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Knee: H. S. Han, S.-B. Kang, and K. S. Yoon High incidence of loosening of the femoral component in legacy posterior stabilised-flex total knee replacement J Bone Joint Surg Br 2007; 89-B: 1457-1461 [Abstract] [Full text] [PDF]

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Successful results with a high flexion posterior stabilised knee prosthesis

Giles R. Scuderi   (21 December 2007)

Successful results with a high flexion posterior stabilised knee prosthesis 21 December 2007
Giles R. Scuderi, Orthopedic Surgeon Insall Scott Kelly Institute, 210 East 64th Street, New York, NY 10021 USA Send letter to journal: Re: Successful results with a high flexion posterior stabilised knee prosthesis GRScuderi{at}aol.com Giles R. Scuderi	Sir, I read this article with interest and was astounded at the authors' 21% femoral loosening rate at a mean interval of 23 months, and even more surprised that femoral components were loosening in less than a year. However, what I find more disturbing is that in this retrospective study in a small group of patients with no control group for comparison, the authors are placing blame on the implant design and the degree of flexion achieved by this limited cohort of patients. It is difficult to imagine that an 11° difference in mean maximum flexion (136° versus 125°) would create such a catastrophic result, especially when both the loosened and well-fixed groups have patients achieving 140° of flexion. In addition, only 26% of patients in the loosened group and 20% in the well-fixed group were capable of prolonged high flexion activities. So, while both groups were achieving high flexion they were not spending much time doing so. The early failure of fixation is probably related to either errors in surgical technique or more likely errors in the cement technique. The published photograph of a retrieved femoral component shows no cement on the back of the prosthesis. This is a very unusual observation. The results in this study are contrary to my own experience with this prosthesis, and I find it incredible that the authors place blame on the implant design. I refer the authors to several publications supporting high flexion knee designs, including the Legacy high flexion posterior stabilised prosthesis. The design features of the LPS-Flex prosthesis have undergone extensive scientific testing and are based on sound principles.1 They have taken into consideration the patient’s need for post-operative flexion,2,3 and the requirement to reduce the contact stress on the tibial polyethylene.4 Several prospective randomised clinical studies have reported excellent results with this prosthetic design in patients with high post-operative knee flexion. Weeden and Schmidt5 compared 50 patients, 25 with a standard cemented implant and 25 with a cemented high flexion posterior stabilised implant. Their findings at one year revealed average flexion in the high flexion group to be 133° with a significant number of patients having flexion greater than 135°. They also reported no evidence of femoral or tibial loosening. Huang et al,6 reported on 25 cemented LPS-Flex prostheses with two-year follow-up having a mean flexion angle of 138° (125° to 150°) with 80% of patients able to squat. In this series of high flexion knees, there was no sign of component loosening or osteolysis. Another report by Kim et al7 randomised 50 patients undergoing bilateral cemented TKA (100 knees). Each patient received an LPS on one side and LPS-Flex on the other. At two-year follow-up, the mean range of motion was comparable for both groups, 136° and 139° respectively, with a similar range (105° to 150°). There were no cases of radiolucent lines or component loosening. Finally, in a series of 3,738 LPS-Flex prostheses implanted by a wide range of surgeons, the Australian Joint Registry reported only 14 loose components.8 This is a loosening rate of 0.37%, similar to their experience with the LPS prosthesis (0.40%). This is significantly less than the authors' loosening rate of 21%. With this vast amount of clinical and scientific data supporting the use of a high flexion posterior stabilised implant, I would suggest that the authors look carefully at their surgical technique and their cement technique before they report such harsh criticism for this successful design. G.R. Scuderi, MD, Orthopaedic Surgeon, Insall Scott Kelly Institute, New York, USA. 1. Argenson JN, Scuderi GR, Komistek RD, et al. In vivo kinematic evaluation and design considerations related to high flexion in total knee arthroplasty. J Biomech 2005;38:277–84. 2. Dennis DA, Komistek RD, Scuderi GR, Zingde S. Factors affecting flexion after total knee arthroplasty. Clin Orthop Relat Res 2007;464:53-60. 3. Victor J, Bellemans J. Physiologic kinematics as a concept for better flexion in TKA. Clin Orthop Relat Res 2006;452:53–8. 4. Sharma A, Komistek RD, Scuderi GR, Cates HE Jr. High-flexion TKA designs: what are their in vivo contact mechanics? Clin Orthop Relat Res 2007;464:117–26. 5. Weeden SH, Schmidt R. A randomized, prospective study of primary total knee components designed for increased flexion. J Arthroplasty 2007;22:349–52. 6. Huang HT, Su JY, Wang GJ. The early results of high-flex total knee arthroplasty: a minimum of 2 years of follow-up. J Arthroplasty 2005;20:674-79. 7. Kim YH, Sohn KS, Kim JS. Range of motion of standard and high-flexion posterior stabilized total knee prostheses. A prospective, randomized study. J Bone Joint Surg [Am] 2005;87-A:1470-5. 8. Australian Orthopaedic Association Annual Report 2006. http://www.aoa.org.au/docs/supp06.pdf (accessed 21/12/2007).