Functional results correlated to laxity with Miller-Galante cemented totalknee prosthesis: A 44 cases study with 6 years of follow-up

Purpose of the study The preservation of the posterior cruciate ligament (PCL) was introduced in total knee arthroplasty to improve the quadriceps efficiency and the range of flexion in stairs. The purpose of this study was to determine if these goals were achieved with the Miller-Galante total knee prothesis and to ass ess the relation between knee laxity and function. Material and Method We assessed retrospectively the results of 48 consecutives Miller-Galante w ith PCL retaining. Four patients were excluded: 2 died, 2 lost to follow-up . Forty-four prostheses were evaluated in 38 patients mean aged 65 (33-79). The preoperative HSS score was 41 +/- 12.4 [21-63]. All the components wer e cemented with patellar resurfacing (25 metal-backed, 19 polyethylene). St ressed Xrays with Telos(TM) device were performed to assess frontal and ant ero-posterior laxity. All radiographic measurements were carried out with a digitizer (Orthographics(TM)). Results After 6 years of follow-up, 8 prostheses (18.1 p. 100) were already revised because of: 1) 3 excessive anterior tibial translations and severe polyeth ylene wear; 2) 5 femoro-patellar disorders. These last 5 knees (4 patellar metal-backed) had a greater patellar thickness [(25 mm +/- 1.2) (p = 0.01)] . The mean HSS knee score for the 36 remaining prostheses was 73.8 +/- 11.3 ( 35-92). Only 5 patients were able to climb stairs without support. The mean mechanical axis was 2.3 degrees in varus, bur 81 percent of the knees were at 5 degrees around neutral position. The mean laxity in valgus was 4 degr ees +/- 2.3 degrees [1-10], and 4.1 degrees +/- 2.1 degrees [1-9] in varus. The mean anterior tibial translation was 5.3 mm +/- 5 [1-17] and posterior laxity was 4.7 mm +/- 2.5 [1-10]. HSS knee score was lowered by 9 points w hen frontal laxity (valgus + varus) was greater than 5 degrees (p = 0.01), and by 9.8 points when posterior laxity was 5 mm or more (p = 0.02). The me an thickness of the patella was 22 mm +/- 2.3 [16-27]. Discussion These results were unsatisfactory considering the high revision rate and th e low functional score observed despite of a correct implant positioning. T he major challenge for PCL retaining (i.e. free stair climbing) was achieve d in few cases. The wide range of posterior laxity underlined the difficult ies to control PCL tension. On the other hand, PCL tension has to be contro led as it could influence knee function. Patello-femoral disorders was the main reason for revision surgery and an insufficient patellar bone resectio n may be contributive. Sagittal anterior laxity was the second reason for r evision and it should be carefully detected as it could drive to catastroph ic polyethylene wear. Conclusion The advantages of PCL retaining were not demonstrated with this low constra ined design. Surgical control of PCL tension could give a wide range of pos terior laxity. Sagittal femoro-tibial laxity and femoro-patellar disorders should be detected before severe polyethylene wear. These results advocates for: I)more congruent designs with PCL retaining or for PCL substituting d esigns, 2) improvement of patello-femoral design.