This randomized, prospective study was performed to evaluate changes in varus-valgus laxity over time and to evaluate the relationship between laxity and retention of the posterior cruciate ligament.
Sixty knees of 60 patients with osteoarthritis received mobile-bearing prostheses. Thirty patients received posterior cruciate ligament-retaining prostheses (average follow-up, 75 months), and 30 patients received posterior cruciate ligament-sacrificing prostheses (average follow-up, 78 months). Varus-valgus laxity was measured with the knee in extension at 6 months, 1 and 2 years after surgery, and at final follow-up examination (average, 77 months).
Varus laxity measurements for patients with posterior cruciate ligament-retaining prostheses at 6 months, 1 year, 2 years, and final examination were 3.7° ± 1.2°, 4.0° ± 1.3°, 4.1° ± 1.7°, and 4.2° ± 1.3°, respectively; corresponding valgus laxity measurements were 3.5° ± 1.1°, 3.5° ± 1.3°, 3.5° ± 1.1°, and 3.6° ± 1.1°, respectively. Varus laxity measurements for patients with posterior cruciate ligament-sacrificing prostheses at 6 months, 1 year, 2 years, and final examination were 4.3° ± 1.9°, 4.3° ± 1.9°, 4.3° ± 1.8°, and 4.4° ± 1.7°, respectively; corresponding valgus laxity measurements were 3.7° ± 1.3°, 3.4° ± 1.3°, 3.5° ± 1.1°, and 3.6° ± 1.3°, respectively.
Prognostic study, See the Guidelines for Authors for a complete description of levels of evidence, Level I.
There were no significant differences in varus and valgus laxities between the two groups. This study demonstrates that coronal laxity does not change over time in either type of knee prostheses and that the posterior cruciate ligament does not affect coronal stability during varus-valgus stress.