Cemented Total Hip Arthroplasty With Boneloc Bone Cement

David C. Markel, MD, Daniel B. Hoard, MD, Charles A. Porretta, MDAuthors and DisclosuresPosted: 04/17/2002; J South Orthop Assoc. 2001;10(4) © 2001 Southern Medical Association www.medscape.com

Abstract

(WK-345, Biomet Inc, Warsaw, Ind) attempted to improve cement characteristics by reducing exotherm during polymerization, lowering residual monomer and solubility, raising molecular weight, and lowering airborne monomer and aromatic amines. To study the efficacy of this cement, a selected group of 20 patients were prospectively enrolled and followed up after hip arthroplasty. All components were cemented. During the enrollment period, approximately 70 other hip arthroplasties were performed. Clinical evaluation was based on the Harris hip score. Radiographic evaluation was based on assessment of position of the components, subsidence, and/or presence of radiolucencies. Patients had follow-up for an average of 42 months (11 to 58 months); 1 was lost to follow-up. Of these, 7 (35%) had failure at last follow-up. Despite its initial promise, Boneloc cement had an unacceptably high failure rate over a relatively short follow-up period and is not recommended for use. Despite the longevity and odor toxicity problems with conventional bone cement, new cement technologies must be approached with caution. Introduction Cemented hip arthroplasty has been performed since the late 1960s.^[1] It became clear over the ensuing years that cemented arthroplasties had a limited longevity and that the mechanical construct would fail via a process of aseptic loosening. In addition, a number of less than desirable characteristics were noted. The fumes of the polymerizing cement were found to be noxious to the operating room staff, and the exotherm of the polymerizing cement was potentially damaging to the bone. To address these concerns, several implant manufactures developed or are developing newer cement technologies.

In 1986, development was begun of a new bone cement, which was later marketed by Biomet Inc (Warsaw, Ind) as Boneloc. The first objective for Boneloc was to create a cement equal to or better than conventional methyl methacrylate/polymethyl methacrylate in both efficacy and longevity. The second objective was to create a product that was safer for operating room personnel.

By decreasing the chemical and thermal damage to bone during implantation, it was believed that the clinical efficacy of conventional polymethyl methacrylate could be improved. It was hoped that by preventing bone necrosis at the bone-cement interface the mechanical grouting action of the cement would be better preserved and perhaps improve the longevity of the construct. Therefore, the first goal was to reduce the exothermic temperature generated during cement polymerization, lower the residual monomer content, and create a product with both a lower solubility and a higher molecular weight. The second objective was protection of operating room personnel. Nursing staff have been noted to complain about the odor of cement and have anecdotally associated exposure to cement fumes with headache, nausea, and/or dizziness. While there is no clear evidence that the cement fumes are teratogenic, pregnant nurses are often not used to staff joint replacement procedures done with cement at many hospitals, including ours. Thus, the second objective would be accomplished by lowering the residual content of the airborne monomer and aromatic amines, as well as containing the noxious airborne material by modifying the cement delivery system.

The resultant Boneloc cement consisted of a two-component self-curing system. The powdered polymer component consisted of butylmethyl methacrylate copolymers in a ratio of 40%:60%. The liquid monomer component contained 50% methyl methacrylate, 30% n-decyl methacrylate and 20% isobornyl methacrylate. An integrated packaging, mixing, and delivery system was developed to minimize operating room staff exposure to the monomer vapor. The system used a double-chambered high-density polyethylene cartridge into which the two cement components were packeted. Within the chambers, an aluminum membrane separated the monomer and polymer. When the separating aluminum membrane barrier was broken, the polymer and monomer mixed, yet the entire process was kept isolated from the operating room environment and staff. Initial reports noted difficulty with the mixing and cement delivery. Therefore, in 1993, a more conventional vacuum mixing and delivery system replaced the cartridge system.

Analysis and evaluation of new technology is, of course, important and is required in the United States by the Food and Drug Administration. The index study and patient population were based on participation in the United States’ Boneloc cement Investigational Device Exemption during the years 1991 to 1993. We present the results of the cemented total hip arthroplasties done at our institution.

Materials and Methods

After agreeing to participate in Biomet’s United States Investigational Device Exemption protocol and after obtaining Institutional Review Board approval, we undertook the study protocol. No financial support was received by the surgeons for participation. All patients properly consented and were free not to participate. Twenty selected patients were ultimately prospectively enrolled for study over an 18-month period. All patients scheduled for cemented hip arthroplasty by one of us (C.A.P.) were invited to participate in the study. The patients were required to be interviewed by the hospital’s surgical physician’s assistant to ensure an understanding of the requirements of participation (follow-up periods, questionnaires, release of information). The patients were required to consent to use of the experimental cement product.

From October 1991 to April 1993, we used the Boneloc bone cement and the dual cartridge injection system to do 20 total hip arthroplasties in 20 patients. The senior investigator (C.A.P.) performed approximately 70 other total hip arthroplasties during this period. The 20 study patients ranged in age from 43.5 to 86.8 years (mean, 67.3 years). Ten patients were men and 10 were women. Seventeen procedures were primary cemented total hip arthroplasties. In all cases, both components (femur and acetabulum) were implanted with the investigational Boneloc bone cement. Of these 17 patients having a primary hip replacement, 13 had a preoperative diagnosis of osteoarthritis, 1 had rheumatoid arthritis, and 3 had osteonecrosis of the femoral head (1 idiopathic, 2 posttraumatic). Each of the 3 patients having revision arthroplasty was believed to have bone stock compatible with cemented revision arthroplasty. One of them had revision of both acetabulum and femur, 1 had revision of a bipolar hemiarthroplasty with removal of the femoral component and conversion to a total hip arthroplasty, and 1 had revision of a femoral head resurfacing arthroplasty to a total hip arthroplasty. As in the primary procedures, all revision components were implanted with the Boneloc cement.

According to the protocol, one of three femoral components was available for use. These included the Biomet nonporous (cemented) Mallory-Head stem, manufactured from a cobalt-chrome-molybdenum alloy; the Biomet Bimetric cemented femoral stem, manufactured from a titanium alloy (Ti-6Al-4V); and the porous coated Biomet Mallory-Head uncemented stem, also manufactured from the titanium alloy. Similarly, the protocol limited acetabular reconstruction to use of one of three acetabular components. These included the molded Mallory-Head acetabular component and the Superior-Loc Acetabular System, both of which were polyethylene-titanium metal-backed shells and both of which could be implanted with or without cement. The third option was the Biomet all-polyethylene acetabular component designed to be implanted with cement. The femoral components used a taper fit modular head manufactured from titanium alloy, cobalt-chrome-molybdenum, or zirconia ceramic. In this study, 19 chrome-cobalt-molybdenum nonporous Mallory-Head stems and 1 titanium alloy Bimetric stem were cemented in place. All had a cobalt-chrome head. A cemented all-polyethylene acetabular component was used in all 20 of the patients in this investigation.

Seventeen of the procedures were done by one surgeon (C.A.P.) and the other 3 by attending surgeons. All cases were performed through an anterolateral approach.^[2] Modern third-generation cementing techniques were used in all cases and included the use of a distal cement restrictor, retrograde filling of the canal, and pressurization of the cement.^[3-5]

Patients were prospectively enrolled and had predetermined regular follow-up with clinical and radiographic evaluation. Clinical evaluation was done immediately before surgery, at 6 months postoperatively, 12 months postoperatively, and annually thereafter for 5 years. The clinical assessment was based on the Harris hip scoring system.^[6] Of the 100 possible points in this system, 44 are based on pain, 47 on function, 4 on the presence or lack of deformity, and 5 on range of motion.^[6]

Radiographic evaluation was based on standard anteroposterior and lateral radiographs of the hip immediately after operation, 6 months and 12 months postoperatively, and annually thereafter for 5 years. The immediate postoperative radiographic evaluation included a baseline assessment of the initial component position as outlined by Yoder et al,^[7] the cement mantle thickness, and the presence of radiolucencies at the bone-cement and cement-prosthesis interfaces. The follow-up radiographic evaluations included assessment of change in component position (rotation, settling) relative to fixed bony points such as the lesser or greater trochanter or the teardrop, fractures of the cement, and/or radiolucency at the bone-cement and cement-prosthesis interfaces. Radiolucencies and/or fractures of cement, if present, were categorized and recorded according to the radiographic zones of Gruen et al^[8] for the femur and of DeLee and Charnley^[9] for the acetabulum. Acetabular loosening was graded by a modification of the systems of Harris and White^[10] and Dorr et al^[11] (definite loosening — component migration; probable loosening — complete radiolucency; possible loosening — radiolucency comprising 2 of 3 Delee and Charnley zones; no loosening — lucency in a single zone or no radiolucency). Femoral component fixation was graded according to the criteria of Harris et al^[12,13] (definite loosening — migration of component or cement; probable loosening — complete radiolucency; possible loosening — radiolucency in >50% of the bone-cement interface).

For the purposes of this study, failure was narrowly defined as either revision surgery or definite radiographic loosening combined with clinical failure (poor Harris hip score, significant complaints of pain, and dysfunction).

Results

At last follow-up, 7 hips showed failure both clinically and radiographically. Of these, 4 had been revised (stem only in 1, cup only in 2, and both stem and cup in 1). All failures occurred between 2 and 5 years postoperatively. Three patients had radiographic evidence of loosening,^[8-13] as well as pain and clinical failure.^[6] Two of them had radiographic evidence of stem subsidence and had pain with weight-bearing and passive range of motion. One patient had radiographic evidence of stem subsidence and a change in position of the cup, as well as pain on weight-bearing and passive range of motion. These 3 patients were awaiting revision surgery.

The 13 patients without either clinical or radiographic signs of loosening had an average follow-up of 42 months (11 to 58 months). The average hip score^[6] at last follow-up was 89.6 (range, 53 to 100). Results were rated as excellent in 8 (61%), good in 4 (31%), and poor in 1 (8%).

The overall failure rate (radiographic loosening of at least one component, clinical failure, and/or revision surgery) was 35% at an average follow-up of 42 months. The femoral component failed at an overall rate of 25% and the acetabular component at an overall failure rate of 20%.

Discussion

Surgical techniques and procedures are always evolving, and surgeons strive to improve on what they know. It is difficult to decide when a new product should be introduced, especially when the new product is designed to replace or improve on an existing product that has a long history of clinical success. This notion is further convoluted by the fact that surgical products are commonly introduced with financial incentives by industry. When a new product or procedure is introduced to the medical community, it is imperative to compare its performance with the established standards of care. The use of cement for component fixation in total hip arthroplasty has a well-documented history with respect to survivorship and clinical success. Therefore, historic controls were readily available for comparison when evaluating Boneloc cement. Polymethyl methacrylate acts as a grout and forms a mechanical link or interlock between an implant and the bone. The cement is a weak link in this bone-cement-prosthesis construct.

Recent data on cemented total hip arthroplasty using conventional bone cements have similarly shown good long-term results. Keisu and Lindgren^[19] had a 10-year revision rate of 5% using the Harris-Design 2 chrome-cobalt femoral implant and an all-polyethylene acetabular implant cemented with CMW-1 (Wright Medical Technologies, Arlington, Tenn) or Palacos (Smith & Nephew, Memphis, Tenn) bone cements. Ziegler and Lachiewicz^[20] reported an acetabular revision rate of 10% and a femoral revision rate of 8.6% at an average follow-up of 9 years in 70 total hip arthroplasties cemented with Simplex-P cement (Stryker-Howmedica-Osteonics, Allendale, NJ). Mulroy and Harris^[4] reported 3% femoral loosening in 105 hips at 10-year follow-up using Simplex-P bone cement and second-generation techniques. Marston et al^[21] reported a 4% revision rate at 6.5 years in 413 hips cemented with Simplex-P cement.

These series reflect the historic standards against which cemented total hip arthroplasties using new technologies must be judged, since it is the expectation that the new technology, products, or procedures should match if not exceed the efficacy, safety, and durability of those that are already established. While one could question the ability to improve on the historic success of cemented arthroplasty using Simplex-P, Palacos, and CMW, Biomet developed Boneloc cement to achieve two objectives: (1) to improve longevity and efficacy by decreasing the chemical and thermal damage to bone during implantation, and (2) to create a product that was safer for operating room personnel.

With the development of Boneloc cement, Biomet created a more biocompatible monomer mixture that polymerized more completely and generated less heat during polymerization (62°C vs 70° to 82°C).^[22] Wykman and Sandersjoo^[23] reported a maximum attained temperature of 43°C at the bone-cement interface in 10 of 11 acetabuli cemented with Boneloc cement. This was a considerable reduction in polymerization exotherm temperature compared with earlier studies using conventional bone cements. In addition, the delivery system appeared to decrease exposure to the noxious cement fumes. Unfortunately, although these goals were attained, the clinical success of the product was poor. The index series (the only US report) revealed a dismal outcome over a relatively short follow-up. European series reflected a similarly unacceptably high rate of failure. In Denmark, Riegels-Nielsen et al^[24] reported loosening in 24 of 43 hips cemented with Boneloc at an average 18-month follow-up. In a Norwegian series, Nilsen and Wiig^[25] reported loosening in 102 of 157 hips at an average follow-up of 2 years. In Finland, Suominen^[26] reported loosening in 4 of 8 stems in hybrid reconstructions after only 32 months of follow-up. Thanner et al^[27] postulated that the failure in these cases was due to poor mechanical properties such as a reduced tensile strength and elastic modulus when compared with a standard cement (Palacos). In addition, an increased amount of monomer appeared to be released from the cement, contrary to one of the original objectives for the Boneloc cement.

Because of these reports of possible early failure of the bone cement at both the femoral and acetabular component interfaces, Boneloc cement was withdrawn from the market in April 1995. Negative publicity, poor sales, and the pending nature of the Food and Drug Administration investigational device exemption contributed to the withdrawal. Although Boneloc cement was never released for general use in the United States, continued follow-up and evaluation of the cement is important. Knowledge of this and other new cements may explain otherwise unclear failure of a cemented construct in a new patient, as well as provide insight into the evaluation of other new cements. The results of this trial certainly provide food for thought when contemplating participation in an investigational protocol or when beginning use of an approved but as yet unproven new product.

Conclusion

Despite initial promise, Boneloc cement was found to have an unacceptably high failure rate over a relatively short follow-up period and is not recommended for use in total hip arthroplasty. Although conventional bone cements and their delivery systems present problems (eg, limited longevity, high exotherm, and noxious airborne material), long-term success has been established. Caution should be exerted before using new cement technology.