What did the study look at?
Tears of the anterior cruciate ligament (ACL) often occur together with injuries to other knee ligaments. Injuries to the structures at the back and outer side of the knee (the posterolateral corner, PLC) can be difficult to recognise. The heel-height test, in which the height of each heel above the examination table is compared with the patient lying on their back, is a simple way of measuring how far the knee bends backwards (hyperextension).
The authors wanted to see how heel height changes when the knee's stabilising structures are cut in sequence: the ACL, the fibular collateral ligament (FCL, the outer side ligament), the popliteus tendon, the popliteofibular ligament and the medial collateral ligament (MCL, the inner side ligament). They also examined whether starting with the ACL or with the FCL made a difference, and whether the backward slope of the top of the shin bone (posterior tibial slope) influenced the results.
How was it done?
This is a cadaveric study: it was carried out in a laboratory on human knees donated for medical research, not in living patients.
- Sixteen knees with no history of injury or surgery, all stable on examination, were used. The mean age of the specimens was 87.7 years (range 76-103).
- The knees were randomly allocated to two groups: one in which the ACL was cut first and one in which the FCL was cut first (8 knees each).
- The popliteus tendon, the popliteofibular ligament and the MCL were then cut in turn.
- At each stage, heel height was measured both with a standardised force (12 N·m) and with a force applied by hand by the same orthopaedic surgeon.
- Tibial slope was measured on side-view X-rays.
What did it find?
- In intact knees, the mean heel height with the standardised force was 3.95 cm.
- Cutting both the ACL and the FCL increased heel height by a mean of 2.85 ± 0.83 cm compared with the intact state.
- With the posterolateral corner also cut, the increase was 3.72 ± 1.02 cm; with the MCL also cut, it was 4.73 ± 1.35 cm.
- Every cutting stage except the popliteofibular ligament produced a significant increase in heel height.
- Whether the ACL or the FCL was cut first did not change the results (P = .863).
- Tibial slope (5.1°-12.5°) was not associated with the increase in heel height (P = .154).
- The hand-applied and standardised forces differed significantly only in the intact knee; no difference was seen after any cutting stage.
The authors' conclusion
According to the authors, combined ACL-FCL, ACL-posterolateral corner and ACL-posterolateral corner-MCL injuries lead to progressively greater heel-height values. Tibial slope did not appear to influence this increase. The authors suggest that the side-to-side difference in heel height may be a clinically relevant examination tool for diagnosing multiligament knee injuries.
Limitations
- Cadaveric knees cannot reproduce the voluntary muscle contraction that living patients may show because of discomfort.
- Testing was done in a single plane only; joint behaviour during movement was not assessed.
- There was no comparison with a healthy opposite knee, and not every structure that limits hyperextension (for example, the oblique popliteal ligament) was assessed.
- The height and weight of the specimens were not recorded, and the reliability of the fixation method was not tested.
- The tibial slope analysis was underpowered (31.6% power).
Reference
Perry AK, Knapik DM, Gürsoy S, Alter TD, Clapp IM, Verma NN, LaPrade RF, Chahla J. Determining the Roles of the Anterior Cruciate Ligament, Posterolateral Corner, and Medial Collateral Ligament in Knee Hyperextension Using the Heel-Height Test. Orthopaedic Journal of Sports Medicine. 2022;10(4):23259671221086669. Licence: CC BY-NC-ND 4.0.
DOI: 10.1177/23259671221086669
Free full text: PubMed Central (PMC9016545)
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.
