Aims: To determine the difference between macroscopic and microscopic appearances of the anterior cruciate ligament (ACL) in patients with osteoarthritis undergoing total knee replacement.

Methods: Patients admitted for routine total knee replacement (TKR) for osteoarthritis were assessed. The integrity of the ACL was noted as normal, moderately damaged (fissured) or complete rupture on a macroscopic level at the time of surgery. The ACL was sacrificed as a normal step in the operation and sent for histological analysis. The macroscopic and microscopic findings of ACL histology were compared using a common grading system (Grade 1 = normal, Grade 2 = moderately diseased, Grade 3 = severely diseased).

Results: The sample contained 48 patients, 17 male and 31 female, age range 55–87 years (mean 73). After exclusions, at surgery 7 ACL ruptures and 8 moderately diseased ligaments (defined by the presence of visible fissuring) were found despite negative pivot shift tests preoperatively. Of the 30 ACL’s that were found to be macroscopically normal, 22 of these (73%) were microscopically moderately or severely diseased.

Conclusion: We have found that a macroscopically normal ACL does not necessarily equate to microscopic integrity in the presence of osteoarthritis. This is an important consideration given the current trend towards unicompartmental knee replacement and highlights the possible need for investigation with appropriate imaging (MRI) and arthroscopy prior to this specific surgery.