Understanding Talotarsal Displacement

Primer on Partial Talotarsal Joint Dislocation

Dislocation –

“the displacement of any part, more especially of a bone”

Dorlands Medical Dictionary

Types of dislocation:

closed, open, complete, incomplete, traumatic, congenital, compound, simple, complicated, fracture, habitual/recurrent, partial, pathologic, subluxation, luxation.

Dislocation

• is a disease process• is not normal• needs to be treated/fixed• failure to fix leads to other

pathologic conditions

Clinical Signs of Talotarsal Joint Dislocation

Aligned TTJBalanced/Aligned hindfoot

Articular facets are in constant congruent contact.

Minimal strain on the supporting soft tissues- ligaments/tendons.

Mal-aligned TTJImbalanced/Malaligned hindfoot

Articular facets are NOT in constant congruent contact.

Excessive strain on the supporting soft tissues- ligaments/tendons.

Radiographic Evidence of TaloTarsal Joint Dislocation

Radiographic Evidence of TaloTarsal Joint Dislocation

Normal TaloTarsal Joint TaloTarsal Joint Dislocation/Displacement

“Open” sinus tarsi Partial to full obliterationof the sinus tarsi

Clinical significance: This immediately indicates that the talus is, at minimum, partially dislocated on the tarsal mechanism. The joints/articular facets are no longer in constant congruent contact.

Radiographic Evidence of TaloTarsal Joint Dislocation

Normal TaloTarsal Joint TaloTarsal Joint Dislocation/Displacement

Normal Talar Declination AngleNormal = < 21 degrees

Abnormal Talar Declination AngleAbnormal = > 21 degrees

Clinical significance: an increased talar declination angle indicates a sagittal plane deformity. Directly responsible for increased strain on the medial column of the foot.

Radiographic Evidence of TaloTarsal Joint Dislocation

Normal TaloTarsal Joint TaloTarsal Joint Dislocation/Displacement

Normal navicular height Navicular drop due to the dislocationClinical significance: navicular drop directly leads to excessive strain to the supporting structures of the medial column of the foot such as the spring ligament, medial band of the plantar fascia and especially the posterior tibial tendon and also disorders of the first ray/hallux.

Radiographic Evidence of TaloTarsal Joint Dislocation

Normal TaloTarsal Joint TaloTarsal Joint Dislocation/DisplacementNormal cyma line Anterior plantar angulated cyma.

Clinical significance: the anterior displacement of the talus forces the navicular forward. This pushes the medial cuneiform forward then the first metatarsal head into the base of the proximal phalanx (hallux) leading to limited joint motion. This also unlocks the midtarsal joint leading to an excessively long period of pronation.

Radiographic Evidence of TaloTarsal Joint Dislocation

Normal TaloTarsal Joint TaloTarsal Joint Dislocation/Displacement

Notice that the calcaneal inclination angle (CIA) is the same.

Clinical significance: a lower than normal CIA indicates a “flat foot” (pes planovalgus). It is possible to have a talotarsal dislocation without a “flat foot”.

Several Examples of Radiographic Evidence of TaloTarsal Joint Dislocation

Normal Talar Second Metatarsal Angle

• Ideal 3-6 degrees• Acceptable is < 16 degrees• Indicator of transverse plane

talotarsal dislocation.

Talar Second Metatarsal Angle

• The bisection of the talus compared to the forefoot or the bisection of the 2nd metatarsal.

• The outer/upper angular range of normal is < 16 degrees.

• > 16 degrees is considered pathologic indicating a medially displaced talus on the tarsal mechanism.

Pathologic Talar Second Metatarsal Angle

Normal Abnormal

Partially Dislocated Talotarsal Joint

PosteriorFacets

Anterior/Middle Facets.

• Talar Second Metatarsal Angle (T2MA) > 16

• Significant transverse plane deformity.

• This shows an anteriomedial talotarsal joint displacement.

Radiographic Evidence of TaloTarsal Joint Dislocation

Radiographic Evidence of TaloTarsal Joint Dislocation

Weightbearing image with talotarsal joint in alignment/

neutral stance position

Weightbearing image exhibiting talotarsal joint displacement/

relaxed stance position.

Clinical significance: The comparison of normal to abnormal flexible dislocation of the talus on the tarsal mechanism. This is a recurrent dislocation.

• Relaxed stance weightbearing radiograph.

• T2MA > 16• Talotarsal joint

displacement

Radiographic Evidence of TaloTarsal Joint Dislocation

Radiographic Evidence of TaloTarsal Joint Dislocation

• Relaxed stance weightbearing radiograph.

• T2MA > 16• Talotarsal joint displacement• Note that there is minimal

anterior displacement.

Radiographic Evidence of TaloTarsal Joint Dislocation

• Relaxed stance weightbearing radiograph.

• T2MA > 16• Talotarsal joint displacement• Note anterior and medial

displacement.

Extra-osseous Talotarsal Stabilization with internal fixation

Clinical significance: Talotarsal joint is realigned, articular facets remain in constant congruent contact. Internal fixation device allows normal/natural talotarsal motion without blocking/limiting motion. Restoration of the pathologic pre-existing deformities both sagittal and frontal plane correction exhibited.

Extra-osseous Talotarsal Stabilization with internal fixation.

Clinical significance: Talotarsal joint is realigned, articular facets remain in constant congruent contact. Internal fixation device allows normal/natural talotarsal motion without blocking/limiting motion. Restoration of the pathologic pre-existing deformity showing transverse plane correction with normalization of the talar second metatarsal angle.

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