Abstract
To ensure implant durability following Modern total knee replacement (TKR) surgery, one long held principle in condylar total knee arthroplasty is positioning the components in alignment with the mechanical axis and restoring the overall limb alignment to 180° ± 3°. However, this view has been challenged recently. Given the high number of TKR performed, clarity on this integral aspect of the procedure is necessary. To investigate the association between malalignment following primary TKR and revision rates. A systematic review of the literature was conducted using a computerised literature search of Medline, CINHAL, and EMBASE to identify English-language studies published from 2000 through to 2014. Studies with adequate information on the correlation between malalignment and revision rate with a minimum follow-up of 6 months were considered for inclusion. A study protocol, including the detailed search strategy was published on the PROSPERO database for systematic reviews. From an initial 2107 citations, eight studies, with variable methodological qualities, were eligible for inclusion. Collectively, nine parameters of alignment were studied, and 20 assessments were made between an alignment parameter and revision rate. Four out of eight studies demonstrated an association between a malalignment parameter and increased revision rates. In the coronal plane, only three studies assessed the mechanical axis. None of these studies found an association with revision rates, whereas four of the five studies investigating the anatomical axis found an association between malalignment and increased revision rate. This study demonstrates the effect of malalignment on revision rates is likely to be modest. Interestingly, studies that used mechanical alignment in the coronal plane demonstrated no association with revision rates. This questions the premise of patient specific instrumentation devices based on the mechanically aligned knee when considering revision as the endpoint.
Highlights
Modern total knee replacement (TKR) is considered an effective treatment for knee arthritis (Callahan et al 1994)
It is suggested that the evidence of poor outcomes secondary to malalignment is largely historic and based on studies of inferior implant designs, some of which have been discontinued (Bach et al 2009; Bonner et al 2011; Matziolis et al 2010; Parratte et al 2010), and the use of poor radiological assessment techniques to assess for malalignment (Lotke and Ecker 1977)
All studies were from single centres apart from one (Kim et al 2014), four studies were from North America (Berend et al 2004; Fang et al 2009; Parratte et al 2010; Ritter et al 2011), three studies from Europe (Bonner et al 2011; Magnussen et al 2011; Morgan et al 2008) and one from Asia (Kim et al 2014)
Summary
Modern total knee replacement (TKR) is considered an effective treatment for knee arthritis (Callahan et al 1994). The choice of target for ideal mechanical alignment has been challenged by proponents of kinematically aligned TKR who have reported promising results (Howell et al 2013a, b). With the removal of osteophytes the original ligament balance can be restored and the tibial component is placed with a longitudinal axis perpendicular to the transverse axis in the femur. Contrast this to conventional and computer assisted mechanically aligned techniques which aim to place the femoral component perpendicular to the mechanical axis of the femur, the tibial component perpendicular to the mechanical axis of the tibia and to rotate the femoral component so that flexion and extension gaps are parallel. As a result a mechanical malalignment (where the components are not positioned at 180° ± 3°) will differ for a kinematically aligned knee where the planned implant alignment is outside the 180° ± 3° range
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