Summary

Patellofemoral osteoarthritis is not a contraindication for doing femorotibial UKA, and it has to be treated in a systematic and stagged manner according to its severity.

Abstract

Introduction

Associated patellofemoral osteoarthritis was classically considered a contraindication for doing unicompartmental knee replacement (UKA) as treatment of femorotibial osteoarthritis, but nowadays this is discussed. The purpose of this article is to examine the functional results, complications and survivorship at midterm of medial or lateral UKA as treatment of femorotibial osteoarthritis, regardless the presence of clinical or radiographic signs of patellofemoral osteoarthritis.

Material And Methods

Retrospective comparative report of patients operated with medial or lateral UKA, despite of the presence of patellofemoral osteoarthritis, with a minimum follow up of 1 year. The patients were classified in groups depending on the patellofemoral osteoarthritis severity valued intraoperatively according to Outerbridge classification. We evaluate the clinical and functional results using the KSS score 2011. In all cases, the patellofemoral osteoarthritis was treated in a systematic and stagged manner with chondral shaving, microfractures, lateral release or lateral patellar facetectomy. Rate of complications and prosthesis survivorship were studied. The ANOVA test and the Kruskal-Wallis test were used with

Significance

level of 5%.

Results

We identified 110 UKA, 81 medial UKA (73.6%) and 29 lateral UKA (26.4%), with a mean follow up of 6 years (1-19.5). Intraoperatively 22 knees (20%) had patellofemoral chondropathy grade 2 according Outerbridge, 59 (53.6%) grade 3 and 29 (26.4%) grade 4. A statistically significant increase in KSS and range of motion was observed compared to the preoperative in the 3 groups. The clinical KSS and flexion contracture improvement were not different between the Outerbridge groups (p=0.07 and p=0.37 respectively). At least one Outerbridge group was different to the others with respect to functional improvement of KSS and maximal flexion (p=0.04 and p=0.04 respectively). The clinical and functional parameters evaluated were not negatively affected by the degree of patellofemoral osteoarthritis. Three cases needed revision (2.7%) because of tibial component aseptic loosening and none were caused by patellofemoral symptoms. Five years survivorship was 100% for 64 arthroplasties, 97% at 7 years for 31 arthroplasties, 93% at 9 years for 15 arthroplasties and 89% at 12 years for 9 arthroplasties.


Discusion: The secondary or associated patellofemoral osteoarthritis occurs in the context of a primary medial or lateral femorotibial osteoarthritis, in which the femorotibial malalignment leads to a medial or lateral patellar hyperpressure. It is usually slightly incapacitating, the pain is internal or external femorotibial and there is clinical-imaging dissociation associated with coronal misalignment. The treatment of the femorotibial osteoarthritis with UKA restores the primitive varus or valgus alignment and leads to clinical upgrade, because patellar alignment improves. Patellofemoral osteoarthritis is asymptomatic in an important proportion of patients, as it is reported in different studies, including our results.

Conclusion

Medial or lateral UKA as treatment for femorotibial osteoarthritis, regardless patellofemoral osteoarthritis, is a safe procedure, with low complication rates and excellent midterm results. Patellofemoral osteoarthritis is not a contraindication for doing UKA, and it has to be treated in a systematic and stagged manner according to its severity.
Proper patient selection, rigorous surgical technique, and trained surgeons are essential to obtain reproducible results.