ACL Deficiency Does Not Reduce the Clinical Effectiveness of Fixed-bearing Partial Knee Arthroplasty

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. ACL deficiency has traditionally been classified as a contra-indication to PKA largely due to concerns of dislocation with mobile-bearing implants. Our experience (of 20 years fixed-bearing PKA) is of excellent functional outcomes and implant longevity in patients with ACL deficiency who no longer experience functional instability. This study (part-supported by The European Knee Society) compares the functional performance of a fixed-bearing PKA in patients with ACL deficiency compared to their ACL-intact counterparts in a large prospective study.

Study Design & Methods
Commencing February 2017, 240 fixed-bearing PKA (Persona Partial Knee, Zimmer Biomet) were performed in 229 consecutive patients with pre-operative, one and two-year assessment of clinical/functional scores documented. Outcome measures included, OKS, KOOS PS, UCLA activity, FJS-12 and patient satisfaction. Scores from patients with ACL-deficient knees (confirmed at surgery) were compared with those with an intact ACL.

Results

Commencing February 2017, 240 fixed-bearing PKA (Persona Partial Knee, Zimmer Biomet) 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). Excellent clinical outcomes were achieved: Mean OKS, KOOS, UCLA and FJS all improved substantially from 24.8, 55.2, 4.8 & 15.2 pre operatively to 43.7, 83, 6.5 & 76.9 at 1 year and 44.8, 84, 6.5 & 82.5 at 2 years.

ACL deficiency was recorded in 22 knees (9%) but there was no significant difference in mean age (65.9yrs) nor BMI (29.9) compared to ACL-intact knees. All outcome scores for the ACL-deficient knees were higher at two years compared to ACL-intact (OKS – 46.7, KOOS PS – 93.4, UCLA 6.9, FJS-12 – 92.1) with KOOS PS and FJS-12 reaching statistical significance p<0.04, unpaired T test). All ACL-deficient patients declared themselves satisfied with their surgery at minimum 2yrs follow-up with no revisions compared to 96.6% and 2 revisions in the ACL-intact knees.

Conclusions

Excellent functional outcomes are confirmed with fixed-bearing PKA for the treatment of severe medial compartmental arthritis. Our study supports the use of isolated fixed-bearing PKA in patients with functionally-stable, ACL deficiency and suggests these patients may achieve greater satisfaction with their surgery. Further evaluation is required to confirm expected long-term implant longevity in these patients.