Flatfoot following anterior cruciate ligament reconstruction using peroneuslongus tendon autografts may be rare, with no reported pain or functional impairment.
In conducted a prospective observational study, investigators recruited 130 patients aged 16 years or older who underwent primary single-bundle anterior cruciate ligament reconstruction (ACLR) using peroneuslongus autografts between May 2024 and December 2025. All procedures were performed by 1 experienced surgeon. Eligible patients had no preexisting flatfoot deformity and at least 12 months of postoperative follow-up. Patients with revision ACLR, multiligament knee injuries, prior surgery involving the affected limb, or neuromuscular and connective tissue disorders were excluded. Clinical and footprint assessments were scheduled at 6, 12, 24, and up to 36 months post surgery.
The investigators assessed incidence of new-onset flatfoot, defined by an Arch Index greater than 0.26 on weight-bearing digital podograms,the Staheli Index, Chippaux-Smirak Index, Clarke angle to characterize foot posture,generalized joint laxity using the Beighton score, and associations between postoperative flatfoot and demographic and anthropometric characteristics.
Among the 130 patients with complete follow-up, 2 developed flatfoot according to the Arch Index, corresponding to an incidence of 1.5%. Both cases occurred on the operated limb, whereas no cases were identified in the contralateral foot. The affected patients remained asymptomatic, with no reported pain, instability, or limitations in daily activities or sports.
However, flatfoot classification varied substantially depending on the measurement method. The Chippaux-Smirak Index identified 2 patients (1.5%), consistent with the primary Arch Index findings. In contrast, the Staheli Index classified 24 patients (18%) as having flatfoot and the Clarke angle classified 61 patients (47%). Despite the higher classification rates with width- and angle-based measurements, the investigators reported no associated pain or functional impairment.
Exploratory analyses found no statistically significant association between postoperative flatfoot and generalized joint laxity, as assessed using the Beighton score. Body mass index, body weight, and height were not significantly associated with flatfoot occurrence. Patients who developed flatfoot were older than those who did not (46 vs. 26 years). However, the investigators cautioned that this association could not be generalized because just 2 patients developed the primary outcome.
Differences among footprint indices may reflect the distinct biomechanical characteristics measured by each method. The Arch Index evaluated midfoot contact area relative to the total plantar footprint, whereas width- and angle-based indices may be more sensitive to variations in footprint contour, stance position, and soft tissue distribution. The discrepancy between the Arch Index and Clarke angle findings highlighted the potential for structural footprint changes to occur without clinically apparent flatfoot deformity or functional donor-site morbidity.
The small number of postoperative flatfoot cases prevented multivariable analysis and restricted conclusions about potential risk factors. Foot posture was assessed using static digital footprints, which may not have fully reflected dynamic foot biomechanics during gait, and radiographic or 3-dimensional imaging was not performed. The study was conducted at a single center, with all procedures performed by 1 surgeon, and about 91% of participants were male, limiting generalizability. The absence of a comparison group receiving alternative grafts also prevented direct assessment of relative donor-site risks.
“Our study showed that ACLR using a [peroneuslongus] autograft carries a minimal risk of clinically significant postoperative flatfoot deformity (1.5% based on the [Arch Index]),” wrote lead study author Ludwig Andre Pontoh, MD, PhD, of Fatmawati Hospital in Indonesia, and colleagues.
The study authors declared no conflicts of interest.
