The function of the posterior tibial tendon (PTT) is to maintain a longitudinal arch, invert the foot, and maintain the hindfoot. PTT dysfunction (PTTD) results when the tendon is torn or inflamed.[1,2] As a result, the PTT may not be able to provide support and stability for the arch of the foot, resulting in acquired flatfoot. An acute injury can tear the PTT or cause it to become inflamed. Repetitive use of the PTT can also tear it. For instance, people who do active sports, such as soccer, tennis, or basketball, may have tears of the PTT from overuse. Once the PTT becomes torn or inflamed, the arch will slowly collapse over time. Additional risk factors include diabetes, hypertension, and obesity.[3–7] Most patients can be treated without surgery, using braces and orthotics. If braces and orthotics do not relieve the discomfort, surgery can be an effective alternative method to help the maintenance of the PTT. Surgery might be repairing a simple tear or removing the inflamed tissue. In several cases, the cause of the acquired flatfoot deformity is PTTD accompanying a PTT injury.[2,8,9] Thus early diagnosis and treatment are very important.
Ankle Magnetic resonance imaging (AMRI) helps the analysis of the pathologic disorders of the PTT.[9–11] Most specialists also consider the AMRI findings when they evaluate the morphology of the PTT for deciding on treatment choices. Previous research evaluated the PTT using one measurement at the “middle” of the PTT. However, partial damage and asymmetrical inflammatory thickening can occur anywhere in the PTT. Accordingly, measurement bias can occur frequently. In contrast to the PTT thickness (PTTT), the PTT cross-sectional area (PTTCSA) does not suffer from this measurement mistake, because the PTTCSA measures the cross-sectional area of the PTT. Therefore, to evaluate the inflammatory reaction of the PTT, we devised the PTTCSA as a new morphological diagnostic parameter. We assumed that the PTTCSA is an important morphologic parameter in PTTD diagnosis. So, we used AMRI to compare the PTTT and PTTCSA between PTTD patients and normal subjects.
The retrospective data of this research were approved by Catholic Kwandong University Institutional Review Board (CKU IRB) center (CKU IRB number: IS19RIS10049). We reviewed individuals who visited the orthopedic clinic with ankle and foot pain from October 2014 to December 2018 and who had taken AMRI
The inclusion criteria of the PTTD group were as follows:
- (1) pain, typically around the inside of the ankle and foot;
- (2) swelling, warmth, and redness along the inside of the foot and ankle
- (3) pain that worsens during activity;
- (4) flattening of the foot;
- (5) inward rolling of the ankle; and
- (6) turning out of the toes and foot.
We excluded subjects if patients had any of the following disorders:
- (1) past surgical history of the ankle;
- (2) peroneal disorder;
- (3) plantar fasciitis; and
- (4) any other neuromuscular disorder.
A total of 14 individuals who met our enrollment criteria were included after PTTD diagnosis was confirmed by a board-certified experienced musculoskeletal radiologist.
There were 9 (64.29%) male patients and 5 (35.71%) female patients, with an average age of 38.64 ± 12.46 years (range, 19 to 57 years) (Table 1). To compare the PTTT and PTTCSA between patients and normal individuals, we enrolled healthy subjects. The normal subjects were individuals who wanted to have AMRIs themselves for a medical examination. In the normal group, 20 individuals (10 males and 10 females) were enrolled, with an average age of 41.15 ± 14.72 years (range, 19 to 63 years).
2.2 Imaging parameters
AMRI analysis was done using a 3T MRI (Siemens health care) and 3T Philips Insignia scanners (Eindhoven, Netherlands). For all AMRI examinations, we acquired transverse T1-weighted turbo-spin echo (TSE) proton-density (PD) images using an intersection gap of 0.9 mm, 150 × 150 cm field of view, repetition time (TR) 3770 ms of/echo time (TE) 38 ms, 448 × 448 matrix, and > 3 ETL, a slice thickness of 3 mm.
2.3 Image analysis
The corresponding author, who was blinded to the group of the ankles, measured the PTTT and PTTCSA. We acquired transverse T1-weighted AMR images at the thickest level of the PTT. We measured the PTTT and PTTCSA on AMRI using an image-analysis program (INFINET, Incheon city, Republic of Korea). (Fig. 1 A, B). The PTTCSA was measured as the cross-sectional area of the margin of the PTT at the most marked portion of hypertrophy in the AMR images.
2.4 Statistical analysis
We compared both the PTTT and PTTCSA between the PTTD and the normal groups using unpaired t-tests. Receiver operating characteristic (ROC) curves were used to compare and describe the diagnostic performances of the PTTT and PTTCSA methods; and a P < .05 was considered significant. Statistical analysis was performed with SPSS (IBM/SPSS, Inc., Chicago, IL) for Windows, version 22.
Demographic data were not significantly different between the 2 groups (Table 1). The average PTTT was 2.43 ± 0.39 mm in the normal group and 3.40 ± 0.42 mm in the PTTD group. The average PTTCSA was 16.10 ± 4.27 mm2 in the normal group and 26.93 ± 4.38 mm2 in the PTTD group. The PTTD patients had significantly higher PTTT (P < .001) and PTTCSA (P < .001) than did the normal subjects (Table 1). A ROC analysis demonstrated that the area under the curve (ACU) was 0.92 (95% CI, 0.84-1.00) in PTTT and 0.95 (95% CI, 0.87-1.00) in PTTCSA (Fig. 2). The best cut-off value for PTTD was 3.07 mm with a sensitivity of 85.7% and a specificity of 85.0% in PTTT (Table 2), and 22.54 mm2 with a sensitivity of 92.9% and a specificity of 90.0% in PTTCSA (Table 3).
The PTT that plays an important role in normal hindfoot function lies beneath the flexor retinaculum and close to the medial malleolus, which binds the tendon to the bone. Since the PTT is the important supporter of the medial aspect of the foot, lack of PTT function results in a gradual flattening of the longitudinal arch of the foot, and, eventually, a hindfoot valgus deformity occurs. Patients suffering from PTTD may have medial ankle pain, clinically. In cases with an inflammatory reaction, there can be edema and tenderness of the PTT. These are most likely to be observed in the distal portion, which is the area most commonly involved in PTT lesions. Because the deformity will develop and progress with delayed or misleading diagnosis, image modalities of acquired flatfoot deformity caused by PTTD require an exact approach to ensure the best therapeutic management. There are multiple available imaging modalities such as AMRI, ultrasonography, bone scintigraphy and high-resolution ultrasound.[13–19] However, the diagnosis of PTTD is still not easy because of the absence of a reliable objective diagnostic parameter. Conti et al. used AMRI to divide PTTD into three grades and insisted that this new classification could be important in predicting the surgical consequences. They concluded that the need for surgical treatment declined when the classification grade was lower. However, surgery is no longer recommended these days, and the usefulness of the classification is not proved.
The talonavicular coverage angle was measured by Sangeorzan et al They have demonstrated that an improvement of 26 degrees can be achieved via lateral column lengthening; however, there was no mention about the actual angle of PTT. Younger et al have demonstrated that the distance was 17.5 mm in a normal situation and 6.3 mm when symptoms of flatfoot were observed. However, they did not evaluate the PTT itself. Acquired flatfoot is only a result, not a cause. Chen et al. reported that the mean diameter of the tendon in the unaffected foot was 3.30 ± 0.34 mm and that of the PTT diameter was 3.64 ± 0.35 mm. They concluded that the increased ratio of the peritendinous area was significantly greater than for the tendinous portion in symptomatic PTT (P < .01). Their measurements were acquired at the middle level between the insertion sites. However, the morphology of the PTT injury can differ, in such ways as having an irregular tendon torn, a wavy or curved contour, elongation, and different signal intensities within the PTT.[23,24] Thus, measuring mistakes could occur frequently.
In this study, we assumed that the cross-sectional tendon area of the PTT on AMRI may predict PTTD better since it would lower measurement mistakes comparing to the thickness of PTT. And we used T1 weighted AMR images because the tendons are clearly seen on AMRI as hypointense anatomies on T1 images. T1 weighted images provide excellent anatomical images at the location of tendon injury.[25–27] Our current results show that the AUC value of ROC for predicting PTTD was 0.95 with a sensitivity of 92.9% and a specificity of 90.0% in PTTCSA, and 0.92 with a sensitivity of 85.7% and a specificity of 85.0% in PTTT. These results suggest that the PTTCSA is a better predictor of PTTD than is the PTTT.
There were multiple limitations to this research. First, alternative diagnostic skills to evaluate PTTD, such as ultrasound analysis[28–34], high-resolution ultrasound, and a grading system, have been used to discriminate PTTD. However, in this research, we assessed only the measurement of the PTTCSA and PTTT on AMRI. Second, there might be a tiny bias associated with measuring the PTTCSA and PTTT on AMRI. Even though we tried to calculate morphologic parameters in the best-shown transverse image of the PTT, the transverse images we calculated to measure the PTTCSA could be irregular because of the cutting level in the AMRI. Third, PTTD was evaluated and classified using 3 grades: in Grade 1, the high signal intensity area is observed and the tendon has become thicker; in Grade 2, the intramural degeneration and several high signal intensity areas are present and the tendon has become thinner; and in Grade 3, the discontinuity has appeared. However, we focused only on the thickened PTT (Grade 1) because our aim was to enable early diagnosis of PTTD to prevent acquired flatfoot. Fourth, the design of this research was a retrospective case-control evaluation. Despite these limitations, this research is the first study to report that PTTCSA is associated with PTTD.
In conclusion, even though the PTTCSA and PTTT were both significantly associated with PTTD, the PTTCSA was a more highly sensitive diagnostic parameter for PTTD than was PTTT. We demonstrated the best cut-off point of the PTTCSA as 22.54 mm2 with a sensitivity of 92.9% and a specificity of 92.0%. When assessing PTTD patients, doctors should carefully evaluate the PTTCSA as a new objective parameter.
All authors thank the International ST. Mary‘s Hospital.
Conceptualization: Young Uk Kim, Joohyun Lee
Data curation: Koeun Kim, Yun-Sic Bang
Methodology: Young Uk Kim, Sangchul Park
Software: Young Uk Kim, Hyung Rae Cho
Formal analysis: Young Uk Kim, Sangchul Park, Hyung Rae Cho
Writing – original draft: Young Uk Kim, Joohyun Lee, Sangchul Park
Writing – review and editing: Young Uk Kim, Joohyun Lee, Hyung Rae Cho
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