New Cruciate-Retaining TKA Implant Does Not Fully Restore In Vivo Articular Contact Kinematics During Strenuous Activities

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A recently introduced cruciate-retaining (CR) implant for total knee arthroplasty (TKA) has concave medial and convex lateral tibial polyethylene bearing components designed to improve functional outcomes.

However, a study at the Bioengineering Laboratory in Massachusetts General Hospital's Department of Orthopaedic Surgery showed this system does not fully restore native knee kinematics during strenuous functional daily activities. The details are published in Knee Surgery, Sports Traumatology, Arthroscopy by Christian Klemt, PhD, research fellow, Young-Min Kwon, MD, PhD, director of the Bioengineering Lab and program director of the Adult Reconstructive Surgery Fellowship Program, and colleagues.

Study Cohort

The study evaluated in vivo kinematics in patients who received the recently introduced cruciate-retaining TKA implant with asymmetric tibial polyethylene bearing geometry implant during TKA. After an average follow-up time of 24.5 months (range, 13–42), all patients had a satisfactory range of motion on knee flexion (average, 98.4°). Radiographs showed no implant malalignment.

In the contralateral knee, all patients had an intact knee ligament and meniscal condition and were without radiographic signs of osteoarthritis.

Study Methods

Using computed tomography, the researchers generated three-dimensional models of the operated knee (with implant) and the contralateral knee of each patient. While being imaged with dynamic fluoroscopy, the patients performed sequential sit-to-stand movements, step-ups and single-leg deep lunges.

The fluoroscopic images and three-dimensional models were imported into a customized software program that determined the in vivo position of each TKA component while patients performed strenuous flexion activities.

Results

The following are the results for the operated knee compared with the contralateral knee:

Sit-to-Stand

• Contact excursions of the lateral condyle were significantly more anteriorly located from 9° to 40° of flexion and from 76° to 90°
• Contact excursions of the medial condyle were significantly more anteriorly located throughout the entire range of flexion angles
• Lateral condyle posterior rollback was not fully restored (9.1 vs. 12.9 mm)
• Lateral pivoting patterns were observed in 80% of patients

Step-ups

• Contact excursions of the lateral condyle were significantly more anteriorly located from 9° to 26° of flexion and from 34° to 51°
• Femoral external rotation was significantly greater
• Lateral pivoting patterns were observed in 73% of patients

Deep Lunges

• Contact excursions of the medial condyle were significantly more anteriorly located throughout the entire range of flexion angles
• Contact excursions of the lateral condyle were significantly less laterally located from 36° to 44° of flexion
• Lateral pivoting patterns were observed in 69% of patients

Counseling Patients

Although in vivo contact kinematics, such as lateral femoral condyle rollback and lateral pivoting patterns, more closely approximated the kinematics of the native knee, the contemporary asymmetrical tibial polyethylene geometry TKA design evaluated in this study did not fully replicate healthy knee contact kinematics during strenuous functional daily activities. These results will be useful for perioperative counseling of patients who are contemplating undergoing, or have undergone, TKA with this specific system.

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Learn more about the Bioengineering Lab at Mass General

Refer a patient to the Mass General Center for Hip & Knee Replacement