Anatomy
Lower Limb
Which of the following synovial joint types best describes the ankle joint:
Answer:
The ankle joint is a hinge type synovial joint formed between the distal ends of the tibia and fibula, and the superior part of the talus.Ankle Joint
Anatomy / Lower Limb / Ankle and Foot Joints
Last Updated: 10th April 2019
Table: Anatomical Overview of the Ankle Joint
| Joint | Ankle |
|---|---|
| Type | Synovial hinge joint |
| Articulations | Talus with the inferior tibia and talus with the medial malleolus of the tibia and the lateral malleolus of the fibula |
| Stabilising factors | Shape of talus bone and articulations with malleoli; Medial and lateral collateral ligaments |
| Movements | Flexion and extension |
Joint articulations
The ankle joint is a hinge type synovial joint formed between the distal ends of the tibia and fibula, and the superior part of the talus.
The tibia and fibula are bound together by strong tibiofibular ligaments forming a deep bracket-shaped socket, which the talus bone then fits into. The talus bone articulates with the tibia in two places; the inferior surface of the tibia forms the roof of the socket and its medial malleolus articulates with the medial surface of the talus bone. The lateral malleolus of the fibula articulates with the lateral surface of the talus bone. The articulation of the talus with the inferior tibia forms the weightbearing surface and the articulations of the talus with the malleoli act to stabilise the joint.
The articular surface of the talus is much wider anteriorly than it is posteriorly, therefore the bone fits more tightly in the socket when the foot is dorsiflexed (and the wider surface of the talus moves into the ankle joint), making the joint more stable in dorsiflexion. Conversely the ankle joint is weakest during plantarflexion (when the narrower part of the talus is in the joint) and it is in this position that the majority of ankle injuries occur - usually as a result of the sudden inversion of the foot.
Ligaments
The ankle joint is supported on each side by the medial (deltoid) and lateral collateral ligaments.
The large strong deltoid ligament is triangular in shape, attached proximally to the medial malleolus at its apex and its broad base attached distally to a line that extends from the tuberosity of the navicular bone anteriorly to the medial tubercle of the talus posteriorly. The medial ligament is subdivided into four parts: the tibionavicular part, the tibiocalcaneal part, the posterior tibiotalar part and the anterior tibiotalar part. It acts to prevent overeversion of the foot and helps maintain the medial longitudinal arch.
The weaker lateral ligament is actually composed of three separate ligaments all originating from the lateral malleolus; the anterior talofibular ligament (attaching to the anterior talus), the posterior talofibular ligament (attaching to the posterior talus) and the calcaneofibular ligament (attaching to the calcaneus). It resists inversion of the foot and is frequently injured in ankle sprain inversion injuries. The most commonly affected ligament is the anterior talofibular ligament followed by the calcaneofibular ligament and then the posterior talofibular ligament.
Ankle Joint. (Image by OpenStax College [CC BY 3.0 , via Wikimedia Commons)
Joint movements
The ankle joint allows dorsiflexion and plantarflexion of the foot.
Table: Movements of the Ankle Joint
| Movement | Main Muscles Involved | Main Nerves Involved |
|---|---|---|
| Dorsiflexion | Tibialis anterior, Extensor hallucis longus, Extensor digitorum longus, Fibularis tertius | Deep fibular nerve |
| Plantarflexion | Gastrocnemius, Plantaris, Soleus, Flexor hallucis longus, Tibialis posterior, Fibularis longus | Tibial nerve, Superficial fibular nerve |
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
