Athletic success depends on the ability to run, jump, and change direction at high rates of speed called pivotal movements. The knee joint and ankle are subjected to extremely high forces such as, torque and compressive. The muscles of the lower limb not only provide stability, but also contribute to the excessive forces during the explosive activities noted above. Dynamic stability is an important goal of lower extremity and upper extremity rehabilitation programs.

     Although the knee has multiple ligaments to support the joint during movement, the 4 primary contributors to its stability are the ACL, posterior cruciate (PCL), medial collateral ligament (MCL), and the lateral collateral ligament (LCL). The most common surgery in the knee is ACL repair. The ACL ligament is the most vulnerable, of the four primary stabilizers noted above, to the stress of high speed pivotal movements in sports. A dynamic rehabilitation program after an ACL surgery is critical for the success of the surgical procedure. The success is measured by the ability of the patient to return to running, jumping, and cutting activities that are necessary in recreational and professional sports.

     Most of the literature supports the use of closed kinetic chain (CKC) exercises as a key component to rehabilitation following ACL ligament surgery. There are many advantages to incorporating CKC exercises as part of the rehabilitation program. CKC exercises take stress off the ACL and enhance dynamic stability by incorporating a co-contraction of the quadriceps and hamstrings muscles and providing a compressive load to the joint surfaces.

     Recently, the Journal of Orthopedic and Sports Physical Therapy (JOSPT) dedicated two issues to current theories how dynamic knee stability may be achieved through neuromuscular control. There is evidence that rehabilitation of the neuromuscular system can improve dynamic control of the knee and provide the mechanisms to prevent knee ligament injuries during athletic activities. Neuromuscular control is defined as a complex interaction between the nervous system and the musculoskeletal system. The sensors in the neuromuscular control system are referred to as mechanoreceptors. (1) These receptors are located in soft connective tissues such as the 4 primary stabilizing ligaments, noted above, that provide stability to the knee. The receptors respond to various forms of mechanical deformation such as tension and compression. Activation of these receptors provides information to the central nervous system (CNS), which modify conditions at the local level by modulating muscle activity.

     A patient who sustains a complete ACL tear may experience a decline in proprioceptive function contributing to the progressive instability and disability often observed after this injury. (2) Stability and balance training and plyometric training produce reductions in voluntary activation times, which may decrease muscle response times so the athlete is more able to perform rapid and unexpected sports maneuvers. (3) External loading of the knee and ACL loading result from flexion loading as observed in straight running. Studies show that during all cutting maneuvers observed in various sporting activities provide a weight acceptance and peak push off that may be critical points for ACL injury. (3)

     Based on the above rationale, a training program to rehabilitate an ACL repair and reduce the risk of ACL injury should consist of (A) increased use and coordination of hamstrings and quadriceps co-contraction. (B) increase the performance of the whole body in coordinated multi-joint movement patterns. (C) exercises to stimulate the knee joint ligament and capsule mechanoreceptors to improve joint stabilization. (D) plyometrics to improve voluntary activation times and strength, especially that of the hamstrings. (E) skill training that teaches players the movements that will produce the least external joint movements and best joint postures when performing cutting maneuvers. (3)

     The Dynamic Edge stands apart from other exercise equipment because it provides all of the above rationale for rehabilitation of ACL repairs, reducing the risk of ACL injury, and for training athletes to improve their performance. The Dynamic Edge provides lateral movement in a CKC position similar to a slide board. While performing lateral movements, the foot plates act as individual tilt boards for proprioception training promoting balance and coordination. The flexion and extension of the knee in the CKC position provides co-contraction of the hamstrings and quadriceps muscles. The side-to-side movements simulate the cutting maneuvers performed during sporting activities by providing varus-valgus and internal-external rotation to the lower leg. However, the push-off and pivotal movement of the weight-bearing leg during cutting is prevented, thus providing limited external joint movements and the best joint postures to safely train the athlete in cutting activities.

     The Dynamic Edge also includes, in the Rehab package, resistance bands to the pelvic and femur providing core muscle strengthening. A wobble board is also available for advanced neuromuscular training. Lastly, a weight-vest has been designed to provide resistance to the eccentric and concentric activity of CKC flexion and extension performed during lateral movements on the Dynamic Edge.

     The latest development is the Dynamic Edge Plyometric Power that provides lateral explosive movements to improve voluntary reaction times and strength of the lower extremity. Finally, the Dynamic Edge provides rehabilitation of the Lower Kinetic Chain and the whole body in coordination and multi-joint movement patterns.

1. Williams GN, Chmielewski T, Rudolph KS, Buchanan TS Synder-Mackler L: Dynamic Knee Stability: Current theory and implications for clinicians and scientists. JOSPT 2001;31:546-566.
2. Risberg MA, Mork M, Jenssen HK, Holm I. Design and implementation of neuromuscular training program following anterior cruciate ligament reconstruction. JOPST 2001;31:620-631.
3. Lloyd DG. Rationale for training programs to reduce anterior cruciate ligament injuries in Australian football. JOSPT 2001;31:645-654.

Robert Donatelli, PhD, PT, OCS, is national director of sports rehabilitation for Physiotherapy Associates in Atlanta.