Our experience with medial unicondylar knee prosthesis

Abstract

The indications for unicondylar knee replacement for osteoarthritis are discussed. Its theoretical advantages against total knee replacement are the small size of the implants, an easier operative technique and faster rehabilitation. But some surgeons assume that tibial osteotomy has the same indications and gives the same long-term results while preserving the natural joint.52 medial resurfacing unicondylar knee prostheses have been followed for a mean time of 4 years, with a minimum of 1 year. There were 16 males and 31 females, with a mean age of 70 years (range 65 to 83 years). The indication was primary (37 cases) or post-traumatic (2 cases) osteoarthritis and necrosis of the medial femoral condyle (13 cases). The Cartier-Mansat prosthesis was most frequently used.Four prostheses were revised because of unexplained pain (1 case), aseptic loosening (2 cases) or osteoarthritic change in the opposite compartment (1 case). 48 prostheses were still in place at the time of this study. The results were studied with Hungerford’s classification, giving the knee joint a maximum score of 100 points.Mean pain score was 42/50, and only 4 patients had significant pain. No abnormal laxity was seen. 45 patients had complete extension, and 3 a deficit between 5 and 10°. 43 patients had over 90° flexion. Quadriceps force was always normal. Only 23 patients had a normal mechanical axis measured on a monopedal stance view, while 19 had a remaining varus deformation and 4 an overcorrection. The mean global score was 85/100, and 33 of the 39 patients with no missing item had a global score over 80/100.Objective and subjective results were very satisfactory. But we were not so pleased with the radiological appearance of the prosthesis. Malposition of both prosthetic components, including global limb malalignment, malalignment of one or both implants, incongruency of both implants or lowering of the joint space with reference to lateral compartment, were very common. The actual influence of these malpositions are not known, but is likely to be significant and the long term survival remains then questionable. A more precise operative technique could decrease the incidence of this disadvantage.