High Yield Overview

TRUNNIONOSIS AND TAPER CORROSION

Mechanically-Assisted Crevice Corrosion at Head-Neck Junction

2-4%Revision rate for ALTR

36mm+High-risk head size

7 ppbCobalt threshold

80%MARS MRI sensitivity

ALVAL SCORE (CAMPBELL)

Low (0-4)

PatternMinimal lymphocytic infiltrate

TreatmentSurveillance if asymptomatic

Moderate (5-6)

PatternPerivascular lymphocytes, some necrosis

TreatmentClose monitoring, consider revision

High (7-10)

PatternDense lymphocytic infiltrate, tissue necrosis

TreatmentRevision surgery indicated

Critical Must-Knows

Trunnionosis = mechanically-assisted crevice corrosion (MACC) at head-neck taper
Risk factors: large heads (36mm+), high offset, long necks, Ti stems, mixed metals
Cobalt more systemically toxic than chromium (cardiotoxicity, neurotoxicity)
MARS MRI is investigation of choice - detects soft tissue destruction
Revision must address soft tissue debridement AND component considerations

Examiner's Pearls

"
Cobalt greater than 7 ppb and Cr greater than 5 ppb are concerning thresholds
"
MoP with large CoCr head on Ti stem = highest risk combination
"
ALTR = Adverse Local Tissue Reaction (umbrella term)
"
ARMD = Adverse Reaction to Metal Debris (same entity, different name)

Critical Exam Concepts

Taper Mechanics Matter

Understand the tribology. Fretting (micromotion) + crevice corrosion (oxygen-depleted environment) = mechanically-assisted crevice corrosion. This is the pathomechanism.

Large Heads = High Risk

Head size is the key modifiable risk factor. Heads 36mm and larger generate greater taper moments and micromotion. Combined with Ti stems, risk is multiplicative.

Metal Ions are Screening

Cobalt and chromium levels guide management. Co greater than 7 ppb is threshold for concern. BUT imaging (MARS MRI) determines tissue damage and surgical decision-making.

Soft Tissue Destruction

ALTR causes extensive tissue necrosis. Pseudotumors, abductor destruction, bone loss. Revision is complex - must debride all necrotic tissue for success.

Taper Corrosion Risk Assessment

Clinical Scenario	Risk Level	Recommended Action	Key Point
MoP THA with 28mm head on CoCr stem	Low	Standard surveillance	Small head, matched metals = low risk
MoP THA with 36mm head on Ti stem	High	Annual metal ions + clinical review	Large head on Ti = high risk combination
MoM resurfacing - well-positioned	Moderate	Annual metal ions, clinical review	Bearing surface wear, not taper
Symptomatic THA with Co greater than 10 ppb	Critical	Urgent MARS MRI + revision planning	High ions with symptoms = tissue damage likely

Mnemonic

THOLTRisk Factors for Taper Corrosion

Titanium stem

Ti alloy stems have worse taper performance than CoCr

Head size large (36mm+)

Larger heads generate greater moments at taper

Offset increased / Neck length

High offset and long necks increase lever arm

Lateral offset design

High offset femoral stems increase torsional loads

Taper mismatch / Mixed metals

CoCr head on Ti stem creates galvanic couple

Memory Hook:A THOLT of caution with large heads on titanium - the taper takes the toll!

Mnemonic

FCGCorrosion Mechanisms

Fretting corrosion

Micromotion between surfaces damages oxide layer

Crevice corrosion

Oxygen-depleted environment accelerates metal dissolution

Galvanic corrosion

Dissimilar metals create electrochemical gradient

Memory Hook:FCG - Fretting, Crevice, Galvanic - the triple threat of taper destruction!

Mnemonic

PUNCHSystemic Effects of Cobalt

Peripheral neuropathy

Sensory and motor nerve dysfunction

Unexplained fatigue

Systemic constitutional symptoms

Neuro-ocular toxicity

Visual and hearing impairment

Cardiomyopathy

Dilated cardiomyopathy - can be fatal

Hypothyroidism

Thyroid dysfunction from cobalt toxicity

Memory Hook:Cobalt can really PUNCH you - systemic toxicity is serious!

Overview and Epidemiology

Definition

Trunnionosis refers to mechanically-assisted crevice corrosion (MACC) occurring at the modular head-neck taper junction of total hip arthroplasty, leading to metal debris release and adverse local tissue reactions (ALTR). It is distinct from bearing surface wear in metal-on-metal articulations.

Epidemiology

Reported in 2-4% of modular THA overall
Higher rates with specific designs (up to 10%)
Male patients may be at higher risk (greater activity)
Recognition increased dramatically post-2010
AOANJRR data shows elevated revision rates for certain stem-head combinations

Historical Context

Modularity introduced 1980s for surgical flexibility
Initial focus on MoM bearing surface failures
Taper corrosion recognized as distinct entity ~2010
MHRA alerts and recalls highlighted problem
Now affects MoP and CoP combinations too

Pathophysiology

The Corrosion Cascade

Fretting disrupts the protective oxide layer → Crevice environment prevents repassivation → Metal ions released → Local tissue toxicity (ALTR) → Possible systemic toxicity. Understanding this cascade is essential.

Morse Taper Fundamentals

Taper design principles:

Morse taper creates interference fit via cold welding
Taper angle varies between manufacturers (5°44' common)
Taper length affects contact area and stability
Impaction force critical for initial fixation

Load transmission:

Axial loads from body weight
Torsional loads from gait (internal/external rotation)
Bending moments from offset/neck length
Larger heads amplify moment arm at taper

Why Large Heads Increase Risk

Moment = Force × Distance. Larger heads increase the lever arm from hip center to taper junction. This amplifies bending moments and torsional stresses at the taper, increasing fretting micromotion. A 36mm head generates approximately 30% more moment than a 28mm head.

Risk Factors

Implant-Related Risk Factors

Factor	Low Risk	High Risk	Mechanism
Head size	28-32mm	36mm+	Larger head = greater taper moment
Stem material	CoCr stem	Titanium stem	Ti has inferior taper performance
Metal combination	Matched metals	CoCr head on Ti stem	Galvanic couple accelerates corrosion
Neck length	Standard	Long (+5, +10)	Increased lever arm at taper
Offset	Standard	High offset	Greater bending moment at taper
Taper design	Manufacturer matched	Mismatch or poor design	Taper angle/roughness mismatch

The worst combination: Large CoCr head (36mm+) on a high-offset titanium stem with extended neck.

High-Risk Combinations to Remember

Titanium stem + Large CoCr head + High offset = Maximum risk. Australian registry data confirms these combinations have the highest revision rates for ALTR. Avoid this combination or implement surveillance protocols.

Clinical Presentation

Local Symptoms

Groin pain (may be insidious onset)
Hip pain with activity
Clicking, squeaking, or grinding
Swelling (pseudotumor)
Progressive weakness (abductor destruction)
Sense of instability
Recurrent dislocation

Systemic Symptoms

Fatigue and malaise
Cognitive changes (memory, concentration)
Peripheral neuropathy
Visual or hearing changes
Palpitations or dyspnea (cardiomyopathy)
Hypothyroidism symptoms
Depression

Clinical Stages

Progression of Trunnionosis

EarlySubclinical Phase

Metal ion release begins. Patient asymptomatic. May only be detected on surveillance bloods. Tissue changes minimal.

IntermediateLocal Symptoms

Groin or hip pain develops. May be mistaken for other causes. Early soft tissue changes on MRI. Metal ions typically elevated.

AdvancedEstablished ALTR

Pseudotumor formation. Abductor destruction. Bone loss possible. Significant functional impairment. High metal ions.

SevereSystemic Toxicity

Cobaltism develops. Cardiac, neurological, thyroid manifestations. May be irreversible. Urgent revision required.

Red Flags for Cobaltism

Systemic cobalt toxicity requires urgent action. Signs include: unexplained cardiomyopathy, peripheral neuropathy, visual/hearing loss, cognitive decline, hypothyroidism. Cobalt levels often greater than 20 ppb. Can be fatal if not addressed. Echo and cardiology referral essential.

Investigations

Serum Metal Ion Testing

Ion	Normal	Concerning	Action Threshold
Cobalt (Co)	Less than 1 ppb	Greater than 4 ppb	Greater than 7 ppb = imaging required
Chromium (Cr)	Less than 1 ppb	Greater than 4 ppb	Greater than 5 ppb = imaging required
Co:Cr ratio	Approximately 1:1	Greater than 2:1	High ratio suggests taper source

Interpretation pearls:

Co:Cr ratio greater than 2:1 suggests taper corrosion (rather than bearing wear)
Levels can fluctuate - trend is important
Some patients develop ALTR with low ion levels (hypersensitivity)
Whole blood samples required (not serum alone)

MHRA guidance (UK) - widely adopted:

Co or Cr greater than 7 ppb = concern, requires imaging
Annual surveillance for at-risk implants

Investigation Protocol for Symptomatic THA

1. Serum metal ions (Co and Cr) → 2. Plain radiographs → 3. MARS MRI if ions elevated or symptoms persist → 4. Aspiration to rule out infection before surgery. Do not skip the aspiration - occult infection can coexist.

Differential Diagnosis

Painful THA - Differential Diagnosis

Diagnosis	Key Features	Distinguishing Investigation
Trunnionosis/ALTR	Elevated metal ions, pseudotumor on MRI	Metal ions + MARS MRI
Periprosthetic infection	Fever, elevated CRP/ESR, positive cultures	Aspiration, WBC count, culture
Aseptic loosening	Start-up pain, progressive, radiolucent lines	Serial X-rays, bone scan
Instability	Recurrent dislocation, sense of giving way	Clinical exam, X-ray, CT for version
Periprosthetic fracture	Acute pain after trauma, may be subtle	X-ray, CT if needed
Referred pain (spine)	Back pain, radicular symptoms	Spine imaging, selective injection
Iliopsoas impingement	Anterior groin pain, worse with flexion	CT (cup position), lidocaine injection

ALTR vs Infection

Must distinguish ALTR from infection before revision. Both can present with pain and elevated inflammatory markers. Aspiration is MANDATORY. ALTR fluid is typically dark/metallic but sterile. Infection requires completely different management.

Management

Non-Operative Surveillance

Indications for surveillance (no immediate surgery):

Asymptomatic patient with at-risk implant
Low-grade metal ion elevation (Co less than 7 ppb)
No significant ALTR on MARS MRI
Well-fixed, well-positioned components

Surveillance protocol:

Annual clinical review
Annual metal ions (Co and Cr)
MARS MRI every 1-2 years if ions elevated
Patient education on warning symptoms

Upgrade to revision if:

Symptomatic progression
Rising metal ion trend
ALTR progression on MRI
Systemic symptoms develop

Soft Tissue Debridement is Critical

The single most important factor for revision success is complete debridement of necrotic tissue. Retained necrotic/reactive tissue leads to persistent inflammation, poor healing, and high complication rates. Be aggressive with debridement.

Surgical Technique Considerations

Surgical Approach

Extensile approach required:

Posterior approach with extended capsulotomy
May need trochanteric osteotomy for access
Must visualize extent of pseudotumor
Direct lateral may limit access posteriorly

Key exposure steps:

Identify and protect sciatic nerve (often displaced by pseudotumor)
Evacuate pseudotumor contents carefully
Complete capsulectomy and synovectomy
Debride all necrotic tissue back to bleeding margins

Titanium Adapter Sleeve

Ti sleeve/adapter devices allow retention of a well-fixed stem with damaged trunnion. The sleeve covers the corroded taper and provides a new surface for head impaction. This avoids stem revision morbidity in selected cases. Check manufacturer compatibility.

Complications

Complications of ALTR and Revision Surgery

Complication	Rate	Risk Factors	Management
Dislocation	10-25%	Abductor loss, revision surgery	Constrained liner, bracing, re-revision
Infection	5-10%	Necrotic tissue, prolonged surgery	Debridement, antibiotics, staged revision
Nerve injury	2-5%	Scarring, pseudotumor displacement	Careful dissection, may recover
Persistent symptoms	15-30%	Incomplete debridement, tissue damage	May need re-revision
Abductor insufficiency	20-40%	Pre-existing damage from ALTR	Gait aids, reconstruction options limited
Fracture	2-5%	Bone loss, osteolysis	May need additional fixation

High Complication Rate

Revision for ALTR has higher complication rates than routine revision THA. Dislocation rates of 10-25% reflect abductor deficiency. Counsel patients appropriately. May require constrained components, brace, or assistive devices long-term.

Outcomes and Prognosis

Prognostic Factors

Good Prognosis:

Early diagnosis before extensive tissue damage
Intact or recoverable abductors
Good bone stock
Low metal ion levels
Complete surgical debridement achieved

Poor Prognosis:

Delayed diagnosis with extensive destruction
Abductor loss/atrophy
Significant bone loss
Very high metal ion levels (cobaltism)
Systemic toxicity (cardiac, neurological)
Multiple prior revisions

Outcomes Data

Re-revision rates after ALTR revision are approximately 15-25% at 5 years - significantly worse than revision for other indications. Dislocation is the most common reason for re-revision. Early diagnosis and meticulous surgery optimize outcomes.

Evidence Base and Key Studies

Langton DJ - Taper Corrosion in Large-Head MoM THA

Langton et al. • J Bone Joint Surg Br (2012)

Key Findings:

First systematic description of taper corrosion as distinct from bearing wear
Larger head sizes associated with increased corrosion
High offset stems increased risk
Titanium stems had worse taper performance

Clinical Implication: Landmark paper establishing trunnionosis as a clinical entity. Head size and stem material are key modifiable risk factors.

Limitation: Retrospective retrieval analysis; may over-represent failures.

AOANJRR - Metal-on-Metal Hip Arthroplasty Analysis

Australian Orthopaedic Association National Joint Replacement Registry • Annual Report (2023)

Key Findings:

MoM bearing has highest revision rate of all bearing couples
Large-head MoM THA has higher revision than resurfacing
ALTR accounts for majority of MoM revisions
Certain stem-head combinations have significantly elevated risk

Clinical Implication: Registry data confirms high failure rates for specific implant combinations. Guides surveillance and patient counselling.

Limitation: Registry data; limited clinical detail on individual cases.

Hart AJ - MARS MRI for ALTR Detection

Hart et al. • J Bone Joint Surg Br (2012)

Key Findings:

MARS MRI highly sensitive for pseudotumor detection (80%+)
Solid lesions associated with worse tissue destruction
MRI findings correlate with intraoperative damage
Metal ions alone not sufficient for diagnosis

Clinical Implication: MARS MRI is investigation of choice for ALTR. Both metal ions AND imaging needed for complete assessment.

Limitation: Single-center study; requires specialized MRI protocol.

Mistry A - Outcomes of Revision for ALTR

Mistry et al. • Bone Joint J (2016)

Key Findings:

Re-revision rate 16% at 5 years
Dislocation most common complication (18%)
Worse outcomes with delayed diagnosis
Complete debridement associated with better outcomes

Clinical Implication: Revision for ALTR has guarded prognosis. Early diagnosis and complete debridement improve outcomes. High dislocation rate requires consideration of constraint.

Limitation: Retrospective; heterogeneous patient population.

Exam Viva Scenarios

Practice these scenarios to excel in your viva examination

VIVA SCENARIOStandard

Scenario 1: Surveillance of At-Risk Implant

EXAMINER

"A 58-year-old man is 5 years post primary THA with a 36mm cobalt-chrome head on a titanium uncemented stem. He is currently asymptomatic but was referred for surveillance due to implant concerns. How would you assess and counsel this patient?"

EXCEPTIONAL ANSWER

This patient has a high-risk implant combination - large CoCr head on Ti stem - which is associated with increased rates of taper corrosion and ALTR. My assessment would begin with detailed history enquiring about hip pain, function, and importantly any systemic symptoms such as fatigue, neurological changes, or cardiac symptoms which might suggest cobaltism. Clinical examination would assess gait, range of motion, abductor strength, and look for any masses or swelling. For investigations, I would check serum cobalt and chromium levels. Given the at-risk implant, I would obtain levels even though asymptomatic. I would obtain AP pelvis and lateral hip radiographs to assess component position and look for osteolysis. If metal ions are elevated (cobalt greater than 7 ppb), I would arrange MARS MRI to look for ALTR. If metal ions are normal and patient asymptomatic with normal X-rays, I would counsel regarding the elevated risk and recommend annual surveillance with clinical review and metal ions. I would educate about warning symptoms requiring earlier review - pain, weakness, swelling, or systemic symptoms. If metal ions are elevated or any symptoms develop, I would proceed to MARS MRI. The key message is this implant combination warrants lifelong surveillance even if asymptomatic.

KEY POINTS TO SCORE

Recognize high-risk combination: large head + Ti stem

Surveillance includes metal ions + clinical review

Cobalt greater than 7 ppb threshold for imaging

MARS MRI is investigation of choice for ALTR

Patient education is essential

COMMON TRAPS

✗Dismissing asymptomatic patient without surveillance

✗Not checking for systemic cobalt toxicity symptoms

✗Ordering wrong type of MRI (must be MARS sequence)

✗Forgetting plain radiographs

LIKELY FOLLOW-UPS

"What if his cobalt level is 12 ppb but he is asymptomatic?"

"What would you see on MARS MRI with ALTR?"

"What are the MHRA surveillance recommendations?"

VIVA SCENARIOChallenging

Scenario 2: Symptomatic ALTR Requiring Revision

EXAMINER

"A 62-year-old woman presents with progressive right hip pain and weakness 7 years after THA. She has a 38mm metal-on-polyethylene bearing on a titanium stem. Her cobalt is 18 ppb and chromium is 6 ppb. MARS MRI shows a large posterolateral pseudotumor with abductor muscle atrophy. How would you manage this patient?"

EXCEPTIONAL ANSWER

This is a case of established ALTR secondary to taper corrosion requiring revision surgery. The significantly elevated cobalt with high Co:Cr ratio greater than 2:1 localizes the problem to the taper rather than bearing surface. My initial assessment would complete the workup by checking for systemic cobalt toxicity - I would enquire about cardiac symptoms and arrange echocardiogram given the very elevated cobalt. I would check thyroid function. I would arrange hip aspiration to rule out infection - this is mandatory before revision. If infection is ruled out, I would proceed to revision planning. The goals of surgery are: complete debridement of pseudotumor and necrotic tissue, removal of the corrosion source, and restoration of a stable hip. Surgical planning would involve careful review of MARS MRI to map the pseudotumor extent and abductor status. CT scan may help assess bone stock. I would plan for a posterior approach with extension as needed for pseudotumor access. Intraoperatively, my key steps would be: protect the sciatic nerve, decompress and excise pseudotumor completely, send tissue for histology and frozen section, assess components. Given significant trunnion damage, I would either use a titanium adapter sleeve if the stem is well-fixed, or revise the stem if loose or severely damaged. I would use a ceramic head, smaller size (32mm), to eliminate metal ion generation. Given abductor atrophy on MRI, I would consider a constrained liner if abductors are non-functional intraoperatively. Post-operatively, I would use protected weight-bearing, hip precautions, and likely an abduction brace given dislocation risk. I would counsel about the guarded prognosis and high complication rate of revision for ALTR.

KEY POINTS TO SCORE

High Co:Cr ratio suggests taper source over bearing

Must rule out infection with aspiration

Check for systemic cobalt toxicity (cardiac, neurological)

Complete debridement is the key surgical principle

Ceramic head eliminates future metal ion generation

Consider constraint given abductor deficiency

COMMON TRAPS

✗Not ruling out infection before revision

✗Not checking for cardiac toxicity with cobalt this high

✗Incomplete pseudotumor debridement

✗Using another metal head at revision

✗Not addressing abductor deficiency with component choice

LIKELY FOLLOW-UPS

"What if her echo shows dilated cardiomyopathy?"

"How would you manage if the stem is well-fixed?"

"What dislocation rate would you quote for this revision?"

VIVA SCENARIOChallenging

Scenario 3: Systemic Cobalt Toxicity

EXAMINER

"A 55-year-old man presents with fatigue, hearing loss, and peripheral neuropathy. He had bilateral THA 6 years ago (large head MoM). His cobalt level is 85 ppb. MARS MRI shows bilateral pseudotumors. His cardiologist has diagnosed new cardiomyopathy. How would you approach this complex case?"

EXCEPTIONAL ANSWER

This is severe systemic cobalt toxicity (cobaltism) - a medical emergency requiring multidisciplinary management. The extremely elevated cobalt with cardiomyopathy, neurotoxicity, and ototoxicity indicates life-threatening metal poisoning. My immediate management would involve multidisciplinary team coordination - cardiology, toxicology, neurology involvement is essential. The priority is stabilizing the patient medically before surgical planning. I would admit for cardiac monitoring given the cardiomyopathy. Medical optimization would focus on cardiac failure management with the cardiology team. There is limited evidence for chelation therapy but it may be considered in consultation with toxicology. For surgical planning, bilateral disease presents a dilemma. I would plan staged bilateral revisions, prioritizing the hip with worse ALTR or if there is a unilateral source. I would not attempt bilateral simultaneous revision given the medical complexity. The interval between staged revisions would depend on medical stability and first side recovery - typically 3-6 months. Surgical principles remain the same - complete debridement, ceramic heads, constrained liners if abductors deficient. Important counselling: Some effects of cobalt toxicity may be irreversible, particularly neurological and cardiac damage. I would be honest about guarded prognosis. Even after revision, metal ions take months to decrease. Close medical follow-up is essential. The key message is that this is a medical emergency requiring urgent multidisciplinary management, with surgery planned as soon as medically appropriate.

KEY POINTS TO SCORE

Cobaltism is a medical emergency requiring MDT approach

Cardiac, neurological, and hearing effects may be irreversible

Staged bilateral revisions - not simultaneous

Cardiac optimization before surgery

Metal ions decrease slowly after revision

Counsel about guarded prognosis

COMMON TRAPS

✗Rushing to surgery without medical optimization

✗Attempting bilateral simultaneous revision

✗Not involving cardiology/toxicology

✗Underestimating severity of systemic toxicity

✗Not counselling about potential irreversibility

LIKELY FOLLOW-UPS

"What is the role of chelation therapy?"

"How quickly do metal ions decrease after revision?"

"What is the evidence for recovery of cardiac function?"

Australian Context

AOANJRR Data

Australia has comprehensive registry data on THA outcomes
MoM THA revision rates significantly higher than other bearings
Registry identified high-risk implant combinations early
Data supports current surveillance recommendations
Specific stem-head combinations flagged for monitoring

TGA Guidance

TGA has issued alerts on MoM hip replacements
Surveillance recommendations align with international guidance
Patient notification requirements for at-risk devices
Reporting of adverse events to TGA encouraged
Database of recalled/monitored devices

AOANJRR Findings on Metal-on-Metal THA

The Australian Orthopaedic Association National Joint Replacement Registry has provided world-leading data on hip arthroplasty outcomes. Key findings relevant to trunnionosis include:

Bearing surface data:

MoM bearings have consistently shown the highest revision rates of all bearing couples
Large-head MoM THA (36mm+) performs worse than resurfacing
Ceramic-on-ceramic and ceramic-on-polyethylene have lowest revision rates

Stem-head combinations:

Specific combinations of titanium stems with large CoCr heads flagged
Revision for ALTR/metal-related pathology increasing as a percentage
Registry data has informed surgeon implant choice and surveillance protocols

Clinical implications for Australian practice:

Surgeons should check registry data before implant selection
Patients with at-risk implants should be in surveillance programs
Registry reporting assists ongoing monitoring of implant performance

Patient Notification

Patients with TGA-flagged implants should be notified and enrolled in surveillance programs. This includes patients with large-head MoM THA and certain high-risk conventional THA combinations. Maintain accurate implant records for all patients.

TRUNNIONOSIS AND TAPER CORROSION

High-Yield Exam Summary

Definition

•Mechanically-assisted crevice corrosion (MACC) at head-neck taper
•ALTR = Adverse Local Tissue Reaction (umbrella term)
•ARMD = Adverse Reaction to Metal Debris (same entity)
•ALVAL = histological pattern of metal hypersensitivity

Risk Factors (THOLT)

•Titanium stem (Ti has worse taper performance)
•Head size large (36mm+ increases taper moment)
•Offset increased / Long neck
•Lateral offset designs
•Taper mismatch / Mixed metals (CoCr on Ti)

Corrosion Mechanisms

•Fretting: micromotion disrupts oxide layer
•Crevice: oxygen-depleted environment accelerates corrosion
•Galvanic: dissimilar metals create electrochemical gradient
•All three combine in MACC

Metal Ion Thresholds

•Cobalt greater than 7 ppb = concern, imaging required
•Chromium greater than 5 ppb = concern
•Co:Cr ratio greater than 2:1 suggests taper source
•Very high levels (greater than 20 ppb) = check for systemic toxicity

MARS MRI Findings

•Pseudotumor (cystic or solid)
•Muscle atrophy (abductors)
•Fluid collections
•Bone involvement/osteolysis

Revision Principles

•Complete debridement of necrotic tissue (most important)
•Ceramic head to eliminate metal ions
•Smaller head size (32mm)
•Ti adapter sleeve if stem well-fixed but taper damaged
•Consider constrained liner if abductors deficient

Systemic Cobalt Toxicity (PUNCH)

•Peripheral neuropathy
•Unexplained fatigue
•Neuro-ocular toxicity (vision/hearing)
•Cardiomyopathy (can be fatal)
•Hypothyroidism

Clinical Scenario

Risk Level

Recommended Action

Key Point

MoP THA with 28mm head on CoCr stem

Low

Standard surveillance

Small head, matched metals = low risk

MoP THA with 36mm head on Ti stem

High

Annual metal ions + clinical review

Large head on Ti = high risk combination

MoM resurfacing - well-positioned

Moderate

Annual metal ions, clinical review

Bearing surface wear, not taper

Symptomatic THA with Co greater than 10 ppb

Critical

Urgent MARS MRI + revision planning

High ions with symptoms = tissue damage likely

Factor

Low Risk

High Risk

Mechanism

Head size

28-32mm

36mm+

Larger head = greater taper moment

Stem material

CoCr stem

Titanium stem

Ti has inferior taper performance

Metal combination

Matched metals

CoCr head on Ti stem

Galvanic couple accelerates corrosion

Neck length

Standard

Long (+5, +10)

Increased lever arm at taper

Offset

Standard

High offset

Greater bending moment at taper

Taper design

Manufacturer matched

Mismatch or poor design

Taper angle/roughness mismatch

Ion

Normal

Concerning

Action Threshold

Cobalt (Co)

Less than 1 ppb

Greater than 4 ppb

Greater than 7 ppb = imaging required

Chromium (Cr)

Less than 1 ppb

Greater than 4 ppb

Greater than 5 ppb = imaging required

Co:Cr ratio

Approximately 1:1

Greater than 2:1

High ratio suggests taper source

Diagnosis

Key Features

Distinguishing Investigation

Trunnionosis/ALTR

Elevated metal ions, pseudotumor on MRI

Metal ions + MARS MRI

Periprosthetic infection

Fever, elevated CRP/ESR, positive cultures

Aspiration, WBC count, culture

Aseptic loosening

Start-up pain, progressive, radiolucent lines

Serial X-rays, bone scan

Instability

Recurrent dislocation, sense of giving way

Clinical exam, X-ray, CT for version

Periprosthetic fracture

Acute pain after trauma, may be subtle

X-ray, CT if needed

Referred pain (spine)

Back pain, radicular symptoms

Spine imaging, selective injection

Iliopsoas impingement

Anterior groin pain, worse with flexion

CT (cup position), lidocaine injection

Non-Operative Surveillance

Indications for surveillance (no immediate surgery):

Asymptomatic patient with at-risk implant
Low-grade metal ion elevation (Co less than 7 ppb)
No significant ALTR on MARS MRI
Well-fixed, well-positioned components

Surveillance protocol:

Annual clinical review
Annual metal ions (Co and Cr)
MARS MRI every 1-2 years if ions elevated
Patient education on warning symptoms

Upgrade to revision if:

Symptomatic progression
Rising metal ion trend
ALTR progression on MRI
Systemic symptoms develop

Soft Tissue Debridement is Critical

Complication

Rate

Risk Factors

Management

Dislocation

10-25%

Abductor loss, revision surgery

Constrained liner, bracing, re-revision

Infection

5-10%

Necrotic tissue, prolonged surgery

Debridement, antibiotics, staged revision

Nerve injury

2-5%

Scarring, pseudotumor displacement

Careful dissection, may recover

Persistent symptoms

15-30%

Incomplete debridement, tissue damage

May need re-revision

Abductor insufficiency

20-40%

Pre-existing damage from ALTR

Gait aids, reconstruction options limited

Fracture

2-5%

Bone loss, osteolysis

May need additional fixation

Modality	Role	Key Findings
Plain radiographs	Baseline, component position, osteolysis	Head position, stem subsidence, bone loss
CT scan	Bone detail, surgical planning	Osteolysis extent, bone stock assessment
Ultrasound	Screening for fluid collections	Pseudotumors, bursae, can guide aspiration
Bone scan	Rule out loosening, infection	Non-specific uptake, limited value

Component	Preferred Choice	Rationale
Bearing surface	Ceramic-on-polyethylene	Eliminates metal ion generation
Head size	32mm or smaller	Reduces taper moment
Head material	Ceramic (BIOLOX)	No corrosion, excellent tribology
Taper adapter	Ti sleeve if available	Salvages damaged stem taper
Stem	Keep if well-fixed, taper salvageable	Avoid unnecessary morbidity
Constraint	May need increased constraint	Abductor insufficiency common

Modality	Role	Key Findings
Plain radiographs	Baseline, component position, osteolysis	Head position, stem subsidence, bone loss
CT scan	Bone detail, surgical planning	Osteolysis extent, bone stock assessment
Ultrasound	Screening for fluid collections	Pseudotumors, bursae, can guide aspiration
Bone scan	Rule out loosening, infection	Non-specific uptake, limited value

Component	Preferred Choice	Rationale
Bearing surface	Ceramic-on-polyethylene	Eliminates metal ion generation
Head size	32mm or smaller	Reduces taper moment
Head material	Ceramic (BIOLOX)	No corrosion, excellent tribology
Taper adapter	Ti sleeve if available	Salvages damaged stem taper
Stem	Keep if well-fixed, taper salvageable	Avoid unnecessary morbidity
Constraint	May need increased constraint	Abductor insufficiency common

Trunnionosis and Taper Corrosion

Trunnionosis and Taper Corrosion

TRUNNIONOSIS AND TAPER CORROSION

ALVAL SCORE (CAMPBELL)

Critical Must-Knows

Examiner's Pearls

Critical Exam Concepts

Taper Mechanics Matter

Large Heads = High Risk

Metal Ions are Screening

Soft Tissue Destruction

Taper Corrosion Risk Assessment

THOLTRisk Factors for Taper Corrosion

FCGCorrosion Mechanisms

PUNCHSystemic Effects of Cobalt

Overview and Epidemiology

Epidemiology

Historical Context

Pathophysiology

The Corrosion Cascade

Morse Taper Fundamentals

Types of Corrosion at the Taper

Adverse Local Tissue Reaction (ALTR)

Risk Factors

Implant-Related Risk Factors

Patient-Related Risk Factors

Intraoperative Considerations

High-Risk Combinations to Remember

Clinical Presentation

Local Symptoms

Systemic Symptoms

Clinical Stages

Progression of Trunnionosis

Investigations

Serum Metal Ion Testing

Metal Artifact Reduction Sequence MRI

Additional Imaging Modalities

Joint Aspiration

Investigation Protocol for Symptomatic THA

Differential Diagnosis

Painful THA - Differential Diagnosis

Management

Non-Operative Surveillance

When to Revise

Surgical Management

Implant Selection at Revision

Soft Tissue Debridement is Critical

Surgical Technique Considerations

Surgical Approach

Soft Tissue Handling

Intraoperative Decision-Making

Complications

Complications of ALTR and Revision Surgery

High Complication Rate

Outcomes and Prognosis

Prognostic Factors

Evidence Base and Key Studies

Langton DJ - Taper Corrosion in Large-Head MoM THA

AOANJRR - Metal-on-Metal Hip Arthroplasty Analysis

Hart AJ - MARS MRI for ALTR Detection

Mistry A - Outcomes of Revision for ALTR

Exam Viva Scenarios

Scenario 1: Surveillance of At-Risk Implant

Scenario 2: Symptomatic ALTR Requiring Revision

Scenario 3: Systemic Cobalt Toxicity

Australian Context

AOANJRR Data

TGA Guidance

AOANJRR Findings on Metal-on-Metal THA

Patient Notification

TRUNNIONOSIS AND TAPER CORROSION

Definition

Risk Factors (THOLT)

Corrosion Mechanisms

Metal Ion Thresholds

MARS MRI Findings

Revision Principles

Systemic Cobalt Toxicity (PUNCH)

Trunnionosis and Taper Corrosion

Trunnionosis and Taper Corrosion