What did the study look at?
One way of assessing ligament injuries on the outer side of the knee is a stress X-ray taken while an inward-bending force is applied to the knee (varus stress radiograph). The amount the outer joint space opens is measured on these images. Earlier studies reported differing results on how much an anterior cruciate ligament (ACL) injury contributes to this opening.
This study set out to examine the effect of cutting the ACL and the structures at the back and outer side of the knee (the posterolateral corner) on lateral compartment opening, in two groups with a randomly assigned cutting order.
How was it done?
This is a biomechanical cadaveric study, carried out in a laboratory on knees donated for medical research.
- Fourteen unpaired cadaveric knees without ligament injury or signs of osteoarthritis were used (10 male and 4 female donors; mean age 49.7 years).
- The knees were randomly allocated to two groups. In the first, the ACL, the fibular collateral ligament (FCL, the outer side ligament), the popliteus tendon and the popliteofibular ligament were cut in that order. In the second, the outer structures were cut first and the ACL last.
- With the knee bent to 20°, a standardised 12 N·m varus moment was applied and fluoroscopic images were taken at each stage.
- Opening was measured on a total of 210 images by three observers working independently of each other.
What did it find?
- With all structures cut, the mean increase in lateral opening was 4.6 ± 1.8 mm (range 1.9-7.7 mm).
- The largest contributions came from cutting the ACL (1.3 ± 0.6 mm) and the FCL (2.2 ± 1.3 mm).
- In both groups, opening greater than 3 mm occurred only after both the ACL and the FCL had been cut.
- For the effect of the ACL, there was no significant difference between cutting it first or last (P = .387).
- Measurement reliability, both within and between observers, was excellent (ICC 0.94 and 0.95).
The authors' conclusion
According to the authors, ACL deficiency significantly increased lateral opening under varus stress regardless of the order of injury. An isolated ACL injury did not cause enough opening to falsely suggest an injury on the outer side. However, the authors state that the effect of the ACL, in addition to the lateral structures, should be taken into account when stress X-rays are used to evaluate knee injuries. They also suggest that opening of more than 3 mm may indicate an ACL injury in addition to an FCL injury.
Limitations
- The knees were unpaired, so the injured knee could not be compared with a healthy opposite knee.
- Knee segments rather than whole lower limbs were used, which may limit clinical applicability.
- Most patients with ligament injuries are younger, so the age of the specimens may affect how far the results apply clinically.
- No hand-applied force was tested and the sample was small; studies with more specimens are needed.
Reference
Gürsoy S, Perry AK, Dandu N, Singh H, Vadhera AS, Yanke A, LaPrade RF, Chahla J. Effect of Sectioning of the Anterior Cruciate Ligament and Posterolateral Structures on Lateral Compartment Gapping: A Randomized Biomechanical Study. Orthopaedic Journal of Sports Medicine. 2022;10(6):23259671221100216. Licence: CC BY-NC-ND 4.0.
DOI: 10.1177/23259671221100216
Free full text: PubMed Central (PMC9178986)
This article summarises a published scientific paper for general information; it does not replace an examination or a personal medical assessment. Please consult your doctor about your symptoms.
