29 November 2016
How to diagnose taper corrosion
Taper junction corrosion in total hip replacements is a growing concern; it is also a multi-faceted problem. With both asymptomatic and symptomatic patient groups, what indications should a surgeon look for when corrosion is suspected? While there is not a single test to isolate corrosion problems, a spectrum of diagnostic tools have been suggested to make a diagnosis.
Corrosion of the head-neck or taper junction in modular total hip implants has increasingly been reported [1,2]. While several co-mingling factors have been identified as contributors to the problem (See Part I of this article series), patients may or may not display symptoms, which can make it challenging to identify corrosion through symptoms. In some cases, corrosion has not been identified or confirmed until during revision, and these patients may experience higher rates of complications . Symptoms patients may display cover a broad range and include, but are not limited to: pain, instability, elevated serum metal levels, adverse local tissue reactions (ALTR), swelling, in rare cases neurological changes, and more.
It can take upwards of eight months to establish corrosion as a diagnosis and perform retrieval  and Kwon cautions against overreliance on any single diagnostic tool . Here we look at a selection of clinical indicators that may help identify or eliminate corrosion and/or associated metal toxicity as a cause for concern.
When to suspect corrosion
Jennings et al  are one of many groups of researchers to point out that diagnosis is generally a process of elimination and more studies are needed to direct diagnosis and treatment. Certainly, if a patient received a metal-on-metal (MoM) implant further investigation is warranted. However, corrosion of the taper junction has been seen in cases regardless of the type of bearing surface. When corrosion products and metal debris are released from the taper junction due to microfracture and accelerated wear, adverse local tissue reaction (ALTR) may transpire .
Diagnosis of taper corrosion can be a challenge. It should be suspected if the patient experiences sudden onset of pain after a post-operative period of one to two years without pain . No matter what symptoms or type of implant a post-operative hip replacement patient may present with, it is advisable to begin with a detailed history and systematic, comprehensive clinical examination . More common causes of pain should be ruled out .
A selection of reported symptoms of taper junction corrosion
- Adverse local tissue reaction (ALTR)
- Discolored joint fluid
- Elevated serum colbalt and chromium levels
- Iliopsoas sign or a sterile iliopsoas abscess
- Symptoms of, or confirmed periprosthetic infection
- Neurological and/or sensory deficits
Pain as a possible initial symptom
Most commonly pain, swelling and instability are reported , although pain itself is not necessarily an indicator of corrosion. Nam et al  found that persistent pain in active patients under the age of 60 was described in at least one location in the hip by 40 percent of study participants 3 years post-operatively. Indeed, McGroryand McKenney  remind us that the majority of cases of “new onset of pain, stiffness, or dysfunction after successful arthroplasty outcome” is not attributed to corrosion or adverse tissue reaction.
When pain presents itself during resisted flexion of the hip (iliopsoas sign) or a sterile iliopsoas abscess is discovered, corrosion should be suspected [12,13]. The common physical exam manifestations of ALTR include pain with straight leg raise, abductor weakness, and limp during ambulation .
Is it an infection?
In a 2015 paper Whitehouse et al  highlighted 17 cases where corrosion was misdiagnosed as periprosthetic infection despite multiple negative pre-and-intra-operative samples for unknown organisms. Serum indicators pointed to a diagnosis of infection (elevated erythrocyte sedimentation rate, C-reactive protein, stromal polymorphonuclear cell counts). Corrosion was identified in all cases during revision for the complication of pseudotumors—all patients had been experiencing pain and were recipients of metal-on-highly cross-linked polyethylene (MoP) joints.
Serum metal levels may be elevated
Once fixation issues and infection have been ruled out for patients with new onset pain, the next diagnostic step that may offer assistance is determining serum cobalt (Co) and chromium (Cr) levels [1,16]. Its been reported that even in well-functioning metal-on-polyethylene hips, serum metal levels are elevated for up to ten years post-operatively, which is attributed to metal release from the modular femoral junction . At present, the costs of toxicity surveillance and revision for every person who has received a modular hip replacement would place an unrealistic burden on health care systems .
Different thresholds for serum metal levels may depend on the type of implant. Using 1 ppb as the minimum serum Co requirement to diagnose corrosion has been advised for patients with metal-on-polyethylene devices; for those with a MoM THA, higher acceptable Co levels should be expected because of surface wear, but a minimum requirement is, at present, unspecified . Over 3 times higher Co levels from baseline were noted in patients with hybrid and Co/Cr hips through 120-months of follow-up .
In a risk stratification algorithm for MoM THA patient management published by Kwon  [See Part III of this article series], the highest-risk category suggesting revision is indicated for patients with high cobalt level (>5 ppb) and high cobalt/chromium ratio (>5). Some have found cobalt levels in ratio to chromium to not be indicative of corrosion or ALTR for MoM THA , others have . Regardless, repeated recommendations for patients with indications of corrosion is to test Co levels regularly to be able to track serum metal level changes.
Evidence of adverse local tissue reaction?
While there is not a single biomarker to indicate adverse local tissue reaction (ALTR) due to corrosion, Whitehouse and colleagues  have asserted that “solid, cystic and mixed soft-tissue lesions” may be noted on imaging. Some researchers have defined ALTR in corrosion cases as metallosis, characterized by aseptic fibrosis, local necrosis, and grey tissue discoloration around the joint. The discoloration of joint fluid, as viewed upon aspiration, is a good visual indication of this .
To further cloud the diagnostic tool kit, Bisseling and co-authors  did not find a relationship between “clinical scoring, metal ion levels and periprosthetic lesions” in their study group of resurfaced and MoM hip patients. In fact, they assert that current MARS-MRI classification systems score conventional soft-tissue collection or effusions as pseudotumors, leading to an overestimation of occurrence.
Use of imaging technology
Radiographic evidence is a useful screening tool  to help identify and determine osteolysis, describing the bony extent of corrosion-related ALTR, as well as device positioning and/or modes of failure. Ultrasound  and metal artifact reducing sequence-MRI (MARS-MRI) [4,22] are suggested as helpful in determining if, and the extent of, synovitis, osteolysis, muscle/tendon destruction, periprosthetic fluid collection and pseudotumors .
Tower  encountered a case of cobaltism in a patient with MoM THA who presented himself with complex symptoms such as, “tinnitus, deafness, vertigo, visual changes, rashes, hypothyroidism, tremor, dyspnea on exertion, mood disorders, dementia, heart failure, and peripheral neuropathy”. Revision caused drastic improvement in the neurological and sensory deficits, but at 66 months post-revision the patient had only returned to two-thirds professional productivity… the patient is a surgeon. Tower reminds us that arthroprosthetic cobaltism should be on the radar.
In 2015 a paper was published on one of the first documented cases of cobalt cardiac toxicity that led to patient death in a case of bilateral MoM THA where the patient died shortly after revision .
It may be challenging to diagnose taper corrosion as the source of a patient’s pain or instability, but it is not impossible. A selection of diagnostic tools are available and as research into the corrosion of modular taper junctions expands, diagnosis is likely to become a more straightforward endeavor.
In Part III of this article series we look at surgical options for revision.
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Taper corrosion, part 2
This is part 2 of a three part series on taper corrosion.