Complications of Metal-on-Metal Bearings

Fig. 15.1

An anteroposterior (AP) radiograph of the right hip revealed a metal-on-metal THA with a DePuy ASR acetabular component , and a Corail stem

Epidemiology: The Nature of the Problem

Metal-on-metal THAs made a resurgence due to their improved wear characteristics, promise of longevity, and lower dislocation rates in the early 2000s [1, 2]. By 2006, 35% of primary THAs in the United States were MoM articulations. It was estimated that over 1,000,000 MoM articulations have been implanted worldwide since 1996 [3]. Recently, adverse local tissue reactions (ALTRs) associated with these bearings have curbed enthusiasm for their use identified, in addition to the traditional failure mechanisms.

The evaluation of a failed MoM THA must begin systematically, and should be similar to the evaluation of any problematic THA. Traditional modes of failures such as instability, infection, tendonitis, aseptic loosening, periprosthetic fracture, and referred pain must be thoroughly evaluated as potential causes of pain before attributing the source of the problem to the metal-on-metal bearing (Table 15.1) [2, 4, 5]. Once these issues have been ruled out, bearing-related problems such as tissue necrosis, modular junction corrosion, skin hypersensitivity, and systematic cobaltism should also be considered.

Table 15.1

Traditional modes of failure for THA that must also be considered during the evaluation of a MoM THA

Modes of failure
Periprosthetic infection
Osteolysis
Aseptic loosening
Dislocation
Periprosthetic fracture
Iliopsoas tendonitis
Referred radicular pain
Trochanteric bursitis

Histologically, ALTRs appear as a lymphocytic inflammatory response that leads to vasculitis-induced necrosis of soft tissue and bone. The terms aseptic lymphocytic vasculitis-associated lesions (ALVAL) , pseudotumor, and metallosis have all been used as umbrella terms in the literature to describe the soft-tissue destruction due to metal-metal junctions and articulations in THA [1, 2, 4–10]. The more commonly accepted term for these problems is adverse local tissue reaction. This chapter presents the evaluation and treatment of complications unique to THA with metal-on-metal articulations.

Risk Stratification

Risk stratification is important in the diagnostic and treatment algorithms of painful MoM THAs. This process is multifactorial as differences in clinical presentation exist. Clinical, laboratory, and radiographic factors help the clinician stratify patients into low-, moderate-, and high-risk categories, which can impact surveillance and treatment (Tables 15.2 and 15.3). A patient who is asymptomatic with normal serum ion levels, appropriately positioned components, and an implant with a low failure rate must be evaluated differently than a patient who is symptomatic with elevated cobalt and chromium levels, a malpositioned cup, and an implant with a high rate of failure. This risk stratification algorithm has been described by Kwon et al. [5].

Table 15.2

The following factors can help surgeons risk stratify patients [5]

Factors to consider for risk stratification

Patient factors

Symptoms

Clinical exam

Implant type

Implant position

Radiographs

Infection workup

Metal ion level

Cross-sectional Imaging

Table 15.3

Guide to management

Risk stratification can help guide management
Who needs cobalt and chromium levels?
Who needs a MARS MRI?
What frequency of surveillance?
Who needs a revision THA?

Prevention

At this point, the main prevention mode to complications associated with metal-on-metal articulations is to discontinue the use of this bearing surface in contemporary THAs.

Diagnosis

The evaluation of a painful MoM THA is multifaceted, focusing on history and physical examination, plain radiographic assessment, laboratory values, and cross-sectional imaging. A thorough review of systems must be performed as systemic cobaltism has been reported [11].

Patient History

A thorough patient history is essential in the evaluation of a patient with a painful MoM THA (Table 15.4).

Table 15.4

Questions to consider in the evaluation of a symptomatic MoM patient

Where is the pain?

How long has the pain occurred?

Was there a pain-free interval ?

Is there start-up pain?

Is there thigh pain? (stem or socket pain)

Is there groin pain? (socket pain)

Do they have mechanical symptoms?

Exacerbating activities?

Alleviating activities?

Constitutional symptoms?

Instability events?

The location, duration, and severity of pain are essential to the evaluation.
The patient should be asked about mechanical symptoms such as popping, clicking, or ratcheting.
Exacerbating or alleviating factors should be noted.
Signs or symptoms of infection must be delineated in the history, as this will change your diagnostic and treatment algorithm .
The skin should be inspected for previous scars, dermal reaction, or signs of infection.

A complete review of systems may also unveil systemic issues due to metallosis (Table 15.5).

Table 15.5

Questions asked during a review of systems

Due to multiorgan toxicity of cobalt and chromium, consider the following questions:

Have you had any change in your vision?

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

Have you experienced recurrent rashes?

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

Do you have shortness of breath ?

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

Physical Examination

Physical examination remains important in the evaluation of any painful total hip arthroplasty. Essential components include the following keys:

The skin should be inspected for previous scars, dermal reactions, or signs of infection.
Palpation should be performed to detect any areas of pain or a soft-tissue mass.
Complete neurovascular examination.
Range of motion of the hip joint and abductor muscle strength testing should be routinely performed.
Any gait abnormalities, such as a Trendelenburg gait, should be noted.
Is the pain reproduced by supine or reverse straight leg raising (radiculopathy)?
Is the pain reproduced by trochanteric palpation (trochanteric bursitis)?
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 the implant type and component position, as well as signs of loosening or osteolysis. One must pay close attention to component malposition, as this has been shown to correlate with increased ion levels and wear [12]. A high-abduction angle or high levels of combined anteversion of the components lead to diminished bearing lubrication leading to increased ion release and soft-tissue reactions [12–16].

Radiographic Analysis

Radiographic evaluation of the failed THA should include an anteroposterior (AP) 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, osteolysis, or ingrowth .
Judet views may be necessary to evaluate for osteolysis or loosening.

Laboratory Evaluation

Following the above evaluation, laboratory testing is important in the diagnostic algorithm of the painful MoM THAs (Table 15.6). Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) should be obtained to rule out periprosthetic joint infection. Unlike MoP THAs, ESR and CRP have been shown to be more nonspecific in the evaluation of MoM THA, as patients with adverse local tissue reactions (ALTR) without infection have also shown elevated markers [17]. Likewise, aspiration results of painful MoM THAs can be misleading and must be interpreted with caution. Traditional values of 3000 WBC/mL combined with >80% PMN indicating periprosthetic infection may not apply to those MoM THA with ALTR with a propensity for falsely positive results [18, 19]. It is therefore important to have a manual rather than an automated cell count performed as automated counts may misinterpret metallic debris leading to spuriously elevated counts. Unfortunately, alpha defensin testing may also be falsely positive in these patients. In general we have a low threshold to aspirate these patients preoperatively in an attempt to more definitely rule in or out infection prior to operative intervention as the intraoperative appearance can also be misleading with purulence commonly identified intraoperatively.

Table 15.6

Laboratory evaluation

Labs
• CRP
• ESR
• Aspiration
• Cobalt
• Chromium

The measurement of serum cobalt and chromium has been used for the evaluation of MoM THA [1, 8, 20]. These metal ions are not only released from the bearing surface during articulation, but also from modular junctions due to corrosion. In 2010, the British Medicine and Healthcare Products Regulatory Agency voiced concern over 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 [10]. Although a useful adjunct, ion levels alone should not be used as a trigger for revision due to 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 [4, 10, 16]. Unfortunately, no current test can predict periarticular necrosis; however biomarkers to detect adverse local tissue reactions are currently under investigation [4, 10].

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