The “correct” rotational alignment and “normal” rotational alignment may not be the same position. Because of natural tibial plateau has average 3° varus but classical TKA method make tibial cut perpendicularly to tibial mechanical axis. Consequently femoral rotational compensation to 3° becomes necessary. While anatomical TKA method performed tibial cut in 3° varus. Then posterior femoral cut will be parallel to posterior condylar axis and component rotation theoretically should be aligned in natural anatomy. This study compares the rotational alignment between two methods. Study conducted on 80 navigated TKAs with modified gap technique. Intraoperative femoral rotation retrieved from navigation. Rotational alignment was calculated using the Berger protocol with postoperative computerised tomography scanning. The alignment parameters measured were tibial and femoral component rotations and the combined component rotations. 57 knees with PS design can be classified into 35 knees as anatomical group and 22 knees as classical group. 23 knees with CR design had 12 knees as anatomical group and 11 knees as classical group. The intraoperative femoral rotation in anatomical group had less external rotation than classical group significantly in PS design (0.77°±1.03° vs 2.86°±1.49°, p = 0.00) and also had the same results in CR design (1.33°±1.37°vs 2.64°±0.81°, p = 0.012). However, the postoperative excessive femoral and tibial component rotation compared with native value and combined rotation had no significant differences between classical and anatomical method in both implant design. Using CAS TKA with gap technique showed no difference in postoperative rotational alignment between classical and anatomical method.
One of four normal people had mechanical alignment of 3 degrees varus and more than so-called “constitutional varus”. Parallel joint line to the floor found in both neutral and varus alignment. Therefore, joint line orientation may play an important role in clinical outcomes after TKA. For reconstituting joint line parallel to the floor advocated by 30 varus tibial cut that was introduced by Hungerford The prospective study conducted on 94 primary varus osteoarthritis knees undergone CAS TKA using either classical method (51 knees) or anatomical method (43 knees). Clinical outcomes including WOMAC scores, Oxford knee scores and ROM were evaluated preoperatively and 6 months postoperatively. Full leg standing hip-knee-ankle were measured mechanical axis, tibial cut angle and tibial joint line angle at 6 months after surgery. The results revealed that postoperative neutral alignment (mechanical axis 0± 3°), 4–5°varus and ≥6°varus showed no significant difference in term of WOMAC scores, Oxford scores and ROM. Including comparison between classical tibial cut and anatomical tibial cut, postoperative joint line parallel to the floor and oblique joint line had no significant in clinical outcomes. Nevertheless, anatomical tibial cut and joint line parallel to the floor had significant WOMAC scores improvement than the others. In conclusion, the joint line parallel to the floor may be one of key successes after TKA more than postoperative limb alignment.
