Patient History

A thorough patient history is essential in the evaluation of a patient with painful MoM THA.

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  The location, duration, and severity of pain are essential to the evaluation.

  
  
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  Exacerbating or alleviating factors should be noted.

  
  
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  Signs or symptoms of infection must be delineated in the history, because this changes the diagnostic and treatment algorithm.

  
  
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  The skin should be inspected for previous scars, dermal reaction, or signs of infection.

  
  
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  One must also assess for potential hypersensitivity reactions, because these may manifest as past dermatitis in those patients with metal allergy to nickel jewelry.

  
  
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  A complete review of systems may also unveil systemic issues caused by metallosis ( Boxes 1 and 2 ).

  
  
  
  

  Box 1

  
  

  
  

  
  

  
  
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    Where is the pain?

    
    
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    How long has the pain occurred?

    
    
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    Was there a pain-free interval?

    
    
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    Is there start-up pain?

    
    
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    Is there thigh pain (stem or socket pain)?

    
    
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    Is there groin pain (socket pain)?

    
    
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    Do they have mechanical symptoms?

    
    
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    Exacerbating activities?

    
    
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    Alleviating activities?

    
    
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    Constitutional symptoms?

    
    
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    Instability events?

  
  

  
  

  Questions to consider in the evaluation of a symptomatic MoM patient
  
  
  
  

  Box 2

  
  

  
  

  
  

  
  
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    Have you had any change in your vision?

    
    
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    Have you experienced any ringing in your ears, difficulty hearing, or dizziness?

    
    
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    Have you experienced recurrent rashes?

    
    
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    Do you have a tremor, difficulty remembering things, or numbness and tingling in your feet and hands?

    
    
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    Do you have shortness of breath?

    
    
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    Do you have mood swings, fatigue easily, or have gained weight lately?

  
  

  
  

  Questions asked during a review of systems because of multiorgan toxicity of cobalt and chromium
  
  

Physical Examination

Physical examination remains important in the evaluation of any painful THA.

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  The skin should be inspected for previous scars, dermal reaction, or signs of infection.

  
  
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  Palpation should be performed to detect any areas of pain or a soft tissue mass.

  
  
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  Complete neurovascular examination.

  
  
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  Range of motion of the hip joint and abductor muscle strength testing should be routinely performed.

  
  
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  Any gait abnormalities, such as a Trendelenburg gait, should be noted.

  
  
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  Is the pain reproduced by supine or reverse straight leg raising (radiculopathy)?

  
  
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  Is the pain reproduced by trochanteric palpation (trochanteric bursitis)?

  
  
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  Is the pain reproduced by resisted hip flexion (iliopsoas tendonitis)?

Radiographic Evaluation

After a complete history and physical, evaluation of a painful MoM THA should proceed with standard radiographs examining implant type and component position, and signs of loosening or osteolysis. One must pay close attention to component malposition, because this has been shown to correlate with increased ion levels and wear. A high abduction angle leads to diminished bearing lubrication leading to increased ion release and soft tissue reactions. Radiographic evaluation of the failed THA should include an anteroposterior view of the pelvis and a cross-table lateral view of the affected hip. Both the acetabular and femoral components should be examined closely for signs of loosening or ingrowth. Judet views may be necessary to evaluate for osteolysis or loosening.

Laboratory Testing

Following initial evaluation, laboratory testing is important in the diagnostic algorithm of the painful MoM THA. Erythrocyte sedimentation rate and C-reactive protein should be obtained to rule out periprosthetic joint infection. Unlike metal-on-polyethylene THA, erythrocyte sedimentation rate and C-reactive protein have been shown to be more nonspecific in the evaluation of MoM THA, because patients with ALTR without infection have also shown elevated markers. Likewise, aspiration results of painful MoM THA can be misleading and must be interpreted with caution. Traditional values of 3000 white blood cells per milliliter combined with greater than 80% polymorphonuclear leukocytes (PMN) indicating periprosthetic infection may not apply to MoM THA with ALTR. It is therefore important to have a manual rather than an automated cell count performed because automated counts may misinterpret metallic debris leading to spuriously elevated counts.

Metal ion levels (cobalt and chromium) have been used for the evaluation of MoM THA. These metal ions are not only released from the bearing surface during articulation, but also from modular junctions because of corrosion. In 2010, the British Medicine and Healthcare Products Regulatory Agency voiced concern about MoM hip implants issuing a safety alert recommending cross-sectional imaging in any MoM hip arthroplasty patient with cobalt or chromium ion levels greater than 7 ppb. Although a useful adjunct, ion levels alone should not be used as a trigger for revision because of their inaccuracy in predicting soft tissue damage in MoM THA. Metal ion levels and their correlation to MoM THA are poorly understood and have been unreliable predictors of soft tissue destruction at the time of revision arthroplasty. Unfortunately, no current test can predict periarticular necrosis; however, biomarkers to detect ALTRs are currently under investigation ( Box 3 ).

The evaluation of a MoM patient is similar to the evaluation of a potential periprosthetic infection. Whereby the clinician cannot rely solely on a single variable to determine the need for intervention, multiple variables must be considered and taken into account as a group ( Fig. 1 ).

Important diagnostic MoM variables. MARS, metal artifact reduction sequence.

Advanced Imaging

Cross-sectional imaging in the form of ultrasound or metal artifact reduction sequence (MARS) MRI has been used in the evaluation of adverse soft tissue reactions. Ultrasound has been able to detect soft tissue lesions, and may differentiate these lesions as solid or cystic. However, this imaging modality remains operator dependent limiting its consistent use in the detailed evaluation of soft tissue lesions. It can be efficient and cost-effective as an initial screening test with high sensitivity.

MARS MRI has become the workhorse imaging modality for the evaluation of ALTRs associated with MoM THAs. MARS MRI allows for early detection of soft tissue lesions and the ability to follow MoM THA patients longitudinally with serial evaluations ( Fig. 2 ).

Cross-sectional MRI of a cystic ALTR lesion ( arrow ) in a MoM THA.

Clinical Presentation

The clinical presentation of a patient with an ALTR remains variable with each patient having an individualized response to metal debris. The initial presenting symptoms may be pain, mechanical symptoms, abductor weakness, instability, or rash.

In addition to symptomatic patients, ALTRs have been identified in asymptomatic patients. A recent investigation has shown a 31% prevalence of cystic ALTRs in asymptomatic MoM patients on MARS MRIs. The natural history of these lesions remains undefined but calls into question the reliability of pain as an indicator of bearing malfunction.