Abstract
The aim of this study was to assess the value of plain AP and lateral radiographs in determining ACL condition in medial unicompartmental osteoarthritis.
Background: A functioning ACL has been shown to be important in the success of certain unicompartmental knee replacements. White (2001) has shown MRI to be too sensitive in this age group of patients. Keyes (1992) suggested that stress radiographs were necessary to accurately assess ACL integrity.
Method: One hundred and twenty-six patients undergoing knee arthroplasty for medial osteoarthritis, had their ACL’s graded as Normal, Frayed or Absent intra-operatively. Standard pre-operative AP and lateral standing radiographs were graded by the Ahlback system. On the lateral view, the plateau was divided into 5 zones from anterior to posterior. The zone, in which the point of deepest wear occurred, was recorded.
Results: There was a significant difference between the occurrence of deepest wear in the anterior three zones versus the posterior two zones for ACL normal and absent knees (2 = 46.85, P< 0.001). There was a significant difference between the occurrence of normal and absent ACL’s in Ahlback grades ≤3 versus ≥4 (2 = 53.8, P< 0.001). There was a moderately strong correlation between both zone of deepest wear on lateral radiograph and Ahlback grade with ACL condition (Spearman’s rho = 0.62 and 0.69 respectively). The Positive Predictive Values for the ACL being normal are 64% for Ahlback grades 3 or less and 67% for Zone of deepest wear in the anterior 3 zones. The Positive Predictive Values for the ACL being intact (but not necessarily normal) are 95% for Ahlback grade 3 or less; 91% for Zone of deepest wear in the anterior 3 zones; and 97% if these criteria are combined.
Combining Ahlback grade ≤3 with wear in the anterior 3 zones also gave a Negative Predictive Value of 92% for the ACL not being normal.
Conclusion: There is a “watershed” in ACL condition between Ahlback grade 3 and 4. Prostheses requiring Normal or Intact ACL’s should only be performed if Ahlback grade is ≤3. Standard radiographs can reliably predict ACL condition with high Positive and Negative predictive values.
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.
