by Richard A. Berger, MD, and Joshua J. Jacobs, MD
Richard A. Berger, MD, is adult reconstruction fellow, department of orthopaedic surgery, Rush Medical College, Chicago.
Joshua J. Jacobs, MD, is associate professor, of orthopaedic surgery, Rush Medical College, Chicago.
Dr. Berger and Dr. Jacobs are members of the Committee on Biomedical Engineering.
Because the medical community has been asked to become increasingly fiscally responsible, cost analysis is being applied to every aspect of health care delivery. When evaluating the expenditures associated with total hip arthroplasty, attention has been concentrated on implant costs. The United States market for hip and knee implants is approximately $1.6 billion annually with a range in price of a primary total hip prosthesis between $2,000 and $6,000. With Medicare paying for 59 percent of all total hip replacements in 1994, the Diagnosis Related Group (DRG) payment method predominates the reimbursement for this procedure. The DRG method reimburses a hospital a fixed fee for a primary total hip replacement, approximately $9,000. The DRG payment covers the cost of the implant and does not vary with the amount of money spent for the implant.
Therefore, prosthesis expense can account for 25 to 60 percent of the average DRG payment. This percentage has increased annually over the last 10 years. For example, at the Lahey Clinic outside of Boston, the expense for total hip implants was 11 percent of the total charge for this procedure in 1981, but rose to 24 percent of the total charge in 1990. Of even greater concern is that, by 1990, implant expenditure consumed 35 percent of their DRG payment for a total hip replacement.
Efforts now are concentrating on cost cutting strategies. From 1993 to 1994, the number of total hip arthroplasties increased by 6.6 percent, to 137,000 procedures, while the total implant expense rose by only about 2 percent. Two factors appear to be responsible for these modest savings. First, manufacturers have reduced the price of the implants to obtain market share. Second, surgeons have been selecting less expensive components.
The surgeon, being the primary consumer of orthopaedic implants, has a significant impact on the overall cost of a total hip replacement. For example, from 1993 to 1994, surgeons increased the use of cemented stems by 12 percent while decreasing the use of more costly cementless stems by about the same. Concurrently, the average cementless stem price rose by 1 percent while the cost of cemented stems fell by 3 percent. This decrease in price in cemented stems is a result of surgeons selecting less expensive options in cemented stems than were previously used. The demands for these lower priced cemented stems have resulted in a greater selection of these stems being offered by manufacturers.
The efforts to reduce the cost of components has led to the concept of the "DRG stem." The term "DRG stem" has become synonymous with a low-priced implant. Note that the DRG payment system has no criteria for prosthesis selection, nor does this system limit or suggest the expense of implants. The idea of implant matching has evolved to help surgeons select an appropriate component to optimize the cost/benefit ratio of the implant selected for each individual patient. With these algorithms, implant selection is based on the individual patient's needs. Older and less active "low demand" patients may do well with less technologically advanced and inexpensive options. Accordingly, younger and more active "higher demand" patients may benefit from the most technologically advanced and expensive options. It is important to realize that there is no hard data on clinical outcomes that validate these matching schemes. They are based on cost/benefit considerations only.
In general, if we are searching for an inexpensive DRG stem, then a cemented stem must be chosen. Porous cementless stems currently do not have low-priced options. In fact, the most expensive cemented stem is about the same price as the least expensive porous cementless stem. The average price of a cemented stem is $1,537 with a range from $400 to $2,150, while cementless stem prices average $2,656 with a range from $2,130 to $3,450.
The first option in choosing a low-priced cemented implant is selecting the material type and manufacturing method. Implants fall into two basic manufacturing methods; casting and forging. Forging is more expensive, but results in a stronger, more fatigue resistant stem. For example, a forged chromium-cobalt stem has, on average, 50 percent more tensile and fatigue strength than a cast chromium-cobalt stem.
There are many other choices which effect stem price. These modifications include precoating with polymethylmethacrylate, textured finishes, modularity, centralizers, hydroxyapatite coatings and attached cement spacers. In addition, ceramic femoral heads and modifications to UHMWPE are new technologies designed to decrease wear-related problems. All these new modifications significantly increase the implant cost. For example, precoating can add $800, a ceramic head can add $700, and a modified UHMWPE liner can add $400 to the cost of the implant. These modifications, while advocated by many, do not have adequate clinical follow up to assess whether the added cost is beneficial, and in which patient they may be appropriate.
In the "low demand" patient, older, less expensive technologies that have stood the test of time are recommended. However, in the "higher demand" patient, where a service lifetime in excess of 20 years is required, innovative design modifications and improvements, which have shown promise in vitro or in animal testing, may be indicated.
Making definitive recommendations is currently quite difficult. First, "low demand" and "high demand" are very subjective terms as is "younger" and "older." Second, very little good data exists on what attributes are clinically helpful for the longevity of total hip arthroplasty. At this juncture, it appears that a forged stem with a contemporary design is important regardless of the patient profile. Centralization, leading to an adequate cement mantle, also appears to be important. Precoated stems, porous coated stems, hydroxyapatite coated stems, ceramic heads, and modified UHMWPE are relatively newer technologies that have not yet been clinically proven to be superior. Head/neck modularity has some definite advantages, provided that modular connections are utilized which minimize or eliminate fretting.
In our practice, we use cemented stems for the majority of our patients. We use only forged stems with some form of centralization in all but the lowest demand patients. For the higher demand patients, precoated cemented stems are an option. We routinely use cementless stems in younger patients, under 60 years old, with good bone quality. We currently do not use ceramic heads or modified UHMWPE.
In conclusion, the cost of total hip replacement must be a secondary concern to the overall patient benefit. A prosthesis chosen solely to minimize cost may not benefit the patient in the short-term and may be cost-ineffective in the long-term. Conversely, the most expensive implants do not necessarily perform better than the modestly-priced alternatives. Better long-term clinical and cost-effectiveness studies will be required to answer these questions.
1. Healy WL: The cost of primary and revision total hip arthroplasty: A dilemma for surgeons and hospitals, in Galante JO, Rosenberg AG, Callaghan JJ (eds): Total Hip Revision Surgery. New York, NY, Raven Press, 1995.
2. 1995 Hip and Knee Implant Review. Orthopedic Network News, Vol 6, No 3, July 1995.