Orthopedics

Metal–Metal Reactivity: Houston, We Have a Problem!

Thomas P. Schmalzried, MD; John V. Tiberi, MD

  • Orthopedics. 2010;33(9)
  • Posted September 1, 2010

Abstract

In this single-surgeon series, both resurfaced hips in 1 woman and a total hip arthroplasty in another were revised for symptomatic pseudotumor (3 of 588 hips; 0.51% overall incidence; 2.2% in women). All 3 hips had 50-mm acetabular components. There was no difference in mean lateral opening angle (mean 38.7° vs 42.8° for the others) but these 3 hips all had increased acetabular anteversion (mean 27.1° vs 16.4° for the others; P<.05). Increased combined anteversion is a mechanical common denominator in pseudotumor formation. Female sex and small component size are variables associated with congenital dysplasia, which typically has a small, shallow socket and high combined anteversion. Thus, native anatomy may predispose to the joint mechanics that lead to pseudotumor formation, and not sex or size. The aggregate results indicate that the determination of satisfactory component position includes (1) assessment of the acetabular component lateral opening, (2) acetabular component version, and (3) femoral version.

A mechanical problem suggests a mechanical solution. To insure capture of the femoral head by the socket and the intended bearing tribology, acetabular lateral opening angles should be <50°, assuming a femoral neck-shaft angle of 130° to 135°. Combined anteversion should not exceed 40°. In resurfacing of dysplastic cases where the neck-shaft angle exceeds 140°, the acetabular lateral opening angle needs to be correspondingly lower to achieve equivalent head capture and bearing contact.

Pseudotumor was described in the American orthopedic literature in 1988 in association with a cementless, metal-on-polyethylene total hip.1 The identified stimulus for the adverse local tissue reaction was corrosion of the cobalt-chrome-to-cobalt-chrome femoral head taper. The histology in this case was similar to what was subsequently coined ALVAL (aseptic lymphocyte-dominated vasculitis-associated lesion).2 The multisurgeon resurfacing experience at Oxford has been characterized by a relatively high occurrence of symptomatic (and asymptomatic) pseudotumors.3 The role of component position was not defined. We investigated acetabular component position associated with pseudotumor development in a single-surgeon series.

In this single-surgeon series, a total of 588 hips (504 patients) received a metal–metal bearing arthroplasty (472 resurfacing and 116 total hip arthroplasty [THA]) from April 1994 through July 2008. Four hundred fifty-three (77%) were in men, and 135 (23%) were in women. Mean patient age and body mass index (BMI) were 50.7 years (range, 14.7-81.9 years) and 27.25 (range, 16.95-44.7), respectively. All were operated through a posterior approach. Minimum follow-up was 1 year (maximum 10 years) with a mean of 4.0 years. Acetabular component position was assessed with edge-detection software (EBRA [Einzel-Bild-Roentgen-Analyse]; University of Innsbruck, Innsbruck, Austria) on the anteroposterior pelvic radiograph for lateral opening angle (abduction angle) and anteversion.

In this series, both resurfaced hips in 1 woman and a monoblock metal–metal bearing THA in another were revised for symptomatic pseudotumor (0.51% overall; 2.2% in women). All 3 hips had 50-mm acetabular components. All had some hip pain and a fluctuant subcutaneous lateral mass within the first postoperative year. There was no difference in mean lateral opening angle (mean 38.7° vs 42.8° for the others), but these 3 hips all had increased acetabular anteversion (mean 27.1° vs 16.4° for the others; P<.05) (Figure). Analysis by computed tomography scan of the THA patient demonstrated femoral anteversion of 22° for a combined anteversion (acetabular plus femoral) of 45°.

The report from Oxford described the development of a pseudotumor in association with 20 metal–metal hip resurfacings in 17 women.3 The histology was consistent with ALVAL.2 Similar demographics, including bilateral occurrence, were seen in the current single-surgeon report. These associations may suggest a primary biologic or immune pathophysiology. However, there is evidence to support a primary mechanical basis for pseudotumor formation. An increase in…

Abstract

In this single-surgeon series, both resurfaced hips in 1 woman and a total hip arthroplasty in another were revised for symptomatic pseudotumor (3 of 588 hips; 0.51% overall incidence; 2.2% in women). All 3 hips had 50-mm acetabular components. There was no difference in mean lateral opening angle (mean 38.7° vs 42.8° for the others) but these 3 hips all had increased acetabular anteversion (mean 27.1° vs 16.4° for the others; P<.05). Increased combined anteversion is a mechanical common denominator in pseudotumor formation. Female sex and small component size are variables associated with congenital dysplasia, which typically has a small, shallow socket and high combined anteversion. Thus, native anatomy may predispose to the joint mechanics that lead to pseudotumor formation, and not sex or size. The aggregate results indicate that the determination of satisfactory component position includes (1) assessment of the acetabular component lateral opening, (2) acetabular component version, and (3) femoral version.

A mechanical problem suggests a mechanical solution. To insure capture of the femoral head by the socket and the intended bearing tribology, acetabular lateral opening angles should be <50°, assuming a femoral neck-shaft angle of 130° to 135°. Combined anteversion should not exceed 40°. In resurfacing of dysplastic cases where the neck-shaft angle exceeds 140°, the acetabular lateral opening angle needs to be correspondingly lower to achieve equivalent head capture and bearing contact.

Pseudotumor was described in the American orthopedic literature in 1988 in association with a cementless, metal-on-polyethylene total hip.1 The identified stimulus for the adverse local tissue reaction was corrosion of the cobalt-chrome-to-cobalt-chrome femoral head taper. The histology in this case was similar to what was subsequently coined ALVAL (aseptic lymphocyte-dominated vasculitis-associated lesion).2 The multisurgeon resurfacing experience at Oxford has been characterized by a relatively high occurrence of symptomatic (and asymptomatic) pseudotumors.3 The role of component position was not defined. We investigated acetabular component position associated with pseudotumor development in a single-surgeon series.

Materials and Methods

In this single-surgeon series, a total of 588 hips (504 patients) received a metal–metal bearing arthroplasty (472 resurfacing and 116 total hip arthroplasty [THA]) from April 1994 through July 2008. Four hundred fifty-three (77%) were in men, and 135 (23%) were in women. Mean patient age and body mass index (BMI) were 50.7 years (range, 14.7-81.9 years) and 27.25 (range, 16.95-44.7), respectively. All were operated through a posterior approach. Minimum follow-up was 1 year (maximum 10 years) with a mean of 4.0 years. Acetabular component position was assessed with edge-detection software (EBRA [Einzel-Bild-Roentgen-Analyse]; University of Innsbruck, Innsbruck, Austria) on the anteroposterior pelvic radiograph for lateral opening angle (abduction angle) and anteversion.

Results

In this series, both resurfaced hips in 1 woman and a monoblock metal–metal bearing THA in another were revised for symptomatic pseudotumor (0.51% overall; 2.2% in women). All 3 hips had 50-mm acetabular components. All had some hip pain and a fluctuant subcutaneous lateral mass within the first postoperative year. There was no difference in mean lateral opening angle (mean 38.7° vs 42.8° for the others), but these 3 hips all had increased acetabular anteversion (mean 27.1° vs 16.4° for the others; P<.05) (Figure). Analysis by computed tomography scan of the THA patient demonstrated femoral anteversion of 22° for a combined anteversion (acetabular plus femoral) of 45°.

Figure A: Osteoarthritis secondary to mild congenital hip dysplasia Figure B: The anteversion, as measured by EBRA
Figure C: A combined anteversion of 45° Figure 1: Preoperative AP radiograph of a woman with osteoarthritis secondary to mild congenital hip dysplasia. Note the small, shallow socket (A). Postoperative AP radiograph of the same patient demonstrating a low acetabular lateral opening angle of 32°. The anteversion, as measured by EBRA, is 23°, which can be difficult to appreciate on the AP radiograph of this metal–metal bearing (B). Johnson’s shoot-thru lateral of the same patient demonstrating the acetabular component anterior opening and the uncovered femoral head. By CT scan, the femoral version was 22°, resulting in a combined anteversion of 45° (C).

Discussion

The report from Oxford described the development of a pseudotumor in association with 20 metal–metal hip resurfacings in 17 women.3 The histology was consistent with ALVAL.2 Similar demographics, including bilateral occurrence, were seen in the current single-surgeon report. These associations may suggest a primary biologic or immune pathophysiology. However, there is evidence to support a primary mechanical basis for pseudotumor formation. An increase in whole blood and serum ion levels has been previously reported in association with higher acetabular component lateral opening angles or anteversion >20°.4 The risk of higher ion levels has been related to the arc of coverage of the resurfacing femoral head.5 The combination of small size and extreme position results in a small contact area and predisposition to edge wear. To further elucidate the pathomechanics, analyses are being conducted of retrieved bearings for wear and evidence of material stress and corrosion, as it is our hypothesis that corrosion products drive pseudotumor formation.1

The current single-surgeon series indicates that increased combined anteversion is a mechanical common denominator in pseudotumor formation. Female sex and small component size are variables associated with congenital dysplasia, which typically has a small, shallow socket and high combined anteversion. Thus, native anatomy may predispose to the joint mechanics that lead to higher ion levels and pseudotumor formation, and not sex or size. The aggregate results indicate that the determination of satisfactory component position includes (1) assessment of the acetabular component lateral opening, (2) acetabular component version, and (3) femoral version.6,7

These findings have implications for surgical technique, at least with current generation metal–metal bearings. A mechanical problem suggests a mechanical solution. To insure capture of the femoral head by the socket and the intended bearing tribology, acetabular lateral opening angles should be <50°, assuming a femoral neck-shaft angle of 130° to 135°. Combined anteversion should not exceed 40°. In resurfacing of dysplastic cases where the neck-shaft angle exceeds 140°, the acetabular lateral opening angle needs to be correspondingly lower to achieve equivalent head capture and bearing contact.

The majority of patients with a metal–metal bearing are doing well. These 3 hips (of 588) all had symptoms within the first year, and early revision of patients with pseudotumor is recommended. Radiographs in multiple planes can demonstrate acetabular component fixation and position. Monoblock cobalt-chromium alloy acetabular components may osseointegrate less reliably than modular titanium alloy components, and the fixation status may be difficult to assess on radiographs.8 A loose acetabular component can cause groin pain. If the lateral opening angle is >55° or anteversion is >20°, the risk of an aberrant wear mechanism (and pseudotumor formation) is increased. In unilateral cases, an elevation of whole blood or serum ion levels >10 parts per billion is consistent with an aberrant wear mechanism and support revision in a symptomatic patient. The value of ion levels in asymptomatic patients is debatable.

References

  1. Svensson O, Mathiesen EB, Reinholt FP, Blomgren G. Formation of a fulminant soft-tissue pseudotumor after uncemented hip arthroplasty. A case report. J Bone Joint Surg Am. 1988; 70(8):1238-1242.
  2. Willert HG, Buchhorn GH, Fayyazi A, et al. Metal-on-metal bearings and hypersensitivity in patients with artificial hip joints. A clinical and histomorphological study. J Bone Joint Surg Am. 2005; 87(1):28-36.
  3. Pandit H, Glyn-Jones S, McLardy-Smith P, et al. Pseudotumours associated with metal-on-metal hip resurfacings. J Bone Joint Surg Br. 2008; 90(7):847-851.
  4. Langton DJ, Jameson SS, Joyce TJ, Webb J, Nargol AV. The effect of component size and orientation on the concentrations of metal ions after resurfacing arthroplasty of the hip. J Bone Joint Surg Br. 2008; 90(9):1143-1151.
  5. De Haan R, Pattyn C, Gill HS, Murray DW, Campbell PA, De Smet K. Correlation between inclination of the acetabular component and metal ion levels in metal-on-metal hip resurfacing replacement. J Bone Joint Surg Br. 2008; 90(10):1291-1297.
  6. Dorr LD, Malik A, Dastane M, Wan Z. Combined anteversion technique for total hip arthroplasty. Clin Orthop Relat Res. 2009; 467(1):119-127.
  7. Schmalzried TP. The importance of proper acetabular component positioning and the challenges to achieving it. Operative Techniques in Orthopaedics. 2009; 19(3):132-136.
  8. Long WT, Dastane M, Harris MJ, Wan Z, Dorr LD. Failure of the Durom Metasul acetabular component. Clin Orthop Relat Res. 2010; 468(2):400-405.

Authors

Dr Schmalzried is from the Joint Replacement Institute at St Vincent Medical Center, Los Angeles, and Dr Tiberi is from Harbor–UCLA Department of Orthopedic Surgery, Torrance, California.

Dr Schmalzried receives royalties from DePuy, Inc, and research funding from DePuy, Inc, Wright Medical Technology, Inc, and Corin Group PLC. Dr Tiberi has no relevant financial relationships to disclose.

Presented at Current Concepts in Joint Replacement 2009 Winter Meeting; December 9-12, 2009; Orlando, Florida.

Correspondence should be addressed to: Thomas P. Schmalzried, MD, 2200 W Third St, Ste 400, Los Angeles, CA 90057 (schmalzried@earthlink.net).

doi: 10.3928/01477447-20100722-45

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