Lower limb bones and fractures
Lower limb bones, fractures, bone tumours, posture and gait for FCPS
Lower limb bones, common fractures and their complications, children's hip disorders, bone tumours around the knee, posture and gait for FCPS Part 1. Links each fracture to its blood supply and each abnormal gait to the weak muscle, nerve or brain region behind it.
Hip bone and femur
- The hip bone forms from the ilium, ischium and pubis, which meet at the acetabulum in a Y-shaped (triradiate) cartilage and fuse at about 15–17 years.
- Femoral neck–shaft angle about 125° (less is coxa vara, more is coxa valga); anteversion about 10–15° in adults.
- Greater trochanter: gluteus medius and minimus, piriformis, obturator internus and gemelli, obturator externus (trochanteric fossa). Lesser trochanter: iliopsoas. Linea aspera: adductors, vasti, short head of biceps.
- The distal femoral epiphysis is the only epiphysis usually present at birth, a sign of a full-term fetus.
Fractures of the femur and their blood supply
| Fracture | Typical patient | Key features | Usual treatment |
|---|---|---|---|
| Intracapsular neck (subcapital) | Elderly osteoporotic woman, minor fall | Leg shortened and externally rotated; retinacular vessels torn, so avascular necrosis and non-union | Undisplaced: screws. Displaced: hemiarthroplasty or total hip replacement |
| Extracapsular (intertrochanteric) | Elderly | Head supply intact; heals well | Dynamic hip screw or nail |
| Femoral shaft | High-energy trauma in the young | Blood loss 1–1.5 litres | Intramedullary nail |
- In a neck fracture the limb shortens because muscles crossing the fracture contract, and rotates outwards mainly through iliopsoas on the lesser trochanter.
- Most neck of femur fractures in older women reflect postmenopausal osteoporosis, worsened by low calcium and vitamin D intake, inactivity and smoking.
- Shock after a femoral fracture is hypovolaemic: blood collects in the thigh, and multiple fractures add up quickly.
| Complication | Timing | Clues |
|---|---|---|
| Fat embolism syndrome | 24–72 hours after long-bone (femur) fracture | Hypoxia and breathlessness, confusion, petechiae in the axillae and conjunctivae, fat globules in urine |
| Pulmonary thromboembolism | Usually from the end of the first week | Sudden breathlessness, pleuritic pain, collapse; an infarct at autopsy points to a thromboembolus |
Tibia, fibula and foot fractures
- Tibial shaft is the commonest long-bone fracture; its anteromedial surface is subcutaneous, so fractures are often open and infected.
- The junction of the middle and lower thirds of the tibia heals slowly: the nutrient artery enters the upper third and runs downwards, the lower third has little muscle cover and depends on a thin periosteal supply. Delayed union (still a fracture line and little callus at six months) is typical even without smoking or infection.
- Tibial plateau: lateral plateau from a valgus force (car bumper). Fibular neck: common peroneal nerve injury and foot drop.
- Calcaneus: fall from height; look for thoracolumbar spine fractures. Talar neck: avascular necrosis of the body.
- March (stress) fracture: neck of the second metatarsal in soldiers and runners.
- Base of fifth metatarsal: avulsion by peroneus brevis in an inversion injury; the Jones fracture, slightly more distal, heals poorly.
Children's hip and knee disorders
| Condition | Typical patient | Features |
|---|---|---|
| Developmental dysplasia of the hip | Newborn girl, breech, first-born, family history | Screen with Ortolani (reduces a dislocated hip) and Barlow (dislocates an unstable hip); ultrasound in infancy |
| Perthes disease | Boy aged 4–8 | Avascular necrosis of the femoral head; limp, hip or knee pain |
| Slipped upper femoral epiphysis | Obese adolescent boy | Hip or knee pain; leg rotates outwards as the hip is flexed; risk of avascular necrosis |
| Osgood–Schlatter disease | Active child, 10–15 years | Tender lump over the tibial tuberosity (traction apophysitis) |
Children with hip disease often present with knee pain because the obturator and femoral nerves supply both joints.
Bone tumours around the knee
The distal femur and proximal tibia are the commonest sites for many bone tumours because their growth plates are the most active.
| Tumour | Age | Site and X-ray | Key fact |
|---|---|---|---|
| Osteochondroma | Under 25 | Metaphysis; bony outgrowth with a cartilage cap, pointing away from the joint | Commonest benign bone tumour |
| Osteoid osteoma | Young adults | Small lucent nidus with dense sclerosis, often tibia or femur | Night pain relieved by NSAIDs |
| Giant cell tumour | 20–40, after skeletal maturity | Epiphysis, eccentric lytic "soap bubble" lesion reaching the joint surface | Multinucleated giant cells in a stromal background; locally aggressive |
| Chondroblastoma | Before skeletal maturity | Epiphysis | An epiphyseal lesion in a child is more likely this |
| Osteosarcoma | Adolescents | Metaphysis; sunburst spicules, Codman triangle | Commonest primary malignant bone tumour |
| Ewing sarcoma | Children | Diaphysis; onion-skin periosteal reaction | Small round blue cells, t(11;22) |
Posture
- In quiet standing the line of gravity passes behind the hip, in front of the knee and in front of the ankle. Hyperextension of the hip is resisted by the iliofemoral ligament, the knee is locked by screw-home rotation, and soleus contracts almost continuously to stop forward sway at the ankle.
- Posture is maintained by antigravity muscles kept in tone by the stretch reflex (muscle spindles and the gamma loop), under the control of vestibulospinal and reticulospinal pathways, with input from the eyes, labyrinths and joint receptors.
Gait
- Stance phase (about 60%): heel strike, foot flat, midstance, heel off, toe off. Swing phase (about 40%): acceleration, midswing, deceleration.
- During single-leg stance the hip abductors (gluteus medius and minimus) of the stance leg keep the pelvis level.
| Gait | Cause |
|---|---|
| Trendelenburg (waddling) | Weak gluteus medius and minimus (superior gluteal nerve, for example a deep buttock wound), DDH, coxa vara; standing on the right leg, the left pelvis sinks if the right abductors are weak |
| High-stepping (foot drop) | Common peroneal palsy, L5 root, peripheral neuropathy |
| Gluteus maximus lurch | Inferior gluteal nerve; trunk thrown back at heel strike |
| Antalgic | Pain; short stance phase on the painful side |
| Scissoring | Spastic diplegia (adductor spasticity) |
| Shuffling (festinant) | Parkinson disease, loss of dopaminergic neurons in the substantia nigra: resting tremor, stooped posture, expressionless face |
| Broad-based ataxic | Cerebellar disease: sways with eyes open and closed, dysdiadochokinesia |
| Stamping (sensory ataxia) | Dorsal column loss: Romberg positive, worse with eyes closed |
Remember The pelvis sinks on the side opposite the weak abductors, the side whose foot is off the ground.
Exam trap A displaced intracapsular neck fracture in the elderly is replaced, not fixed, because the head's blood supply is lost.
Exam trap An epiphyseal "soap bubble" lesion after skeletal maturity is a giant cell tumour; before maturity think chondroblastoma.
How FCPS asks about this
- Displaced intracapsular neck of femur fracture in an 80-year-old: hemiarthroplasty or total hip replacement.
- Breathlessness, confusion and petechiae 2–3 days after a femoral fracture: fat embolism; shock earlier is hypovolaemic.
- Delayed union at the junction of middle and lower thirds of the tibia: poor blood supply with little muscle cover.
- Commonest benign bone tumour: osteochondroma; epiphyseal soap bubble in an adult is giant cell tumour.
- Standing on the right leg, the left pelvis sinks: right superior gluteal nerve or right gluteus medius and minimus.
- Resting tremor, stooped posture and shuffling gait: substantia nigra (Parkinson disease).
- Line of gravity in standing: behind the hip, in front of the knee and ankle; soleus prevents forward sway.
Test yourself on this topic
5 of the 11 questions in our bank on this topic. Choose an answer to see why every option is right or wrong.
A builder falls 4 m onto his heels and fractures his calcaneus. Which of the following associated injuries should be specifically sought?
Answer: Thoracolumbar vertebral fracture
A fall from height onto the heels sends a large axial load through the calcaneus, up the lower limbs and pelvis to the spine. About one in ten such patients has a compression or burst fracture of the thoracolumbar spine, which can be missed when attention is on the painful heel. Both heels should also be X-rayed. Clavicle and scaphoid fractures follow falls on the shoulder or outstretched hand, and posterior shoulder dislocation is typical of seizures or electric shock.
Fall onto the heels
- Axial load through the heel
- Look for thoracolumbar fracture
- X-ray both heels
- Check the spine in every calcaneal fracture
Remember Broken heel: examine the back.
Exam trap Pain from the heel can distract from a spinal fracture, so the back must be examined and imaged.
Why the other options are wrong
- Fracture of the clavicle Follows a fall on the shoulder.
- Fracture of the scaphoid Follows a fall on the outstretched hand.
- Posterior dislocation of the shoulder Typical of seizures or electrocution.
- Fracture of the mandible Follows a direct blow to the jaw.
Surface EMG is recorded from the leg muscles of a healthy man standing quietly at ease. The line of gravity falls just in front of his ankle joints. Which of the following muscles shows continuous low-level activity?
Answer: Soleus
In relaxed standing, the line of gravity passes slightly behind the hip, in front of the knee and in front of the ankle. Because it lies in front of the ankle, the body tends to sway forwards, and soleus, a slow-twitch postural muscle, contracts continuously to pull the leg back on the foot. The knee is held straight by ligaments with little quadriceps activity, and the hip is braced by the iliofemoral ligament. Tibialis anterior is largely silent unless the body sways backwards.
Quiet standing
- Gravity line in front of ankle
- Soleus works all the time
- Knee: locked by ligaments
- Hip: iliofemoral ligament braces it
Remember Standing still is a soleus job.
Exam trap Gastrocnemius also plantarflexes, but soleus, rich in slow fibres, is the main postural muscle.
Why the other options are wrong
- Tibialis anterior Active only when the body sways backwards.
- Quadriceps femoris The knee is locked passively; little activity is needed.
- Gluteus maximus Silent in quiet standing; works in climbing and rising.
- Iliopsoas The iliofemoral ligament resists hip extension instead.
An 80-year-old woman falls and cannot bear weight. Her leg is shortened and externally rotated. X-ray shows a displaced intracapsular femoral neck fracture. What is the usual treatment?
Answer: Hemiarthroplasty or total hip replacement
Hip fractures in the elderly typically follow a fall on osteoporotic bone. The leg is shortened (muscle pull across the fracture) and externally rotated (iliopsoas acting on the lesser trochanter and gravity). Intracapsular fractures (subcapital, transcervical) disrupt the retinacular vessels; if displaced (Garden III–IV), the head is replaced—hemiarthroplasty, or total hip replacement in fit, mobile patients. Undisplaced intracapsular fractures (Garden I–II) can be fixed with cannulated screws. Extracapsular (intertrochanteric) fractures are fixed with a dynamic hip screw; subtrochanteric fractures with an intramedullary nail. Early surgery (within 36 hours) and mobilisation reduce mortality.
Hip fracture management
- Leg shortened and externally rotated
- Intracapsular displaced (Garden III–IV): hemiarthroplasty / THR
- Intracapsular undisplaced: screws
- Intertrochanteric: dynamic hip screw
- Surgery within 36 hours
Remember Inside and displaced: replace; outside: fix.
Why the other options are wrong
- Dynamic hip screw fixation For extracapsular intertrochanteric fractures.
- Skin traction for 12 weeks Causes complications in the elderly.
- Cast immobilisation Not used.
- Intramedullary nail of the femoral shaft For shaft or subtrochanteric fractures.
A 30-year-old has knee pain. X-ray shows an eccentric lytic 'soap bubble' lesion in the distal femoral epiphysis reaching the joint surface. What is the most likely tumour?
Answer: Giant cell tumour
Giant cell tumour of bone occurs at 20–40 years after the growth plate closes, in the epiphysis of long bones (around the knee, distal radius). It is lytic, eccentric and expansile ('soap bubble'), extending to subchondral bone. Histology shows osteoclast-like giant cells. It is locally aggressive and recurs after curettage; rarely it metastasises to the lungs. Denosumab (RANKL inhibitor) is used in some cases.
Giant cell tumour
- Age 20–40
- Epiphysis (after fusion)
- Soap bubble, eccentric
- Osteoclast-like giant cells
- Locally aggressive
Remember Grown-up epiphysis with soap bubbles.
Exam trap Before skeletal maturity, an epiphyseal lesion is more likely a chondroblastoma.
Why the other options are wrong
- Osteosarcoma Metaphysis; sunburst, Codman triangle; adolescents.
- Ewing sarcoma Diaphysis; onion skin; children.
- Osteochondroma Bony outgrowth from the metaphysis.
- Simple bone cyst Metaphysis in children; fallen fragment sign.
A 28-year-old motorcyclist has a displaced fracture of the neck of the talus after violent dorsiflexion of the foot against the footrest. Which of the following complications is most directly explained by the pattern of blood supply to this bone?
Answer: Avascular necrosis of the talar body
Most of the talus is covered by articular cartilage, so vessels enter mainly through the neck and the sinus tarsi and tarsal canal, then run backwards into the body. A displaced neck fracture cuts these vessels, leaving the body without supply, so it may undergo avascular necrosis, seen as increased density on X-ray. The head keeps its supply from the neck vessels and talonavicular region. This retrograde pattern is similar to the scaphoid and the femoral head.
Talus blood supply
- Mostly covered in cartilage
- Vessels enter at the neck and run back
- Neck fracture: body loses supply
- Retrograde like scaphoid and femoral head
Remember Talar neck broken: watch the body die.
Exam trap It is the proximal part (body), not the distal head, that loses its blood supply.
Why the other options are wrong
- Avascular necrosis of the talar head The head keeps its supply from the neck region.
- Non-union of the calcaneus The calcaneus is not fractured here.
- Compartment syndrome of the leg A leg complication, not related to talar blood supply.
- Fat embolism syndrome Related to long bone fractures, not talar vessels.
Where this sits in the CPSP syllabus
- Paper 1: Lower limb, Lower limb bones and fractures; posture and gait
- Surgery & Allied, Paper 2: Lower limb, Lower limb bones and fractures; posture and gait