Early failure of minimally invasive unicompartmental knee arthroplasty is associated with obesity

There has been increasing use of and expanding indications for unicompartmental knee arthroplasty using minimally invasive techniques. We sought to define contraindications by examining failures. We retrospectively reviewed the early results of a consecutive series of minimally invasive medial unicompartmental knee arthroplasty using two implant designs. Seventy-nine consecutive unicompartmental knee arthroplasty cases (48 instrumented and 31 noninstrumented) with minimum 2-year followup were reviewed. Patients with radiographic involvement with or without pain referable to the lateral compartment or to the patellofemoral joint were not considered candidates. Failure was defined as revision or pending revision. The average followup was 40.2 months. There were 16 failures (six tibial loosening, three plateau fracture, four persistent medial pain, one progressive arthritis, and two sepsis). Age, gender, disease severity and implant design did not predict failure. Body mass index greater than 32 did predict failure and was associated with a reduction in survivorship by log-rank and Wilcoxon analyses. These results show reliable success if obesity is considered a contraindication and technical errors resulting in fracture are eliminated. Better defining the ideal candidate for unicompartmental knee arthroplasty, with obesity remaining a contraindication, will make this a more predictable and reliable procedure.