By Michael J. Mullaney, MPT
Joint stability is the state of a joint remaining or promptly returning to proper alignment through equalization of forces.1 Restoring joint stability is an essential component of any rehabilitation program, especially one designed for an athlete following a lower extremity injury. Lower extremity joint stability is dependent on various components. Joint structure or surface topography is the first anatomical level of joint stability. It is evident in our anatomical design that we often sacrifice this first level of joint stability for a more mobile joint. This sacrifice of anatomical joint stability predisposes our mobile joints to injury. Our second level of joint stability is achieved through non-contractile, soft-tissue components like ligaments, accessory cartilage and joint capsules. Our final and most influential level of stability is gained through contractile, muscular components. This contractile component of a joint's stability provides us the opportunity to train and increase the level of joint stability.
Although anatomical and non-contractile components of joint stability can be addressed with surgical interventions, a properly design rehabilitation program can positively affect the contractile components to provide an athlete with a greater level of dynamic stability. For recovering athletes to perform at their optimal level, they must have the dynamic ability to gradate muscle force and contraction type to prevent joint disruption.2,3 In recent years this form of dynamic stability training has been referred to as neuromuscular training.4,5,6
Neuromuscular Control and Proprioceptive Input
From a joint stability perspective, neuromuscular control represents an unconscious activation of dynamic restraints occurring in preparation for and in response to joint motion and loading for the purpose of maintaining and restoring functional joint stability.1 According to Risberg et al.,6 the objective of neuromuscular training is to improve the nervous system's ability to generate a fast and optimal muscle firing pattern, to increase dynamic joint stability, decrease joint forces and relearn movement patterns and skills.6 Neuromuscular control can improve knee joint stability by enhancing unconscious motion responses through stimulating both afferent signals and control nervous system centers responsible for maintaining dynamic joint stability.
Training this continual feedback control system improves one's ability to utilize proprioceptive information. Proprioceptive information is attained from joint receptor input originating from muscle spindles, tendons, and joints. These receptors can detect joint position and movement as well as delineate direction, amplitude and speed of joint motion. In theory, a joint that possesses a high level of neuromuscular control and a highly sensitive proprioceptive feedback system can respond appropriately to variations in forces placed upon it during activity and decrease risk of injury. Therefore, the premise for implementing a proprioceptive training program is to train joint proprioceptors to adapt to stimuli received either during or prior to initiation of a deleterious movement.5
Prior to any motor task or action, a series of subtle events prepare the body to maintain both postural and joint stability.7 Following an anterior cruciate ligament injury, compensatory motor patterns develop to maintain these two types of stability. These adaptive motor patterns involve increased hamstring activation before joint loading and produce alterations in knee joint angles during load acceptance. 8,9,10 Colby et al10 found that patients having undergone an ACL reconstruction had a greater time to stabilization on the involved extremity when compared to that of the uninvolved extremity. These changes in muscular programming may be related to a loss of mechanical stability or a loss of proprioceptive input and need to be addressed during the progression of a functional rehabilitation program. Regardless of why these changes in motor programming occur, as clinicians, we have the ability to train these missing links.
Why Train Joint Stability?
The concept of training joint stability has been well examined in the ankle joint. Studies have shown that patients had improved selective sequential muscle contractions in the ankle following a well-designed neuromuscular program using a balance disc. Sheth et al11 reported altered muscular activation timing during a simulated lateral ankle sprain following an ankle disc training program. These researchers placed fine-wire electrodes in each subject's anterior tibialis, posterior tibialis, peroneus longus, and flexor digitorum longus muscles. Prior to the training protocol, all muscles fired simultaneously during the replication of the lateral ankle sprain. Following the 8-week training program, EMG activity revealed a delay in anterior and posterior tibialis contractions during replication of a lateral ankle sprain. This delay favors the correction of excessive ankle inversion. This study demonstrates the importance of utilizing proprioceptive stability training to improve muscle reaction timing. This concept of preventative proprioceptive training is now becoming a highly utilized technique of training stability for various joint complexes.
In recent years clinicians have used neuromuscular training programs for the prevention of ACL injuries4,5,12 the rehabilitation of the ACL deficient knee,13 and the core component of a post-surgical rehabilitation program.6 Hewett et al.4 introduced a six-week, pre-season jump-training program designed to prevent knee injuries in female athletes. Phase I was used to train subjects in proper jumping techniques. Phase II concentrated on building a base of strength, power and agility. Phase III focused on achieving maximum vertical jump height. These researchers reported a decreased incidence of injury in the trained female athlete group when compared to the untrained group. These findings are relevant when we consider that the jump landing sequence places an increased degree of stress on the stabilizing structures of the knee and is often a common mechanism of injury for many athletes.14 Furthermore, using training programs and implementing augmented feedback instructions can reduce impact landing forces during jump landing.15 Studies of this type demonstrate the ability to develop training programs that enhance the coordination, strength and dynamic stability of patients and decrease the rate of injury.
Implementing a Joint Stability Training
Neuromuscular training to restore knee joint stability in patients with ACL deficient knees was originally evaluated by Ihara and Nakayama.16 By implementing a balance program with perturbation training, they concluded that that the program improved muscular reaction time. Beard et al.13 assigned ACL deficient subjects to either a proprioceptive training program or a traditional strengthening program. The proprioceptive program utilized balance, dynamic joint stability and perturbation training. Traditional strengthening program was based on strengthening the lower extremity musculature. The study demonstrated a significant improvement in hamstring contraction latency and a higher Lysholm functional score in the proprioceptive neuromuscular training group.
Risberg et al.6 have designed an evidence-based neuromuscular training program to be implemented following ACL reconstruction. This training program was developed using the latest knowledge on graft healing response, ACL strain values during exercise, function of ligament mechanoreceptors and neuromuscular control. The authors developed a comprehensive program consisting of balance exercises, dynamic joint stability exercises, plyometric exercises, agility drills and sports-specific exercises. The effectiveness of this rehabilitation program on short and long term outcomes is not known at this time; however, it focuses on restoring joint stability in order to return the patient to the highest level of function.
The purpose of this article is to highlight the importance of using neuromuscular control in treating patients with lower extremity impairments. As clinicians in today's healthcare spectrum, we need to possess the tools that will allow us to treat patients in a thorough and timely fashion. By training joint stability with proprioceptive enhancement programs, we are offering exercises that address multiple areas of concern: strength, balance, proprioception, neuromuscular control, and biomechanics.
As with any training program, patients must be progressed appropriately. To introduce neuromuscular training in a rehabilitation program, the clinician must introduce the balance portion prior to adding highly dynamic joint stability exercises. This progression provides the feedback system a chance to start from the bottom up and build from a base of low-level stability training. Progressing to dynamic stability training following familiarization with balance training will enhance the likelihood of the neuromuscular program's success. One should always consider the readiness for dynamic exercise progression. Patients with increased pain or swelling should not progress to high-level dynamic stability training. As patients progress through the stability program, physical therapists should always consider the quality of the movement, the level of postural stability and the coordination between joints. Like any neuromuscular training program, the amount of exercises is limited to the imagination of the clinician. The more creative, challenging and applicable the exercises are, then the more motivated the patient will be to participate.
These ideas are not intended to replace traditional strengthening programs; however, they can add a component of training that is often neglected. In our clinic, dynamic joint stability training following a lower extremity injury is an essential component to our rehabilitation programs. The following list highlights joint stability training exercises designed to improve joint stability.
Proprioceptive Balance Training
- Balance board with perturbation
- Balance board with ball toss
- Single limb balance (floor, disc, board) with rotational reach:
Mini-squats on balance board:
Dynamic Joint Stability Training- "Star" heel taps
- "Star" balance and reach
- Step up on onto disc or balance board:
Step down onto disc or balance boardLunge onto Bosu trainer:
- Leap onto Bosu trainer and hold (bilateral and single limb):
Lateral plyometrics: step down step and leap laterally onto next step (bilateral and single limb)- Single-limb hops for distance; concentrate on "sticking" landing
- Single-limb dot hopping; hop from spot to spot on floor:
- Reactive number hopping; place numbered pieces of tape on floor as clinician calls out a number, patient must hop to that number
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