Precoated femoral component in primary hybrid total hip arthroplasty: Results at a mean 10-year follow-up

The Journal of Arthroplasty Vol. 18 No. 1 2003

Precoated Femoral Component in Primary Hybrid Total Hip Arthroplasty Results at a Mean 10-Year Follow-Up Paul F. Lachiewicz, MD, and Peter Messick, BA

Abstract: This is a mid-term report at 10 years’ mean follow-up of a study of a precoated femoral component used in primary hybrid total hip arthroplasty (THA). Of an original cohort of 98 hips undergoing THA performed by one surgeon, 75 hips in 65 patients (mean age, 67 years) were prospectively followed up for 7 to 12 years (mean, 10 years). All hips had the same porous coated acetabular component and a precoated femoral component (with an oval cross-section) implanted using Simplex bone cement (Howmedica, Rutherford, NJ). There was no femoral component loosening or revision. Two acetabular components in patients with rheumatoid arthritis and protrusio acetabulae had radiographic loosening; however, only 1 was symptomatic and was revised. Acetabular osteolysis was seen in 4 hips (5.3%), and minor femoral osteolysis was seen in 3 hips (4%). Used in this manner in this patient population, precoating is not detrimental to successful fixation at 10 years’ mean follow-up of primary hybrid THA. Key words: hip arthroplasty, femoral component, precoat, hybrid arthroplasty. Copyright 2003, Elsevier Science (USA). All rights reserved.

The optimum surface finish for a total hip arthroplasty (THA) femoral component implanted with cement remains controversial. Femoral components are available with a smooth, highly polished surface; a rough or matte finish; a macrotextured surface; or precoated with a thin layer of polymethyl methacrylate. Various combinations of these surfaces are also available. Precoating on the proximal surface of a cemented femoral component enhances the proximal stem– cement bond. Biome-

chanical studies have shown that this enhanced stem– cement bond increases cement–metal interface shear and torsional fatigue strength and reduces strain in the distal cement mantle [1– 4]. However, there has been some discrepancy between these theoretical and biomechanical studies and several clinical reports that show a high rate of failure of precoated femoral component [5–7]. This discrepancy may possibly be explained by differences in stem geometries and offsets, patient populations, and femoral canal preparation and cementing techniques. The authors previously reported the clinical and radiographic results of hybrid THA with a precoated femoral component in 98 hips at a mean of 6.5 years [8]. Although the cement mantle was relatively poor in 90% of the hips, only 2 femoral components were revised for definite loosening and 1 well-fixed femoral component was removed at 5 years because of late hematogenous infection. The purpose of this study is to

From the Department of Orthopaedics, University of North Carolina, Chapel Hill, Chapel Hill, North Carolina. Submitted October 18, 2001; accepted August 12, 2002. Funds were received in support of the research material described in this article from Zimmer, Warsaw, IN. Reprints requests: Paul F. Lachiewicz, MD, Department of Orthopaedics, University of North Carolina, Chapel Hill, 242 Burnett-Womack Bldg, CB 7055, Chapel Hill, NC 27599. Copyright 2003, Elsevier Science (USA). All rights reserved. 0883-5403/03/1801-0008$35.00/0 doi:10.1054/arth.2003.50017

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2 The Journal of Arthroplasty Vol. 18 No. 1 January 2003 report the mean 10-year clinical and radiographic results, using prospectively obtained data, for the 95 remaining hips with a hybrid precoated THA.

Materials and Methods Because of the continued controversy concerning precoated femoral components, the remaining original 82 patients (95 hips) still living were followed up prospectively at yearly or 2-year intervals or until death [8]. This was a consecutive series of patients who had undergone a THA with a cemented femoral component of a single design. Regarding the present study, 13 patients (16 hips) had died due to unrelated causes with the implants in place. Three patients (3 hips) were lost to followup, and 3 patients (4 hips) were contacted by telephone but could not return for re-evaluation due to serious medical problems. The hips in these 3 groups of patients had been well-fixed radiographically at the previous follow-up. Therefore, the study group consisted of 75 hips in 63 patients who underwent complete clinical and radiographic evaluation. Of these patients, 48 were women (59 hips) and 15 were men (16 hips). The mean age at surgery was 67.4 years (range, 44 – 86 years) and the mean age at follow-up was 76.4 years (range, 55–96 years). The mean weight at surgery was 72.4 kg (range, 41–101 kg). The preoperative diagnosis was osteoarthritis in 54 hips, rheumatoid arthritis in 15 hips, osteonecrosis in 3 hips, post-traumatic arthritis in 2 hips, and an acute femoral neck fracture in 1 hip. Preoperatively, 22 hips (22 patients) had Charnley Class A function; 28 hips (19 patients) had Charnley Class B function, and 25 hips (22 patients) had Charnley Class C function. The mean follow-up time was 10 years (range, 7–12 years). Institutional Review Board approval was obtained for the clinical review of these patients. The arthroplasties were performed by 1 surgeon through the posterolateral approach. However, 1 hip had, in addition, an advancement of the greater trochanter. The femoral component was modular, fabricated of chromium-cobalt alloy with an oval cross-section, and precoated proximally with a thin layer of polymethyl methacrylate by the manufacturer. The femoral component in all hips was a Precoat or Precoat plus (with small dimples in the proximal precoated anterior and posterior aspects of the component) made by the same manufacturer (Zimmer, Warsaw, IN). A 28-mm femoral head was used in 74 hips, and a 22-mm femoral head was used in 1 hip. A small stem was used in 11 hips, a

medium stem in 40 hips, a large stem in 10 hips, an extra-large stem in 3 hips, and a precoated congenital dislocation of the hip stem in 1 hip. A short neck was used in 9 hips, a medium neck in 60 hips, and a long neck in 6 hips. The acetabular component was an uncemented porous-coated hemisphere fixed with multiple screws (Harris-Galante, Zimmer, Warsaw, IN) [9]. The minimum polyethylene thickness used was 6.3 mm. So-called “third-generation” cement techniques were used. The femoral canal was prepared using hand broaching to the largest rasp that would fit. Power reamers were not used in the femoral medullary canal. The medial neck and calcar were prepared for the collar using a circular reamer. An intramedullary polyethylene cement restrictor was placed 1.5 to 2.5 cm below the anticipated tip of the prosthesis. The intramedullary canal was cleansed of blood and debris using pulsatile lavage (Stryker, Kalamazoo, MI) and packed with gauze containing a thrombin solution (10,000 U/10 mL). Polymethyl methacrylate (Simplex-P, Howmedica, Rutherford, NJ) was prepared using a vacuum mixer (Stryker) and introduced in a retrograde fashion using a cement gun. The proximal cement was pressurized at least 3 times manually with a rubber dam. The prosthesis was inserted in the middle of the cement mantle by hand in 1 motion, and the collar was placed on the medial neck. Full weight bearing as tolerated with crutches or a walker was recommended for the first 6 weeks after surgery. All hips were evaluated clinically postoperatively by an orthopaedic research nurse at the most recent follow-up using the Harris hips score [10]. Using previously reported methods, standardized anteroposterior (AP) pelvis radiographs centered over the pubis and AP and frog leg lateral views of the femoral component were analyzed using the 6-week postoperative and subsequent radiographs by 1 investigator (PM) who did not perform the arthroplasties [1,8,9,11,12–17].

Results Clinical Results The mean preoperative Harris hip score was 44 points (range, 0 to 70) for the seventy-five hips in this study. No femoral components were removed or revised since the initial report [8]. However, 1 acetabular component was revised at 8 years for symptomatic loosening. The mean postoperative Harris hip score for all 75 hips (63 patients) was 86 points (range, 30 –100 points) at a mean follow-up of 10 years. The clinical results were excellent in 30

Precoated Femoral Component • Lachiewicz and Messick

hips (26 patients), good in 32 hips (27 patients), fair in 8 hips (8 patients), and poor in 5 hips (5 patients). Therefore, 62 of 75 hips (83%) had an excellent or good clinical result. Three of the 5 patients with a poor hip score were elderly patients with Charnley Class C function before surgery and with multiple systemic medical problems. One poor result was in the patient with symptomatic loosening of the acetabular component. The fifth poor result was in a patient with severe arthritis of both knees who had limited ambulation and function. Pain was absent in 56 (74.6%) hips (44 patients), slight or occasional in 15 (20%) hips (15 patients), mild in 2 (2.6%) hips (2 patients), moderate in 1 (1.3%) hip (1 patient), and severe in 1 (1.3%) hip (1 patient). Forty-eight patients (60 hips; 76%) walked with no limp, 10 patients (10 hips; 13.3%) walked with a slight limp, 4 patients (4 hips; 6.3%) walked with a moderate limp, and 1 patient (1 hip; 1.5%) was unable to walk. Thirty-four patients (40 hips; 54%) used no support, 15 patients (20 hips; 24%) used a cane for long walks, 7 patients (8 hips; 11%) used a cane full time, 6 patients (6 hips; 9.5%) used 2 supports or a walker, and 1 patient (1 hip, 1.5%) was unable to walk. Twenty patients (32 hips; 32%) were able to walk unlimited distances, 4 patients (5 hips; 6%) were able to walk 6 blocks, 30 patients (38 hips; 48%) were able to walk 2 to 3 blocks, 8 patients (8 hips; 13%) were limited to walking indoors, and 1 patient (1 hip; 1.5%) could perform only bed to chair transfers. Complications Of the original cohort of 98 hips, there were 2 early failures of femoral component fixation and 1 component that was removed for late infection. All were previously reported [8]. One acetabular component, previously mentioned, was revised for loosening at 8 years. Radiographic Results In the current review, there were no femoral components with possible, probable, or definite loosening of the component. Three hips had an isolated radiolucent line in 1 femoral zone (Fig. 1). Small areas of focal femoral osteolysis were seen in 3 hips at 7 years, but there was no progression at 10 years. These areas measured between 3 to 5 mm in size. Calcar resorption was seen in 21 hips, with mean resorption of 3.9 mm (range, 1– 8 mm). The initial position of the femoral component was valgus (2°– 4°) in 10 hips (13.3%), neutral in 58 hips (77.3%) and varus (1°–2°) in 7 hips (9.3%). Corti-

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Fig. 1. Ten-year postoperative anteroposterior radiograph of a 75-year-old woman who had undergone THA for a displaced femoral neck fracture. There is an incomplete radiolucent line in Gruen zone 1 of the femur and 3 mm of calcar resorption.

cal hypertrophy was seen in Gruen zones 3 and 5 in 6 hips (8%). The femoral cement mantle was classified as grade A in only 2 hips (2.6%) and Grade B in 3 hips (4%). In 56 hips (74.6%), the cement mantle was classified as grade C-1 (presence of small bubbles in the cement mantle), and in 14 hips (18.6%) the cement mantle was classified as grade C-2 (thin cement mantle ⱕ 1 mm in zones 2, 3, and 5). The mean amount of cement distal to the femoral component was 15 mm (range, 5– 45 mm). Seventy-three of 75 acetabular components were stable according to the criteria of Massin, Schmidt, and Engh [16]. One was revised for loosening, and the other had asymptomatic migration but was not revised. Periacetabular osteolysis was seen in 4 hips (3 patients): 2 in the ischium and 2 in the ilium. There were no loose or broken acetabular screws. Radiolucent lines were visible at the bone-prosthesis interface in 13 (17.8%) acetabular components. In 11 hips, the radiolucent line was in 1 zone, and in 2 hips, it was in 2 zones. The mean linear polyethylene wear rate was 0.05 mm/y (range, 0 – 0.17 mm/y) with a standard deviation of 0.04 mm/y.

Discussion This study was a mid-term review at 10 years’ mean follow-up of prospectively obtained data on

4 The Journal of Arthroplasty Vol. 18 No. 1 January 2003 75 consecutive primary hybrid THAs with a precoated femoral component implanted using thirdgeneration cement techniques. In the previous report from this institution, there had been 2 femoral component loosenings and revisions and 1 late infection requiring component removal in 98 hips, which had been followed up for a mean of 6.5 years [8]. The important finding was that there were no femoral component loosenings since the initial report. These patients were predominantly women, with a mean age of 67 years and a mean weight of 72 kg at the time of implantation and a mean age of 76 years at the time of last review. It was the senior author’s (P. F. L.) policy that patients younger than 60 years of age were strongly encouraged to have a cementless femoral component during the time of this study. However, some patients refused a cementless device. In addition, the overall functional level of these patients, as described by Charnley Class, changed with time, and more patients developed other orthopaedic, medical, or neurologic problems that limited their function. Only 20 patients with 23 hips were able to walk an unlimited distance, and 34 patients with 43 hips were able to walk short to moderate distances outdoors. Thus, many of these patients had limited their activities due to problems other than the THA. The results of using this prosthesis in a younger, more active patient population might have been different from the results for this group. In addition to the variable of femoral component surface finish, additional variables of stem geometry and offset [5,18], operative techniques [6,19], and patient population, may all play critical roles in the durability of a roughened precoated femoral component [2]. The polyethylene wear rate was low in this series, and in only 4 hips was there measurable wear greater than 1 mm. Periacetabular osteolysis was seen in 4 hips, but the patients were asymptomatic. The low polyethylene wear rate observed in these patients is likely typical of patients over the age of 70 who have a low activity level, such as this patient population. Femoral osteolysis was seen in only 3 hips, and these were small lesions. In this study of hybrid THAs with a precoated femoral component, the surface finish was not detrimental to secure fixation at a mean of 10 years. Femoral and periacetabular osteolysis are a minor problem in patients who have a hybrid THA at an age ⬎ 60 years. When considering the results of THAs, it is important to remember that all hybrids and all precoated femoral components are not alike. There are major differences in design and technique

that can influence the early and long-term survival of the implant.

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