No abstract

Abnormal patellar tracking results in patello-femoral (PF) joint disorders and frequently in failure of total knee arthroplasty (TKA). It is fundamental to assess this tracking intra-operatively, i.e. since the implantation of the femoral and tibial components. The aim of this study was to assess the feasibility of three-dimensional anatomical-based patellar tracking intra-operatively in standard TKA. A surgical navigation system was utilized to test the new technique in-vitro. An original tracking device and a reference frame were designed and an articular convention for the description of PF joint kinematics was adopted. Six fresh-frozen amputated legs were analyzed with the new technique. Landmark digitations were used to define anatomical reference frames for the femur, tibia, and patella. Five trials of passive flexion were performed with 100 N force on the quadriceps, before and after standard knee arthroplasty. Patellar flexion, tilt, rotation and shift were calculated in addition to standard tibio-femoral (TF) joint kinematics. An intra-specimen repeatable path of motion over repetitions and a coupled path of motion throughout the flexion-extension cycle were observed in all intact knees, both at the TF and PF joints. Replication of the original PF motion in the intact knee was not fully accomplished in the replaced knee. These results revealed the feasibility and the necessity of patellar tracking during TKA. By monitoring intra-operatively also the PF kinematics, the surgeon has a more complete prediction of the performance of the final implant and therefore a valuable support for the most critical surgical decisions.

Prognostic studies-retrospective study, Level II.

After total knee arthroplasty, changes in articular surface geometry, soft tissue treatment, and component alignment can alter normal lower limb function. The guided motion bi-cruciate substituting prosthesis was designed specifically to restore physiological knee joint motion. We determined whether this design could in vivo normal kinematics and kinetics, not only at the replaced knee, but also throughout both lower limbs. Sixteen patients (4 male, 12 female, mean age of 68.2 years with a range from 58 to 79 years) with primary knee osteoarthritis were implanted with the bi-cruciate substituting prosthesis. At 6-month follow-up, knee joint kinematics was assessed by video-fluoroscopy during stair-climbing, chair-rising/sitting, and step-up/down. Lower limb overall function was also assessed on the same day by standard gait analysis with simultaneous electromyography during level walking. By video-fluoroscopy, mean anteroposterior translations between femoral and tibial components during the three motor tasks were 9.7 AE 3.0, 10 AE 2.6, and 6.9 AE 3.5 mm on the medial compartment, and 14.3 AE 3.5, 18.5 AE 3.0, and 13.9 AE 3.8 mm on the lateral compartment, respectively. Axial rotation ranged from 5.68 to 26.28. Gait analysis revealed restoration of nearly normal walking patterns in most patients. This rare combination of measurements, i.e., accurate rotation-translation at the replaced knee and complete locomotion patterns at both lower limb joints, suggested that bi-cruciate substituting arthroplasty can restore physiological knee motion and normal overall function. ß

In-depth comprehension of human joint function requires complex mathematical models, which are particularly necessary in applications of prosthesis design and surgical planning. Kinematic models of the knee joint, based on one-degree-of-freedom equivalent mechanisms, have been proposed to replicate the passive relative motion between the femur and tibia, i.e., the joint motion in virtually unloaded conditions. In the mechanisms analysed in the present work, some fibres within the anterior and posterior cruciate and medial collateral ligaments were taken as isometric during passive motion, and articulating surfaces as rigid. The shapes of these surfaces were described with increasing anatomical accuracy, i.e. from planar to spherical and general geometry, which consequently led to models with increasing complexity. Quantitative comparison of the results obtained from three models, featuring an increasingly accurate approximation of the articulating surfaces, was performed by using experimental measurements of joint motion and anatomical structure geometries of four lower-limb specimens. Corresponding computer simulations of joint motion were obtained from the different models. The results revealed a good replication of the original experimental motion by all models, although the simulations also showed that a limit exists beyond which description of the knee passive motion does not benefit considerably from further approximation of the articular surfaces.