[Medin modular implant for total knee arthroplasty--mid-term results]

PURPOSE OF THE STUDY To evaluate the mid-term results of total knee arthroplasty (TKA) using a Medin Modular joint prosthesis in a standard design preserving the posterior cruciate ligament. MATERIAL The study comprised 206 consecutive total knee arthroplasties, 10 bilateral, 60 in men and 136 in women. Twelve patients died of causes unrelated to the surgery and 14 knee replacements were lost to follow-up. A total of 180 were evaluated at an average follow-up of 6.5 years (range, 5 to 8.7 years). The patients ranged in age from 43 to 84 years (average, 69.5 years). The basic indication for surgery was osteoarthritis in 179 and rheumatoid arthritis in 37 cases. METHODS Pain, range of motion, stability and function were scored on a 100-point scale of the Hospital for Special Surgery (HSS) Scoring System. Subjective satisfaction was essessed by the patient's willingness to undergo the surgery again. At yearly intervals, radiographs in two projections were examined for radiolucent lines around the implant. The Kaplan-Meier survival curve was evaluated for the whole group and compared with that for non-infected cases only. The mechanical properties of the implant were most reliably shown by the survival curve for the subgroup of knee replacements free of infection. RESULTS At the final follow-up out of 180 knees, 169 were fully functioning and 11 required revision arthroplasty for the following reasons: polyethylene wear, one knee; instability, two; infection, six; patellar fracture, one; and problems associated with the femoro-patellar joint, one knee. The Kaplan-Meier curve for the whole group showed survival of 92 % of the implants at the end of the 9-years follow-up time. In the infection-free subgroup, in which aseptic loosenings were only included, there was a 95 % survival. The average range of flexion was over 106 degrees, and only 11 knees had flexion below 90 degree lack of. Extension from 5 to 10 degrees was found in four knees. Thirteen knees showed instability that did not interfere with function. In 191 knees, after surgery alignment was optimal, between 0 and 5-degree valgus; in 11 knees varus up to 5 degrees and valgus up to 10 degrees were found. No pain was recorded in 123 knees, occasional pain with no effect on function in 36 cases, and moderate pain after weight-bearing in 10 knees. By the HSS score, 136 knees had excellent and very good (over 90 points) outcomes and 21 had unsatisfactory or poor outcomes (below 85 points); the remaining 23 had satisfactory outcomes (between 89 and 85 points). The subjective evaluation was positive for 156 knees. Of 169 TKA evaluated radiographs, 141 were without signs of radiolucency, 17 showed a slight marginal radiolucent line and 11 had a more pronounced radiolucent line up to 1 mm in width, but without progression. DISCUSSION A total of 93 % of total replacements were evaluated and 7 % were lost to follow-up. Therefore, the number of remaining patients is big enough to make the group valid for assessment. The rate of complications, including 2.9 % of infected knees, is in agreement with the reported values. The occurence of polyethylene wear was negligible. A comparison of the cumulative survival curve for the whole group with that for the infection-free subgroup showed that the effect of infection on the TKA outcome was statistically significant (p=0.0431), and that late infection remains the most serious complication. Aseptic loosening plays a less important role in implant survival evaluated at mid-term intervals. CONCLUSIONS The rate of complications for Medin Modular implants evaluated at an average follow-up of 6.5 years is not different from the values reported for similar prostheses. The most serious complication is late infection. Persistent pain is usually located to the femoro-patellar articulation, but it seldom markedly affects joint function. The cumulative survival curve for the whole group was 92 % at a 9 years. The HSS evaluation of the whole group showed that 75 % of the knees achieved mor than 90 points.