Proprioception and Anterior Cruciate Ligament Reconstruction

Introduction

Most rehabilitation programs for patients who have undergone anterior cruciate ligament (ACL) reconstruction include exercises and drills that are directed toward improving neuromuscular function and coordination. They are often loosely referred to as proprioceptive training exercises. This chapter explores the basis for the incorporation of such exercises into rehabilitation following ACL reconstruction.

The human ACL has been shown to contain mechanoreceptors, including Golgi tendon organs, Pacinian corpuscles, and Ruffini nerve endings. These receptors contribute to proprioception about the knee joint and also form part of a reflex arc, in which electrical stimulation of the ACL results in hamstring muscle contraction. Such a reflex presumably serves to protect the knee, and the ACL in particular, when the tibia is anteriorly displaced. ACL rupture can therefore be expected to result in disruption or alterations of these pathways.

Evaluating Proprioception

The term proprioception has proved difficult to define succinctly and has similarly been tested and measured using a variety of techniques. Proprioception is generally accepted to include joint position sense and the ability to detect joint movement (kinesthesia). These have been measured by joint position-matching tasks, and by threshold to detection of passive movement tasks, respectively. Overall, it appears that threshold to detection methods have proved more reliable, although the two test types address different aspects of proprioception.

Another approach has been to use tests of neuromuscular function. These involve both afferent and efferent components and therefore test not only proprioception but also the muscular response. Examples of such tests are the measurement of the latency of hamstring muscle contraction following the application of an anterior displacement force to the tibia, and assessment of postural control, typically during single-leg stance. This can be static or dynamic, as in the response to a perturbation or on an unstable platform. More global functional tests include the various hop tests.

When assessing proprioception or neuromuscular function following ACL rupture and subsequent reconstruction, there are some fundamental issues that need to be considered. Alterations in the uninjured limb have been widely reported, although deficits may be greater in the injured limb. A variety of mechanisms have been proposed, including loss of afferent information affecting the contralateral limb, central motor control mechanisms being unable to cope with differential sensory deficits and therefore adjusting the contralateral limb to the injured limb, and general deconditioning as a result of the ACL injury. In assessing neuromuscular function, it may therefore be useful to include a group of control subjects.

Deficits have been demonstrated to change over time following both injury and reconstructive surgery. Thus, longitudinal studies may be of greater benefit than studies using only one point in time. It is also important to note the type of graft used for reconstructive procedures (e.g., hamstring harvest may affect tests involving a hamstring muscle response), to correct results for height, and to consider the gender of subjects, as these may all be confounding factors.