The Healing Response Technique: A Minimally Invasive Procedure to Stimulate Healing of Anterior Cruciate Ligament Injuries Using the Microfracture Technique

J. Richard Steadman

William G. Rodkey

Defects in the anterior cruciate ligament (ACL) rarely heal spontaneously. The torn ACL sometimes scars to the posterior cruciate ligament (PCL), but this aberrant healing probably does not result in any significant biomechanical function. ACL injuries continue to present a difficult problem for orthopaedic surgeons because it is difficult to predict whether such injuries will cause severe disability or only minimal impairment.

Primary repair of cruciate ligament injuries has often produced less than rewarding results.¹^,²^,³^,⁴ Both clinical and experimental studies have demonstrated poor healing of these intra-articular ligaments.¹^,²^,³^,⁴^,⁵^,⁶^,⁷^,⁸^,⁹^,¹⁰^,¹¹ This failure to heal completely is thought to be because of the inhibitory effects of the intra-articular environment (poor hematoma formation and a lack of cytokine stimulation) and the inherent inability of the cruciate ligament cells themselves to mount a significant reparative response.¹^,⁷^,¹²^,¹³ Several studies have shown that cruciate ligament cells are less responsive to cytokine stimulation (chemotaxis, mitogenesis, and metabolic activity) than cells from extra-articular ligaments (i.e.,
medial collateral ligament).¹^,⁵^,¹²^,¹⁴ Furthermore, the lack of an additional source of reparative cells in the intra-articular environment may further limit the healing response of these intra-articular ligaments.

A similar problem exists in articular cartilage injuries. The inability of chondrocytes to mount a reparative response and the lack of adjacent reparative cells naturally migrating into the wound make the treatment of these lesions very challenging. However, clinical and experimental studies have shown that accessing mesenchymal cells, as well as an array of cytokines, through surgically created connections to the underlying bone marrow (“microfracture” technique), stimulates a “healing response” sufficient enough to repair the defect.¹⁵^,¹⁶^,¹⁷^,¹⁸^,¹⁹^,²⁰^,²¹^,²²^,²³ The efficacy of the microfracture technique to treat articular cartilage defects has been demonstrated both experimentally and clinically.¹⁶^,¹⁷^,¹⁸^,²⁰^,²² Theoretically, using this same technique to access bone marrow elements might be useful to stimulate intra-articular ligament healing. Hence, a direct extension of the microfracture procedure involves the use of a surgical awl to produce between three and ten microfracture holes in the cortical bone at the femoral footprint of the origin of the injured ACL, or other ligaments intra-articularly, as well as making numerous perforations in the injured ligament itself. In this way, a marrow clot is surgically induced. The clot, which forms after the bone perforations are made, captures the ends of the damaged ligament and provides a rich environment for tissue repair. Previous reports describe the use of microfracture to treat chondral lesions,¹⁶^,¹⁷^,¹⁸^,²⁰^,²² but until recently there have been no reports on use of the microfracture technique to treat intra-articular ligament injuries.²⁴^,²⁵

The healing response, the term given by the senior author (JRS) who developed this procedure to treat intra-articular ligament injuries, is partly a response to findings by Daniel and coworkers,²⁶^,²⁷ who reported the increased risk of degenerative arthritis following ACL reconstruction. They concluded that a large group of patients with ACL disruption would not benefit from intra-articular reconstruction of the ligament. In fact, such procedures may be detrimental in certain patients. Laboratory studies in primates by McCarthy et al.²⁸ supported the clinical observations by Daniel and associates.²⁶^,²⁷ Although historically, it has been stated that intra-articularly injured ligaments are not expected to heal,¹^,²^,⁴^,⁷^,⁸^,⁹^,¹⁰ use of the microfracture procedure to stimulate healing may be an alternative to intra-articular ligament reconstruction.

This healing response procedure was originally conceived especially for proximal-third ACL injuries, the type frequently seen in skiers. Nonetheless, it has proven its utility in many types of ACL injuries regardless of the injury mechanism. We believe that the healing response procedure has significant advantages that outweigh the potential disadvantages. It is a technically easy procedure for the surgeon to perform, with minimal downside risk. We recently completed a canine study to investigate the morphologic, cellular, and molecular events that occur within the surgically induced clot and ligament during the healing process.²⁴ With this new understanding of the basic science of the healing response technique, we were able to assess and better understand our observations in clinical patients.²⁵

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