High Yield Overview
Classic Radiological Signs: Arthritis
—OA Key Features
4cardinal signs
—RA Key Features
—Periarticular changes
—Gout Key Features
—Overhanging edge
Arthritis Pattern Recognition
Degenerative (OA): Weight-bearing, sclerosis, osteophytes
Inflammatory (RA): Symmetric, periarticular osteopenia, erosions
Crystal (Gout): Asymmetric, preserved density, soft tissue tophi
Seronegative: Asymmetric, enthesitis, sacroiliitis
Key: Distribution and associated features distinguish arthritis types
Critical Must-Knows
- OA: Joint space narrowing, osteophytes, subchondral sclerosis, cysts
- RA: Periarticular osteopenia, marginal erosions, symmetric
- Gout: Punched-out erosions with overhanging edges, preserved density
- Psoriatic: Pencil-in-cup, periostitis, DIP involvement
Examiner's Pearls
- "OA vs inflammatory: Distribution and presence of osteopenia
- "Gull-wing sign: Erosive OA of hands
- "Rat-bite erosions: RA marginal erosions
- "Ivory phalanx: Psoriatic arthritis
Exam Warning
Arthritis radiological signs are commonly tested. You must distinguish OA from inflammatory arthritis patterns, know the distribution of different arthropathies, and recognise classic signs like overhanging edges in gout and pencil-in-cup in psoriatic arthritis.
Osteoarthritis Signs
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Mnemonic
LOSSOA Cardinal Signs
L
L = Loss of joint space (narrowing)
O
O = Osteophytes (bone spurs)
S
S = Subchondral sclerosis (eburnation)
S
S = Subchondral cysts (geodes)
Memory Hook:Joint space narrowing is the hallmark; the other features develop as the disease progresses
OA Radiological Signs by Joint
| Joint | Distribution | Specific Signs |
|---|---|---|
| Hip | Superior (weight-bearing) | Superior migration, osteophyte ring |
| Knee | Medial greater than lateral usually | Bone-on-bone, varus/valgus deformity |
| Hand DIP/PIP | Heberden's/Bouchard's nodes | Osteophytes at DIP/PIP |
| 1st CMC | Thumb base arthritis | Radial subluxation, squaring |
| Spine | Facet, uncovertebral | Disc space narrowing, osteophytes |
Erosive OA
Erosive OA is an aggressive form affecting DIP and PIP joints with central erosions creating a 'gull-wing' or 'seagull' appearance. Distinguished from inflammatory arthritis by DIP involvement and lack of periarticular osteopenia.
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Rheumatoid Arthritis Signs
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RA Radiological Signs
| Sign | Description | Location |
|---|---|---|
| Periarticular osteopenia | Reduced density around joints | Early sign, juxta-articular |
| Symmetric joint space narrowing | Uniform narrowing (not just weight-bearing) | All compartments affected |
| Marginal erosions | 'Rat-bite' erosions at bare areas | MCP, PIP, MTP joints |
| Soft tissue swelling | Fusiform swelling around joints | Early sign |
| Subluxations/deformities | Ulnar drift, swan neck, boutonniere | Late disease |
| Atlantoaxial subluxation | AADI greater than 3mm | Cervical spine involvement |
RA Hand Distribution
Classic RA affects MCP and PIP joints (spares DIP). Compare with OA which affects DIP and 1st CMC. Wrist involvement is common in RA. The distribution is typically symmetric between hands.
Crystal Arthropathy Signs
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Gout Radiological Signs
| Sign | Description | Significance |
|---|---|---|
| Punched-out erosions | Well-defined erosions with sclerotic margins | Tophaceous deposits |
| Overhanging edges | Erosion edge overhangs (Martel sign) | Pathognomonic for gout |
| Preserved bone density | No periarticular osteopenia | Unlike RA |
| Soft tissue tophi | Dense soft tissue masses | May calcify |
| Asymmetric distribution | 1st MTP, midfoot, ankle | Podagra classic |
| Preserved joint space | Until late disease | Unlike OA/RA |
Seronegative Arthropathy Signs
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Seronegative Spondyloarthropathy Signs
| Condition | Classic Signs | Distribution |
|---|---|---|
| Psoriatic arthritis | Pencil-in-cup, ivory phalanx, periostitis | DIP, asymmetric, dactylitis |
| Ankylosing spondylitis | Bamboo spine, SI fusion, squaring | Axial, symmetric SI joints |
| Reactive arthritis | Asymmetric oligoarthritis, calcaneal spurs | Lower limb, entheses |
| Enteropathic | Similar to AS, less severe | Axial, peripheral can occur |
Pencil-in-Cup Deformity
Pathognomonic for psoriatic arthritis. Central erosion of the proximal phalanx (cup) with pointed distal phalanx (pencil) of the adjacent bone. Associated with arthritis mutilans in severe cases.
Differentiating Features
Differentiating Arthritis Types
| Feature | OA | RA | Gout | Psoriatic |
|---|---|---|---|---|
| Distribution | Weight-bearing, asymmetric | Symmetric, MCP/PIP | Asymmetric, 1st MTP | Asymmetric, DIP, ray pattern |
| Bone density | Normal/sclerotic | Periarticular osteopenia | Preserved | Preserved or proliferative |
| Erosions | No (except erosive OA) | Marginal, rat-bite | Punched-out, overhanging edge | Marginal + central |
| Osteophytes | Yes | Uncommon | Uncommon | Uncommon |
| Periostitis | No | No | No | Yes |
| Soft tissue | Minimal | Fusiform swelling | Tophi | Dactylitis (sausage digit) |
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
VIVA SCENARIOStandard
EXAMINER
"A patient presents with a painful, swollen 1st MTP joint. X-ray shows well-defined erosions with overhanging edges and preserved bone density."
EXCEPTIONAL ANSWER
The diagnosis is gout. The classic radiological features are: (1) Punched-out erosions - well-defined erosions with sclerotic margins from tophaceous deposits. (2) Overhanging edges (Martel sign) - the erosion edge characteristically overhangs, which is pathognomonic for gout. (3) Preserved bone density - unlike RA, there is no periarticular osteopenia. (4) Asymmetric distribution - typically affecting the 1st MTP (podagra), midfoot, and ankle. (5) Preserved joint space until late disease. (6) Soft tissue tophi - may be visible as dense soft tissue masses that can calcify. The combination of punched-out erosions with overhanging edges and preserved bone density is virtually diagnostic of gout.
KEY POINTS TO SCORE
Overhanging edges (Martel sign) pathognomonic
Punched-out erosions with sclerotic margins
Preserved bone density (unlike RA)
1st MTP classic location (podagra)
Preserved joint space until late
COMMON TRAPS
✗Confusing with RA (RA has osteopenia)
✗Missing the overhanging edge
✗Not recognising soft tissue tophi
VIVA SCENARIOStandard
EXAMINER
"A patient with long-standing psoriasis has hand pain. X-ray shows DIP joint erosions with a 'pencil-in-cup' appearance and periostitis along the phalanges."
EXCEPTIONAL ANSWER
This is psoriatic arthritis. The pencil-in-cup deformity is pathognomonic - the proximal phalanx is eroded centrally (cup) while the distal phalanx becomes pointed (pencil). Key differences from RA: (1) Distribution - psoriatic affects DIP joints (RA spares DIP), can have ray pattern (whole digit), and is often asymmetric. (2) Periostitis - fluffy periosteal new bone is seen in psoriatic but not RA. (3) Bone density - preserved or even proliferative in psoriatic, whereas RA has periarticular osteopenia. (4) Dactylitis - sausage digit from soft tissue and joint swelling is classic for psoriatic. (5) Enthesitis - bone proliferation at tendon insertions. (6) Nail changes - clinically important as nail disease correlates with joint disease.
KEY POINTS TO SCORE
Pencil-in-cup pathognomonic for psoriatic
DIP involvement (RA spares DIP)
Periostitis present (absent in RA)
Preserved bone density (RA has osteopenia)
Asymmetric, ray pattern involvement
COMMON TRAPS
✗Confusing with RA (different distribution)
✗Missing the periostitis
✗Not looking for associated skin/nail changes
VIVA SCENARIOStandard
EXAMINER
"An elderly patient has hand X-rays showing joint space narrowing, osteophytes, and central erosions at the DIP joints with a 'gull-wing' appearance."
EXCEPTIONAL ANSWER
This is erosive osteoarthritis (EOA), an aggressive inflammatory variant of OA primarily affecting the DIP and PIP joints of the hands. The 'gull-wing' or 'seagull' sign describes the central collapse and marginal proliferation at the DIP joints creating a shape resembling a seagull in flight. Differences from standard OA: (1) Erosions - central erosions are present (standard OA has no erosions). (2) Inflammatory features - more swelling, redness, and pain than typical OA. (3) Characteristic pattern - affects DIP and PIP with gull-wing deformity. (4) Progression - can lead to ankylosis. Differences from inflammatory arthritis: (1) No periarticular osteopenia. (2) DIP involvement (RA spares DIP). (3) No systemic features or positive serology.
KEY POINTS TO SCORE
Erosive OA = aggressive OA with central erosions
Gull-wing sign at DIP joints
Affects DIP/PIP (like OA distribution)
No periarticular osteopenia (unlike RA)
Can progress to ankylosis
COMMON TRAPS
✗Misdiagnosing as inflammatory arthritis
✗Missing the central erosion pattern
✗Not recognising the gull-wing sign
Arthritis Signs Quick Reference
High-Yield Exam Summary
OA Signs (LOSS)
- •L = Loss of joint space
- •O = Osteophytes
- •S = Subchondral sclerosis
- •S = Subchondral cysts
RA Signs
- •Periarticular osteopenia
- •Marginal erosions (rat-bite)
- •Symmetric MCP/PIP involvement
- •Soft tissue swelling
Gout Signs
- •Overhanging edges (Martel sign)
- •Punched-out erosions
- •Preserved bone density
- •Soft tissue tophi
Psoriatic Signs
- •Pencil-in-cup deformity
- •Periostitis
- •DIP involvement
- •Dactylitis (sausage digit)