Ligament releases are necessary for contemporary non-conforming femoral-tibial articulations. Most total knee arthroplasty prostheses are designed to be non-conforming at the articulation between the femoral and tibial components. This design is chosen on the arthroplasty principle that “constraint causes loosening” and conforming surfaces have been considered constrained. To provide stability the ligaments are adjusted so that tension in the ligament can provide stability for the total knee replacement. Ligament releases are NOT necessary for contemporary conforming femoral-tibial articulations. Through the majority of the range of motion, the normal human knee is not stabilised by ligament tension. Rather, it is the geometrical conformity of the femur and tibia, especially on the medial side, that provides stability. The ligaments are present and ready to restrain the knee from excess varus-valgus or anterior-posterior loads. In a knee design that is congruent, ligaments may be left intact as in the normal knee, ready to provide restraint but not necessarily to provide stability except when excess loads are applied to the knee. When designing and using the ADVANCE Medial Pivot total knee, the author has left ligaments in the toe-region of the stress-strain curve rather than releasing and tensioning the ligaments. Patient satisfaction survey data at routine follow-up visits for patients at 7–15 years after arthroplasty with this type of reconstruction indicate high satisfaction despite medial and lateral opening (on valgus and varus stress) that would be considered “mid-flexion instability” for non-conforming joints that require careful ligament releases and tensioning.
Background. Patellofemoral complications have dwindled with
Medial pivot (MP) total knee arthroplasties (TKAs) were designed to mimic native knee kinematics with their deep medial congruent fitting of the tibia to the femur almost like a ball-on-socket, and a flat lateral part. GMK Sphere is a novel MP implant. Our primary aim was to study the migration pattern of the tibial tray of this TKA. A total of 31 patients were recruited to this single-group radiostereometric analysis (RSA) study and received a medial pivot GMK Sphere TKA. The distributions of male patients versus female patients and right versus left knees were 21:10 and 17:14, respectively. Mean BMI was 29 kg/m2 (95% confidence interval (CI) 27 to 30) and mean age at surgery was 63 years (95% CI 61 to 66). Maximum total point motions (MTPMs), medial, proximal, and anterior translations and transversal, internal, and varus rotations were calculated at three, 12, and 24 months. Patient-reported outcome measure data were also retrieved.Aims
Methods
Restoring the overall mechanical alignment to neutral has been the gold standard since the 1970s and remains the current standard of knee arthroplasty today. Recently, there has been renewed interest in alternative alignment goals that place implants in a more “physiologic” position with the hope of improving clinical outcomes. Anywhere from 10 – 20% of patients are dissatisfied after knee replacement surgery and while the cause is multifactorial, some believe that it is related to changing native alignment and an oblique joint line (the concept of constitutional varus) to a single target of mechanical neutral alignment. In addition, recent studies have challenged the long held belief that total knee placed outside the classic “safe zone” of +/− 3 degrees increases the risk of mechanical failure which theoretically supports investigating alternative, more patient specific, alignment targets. From a biomechanical, implant retrieval, and clinical outcomes perspective, mechanical alignment should remain the gold standard for TKA. Varus tibias regardless of overall alignment pattern show increased polyethylene wear and varus loading increases the risk of posteromedial collapse. While recently questioned, the evidence states that alignment does matter. When you combine