III.

Systematic review, Level IV.

IV (retrospective cohort study).

Case series, Level IV.

Cutibacterium acnes is a commensal skin bacterium, regularly implicated in prosthetic joint infection, particularly of the shoulder. Diagnosis has been improved by progress in bacteriological techniques: longer culture time, liquid medium culture, MALDI-TOF mass spectrography, and universal 16S rRNA PCR, associated by some authors to sonication of ablated implants. C. acnes pathogenicity involves many virulence factors, notably including biofilm formation. C. acnes may lead to infection that is clinically evident or, frequently, relatively asymptomatic. C. acnes is an anaerobic Gram-positive bacterium, susceptible to many antibiotics that are regularly used in bone and joint infection: beta-lactams, quinolone, rifampicin and clindamycin. It shows increasing resistance to clindamycin and natural resistance to metronidazole. Treatment is medical and surgical, associating synovectomy or complete 1- or 2-step revision depending on time to treatment, and antibiotic therapy. Antibiotic therapy is typically for three months with an initial 2-6 weeks' intravenous phase. Prognosis is generally favorable with well-conducted treatment. Late discovery of positive samples after apparently aseptic implant change is an at-risk situation, usually managed by antibiotic therapy, but with late initiation and hence increased risk of failure. Adverse secondary progression requires repeat revision under good conditions.

Recession wedge trochleoplasty is a feasible additional procedure addressing bony trochlear abnormality in the surgical treatment of patellar instability. Our attitude is to perform it never in isolation but associated to realignment of the extensor apparatus according to the à la carte surgery concept. It seems to be effective in preventing future patellar dislocation and reducing anterior knee pain in case of painful patellofemoral instability with a major dysplastic trochlea, or in revision cases when other realignment procedures have failed.

Retrospective study, Level IV.

Prospective cohort study Level IV.