Cementless Acetabular Fixation With and Without Screws

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1 Cementless Acetabular Fixation With and Without Screws Analysis of Stability and Migration The Journal of Arthroplasty Vol. 25 No Richard Iorio, MD,* Brian Puskas, MD,y William L. Healy, MD,* John F. Tilzey, MD,* Lawrence M. Specht, MD,* and Michael S. Thompson, MD* Abstract: The purpose of this study was to compare initial stability and late migration of 775 cementless acetabular components with and without screw fixation. Screw fixation was used in 509 cups and no screws in 266 cups. Average follow-up in the screw fixation group was 6.32 years (range, 2-10 years) and 6.9 years (range, 2-10 years) in the no-screw group. One component (0.2%, osteolysis) in the screw group and one (0.4%, loss of fixation) in the no-screw group required revision. Osteolytic lesions more than 4 cm 2 were noted in 8 (1.6%) screw fixation cups and 2 (0.75%) no-screw fixation cups. No cups in either cohort had radiographic evidence of migration. Screw fixation did not have a favorable or adverse effect on the outcome of acetabular reconstruction. Keywords: cementless, acetabular, fixation, with screws, without screws Published by Elsevier Inc. Cementless porous-coated acetabular components can be successfully implanted with and without screw fixation for primary total hip arthroplasty (THA) [1-5]. Screw fixation has been advocated by some hip surgeons to achieve initial stability and osseointegration of the acetabular component and to prevent late migration of the acetabular implant [1,3,6-9]. Advocates for insertion of porous-coated acetabular components without screw fixation have suggested that a press-fit technique with underreaming of the acetabular socket provides adequate initial fixation and adjunctive screw fixation is unnecessary to prevent late migration [1,2,9-12]. In addition, avoidance of screw holes in the acetabular shell may prevent potential egress of polyethylene particles through the shell. Decreasing the amount of polyethylene wear debris introduced to the pelvis may decrease pelvic osteolysis [3]. The elimination of screw fixation may also decrease From the *Department of Orthopaedic Surgery, Lahey Clinic Medical Center, Burlington, Massachusetts; and ydepartment of Orthopaedic Surgery, Boston Medical Center, Boston, Massachusetts. Submitted September 9, 2008; accepted January 30, Benefits or funds were received in partial or total support of the research material described in this article. Institutional Educational Support was received from DePuy Orthopedics (Warsaw, IN). One Author (WLH) is a consultant and implant designer for DePuy Orthopedics (Warsaw, IN). Reprint requests: Richard Iorio, MD, Department of Orthopaedic Surgery, Lahey Clinic Medical Center, 41 Mall Road, Burlington, MA Published by Elsevier Inc /09/ $36.00/0 doi: /j.arth operative time for primary insertion of the acetabular implant and for removal of the acetabular implant during revision operation [2]. Avoiding screw fixation prevents complications associated with screw penetration and location such as vascular and nerve injury [6]. Furthermore, the avoidance of screws has a theoretical cost reduction of $50 to $150 per screw implanted for institutions that do not use single price/case purchasing programs [13,14]. Acetabular implant design and materials have improved markedly for the past 2 decades. Improved conformity of the liner with the metal shell of the acetabular component, reduced roughness or improved polishing of the internal surface of the cup, improved liner locking mechanism fixation, improved congruity of the screw heads in the acetabular shell, improved bearing surfaces, and improved polyethylene sterilization techniques and packaging have all greatly increased the survivorship of cementless acetabular components [1-4]. Evaluation of clinical (reoperations, outcome data) and radiographic parameters (osteolysis, bone loss, radiolucency, radiodensity) associated with cementless porous-coated acetabular component design and polyethylene that is sterilized in an inert environment and stored in a vacuum provided by barrier packaging should allow a more equitable study of acetabular fixation than was possible in the past. The purpose of this study was to compare initial acetabular implant stability and late acetabular implant migration with and without screw fixation of the acetabular component. This study attempts to answer

2 310 The Journal of Arthroplasty Vol. 25 No. 2 February 2010 the very specific question of whether screws are necessary for the fixation of the acetabular component in cementless primary THA with current design features. Materials and Methods Seven hundred seventy-five cementless hemispheric porous-coated acetabular components were implanted during primary total hip operations at Lahey Clinic, Burlington, MA, and were available with at least 2 years of follow-up. Exclusions included acetabular cups implanted during conversion of previous hip surgery to total hip operations, revision total hip operations, primary total hip operations with Crowe III or IV dysplastic acetabulums, primary total hip operations with cemented acetabular components, and patients without at least 2 years of follow-up. Five hundred nine acetabular implants (66%) were implanted with screws, and 266 acetabular implants (34%) were inserted without screws. There were no significant differences in sex distribution between the 2 cohorts with slight female predominance (P =.635) (Table 1). The reason for operation was osteoarthritis or posttraumatic arthritis in 475 (93.3%) of 509 cases in the screw fixation cohort and 252 (94.7%) of 266 cases in the no-screw fixation cohort. The remaining diagnoses were inflammatory arthritides or osteonecrosis in each cohort with no significant difference in the distribution of diagnoses between cohorts (Table 1). The Charnley functional categories of the patients in each cohort were significantly different for each category. The screw fixation cohort had significantly more Charnley A (unilateral hip disease) and Charnley B (bilateral hip disease) patients, and the no-screw fixation cohort had significantly more Charnley C patients (unilateral or bilateral hip disease with other disability) (Table 1). Acetabular preparation was performed similarly in both cohorts with concentric underreaming of the socket by 1 mm, and the acetabular component was impacted into place. Three surgeons (471 cases) always used adjunctive screw fixation, and 3 surgeons used both screw fixation and no-screw fixation. One surgeon primarily used noscrew press-fit fixation (237 no screw, 20 with screw fixation) and used adjunctive screw fixation when the initial press-fit was not stable. Two surgeons used screw fixation (18 cases) and no-screw press-fit only fixation (29 cases) variably. The 3 surgeons who used screw fixation variably attempted to implant all acetabular components without screw fixation. When the reamer reached maximal medial depth of the acetabulum and the anteriorposterior diameter of the acetabulum had been maximized, the fit of the acetabular reamer was assessed. If the reamer was tight with minimal or no motion, an acetabular component without holes 1 mm larger was chosen for implantation. If maximal reaming had been Table 1. Preoperative and Intraoperative Data Acetabular Fixation With Screws Without Screws No. of implants 509 (66%) 266 (34%) No. of patients Follow-Up (y) 6.32 (2-11) 6.9 (2-11).196 Age (y) (32-89) (39-88).288 Sex Male 232 (45.6%) 126 (47.4%).635 Female 277 (54.4%) 140 (52.6%) Diagnosis Osteoarthritis/ 475 (93.3%) 252 (94.7%).437 Posttraumatic Inflammatory 15 (2.9%) 5 (1.9%).374 Osteonecrosis 19 (3.8%) 9 (3.4%).805 Functional category Charnley class A 265 (52%) 111 (42%).006 * B 128 (25%) 40 (15%).001 * C 116 (23%) 115 (43%) * Types of socket Pinnacle 82 (16.1%) 39 (14.7%) * 100 (no holes) 0 39 Sector (3 holes) 72 Multihole 10 Duraloc 354 (69.5%) 157 (59%).003 * 100 (no holes) 157 Sector (3 holes) 293 Multihole 61 PFC 73 (14.4%) 70 (26.3%) * No holes 41 2 holes Multihole Head size (92.3%) 263 (98.9%) * (7.7%) 3 (1.1%) b.01 * Bone grafts 31 (6.1%) 12 (4.5%).362 (all nonstructural) Morselized 29 (5.7%) 11 (4.1%).351 autograft Morselized 2 (0.4%) 1 (0.4%).971 allograft Type of stem Cementless 376 (73.9%) 122 (45.9%) b.01 * Cemented 133 (26.1%) 144 (54.1%) b.01 * *Significant value at P b.05. achieved and concern remained about the fit of the reamer, a component with holes was chosen. After implantation of the acetabular component, the cup was tested by pulling on the rim with a Kocher clamp. If no motion was noticed with this maneuver, screws were not used and the apex hole eliminating cover was placed, followed by the acetabular liner. If motion was detected when either the cup was challenged with the Kocher clamp or while inserting the apex hole cover, then screws were used for adjunctive fixation after reimpacting the component. One surgeon would use an acetabular trial when unsure of the rim fit. If any doubt about rim fit remained, a cup with screw holes was chosen to insure the ability to use screws and obtain secure fixation. Nonused screw holes were not filled in the screw fixation cohort. P

3 Cementless Acetubular Fixation With and Without Screws Iorio et al 311 Three different porous-coated acetabular components were evaluated in this study. The Press-Fit Condylar (PFC, DePuy Orthopedics, a Johnson & Johnson company, Warsaw, IN) modular component was used from January 1, 1998, to 1999 (143 cases). The Duraloc cup was used from 1999 to 2004 (511 cases). The Pinnacle cup was used from 2004 to December 31, 2005 (121 cases). All 3 acetabular components used had favorable oxidation minimizing polyethylene sterilization, modern locking mechanisms, and a porous coating with enduring survivorship. These similar characteristics of the 3 cup designs in this study allowed screw or no-screw fixation to be evaluated fairly. The PFC cup was a modular, second-generation component with hemispheric geometry. It featured a beaded porous coating and was made from cast cobaltchromium alloy. The PFC cup came in a no-hole, 2-hole, and a multihole variant. The locking mechanism was a 12-position rotational design with 4 antirotation tabs, which locked the peripheral rim of the polyethylene to the shell. The polyethylene was γ sterilized in a vacuum with a foil package. Screw fixation was used in 73 (14.4% of the screw fixation cases) PFC cups, and no-screw fixation was used in 70 (26.3% of the no-screw fixation cases) PFC cups (Table 1). The Duraloc cup was a modular, second-generation porous-coated socket with a wire ring locking mechanism. It featured a porous beaded surface and was made from titanium. The Duraloc cups used in this series were the Duraloc 100 (no-holes), Duraloc sector (3 holes), and the Duraloc 1200 series (a multihole component). The no-hole design had a threaded insertion hole at the apex of the hemisphere that could be filled with a hole eliminator after insertion. A hole eliminator was used in each case in this series. The Enduron polyethylene was plasma sterilized in an inert environment with barrier packaging. Screw fixation was used in 354 (69.5% of the screw fixation cases) Duraloc cups, and no-screw fixation was used in 157 (59% of the no-screw fixation cases) Duraloc cups. The most recently designed Pinnacle cup is a hemispheric titanium cup with a porous beaded surface. The locking mechanism is a Morse taper fit that can accommodate polyethylene, metal, and ceramic liners. The Pinnacle cup has no-hole, 3-hole, and multihole varieties. The threaded dome apex insertion hole can be plugged with a hole eliminator. A hole eliminator was used in each case in this series. Marathon crosslinked polyethylene has been used in the Pinnacle cups since its introduction in No metal-on-metal or ceramic-on-ceramic hips were performed during this study. Screw fixation was used in 82 (16.1%) Pinnacle cups, and no-screw fixation was used in 39 (14.7%) Pinnacle cups. Clinical evaluation was performed preoperatively at 1 year postoperatively and every 2 years thereafter. All clinical and patient-generated outcome data were recorded in a total joint arthroplasty database. All patients were asked to fill out patient questionnaires that included Short Form-36, Western Ontario and McMaster University Osteoarthritis Index, Harris hip score, and other outcome information at each visit that was not germane to this particular study. Radiographic evaluation included an anterior/posterior radiograph of the pelvis centered on the pubic symphysis with inclusion of the proximal part of the femur, distal to the tip of the femoral stem, and a cross-table lateral x-ray of the hip. The radiographs were stored in a digital radiographic archive. Postoperative radiographs could be corrected for magnification by using the known diameter of the femoral head. Postoperative evaluation was carried out by the operative surgeons, and all postoperative radiographs were evaluated by an independent evaluator (BP) not involved in the surgical procedures or ongoing care of the patients. Evidence of acetabular component migration were measured on serial radiographs, and a linear change of greater than 3 mm was considered indicative of migration [5]. Postoperative gaps, radiolucent lines, bone loss, osteolytic lesions, and radiodensities were identified and followed on sequential radiographs to look for progressive lesions noted in the 3 acetabular zones, previously described by DeLee and Charnley [15]. Clinically significant osteolytic lesions defined as greater than 4 cm 2 were separately noted. Reoperation of any type was identified. Acetabular component revision for instability or loosening were individually identified. Statistical analysis performed with the use of SPSS version 11.5 software (SPSS, Chicago, IL). χ 2 tests were used to analyze the relationship of screw fixation and nonscrew fixation with the other variables. Continuous correction was used for 2 2 tables. Institutional review board permission was granted to review the medical records and radiographs of all patients involved in the study. Institutional educational support was received from DePuy Orthopedics. However, this funding was for fellowship education and was not linked to this study. One author (WLH) has a consulting and a product development contract with DePuy Orthopedics. Results Screw fixation was used in 509 hips (470 patients, 66%), and no-screw fixation with the press-fit only technique was used in 266 hips (243 patients, 34%). In the screw fixation cohort, 109 (21.4%) hips had 1 screw placed in the acetabular shell for fixation, 335 (65.8%) hips had 2 screws placed, 59 (11.6%) hips had 3 screws placed, and 6 (1.2%) had 4 or more screws placed. Average follow-up for the screw fixation cohort was 6.32 years (2- to 10-year follow-up), and average follow-up for the no-screw fixation cohort was 6.9 years (2- to 10- year follow-up) (P =.196).

4 312 The Journal of Arthroplasty Vol. 25 No. 2 February 2010 In the screw fixation cohort, there were 73 two-hole PFC cups, 293 Duraloc sector cups, 61 Duraloc multihole 1200 series cups, 72 Pinnacle sector cups, and 10 Pinnacle multihole cups. In the no-screw fixation press-fit cohort, there were 41 no-hole PFC cups inserted and 29 two-hole PFC cups inserted. In the no-screw press-fit fixation cohort, there were 157 Duraloc 100 series cups inserted with no holes and 39 Pinnacle cups inserted with no holes. When the 2-hole PFC cup was inserted without screws, the cup was rotated so that the screw holes were placed on the inferior surface of the acetabulum away from the lines of force of the femoral head. This method theoretically would prevent polyethylene from extruding through the screw holes due to pressure of the femoral head on the polyethylene liner and the unfilled holes in the acetabular shell. The 2-hole cup was chosen in 29 of 70 cases when there was concern that insertion of the cup may require additional fixation. Cementless stems were used in 376 cases (73.9%) of the screw fixation cohort and 122 cases (45.9%) of the noscrew fixation cohort (P b.01). Cemented stems were used in 133 cases in the screw fixation cohort (26.1%) and in 149 cases (54.1%) in the no-screw fixation cohort (P b.01). The 28-mm heads were used in 470 cases (92.5%) in the screw fixation cohort and 263 cases (98.8%) in the noscrew fixation press-fit only group. The 32-mm heads were used in 39 (7.7%) cases of the screw fixation group and 3 (1.1%) cases of the no-screw fixation cohort. No structural allografts were used in these cases. There were 6 total reoperations in each cohort (Table 2) (P =.249). There were no cups revised for loosening in the Table 2. Postoperative Follow-Up Data Acetabular Fixation With Screws Without Screws No. of implants Reoperations Total 6 (1.2%) 6 (2.3%).249 Acetabulum only 5 (0.98%) 5 (1.9%).249 Infections/Resections 1 (0.2%) 1 (0.4%).971 Periprosthetic 0 1 (0.4%).166 fracture/orif Periprosthetic fracture/ 1 (0.2%) Femoral revision Cup revision/osteolysis 1 (0.2%) Cup revision/instability 3 (0.5%) 3 (1.1%).417 Cup revision/loosening 0 1 (0.4%).166 Acetabular radiolucency Total 47 (9.2%) 19 (7.1%).322 Zone 1 30 (5.9%) 6 (2.3%).022 * Zone 2 21 (4.1%) 8 (3.0%).436 Zone 3 9 (1.8%) 18 (6.8%).0003 * Radiodensity 1 (0.2%) 1 (0.4%).640 Osteolysis, 8 (1.6%, 6 2 (0.75%,.337 N4 cm 2 lesion Duraloc, 2 PFC) 2 Duraloc) Bone loss of any kind 42 (8.3%) 31 (11.6%).124 Migration 0 0 ORIF indicates Open Reduction Internal Fixation. *Significant value at P b.05. P screw fixation cohort. One hip (0.4%) was revised for loss of position in the no-screw fixation group on postoperative day 1 (P =.166). This cup was revised with a screw fixation socket without further complications. One cup (0.2%) was revised in the screw fixation cohort due to osteolysis. Three cups in each group were revised for instability (recurrent dislocation) (P =.417). All were well fixed. One acetabular component (0.2%) was revised in the screw fixation cohort due to infection and 1 (0.4%) in the no-screw fixation cohort. Radiographic analysis of the remaining hips revealed no cups in either cohort with migration greater than 3 mm. Acetabular radiolucencies were seen in 47 (9.2%) hips in the screw fixation cohort and 19 (7.1%) cups in the noscrew fixation cohort (P =.322). Osteolytic lesions greater than 4 cm 2 were seen in 8 (1.6%) cases of the screw fixation group and 2 (0.75%) cases of the no-screw fixation group (P =.337) (Table 2). There were 36 deaths involving 39 (7.7%) THA operations in the screw fixation cohort. The deaths occurred at an average of 5.4 ( ) years after total hip operation. There were 16 deaths in 16 (6.0%) THA patients in the no-screw fixation cohort. The deaths occurred at an average of 4.7 ( ) years after total hip operation. All surviving patients were available for at least 2 years of clinical follow-up. Discussion The results of this series confirm previous reports of equivalent results of primary THA performed with porous-coated hemispheric acetabular components inserted with a 1-mm underreamed press-fit technique with and without screw fixation [7-11,16]. For cups implanted with screws, previous reports were concerned about polyethylene wear debris and an increased risk of osteolysis due to egress of polyethylene into the pelvis through screw holes and along the tract of fixation screws [2,4,12,16]. In the past, it was not clear whether osteolysis associated with cementless acetabular fixation may be due to high wear rates of polyethylene secondary to sterilization and storage in an oxidative environment or may be due to acetabular component design. The cups used in this series were designed with locking mechanisms that decreased micromotion and back-side wear that were intended to reduce wear debris and osteolysis. The cups used in this series also had congruency of the acetabular liner with the acetabular metal shell that also decreased backsided wear. This is one of the first series that has looked at stability, migration, and osteolysis of cementless porous-coated acetabular components that had polyethylene sterilized and packaged in an inert environment and stored in a vacuum with barrier packaging to minimize oxidation. In this series, no acetabular components with or without screw fixation were found to be loose or migrated secondary to polyethylene wear or osteolysis

5 Cementless Acetubular Fixation With and Without Screws Iorio et al 313 that may validate the changes in cup design. At intermediate-term follow-up, cementless acetabular fixation with a porous-coated cementless cup with and without screw fixation is acceptable with modern polyethylene sterilization and preparation techniques. Cups can be successfully stabilized and fixed with or without screw fixation. Laboratory studies have also demonstrated that press-fit cups without screw fixation show less micromotion than cups with screw fixation [17]. Screw fixation may be necessary whenever patients have soft bone due to osteoporosis, a deficient acetabulum with inadequate rim coverage, and an inability to obtain a stable mechanical press-fit with underreaming of the acetabulum [2,15]. The inclusion of 3 different acetabular implant designs for 3 different periods is a limitation of this study. The inclusion of different locking mechanisms, polyethylene types, and fixation coatings is a limitation of this study. However, the use of screw or no-screw fixation did not affect initial or early stability, survivorship, or late migration in any one of the 3 cup types. In this series, there does not appear to be any advantage or disadvantage to using screw fixation for acetabular reconstruction in primary THA. The advances in the quality of polyethylene available today including crosslinked varieties has muted the concerns regarding the relationship of screw fixation, polyethylene wear, and osteolysis [18,19]. At intermediate-term follow-up, cementless porous-coated press-fit acetabular fixation with and without screw fixation can be used successfully for primary THA. References 1. Roth A, Winzer T, Sander K, et al. Press-fit fixation of cementless cups: how much stability do we need indeed. Arch Orthop Trauma Surg 2006;126: Dorr LD, Wan Z, Cohen J. Hemispheric titanium porous coated acetabular component without screw fixation. Clin Orthop Relat Res 1998; Della Valle AG, Zoppi A, Peterson MG, et al. Clinical and radiographic results associated with a modern, cementless modular cup design in total hip arthroplasty. J Bone Joint Surg Am 2004;86-A: Engh CA, Hopper Jr RH, Engh Jr CA. Long-term porouscoated cup survivorship using spikes, screws, and pressfitting for initial fixation. J Arthroplasty 2004;19: Massin P, Schmidt L, Engh CA. Evaluation of cementless acetabular component migration. An experimental study. J Arthroplasty 1989;4: Wasielewski RD, Cooperstein LA, Kruger MP, et al. Acetabular anatomy and the tansacetabular fixation of screws in total hip arthroplasty. J Bone Joint Surg 1990;2A: Archibeck MJ, Showalter D, Kavanaugh TS, et al. A comparison of cementless acetabular components of the same design: spiked versus supplemental screws. J Arthroplasty 2003;18: Kwong LM, O'Connor DO, Sedlacek RC, et al. A quantitative in vitro assessment of fit and screw fixation on the stability of a cementless hemispherical acetabular component. J Arthroplasty 1994;9: Thanner J, Kärrholm J, Herberts P, et al. Hydroxyapatite and tricalcium phosphate-coated cups with and without screw fixation: a randomized study of 64 hips. J Arthroplasty 2000; 15: Schmalzried TP, Wessinger SJ, Hill GE, et al. The Harris- Galante porous acetabular component press-fit without screw fixation. Five-year radiographic analysis of primary cases. J Arthroplasty 1994;9: Torga Spak R, Stuchin SA. Cementless porous-coated sockets without holes implanted with pure press-fit technique. J Arthroplasty 2005;20: Udomkiat P, Dorr LD, Wan Z. Cementless hemispheric porous-coated sockets implanted with press-fit technique without screws: average ten-year follow-up. J Bone Joint Surg Am 2002;84-A: Mendenhall S hip and knee implant review. Orthopedic Network News 2008;19: Healy WL, Iorio R, Lemos MJ, et al. Single price/case price purchasing in orthopaedic surgery: experience at the Lahey Clinic. J Bone Joint Surg Am 2000;82A: DeLee JG, Charnley J. Radiological demarcation of cemented sockets in total hip replacement. Clin Orthop Relat Res 1976; Röhrl SM, Nivbrant B, Ström H, et al. Effect of augmented cup fixation on stability, wear, and osteolysis: a 5-year follow-up of total hip arthroplasty with RSA. J Arthroplasty 2004;19: Won CH, Hearn TC, Tile M. Micromotion of cementless hemispherical acetabular components. Does press-fit need adjunctive screw fixation. J Bone Joint Surg Br 1995;77: Egawa H, Ho H, Hopper RH, et al. The relationship between acetabular osteolysis and cup lesion interface involvement in cementless arthroplasty. In: American Association of Hip and Knee Surgeons Scientific Program; Rosemont; IL: AAHKS; 2007;. p. 88. [Poster 231]. 19. Schmalzried TP, Guttmann D, Grecula M, et al. The relationship between the design, position, and articular wear of acetabular components inserted without cement and the development of pelvic osteolysis. J Bone Joint Surg Am 1994;76:677 [Comment in: J Bone Joint Surg Am. 1995;77(8):1290-1].