Classifications in Brief: Johnson and Strom Classification of Adult-acquired Flatfoot Deformity
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- Abousayed, M.M., Tartaglione, J.P., Rosenbaum, A.J. et al. Clin Orthop Relat Res (2016) 474: 588. doi:10.1007/s11999-015-4581-6
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The posterior tibial tendon functions mainly as a dynamic support of the medial arch. It also inverts the foot and aids in ankle plantar flexion. Dysfunction of the posterior tibial tendon usually manifests early with pain and swelling along the medial aspect of the foot and behind the medial malleolus. The pain is worse with prolonged standing and activities, and usually is associated with tenderness along the length of the tendon. In advanced posterior tibial tendon dysfunction, collapse of the medial arch occurs, leading to the characteristic pes planus deformity with hindfoot valgus; initially, this deformity is flexible, but in more-advanced stages it can become fixed and associated with forefoot abduction. The single-heel rise test can assess the function of the tendon, where varus alignment of the hind foot is indicative of a healthy tendon. Lateral-sided ankle pain occurs eventually in some patients, a result of subfibular impingement.
In 1989, Johnson and Strom created a three-stage posterior tibial tendon dysfunction classification system based on the condition of the posterior tibial tendon, the position of the hindfoot, and flexibility of the deformity . Although a fourth stage in this system is commonly attributed to Myerson , this stage was described in the original article by Johnson and Strom . It helps guide treatment in patients with deltoid ligament insufficiency and ankle joint involvement.
Better understanding of the biomechanics of the foot, particularly the medial arch and its supporting structures, has led to more precise understanding of the development of adult-acquired flatfoot deformity [3, 4, 5, 7, 10, 13, 15, 20, 25, 27]. Although numerous authors have devised their own classification systems [4, 5, 15, 25], all used the original structure described by Johnson and Strom .
Historically, adult-acquired flatfoot deformity has been attributed to posterior tibial tendon dysfunction [16, 19]. Nevertheless, adult-acquired flatfoot deformity in its current form includes a wide range of deformities affecting the hindfoot, mid-foot, and the ankle. Although diagnosis of flat foot can be relatively easy, accurate identification of the different aspects of the deformity can be challenging. The Johnson and Strom classification is clinical and anatomic, and it was the first to look at flatfoot as a spectrum of deformities and guide treatment strategies. Similar to other classification systems, in addition to guiding treatment and facilitating communication among surgeons, it provides useful prognostic information. Many patients with milder forms of tendon dysfunction as graded by this classification system will respond to conservative measures, whereas more patients with more-severe forms of the condition will undergo surgical interventions to treat pain or disability [4, 5, 8, 18, 24, 27].
Johnson and Strom classification
Mild, medial pain
Moderate, medial pain
Severe, medial and lateral pain
Swelling and tenderness
Mild swelling and tenderness along posterior tibial tendon
Moderate swelling and tenderness along posterior tibial tendon
Not much swelling but marked tenderness along posterior tibial tendon
“Too many toes” sign
Normal tendon length, paratendinitis
Elongated with longitudinal tears
Disrupted with visible tears
Deformity and diffuse arthritic changes
Flexor digitorum longus transfers
In Stage I of the disease, patients may report mild pain along the medial aspect of the ankle that is exacerbated by activities. On examination, swelling, fullness, and tenderness are localized to the course of the posterior tibial tendon. Tendon length is usually normal. Pathologic examination of the tendon will reveal synovial proliferation . Other findings include paratendinitis, normal alignment, and mild weakness on single-heel rise test. No changes in bony architecture are expected on routine standing radiographic images. Treatment at this stage consists initially of conservative measures including rest, antiinflammatory agents, arch supports, and orthotics. Treatment is continued for 3 months, and if no improvement is noticed, tenosynovectomy and débridement or repair of tendon tears may be considered.
In Stage II, pain is moderate although usually more debilitating, and localized along a longer segment of the tendon. Swelling, fullness, and tenderness are more pronounced. There is elongation of the posterior tibial tendon, which results in the characteristic pes planus deformity. Pathologic examination shows degeneration with multiple longitudinal tears . Single-heel rise test reveals marked weakness (Fig. 2). Visible deformity and malalignment of the hind foot are present, although mobile, and the “too many toes” sign can be seen (Fig. 3). Standing radiographs will show forefoot abduction in relation to the hindfoot and talonavicular subluxation. The surgical treatment we prefer for patients with Stage II deformity who elect to undergo surgery is flexor digitorum longus tendon transfers.
In Stage III, pain can be severe and may be evident on the lateral foot at the sinus tarsi in addition to the medial arch. There is severe elongation and disruption of the tendon. On examination, the swelling and fullness might be less evident but the deformity is more pronounced. On pathologic examination, the tendon is disrupted with visible tears . Single-heel rise is painful and shows marked tendon weakness. Hindfoot eversion and forefoot abduction are present and the deformity usually is fixed. The “too many toes” sign is still present. The same changes as seen in Stage II on plain films can be appreciated in addition to degenerative arthritic changes in the subtalar, talonavicular, and calcaneocuboid joints. Treatment for patients presenting with Stage III pain may include subtalar arthrodesis.
Johnson and Strom  alluded to a possible Stage IV in which the fixed valgus deformity of the hindfoot results in lateral talar tilt in the ankle mortise. They suggested tibiotalocalcaneal fusion as a possible treatment for such deformity. Myerson  was credited for Stage IV modification of the original classification. He described valgus deformity of the ankle associated with deltoid ligament insufficiency, which sometimes can be associated with lateral tibiotalar arthritis. He further subdivided Stage IV into type A with flexible ankle deformity amenable to deltoid ligament reconstruction with triple arthrodesis or type B with fixed deformity and requiring pantalar arthrodesis.
Although the treatment modalities originally suggested by Johnson and Strom still are helpful, they are not—and need not be—consistently applied. For example, some surgeons may elect to prolong the period of conservative treatment longer than 3 months before considering surgical options. Additionally, newer methods of immobilization have been proposed, and some patients are not good surgical candidates, or opt not to have surgery. The same concerns apply to Stages II through IV, where numerous other surgical options have been suggested, of which many are effective [5, 8, 13, 14, 25, 26, 27].
To our knowledge, the validity and reliability of the Johnson and Strom classification have not been studied. Reliability here would refer to the ability of a classification to persistently classify a specific stage among reviewers (interobserver reliability) and by the same reviewer along different intervals (intraobserver reliability). Validity in this setting represents the ability to accurately associate physical examination with the radiographic and pathologic findings in each stage.
Grading a patient according to this classification system requires history, physical examination, and radiographic evaluation. As such, it can be impractical to have different observers evaluate the same patient to assess the system’s interobserver reliability. In addition, the condition can evolve with time, making measurement of intraobserver reliability impossible. In addition, to confirm validity of this system, pathologic specimens might be required. This might be impractical because many patients will be treated conservatively and will not undergo surgery. Accordingly, validation of the Johnson and Strom classification has been difficult. Despite the inherent limitations of using a system that has not been validated, advancement of technology allowing better understanding of the deformity, and availability of more-complex and more-detailed classification systems, the Johnson and Strom classification persists widely, which may indicate the value to this system to users [4, 5, 8, 9, 12, 13, 24, 26, 27].
The main limitation of the Johnson and Strom classification system for adult-acquired flatfoot deformity is its failure to include all anatomic aspects of the pes planus deformity; by focusing on the role of the posterior tibial tendon, this system misses the importance of the spring ligament, deltoid ligament, naviculocuneiform joint, and tarsometatarsal joints, all of which have been shown to be involved, as have the hindfoot and forefoot in the deformity [8, 9, 12, 21, 22]. As a result, numerous authors [5, 9, 20, 24, 27] have expanded the original classification system in an attempt to include the various structures involved. In addition, in a given stage in the Johnson and Strom classification, there may be important variations, and deformities do not necessarily progress in a linear or inevitable way.
Classification system of Bluman et al.
Tenderness along posterior tibial tendon, normal anatomy
Immobilization, orthosis, NSAIDs, tenosynovectomy
Tenderness along posterior tibial tendon, normal anatomy
Slight hindfoot valgus, normal anatomy
Slight hindfoot valgus
Supple hindfoot valgus, flexible forefoot varus
Meary’s line disrupted
Loss of calcaneal pitch
Orthosis, medial displacement calcaneal osteotomy, tendoAchilles lengthening or Strayer procedure and flexor digitorum longus transfer if deformity corrects only with ankle plantar flexion
Supple hindfoot valgus, fixed forefoot varus
Orthosis, medial displacement calcaneal osteotomy, flexor digitorum longus transfer, cotton osteotomy
A2+ forefoot abduction
Talonavicular uncovering, forefoot abduction
Orthosis, medial displacement calcaneal osteotomy, flexor digitorum longus transfer, lateral column lengthening
B+ medial column instability, first ray dorsiflexion with hindfoot correction, sinus tarsi pain
First tarsometatarsal plantar gapping
Medial displacement calcaneal osteotomy, flexor digitorum longus transfer, cotton osteotomy or medial column fusion
Rigid hindfoot valgus, pain in sinus tarsi
Subtalar joint space loss, angle of Gissane sclerosis, hindfoot valgus
Triple arthrodesis or custom bracing if not surgical candidate
A+ forefoot abduction
A+ forefoot abduction
A+ lateral column lengthening
Supple ankle valgus
Hindfoot and ankle valgus
Surgery to have a plantigrade foot+ deltoid reconstruction
Rigid ankle valgus
Classification system of Raikin et al.
Posterior tibial tendon tenosynovitis
Posterior tibial tendon tendinitis without deformity
Mild flexible mid-foot supination
Mild valgus < 5°
Flexible planovalgus (< 40% talar uncoverage, < 30° Meary’s angle, incongruency angle 20°–45°)
Mid-foot supination without radiographic instability
Valgus with deltoid insufficiency
Flexible planovalgus (> 40% talar uncoverage, > 30° Meary angle, incongruency angle > 45°)
Mid-foot supination with instability
Valgus with deltoid insufficiency and tibiotalar arthritis
Fixed planovalgus (< 40% talar uncoverage, < 30° Meary’s angle, incongruency angle 20°–45°)
Arthritic changes isolated to medial column
Valgus secondary to bone loss in lateral ankle compartment (deltoid normal)
Fixed planovalgus (> 40% talar uncoverage, > 30° Meary’s angle, incongruency angle > 45°)
Medial and middle-column mid-foot arthritic changes
Valgus secondary to bone loss in lateral ankle compartment and deltoid insufficiency
Although these classifications have addressed some of the concerns associated with the Johnson and Strom classification, these newer and yet-more-complex classifications have not been validated either. This lack of validation has to be considered when evaluating any research studies on flatfoot deformity. The lack of proof that these systems possess a high degree of interobserver and intraobserver reliability means that readers need to use them with great care. To the degree that one observer may classify a patient as having Stage II posterior tibial tendon dysfunction, and another observer may perceive the same patient to have a Stage III deformity, important differences in care could result. The same problem might arise when a reader wishes to interpret research using these systems, and apply that work in his or her practice.
The Johnson and Strom classification  describes the various stages associated with adult-acquired flatfoot deformity. It is composed of clinical, radiographic, and pathologic findings that correlate with the natural progression of the deformity, and it helps guide our understanding of the disease process. Despite the limitations associated with the classification, it remains widely used and accepted among foot and ankle surgeons, and is the most-commonly cited classification for research on adult-acquired flatfoot deformity.