To obtain a good outcome in TKA is mandatory to reach a balanced flexion-extension gap. That requires, during surgery, to choose the amount of bone resection and the position of the prosthetic component, mainly the femoral one. These choices are based upon some bone landmarks, but overall could be based upon a proper ligament’s tension, as a preview of ideal kinematics.> About this topic several Authors published in the last decade, but the determination of a value of ligament’s tension still remains a big issue.

So we made an hydraulic knee analyzer (HKA® ) computer integrated and we tested and validated by a cadaveric study. Aims of this study are: to validate the reproducibility, in vivo, of the results of the cadaveric study, and subsequently to evaluate the outcome between two groups of patients undergone to surgery, one by conventional technique and the other by C.A.S. The previous cadaveric study, that was done on ten fresh knees by HKA®, highlighted a relation between ligament’s tension in flexion and in extension, 4 bar vs 6 bar. Twenty patients were operated by C.A.S. (Navitrack® Centerpulse-Zimmer) and HKA®, Twenty patients were operated conventionally, by the same surgeon and utilizing the same prosthesis (Innex® Centerpulse-Zimmer). Preoperative and postoperative study was performed by: long lenghth lower limb x-ray, IKSS score and SF 36 score.

In all the C.A.S. patients it’s got a rectangular and balanced gap, both in flexion and extension, utilizing a 4 bar in flexion and 6 bar in extension, as shown in the cadaveric study.

The comparison between two groups of patients has underlined a better functional outcome in the C.A.S. group.

A comparative prospectic randomized study has been performed between two groups of patients, one undergone to surgery by conventional technique (A) and the other by CAS (B). In all the patients the same type of prosthesis, Innex Ucor® (Zimmer), was implanted by the same surgeon. The surgical technique has been “tibia first” with preliminary ligament balance in both groups.

In CAS technique has been utilized the Navitrack® (Orthosoft) system integrated by an hydraulic tensor, Hydraulic Knee Analyzer® (Zimmer), able to measure the applied force and the obtained space.

Evaluation criteria have been: x-ray alignment (HKA), IKSS, SF-36. Minimum follow-up has been 12 months.

The data shows a statistically significant difference in the group B related to HKA (p< 0,0001) and functional score (p= 0,009). The knee score is “non significant” but it has a “tendency value”, even if the pain score is “significant” (p=0,008). SF-36 isn’t “significant”.

The group B has shown an important reduction of clinical and radiographic outliers.