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1 Both authors: Department of Radiology, P. O. Box 3808, Duke University Medical Center, Durham, NC 27710.
Received June 29, 2000;
accepted after revision October 26, 2000.
Presented at the annual meeting of the American Roentgen Ray Society,
Washington, DC, May 2000.
Abstract
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MATERIALS AND METHODS. MR images from 25 patients with advanced posterior tibial tendon injury were retrospectively examined for spring ligament, sinus tarsi, and plantar fascia abnormalities. These images were randomly compared with those obtained from 25 control patients with normal-appearing posterior tibial tendons.
RESULTS. The spring ligament was abnormal in 23 (92%) of 25 patients with a posterior tibial tendon injury and seven (28%) of 25 patients with a normal posterior tibial tendon (p < 0.0001). The sinus tarsi was abnormal in 18 (72%) of 25 patients with posterior tibial tendon injury and nine (36%) of 25 patients with a normal posterior tibial tendon (p < 0.0132). The plantar fascia was abnormal in seven (32%) of 22 patients with posterior tibial tendon injury and two (9%) of 22 patients with a normal posterior tibial tendon (p < 0.0768). Two or more associated abnormalities were present in 20 (80%) of 25 patients with posterior tibial tendon injury and four (16%) of 25 patients with a normal posterior tibial tendon (p < 0.0001).
CONCLUSION. Advanced posterior tibial tendon injury has a high association with spring ligament and sinus tarsi abnormalities on MR imaging. There was a low association between advanced posterior tibial tendon injury and plantar fascia abnormality. Patients with posterior tibial tendon injury often have abnormalities of two or more associated structures.
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The association between tear of the posterior tibial tendon and injury of the spring ligament has been reported in the orthopedic literature [2]. As expected, patients with both injuries may have more severe abnormalities of the hindfoot. Gazdag and Cracchiolo [3] have advocated that the spring ligament should be inspected and damage repaired during surgery for posterior tibial tendon insufficiency. Yao et al. [2] described the MR imaging appearance of spring ligament insufficiency and noted its association with posterior tibial tendon tear. To our knowledge, the frequency of spring ligament insufficiency on MR imaging in a group of patients with posterior tibial tendon injury has not been reported.
Two of the ligaments in the sinus tarsi assist the posterior tibial tendon and spring ligament in maintaining the longitudinal arch of the foot. These ligaments, the talocalcaneal interosseus ligament and the cervical ligament, maintain stability between the calcaneus and the talus and prevent talar flexion or rotation on the calcaneus. Klein and Spreitzer [4] examined patients with sinus tarsi syndrome and found an increased incidence of posterior tibial tendon tear, especially when the lateral ligaments of the ankle were normal. We are not aware of any studies that have examined patients with a posterior tibial tendon injury to determine the frequency of associated sinus tarsi abnormality.
The plantar fascia also helps maintain the normal arch of the foot. Cadaveric studies of the arch during simulated weight bearing showed that the plantar fascia was a major factor in maintaining the longitudinal arch of the foot [5, 6]. The MR imaging appearance of plantar fasciitis has been described [7, 8]. To our knowledge, an association with posterior tibial tendon insufficiency has not been reported in the radiology literature.
The purpose of this study was to investigate the frequency of abnormalities of the spring ligament, sinus tarsi, and plantar fascia on MR imaging in a group of patients with advanced injury of the posterior tibial tendon. This frequency was compared with a control group of patients with normal posterior tibial tendons.
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The study group comprised 25 ankles in 25 patients (20 women and five men; age range, 35-76 years; average age, 55.4 years). There were 25 control patients who did not have an abnormality of the posterior tibial tendon (11 women and 14 men; age range, 19-76 years; average age, 45.8 years). All patients were scanned with a Signa 1.5-T MR scanner (General Electric Medical Systems, Milwaukee, WI). The following sequences were used: T1-weighted spin echo (400-600/9-17 [TR range/TE range], 256 x 192 matrix, 12- to 16-cm field of view, 1-2 excitations, 3-mm slice thickness, 1-mm spacing), proton density—weighted spin echo (1800-3050/15-40, 256 x 192 matrix, 12- to 16-cm field of view, 1 excitation, 3-mm slice thickness with 1-mm spacing), T2-weighted spin echo (2000-3000/70-80, 256 x 192 matrix, 12- to 16-cm field of view, 1 excitation, 3-mm slice thickness with 1-mm spacing), and T2-weighted fast spin echo with fat saturation (3083-5000/80-108 [TR range/effective TE range), 256 x 192 matrix, 12- to 16-cm field of view, 2-3 excitations, 3-mm slice thickness with 1-mm spacing. Images were obtained in the axial, coronal, and sagittal planes. All sequences were not performed in every patient.
The control and study groups were randomly reviewed. Reviewers were unaware of the initial interpretation. The sinus tarsi, plantar fascia, and spring ligament were evaluated before the posterior tibial tendon was inspected. The images were evaluated by consensus by two musculoskeletal radiologists. The spring ligament, sinus tarsi, and plantar fascia were described as normal (Figs. 1 and 2) or abnormal. Spring ligament abnormality was noted when the superomedial calcaneonavicular portion of the ligament was thickened to more than 5 mm, attenuated, or showed heterogeneous signal in the ligament. The thickness was primarily evaluated in the axial plane [2]. Criteria for sinus tarsi abnormality were replacement of the normal fat signal surrounding the ligaments of the sinus tarsi by low signal on T1-weighted images and either increased or decreased signal on T2-weighted images [4]. Plantar fasciitis was reported when the fascia was thickened or showed increased signal [7,8,9]. The plantar fascia was not evaluated when it was outside the field of view on all the planes. Advanced injury to the posterior tibial tendon was diagnosed for patients with marked tendinosis (marked thickening and increased signal within the tendon), a partial tear (attenuation or a split tear of the tendon), and a complete tear (disruption of the tendon) [10]. Surgical results were reviewed when available. Fischer's exact test was used to compare the group with posterior tibial tendon tear and the control group.
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There were 25 control patients who did not have an abnormality of the posterior tibial tendon. The spring ligament was abnormal in seven patients (28%). The sinus tarsi was abnormal in nine patients (36%). The plantar fascia was abnormal in two (9%) of 22 patients. The plantar fascia was outside the field of view in three of the control patients and could not be evaluated. Coincidentally, this was the same number of times the plantar fascia lay outside the field of view in the posterior tibial tendon injury group. Four control patients (16%) had two associated structures injured; one control patient (4%) had injury to all three associated structures.
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There are many factors implicated as a cause of posterior tibial tendon failure: impingement at the fibroosseous groove, constriction by the overlying flexor retinaculum, an accessory navicular bone weakening the insertion, hypovascularity of the tendon at the medial malleolus, inflammatory arthropathies, acute trauma, corticosteroid injection, and chronic mechanical overload [1, 11]. Surgical biopsy specimens show degenerative tendinosis without evidence of inflammation [1]. The posterior tibial tendon most commonly fails at the level of the medial malleolus [11]. The typical patient is a middle-aged woman [2, 3, 10, 12]. A similar patient profile was seen in our group with 80% women and an average age of 55.4 years.
Without a functioning tendon, the Achilles tendon remains lateral to the axis of rotation during the flatfoot portion of the gait cycle and the hindfoot is not fixed during toe off [1]. The gastrocnemius-soleus complex acts at the talonavicular joint instead of the metatarsal heads [3]. The plantar ligaments of the foot are subjected to the forces of this powerful muscle complex [1]. Over time, these unchecked forces result in acquired flatfoot characterized by valgus deformity of the hindfoot and plantar flexion of the talus [3]. This altered alignment has been previously reported as a secondary sign of posterior tibial tendon tear [12] (Fig. 7A).
Prospective MR imaging is a useful modality for diagnosis of injury of the posterior tibial tendon in patients with medial ankle pain or acquired flatfoot deformity. With insufficiency and subsequent flatfoot deformity, the other structures in the foot responsible for supporting the arch may also fail. Three of these other structures are the spring ligament, ligaments of the sinus tarsi, and the plantar fascia. As our study shows, there is an increased incidence of abnormality on MR imaging of these three other structures in patients with advanced posterior tibial tendon injury.
The spring ligament acts to prevent plantar flexion of the talus by stabilizing the talocalcaneonavicular joint [13]. This ligament is actually formed by two distinct structures: the larger superomedial calcaneonavicular portion and the inferior calcaneonavicular portion. The superomedial calcaneonavicular portion arises from the superomedial sustentaculum tali and inserts on the medial articular border of the navicular bone [14]. When examining patients with surgically proven spring ligament tear, Yao et al. [2] found that this superomedial portion was thickened and showed heterogeneous signal as it ran along the medial aspect of the talar head (Fig. 3B). Superiorly, the superomedial calcaneonavicular portion blends with the superficial portion of the deltoid ligament [14, 15] (Figs. 3B and 4B). Distally, it merges with the posterior tibial tendon to insert in a conjoined manner on the medial aspect of the navicular [14, 15]. The superomedial calcaneonavicular portion lies just deep in relation to the posterior tibial tendon [14, 15] (Figs. 3A and 4A,4B). The inferior calcaneonavicular portion of the spring ligament is a separate and smaller structure. Originating medial to the superomedial calcaneonavicular portion on the sustentaculum talus, it is a fasciculated flat band that runs longitudinally and medially along the plantar surface of the talar head to insert on the inferior surface of the navicular. Laterally, the inferior calcaneonavicular portion is contiguous with the medial band of the bifurcate ligament [15]. Biomechanical analysis has shown that the inferior calcaneonavicular portion has a minor role in stabilizing the talocalcaneonavicular joint and the longitudinal arch of foot [14].
Abnormality of the spring ligament had a high association (92%) with advanced posterior tibial tendon injury in our study. Twenty-eight percent of our control population was found to have spring ligament abnormality, which may represent a lower specificity than the 100% specificity reported by Yao et al. [2]; however, surgical follow-up would be needed to confirm this.
The ligaments within the sinus tarsi provide subtalar stability and maintain the alignment between the talus and the calcaneus. Kitaoka et al. [13] studied the effect of sectioning various ligaments on the longitudinal arch with simulated weight bearing in cadavers. They found that the calcaneus-to-talus alignment was altered the most with sectioning of the talocalcaneal interosseous ligament. Another cadaveric study found an increase in the talocalcaneal motion with sectioning of either the interosseous or cervical ligament [16]. The talar plantar flexion and hindfoot valgus resulting from posterior tibial tendon insufficiency place increased stress on these ligaments and predispose to their failure. Insufficiency of these ligaments is seen in sinus tarsi syndrome, a clinical condition of pain over the sinus tarsi region of the foot and a sensation of hindfoot instability. The key MR imaging feature of sinus tarsi syndrome is replacement of the normal fat signal surrounding the injured ligaments. The abnormal tissue most often shows low signal on T1-weighted images and high signal on T2-weighted images. At pathologic examination, this tissue has been shown to represent inflammatory infiltrate and fibrosis [17]. The abnormal tissue may also show low signal on both T1- and T2-weighted images; however, this type of change is less common and presumably results when the fibrotic change is more pronounced.
We found a high association (72%) between advanced posterior tibial tendon injury and abnormal signal within the sinus tarsi. The moderate incidence of sinus tarsi abnormality in our control population is not unusual because these patients were scanned for ankle pain. Sinus tarsi abnormality is known to be associated with several other types of ankle injuries [4].
The normal appearance of the plantar fascia is of homogeneous low signal intensity with either uniform thickness or minimal tapering along its course [7]. Plantar fasciitis can be seen as thickening or increased signal within the fascia. Plantar fasciitis had a low association with advanced posterior tibial tendon injury in our study. Twenty-eight percent of patients with a posterior tibial tendon injury showed an abnormality of the plantar fascia. This is explained by the role of the plantar fascia in supporting the longitudinal arch. This role was seen in cadaveric studies of the arch after sectioning the plantar fascia and noting the effect on simulated weight bearing in two gait phases [5, 6]. The low incidence (9%) of plantar fasciitis in our control population is a reasonable incidence in a group of patients undergoing MR imaging for ankle pain. The low association between posterior tibial tendon injury and plantar fasciitis did not reach statistical significance in our study.
Treatment options for patients with posterior tibial tendon insufficiency depend on the presence and severity of the acquired flatfoot deformity. Nonsurgical treatment with a brace may benefit a patient with no deformity. Surgical repair is often advocated in an active patient who has developed a deformity: the type of repair is also dependent on the degree of deformity [1]. Surgical repair addresses the torn posterior tibial tendon and the altered mechanics that subsequently develop. Gazdag and Cracchiolo [3] recommend repair of the spring ligament if it is torn. A preoperative assessment of the spring ligament, sinus tarsi, and plantar fascia can help a surgeon plan treatment. In patients with advanced posterior tibial tendon, extra attention should be focused on these structures.
There are several limitations of this study. First, our criteria for posterior tibial tendon abnormality restricted our study group to those patients with an advanced injury. Patients with mild to moderate injury may not have as high a degree of associated injuries as patients with advanced injury. The second limitation is the small sample size. Whereas a statistically significant association was found between posterior tibial tendon injury and both spring ligament and sinus tarsi abnormalities, the association between posterior tibial tendon injury and plantar fasciitis did not reach statistical significance. Increased numbers may have allowed us to show a statistically significant association in all patients. The third limitation is that the evaluation of the spring ligament required looking in the region of the posterior tibial tendon. Although the posterior tendon was evaluated last in our search pattern, injury to this tendon was at times apparent during earlier evaluation of the spring ligament, thereby introducing possible bias into our interpretation of the spring ligament. The final limitation is the limited surgical correlation. A follow-up study that examines patients undergoing repair of a posterior tibial tendon injury would be useful. As inspection of the spring ligament at the time of surgery becomes more common, future studies investigating the sensitivity and specificity of MR imaging for diagnosing spring ligament tears will be easier to perform.
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