Adult Acquired Flatfoot Deformity
Adult acquired flatfoot deformity (AAFD), most commonly caused by posterior tibial tendon (PTT) insufficiency, consists of a spectrum of deformities. It typically consists of a combination of plantar sag, midfoot abduction, and heel valgus. It results from a combination of PTT insufficiency and failure of both capsular and ligamentous structures (spring ligament, deltoid ligament).
AAFD has a multifactorial etilogy. The primary risk factors include a pre-existing flatfoot, female gender, age (peak at 55), obesity, gastrocnemius contracture, ligamentous laxity, trauma, high impact sports and diabetes.
Johnson and Strom (1989)
Modified by Myerson (2007)
However, Myerson and colleagues (2020) in their publication stated that there were inconsistencies with the use of the existing classification systems for these deformities. They proposed a system that better incorporates the most recent data and understanding of the condition and better allows for standardisation of reporting. The consensus group proposed the adoption of the nomenclature “Progressive Collapsing Foot Deformity” (PCFD) and a new classification system aiming at summarising recent data published on the subject and to standardise data reporting regarding this complex 3-dimensional deformity.
Appropriate history with identification of risk factors, presence of medial sided pain, the intensity of pain may not necessarily reflect the severity of the stage, progressive lateral pain due to impingement.
A complete examination of the foot and ankle including toe-many toes sign, palpation along the distal portion of the PTT, pain at the lateral aspect of the hindfoot (suggestive of lateral impingement), pain on palpation of arthritic joints in stage III and IV (talonavicular, subtalar, calcaneocuboid, and ankle), inability to perform a single heel rise (highly suggestive of PTT insufficiency), range of motion of ankle must also be evaluated, gastrocnemius/Achilles tendon tightness (Silverskiold’s test).
Weight-bearing plain AP and lateral radiographs of the foot ankle to assess arch collapse (by Meary’s or the lateral first tarsometatarsal angle), forefoot abduction (at the talonavicular joint), talar head uncoverage (>30%or <30%) and talar tilt (stage IV AAFD). Hindfoot valgus can be evaluated with either a hindfoot alignment view or long axial view. All radiographs should be carefully examined to identify arthritic changes that could substantially affect treatment choice.
MRI, although not essential but a very useful modality to assess the extent of cartilage, tendon, and ligament involvement, bone oedema (may reveal signs of lateral bony impingement) and spring ligament integrity.
Regardless of the stage, the first line of management for all patients is conservative before considering surgery. This includes physiotherapy, NSAIDs, orthotics, bracing (medial arch or ankle brace), a low-articulating ankle-foot orthosis (LAFO) or similar AFO, cast-boot (cam walker) or shoe modifications.
In cases of stage I disease, Nielson et al. reported an 87 % success rate with these modalities defined as not requiring further surgical treatment. Similar results have been reported by other authors including Chao et al. Augustine et al. and Alvarez et al. (67%-90%) for stage I and II disease.
Saltzman et al reported on patients with stage I to II deformity utilising a structured nonoperative protocol consisting of an orthosis and aggressive exercise/stretching and stated that it resulted in improved function and satisfaction in nearly 90% of patients, with only 11% requiring surgery in the 2-year study period.
Pomrantz et al, in a randomised controlled trial of stage I to II patients, found that the combination of orthoses, stretching, and eccentric exercise reduced the pain and improved perceived function.
A study by Malay et al found that after 27 months of nonoperative treatment, only 12.5% of patients required surgery.
Surgical intervention is recommended for patients who remain symptomatic after exhausting 6 months of nonoperative treatment, however, this time period may be shorter or longer depending on the patient's deformity and planned surgery.
Surgery aims to improve pain, function, and quality of life with continued improvement demonstrated in the available studies. A variety of surgical options exists and the final choice depends on the deformity and surgeon's familiarity and preference.
As much as the surgical intervention is avoided in stage I, in some cases of disease progression with worsening symptoms after a period of at least 6 months, surgery may be considered. A combination of soft tissue and bony procedures is recommended instead of only soft tissue procedures. Preferred option in stage I is medialising calcaneal osteotomy with PTT procedures (tenosynovectomy, repair, or transfer).
Subtalar arthroereisis screw has been used in pediatric patients, but there is limited evidence of its utility in adults as an adjunct for additional correction.
For stage IIa, medialising calcaneal osteotomy, flexor digitorum longus (FDL) transfer, with or without gastrocnemius recession or TA lengthening represent the treatment of choice in stage IIa AAFD. A medialising calcaneal osteotomy realigns the hindfoot, offloads the spring ligament and increases the inversion moment arm of the gastrocsoleus complex.
The FDL transfer to the navicular compensates for the lost function of the degenerated PTT. An elevated medial column can be lowered to treat forefoot supination or varus persisting after hindfoot realignment. If the first TMT joint is not hypermobile, an opening wedge medial cuneiform osteotomy (Cotton osteotomy) can be performed to bring down the first ray. If the 1st TMT joint is hypermobile or arthritic, this can be addressed with a fusion of the joint in the desired position.
The spring (calcaneonavicular) ligament is a primary static stabiliser of the medial arch. There is emerging data available to support that the spring ligament reconstruction supplements the correction of midfoot deformity and improves the outcomes. Multiple techniques have been described for its reconstruction and the use of speedbridge system is commonly used in practice.
Myerson et al. reported the results of 129 patients treated with above combined procedure for stage II AAFD, with average age of 53 years and an average follow up of 5.2 years. Their results showed significant correction of radiographic parameters, 91% patient-satisfaction, 97% pain relief, 94% improvement of function, 87% improvement in the arch of the foot, and 84% patients were able to wear shoes comfortably without shoe modifications or orthotic arch support.
Deland et al. reported the results of the above procedure in 34 patients below 50 years of age (average 41 years), and average follow up of 44 months. Their results showed a significant improvement of functional scores (AOFAS).
Kou et al. reported excellent functional outcome and a high patient-satisfaction rate after medial calcaneal osteotomy, FDL transfer and gastrocnemius recession for stage II disease in 23 patients at 2-year follow up.
For stage IIb, more severe flexible deformity, the treatment strategy is the same as above, with a possible addition of lateral column lengthening which can be achieved either via an osteotomy at the anterior calcaneus or distraction arthrodesis at calcaneocuboid joint. It achieves correction of TN abduction and increases the arch. It can be performed either by an Evan’s procedure or CC distraction.
However, lateral column lengthening has is rarely performed due to stiffness and high rates (up to 40%) of nonunion. In a retrospective comparison study by Thordarson and colleagues, patients who underwent osteotomies had better outcomes and lower rates of hardware removal than those who had CC arthrodesis.
Hindfoot values with too-many-toes sign
Medial arch support
Hindfoot values with too-many-toes sign
Stage III AAFD consists of fixed deformity involving the subtalar, calcaneocuboid and talonavicular joints. Correction is achieved by fusing the talonavicular and subtalar joints (Double fusion), where most of the deformity occurs and the calcaneocuboid joint may be spared (traditional Triple fusion), unless arthritic and symptomatic. Double fusion in comparison to triple fusion improves the ability to adapt to uneven grounds and reduces the potential risk of developing ankle arthritis.
The heel should be fused in ≤5° of valgus with the forefoot in neutral, avoiding supination, pronation or elevation of the first ray. If heel valgus persists after achieving neutral of the forefoot and triple-joint complex, then a medialising calcaneal osteotomy may be needed additionally. It is important to avoid overcorrection of the deformity as lateral overload can result from fixed supination deformity. If the first ray is elevated, a first TMT procedure (fusion or osteotomy) may need to be added.
Fusion surgery is best used in fixed flatfoot deformity but also may be used to treat severe flexible deformity where the spring ligament is severely compromised and is not considered reconstructable. The patient’s age may be considered as well, as older patients with lower demands may be better off with one definitive surgery. However, there are no studies showing worse outcomes of reconstruction based on age.
Stage IVa deformity can potentially be treated with foot reconstruction without requiring fusion or replacement of the ankle joint. Deltoid ligament reconstruction can be performed with a variety of techniques employing autografts, allografts, or tendon transfers. The correction of deformity in the foot must be done at the same time so the first ray is stable and the valgus of the heel and ankle are corrected.
The only available study is by Deland et al., which described long-term clinical and radiographic results. In a small cohort of patients at 9 years follow-up, the results were encouraging.
In rigid deformity with ankle involvement (stage IVb), a double or triple arthrodesis with ankle replacement or pantalar fusion is used. However, the optimal use of either procedure has not been well studied. There are anecdotal descriptions of staged procedures (ie, reconstructive procedures in the foot and deltoid ligament reconstruction first, followed by total ankle replacement), but there are no studies supporting or refuting this.
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