[Laxity and functional results of Miller-Galante total knee prosthesis with posterior cruciate ligament sparing after a 6-year 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 assess the relation between knee laxity and function.

MATERIALS AND METHOD: We assessed retrospectively the results of 48 consecutive Miller-Galante with 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 were cemented with patellar resurfacing (25 metal-backed, 19 polyethylene). Stressed X-rays with Telos device were performed to assess frontal and antero-posterior laxity. All radiographic measurements were carried out with a digitizer (Orthographics).

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 polyethylene 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, but 81 percent of the knees were at 5 degrees around neutral position. The mean laxity in valgus was 4 degrees +/- 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 when 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 mean thickness of the patella was 22 mm +/- 2.3 [16-27].

DISCUSSION: These results were unsatisfactory considering the high revision rate and the low functional score observed despite of a correct implant positioning. The major challenge for PCL retaining (i.e. free stair climbing) was achieved in few cases. The wide range of posterior laxity underlined the difficulties to control PCL tension. On the other hand, PCL tension has to be controlled as it could influence knee function. Patello-femoral disorders was the main reason for revision surgery and an insufficient patellar bone resection may be contributive. Sagittal anterior laxity was the second reason for revision and it should be carefully detected as it could drive to catastrophic polyethylene wear.

CONCLUSION: The advantages of PCL retaining were not demonstrated with this low constrained design. Surgical control of PCL tension could give a wide range of posterior laxity. Sagittal femoral-tibial laxity and femoro-patellar disorders should be detected before severe polyethylene wear. These results advocates for: 1) more congruent designs with PCL retaining or for PCL substituting designs, 2) improvement of patello-femoral design.