Sports Medicine: Just the Facts

62 ANKLE INSTABILITY

Todd R Hockenbury, MD

DEFINITION OF ANKLE SPRAIN

• An ankle sprain is a tear of the ligaments supporting
  the ankle joint.


• Ankle sprains are common. They constitute 25% of all
  sports-related injuries (Mack, 1982).


• Ankle sprains make up 21–53% of basketball injuries
  and 17–29% of all soccer injuries (Ekstrand and
  Tropp, 1990; Garrick and Requa, 1988).

ANATOMY AND PATHOPHYSIOLOGY

ANATOMY

• The ankle, or talocrural, joint comprises the talus,
  tibial plafond, medial malleolus, and lateral malleo-
  lus. The distal tibia and lateral malleolus form a mor-
  tise, in which the talus sits.


• The talus is wider anteriorly than posterior, thus result-
  ing in a tighter fit and more stable articulation between
  the talus and mortise during ankle dorsiflexion.


• Ankle joint stability depends on joint congruency and
  the supporting ligamentous structures.


• The lateral ankle ligaments are the anterior talofibular
  ligament (ATFL), calcaneofibular ligament (CFL),
  and posterior talofibular ligament (PTFL). The
  medial ankle ligaments are the deep and superficial
  portions of the deltoid ligament.


• The relative strengths soft the ankle ligaments from
  weakest to strongest are ATFL, CFL, PTFL, and del-
  toid (Attarian et al, 1985).


• The syndesmotic ligaments connect and stabilize the
  distal fibula to the distal tibia. The syndesmotic liga-
  ments are the anterior tibiofibular ligament, posterior
  tibiofibular ligament, transverse tibiofibular ligament,
  interosseous ligament, and interosseous membrane.


• The subtalar (talocalcaneal) joint lies inferior to the
  ankle joint and is responsible for hind foot inversion and
  eversion. Up to 50% of clinical ankle inversion occurs at
  the subtalar joint (Stephens and Sammarco, 1992).

JOINT MECHANICS

• The ankle is a hinge joint that permits flexion, exten-
  sion, and rotation. The talus externally rotates with

ankle dorsiflexion, and internally rotates during plan-

tar flexion (Sammarco and Hockenbury, 2001).

• The distal fibula externally rotates during ankle dorsiflex-
  ion and moves distally during weight bearing, thus deep-
  ening and stabilizing the ankle mortise (Wang et al,1996).


• The ankle mortise widens with ankle dorsiflexion and
  with weight bearing.


• The ATFL and CFL act synergistically to resist ankle
  inversion forces. The ATFL resists ankle inversion in
  plantar flexion and the CFL resists ankle inversion
  during ankle dorsiflexion.


• The CFL spans both the lateral ankle joint and lateral
  subtalar joint, thus contributing to both ankle and sub-
  talar joint stability (Stephens and Sammarco, 1992).


• The PTFL limits posterior talar displacement and
  external rotation (Sarrafian, 1993).


• The deltoid ligament resists ankle eversion, external
  rotation, and planter flexion. In cases of distal fibular
  fracture and mortise instability, it restrains lateral talar
  translation (Harper, 1987).

INJURY MECHANISMS

• The most commonly sprained ankle ligament is the
  ATFL, followed by the CFL. An isolated CFL tear is
  rare. A CFL tear is almost always preceded by a tear
  of the ATFL.


• Lateral ankle sprains occur as a result of landing on a
  plantar flexed and inverted foot. These injuries occur
  while running on uneven terrain, stepping in a hole,
  stepping on another athlete’s foot during play, or land-
  ing from a jump in an unbalanced position.
  •A syndesmotic ankle sprain or high ankle sprain
  occurs as a result of forced external rotation of the
  foot or during internal rotation of the tibia on a fixed
  planted foot. A common mechanism is a direct blow
  to the back of the ankle while the patient is lying
  prone with the foot externally rotated (Wuest,
  1997).


• Isolated deltoid ligament sprains are rare and are usu-
  ally accompanied by a lateral malleolar fracture
  and/or syndesmotic injury. The deltoid ligament is
  injured through a mechanism or external rotation or
  eversion.

LIGAMENT PATHOPHYSIOLOGY

• Ligamentous injuries undergo a series of phases
  during the healing process: hemorrhage and inflam-
  mation, fibroblastic proliferation, collagen protein
  formation, and collagen maturation (Akeson et al,
  1984; Chvapil, 1967).

366 SECTION 4 • MUSCULOSKELETAL PROBLEMS IN THE ATHLETE