Back to ISAWE Scenarios
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).
Open Full Size

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)