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Zimmer - Gender Solutions


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Zimmer - Gender Solutions

  1. 1. Issue 20 What’s NewZan educational service from Zimmer The outcomes achieved with standard femoral implants used in total knee arthroplasty (TKA) are satisfactory for most patients, however there are significant reasons for developing a gender specific knee implant for women. Standard implants can be a contributing cause of post-operative morbidity in women, said Dr Robert E. Booth Jr, Clinical Professor of Orthopaedic Surgery at the University of Pennsylvania School of Medicine, Philadelphia. “Even though most women are happy with their results after joint replacement, some still have residual pain in the front of the knee…or say their artificial knee just doesn’t feel or move the way their own knee did when it was healthy,” said Dr Robert Booth. The problem is that while standard implants are currently available in variable sizes, they are based on the combined average of male and female anatomy that doesn’t take into account shape-related anatomical differences between the genders, he said. Standard implants are currently available in variable sizes, but are based on the combined average of women and men’s anatomy that don’t take into account shape- related gender differences These differences have been reported in a number of studies1,2,3,4,5 but have been difficult to quantify with a high degree of precision and accuracy. As a result women undergoing TKA have continued to be treated simply as smaller versions of men with regards to implant selection, said Dr Booth. The growing number of women who require TKA has also led to an increased demand for improved outcomes. Women made up 58.1% of primary TKA in 2004-5, the fastest growing major joint replacement in Australia (18.1% increase from 2002-3 to 2004-5), according to Australian Joint Replacement Registry data.6 This trend is set to increase with the ageing population. Research also shows that women are three times less likely than men to undergo arthroplasty although they suffer from a higher prevalence of arthritis, more severe symptoms and greater disability.7 With an implant “shaped to fit women’s anatomy” there is an expectation that “far more women will want to consider knee replacement,” said Dr. Booth. In addition, a better fitting implant may require fewer intraoperative adjustments to accommodate anatomical differences, contributing to reduced operating time. In this issue The need for a knee implant designed specifically for women ..... 1 Best of both worlds - The Zimmer Gender Solutions High-Flex Knee ....2 Three distinct differences in shape .........................................2 (1) Modified Aspect Ratio – to better fit the shape of a woman’s trapezoidal distal femur............. 2 - 3 (2) Modified Anterior Flange – reduced thickness to equal the amount of bone removed and avoid overstuffing ....................................4 (3) Lateralised Sulcus – to provide more natural patella tracking for a woman’s greater Q-angle ................4 The need for a knee implant designed specifically for women Dr Robert E. Booth Jr. MD Clinical Professor of Orthopaedic Surgery at the University of Pennsylvania, School of Medicine, Philadelphia
  2. 2. What’s NewZ Issue 0 “Knee implants have been functioning very well for men and women, but we want to meet women’s unique needs by making knee replacements that feel, fit and function even better,” said Dr Booth. “The Gender Solutions Knee is the best of both worlds. It’s based on the NexGen® Knee, a highly successful implant with great mechanics and ten years of clinical success. Only the shape is different, to make it feel more natural,” he said. The Gender Solutions Knee is based on the NexGen® Knee, a highly successful implant with great mechanics, only the shape is different, to make it feel more natural Three distinct differences in shape The Gender Solutions High-Flex Knee has the potential to achieve substantial intraoperative and post-operative benefits for TKA patients by addressing three distinct shape-related differences of a woman’s knee. (1) Decreased medial-lateral (M/L) dimension reduces implant overhang Previous research has reported differences in knee anatomy between women and men.1,2,3,4,5 Poilvache et al conducted measurements including trans- epicondylar width and AP dimensions before and after resection in their 1996 study of 54 female and 46 male knees undergoing TKA.1 They found “a significant, although small, difference…between males and females in the ratio between the transepicondylar width and the mean height of the condyles…suggesting that females had narrower femurs than males. The difference was even greater when subtracting the anterior extent of the trochlea (anterior cuts) from the height of the condyles.”1 In 2002 Chin et al conducted intra- operative measurements of 100 female and 100 male femurs after making the distal femoral cut. Their data found that “for any given A/P femoral dimension, women tend to have a narrower M/L dimension than men, independent of A/P height.”2 In 2003 Hitt et al also measured the amount of M/L implant overhang in both genders in addition to confirming that the female femurs were narrower. They observed that the overhang was greater in females regardless of the brand of implant.3 Despite the insights achieved by these and other studies, the methods used for the intra-operative measurements, including calipers and rulers, were limited by a lack of precision and variability. Zimmer® Gender Solutions™ NexGen® High-Flex Knee Best of both worlds: The Zimmer® Gender Solutions™ NexGen® High-Flex Knee
  3. 3. What’s NewZ Issue 0 Research conducted for Zimmer by a team led by Mohamed Mahfouz, Ph.D., director of Computational Bioengineering at the University of Tennessee, Knoxville, set out to accurately quantify these differences. A continually growing knee bone atlas based on more than 800 knees and patellae was created for Zimmer by Dr Mahfouz. Bone atlases have been used in the past to create knee replacements; however the data were two-dimensional and interpreted differently. In contrast, Dr Mahfouz and co- researchers utilised three- dimensional computed tomography (CT). Data was collected for the femoral condyle dimensions to create highly detailed virtual blueprints of the knee as it looks after resection when the bone is ready for the implant. Based on findings from this research that was reported earlier this year, a graph that plots the mid-box medial-lateral (M/L) dimension versus the overall anterior-posterior (A/P) dimension confirms the findings of the earlier research that the average female knee had a decreased M/L dimension compared to men’s or ‘the male knee’ with the same overall anterior-posterior (A/P) dimension.8 The female knee has a decreased M/L dimension when compared to the male knee anatomy. A consequence of the narrower M/L dimension is that female knees were found to be more trapezoid-shaped, whereas male knees were characterized by a rectangle-shape. Overhang is reduced at the M/L interface leading to potential intraoperative and post-operative benefits. The decreased M/L dimension was incorporated into the Zimmer® Gender Solutions™ High-Flex Knee design, with the aim of reducing implant overhang, which has the potential to achieve intraoperative and post-operative benefits. Overhang can press on or damage surrounding soft tissues and may possibly cause pain and reduced function. Intraoperative adjustments to compensate for the overhang are often required.2 Overhang can occur because a patient’s implant size is usually selected based on the A/P dimension, which is the key to achieving normal knee kinematics and maximizing the potential for full flexion. However standard non-gender specific implant designs that provide a good A/P fit are often too wide in the M/L dimension leading to overhang at the distal, anterior and posterior M/L interfaces.1 Femoral condyle mid-box medial-lateral (M/L) dimension versus overall anterior-posterior (A/P) dimension Difference in the distal femur shape: Females (pink) compared to males (blue) A/P M/L Mid-Box A/P A standard implant may overhang at the distal, anterior and posterior M/L interfaces compared to the reduced or eliminated overhang of the Gender Solutions High-Flex Knee The new computational method devised by Zimmer for predetermining the contour of a resected bone and fit of an implant that was used in the development of Gender Solutions High-Flex Knee
  4. 4. What’s NewZ Issue 0 () Reduced anterior flange thickness decreases implant protrusion Research has shown that the female knee has a less pronounced anterior condyle compared to males due to decreased bone thickness.2, 9 In the 1996 Poilvache et al study cited earlier, measurements were also taken of the resected thickness of the anterior condyles. The average lateral and medial condyle thickness in males was statistically significantly greater than for females.1 Zimmer data has confirmed the gender difference in thickness – 0.8 mm less in females on the lateral condyle and 1.3 mm less on the medial condyle.9 In addition the M/L dimension of the resected anterior flange bone is narrower in women.9 The Gender Solutions High-Flex Knee addresses the distinctive anterior condyle differences by reducing the anterior flange thickness as well as narrowing the implant anteriorly decreasing the M/L dimension of the implant. To compensate for reduced anterior flange thickness, the anterior condyles have been lowered and the patella sulcus has been recessed, while retaining the NexGen® patella articulation. Reduced anterior flange thickness of the implant decrease anterior protrusion of the joint The advantage of the reduced anterior flange thickness of the Zimmer® Gender Solutions™ High-Flex Knee implant is decreased anterior protrusion of the joint, which can reduce pain from overstuffing the joint. In addition to reducing bulkiness, patients may experience improved function and there may be less need for intraoperative adjustments. This is due, in part, to a reduction in the stress on the patella ligament as the knee moves into overstuffing on angles. To compensate for this, a surgeon’s only option (in the past) was to translate the entire femoral component inferiorly. This intra-operative compromise could result in either matching of the femoral anterior cortex or overstuffing the flexion gap. A knee designed with a thinner anterior flange demonstrates the need for this compromise. () Greater Q-angle reduces implant patella maltracking While patella maltracking remains a concern for all patients following TKA, it is a particular concern for females due to their patellofemoral joint biomechanics, which predisposes them to pain associated with patella malalignment and quadriceps weakness.10 One of the main features of female patellofemoral joint biomechanics is a statistically significant higher quadriceps femoral angle (Q-angle) compared to men.11,12,13, 14 Aglietti et al found a 3º greater Q-angle in the women compared to males when measured with a goniometer in supine in their 1983 study of 240 male and female university-aged subjects.11 Gender Solutions High-Flex Femoral Implant Traditional implant The Gender Solutions High-Flex Knee addresses the distinctive anterior flange differences Traditional implant Gender Solutions High-Flex Femoral Implant
  5. 5. What’s NewZ Issue 0 In 1990 Hsu et al measured the Q-angle of 60 knees of subjects aged 25-40 years and 60 aged 41-60 years using x-rays in standing, full weight- bearing position. They found a 3.7º difference in the women in the young group and 2.7º in the older group.12 Two years later Woodland et al measured the Q-angle of 269 male and 257 female university-aged subjects in supine and standing using a goniometer and found it was 3.1º greater for the females in supine and 3.4º in standing.13 Emulating the greater Q-angle reduces patella maltracking The Zimmer® Gender Solutions™ High-Flex Knee emulates the Q-angle difference by increasing the patella sulcus angle 3º laterally. The potential benefit is reduced patella maltracking and decreased associated post-operative morbidity. The early Australian experience The first orthopaedic surgeon in Australia to use a Zimmer® Gender Solutions™ High-Flex Knee implant, Dr Brett Courtenay, from the St Vincent’s Clinic in Sydney, says the improved fit was immediately clear to see in the operating theatre. “In many patients there is considerable overhang of the femoral component when the correct sizes [of standard implants] are used. This implant clearly reduces this overhang without any changes to the bone cuts. The decision is made at the time of using the trial implant,” he says. “Having used the new implant I would feel fairly confident that it will allow me to use a more correct sized prosthesis with my patients.” Dr Courtenay says “in the past when I was worried about overhang I tended to slightly undersize which is generally not a good thing to do because it can lead to instability in flexion and less efficient movement of the prosthesis.” In the past when I was worried about overhang I tended to slightly undersize. “The trouble is that if you put a smaller prosthesis in it might feel stable when the knee is extended but it is not going to be as stable when the knee is flexed.” One of the key benefits offered by the Gender Solutions™ High-Flex Knee implant is increased variability. “Previously we had one prosthesis that was meant to fit all. Now we’re going to have slimmer and broader prostheses. I feel very comfortable that this step is one to address a problem that we have had with sizes of prostheses,” says Dr Courtenay. “It allows me to use the correct size according to the measurements without the risk of an overhang,” he says. The Gender Solutions High-Flex Knee allows me to use the correct size according to the measurements without the risk of an overhang. Greater Q-angle of the Gender Solutions High-Flex Knee
  6. 6. What’s NewZ Issue 0 “Time will tell how effective it will be with regards to functional outcome. But we’re coming from a prosthesis that really has demonstrated that it is very good at returning bend to the knee. The [Zimmer High-Flex Knee] prosthesis, the basic one in its design, is safe to 155 degrees. The Gender Solutions is another step in that process and very definitely warrants encouragement.” Additional sizes and half sizes don’t address the gender issue Even though many standard implants are provided in additional sizes or half sizes, such as the Stryker Triathlon implant, they do not address the main gender issue, which is the shape difference between women and men. Patient selection The Zimmer® Gender Solutions™ NexGen® High-Flex Knee may be suitable for: Female patients requiring a primary total knee arthroplasty (TKA) Some female patients requiring revision total knee arthroplasty (TKA), to the extent that primary TKA implants are currently used by the surgeon for revision TKA A small proportion of male patients with a narrower M/L dimension for a given A/P when compared to the rest of the male population. • • Zimmer systems and techniques The Zimmer® Gender Solutions™ NexGen® High-Flex Knee not only retains all of the elements of Zimmer’s clinically successful NexGen® standard knee system, but also provides the added bonus of safely accommodating up to 155 º of flexion for patients with the desire and ability to achieve overstuffing on. In addition it is compatible with other Zimmer surgical techniques, including Minimally Invasive Solutions™ procedures, which typically offer smaller scars, shorter hospitalization and quicker rehabilitation and recovery. Femoral condyle mid-box medial-lateral (M/L) dimension versus the overall anterior-posterior (A/P) dimension of standard implants and Gender Solutions High-Flex Knee. As seen on a graph that plots the femoral condyle mid-box medial- lateral (M/L) dimension versus overall anterior-posterior (A/P) dimension, standard implants still tend to follow the same curve line, which is based on the average of both women and men, whereas the Gender Solutions High-Flex Knee stands out as having a decreased M/L dimension. In addition, standard implants do not have the decreased anterior flange thickness and greater Q-angle that the Gender Solutions High-Flex Knee implant exhibits.
  7. 7. What’s NewZ Issue 0 NOTES AND QUOTES “We have known for years that there are differences between men and women. And we’ve accommodated…that with our surgery technique. [But] as our patients are becoming more active, wanting a better result, expecting more for their total knee replacements I think we have to accommodate that by having gender specific knees.” Dr Richard A. Berger, Rush University Medical Center, Chicago “If we think back twenty-five years ago, we had knees that weren’t even left and right. Twenty-five years ago, we figured you had to have left and rights. Twenty-five years later, we find out you have to have male and female…we’re realizing that the size difference and the ratio of medial to lateral and anterior to posterior [femoral condyle dimensions] are different for females.” Dr Aaron A. Hoffman, University of Utah Medical Center, Salt Lake City “I think if a surgeon questions whether or not if this is a real advance…he can answer that question in the operating room as he puts a trial prosthesis on and sees that it overhangs significantly and then puts the gender specific prosthesis on and sees that it conforms accurately to the dimensions of that particular knee. He’ll be instantly convinced that there is a place for this particular prosthesis.” Dr Kim C. Bertin, Utah Hip and Knee Center, Salt Lake City The Zimmer® Gender Solutions™ High-Flex Knee Advantage A gender specific femoral implant design helps to meet the expectations of female patients by providing a better anatomical fit leading to potential benefits: Reduced pain Decreased feelings of bulkiness and overstuffing Improved function and biomechanics, particularly patella tracking Reduced need for intraoperative adjustments • • • • REFERENCES 1. 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 Oct;331:35-46. 2. 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 Fall;15(4):213-7. 3. Hitt K, Shurman JR 2nd, Greene K, et al. Anthropometric measurements of the human knee: correlation to the sizing of current knee arthroplasty systems. J Bone Joint Surg Am, 2003;85-A Suppl 4:115-22. 4. Vaidya SV, Ranawat CS, Aroojis A, Laud NS. Anthropometric measurements to design total knee prostheses for the Indian population. J Arthroplasty 2000 Jan;15(1):79-85. 5. Urabe K, Miura H, Kuwano T, et al. Comparison between the shape of resected femoral sections and femoral prostheses used in total knee arthroplasty in Japanese patients: simulation using three-dimensional computed tomography. J Knee Surg 2003 Jan;16(1):27-33. 6. Graves S, Davidson D, Ingerson L, et al. Australian Orthopaedic Association National Joint Replacement Registry annual report. Adelaide: Australian Orthopaedic Association, 2006. 7. Hawker GA, Wright JG, Coyte PC, et al. Differences between men and women in the rate of use of hip and knee arthroplasty. N Engl J Med 2000 Apr 6;342(14):1016-22. 8. Mahfouz M, Booth R Jr, Argenson J, et al. Analysis of variation of adult femora using sex specific statistical atlases. Presented at: Computer Methods in Biomechanics and Biomedical Engineering Conference; 2006 9. Data on file at Zimmer. 10. Csintalan RP, Schulz MM, Woo J, et al. Gender differences in patellofemoral joint biomechanics. Clin Orthop Relat Res 2002 Sep;(402):260-9. 11. Aglietti P, Insall JN, Cerulli G. Patella pain and incongruence. I: Measurements of incongruence. Clin Orthop Relat Res 1983 Jun;(176):217-24. 12. Hsu RW, Himeno S, Coventry MB, Chao EY. Normal axial alignment of the lower extremity and load-bearing distribution at the knee. Clin Orthop Relat Res 1990 Jun;(255):215-27. 13. Woodland LH, Francis RS. Parameters and comparisons of the quadriceps angle of college-aged men and women in the supine and standing positions. Am J Sports Med 1992 Mar-Apr;20(2):208-11 14. Livingston LA. The quadriceps angle: a review of the literature. J Orthop Sports Phys Ther. 1998 Aug;28(2):105-9.
  8. 8. What’s NewZ Issue 0 The Zimmer® Gender Solutions™ High-Flex Knee Total Knee Arthroplasty implant that emulates three distinct and scientifically documented anatomical shape features of women’s knees (1) Decreased mid-box medial-lateral (M/L) dimension versus overall A/P dimension leads to an improved fit of the implant leading to reduced overhang at the distal, anterior and posterior M/L interfaces → () Reduced anterior flange thickness of the implant decreases anterior protrusion → () Greater Q-angle of the implant improves patella tracking → A Special Thank You On behalf of John Cooper, Vice President, Australia, New Zealand and India we would like to thank our guests for celebrating the launch of the revolutionary Gender Knee at the Zimmer ‘Art of the Knee’ Gala Dinner held 10th October at the National Gallery of Australia. For those people who were unable to attend the event, Professor Betty Churcher introduced guests to the mysterious yet fascinating world of academic art history. Guests experienced an informative and entertaining journey that encompassed the representation of the human anatomy from the 10th century Nordic tradition to present pieces produced by Australian contemporary photographer Bill Henson. How artists depicted female nudes was not only interesting but it was apparent that art and science can portray entirely different facts about the human body. To discuss the scientific attributes was international guest speaker Dr Robert Booth, Chief of Orthopaedic Surgery, Pennsylvania Hospital, Philadelphia, USA. Dr Booth was one of the key orthopaedic surgeons on the Zimmer® Gender Solutions™ NexGen® Knee Development Team. His presentation titled ‘The EVEolution’ of the TKA’ presented our learned audience with hard clinical evidence that supported the design, development and manufacturing of a femoral prosthesis shaped to fit the female anatomy. The positive feedback that we have received from both orthopaedic surgeons and partners alike has been overwhelming. Once again, we would like to thank you for being a part of our very special evening. Gender Solutions High-Flex Femoral Implant on female bone Traditional implant overhangs female bone Gender Solutions High-Flex Femoral Implant Traditional implant (1) () () Please complete the details below and fax to: Att: Marketing Assistant Fax: Australia (02) 9975 1438 New Zealand 0800 427 597 Name: ________________________________________________________________________________________________ Address: ______________________________________________________________________________________________ Phone:________________________________________________________________________________________________ p Please tick here if you no longer wish to receive future issues of What’s NewZ. Zimmer Australia, Unit 1, 1-2 Skyline Place, Frenchs Forest NSW 2086 Australia Tel: +612 9950 5400 Zimmer New Zealand, 210 Khyber Pass Road, Grafton, Auckland New Zealand Tel: +64 9368 1490