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.

First-Ray (FR) stability allows for foot propulsion in-stance, taking 60% weight. First-ray instability (FRI) is associated with middle column overload, synovitis, deformity and osteoarthritis. Clinical detection can still be challenging. We propose to develop a clinical test that helps identify FRI using two simple manual manoeuvres. 10 patients with unilateral FRI were recruited. Unaffected contralateral feet were used as controls. Stringent exclusion criteria were applied including hallux MTP pain, laxity, inflammatory arthropathy and collagen disorders. A Klauemeter directly measured the sagittal plane dorsal first metatarsal head translation of affected vs unaffected feet. Maximum passive proximal phalanx 1st MTP joint dorsiflexion was measured using a video capture and Tracker motion software analysis with and without applying a dorsal force at the 1st metatarsal head using a Newton meter. Proximal phalanx motion was compared in affected vs unaffected feet with and without dorsal metatarsal head force application and compared to direct measurements using the Klaumeter. P value of < 0.05 was considered significant. FRI feet had dorsal translation greater than 8 mm (median, 11.94; interquartile range [IQR], 10.23-13.81) vs 1.77 for unaffected control feet was (median, 1.77; interquartile range [IQR], 1.23-2.96) using the Klauemeter. The percentage reduction in 1st MTP joint dorsiflexion ROM when applying the double dorsiflexion test FRI (mean reduction of 67.98%) when compared to control feet (mean reduction of 28.44%)(P < 0.01). Receiver operating characteristic (ROC) analysis showed that a 50% reduction in dorsiflexion ROM of 1st MTPJ when performing the double dorsiflexion test achieved a specificity of 100% and sensitivity of 90% (AUC =0.990, 95%CI [0.958-1.000], P > 0.0001). The double dorsiflexion (DDF) is easy to perform with two relatively simple manual manoeuvres that avoids the need for complex instrumented and radiation-based assessment. Greater than 50% decrease in proximal phalanx motion has an over 90% sensitivity in identifying feet with FRI. This was a prospective case-controlled study of consecutive cases of a level II evidence.

The progressive ligament instability associated with flatfoot deformity may result in altered foot biomechanics and represent a risk factor for the development of Achilles Tendinopathy (AT). The aim of this study was to determine whether an increased tendo-Achilles (TA) force was required to generate a set heel lift in a cadaveric flatfoot model. Thirteen fresh (previously frozen) cadavers, with no previous foot pathology and sectioned from the knee were mounted on a testing frame. The frame maintained a dorsiflexed ankle position, to simulate the terminal stance phase of gait, and allowed a constant axial load to be applied through the tibia. The heel was elevated 3 cm by a measured traction force through the TA to a pre-determined laser mark. The flatfoot model was created by sequential sectioning of the medial arch supporting structures, creating progressive midfoot instability and flatfoot deformity, from mild to severe. The force (N) required to generate heel lift was recorded at each stage of the development of the flatfoot. Initially, following Spring ligament and Tibialis Posterior sectioning, the force required to generate heel lift decreased. However, as the flatfoot deformity progressed the force required for heel lift increased. A severe flat foot deformity, characterised by medial ray destabilisation significantly increased the force required to generate a heel lift (5.1 ± 7.2 N, p = 0.02) as did sectioning of the (ii) short and long plantar ligaments (5.5 ± 8.7 N, p = 0.03). Progressive ligament failure associated with acquired flatfoot deformity may be a risk for AT overload due to increased TA force required for heel lift, resulting in TA overload symptoms. The paradoxical decrease in force required to generate heel lift with isolated SL sectioning has not been previously described. This biomechanical study raises the possibility that interventions that support the medial longitudinal arch, such as orthotics, may protect against TA overload.