U. Szeimies
Syndesmotic Instability Definition
This condition is defined as persistent instability of the ankle syndesmosis after a fibular fracture with syndesmotic involve-ment or after an isolated syndesmosis tear.
Symptoms
●Diffuse ankle pain and subjective instability with no clinically detectable increase in joint space opening
●Complaints aggravated by physical activity
●Possible local tenderness over the syndesmosis
●Pain on external rotation of the foot
●Diagnosis confirmed by trial infiltration of the syndesmosis with local anesthetic
Predisposing Factors
Prior history of ankle trauma with an unrecognized or inad-equately treated syndesmosis injury.
Anatomy and Pathology
The syndesmotic instability can range from weakness to a com-plete loss of function. The tibiofibular space may be occupied by scar tissue, or there may elongation of the anterior, central, and posterior syndesmotic ligaments.
Imaging
RadiographsA widening of the syndesmosis up to more than 4–6 mm in the AP view is suspicious of a syndesmotic injury. Due to the high variability further imaging is recommended. Stress radiographs with rotation may show abnormal widening of the tibiofibular clear space.
Ultrasound
Color duplex ultrasound scanning may show increased soft tissue in the anterior tibiofibular space. A dynamic examination can be performed with rotation and weight bearing. Stress test-ing of the syndesmosis consists of maximum passive dorsiflexion Fig. 3.55 Activated os trigonum in a 20-year-old soccer player.
Sagittal PD-weighted fat-sat image shows the os trigonum with its fibrous attachment to the talus, bone marrow edema, and associated irritation.
and eversion. Instability is present if the tibiofibular gap is great-er on the affected side than on the opposite side.
CT
CT can define the precise width of the anterior syndesmosis, and ankle joint congruity can be accurately assessed. Normal CT findings do not exclude syndesmosis instability, however. CT cannot evaluate fiber structures, scarring, activation around the syndesmosis, or initial secondary degenerative changes.
MRI
Interpretation Checklist
●Continuity and quality of the anterior syndesmosis fibers
●Complete disruption
●Elongation
●Old avulsion
●Extent of scarring and fibrovascular activation
●Possible scar impingement
●Secondary degenerative changes in the ankle joint
●Evaluation of cartilage quality
●Signs of chronic instability with synovitis
●Evaluation of ligament structures about the lateral and medial malleolus
Examination Technique
●Standard protocol: prone position, high-resolution multi-channel coil
●Sequences:
○Coronal and sagittal PD-weighted fat-sat
○Coronal T1-weighted
○Axial T2-weighted
○Oblique sagittal PD-weighted fat-sat, angled parallel to the syndesmosis fibers in the anterior superior corner of the ankle joint
○T1-weighted fat-sat, true axial (angled to joint plane) and sagittal after IV contrast administration
MRI Findings (▶Fig. 3.56)
●Absence of well-defined, hypointense fiber structure in the anterior syndesmosis
●Thickened, enhancing fibrovascular scar tissue in the syndes-mosis with reactive synovitis in the ankle joint, predomi-nantly on the anterior side
●Evidence of syndesmotic impingement
●Coronal projection may show incongruity with joint-space widening on the medial side
●Possible cartilage lesions due to chronic instability, most pro-nounced on the anterior side
Imaging Recommendation
Modality of choice: MRI for direct visualization of the syndes-mosis and secondary changes.
Differential Diagnosis
●Lateral ankle instability
●Fibular fracture
●Osteoarthritis of the ankle joint
●Anterolateral ankle impingement
Treatment
Conservative●For functional instability without frank dehiscence: steroid injections
●For persistent complaints: injection of platelet-derived growth factor plus TightRope or screw fixation of the syndesmosis
Operative
Syndesmoplasty in cases where imaging shows definite diasta-sis of the syndesmodiasta-sis.
Prognosis, Complications
Even with surgical reconstruction of the syndesmosis, function-al deficits of the ankle joint may persist in young, athleticfunction-ally active patients. A chronic ankle pain syndrome may develop.
Persistent instability may lead to early degenerative changes in the ankle joint.
Fig. 3.56 a, b Injury of the anterior syndesmosis following an ankle sprain in a 42-year-old woman. The patient presented 6 months after conservative therapy with persistent focal com-plaints over the anterior syndesmosis, especially on weight bearing.
a Axial T1-weighted fat-sat image after contrast administration shows intense focal enhancement of fibrovascular scar tissue in the anterior syndes-mosis consistent with chronic irritation and insta-bility (arrow).
b Oblique sagittal PD-weighted fat-sat image in the plane of the syndesmosis shows overall con-tinuity of the syndesmotic fibers. Individual fiber bands are thickened, especially on the fibular side, and are poorly delineated (arrow).
Ankle Instability Definition
This condition is defined as mechanical instability of the ankle joint due to insufficiency of the lateral ligaments and/or deltoid ligament, usually as a result of trauma.
Symptoms
●Subjective instability
●Increased lateral joint-space opening
●Anterior translation of the tibia
●Unsteadiness on weight bearing and when walking on uneven ground
●Nonspecific ankle pain
Predisposing Factors
●General laxity of capsule and ligaments
●Prior history of ankle sprains
●Pes cavus
●Hindfoot varus
●Peroneal tendon pathology
Anatomy and Pathology
Mechanical insufficiency of the lateral capsule and ligaments leads to increased joint-space opening and anteroposterior translation of the tibia in the ankle mortise.
Imaging
RadiographsAP stress radiographs may be taken and evaluated in a side-to-side comparison. Lateral views may also be obtained. The radio-graphs may show joint incongruity, and a side-to-side compari-son may show increased opening of the ankle joint space on the affected side.
Ultrasound
A dynamic ultrasound examination can be performed. A longi-tudinal scan over the anterior talofibular ligament will show a ligament defect with associated instability on stress testing. The examiner can measure translational motion between the poste-rior tibia and calcaneal tuberosity by performing a longitudinal scan of the posterosuperior quadrant of the ankle joint in the prone position and watching the monitor while heel pressure is applied. The advantage of this method is that it allows for very brief, precisely controlled stress testing of the ankle joint.
MRI
Interpretation Checklist
●Direct evaluation of the capsule and ligaments
●Scar tissue in older injuries
●Signs of impingement
●Excessive scar formation
●Assessment of cartilage quality
●Degree of effusion and synovitis
●Accurate localization of capsule and ligament pathology
●Early secondary degenerative changes
●Bone marrow edema
●Condition of the subtalar joint
●Overloading of hindfoot tendons
●Sinus tarsi ligaments
Examination Technique
●Standard protocol: prone position, high-resolution multi-channel coil
●Sequences:
○Coronal and sagittal PD-weighted fat-sat
○Coronal T1-weighted
○Axial T2-weighted
○T1-weighted fat-sat, true axial (angled to joint plane) and sagittal after IV contrast administration
MRI Findings (▶Fig. 3.57,▶Fig. 3.58)
MRI cannot supply an accurate diagnosis, which must rely on a combination of subjective complaints (feeling of instability, nonspecific pain), clinical findings (increased laxity of capsule and ligaments, especially in a side-to-side comparison), and MRI findings (effusion and synovitis in the ankle joint with lit-tle or no associated pathology). The capsule and ligaments may appear fully intact on MRI.
! Note
The detection of pre-existing secondary degenerative changes and impending cartilage defects is important for treatment planning.
Imaging Recommendation
Modalities of choice: radiography and ultrasound. MRI is a useful adjunct for planning treatment and narrowing the dif-ferential diagnosis.
Differential Diagnosis
●Osteochondral lesion of the talus
●Peroneal tendon lesion
●Arthritis
●Ankle joint impingement
●Subtalar joint disease
●Pes supinatus/varus
●Palsy
Treatment
Conservative●Proprioception exercises
●Strengthening of the peroneus longus and brevis
●Ankle brace
●High-top shoes
Surgical
●Anatomic reconstruction of damaged ligaments (Broström)
●If tissue quality is deficient: augmentation with plantaris lon-gus tendon or an allograft
●Tenodesis (Watson–Jones and similar procedures have poorer long-term results than an anatomic reconstruction)
Prognosis, Complications
PrognosisPatients who respond well to conservative therapy have a good prognosis. In cases that require surgical treatment, possible complications include adhesion formation, scar impingement, and limited motion. Recurrent sprains may give rise to secon-dary degenerative changes.
Possible Complications
●Osteochondral lesion of the talus
●Peroneal tendon overload
●Rupture of the peroneus brevis tendon
Subtalar Joint Instability Definition
Instability of the subtalar joint is manifested as hypermobility of the joint.
Symptoms
●Nonspecific pain at the level of the subtalar joint
●Subjective ankle instability
●Pain relieved by diagnostic local anesthesia
●With a stable ankle: increased joint-space opening in the sub-talar joint (tested with the ankle joint in dorsiflexion)
●Increased mediolateral translation in the subtalar joint
Predisposing Factors
Subtalar joint instability may develop after a sprain injury that tears the interosseous talocalcaneal ligament and calcaneofibu-lar ligament.
Fig. 3.57 a, b Ankle instability in a 26-year-old man who had a prior ankle sprain with rupture of the anterior talofibular ligament. He presented with ankle pain and swelling, aggravated by exercise, and subjective ankle instability.
a Axial T2-weighted MRI (angled to the joint plane) shows moderate effusion and a complete tear of the anterior talofibular ligament.
b Axial T1-weighted fat-sat image after contrast administration shows intense synovitic enhance-ment encircling the ankle joint due to chronic an-kle instability with fibrovascular activation along the deltoid ligament.
Fig. 3.58 a, b Ankle instability in a 37-year-old man 3 months after a pronation injury. He complained now of increasing pain on weight bearing, predominantly on the medial side.
a Coronal PD-weighted fat-sat image. The deltoid ligament is seen to be structurally intact, but all portions of the ligament are thickened and expanded.
b Axial T1-weighted fat-sat image after contrast administration shows marked fibrovascular acti-vation along the deltoid ligament associated with severe ligament dysfunction. Soft-tissue activation is seen anterolaterally over the later-al mlater-alleolus.
Anatomy and Pathology
A sprain of the subtalar joint causes elongation or tearing of the interosseous talocalcaneal ligament and calcaneofibular liga-ment, resulting in increased joint laxity with complaints related to overloading of the joint capsule.
Imaging
RadiographsThe Broden view with 45° of internal rotation and a varus stress shows abnormal passive opening of the subtalar joint space.
Ultrasound Not indicated.
MRI
Interpretation Checklist
●Carefully evaluate the subtalar ligament structures and the ligaments in the sinus tarsi, giving particular attention to the interosseous ligament and calcaneofibular ligament (elonga-tion, discontinuity, thickening due to scarring).
●Evaluate the articular cartilage in the subtalar joint, the joint capsule, and subchondral bone.
●Edema
●Enhancing reactive tissue
●Synovitis
●Transition to degenerative arthritis
●Evaluation of the tendons of the hindfoot and midfoot
Examination Technique
●Standard protocol: prone position, high-resolution multi-channel coil
●Sequences:
○Coronal and sagittal PD-weighted fat-sat
○Coronal T1-weighted
○Axial T2-weighted
○T1-weighted fat-sat, true axial (angled to the joint plane) and sagittal after IV contrast administration
MRI Findings (▶Fig. 3.59)
●Effusion and synovitis in the subtalar joint
●Signs of overload
●Thickened joint capsule
●Poor delineation, thickening, and possible enhancement of the fibers of the interosseous ligament and calcaneofibular ligament
●Possible wavy contours (like the findings in sinus tarsi syn-drome). See 3.2.10 Subtalar Joint: Sinus Tarsi Syndrome (p. 120)
●Complete tear of the interosseous ligament (extremely rare)
! Note
Instability may be present, even if the ligament structures ap-pear morphologically normal! Subtalar instability is often diffi-cult to recognize and may have equivocal clinical findings. Be alert for subtle changes, especially in the sinus tarsi.
An early sign is a fibrovascular reaction in the sinus tarsi, which is sometimes accompanied by mild irritative synovitis in the subtalar joint. Cartilage involvement is found only in advanced stages. A helpful study is post-exercise MRI (imaging after strenuous treadmill exercise), which will usually demonstrate subtalar effusion and synovitis.
! Note
Sinus tarsi syndrome should not be offered as an interpretation.
It is not a diagnosis in the strict sense, but describes a fibrovas-cular activation chiefly involving the ligaments in the presence of subtalar instability.
Imaging Recommendation
Modality of choice: MRI is useful for evaluating secondary de-generative joint changes and for narrowing the differential diagnosis.
Fig. 3.59 a, b Significant chronic subtalar in-stability in a 40-year-old active soccer player.
Findings include massive fibrovascular tissue in the sinus tarsi, adjacent bone edema in the calcaneus and, to a lesser degree, in the talus with no significant degenerative changes.
a Sagittal T1-weighted fat-sat image after con-trast administration shows marked synovitic en-hancement, most notably in the posterior recess of the subtalar joint. There is no evidence of deep cartilage lesions in the posterior facet of the sub-talar joint.
b Axial T1-weighted fat-sat image after contrast administration shows fibrovascular enhancement along the interosseous ligament with bone marrow edema in the anterior process of the cal-caneus.
Differential Diagnosis
●Primary osteoarthritis of the subtalar joint
●Osteochondral injury in the subtalar joint
●Coalition
●Instability of the ankle joint
Treatment
Conservative●Exercises to improve active stabilization
●Proprioception exercises
●Shoe inserts and ankle brace
Operative
●Plication of the calcaneofibular ligament and lateral joint capsule
●Plus augmentation of the interosseous talocalcaneal ligament, if required
Prognosis, Complications
Secondary degenerative changes may develop in the subtalar joint, and a chronic pain syndrome may develop. To date, few data have been published on the clinical results of surgical sta-bilization of the subtalar joint.