Abstract
The aim of this study was to assess the distribution of wear down to bone in lateral compartment osteoarthritis and to analyse the effect of ACL condition and Ahlbach grading on this distribution.
Background: The distribution of medial compartment wear is now well described and shows posterior progression and increased area of wear with worsening AhIback grade and ACL condition (Porteous 2000). Harman (1998) described wear situated more posteriorly in the lateral compartment but did not show any change to this with altering ACL function, and did not assess the severity of the arthritis.
Method: Forty two tibial plateaus resected at total or unicompartmental replacement for lateral compartment osteoarthritis were analysed for the anterior and posterior extent of wear, as well as the point of deepest wear and the size of lesion. The plateau was divided into five zones from anterior to posterior. The ACL condition at surgery was graded as Normal, Frayed or Absent. Radiographs were classified by Ahlbach grade. Analysis using Mann-Whitney U-test, Fisher’s exact test and Spearman’s rank correlation were performed.
Results: The significant changes with increasing Ahlbach grade were that: the point of deepest wear moved posteriorly, the posterior extent of wear moved posteriorly and the size of the lesion increased. With ACL deterioration and rupture, the anterior extent of the wear moved forward and the size of lesion increased, but this did not occur through posterior migration of the posterior extent of the wear. There was a significant difference between the Ahlbach grade of ACL Normal and Absent knees.
Conclusion: In early disease, the wear is situated more posteriorly than in medial disease. The wear size increases with ACL insufficiency, but the further posterior progression of wear associated with posterior femoral subluxation seen in advanced disease seems to be more dependant on the loss of bone reflected in the Ahlbach grading.
The abstracts were prepared by Mr Roger Smith. Correspondence should be addressed to him c/o British Orthopaedic Association, Royal College of Surgeons, 35-42 Lindoln’s Inn Fields, London WC2A 3PN.
