[Unicompartmental arthroplasty (Lotus type) in the treatment of lateralized gonarthrosis in the elderly. Outcome after more than 5 years of 56 prostheses analyzed in 1981].

The progress of 56 uni-compartmental knee arthroplasties has been studied. Five were lost to follow-up after 3 or 4 years: at that time the knees were pain-free and the radiological appearances were good. Seven knees had to be operated on again because of pain after 3.5 years following insertion of the prosthesis. Forty-four prosthesis were still in place after 5 years (average follow-up 6.7 years), 35 of them being almost painless. The knees which became painful did so during the first 3 years and were associated with radiological deterioration. There were 2 loosenings, 11 narrowings of the non-prosthetic tibio-femoral compartment and 3 antero-posterior subluxations with laxity. The authors consider that the main reasons for loosenings were increased stresses and over-correction for narrowing of the non-prosthetic compartment. Subluxation was aggravated by joint obliquity. it is concluded that uni-compartmental knee prosthesis for single compartment arthrosis is a valuable procedure provided that there is good surgical technique and correct indications for operation. However, the long-term prognosis is uncertain because the design of the prosthesis cause increased stresses and some degree of permanent anteroposterior obliquity.