Posterior tibial tendon dysfunction (PTTD) is a common foot condition, with a prevalence of 3.3% among women older than 40 years.1 This condition develops as tenosynovitis, which becomes aggravated and progresses to an elongated, partially ruptured, or even completely ruptured tendon. During this process, functional loss of the tibialis posterior tendon causes pes planovalgus, which is also known as adult-acquired flatfoot.1,2
The degree of planovalgus foot deformity can be evaluated with weight-bearing radiography, by measuring the bony alignment of the forefoot relative to the hindfoot, such as the anteroposterior or lateral talus-first metatarsal angle.3 However, direct visualization and evaluation of the tibialis posterior tendon traditionally has been performed with ultrasonography or magnetic resonance imaging.4 A previous study reported that ultrasonography is more reliable than magnetic resonance imaging for predicting intraoperative posterior tibial tendon pathology.5 The extent of PTTD surgery is determined based on the condition of the tibialis posterior tendon. Surgeons also must consider whether surgery on the medial soft tissue structure (eg, spring ligament reconstruction or flexor digitorum longus tendon transfer) with calcaneal osteotomy is required.6
Recent advances in radiography have facilitated more sophisticated evaluations of the soft tissue of the musculoskeletal structure,7,8 in addition to the traditional “fat pad sign” after elbow fracture9 and “Kager's triangle” after Achilles tendon rupture.10 The current authors hypothesized that the posterior tibial tendon could be evaluated with simple radiography. The goal of this study was to examine the reliability and accuracy of evaluating posterior tibial tendon integrity with plain foot radiography as a screening method.
Materials and Methods
This study was approved by the institutional review board at the authors' institution, and the requirement for informed consent was waived because of the retrospective nature of the study. The authors included consecutive patients who underwent bilateral weight-bearing foot radiography and ultrasonography based on suspicion of posterior tibial tendinopathy between May 2016 and August 2017. The exclusion criteria were: (1) age younger than 20 years, (2) presence of an infection or tumor, (3) presence of congenital anomalies, (4) presence of neuromuscular diseases, and (5) cases with non–weight-bearing foot radiographs.
Evaluating Posterior Tibial Tendon Integrity With Foot Radiographs
Weight-bearing anteroposterior foot radiographs were obtained with a UT 2000 radiograph machine (Philips Research, Eindhoven, the Netherlands) set to 50 kVp and 5 mAs, with a source-to-image distance of 100 cm. Digital radiographic images were retrieved from the authors' picture archiving and communication system (PACS) (IMPAX; Agfa Healthcare, Mortsel, Belgium) and evaluated with the PACS software. The integrity of the posterior tibial tendon was evaluated independently by 2 orthopedic surgeons (S.Y.L., J.H.C.) who had 8 years and 3 years of experience (observers 1 and 2, respectively) and were blinded to the patient's clinical status. The brightness and contrast for each radiographic image were adjusted with the PACS software to provide optimal resolution at the posterior tibial tendon. The surgeons manually traced the soft tissue shadow of the posterior tibial tendon under the skin, from the retromalleolar groove (medial malleolus), across the radiopaque medial malleolus, and curvilinearly to the navicular insertion.
Based on radiographic evaluation, tendon integrity was scored as normal or abnormal. When the posterior tibial tendon shadow showed a regular, definite margin with symmetrical thickness, tendon integrity was scored as normal (Figure 1). Tendon integrity was scored as abnormal if a wavy pattern or an irregular margin for the tendon shadow was seen or if the tendon thickness differed (>2 mm difference over the medial end of the talar head) from the contralateral side (Figure 2).
Normal posterior tibial tendon integrity on a plain weight-bearing anteroposterior foot radiograph. Posterior tibial tendon density is shown as a normal and symmetrical delineated soft tissue shadow (arrowheads) near the navicular insertion.
Abnormal posterior tibial tendon integrity on plain weight-bearing anteroposterior foot radiographs. A wavy pattern of soft tissue (arrows) medial to the talar head on the right foot corresponds to the posterior tibial tendon. Intact density of the posterior tibial tendon (arrowheads), which inserts on the navicular bone, is seen on the left foot (A). Compared with the well-delineated soft tissue shadow (arrowheads) of the right posterior tibial tendon, the left tendon shadow (arrows) is not well delineated (B). More severe pes planovalgus deformity of the right foot is seen, with a different thickness of soft tissue density just proximal to the navicular insertion. Compared with the left side (arrowheads), the right side shows thin, low-density soft tissue (arrows) along the posterior tibial tendon near the navicular insertion (C).
Ultrasonographic examination was performed by a single radiologist with 11 years of specialized experience in musculoskeletal radiology. High-frequency ultrasonography was used to assess the integrity of the tibialis posterior tendon and was performed with an iU 22 scanner (Philips Healthcare, Bothell, Washington). Ultrasonographic findings were scored as intact posterior tibial tendon, tenosynovitis, tendinopathy (tendinosis), or loss of tendon continuity (Figure 3). An intact posterior tibial tendon was defined as normal echogenic striation of the tendon fibers, and tenosynovitis was defined as normal tendon fibers that were surrounded by low echogenic fluid collection along the tendon. Tendinopathy was defined as alterations in the normal striations of the tendon fibers, with echogenicity or calcifications (a low echogenic shadow behind the high echogenic lesion) in some cases. Loss of tendon continuity was defined as a torn or ruptured tendon that showed an empty low echogenic space near the navicular insertion of the posterior tibial tendon as a result of retraction of the tendon. Ultrasonographic examination is considered the gold standard for evaluating posterior tibial tendon integrity. The authors compared the radiographic and ultrasonographic findings to evaluate the surgeons' diagnostic accuracy and categorized normal tendon integrity as ultrasonography-confirmed intact posterior tibial tendon or tenosynovitis and abnormal tendon integrity as tendinopathy or loss of tendon continuity.
Ultrasonographic findings of the posterior tibial tendon. Intact echogenic fibrous tissue of the posterior tibial tendon near the navicular insertion and accessory navicular is seen (N, navicular bone; O, accessory navicular; T, talus; TP, posterior tibial tendon) (A). Intact echogenic fibrous tissue of the posterior tibial tendon (asterisks) is seen, with surrounding low echogenic fluid collection (arrows), consistent with tenosynovitis (B). Diffuse thickening of tendon fibers and focal decreased echogenicity of the posterior tibial tendon (arrows) is seen, consistent with tendinopathy (TP, posterior tibial tendon) (C). A torn and retracted posterior tibial tendon from the navicular insertion is seen. The wavy pattern of fibrous tissue (arrows) may be caused by loss of normal tension of the tendinous fibers (N, navicular bone; PTT, posterior tibial tendon; T, talar head). The double arrow represents the amount of tendon retraction (D). Absence of a posterior tibial tendon shadow (TP) is noted just proximal to the navicular insertion, which is normally a high-echogenic shadow. The distal end of the torn and retracted posterior tibial tendon was located at the retromalleolar groove (N, navicular bone; T, talar head) (E).
Results were reported with descriptive statistics, such as mean, SD, and proportion. Interobserver agreement was analyzed with kappa statistics, and the accuracy of the evaluation was reported as percentage of agreement between radiographic and ultrasonographic findings. All analyes were performed with SPSS version 20.0 software (IBM Corp, Armonk, New York), and P<.05 was considered statistically significant.
This study included 21 patients (5 men, 16 women) who underwent weight-bearing foot radiography and ultrasonography. Patient age was 51.5±15.7 years. Ultrasonographic examination showed that 4 patients had normal tendon integrity, 6 patients had tenosynovitis, 8 patients had tendinopathy, and 3 patients had loss of continuity (Table 1). When the authors compared the 2 surgeons' radiographic findings, they found agreement for 17 of the 21 cases (81%; kappa=0.576, P=.007). They found disagreement for 3 cases of ultrasonographically confirmed tendinopathy and 1 case of an intact tendon. When the authors compared the ultrasonographic and radiographic findings, they found agreement for 16 of 21 cases (76.2%) for the surgeon with 8 years of experience (observer 1) and 13 of 21 cases (61.9%) for the surgeon with 3 years of experience (observer 2).
Refinement of radiographic equipment and techniques has improved the resolution of radiographic images and enabled screening of soft tissue conditions in musculoskeletal structures.8 This study investigated the possibility that weight-bearing anteroposterior foot radiography could be used as a screening tool to determine the integrity of the posterior tibial tendon. The results showed fair interobserver agreement between the 2 orthopedic surgeons' radiographic findings (kappa=0.576) and diagnostic accuracy of 76.2% and 61.9% for the surgeons with 8 years and 3 years of experience, respectively.
This study had several limitations that should be considered. First, the ultrasonographic examination was performed unilaterally, and the radiographic evaluation typically compared the integrity of both posterior tibial tendons. However, unilateral ultrasonographic examination could not confirm that the contralateral posterior tibial tendon was completely intact, which may have affected the surgeons' radiographic comparisons. Second, the current results cannot be generalized because of the small sample size and differences in clinical settings and equipment at other hospitals. This retrospective study was performed at a tertiary referral center. A larger prospective study is needed to validate and generalize these findings.
The tibialis posterior muscle is a key stabilizer as well as a strong inverter and plantar flexor of the foot and ankle. It also acts as a key muscle in supporting the medial arch of the foot. When muscle and tendon function is lost or when the structure loses its continuity, acquired pes planovalgus deformity (a combination of forefoot abduction, medial arch collapse, and heel valgus) develops.11 Screening of the structural integrity of the posterior tibial tendon is important for diagnosing the cause and planning treatment and follow-up.
The current results suggest that radiographic evaluation of the posterior tibial tendon is an appropriate screening tool, although it may not provide a definitive diagnosis. For example, the surgeons could detect loss of tendon continuity and severe tendinopathy based on changes in tendon thickness or calcification on radiographs, but they could not detect tenosynovitis or mild tendinopathy without changes in tendon thickness. Therefore, radiographs have limited accuracy, especially for early PTTD, and may be more appropriate as a screening tool for advanced PTTD, which is more likely to be surgically treated.
As shown in Figure 4, resolution of the posterior tibial tendon shadow was often variable and depended on the condition of the surrounding soft tissue. Soft tissue swelling may affect the resolution of the posterior tibial tendon shadow, although further studies are needed to identify additional factors that may affect the reliability of radiographic evaluation. In addition, the optimal radiographic settings and foot position for visualizing the posterior tibial tendon are not known. A previous study used diffraction-enhanced radiography (a radiographic technique used in mammography) to clearly visualize the soft tissues in the foot and ankle, such as the tendon, skin, and plantar fascia.12 However, the authors believe that further improvements in musculoskeletal radiography can facilitate simpler, low-cost diagnosis of soft tissue conditions, such as tendinopathy.
Resolution of the posterior tibial tendon shadow can be variable, depending on the condition of the surrounding soft tissue. The tendon shadow (arrowheads) on foot radiographs can be poorly delineated (A) or well delineated (B) for the intact posterior tibial tendon.
Radiographic evaluation of the integrity of the posterior tibial tendon depends considerably on its reliability and the accuracy of comparison with the contralateral side. Therefore, radiographic detection of abnormal posterior tibial tendon integrity may be possible when the contralateral side has normal tendon integrity or less severe tendinopathy. However, when both sides are symmetrically abnormal, it may be difficult to identify abnormal integrity radiographically. Therefore, orthopedic surgeons must consider patient discomfort and history when evaluating PTTD radiographically.
Foot radiographs showed reasonable and consistent findings compared with ultrasonographic examination in evaluating the integrity of the posterior tibial tendon. One patient in the current cohort was a 28-year-old man who had undergone a Kidner procedure13 for a painful accessory navicular 10 months before presentation. He reported postoperative medial foot pain and recent aggravation of pes planovalgus deformity. Weight-bearing foot radiographs showed a soft tissue shadow with a wavy pattern just proximal to the navicular bone (Figure 2A), corresponding to a torn and retracted posterior tibial tendon on ultrasonography (Figure 3D). Another patient was a 66-year-old woman who presented to the authors' outpatient clinic because of recent aggravation of pes planovalgus deformity of the right foot. Her symptoms were concurrent with weakness and inability to perform single-heel raise on the right side. Ultrasonography showed a completely ruptured posterior tibial tendon, with the torn and retracted distal end located at the retromalleolar groove and an empty shadow near the navicular insertion (Figure 3E). Weight-bearing foot radiographs showed a different thickness of soft tissue density between the right and left medial foot, just proximal to the navicular insertion, suggesting absence of normal posterior tibial tendon density on the right side (Figure 2C). The clinical implication of these findings is that radiography may be able to predict prognosis or aggravation for patients with PTTD, although a longitudinal study is needed to validate this concept. Patients with severe tendinopathy or loss of tendon continuity are more likely to aggravate planovalgus deformity compared with patients with normal tendon integrity, tenosynovitis, or mild tendinopathy without changes in tendon thickness. A subgroup of patients with PTTD who need surgical treatment may show abnormal tendon integrity on foot radiographs, which would indicate the need for additional medial soft tissue reconstruction with medial displacement calcaneal osteotomy or lateral column lengthening. Foot radiography also can help to detect the integrity of the posterior tibial tendon after surgery, such as the Kidner procedure. Therefore, foot radiography may help to predict the prognosis during outpatient follow-up and help the surgeon to select the appropriate extent for surgical treatment and detect the postoperative integrity of the posterior tibial tendon.
In this study cohort, radiographic evaluation of posterior tendon integrity provided an excellent positive predictive value and a lower negative predictive value. This modality detected all 3 cases of loss of tendon continuity and most cases of severe tendinopathy and changes in tendon thickness. Unfortunately, the modality was not sensitive for mild tendinopathy without changes in tendon thickness. Therefore, the radiographic appearance of normal posterior tibial tendon integrity does not guarantee that the tendon is not compromised, although the finding of abnormal tendon integrity is a good indicator of either severe tendinopathy or loss of tendon continuity.
The authors found that the integrity of the posterior tibial tendon could be screened with weight-bearing anteroposterior foot radiography. Severe tendinopathy with changes in tendon thickness and loss of tendon continuity could be visualized on foot radiographs, although milder tendinopathy was not detected accurately. Therefore, the authors conclude that foot radiography may allow orthopedic surgeons to predict the aggravation of adult-acquired flatfoot in patients with PTTD during outpatient follow-up and help them to select an appropriate extent for subsequent surgery. Refinements to the radiographic technique and setting are needed to improve the resolution of this modality.
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|Age, mean±SD, y||51.5±15.7|
|Sex, male/female, No.||5/16|
|Ultrasonography finding, No.|
| Loss of continuity||3|
|Integrity, normal/abnormal, No.||10/11|