gms | German Medical Science

Contemporary total knee arthroplasty implants provide reliable pain relief and restoration of moderate levels of function for patients suffering from severe arthritis and degeneration of the knee. However, regaining normal levels of functional strength and range of motion remain significant challenges for the patient, surgeon and physical therapist. Many studies have demonstrated a link between prosthesis design and patient function [1], [2], [3] and newer designs attempt to incorporate these findings to improve patient function.

Based on in vivo kinematic studies and retrieved implant analysis, the 3D Knee™ prosthesis (Encored Medical, Austin, TX) was designed with the goal of providing better patient strength, improved range of motion, and enhanced durability. The 3D Knee™ is a fixed-bearing total knee prosthesis designed to allow full retention of the posterior cruciate ligament. The implants incorporate a hemispherical lateral condyle and tibial articulation to provide definitive anteroposterior translational control while freely allowing endo-exorotation. The femoral component has a wider medial condyle to provide greater contact area, and the posterior condyles are shaped to provide maximum posterior condylar offset late in the flexion are to enhance flexion.

The purpose of this evaluation was to quantify the early clinical, gait, and kinematic performance of patients receiving the 3D Knee in a single-surgeon, consecutive case series.

Clinical - Data were gathered from the clinical records for all patients seen in the clinic at least 12 months after surgery.

Gait Laboratory - Six patients with unilateral 3D Knee™ arthroplasty were studied in the gait laboratory using motion analysis, force platforms and surface electromyography. The patients were studied during free-speed walking and stepping onto and over a 20cm box. Full body kinematics and lower extremity kinetics were analyzed.

Fluoroscopic - Ten patients with 15 3D Knee™ arthroplasties were studied during maximum kneeling activities. Lateral fluoroscopic images were acquired and the 3D position and orientation of the components was determined using shape matching techniques.

Clinical Results - 31 knees had been seen at minimum 12 months. One knee had been revised due to infection following lumbar laminectomy and one knee had been revised due to severe adhesive capsulitis secondary to diabetic episodes. Average pre-op Knee Society Knee/Function scores were 45±15/48±13 and improved to 94±10/92±13 at the 12 month clinic visit. Range of motion increased from an average of 104°±9° pre-op to 118°±11 at 12 months post-op. 87% of knees had greater flexion at twelve months post-op, and 55% of knees had greater than 120° flexion.

Gai Laboratory Results - There were no statistically significant differences in knee kinematics during the gait or step-over activities comparing the normal and operated knees. Peak knee moments were 84% of normal for the operated knees during the step-over activity. The operated knees exhibited reduced lateral hamstrings acitivity during the ascent phase of the step-over acitivity.

Fluoroscopic Results - Maximum skeletal flexion averaged 134°±11° (116°-155°) for the kneeling activity. Tibial endorotation averaged 11°±4° (3°-18°), and condylar rollback averaged 3mm medially and 11mm laterally.

Early results with this fixed-bearing posterior cruciate retaining knee prosthesis are encouraging. Clinical scores and complication rates are equivalent or better than experienced with previous devices in the same clinic. Patient strength during demanding dynamic activities is equivalent to the strongest knee arthoplasties reported in the literature [2], and significantly better than values reported for other prostheses [4]. Maximum flexion in this PCL retaining TKA is equivalent to the best performing posterior stabilized knee arthroplasties in North American patients [5]. These clinical, gait, and fluoroscopic studies are ongoing to provide mild-term outcomes for patients with a prosthesis designed to better control knee kinematics to achieve enhanced functional performance.

These studies were sponsored by The BioMotion Foundation with grant support from Encore Medical, Inc.