title: Maximizing tibial coverage is detrimental to proper rotational alignment.
abstract: BACKGROUND
  Traditionally, the placement of the tibial component in total knee arthroplasty (TKA) has focused on maximizing coverage of the tibial surface. However, the degree to which maximal coverage affects correct rotational placement of symmetric and asymmetric tibial components has not been well defined and might represent an implant design issue worthy of further inquiry.
  
  
  OBJECTIVE
  Using four commercially available tibial components (two symmetric, two asymmetric), we sought to determine (1) the overall amount of malrotation that would occur if components were placed for maximal tibial coverage; and (2) whether the asymmetric designs would result in less malrotation than the symmetric designs when placed for maximal coverage in a computer model using CT reconstructions.
  
  
  METHODS
  CT reconstructions of 30 tibial specimens were used to generate three-dimensional tibia reconstructions with attention to the tibial anatomic axis, the tibial tubercle, and the resected tibial surface. Using strict criteria, four commercially available tibial designs (two symmetric, two asymmetric) were placed on the resected tibial surface. The resulting component rotation was examined.
  
  
  RESULTS
  Among all four designs, 70% of all tibial components placed in orientation maximizing fit to resection surface were internally malrotated (average 9°). The asymmetric designs had fewer cases of malrotation (28% and 52% for the two asymmetric designs, 100% and 96% for the two symmetric designs; p < 0.001) and less malrotation on average (2° and 5° for the asymmetric designs, 14° for both symmetric designs; p < 0.001).
  
  
  CONCLUSIONS
  Maximizing tibial coverage resulted in implant malrotation in a large percentage of cases. Given similar amounts of tibial coverage, correct rotational positioning was more likely to occur with the asymmetric designs.
  
  
  CONCLUSIONS
  Malrotation of components is an important cause of failure in TKA. Priority should be given to correct tibial rotational positioning. This study suggested that it is easier to balance rotation and coverage with asymmetric tibial baseplates; clinical research will need to determine whether the observed difference affects patellar tracking, loosening rates, or the likelihood of revisions after TKA.
authors: Methodist Center for Orthopaedic Surgery, 6550 Fannin, Suite 2600, Houston, TX, 77030, USA.
authors: Stacey
authors: S
authors: Martin
authors: Alex
authors: A
authors: Saurez
authors: Sabir
authors: S
authors: Ismaily
authors: Kashif
authors: K
authors: Ashfaq
authors: Philip
authors: P
authors: Noble
authors: Stephen J
authors: SJ
authors: Incavo
mesh_terms: D019645:Arthroplasty, Replacement, Knee / Q000295:instrumentation / Q000379:methods*; D001696:Biomechanical Phenomena / Q000502:physiology; D003198:Computer Simulation; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000502:physiology / Q000601:surgery*; D011859:Radiography; D016059:Range of Motion, Articular / Q000502:physiology*; D012399:Rotation; D013977:Tibia / Q000000981:diagnostic imaging / Q000502:physiology / Q000601:surgery*
references: J Arthroplasty. 2003 Dec;18(8):1048-55
references: 14658111
references: Clin Orthop Relat Res. 1989 Nov;(248):135-44
references: 2805471
references: Clin Orthop Relat Res. 2007 May;458:131-6
references: 17224835
references: Knee Surg Sports Traumatol Arthrosc. 2013 Oct;21(10):2288-95
references: 22476525
references: Clin Orthop Relat Res. 2008 Nov;466(11):2751-5
references: 18825470
references: Orthop Clin North Am. 2001 Oct;32(4):639-47, ix
references: 11689376
references: Clin Orthop Relat Res. 2005 Jul;(436):172-6
references: 15995437
references: Clin Orthop Relat Res. 2011 Aug;469(8):2346-55
references: 21533528
references: J Arthroplasty. 2011 Feb;26(2):260-7.e1-2
references: 20452177
references: Clin Orthop Relat Res. 1994 Dec;(309):163-75
references: 7994956
references: J Arthroplasty. 2011 Sep;26(6 Suppl):53-58.e1
references: 21723702
references: BMC Musculoskelet Disord. 2010 Mar 25;11:57
references: 20338042
references: J Arthroplasty. 2003 Aug;18(5):643-8
references: 12934219
references: Clin Orthop Relat Res. 2006 Nov;452:35-43
references: 16967035
references: J Bone Joint Surg Br. 2010 Sep;92(9):1238-44
references: 20798441
references: Clin Orthop Relat Res. 1989 Nov;(248):15-9; discussion 19-20
references: 2805473
references: Clin Orthop Relat Res. 2010 Oct;468(10):2734-8
references: 20352384
references: Clin Orthop Relat Res. 1994 Feb;(299):81-5
references: 8119041
references: Clin Orthop Relat Res. 2002 Nov;(404):7-13
references: 12439231
references: J Orthop Res. 2011 Jul;29(7):969-75
references: 21567450
references: Orthop Traumatol Surg Res. 2011 Nov;97(7):699-704
references: 21993150
references: Clin Orthop Relat Res. 1993 Jan;(286):40-7
references: 8425366
references: Zhongguo Xiu Fu Chong Jian Wai Ke Za Zhi. 2007 Mar;21(3):226-30
references: 17419197
references: J Arthroplasty. 2004 Oct;19(7):906-10
references: 15483808