Anatomy chapters
Lower limb injuries and deformities
Connect common hip, knee, ankle and foot injuries to the vessels, nerves, ligaments and tendons they threaten.
- Femoral-neck fractures threaten head perfusion; posterior hip dislocation threatens sciatic.
- Knee dislocation threatens popliteal artery; fibular-neck trauma threatens common fibular nerve.
- Define the lost movement, direction of displacement and damaged structure.
On this page
Overview
Lower-limb injuries threaten both weight-bearing structures and neighbouring neurovascular bundles. A recognisable deformity is useful, but the functional loss and the structures lying beside the injury explain its importance.
Work from the injured level to its anatomical neighbours. Then examine perfusion, sensation and individual movements rather than assuming that a fracture name already describes all associated damage.
Hip fractures and dislocations
| Pattern | Anatomical failure | Structure at risk | Expected consequence |
|---|---|---|---|
| Intracapsular femoral-neck fracture | Fracture within capsular attachment | Retinacular vessels along neck | Head ischaemia, avascular necrosis and non-union risk |
| Intertrochanteric fracture | Extracapsular fracture between trochanters | Bleeding from cancellous bone and surrounding vessels | Shortened externally rotated limb; head supply generally better preserved |
| Posterior hip dislocation | Head displaced behind acetabulum | Sciatic nerve and head circulation | Flexed, adducted, internally rotated posture |
| Anterior hip dislocation | Head displaced anteriorly | Anterior neurovascular structures | Abducted, externally rotated posture, varying with subtype |
| Femoral shaft fracture | Major weight-bearing shaft disrupted | Deep thigh vessels and soft tissue | Substantial concealed blood loss and deformity |
The adult head relies mainly on retinacular vessels from the circumflex system, especially medial circumflex femoral. The artery within the head ligament does not reliably replace this supply after displacement.
Snell highlights posterior acetabular-rim and possible femoral-head fractures with posterior fracture-dislocation. An apparently simple joint displacement may therefore include an articular fracture.
Intracapsular neck fracture threatens retinacular perfusion; posterior hip dislocation also requires sciatic assessment.
Knee ligament and extensor injuries
| Pattern | Mechanism/anatomy | Lost restraint or action | Useful sign |
|---|---|---|---|
| ACL injury | Pivoting or hyperextension loads ligament | Restraint to anterior tibial translation | Increased Lachman/anterior drawer movement |
| PCL injury | Posterior force on proximal tibia with knee flexed | Restraint to posterior tibial translation | Posterior sag or drawer |
| MCL injury | Valgus force opens medial joint | Medial stability | Pain or laxity under valgus stress |
| LCL injury | Varus force opens lateral joint | Lateral stability | Varus laxity; assess nearby common fibular nerve |
| Meniscal tear | Twisting loaded joint traps fibrocartilage | Congruence and smooth motion | Joint-line pain, catching or mechanical locking |
| Patellar fracture or tendon rupture | Extensor chain interrupted | Active knee extension | Failure of straight-leg raise when disruption is complete |
The classical “unhappy triad” names ACL, MCL and medial meniscus. The medial meniscus is tethered to MCL, as Snell emphasises; actual combined sports injuries can involve other patterns, so the mnemonic is not a universal injury rule.
The patella sits within quadriceps tendon and connects to the tibial tuberosity through the patellar ligament. Disruption above, through or below it can interrupt the same functional chain.
Intact retinacula may preserve some extension despite a patellar fracture.
Knee dislocation and fibular-neck injury
The popliteal artery lies close to the posterior knee and is tethered across the region. Major displacement can damage its wall even if the joint has already reduced before examination.
The common fibular nerve is exposed as it winds around the fibular neck. A fracture, lateral knee injury, cast pressure or prolonged compression can impair both its deep and superficial branches.
| Name | Origin/roots | Supply/action | Clinical note |
|---|---|---|---|
| Sciatic | L4–S3 | Hamstrings and distal tibial/fibular pathways | Posterior hip injuries can cause combined distal deficits |
| Common fibular | L4–S2 | Dorsiflexion/toe extension and eversion through its branches | Fibular-neck palsy causes foot drop with relatively preserved inversion |
| Tibial | L4–S3 | Plantarflexion, long toe flexors and sole muscles | Weak inversion/plantarflexion suggests a broader lesion than fibular palsy |
| Saphenous | Femoral, mainly L3–L4 | Medial leg/foot sensation | May remain intact after sciatic injury |
Foot drop does not identify a single lesion level. Test inversion, eversion, plantarflexion and proximal muscles.
Leg and ankle injuries
The tibial shaft has a subcutaneous anterior and medial surface, so displaced fractures may have important skin and soft-tissue injury. Bleeding and swelling can also raise pressure inside the closed leg compartments.
An inversion sprain, particularly in plantarflexion, commonly loads anterior talofibular ligament first. More severe injury can involve calcaneofibular and other lateral restraints. The stronger medial deltoid complex resists eversion.
Eversion or rotational ankle trauma can fracture a malleolus or disrupt the syndesmosis. A high fibular fracture associated with ankle syndesmotic injury is a Maisonneuve pattern: the painful ankle should not prevent examination of the proximal fibula.
The term Pott's fracture has been used for ankle fracture patterns, but a precise description of malleolar fractures, talar displacement and syndesmotic integrity is more informative than the eponym alone.
Knee displacement threatens popliteal artery; fibular-neck injury threatens common fibular nerve.
Foot fractures and tendon disruption
| Pattern | Anatomical issue | Clinical implication |
|---|---|---|
| Talar-neck fracture | Disruption of vessels reaching talar body | Avascular necrosis risk |
| Calcaneal fracture | Axial load through hindfoot | Loss of heel height/shape; consider associated axial injuries |
| Fifth metatarsal tuberosity avulsion | Traction near fibularis brevis attachment | Lateral foot pain after inversion |
| Proximal fifth metatarsal junction fracture | Different location from tuberosity avulsion | Healing behaviour differs; do not call every base fracture the same injury |
| Lisfranc injury | Tarsometatarsal complex disrupted | Midfoot instability; second metatarsal base is a key alignment landmark |
| Achilles rupture | Calf tendon loses continuity | Weak push-off and impaired heel rise |
The long plantar and spring ligaments, plantar aponeurosis and muscle tendons normally distribute load across the arches. An injury affecting one support can change loading elsewhere rather than producing pain only at the damaged attachment.
Alignment and foot deformities
Coxa vara means a reduced femoral neck–shaft angle; coxa valga means an increased angle. Genu varum is bow-leg alignment; genu valgum is knock-knee alignment. Describe these at the relevant joint rather than applying one term to the entire limb.
Pes planus is a lowered medial longitudinal arch. It may be flexible or rigid; posterior tibial tendon dysfunction is an important acquired cause. Pes cavus describes an abnormally high arch and may accompany muscle imbalance.
Congenital talipes equinovarus combines hindfoot varus, equinus, forefoot adduction and cavus. Equinus means plantarflexed ankle posture; it is not a synonym for the whole deformity.
Clinical relevance
Compartment syndrome
How it happens: swelling or bleeding raises pressure inside a closed leg compartment and compromises muscle and nerve perfusion.
What you see: severe pain, especially on passive stretch of involved muscles, followed by sensory or motor change. Pulses can remain present because large-artery flow may persist while tissue perfusion fails.
Achilles tendon rupture
How it happens: the tendon transmitting gastrocnemius and soleus force ruptures.
What you see: weak push-off, impaired heel rise and reduced plantarflexion on calf squeeze. Other plantarflexors may still produce some active movement.
Posterior tibial tendon dysfunction
How it happens: the tendon loses its dynamic support of the medial arch and hindfoot.
What you see: acquired arch flattening, heel valgus and difficulty with single-leg heel rise. Deformity may progress from flexible to more fixed.
Popliteal arterial injury
How it happens: knee trauma stretches or tears the arterial wall, possibly producing an intimal flap and later thrombosis.
What you see: distal perfusion may deteriorate after an initially reassuring examination. A palpable early pulse does not exclude the injury.
Match fracture or dislocation level to its endangered artery, nerve or tendon mechanism. Separate intracapsular from extracapsular hip fractures, and common fibular palsy from a higher sciatic lesion. Describe deformity by joint, direction and lost function before using its eponym.
Quick revision
- Intracapsular neck fractures threaten femoral-head blood supply.
- Posterior hip dislocation classically internally rotates and adducts the limb.
- ACL limits anterior and PCL posterior tibial translation.
- Knee dislocation threatens popliteal artery.
- Fibular-neck injury can cause common fibular foot drop.
- ATFL is commonly injured in plantarflexed inversion.
Sources: Snell's Clinical Anatomy by Regions, supplied Lower Limb chapter, for fracture-neurovascular relationships and regional anatomy; supplementary standard orthopaedic injury definitions and clinical examination conventions. UHS PGET Paper I MBBS TOS. Picture links are visual study resources. Original wording and tables.
FAQ
Why can some plantarflexion remain after Achilles rupture?
Tibialis posterior, long toe flexors and fibularis muscles can still plantarflex, although the powerful calf contribution and push-off are impaired.
What distinguishes a common fibular lesion from complete sciatic injury?
Relative preservation of tibial functions, especially inversion through tibialis posterior and plantarflexion, favours an isolated common fibular lesion.
Is every fifth metatarsal base fracture a Jones fracture?
No. Tuberosity avulsion and the more distal metaphyseal–diaphyseal junction fracture are distinct patterns.
Does a normal pulse exclude compartment syndrome?
No. Compartment tissue perfusion can fail while flow through the major artery remains detectable.