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The Journal of Bone and Joint Surgery 78:1486-90 (1996)
© 1996 The Journal of Bone and Joint Surgery, Inc.

Failure of a Non-Porous-Coated Acetabular Component Inserted without Cement in Primary Total Hip Arthroplasty*{dagger}

LIEUTENANT COMMANDER MICHAEL P. MULDOON, {ddagger}, MEDICAL CORPS, DOUGLAS E. PADGETT, M.D.§, SAN DIEGO, LIEUTENANT ROBERTA ROTHEN, {ddagger}MEDICAL CORPS,UNITED STATES NAVY, GERALD W. CADY, M.D.{ddagger},SAN DIEGO,CALIFORNIA and LIEUTENANT COMMANDER ANTHONY S. MELILLO, {ddagger},MEDICAL CORPS,UNITED STATES NAVAL RESERVE

Investigation performed at the Departments of Orthopedics and Clinical Investigation, Naval Medical Center, San Diego


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Thirty-four patients (thirty-eight hips) had a primary total hip arthroplasty with insertion of a non-porous-coated titanium-alloy acetabular component without cement. This component is initially stabilized with use of a central acetabular polyethylene peg, which is inserted into the pelvis, as well as supplementary cortical-bone screws inserted into the ilium. The original diagnosis was degenerative joint disease in thirty-four hips and avascular necrosis in four hips. Twenty-five femoral components were inserted with cement, and thirteen non-porous-coated femoral implants were inserted without cement. The acetabulum was prepared with so-called line-to-line reaming. Thirty-five hips in thirty-one patients were available for clinical and radiographic follow-up at a mean of 4.5 years (range, two to seven years). Serial measurements of the position of the acetabular component revealed that eighteen cups (51 per cent) had migrated. Of these, eleven had been revised. Radiolucent lines of at least one millimeter in thickness at the bone-prosthesis interface were noted adjacent to all but six of the acetabular components. Although this series was small, it demonstrates an unacceptably high rate of failure of non-porous-coated acetabular components after a relatively short duration. We question the efficacy of this acetabular component, inserted without cement, as part of a primary total hip arthroplasty.


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
The clinical success of total hip arthroplasty has made it one of the most commonly performed orthopaedic procedures. Since the introduction of modern total hip arthroplasty by Charnley, attempts have been made to improve the quality and longevity of the results. A review3 of the intermediate-term results of total hip arthroplasties performed in the 1970's revealed several troubling problems. Most notably, aseptic loosening became one of the most common causes of failure of an implant, and the rate of loosening appeared to increase with time. Of particular concern was the increased prevalence of failure of the acetabular component with time. Symptomatic aseptic loosening manifested by radiographic radiolucent lines and migration of a component became increasingly frequent as more series with more than ten years of follow-up were reported12,14,15. Many authors questioned the role of the acrylic cement in this problem, and investigation of alternative methods of fixation was begun1,2,5,11,13.

A press-fit acetabular component designed for insertion without cement was suggested as an alternative to implants fixed with cement. This suggestion was based on the principle of mechanical locking of the implant into viable bone without reliance on bone ingrowth5,11. While the concept of fixation with biological ingrowth was attractive, concerns regarding the predictability of such fixation as well as the relatively large metallic surface area exposed to bone prompted several clinical trials on polyethylene components inserted without cement2,5,11. It was thought that use of a relatively inert substance, such as ultra-high molecular weight polyethylene, might result in a so-called mechanical macro-interlock, thereby stabilizing the implant5,7. While early clinical results were encouraging, questions arose regarding whether abrasion of loose polyethylene components against bone would yield an intensive histiocytic response and resultant osteolysis. Therefore, in 1983, Freeman et al.5 modified Freeman's original polyethylene-pegged acetabular component designed for insertion without cement by adding a metal backing. It was hoped that this backing would minimize concerns regarding abrasive wear. The early report of the results was relatively enthusiastic, with 94 per cent (134) of 143 patients reporting no or mild pain and 80 per cent (114) reporting the ability to walk for more than thirty minutes at the time of the one-to-three-year follow-up6. Only two patients had radiographic evidence of migration of the implant, and only one hip was revised for loosening of the femoral component.

The purpose of the present study was to evaluate our experience with this non-porous-coated metal-backed acetabular component to determine if the favorable early clinical results were maintained.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Thirty-four patients (thirty-eight hips) had a primary total hip arthroplasty with a non-porous-coated metal-backed acetabular component that was fixed with a polyethylene peg (Protek, Berne, Switzerland) and without cement, between 1985 and 1988. The thirteen women and twenty-one men were a mean of 61.7 years old (range, twenty-four to seventy-two years old). This was a non-consecutive series of patients who met the criteria of the senior surgeon (G. W. C.) for hybrid total hip arthroplasty (insertion of the femoral component with cement and the acetabular component without cement) or total hip arthroplasty performed entirely without cement. These criteria include adequate bone stock, absence of inflammatory arthropathy, and good over-all health. The diagnosis was osteoarthrosis in thirty-one patients (thirty-four hips) and avascular necrosis in three patients (four hips). Twenty-five hips had a femoral component (Duolock; DePuy, Warsaw, Indiana) inserted with cement, ten had a CLS stem (Protek) inserted without cement, and three had a Zweymüller stem (Protek) inserted without cement. All operations were performed under the supervision of the senior surgeon, who was trained in the technique of insertion of this acetabular component by one of the developers of the implant.

The hip is exposed through a posterolateral approach with use of a modification of the technique described by Bertin et al. The acetabulum is reamed with sequentially larger reamers, with care taken to preserve as much subchondral bone as possible. After a hemispherical cavity is prepared, a trial component is inserted in approximately 45 degrees of abduction and 10 degrees of anteversion. A central drill-hole is made through a template, and two superolateral slots are cut. The metal-backed acetabular component is impacted into position and is held in place by the fins of the superomedial polyethylene peg and by 4.5-millimeter cortical-bone screws into the ilium (Fig. 1). The femoral component is then inserted, with or without the use of cement. In this series, the decision to insert the stem without cement was made on the basis of the age of the patient, the level of activity, and the quality of the bone at the time of the operation. Patients were advised to use crutches with protected weight-bearing for six weeks postoperatively.



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  		Photograph of a retrieved Freeman acetabular component with metal backing.

 
The patients were evaluated both clinically and radiographically at six weeks, three months, and six months and at yearly intervals thereafter. Measurements were made on the radiographs relative to the interteardrop line. The horizontal distance; the vertical distance; the position of the acetabular component relative to the Kohler line (the K distance); and the cup angle, as described by Callaghan et al., were determined on all of the radiographs (Fig. 2). All measurements were corrected for magnification with use of the known diameter of the femoral head as a reference. Migration of the acetabular component was defined as a change of more than three millimeters in the horizontal distance, the vertical distance, or the K distance or a change of more than 2 degrees in the cup angle. Any radiolucent line of more than one millimeter in width at the bone-acetabular component interface, as described by one of us (D. E. P.) and colleagues9, was noted. Any broken screws were also noted. We subdivided the hips that were available for follow-up into those with an acetabular component that was determined to be stable radiographically and those with a component that either had been revised for aseptic loosening or had been determined to be loose but had not yet been revised.



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  		Illustration demonstrating how the position of the cup is assessed by measurement of the horizontal (H) and vertical (V) distances relative to the interteardrop line and the distance from the Kohler line (K) of the center of the femoral head. The cup angle was measured relative to the interteardrop line. The hip to the left demonstrates the acetabular zones described by Padgett et al. to classify acetabular lucency.

 

Statistical Analysis
The relationship of variables related to the position of the acetabular component (such as the horizontal distance, the vertical distance, the K distance, and the cup angle) to migration or loosening, or both, was assessed with the unpaired Student t test. Results were considered to be significant when the p value was less than 0.05.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
Of the thirty-four patients (thirty-eight hips), two patients (two hips) died at eighteen and twenty-three months after the index operation and one patient (one hip), who had last been evaluated six months after the operation, could not be reached for follow-up. Thus, thirty-one patients (thirty-five hips) were available for clinical and radiographic follow-up, at a mean of 4.5 years (range, two to seven years). There were fifteen women (seventeen hips) and sixteen men (eighteen hips). Eleven hips in nine patients (seven hips in five women and four hips in four men) had been revised by the time of the latest follow-up examination. There were no failures due to infection.

Clinical Findings
Fourteen patients (45 per cent) had moderate or severe pain. Seventeen patients (55 per cent) walked with a limp, and thirteen of them (42 per cent of the series) needed some sort of assistive device in order to walk.

Radiographic Findings
At six weeks, the mean cup angle was 46.7 degrees (range, 31 to 69 degrees). The mean horizontal distance was 43.5 millimeters (range, thirty-one to fifty-five millimeters) lateral to the teardrop, the mean vertical distance was 23.1 millimeters (range, twelve to forty-three millimeters) proximal to the interteardrop line, and the mean K distance was 8.5 millimeters lateral (range, three millimeters medial to sixteen millimeters lateral) to the Kohler line (Table I).


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  		TABLE I RADIOGRAPHIC MEASUREMENTS OF THE ACETABULAR COMPONENTS MADE AT SIX WEEKS POSTOPERATIVELY*

 
Eighteen (51 per cent) of the thirty-five acetabular components had migrated more than three millimeters or had a change of more than 2 degrees in the cup angle (Figs. 3-A and 3-B). Of these eighteen loose, migrated components, eleven were replaced with a hemispherical, porous-coated acetabular component without cement and with supplemental screw fixation.



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  		Figs. 3-A and 3-B: Radiographs of the hip of a fifty-three-year-old man who had osteoarthrosis. Fig. 3-A: Early postoperatively, there is adequate alignment of the cup.

 


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  		Five years postoperatively, there is migration of the cup and a cortical-bone screw has broken.

 
There were no significant differences between the initial (six-week) horizontal, vertical, and K distances or the cup angles in the hips in which the acetabular component was thought to be stable at the time of follow-up and those in which the cup was revised or determined to be loose radiographically at the time of follow-up (Table I).

With the number of hips available for this study, we could detect no significant difference between the femoral stems inserted with cement and those inserted without cement with regard to migration of the acetabular component.

Radiolucent lines adjacent to the acetabular component were common. Of the twenty-four original cups that were still in situ at the time of the latest follow-up, only six had no adjacent radiolucent lines. The remaining cups had at least one. Eleven hips had a radiolucent line in Zone A-1; eleven, in Zone A-2; twelve, in Zone B-1; thirteen, in Zone B-2; and fifteen, in Zone C (Fig. 2). Eight components were surrounded by a complete radiolucent line; seven of these had migrated, as determined on the serial radiographs.

Ten of the eleven revised components and five of the seven acetabular components with radiographic evidence of migration had a broken cortical-bone screw.


   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
The purpose of this study was to review our experience with a non-porous-coated acetabular component inserted without cement. Our results revealed an unacceptably high rate of failure.

Many reports of the apparent deterioration of the results of total hip arthroplasty and radiographic evidence of loosening of the acetabular cup with time led to attempts to improve the longevity of this component12,14,15. The concept of a polyethylene cup inserted without cement as part of a total hip arthroplasty was pioneered by several authors5,7,11,16, who contended that the use of a material that was isoelastic with respect to the host bone would lead to a decreased stress differential between the implant and the bone and improve the longevity of the implant. However, damage due to the abrasion of polyethylene against living bone prompted the addition of a non-porous-coated metal backing6. In 1985, Freeman et al. reported, to The Hip Society, the short-term (six-month to three-year) results of their first forty procedures with a non-porous-coated metal-backed acetabular component fixed with polyethylene pegs6. Two implants had migrated. On the basis of these early results, this acetabular system gained in popularity.

Our results demonstrate that the rate of migration and failure of this component is unacceptably high (51 per cent; eighteen of thirty-five components). It is higher than that reported for non-metal-backed acetabular components inserted without cement. Nunn reported favorable results in 1488 patients two to seven years after replacement with a Ring plastic-on-metal hip prosthesis that included a polyethylene acetabular component inserted without cement. Ninety-three per cent of the patients had an excellent clinical result, the rate of revision for the entire series was 1.5 per cent, and the rate of radiographic loosening of the acetabular component was 3.1 per cent. Wilson-MacDonald et al., however, reported a 28 per cent rate of loosening eight years after insertion of a non-metal-backed, all polyethylene acetabular component inserted without cement in 421 patients (445 hips). Those authors observed that lack of fixation of the component led to abrasion of the polyethylene against bone, osseous erosion, and ultimately migration of the implant. They concluded that direct contact between bone and the polyethylene of the acetabular component should be avoided, and they also believed that female patients who have osteoporotic bone and a smaller cup were at greatest risk for loosening16.

In our experience, the metal-backed version of the polyethylene component fixed with a peg has fared no better than the non-metal-backed version. Our observation of progressive radiolucent lines and migration of implants is similar to that of Wilson-MacDonald et al. after breakage of cortical-bone screws. While several of the acetabular components cups in our series migrated without evidence of broken screws, there were no broken screws associated with stable implants.

The concept of acetabular implantation without cement is appealing. The advantages are the preservation of the acetabular bone stock and the elimination of potential sources of particulate debris capable of inducing histiocytic reactions. Various methods have been tried to obtain skeletal fixation and stability without the use of cement. However, complete reliance on a so-called mechanical macro-interlock with use of threaded screw-rings, as well as the use of polyethylene pegs, have not proved effective1,5,16.

Excellent short-term results have been reported for porous-surfaced implants inserted without cement for acetabular reconstruction. Engh et al. reported no clinical or radiographic loosening of 285 porous-coated acetabular components at a mean of 4.8 years postoperatively. Similarly, Schmalzried and Harris reported the survival of eighty-one of eighty-three acetabular components at a minimum of five years postoperatively. The results with non-porous-coated metal-backed acetabular components inserted without cement are clearly inferior, as demonstrated by the fact that 51 per cent (eighteen) of the thirty-five implants in our study became unstable.

We were not able to demonstrate any relationship between the position of the implant six weeks after insertion and the eventual development of loosening. Ranawat et al. found that positioning of the acetabular component outside of the so-called anatomical triangle was associated with the development of progressive radiolucent lines around and loosening of cemented sockets. In our study, the components appeared to have been placed in a technically acceptable position with respect to the hip center and the cup angle; therefore, we could not attribute our high rate of failure to error related to the initial position of the component.

On the basis of our study, we do not recommend the use of this non-porous-coated acetabular component inserted without cement in primary total hip arthroplasty. The migration of eighteen of the thirty-five components and the revision of eleven components at a mean of 4.5 years support our contention that this metal-backed implant with a polyethylene peg does not provide sufficient stability. We recommend close observation of all patients who have had a total hip arthroplasty with use of this implant, and we recommend special attention to radiographic signs of migration. In addition, we alert surgeons to the observation that broken screws are often a harbinger of subsequent migration of this implant.


   Footnotes
 
*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. The Chief, Bureau of Medicine and Surgery, Navy Department, Washington, D.C., Clinical Investigation Program sponsored this study, number S-90-072, as required by HSETCINST 6000.41A.

{dagger}The views expressed in this article are those of the authors and do not reflect the official policy or position of the Department of the Navy, Department of Defense, or United States Government.

{ddagger}Department of Clinical Investigation, Naval Medical Center, San Diego, California 92134-5000.

§The Hospital for Special Surgery, 535 East 70th Street, New York, N.Y. 10021.


   References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

  1. Apel, D. M.; Smith, D. G.; Schwartz, C. M.; and |and |Paprosky, W. G.: Threaded cup acetabuloplasty. Early clinical experience. Clin. Orthop., 241: 183-189, 1989.
  2. Bertin, K. C.; Freeman, M. A.; Morscher, E.; Oeri, A.; and |and |Ring, P. A.: Cementless acetabular replacement using a pegged polyethylene prosthesis. Arch. Orthop. and Trauma Surg., 104: 251-261, 1985.
  3. Callaghan, J. J.; Dysart, S. H.; and |and |Savory, C. G.: The uncemented porous-coated anatomic total hip prosthesis. Two-year results of a prospective consecutive series. J. Bone and Joint Surg., 70-A: 337-346, March 1988.[Abstract/Free Full Text]
  4. Engh, C. A.; Griffin, W. L.; and |and |Marx, C. L.: Cementless acetabular components. J. Bone and Joint Surg., 72-B(1): 53-59, 1990.
  5. Freeman, M. A.; McLeod, H. C.; and |and |Levai, J. P.: Cementless fixation of prosthetic components in total arthroplasty of the knee and hip. Clin. Orthop., 176: 88-94, 1983.
  6. Freeman, M. A.; Rasmussen, G. L.; and Choy, W. S.: Replacement of the acetabulum with pegged press-fit components. In The Hip. Proceedings of the Thirteenth Open Scientific Meeting of The Hip Society, pp. 261-268. St. Louis, C. V. Mosby, 1985.
  7. Morscher, E. W., and |and |Dick, W.: Cementless fixation of "isoelastic" hip endoprotheses manufactured from plastic materials. Clin. Orthop., 176: 77-87, 1983.
  8. Nunn, D.: The Ring uncemented plastic-on-metal total hip replacement. Five-year results. J. Bone and Joint Surg., 70-B(1): 40-44, 1988.
  9. Padgett, D. E.; Kull, L.; Rosenberg, A.; Sumner, D. R.; and |and |Galante, J. O.: Revision of the acetabular component without cement after total hip arthroplasty. Three to six-year follow-up. J. Bone and Joint Surg., 75-A: 663-673, May 1993.[Abstract/Free Full Text]
  10. Ranawat, C. S.; Dorr, L. D.; and |and |Inglis, A. E.: Total hip arthroplasty in protrusio acetabuli of rheumatoid arthritis. J. Bone and Joint Surg., 62-A: 1059-1065, Oct. 1980.[Abstract/Free Full Text]
  11. Ring, P. A.: Ring UPM total hip arthroplasty. Clin. Orthop., 176: 115-123, 1983.
  12. Salvati, E. A.; Wilson, P. D., Jr.; Jolley, M. N.; Vakili, F.; Aglietti, P.; and |and |Brown, G. C.: A ten-year follow-up study of our first one hundred consecutive Charnley total hip replacements. J. Bone and Joint Surg., 63-A: 753-767, June 1981.[Abstract/Free Full Text]
  13. Schmalzried, T. P., and |and |Harris, W. H.: The Harris-Galante porous-coated acetabular component with screw fixation. Radiographic analysis of eighty-three primary hip replacements at a minimum of five years. J. Bone and Joint Surg., 74-A: 1130-1139, Sept. 1992.[Abstract/Free Full Text]
  14. Stauffer, R. N.: Ten-year follow-up study of total hip replacement. J. Bone and Joint Surg., 64-A: 983-990, Sept. 1982.[Abstract/Free Full Text]
  15. Sutherland, C. J.; Wilde, A. H.; Borden, L. S.; and |and |Marks, K. E.: A ten-year follow-up of one hundred consecutive Müller curved-stem total hip-replacement arthroplasties. J. Bone and Joint Surg., 64-A: 970-982, Sept. 1982.[Abstract/Free Full Text]
  16. Wilson-MacDonald, J.; Morscher, E.; and |and |Masar, Z.: Cementless uncoated polyethylene acetabular components in total hip replacement. Review of five- to 10-year results. J. Bone and Joint Surg., 72-B(3): 423-430, 1990.

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