|Abstract / Summary
Medial osteoarthritis (OA) of the knee can be treated with a medial unicompartmental knee
arthroplasty (UKA). UKA offers a good clinical outcome and compared to total knee
arthroplasty (TKA) fewer complications. Nevertheless, the survival rate of UKA is lower than
the survival rate of TKA. The overall aim of this dissertation was therefore to identify aspects
that have an influence on the selection, treatment, and outcome of patients with medial
tibiofemoral (TF) OA treated with a medial UKA.
One of the selection criteria for a medial UKA is that there is full-cartilage thickness in the
lateral TF joint. On regular weight-bearing radiographs, the lateral TF compartment is
unloaded, and cartilage thickness cannot be sufficiently evaluated. As a supplement to weightbearing
radiographs, valgus-stress radiographs can be taken to evaluate the lateral TF
In Study I, we evaluated the reproducibility of valgus-stress radiography with the Telos stress
device for assessment of lateral TF OA. We found that the assessment of OA in the lateral TF
compartment was most reliable when based on measurement of the joint space width (JSW),
showing an almost perfect intra-rater reliability and a substantial inter-rater reliability.
Early implant migration is a predictor for late implant loosening, which is the primary cause for
revision surgery. Migration can be measured with radiostereometric analysis (RSA).
In Studies II and III, we evaluated migration of a fixed-bearing (FB) UKA and a mobilebearing
(MB) UKA with RSA. Due to design features of the tibial component and the
polyethylene bearing, the loading and bone-implant fixation of FB and MB UKAs may be
different, and the implants may migrate differently. We showed that fixation was similar and
good with both the FB UKA and the MB UKA.
A low mid- to long-term (5- to 10-year) revision rate can therefore be expected for both
implants. However, in Study II, continuous migration of the tibial component of the FB UKA
was found in 30% of cases. Continuous migration poses a risk for loosening and consequently
revision. This was not found in Study III. Patients in the FB UKA and the MB UKA group
showed similar improvements in clinical outcome scores.
Bone mineral density (BMD) may be of importance in fixation of orthopedic implants and
implant survival. There are only a few studies comparing tibial component migration and periprosthetic
BMD, and they show contradictory results.
In Study IV, we investigated the influence of systemic and peri-prosthetic BMD on migration
of the tibial component of a cemented medial UKA. During the first 12 months after surgery, a
similar reduction of the peri-prosthetic BMD was seen in both the operated and the non2
operated knee. This suggests that a natural reduction in BMD due to aging is partly responsible
for the BMD loss. Tibial component migration (MTPM) was associated with neither preoperative
systemic BMD nor with post-operative change in peri-prosthetic BMD, suggesting
that long-term fixation is not influenced by BMD.
The findings of this thesis add new knowledge in the treatment of patients with medial OA of
the knee. The thesis emphasizes on aspects of influence in patient selection, treatment, and
outcome of treatment with a medial UKA.