- The research team found no significant differences between operated bicruciate-retaining total knees and contralateral knees in anterior-posterior translation or varus rotation during the stance phase
- However, sagittal plane motion and tibiofemoral articular contact characteristics, including pivoting patterns, differed significantly in bicruciate-retaining total knee arthroplasty
- The difference in femoral external/internal rotation observed in this study may lead to altered gait biomechanics that affect joint loading and associated muscle loading
Patient dissatisfaction with conventional total knee arthroplasty (TKA) may be due to abnormal knee kinematics and paradoxical anterior femoral translation. Several studies have demonstrated the recently introduced bicruciate-retaining total knee arthroplasty (BCR TKA) has the potential restore knee in vivo kinematics as it preserves both anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL).
Young-Min Kwon, MD, PhD, program director of the Adult Reconstructive Surgery Fellowship Program and director of the Bioengineering Laboratory, and colleagues in the Massachusetts General Hospital Department of Orthopaedic Surgery became the first to evaluate in vivo kinematics in patients with currently available BCR TKA design for factors that affect clinical outcomes and wear performance during functional activities.
In the Journal of Orthopaedic Research, the research team found no significant differences between operated knees and contralateral knees in anterior-posterior translation or varus rotation during the stance phase. However, sagittal plane motion and tibiofemoral articular contact characteristics, including pivoting patterns, were not restored by BCR TKA.
Study Participants and Design
The researchers evaluated patients who underwent unilateral BCR TKA for degenerative osteoarthritis. A single surgeon performed all procedures using a standard medial parapatellar approach. The in vivo kinematics of the operated and healthy knees were analyzed with a dual fluoroscopic imaging tracking system in the Bioengineering Laboratory while patients performed functional activities including gait. Kinematics in healthy knee controls from previous research were also used for comparison.
Kinematics During Gait
Compared with the healthy knee, the operated knee did not demonstrate any difference with respect to varus/valgus rotation or anterior-posterior translations. However, operated knees showed smaller external rotation range of motion during gait.
There was considerable variation in knee internal-external rotation, and 23% of patients exhibited external tibial rotation.
Medial Lowest Point
- In the stance phase, the average medial lowest point trajectory of the operated knee ranged from −4 to 1 mm in the anterior-posterior direction, whereas the healthy knee ranged from 1.5 to 5 mm
Lateral Condylar Lowest Point
- The average lateral condylar lowest point trajectory of the operated knee during gait demonstrated less translation than the medial condylar lowest point along the anterior-posterior axis and remained entirely on the posterior part of the insert
- However, the average lateral condylar lowest point trajectory of the healthy knee during the stance phase ranged from −0.7 to −0.9 mm in the anterior-posterior direction
Medial Condylar Lowest Point
- The medial condylar lowest point of the operated knee moved backward in loading response, forward in mid- and terminal stance, backward in preswing, forward in acceleration swing and backward in deceleration swing
- In contrast, the medial condylar lowest point of the normal healthy knee moved forward in loading response, backward in midstance and forward in terminal stance and preswing
- In the operated knee, the average pivoting point was located in the lateral compartment in the stance phase and moved to the medial compartment in the swing phase
- In the healthy knee, the average pivoting point was located in the lateral compartment and moved in the lateral medial direction during the stance phase
- Lateral pivoting was observed during the loading response, terminal stance and preswing phase in 60% of subjects; medial pivoting patterns were observed in the others
Comparisons with the Literature on Healthy Knees
As the average pivoting of the operated knee occurred in the opposite direction to the healthy knee, this research illustrates that BCR TKA does not restore the tibiofemoral contact kinematics of the normal knee. In addition, BCR TKA did not restore native tibial rotation and femoral rollback characteristics during gait, compared with several studies of cruciate-retaining and posterior-stabilized TKA systems.
The lateral pivoting pattern observed in 60% of patients during the stance phase is also inconsistent with published reports on healthy knees. In addition, this pattern does not necessarily indicate restoration of physiologic gait patterns because operated knees demonstrated external femoral rotation while healthy knees exhibited internal femoral rotation. In fact, the difference in femoral external/internal rotation may lead to altered gait biomechanics that affect joint loading and associated muscle loading.
Therefore, as sagittal plane motion and tibiofemoral articular contact characteristics including pivoting patterns were not fully restored in BCR TKA patients during gait, the study finding suggests that BCR TKA does not restore native tibiofemoral articular contact kinematics.
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