Gradual-radius femoral component with s-curve post-cam provides stable kinematics at mid-flexion after total knee arthroplasty

Effect of single-radius design on in vivo kinematics during stair activities after total knee arthroplasty

BACKGROUND

The single-radius design is one of the major total knee arthroplasty (TKA) designs and widely used all over the world. The objective of this study was to compare in vivo kinematics between the anteroposterior (AP) single-radius design with mediolateral (ML) single-radius (Non Restricted Geometry; NRG) and ML dual-radius (Triathlon) during stair activities.

METHODS

A total of 21 knees in 18 patients (NRG group: 10 knees in 7 patients, Triathlon group: 11 knees in 11 patients) with a clinically successful posterior stabilized TKA were examined. Under fluoroscopic surveillance, each patient performed stair ascending and descending motions. In vivo kinematics were analyzed using 2D/3D registration technique. The knee flexion angle, rotation angle, varus-valgus angle, AP translation of the femorotibial contact point for both the medial and lateral sides of the knee, and post-cam engagement were evaluated.

RESULTS

There were no significant differences between the two groups in rotation angle and AP translation at each flexion angle. Examining the varus-valgus angle, the NRG group showed varus position at an early flexion angle during both stair activities.Post-cam engagement was observed in both groups during both stair activities. The mean flexion angle of engagement in the NRG group, the post of which was located anterior to the Triathlon, was larger than that in the Triathlon group during both stair activities.

CONCLUSION

Despite the same AP single-radius TKA, ML single-radius might affect varus motion at an early flexion angle.

Clinical advantages of gradually reducing radius versus multi-radius total knee arthroplasty: a noninferiority randomized trial

BACKGROUND

The rationale for gradually reducing radius (GR) femoral component aims to prevent flexion instability by gradually change the center of femoral rotation, unlike a discrete change by the multi-radius (MR) which is more common for most of total knee arthroplasties (TKA). However, no strong evidence has been reported the clinical significance of the GR design.

METHODS

This patient-blinded, parallel, non-inferiority trial conducted between January 2018-December 2020. Patients with knee osteoarthritis consented for cruciate retaining TKA were randomly allocated to a GR or MR group. Primary outcome measures were knee functions at postoperative 6 and 12 months using the Knee injury and Osteoarthritis Outcome Score (KOOS). Secondary outcome measures were performance-based tests (30-s chair stand test, 40-m fast paced walk test, and 3-m timed up and go test), and knee motions.

RESULTS

Sixty patients were enrolled and randomized; GR (n = 30) and MR (n = 30) group. The changes of KOOS at 6 and 12 months from baseline showed clinical meaningful for both GR and MR group. At 6 and 12 months postoperatively, there was no significant difference between both groups in all KOOS subscales. The length of stay was not different between GR and MR group (5.93 ± 1.44 vs 6.17 ± 1.86 days, p = 0.59). Patients on both groups presented similar performance-based tests. However, the improvement in degrees of knee motion for the GR group was significantly greater than the MR group (34.67 ± 12.52 vs 23.67 ± 12.59, p = 0.001).

CONCLUSION

GR was noninferiority to MR for the functional outcomes and performances after TKA. The GR femoral component gave more knee motions than did the MR prostheses.

LEVEL OF EVIDENCE

Level I, therapeutic study.

Comparison of in vivo knee kinematics before and after bicruciate-stabilized total knee arthroplasty during squatting

Background

No studies have directly evaluated kinematic changes during squatting before and after bicruciate-stabilized total knee arthroplasty (BCS-TKA) with the dual cam-post mechanism and asymmetric surfaces. This study investigated the effect of BCS-TKA on changes to pre- and postoperative skeletal knee kinematics, to identify factors associated with postoperative skeletal kinematic parameters.

Methods

Seventeen knees in 17 patients were prospectively recruited before primary TKA for advanced medial knee osteoarthritis. Subjects underwent BCS-TKA and were evaluated more than 1 year postoperatively. In vivo dynamic skeletal knee kinematics were evaluated using periodic radiographic images collected during squatting to quantify the tibiofemoral functional extension/flexion angle, anteroposterior (AP) translation, and axial rotation angle using image-matching techniques. Rotational alignments of femoral and tibial components were measured postoperatively using computed tomography images.

Results

The pre- and postoperative tibiofemoral functional extension/flexion angles during squatting were 12.2° ± 6.7°/100.1° ± 16.8° and 9.6° ± 8.6°/109.4° ± 16.8°, respectively, with a significant difference in flexion angle (p < .05). Total AP translation was significantly larger postoperatively than preoperatively (10.8 mm ± 3.7 mm vs. 14.4 mm ± 4.2 mm, respectively; p < .05). The pre- and postoperative total rotation angles were 6.6° ± 3.0° and 6.4° ± 3.7°, respectively, indicating no significant difference. The pre- and postoperative tibiofemoral functional flexion angles were significantly associated with each other (p = .0434, r = .49). The postoperative total rotation angle was significantly smaller when the total component rotational mismatch angle between the femoral and tibial components was above 5° vs. below 5° (4.6° ± 2.7° vs. 8.3° ± 3.9°, respectively; p < .05).

Conclusions

BCS-TKA significantly increased the tibiofemoral functional flexion angles, with larger AP translation postoperatively. Both preoperative skeletal kinematics and surgical techniques affected the skeletal kinematics of the replaced knee. A total component rotational mismatch angle greater than 5° significantly decreased postoperative total knee rotation during squatting.