LIVRE JDG 2014

T. Ait Si Selmi, D. Shepherd, M.Bonnin

improve functional outcomes [72], however

literature does not support any superiority of

high flexion devices [73, 74].

The bearing platform itself has variations of

posterior stabilized, cruciate retaining, rotating

platforms and deep dished platforms to try and

enhance kinematics such as deep flexion and

maintain flexion stability. There is controversy

over whether any are more superior. There

appears to be no difference between fixed or

rotating platforms [75], and they fail to achieve

the anteroposterior stability of the native knee,

furthermore some designs have failed to

prevent paradoxical rollback/tibial external

rotation.Cruciateretainingdesignstheoretically

may improve function by maintaining

proprioception [76], whereas posterior

stabilized designs have evolved to enhance

flexion. Whilst posterior stabilized knees may

provide deeper flexion [77], the evidence in the

literature shows that there is no difference in

outcomes functionally between the two groups

[77, 78, 79].

Overall, despite best attempts to improve the

performance of knee arthoplasty, these

modifications to existing implant design and

rationale have not necessarily improved

outcomes in active patients [80]. All in all, the

trend that we all see is clearly an attempt to

attain a prosthetic design that can better match

the native knee, and current ‘off the shelf’

designs still utilize the model whereby the knee

is made to fit the prosthesis, rather than the

prosthesis fitting the knee, such that

intraoperative modifications of one parameter

will have consequences on another.

The question then remains, why are we not

attempting to leapfrog these steps to a

customized prosthesis?

The concept of

customized knee

arthroplasty

The general idea of customization is to prevent

the need for compromises that the surgeon is

forced to make during standard TKR insertion

and to minimize the accumulation of

approximations from preoperative planning to

final implant insertion. Customization is an

appealing option but 3 principle questions

arise:

, What type of deformity can be

addressed or what (native) residual alignment

is acceptable?

What parts of a TKR may

benefit from customization?

How to execute

it at an industrial level?

Reaching the native alignment

The amount of acceptable native alignment

(incorrectly termed “deformity”) is somewhat

difficult to determine, but as mentioned

previously, 3 to 5 degrees of residual alignment

may be acceptable, as recommended in

unicondylar knee arthroplasty. This amount of

angulation is acceptable provided that the

ligaments (including the cruciates) are intact,

and probably in patients under a maximum

weight or BMI. These criteria would make the

customized knee ideal for patients where both

cruciates are intact. But in TKR the stabilization

mechanism can be used to compensate for the

absence of one or two cruciates, and thus

customization can presumably be extended to

more patients. On the other hand, fixed

deformities, major ligament instability, or

severe extra-articular deformities should be

contraindications.

The native alignment does not cover the limb

alignment alone but includes the joint line

obliquity. In a customized knee concept this

native angulation can be respected. This has

consequences on ligament balancing, making it

simpler because it does not create a flexion-

extension miss-match from a femoral origin.

Keeping the native joint obliquity results in

restoring – or approaching – the individual

medial-lateral femoral contours. In principle,

in keeping the native knee contour there should

be no further need for ligament release or it

should be limited to address limited contractures

(fig. 5). Such a design, while reducing the

flexion extension imbalance may provide a

smoother stability across the range of motion,

thus reducing the mid flexion instability. Along