The ultrasonographic dynamic heel-rise test of the Achilles tendon

The Achilles tendon (AT) is made of tendinous bands arising from the heads of the triceps surae muscle attaching to the calcaneal tuberosity. Despite being the largest and strongest tendon in the human body, the AT can become ruptured. The injury often occurs in physically active individuals who expect to resume full sports activity after treatment. The treatment of a ruptured AT attempts to restore its primary anatomical structure and principal biomechanical properties. To ensure optimal healing and restore the length of the tendon, various surgical techniques to connect or bring closer the torn tendon stumps are used, including open repair and percutaneous repair.

The patient’s foot alignment and Thompson squeeze tests as well as Achilles tendon resting angle (ATRA) are considered the testing modalities designed to assess the normal resting function of the AT. Based on these tests, a traumatic tendon rupture or secondary rupture can be suspected quite clearly. Yet still, postoperative clinical assessment of the recovery progress may be difficult and require an appropriate level of experience. Moreover, it may be further impeded by the formation of adhesions in the tissues surrounding the healing tendon, which often makes the clinical evaluation of the tendon difficult. Diagnostic imaging plays a supportive role in the clinical assessment of the patient. It allows to monitor the recovery in terms of the tendon’s structure status as well as biomechanical properties through dynamic evaluation. Radiological imaging provides information about two major aspects of the patient’s progress: tendon morphology following the reconstruction, and healing process assessment pointing to possible issues occurring throughout the postoperative treatment protocol, including physical therapy. The overall condition of a particular patient and the characteristics of the tendon healing process should also be taken into account.

The diagnostic imaging modalities used to assess the healing process of a torn AT include ultrasonography (US) and magnetic resonance imaging (MRI). Both methods are suitable for evaluating the condition of the tendon’s healing structure following injury. In addition, US offers the advantage of a dynamic assessment of the tendon.

The development of the US heel-rise test and its implementation into the ultrasound AT assessment protocol stems from observations made during orthopaedic clinical examinations done routinely at our Clinic. During the examination, the orthopaedist asks the patient to flex the ankle actively against the resistance from their hand and then evaluates the tension of the AT through palpation. In some patients, we observed that despite bending the ankle with the maximum force achievable by the patient, one could feel with the fingers that the AT was loose over the upper outline of the calcaneus. In such cases, after applying the US transducer, we observed that the AT was not tight, but wavy. This observation gave the authors the idea to perform the test on a regular basis.

This, in turn, means that during the US heel-rise test the patient flexes the ankle actively using the strength of the other flexor muscles instead of the triceps calf muscle and the AT.

This report aims to present a complementary dynamic ultrasound AT evaluation method that employs an element of the clinical examination protocol (dynamic heel-rise test), albeit with direct ultrasound monitoring of tendon activity.

Dynamic US test is performed to assess AT traction – the transfer of the force of the triceps surae muscle contraction to the distal tendon. The dynamic test enables the diagnostician to observe the presence of AT tension during resisted active plantar flexion of the ankle joint. Such an evaluation allows to identify potential tendon undulation^(1,2) due to the lack of tendon activity and its passiveness during foot movement executed by other plantar flexors. This additional test, while included in the ultrasound examination protocol, offers a fast and reliable way to determine the tension of the AT and may be performed during any ultrasound appointment.

A routine postoperative protocol for AT patients at our Clinic includes regular follow-up orthopaedic appointments combined with ultrasound examinations including the US heel-rise test at 3 and 6 weeks, 3, 6, and 9 months, as well as 1 year after AT surgery.

The ultrasound-guided assessment of the biomechanical behaviour of a reconstructed tendon is performed in two positions: at rest and during active ankle plantar flexion against resistance.

Stage one: the patient is in a prone position with both feet at rest, placed beyond the edge of the examination table to allow for unrestricted foot movement. A linear transducer is applied longitudinally to the AT above the calcaneal tuberosity to obtain the best possible image of the longitudinally arranged tendon fibres (Fig. 1).

Fig. 1.

If resting tension is present in the muscle-tendon unit, a fibrillar structure of the AT should be evident in the image (Fig. 2). The absence of a fibrillar structure in the tendon indicates the lack of resting tension in the muscle-tendon unit (Fig. 3).

Fig. 2.

Fig. 3.

Stage two: the patient is in a prone position with both feet at rest, placed beyond the edge of the examination table. The linear transducer is again applied longitudinally to the AT, above the upper outline of the calcaneal tuberosity. The transducer is placed so that the image of longitudinally arranged tendon fibres during tendon movement can be observed. The patient is asked to perform a maximum pain-free plantar flexion of the ankle. Fig. 4 shows the hand of the diagnostician placed on the metatarsus, providing resistance against the foot during active plantar flexion, and thus forcing active muscle tension in the lower leg, including the triceps surae muscle and consequently the AT, similarly to the heel-rise test.

Fig. 4.

Our experience indicates that active plantar flexion of the ankle joint with the patient in a prone position is safe if performed carefully, even in the early postoperative period – (1 week). The resistance applied against the foot may be gradually increased, with the major indicator of the maximum strength allowed being the pain threshold of each individual patient. This means that, over time, the applicable resistance would increase from low to high at the more advanced phases of tendon healing which occur at 6 months up to 1 year after Achilles tendon surgery⁽³⁾. The examiner’s hand resists pressure from the patient’s foot. The presence of tensed fibres of the AT should be monitored on the ultrasound during active foot movement against resistance (Fig. 5). Tendon fibre undulation could be identified on the ultrasound images throughout the entire movement, or in some cases, only at the end-stage of plantar flexion of the ankle. In both scenarios, the lack of tension of the AT suggests its elongation during postoperative period (Fig. 6). In the case of AT elongation, the ankle joint does not bend as a result of the triceps surae muscle activity but through the employment of the other plantar flexors, hence no AT tension is observed.

Fig. 5.

Fig. 6.

The presence of both resting and active tension of the AT is indicative of good condition of the muscle-tendon unit both in terms of anatomy and structure⁽⁴⁾. The presence of tendon tension during motion in a closed kinematic chain is a sign of restoration of good tendon function and is of particular importance for the clinical assessment (Fig. 7).

Fig. 7.

Elongation of the AT scar after suturing a completely ruptured tendon is believed to be the cause of treatment failure. Studies have shown that surgical restoration of the length of a ruptured tendon prevents the loss of strength in the calf triceps muscle⁽⁵⁾.

A specific task of the AT is to maintain tension during the final phase of plantar flexion – for example during jumping and sprinting. Therefore, evaluating this feature is essential for monitoring the tendon function. Elongation of the AT by about 2–3 centimetres after the treatment of tendon rupture, although seemingly insignificant, disturbs the function of plantar flexion of the ankle joint. This, in turn, results in permanent impairment of the ankle joint biomechanics. The resulting loss of proper function of the muscles of the lower leg and the knee escalates further during walking, running and jumping, i.e. basic sports activities^(6,7).

The lack of tension may result from tendon elongation, inadequate activation of the calf triceps muscle, adhesions around the muscles and tendon, or a combination thereof. The presence of undulations, i.e. the lack of tension in the AT^(2,8), especially in the final phase of plantar flexion (Fig. 8 and Fig. 9), indicates that the movement is not performed with the force of the triceps surae muscle, but with the strength of plantar flexors, i.e. a heel rise is possible, but without the involvement of the triceps surae muscle/AT⁽⁹⁾.

Fig. 8.

Fig. 9.

Improper AT healing with its elongation correlates with reduced strength of plantar flexion assessed by biomechanical testing⁽⁸⁾ and abnormal heel-rise test. Interestingly, biomechanical impairment may also develop in the other limb, most likely as a result of adjustment to the limitations of the affected limb⁽⁹⁾.

In case of a classical heel-rise test, reduced calf muscle strength in the final phase of plantar flexion is caused by elongation of the AT^(5,8), which results in a reduced number of heel-rise test repetitions, lower heel-rise height or inability to perform the test. The benefit of the US heel-rise test is that it may be performed in cases where the classical test is not yet possible. This is a significant advantage, as the test can be performed at 6 weeks up to 6 months after the injury when the tendon scar lengthens the most^(10,11), and information on the tendon healing process is crucial. The US heel-rise test can be frequently repeated and is particularly clinically useful when healing disorders occur.

The US heel-rise test is cost-effective and accessible, and moreover it does not require any additional ultrasound equipment. An ultrasound device with a linear transducer is sufficient. The results are assessed qualitatively for the presence or absence of AT tension during plantar flexion.

The US heel-rise test is dedicated to monitoring the function of the Achilles tendon regardless of the surgical technique used or in the evaluation of conservative treatment. The test is not meant to measure the length of the tendon. It only shows the tendon tension or lack thereof. The surgical techniques were not discussed because, regardless of the treatment, the ultimate goal is to regain the function of the AT. The lack of tension on the AT equals unsatisfactory AT function.

Insufficient AT function may have a complex aetiology which is not the subject of this brief report. Of course, in the daily practice, a full clinical and radiological evaluation of the patient is considered, especially in cases of treatment failure.

The ultrasound heel-rise test is a simple yet significant addition to the Achilles tendon function assessment protocol. It brings together the elements of both clinical and ultrasound examinations.

The question for the orthopaedic surgeons as well as diagnosticians is whether the US heel-rise test is something they need in their everyday practice, and if it can aid their evaluation process and help optimise the treatment.

The authors believe that the test has value for several reasons. It provides a “second”, independent opinion concerning the structural condition, but more importantly, the function of the healing tendon. Such input gives the surgeon a significant argument for or, as the case may be, against allowing the patient to extend the set of permitted activities. Secondly, the test can be performed by the orthopaedist during the appointment, thus offering a complementary tool that could be used during the clinical examination, especially when adhesions surrounding the AT make palpation difficult. Additionally, the test can be done by a physiotherapist as a form of biofeedback allowing to optimise the physical therapy protocol.

All in all, the test offers considerable benefits at little to no cost.