Characterisation of the neurosensory elements of the feline cranial cruciate ligament.

The identification and distribution of mechanoreceptors in the cranial cruciate ligament of the cat (analogous to the anterior cruciate ligament in other species) was studied histologically using a modified celloidin embedding technique to achieve serial sectioning of bone-ligament-bone preparations with gold chloride staining. We identified distinctive large elongated structures situated between the collagen bundles of the ligament (resembling endings described as Freeman and Wyke type III; also termed Golgi tendon receptors). These endings were found near the middle of the ligament well away from the bone-ligament junction. Axons seen entering only one end of each type III ending helped to confirm its neural basis. While we saw structures resembling types I and II endings (i.e. Ruffini and pacinian endings, respectively) in individual sections, serial sections failed to reveal convincing evidence of their existence. Such structures almost always appeared to be vascular in nature on adjacent sections, with vessels entering and exiting. We conclude that serial sections are critical to interpreting the presence or absence of mechanoreceptors.