- Advantages: 
    - larger heads helps avoid dislocation:
    - avoidance of screws
    - larger heads allows greater ROM

- Disadvantages:
     - metallosis
     - contraindictated in renal insufficiency;

- Levels:
     - normal cobalt:
           - mean serum cobalt level of 0.24 µg/L (range: 0.08 to 0.50 µg/L)
           - highest safe level: 5 µg/L and 60 µg/L for cobalt in urine
           - references:
                  - Serum metal ion concentrations after unilateral vs bilateral large-head metal-on-metal primary total hip arthroplasty.
                  - Systemic cobalt toxicity from total hip arthroplasties: review of a rare condition Part 1 - history, mechanism, measurements, and pathophysiology.
                  - Systemic cobalt toxicity from total hip arthroplasties: review of a rare condition Part 2. measurement, risk factors, and step-wise approach to treatment.

       - normal chromium: mean serum chromium level of 0.28 µg/L (range, 0.06 to 0.93 µg/L)
           - note potential variation in the levels of chromium in plasma compared with those in serum (hence need to assess whole-blood
                    levels rather than levels in plasma, serum, or red blood cells alone)
           - highest safe level: 17 µg/L for chromium in blood and 20 µg/L for chromium in urine;
           - references:
                   - Release of hexavalent chromium from corrosion of stainless steel and cobalt-chromium alloys
                   - The effect of the diameter of metal-on-metal bearings on systemic exposure to cobalt and chromium
     - references:  
           - Blood and urine metal ion levels in young and active patients after Birmingham hip resurfacing arthroplasty: four-year results of a prospective longitudinal study.
           - How do serum cobalt and chromium levels change after metal-on-metal hip resurfacing?  
           - Metal-on-metal bearings total hip arthroplasty: the cobalt and chromium ions release concern
           - Sensitivity and specificity of blood cobalt and chromium metal ions for predicting failure of metal-on-metal hip replacement

- Pseudotumor: 
       - Pseudotumors in association with well-functioning metal-on-metal hip prostheses: a case-control study using three-dimensional computed tomography and magnetic resonance imaging.

- Trunion:
      - Comparison of Whole-Blood Metal Ion Levels Among Four Types of Large-Head, MoM THA Implants

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M2 a Magnum: Large Metal Articulation Design Rationale

Arthroprosthetic cobaltism: neurological and cardiac manifestations in two patients with metal-on-metal arthroplasty: a case report.

Metal-on-Metal Hip Resurfacing Arthroplasty

Survivorship and Retrieval Analysis of Sikomet Metal-on-Metal Total Hip Replacements at a Mean of Seven Years.

The effect of the diameter of metal-on-metal bearings on systemic exposure to cobalt and chromium.

Metal-on-metal total hip arthroplasty with large heads may prevent early dislocation.

The rationale for metal-on-metal total hip arthroplasty.

Renal Clearance of Cobalt in Relation to the Use of Metal-on-Metal Bearings in Hip Arthroplasty

Understanding Why Metal-on-Metal Hip Arthroplasties Fail: A Comparison Between Patients with Well-Functioning and Revised Birmingham Hip Resurfacing Arthroplasties AAOS Exhibit Selection

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- articles which argue against metal on metal: 
       - Chronic cobalt poisoning in endoprosthetic replacement
       - Metal-on-metal resurfacing arthroplasty: no way under the sun!--in the affirmative.                                            
       - Painful metal-on-metal total hip arthroplasty.
       - Possible Prosthetic Poison
       - "Asymptomatic" Pseudotumors After Metal-on-Metal Hip Resurfacing Arthroplasty: prevalence and metal ion study. 
       - No Superiority of Cemented Metal-on-Metal vs Metal-on-Polyethylene THA at 5-Year Follow-up 
       - Reduced Articular Surface of One-piece Cups: A Cause of Runaway Wear and Early Failure
       - Case Report. Cystic Lesion of the Groin due to Metallosis: A Rare Long-Term Complication of Metal-on-Metal Total Hip Arthroplasty
       - A benign psoas mass following metal-on-metal resurfacing of the hip.
       - Metal-on-metal resurfacing arthroplasty: no way under the sun!--in opposition.
       - Metallosis After Contemporary Metal-on-Metal Total Hip Arthroplasty. Five to Nine-Year Follow-up. 
       - Has MOM worn out its welcome?
       - Metal-on-Metal Total Hip Arthroplasty: Causes and High Incidence of Early Failure
       - Polyneuropathy caused by cobalt-chromium metallosis after total hip replacement.
       - Adverse Local Tissue Reaction Arising from Corrosion at the Femoral Neck-Body Junction in a Dual-Taper Stem with a Cobalt-Chromium Modular Neck