This article is more than 5 years old. Information may no longer be current.

Providing lifetime function with THR

Issue: June 2006

ByRoger H. Emerson Jr., MD

Add topic to email alerts

Receive an email when new articles are posted on

Please provide your email address to receive an email when new articles are posted on .

Subscribe

Added to email alerts

You've successfully added to your alerts. You will receive an email when new content is published.

Click Here to Manage Email Alerts

You've successfully added to your alerts. You will receive an email when new content is published.

Click Here to Manage Email Alerts

Back to Healio

We were unable to process your request. Please try again later. If you continue to have this issue please contact customerservice@slackinc.com.

Back to Healio

The goal of total hip replacement is to provide a prosthesis that lasts a patient’s lifetime. At the outset, this goal could only be achieved through careful patient selection, specifically by only operating on elderly and minimally active patients. In fact, young age was considered a contraindication to total joint replacement. All patients with total hip replacements were admonished to maintain strict observance of activity restrictions.

The problem of a young patient with debilitating degenerative hip disease was, nonetheless, appreciated. Burton wrote in 1975 that total hip replacement (THR) was indicated for “those younger patients for whom no other form of therapy is possible to provide pain-free function.”¹ Results in young patients were not encouraging. Dorr et al reported only 58% clinically satisfactory results in patients younger than 45 years at nine to 10 years of follow-up in hip replacements from this same era.² The revision rate tripled between follow-up intervals of an average 4.5 years and an average 9.2 years. The patients who achieved the best results in this age group were those with systemic inflammatory arthritis. Young patients learned to expect a limited life expectancy for a total hip prosthesis.

Limited survivorship

Generally, implant survivorship for THRs performed in the late 1970s was limited. Dobbs et al reported a life table survivorship of 88% at only eight years for metal-on-plastic hips placed between 1969 and 1972.³

Twenty-five-year survivorship of the Charnley prosthesis free of reoperation at the Mayo Clinic as reported by Berry et al was 77.5%.⁴ Twenty-five-year survivorship free of revision for aseptic loosening was poorer for each decade earlier in life at which the procedure was performed. The survivorship ranged from 68.7% for patients younger than 40 years to 100% for patients who were at least 80 years old. Men had a twofold higher rate of revision for aseptic loosening than women. Age, gender and underlying diagnosis affected the likelihood of long-term survivorship of the acetabular and femoral components used in a Charnley THR.

In addition to concerns about surgery durability, there were also concerns about the safety of THR surgery. Schoning et al reported a mortality rate of 5.7% in a series of 1322 total hip replacements performed between 1967 and 1975.⁵

Bearing wear was identified early as a limiting factor in total hip survivorship. In 1975 Charnley and Halley reported on a series of low-friction arthroplasties looking at polyethylene wear and found that 68% of hips wore at a rate of 0.15 mm/yr but that 15% of hips wore at a rate of 0.25 mm/yr.⁶

Total hip-replacement failure was also shown to be dependent on surgical technique, implant design and material variables. Pelicci et al reported that two-thirds of the revisions done at the Hospital for Special Surgery between 1971 and 1977 were due to technical problems with the primary replacement.⁷ Six out of 35 revisions were for stem breakage in young and active men, and seven THRs were revised for recurrent dislocations. The authors advised careful patient selection and stem positioning in valgus and optimal cementing technique to avoid failures.

Evolution

With the goal of producing increasingly durable and predictable total joint implants, surgical technique and implant design evolved. Super alloys all but eliminated the problem of implant breakage. Cobalt chrome material with a high modulus of elasticity is better than other materials for cemented stems, and titanium is a better material for cementless stems.

Although acrylic cement fixation produced reliable fixation compared with the early-generation pressfit implants, durability in the first generation of cemented implants was not optimal. The orthopedic community responded with second- and third-generation cementing techniques, which included distal-to-proximal cement delivery with a gun, canal plugging, cement pressurization, porosity reduction and canal centralization. The implants were modified for cemented fixation with metal backing for the acetabulum and changes in femoral stem geometry, as well as changes in surface roughness, with options such as pre-coating with methylmethacrylate.

Follow-up studies will establish to what extent these changes will alter the results of the gold standard of cemented fixation represented by the Charnley prosthesis. At this time, it seems that smoother finished stems have longer survivorship than rougher finished stems.⁸

Cement fixation permits predictable initial fixation but probably will not demonstrate consistent long-term fixation, especially in young, active patients. The inherent mechanical weakness of the bone-cement-implant composite cannot be completely eliminated by changes in surgical technique and design.

Biologic fixation

Biologic fixation, which is bone ingrowth into a porous surface, is a theoretically self-restoring interface that holds the potential for long-term or possibly indefinite fixation. Bone ingrowth fixation using titanium, plasma-spray, porous-coated components provides predictable and durable fixation.

In my practice, using titanium porous-coated Mallory-Head femoral components (Biomet Orthopedics, Inc., Warsaw, Ind.) from 1987 through 2005, a total of 1760 stems show survivorship of 99%, and only seven stems were revised for loosening.

We showed that circumferentially porous-coated stems are more resistant to osteolysis than partially porous-coated stems.⁹ At 15 years of follow-up, late failure mode for this type of stem is not apparent.

Comparable straight-tapered titanium stems, such as the Zweymuller (Wright Medical Technology, Arlington, Tenn.), have similar survivorship, with 100% at 10 years as reported by Swanson.¹⁰ In young patients with an average age of 37 years, McLaughlin and Lee showed no revisions for mechanical loosening at eight to 13 years of follow-up in a series of 108 hips using the Taperloc porous-coated, titanium-tapered stem.¹¹ No hips were lost to follow-up in the series.

In the past decade the most common cause of revision in our practice was polyethylene wear and resulting osteolysis. This is almost exclusively from conventional polyethylene, ram-extruded and sterilized in air, in first-generation acetabular designs. The key role of wear debris generation as a cause of implant failure, especially the acetabulum, is now appreciated. The introduction of ArCom polyethylene (Biomet Orthopedics, Inc., Warsaw, Ind.) in 1993, with the improved hemispherical cup design and RingLoc (Biomet Orthopedics, Inc., Warsaw, Ind.) locking mechanism, dramatically reduced the amount of polyethylene wear-related failures that surgeons see. Wear studies show a 40% decrease in wear rates with the ArCom product compared with conventional polyethylene.

Highly cross-linked polyethylene holds great promise for diminishing the amount of wear in metal-polyethylene hips. Dorr et al recently published five-year results showing linear wear rates, after bedding in, of 0.029 mm/yr for the cross-linked material, Durasul (Sulzer Medica, Winterthur, Switzerland), compared with 0.065 mm/yr for conventional polyethylene.¹² A significant concern for such first-generation cross-linked polyethylene, however, is the loss of mechanical properties created by the manufacturing process, increasing the risk of breakage of these polyethylene components. The loss of mechanical properties is clinically documented in thin cup inserts, especially if vertically oriented in the patient.

Newer polyethylene technologies designed to enhance mechanical properties, such as ArComXL (Biomet Orthopedics, Inc., Warsaw, Ind.), hold the promise of extended survivorship by diminishing the concerns about fracture but maintaining the low wear rates.

A multifaceted problem

Hip dislocation is a major source of implant failure and a multifaceted problem related to patient selection, surgical technique and implant design. The past necessity of a small, non-anatomic-sized femoral head to permit the required thickness of polyethylene, builds in a risk of dislocation because the head has a reduced distance to travel to escape the cup.

Any design change that permits a large femoral head will minimize the dislocation problem. When combined with modern, soft-tissue-preserving surgical techniques, the likelihood of substantially lowering, possibly eliminating, the problem of hip dislocation can be discussed. With conventional polyethylene, a small head size produces less friction and reduces wear particle generation. The cross-linked polyethylene is less sensitive to this friction issue, by virtue of its wear resistance, and permits use of the larger 32-mm and 36-mm heads available at this time.

Metal-on-metal holds the promise of a durable articulation.¹³ Brown et al reported 20-year survivorship for the McKee-Farrar hip of 84%, which is better than the Charnley.¹⁴ Smith et al showed that increasing the head size in metal-on-metal hips decreased the wear due to enhanced fluid film lubrication with large surface areas.¹⁵ Therefore, larger metal-on-metal head diameters will diminish wear and enhance stability. With the stronger metal material in the cup, the previous requirement for a small femoral head is eliminated. Designs such as the Magnum cup (Biomet Orthopedics, Inc., Warsaw, Ind.), where the head size is always 6 mm smaller than the cup’s outer diameter, permit the use of almost anatomic-sized femoral heads, conferring natural stability back to the prosthetic hip.

Lifetime function

Forty years of total hip development produced super alloy implants with biologic fixation, near-anatomic dimensions and bearings that wear little. At this time, I believe the orthopedic community can speak of lifetime survivorship of the current generation of hip replacements. In the past, surgeons were hesitant to speak of this possibility and underestimated the survivorship of implants to avoid being perceived as making unsupported and reckless claims. The first hip replacements were done in the late 1960s, and now the available designs bear little resemblance to the first components. Young patients with debilitating hip disease can look forward to near-normal hip function and expect many years of total hip function.

The orthopedic community, however, must still monitor implant function because early and asymptomatic implant failure can be identified. Nothing more sophisticated than a routine X-ray is needed to assess the status of a hip prosthesis. Surgeons can now speak of lifetime implant function and reassure even the young and active patient that, with sensible orthopedic surveillance, lifetime joint comfort and normal joint function can be achieved and maintained.

References

1. Burton DS. The current status of hip replacement. Prim Care. 1975;2:47-255.
2. Dorr LD, Luckett M, Conaty JP. Total hip arthroplasties in patients younger than 45 years, A nine- to ten- year follow-up study. Clin Orthop. 1990;260:215-219.
3. Dobbs HS. Survivorship of total hip replacements. J Bone Joint Surg. 1980;62-B:168-173.
4. Berry DJ, Harmsen WS, Cabanela ME, Morrey BF. Twenty-five-year survivorship of two thousand consecutive primary Charnley total hip replacements: factors affecting survivorship of acetabular and femoral components. J Bone Joint Surg. 2002;84-A:171-177.
5. Schoning B, Schulitz KP, Pfluger T. Statistical analysis of perioperative and postoperative mortality of patients with prosthetic replacement of the hip. Arch Orthop Traum Surg. 1980;97:21-26.
6. Charnley J, Halley DK. Rate of wear in total hip replacement. Clin Orthop. 1975;112:170-179.
7. Pelicci PM, Salvati EA, Robinson HJ. Mechanical failures in total hip replacement requiring reoperation. J Bone Joint Surg. 1979;61-A:28-36.
8. Della Valle AG, Zoppi A, Peterson MG, Salvati EA. A rough surface finish adversely affects the survivorship of a cemented femoral stem. Clin Orthop. 2005;436:158-163.
9. Emerson RH, Sanders SB, Head WC, Higgins L. Effect of circumferential plasma-spray porous coating on the rate of femoral osteolysis after total hip arthroplasty. J Bone Joint Surg. 1999;81-A:1291-1298.
10. Swanson TV. The tapered press fit total hip arthroplasty: A European alternative. J Arthoplasty. 2005;20:63-67.
11. McLaughlin JR, Lee KR. Total hip arthroplasty in young patients, 8- to 13-year results using an uncemented stem. Clin Orthop. 2000;373:153-163.
12. Dorr LD, Wan Z, Shahrdar C, et al. Clinical performance of a Durasul highly cross-linked polyethylene acetabular liner for total hip arthroplasty at five years. J Bone Joint Surg. 2005;87-A:1816-1821.
13. Dorr LD, Wan Z, Longjohn DB, et al. Total hip arthroplasty with use of the Metasul metal-on-metal articulation. Four to seven-year results. J Bone Joint Surg. 2000;82-A:789-798.
14. Brown SR, Davies WA, De Heer DH, Swanson AB. Long-term survival of McKee-Farrar total hip prostheses. Clin Orthop. 2002;402:157-163.
15. Smith SL, Dowson D, Goldsmith AA. The effect of femoral head diameter upon lubrication and wear of metal-on-metal hip replacements. Proc Inst Mech Eng. 2001;215:161-70.

Roger H. Emerson, Jr, MD, practices at Texas Center for Joint Replacement, Plano, Texas.