The key to a successful knee replacement is restoring normal kinematics with a neutral alignment, thus a hip-knee-ankle (HKA) angle of 180° (within 3° limits). Conventional TKR is proven to have excellent results but relies in extensive visual referencing of bony landmarks. Customised cutting blocks provide accurate bone cuts, also lowering the risk of fat embolism, blood loss and operating time.
We share our experience comparing two different TKA techniques using patient specific instrumentation (PSI) with the Visionaire knee and conventional instrumentation (CVI) from the same system (Genesis II Smith&Nephew). A total number of 80 knees were divided into two equal groups, 40 PSI and 40 CVI respectively, operated between April 2013 and August 2014. One female patient had bilateral TKR during this period, at six months interval, both with the PSI.
All operated knees had varus deformity, with a mean HKA of 168° (PSI) vs 163° (CVI). We used tranexamic acid (double-dose scheme) and suction drains for 48 hours, with a mean blood drainage in the PSI group of 185 ml and Hb levels of 11.2 g/dl at three days post, compared to 260 ml and 10.7 g/dl in the CVI. Mean blood loss was 3.5 g/dl in PSI, and 4.2 g/dl in the CVI. On the long leg standing radiograph at six weeks, all knees were aligned in frontal plane, with simillar HKA values (178.9° PSI vs 178.6° CVI). Bone cuts measured intraoperatively proved to be accurate within a 1 mm limit.
We cannot recommend PSI-TKR for a better outcome. It is an alternative to conventional and computer-assisted TKR, but further studies are needed to evaluate weather surgical or economic benefits may be achieved by choosing customised instruments.