Influence of the anterior notch in mobile-bearing UKA on patellofemoral radiotracer uptake and clinical outcome

BACKGROUND: Previous studies reported that in partial knee arthroplasty smooth transitions to the remaining native parts of the knee are important. However, in mobile-bearing unicondylar knee arthroplasty (UKA) it is mandatory to create an anterior osteochondral notch adjacent to the femoral component to get clearance for the anterior lip of the bearing in full knee extension. This notch is, however, part of the femoral trochlea. It was the aim of the study to test for a potential association between a) an obligatory anterior notch in mobile-bearing UKA located at the margin of the medial aspect of the femoral trochlea and b) postoperative patellofemoral joint (PFJ) bone remodelling and discomfort. METHODS: In patients who underwent routine mobile-bearing UKA (11 male, 13 female; 64.5 years / IQR 14) the following parameters were prospectively determined i) size of the surgically created anterior notch, ii) knee score sensitive to PFJ disorders, iii) bone remodelling in the PFJ (radiotracer uptake in SPECT-CT). RESULTS: Notch size was not correlated with radiotracer uptake at the PFJ. Similarly, no significant correlations were observed between radiotracer uptake (patella or trochleocondylar junction) and knee scores (KOOS or Kujala Score). Significant positive correlations were found between notch size and knee scores. CONCLUSIONS: From the findings made in our study it is concluded that a larger size of the anterior notch in mobile-bearing medial Oxford UKA is not associated with increased osteochondral remodelling processes at the patella or the trochleocondylar junction. Neither is a larger sized notch associated with worse clinical PFJ outcome. Surprisingly, a larger notch was even associated with superior clinical outcome. The exact mechanism for this contraintuitive finding remains unclear but may be the basis for future research. TRIAL REGISTRATION: The study is registered in a public trials registry. Link: (9/12/2017) ClinicalTrials.gov. NCT01407042; Date of registration: July, 26, 2011.