Incidence of flatfoot after peroneuslongus ACL grafting

Investigators found few cases of postoperative arch collapse, but alternative footprint measurements classified substantially more cases of flatfoot.

By
Andrea Surnit
November 4, 2026
4 min

MDSpire News

At a Glance

Category	Detail
Condition	New-onset flatfoot after anterior cruciate ligament reconstruction (ACLR) using peroneuslongus tendon autografts
Key Mechanisms	Foot posture was assessed with static digital footprints using the Arch Index, Staheli Index, Chippaux-Smirak Index, and Clarke angle; these measures classified flatfoot at different rates.
Target Population	Patients aged 16 years or older undergoing primary single-bundle ACLR with a peroneuslongus autograft, without preexisting flatfoot deformity
Care Setting	Single-center prospective observational study of postoperative patients, with clinical and footprint assessments scheduled from 6 to 36 months

Key Highlights

Among 130 patients with complete follow-up, 2 (1.5%) developed flatfoot by the Arch Index; both cases were on the operated limb.
The two patients classified as having flatfoot by the Arch Index remained asymptomatic, with no reported pain, instability, or activity limitations.
Flatfoot classification varied by measure: 1.5% by the Chippaux-Smirak Index, 18% by the Staheli Index, and 47% by the Clarke angle.
Exploratory analyses found no statistically significant association with Beighton score, BMI, body weight, or height; only two primary outcome cases limited risk-factor analysis.
The study had no alternative-graft comparison group and was limited by its single-center design, one surgeon, predominantly male sample, and static footprint assessments.

Guideline-Based Recommendations

Diagnosis

The study defined new-onset flatfoot using an Arch Index greater than 0.26 on weight-bearing digital podograms.
The investigators also assessed foot posture using the Staheli Index, Chippaux-Smirak Index, and Clarke angle; classification rates differed substantially across measures.

Management

Monitoring & Follow-up

Clinical and footprint assessments were scheduled at 6, 12, 24, and up to 36 months after surgery.

Risks

The study reported a 1.5% incidence of flatfoot by the Arch Index among 130 patients with complete follow-up.
The authors cautioned that the association between older age and flatfoot could not be generalized because only two patients developed the primary outcome.
Static footprints may not fully reflect dynamic foot biomechanics; radiographic and 3-dimensional imaging were not performed.

Patient & Prescribing Data

130 patients aged 16 years or older who underwent primary single-bundle ACLR with peroneuslongus autografts and had at least 12 months of follow-up; patients with preexisting flatfoot and specified revision, multiligament, prior-limb-surgery, neuromuscular, or connective-tissue conditions were excluded.

Two patients (1.5%) developed flatfoot by the Arch Index after ACLR; both were asymptomatic. The study did not compare peroneuslongus grafts with alternative grafts.

Clinical Best Practices

Interpret footprint-based flatfoot classifications in light of the measurement method, as the indices produced substantially different rates in this study.
Do not generalize the exploratory age association or infer risk factors from this study; only two patients met the primary outcome.
Recognize that the study assessed static footprints and did not evaluate foot posture with radiographic or 3-dimensional imaging.