Case Report #5: Clinically Silent Acetabular Osteolysis

Scott I. Berkenblit, M.D., Ph.D. and
David S. Hungerford, M.D.

History

The patient is an 80-year-old male who had undergone a cementless right total hip replacement 10 years ago and cementless left THR 16 years ago, both for osteoarthritis. He presented for routine periodic follow-up, having last been seen 2 years ago. He had no complaints except for intermittent slight discomfort over both greater trochanters. He remained physically active, playing several rounds of golf every week. Overall, he was quite pleased with the outcome of both hip replacements.

Physical Examination

On examination, the patient appeared younger than his stated age. His gait was normal. He had unrestrained, painless motion of both hips. Sensory and motor testing were normal and he had palpable pulses in both lower extremities.

Radiology Studies

An AP view of the left hip (Figure 1) reveals significant asymmetric wear of the polyethylene liner, with superior migration of the 32mm femoral head. A large lytic lesion is seen beneath DeLee and Charnley zone 2 of the acetabulum; this had increased in size since the patient’s previous films 2 years ago (Figure 2). In the femur, there is loss of the normal trabecular pattern in the region of the greater and lesser trochanters, with a small break in the medial cortex. This lytic region has also expanded since the last films. Distally, the stem appears to be well fixed. There has been no change in position of either component. Views of the right hip were unremarkable.

Diagnosis

Osteolysis of left acetabulum and proximal femur (clinically silent).

Discussion

Osteolysis is the most common long-term complication of total hip replacement [1]. Although originally termed “cement disease” [4] because it was thought to be a response to particles of PMMA bone cement, the process occurs with cementless implants as well. Osteolysis is, in fact, a response to wear debris, most commonly polyethylene (although it can also occur in response to other materials, such as ceramics [11], if the particles are of the appropriate size).

The development of osteolysis around a hip implant requires generation of wear particles, access of those particles to the implant-bone interface, and the biologic response of the host to those particles. The most common source of wear debris is adhesive-abrasive wear between the femoral head and polyethylene liner, which can produce as many as 500,000 particles per gait cycle [10]. Some studies have demonstrated an increased volumetric wear rate with larger femoral heads, as well as increased wear if the cup is positioned excessively vertical [10]. Material properties of the polyethylene also play a role, and it is hoped that recent developments, including avoidance of gamma-irradiation in air and the development of new highly crosslinked polyethylenes, will result in decreased long-term wear rates in vivo. Patient factors, including weight and activity level, also affect the wear rate.

Schmalzreid et al [8] coined the term “effective joint space” to refer to all periprosthetic regions to which joint fluid, and hence wear debris, can gain access. In the acetabulum, wear debris can reach the interface through unfilled screw holes or via non-ingrown areas of the shell. On the femoral side, use of circumferential porous coating (as compared to earlier “patch coating” techniques) has reduced the incidence of diaphyseal osteolysis by blocking access of wear particles.

The biologic reaction to wear particles is a nonspecific foreign-body reaction. Particles in the submicron size range undergo phagocytosis by macrophages [2,3]; the activated macrophages, in turn, release a variety of cytokines which ultimately stimulate osteoclasts to resorb bone. Bisphosphonates have been shown to prevent this bone resorption in an in vitro model [9], as has pentoxifylline, which inhibits production of the cytokine tumor necrosis factor-alpha [6]. These agents may eventually provide a pharmacologic form of treatment or prophylaxis.

Clinically, osteolysis is usually asymptomatic until the lesions become very large.  Routine follow-up at regular intervals is indicated following any total joint arthroplasty in order to detect any osteolytic defects at a stage when they can be more easily treated, thus preserving bone stock and preventing catastrophic failure such as pelvic fracture.

At present, surgery is the main treatment for osteolysis, although the timing remains controversial. The basic principle of surgery for osteolysis is to both treat the bony lesions and to remove the particle generator (in order to prevent recurrence) [7]. With a stable acetabular component in acceptable alignment and with a modular liner, debridement and bone grafting of the lesions with retention of the acetabular shell and replacement of the polyethylene liner has been demonstrated to be successful at 2-year follow-up [5]. If the acetabular shell is loose or malpositioned, however, then revision of the component is indicated.

Clinical Course

Given the large size of the osteolytic lesions and the presence of extensive polyethylene wear, it was recommended to the patient that he undergo a revision left hip arthroplasty. He elected to proceed. Preoperatively, the plan was to replace the polyethylene liner and femoral head, possibly revise the acetabular and/or femoral components, and bone graft the osteolytic defects.

The hip was approached via a direct lateral approach, using the previous skin incision. Once the hip was dislocated, examination of the acetabular liner revealed extensive polyethylene wear, extending almost down to the underlying metal superiorly. Examination of the femur revealed large lytic defects involving the greater and lesser trochanters; these were debrided using a curette. The cementless stem was found to be solidly fixed and in acceptable version and thus was not revised.

The acetabular shell was removed using only a small amount of force, revealing a large underlying central osteolytic defect extending through the medial wall as well as a smaller contained defect which did not penetrate the wall. Wear debris and fibrous tissue were removed from both defects using a curette. Acetabular reaming was then performed up to 58mm, and the reamed bone was used to fill the bony defects in the acetabulum. A 60mm porous-coated cup was implanted, supplemented by a single screw in the posterosuperior quadrant. A highly cross-linked polyethylene liner (28mm inner diameter) was placed into the shell.

For the femur, a frozen distal femoral allograft was obtained from the bone bank, morcellized using a bone mill, and used to pack the proximal lytic defects. A 28mm head was impacted onto the trunnion, the hip was reduced, and the wound was closed in the usual fashion. The patient has been doing well postoperatively. His most recent radiographs (Figure 3) show good alignment of the components, incorporation of the bone graft, and no progression of the osteolytic lesions.

Figure 3

Case Discussion

Although this patient was completely asymptomatic, radiographs revealed large acetabular and femoral defects associated with severe polyethylene wear. Contributing factors included the long interval since surgery (16 years) and possibly the large head size (32mm). Early surgical intervention was felt to be indicated in order to treat the lesions, replace the polyethylene liner, and avoid possible catastrophic failure such as cup migration or pelvic fracture. Although the acetabular component had not migrated, it was revised because of the large size of the lesion and in order to allow full access to the lesion for debridement and bone grafting.

References

1. Harris WH. Wear and prosthetic osteolysis: The problem. Clin Orthop 393:66-70 (2001).
2. Etiology, prosthetic factors, and pathogenesis. AAOS Instructional Course Lectures 49:71-82 (2000).
3. Jacobs JJ, Roebuck KA, Archibeck M, Hallam NJ, Glant TG. Osteolysis: Basic science. Clin Orthop 393:71-77 (2001).
4. Jones LC, Hungerford DS. Clin Orthop 225:192-196 (1987).
5. Maloney WJ, Herzwurm P, Paprosky W, Rubash HE, Engh CA. Treatment of pelvic osteolysis associated with a stable acetabular component inserted without cement as part of a total hip replacement. J Bone Joint Surg [Am] 79-A:1628-1634 (1997).
6. Pollice PF, Rosier RN, Cooney RJ, Puzas JE, Schwarz EM, O’Keefe RJ. Oral pentoxifylline inhibits release of tumor necrosis factor-alpha from human peripheral blood monocytes: A potential treatment for aseptic loosening of total joint components. J Bone Joint Surg [Am] 83-A:1057-1061 (2001).
7. Rubash HE, Sinha RK, Maloney WJ, Paprosky WG.  Osteolysis:  Surgical treatment.  AAOS Instructional Course Lectures 47:321-329 (1998).
8. Schmalzreid TP, Jasty M, Harris WH.  Periprosthetic bone loss in total hip arthroplasty:  Polyethylene wear debris and the concept of the effective joint space.  J Bone Joint Surg [Am] 74-A:849-863 (1992).
9. Shanbhag AS, Hasselman CT, Rubash HE.  Inhibition of wear debris mediated osteolysis in a canine total hip arthroplasty model.  Clin Orthop 344:33-43 (1997).
10. Wright TM, Goodman SB, eds.  Implant Wear in Total Joint Replacement.  Rosemont, IL: AAOS (2001).
11. Yoon TR, Rowe SM, Jung ST, Seon KJ, Maloney WJ.  Osteolysis in association with a total hip arthroplasty with ceramic bearing surfaces.  J Bone Joint Surg [Am] 80-A:1459-1468 (1998).

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