The effect of the preoperative bone quality on the fixation of the tibial component in total knee arthroplasty

The relationship between the preoperative level of bone mineral density (BMD) in the proximal tibia and the migration of the tibial component 2 years after total knee arthroplasty was investigated in 28 knees with osteoarthrosis (10 men, 18 women; mean age, 71). Sixteen components were inserted uncemented and 12 were cemented. Mean average BMD measured 10 mm below the joint level was 0.81 g/cm² (range, 0.15-1.33 g/cm²) and was not influenced by gender, age, weight, or preoperative alignment. Local BMD measured in the medial and lateral condyles was influenced by the preoperative alignment. In knees with uncemented fixation, most of the tibial component migration (ie, subsidence and lift-off) occurred within the first months, and thereafter the implants seemed to stabilize. In the uncemented implants, there was a significant relationship between average BMD and migration (regression analysis with curve-fit estimation). The least migration was seen when average BMD was 0.6 to 1.0 g/cm². Beyond this range, increased subsidence and lift-off was seen. There was no relationship between BMD and the change in maximum migration between 1 and 2 years postoperatively, however. In knees with cemented fixation, subsidence was initially small but continuously increasing. There were no relationships between BMD and subsidence, lift-off, and maximum migration, indicating that bone-cement can compensate for variations in bone quality, at least in the early period after operation.