Spatiotemporal and Gait Symmetry Changes Following Osseointegration in Transfemoral Prosthesis Users: A Longitudinal Study

Abstract

Background/Objectives: Bone-anchored prostheses provide an alternative to socket prostheses, directly connecting the prosthesis to the residual limb via osseointegration. However, limited evidence exists on how spatiotemporal gait parameters and gait symmetry change over time following osseointegration in individuals with unilateral transfemoral amputation. This study aimed to examine changes in spatiotemporal and gait symmetry parameters before osseointegration and at 6 and 12 months post-surgery. Methods: Common spatiotemporal parameters were collected from six individuals with unilateral transfemoral amputation at baseline (with socket prosthesis) and at 6 and 12 months post-osseointegration using a motion analysis system. Group-level differences were assessed using repeated measures ANOVA. Gait symmetry was evaluated using selected spatiotemporal parameters. Results: Following osseointegration, individuals with unilateral transfemoral amputation experienced significant spatiotemporal changes over time. At the group level, walking velocity and stride length decreased at 6 months, with stride length increasing at 12 months. Step width and prosthetic-side step length increased at 12 months relative to 6 months, while intact-side step length decreased. Prosthetic-side toe-off timing was shorter at 12 months. Gait symmetry responses varied individually: some with poor baseline symmetry improved, while those with better baseline symmetry became more asymmetric, indicating heterogeneous outcomes. Conclusions: This study highlights longitudinal changes in gait biomechanics following osseointegration in individuals with unilateral transfemoral amputation. Gait adaptations were highly variable across individuals and time points. Future research should involve larger, more homogeneous samples and incorporate kinetic, muscle activity, and functional outcome measures to better understand the impact of bone-anchored prostheses on gait and mobility.

1. Introduction

Dependence on a prosthesis is essential for restoring walking after a transfemoral amputation. While most affected individuals use a socket prosthesis, many of them experience problems such as skin irritation, residual limb pain, and poor force transfer between the limb and socket, which can reduce gait stability and quality of life [1,2,3,4,5]. Instrumented gait analysis provides an objective way to identify deviations from typical walking by quantifying spatiotemporal, kinematic, kinetic, and electromyography (EMG) data [6]. Compared with individuals without disabilities, transfemoral socket prosthesis users showed decreased walking speed [7,8,9,10] as well as increased stance and double support durations [5,11,12].

Bone-anchored prostheses (BAP) were developed to address limitations of socket systems by directly connecting the prosthesis to the femur, which may improve comfort, force transmission, and gait [13,14,15]. Altered biomechanics for unilateral transfemoral BAP users [16] resulted in a higher cadence [17,18], a shorter step width [19,20,21], and a shorter support (stance) phase duration on the prosthetic side [17] compared to gait using a socket prosthesis. However, compared to healthy participants, unilateral BAP users still showed a lower speed [22], lower cadence [23], lower symmetry [22,24], and a longer duration of the swing phase [17,18]. When assessing gait symmetry, previous studies have shown that individuals with unilateral transfemoral amputation typically demonstrate asymmetrical gait patterns [19,25,26]. In this context, factors such as an increased walking speed [11], prescribed gait training [25], osseointegration (OI) surgery [19], and the use of a microprocessor-controlled prosthetic knee [27] have been associated with reduced gait asymmetry.

Recent studies have begun to investigate longitudinal changes in gait following osseointegration. For example, Toderita et al. [21] reported diverse adaptation patterns in walking within the first year after BAP compared to the pre-surgery time point. Similarly, Ranaldi et al. [20] examined walking ability in individuals using transfemoral BAP and identified differences in spatiotemporal gait parameters compared with conventional prosthetic users. Although these studies suggest that osseointegration can improve certain biomechanical aspects of gait, important gaps remain. In particular, few studies have examined spatiotemporal changes at multiple postoperative time points, such as 6 and 12 months, making it difficult to fully understand the trajectory of gait adaptation during the rehabilitation period. Spatiotemporal parameters and gait symmetry are clinically relevant indicators of walking stability, functional mobility, and rehabilitation progress, and may ultimately influence independence and quality of life for individuals with transfemoral amputation. However, gait symmetry after osseointegration surgery has received limited investigation despite its value for comparing outcomes across individuals and time and for monitoring rehabilitation progress. Therefore, the present study aimed to examine changes in spatiotemporal gait parameters and gait symmetry at baseline, 6 months, and 12 months following osseointegration.

To address these gaps, this study examined longitudinal changes in spatiotemporal parameters and gait symmetry before osseointegration and at 6 and 12 months post-surgery. Given the limited evidence on how quickly gait improves following osseointegration, the 6-month evaluation captured gait immediately after completing gait training and rehabilitation, whereas the 12-month assessment reflected longer-term, habitual gait without further intervention. This design allowed us to examine both early post-training adaptations and subsequent changes over time. Gait symmetry was evaluated using the gait symmetry index [28] to determine whether symmetry improvements after OI were achieved and maintained, providing additional information on gait changes associated with BAP use compared with socket prosthesis use. Accordingly, the study addressed the following research questions: (1) Do spatiotemporal gait parameters change after osseointegration compared with pre-surgery socket prosthesis use? and (2) Does gait symmetry improve over time following osseointegration?

2. Materials and Methods

Six adult participants (four males and two females; age 45.5 ± 12.8 years; weight 74.1 ± 7.7 kg; height 174.3 ± 5.7 cm;

Table 1. Overview details of the participants with amputation, including sex, age at time of osseointegration surgery, weight, height, the amputated side, and the type of prosthetic knee joint and foot; M = male, F = female.

Participant	Sex	Age at Time of Surgery (Years)	Years Between Primary Amputation and Osseointegration Surgery (Years)	Weight at Baseline (kg)	Height (cm)	Amputated Side	Length of Residual Limb (cm)	Type of Prosthetic Knee	Type of Prosthetic Foot
1	F	35	7	82.1	171	Left	37	Össur Symbionic® *	Össur Symbionic® *
2	M	55	4	66.0	169	Left	31	Ottobock Genium X3 **	Össur Pro-Flex® LP Torsion *
3	M	39	3	63.0	177	Right	27	Ottobock Genium X3 **	Össur Cheetah® Xceed *
4	F	60	7	73.5	167	Right	26	Ottobock C-Leg 4 **	Össur Pro-Flex® LP Torsion *
5	M	58	38	84.2	179	Left	21	Ottobock 3R85 **	Össur Pro-Flex® LP Torsion *
6	M	26	2	75.6	183	Left	32	Ottobock C-Leg 4 **	Össur Pro-Flex® LP Torsion *

* Össur: Össur, Reykjavík, Iceland; ** Ottobock: Ottobock, Duderstadt, Germany.

) with unilateral transfemoral amputation who received an osseointegrated prosthetic limb implant (Permedica, S.p.A, Italy) participated in this study. The sample size reflects the limited number of individuals undergoing osseointegration surgery who met the study inclusion criteria during the recruitment period, which was further affected by restrictions related to the COVID-19 pandemic that limited participant recruitment and data collection. Study procedures were approved by the University of Alberta Research Ethics Board (Pro00091604), and all participants provided written informed consent. Spatiotemporal data were collected at baseline with a socket prosthesis and at 6 and 12 months after OI surgery using a transfemoral BAP. All gait assessments were conducted in the same motion analysis laboratory to maintain a consistent testing environment. Participants were allowed to wear their own footwear during data collection, as this reflected the shoes they typically wear in daily walking and ensured comfortable, natural gait performance.

Trunk and lower-limb markers were tracked at 120 Hz during walking at a comfortable speed using an 8-camera motion-capture system (Eagle, Motion Analysis Corporation, Rohnert Park, CA, USA). In addition, ground reaction forces were recorded at 2400 Hz using three force plates (AMTI, Watertown, MA, USA). Three trials per time point (pre-OI, 6-month post-OI, and 12-month post-OI) were selected based on clear force-plate contacts, and marker data were low-pass filtered with a cut-off frequency of 6 Hz. A standard Helen Hayes model [29] was used to place markers on the following anatomical landmarks: the acromion, seventh cervical spinous process (C7), sacrum, anterior superior iliac spine (ASIS), anterior thigh, medial and lateral knee defining the knee’s flexion-extension axis, shank on the medial tibia, medial and lateral malleoli, heel level with the forefoot, and forefoot between the 2nd and 3rd metatarsal heads. Equivalent marker locations were identified on the prosthesis, with an additional marker placed on the implant stem above the knee joint connector at 6 and 12 months post-OI [30,31]. The Visual3D software (v4.96.11, C-motion, Germantown, MD, USA) was used to scale a generic musculoskeletal model using anthropometric calibration data acquired while the participant stood in a static anatomical position for one second.

No missing data was observed during data acquisition. The recorded time series data were used to calculate the following measures: cadence, walking velocity, step width, stride length, single support duration (prosthetic and intact sides), double support duration, and toe-off timing for both limbs. The velocity values presented in the results were calculated from cadence and stride length, whereas the Supplementary Materials contains trial-level velocity directly computed by the motion capture system, which may result in minor differences between the two outputs. Normative spatiotemporal data, used for comparison, were previously collected from 16 individuals without impairments (six males and ten females; age 30.7 ± 12.3 years; weight 68.5 ± 8.8 kg; height 170.8 ± 6.2 cm) under the same conditions.

We assessed the normality of each variable across all participants using the Shapiro–Wilk test. As the assumption of normality was met, group-level analyses were conducted using one-way repeated measures ANOVA. Outliers were assessed using boxplots, and the assumption of sphericity was assessed using Mauchly’s test of sphericity. If the assumption of sphericity was violated, the Greenhouse–Geisser corrected value was used instead. For significant main effects, a post hoc comparison with Bonferroni correction was conducted. All statistical analyses were conducted using SPSS (v29.0.2.0, IBM, Armonk, New York, NY, USA), with a significance level set at p < 0.05. Given the small sample size (n = 6), this study was designed as an exploratory longitudinal investigation, and the statistical power of group-level analyses is limited; therefore, results from the repeated measures ANOVA should be interpreted with caution. To address the limited statistical power, individual-level data were also examined for consistency with the group trends.

The gait symmetry index (SI) quantifies differences between the intact and prosthetic limbs using spatiotemporal, kinematic, or kinetic measures. An SI of 0% indicates perfect symmetry, with higher values reflecting greater asymmetry, with SI ≥ 100% suggesting complete asymmetry (e.g., non-use of one limb) [28]. In the present study, spatiotemporal parameters, including step length, single and double limb support times, and toe-off timing, were used to assess gait symmetry and its changes following OI surgery in individuals with unilateral transfemoral amputation. To calculate the gait symmetry index, the values of the selected variable for both the intact and prosthetic limbs (X_intact and X_Prosthetic) were used, as defined by Equation (1) [28].

$$\mathrm{SI}={\displaystyle \frac{\left|{\mathrm{X}}_{\mathrm{Intact}}-{\mathrm{X}}_{\mathrm{Prosthetic}}\right|}{0.5\left|{\mathrm{X}}_{\mathrm{Intact}}+{\mathrm{X}}_{\mathrm{Prosthetic}}\right|}}\times 100\%$$

(1)

3. Results

3.1. Spatiotemporal Parameters

A summary of group mean values for the spatiotemporal parameters is presented in

Table 2. Group mean ± standard deviation of spatiotemporal parameters at baseline, 6 months post-OI, and 12 months post-OI, compared to normative values.

Spatiotemporal Parameters	Normative Values	Baseline	6 Months Post-OI	12 Months Post-OI
Velocity (m/s)	1.39 ± 0.12	1.11 ± 0.21	1.04 ± 0.18 *	1.09 ± 0.19
Step length on prosthetic side (m)	0.70 ± 0.05	0.65 ± 0.11	0.63 ± 0.10	0.65 ± 0.08 **
Step length on intact side (m)	0.70 ± 0.05	0.66 ± 0.07	0.61 ± 0.08 *	0.62 ± 0.07 ***
Stride length (m)	1.39 ± 0.09	1.31 ± 0.16	1.23 ± 0.17 *	1.28 ± 0.15 **
Step width (m)	0.11 ± 0.03	0.17 ± 0.03	0.16 ± 0.04	0.19 ± 0.03 **
Toe-off on the prosthetic side (% Gait Cycle)	60.50 ± 1.34	59.25 ± 1.38	59.12 ± 1.94	57.87 ± 1.88 ***
Toe-off on the intact side (% Gait Cycle)	60.50 ± 1.34	67.93 ± 3.72	69.31 ± 3.25	67.19 ± 2.58 **

* Significant difference between baseline and 6 months, ** Significant difference between 6 months and 12 months, *** Significant difference between baseline and 12 months.

, with significant differences across time points indicated. No significant changes were observed in cadence or in the single- and double limb support duration on either the prosthetic or intact sides. However, statistically significant changes were identified for velocity, stride length, step width, step length, and toe-off timing on both the prosthetic and intact sides, as indicated in Table 2, with heterogeneous changes observed across different time points and participants.

Walking velocity differed across time points (F(2, 34) = 3.893, p = 0.030, η_p² = 0.186), with a trend toward a decrease from baseline to 6 months post-OI (p = 0.089), while no significant differences were observed between baseline and 12 months or between 6 and 12 months post-OI. Stride length also differed significantly across time points (F(2, 34) = 11.528, p < 0.001, η_p² = 0.404), decreasing from baseline to 6 months post-OI (p < 0.001) and increasing from 6 to 12 months post-OI (p = 0.017), with no significant difference between baseline and 12 months. Step length on the prosthetic side showed a near-significant main effect (F(2, 34) = 3.235, p = 0.052, η_p² = 0.160), with post hoc analysis indicating a significant increase from 6 to 12 months post-OI (p = 0.044), but no differences between baseline and the other time points. On the intact side, step length differed significantly across time points (F(2, 34) = 9.105, p < 0.001, η_p² = 0.349), with reductions observed at both 6 months (p = 0.006) and 12 months (p = 0.013) compared to baseline. Step width also differed across time points (F(2, 34) = 3.702, p = 0.035, η_p² = 0.179), increasing significantly from 6 to 12 months post-OI (p = 0.013). However, this was largely due to participant six, whose step width nearly doubled; when participant six was excluded from the group analysis, no significant changes across time points were observed (F(2, 28) = 1.593, p = 0.221, η_p² = 0.102). Toe-off timing on the prosthetic side showed a significant main effect (F(2, 34) = 3.529, p = 0.040, η_p² = 0.172), although post hoc comparisons did not reach statistical significance, with a trend toward an earlier toe-off at 12 months compared to baseline (p = 0.055). On the intact side, toe-off timing differed significantly across time points (F(2, 34) = 5.850, p = 0.007, η_p² = 0.256), with a significant decrease from 6 to 12 months post-OI (p = 0.002).

At the individual level (Appendix A), consistent with the group-level findings, most participants demonstrated decreased walking velocity (

Table A1. Individual and group mean ± standard deviation for walking velocity (m/s) at baseline, 6, and 12 months post-OI.

Velocity (m/s)
Participant	Baseline	6 Months Post OI	12 Months Post OI
1	1.22 ± 0.02	1.00 ± 0.01	1.08 ± 0.01
2	1.26 ± 0.03	1.24 ± 0.06	1.17 ± 0.04
3	1.41 ± 0.04	1.22 ± 0.02	1.43 ± 0.07
4	0.85 ± 0.01	0.82 ± 0.01	0.92 ± 0.01
5	0.87 ± 0.02	0.80 ± 0.02	0.84 ± 0.03
6	1.05 ± 0.01	1.14 ± 0.01	1.11 ± 0.03
Mean	1.11 ± 0.21	1.04 ± 0.18	1.09 ± 0.19

) and stride length (

Table A2. Individual and group mean ± standard deviation of stride length (m) at baseline, 6, and 12 months post-OI.

Stride Length (m)
Participant	Baseline	6 Months Post OI	12 Months Post OI
1	1.31 ± 0.05	1.18 ± 0.03	1.22 ± 0.03
2	1.38 ± 0.01	1.31 ± 0.02	1.29 ± 0.02
3	1.52 ± 0.06	1.38 ± 0.01	1.48 ± 0.05
4	1.06 ± 0.09	0.99 ± 0.04	1.09 ± 0.02
5	1.20 ± 0.04	1.08 ± 0.01	1.15 ± 0.03
6	1.42 ± 0.04	1.45 ± 0.04	1.43 ± 0.04
Mean	1.31 ± 0.16	1.23 ± 0.17	1.28 ± 0.15

) from baseline to 6 months post-OI, with the exception of participant six. At the individual level, step width (

Table A3. Individual and group mean ± standard deviation of step width (m) at baseline, 6, and 12 months post-OI.

Step Width (m)
Participant	Baseline	6 Months Post OI	12 Months Post OI
1	0.18 ± 0.01	0.18 ± 0.00	0.20 ± 0.04
2	0.16 ± 0.03	0.15 ± 0.00	0.16 ± 0.02
3	0.21 ± 0.01	0.15 ± 0.01	0.18 ± 0.02
4	0.17 ± 0.01	0.19 ± 0.02	0.21 ± 0.02
5	0.21 ± 0.01	0.20 ± 0.02	0.21 ± 0.03
6	0.11 ± 0.06	0.08 ± 0.02	0.16 ± 0.02
Mean	0.17 ± 0.03	0.16 ± 0.04	0.19 ± 0.03

) increased at 12 months compared to 6 months for all participants, showing wider steps than the normative data at all time points except for participant six at baseline and 6 months post-OI. Based on individual data, four of six participants showed increased step length on the prosthetic side (

Table A4. Individual and group mean ± standard deviation of step length on the prosthetic side (m) at baseline, 6, and 12 months post-OI.

Step Length on the Prosthetic Side (m)
Participant	Baseline	6 Months Post OI	12 Months Post OI
1	0.68 ± 0.03	0.63 ± 0.01	0.66 ± 0.02
2	0.73 ± 0.01	0.67 ± 0.02	0.69 ± 0.02
3	0.77 ± 0.03	0.71 ± 0.05	0.73 ± 0.01
4	0.48 ± 0.04	0.47 ± 0.01	0.55 ± 0.01
5	0.54 ± 0.02	0.55 ± 0.03	0.55 ± 0.02
6	0.71 ± 0.02	0.74 ± 0.02	0.74 ± 0.03
Mean	0.65 ± 0.11	0.63 ± 0.10	0.65 ± 0.08

) at 12 months compared to 6 months post-OI, whereas participants five and six exhibited no change. Most participants demonstrated a reduction in step length on the intact side (

Table A5. Individual and group mean ± standard deviation of step length on the intact side (m) at baseline, 6, and 12 months post-OI.

Step Length on the Intact Side (m)
Participant	Baseline	6 Months Post OI	12 Months Post OI
1	0.65 ± 0.05	0.57 ± 0.02	0.57 ± 0.01
2	0.62 ± 0.02	0.63 ± 0.02	0.62 ± 0.02
3	0.75 ± 0.01	0.69 ± 0.02	0.72 ± 0.06
4	0.57 ± 0.05	0.51 ± 0.03	0.54 ± 0.01
5	0.64 ± 0.02	0.53 ± 0.02	0.59 ± 0.02
6	0.71 ± 0.01	0.72 ± 0.02	0.69 ± 0.02
Mean	0.66 ± 0.07	0.61 ± 0.08	0.62 ± 0.07

) at 6 months post-OI relative to baseline, except for participants two and six, who showed small (approximately 1 cm) increases. At 12 months post-OI, step length on the intact side either decreased or remained unchanged compared to baseline across all participants. Similarly, toe-off timing on the prosthetic side (

Table A6. Individual and group mean ± standard deviation of toe-off on the prosthetic side (% Gait Cycle) at baseline, 6, and 12 months post-OI.

Toe-Off on the Prosthetic Side (% Gait Cycle)
Participant	Baseline	6 Months Post OI	12 Months Post OI
1	59.60 ± 0.94	60.10 ± 0.58	58.90 ± 0.44
2	60.20 ± 0.91	56.50 ± 0.30	58.10 ± 0.67
3	57.90 ± 0.16	58.00 ± 0.70	53.90 ± 2.70
4	61.50 ± 1.95	61.90 ± 1.05	59.90 ± 1.22
5	57.40 ± 2.51	60.80 ± 0.61	58.00 ± 0.91
6	58.90 ± 0.14	57.40 ± 0.65	58.40 ± 0.24
Mean	59.25 ± 1.38	59.12 ± 1.94	57.87 ± 1.88

) either decreased or showed little change from baseline to 12 months post-OI for all participants. On the intact side (

Table A7. Individual and group mean ± standard deviation of toe-off on the intact side (% Gait Cycle) at baseline, 6, and 12 months post-OI.

Toe-Off on the Intact Side (% Gait Cycle)
Participant	Baseline	6 Months Post OI	12 Months Post OI
1	66.70 ± 0.54	68.70 ± 2.55	65.30 ± 2.88
2	63.20 ± 0.89	67.70 ± 0.97	67.50 ± 1.69
3	64.10 ± 1.13	65.00 ± 0.02	63.90 ± 0.93
4	72.10 ± 2.82	73.50 ± 0.54	68.40 ± 0.58
5	73.10 ± 1.45	72.80 ± 1.53	70.40 ± 1.80
6	68.40 ± 0.90	68.10 ± 0.49	67.70 ± 0.44
Mean	67.93 ± 3.72	69.31 ± 3.25	67.19 ± 2.58

), most participants showed minimal change or a decrease in toe-off timing at 12 months compared to 6 months post-OI.

3.2. Gait Symmetry Index

All participants demonstrated gait asymmetry at baseline, as reflected by non-zero gait symmetry index values across step length, single support, double support, and toe-off timing (

Table 3. Gait symmetry index (SI) for spatiotemporal parameters, including step length, single support time, double support time, and toe-off timing, expressed as percentages, for 6 participants with unilateral transfemoral amputation, assessed at three time points: baseline, 6, and 12 months post-OI.

Step Length
Participants	Baseline	6 Months Post-OI	12 Months Post-OI
1	4.82	9.54	13.66
2	16.16	6.03	10.12
3	2.10	2.42	0.83
4	18.46	8.61	3.13
5	16.17	3.51	5.78
6	0.85	2.47	7.57
Single Support
Participants	Baseline	6 Months Post-OI	12 Months Post-OI
1	17.80	22.40	15.38
2	12.06	28.88	24.66
3	17.28	18.23	32.31
4	34.40	37.15	28.66
5	44.41	36.55	33.33
6	26.59	26.61	23.89
Double Support
Participants	Baseline	6 Months Post-OI	12 Months Post-OI
1	1.57	1.44	1.64
2	4.99	2.00	1.52
3	1.75	0.88	7.41
4	2.06	1.13	3.96
5	2.84	0.90	3.33
6	0.36	2.42	2.21
Toe-Off
Participants	Baseline	6 Months Post-OI	12 Months Post-OI
1	11.24	13.35	10.31
2	4.86	18.04	14.97
3	10.16	11.38	16.98
4	15.87	17.13	13.25
5	24.06	17.96	19.31
6	14.93	17.05	14.75

). Improvements in step length symmetry were observed for participants two, three, four, and five after OI surgery, whereas participants one and six demonstrated increased asymmetry at post-surgery time points compared to baseline. For single support, minimal changes or increased asymmetry were observed for most participants (participants one, two, three, four, and six), with the exception of participant five, who showed improved symmetry at 6 months post-OI compared to baseline. At 12 months post-OI, there was decreased asymmetry for participants one, two, four, five, and six compared to 6 months post-OI. Regarding double support, gait symmetry index values were very low at baseline (0.36–4.99%), indicating near-symmetric timing. At 6 months post-OI, asymmetry decreased for participants one, two, three, four, and five, while participant six showed an increase. By 12 months, asymmetry increased for participants one, three, four, five, and six, whereas participant two maintained improved symmetry. The absolute changes were generally small, with the largest individual change observed in participant three (0.88% at 6 months to 7.41% at 12 months), suggesting that many fluctuations may be within measurement variability given only three trials per participant. In terms of toe-off timing, only participant five exhibited a reduction in gait asymmetry following surgery compared to baseline. Overall, while most participants improved in step length symmetry, other parameters such as single and double support and toe-off timing exhibited less consistent trends.

4. Discussion

This study examined longitudinal changes in spatiotemporal gait parameters before osseointegration and at 6 and 12 months post-surgery. Significant group-level changes were observed in velocity, step length, stride length, step width, and toe-off timing. Walking velocity decreased by ~0.07 m/s at 6 months post-OI, which was statistically significant but below the minimal clinically important difference (0.21 m/s) for individuals with lower-limb amputation [32], suggesting limited functional impact. The decline in velocity observed at 6 months in the present study could be attributed to the initial use of assistive devices after surgery (e.g., using crutches until 4–6 months after BAP depending on each participant’s loading protocol) and to temporary adaptive gait strategies characterized by slower, more stable, and less dynamic walking, typically adopted shortly after transitioning off gait aids.

No significant group-level differences were found in cadence or single and double support times, unlike some previous BAP studies [17,18,20]. Step length on the prosthetic side increased from 6 to 12 months, while step length on the intact side decreased from baseline, indicating greater step length asymmetry after OI. These results contrast with previous reports of unchanged step length between BAP and socket users [33]. Step length asymmetry is a common challenge for individuals with unilateral transfemoral amputation [34], primarily due to the reduced propulsion-generating capacity of the prosthetic leg [11], loss of muscle function following amputation, and changes in the inertial properties of the prosthetic limb [25,34]. The reduced stride length at 6 months was mainly driven by shorter intact-side steps, whereas the increase at 12 months was driven by longer prosthetic-side steps, reflecting ongoing adaptation after removal of gait aids. However, stride length generally did not return to normative values by 12 months. Toe-off timing asymmetry also persisted in most participants, indicating continued reliance on the intact limb during stance.

Group-level step width increased from 6 to 12 months post-OI (mean change: 0.03 ± 0.05 m), contrasting with previous studies reporting no change or narrower step width in BAP users [19,20,21]. Although this represents a ~30–38% increase relative to normative values (8–10 cm), the effect was largely driven by participant six, whose step width doubled, while others changed by only 1 to 3 cm. This participant, who showed several trends against the group mean, experienced pain in the osseointegration limb and infection complications requiring two surgical debridements, which likely affected their gait pattern. However, the smaller but consistent increase in step width in the remaining participants could reflect altered hip abductor mechanics, as reduced strength and increased muscle tightness can lead to a wider step width to maintain lateral stability [35]. In the absence of kinetic or muscle activation data, it is not possible to confirm whether changes in hip abductor function contributed to this adaptation. Osseointegration eliminates the socket interface and allows direct skeletal load transfer between the prosthesis and the residual limb, which may alter mechanical coupling and load distribution during gait compared to socket suspension. These changes could influence frontal-plane stability strategies, potentially contributing to variations in step width. Nevertheless, further studies incorporating kinetic and muscle activation analyses are required to better understand the mechanisms underlying these adaptations.

The relatively small gait changes observed likely relate to the fact that all participants were high-functioning prosthesis users at baseline, able to walk independently, and manage daily activities despite socket-related discomfort. Osseointegration improved comfort and prosthesis wear time, but these functional gains may not fully translate into measurable biomechanical changes in a controlled lab setting [36,37]. Residual limb muscle weakness [35] and long-established compensatory strategies may have further limited adaptations. A fuller characterization of prosthetic use and mobility in daily life would be important to consider in the absence of biomechanically measured changes.

Limitations of this study include a small sample size, trauma-only etiology, heterogeneous prosthetic components, and the absence of age-matched normative data, all of which limit generalizability. Participants used different prosthetic knees, ranging from passive mechanical devices to fully integrated microprocessor-controlled systems, as well as various foot–ankle assemblies. This heterogeneity is known to influence spatiotemporal gait parameters [38,39] and may have contributed to the inter-individual variability observed in our cohort. Because of the small sample size, adjustment or sensitivity analyses were not feasible; therefore, the influence of prosthetic component design should be considered when interpreting changes attributed to osseointegration. Future studies should aim for greater consistency in prosthetic components, either by standardizing devices across participants or by grouping participants according to prosthesis type for analysis, as demonstrated in previous studies [38,39,40,41]. Such approaches would help control device-related variability and allow clearer interpretation of gait adaptations associated with osseointegration.

All participants in both the control and amputation groups were adults aged 21–60; however, normative data were not collected specifically for this study, preventing precise age-matching between groups. This may have influenced observed gait differences, as age-related changes in muscle strength, joint mobility, and walking patterns can occur within this range [42,43,44]. Future studies should include larger, more homogeneous samples, standardize prosthetic components, and account for demographic and device-related variability to better interpret gait adaptations following OI. While the gait symmetry index provides useful information about individual adaptations, caution is warranted when interpreting small absolute changes, particularly for parameters that are inherently stable and have low baseline asymmetry. Reporting minimal detectable change (MDC) values or incorporating repeated measures may improve reliability in future assessments of the gait symmetry index.

Interpreting the 6-month follow-up is influenced by the initial gait rehabilitation. At this point, participants’ gait reflects a mix of ongoing surgical recovery, use of assistive devices, and newly learned walking strategies. These factors may recover at different rates, making it difficult to separate the specific effects of osseointegration from rehabilitation. In addition, the study focused solely on biomechanical parameters collected in a laboratory setting and did not include functional performance tests or patient-reported outcome measures. Consequently, the extent to which the observed biomechanical changes translate into functional improvements in daily mobility cannot be determined. Nevertheless, understanding changes in spatiotemporal gait parameters and symmetry may help clinicians monitor adaptation following osseointegration and guide the progression of gait rehabilitation programs. Future studies should incorporate validated functional assessments (e.g., Timed Up and Go, 6-Minute Walk Test) and patient-reported measures to better establish the clinical relevance of gait adaptations following osseointegration.

5. Conclusions

This study examined longitudinal changes in spatiotemporal gait parameters and gait symmetry following osseointegration surgery in individuals with unilateral transfemoral amputation. Assessing participants at 6 and 12 months post-OI provided insight into the progression of gait adaptations over time. Post-surgery, participants showed variable changes in cadence, step length, stride length, step width, and toe-off timing, as well as in gait symmetry, highlighting that adaptations are highly individualized. Factors such as residual limb characteristics, muscle strength, prosthetic alignment, and personal strategies likely influenced these patterns. Future studies with larger, more homogeneous cohorts are needed to further clarify spatiotemporal and symmetry outcomes and their functional relevance.