Preoperative Evaluation and Imaging



Preoperative Evaluation and Imaging


RICHARD D. FERKEL

GREGORY R. APPLEGATE



The ankle and foot are complex structures composed of multiple joints and anatomic structures. Evaluation of the ankle and foot requires a thorough knowledge of the intra- and extra-articular anatomy, normal variants, kinesiology, and imaging appearance. It is important to be able to separate normal from abnormal complaints and findings and to understand how the ankle and foot relate to the rest or the body.

The most important methods of evaluation are a careful history and a physical examination. Plain radiographs are then obtained, and a preliminary diagnosis is made. Sometimes the diagnosis is not obvious, and various etiologies must be considered in the differential diagnosis. In these cases, additional diagnostic tests may be necessary. Many different tests are useful in the ankle and foot, but they must be used judiciously and a “shotgun” approach avoided (Table 2-1). A keen understanding of the indications and limitations of each test is mandatory for cost-effectiveness; they vary from case to case.






RADIOLOGIC IMAGING

After a careful history and physical examination, radiologic evaluation is critical to the proper diagnosis and treatment of ankle and foot disorders. Over the last 10 to 15 years, newer imaging techniques have given us the opportunity to better understand numerous pathologic disorders and sometimes to diagnose previously unknown conditions.7


Routine Radiography

At least two orthogonal radiographs should be performed. The anterior/posterior (AP) radiograph is the best overview of the ankle and is particularly valuable to verify that an intact distal tibiofibular joint is present (Fig. 2-19A). On the lateral view, the articular space between the talus and tibia is seen, as well as the articulation of the talus with the navicular and calcaneus (see Fig. 2-19B). Weight-bearing AP and lateral ankle x-rays demonstrate standing alignment and accentuate non-weight-bearing deformities.






FIGURE 2-18. Pain in the foot can be referred from the back, hip, or knee. (Illustration by Susan Brust.)







FIGURE 2-19. Normal ankle x-rays. (A) Anterior/posterior view of the ankle. The medial clear space is well seen with overlap of the fibula with the distal tibia and talus. (B) Lateral view of the ankle. Both the distal anterior and posterior portions of the tibia can clearly be seen, as can the space between the distal tibia and talus and subtalar joint. (C) Mortise view of the ankle. Normally, the medial clear space measures 2 mm as does the tibiofibular syndesmosis. The zone of rarefaction in the talus shows the posterior facet of the subtalar joint.

The ankle mortise is best evaluated by having the patient recumbent with the leg and foot rotated internally 20° or 30° (see Fig. 2-19C). If the radiograph is properly performed, the medial and lateral clear spaces and the distal tibiofibular syndesmosis can be well seen.

The tibiofibular clear space, the tibiofibular overlap, and the medial clear space are measured on the AP and mortise views (Fig. 2-20). The tibiofibular clear space is the distance between the incisura fibularis of the posterior tibia and the medial border of the fibula, measured
1 cm proximal to the tibial plafond articular line on the AP and mortise views. This space is usually considered within normal limits if it is <6 mm. The tibiofibular overlap is the distance between the medial border of the fibula and the lateral border of the anterior tibia, measured 1 cm proximal to the tibial plafond articular line. A normal tibiofibular relationship is indicated by at least 1 mm overlap of the tibia and the fibula on the AP and mortise views. The medial clear space is the distance between the medial border of the talar dome and the lateral border of the medial malleolus, measured 1 cm distal from the tibial plafond articular line. The distance defines the integrity of the ankle mortise and is normally 2 to 3 mm. A medial clear space of more than 3 to 4 mm is associated with ankle fractures or syndesmotic injuries in which the talus shifts laterally. This finding also indicates a rupture of the deltoid ligament. In addition, a detailed evaluation of the tibiotalar joint congruity on the lateral view can be important in the overall evaluation of a syndesmosis injury. Anterior widening of the tibiotalar joint is consistent with a syndesmotic injury. It is always important to obtain comparison radiographs of the contralateral ankle to help with the assessment.8






FIGURE 2-20. Normal radiographic relationships that are important in evaluation of the tibiofibular articulation. (A, tibiofibular clear space; B, tibiofibular overlap; C, medial clear space.) (Illustration by Susan Brust.)

Less common projections include the Harris-Beath view or the axial view of the calcaneus. This is useful for evaluating subtle calcaneal fractures, injuries to the subtalar joint, and talocalcaneal coalitions. The Broden view is helpful in visualizing the posterior facet of the subtalar, talofibular, and tibiofibular joints. Different portions of the subtalar joint can be seen depending on the tube angle. The Cobey view, used to evaluate the position of the calcaneus relative to the tibial axis and the ankle joint, is particularly helpful in looking at varus and valgus alignment.9

Weight-bearing AP and lateral views of the foot are routinely taken to evaluate foot disorders, and oblique x-rays are often helpful to better demonstrate the sinus tarsi, calcaneocuboid, and tarsometatarsal arrangements (Fig. 2-21A-C).


Hindfoot Alignment View

Saltzman and Ek-Khoury have popularized the coronal plane hindfoot alignment view.10 Using this view, the moment arm between the weight-bearing axis of the leg and the contact point of the heel can be estimated. They presented normative data on 57 asymptomatic patients. This is particularly helpful in determining varus and valgus malalignments in the coronal plane (Fig. 2-22).


Stress Radiographs

Stress x-rays are used to evaluate ligamentous integrity about the ankle and subtalar regions. These x-rays may be done manually by the physician or an experienced assistant or by a mechanical device or jig. Comparison x-rays are essential because there is a large variation in normal ligamentous laxity. To generate a reproducible amount of stress, the Telos device can be used11 (Fig. 2-23). A maximum stress of 15daN (decaNewtons) is applied in eversion, inversion, or anterior drawer, as indicated. The Telos device has advantages that include the following:


1. No radiation exposure to the examining physician

2. Reproducible patient motion

3. Gradual and accurate application of stress, which avoids muscle splinting

4. Reproducible fixation in 18° internal rotation to approximate the mortise view during stress

Stress views are most useful for evaluating the lateral and medial ligament complexes. Plantarflexion/inversion stress is a better indicator of the integrity of the anterior talofibular ligament; dorsiflexion/inversion stress is best for testing the calcaneofibular ligament.11 Sauser and coworkers,12 using the Telos device, found that a talar tilt of 10° or more was associated with a lateral ligament injury in 99% of cases. Normal values for talar tilt reportedly range from 5° to 23°.13 Chrisman and Snook14 noted when comparing both ankles that a difference of more than 10° was significant when measuring the anterior talofibular and calcaneofibular ligaments (Fig. 2-24). Cox and Hewes15 noted that a 5° difference in talar tilt between the two ankles was clinically significant, and we use this number to help assist us in determining which patients need ankle ligament reconstruction.

The anterior drawer stress test specifically tests the integrity of the anterior talofibular ligament and is the most
reliable indicator of injury to it. Gould and colleagues16 found that an increase of 4 mm indicated instability in the anterior drawer test. However, Laurin and associates17 considered an increase of more than 9 mm to be abnormal. Overall values of up to 4 mm separation between the talus and distal tibia are considered normal, values of 4 to 10 mm are probably abnormal, and values over 10 mm are grossly abnormal. These measurements are best performed at the posterior aspect of the talar and distal tibial articular surfaces (Fig. 2-25).






FIGURE 2-21. Normal foot x-rays. Degenerative joint disease, subluxation or dislocation, avascular necrosis, accessory bones, and other abnormalities can be noted on these x-rays. (A) Anterior posterior view; (B) true lateral view; (C) oblique view.

Subtalar instability can also be tested with the Telos device. Although this is more difficult to diagnose, the stress x-ray can detect laxity in the joint when done properly (Fig. 2-26).18, 19 Using the device, a Broden stress view of the subtalar joint when positive will show loss of talus and calcaneus facet parallelism. In addition, a lateral view of the subtalar joint with inversion stress of the hindfoot can demonstrate anterior translation of the posterior facet of the calcaneus relative to the posterior facet of the talus.


Tomography

In tomography, a focal point for each image is established and the structures anterior and posterior to this fulcrum are blurred out of focus by the movement of the x-ray tube and film in tandem. The tube and film can move in several different motions to optimize detail
in different planes. Tomograms can be unidirectional (linear tomography) or pluridirectional (complex). The main indications for tomography include evaluations for nonunions, most arthrodeses, and occasionally Lisfranc fracture-dislocations. Infrequently, they are used to evaluate osteochondral fractures of the talus, navicular stress fractures, calcaneal fractures, and subtalar arthritis. The disadvantages of tomography include high radiation exposure and an inaccurate picture of the structures not exactly perpendicular to the plane of the tube motion. Conventional tomography is no longer widely available and has been replaced by CT. Recently, however, with digital radiography (DR), some manufacturers have included a tomographic technique into their DR systems, which may have limited utility.

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Sep 25, 2018 | Posted by in RHEUMATOLOGY | Comments Off on Preoperative Evaluation and Imaging
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