By R. Michael Meneghini, MD
Cement fixation is currently the gold standard in total knee replacement, with >95% success rates being reported at more than fifteen years of follow-up1. In addition, cementless fixation in total knee arthroplasty has enjoyed limited use in recent decades due to past failures in the early generation of cementless designs. Screw-track osteolysis, poor polyethylene, and patch-porous-coating and metal-backed patellar component failures have contributed to a controversial track record and created a reluctance to embrace cementless fixation in total knee arthroplasty. However, total knee arthroplasty is being performed in younger patients than in the past, and reports exist of decreased survivorship of cemented knee implants in patients who are younger than fifty-five years of age2. A need therefore exists for a more durable long-term fixation, such as cementless osseointegration, to address the concern for a decrease in survivorship after the first ten to fifteen years, particularly in younger patients undergoing total knee arthroplasty.
Long-term results of certain cementless knee designs have shown a success rate (>95% survivorship at fifteen years and beyond in some series) that is nearly equal to the success rate achieved with cemented designs. A cementless total knee system, consisting of monoblock tibial and femoral components with a plasma-sprayed porous titanium surface and inserted without supplemental screw fixation (Fig. 1), has been associated with a survivorship of 97% after a follow-up period of twenty years3. In addition, the causes of past cementless knee replacement failures are likely correctable through improvements in biomaterials, implant design, patient selection, and surgical technique. The recent development of improved biomaterials has facilitated a renewed interest in cementless total knee replacement. Highly porous metals composed of tantalum and titanium may provide greater osseointegration and more isoelastic behavior with adjacent bone, which may minimize stress-shielding and facilitate long-term bone preservation. Early clinical results of porous tantalum tibial component fixation demonstrate reliable osseointegration at a minimum of three years4. Furthermore, newly developed highly cross-linked polyethylene5, in addition to improved locking mechanisms and avoidance of supplemental screw fixation, are likely to minimize the occurrence of wear-related osteolysis in cementless knee replacement. Finally, as our medical environment continues to evolve, the decreased surgical time afforded with cementless fixation will be advantageous and may contribute to subsequent improvements in operating-room efficiency and minimize perioperative infection.
As has been established with total hip replacement, improved long-term survivorship with cementless fixation should be anticipated with regard to total knee replacement. Highly porous metals, biomaterials with elastic properties more similar to bone, and highly cross-linked polyethylene are likely to provide optimal biologic fixation, bone preservation, and improved long-term outcomes after cementless total knee replacement.
Does the Sex of the Patient Matter?
By Robert E. Booth Jr., MD
For three decades, joint arthroplasty has been performed in a very androgynous fashion. Total knee replacements, in particular, have been implanted in a manner irrespective of the sex of the patient. Little accommodation has been made for known and observable differences in anatomy, physiology, and psychology in joint replacement.
Many factors are currently promoting our differentiation of male and female pathologies. Women are living longer, are more athletic, and are more empowered with regard to decision-making for themselves and their families, and they are clearly the target population for future arthroplasties. Indeed, the postmenopausal, obese woman with osteoporosis will be the most likely recipient of a total knee prosthesis in the first half of the twenty-first century.
Most orthopaedic surgeons are subliminally aware of, if not consciously able to articulate, the sex differences with which they deal every day. Skin turgor, fat distribution, limb alignment, ligamentous laxity, and metabolic issues are all well known if not consciously verbalized. Twenty-five years ago, John Insall created a subset of femoral components to accommodate the variational anatomy of the femur in women. We know full well that the anterior-posterior and medial-lateral diameter of the femur of women is quite different from that of men. The 0.8 aspect ratio to which most implant designers subscribe is indeed only an average that actually favors the male population. Women's knees are quite different, as are knees in individuals with inflammatory arthropathy, epiphyseal dysplasia, and autoimmune diseases. Interestingly, the ratio between the anterior-posterior and medial-lateral dimensions of the knee in Asian populations is actually the reverse of that in the occidental world.
The kinematics of a "natural knee" are still imperfectly understood even after all of these years. Most surgeons still make subconscious accommodations for women's knees in the face of patellofemoral arthritis, obesity, medial fat-pad adiposity, and lateral femoral condylar hypoplasia. Problems such as recurvatum deformity remain unresolved, as none of us knows whether to accommodate or anticipate that phenomenon when performing a total knee replacement.
From an instrumentation standpoint, there are clear decision points that need to be evaluated. The conventional wisdom that posterior stabilized knees when "in between sizes" should be upsized and that cruciate-retaining knees in similar circumstances should be downsized, tends to aggravate the overhang problem for women and accentuate the sizing problem for men. On the other hand, those who favor the anterior-posterior diameter play into the concept of kinematics, while those who prioritize the medial-lateral diameter enhance the contact area and force distribution issues that are germane to the needs of men.
Further sophistication is clearly needed, and this is probably the most favorable outcome of the computerized navigation systems extant today. Our ability to define the differences in the knees of men and women and to accommodate them from both an implant and an instrumentation viewpoint will define the next generation of knee arthroplasty.
Merchant AC, Arendt EA, Dye SF, Fredericson M, Grelsamer RP, Leadbetter WB, Post WR, Teitge RA. The female knee: anatomic variations and the female-specific total knee design. Clin Orthop Relat Res.2008;466:3059-65.4663059
2008
[PubMed][CrossRef]
Singh JA, Gabriel S, Lewallen D. The impact of gender, age, and preoperative pain severity on pain after TKA. Clin Orthop Relat Res.2008;466:2717-23.4662717
2008
[CrossRef]
Berend ME, Small SR, Ritter MA, Buckley CA, Merk JC, Dierking WK. Effects of femoral component size on proximal tibial strain with anatomic graduated components total knee arthroplasty. J Arthroplasty.2008 Dec 17. [Epub ahead of print]
2008
Chin KR, Dalury DF, Zurakowski D, Scott RD. Intraoperative measurements of male and female distal femurs during primary total knee arthroplasty. J Knee Surg.2002;15:213-7.15213
2002
What Is the Evidence for Sex-Based Total Knee Arthroplasty?
By Michael A. Mont, MD, Mike S. McGrath, MD, and Michael G. Zywiel, MD
Differences in knee dimensions between women and men have been documented in multiple studies, and there is concern about the effects of this difference on the outcomes of total knee arthroplasty1-3.
Specifically, women typically have smaller mean femoral medial-lateral dimensions relative to the anterior-posterior axis than men do1,3,4. As a result, knee arthroplasty prosthetic designs may be too wide for women. As a result, knee arthroplasty prosthetic designs may cause medial-lateral overhang of the prosthesis, which might affect collateral ligament balancing and patellofemoral stresses. If the component is matched to the knee according to the medial-lateral axis, then the prosthesis may be too small in the anterior-posterior dimension, which may cause increased wear or impingement of the implant or notching of the anterior cortex1.
Other differences between sexes have been documented. When compared with men, women may have a significantly shorter femoral condyle height (although this may be more directly associated with bone size than with sex)3, larger quadriceps angles (Q angles)5,6 (although this may be more directly correlated with height than with sex)6, and different orientations of the trochlear groove3. These variations may affect flexion and patellofemoral tracking, although the clinical importance of this is unknown.
Multiple studies have compared the long-term results of total knee arthroplasties in men and women, and the results have shown similar ranges of motion, knee as well as pain scores, and survival rates at ten to fifteen years of follow-up. Several reports noted higher function scores for men7,8, but other reports of large, long-term studies found that men had higher revision rates than women did9,10.
Total knee replacement systems have been developed that incorporate sex-specific sizing, including multiple prosthetic widths to match the medial-lateral dimensions of the knee for both men and women. Excellent short-term clinical outcomes have been reported in association with these systems although no differences in clinical outcomes between men and women have been found11,12. However, one report described significant radiographic improvements in women who received sex-specific implants13.
In summary, it is not clear whether the anatomic differences between the knees of men and women might affect clinical outcome after total knee arthroplasty. Currently, no significant differences in clinical outcomes have been noted with regard to sex-specific implants, but further study, including direct comparisons between sex-specific implants and sex-neutral implants, might be useful.
Hitt K, Shurman JR 2nd, Greene K, McCarthy J, Moskal J, Hoeman T, Mont MA. Anthropometric measurements of the human knee: correlation to the sizing of current knee arthroplasty systems. J Bone Joint Surg Am.2003;85 Suppl 4:115-22.85115
2003
[CrossRef]
Merchant AC, Arendt EA, Dye SF, Fredericson M, Grelsamer RP, Leadbetter WB, Post WR, Teitge RA. The female knee: anatomic variations and the female-specific total knee design. Clin Orthop Relat Res.2008;466:3059-65.4663059
2008
[PubMed][CrossRef]
Poilvache PL, Insall JN, Scuderi GR, Font-Rodriguez DE. Rotational landmarks and sizing of the distal femur in total knee arthroplasty. Clin Orthop Relat Res.1996;331:35-46.33135
1996
[CrossRef]
Chin KR, Dalury DF, Zurakowski D, Scott RD. Intraoperative measurements of male and female distal femurs during primary total knee arthroplasty. J Knee Surg.2002;15:213-7.15213
2002
Aglietti P, Insall JN, Cerulli G. Patellar pain and incongruence. I: measurements of incongruence. Clin Orthop Relat Res.1983;176:217-24.176217
1983
Grelsamer RP, Dubey A, Weinstein CH. Men and women have similar Q angles: a clinical and trigonometric evaluation. J Bone Joint Surg Br.2005;87:1498-501.871498
2005
[CrossRef]
Ritter MA, Wing JT, Berend ME, Davis KE, Meding JB. The clinical effect of gender on outcome of total knee arthroplasty. J Arthroplasty.2008;23:331-6.23331
2008
[CrossRef]
MacDonald SJ, Charron KD, Bourne RB, Naudie DD, McCalden RW, Rorabeck CH. Gender-specific total knee replacement: prospectively collected clinical outcomes. Clin Orthop Relat Res.2008;466:2612-6.4662612
2008
[CrossRef]
Gioe TJ, Novak C, Sinner P, Ma W, Mehle S. Knee arthroplasty in the young patient: survival in a community registry. Clin Orthop Relat Res.2007;464:83-7.46483
2007
Rand JA, Trousdale RT, Ilstrup DM, Harmsen WS. Factors affecting the durability of primary total knee prostheses. J Bone Joint Surg Am.2003;85:259-65.85259
2003
Harwin SF, Greene KA, Hitt K. Early experience with a new total knee implant: maximizing range of motion and function with gender-specific sizing. Surg Technol Int.2007;16:199-205.16199
2007
Emerson RH Jr, Martinez J. Men versus women: does size matter in total knee arthroplasty? Clin Orthop Relat Res.2008;466:2706-10.4662706
2008
[CrossRef]
Clarke HD, Hentz JG. Restoration of femoral anatomy in TKA with unisex and gender-specific components. Clin Orthop Relat Res.2008;466:2711-6.4662711
2008
[CrossRef]