Dynamic EMG analysis of anterior cruciate deficient legs with and without bracing during cutting

Abstract

The purpose of this research was to determine if bracing altered muscle firing amplitude, duration, or timing, creating improved dynamic stability. We hypothesized that a derotational knee brace improved the stability of an ACL deficient knee by augmenting limb proprioception, causing hamstring muscles to increase in activity and/or to contract earlier during a side-step cut. Ten subjects with documented unilateral isolated ACL deficient knees and five normal controls participated. A strap dominant brace (Lenox Hill, Lenox Hill Brace, Inc., Long Island City, NY) and a shell dominant brace (CTi, Innovation Sports, Irvine, CA) were selected for study. Using footswitches and dynamic EMG, we tested each subject during performance of a side-step cutting maneuver. Subjects completed 15 trials: 5 without bracing, 5 with the strap dominant brace, and 5 with the shell dominant brace. Normals cut 10 times each on their dominant limb. In swing phase, subjects had 38% more and 32% higher lateral hamstring EMG activity than normals; in stance phase, subjects had less quadriceps and gastrocnemius activity but more medial hamstring activity. When braced during stance phase, the ACL deficient legs demonstrated a further reduction of 18% in quadriceps total activity and 14% in peak activity compared to the unbraced situation. The hamstrings showed a concomitant decrease of 18% in total activity. No timing differences were noted between the braced and unbraced conditions during swing or stance phase.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of functional knee bracing: an in vivo three-dimensional kinematic analysis of the anterior cruciate deficient knee

“…Previous manual knee evaluations including the anterior drawer test, the pivot shij? test, and Lnchman 's test have al1 rneasured tibial displacements during simulated static loading conditions but they do not reflect true physiologic loading (Branch et al, 1989).…”

“…Early studies reported fewer syrnptoms of instability with improved athletic performance during brace use although evaluations were anecdotal and subjective in nature (Vailas et ai., 1990 However, braces seem to fail in situations where high loads are encountered or when the load is applied in an unpredictable manner (Branch et al, 1989).…”

“…Branch and Hunter (1 990) found that ACLD subjects during the performance of a lateral side step and straight ahead m i n g compensate the way they perform certain athletic manoeuvres. During small athletic manoeuvres such as walking and ruming, hinctional braces appeared to be effective and the compensatory mechanisms employed arnong the ACL deficient group was disrupted (Branch et al, 1989).…”

“…Traditionally, force platforms have been used in biomechanics for quantifj6ng extemal forces during human gait (Branch et al, 1989;Branch and Hunter, 1990;Winter, 1990). Ground reaction forces are a reflection of forces imparted to the foot by the ground and composed of the sum of multiple forces generated by the body as a system during an event (Branch et al, 1989).…”

“…Ground reaction forces are a reflection of forces imparted to the foot by the ground and composed of the sum of multiple forces generated by the body as a system during an event (Branch et al, 1989).…”