Abstract
Restoration of the mechanical axis is thought to be a critical factor in determining the Outcome of knee replacement surgery. There is strong theoretical evidence that reproduction of this axis improves mechanical loading and hence longevity of the implant. Clinical studies are small in number.
Per-operative use of intra-and-extra-medullary alignment jigs help to determine the distal femoral and proximal tibial cuts. Studies have shown large margins of error using the standard jigs provided with most total knee replacement systems. On this basis computer assisted guidance systems are being introduced such as Orthopilot and BrainLab. These systems allow more accurate placement of the bony cuts and hence improve overall lower limb alignment.
No study has shown conclusively that accurately reproducing the mechanical axis of the lower limb improves survivorship of the implant. Prior to investing in these systems we felt it would be prudent to investigate how critical reproduction of the mechanical axis was in the primary total knee replacement.
We assessed 100 primary kinematic total knee replacements performed in 1990. All case notes were reviewed looking for basic demographics, pathology and clinical outcome.
All cases had a long leg film weight-bearing alignment film taken post-operatively. These were digitised and then analysed using Design CAD 97 software and from this the mechanical axis calculated.
Using these data the patients were divided into two groups. The first were within 3 degrees varus/valgus of the mechanical axis. The second were outside this range. These two groups were then correlated to clinical outcome.
Conclusions: Our results suggest that accurate reproduction of the lower limb alignment and the mechanical axis improves clinical outcome and survivorship of the implant using revision as an endpoint. Our data would support the introduction and use of intra operative computer aided guidance systems.
The abstracts were prepared by Mr Tim Briggs. (Editoral Secretary 2003/4) Correspondence should be addressed to him at Lane Farm, Chapel Lane, Totternhoe, Dunstable, Bedfordshire LU6 2BZ, United Kingdom
