Chronic infection of unicompartmental knee arthroplasty: one-stage conversion to total knee arthroplasty

BACKGROUND

The main reasons for revision of unicompartmental knee arthroplasty (UKA) are loosening, wear, extension of osteoarthritis to another compartment, and infection. There have been no studies of the management of infected UKA, whose incidence varies from 0.2% to 1%. Our objective was to describe infection-related and mechanical outcomes of chronic UKA infection managed by one-stage conversion to total knee arthroplasty (TKA).

PATIENTS AND METHODS

Consecutive patients with chronic UKA infection managed by one-stage conversion to TKA between January 2003 and December 2010 were included in a retrospective single-center study. All patients also received appropriate dual antibiotic therapy intravenously for 6 weeks then orally for 6 additional weeks.

RESULTS

During the study period, among 233 cases of infected knee arthroplasty managed at our center, 9 met the study inclusion criteria. The UKA was medial in 6 patients, lateral in 2, and patellofemoral in 1. Median age was 67 years (range, 36-83 years) and median infection duration was 9months. In 5 patients, previous treatment with synovectomy, joint lavage, and antibiotics had failed. The following bacteria were identified: oxacillin-susceptible Staphylococci, n=6 (S. epidermidis, n=4; S. capitis, n=1; and S. lugdunensis, n=1); nutritionally deficient Streptococcus, n=1; Enterococcus durans, n=1; and Escherichia coli, n=1. Median follow-up was 60 months (range, 36-96 months). No patient experienced recurrent infection or required revision surgery for infection. No medical complications limiting the use of appropriate antibiotic therapy were recorded. The mean preoperative knee and function scores were 60 and 50, respectively; corresponding mean postoperative values were 75 and 65, respectively.

DISCUSSION

UKA infection involves both the prosthesis and the native cartilage, neither of which can be treated conservatively in chronic forms. After identification of the causative organism, synovectomy and joint excision followed by same-stage TKA and combined with appropriate antibiotic therapy for 3 months is effective.

LEVEL OF EVIDENCE

IV, retrospective cohort study.

Unicompartmental knee arthroplasty: 11-year experience from 3929 implants in RIPO register

BACKGROUND

Since 2000, the Register of Prosthetic Orthopedic Implants (RIPO) has been following all hip, knee, and shoulder arthroplasties in the Emilia-Romagna region, comprising 4.5 million inhabitants, in northern Italy. The aim of the present analysis was to present the main figures of unicompartmental knee implants processed from the Registry.

METHODS

During the period 2000-2011, 3929 unicompartmental knee arthroplasties were performed on 3645 resident patients, of which 71% were females. The medial condyle was treated in 94% of cases, where mean age at surgery was 67.3 years and mean body weight was 76.6 kg. The main outcome measure was time to revision of at least one single component. The Kaplan-Meier survival and Cox multivariate analyses have been applied.

RESULTS

At 10-year follow-up, the percentage of survival was 86.8% (confidence interval (CI) at 95% was 84.1-89.5); total aseptic loosening represented 42% of the causes of failure, pain represented 15%, and sepsis represented 11%. Age at surgery significantly influences the survival of the prosthesis, whatever the reason for revision, while the type of tibial component (monoblock or metal tray) does not appear to be a determinant. Septic failure is not prevented by the use of antibiotic-loaded cement.

CONCLUSION

Results are comparable to main orthopedic registries from Scandinavia, Australia, and New Zealand, even if some differences can be highlighted.

Do bone loss and reconstruction procedures differ at revision of cemented unicompartmental knee prostheses according to the use of metal-back or all-polyethylene tibial component?

INTRODUCTION

Results of unicompartmental knee arthroplasty (UKA) revision are known but the severity of bone loss and the need for reconstruction are not detailed for different tibial implants.

HYPOTHESIS

Metal-backing UKA revision exposes the patient to more severe tibial bone loss and requires more substantial reconstruction procedures than cemented polyethylene UKA revision.

MATERIALS AND METHODS

This retrospective series of 23 revisions of UKA to total knee arthroplasty (TKA) compared 11 all-polyethylene UKAs with 12 metal-backing UKAs. Factors that contributed to failure were aseptic loosening (n=12) and osteoarthritis evolution (n=11). Both groups were similar regarding the demographic and clinical features. We reported bone loss and the reconstruction procedure to fill it according to the initially used tibial implant. The results were evaluated with the IKS score to a follow-up of 37 months (range, 24-67 months).

RESULTS

There were more tibial segmental bone loss (10 versus 3) and more metal wedges (8/12 versus 2/11) in metal-backing UKA revision (P<0.05). Tibial stems were more often used in metal-backing UKA revision (12/12 versus 7/11) (P=0.04). The results of TKA at follow-up did not differ according to whether the revised tibial implant was all polyethylene (IKS=155 [range, 107-195]) or metal-back (IKS=155 [range, 127-172]).

DISCUSSION

This study suggests that metal-backing UKA revision exposes the patient to more severe tibial bone loss requiring more substantial reconstruction. These results must be confirmed on a larger population, but surgeons should be alerted to this kind of revision surgery, which warrants having available a revision knee prothesis.

LEVEL OF EVIDENCE

Level III, case-control study.

Unicompartmental knee prosthetization: Which key-points to consider?

Unicompartmental knee arthroplasty (UKA) has evolved into a suitable option for diseased knees that cannot be managed with arthroscopic treatment and at the same time are not good candidates for total knee replacement. Since meticulous execution of the surgical technique is essential to optimizing UKA outcome, some procedural key-points are mandatory. Templates (phantoms) are then used to size the required prosthetic component (using these radiographs. Arthritic varus (or valgus) knees with an asymptomatic patello-femoral joint are typically ideal for UKA. Metal-backed tibial components should be favourite instead of all-polyethylene tibial components to avoid polyethylene creep that may occur in fixed bearings. Moreover, a proper thickness of the polyethylene layer is mandatory, in order to avoid early failure.