Review of Classification Systems for Adult Acquired Flatfoot Deformity/Progressive Collapsing Foot Deformity and the Novel Development of the Triple Classification Delinking Instability/Deformity/Reactivity and Foot Type

Background: Classifications of AAFD/PCFD have evolved with an increased understanding of the pathology involved. A review of classification systems helps identify deficiencies and respective contributions to the evolution in understanding the classification of AAFD/PCFD. Methods: Using multiple electronic database searches (Medline, PubMed) and Google search, original papers classifying AAFD/PCFD were identified. Nine original papers were identified that met the inclusion criteria. Results: Johnson's original classification and multiple variants provided a significant leap in understanding and communicating the pathology but remained tibialis posterior tendon-focused. Drawbacks of these classifications include the implication of causality, linearity of progression through stages, an oversimplification of stage 2 deformity, and a failure to understand that multiple tendons react, not just tibialis posterior. Later classifications, such as the PCFD classification, are deformity-centric. Early ligament laxity/instability in normal attitude feet and all stages of cavus feet can present with pain and instability with minor/no deformity. These may not be captured in deformity-based classifications. The authors developed the 'Triple Classification' (TC) understanding that primary pathology is a progressive ligament failure/laxity that presents as tendon reactivity, deformity, and painful impingement, variably manifested depending on starting foot morphology. In this classification, starting foot morphology is typed, ligament laxities are staged, and deformity is zoned. Conclusions: This review has used identified deficiencies within classification systems for AAFD/PCFD to delink ligament laxity, deformity, and foot type and develop the 'Triple classification'. Advantages of the TC may include representing foot types with no deformity, defining complex secondary instabilities, delinking foot types, tendon reactivity/ligament instability, and deformity to represent these independently in a new classification system. Level of Evidence: Level V.

The Role of the Transverse Arch in Progressive Collapsing Foot Deformity

BACKGROUND

The transverse arch (TA) has recently been shown to significantly increase the intrinsic stiffness of the midfoot when coupled with the medial longitudinal arch (MLA). Progressive collapsing foot deformity (PCFD) is a complex deformity that ultimately results in a loss of stiffness and collapse of the MLA. The role of the TA has not been investigated in patients diagnosed with this disorder using weightbearing CT (WBCT). Therefore, this study aims to answer the following questions: (1) Is the curvature of the TA decreased in PCFD? (2) Where within the midfoot does TA curvature flattening happen in PCFD?

METHODS

A retrospective review of weightbearing CT images was conducted for 32 PCFD and 32 control feet. The TA curvature was assessed both indirectly using previously described methods and directly using a novel measurement termed the transverse arch plantar (TAP) angle that assesses the angle formed between the first, second, and fifth metatarsals in the coronal plane. Location of TA collapse was also assessed in the coronal plane.

RESULTS

The TAP angle was significantly higher in PCFD (mean 115.2 degrees, SD 10.7) than in the control group (mean 100.8 degrees, SD 7.9) (P < .001). No difference was found using the calculated normalized TA curvature between PCFD (mean 17.1, SD 4.8) and controls (mean 18.3, SD 4.0) (P = .266). Location of collapse along the TA in PCFD was most significant at the second metatarsal and medial cuneiform.

CONCLUSION

The TA is more collapsed in PCFD compared to controls. This collapse was most substantial between the plantar medial cuneiform and the plantar second metatarsal. This may represent a location of uncoupling of the TA and MLA.

LEVEL OF EVIDENCE

Level III, retrospective case control.

Deformities Influencing Different Classes in Progressive Collapsing Foot

Background

The current classification system of progressive collapsing foot deformity (PCFD) is comprised of 5 possible classes. PCFD is understood to be a complex, three-dimensional deformity occurring in many regions along the foot and ankle. The question remains whether a deformity in one area impacts other areas. The objective of this study is to assess how each one of the classes is influenced by other classes by evaluating each associated angular measurement. We hypothesized that positive and linear correlations would occur for each class with at least one other class and that this influence would be high.

Methods

We retrospectively assessed weight bearing CT (WBCT) measurements of 32 feet with PCFD diagnosis. The classes and their associated radiographic measurements were defined as follows: class A (hindfoot valgus) measured by the hindfoot moment arm (HMA), class B (midfoot abduction) measured by the talonavicular coverage angle (TNCA), class C (medial column instability) measured by Meary's angle, class D (peritalar sub-luxation) measured by the medial facet uncoverage (MFU), and class E (ankle valgus) measured using the talar tilt angle (TTA). Multivariate analyses were completed comparing each class measurement to the other classes. A p-value <0.05 was considered significant.

Results

Class A showed substantial positive correlation with class C (ρ=0.71; R2=0.576; p=0.001). Class B was substantially correlated with class D (ρ=0.74; R2=0.613; p=0.001). Class C showed a substantial positive correlation with class A (ρ=0.71; R2=0.576; p=0.001) and class D (ρ=0.75; R2=0.559; p=0.001). Class D showed substantial positive correlation with class B and class C (ρ=0.74; R2=0.613; p=0.001), (ρ=0.75; R2=0.559; p=0.001) respectively. Class E did not show correlation with class B, C or D (ρ=0.24; R2=0.074; p=0.059), (ρ=0.17; R2=0.071; p=0.179), and (ρ=0.22; R2=0.022; p=0.082) respectively.

Conclusion

This study was able to find relations between components of PCFD deformity with exception of ankle valgus (Class E). Measurements associated with each class were influenced by others, and in some instances with pronounced strength. The presented data may support the notion that PCFD is a three-dimensional complex deformity and suggests a possible relation among its ostensibly independent features. Level of Evidence: III.

Effect of Peritalar Subluxation Correction for Progressive Collapsing Foot Deformity on Patient-Reported Outcomes

BACKGROUND

Peritalar subluxation (PTS) is part of progressive collapsing foot deformity (PCFD). This study aimed to evaluate initial deformity correction and PTS optimization in PCFD patients with flexible hindfoot deformity undergoing hindfoot joint-sparing surgical procedures and its relationship with improvements in patient-reported outcome measures (PROMs) at latest follow-up. We hypothesized that significant deformity/PTS correction would be observed postoperatively, positively correlating with improved PROMs.

METHODS

A prospective comparative study was performed with 26 flexible PCFD patients undergoing hindfoot joint-sparing reconstructive procedures, mean age 47.1 years (range, 18-77). We assessed weightbearing computed tomography (WBCT) overall deformity (foot and ankle offset [FAO]) and PTS markers (distance and coverage maps) at 3 months, as well as PROMs at final follow-up. A multivariate regression model assessed the influence of initial deformity correction and PTS optimization in patient-reported outcomes.

RESULTS

Mean follow-up was 19.9 months (6-39), and the average number of procedures performed was 4.8 (2-8). FAO improved from 9.4% (8.4-10.9) to 1.9% (1.1-3.6) postoperatively (P < .0001). Mean coverage improved by 69.6% (P = .012), 12.1% (P = .0343) and 5.2% (P = .0074) in, respectively, the anterior, middle, and posterior facets, whereas the sinus tarsi coverage decreased by an average 57.1% (P < .0001) postoperatively. Improvements in patient-reported outcomes were noted for all scores assessed (P < .03). The multivariate regression analysis demonstrated that improvement in both FAO and PTS measurements significantly influenced the assessed PROMs.

CONCLUSION

This study demonstrated significant improvements in the overall 3D deformity, PTS markers, and PROMs following hindfoot joint-sparing surgical treatment in patients with flexible PCFD. More importantly, initial 3D deformity correction and improvement in subtalar joint coverage and extraarticular impingement have been shown to influence PROMs significantly and positively. Addressing these variables should be considered as goals when treating PCFD.

LEVEL OF EVIDENCE

Level II, prospective cohort study.

Three-Dimensional Distance Mapping to Identify Safe Zones for Lateral Column Lengthening

BACKGROUND

Evans (E-LCL) and Hintermann LCL (H-LCL) lateral column lengthening osteotomies are standard surgical solutions for flexible, progressive collapsing feet. E-LCL is performed between the anterior and middle facets and endangers specific os calcis subtalar joint (OCST) subtypes without distinct facets. H-LCL is oriented between the posterior and middle facets and should be suitable for all OCSTs. Both osteotomies are associated with increased subtalar osteoarthritis, indicating iatrogenic damage. Distance mapping (DM) enables visualization of the relative distance between 2 articular surfaces represented by color patterns. This study aims to measure the safe zones for LCL using 3-dimensional (3D) models and DM; we hypothesize that it could be measured with high reproducibility.

METHODS

Two raters categorized 200 feet across 134 patients into OCSTs based on the Bruckner classification. Four angles were measured independently. The proximal and distal extents of the posterior safe zone (PSZ) angles were determined for H-LCL osteotomies; similarly, the proximal and distal extents of the anterior safe zone (ASZ) angles were identified for E-LCL osteotomies. Consequently, the surface available for safe osteotomies were calculated. An interclass correlation was used to assess the agreement between the 2 raters. Additionally, analysis of variance and Mann-Whitney U test were used to compare the safe zones between OCSTs.

RESULTS

The mean proximal and distal extents of the PSZ angles were 68 ± 7 and 75 ± 5 degrees from a line parallel to the lateral border of the calcaneus, respectively, and the proximal and distal extent of the ASZ angles were 89 ± 6 and 95 ± 5 degrees, respectively. There were no statistically significant differences between the OCSTs. Two raters measured the angles with good to excellent interrater and intrarater agreement. In 18 cases, we were unable to plan for H-LCL or E-LCL osteotomies.

CONCLUSION

Distance mapping could be used to measure the safe zone, tailor a preoperative plan, and potentially reduce the risk for iatrogenic damage in LCL. 3D models and DM can increase the reliability of preoperative plans in bones with complex 3D structures.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

A comparison between the Bluman et al. and the progressive collapsing foot deformity classifications for flatfeet assessment

INTRODUCTION

Bluman et al., flatfoot classification is based on posterior tibial tendon (PTT) dysfunction leading to a chronological appearance of several foot deformities. An expert consensus recently proposed a new classification named Progressive Collapsing Foot Deformity (PCFD) in which the focus was shifted to five different independent foot and ankle deformities and their flexibility or rigidity. The aim of this study was to compare Bluman and PCFD classifications. We hypothesize that both classifications will be reliable and that the PCFD classification will allow a larger distribution of the different types of foot deformity.

MATERIALS AND METHODS

We performed a retrospective IRB-approved study including 92 flatfeet. Three foot and ankle surgeons reviewed patient files and radiographs to classify each foot using both classifications. Bluman classification was performed one time as initially described and a second time after removing the Angle of Gissane sclerosis sign. Interobserver reliabilities were determined with Fleiss' kappa values.

RESULTS

Interobserver reliabilities of Bluman and PCFD classifications were, respectively, substantial 0.67 and moderate 0.55. PCFD Class C and D reliabilities were, respectively, slight 0.07 and fair 0.28. The 276 readings were spread into 10 substages in Bluman and 65 subclasses in PCFD. The progressivity of the Bluman classification prevented the combination of flexible hindfoot valgus (II Bluman, 1A PCFD), midfoot abduction (IIB, 1B) and medial column instability (IIC, 1C) which was frequent in our study (112/276 readings, 40.6%). By removing the Angle of Gissane sclerosis sign from the Bluman classification, the prevalence of stage III decreased from 44.2 to 10.1%.

CONCLUSIONS

Bluman and PCFD classifications were reliable. The PCFD classification showed a larger distribution of different types of flatfeet but Classes C and D need better definition. The progressivity of Bluman classification causes inconsistencies and Gissane angle sclerosis sign is inappropriately used and might lead to incorrect surgical indications.

Influence of Weightbearing Computed Tomography in the Progressive Collapsing Foot Deformity Classification System

BACKGROUND

The objective of this study was to compare progressive collapsing foot deformity (PCFD) classifications performed using clinical and conventional radiographs (CR) with classifications established using clinical and weightbearing computed tomography (WBCT).

METHODS

This retrospective comparative study evaluated 89 consecutive PCFD feet (84 patients). Three readers performed chart reviews and CR evaluations, determining PCFD classifications that were previously published. After a washout period, the sequence was randomized, and a new classification was executed using clinical and WBCT assessment. One of the readers repeated the WBCT evaluation for intrarater reliability.

RESULTS

Interrater reliability for the WBCT was found moderate (0.55) and intrarater excellent (0.98). Evaluation using WBCT produced 29.6% of 1ABC (CR: 25.4%, P = .270), 11.6% of 1ABCD (CR: 6.9%, P = .081), and 6.4% of BC (CR: 3.3%, P = .090) as most prevalent. Class A was presented in 83.9% (CR: 89.5%, P = .55), class B in 89.9% (CR: 76.4%, P < .001), class C in 93.6% (CR: 86.2%, P = .004), class D in 46.4% (CR: 34.8%, P = .006), and class E in 27.7% (CR: 22.5%, P = .158) of the classifications performed by WBCT.

CONCLUSION

WBCT showed a different rate of deformity recognition, which increased the incidence of all classes, especially B, C, and D. An excellent intrarater agreement was found, which infers assessment reliability combining clinical and WBCT evaluation. The obtained information could enhance disease understanding and supply patients with more precise care.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

Prevalence and pattern of lateral impingements in the progressive collapsing foot deformity

INTRODUCTION

The prevalence of lateral bony impingements [i.e., Sinus Tarsi (STI), Talo-Fibular (TFI) and Calcaneo-Fibular (CFI)] and their association with Peritalar Subluxation (PTS) have not been clearly established for progressive collapsing foot deformity (PCFD).This study aims to assess the prevalence of STI, TFI and CFI in PCFD, in addition to their association with PTS. We hypothesized that STI and TFI would be more prevalent than CFI.

MATERIALS AND METHODS

Seventy-two continuous symptomatic PCFD cases were retrospectively reviewed. Weightbearing computed tomography (WBCT) was used to assess lateral impingements and classified as STI, TFI and CFI. PTS was assessed by the percent of uncovered and the incongruence angle of the middle facet, and the overall foot deformity was determined by the foot and ankle offset (FAO). Data were collected by two fellowship-trained independent observers.

RESULTS

Intra-observer and inter-observer reliabilities for impingement assessment ranged from substantial to almost perfect. STI was present in 84.7%, TFI in 65.2% and CFI in 19.4%. PCFD with STI showed increased middle facet uncoverage (p = 0.0001) and FAO (p = 0.0008) compared to PCFD without STI. There were no differences in FAO and middle facet uncoverage in PCFD with TFI and without TFI. PCFD with CFI was associated with STI in 100% of cases. PCFD with CFI showed decreased middle facet incongruence (p = 0.04) and higher FAO (p = 0.006) compared to PCFD without CFI.

CONCLUSIONS

STI and TFI were more prevalent than CFI in PCFD. However, only STI was associated with PTS. Conversely, CFI was associated with less PTS, suggesting a different pathological mechanism which could be a compensatory subtalar behavior caused by deep layer failure of the deltoid ligament and talar tilt.

Diagnostic accuracy of measurements in progressive collapsing foot deformity using weight bearing computed tomography: A matched case-control study

BACKGROUND

We aimed to investigate the diagnostic accuracy of known two-dimensional (2D) and three-dimensional (3D) measurements for Progressive Collapsing Foot Deformity (PCFD) in weight-bearing computed tomography (WBCT). We hypothesized that 3D biometrics would have better specificity and sensitivity for PCFD diagnosis than 2D measurements.

METHODS

This was a retrospective case-control study, including 28 PCFD feet and 28 controls matched for age, sex and Body Mass Index. Two-dimensional measurements included: axial and sagittal talus-first metatarsal angles (TM1A and TM1S), talonavicular coverage angle (TNCA), forefoot arch angle (FFAA), middle facet incongruence angle (MF°) and uncoverage percentage (MF%). The 3D Foot Ankle Offset (FAO) was obtained using dedicated semi-automatic software. Intra and interobserver reliabilities were assessed. Receiver Operating Characteristic (ROC) curves were calculated to determine diagnostic accuracy (Area Under the Curve (AUC)), sensitivity and specificity.

RESULTS

In PCFD, mean MF% and MF° were respectively 47.2% ± 15.4 and 13.3° ± 5.3 compared with 13.5% ± 8.7 and 5.6° ± 2.9 in controls (p < 0.001). The FAO was 8.1% ± 3.8 in PCFD and 1.4% ± 1.7 in controls (p < 0.001). AUCs were 0.99 (95%CI, 0.98-1) for MF%, 0.96 (95%CI, 0.9-1) for FAO, 0.90 (95%CI, 0.81-0.98) for MF°. For MF%, a threshold value equal or greater than 28.7% had a sensitivity of 100% and specificity of 92.8%. Conversely, a FAO value equal or greater than 4.6% had a specificity of 100% and a sensitivity of 89.2%. All other 2D measurements were significantly different in PCFD and controls (p < 0.001).

CONCLUSIONS

MF% and FAO were both accurate measurements for PCFD. MF% demonstrated slightly better specificity. FAO better sensitivity. A combination of threshold values of 28.7% for MF% and 4.6% for FAO yielded 100% sensitivity and specificity.

Does tibialis posterior dysfunction correlate with a worse radiographic overall alignment in progressive collapsing foot deformity? A retrospective study

BACKGROUND

Posterior Tibial Tendon (PTT) dysfunction is considered to have an important role in Progressive Collapsing Foot Deformity (PCFD). The objective of our study was to assess the relationship between PTT status and three-dimensional foot deformity in PCFD.

METHODS

Records from 25 patients with PCFD were included for analysis. The PTT was considered deficient in patients with a positive single heel rise test or a deficit in inversion strength. Three-dimensional foot deformity was assessed using the Foot and Ankle Offset (FAO) from Weight-Bearing-CT imaging. Hindfoot valgus, midfoot abduction and medial longitudinal arch collapse were assessed on X-Rays using hindfoot moment arm, talonavicular coverage angle and Meary's angle respectively. Deland and Rosenberg MRI classifications were used to classify PTT degeneration.

RESULTS

PCFD with PTT deficit (13/25) had a mean FAO of 7.75 + /- 3.8% whereas PCFD without PTT deficit had a mean FAO of 6.68 + /- 3.9% (p = 0.49). No significant difference was found between these groups on the hindfoot moment arm and the talonavicular coverage angle (respectively p = 0.54 and 0.32), whereas the Meary's angle was significantly higher in case of PCFD with PTT deficit (p = 0.037). No significant association was found between PTT degeneration on MRI and FAO.

CONCLUSION

PCFD associated three-dimensional deformity, hindfoot valgus and midfoot abduction were not associated with PTT dysfunction. PTT dysfunction was only associated with a worse medial longitudinal arch collapse in our study. Considering our results, it does not appear that PTT is the main contributor to PCFD.

LEVEL OF EVIDENCE

Level III, Retrospective Comparative Study.

Injuries to the Spring Ligament: Nonoperative Treatment

The fibrocartilage within the superomedial calcaneonavicular (spring) ligament is part of an interwoven complex of ligaments that span the ankle, subtalar, and talonavicular joints. Acute isolated rupture of the spring ligament has been reported in association with an eversion ankle sprain. Attenuation and failure of the spring ligament causes complex 3D changes called the progressive collapsing foot deformity (PCFD). This deformity is characterized by hindfoot eversion, forefoot supination, collapse of the medial longitudinal arch, and forefoot abduction. Nonoperative treatment of an isolated spring ligament rupture and PCFD using various designs of orthoses have shown promising results.

Managing Complications of Foot and Ankle Surgery: Reconstruction of the Progressive Collapsing Foot Deformity

Our understanding of the cause and principles of treatment of progressive collapsing foot deformity (PCFD) has significantly evolved in recent decades. The goals of treatment remain improvement in symptoms, correction of deformity, maintenance of joint motion, and return of function. Although notable advancements in understanding the deformity have been made, complications still occur and typically result from (1) poor decision making, (2) technical errors, and (3) patient-related conditions. In this article, we discuss common surgical modalities used in the treatment of PCFD and further highlight the common complications that occur and the techniques that can be used to prevent them.

Intra- and Interobserver Reliability of the New Classification System of Progressive Collapsing Foot Deformity

BACKGROUND

Historical concept of flatfoot as posterior tibial tendon dysfunction (PTTD) has been questioned. Recently, the consensus group published a new classification system and recommended renaming PTTD to Progressive Collapsing Foot Deformity (PCFD). The new PCFD classification could be effective in providing comprehensive information on the deformity. To date, there has been no study reporting intra- and interobserver reliability and the frequency of each class in PCFD classification.

METHODS

This was a single-center, retrospective study conducted from prospectively collected registry data. A consecutive cohort of PCFD patients evaluated from February 2015 to October 2020 was included, consisting of 92 feet in 84 patients. Classification of each patient was made using characteristic clinical and radiographic findings by 3 independent observers. Frequencies of each class and subclass were assessed. Intraobserver and inteobserver reliabilities were analyzed with Cohen kappa and Fleiss kappa, respectively.

RESULTS

Mean sample age was 54.4, 38% was male and 62% were female. 1ABC (25.4%) was the most common subclass, followed by 1AC (8.7%) and 1ABCD (6.9%). Only a small percentage of patients had isolated deformity. Class A was the most frequent component (89.5%), followed by C in 86.2% of the cases. Moderate interobserver reliability (Fleiss kappa = 0.561, P < .001, 95% CI 0.528-0.594) was found for overall classification. Very good intraobserver reliability was found (Cohen kappa = 0.851, P < .001, 95% CI 0.777-0.926).

CONCLUSION

Almost half (49.3%) of patients had a presentation dominantly involving the hindfoot (A) with various combinations of midfoot and/or forefoot deformity (B), (C) with or without subtalar joint involvement (D). The new system may cover all possible combinations of the PCFD, providing a comprehensive description and guiding treatment in a systematic and individualized manner, but this initial study suggests an opportunity to improve overall interobserver reliability.

LEVEL OF EVIDENCE

Level III, retrospective diagnostic study.

Early results and complication rate of the LapiCotton procedure in the treatment of medial longitudinal arch collapse: a prospective cohort study

INTRODUCTION

Instability/collapse of the medial column has been associated with many conditions, particularly progressive collapsing foot deformity (PCFD), hallux valgus (HV), and midfoot arthritis (MA). Restoration of first ray length and sagittal plane alignment to restore the foot tripod is essential when treating these deformities. This study aimed to assess early results, healing, and complication rate of a distraction dorsal opening plantarflexion wedge allograft first tarsometatarsal joint fusion (LapiCotton Procedure) in patients with collapse/instability of the medial column.

METHODS

In this prospective cohort study, we included PCFD, HV, and MA patients that underwent a LapiCotton procedure. Fusion site healing was defined by > 50% bone bridging in both interfaces between allograft wedge and host bone using weight-bearing computed tomography (WBCT) after 3 months. First ray collapse radiographic correction and minor and major complications (deep dehiscence, deep infection, and reoperation) were assessed.

RESULTS

A total of 22 patients (22 feet) were included (11 PCFD, 6 MA, and 5 of HV patients). Mean follow-up was 5.9 months (range 3-12) and median allograft size was 8 mm (range 5-19 mm). Bone healing was observed in 91% of cases. Two minor complications (9%, both superficial dehiscence) and one major complication (4.5%, deep infection) were observed. Statistically significant improvement of the sagittal plane talus-first metatarsal angle was observed, with mean improvement of 9.4° (95% CI 6.7-12.1°; p < 0.0001).

CONCLUSION

In this prospective cohort study of 22 patients treated with the LapiCotton procedure for medial longitudinal arch collapse/instability, we observed a low complication rate (9% minor, 4.5% major), high healing rate after 3 months (91%), one clinically stable radiographic non-union (4.5%) and one unstable non-union (4.5%) needing reoperation. Our results demonstrate promising initial results for LapiCotton technique in treating collapse of the medial longitudinal arch in patients with PCFD, MA and HV deformities. Long-term results are needed to confirm these promising results.

LEVEL OF EVIDENCE

Level II, prospective cohort study.

Association Between Middle Facet Subluxation and Foot and Ankle Offset in Progressive Collapsing Foot Deformity

BACKGROUND

Subtalar middle facet (MF) subluxation was recognized as a reliable marker for progressive collapsing foot deformity (PCFD) diagnosis. Foot and Ankle Offset (FAO) is an established measurement, predictive of malalignment severity. The objective of this study was to assess the potential association between MF subluxation and FAO in PCFD patients.

METHODS

56 individuals with flexible PCFD (74 feet) were assessed. Two blinded foot and ankle surgeons calculated MF uncoverage, MF incongruence, and FAO. Agreement was quantified using intraclass correlation coefficient (ICC). A multivariate regression analysis and partition prediction models were applied to assess relationship between values.

RESULTS

All ICCs were >0.80. MF subluxation and FAO were found to be correlated (r_s = 0.56; P < .0001). Changes in the MF subluxation were noticeably explained by FAO and BMI (R² = 0.33). MF incongruence was not correlated with the assessed variables (P = .10). In this cohort, an MF subluxation of 27.5% was a threshold for increased FAO (FAO of 3.4%±2.4% when below; FAO of 8.0% ±3.5% when above).

CONCLUSION

We found a correlation between MF subluxation and FAO. An MF subluxation of 27.5% was found to be a threshold for higher FAO, which corresponded to a greater malalignment. These data may help surgeons optimize treatment decisions in PCFD patients.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

Spring and Deltoid Ligament Insufficiency in the Setting of Progressive Collapsing Foot Deformity. An Update on Diagnosis and Management

The spring ligament and deltoid ligament are important stabilizers of the medial ankle. Together, they form a complex along the medial ankle and foot that is critical to stability of both the ankle and the medial longitudinal arch. Incompetence of the spring and deltoid ligament is a component of both the early and late stages of progressive collapsing foot deformity. As the importance of this medial ligament complex has been recognized, repair and reconstruction of these ligaments have progressively evolved, initially as separate reconstructions, and more recently as combined techniques.

What Are the Updates on Epidemiology of Progressive Collapsing Foot Deformity?

Progressive collapsing foot deformity is one of the most controversial topics in foot and ankle surgery. Much research has been done regarding anatomy, biomechanics, and etiology behind this complex deformity and there is interest in studying metabolic or genetic conditions that could influence the development of this multifactorial disorder. Relevant anatomy includes osseous and soft tissue structures. Several risk factors like obesity, genetics, and flat foot during childhood have been proposed in literature. It occurs 3 times more often in women, the peak incidence happening at age 55, and is more common in white, obese, diabetic, rheumatic, and hypertensive patients.

Three-Dimensional Distance and Coverage Maps in the Assessment of Peritalar Subluxation in Progressive Collapsing Foot Deformity

BACKGROUND

Progressive collapsing foot deformity (PCFD), formerly termed adult-acquired flatfoot deformity, is a complex 3-dimensional (3D) deformity of the foot characterized by peritalar subluxation (PTS). PTS is typically measured at the posterior facet, but recent studies have called this into question. The objective of this study was to use 3D distance mapping (DM) from weightbearing computed tomography (WBCT) to assess PTS in patients with PCFD and controls. We hypothesized that DMs would identify the middle facet as a superior marker for PTS.

METHODS

We analyzed WBCT data of 20 consecutive stage I patients with PCFD and 10 control patients with a novel DM technique to objectively characterize joint coverage across the entire peritalar surface, including both articular and nonarticular regions. Joint coverage was defined as the percentage of articular area with DMs <4 mm and impingement when distances were <0.5 mm. Comparisons were performed with independent t tests or Wilcoxon tests. P values <.05 were considered significant.

RESULTS

Overall, coverage was decreased in articular regions and impingement was increased in nonarticular regions of patients with PCFD with a significant increase in uncoverage in the middle (46.6%, P < .001) but not anterior or posterior facets. Significant increases in sinus tarsi coverage were identified (98.0%, P < .007) with impingement in 6 of 20 patients with PCFD. Impingement of the subfibular region was noted in only 1 of 20 cases but narrowing greater than 2 standard deviations was noted in 17 of 20 patients.

CONCLUSION

Objective DMs identified significant markers of PTS in the middle but not posterior or anterior facets. We confirmed prior 2-dimensional data that suggested uncoverage of the middle facet provided a more robust and consistent measure of PTS than measures in the posterior facet.

LEVEL OF EVIDENCE

Level III, case-control study.

Patient-Reported Outcomes and Radiographic Assessment in Primary and Revision Stage II, III, and IV Progressive Collapsing Foot Deformity Surgery

BACKGROUND

Progressive collapsing foot deformity (PCFD) is a progressive hindfoot and midfoot deformity causing pain and disability. Although operative treatment is stage dependent, few studies have looked at patient-reported and radiographic outcomes stratified by primary vs revision stage II, III, and IV reconstruction surgery. Our goal was to assess operative improvement using Patient-Reported Outcomes Measurement Information System (PROMIS) and to determine whether radiographic parameter improvement correlates with patient-reported outcomes.

METHODS

PROMIS Physical Function (PF) and Pain Interference (PI) scores were prospectively obtained on 46 consecutive patients who underwent PCFD reconstruction between November 2013 and January 2019. Thirty-six patients completed pre- and postoperative PROMIS surveys, 6 patients completed only preoperative PROMIS surveys, and 4 patients completed 12-month postoperative PROMIS surveys but did not complete preoperative PROMIS surveys. Minimum follow-up was 12 (average, 23) months. Radiographic correction was measured with pre- and postoperative weightbearing radiographs and correlated with PROMIS scores. Measurements included the talonavicular uncoverage angle, talonavicular uncoverage percentage, anteroposterior talo-first metatarsal angle, Meary angle, medial cuneiform height (MCH), and medial cuneiform-fifth metatarsal height.

RESULTS

For the overall cohort, PROMIS PF increased significantly from 37.5±5.6 to 42.3±7.1 (P = .0014). PROMIS PI improved significantly from 64.5±6.0 to 55.1±9.8 (P < .0001). Preoperative, postoperative, and change in PROMIS scores were not statistically different between PCFD stages. Change in PROMIS PI was significantly greater in primary (-12.3) vs revision (-3.7) surgery (P = .0157). Change in PROMIS PF was greater in primary (+6.0) vs revision surgery (+2.3) but did not reach statistical significance. All radiographic measurements improved significantly (P < .05). In primary stage II PCFD, postoperative PROMIS scores correlated with postoperative MCH (PF: r = 0.7725, P = .0020; PI: r = -0.5692, P = .0446).

CONCLUSION

Patient-reported and radiographic outcomes improved significantly after PCFD reconstruction. We found no significant difference in preoperative, postoperative, or change in PROMIS scores between PCFD stages. However, stage III patients had smaller improvements in PROMIS PF, which we feel may be secondary to change in function after arthrodesis. Primary operations had better patient-reported outcomes compared to revision operations. In primary stage II PCFD, reconstructing the medial arch height correlated significantly with improvement in pain and functionality.

LEVEL OF EVIDENCE

Level II, prospective cohort study.

Progressive Collapsing Foot Deformity: Consensus on Goals for Operative Correction

RECOMMENDATION

In the treatment of progressive collapsing foot deformity (PCFD), the combination of bone shape, soft tissue failure, and host factors create a complex algorithm that may confound choices for operative treatment. Realignment and balancing are primary goals. There was consensus that preservation of joint motion is preferred when possible. This choice needs to be balanced with the need for performing joint-sacrificing procedures such as fusions to obtain and maintain correction. In addition, a patient's age and health status such as body mass index is important to consider. Although preservation of motion is important, it is secondary to a stable and properly aligned foot.

LEVEL OF EVIDENCE

Level V, consensus, expert opinion.

Consensus for the Use of Weightbearing CT in the Assessment of Progressive Collapsing Foot Deformity

RECOMMENDATION

There is evidence that the use of WEIGHTBEARING imaging aids in the assessment of progressive collapsing foot deformity (PCFD). The following WEIGHTBEARING conventional radiographs (CRs) are necessary in the assessment of PCFD patients: anteroposterior (AP) foot, AP or mortise ankle, and lateral foot. If available, a hindfoot alignment view is strongly recommended. If available, WEIGHTBEARING computed tomography (CT) is strongly recommended for surgical planning. When WEIGHTBEARING CT is obtained, important findings to be assessed are sinus tarsi impingement, subfibular impingement, increased valgus inclination of the posterior facet of the subtalar joint, and subluxation of the subtalar joint at the posterior and/or middle facet.

LEVEL OF EVIDENCE

Level V, consensus, expert opinion.

Consensus on Indications for Medial Cuneiform Opening Wedge (Cotton) Osteotomy in the Treatment of Progressive Collapsing Foot Deformity

RECOMMENDATION

Forefoot varus is a physical and radiographic examination finding associated with the Progressive Collapsing Foot Deformity (PCFD). Varus position of the forefoot relative to the hindfoot is caused by medial midfoot collapse with apex plantar angulation of the medial column. Some surgeons use the term forefoot supination to describe this same deformity (see Introduction section with nomenclature). Correction of this deformity is important to restore the weightbearing tripod of the foot and help resist a recurrence of foot collapse. When the forefoot varus deformity is isolated to the medial metatarsal and medial cuneiform, correction is indicated with an opening wedge medial cuneiform (Cotton) osteotomy, typically with interposition of an allograft bone wedge from 5 to 11 mm in width at the base. When the forefoot varus is global, involving varus angulation of the entire forefoot and midfoot relative to the hindfoot, other procedures are needed to adequately correct the deformity.

LEVEL OF EVIDENCE

Level V, consensus, expert opinion.

Consensus for the Indication of Lateral Column Lengthening in the Treatment of Progressive Collapsing Foot Deformity

RECOMMENDATION

Progressive collapsing foot deformity (PCFD) is a complex 3D deformity with varying degrees of hindfoot valgus, forefoot abduction, and midfoot supination. Although a medial displacement calcaneal osteotomy can correct heel valgus, it has far less ability to correct forefoot abduction. More severe forefoot abduction, most frequently measured preoperatively by assessing talonavicular coverage on an anteroposterior (AP) weightbearing conventional radiographic view of the foot, can be more effectively corrected with a lateral column lengthening procedure than by other osteotomies in the foot. Care must be taken intraoperatively to not overcorrect the deformity by restricting passive eversion of the subtalar joint or causing adduction at the talonavicular joint on simulated AP weightbearing fluoroscopic imaging. Overcorrection can lead to lateral column overload with persistent lateral midfoot pain. The typical amount of lengthening of the lateral column is between 5 and 10 mm.

LEVEL OF EVIDENCE

Level V, consensus, expert opinion.

CONSENSUS STATEMENT ONE

Lateral column lengthening (LCL) procedure is recommended when the amount of talonavicular joint uncoverage is above 40%. The amount of lengthening needed in the lateral column should be judged intraoperatively by the amount of correction of the uncoverage and by adequate residual passive eversion range of motion of the subtalar joint.Delegate vote: agree, 78% (7/9); disagree, 11% (1/9); abstain, 11% (1/9).(Strong consensus).

CONSENSUS STATEMENT TWO

When titrating the amount of correction of abduction deformity intraoperatively, the presence of adduction at the talonavicular joint on simulated weightbearing fluoroscopic imaging is an important sign of hypercorrection and higher risk for lateral column overload.Delegate vote: agree, 100% (9/9); disagree, 0%; abstain, 0%.(Unanimous, strongest consensus).

CONSENSUS STATEMENT THREE

The typical range for performing a lateral column lengthening is between 5 and 10 mm to achieve an adequate amount of talonavicular coverage.Delegate vote: agree, 100% (9/9); disagree, 0%; abstain, 0%.(Unanimous, strongest consensus).

Consensus on Indications for Isolated Subtalar Joint Fusion and Naviculocuneiform Fusions for Progressive Collapsing Foot Deformity

RECOMMENDATION

Peritalar subluxation represents an important hindfoot component of progressive collapsing foot deformity, which can be associated with a breakdown of the medial longitudinal arch. It results in a complex 3-dimensional deformity with varying degrees of hindfoot valgus, forefoot abduction, and pronation. Loss of peritalar stability allows the talus to rotate and translate on the calcaneal and navicular bone surfaces, typically moving medially and anteriorly, which may result in sinus tarsi and subfibular impingement. The onset of degenerative disease can manifest with stiffening of the subtalar (ST) joint and subsequent fixed and possibly arthritic deformity. While ST joint fusion may permit repositioning and stabilization of the talus on top of the calcaneus, it may not fully correct forefoot abduction and it does not correct forefoot varus. Such varus may be addressed by a talonavicular (TN) fusion or a plantar flexion osteotomy of the first ray, but, if too pronounced, it may be more effectively corrected with a naviculocuneiform (NC) fusion. The NC joint has a curvature in the sagittal plane. Thus, preserving the shape of the joint is the key to permitting plantarflexion correction by rotating the midfoot along the debrided surfaces and to fix it. Intraoperatively, care must be also taken to not overcorrect the talocalcaneal angle in the horizontal plane during the ST fusion (eg, to exceed the external rotation of the talus and inadvertently put the midfoot in a supinated position). Such overcorrection can lead to lateral column overload with persistent lateral midfoot pain and discomfort. A contraindication for an isolated ST fusion may be a rupture of posterior tibial tendon because of the resultant loss of the internal rotation force at the TN joint. In these cases, a flexor digitorum longus tendon transfer is added to the procedure.

LEVEL OF EVIDENCE

Level V, consensus, expert opinion.

Classification and Nomenclature: Progressive Collapsing Foot Deformity

RECOMMENDATION

The historical nomenclature for the adult acquired flatfoot deformity (AAFD) is confusing, at times called posterior tibial tendon dysfunction (PTTD), the adult flexible flatfoot deformity, posterior tibial tendon rupture, peritalar instability and peritalar subluxation (PTS), and progressive talipes equinovalgus. Many but not all of these deformities are associated with a rupture of the posterior tibial tendon (PTT), and some of these are associated with deformities either primarily or secondarily in the midfoot or ankle. There is similar inconsistency with the use of classification schemata for these deformities, and from the first introduced by Johnson and Strom (1989), and then modified by Myerson (1997), there have been many attempts to provide a more comprehensive classification system. However, although these newer more complete classification systems have addressed some of the anatomic variations of deformities encountered, none of the above have ever been validated. The proposed system better incorporates the most recent data and understanding of the condition and better allows for standardization of reporting. In light of this information, the consensus group proposes the adoption of the nomenclature "Progressive Collapsing Foot Deformity" (PCFD) and a new classification system aiming at summarizing recent data published on the subject and to standardize data reporting regarding this complex 3-dimensional deformity.

LEVEL OF EVIDENCE

Level V, consensus, expert opinion.

CONSENSUS STATEMENTS VOTED

CONSENSUS STATEMENT ONE: We will rename the condition to Progressive Collapsing Foot Deformity (PCFD), a complex 3-dimensional deformity with varying degrees of hindfoot valgus, forefoot abduction, and midfoot varus.Delegate vote: agree, 100% (9/9); disagree, 0%; abstain, 0%.(Unanimous, strongest consensus)CONSENSUS STATEMENT TWO: Our current classification systems are incomplete or outdated.Delegate vote: agree, 100% (9/9); disagree, 0%; abstain, 0%.(Unanimous, strongest consensus)CONSENSUS STATEMENT THREE: MRI findings should be part of a new classification system.Delegate vote: agree, 33% (3/9); disagree, 67% (6/9); abstain, 0%.(Weak negative consensus)CONSENSUS STATEMENT FOUR: Weightbearing CT (WBCT) findings should be part of a new classification system.Delegate vote: agree, 56% (5/9); disagree, 44% (4/9); abstain, 0%.(Weak consensus)CONSENSUS STATEMENT FIVE: A new classification system is proposed and should be used to stage the deformity clinically and to define treatment.Delegate vote: agree, 89% (8/9); abstain, 11% (1/9).(Strong consensus).

Consensus for the Indication of a Medializing Displacement Calcaneal Osteotomy in the Treatment of Progressive Collapsing Foot Deformity

RECOMMENDATION

There is evidence that the medial displacement calcaneal osteotomy (MDCO) can be effective in treating the progressive collapsing foot deformity (PCFD). This juxta-articular osteotomy of the tuberosity shifts the mechanical axis of the calcaneus from a more lateral position to a more medial position, which provides mechanical advantage in the reconstruction for this condition. This also shifts the action of the Achilles tendon medially, which minimizes the everting deforming effect and improves the inversion forces. When isolated hindfoot valgus exists with adequate talonavicular joint coverage (less than 35%-40% uncoverage) and a lack of significant forefoot supination, varus, or abduction, we recommend performing this osteotomy as an isolated bony procedure, with or without additional soft tissue procedures. The clinical goal of the hindfoot valgus correction is to achieve a clinically neutral heel, as defined by a vertical axis from the heel up the longitudinal axis of the Achilles tendon and distal aspect of the leg. The typical range when performing a MDCO, while considering the location and rotation of the osteotomy, is 7 to 15 mm of correction.

LEVEL OF EVIDENCE

Level V, consensus, expert opinion.

Titrating the Amount of Bony Correction in Progressive Collapsing Foot Deformity

RECOMMENDATION

There is evidence indicating that the amount of bony correction performed in the setting of progressive collapsing foot deformity reconstructive surgery can be titrated within a recommended range for a variety of procedures. The typical range when performing a medial displacement calcaneal osteotomy should be 7 to 15 mm of medialization of the tuberosity. The typical range when performing an Evans lateral column lengthening should be 5 to 10 mm of a laterally based wedge in the anterior calcaneus. The typical range when performing a plantarflexion opening wedge osteotomy of the medial cuneiform (Cotton) osteotomy should be 5 to 10 mm of a dorsal wedge.

LEVEL OF EVIDENCE

Level V, consensus, expert opinion.

Indications for Deltoid and Spring Ligament Reconstruction in Progressive Collapsing Foot Deformity

RECOMMENDATION

There is evidence supporting medial soft tissue reconstruction, such as spring and deltoid ligament reconstructions, in the treatment of severe progressive collapsing foot deformity (PCFD). We recommend spring ligament reconstruction to be considered in addition to lateral column lengthening or subtalar fusion at the initial operation when those procedures have given at least 50% correction but inadequate correction of the severe flexible subluxation of the talonavicular and subtalar joints. We also recommend combined flatfoot reconstruction and deltoid reconstruction be considered as a joint sparing alternative in the presence of PCFD with valgus deformity of the ankle joint if there is 50% or more of the lateral joint space remaining.

LEVEL OF EVIDENCE

Level V, expert opinion.