Cementless medial pivot design demonstrates equal or better outcomes compared to cementless cruciate-retaining design following total knee arthroplasty

Cementless Total Knee Arthroplasty Using an Ultraconforming Tibial Bearing: Outcomes at Minimum 5-Year Follow-Up

BACKGROUND

Cementless fixation for primary total knee arthroplasty (TKA) continues to increase in the United States. However, compared to cemented TKA, reports on revision rates have been mixed. A confounding variable may include the tibial insert design. This study aimed to assess the minimum 5-year survivorship and outcomes of a cementless TKA using an ultracongruent (UC) articulation.

METHODS

A consecutive series of 242 cementless TKAs were implanted at two institutions between 2017 and 2019 using an UC kinematic tibial insert. Of the patients, 56% were men. The average age was 60 years. Patients were followed using Knee Injury and Osteoarthritis Outcome Score for Joint Replacement (KOOS-JR) and Knee Society clinical and radiographic scores. Preoperative and postoperative radiographs were classified according to the Coronal Plane Alignment of the Knee (CPAK) type. The average follow-up was 5.6 years (range, five to 7.5).

RESULTS

At the final follow-up, KOOS-JR scores averaged 84.0. Knee Society scores averaged 94. Flexion averaged 116°. There were seven manipulations (2.9%), one patella fracture, and no deep infections. There were seven knees (2.9%) revised (three for flexion instability, one for pain, one for femoral fibrous ingrowth, one for distal femur fracture, and one for arthrofibrosis). At 5 years, survivorship free from aseptic loosening was 99.6%. Change in CPAK type did not correlate with final KOOS-JR, pain, University of California Los Angeles activity score, or satisfaction scores.

CONCLUSIONS

Cementless TKA using this conforming design has provided excellent clinical results out to 5 years. Once initial component stability is achieved, the UC nature of this articulation does not appear to adversely influence the durability of implant fixation, regardless of whether the CPAK type was changed.

Mobile medial pivot (lateral slide)-type total knee arthroplasty exhibited different motion patterns between under anaesthesia and weight-bearing condition

PURPOSE

Total knee arthroplasty (TKA), which has medial pivot and mobile-bearing mechanisms, has been developed and clinically used. However, the in vivo dynamic kinematics of the mobile medial pivot-type TKA (MMPTKA) is unclear. This study analysed the in vivo kinematics of MMPTKA in weight-bearing and nonweight-bearing conditions.

METHODS

The study included 10 knees that underwent primary TKA using MMPTKA. After TKA, lateral view radiographs of the knee in full extension, 90° of flexion and passive full flexion were taken under general anaesthesia in the nonweight-bearing condition. At least 6 months postoperatively, knee motion during squatting from a weight-bearing standing position was observed using a flat-panel detector and analysed using the three-dimensional-to-two-dimensional image registration technique.

RESULTS

Under anaesthesia: in passive full flexion, the anteroposterior (AP) locations of the femoral component's medial and lateral distal points were 10.2 and 16.0 mm posterior, and the rotational angles of the femoral component's X-axis (FCX) and insert were 8.1° external rotation and 18.5° internal rotation to full extension, respectively. Squatting: the AP translations of the femoral component's medial and lateral most distal points were 2.2 and 6.4 mm, and the rotational angles of the FCX and insert were 5.7° and 1.6° external rotation, respectively. Significant differences were observed in the AP translation of the femoral component's medial and lateral most distal points and changes in the insert's rotational angle when comparing under anaesthesia and squatting.

CONCLUSIONS

The kinematics of the insert in MMPTKA was significantly influenced by loading and muscle contraction. The femoral component exhibited substantial external rotation and posterior translation under anaesthesia, which may contribute to achieving an optimal range of motion. The insert remained relatively stable during squatting and minimal rotation was observed, indicating good stability. MMPTKA was expected to demonstrate rational kinematics by incorporating mobile and medial pivot mechanisms.

LEVEL OF EVIDENCE

Level IV, prospective biomechanical case series study.