Background: As many as 20% of all patients after total knee arthroplasty (TKA) are not satisfied with their result. Different factors affecting clinical outcome include leg alignment, rotational alignment, soft tisssue-balancing, the femoro-patellar joint, and patient-related factors. The purpose of this study was to assess relationships between prosthesis rotational alignment, function score and knee kinematics after TKA.

Materials and Methods: From initially eighty patients with a cemented, unconstrained, cruciate-retaining TKA with a rotationg platform without patellar resurfacing seventy-three patients were available for post-operative physical and radiological examination after a median of 20 months follow-up.

Results: Nine patients had more than 10° rotational mismatch between the femoral and tibial component in the postoperative CT-scans. These patients were not different from the remaining 64 patients in the KSS Knee score (both groups 89 points at follow-up) and EQ 5D VAS (65 points vs 70 points at follow-up) but showed significantly worse results in the KSS Function score. While the normal patients with less than 10° rotational mismatch impoved from a median preoperative 55 points to a median 70 points at follow-up, the group with more than 10° mismatch deteriorated from a median 60 points preoperatively to a median 50 points at follow-up (p = 0.001).

For seven of these nine patients, kinematic analysis was available during passive flexion from approximately 0° to 120°. There were no substantial differences in the average range of total axial rotation achieved in this group compared to the normal group, but the pattern of motion during that range was quite different. While external rotation steadily increased with knee flexion in the normal group, there was internal rotation between 30° and 80° of flexion in the group with more than 10° rotational mismatch.

Conclusion: Rotational mismatch between femoral and tibial components exceeding 10° resulted in different kinemtics after TKA. This might contribute to worse clinical results observed in those patients and should therefore be avoided.

Mobile-bearing total knee replacement (TKR) designs are advocated for their theoretical ability to self-align and accommodate small errors in rotational (axial) alignment. However, for many mobile-bearing TKR, the relationships between axial alignment, knee axial rotation and bearing motion during knee flexion are undefined. This study evaluates whether mobile-bearing TKR with axial alignment outside surgical norms have different rotations and motions compared to well-aligned TKR.

This prospective study included 67 patients implanted with cruciate-retaining mobile-bearing TKR with a rotating platform polyethylene bearing (Scorpio PCS, Stryker). Axial alignment of femoral components relative to the transepicondylar axis and tibial components relative to the medial tibial tuberosity was measured from postoperative CT scans. TKR were categorized as “normal” or “outliers” according to defined tolerances for surgical axial alignment relative to anatomic landmarks (+3° for femur, +10° for tibia) and combined axial mismatch (+5° between femoral and tibial components). Knee kinematics and axial rotation were measured from fluoroscopic images acquired immediately after TKR during 0° to 120° of passive knee flexion. Total knee axial rotation (relative motion between the femoral component and tibial baseplate), femoral component axial rotation on the bearing articular surface, and bearing axial rotation on the tibial baseplate were determined using published shape-matching techniques.

External rotation during knee flexion averaged 8.4°+6.1°, with two phases of axial rotation motion distinguished in all groups. External rotation from 0°–80° occurred primarily due to bearing axial rotation on the tibial baseplate. Beyond 80°, there was combined bearing rotation and external rotation of the femoral component on the polyethylene articular surface, with the latter dominating the motion pattern. Axial rotation varied with the component axial alignment. Among TKR with normal axial alignment, external rotation steadily increased with knee flexion. Among anatomic landmark outliers, there was a transition to internal rotation from 20°–50° and limited (< 1°) axial rotation beyond 80°. Among combined axial mismatch outliers, the magnitude of axial rotation was significantly less than normal TKR throughout the flexion range (p< 0.001) due to opposite rotations between the femoral component and polyethylene bearing.

Achieving appropriate axial alignment using defined bony landmarks remains a challenge. In this study, approximately 30% of TKR did not have suitable axial alignment, with notable combined axial mismatch in tibial-femoral alignment. Axial rotation misalignment affected the kinematics and knee rotation motions over the passive flexion range and appears to result in opposite rotations of the femur-bearing and bearing-base-plate articulations.

Background: Correct rotational alignment of the femoral and tibial component is an important factor for successful TKA. The transepicondylar axis is widely accepted as a reference for the femoral component. There is no such reference for the tibial component. CT scans were used in this study to measure which tibial landmark most reliably reproduces a correct femoro-tibial rotational alignment in TKA. Furthermore, the impact of computer-assisted navigation on rotational alignment is investigated.

Materials and Methods: After informed consent, 80 patients were randomized to receive either navigated or conventional TKA. All patients received a cemented, unconstrained, cruciate-retaining TKA with a rotating platform. CT scans were performed 5–7 days postoperatively but before discharge. The rotational variance between the femoral and tibial components was measured.

Results: There was notable rotational variance between the femoral and tibial components in both groups. In the navigated group, the median variance was 1.2° relative external rotation of the femur (range: 16.2° relative external to 12.7° relative internal rotation of the femur). In the conventional group, the median variance was 1.7° relative internal rotation of the femur (range: 9.0° relative external to 14.4° relative internal rotation of the femur). Using the medial third of the tuberosity as reference for tibial rotational alignment, 67.5% of all TKA had a femoro-tibial variance within ± 5°, 85% within ± 10° and 97.5% within ± 20°. Using the medial border of the tibial tubercle as reference this variance was greater, 3.8% had a femoro-tibial variance within ± 5°, 15% within ± 10° and 68.8% within ± 20°.

Conclusion: Using fixed bone landmarks for rotational alignment leads to a notable variance between femoral and tibial component. Computer-assisted navigation did not reduce this variance.

Referencing the tibial rotation on a line from the lateral border of the medial third of the tibial tubercle to the center of the tibial tray resulted in a better femoro-tibial alignment than using the medial border of tibial tubercle as landmark. Surgeons using fixed bearings with a high conformity between the inlay and the femoral component should be aware of this effect to avoid premature polyethylene wear.

Background: Computer-assisted navigation systems are supposed to improve the precision of implant positioning and therefore the longevity of the knee arthroplasty. Several studies have demonstrated a better mechanical axis or axial component alignment in navigated compared to conventional TKA at least less outliers from a range of 3° of varus or valgus. It is still unclear wether navigation can improve rotational alignment.

Materials and Methods: After informed consent 80 patients were randomized to navigated or conventional TKA. In all patients, a cemented, unconstrained, cruciate-retaining TKA with a rotating platform was implanted. A full-length standing and a lateral radiograph and CT Scans of the hip, knee and ankle joint were done 5 to 7 days postoperatively before discharge.

Results: The navigated group showed a median deviation from the mechanical axis of 1,5° with a range between 5,9° valgus and 4,6 varus malalignment. The conventional implanted arthroplasties showed a median deviation from the mechanical axis of 1,6° with a range between 5,9° valgus and 7,2° varus malalignment. 5 navigated and 7 conventional implanted arthroplasties were outside a tolerance level of 3°.

The femoral component showed a median deviation from the transepicondylar axis of 1,7° (range: 3,1° external rotation to 4,4° internal rotation) in the navigated group and of 1,0° (range: 3,4° external rotation to 4,3° internal rotation) in the conventional implantations.

The tibial component showed a much greater range of rotational deviation from the medial third of the tuberosity in median 5,3° (range: 14,9° external rotation to 26° internal rotation) in the navigated group and 4,8° (range: 6,5° external rotation to 23,8° internal rotation) in the conventional implantations.

Conclusion: We could not find a difference between Computer-assisted navigation and conventional implantation for rotational alignment of the femoral or tibial component. While the deviation from the transepicondylar axis was quite low and nearly all implantations were within a range of 3° of internal and external rotation there was a considerable range of deviation for the tibial rotational alignment.