Purpose of the study: How does a total knee arthroplasty (TKA) function? Do all prostheses provide the excellent results reported in the literature? This gait analysis compared patients with a TKA versus normal subjects in order to obtain a 3D quantification of the kinematic and dynamic differences between patients with a very good functional result and controls.

Material and methods: Twenty patients who had a TKA for less than one year and whose functional outcome was scored very good (KSS knee > 85/100, VAS ≤1/10) were compared in a double blind study with 20 normal controls. The knees were masked so that the investigators were unaware of the type of subject (operated or not), the side operated, or the type of implant. The analysis as performed on an AMTI platform with six infrared cameras which followed the displacements of 36 reflectors. Motion Analysis software was applied. The gait parameters recorded were: speed, step length, flexion angle, duration of weight bearing/oscillation phases, and dynamic variables: flexion-extension moment, varus-valgus moment, internal/external rotation moment.

Results: Adjusted for age and height, step length, walking speed, and duration of the weight bearing phase were identical in the operated and control populations. Kinematic and dynamic variables demonstrated significant differences. At lift-off, all of the TKA subjects were in functional permanent flexion (m=10); the flexion moment of the quadriceps was less than in the non-operated subjects. In the frontal plane, the weight-bearing phase was identical between the operated subjects and controls, but with a varus dynamic (m=4) during the oscillating phase. In the horizontal plane, there was an external rotation of the tibia (m=+5) during weight bearing.

Discussion: Gait analysis provides quantitative information which is not perceptible at physical examination nor with videoscopic explorations. Even patients with an excellent KSS score exhibit important anomalies despite the fact that the physical exam finds a normal range of motion and normal muscle force. The degree by degree 3D gait analysis reveals the difference.

Conclusion: Despite a clinical score considered to be very good, patients with a TKA have a functional deficit of the extensor system during take-off, even when the knee has complete active extension; the weight-bearing phase of the step is in external rotation and the oscillating phase exhibits varus laxity.

This is a prospective gait laboratory case matched cohort study of patients after total knee arthroplasty.

20 patients who had TKA with a good functional result and a follow-up superior to 2 years were compared with 20 “normal” knees.

The examiners were blinded to the group. A standardized gait analysis was performed, measuring gait kinematics, kinetics and force plate recordings using Motion Analysis computer software.

All patients had a single surgeon and the same brand mobile bearing platform.

The kinematics parameters were identical in both groups

However the dynamic parameters showed a statistically significant difference

At terminal swing and heel strike the operated patients had a 10-degree extension deficit in their gait analysis, despite of the fact that clinically all patients had a full extension with no quadriceps lag.

The coronal plane kinetics of TKA showed valgus moment in stance despite having radiological normal (180° +/−1°) mechanical axis. (p< 0,02)

In the axial plane, all operated patients had an external rotation moment greater than normals. (p< 0,01)

Despite good clinical ROM and quadriceps strength, the TKA demonstrated a lack of extension in early stance.

This may be due to insufficient extension gap at surgery.

The valgus resultant pattern poses a more challenging question:

Are we aiming for the wrong goals in the mechanical axis, or should we consider undercorrection?

Gait analysis of the TKA patients compared to normals demonstrates dynamic differences in relation with the surgical positioning of the implant.

Purpose: This comparative study of femoropatellar function in four types of total knee arthroplasty (TKA) was conducted to demonstrate the relation between the form of the femoropatellar articulation and the function outcome achieved with these prostheses.

Material and methods: Forty patients who had undergone first-intention TKA for primary degenerative joint disease were selected at random. Minimum follow-up was one year. The functional IKDC score was greater than 85/100. All TKA had been inserted without preservation of the posterior cruciate ligament. Four types of prostheses were used:

- posterior stabilised prosthesis with a fixed plateau, toric trochlea, cemented dome patella (n=10);

The following parameters were studied prospectively:

- pain assessed on a visual analogue scale;

Results: The kinematic data demonstrated a significant difference between:

- TKAs with a dome patella and those with an anatomic patella;

This difference basically involved the patellar tilt, lateral subluxation of the patella, and especially, the patellar trajectory between 20° and 90°, the toric trochlae with a dome patella having a more anterior trajectory than the normal knee.

The clinical and functional study showed that:

- the percentage of totally pain-free femoropatellar articulations was higher for the hollow anatomic trochlae (96%) than for the three other types (75%) (p = 0.04);

Discussion and conclusion: This study confirms the theoretic work reported by Walker and the clinical work reported by Andriacchi on the anterior curvature of the trochlae and the kinematic work reported by Stichl on the advantage of anatomic trochlae. These findings point out the advantage of the hollow anatomic trochlae where the patella is applied on the trochlear groove situated at the same depth as the normal trochlae, which is not the case with most TKAs. This advantage is seen by the absence of pain and by the propulsion when climbing stairs.