arthroplasty
Metal-on-Metal Hip Complications and ALTR
advanced
6 min
20 marks
7 questions
Clinical Scenario
A 55-year-old female with bilateral metal-on-metal hip resurfacing performed 8 years ago presents with right groin pain and clicking for 6 months. Initially pain-free for 6 years. She also reports new onset of lateral thigh numbness. Routine surveillance shows whole blood cobalt level of 45 μg/L (previously 5 μg/L two years ago).
MARS MRI (Metal Artifact Reduction Sequence) showing large posterolateral fluid collection/pseudotumour with abductor muscle involvement. This represents ARMD (Adverse Reaction to Metal Debris).
Image source: Open Access medical literature (NIH/PubMed Central) • CC-BY License
Questions
Question 1 (3 marks)
What are the complications specific to metal-on-metal bearing surfaces and what is the underlying pathophysiology?
Question 2 (3 marks)
What is the surveillance protocol for metal-on-metal hip arthroplasty?
Question 3 (4 marks)
This patient has elevated cobalt (45 μg/L) with MARS MRI showing pseudotumour and muscle destruction. What is your management plan?
Question 4 (3 marks)
What are the key surgical principles for revision of MoM hip with ALTR?
Question 5 (3 marks)
What factors predict poorer outcome after revision for ALTR?
Question 6 (2 marks)
Explain trunnionosis and how it differs from bearing surface wear.
Question 7 (2 marks)
What would you counsel this patient regarding revision outcomes?
Exam Day Cheat Sheet
Must Mention
- •ALTR/ARMD = Adverse Reaction to Metal Debris
- •Cobalt >7μg/L = concerning, triggers MARS MRI
- •MARS MRI = gold standard for soft tissue assessment
- •Annual surveillance for ALL MoM hips
- •Revise to ceramic-on-poly or ceramic-on-ceramic
- •EXTENSIVE debridement essential
- •Dual mobility for abductor deficiency/tissue damage
Common Pitfalls
- •Monitoring without revision despite progression
- •Not imaging elevated ions even if asymptomatic
- •Incomplete debridement at revision
- •Missing contralateral hip in bilateral MoM
- •Forgetting trunnionosis (modular junctions)