Abstract
Background and objectives
Progressive Collapsing Foot Deformity (PCFD), a multifactorial disorder, involves the synergistic failure of dynamic restraints, primarily the posterior tibial tendon (PTT), and static restraints, chiefly the calcaneonavicular ligament (SL). The necessity of routinely reconstructing the SL complex in the early, flexible stages of the disease is a significant clinical debate.To clarify this, this study aimed to assess whether measurable macro-structural changes, specifically alterations in the ultrasonographic thickness of the supramedial fasciculus of the calcaneonavicular ligament, are already established in patients presenting with symptomatic, flexible PCFD compared with healthy controls.
Methods
An observational cross-sectional study (level of evidence: III, prognostic study) included 108 adult subjects: a symptomatic flexible PCFD group (n = 55) and a control group (n = 53). Exclusion criteria were strictly implemented to prevent the inclusion of advanced, rigid deformities, specifically excluding patients presenting with talar uncoverage greater than 50% on weight-bearing anteroposterior radiographs or a plantar sag indicative of severe collapse on lateral radiographs. The thickness of the calcaneonavicular ligament (SL) was the primary outcome measure measured using high-frequency ultrasound. Secondary measures included PTT thickness to confirm the pathological status of the experimental cohort.
Results
The mean thickness of the calcaneonavicular ligament showed no statistically significant difference between the control group (5.07 mm, SD = 0.116) and the PCFD group (4.81 mm, SD = 0.119) (p = 0.368). This demonstrates the structural integrity of the SL complex in the early, flexible stage of the deformity. In contrast, all measurements of the PTT demonstrated significant thickening in the experimental group, confirming established tendinosis (p < 0.001).
Conclusions
In symptomatic, flexible Progressive Collapsing Foot Deformity dynamic tissue pathology (PTT tendinosis) is established, yet the structural thickness of the superomedial calcaneonavicular ligament remains stable. This supports a temporal pathomechanical sequence in which the dynamic restraint failure precedes the gross dimensional collapse of the primary static stabilizer. The preservation of SL structural stability in early disease stages argues against the routine, mandatory exploration and reconstruction of the medial soft tissues unless functional dynamic imaging reveals severe laxity.
Level of Evidence
III
Keywords: Spring ligament, Posterior tibial tendon, Progressive collapsing foot deformity, Ultrasonography
Introduction
Progressive Collapsing Foot Deformity (PCFD) represents a complex, three-dimensional instability characterized by the synergistic failure of both dynamic and static medial column stabilizers [1]. While the posterior tibial tendon (PTT) acts as the primary dynamic restraint, the superomedial fasciculus (SMF) of the calcaneonavicular or “Spring” ligament (SL) complex serves as the fundamental static support for the talonavicular joint and the acetabulum pedis [2]. Although advanced stages of PCFD are marked by gross SL attenuation or rupture, leading to irreversible talar migration and arch collapse, the structural integrity of this ligament during the early, flexible stages of the disease remains a subject of significant clinical debate [3].
The clinical relevance of the SMF is underscored by its unique histological properties; its fibrocartilaginous gliding zone and limited microvascularity suggest a poor intrinsic potential for biological repair once structural damage occurs [3]. Consequently, the surgical management of early-stage, flexible PCFD often involves a conflict between corrective bony procedures—intended to mechanically de-stress the medial column—and formal soft-tissue reconstruction of the SL complex [4, 5]. If the SL maintains its macro-structural integrity during the symptomatic but flexible phase, routine reconstruction may be unnecessary, thereby avoiding the morbidity associated with complex ligamentous transfers or augmentations [6, 7].
High-frequency ultrasonography has emerged as a reliable, non-invasive modality for assessing the SL complex, offering spatial resolution comparable to magnetic resonance imaging [8]. However, there is a lack of consensus in the literature regarding normative thickness values and whether measurable dimensional changes occur before the onset of rigid deformity. Characterizing the relationship between dynamic failure (PTT tendinosis) and static restraint status is essential to delineate the temporal pathomechanical sequence of PCFD.
Therefore, the objective of this study was to evaluate whether measurable macro-structural alterations, specifically changes in the ultrasonographic thickness of the superomedial fasciculus of the calcaneonavicular ligament, are present in patients with symptomatic, flexible PCFD compared with healthy controls.
Materials and methods
Study design, setting, and ethics
This investigation was structured as an observational, cross-sectional study (Level III, Prognostic study) conducted from January to December 2022, according to the STROBE guidelines. The Ethics Committee approved the study (PEIBA 2019102316500), and all procedures adhered to the guidelines established by the Declaration of Helsinki.
Participant selection and enrollment
A consecutive sample of 108 adult subjects was recruited and divided into an experimental group diagnosed with symptomatic, flexible PCFD (n = 55) and a control group (n = 53). The mean of the age PCFD cohort was 54.06 years, with a mean of 78.77 Kg of weight (This involves a prevalence of overweight of 36.1%) The percentage of females in the PCFD Stage I was 35.2%. The control group mean age was 46.5 years and 69.73 Kg (overweight prevalence of 18.5%), in this group the percetange of females was 31.5%.
The inclusion criteria for the experimental group were symptomatic medial foot pain and clinically flexible deformity confirmed by standard physical examination. Both groups agreed to undergo high-frequency ultrasound and standard weight-bearing anteroposterior (AP) and lateral radiography.
The exclusion criteria were strictly implemented to ensure that the study population represented the early, flexible stages of the disease, barring subjects with
Previous history of trauma or surgery in the foot/ankle.
BMI > 40 (morbid obesity).
Inflammatory arthropathies or congenital malformations.
Repeated ankle sprains with medial involvement, tarsal coalitions, previous history of fractures or surgeries in the studied foot, or lateral pain of the foot-ankle.
- Radiographic evidence of advanced collapse on weight-bearing views, specifically [9, 10]:
- Talar uncoverage greater than 50% on the AP view (indicating severe forefoot abduction/talonavicular subluxation).
- Significant plantar sag in the lateral radiograph (indicative of fixed bony or advanced ligamentous failure and collapse of the talonavicular joint).
Ultrasound protocol: calcaneonavicular ligament assessment
Measurements were performed by a single experienced examiner. While intraobserver reliability was not assessed for this specific cohort, in a prior interobserver agreement analysis published by our research team [11] the ICC was 0.91 (95% CI: 0.698–0.977). This demonstrates a high degree of consistency between the orthopedic surgeon and the radiologist, supporting the reliability of the protocol.
All imaging examinations were performed using the same ultrasound equipment (MB-Turbo) and a single high-frequency linear probe (15 − 6 MHz) by a single specialized orthopedic surgeon. The primary outcome measure was the thickness of the superomedial fasciculus (SMF) of the calcaneonavicular ligament.
The transducer was placed parallel to the long axis of the foot on the medial longitudinal arch at the level of the head of the talus and the navicular. This standardized longitudinal view allowed for the measurement of the SMF thickness, which was verified by cross-referencing the short-axis view [6]. Figure 1.
Fig. 1.
Longitudinal axis and specified sonographic of the PTT and SML
Secondary measurements were obtained for the PTT (longitudinal thickness and major and minor diameters at the retromalleolar level) to confirm the presence of tendinosis in the experimental cohort. Figure 2.
Fig. 2.
Short-axis ultrasonographic image of the posterior tibial tendon (PTT) 2. Short-axis ultrasonographic image of the SML (superomedial Spring Ligament)
Statistical analysis
The Wilcoxon-Mann-Whitney U test was used for the comparative analysis of continuous variables (SL and PTT thickness) between the groups. Due to significant baseline differences in age and weight/BMI, a multivariable regression analysis was used to assess the association between PTT thickening and PCFD status, adjusting for the effects of these known confounding variables, further validating the pathological state of the experimental cohort.
Results
Demographic and anthropometric characteristics
The study included 53 control subjects (49.1%) and 55 PCFD subjects (50.9%). The PCFD cohort was significantly older (mean 54.06 years vs. 46.5 years) and heavier (mean weight 78.77 Kg vs. 69.73 Kg), with a higher prevalence of overweight/obesity (36.1% vs. 18.5%) compared to the controls (p = 0.002 in all comparisons).
Comparative Analysis of the Baseline Demographic and Anthropometric Characteristics are shown in Table 1.
Table 1.
Comparative analysis of the baseline demographic and anthropometric characteristics
| Variable | Control group mean (SD) | PCFD group mean (SD) | Statistical comparison (p-value) |
|---|---|---|---|
| Age (Years) | 46.5 (10.96) | 54.1 (13.19) | 0.002 |
| Weight (Kg) | 69.73 (13.23) | 78.77 (14.80) | < 0.001 |
| BMI status (Overweight/Obesity, %) | 18.5% | 36.1% | < 0.001 |
| Gender (Female, %) | 31.5% | 35.2% | 0.276 |
Primary outcome: calcaneonavicular ligament structural assessment
The comparative analysis of the primary outcome demonstrated no statistically significant difference in the mean thickness of the calcaneonavicular ligament (SL) between the groups (p = 0.368).
Ultrasound Measurements of Calcaneonavicular Ligament Thickness (Primary Outcome). Table 2.
Table 2.
Ultrasound measurements of calcaneonavicular ligament thickness (Primary Outcome)
| Structure measured | Control group mean (mm, SD) | PCFD group mean (mm, SD) | P-value | Result |
|---|---|---|---|---|
| Spring ligament (SL) thickness | 5.07 (0.116) | 4.81 (0.119) | 0.368 | Structural stability maintained |
Secondary outcome: posterior tibial tendon pathology confirmation
The secondary outcome measures confirmed the presence of an established pathology in the experimental cohort, consistent with tendinosis. All PTT thickness measurements (LPTT, DmTP, DMTP) were significantly greater in the PCFD group (p < 0.001). This significant thickening remained stable and independent of the confounding effects of age and BMI in the multivariate analysis. Table 3.
Table 3.
Ultrasound measurements of the posterior tibial tendon dimensions (secondary outcome)
| Structure measured | Control group mean (mm, SD) | PCFD group mean (mm, SD) | P-value | Result |
|---|---|---|---|---|
| PTT long axis (LPTT) | 3.59 (0.076) | 4.39 (0.112) | < 0.001 | Significant thickening |
| PTT minor diameter (DmTP) | 3.37 (0.065) | 4.40 (0.145) | < 0.001 | Significant thickening |
Discussion
The most important finding of this study was the clear discordance in morphological changes between the primary static and dynamic restraints of the medial arch in symptomatic, flexible PCFD. Specifically, we observed a statistically significant thickening of the posterior tibial tendon (PTT), indicative of tendinosis (p < 0.001), but no statistically significant difference in the ultrasound thickness of the superomedial calcaneonavicular ligament (SL) between the healthy and pathological individuals (p = 0.368).
This finding suggests that while PTT changes are an early and significant feature of this deformity, the Spring ligament may not yet show the thinning or thickening commonly associated with more advanced stages. This structural stability strongly supports the sequential pathomechanical hypothesis that dynamic overload precipitates PTT tendinosis and that this dynamic failure precedes the macroscopic, dimensional collapse of the primary static stabilizer.
Calcaneonavicular ligament structural assessment: comparison with the literature
In our study, no statistically significant differences were found in the ultrasound thickness of the SL between healthy and pathological individuals. The mean SL thickness in the control group was 5.07 mm, whereas the mean SL thickness in the pathological group was 4.81 mm.
It must be considered that the middle portion of the superomedial fascicle of the SL may show a thickening of the damaged fibrocartilaginous portion in chronic injuries. This finding is consistent with the hypothesis that the SL may not be the primary site of early-stage pathology.
Our observed mean SL thickness values must be compared with published normative data to accurately contextualize the stability finding:
Tryfonidis et al. [12] reported a mean thickness of the SL in healthy persons of 4 mm (range 2.5–5.5 mm). In contrast, patients with SL insufficiency demonstrated a median thickening of 5.5 mm with a loss of the fibrillar pattern and increased vascularity.
Harish et al. [13] obtained a mean of 3 mm (range 1.9–4.7 mm) in healthy subjects.
Mansour et al. [14] measured means in healthy subjects using the short-axis ultrasound, finding proximal measurements at 4 mm (range 3.4–5.3 mm, SD 0.6) and distal measurements at 3.6 mm (range 2.4–5.2 mm, SD 2.0).
The proximal and distal portions of the SL measured by Mansour et al. [14] are narrower than the central zone used for measurement in this article, where, as mentioned earlier, thickening occurs in chronic injuries. Harish et al. [13] measured only the short axis in a single portion, so variations along the length of the ligament are not considered. Our control mean of 5.07 mm is at the upper end of, or slightly exceeds, the ranges reported by these authors. However, despite the known propensity of the SL to show thickening in chronic pathology, the PCFD group in our study (mean 4.81 mm) showed no significant increase compared with our healthy controls (mean 5.07 mm), reinforcing the notion that the SL retains structural thickness in flexible PCFD and may not be the primary site of early-stage, measurable macroscopic pathology.
The PCFD cohort was significantly older (mean 54.06 years vs. 46.5 years). The role of age in the SL damage is documented in the bibliography. Raikin and colleagues [15] defined age as an independent predictor of SL degeneration or rupture; with each additional year of age, the probability of damage increased (OR = 1.10, p = 0.003), and older age was associated with a greater percentage of talonavicular uncoverage [16].
PTT thickening confirms the pathological status
In contrast to the SL findings, the statistically significant PTT thickening observed across all measured diameters (p < 0.001) strongly confirmed the presence of established tendinosis and dynamic failure in the experimental cohort. Overload of the posterior tibial tendon, secondary to repetitive microtraumas and excessive pronation, results in degeneration and replacement by fibrous tissue as it degenerates. This often occurs in the microvascularized retromalleolar zone, likely due to the pressure of the medial malleolus on the tendon at this level [17, 18]. Hence, the area of pressure stress and decreased vascularization at the retromalleolar level is the most problematic for the development of PTT tendinopathy. We found a thickened tendon, a result of tendon synovitis and metaplasia of the tendinopathy causing this thickening. This PTT pathology is validated as an independent finding, as the multivariable analysis confirmed that the thickening was significant even after adjusting for the confounding factors of age and BMI [19, 20].
Clinical interpretation and surgical implications
The maintenance of structural integrity in the calcaneonavicular ligament in flexible PCFD carries profound implications for contemporary surgical planning. The structural stability observed argues against the routine, mandatory surgical exploration and primary soft tissue reconstruction of the medial column in flexible PCFD.
Our findings support a targeted surgical approach in early-stage, flexible PCFD, focusing primarily on achieving mechanical realignment through precise bony corrections. The objective of these procedures is to relieve the excessive mechanical strain currently being borne by the structurally intact SL. Regarding the posterior tibial tendon, the decision to perform a synovectomy or FCD transfer may depend on the severity of fibrous metaplasia and synovitis, which can be effectively assessed via dynamic ultrasonography [21].
While some authors advocate for early ligament reconstruction to ensure stability [2, 4], our data complement these viewpoints by characterizing a specific subgroup—patients with early, flexible deformities and preserved ligamentous structure—where bony realignment alone might suffice [22, 23]. Consequently, Spring Ligament reconstruction might be best reserved for cases where advanced instability or structural rupture is confirmed. Surgical decision-making should ideally integrate clinical examination, dynamic imaging, and intraoperative findings, looking for objective markers such as [10]:
Significant Plantar Sag: Evidence of talonavicular collapse in the lateral view under weight-bearing conditions (Weight-bearing CT SCAN or X-ray).
Talar Uncoverage Greater than 50%: Indicating severe talonavicular subluxation and failure of the static restraints in the anteroposterior view under weight-bearing conditions.
Future research should integrate static structural findings with dynamic, stress-based ultrasound protocols to precisely identify the critical point where the calcaneonavicular ligament transitions to functional laxity, thereby refining prognostic markers for surgical necessity.
Limitations
We acknowledge several limitations in this study. First, the cross-sectional design restricts our ability to establish a definitive temporal progression of the disease; while we observed a correlation between PTT degeneration and early PCFD, longitudinal studies would be required to confirm the exact sequence of structural failure. Second, regarding the ultrasound assessment, an interobserver agreement analysis was performed. The intraclass correlation coefficient for measurements between observers (orthopedic surgeon and radiologist) was 0.91 (CI95%: 0.698–0.977), which denotes a high degree of similarity between the clinician and the radiologist [11]. However, we acknowledge that this remains a single-center study and intraobserver reliability was not assessed for the entire cohort. Third, the ultrasound assessments of the spring ligament were static and not performed under weight-bearing conditions. Consequently, while we demonstrated anatomical preservation, functional insufficiency under load cannot be entirely ruled out.
Conclusion
This study demonstrates that in symptomatic flexible PCFD, dynamic component failure, as evidenced by PTT tendinosis, is established, while the primary static stabilizer, the superomedial calcaneonavicular ligament, maintains its structural thickness. The absence of a statistically significant difference in SL thickness could support a sequential pathomechanical process in which dynamic overload precedes the gross structural collapse of the static ligament. This preservation of SL thickness in the early stages challenges the routine surgical procedure of the calcaneonavicular ligament, guiding surgical focus toward bony realignment.
Acknowledgements
We would like to thank the patients who agreed to participate in this study, as well as our colleagues who collaborated to make the preparation of this manuscript possible.
Author contributions
BMS: collected the patients’ data and designed the study.ST and SF: obtained patient data, collected the images for the figures, and drafted part of the discussion.ELR: collaborated in designing the study and helped write the introduction and the abstractFJMB y MGA: they prepared the tables and analyzed the results.
Funding
This research did not receive funding.
Data availability
We generate a database from patients in our hospital that is available in excel format.
Declarations
Ethics approval and consent to participate
The Ethics Committee granted approval to the study (PEIBA 2019102316500), which was carried out according to the guidelines of the Declaration of Helsinki. All the authors consent to participate in this manuscript.
Consent for publication
I confirm the corresponding author has read the journal policies and submit this manuscript in accordance with those policies.
Competing interest
The authors declare no competing interests.
Footnotes
Publisher’s note
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Contributor Information
Beatriz Martínez-Sañudo, Email: bmartinezsanudo@gmail.com.
Sergio Tejero, Email: sertejgar@us.es.
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Associated Data
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Data Availability Statement
We generate a database from patients in our hospital that is available in excel format.