Orthopedics

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Case Reports 

Massive Wear and Metallosis of an Acetabular Cup System Presenting as Pseudodislocation

Sathappan S. Sathappan, MD; James Wee, MBBS; Daniel Ginat, BS; Patrick Meere, MD

Abstract

In primary and revision total hip arthroplasty (THA), the acetabular component continues to pose greater challenges than the femoral component. Numerous factors lead to polyethylene wear, which subsequently affects primary THA survival. Progressive polyethylene wear is associated with the occurrence of osteolysis, especially overlying the acetabulum, which can lead to component loosening and subsequent revision.

Polyethylene failure usually manifests as massive liner wear up to the metal shell, fracture of the liner, or a combination of both. There is often a small amount of metallosis associated with this pathology. To our knowledge, massive wear of the acetabular metal shell, however, has not previously been reported in the literature.

This article describes a case of massive wear through a polyethylene liner and the acetabular metal shell of an Acetabular Cup System (DePuy, Leeds, United Kingdom) that presented as an apparent dislocation 13 years following the index operation. The pseudodislocation was intraoperatively found to be penetration of the femoral head through the acetabular shell. The acetabular component was consequently revised to a larger cementless cup. The femoral component was mechanically stable and required no revision.

Patients with long-standing Acetabular Cup System THA may experience acetabular metal shell wear-through phenomena presenting as a pseudodislocation, and this possibility should be taken into consideration during preoperative planning.

In primary and revision total hip arthroplasty (THA), the acetabular component continues to pose greater challenges than the femoral component. Numerous factors lead to polyethylene wear, which subsequently affects primary THA survival. Progressive polyethylene wear is associated with the occurrence of osteolysis, especially overlying the acetabulum, which can lead to component loosening and subsequent revision.

This article describes a case of a patient with a previous revision left THA who presented with clinical features suggestive of left hip dislocation.

An 85-year-old woman who was 64 inches tall with a body mass index of 23 had a history of a left primary THA performed approximately 25 years ago. In addition, she had a left revision THA with trochanteric osteotomy performed approximately 13 years ago. Her left revision THA consisted of an Anatomic Medullary Locking Plus uncemented metal stem (DePuy, Warsaw, Indiana) with a 56-mm Acetabular Cup System polyethylene liner (DePuy, Leeds, United Kingdom).

The patient presented with a history of severe left groin pain, limp, and an inability to bear weight for a prolonged period on the left lower limb. She described the pain as radiating to her left knee. In the first 2 months postinjury, she had been dependant on a cane and was a minimal ambulator. During the third month she was unable to bear any weight on the affected limb. Constitutional symptoms were unremarkable and there was no history of fever.

Examination of her left hip revealed a shortened and externally rotated limb. The left hip had a bulge on the anterior aspect of the acetabulum that was palpable and associated with exquisite tenderness to touch and internal rotation. There was a posterolateral scar from the previous surgical procedures. There was also wasting of the left gluteal musculature associated with a positive Trendelenburg’s test. In contrast, the right hip was asymptomatic and the physical examination unremarkable. There was a 25-mm lower limb-length discrepancy, with the left side being shorter. The neurovascular status of the limb was intact. Clinical examination ruled out the presence of spinal stenosis, as well as any clinically significant pathology in the knees. There were neither draining sinuses nor erythema around the wound.

All laboratory test markers for infection, including C-reactive protein, erythrocyte sedimentation rate, and leukocyte counts, were within normal ranges. Based on the clinical assessment and the radiographs (Figure 1), the…

Abstract

In primary and revision total hip arthroplasty (THA), the acetabular component continues to pose greater challenges than the femoral component. Numerous factors lead to polyethylene wear, which subsequently affects primary THA survival. Progressive polyethylene wear is associated with the occurrence of osteolysis, especially overlying the acetabulum, which can lead to component loosening and subsequent revision.

Polyethylene failure usually manifests as massive liner wear up to the metal shell, fracture of the liner, or a combination of both. There is often a small amount of metallosis associated with this pathology. To our knowledge, massive wear of the acetabular metal shell, however, has not previously been reported in the literature.

This article describes a case of massive wear through a polyethylene liner and the acetabular metal shell of an Acetabular Cup System (DePuy, Leeds, United Kingdom) that presented as an apparent dislocation 13 years following the index operation. The pseudodislocation was intraoperatively found to be penetration of the femoral head through the acetabular shell. The acetabular component was consequently revised to a larger cementless cup. The femoral component was mechanically stable and required no revision.

Patients with long-standing Acetabular Cup System THA may experience acetabular metal shell wear-through phenomena presenting as a pseudodislocation, and this possibility should be taken into consideration during preoperative planning.

In primary and revision total hip arthroplasty (THA), the acetabular component continues to pose greater challenges than the femoral component. Numerous factors lead to polyethylene wear, which subsequently affects primary THA survival. Progressive polyethylene wear is associated with the occurrence of osteolysis, especially overlying the acetabulum, which can lead to component loosening and subsequent revision.

This article describes a case of a patient with a previous revision left THA who presented with clinical features suggestive of left hip dislocation.

Case Report

An 85-year-old woman who was 64 inches tall with a body mass index of 23 had a history of a left primary THA performed approximately 25 years ago. In addition, she had a left revision THA with trochanteric osteotomy performed approximately 13 years ago. Her left revision THA consisted of an Anatomic Medullary Locking Plus uncemented metal stem (DePuy, Warsaw, Indiana) with a 56-mm Acetabular Cup System polyethylene liner (DePuy, Leeds, United Kingdom).

The patient presented with a history of severe left groin pain, limp, and an inability to bear weight for a prolonged period on the left lower limb. She described the pain as radiating to her left knee. In the first 2 months postinjury, she had been dependant on a cane and was a minimal ambulator. During the third month she was unable to bear any weight on the affected limb. Constitutional symptoms were unremarkable and there was no history of fever.

Examination of her left hip revealed a shortened and externally rotated limb. The left hip had a bulge on the anterior aspect of the acetabulum that was palpable and associated with exquisite tenderness to touch and internal rotation. There was a posterolateral scar from the previous surgical procedures. There was also wasting of the left gluteal musculature associated with a positive Trendelenburg’s test. In contrast, the right hip was asymptomatic and the physical examination unremarkable. There was a 25-mm lower limb-length discrepancy, with the left side being shorter. The neurovascular status of the limb was intact. Clinical examination ruled out the presence of spinal stenosis, as well as any clinically significant pathology in the knees. There were neither draining sinuses nor erythema around the wound.

All laboratory test markers for infection, including C-reactive protein, erythrocyte sedimentation rate, and leukocyte counts, were within normal ranges. Based on the clinical assessment and the radiographs (Figure 1), the patient was diagnosed with chronic left hip anterior dislocation with retroacetabular osteolysis. Since there was no significant loosening of the femoral component, the surgical plan was to perform a left acetabular revision.

After obtaining spinal anesthesia, a posterior approach to the hip was used. Following a deep fascial incision, high-pressure metallosis liquid was expelled. A total of 80 mL was aspirated. External rotators were identified and peeled subperiosteally from the femur. It was noted that >50% of the musculature had been damaged by the metallosis. All 4 quadrants of the hip were debrided until clear of the exuberant metallosis and synovitis. Biopsies were taken of the capsule and frozen section analyses were negative for acute inflammation.

It was noted that there was no true dislocation of the hip. Instead, there was gross loosening of the acetabular component with penetration of the femoral head through both the acetabular polyethylene liner and the metal shell. The patient, therefore, had a pseudodislocation with perforation of the acetabular dome of >25%. The acetabular polyethylene liner was also cracked in several places. The acetabular component was removed with the adjoining screws (Figure 2).

Figure 1: Anterior dislocation of the left hip Figure 2A: Retrieved Acetabular Cup System polyethylene liner revealing rim fragmentation Figure 2B: Severe wear of the Acetabular Cup System metal shell

Figure 1: AP radiograph of an 85-year-old woman with left groin pain showing an apparent anterior dislocation of the left hip. Figure 2: Retrieved Acetabular Cup System polyethylene liner revealing rim fragmentation (A). Severe wear of the Acetabular Cup System metal shell in the superior pole (B). The femoral head had penetrated through the latter.

Assessment of the acetabular bone revealed a deficiency in the medial wall. There was also a combined segmental and cavitary lesion involving the superior dome of the acetabulum. The anterior column of the acetabulum showed 20% bone loss, while the posterior column revealed 60% loss of bone stock. In keeping with the initial radiographic assessment, there was a deep retroacetabular and periacetabular lesion; all fibrous metallosis debris was subsequently curetted. The femoral stem was mechanically stable, with limited etching of the superior dome of the femoral head. The femoral head diameter was 32 mm.

Based on the intraoperative findings, the following options were taken into consideration: resection arthroplasty; cemented all-polyethylene acetabular component with the use of a wire mesh to augment the medial wall defect; use of an anti-protrusio cage with a polyethylene cup cemented onto the latter; and use of a jumbo cup.

Since there was sufficient acetabular bone quantity peripherally, the final option was undertaken. Following gentle peripheral reaming, a uniform hemispherical cavity was attained, allowing the placement of a 64-mm Pinnacle cementless shell (DePuy) with multiple holes, which was press-fitted into the acetabulum. Anteversion was kept to approximately 15°. For additional stability, 2 posterosuperior screws measuring 40 mm and 25 mm and 1 anterior screw measuring 15 mm were inserted. A highly cross-linked 32-mm polyethylene liner was used.

The hip was reduced and the range of motion of the hip was as follows: 0° of extension, 105° of flexion, 45° of abduction, 50° of external rotation, and 60° of internal rotation. No anterior instability was noted and the push-pull test revealed satisfactory soft tissue tension. Following copious irrigation, the external rotators were sutured to the greater trochanter and the gluteal fascia was closed. The estimated blood loss was 250 mL.

Figure 3: AP radiograph after revision of the acetabulum
Figure 3: AP radiograph after revision of the acetabulum.

Postoperative radiographs were satisfactory (Figure 3) and no periprosthetic fractures were seen. The patient had an uneventful postoperative recovery and was discharged on postoperative day 8. She ambulated with weight bearing as tolerated on the left lower limb with the aid of a walker.

Discussion

The use of cemented polyethylene cups is time-tested since the early development of THA by Charnley.1,2 The goal of cementless cup fixation was to avoid problems of osteolysis seen with cemented acetabular cups. However, osteolysis has also been noted to occur around cementless cups.3-6 In the latter, there are also issues with regard to wear.7 Massive wear of the polyethylene liner has been described in the literature with various system designs.8-11 Usually polyethylene failure either manifests as massive liner wear up to the metal shell, fracture of the liner, or a combination of both. There is often a small amount of metallosis associated with this pathology. To our knowledge, there are no previous reports in the literature of massive wear of the acetabular metal shell.

Patel et al9 have previously reported on 5 cases of severe polyethylene wear associated with the use of the Acetabular Cup System. In all 5 cases, only wear and fracture through the polyethylene were described. In this design, the liner shares the load with the metal shell at its periphery. In their series, the average polyethylene rim thickness was between 2.5 and 4.5 mm. Inevitably, whenever the polyethylene thickness is <6 mm, excessively high stress results in massive polyethylene wear.8,12,13 In all their patients, the metal shells were noted to be securely fixed despite metallosis.

The approximate time to failure of the Acetabular Cup System in our patient was approximately 13 years, which is significantly longer than the previously reported maximum time of 7.4 years.9 The polyethylene thickness, especially at the rim of the failed polyethylene liner, was found to be thin.9,14 In our patient, significant destruction and metallic wear had occurred around the superior screw hole present within the metallic acetabular shell. It is highly probable that micromotion between the screw, the thin polyethylene cup, and the metal shell led to the rapid generation of metallic and polyethylene debris. This particulate debris could have accelerated the wear of the polyethylene liner. Furthermore, our patient had a large 32-mm femoral head in conjunction with a thin liner; these factors have been shown in the literature to be associated with a greater linear wear rate.9,14-16

In addition, as an older design, the liner was likely gamma irradiated in air, which has also been shown to be associated with unsatisfactory material and wear properties. Since our patient had prior placement of the Acetabular Cup System at another institution, we were unable to confidently determine the method used for sterilization of the liner. The failed liner eventually led to the articulation of the metallic femoral head with the inner surface of the metal shell. The way in which this articulation was produced caused eccentric loading on the shell. Ultimately, this resulted in the penetration of the femoral head through the metal shell.

Current cementless systems have produced good clinical outcomes despite an increase in the incidence of revisions arising from polyethylene wear.17,18 The older Acetabular Cup System design, however, is mechanically unsound and has been associated with massive wear of the polyethylene liner.9,15 Because the implant was in vivo for a long period of time (13 years), the femoral head penetration had become so extensive that it resulted in radiographs suggestive of hip dislocation. Therefore, in patients who have had the Acetabular Cup System for an extended time period and who subsequently present with an apparent dislocation, the possibility of a femoral head penetration should be taken into consideration during preoperative planning. In retrospect, the correct diagnosis could have been established preoperatively by using computed tomography scanning with metal subtraction. To our knowledge, this is the first reported case of wear through the Acetabular Cup System metal shell presenting as a pseudodislocation.

References

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  2. Malchau H, Herberts P, Ahnfelt L. Prognosis of total hip replacement in Sweden. Follow-up of 92,675 operations performed 1978-1990. Acta Orthop Scand. 1993; 64(5):497-506.
  3. Cooper RA, McAllister CM, Borden LS, Bauer TW. Polyethylene debris-induced osteolysis and loosening in uncemented total hip arthroplasty. A cause of late failure. J Arthroplasty. 1992; 7(3):285-290.
  4. Devane PA, Robinson EJ, Bourne RB, Rorabeck CH, Nayak NN, Horne JG. Measurement of polyethylene wear in acetabular components inserted with and without cement. A randomized trial. J Bone Joint Surg Am. 1997; 79(5):682-689.
  5. Barrack RL, Folgueras A, Munn B, Tvetden D, Sharkey P. Pelvic lysis and polyethylene wear at 5-8 years in an uncemented total hip. Clin Orthop Relat Res. 1997; (335):211-217.
  6. Engh CA Jr, Claus AM, Hopper RH Jr, Engh CA. Long-term results using the anatomic medullary locking hip prosthesis. Clin Orthop Relat Res. 2001; (393):137-146.
  7. Hernandez JR, Keating EM, Faris PM, Meding JB, Ritter MA. Polyethylene wear in uncemented acetabular components. J Bone Joint Surg Br. 1994; 76(2):263-266.
  8. Berry DJ, Barnes CL, Scott RD, Cabanela ME, Poss R. Catastrophic failure of the polyethylene liner of uncemented acetabular components. J Bone Joint Surg Br. 1994; 76(4):575-578.
  9. Patel J, Scott JE, Radford WJ. Severe polyethylene wear in uncemented acetabular cup system components: a report of 5 cases. J Arthroplasty. 1999; 14(5):635-636.
  10. Petersen MB, Poulsen IH, Thomsen J, Solgaard S. The hemispherical Harris-Galante acetabular cup, inserted without cement. The results of an eight to eleven-year follow-up of one hundred and sixty-eight hips. J Bone Joint Surg Am. 1999; 81(2):219-224.
  11. Puolakka TJ, Pajamäki KJ, Pulkkinen PO, Nevalainen JK. Poor survival of cementless Biomet total hip: a report on 1,047 hips from the Finnish Arthroplasty Register. Acta Orthop Scand. 1999; 70(5):425-429.
  12. Bartel DL, Bicknell VL, Wright TM. The effect of conformity, thickness, and material on stresses in ultra-high molecular weight components for total joint replacement. J Bone Joint Surg Am. 1986; 68(7):1041-1051.
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  15. Bono JV, Sanford L, Toussaint JT. Severe polyethylene wear in total hip arthroplasty. Observations from retrieved AML PLUS hip implants with an ACS polyethylene liner. J Arthroplasty. 1994; 9(2):119-125.
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Authors

Drs Sathappan and Meere are from the Department of Orthopedic Surgery, NYU Hospital for Joint Diseases, and Mr Ginat is from NYU School of Medicine, New York, New York; and Dr Wee is from the Department of Orthopedic Surgery, Tan Tock Seng Hospital, Singapore.

Drs Sathappan, Wee, and Meere and Mr Ginat have no relevant financial relationships to disclose.

Correspondence should be addressed to: Sathappan S. Sathappan, MD, Department of Orthopedic Surgery, Tan Tock Seng Hospital, 11 Jalan Tan Tock Seng, Singapore 308433.

DOI: 10.3928/01477447-20090511-23

10.3928/01477447-20090511-23

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