Friday, January 8, 2010

The lateral ankle joint

Bony Anatomy

• Curved trochlear surface of talus produces a cone-shaped articulation whose apex is directed medially; thus the fan-shaped deltoid is all that is needed for support medially
• A larger area of movement and the subtalar joint articulation laterally dictates more soft tissue involvement to produce stability, thus, more commonly injured

Anatomy of Ligaments

• The lateral ligaments should include not only the ATFL, CFL, and PTFL of the tibiotalar joint, but should also include the subtalar joint which is supported by the CFL, inferior extensor retinaculum, the lateral talocalcaneal ligament, the cervical ligament, and the interosseous talocalcaneal ligament
• Note: the CFL is included in both these joints and is crucial to the proper biomechanics of both joints
• ATFL - originates at the distal anterior fibula and inserts on the body of the talus just anterior to the articular facet (not unto the talar neck). ATFL - Makes an angle of approximately 75° with the floor from its fibular origin
• PTFL - originates from the medial surface of the lateral malleolus and courses medially in a horizontal manner to nearly the entire posterior lip of the talus
• CFL - originates from the anterior border of the distal lateral malleolus just below the origin of the ATFL and courses medially, posteriorly, and inferiorly from its fibular origin. It’s attachment on the calcaneus blends with the peroneal tendon sheath and inserts on a small tubercle posterior and superior to the the peroneal tubercle. It runs approximately 10° to 45° posterior to the line of the longitudinal axis of the fibula
• Burks and Morgan showed ATFL and CFL had adjacent attachments on the anterior distal fibula 8 to 10 mm from the tip
• Inferior extensor retinaculum is composed of 3 (lateral , intermediate, and medial); the CFL, LTCL, and the lateral root constitutes the superficial ligamentous support of the subtalar joint
• Lateral talocalcaneal ligament- originates from the lateral wall of the calcaneus just anterior to the calcaneal origin of the CFL and inserts on the body of the talus just inferior to the ATFL. This often blends with the CFL and ATFL (arcuate type)
• Cervical ligament- lies in the sinus tarsi and connects the neck of the talus to the superior surface of the calcaneus
• Interosseous talocalcaneal ligament – located at the most medial aspect of the sinus tarsi and extends from a ridge at the sulcus tali
• The angle of CFL and ATFL in the sagittal plane averages 105°; this is clinically important in both the etiology of instability and for reconstruction
• Passing from dorsiflexion to plantarflexion causes a moment in time in which there may be decreased stability
• At 105° this is unusual, however, with an anatomical variant that displays a larger angle, there may be a larger interval of vulnerablity

Biomechanics of Ligaments

• CFL is parallel to the subtalar joint axis in the sagittal plane; as the ankle is dorsi and plantar flexed, CFL and subtalar relationship does not change
• CFL is designed to allow motion in two joints simultaneously
• Neutral position, CFL is angulated posteriorly; in dorsiflexion it is brought in line with the fibula and becomes a true collateral ligament
• CFL in plantar flexion becomes parallel with the ground, and thus provides little support with resisting inversion
• ATFL is in line with fibula when the ankle is plantar flexed: collateral ligament
• ATFL in dorsiflexion positions the ligament horizontal to the ground and provides little resistance to inversion

Biomechanics of Ligaments can be studied under

1. Relationship in neutral
2. Relationship in plantarflexion
3. Relationship in Dorsiflexion

• PTFL is maximally stressed in dorsiflexion and prevents external rotation in dorsiflexion
• Attarin et al. ATFL has a lower load to failure than the CFL (CFL 2-3.5 times greater)
• However, the ATFL is capable of undergoing greater strain which allows for the internal rotation of the talus during plantar flexion
• The ATFL inhibits internal rotation primarily; in plantar flexion it also prevents adduction
• CFL prohibits adduction and acts almost independently in the neutral and dorsiflexed positions. In plantar flexion it prevents adduction in conjunction with the ATFL

Biomechanics in Injury

• Forced dorsiflexion, PTFL ruptures
• Forced internal rotation ATFL ruptures followed by injury to the PTFL
• Extreme external rotation produces disruption of the deep deltoid lig.
• Adduction forces in neutral and dorsiflexion positions cause disruption of the CFL whereas in plantar flexion the ATFL is primarily injured
• Kjaersgaard-Anderson et al. – cutting of CFL increased talocalcaneal rotation by 20% and increased tibiotalar adduction by 61%-77%

Biomechanics: Subtalar motion

• Allows the leg to undergo an additional amount of internal and external rotation
• Joint moves around a single inclined axis and functions essentially like a hinge connecting the talus and calcaneus
• The axis in the transverse plane deviates approx. 23° medial to long axis of foot, and in the horizontal plane, the axis is approx. 41° to the floor
• CFL and subtalar joint relationship: subtalar deviates from medial to lateral as it passes from dorsal to plantar direction
• Axis is defined from head of talus to lateral calcaneus, and forms a cone shape motion with its apex intersecting with the calcaneal attachment site of the CFL
• This cone shape arc and the position of the CFL allows unrestricted motion of the ankle and subtalar joint
• Two boards attached with a 45° hinge illustrates a one to one relationship of torque.
• A more horizontal hinge creates more rotation of the horizontal member (acts much like a torque converter)
• To prevent the horizontal member from participating in the displacement, it can be divided into 2 members: a short proximal segment and long distal segment
• The distal segment remains stationary by pivoting with the short segment (the transverse tarsal joint): this short segment acts just like the subtalar joint
• Conversion of the distal segment into rays will create an anatomical foot model where external rotation of the leg causes inversion of the heel, elevation of the medial side of foot, and depression of lateral side.
• Clinical: Patients with pes planus have a more horizontal subtalar joint so that with little leg rotation, they have more supination and pronation

Epidemiology of injuries

• Acute sprains account for 16%-21% for all athletic injuries
• Lateral injuries account for 85% of all ankle sprains
• 10%-30% of all acute sprains result in chronic symptomatology
• Instability can be thought of in two ways: functional and mechanical
• Functional = subjective complaint with proprioceptive disorder that is rehab able
• Mechanical = objective instability that is determined by anterior drawer and talar tilt stress tests and often requires surgical intervention
• O’Donaghue classification most commonly used: Grade I, II, III

Examining the part

• Anterior drawer test- performed in relaxed plantar flexion
• Talar tilt test performed in neutral with hindfoot locked
• Freeman described modified Romberg’s test performed on injured and uninjured leg (positive = proprioceptive defects, rehab)
Telos stress test:
a. anterior draw > 10mm and talar tilt > 9°.
b. difference of anterior drawer of symptomatic ankle from asymptomatic should be > 3mm.
c. difference between talar tilt of symptomatic versus asymptomatic should be > 3°. Karlsson et al. found > 90% sensitivity, specificity, and predictive values with above criteria

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