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The effect of postoperative mechanical axis alignment on the revision rate of primary total knee arthroplasty after a follow up of 10 years

7 pagesPublished: June 27, 2017

Abstract

The purpose of this study is to evaluate the effect of postoperative mechanical alignment on clinical outcomes and revision rate by comparing acceptable mechanical axis group from neutral and an outlier mechanical axis.
Between 2000 and 2006, clinical and radiographic data of 334 primary TKAs were retrospectively reviewed. Post-operative mechanical axis was investigated within 1 month after TKA. The first group was an acceptable group of 286 knees (85.6%, with mechanical axis of 0°±3°). The second group was an outlier group of 48 knees (14.4%, with mechanical axis of beyond 0°±3°). Clinical outcomes before surgery and at the final follow up were analyzed using scoring method such as Hospital for Special Surgery, Knee Society Score, and Western Ontario & McMaster Universities Osteoarthritis Index (WOMAC) score. Radiologic outcomes including changes of mechanical axis between immediate postop and last follow-up were evaluated. Postoperative complications and revision rates were also evaluated.
The mean degrees in change of mechanical axis between immediate postop and last follow-up were greater in the outlier group (1.6°±2.7) than acceptable group (0.8°±2.4). No significance difference in clinical outcome was found between the two groups. The incidence of aseptic loosening, instability, polyethylene wear, polyethylene breakage, and periprosthetic fracture was 2/4/2/2/2 each in the acceptable group and 1/1/2/0/0 each in the outlier group. Six (2.1%) of 286 in the acceptable group and 4 (8.3%) of 48 in the outlier group were revised (p=0.04). The Kaplan-Meier survival analysis showed a tendency towards improved survival with restoration of neutral mechanical axis. However, such improvement was not statistically significant (p=0.25).
Restoration of neutral limb alignment is a factor of total knee arthroplasty that can result in less revision rate and higher longevity. However, there are no significant differences in clinical outcomes between the two groups.

Keyphrases: Total knee arthroplasty, Mechanical alignment, Acceptable, Outlier

In: Klaus Radermacher and Ferdinando Rodriguez Y Baena (editors). CAOS 2017. 17th Annual Meeting of the International Society for Computer Assisted Orthopaedic Surgery, vol 1, pages 269--275

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