Pattern of ultrasonographic findings of disorders of the ankle joint complex in patients presenting with ankle pain at the department of diagnostic imaging, university of Nairobi

Introduction the ankle joint is a frequently injured joint. It is also affected by inflammatory, infectious and tumoral lesions. Ultrasound is a safe and cost-effective imaging tool when evaluating the ankle joint, as most structures are superficial and accessible. The aim of the study was to determine the pattern of ultrasonographic findings of disorders of the ankle joint complex in patients presenting with ankle pain. Methods a total of 43 consecutive patients with ankle pain referred for an ankle radiograph or ankle ultrasound were examined. Statistical analysis was done using SPSS version 20. Results abnormalities were found in 60% of the examinations performed. The abnormalities were more common in female patients accounting for 61.4% of the abnormalities detected. The most common finding was synovial hypertrophy seen in 26% of the patients. Conclusion ankle ultrasound was able to identify a large number of pathologies. This demonstrates the usefulness of ultrasound in the evaluation of a patient with ankle pain.


Introduction
The use of musculoskeletal ultrasound by radiologists has taken a back seat not only in Kenya but also in the developed world. The reason for this is that many believe musculoskeletal ultrasound is difficult and has a steep learning curve [1]. Most radiology residency programs do not incorporate musculoskeletal sonography in their curriculums, hence the reluctance of radiologists in performing the examination [1]. Another aspect is the higher remunerations involved in reading Magnetic Resonance Imaging (MRI) examinations as compared to performing sonography [1] leading to the preferential use of MRI over sonography. This has resulted to the increasing use of musculoskeletal ultrasound by non-radiologists. It has been shown that between the period of 2000 and 2009, in the United States, 71.8% of ultrasounds done in the office setting were done by nonradiologists [2]. Preference is given to MRI because it has more standardized protocols, its high spatial resolution, wide field of view and its ease of interpretation [1]. While these statements are largely true, in experienced hands musculoskeletal ultrasound has shown to be a complementary or even an alternative to MRI examinations [1].
Ultrasound is a cost-effective, readily available imaging modality. Its added advantages include; it is patient friendly, allows for dynamic evaluation and facilitates bilateral comparison. Physiologic information can also be provided by the use of color and power Doppler [1]. It can also be used in guiding therapeutic interventions.
One of its disadvantages is its lack of ability to interrogate deeper structures. With recent advances, ultrasound probes can interrogate superficial structures with better resolution. A 15MHz probe gives a resolution of 200µm, greater than routine MRI [3]. The ankle joint is the most frequently injured joint, and it commonly involves the lateral compartment [4]. Although most injuries are treated conservatively, adequate assessment of injuries is required. Most of the structures that comprise the joint are superficial and easily identifiable and accessible to ultrasound [5]. Ultrasound has been shown to be useful in detecting injuries in patients with acute ankle injury, or in patients who present with symptoms of chronic ankle pain [6]. Ankle sprains represent 5% of all casualty consultations in the United Kingdom [7].
The ankle joint is initially imaged using plain radiography with the antero-posterior, the mortise view and lateral views. Radiography evaluates the bony elements of the joint but does not interrogate the soft tissue structures around it. A normal radiograph of the ankle joint does not completely rule out injury to the surrounding soft tissue structures [8]. The ankle joint is surrounded by tendons, blood vessels, ligaments and nerves which need to be evaluated in a patient presenting with ankle pain. Further evaluation is usually performed by MRI [8]. While MRI is excellent for assessing musculoskeletal disorders it is an expensive imaging modality [9]. The ankle joint can be affected by traumatic injuries, inflammatory conditions, instability and osteoarthritis [10]. Traumatic injuries could involve fractures or ligamentous injuries. The most common cause of ankle pain results from an ankle sprain [10]. This is more evident in sports related injuries [11]. Ultrasound has been shown to have high accuracy rates in detecting ankle tendon and ligamentous tears. In a study by Rockett et al. [12], ultrasound was found to be more accurate and sensitive than MRI in diagnosis of ankle tendon tears. Ultrasound showed a sensitivity of 100% and accuracy of 94.4% while MRI showed a sensitivity of 23.4% and an accuracy of 65.75%. Grant et al. [13] correlated the findings of peroneal tendon tears with surgical findings. Results revealed ultrasound had 100% sensitivity, 85% specificity and 90% accuracy in diagnosing peroneal tendon tears. It is cheaper and readily available in most regional hospitals. It is also able to visualize the soft tissue structures around the ankle joint and give a diagnosis with high sensitivity, specificity and accuracy. The aim of this study is to demonstrate the usefulness of sonography in evaluating the ankle joint and by extension increase the awareness of sonography as an alternative imaging modality when evaluating joints in general.

Methods
This study was a cross-sectional study and was conducted at the  Table 1). The common abnormality identified was joint effusion and joint erosions. Edema represented 21% of the lesions identified. One patient was found to have plantar fasciitis which constituted 3% of the lesions seen. A mass was also seen in 1(3%) patient. The lesion did not fit any imaging criteria for a diagnosis of a specific condition

Discussion
The ankle joint is the most commonly injured joint in the body.
Although underutilized, musculoskeletal ultrasound is a cheap, easily available imaging modality with comparable sensitivity and specificity to MRI. This would be highly applicable in a resource poor setting.
The examinations were performed in 28(65%) female patients and 15(35%) male patients. The mean age of the patients was 42.4 years. Similar findings were demonstrated by Artul S et al [15]. The most common symptom was ankle pain seen in 35(81%) patients. The second most common symptom was ankle swelling seen in 24(56%).
The same was shown in Shalaby MH et al.'s study [16]. Synovial hypertrophy was the most prevalent pathology identified accounting for 26% of the lesions. This was higher than in studies by Artul S et al. [14] and Shalaby MH et al. [16] where the prevalence was 3% and 10.7% respectively. This could be explained by the fact that majority of the patients referred to us for ultrasound were from the rheumatology clinic. Tendon pathology was seen in 7(18%) of the patients examined. The most common tendon affected was the Achilles tendon representing 57.2% of the tendon lesions. The most common pathology demonstrated was tendinopathy accounting for 57.2% of the tendon pathologies seen. The anterior talofibular ligament was the ligament injured in all the ligamentous injuries seen. 75% represented partial tears. These findings are similar to the ones found in N. El-Liethy et al [10]. The major difference was the increased involvement of the FDL tendon in our study. Joint erosions and joint effusion were seen in association with other pathologies.
Plantar fasciitis was seen in one case representing 3% of the lesions. This was lower than what was found by Shalaby MH et al. [16] and Artul S et al. [15]. Most patients with heel pain are referred for a radiograph, not ultrasonography. This would explain the discrepancy.
In this study one case accounting for 3% of the lesions was diagnosed to have a mass. The lesion did not fit any particular imaging criteria for a diagnosis of a specific condition.          Longitudinal ultrasound of the Achilles tendon shows an enlarged thickened tendon with loss of the normal fibrillary echo-texture.