MoM

Clinical image

Metal-on-metal prosthetic hip. Source: Wikimedia Commons — James Heilman, MD; CC BY-SA 4.0. Image binary is embedded locally in this package; original source and licence are retained.

Why?

• Improved ROM
• Better gait
• reduced dislocation
• Reduced stress shielding
• Less infection
• Less DVT/PE
• Preserves bone stock
• Preserved BMD in Gruen 7 zone

Key points

Look for

• Abduction angle (40 degree)
• Mention Head size (minimum 46 mm)
• Metaphysial radiolucency
• Narrowing/fracture of neck
• Divot sign:Depression of neck contour just below the junction with femoral component, often associated with reactive exostosis. Sign of impingement

Indications

• Young man with normal anatomy and primary OA
• C/I
  • Small head and neck, deformed acetabulum
  • Progressive disease: inflammatory disease
  • Large cyst/ AVN
  • Female who want children
  • Large BMI>35kg/m2
  • Osteoporosis

Complications

• Femoral neck # 1-3%
  • Parient causes
    • Female, bone quality
  • Surgeon causes
    • Experience
  • Technical causes
    • Head size
    • notching
    • component malposition
  • Inadequate blood supply
    • Posterior approach

Technical cause reduction

• Templating
• Upsizing head
• Proper jig
• Surgeon experience (De Smith JBJS Am)
  • Minimum 200 THA before resurfacing
  • learning curve 20-50 resurfacing to overcome
• Computer navigation to prevent mal position

Compli

• Loosening: More common in females
• Metallosis: Macroscopic staining of soft tissue and is associated with abnormal wear

ALVAL and Pseudotumour

• Aseptic lymphocyte dominated Vasculitis associated lesion is cause by metal particle debris.
• Patient presents with localised pain and osteolytic reaction. More severe form is pseudotumor

ALVAL and Pseudo Tr

• ALVAL is Delayed Hypersensitivity reaction
• Ps Tr is a characterised by formation of synovial like bio-membrane which can produce collagenase, IL1 and TNF, leading to bone resorption and osteolysis. It is neither malignant nor infective
• Diagnosis by USG and MARS

pathology

• Wear
• Hypersensitivity
• Combination of two
• Unknown

Causes

- Component malposition
- Abduction angle of acetabulum >35 degree
- Jumbo head in THA
- Small head resurfacing
- female
- Trunnionosis: Narrow Head neck taper and large head leading to corrosive wear at trunnion

Painful MoM

• I will first exclude infection
• Causes can be extrinsic or intrinsic
• Exclude
  • Referred pain
  • Soft tissue causes: psoas/abductor tendinosis, impingement
  • POVD
  • Stress fracture
  • Component malposition
  • Femoral neck fracture
  • Aseptic loosening
  • Heterotropic ossification
• I will follow BHS guideline for MoM once these causes are excluded

Rule out ARMD

• Look for groin swelling, hip pain, limping and decreased ROM
• Measure metal ions: may not be raised in MoM THA
• MARS/USG: most important,(Look for muscle/bone damage)
  • then observe
    • if no fluid collection, mass
    • ions static

Followup MoM

• ASR
• Female resurfacing
• Male small resurfacing < 48
• Jumbo THA head >36
• Other Symptomatic MoM
• Oxford HS
• Blood metal ions
• Annual follow up
• MARS/USG if
  • worsening OHS

  • 7ppb metal ions

Other Asymptomatic

• ODEP rated: First year, 7th year the 3 yearly
• Non ODEP rated: Yearly for 5 years, 2 yearly for 10 years, the 3 yearly afterwards

Management of pseudotumor

• Get second opinion
• Aggressive debridement
• Keep the option of constrained cup as soft tissue may be defective
• MoP, uncemented

ASR

• Sub hemispherical cup to reduce impingement
• Internal groove design to accommodate insert
• effective arc was reduced, edge loading occurs
• Suboptimal manufacturing of CCM
• High failure rate