Abstract

Progressive Collapsing Foot Deformity (PCFD), previously termed Adult Acquired Flatfoot Deformity (AAFD), is a progressive condition characterized by failure of medial soft tissue structures leading to painful biomechanical dysfunction. Traditional reconstructions often rely on nonanatomic osteotomies, such as lateral column lengthening, which carry notable risks. This study evaluates a novel soft tissue reconstruction of the spring-deltoid ligament complex combined with medial column osteotomies for stage II PCFD.

Methods: A retrospective case series was performed on 9 feet in 8 patients (mean age 44.7 years) treated between September 2021 and December 2024. The surgical technique included spring ligament InternalBrace™ augmentation with Flexor Digitorum Longus (FDL) transfer, Cotton osteotomy with titanium wedge and minimally invasive Medial Calcaneal Osteotomy (MICO). Pre- and postoperative radiographs were analyzed for Meary’s angle, talocalcaneal angle, calcaneal inclination angle, calcaneocuboid angle and intermetatarsal angle. Functional outcomes were assessed using FAOS and AOFAS hindfoot scores. Paired t-tests determined statistical significance (p < 0.05).

Results: All radiographic parameters demonstrated significant improvement: Meary’s angle (14.56° → 2.11°), talocalcaneal angle (28.11° → 18.44°), calcaneal inclination (11.67° → 15.89°), calcaneocuboid angle (21.11° → 12.11°) and intermetatarsal angle (11.11° → 6.67°) (all p < 0.05). Functional outcomes also improved, with mean FAOS of 79.1 ± 10.5 and mean AOFAS of 84.3 ± 3.8 at an average of 21 month follow-up. No patients required adjunctive lateral column lengthening and no construct failures or major complications were observed.

Conclusion: Spring-deltoid ligament reconstruction with InternalBrace™ augmentation, combined with MICO and Cotton osteotomy, achieved significant radiographic and functional correction in stage II PCFD without the need for nonanatomic lateral column lengthening. This technique may provide a safer, anatomic alternative to traditional reconstructions, offering reliable restoration of medial column stability and improved patient-reported outcomes.

Level of Evidence: IV (Retrospective case series).

Keywords: Progressive Collapsing Foot Deformity (PCFD); Adult Acquired Flatfoot Deformity (AAFD); Flatfoot; Spring Ligament; Deltoid Ligament; InternalBrace™ Augmentation; Medial Calcaneal Osteotomy (MICO); Cotton Osteotomy; Flexor Digitorum Longus (FDL) Transfer; Soft Tissue Reconstruction; Foot and Ankle Surgery

Introduction

Progressive Collapsing Foot Deformity (PCFD) arises from multiple anatomic and biomechanical factors, with aspects of both its origin and techniques remain controversial.  The incidence of flatfoot is often underreported, but recent studies suggest that Adult Acquired Flatfoot Deformity (AAFD) occurs in approximately 3.3% of women over the age of 40 [1]. AAFD can be life-changing, ranking second only to ankle arthritis in terms of preoperative pain and limitation of function based on long term outcome scores [1]. The deformity is progressive, accentuated by the loss  of the integrity of tendons and ligaments that support the talus, allowing the deformity to worsen [2]. AAFD has been applied to previously described classification systems that were originally designed for Posterior Tibial Tendon Dysfunction (PTTD). Further revisions have been developed to aid surgeons in addressing patient specific deformities, as there is not a “one size fits all” flatfoot deformity. However, core tenants can be addressed to improve long term outcomes [1]. Multiple updates have been made to the accepted classification of PTTD, ranging from 1-IV, now called Progressive Collapsing Foot Deformity (PCFD). This paper will focus on the flexible aspect of the classification and describe a novel technique to address both the soft tissue as well as osseous sequelae of stage II PCFD [3].

Failure of soft tissue structures including ligaments, tendons and support structures allows osseous structures to become misaligned and over time lead to painful biomechanics [1]. Recent ligament mapping using attachment-based dissection has further clarified the functional roles of the medial collateral and spring ligaments [2]. There is ongoing debate regarding whether the medial collateral ligament complex is part of the medial deltoid ligament apparatus or the spring ligament. Two components of the medial collateral complex are widely accepted: the superficial and the deep portions. The superficial portion consists of the tibionavicular, tibiospring, superficial posterior tibiotalar and talocalcaneal ligaments, while the deep portion consists of the deep posterior and deep anterior tibiotalar ligaments.

The spring ligament complex consists of both the superioromedial calcaneonavicular ligament, which provides longitudinal arch support and is frequently attenuated or injured in patients with PCFD, as well as the inferior calcaneonavicular ligament whose precise role remains unclear. Although the medial collateral complex and the spring ligament serve distinct functions, they are interconnected via the superomedial calcaneonavicular ligament [2]. This anatomic relationship forms the foundation of the core tenet underlying the novel technique described in this paper.

A common presentation of PCFD includes a patient with flexible hindfoot valgus, forefoot abduction, a painful Posterior Tibial (PT) tendon, medial column sag and talonavicular uncovering consistent with a stage II deformity. Such cases have been shown to respond more favorably to surgical treatment than to conservative measures. Houck, et al., performed a Randomized Control Trial (RCT) comparing orthotics alone with orthotics plus stretching finding only mild improvement in activity and pain at 12 weeks [4].

In 2019, Aynardi, et al., performed a cadaveric study to evaluate the biomechanical impact of spring ligament augmentation using FiberTape™ in a flatfoot model. They demonstrated the FiberTape™ augmentation was safe and effective under cyclic loading. In contrast, 8/8 suture only repairs failed due to suture cut-through (n=5), structure fatigue (n=2)  or knot failure (n=1). Only one of the Fiber Tape™ augmented repairs failed after cyclic loading (P=0.0014). At forces of 1600 N (P=0.03) and 1700 N (P= 0.02), there were statistically significant differences favoring Fiber Tape™ augmentation compared to suture-only techniques, with greater collapse of the lateral Meary’s talo-first metatarsal angles in the control group [5].

The goals of radiographic restoration in PCFD reconstruction include improvement of the calcaneocuboid angle, reduction of talar head uncovering, correction of Kite’s angle, correction of calcaneal valgus on axial radiographs and resolution of the medial column “sag.” Surgeons must address both rearfoot valgus and forefoot alignment, which may present in supinatus or varus [1]. The role of forefoot abduction relative to the rearfoot remains controversial. Previous principles of flatfoot reconstruction recommended an Evans osteotomy to achieve triplanar correction and directly address the abduction deformity.

Valgus malposition of the heel, due to loss of integrity of the medial column soft tissue apparatus, produces the “too many toes sign.” This transverse deformity can be addressed without lateral column lengthening, despite the historical popularity of the Evans osteotomy since 1975. However, recent studies have shown that while the Evans osteotomy can reliably correct the transverse radiographic deformity, it carries notable sequelae, including calcaneocuboid degeneration (30%), subtalar degeneration (25%), sural neuritis (11%) and lateral column overload (4%), with an overall complication rate of 15.2% [6-8]. Given these complication rates, there is a growing need for less extensive, procedures. Soft tissue balancing techniques may achieve adequate correction while avoiding the risks of aggressive non anatomic structural procedures.

Multiple considerations should be made regarding whether to address the medial column alone or to include the lateral column. These include obesity, osteoarthritis, degenerative joint disease, joint preservation and ankle involvement. For ease of use, this authors’ algorithm was simplified to address four core deformities: equinus, valgus hindfoot, soft tissue insufficiency and osseous deficiency.

Equinus correction: Taloachilles Lengthening (TAL), Endoscopic Gastrocnemius Recession (EGR)

Valgus correction: Medializing Calcaneal Osteotomy (MCO), Minimally Invasive Calcaneal Osteotomy (MICO)

Soft tissue correction: Flexor Digitorum Longus (FDL) transfer, Spring Ligament with deltoid repair

Osseous supplementation: Cotton, Lapidus

For stage II patients with obesity (BMI> 40), treatment consists of soft tissue repair with isolated fusion in the absence of Degenerative Joint Disease (DJD) of the Subtalar Joint (STJ), Talonavicular (TN)  or Calcaneocuboid (CC) joints. If DJD is present, soft tissue repair is combined with double or triple arthrodesis. Stage III patients typically undergo soft tissue repair with isolated fusion, including double or triple arthrodesis, to address hindfoot valgus. Stage IV patients with ankle involvement may benefit from staged reconstruction, first addressing foot alignment to restore the mechanical axis, followed by treatment of the ankle. This paper focuses on soft tissue correction, specifically restoration of the spring/deltoid ligament complex to treat stage II flexible flatfoot reconstruction. We aim to demonstrate that the spring ligament Internal brace™ ligament augmentation provides adequate deformity correction without requiring nonanatomic reconstructive procedures, the Fiber Tape™ augmentation of the spring ligament is biomechanically safe and effective under cyclic loading, combined deltoid and spring ligament repair yields superior long term success and that the spring ligament repair with Internal brace™ provides both radiographic and clinical improvement.

Methodology

A retrospective case series was conducted of patients undergoing surgical correction for progressive collapsing flatfoot deformity using the authors’ novel soft tissue balancing technique, which included the spring ligament reconstruction with corresponding Cotton osteotomy with titanium wedge placement and MICO. All patients were provided informed consent for inclusion in this study. Inclusion criteria included diagnosis of stage II adult flatfoot without end stage arthritis that had failed conservative measures. Exclusion criteria included a rigid flatfoot, end stage arthritis, neuromuscular disease, history of charcot  or infection. We included 9 feet, composed of 8 patients between September 2021 and December 2024 who met inclusion criteria.

Operative Technique Guide

Setup: Patients were positioned supine with an ipsilateral hip bump.

We developed the current technique to reconstruct both the calcaneonavicular and tibiospring ligaments of the deltoid ligament.

1. Through a standard medial approach over the PTT, the primary insertion of the PTT was reflected off the navicular, leaving the secondary insertion plantarly. The tendon was appropriately debrided and left intact to advance and provide a side-to-side tenodesis with the FDL to the PTT after transfer
2. The spring ligament was approached with a transverse incision and a wedge resection was performed for imbrication after reconstruction
3. The FDL was identified deep and proximal to the PTT, reflecting the PTT inferiorly to locate the FDL
4. The FDL was transected proximal to the knot of Henry
5. Arthrex suture tape FiberLoop™ was used to create a Krackow-type suture through the FDL. The Keith needle was protected with a clamp and set aside for later tendon transfer
6. The sustentaculum tali was identified just distal to the tip of the medial malleolus (approximately one thumb length) and deep to the prepared FDL tendon
7. The cannulated Internal Brace System (Arthrex)™ was used, with a guidewire placed in the sustentaculum (Fig. 1) Fluoroscopy (lateral and calcaneal axial views) confirmed placement
8. A 2.7 mm drill for a 3.5 SwiveLock Anchor™ was used over the guidewire, followed by tapping. The guidewire was then removed
9. A 3.5 mm anchor double-loaded with Fibertape™ (Fig. 2) was placed into the prepared drill hole in the sustentaculum. Due to the size of the anchor and the double-loaded suture, the resistance and feedback can be tight. The suture was clamped and set aside
10. A MICO was performed to medialize ankle forces and protect the soft tissue reconstruction. The osteotomy was fixated with two screws perpendicular to the osteotomy (Fig. 3,4)
11. A medial cuneiform osteotomy was prepared at this stage but not fixated until later to allow appropriate positioning. This also allows the cut to take place prior to soft tissue repair in order to prevent final malalignment of the osteotomy
12. A guidewire was placed in the medial talus, distal to the ankle joint, and distal to the medial cartilage of the talus and confirmed with fluoroscopy (Fig. 5). A cannulated 3.4 mm drill was used, followed by tapping. One arm of the sustentaculum suture was fixed with an Arthrex 4.75 SwiveLock™ anchor under tension (Fig. 6)
13. A guidewire was then placed into the medial malleolus, confirmed on fluoroscopy (Fig. 7). A cannulated 3.4mm drill and tap were used and one arm from the sustentaculum and the remaining talus suture were fixed with another Arthrex 4.75 SwiveLock™ anchor under neutral ankle positioning (Fig. 8).
14. The remaining two arms from the sustentaculum were used for the FDL transfer. The tendon was pulled through a prepared navicular tunnel using a pull-through technique and fixed with Arthrex bio-tenodesis anchor™ (Fig. 9,10)
15. The medial cuneiform osteotomy was sized and fixed with an Arthrex Biosync™ cotton cage (Fig. 11)
16. The native spring ligament was imbricated in a pants-over-vest fashion using 2-0 vicryl
17. An endoscopic gastrocnemius or Achilles lengthening was then performed if equinus was present. TAL versus EGR was performed in order to eliminate cephalad pull from the Achilles
18. 12 before and after innovative technique/correction

Figure 1: The cannulated Internal Brace System (Arthrex)™.

Figure 2: A 3.5 mm anchor double-loaded with Fibertape™.

Figure 3: A MICO was performed to medialize ankle forces.

Figure 4: Osteotomy was fixated with two screws perpendicular to the Osteotomy.

Figure 5: A guidewire was placed in the medial talus, distal to the ankle joint and distal to the medial cartilage of the talus.

Figure 6: One arm of the sustentaculum suture was fixed with an Arthrex 4.75 SwiveLock™ anchor under tension.

Figure 7: Confirm anchor placement is not within the ankle joint under fluoroscopy.

Figure 8: Neutral ankle positioning, place anchor into the medial malleolus.

Figure 9: Used the remaining two arms from the sustentaculum for FDL transfer. The tendon was pulled through a prepared navicular tunnel using a pull-through technique and fixed with Arthrex bio-tenodesis anchor™.

Figure 10: Final positioning of all anchors to recreate native anatomy of the deltoid-spring ligament complex.

Figure 11: Cotton cage was then sized and placed after anchors were placed.

Figure 12: Before/After demonstrating flatfoot reconstruction utilizing novel technique.

Postoperative Protocol

Splint immediately post op, transition to CAM boot at 2 weeks. Strict non-weight bearing 4-6 weeks unless its a fusion then 6-8 weeks. Partial weight bearing (50-75%) at 4 weeks. Aggressive physical therapy with gait training, compression and Alter-G treadmill. Transition to shoes at 8 weeks.

Outcome Scores

Outcomes included the Foot and Ankle Outcome Score (FAOS), which has been validated for PCFD, 1,9 and the AOFAS score for comparison with prior literature.

Radiographs

Weightbearing radiographs were obtained pre- and post-operatively. Angles measured included Meary’s angle, talocalcaneal angle, calcaneal inclination, calcaneocuboid angle and intermetatarsal angle. Measurements were performed by a single author and averages were recorded.

Statistical Analysis

Paired t-tests compared preoperative and postoperative angular measurements, with significance at p < 0.05. Descriptive statistics mean ± standard deviation were calculated for continuous variables. Demographics including age, sex and follow up duration were reported.             

Results

Eight patients (9 feet, including one bilateral case) underwent spring ligament InternalBrace™ augmentation with the authors’ technique (MICO + Cotton osteotomy).

Radiographic Outcomes

• Calcaneal Inclination Angle increased from 11.67° ± 3.77° to 15.89° ± 2.98°
• Meary’s Angle decreased from 14.56° ± 5.36° to 2.11° ± 1.90°
• Talocalcaneal Angle decreased from 28.11° ± 4.73° to 18.44° ± 4.03°
• Calcaneocuboid Angle decreased from 21.11° ± 6.86° to 12.11° ± 5.69°
• Intermetatarsal Angle decreased from 11.1° ± 3.41° to 6.67° ± 1.73°

All changes were statistically significant (p < 0.05), supporting meaningful correction of midfoot and hindfoot alignment.

Functional Outcomes

• FAOS: 79.1 ± 10.5, indicating substantial improvement in pain, function and quality of life
• AOFAS: 84.3 ± 3.8, consistent with favorable recovery, although not validated for AAFD

No correlation was found between age and outcomes.

1. A statistical description of the case series (N = 9). Gender, mean age, standard deviation (Table 1)