Healio
Healio
Issue: June 2006
ByThomas H. Mallory, MD, FACS
ByWilliam C. Head, MD
June 01, 2006
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History and clinical outcomes support proximally coated titanium hips

Issue: June 2006
ByThomas H. Mallory, MD, FACS
ByWilliam C. Head, MD

William C. Head, MD [photo]
William C. Head

This symposium investigates the long-term clinical and radiological results of a cementless, titanium, tapered, primary hip replacement prosthesis. The design has a proximal-to-distal tapered geometry, and the proximal one-third has circumferential plasma-sprayed porous coating. Titanium tapered stems have been in clinical use for over 20 years. The early application was felt to be appropriate for only Dorr A and B femurs.1 Experience has demonstrated that they are suitable for type C, as well.

Survivorship

Between 1987 and 1990, 166 procedures were performed using a Mallory-Head porous femoral component (Biomet Orthopedics, Inc., Warsaw, Ind.) (Figure). Current data is available on 100 implants with a minimum 15-year follow-up. Thirty-three patients are deceased and another 30 lost to follow-up. Another study was conducted assessing the long-term survivorship of patients age 65 years or older with a minimum follow-up of 10 years and an average follow-up of 13.2 years using the same Mallory-Head component.2 The minimum age was 65 years, and the average age was 70 years. There were 91 hips in the study. None were lost to follow-up. Between February 1987 and April 2005, 1760 primary cases were performed. The implant design remained unchanged from 1987 to the present.

Both studies have a 100% survivorship. There have been no revisions in either series. The 65-and-older age group study contains 40 Dorr type C femurs. To date, in the total series of 1760 cases, there were seven revisions: four for infection and three for aseptic loosening. The projected survivorship at 19 years is 99.5%.

Figure
Figure. The Mallory-Head porous femoral component.

Source: Head WC

Taper design and material

The taper design gains its initial fixation via two modes. A rough porous surface settles into the proximal viso-elastic femur. The tapered stem achieves a three-point fixation as a result of a straight stem being placed into a femur with an anterior bow. Rapid and proliferate bone ongrowth and ingrowth occurs. Two explants at three and four months demonstrated abundant bone ingrowth and ongrowth. Proximal circumferential porous coating provides a seal to the effective joint space.3

Titanium-aluminum-vanadium alloy prostheses have been in use since the mid-1980s. Titanium was chosen for flexibility, strength and biocompatibility. Titanium implants have a lower modulus of elasticity than cobalt chrome. Titanium has superior osteoconductive properties. Medical-grade titanium, when exposed to air and bodily fluids, has a layer of titanium oxide along its surface. This titanium oxide layer establishes a dielectric constant (flux), which acts similar to water. This electrical flux attracts morphogenetic proteins that have reportedly stimulated bone growth, signaling and bonding.4,5 The rougher the titanium surface, the greater the surface area upon which the titanium oxide layer is established.

Long-term femoral remodeling

Clinical radiographs from 35 randomly selected Mallory-Head femoral components were reviewed.6 Standardized measurements of the proximal, middle and diaphyseal bone thickness were taken from preoperative and long-term follow-up radiographs. Radiographic follow-up averaged 11.5 years. Proximal medial cortical thickness increased an average of 14%, with 80% showing an increase or no change. The combined thickness of the proximal femur increased an average of 10%, with 71% showing an increase or no change in combined thickness. Near the tip of the stem the average cortical thickness increased 13%; cortical thickness was stable or increased for 89%. Along the distal diaphyseal cortex, an average increase of 3% was noted; thickness was stable or increased for 60% of femurs. These results are in contrast to the recent work of Berry et al that demonstrated time-dependent proximal cortical thickness loss in cemented stems, diaphyseal fixation stems and metaphyseal fixation stems.7 This titanium-tapered, plasma-sprayed, porous femoral component does not cause radiographic signs of stress shielding. Instead, the majority of cases demonstrate increased cortical thickness at all three locations. This lack of stress shielding is a result of the tapered stem geometry and the titanium substrate.

There are numerous published reports regarding the clinical use of titanium tapers.8-12 To date, there are no negative or critical reports of this design in the literature. Titanium-tapered implants universally demonstrate high survivorships, little or no thigh pain, an absence of distal lysis and no late failure modes.13-15 Stress shielding and bone atrophy occur in a small percentage of cases. This design is compatible with all bone types. There is ample clinical and published evidence to support this prosthesis design as the new gold standard in primary hip replacement.

References

  1. Dorr LD, Faugere MD, Mackel AM, et al. Structural and cellular assessment of bone quality of proximal femur. Bone. 1993;14:231-242.
  2. Reitman RD, Emerson R, Higgins L, et al. Thirteen-year results of total hip arthroplasty using a tapered titanium femoral component inserted without cement in patients with type-C bone. J Arthroplasty. 2003;18:116.
  3. 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.
  4. Wieland M, Sittig C, Brunette DM, et al. Measurement and evaluation of the chemical composition and topography of titanium implant surface. In: Davies JE, ed. Bone Engineering. Toronto: em squared, inc.;2000:163-182.
  5. Sittig C, Wieland M, Vollotton PH, et al. Surface characterization of implant materials c.p. Ti, Ti-6Al-7Nb and Ti-6Al-4V after different pretreatment. J Mater Sci Mater Med. 1999;10:35-46.
  6. Berend KR, Mallory TH, Head WC, Lombardi AV. The titanium taper: the new gold standard in primary hip replacement. Minimum 15-year follow-up of the Mallory-Head porous femoral component. Poster presented at: The 118th Annual Meeting of the American Orthopaedic Association; June 22-25, 2005; Huntington Beach, Calif.
  7. Berry DJ, Collins DC, Harmsen W, et al. How does prosthesis fixation type alter long-term femoral cortical bone remodeling around THA? Poster presented at: The 72nd Annual Meeting of the American Academy of Orthopaedic Surgeons; February 23-27, 2005; Washington.
  8. Head WC, Mallory TH, Emerson RH. The proximal porous coating alternative for primary total hip arthroplasty. Orthopedics. 1999;22:813-815.
  9. Bourne RB, Rorabeck CH, Patterson JJ, Guerin J. Tapered titanium cementless total hip replacements: A 10- to 13-year followup study. Clin Orthop Relat Res. 2001;393:112-120.
  10. Mallory TH, Lombardi AV, Leith JR, et al. Minimal 10-year results of a tapered cementless femoral component in total hip arthroplasty. J Arthroplasty. 2001;16:49-54.
  11. Mallory TH, Lombardi AV, Leith JR, et al. Why a taper? J Bone Joint Surg Am. 2002;84-A: 81-89.
  12. McLaughlin JR, Lee KR. Total hip arthroplasty in young patients. 8- to 13-year results using an uncemented stem. Clin Orthop Relat Res. 2000;373:153-63.
  13. Rothman RH. Hip arthroplasty: assessment and choices. Fit and fill: fact of fiction? Orthopedics. 1994;17:803.
  14. Mulliken BD, Bourne RB, Rorabeck CH, Nayak N. A tapered titanium femoral stem inserted without cement in a total hip arthroplasty. Radiographic evaluation and stability. J Bone Joint Surg Am. 1996;78:1214-1225.
  15. Mallory TH, Head WC, Lombardi AV Jr, et al. Clinical and radiographic outcome of a cementless, titanium, plasma spray-coated total hip arthroplasty femoral component. Justification for continuance of use. J Arthroplasty. 1996;11:653-660.

William C. Head, MD, is retired from practice at the Texas Center for Joint Replacement in Plano, Texas. Thomas H. Mallory, MD, FACS, is founder of Joint Implant Surgeons, Inc. in New Albany, Ohio.

History

Thomas P. Schmalzried, MD: In the 1980s, cemented femoral components were an established technology. Debate about cementless fixation and the optimal alloy existed. What are your recollections of your thoughts at that time?

William C. Head, MD: At that time, three issues were important: titanium as a material, plasma spray and the tapered shape. The original concept of the tapered design was to fill the proximal femur and then offload in a more physiologic fashion. My colleagues and I found that by putting a straight, tapered stem in the femur with the anterior bow, the implant would be stable but not completely filled proximally. This outcome led us to recognize the three-point fixation issue.

Plasma spray proved intriguing because the material can be applied to the implant without heating the implant, resulting in less danger of weakening the metal. In 1984, I had an opportunity to look at two retrievals removed because of infection. I observed a florid bone response with bone ingrowth, reinforcing the concept that plasma spray does not weaken the substrate metal.

Titanium was chosen because of its biocompatibility. We knew titanium was less stiff than cobalt chrome, but at the time, clinicians did not understand its osteoconductive properties.

Schmalzried: When did you recognize that proximally porous-coated tapered stem technology was working for your patients?

Head: I became comfortable with cementless technology by 1986. The early prosthesis design had high anterior and posterior fins, causing some femurs to split. If a crack is above the lesser trochanter, then it can be easily handled with a wire or cable. A crack below the lesser trochanter or free fragment, however, is not easily resolved.

Schmalzried: Did you develop any radiographic criteria for a stable implant to classify a patient’s progress during follow-up?

Head: My colleagues and I applied the Engh radiograph evaluation, which classified an implant as having bone ingrowth or being loose or stable fibrous. Right away we observed that no implants were stable fibrous because the implants either ingrew or did not. Bone densing was quickly observed, particularly medially and in Zone 2 where streams of bone densing occurred.

We also identified undersizing as the only mechanism for aseptic loosening. A stable implant that went in place and did not become infected would consistently bone ingrow. I never observed any long-term stable fibrous implants.

Schmalzried: In your practice, do you prefer cementless or cemented femoral fixation?

Roger H. Emerson, Jr, MD: From the late 1990s, I became increasingly confident in cementless implants. Currently, I use a cementless femoral component in almost 99.9% of patients.

Limitations

Schmalzried: Are there limitations to the technology of proximally porous-coated hip systems?

Emerson: Trunnion failure during a patient’s third or fourth decade with the implant is a concern. Surgeons know that removing a well-fixed stem is difficult, and trunnion failure adds a significant challenge to removing a stem.

Schmalzried: Is trunnion failure due to corrosion or fatigue failure?

Emerson: Both could cause trunnion failure. A bending-lever mode of failure with well-fixed stems, especially with higher offset stems, causes a problem with long-term use. The constant bending movement over millions of cycles is problematic. Trunnion failure is unlikely to occur, however. I am aware of only one traumatic trunnion failure with the Mallory-Head stem.

One of my patients with a polyethylene revision had a skirted head. I revised the surgery using the same length head without a skirt, and damage to the trunnion underneath the skirt resulted. I was concerned about the trunnion damage and that a non-skirted head would be a problem. The manufacturer took radiographs, determined the extent of the damage, notched the trunnion and cycled it millions of times. The trunnion did not break, and the patient is doing well after 10 years of follow-up.

Schmalzried: What is the next limitation of total hip arthroplasty?

John M. Cuckler, MD: A damaged tapered stem or prosthetic femoral neck may be a source of mechanical failure. Titanium is a notch-sensitive material. If improper component placement allows impingement of the neck against the rim of the acetabular prosthesis, then that notch will concentrate stress, altering the stress-strained performance of the materials. Mechanical failure due to this type of damage is most likely rare, however.

Another source of late failure may be biologic. Changes in bone metabolism, possibly due to senescence, and dietary changes, possibly related to medications used for other maladies, will lead to implant loosening after 20 to 30 years or more of otherwise successful service. Surgeons will also continue to treat patients with late sepsis and trauma and fracture around the implants.

With proximally porous-coated hip systems, surgeons will not likely observe massive osteolysis, which comprises a major part of my revision practice. Proximally porous-coated hip systems will alter the form of failure and substantially decrease the number of failures with modern articular couples.

Schmalzried: How does plasma spray coating affect fixation or osteolysis?

Jeffrey R. McLaughlin, MD: Plasma spray porous coating is associated with excellent fixation. In my experience with proximally porous-coated titanium hips, an average follow-up of 15 years shows femoral loosening present in 1% of patients, and osteolysis occurring in only 7%. The rate of survivorship is 95%.

Early weight-bearing

Schmalzried: In the past, surgeons were insecure about initial stability of cementless implants and advised patients to stay on crutches for six weeks or more. Why did you decide to move to an early weight-bearing protocol?

Barry J. Waldman, MD: Early in my practice, I felt that the three-point fixation obtained with cementless components was equivalent to that obtained with cemented components. I recommended early weight-bearing from the start of my practice, and because my colleagues and I did not observe any adverse effects, we continue to do so today.

In my regular review of radiographs, I have noticed a small number of patients with subsidence of 1 mm to 2 mm. No clinical detriment was observed in any of the patients who had that subsidence, however, and I felt fairly confident in my decision to advise early weight-bearing.

McLaughlin: My protocol has been full weight-bearing after surgery for the past 15 years. Regardless of any recommended restrictions, patients will bear full weight as soon as they are comfortable. It is not uncommon to see patients off crutches 2 to 3 weeks after surgery.

Emerson: Most surgeons do not recommend protective weight-bearing but should advise patients to weight-bear with support. I recommend patients start with two-arm support and then monitor their symptoms. Occasionally, a patient will be non-compliant and develop discomfort, usually in the thigh or groin. A patient who develops discomfort must return to using support to rapidly diminish any pain.

Adolph V. Lombardi, Jr, MD, FACS: The real proof of immediate weight-bearing is observed in patients with bilateral hip replacements. Surgeons treating patients with bilateral Taperloc (Biomet Orthopedics, Inc., Warsaw, Ind.) hips allow patients with double support, such as a walker or crutches, to ambulate. Success with bilateral hip replacements in my patients and patients at the Rothman Institute in Philadelphia demonstrates that immediate weight-bearing is satisfactory with proximally porous-coated hip stems.