Orthopedics

Acetabular Options: Notes From the Other Side

Kristoff Corten, MD; Keegan Au, MD, FRCS; Robert B. Bourne, MD, FRCS

Abstract

The socket remains the weakest link of primary total hip arthroplasty (THA). The revision rates of the socket are higher than those of the stem, with aseptic loosening and polyethylene wear being the most frequent indications for revision THA. Both cemented all-polyethylene cups and cementless sockets have benefited from stepwise improvements in surgical techniques and designs. In many countries, cementless sockets have replaced cemented cups during primary THA, with >90% of the acetabular components using a cementless fixation mode. The long-term prospective data of cementless sockets from high-volume centers show excellent and equivalent survivorship to cemented implants, but the insertion technique is easier and quicker. In addition, cementless sockets are more versatile than cemented all-polyethylene cups. With cementless sockets there is a move to increased porosity of the ingrowth surface, tri-bearing options, and enhanced locking mechanisms. There is a role for well-conducted randomized controlled trials to assess these new designs because data from various national registries show that the socket remains the weakest link of primary THA. Factors like sex, age, diagnosis, and bearing couples have a different and significant influence on the intermediate to long-term survivorship of contemporary cemented and cementless THA.

Total hip arthroplasty (THA) has been associated with excellent survival rates in older age groups, but the longevity of these implants in young patients remains a concern.1,2 The acetabular socket is at least as important as the stem for a successful THA. The cup has higher revision rates than the stem in various national joint replacement registries, and aseptic loosening of the socket and polyethylene wear were by far the most frequent indications for revision of THA after 3 years.1-5

Debate continues as to whether cemented or cementless sockets have the best survival rates. Prospective long-term follow-up studies of cemented all-polyethylene cups and cementless sockets have shown reliable survival rates of >90% (Table 1). More than 85% of the sockets are cemented in the Scandinavian countries, whereas in Australia and North America, >90% of the sockets are cementless.1-5

A randomized controlled trial is the best way to assess and compare the results of different fixation modes in THA. Two hundred fifty patients were recruited in a randomized controlled trial at our institution between October 1987 and January 1992. In 20 years of follow-up, Kaplan-Meier survivorship analysis with failure of either component as the endpoint revealed a significantly increased overall revision rate in the cemented group (P=.02). Failure of the socket accounted for most of the revisions, with cementless sockets outperforming cemented cups (84% vs 64% survivorship, respectively; P<.0001). Similarly, the revision rate of the cemented stems was significantly higher than that of the cementless stems (P<.0001).14

Despite the strengths of randomized controlled trials, some important shortcomings exist, including the expense, length of follow-up with the risk of the implants studied becoming obsolete, and generalizability of results from 1 specific implant to others becoming difficult. Therefore, the results of randomized controlled trials should be combined and compared with data from national joint replacement registries. For example, in Australia, sockets were more frequently revised than stems, and an equal percentage (44%) of component revisions of cemented and cementless THAs were directed toward the cup only.1 In New Zealand, however, the 9-year revision rate of cementless sockets for aseptic loosening was significantly lower (P<.001) than those in cemented THA, across all age groups.3 The findings in our randomized controlled trial study were similar.14

Despite the variable follow-up times in different national joint replacement registries, they all showed that factors such as age, sex, diagnosis, fixation mode, and bearing couple play an important role in the survival rates of primary THA.1-5…

The socket remains the weakest link of primary total hip arthroplasty (THA). The revision rates of the socket are higher than those of the stem, with aseptic loosening and polyethylene wear being the most frequent indications for revision THA. Both cemented all-polyethylene cups and cementless sockets have benefited from stepwise improvements in surgical techniques and designs. In many countries, cementless sockets have replaced cemented cups during primary THA, with >90% of the acetabular components using a cementless fixation mode. The long-term prospective data of cementless sockets from high-volume centers show excellent and equivalent survivorship to cemented implants, but the insertion technique is easier and quicker. In addition, cementless sockets are more versatile than cemented all-polyethylene cups. With cementless sockets there is a move to increased porosity of the ingrowth surface, tri-bearing options, and enhanced locking mechanisms. There is a role for well-conducted randomized controlled trials to assess these new designs because data from various national registries show that the socket remains the weakest link of primary THA. Factors like sex, age, diagnosis, and bearing couples have a different and significant influence on the intermediate to long-term survivorship of contemporary cemented and cementless THA.

Total hip arthroplasty (THA) has been associated with excellent survival rates in older age groups, but the longevity of these implants in young patients remains a concern.1,2 The acetabular socket is at least as important as the stem for a successful THA. The cup has higher revision rates than the stem in various national joint replacement registries, and aseptic loosening of the socket and polyethylene wear were by far the most frequent indications for revision of THA after 3 years.1-5

Debate continues as to whether cemented or cementless sockets have the best survival rates. Prospective long-term follow-up studies of cemented all-polyethylene cups and cementless sockets have shown reliable survival rates of >90% (Table 1). More than 85% of the sockets are cemented in the Scandinavian countries, whereas in Australia and North America, >90% of the sockets are cementless.1-5

Table 1: Long-Term Prospective Survival Rates of Cemented and Cementless Sockets

A randomized controlled trial is the best way to assess and compare the results of different fixation modes in THA. Two hundred fifty patients were recruited in a randomized controlled trial at our institution between October 1987 and January 1992. In 20 years of follow-up, Kaplan-Meier survivorship analysis with failure of either component as the endpoint revealed a significantly increased overall revision rate in the cemented group (P=.02). Failure of the socket accounted for most of the revisions, with cementless sockets outperforming cemented cups (84% vs 64% survivorship, respectively; P<.0001). Similarly, the revision rate of the cemented stems was significantly higher than that of the cementless stems (P<.0001).14

Despite the strengths of randomized controlled trials, some important shortcomings exist, including the expense, length of follow-up with the risk of the implants studied becoming obsolete, and generalizability of results from 1 specific implant to others becoming difficult. Therefore, the results of randomized controlled trials should be combined and compared with data from national joint replacement registries. For example, in Australia, sockets were more frequently revised than stems, and an equal percentage (44%) of component revisions of cemented and cementless THAs were directed toward the cup only.1 In New Zealand, however, the 9-year revision rate of cementless sockets for aseptic loosening was significantly lower (P<.001) than those in cemented THA, across all age groups.3 The findings in our randomized controlled trial study were similar.14

Despite the variable follow-up times in different national joint replacement registries, they all showed that factors such as age, sex, diagnosis, fixation mode, and bearing couple play an important role in the survival rates of primary THA.1-5 Therefore, these factors should be kept in mind when results of THA are being investigated.

Cemented Sockets

The surgical techniques have been optimized (Table 2), which has led to reliable long-term results of all-polyethylene cemented sockets (Table 1). Poor designs such as cemented metal-backed sockets were identified.4,6,14 Our 20- to 25-year results of the matte-finished Harris Design-2 THA (Stryker, Mahwah, New Jersey) showed a 93±3% survivorship of the polyethylene cup for aseptic loosening.7 The survivorship is strongly influenced by multiple factors, with age and sex likely being the most important parameters. Berry et al9 identified female sex, older age at time of surgery, and inflammatory diseases as strong predictors for an improved survivorship in a large series of 2000 cemented Charnley THAs (DePuy International, Leeds, United Kingdom) followed for 25 years. In addition, almost all cemented designs did well in patients older than 75 years in Finland, but none could provide a 15-year survival of >85% in the 55- to 64-year age group.4 Furthermore, the data from New Zealand showed that in patients younger than 65 years, cementless THA had significantly lower revision rates than cemented designs (P<.01), with loosening of the cemented socket being the most frequent reason for revision.3

Table 2: Stepwise Modifi cations of Surgical Techniques and Design Features of Cemented and Cementless Sockets

Cementless Sockets

The bony ingrowth of contemporary cementless sockets with surface porosities of 30% to 45% is good and reliable, but the polyethylene liner remains the weakest link.11,13 Monoblock cementless sockets have been reported to have excellent survivorship at 20 years,12 but the results of modular designs in cementless and hybrid THA are promising as well (Table 1).10-13 Recently, Utting et al11 showed that the cumulative survival of the Harris-Galante cementless component (Zimmer, Warsaw, Indiana) in hybrid THA was 94% at 16 years in a patient group younger than 50 years, whereas the survivorship of the liner was 84%.

Sex can be an important prognosticator for survival of cementless THA. We found that women had significantly lower acetabular survival rates of the Porous Coated Anatomic socket (Stryker) than men at 14 years (87% and 96%, respectively; P5.03). In addition, thicker polyethylene liners had significantly better survival rates.13 Similar to Utting et al,11 we concluded that osteolysis and wear of the polyethylene liner became major problems associated with early-design cementless sockets.13

Hybrid THA was introduced to improve the survival of THA in young patients in whom cemented cup failure was the main cause of early revision. However, hybrid THA performed only better than other designs in the 55- to 64-year age groups in Australia and New Zealand.1,3

Algorithm and Future Directions

Failure of the Porous Coated Anatomic acetabular component has resulted from the combination of a poor polyethylene locking mechanism, polyethylene wear, acetabular osteolysis, and migration.13 Based on our experiences,13,14 we currently use cementless THA with a tapered stem and a third-generation solid titanium shell with a polished inner surface and an improved locking mechanism in >98% of primary THAs, in all ages and all activity levels. Cemented fixation (<2%) is most often preserved for more special indications such as prior pelvic irradiation or when structural allografts are being used.

Stepwise changes and improvements in surgical techniques and design features have led to reliable and comparable survival rates of cemented and cementless sockets. Our long-term randomized controlled trial demonstrated the importance of post-market surveillance and evidence-based improvements in THA design.14 However, this randomized controlled trial also questioned the generalizability of the results of such randomized controlled trials due to the extended time frame required to draw any firm conclusions. In addition, data from the registries and prospective follow-up studies have shown that multiple factors significantly influence the long-term survivorship of THA. These factors should be implemented in any analysis of new designs and techniques.

Several changes in cementless socket designs can be expected and will need thorough clinical investigations. There is a trend toward manufacturing cups with an increased porosity (60%-73%) to improve the bone ingrowth potential. This also leads to higher coefficients of friction, which has been shown in radiostereometric analysis studies to be beneficial for stability at 6 months to 1 year,15 but it is useful in difficult cases with poor bony coverage. The modularity of the liners will also be improved. There is a trend toward tri-bearing options, which provide the surgeon a greater versatility in terms of bearing couples and in terms of intraoperative adaptations to certain biomechanical requirements like providing an offset option in the liner. Currently, the most frequently used bearing couple is metal-on-polyethylene. Not only will the mechanical properties of the polyethylene further be improved, but the locking mechanism of the liner in the shell will also be optimized. Deeper fixation and a larger fixation area will decrease the risk of fracture of the polyethylene liner, which will also be less prone to seating errors. Moreover, the improvements of the polyethylene liner may lead to the increased use of larger diameter articulating surfaces, but close clinical surveillance of this trend is mandatory.

An interesting area of controversy regarding cementless sockets is whether the advantages and the versatility of modular sockets should be sacrificed for the elimination of backside wear with the use of monoblock cups, which have been reported with excellent long-term results.12

Conclusion

Using contemporary techniques, both cemented and cementless sockets can yield good results. In the majority of national registries, particularly those in North America, Australia, and New Zealand, most of the sockets are inserted without cement, likely because it is easier, quicker, and perhaps more versatile for the surgeon. Future changes in cementless socket designs should be investigated in well-conducted randomized controlled trials and closely monitored in the registries.

References

  1. Australian Orthopaedic Association National Joint Replacement Registry. Annual Report. Adelaide, Australia: Australian Orthopaedic Association; 2008.
  2. Kärrholm J, Garellick G, Herberts P. Swedish Hip Arthroplasty Register Annual Report 2006. Gothenburg, Sweden: Sahlgrenska University Hospital; 2007.
  3. Hooper GJ, Rothwell AG, Stringer M, Frampton C. Revision following cemented and uncemented primary total hip replacement: a seven-year analysis from the New Zealand Joint Registry. J Bone Joint Surg Br. 2009; 91(4):451-458.
  4. Mäkelä K, Eskelinen A, Pulkkinen P, Paavolainen P, Remes V. Cemented total hip replacement for primary osteoarthritis in patients aged 55 years or older: results of the 12 most common cemented implants followed for 25 years in the Finnish Arthroplasty Register. J Bone Joint Surg Br. 2008; 90(12):1562-1569.
  5. Johnsen SP, Sørensen HT, Lucht U, Søballe K, Overgaard S, Pedersen AB. Patient-related predictors of implant failure after primary total hip replacement in the initial, short- and long-terms. A nationwide Danish follow-up study including 36,984 patients. J Bone Joint Surg Br. 2006; 88(10):1303-1308.
  6. Callaghan JJ, Liu SS, Firestone DE, et al. Total hip arthroplasty with cement and use of a collared matte-finish femoral component: nineteen to twenty-year follow-up. J Bone Joint Surg Am. 2008; 90(2):299-306.
  7. Skutek M, Bourne RB, Rorabeck CH, Burns A, Kearns S, Krishna G. The twenty to twenty-five-year outcomes of the Harris design-2 matte-finished cemented total hip replacement. A concise follow-up of a previous report. J Bone Joint Surg Am. 2007; 89(4):814-818.
  8. Buckwalter AE, Callaghan JJ, Liu SS, et al. Results of Charnley total hip arthroplasty with use of improved femoral cementing techniques. a concise follow-up, at a minimum of twenty-five years, of a previous report. J Bone Joint Surg Am. 2006; 88(7):1481-1485.
  9. Berry DJ, Harmsen WS, Cabanela ME, Morrey BF. Twenty-five-year survivorship of two thousand consecutive primary Charnley total hip replacements: factors affecting survivorship of acetabular and femoral components. J Bone Joint Surg Am. 2002; 84(2):171-177.
  10. Gaffey JL, Callaghan JJ, Pedersen DR, Goetz DD, Sullivan PM, Johnston RC. Cementless acetabular fixation at fifteen years. A comparison with the same surgeon’s results following acetabular fixation with cement. J Bone Joint Surg Am. 2004; 86(2):257-261.
  11. Utting MR, Raghuvanshi M, Amirfeyz R, Blom AW, Learmonth ID, Bannister GC. The Harris-Galante porous-coated, hemispherical, polyethylene-lined acetabular component in patients under 50 years of age: a 12- to 16-year review. J Bone Joint Surg Br. 2008; 90(11):1422-1427.
  12. Belmont PJ Jr, Powers CC, Beykirch SE, Hopper RH Jr, Engh CA Jr, Engh CA. Results of the anatomic medullary locking total hip arthroplasty at a minimum of twenty years. A concise follow-up of previous reports. J Bone Joint Surg Am. 2008; 90(7):1524-1530.
  13. Kawamura H, Dunbar MJ, Murray P, Bourne RB, Rorabeck CH. The porous coated anatomic total hip replacement. A ten to fourteen-year follow-up study of a cementless total hip arthroplasty. J Bone Joint Surg Am. 2001; 83(9):1333-1338.
  14. Au K, Corten K, Rorabeck CH, Laupacis A, Bourne RB. Cemented and cementless total hip arthroplasty: a randomized controlled rial at 17 to 21 years of follow-up. Paper presented at: Canadian Orthopaedic Association 64th Annual Meeting; July 3-6, 2009; Whistler, British Columbia, Canada.
  15. Bourne RB, McCalden RW, Naudie D, Charron KD, Yuan X, Holdsworth DW. The next generation of acetabular shell design and bearing surfaces. Orthopedics. 2008; 31(12 Suppl 2). pii:orthosupersite.com/view.asp?rID=37179.

Authors

Drs Corten, Au, and Bourne are from the London Health Sciences Centre, London, Ontario, Canada.

Drs Corten and Au have no relevant financial relationships to disclose. Dr Bourne is a consultant for Smith & Nephew.

Presented at Current Concepts in Joint Replacement 2008 Winter Meeting; December 10-13, 2008; Orlando, Florida.

Correspondence should be addressed to: Kristoff Corten, MD, Weligerveld 1, 3212 Pellenberg, University Hospital Pellenberg, Belgium.

DOI: 10.3928/01477447-20090728-10

10.3928/01477447-20090728-10

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