The effect of post-operative mechanical axis alignment on the survival of primary total knee replacements after a follow-up of 15 years.
J Bone Joint Surg Br. 2011 Sep;93(9):1217-22.
Bonner TJ, Eardley WG, Patterson P, Gregg PJ
Source: Queen Elizabeth Hospital, Sheriff Hill, Gateshead, Tyne and Wear NE9 6SX, UK. firstname.lastname@example.org
Background: Correct positioning and alignment of components during primary total knee replacement (TKR) is widely accepted to be an important predictor of patient satisfaction and implant durability. The apparent benefits of achieving a neutral mechanical axis (angle of 0°) of the lower limb during TKR surgery has encouraged surgeons and manufacturers to invest time and resources into achieving this alignment target. This retrospective study reports the effect of the post-operative mechanical axis of the lower limb in the coronal plane on implant survival following primary TKR.
Materials and Methods: A total of 501 TKRs in 396 patients were divided into an aligned group with a neutral mechanical axis (± 3°) and a malaligned group where the mechanical axis deviated from neutral by > 3°.
Results: At 15 years' follow-up, 33 of 458 (7.2%) TKRs were revised for aseptic loosening. Kaplan-Meier survival analysis showed a weak tendency towards improved survival with restoration of a neutral mechanical axis, but this did not reach statistical significance (p = 0.47). The pre-operative alignment, type of fixation and primary pathology did not predict either the accuracy of alignment of the mechanical axis or the survival pattern in either group
Discussion: Interest in the accurate positioning and alignment of arthroplasty components has been the subject of controversy, particularly following the development of computer navigated surgery. Justification for using computer navigation and its cost-effectiveness is based on the implication that accurate alignment improves implant survival, thereby reducing the rate of costly revision, but the evidence supporting this is scarce. In present Study the effect of post-operative alignment of the mechanical axis, measured using long-leg radiographs, on the long-term risk of revision surgery demonstrate only a weak relationship between alignment and the risk of revision surgery. Thus, the reported cost-benefit ratio of computer navigated TKR surgery using 3° as the primary outcome measure alone may exaggerate its benefit, with the effect of computer-navigated TKR on long-term implant survival remaining unproven.
Conclusion: We found that the relationship between survival of a primary TKR and mechanical axis alignment is weaker than that described in a number of previous reports.
LEVEL OF EVIDENCE: Level - IV
IORG Arthroplasty Update