Background

Partial knee arthroplasty (PKA) is now accepted by an increasing proportion of clinicians as the treatment of choice for severe medial osteoarthritis. PKA can achieve superior functional outcomes with reduced surgical risk compared to total knee arthroplasty (TKA) with revision rates for the best performing fixed-bearing implants approaching those of TKA. Many surgeons remain reluctant to expand their selection criteria, limiting the substantial advantages of PKA to a small proportion of their patients. This study (part-supported by The European Knee Society) was designed to prospectively assess clinical outcomes from a large consecutive series of fixed-bearing medial PKA with broad selection criteria including those with severe patello-femoral osteoarthritis (PFJOA)

Study Design & Methods
We prospectively studied 240 consecutive, fixed-bearing PKA (Persona Partial Knee, Zimmer Biomet) cases. Broad selection criteria included patients with PFJOA providing it was not significantly symptomatic. Patients diagnosed with severe lateral PFJOA were excluded. Pre and post-operative (1 and 2-year) data including Oxford Knee Score (OKS), KOOS PS, UCLA, Forgotten Joint Score (FJS-12) and patient satisfaction was collected. Intra-operative assessment of the severity and site of PFJOA was recorded.

Results

From February 2017, 240 fixed-bearing PKA were performed in 229 consecutive patients. Mean age at time of surgery was 65.8yrs (range 41-89), mean BMI 29.2 (range 20 - 47).
Mean OKS (0-48) increased from 24.8 (pre-op) to 43.7 and 44.8 at one and two years respectively. Mean KOOS PS, UCLA (1-10) and FJS-12 all showed substantial improvements from 55.2, 4.8 and 15.2 pre-operatively to 83.0, 6.5 and 76.9 (one year) and 84.4, 6.5 and 82.5 (two years). 96.8% were satisfied with their PKA at 2 years and only two patients have required a revision procedure (tibial loosening and lateral OA respectively) - mean 3 years follow-up.
Grade III or IV osteoarthritis of the medial, central and lateral PFJ was observed in 100, 87 and 28 cases respectively with approximately 60% patients having severe PFJOA in some part of the joint. No significant difference was demonstrated in 1 or 2-year post-operative outcomes with comparison of cases demonstrating nil significant PFJOA vs those with grade III / IV PFJOA involving medial, central or even lateral facets.

Conclusions

Excellent functional outcomes are confirmed with fixed-bearing PKA for the treatment of severe medial compartmental arthritis. Whilst the patella-femoral joint cannot be completely ignored, our study supports the use of isolated fixed-bearing PKA in patients with severe PFJOA and such patients should be included in the selection criteria although severe lateral PFJOA remains a relative contraindication. Extended selection criteria can increase the proportion of patients able to take advantage of the substantial benefits of PKA by 60-70% in most surgeon's practice.