Gait Retraining After Anterior Cruciate Ligament Reconstruction

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Gait Retraining After Anterior Cruciate Ligament Reconstruction Michael J. Decker, MS, Michael R. Torry, PhD, Thomas J. Noonan, MD, William I. Sterett, MD, J. Richard Steadman, MD ABSTRACT. Decker MJ, Torry MR, Noonan TJ, Sterett WI, Steadman JR. Gait retraining after anterior cruciate ligament reconstruction. Arch Phys Med Rehabil 2004;85:84856. Objectives: To examine the effects of 2 gait retraining protocols on the gait patterns of patients with bone–patellar tendon– bone anterior cruciate ligament (ACL) reconstruction. Design: Randomized control, repeated-measures design. Setting: Private orthopedic center and research facility. Participants: Sixteen patients with bone–patellar tendon– bone ACL reconstruction, randomly subdivided into 2 groups (group 1, n⫽8; group 2, n⫽8), and a healthy control group of 8 subjects. Intervention: The 16 subjects with ACL reconstruction were randomly assigned to 2 different gait retraining protocols over a 6-week training interval: (1) a protocol using a predicted stride frequency calculated from the resonant frequency of a force-driven harmonic oscillator (FDHO) model or (2) a protocol using the preferred stride frequency (PSF). Main Outcome Measures: Gait analyses examining the lower-extremity kinematic, kinetic, and energetic gait patterns of each group. Results: Gait retraining with the FDHO model showed improvements in lower-extremity positions, hip and knee extensor angular impulse, and work parameters. Gait retraining with the PSF demonstrated no statistical improvements. The FDHO training protocol facilitated a greater midstance knee range of motion (ROM) and greater rates of improvement for midstance ROM, hip extensor angular impulse, and concentric hip extensor work. Conclusions: Gait retraining with the resonant frequency of an FDHO model facilitated a greater recovery of gait function compared with training with the PSF. Key Words: Anterior cruciate ligament; Gait; Knee; Rehabilitation. © 2004 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation

From the Biomechanics Research Laboratory, Steadman-Hawkins Sports Medicine Foundation, Vail, CO. Presented in part at the International Society of Biomechanics’ 18th Annual Meeting, 2001, Zurich, Switzerland. Supported in part by the NFL Charities and the Steadman-Hawkins Sports Medicine Foundation. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated. Correspondence to Michael R. Torry, PhD, Biomechanics Research Laboratory, Steadman-Hawkins Sports Medicine Foundation, 181 West Meadow Dr, Ste 1000, Vail, CO 81657, e-mail: [email protected]. Reprints are not available from the authors. 0003-9993/04/8505-8133$30.00/0 doi:10.1016/j.apmr.2003.07.014

Arch Phys Med Rehabil Vol 85, May 2004

AIT RETRAINING PROGRAMS ARE a vital compoG nent of current therapy protocols for patients with anterior cruciate ligament (ACL) reconstruction. Despite a focused 1-7

effort, it is commonly reported that patients with ACL reconstruction walk with reduced stride frequencies (cadence) and stride lengths, with decreased stance phase knee range of motion (ROM), and with increased hip extensor and decreased knee extensor torque and power within the first year after surgery.1,8-10 These gait adaptations have been found to be related with quadriceps weakness1,3,11 and associated with low patient satisfaction with outcome after ACL reconstruction,12 decreased functional performance,13,14 and several postoperative complications,15,16 including osteoarthritis.17 Even though several authors have advocated gait retraining programs after ACL reconstruction, few have described the actual design of the program or have provided information for evaluation of the efficacy of such a program.2,4-7,18 Therefore, the design and refinement of efficient gait retraining protocols remains an important challenge for clinicians. Although there are many analyses and variables to describe gait, the simple variables of stride frequency and stride length are highly indicative of appropriate human gait characteristics. These variables relate well to kinetic measures of muscle performance and represent the endpoint manifestations of numerous neuromuscular processes. In a population with ACL reconstruction, stride frequency as well as lower-extremity joint ROM and moments are drastically reduced at the time when these patients begin gait rehabilitation.8,11 Although an early rehabilitation goal for this population is to reestablish normal gait parameters, preinjury gait parameters are usually unknown to the clinician, thus, the patients often develop adapted gait strategies.8,9,19 At freely selected gait speeds, however, it has been shown that healthy subjects naturally select a preferred stride frequency (PSF) that is predictable by the resonant frequency of the limbs, modeled as forcedriven harmonic oscillators (FDHOs).20-23 Subject-specific inputs of leg length and mass into this resonance formula has empirically been shown to accurately predict minimum metabolic cost, which occurred at the PSF with a mean prediction error near 1%.23 Because ACL reconstruction does not change the length and weight of the leg, using the resonance formula for an injured population may provide a means to predict a preinjured stride frequency, which can be used to reestablish a normal gait. It has been well documented that rehabilitation procedures that use repetitive audio signals to entrain a desired stride frequency that is typically faster than the PSF are effective at improving gait.24-26 This gait frequency– based strategy is a means to manipulate the PSF to alter sensory and motoneuron signals, training stimuli, and resultant motor learning. Thus, the purpose of this study was to examine the therapeutic effects of 2 gait retraining protocols on the gait patterns of patients with bone–patellar tendon– bone ACL reconstruction: a protocol designed with the resonant frequency of a modified FDHO and a protocol using the patient’s PSF. It was hypothesized that gait retraining with the resonant frequency would facilitate greater

GAIT RETRAINING AFTER ACL RECONSTRUCTION, Decker

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Fig 1. Patient enrollment and randomization protocol. Abbreviations: IRB, institutional review board; PT, physical therapy. *Assignment of a number was conducted at random as patients were discharged from the clinic and as they agreed to participate in the study. Numbers were assigned to subjects in ascending and then descending (1,2,2,1) order until the sample size of the subgroups were determined to be statistically adequate with regard to study variables of interest.

gains in knee ROM, knee torque and power, and reductions in hip torque and power, as compared with gait retraining with the PSF. METHODS Participants A total of 16 patients (mean age, 27.8⫾7.4y; weight, 75.5⫾12.5kg; height, 1.8⫾0.1m) who had arthroscopically assisted bone–patellar tendon– bone ACL reconstruction and 8 healthy (age, 28.3⫾4.3y; weight, 71.5⫾11.1kg; height, 1.7⫾0.1m) control subjects participated in this study. All subjects with ACL injuries had reconstruction by the same orthopedic surgeon, participated in an accelerated rehabilitation strength and ROM protocol,27 and were restricted from recreational and sporting activities for the first 12 weeks after surgery. Exclusion criteria were knee flexion contractures that prevented full knee extension; chronic knee joint effusion; and concomitant injuries that prevented, or delayed, early weight bearing (chondral defects, meniscal tears, multiple ligamentous ruptures). All subjects were allowed to bear weight as tolerated immediately after the surgery. Before any testing, each participant provided written informed consent according to a protocol approved by the Vail Valley Medical Center’s Internal Review Board.

The ACL reconstruction group was randomly subdivided into 2 groups and given different walking protocols lasting 6 weeks, beginning at 6 weeks postoperation (enrollment and randomization protocol is provided in figure 1). Group 1 (age, 25.9⫾6.8y; weight, 74.9⫾8.0kg; height, 1.8⫾0.1m) walked with the aid of a metronome at a stride frequency calculated from the resonant frequency of a modified FDHO model.21,22 The only instruction given to the subjects regarding metronome use was to match consecutive heel strikes with the audio signals. The resonant frequency was calculated from the following equation.21,22 f⫽1/(2 ␲ ⫻[L/2g]1/2)

(1)

where L is a simple pendulum equivalent length, ␲ equals 3.1416, and g equals 9.81m/s. The simple pendulum equivalent length required inputs of body weight and thigh, shank, and foot lengths. The same experimenter made all measurements at the first test session. The gravitational constant value of 2 is the modification to the model that has been added to compensate for dampening attributes of the biologic system.21,22 For a comprehensive review of the calculation, see Schot and Decker.20 Group 2 (age, 29.8⫾6.9y; weight, 76.1⫾15.0kg; height, 1.7⫾0.1m) walked at their PSF without a metronome. Both groups were instructed to walk a minimum of 3 days a week for Arch Phys Med Rehabil Vol 85, May 2004

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20 to 30 minutes for each exercise bout. Each subject maintained an exercise log that documented exercise frequency and duration. Periodic telephone calls were placed to each subject to evaluate the level of participation and ensure protocol adherence. To assess the effectiveness of the 2 training regiments, gait analyses were performed with self-selected velocities and PSFs 6 and 12 weeks after surgery. Before each gait test, the subjects were fitted with a standardized court shoea and allowed to warm-up on a treadmillb for 5 minutes and then familiarize themselves with the walkway and testing apparatus. Each participant practiced walking on the walkway until they showed consistent foot strikes on the force platform. Ten walking trials were collected at each test period and only trials within 2.5% of the self-selected speed, and where full foot placement was achieved on the force platform,c were considered acceptable for analysis. Instrumentation Thirteen retroreflective, spherical markers (diameter, 2.6cm) attached to select anatomic landmarks in a simplified Helen Hays marker set,28 defined a 4-segment, rigid-link model of the body. A 5-camera motion analysis system,d synchronized with infrared strobe lights, was used to capture 3-dimensional motion of the hip, knee, and ankle at a frequency of 60Hz. The cameras were calibrated with mean residuals ranging from 1.8 to 2.5mm over a volume of 1.50⫻1.10⫻1.50m. The kinematic data were smoothed by using a Butterworth filter with a 5-Hz cutoff frequency for marker trajectories. Segmental masses and the mass center locations of the trunk, thigh, shank, and foot were estimated from each subject’s anthropometric data according to Dempster29 and Hanavan.30 Ground reaction forces were collected at a frequency of 1200Hz. Center of pressure was calculated according to Winter.31 Joint moments were calculated by combining the anthropometric, kinematic, and forceplate data in an inverse dynamics analysis.31 Joint moments acting in the direction of hip and knee extension and ankle dorsiflexion were assigned to be positive. Instantaneous mechanical power for each joint was calculated by the taking the product of the joint moment and joint angular velocity. Both the joint moment and muscle power curves were mathematically integrated to calculate angular impulse and work parameters, respectively. Angular impulse represents the total contribution of a joint torque in producing movement at a joint and accounts for any joint torque alterations produced by a muscle group.8,9,32,33 Positive and negative work phases indicate energy production and absorption through concentric and eccentric muscular actions, respectively. All kinetic and energetic parameters were normalized to the product of body weight and height (%BW⫻ht).34 Analysis Sagittal plane, lower-extremity ROM, contact and average joint positions were derived from the position curves during the stance phase. Weight-acceptance knee ROM was calculated as the difference between initial contact position and maximum flexion.35 Midstance knee ROM was calculated from maximum flexion during weight acceptance to maximum extension during midstance.35 Hip and knee extensor angular impulses were calculated for the first half of the stance phase from the joint moment curves. Concentric hip extensor work (H1) was calculated from 0% to 75% of stance from the hip power curves. Eccentric (K1) and concentric (K2) knee extensor work values were calculated Arch Phys Med Rehabil Vol 85, May 2004

from 0% to 25% and 26% to 50% of stance from the knee power curves.36 Group effects at each time period (1-way analysis of variance [ANOVA]) and gait recovery effects (2-way mixed-factor ANOVA) were contrasted for all dependent variables. Tukey post hoc testing evaluated the within-group time effects between 6 and 12 weeks after surgery. Alpha was set a priori at P equal to .05 or less. RESULTS Group Characteristics and Protocol Adherence The time from injury to surgery was similar between the 2 ACL reconstruction groups (FDHO group, 120.1⫾104.5d; range, 5–348d; PSF group, 120.3⫾107.3d; range, 11–380d). Physical examination revealed all subjects to possess full passive knee extension at both test periods and that body mass did not fluctuate by more than 1kg. Review of the exercise logs demonstrated that all patients complied with the walking program, and that the training load over the 6-week protocol was equal between the 2 groups. The FDHO group walked an average of 3.3⫾0.7 days a week for 27.2⫾5.7 minutes a session, and the PSF group walked an average of 3.1⫾0.6 days a week for 27.0⫾7.0 minutes a session. One subject from the FDHO group and 2 subjects from the PSF group reported minor knee pain with no noticeable effusion during the second week of the protocol, but these issues tended to subside by the third week of the protocol and did not hamper their rehabilitation progress. Three subjects from the PSF group reported discomfort in their hip musculature during weeks 4 and 5 of the protocol, but the subjects stated that it did not affect their protocol adherence. Stride Characteristics Both ACL reconstruction groups walked with reduced stride frequencies and gait velocities compared with the healthy group 6 weeks after surgery (both P⬍.05). Stride frequencies and lengths were similar between the healthy and ACL reconstruction groups 12 weeks after surgery (all P⬎.05). Although both ACL reconstruction groups showed normal gait velocities and stride characteristics at 12 weeks, the recoveries were distinctly different (table 1). The FDHO group increased stride length and frequency (both P⬍.05), whereas the PSF group maintained a similar stride length (P⬎.05) but increased stride frequency (P⬍.05). Compared with the predicted, resonant frequency of the FDHO model (table 2), both ACL reconstruction groups used a slower PSF 6 weeks after surgery (both P⬍.05), and only the PSF group had a slower frequency at 12 weeks after surgery (P⬍.05). Gait Testing Means and standard deviations (SDs) for the kinematic, kinetic, and energetic variables are listed in table 3 and graphically represented in figures 2 to 4. No gait performance differences were found between the ACL reconstruction groups at 6 weeks after surgery (all P⬎.05). Kinematics Compared with the healthy group, at 6 weeks after surgery, both ACL reconstruction groups were qualitatively more flexed throughout the stance phase of gait and used on average 34% and 65% less knee ROM during weight acceptance and midstance (both P⬍.05). Knee position at initial contact with the force platform, weight acceptance, and midstance knee ROM for the FDHO group improved 65%, 40%, and 96%, respec-

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GAIT RETRAINING AFTER ACL RECONSTRUCTION, Decker Table 1: Stride Characteristics for the Healthy and ACL Reconstruction Groups FDHO

Stride length (m) Stride frequency (cycles/s) Velocity (m/s)

PSF

Healthy

6 Weeks

12 Weeks

6 Weeks

12 Weeks

1.56⫾0.11 0.93⫾0.06 1.46⫾0.03

1.52⫾0.12 0.83⫾0.11 1.26⫾0.17

1.66⫾0.15 0.90⫾0.09 1.49⫾0.11

1.53⫾0.14 0.86⫾0.06 1.31⫾0.13

1.61⫾0.23* 0.89⫾0.05*†‡㛳 1.43⫾0.18*†‡㛳

NOTE. Values are mean ⫾ standard deviation (SD). *Healthy vs FDHO group week 6 (P⬍.05). † Healthy vs PSF group week 6 (P⬍.05). ‡ FDHO group week 6 vs week 12 (P⬍.05). 㛳 PSF group week 6 vs week 12 (P⬍.05).

tively, 12 weeks after surgery compared with 6 weeks after surgery (all P⬍.05), whereas the PSF group showed no statistical improvements in these variables (all P⬎.05). Although deficits in midstance knee ROM remained for both ACL reconstruction groups 12 weeks after surgery compared with the healthy group (both P⬍.05), the FDHO group had a greater rate of functional improvement than the PSF group (interaction term P⬍.05). Additionally, the FDHO group was significantly more extended at initial ground contact and used more midstance knee ROM compared with the PSF group 12 weeks after surgery (both P⬍.05). Kinetics Compared with the healthy group, both ACL reconstruction groups 6 weeks after surgery showed on average a 36% increase in hip extensor angular impulse, and a 53% decrease in knee extensor angular impulse. Statistically, however, only the FDHO group used less knee extensor angular impulse compared with the healthy group (P⬍.05). Compared with 6 weeks after surgery, the FDHO group decreased hip extensor angular impulse by 23% and increased knee extensor angular impulse

by 55% 12 weeks after surgery (both P⬍.05), and the PSF group showed no changes (both P⬎.05). The PSF group was observed to have an 18% increase in hip extensor angular impulse 12 weeks after surgery compared with 6 weeks, but this did not differ statistically. However, this increase in hip extensor angular impulse showed by the PSF group revealed the interaction term of the hip extensor angular impulse comparisons to be statistically significant (P⬍.05), indicating that the training programs facilitated different effects from the hip extensor muscles. Energetics At 6 weeks after surgery, both ACL reconstruction groups had an average of 38% greater concentric hip extensor work (H1) values compared with the healthy group (P⬎.05) and used an average of 60% and 73% less eccentric (K1) and concentric (K2) knee extensor work (both P⬍.05). The FDHO group increased K1 and K2 by 113% and 100%, respectively, over the course of the 6-week training period (both P⬍.05), and the PSF group showed no statistical changes (all P⬎.05). Compared with the healthy group, these results indicated the

Table 2: Anthropometric Characteristics, Predicted Resonant Frequencies, and Actual Stride Frequencies for Both ACL Reconstruction Groups at 6 and 12 Weeks After Surgery

Subject No.

FDHO 1 2 3 4 5 6 7 8 Mean SD PSF 9 10 11 12 13 14 15 16 Mean SD

Body Weight (N)

Actual Stride Frequency (cycles/s)

Femur Length (m)

Shank Length (m)

Foot Length (m)

Resonant Frequency

6 Weeks

12 Weeks

618 749 913 696 702 760 727 705 733.8 84.3

.380 .410 .460 .460 .420 .415 .430 .410 .423 .027

.395 .470 .490 .450 .400 .395 .490 .445 .442 .041

.150 .150 .160 .145 .140 .130 .150 .145 .146 .009

.957 .903 .868 .885 .930 .937 .884 .915 .910 .030

.838 .839 .870 .682 .842 .920 .797 .829 .827 .069

.957 .914 .870 .846 .964 .941 .827 .877 .899 .052

756 736 667 644 673 747 1115 624 745.3 157.3

.410 .435 .400 .390 .400 .360 .350 .385 .391 .027

.420 .420 .395 .380 .410 .430 .405 .365 .403 .022

.140 .120 .135 .130 .160 .130 .140 .130 .136 .012

.927 .914 .946 .961 .935 .955 .974 .972 .948 .021

.803 .853 .864 .885 .824 .932 .821 .880 .858 .042

.853 .898 .833 .893 .899 .948 .883 .919 .891 .036


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GAIT RETRAINING AFTER ACL RECONSTRUCTION, Decker Table 3: Mean Kinematic, Kinetic, and Energetic Values for Both Groups FDHO Variable

Kinematic (deg) Average hip position Average knee position Knee contact position Knee weight acceptance ROM Knee midstance ROM Kinetic (%BW ⫻ ht) Hip extensor impulse (0%–50%) Knee extensor impulse (0%–50%) Energetic (%BW ⫻ ht) H1-concentric hip work (0%–75%) K1-eccentric knee work (0%–25%) K2-concentric knee work (26%–50%)

Healthy

Week 6

PSF Week 12

Week 6

⫺6.94⫾4.39 ⫺19.18⫾3.76 ⫺3.74⫾3.48 21.90⫾3.42 15.10⫾3.25

⫺7.64⫾6.09 ⫺20.87⫾3.75 ⫺7.76⫾3.67 14.33⫾4.53 5.41⫾3.07

⫺6.44⫾3.77 ⫺17.68⫾3.72 ⫺2.74⫾3.16 20.08⫾3.58 10.61⫾2.66

⫺7.72⫾8.82 ⫺20.55⫾7.56 ⫺9.08⫾5.20 14.68⫾5.29 5.28⫾1.94

0.86⫾0.35 0.54⫾0.26

1.38⫾0.31 0.22⫾0.15

1.06⫾0.33 0.34⫾0.15

1.01⫾0.53 0.29⫾0.23

0.66⫾0.31 ⫺0.53⫾0.20 0.26⫾0.21

1.02⫾0.42 ⫺0.15⫾0.13 0.07⫾0.06

0.81⫾0.28 ⫺0.32⫾0.15 0.14⫾0.11

0.80⫾1.03 ⫺0.25⫾0.21 0.07⫾0.06

Week 12

⫺8.52⫾6.48 ⫺20.92⫾3.31 ⫺6.44⫾3.44‡¶** 18.53⫾4.65*‡¶ 6.79⫾3.06*†‡㛳¶**†† 1.19⫾0.47¶†† 0.37⫾0.22*¶ 1.03⫾0.39†† ⫺0.28⫾0.18*‡㛳¶ 0.11⫾0.08*‡¶

NOTE. Values are means ⫾ SD. *Healthy vs FDHO group week 6 (P⬍.05). † Healthy vs FDHO group week 12 (P⬍.05). ‡ Healthy vs PSF group week 6 (P⬍.05). 㛳 Healthy vs PSF group week 12 (P⬍.05). ¶ FDHO group week 6 vs week 12 (P⬍.05). ** FDHO group week 12 vs PSF group week 12 (P⬍.05). †† Significant interaction (P⬍.05).

FDHO group did not differ in hip and knee work, but K1 remained statistically lower for the PSF group at 12 weeks after surgery (P⬍.05). Additionally, the FDHO group decreased H1 by 21% over the 6-week training period, whereas the PSF group was observed to have a 29% increase, but neither were statistically significant (both P⬎.05). However, a significant statistical interaction (P⬍.05) for H1 indicated that the 2 training programs facilitated opposite effects in concentric work from the hip extensor muscles. DISCUSSION Numerous studies have found that subjects with ACL reconstruction use neuromuscular adaptations during gait1,3,8,9,33,37,38 and functional activities.1,10,11,35,39 From these studies, it appears that the hip extensor moments and powers progressively increase during the first 6 months after surgery, whereas the knee extensor moments and powers progressively decrease. In our study, both ACL reconstruction groups showed these classical gait adaptations 6 weeks after surgery. Over the 6-week training period, the PSF group showed gait patterns that followed the same time course, whereas the FDHO group decreased hip extensor work and power and increased knee extensor work and power. In addition, this mode of training was found to be superior to training with the PSF in promoting knee motion during midstance and facilitating reductions in the hip extensor moments and powers. Thus, gait retraining with the resonant frequency of a modified FDHO model had a greater therapeutic effect on the recovery of gait function for people with bone–patellar tendon– bone ACL reconstruction as compared with gait retraining using the PSF. This study supports the notion that gait retraining programs predicted and designed from the mechanical attributes of the legs can beneficially affect the learning process and development of neuromuscular function. Prolonged gait adaptations may contribute to quadriceps weakness. During the early phases of rehabilitation, decreased quadriceps function is clinically observed as a protective limp that is designed to prevent pain or further injury of the patellar tendon graft or graft harvest site. It is our perspective that this Arch Phys Med Rehabil Vol 85, May 2004

limp is a conscious selection to reduce quadriceps function and is manifested by a reduced knee extensor moment that, in turn, requires a greater hip extensor moment for propulsion and total support; over time, this becomes accentuated and engrained into the locomotor programs. As a consequence, these gait adaptations may be the origin of the quadriceps weakness noted for this population.1,3,11,35 Indeed, several gait parameters, such as decreased weight acceptance and midstance knee ROM and a decreased knee extensor moment, have been found to be related to quadriceps weakness.1,11,35 Although quadriceps strength was not measured in this study, only the FDHO group showed statistical improvements in these gait parameters. This may indicate that training with the resonant frequency of a modified FDHO model might have promoted a more normal gait pattern, which in turn facilitated a greater recovery of quadriceps strength compared with training with the PSF. Although knee extensor torque during gait has been related to quadriceps strength, it may not necessitate normal quadriceps function. A net knee extensor moment during the first 50% of the stance phase of gait is primarily derived from eccentric and concentric muscular contractions of the quadriceps muscles. In agreement with other studies,8,9 both ACL reconstruction groups had reduced knee extensor moments and eccentric and concentric knee extensor work 6 weeks after surgery, compared with the healthy group. At the end of the 6-week training protocol, both ACL reconstruction groups had knee extensor moments that did not differ statistically from the normal group, but deficits in eccentric quadriceps work remained for the PSF group. Although both ACL reconstruction groups increased their gait velocity, the FDHO group walked with greater extension at 12 weeks compared with 6 weeks after surgery, and the PSF group walked with greater flexion. A knee that is more flexed during and after initial ground contact may not be conducive to adequate shock absorption from the quadriceps muscles40; this may account for the eccentric knee work reductions noted in the PSF group. Given the same gait velocity, the results of our study are interpreted to indicate that the knee extensor moment for the FDHO group was generated with a relatively normal quadriceps muscle function, whereas


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Fig 2. Mean hip and knee position curves (degrees) during the stance phase for the healthy group (O) and both ACL reconstruction groups at 6 weeks (FDHO group, {; PSF group, 䊐) and at 12 weeks (FDHO group, }; PSF group, ) postsurgery. Negative values indicate hip and knee flexion.

the knee extensor moment for the PSF group was influenced by a flexed knee position. Thus, training with the resonant frequency of a modified FDHO model might have facilitated greater quadriceps muscle function compared with training with the PSF. Differences in gait recovery were found between the 2 ACL reconstruction groups despite identical rehabilitation protocols and training loads. Enforcing a normal stride frequency for the FDHO group may have influenced the differences between training protocols. It is well documented that rehabilitation procedures that involve repetitive, rhythmically patterned movements that are matched to an audio signal are effective at improving stride lengths and gait velocities.24-26 The immediate effects of enforcing a faster frequency for the FDHO group at 6 weeks after surgery also promoted a more normal gait with increased stride lengths and gait velocities,19 both of which require a greater muscular output from the quadriceps muscles.28,41,42 Promoting a more normal gait earlier than the PSF

group probably encouraged earlier quadriceps return and accounts for the differences in gait performance at the end of the training period. Gait improvements from intensive quadriceps strengthening,11,43 therefore, may only be temporary if the patient uses and maintains an adapted gait with reduced knee extensor joint moments and powers. Limitations of this study are recognized. First, we used the predictive power of the FDHO model as a basis for the initiation of a gait retraining protocol. Although the mean predictive error has been shown to be as low as 1% for healthy subjects, some subjects may choose to walk at percentages even greater than those that were predicted. Thus, slower preferred stride frequencies compared with those predicted by the model may not be a gait adaptation to ACL reconstruction. Second, the patient’s selection to perform gait adaptations may be reasonably used and designed to protect the ACL graft and harvest site from deleterious forces to allow adequate healing. We were initially conArch Phys Med Rehabil Vol 85, May 2004

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Fig 3. Mean hip and knee internal joint moment curves (%BWⴛht) during the stance phase for the healthy group (O) and both ACL reconstruction groups at 6 weeks (FDHO group, {; PSF group, 䊐) and at 12 weeks (FDHO group, }; PSF group, ) postsurgery. Positive values indicate hip and knee extensor joint moments.

cerned that forcing the patient to walk faster with a greater stride frequency may be harmful. However, isokinetic strength testing and functional agility programs, which often produce very large knee shear forces and knee torques, are commonly performed as early as 4 weeks after surgery without incident.5,6,44 In support of this, Shelburne et al45 recently determined that ACL force during walking for healthy subjects is well below most quadriceps strengthening exercises that are being performed at this phase in the rehabilitation program. Last, in this study design, gait retraining was used between 6 and 12 weeks after bone– patellar tendon– bone ACL. We chose this time period because the rehabilitation protocol used in our clinic begins to focus on gait at 6 weeks after surgery in preparation for higher demand activities beginning at 12 weeks after surgery. It is unknown whether gait retraining for a longer time period, or within another time period, would facilitate a different effect on gait recovery. Arch Phys Med Rehabil Vol 85, May 2004

CONCLUSIONS Gait retraining with the FDHO model showed improvements in lower-extremity positions, hip and knee extensor angular impulse, and work parameters, whereas gait retraining with the PSF showed no statistical improvements. The FDHO mode of training was superior to the PSF protocol in promoting midstance knee ROM and facilitating normal hip extensor function. These gait performance improvements were proposed to stem from an audio signal that accessed locomotor programs and promoted a greater recovery of quadriceps strength and function. This study provides evidence that the gait of patients with ACL reconstruction can be improved with the addition of focused gait retraining protocols. Acknowledgments We acknowledge Chris Rich and Mike Kain for their contributions to the data reduction process. We also thank Kevin Shelburne, PhD, for his critical review and contributions to the final manuscript.


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Fig 4. Mean hip and knee internal joint power curves (%BWⴛht/s) during the stance phase for the healthy group (O) and both ACL reconstruction groups at 6 weeks (FDHO group, {; PSF group, 䊐) and at 12 weeks (FDHO group, }; PSF group, ) postsurgery. Positive values indicate energy generation from concentric muscle actions, and negative values indicate energy absorption through eccentric muscle actions.

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