Abstract
PURPOSE:
Unicompartmental knee arthroplasty (UKA) is becoming more commonly performed and is more technically challenging than total knee replacement. Retention of the anterior and posterior cruciate ligaments requires more accurate re-creation of the patient's normal anatomic posterior slope with UKA. Purpose of this study was to accurately determine the posterior tibial slope in patients having medial or lateral UKA performed.
METHODS:
Retrospective review was performed of 2,395 CT scans performed for a customized UKA implant. Standard CT technique was used and the posterior slope was measured on the involved side of the proximal tibia.
RESULTS:
CT measurements from 2031 knees undergoing medial UKAs had an average pre-operative posterior slope of 6.8 deg (SD 3.3), in these patients the posterior slope was between: 0–4 deg in 430 knees (21.2%), 4–7 deg in 696 knees (34.3%), 7–10 deg in 545 knees (26.8%), >10 deg in 360 knees (17.7%), and 13 knees (0.6%) had a reversed (anterior) tibial slope. Measurements from the 364 knees undergoing lateral UKAs showed an average pre-operative posterior slope of 8.0 deg (SD 3.3), in these patients the posterior slope was between: 0–4 deg in 43 knees (11.8%), 4–7 deg in 100 knees (27.5%), 7–10 deg in 118 knees (32.4%), >10 deg in 103 knees (28.3%), and 1 knee (0.3%) had a reversed (anterior) tibial slope.
CONCLUSION:
There is marked variability in the posterior slope of the proximal tibial with 44.5% of medial plateaus and 60.7% of lateral plateaus having more than 7 deg of posterior slope pre-operatively. This is the first large CT based review of posterior slope variation of the proximal tibia. If attempting to match the patient's proximal slope during UKA, a routine setting of 5 degrees posterior slope will produce a posterior slope less than the patient's native anatomy in more than 50% of patients.
