Cemented Total Hip Arthroplasty With Boneloc Bone Cement

David C. Markel, MD, Daniel B. Hoard, MD, Charles A. Porretta, MD

Disclosures

J South Orthop Assoc. 2001;10(4) 

In This Article

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. Unfavorable mechanical properties such as low tensile or fatigue strength, poor fracture toughness, and a low elastic modulus compared with cortical bone or prosthetic metals may lead to cement failure.[14] When disrupted by bony resorption or mechanical failure of the cement, the interlock is lost and loosening results. Loosening therefore can be the result of biologic or mechanical factors. The primary objective for Boneloc was to create a cement that improved the mechanical and chemical properties of conventional polymethyl methacrylate. It was believed that the efficacy would be improved by decreasing bone necrosis as well as more subtle chemical and thermal damage to bone during implantation. Therefore, the material was designed to reduce the exothermic temperatures generated during polymerization, to lower residual monomer content, and to have a lower solubility and a higher molecular weight. Charnley performed what is considered to be the benchmark series of cemented total hip arthroplasties even without the use of what are considered modern cement techniques.[4,12,13,14] In 1973, Charnley and Cupic[1] reported a 92% satisfactory outcome at 9 and 10 years of follow-up. In 1986, Wroblewski[15] reviewed the Charnley and Cupic series at a 15- to 21-year follow-up and found that 85% of the survivors with an intact implant were pain free and 11% had only occasional discomfort. Several other reports cite excellent survivorship over long-term follow-up. Hozack et al[16] reported 99% survivorship of the acetabular component and 96% survivorship of the femoral component of 1,041 Charnley total hip arthroplasties at 10-year follow-up. McCoy et al[17] reported a survivorship of 91% at 15 years in 100 Charnley low-friction arthroplasties. The acetabular survivorship was 98% and femoral survivorship 93%, with 87% good or excellent clinical scores. Sarmiento et al[18] reported an 11-year survivorship of 91.4% and 92.7% when Charnley and Sarmiento prostheses were compared.

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.

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