LIVRE JDG 2010

DISCUSSION

The kinematics of the Journey CR knee

implant are on average comparable to the kine-

matic pattern of the native knee in these tests.

Apparently the joint surfaces of the anatomic

knee design with a dished medial insert surfa-

ce and a convex lateral insert surface and a

3 degrees varus of the joint line is guiding the

motion towards that of a normal knee joint. We

feel that correct balancing of the PCL during

implantation is of major importance in achie-

ving these results. The step-off guided spacer

technique to balance the PCL seems to work

well in this experiment, no lift off of the tibia

inserts occurred during trail implantation. The

preparation of the PCL with preservation of

the bony insertion was also safe since no liga-

ment ruptures occurred during the tests.

It is clear that the PCL is the main and largest

ligament structure in the flexion gap, and it

dictates the position of the contact point of

femur on tibia. The precise preparation of the

gaps is also important in achieving correct

kinematics. In two out of eight cases we nee-

ded to increase the slope of the tibia with 2-

3 degrees, thereby increasing the flexion gap

with 2-3mm. The described technique therefo-

re can be used easily.

We did not not use a PCL release in the tight

knees in this experiment since effects of

releases on roll-back and contact points were

not available in the literature and thus uncer-

tain. Moreover we feel that in case of a tight

flexion gap the PCL is not the cause of the pro-

blem but the gaps are not correct. As Christen

et al.

[3] have shown a 1-2mm flexiongap

increase causes a contactpoint change of 2-

4mm with the tibia moving anterior. This

explains why a limited increase of the tibia

slope with 2-3 degrees was sufficient to cor-

rectly balance the flexiongap and create a cor-

rect contact point.

In summary the kinematics of the anatomic

Journey CR total knee design seem to be simi-

lar to the kinematics of the native knee using a

measured bone resection technique and a spa-

cer guided PCL balancing.

JOURNÉES LYONNAISES DE CHIRURGIE DU GENOU

194

Fig. 3 : Loaded contact points Journey CR

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