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Abstract

Background:

A controlled ankle movement (CAM) walking boot introduces an artificial leg length discrepancy (LLD), which alters gait mechanics and may increase pain. Using a contralateral shoe lift in conjunction with the CAM boot is a common strategy to address this discrepancy; however, the extent to which the shoe lift restores gait biomechanics remains understudied. This study investigates the effects of the combination of CAM boot and contralateral shoe lift on gait parameters compared to normal (shod) conditions.

Methods:

Thirty healthy adults (mean age 24.6 ± 7.9 years), including 15 men and 15 women, walked overground under 3 conditions: normal shod walking, unilateral CAM boot, and CAM boot with a contralateral shoe lift. A Vicon motion capture system tracked 16 markers to calculate spatiotemporal gait parameters as well as hip and knee kinematics and kinetics using the Plug-in-Gait model. A 1-way analysis of variance followed by Tukey pairwise comparisons identified significant effects of walking condition on various gait characteristics.

Results:

The CAM boot with shoe lift restored kinematic parameters, including hip flexion (P = .036), knee flexion (P = .023), and hip abduction (P = .038), as well as kinetic parameters including knee axial compression force (P = .014) and hip medial-lateral force (P = .007), to normal walking levels on the booted limb. The reported P values reflect differences observed with the CAM boot alone, which were eliminated by the shoe lift.

Conclusion:

A corrective contralateral shoe lift used with a CAM boot can restore some of the knee and hip kinematic and kinetic alterations introduced by the CAM boot. However, it has limited effect on other gait parameters and does not fully replicate the mechanics of normal shod walking.

Level of Evidence:

Level IV, case series.

Graphical Abstract

Keywords

gait studies gait gait parameters gait analysis controlled ankle movement walking kinematics CAM athletic shoe

Introduction

The controlled ankle movement (CAM) walking boot is considered a viable alternative to fiberglass casts for postoperative recovery, offering several benefits^15,17,20: it helps to offload weight from the injured limb while allowing limited but functional motion during ambulation²⁰; furthermore, it maintains the foot and ankle in a neutral position, providing adequate stability to the affected limb.¹⁸ Despite these advantages, CAM boots restrict the ankle joint’s ability to perform work effectively during walking, leading to compensatory mechanisms at the ipsilateral and contralateral hip and knee joints.²³ In addition, it introduces an artificial leg length discrepancy (LLD) caused by the CAM boot’s sole,²⁰ which can negatively impact gait and balance. This discrepancy may lead to secondary issues such as back, knee, and hip pain,⁹ similar to those observed in individuals with naturally occurring LLD.^7,16,24 The gait alterations caused by the CAM boot affect movement in the sagittal, frontal, and transverse plane in the booted limb. For instance, gait with a CAM boot involves pelvic protraction and thoracic lateral flexion toward the booted limb,⁸ both of which are associated with disc degeneration and other musculoskeletal issues.⁵ These alterations can lead to pain and discomfort, potentially reducing adherence to using the CAM boot, which can slow down recovery.¹⁶

Some attempts have been made to compensate for the artificial LLD by using custom heel-lifts. However, it was found that these custom heel-lifts cause new gait asymmetry not observed when wearing the CAM boot alone.¹⁹ Another alternative to address the artificial LLD is the use of shoe lifts, which elevate the entire contralateral limb to align with the booted limb. Studies have shown that the use of shoe lifts, in conjunction with the CAM boot, can decrease pain and increase functionality.^4,10 The use of a contralateral shoe lift has been shown to reduce variability in walking velocity and decreased stance time for the booted foot.⁴ In addition, shoe lift increased the absolute work done and relative contribution of the contralateral limb when worn in combination with the CAM boot.²⁵ These findings suggest promising results for enhancing gait with the implementation of contralateral shoe lifts.

Shoe lifts are a promising intervention to reduce perceived pain in CAM boot wearers and correct gait deviations resulting from artificial LLD. A recent study by Walker et al²⁵ measured biomechanical responses of 12 participants wearing a CAM boot and shoe lift in the contralateral limb. Results showed that a shoe lift can partially mitigate compensatory mechanisms. However, to date, no studies have investigated the impact of shoe lifts on 3-dimensional (3D) gait patterns and mechanics using overground gait analysis, which differs from treadmill-based assessments,²¹ in a larger sample with an equal distribution of sexes. Therefore, the purpose of this study was to evaluate whether compensatory mechanisms associated with CAM boot use can be mitigated by wearing a contralateral shoe lift, in comparison to normal shod walking. We hypothesized that the combination of a CAM boot and shoe lift would restore certain gait parameters and mechanics toward those observed during normal shod walking conditions. Results of the current work will inform clinicians about potential compensatory gait strategies resulting from this common intervention.

Methods

Participants

A prospective cohort study involving 30 participants was conducted. The Institutional Review Board (IRB ID: 1952671 and 1970383/20221099) approved the experimental protocol. All participants received detailed information about the study methods, provided written consent before commencing the experiment, and had the option to withdraw at any time. Recruitment was facilitated through advertisement flyers. Inclusion criteria consisted of adults aged 18 years or older with no current musculoskeletal injury or medical condition that could hinder participation in the planned activity. Participants were excluded if they were pregnant, had sustained a musculoskeletal injury within the past 6 months, or had a body mass index (BMI) of 30 and higher, classified as obese according to the World Health Organization (WHO) standards.²⁷ We excluded participants with BMI >30 to isolate the effects of the CAM boot and shoe lift, as higher BMI can alter gait biomechanics.²⁶ The study sample consisted of 30 participants (50% males, n = 15; 50% females, n = 15) with a mean age of 24.6 years (SD = 7.9; SD = standard deviation), mean weight of 70.7 kg (SD = 12.2), mean height of 1.72 m (SD = 0.09), and mean BMI of 23.8 (SD = 3.85) (see Table 1).

Table 1.

Age and Anthropometric Data of Participants.^a

	Age, y	Weight, kg	Height, m	BMI, kg/m²
Men (n = 15)	24.2 ± 8.2	70.9 ± 11.2	1.79 ± 0.05	22.1 ± 2.89
Women (n = 15)	25.0 ± 7.7	70.5 ± 13.2	1.66 ± 0.07	25.5 ± 3.94
Total (n = 30)	24.6 ± 7.9	70.7 ± 12.2	1.72 ± 0.09	23.8 ± 3.85

Abbreviation: BMI, body mass index.

All the data are reported as mean ± SD.

Data Collection

Each participant performed walking under 3 conditions: (1) wearing only shoes bilaterally, (2) wearing an Aircast Airselect CAM boot (DJO, Vista, CA) on the right foot and a shoe on the left foot, and (3) wearing an Aircast Airselect CAM boot on the right foot with a Procare ShoeLift (DJO) on the left foot. The size of the CAM boot and shoe lift (small, medium, or large) was selected based on the participant’s shoe size, following the manufacturer’s recommendation. All shoe lifts, regardless of the size, provided a 1-inch lift. The walking distance for each trial was standardized to 6 m at a habitual gait speed. We determined habitual gait speed using a minimum of 5 test trials. A 15-minute walking period was provided for participants to familiarize themselves with the change in footwear. Next, each participant completed 3 trials per condition at their habitual gait speed.

Data Processing

A Vicon Motion Capture System using Nexus data capture software (2.15, Vicon Motion Systems, Inc, Oxford, England) was used for 3D motion analysis. Eight Vantage infrared cameras (Vicon Motion Systems, Inc) were used to track reflective markers, whereas 4 staggered and embedded force plates (Kistler Instrument AG, Winterthur, Switzerland) quantified ground reaction forces. A total of 16 reflective markers were placed on the pelvis and lower limbs following the guidelines of the Vicon’s Plug-in Gait (PiG) model.⁶ Anthropometric measurements, including the distance from the right and left anterior superior iliac spine to the respective medial malleolus (leg length), the knee width about the flexion axis, and the ankle width about the medial and lateral malleoli, were collected to run the PiG model. Markers on the CAM boot were placed according to the anatomic landmarks from the PiG model, based on palpation before the CAM boot was adjusted. Vicon’s PiG model has been previously used in our laboratory to estimate kinematic and kinetic outcomes, as well as gait parameters,^2,13 and it has also been employed in prior studies to estimate gait parameters with markers placed directly on a CAM boot.^8,25 Kinematic and kinetic data were collected at 500 Hz and processed with the PiG model and Vicon’s gait cycle parameters. Data post-processing provided spatiotemporal gait parameters for left (shod and shoe-lifted) and right (booted) legs (walking speed, time spent in step/stride, contact times, stride length, and step length and width) as well as lower limb kinematics and kinetics. Kinematic outputs included hip and knee joint angles in the sagittal plane (flexion-extension), frontal plane (abduction-adduction), and transverse plane (internal-external rotation). Kinetic outputs included joint forces in the anterior-posterior (AP), medial-lateral (ML), and axial/compression (AC) directions, as well as joint moments in flexion-extension (FE), varus-valgus (V), and internal-external (IE) rotation at both the hip and knee.

Statistical Analysis

Peak joint angles, forces, and moments for each participant were determined by averaging their values across all 3 trials (MATLAB R2023b; MathWorks Inc, Natick, MA). Descriptive statistics (means and SDs) were computed for each spatiotemporal gait parameter and biomechanical output. Subsequent statistical analyses were computed using Minitab (20.2, Minitab LLC, State College, PA). A significance level of 95% (α = .05) was used for all statistical tests. Outliers were identified using Grubb test but retained, as they may reflect true individual differences. Comparisons between gait variables were performed using a 1-way analysis of variance, with walking condition (3 levels) as the factor. Assumptions of analysis of variance, including homogeneity of variances (assessed with the Levene test) and normal distribution of residuals (evaluated with the Shapiro-Wilk test), were satisfied. Tukey pairwise comparisons were conducted to determine significant differences between groups. Omega squared (ω²) was used to estimate effect size, with ω² ≥ 0.14 interpreted as a large effect.¹² To assess the precision of these estimates, 95% CIs for ω² were also computed. Analyses were organized into 3 sections: gait parameters, kinematics, and kinetics.

Results

Spatiotemporal Gait Parameters

A summary of all discrete spatiotemporal gait parameters, organized by walking condition, is presented in Table 2. Step width was the only parameter significantly affected by walking condition in both limbs (P < .001), with a shorter width observed during normal walking (0.16 m) compared to walking with the CAM boot (0.20 m) and the combination of a CAM boot and shoe lift (0.22 m). Furthermore, walking speed (P < .001) was higher during normal gait (1.20 m/s) compared to walking with the CAM boot (1.01 m/s) and the combination of the CAM boot and shoe lift (1.02 m/s). Step time (P = .021) and single support time (P < .001) were also shorter during normal gait (0.61 and 0.42 seconds, respectively) compared with walking with the CAM boot (0.67 and 0.49 seconds) or the CAM boot and shoe lift (0.68 and 0.49 seconds). A large effect size (ω² ≥ 0.14) was found for all gait parameters that were significantly affected by walking condition.

Table 2.

Gait Parameters by Walking Conditions.^a

Gait Parameters	Limb	P Value	C1	C2	C3	ω²	95% CI (ω²)
Walking speed, m/s	N/A	<.001***	1.20 ± 0.10^a	1.01 ± 0.13^b	1.02 ± 0.18^b	0.191	[0.070, 0.374]
Stride time, s	N/A	.315	1.17 ± 0.16	1.22 ± 0.12	1.23 ± 0.23	0.002	[<0.001, 0.108]
Step time, s	Right	.021*	0.61 ± 0.08^b	0.67 ± 0.08^{a b}	0.68 ± 0.12^a	0.066	[<0.001, 0.220]
	Left	.126	0.60 ± 0.09	0.63 ± 0.09	0.64 ± 0.08	0.012	[<0.001, 0.155]
Single support, s	Right	<.001***	0.42 ± 0.02^b	0.49 ± 0.01^a	0.49 ± 0.01^a	0.121	[0.007, 0.298]
	Left	.138	0.44 ± 0.09	0.50 ± 0.12	0.49 ± 0.12	0.023	[<0.001, 0.134]
Double support, s	N/A	.885	0.43 ± 0.04	0.42 ± 0.05	0.40 ± 0.02	<0.001	[<0.001, 0.068]
Stride length, m	N/A	.287	1.17 ± 0.19	1.10 ± 0.19	1.17 ± 0.19	0.006	[<0.001, 0.128]
Step length, m	Right	.319	0.61 ± 0.12	0.60 ± 0.10	0.65 ± 0.17	0.004	[<0.001, 0.140]
	Left	.141	0.61 ± 0.13	0.56 ± 0.12	0.56 ± 0.08	0.024	[<0.001, 0.180]
Step width, m	Right	<.001***	0.16 ± 0.04^b	0.20 ± 0.04^a	0.22 ± 0.06^a	0.183	[0.071, 0.367]
	Left	<.001***	0.16 ± 0.04^b	0.21 ± 0.05^a	0.22 ± 0.05^a	0.206	[0.094, 0.377]

P values, mean values, and Tukey groupings for gait parameters categorized by walking condition: C1 (condition 1: Normal walking with athletic shoes), C2 (condition 2: CAM boot on the right foot and an athletic shoe on the left foot), and C3 (condition 3: CAM boot on the right foot and a shoe lift on the left foot). Superscripts (eg, a, ab, b) indicate results of Tukey post hoc comparisons: means that do not share a common letter are significantly different (eg, a ≠ b), whereas shared letters (eg, ab) indicate no significant difference from either a or b. Superscript letters are assigned such that a corresponds to the group with the highest mean value. ***P ≤ .001; *.01 < P ≤ .05, level of significance of effects.

Gait Kinematics

Analysis of discrete kinematic variables showed a significant effect of walking condition on the booted limb (Figure 1 and Table 3) in hip abduction (P = .038), hip flexion (P = .036), and knee flexion (P = .023). Notably, the combination of a CAM boot and shoe lift restored booted-limb angles to values observed during normal walking, in contrast to walking with the CAM boot alone. Additionally, walking conditions significantly affected the shod/shoe-lifted limb, particularly knee external rotation (P < .024), with normal walking showing less rotation compared to walking with either the CAM boot alone or the combination of CAM boot and shoe lift. Small to large effect sizes (ω² = 0.01-0.14) were observed in the kinematic variables that were significantly affected by walking condition.

Figure 1.

Hip and knee walking kinematics. Time-series plots of left- and right-side hip and knee angles across 3 walking conditions: C1 (normal walking in athletic shoes), C2 (CAM boot on the right foot and athletic shoe on the left), and C3 (CAM boot on the right foot and shoe lift on the left). Solid lines represent the mean angle across participants, whereas dashed lines indicate the upper and lower bounds of 1 SD. The first column shows flexion-extension in the sagittal plane, the second shows abduction-adduction in the frontal plane, and the third shows internal-external rotation in the transverse plane.

Table 3.

Kinematics by Walking Condition.^a

Joint angles	Limb	P value	C1	C2	C3	ω²	95% CI (ω²)
Hip extension, degrees	Right	.830	−18.42 ± 9.68	−19.67 ± 9.56	−18.55 ± 9.41	<0.001	[<0.001, 0.064]
	Left	.910	−16.51 ± 10.19	−16.31 ± 9.90	−17.33 ± 9.89	<0.001	[<0.001, 0.062]
Hip flexion, degrees	Right	.036*	28.66 ± 9.38^a	23.78 ± 8.87^b	28.28 ± 9.86^a	0.033	[<0.001, 0.160]
	Left	.714	27.80 ± 10.03	28.75 ± 9.01	26.98 ± 9.08	<0.001	[<0.001, 0.076]
Hip abduction, degrees	Right	.038*	−11.21 ± 3.56^{a b}	−12.61 ± 4.20^b	−9.90 ± 4.22^a	0.051	[<0.001, 0.194]
	Left	.149	−9.87 ± 4.13	−7.81 ± 3.88	−9.48 ± 4.54	0.022	[<0.001, 0.162]
Hip adduction, degrees	Right	.139	4.74 ± 3.42	2.79 ± 5.66	4.77 ± 3.98	0.024	[<0.001, 0.195]
	Left	.408	6.86 ± 4.99	4.13 ± 4.33	4.33 ± 4.57	<0.001	[<0.001, 0.110]
Hip external rotation, degrees	Right	.996	−12.06 ± 5.29	−11.89 ± 6.08	−12.13 ± 4.77	<0.001	[<0.001, 0.061]
Hip external rotation, degrees	Left	.981	−13.33 ± 8.86	−13.72 ± 8.16	−13.63 ± 8.77	<0.001	[<0.001, 0.059]
Hip internal rotation, degrees	Right	.946	7.72 ± 5.99	7.55 ± 8.27	6.82 ± 6.70	<0.001	[<0.001, 0.065]
Hip internal rotation, degrees	Left	.359	5.57 ± 8.15	4.49 ± 8.80	4.87 ± 8.89	<0.001	[<0.001, 0.105]
Knee flexion, degrees	Right	.023*	59.62 ± 8.62^{a b}	55.39 ± 8.18^b	60.90 ± 7.10^a	0.061	[<0.001, 0.208]
	Left	.078	61.26 ± 6.98	57.56 ± 7.85	57.41 ± 7.40	0.034	[<0.001, 0.164]
Knee abduction, degrees	Right	.764	−1.52 ± 2.46	−3.37 ± 2.15	−1.66 ± 2.23	<0.001	[<0.001, 0.067]
Knee abduction, degrees	Left	.414	−2.08 ± 1.86	−4.81 ± 1.57	−4.66 ± 1.89	<0.001	[<0.001, 0.116]
Knee adduction, degrees	Right	.991	1.23 ± 1.51	1.48 ± 1.59	1.29 ± 1.32	<0.001	[<0.001, 0.055]
Knee adduction, degrees	Left	.074	1.10 ± 1.91	−1.59 ± 1.83	−1.17 ± 1.88	0.032	[<0.001, 0.174]
Knee external rotation, degrees	Right	.961	−16.45 ± 7.73	−15.58 ± 3.60	−15.00 ± 4.33	<0.001	[<0.001, 0.065]
Knee external rotation, degrees	Left	.024*	−17.77 ± 6.37^a	−20.89 ± 5.27^b	−20.60 ± 6.78^b	0.161	[0.057,0.324]
Knee internal rotation, degrees	Right	.848	13.09 ± 4.07	11.74 ± 4.13	14.81 ± 4.07	<0.001	[<0.001, 0.074]
Knee internal rotation, degrees	Left	.289	12.22 ± 5.75	8.61 ± 8.30	8.88 ± 8.18	0.005	[<0.001, 0.115]

P values, mean values, and Tukey groupings for gait parameters categorized by walking condition: C1 (condition 1: Normal walking with athletic shoes), C2 (condition 2: CAM boot on the right foot and an athletic shoe on the left foot), and C3 (condition 3: CAM boot on the right foot and a shoe lift on the left foot). Superscripts (eg, a, ab, b) indicate results of Tukey post hoc comparisons: means that do not share a common letter are significantly different (eg, a ≠ b), whereas shared letters (eg, ab) indicate no significant difference from either a or b. Superscript letters are assigned such that a corresponds to the group with the highest mean value. *Indicates a statistically significant effect (01 < P ≤ .05).

Gait kinetics

Hip ML force (P = .007) and knee AC force (P = .014) in the booted limb returned to levels observed during normal walking when using the CAM boot and shoe lift, compared with walking with only the CAM boot (Table 4). In the shod/shoe-lifted limb, knee AP force (P = .022) and ML force (P < .001) were also significantly affected by walking condition. Medium to large effect sizes (ω² = 0.06-0.14) were observed in the kinetic variables that were significantly affected by walking condition.

Table 4.

Kinetics by Walking Condition.^a

Kinetics	Limb	P Value	C1	C2	C3	ω²	95% CI (ω²)
Hip force–AP, N/kg	Right	.706	0.75 ± 0.45	0.86 ± 0.59	0.76 ± 0.56	<0.001	[<0.001, 0.074]
	Left	.780	0.94 ± 0.67	0.96 ± 0.73	1.06 ± 0.73	<0.001	[<0.001, 0.063]
Hip force–ML, N/kg	Right	.007**	0.39 ± 0.09^b	0.52 ± 0.22^a	0.41 ± 0.11^b	0.067	[<0.001, 0.237]
	Left	.416	0.42 ± 0.14	0.48 ± 0.04	0.49 ± 0.04	<0.001	[<0.001, 0.101]
Hip force–AC, N/kg	Right	.389	0.95 ± 0.13	0.99 ± 0.14	0.95 ± 0.10	<0.001	[<0.001, 0.067]
	Left	.568	0.93 ± 0.13	0.95 ± 0.11	0.95 ± 0.09	<0.001	[<0.001, 0.084]
Knee force–AP, N/kg	Right	.902	0.51 ± 0.09	0.50 ± 0.16	0.52 ± 0.17	0.001	[<0.001, 0.090]
	Left	.022*	0.64 ± 0.26^a	0.48 ± 0.25^b	0.48 ± 0.25^b	0.069	[<0.001, 0.224]
Knee force–ML, N/kg	Right	.231	0.26 ± 0.11	0.31 ± 0.18	0.26 ± 0.09	<0.001	[<0.001, 0.068]
	Left	<.001***	0.27 ± 0.15^b	0.39 ± 0.14^a	0.38 ± 0.12^a	0.120	[0.031, 0.322]
Knee force–AC, N/kg	Right	.014*	1.03 ± 0.08^b	1.09 ± 0.07^a	1.05 ± 0.08^b	0.083	[0.004, 0.236]
	Left	.172	1.04 ± 0.08	1.06 ± 0.08	1.09 ± 0.11	0.014	[<0.001,0.122]
Hip moment–FE, Nm/kg	Right	.563	3.45 ± 1.20	3.44 ± 1.34	3.12 ± 1.18	<0.001	[<0.001, 0.065]
	Left	.493	4.45 ± 2.59	4.65 ± 3.29	3.88 ± 1.71	<0.001	[<0.001, 0.060]
Hip moment–V, Nm/kg	Right	.934	1.89 ± 0.64	1.94 ± 0.70	1.87 ± 0.74	<0.001	[<0.001, 0.073]
	Left	.367	1.90 ± 0.54	2.03 ± 0.54	1.84 ± 0.41	<0.001	[<0.001, 0.068]
Hip moment–IE, Nm/kg	Right	.918	0.52 ± 0.19	0.54 ± 0.20	0.55 ± 0.27	<0.001	[<0.001, 0.062]
	Left	.436	0.54 ± 0.19	0.46 ± 0.17	0.50 ± 1.23	<0.001	[<0.001, 0.060]
Knee moment–FE, Nm/kg	Right	.588	1.49 ± 0.58	1.57 ± 0.50	1.67 ± 0.87	<0.001	[<0.001, 0.089]
	Left	.417	1.65 ± 0.71	1.68 ± 0.88	1.94 ± 1.06	<0.001	[<0.001, 0.101]
Knee moment–V, Nm/kg	Right	.105	0.78 ± 0.32	1.09 ± 0.47	0.90 ± 0.46	0.030	[<0.001, 0.160]
	Left	.225	0.78 ± 0.43	0.95 ± 0.41	0.82 ± 0.33	<0.001	[<0.001, 0.126]
Knee moment–IE, Nm/kg	Right	.330	0.25 ± 0.13	0.30 ± 0.13	0.28 ± 0.12	0.003	[<0.001, 0.134]
	Left	.890	0.23 ± 0.12	0.24 ± 0.12	0.23 ± 0.12	<0.001	[<0.001, 0.065]

Abbreviations: AC, axial/compression direction; AP, anterior-posterior direction; FE, flexion-extension rotation; IE, internal-external rotation; ML, medial-lateral direction; V, varus-valgus rotation.

P values, mean values, and Tukey groupings for gait parameters categorized by walking condition: C1 (condition 1: Normal walking with athletic shoes), C2 (condition 2: CAM boot on the right foot and an athletic shoe on the left foot), and C3 (condition 3: CAM boot on the right foot and a shoe lift on the left foot). Superscripts (e.g., a, ab, b) indicate results of Tukey post hoc comparisons: means that do not share a common letter are significantly different (e.g., a ≠ b), whereas shared letters (eg, ab) indicate no significant difference from either a or b. Superscript letters are assigned such that a corresponds to the group with the highest mean value. ***P ≤ .001; **.001 < P ≤ .01; *.01 < P ≤ .05, level of significance of effects.

Discussion

The purpose of this study was to evaluate and compare gait parameters and mechanics in a group of healthy adult subjects without any physical impairments when wearing regular shoes, walking with the CAM boot, and wearing the CAM boot with a shoe lift in the contralateral limb. Previous studies have shown improved comfort and gait when wearing the shoe lift in the contralateral limb in combination with the CAM boot.⁵ Shoe lifts offer some mitigation in the ipsilateral leg because of the reduced LLD, but it does not allow the contralateral limb to maintain normal biomechanical functions due to the restriction of the ankle joint range of motion.²⁵ To the authors’ best knowledge, this is the first study evaluating the effects of wearing the shoe lift in combination with the CAM boot using overground biomechanics, while also expanding into the previous analysis of gait parameters and gait mechanics.^5,25 Our overall results show significant compensatory mechanisms adopted by the use of the CAM boot in terms of gait mechanics.

Walking conditions significantly impacted gait parameters and mechanics in the present study. Walking speed, as well as step time and single support time on the booted leg, were significantly longer in both walking conditions with CAM boots compared to shod walking. Our results partially align with previous studies. Bruening et al³ found a significant decrease in walking speed and cadence when wearing a spring-loaded CAM boot with a contralateral shoe lift compared with regular shoes, but not with a traditional or hinged CAM boot and shoe lift. Similarly, Walker et al²⁵ reported significant differences between shod walking and walking with a CAM boot alone, but not with the combination of a CAM boot and shoe lift, unlike our findings. We attribute these differences to variations in habitual walking speed among study samples. Our study included 15 males and 15 females, whereas Walker et al examined 8 males and 4 females, and Bruening et al studied 10 males. Because females generally have shorter stride lengths, which contribute to lower walking speeds,^1,3,11 sample composition may have influenced the results. Although the combination of a CAM boot and shoe lift may partially maintain walking speed, a deeper understanding of its interaction with sex is needed.

Previous studies have found significant differences in knee flexion, hip flexion, and hip abduction when using the CAM boot.^3,8 Our study showed that although ambulating with a CAM boot decreased hip and knee flexion in the booted limb by 17.0% and 7.0%, respectively, compared to walking with regular shoes, this was corrected with the use of a shoe lift. Notably, Bruening et al⁴ also found the contralateral shoe lift to correct hip and knee flexion closer to the normal angle values seen in ambulation with regular shoes. Walker et al²⁵ also found that the use of the shoe lift partially mitigated the alterations in the hip abduction angle,¹⁴ which aligns with our findings, where hip abduction was also reduced, but only in the booted limb.

Analogous to our results, previous studies have found that most kinetic changes occur at the level of the knee joint, with a walking boot having minimal change in the hip.^8,18 Walker et al²⁵ showed that the use of a shoe lift in the contralateral limb increased absolute work done and relative contribution of the shoe-lifted limb. The present study showed that the knee on the booted limb was compensated in the AC force when wearing the shoe lift, having only a 2.0% difference compared to that walking with regular shoes. In terms of hip kinetics, previous studies found a significant decrease in the shoe-lifted hip abductor moments.^8,18 However, we did not find significant changes in hip moments. Severin et al²² conducted a study similar to ours in terms of walking conditions (athletic shoes, walking CAM boot, and CAM walking boot plus a contralateral heel lift). Similar to our findings, they found that several of the moments that were altered by the boot were returned closer to normal values when the contralateral lift was introduced, but knee moments typically remained altered.²² We found that the use of a shoe lift slightly restored hip ML force in the booted limb but had minimal ability to restore knee AP force or ML force in the shoe-lifted limb.

One potential limitation of the current study is that, during walking trials involving the CAM boot, kinematic and kinetic data were collected using markers placed on the exterior of the boot rather than directly on the skin. However, care was taken to align marker placement with anatomical landmarks using standardized CAM boot modifications and consistent placement protocols across participants. Previous studies have shown that when marker placement over rigid surfaces such as orthopaedic boots is performed systematically, joint kinematics can still be estimated with acceptable accuracy, particularly for within-subject comparisons across conditions.^8,23,25 A second limitation concerns the participant sample: all volunteers were healthy and uninjured, whereas CAM boots are typically prescribed for individuals recovering from lower-limb injury or surgery. Although studying a healthy cohort allowed us to isolate the mechanical effects of the boot and shoe lift without confounding factors such as pain or impaired neuromuscular control, readers should be cautious when generalizing these findings to clinical populations. Future research should examine whether gait adaptations differ by sex using the current study design, as sex-specific biomechanical patterns may influence rehabilitation strategies. Furthermore, the sample size and effect sizes reported in the present study may help inform a priori power analyses for future studies involving CAM boots and shoe lifts.

Conclusion

In conclusion, walking with a CAM boot alone partially alters gait biomechanics because it produces an artificial LLD. The use of a corrective contralateral shoe lift with a CAM walking boot can restore some of the differences; however, it does not fully normalize gait biomechanics observed during normal gait with regular shoes. This is primarily due to the CAM boot’s intended restriction of ankle motion, which limits multiple phases of the gait cycle. Additionally, the boot imposes supraphysiologic traction on proximal joints such as the knee and hip. These factors are inherent to CAM boot use and can only be partially mitigated. Overall, these findings suggest that using a contralateral shoe lift may improve functional gait mechanics and enhance comfort during recovery. However, prolonged use may introduce secondary issues, which has important implications for clinicians when developing rehabilitation strategies and determining treatment duration. Our comparisons to normal shod walking provide practical reference values that may help clinicians assess gait restoration and make informed decisions about the length and monitoring of CAM boot and shoe lift use.

Supplemental Material

sj-pdf-1-fao-10.1177_24730114251387680 – Supplemental material for Impact of Contralateral Shoe Lifts on Gait Parameters and Mechanics When Wearing a Controlled Ankle Movement (CAM) Boot

Supplemental material, sj-pdf-1-fao-10.1177_24730114251387680 for Impact of Contralateral Shoe Lifts on Gait Parameters and Mechanics When Wearing a Controlled Ankle Movement (CAM) Boot by Dino Fanfan, Sergio A. Lemus, Taylor Schnepp, Daniel Murray, Samantha Trynz, Francesco Travascio and Cary B. Chapman in Foot & Ankle Orthopaedics

Footnotes

ORCID iDs

Sergio A. Lemus, PhD,

Taylor Schnepp, MS,

Samantha Trynz, MD,

Francesco Travascio, PhD,

Cary B. Chapman, MD,

Ethical Considerations

This study has been approved under Baptist Health Institutional Review Board (IRB Nos. 1952671 and 1970383) and the University of Miami Institutional Review Board (IRB No. 20221099).

Competing Interests

The authors have no relevant financial or nonfinancial interests to disclose.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Declaration of Conflicting Interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article. Disclosure forms for all authors are available online.

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