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Document Title: Barrack-AJSM-Mar97
Article Title: Evidence of reinnervation of free patellar tendon autograft used for anterior cruciate ligament reconstruction
Author: Robert L Barrack, Peter J Lund, Barry G Munn, Carole Wink, Leo Happel.
Publication: The American Journal of Sports Medicine
ISSN: 03635465
Date: March-April 1997.
(Figures included. Reference-denoting numbers appear in the same point size as document text.)
Volume: 25
Issue: 2
Pages: 196-202
Key Words: Sports medicine, ACL, ligaments, tissue grafts, proprioception, reinnervation, reconstruction.
This article, based on research in dogs (given the relative ease with which invasive histological investigations can be performed), shows that with the patellar-tendon autograft, there is good evidence that reinnervation occurs in the surrogate ligament. While it is still uncertain whether such regrown nerve endings enable regainment of pre-injury-style proprioception, at least it is realistic for useful nerve-ending regrowth to occur. Indeed, Barrack did observe that the newly developed nerve endings did respond to stimulation, and that this strongly implies that the neural pathway between the ACL and the central nervous system is eventually reestablished. This, in turn, shows that the grafted ACL does have the potential for providing meaningful sensory input. Therefore, a successful ACL reconstruction provides not only a mechanical restraint to abnormal knee movement, but could also reestablish some degree of propriopceptive (or quasi-proprioceptive) feedback to the brain. (Note: This is still an area of active research. The nerve-ending-regrowth-and-reconnection aspects would, in any case, take several years to occur. Remember, too, that there is no guarantee that such regrowth-and-reconnection will occur...and in fact, some later studies clearly show how uncertain occurrence of the regrowth-and-reconnection phenomenon is. In this regard, the only certainty seems to be that the outcome varies from person to person.) Barrack was one of the first to note the proprioceptive function of the ACL, in 1989. (Anyone who still thinks the ACL is completely devoid of nerve tissue would do well to read Barrack's studies!)
ABSTRACT
We studied six adult male dogs to determine whether free patellar tendon grafts show evidence of reinnervation when used for anterior cruciate ligament reconstruction. Histologic return of neural elements and return of a somatosensory-evoked potential defined evidence of reinnervation. Before removal, the native anterior cruciate ligament was electrically stimulated with a bipolar electrode and a somatosensory-evoked potential was recorded from a scalp electrode. The ligament was excised and reconstructed using an autogenous patellar tendon graft. Somatosensory-evoked potential was attempted immediately after reconstruction. Histology for nerve endings was performed on the native ligaments. Each animal underwent repeat arthrotomy 6 months later. The grafts were isolated and somatosensory-evoked potentials were attempted. An evoked potential was seen in all six dogs before reconstruction. No graft demonstrated a somatosensory-evoked potential acutely; however, 6 months postoperatively, the somatosensory-evoked potential returned in two cases. Histology of native ligaments showed that 25% of the 100 sections evaluated contained neural elements. Of the receptors present, 89% were mechanoreceptors and 11% were free nerve endings. Histologic examination of the graft tissue 6 months postoperatively revealed that all six grafts also contained neural elements. Mechanoreceptors and free nerve endings were present in approximately equal numbers in the grafts. The results of histology and somatosensory-evoked potential demonstrate that in at least some cases, free patellar tendon grafts show evidence of reinnervation when used for anterior cruciate ligament reconstruction.
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