Point/Counter

Is switching from cobalt-chrome to non-cobalt-chrome femoral heads the best way to mitigate taper corrosion problems?

Click here to read the Cover Story, "Suspicion is of the essence with taper corrosion diagnosis."

POINT

Non-cobalt-chrome head is best option

Brian J. McGrory, MD, MS
Brian J. McGrory

Taper corrosion or mechanically assisted crevice corrosion is commonly noted in contemporary THA retrieval specimens and is becoming more recognized as a clinical diagnosis. Issues related to mechanically assisted crevice corrosion (MACC) include symptoms, such as stiffness and pain, adverse local tissue reaction (ALTR) including necrosis of tissues, and secondary instability, even systemic reactions. These problems appear to be related to fretting and corrosion debris from the cobalt-chromium alloy femoral head. Non-cobalt-chrome femoral heads, such as ceramic, oxidized zirconium and stainless steel, may also be susceptible to MACC at the trunion-bore junction, but they do not produce the cobalt-rich fretting and corrosion products that appear to be responsible for many MACC-associated problems. Interestingly, even in THA taper corrosion failure with a cobalt-chrome alloy (CoCr) stem, switching to a revision ceramic head appears to decrease symptoms and serum Co. Another area of concern is gross trunion failure (GTF), for which some believe corrosion is an inciting factor. This failure mode has rarely been described with non-CoCr heads and switching to a ceramic revision head is suggested as a strategy for treatment of early corrosion when the trunion is intact, even in prostheses at high risk for GTF. Until we more completely understand the etiology of MACC, I strongly believe a non-CoCr alloy head should be used preferably in primary surgery. Likewise, if a patient presents with symptomatic MACC, I think revision to a non-cobalt-chromium femoral head is the best treatment option in most cases, if the trunion is not significantly damaged.

Brian J. McGrory, MD, MS, is a clinical professor at Tufts University School of Medicine and orthopedic surgeon at Maine Medical Center in Portland, Maine.
Disclosure: McGrory reports he is an editor for Arthroplasty Today, receives royalties from Innomed Orthopedic Instruments and is a consultant for Smith & Nephew.

COUNTER

Potential tradeoffs

Steven M. Kurtz, PhD
Steven M. Kurtz

I mostly agree with this statement but take issue with the concept that all “non-cobalt-chrome” femoral heads are clinically equivalent. Further, making reactionary switches away from a historically and internationally well-accepted biomaterial like CoCr alloy is not necessarily the “best” way for orthopedics to proceed when confronted with a rare, clinically significant, but poorly understood reason for revision. Retrieval studies have shown the vast majority of Co and Cr in a modular taper is released from the CoCr femoral head taper surface, even when the stem is fabricated from CoCr alloy. On the other hand, titanium (Ti) wear debris and corrosion products can still cause metallosis and osteolysis, although Ti has generally not been associated with ALTRs that require revision. From a practical perspective, switching femoral head materials from CoCr alloy to ceramic is a straightforward way to address taper corrosion problems associated with ALTRs. Using a Ti alloy acetabular shell and stem, the surgeon can readily exclude CoCr alloy from the entirety of modern THA constructs. I will note that surgeons have been able to make such a choice for more than a decade. There are potential tradeoffs with widespread turning away from CoCr femoral heads, especially if the alternative material is more expensive and itself carries unique risks. With ceramic materials, the health economic implications and fracture risk have been studied and seem to be clinically acceptable with the data available today. Introduction of a new and unproven alternative femoral head material, such as a novel ceramic-coated head or a new femoral-head alloy, would likely face economic and regulatory challenges in today’s health care and litigation environment.

Steven M. Kurtz, PhD, is director of the Implant Research Center and a research professor at Drexel University in Philadelphia.
Disclosure: Kurtz reports he is an officer and shareholder of Exponent, which receives fees for his presentations and consulting services; receives research support as a principal investigator from Stryker, Zimmer Biomet, Invibio, Stelkast, Wright Medical Technology, Ceramtec, Celanese, Simplify Medical and Ferring Pharmaceuticals; and receives royalties, financial or material support from Elsevier.

Click here to read the Cover Story, "Suspicion is of the essence with taper corrosion diagnosis."

POINT

Non-cobalt-chrome head is best option

Brian J. McGrory, MD, MS
Brian J. McGrory

Taper corrosion or mechanically assisted crevice corrosion is commonly noted in contemporary THA retrieval specimens and is becoming more recognized as a clinical diagnosis. Issues related to mechanically assisted crevice corrosion (MACC) include symptoms, such as stiffness and pain, adverse local tissue reaction (ALTR) including necrosis of tissues, and secondary instability, even systemic reactions. These problems appear to be related to fretting and corrosion debris from the cobalt-chromium alloy femoral head. Non-cobalt-chrome femoral heads, such as ceramic, oxidized zirconium and stainless steel, may also be susceptible to MACC at the trunion-bore junction, but they do not produce the cobalt-rich fretting and corrosion products that appear to be responsible for many MACC-associated problems. Interestingly, even in THA taper corrosion failure with a cobalt-chrome alloy (CoCr) stem, switching to a revision ceramic head appears to decrease symptoms and serum Co. Another area of concern is gross trunion failure (GTF), for which some believe corrosion is an inciting factor. This failure mode has rarely been described with non-CoCr heads and switching to a ceramic revision head is suggested as a strategy for treatment of early corrosion when the trunion is intact, even in prostheses at high risk for GTF. Until we more completely understand the etiology of MACC, I strongly believe a non-CoCr alloy head should be used preferably in primary surgery. Likewise, if a patient presents with symptomatic MACC, I think revision to a non-cobalt-chromium femoral head is the best treatment option in most cases, if the trunion is not significantly damaged.

Brian J. McGrory, MD, MS, is a clinical professor at Tufts University School of Medicine and orthopedic surgeon at Maine Medical Center in Portland, Maine.
Disclosure: McGrory reports he is an editor for Arthroplasty Today, receives royalties from Innomed Orthopedic Instruments and is a consultant for Smith & Nephew.

PAGE BREAK

COUNTER

Potential tradeoffs

Steven M. Kurtz, PhD
Steven M. Kurtz

I mostly agree with this statement but take issue with the concept that all “non-cobalt-chrome” femoral heads are clinically equivalent. Further, making reactionary switches away from a historically and internationally well-accepted biomaterial like CoCr alloy is not necessarily the “best” way for orthopedics to proceed when confronted with a rare, clinically significant, but poorly understood reason for revision. Retrieval studies have shown the vast majority of Co and Cr in a modular taper is released from the CoCr femoral head taper surface, even when the stem is fabricated from CoCr alloy. On the other hand, titanium (Ti) wear debris and corrosion products can still cause metallosis and osteolysis, although Ti has generally not been associated with ALTRs that require revision. From a practical perspective, switching femoral head materials from CoCr alloy to ceramic is a straightforward way to address taper corrosion problems associated with ALTRs. Using a Ti alloy acetabular shell and stem, the surgeon can readily exclude CoCr alloy from the entirety of modern THA constructs. I will note that surgeons have been able to make such a choice for more than a decade. There are potential tradeoffs with widespread turning away from CoCr femoral heads, especially if the alternative material is more expensive and itself carries unique risks. With ceramic materials, the health economic implications and fracture risk have been studied and seem to be clinically acceptable with the data available today. Introduction of a new and unproven alternative femoral head material, such as a novel ceramic-coated head or a new femoral-head alloy, would likely face economic and regulatory challenges in today’s health care and litigation environment.

Steven M. Kurtz, PhD, is director of the Implant Research Center and a research professor at Drexel University in Philadelphia.
Disclosure: Kurtz reports he is an officer and shareholder of Exponent, which receives fees for his presentations and consulting services; receives research support as a principal investigator from Stryker, Zimmer Biomet, Invibio, Stelkast, Wright Medical Technology, Ceramtec, Celanese, Simplify Medical and Ferring Pharmaceuticals; and receives royalties, financial or material support from Elsevier.