REIDER PART 230

290 Charter 7_Lower Leg, Foot, and Ankle

Figurę 7-65. Assessing inver$ion slrength.

Although completely isolated testing of the tibialis posterior is not possible, most of the effect of the tibialis anterior can be eliminated by modifying the test to have the patient begin the maneuver in the everted position.

Tibialis posterior function may also be assessed by asking the patient to rise up on the toes while the exam-iner observes from behind. If tibialis posterior function is normal, the heels should be observed to invert as they rise off the ground (see Fig. 7-34). The examiner should be aware, however, that stiffness in the subtalar joint may also prevent inversion of the heel, even in the presence of normal tibialis posterior strength.

Sensation Testing

The average distribution of the principal sensory nerves about the leg, ankle, and foot is delineated in Figurę 7-66. The anatomy of the sensory nerves is quite vari-able; therefore, the exact pattern can vary considerably from one individual to another. Light touch or sharp-dull discrimination testing is generally used to screen for areas of altcrcd sensation. Semmes-Weinstein monofila-ments can be used to assess morę accurately for altered sensation when suspected in those with peripheral neu-ropathy, such as in diabetes mellitus. Reduction in the sensory threshold beyond the 5.07 Semmes-Weinstein monofilaments suggests an inereased risk for uleeration and amputation, which can identify those individuals needing specialized cducation and protective shoe wear.

To detect a sural nerve deficit, the lateral border of the ankle and foot is usually tested. The deep peroneal nerve normally supplies the first web space between the great toe and the second toc, and the superficial peroneal nerve supplies most of the rest of the dorsum of the foot.

The saphenous nerve, which is the most often injured or entrapped on the medial aspect of the knee, supplies most of the medial leg, usually extending down to the ankle or hindfoot.

Branches of the posterior tibial nerve supply most of the sensation to the plantar aspect of the heel and foot. These include the medial calcaneal nerve, which supplies the medial heel on both its medial and its plantar aspects, and the medial and lateral plantar nerves, which supply the medial and the lateral plantar surfaces of the foot, respectively.

Numbness in the distribution of the individual digi-tal nerve branches can develop in the advanced stages of iMortons neuroma. Because these neuromata normally occur at an interspace, the adjacent sides of the digits that define the interspace can develop altered or decreased sensation. For example, the most common location of Mortons neuroma is at the interspace between the third and the fourth metatarsal heads. In the advanced stages of this condition, altered sensation is detectable along the lateral aspect of the third toe and the medial aspect of the fourth toe.

Special Tests

Stability Testing

Two manipulative tests havc been described for testing the passive laxity of the lateral ankle ligaments. The anterior talofibular ligament and the calcaneofibular ligament are the most common ankle ligaments to be injured and the most common to be associated with pathologic laxity. The test described may be performed after an acute injury or for evaluation of chronic instability, although cxami-nation in the face of an acute injury is morę difficult owing to associated pain.

Anterior Drawer Test. The anterior talofibular ligament is assessed with the anterior drawer test. This test is performed with the patient seated on the examination table with the lower limb relaxed and hanging loosely off the side of the table. With one hand, the examiner grasps the patients leg just proximal to the ankle joint to stabilize it. The examiner should grasp the patients foot and gently oscillatc the ankle to verify that the patient is relaxcd. The examiner then grasps the patienfs heel with the free hand and pulls forward while pushing posteriorly on the leg in a reciprocating manner (Fig. 7-67). The examiner focuscs on the skin over the anterolateral domc of the talus to watch for anterior motion of the talus with this maneuver. The examiner assesses the amount of anterior translation by the feel as well as by the appearance of the talus. When greater degrees of displacement are present, the anterolateral domc of the talus is often seen tenting the skin. Because the deltoid ligament is usually intact, the talus tends to intcrnally rotate in response to the anterior drawer stress. The examiner can maximize the excursion of the talus by internally rotating the foot as it is pulled forward.