We describe a case of middle-aged woman who had undergone a total knee arthroplasty with a Zimmer NexGen Legacy Constrained Condylar Knee (LCCK) (Warsaw, IN). Nine years later, an atraumatic failure of the locking mechanism of the polyethylene insert and the tibial base plate occurred. There was no evidence of loosening of either tibial or femoral components. The patient underwent revision surgery with reinsertion of another tibial base plate and locking mechanism.
The additional constraint has shown to lead to increased stresses on the cement-implant interfaces as well as increase in micromotion between the insert and the tibial base plate that may cause backside wear and subsequent osteolysis.16 Some constrained designs use supplemental screw fixation to decrease micromotion. Only a few cases have reported on the disengagement of the locking screw from the tibial insert causing mechanical symptoms.9 The exact mechanism of this unusual complication has not been fully elucidated. Rapuri et al.9 hypothesized that counterclockwise torque which is created between the insert and the tibial tray due to the rotation of the femur on the tibia can cause disengagement. The authors postulated that micromotion at the backside of the insert on the baseplate likely allows this force to be transferred to the screw, and, over many cycles, may lead to screw loosening.
loosening of the knee prosthesis ..
Basics Description Skeletal scintigraphy is a nuclear medicine imaging method for bone disease. Advantages: High sensitivity for early detection of disease Whole body survey Disadvantage: Limited specificity Diagnosis Signs and Symptoms Indications Whole body skeletal scintigraphy: Primary bone tumors Osteomyelitis Joint prosthesis pain Occult fractures Stress fractures and shin splints Spondylosis Reflex sympathetic dystrophy […]
The distribution of activity around the right knee prosthesis ..
Another experimental hypothesis is that different material properties of polyethylene may be subject to creep under loading and, thus, the locking screw preload decreases with time, reducing the torque needed to loosen the locking screw.17 The major concern of disengagement of a modular object in knee arthroplasty is the development of metallic wear, fretting and corrosion that ultimately could lead to a severe inflammatory response causing arthrofibrosis or osteolysis with the potential need for early intervention.
prosthetic infection from loosening in hip or knee ..
In our patient, the LCCK was implanted for severe deformity as a primary total knee arthroplasty. It remained asymptomatic for nine years without signs of radiographic osteolysis. It suddenly became symptomatic once the locking screw migrated into the knee joint. The disengagement process was probably the cause for the severe metallosis in the knee synovial tissue over an extended period. In contrast to the case reports by Rapuri et al.,9 our patient did not experience a traumatic event that may have incited the disengagement. The evidence of backside wear of the tibial polyethylene supports the theory of micromotion at the backside of the insert translating into slow loosening of the screw-thread interface. Therefore, it is important to monitor for any signs of screw loosening to prevent premature wear of the tibial insert or osteolysis around the components on an annual basis.
loosening around the prosthesis.
The total knee implant is made up of four components: the femoral component, the tibial component, the patellar component and an intermediary plastic component which provides a slick surface between the femur and the tibia (figures 1 and 2).
The stability of the implant is ensured by the ligaments, which are like ribbons of varying elasticity connecting the femur to the tibia. The functioning of the implant is ensured by all the tendons connecting the muscles to the bone, particularly the extensor mechanism formed by the quadriceps, the patella and the patellar tendon.
Over time, the intermediary component wears and the fixation of the implant to the bone deteriorates. Little by little the cement between the implant and the bone deteriorates. This leads to the progressive loosening of the implant resulting in mobility in relation to the bone (figures 3 and 4). Causes other than natural wear, such as a chronic infection or poor positioning of the implant, can result in this developing more rapidly after the operation.
The loosening will cause pain, limping, even a deformation of the limb, as well as stiffness, progressively decreasing the functional possibilities of the implant.