to describe the anatomy and coronal alignment of the leg , a number of descriptive terms are used .
the anatomical axis of each bone refers to a line drawn along the centre of the intramedullary canal .
the mechanical axis of the femur refers to a line drawn from the centre of the femoral head to the centre of the knee . for the tibia
, the mechanical axis refers to a line between the centre of the knee and the centre of the ankle .
the anatomical and mechanical axes of the femur form an angle of approximately 6 , while the two axes of the tibia are usually equivalent ( fig .
right leg demonstrates mechanical axis ( white line ) and anatomical axis ( purple line ) of the femur .
the anatomical and mechanical axes of the tibia are usually the same ( red line ) . on the left leg ,
maquet s line passes through the medial compartment of the knee , indicating varus alignment .
the global mechanical axis , sometimes referred to as maquet s line , describes a line drawn from the centre of the femoral head to the centre of the talus ( fig .
normally , this line passes through the centre of the knee . the anatomical femorotibial angle ( afta )
describes the angle between the anatomical axes of the femur and tibia , and is usually about 6 of valgus .
the mechanical femorotibial angle ( mfta ) , formed by the mechanical axes of the two bones , is usually 0 or neutral , although variation exists in nature .
this is sometimes referred to as the hip - knee - ankle angle ( hka ) .
variance in limb rotation and knee flexion may have significant impact on the observed angles . in a valgus knee model with a true afta of 18 ,
swanson measured a change of almost 7 in the apparent afta with 20 of internal and external rotation .
in general , the closer an extra - articular deformity to the knee , the greater is its importance .
in 1977 , lotke and ecker first examined the correlation between implant positioning and functional outcome in 70 tkas .
they noted a significant correlation between good clinical results and good alignment . in four of their five failures ,
denham and bishop , in a 1978 study of biomechanics in relation to knee reconstruction , defined optimal positioning to be 7  4 of anatomical valgus for the femoral component and 90  4 to the anatomical axis for the tibia , to ensure the weight - bearing line passed through the centre of the joint .
hvid and nielsen reported an increased incidence of radiolucent lines at two years surrounding tibial components implanted with > 4 tilt in any direction , with the interesting exception of varus angulation in osteoarthritic knees . in an important 1991 study ,
jeffrey et al published the results of 115 early denham knee arthroplasties , with a median follow - up of eight years . using long - leg radiographs to assess coronal plane alignment , they found a significant difference in the rate of loosening between those aligned within  3 of the mechanical axis maquet s line ( 3% loosening ) , and those outside these limits ( 27% loosening ; p = 0.001 ) .
these studies are summarised in table i. summary of early studies supporting neutral mechanical alignment interestingly , not all studies from this period supported a neutral mechanical axis .
bargren et al reported a failure rate of 2.3% for the freeman swanson ( iclh ) knee when aligned between 1 to 5 of anatomical valgus ( 1 to 5 varus mechanical alignment ) , against an overall failure rate of 27% .
in the last few years , several reports have been highlighted challenging the superiority of neutral mechanical alignment .
summary of studies challenging the aim of neutral alignment notes : kss , knee society score ; womac , western ontario and mcmaster university osteoarthritis index ; iks , international knee society score ; sf-36 , short form-36 ; adl , activities of daily living .
regarding survival , in 2007 morgan et al reviewed the outcomes of 197 kinemax tkas at a mean of nine years post - operatively , and found no difference in revision rate between those in neutral , varus or valgus alignment . in a larger study ,
parratte et al published a retrospective review of 398 cemented primary knee arthroplasties performed at the mayo clinic using three modern prostheses .
 3. they found no difference in survivorship at 15 years between the well - aligned and outlier groups , and concluded that describing alignment as a dichotomous variable was of little value for predicting durability .
in a similar study of 501 tkas using a single prosthesis , bonner and co - workers found a weak trend towards a higher revision rate in those outside the 0  3 range ; however , this fell short of statistical significance ( p = 0.47 ) .
they concluded that the relationship between mechanical alignment and survival for primary tka is weaker than previously reported . with regards
to function , two medium - term studies have suggested that functional outcome is not adversely affected by residual post - operative varus alignment . from a series of 218 primary tkas , matziolis and
colleagues compared the results of the 30 knees with the greatest post - operative varus alignment , to neutrally aligned , matched controls .
the varus group had a mean post - operative mechanical axis deviation of 6.3 ( 3.9 to 10.7 ) .
there was no difference in functional results using multiple validated measures , and no revisions in either group at a minimum five - year follow - up .
magnussen and colleagues , from the centre albert trillat in lyon , examined the results of 553 tkas for varus osteoarthritis , comparing those with neutral post - operative mechanical alignment ( 0  3 ) and those with residual varus alignment >
they found no difference in knee society score ( kss ) or revision rate between the two groups , provided the residual varus was femoral in origin .
one recent study has found superior functional results for tkas with mild residual varus . in a study of 143 consecutive
tkas for varus osteoarthritis , vanlommel et al observed that the 46 knees with residual varus of 4 to 7 ( ftma 174 to 177 ) demonstrated significantly better kss and western ontario and mcmaster university osteoarthritis index ( womac ) scores than the neutral and significant varus groups at a mean of 7.2 years .
a number of criticisms have been made of early studies showing decreased survivorship with non - alignment of the mechanical axis .
most used only short - leg radiographs for assessment and involved early prosthesis designs no longer in use today .
polyethylene quality was inferior , and the sterilisation methods employed are now known to cause material property degradation .
most data comes from studies into navigation in tka , examining short- to medium - term results .
a systematic review in 2012 concluded that there was improved coronal plane alignment but no functional improvement with navigation ; however , a recent meta - analysis did find improved function in the navigation group .
recently , bellemans and co - workers have introduced the concept of constitutional varus , suggesting a neutral mechanical axis may be abnormal and even undesirable for many patients . in their study , 32% of men and 17% of women had a natural mechanical alignment  3 of varus .
similarly , others have explored the cylindrical axis of the knee and the concept of kinematic alignment .
kinematic alignment is based on the finding that the true axis about which knee flexion and extension occur is not perpendicular to the mechanical axis , and places the femoral and tibial components accordingly to recreate this anatomical axis . howell and co - workers reported equivalent or slightly better womac and oxford knee scores ( oks ) for varus and valgus outlier groups in 198 kinematically - aligned tkas , although this did not reach significance . a more recent study of 219 consecutive , kinematically - aligned tkas from the same author reported a comparable revision rate to registry data for the same prosthesis at six years , regardless of tibial component varus or overall limb alignment .
there were three revisions reported , including one for tibial component loosening , with two further revisions pending for patellar component loosening .
dossett et al , in a randomised control trial , evaluated the short - term outcomes of 41 kinematically- and 41 mechanically - aligned tkas . while the overall limb alignment was similar , the kinematic alignment group had 2.3 more tibial component varus and 2.4 more femoral component valgus .
kss , womac and oks were superior in the kinematically - aligned group . while there were no catastrophic early failures in these studies , the long - term survival of kinematically - aligned tkas is unknown .
ishikawa et al , in a recent computer simulator and finite element analysis , found near - normal knee kinematics in kinematically - aligned tkas ; however , both patellofemoral and tibiofemoral peak contact stresses were increased by as much as 200% and 270% respectively in the kinematically - aligned model .
furthermore , the accuracy of the patient - specific instrumentation systems typically required to achieve kinematic alignment are still being investigated and may be inferior to traditional or navigated systems .
contrary to these results , a number of authors have reported inferior results associated with tibial component varus . berend and colleagues , in a study of a cohort of 3152 knees with a mean five - year follow - up , found tibial component varus > 3 to significantly increase the odds of failure ( hazard ratio 17.2 , p < 0.0001 ) . in a later study from the same centre on an expanded cohort of 6070 tkas , ritter et al found increased revision rates when the tibial component was implanted in varus , when the femoral component was implanted with > 8 of anatomical valgus , and when one component was implanted to 
correct  for malalignment of the other component , despite resulting in neutral global limb alignment .
there was no difference in survivorship between those with neutral tibial component and neutral overall alignment and those with neutral tibial alignment and overall varus limb alignment ( < 2.5 ) , suggesting some residual varus global alignment in itself does not compromise results .
karachalios et al found residual deformity to be much more common in valgus knees and associated with significantly inferior clinical results using the bristol knee score .
fang et al reported a revision rate of 1.5% for those with post - operative valgus alignment compared with 0.5% for those in neutral alignment , noting that those with residual valgus tended to fail from ligament instability .
koskinen , in a study of 48 valgus knees implanted with cruciate - retaining prostheses , found residual valgus deformity to significantly increase the risk of revision with an odds ratio of 2 ( 95% confidence interval 1 to 3 , p = 0.025 ) .
eight of the 14 revisions were for progressive medial collateral ligament ( mcl ) instability .
consistent with these clinical reports , bryant and coworkers , in a recent cadaveric study , found valgus loading of a tka to significantly increase lateral tibio - femoral contact pressures and mcl strain .
as noted by tew and waugh in 1985 , while coronal alignment is certainly a factor in the outcome of tka , it may not be the most important factor and may serve to compound failure from other causes .
other technical factors , such as sagittal and rotational alignment , joint line restoration , and soft - tissue balance all influence the final outcome .
recent work on kinematic alignment would suggest that the ideal alignments for patient function and prosthesis longevity may in fact be different .
if so , advances in materials technology may allow for implant survival in a more functional but non - optimal mechanical environment . while mild residual global varus deformity may not negatively impact outcomes , survivorship may be negatively affected by varus of the tibial component .
this research received no specific grant from any funding agency in the public , commercial , or not - for - profit sectors .
 recent studies have challenged the long - held notion that neutral mechanical alignment after total knee arthroplasty leads to optimal function and survivorship.the ideal alignment for function and survivorship may actually be different.kinematic alignment , where components are implanted to re - create the natural flexion / extension axis of the knee , may lead to improved functional results.residual varus alignment may not adversely impact survivorship provided the tibial component is implanted in neutral alignment.cite this article : lording t , lustig s , neyret p. coronal alignment after total knee arthroplasty . 
 efort open rev 2016;1:12 - 17 . 
 doi : 10.1302/2058 - 5241.1.000002 . 
Anatomy and deformity
Historical evidence supporting neutral alignment
Recent evidence challenging neutral alignment
Discussion
Tibial component varus
Conclusion
Funding