
"
The disc is avascular in adults - infection starts in the vertebral endplate.
"
IVDU patients are prone to Pseudomonas (Gram Negative).
"
Epidural Abscess is the most feared complication (Cord Compression).

Clinical Imaging

Imaging Gallery

Sagittal T1 Short T1 Inversion Recovery (A) and postcontrast T1 fat-saturated (B) images demonstrate confluent epidural enhancement with mass effect upon the thecal sac. There are also two small T2 hy — Sagittal T1 Short T1 Inversion Recovery (A) and postcontrast T1 fat-saturated (B) images demonstrate confluent epidural enhancement with mass effect uCredit: Moudgal V et al. via Open Forum Infect Dis via Open-i (NIH) (Open Access (CC BY))

Pyogenic spondylodiscitis.67-year-old woman with lower back pain. Axial T1-weighted imaging (T1WI) showed abnormal low signal intensity (arrow) (A), and axial T2-weighted imaging showed corresponding — Pyogenic spondylodiscitis.67-year-old woman with lower back pain. Axial T1-weighted imaging (T1WI) showed abnormal low signal intensity (arrow) (A), aCredit: Open-i / NIH via Open-i (NIH) (Open Access (CC BY))

Critical Errors

At a Glance

Pyogenic vs TB Spine

Feature	Pyogenic	Tuberculosis (Pott's)
Disc Space	Destroyed Early	Preserved Late
Levels	Usually 2 (contiguous)	Multiple (skip lesions)
Abscess	Small / Epidural	Large / Psoas (Cold Abscess)
Kyphosis	Less Common	Common (Gibbus)

Mnemonics

Mnemonic

DISCITISRisk Factors

Diabetes

Immunocompromised

IV Drug Use

Pseudomonas risk

Steroids

Chronic use

Cancer

Metastatic or primary

Infection

Recent UTI/Pneumonia

Trauma

Or surgery

Immunity

HIV/Chemo

Surgery

Post-op infection

Memory Hook:Who gets infected?

Mnemonic

SEC POrganisms

Staph aureus

Most common (over 50%)

E. coli

From UTI

Cutibacterium

Post-op (Slow growing)

Pseudomonas

IVDU

Memory Hook:Common bugs.

Mnemonic

BIOPSYManagement

Blood Cx

First step

Imaging

MRI Gadolinium

Off Abx

Hold until cultures

Percutaneous

CT Guided Biopsy

Surgery

If unstable/neuro/sepsis

Yield

Repeat if negative

Memory Hook:Workflow.

Overview and Epidemiology

Pathophysiology In adults, the intervertebral disc is avascular. Bacteria lodge in the end-arterioles of the vertebral metaphysis (endplate). The infection sets up an osteomyelitis, then breaks through the endplate into the disc, rapidly destroying it (proteolytic enzymes). From the disc, it spreads to the adjacent vertebra.

Spread

Hematogenous (Arterial): Nutrient arteries.
Hematogenous (Venous): Batson's Plexus (valveless venous system connecting pelvis/bladder to spine). Explains UTI link.

Epidemiology

Bimodal distribution (under 20yo and over 50yo).
Lumbar > Thoracic > Cervical.
Note: TB spine prefers Thoracic.

Pathophysiology and Mechanisms

The Intervertebral Disc

Adult: Avascular. Nutrition via diffusion from endplates.
Child: Vascular channels persist (explains direct discitis in children).

The Endplate

The "Metaphysis" of the spine.
Rich vascular loop system (slow flow) → Predisposes to bacterial lodging.

Venous Anatomy (Batson's Plexus)

A valveless system of vertebral veins.
Connections: It communicates freely with the pelvic, abdominal, and thoracic venous systems.
Mechanism: Increases in intra-abdominal or intra-thoracic pressure (e.g., coughing, straining, lifting) can reverse blood flow.
Clinical Relevance: This retrograde flow allows bacteria from the pelvis (UTI, Prostatitis) or abdomen to bypass the liver/lung filters and lodge directly in the spine.
This explains the strong association between Urinary Tract Infections and Vertebral Osteomyelitis.

Biomechanics

Infection weakens the anterior column (body/disc).
Leads to Kyphosis (Gibbus deformity).
If greater than 50% body destruction → Mechanical Instability.

Classification Systems

Polal Classification (Modified) Used for surgical decision making.

Type A: Discitis without neurological deficit or instability. (Conservative).
Type B: Associated with Epidural Abscess but Neurology intact. (Conservative/Surgery).
Type C: Neurological Deficit. (Surgery).
Type D: Spinal Instability / Deformity. (Surgery).

Clinical Assessment

History

Pain: Constant, non-mechanical (night pain), progressively worsening.
Constitutional: Fever, rigors, weight loss (often absent).
Neurology: Weakness/Numbness (Epidural abscess).

Examination

Tenderness: Percussion tenderness is highly sensitive.
Spasm: Paravertebral muscle spasm ("Board-like").
Neurology: Detailed myotomal/dermatomal exam.

Imaging and Investigations

Workup Protocol

LabsInflammatory Markers

ESR/CRP: Elevated in over 90%. Used to monitor response.
WCC: Often normal!
Blood Cultures: Positive in ~50%. If positive, may avoid biopsy.

MRIGold Standard

T1: Hypointense (Dark) disc and endplates.
T2: Hyperintense (Bright) "Fluid in the disc".
T1+Gad: Enhancement of disc/endplates/abscess.
"Hot Disc Sign": Highly specific.

Multimodal imaging of femoral osteomyelitis showing X-ray, MRI, and surgical fixation — Comprehensive osteomyelitis imaging and management: (A) Initial AP radiograph showing periosteal reaction and cortical irregularity in the proximal femur. (B-C) Coronal MRI sequences demonstrating bone marrow edema and soft tissue extension. (D) Post-operative radiograph showing debridement with plate and screw fixation for mechanical stability. (E) Follow-up X-ray showing healing with hardware in situ. This illustrates the typical progression from diagnosis through surgical management of chronic osteomyelitis.Credit: Open-i/PMC - CC BY 4.0

Workup Protocol (continued)

BiopsyDefinitive

CT Guided: Standard of care.
Yield: Only 50-70%.
Must hold antibiotics for 48-72hrs prior if safe.

Management Algorithm

Clinical Algorithm— Infection Management

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Treatment Protocols

Antimicrobial Therapy

Empiric: Vancomycin + Ceftriaxone (coverage for MRSA and Gram Negatives).
Targeted: Narrow spectrum based on sensitivities.
Duration: Traditionally 6 weeks IV. Modern evidence (OVIVA Trial) suggests Oral is non-inferior if bioavailable.

Bracing

TLSO: Often used for pain control and to prevent deformity (kyphosis).
Worn for 6-12 weeks while bone heals.

Surgical Technique

Decompression (Laminectomy)

Indication: Epidural Abscess with cord/cauda equina compression.
Technique:
1. Midline approach.
2. Laminectomy (wide).
3. Drainage of abscess (often minimal 'pus', mostly granulation tissue).
4. Do NOT destabilize the facets if possible.
Pitfall: Laminectomy alone in a destroyed spine causes rapid kyphosis. Must instrument if unstable.

Complications

Complication	Risk	Note
Epidural Abscess	15-20%	Can cause rapid onset paraplegia.
Pseudoarthrosis	10%	Infection inhibits fusion.
Kyphosis	Common	Collapse of disc and endplates.
Endocarditis	1-5%	Always auscultate the heart (Echo if murmur).

Postoperative Rehab

Antibiotics

Continue for 6 weeks minimum.
Stop when CRP normalizes and radiographic healing seen.

Follow-up

Weekly CRP.
X-rays at 6 weeks/3 months to check fusion/alignment.
MRI only if symptoms worsen (post-op changes mimic infection).

Outcomes and Prognosis

Mortality

High (2-20%) depending on comorbidities (Age, Diabetes).
Higher in MRSA infections.

Recurrence

5-10%.
Risk factors: Inadequate duration of Abx, Undrained abscess, Retained hardware (if loose).

Functional Outcome

Majority (greater than 70%) have significant residual back pain.
Functional impairment is worse than standard degenerative spine surgery.

Long-term Sequelae

Chronic Pain: Due to facet joint destruction and altered biomechanics (kyphosis).
Instability: Degenerative spondylolisthesis may develop years later above or below the fused level (Adjacent Segment Disease).
Quality of Life: Studies (e.g., Carragee et al.) show scores similar to chronic heart failure.

Prognostic Factors (Poor Outcome)

Age greater than 60.
Concurrent Endocarditis.
Disseminated S. aureus infection.
Delay in diagnosis (greater than 3 months).
Presence of neurological deficit at presentation (often permanent).

Evidence Base

OVIVA Trial

Li et al • NEJM (2019)

Key Findings:

Oral vs Intravenous Antibiotics for Bone and Joint Infection.
1000+ patients randomized.
Found Oral therapy was NON-INFERIOR to IV therapy.
Huge shift in practice (previously 6 weeks IV was dogma).

Clinical Implication: Oral antibiotics are safe and effective for discitis.

Duration of Therapy

Bernard et al • Lancet (2015)

Key Findings:

6 weeks vs 12 weeks of antibiotics.
Found 6 weeks was non-inferior for pyogenic vertebral osteomyelitis.
Reduced antibiotic burden and resistance.

Clinical Implication: 6 weeks is the standard duration (if CRP normalizes).

Biopsy Yield

Marschall et al • Spine J (2011)

Key Findings:

CT Guided Biopsy yield is only 52%.
Blood cultures are positive in 58%.
Combined yield increases to ~70%.
Negative biopsy does NOT rule out infection.

Clinical Implication: Low threshold for repeat or open biopsy.

Titanium Safety

Oga et al • Spine (1993)

Key Findings:

Compared bacterial colonisation on Stainless Steel vs Titanium.
Stainless steel had heavy biofilm formation.
Titanium had minimal adherence.
Concluded Titanium is safer in infection.

Clinical Implication: Use Titanium implants.

Epidural Abscess

Darouiche et al • NEJM (2006)

Key Findings:

Spinal Epidural Abscess (SEA) is a surgical emergency.
Classic Triad: Fever, Back Pain, Neurology (only seen in less than 15%).
MRI is mandatory for any back pain + fever.
Early decompression improves neurological recovery.

Clinical Implication: High index of suspicion for SEA.

Exam Viva Scenarios

Practice these scenarios to excel in your viva examination

VIVA SCENARIOStandard

The Negative Biopsy

EXAMINER

"60M with L4/5 Discitis. Blood Cx neg. CT Biopsy neg. CRP 150. Stable Neuro. What now?"

EXCEPTIONAL ANSWER

This is a common dilemma. 1. **Do NOT start empiric Abx** yet (unless sepsis). 2. **Repeat Biopsy**: A second percutaneous biopsy increases yield by ~15%. 3. **Open Biopsy**: If second biopsy negative, proceed to surgery for 'Open Biopsy & Debridement'. 4. **Rationale**: Treating without a bug commits patient to broad spectrum Abx for 6 weeks with unknown efficacy. **Exceptions**: Sepsis, severe comorbidities making surgery unsafe.

KEY POINTS TO SCORE

Bug is King

Don't treat culture-negative blindly

Open biopsy is safe and effective

COMMON TRAPS

✗Starting Vancomycin because 'CRP is high'

✗Ignoring the possibility of TB or Tumor

VIVA SCENARIOStandard

Implant Safety

EXAMINER

"You need to stabilize an L3/4 infection. Is it safe to put Titanium screws into pus?"

EXCEPTIONAL ANSWER

**Yes**. **Evidence**: Multiple studies show that in the presence of adequate debridement (radical removal of necrotic tissue), titanium instrumentation is safe and rarely requires removal. **Mechanism**: - Titanium is relatively resistant to biofilm. - Stability promotes healing (Wolf's Law vs Infection). - Instability perpetuates infection.

KEY POINTS TO SCORE

Debridement is key

Stability aids clearance

One-stage surgery is standard

COMMON TRAPS

✗Thinking you must do 2-stage (Debride now, Fuse later)

✗Using stainless steel (historic)

MCQ Practice Points

Diagnosis

Q: What is the earliest MRI sign of discitis? A: Endplate Edema. High signal on T2/STIR in the subchondral bone.

Anatomy

Q: Why does infection start in the endplate, not the disc? A: Vascular Supply. The adult disc is avascular. Bacteria lodge in the vascular loops of the endplate.

Pathogen

Q: Most common organism in IV Drug Users? A: Pseudomonas aeruginosa. (Though S. aureus is still common).

Complication

Q: What clinical sign suggests an Epidural Abscess? A: Neurological Deficit or severe radicular pain.

Treatment

Q: What is the primary indication for surgery in discitis? A: Neurological Deficit. Failure of medical management and instability are secondary.

Australian Context

Epidemiology

Indigenous population has higher rates of Rheumatic Fever? No, but higher rates of S. aureus bacteremia.
"Bush Walking" or rural exposure? Think Cryptococcus or atypical organisms.

Exam Day Cheat Sheet

Discitis Summary

High-Yield Exam Summary

Key Facts

•S. aureus #1
•MRI is Gold Standard
•Biopsy BEFORE Abx
•6 weeks Tx

Red Flags

•Neuro Deficit (Abscess)
•Sepsis (Systemic)
•IVDU (Pseudomonas)
•Endocarditis

Workup

•Blood Cx x3
•MRI Gadolinium
•CT Biopsy
•Echo

Risks

•Paralysis
•Sepsis
•Deformity (Kyphosis)
•Chronic Pain

Image Manifest

[1-mri-lumbar-spinefigure-1-mri-of-lumbar-spine-with-.png]: Acute Discitis Endplate destruction
- [2-lumbar-spine-magnetic-resonance-imaging-a-fat-supp.png]: Fat Sat MRI showing edema
- [3-mri-of-lumbar-spine-after-antibioticsfigure-3-sagi.png]: Post-treatment MRI

Feature

Pyogenic

Tuberculosis (Pott's)

Disc Space

Destroyed Early

Preserved Late

Levels

Usually 2 (contiguous)

Multiple (skip lesions)

Abscess

Small / Epidural

Large / Psoas (Cold Abscess)

Kyphosis

Less Common

Common (Gibbus)

Complication

Risk

Note

Epidural Abscess

15-20%

Can cause rapid onset paraplegia.

Pseudoarthrosis

10%

Infection inhibits fusion.

Kyphosis

Common

Collapse of disc and endplates.

Endocarditis

1-5%

Always auscultate the heart (Echo if murmur).

OVIVA Trial

Li et al • NEJM (2019)

Key Findings:

Oral vs Intravenous Antibiotics for Bone and Joint Infection.
1000+ patients randomized.
Found Oral therapy was NON-INFERIOR to IV therapy.
Huge shift in practice (previously 6 weeks IV was dogma).

Clinical Implication: Oral antibiotics are safe and effective for discitis.

Duration of Therapy

Bernard et al • Lancet (2015)

Key Findings:

6 weeks vs 12 weeks of antibiotics.
Found 6 weeks was non-inferior for pyogenic vertebral osteomyelitis.
Reduced antibiotic burden and resistance.

Clinical Implication: 6 weeks is the standard duration (if CRP normalizes).

Biopsy Yield

Marschall et al • Spine J (2011)

Key Findings:

CT Guided Biopsy yield is only 52%.
Blood cultures are positive in 58%.
Combined yield increases to ~70%.
Negative biopsy does NOT rule out infection.

Clinical Implication: Low threshold for repeat or open biopsy.

Titanium Safety

Oga et al • Spine (1993)

Key Findings:

Compared bacterial colonisation on Stainless Steel vs Titanium.
Stainless steel had heavy biofilm formation.
Titanium had minimal adherence.
Concluded Titanium is safer in infection.

Clinical Implication: Use Titanium implants.

Epidural Abscess

Darouiche et al • NEJM (2006)

Key Findings:

Spinal Epidural Abscess (SEA) is a surgical emergency.
Classic Triad: Fever, Back Pain, Neurology (only seen in less than 15%).
MRI is mandatory for any back pain + fever.
Early decompression improves neurological recovery.

Clinical Implication: High index of suspicion for SEA.