Bones of the Lower Limb

Part 3 · The lower limb

Pelvis to phalanges, the weight-bearing chain, and the palpable landmarks

The design brief, reversed

Figure 1 · How body weight reaches the ground

The upper limb traded stability for reach. The lower limb made the opposite bargain, and every feature of its skeleton follows from it:

• The girdle is fused to the axial skeleton, not slung from it. The sacroiliac joints transmit the entire body weight and move only a few degrees.
• The sockets are deep. The acetabulum encloses more than half the femoral head; the glenoid encloses a third of the humeral head.
• The bones are massive. The femur is the longest, heaviest and strongest bone in the body, withstanding compressive loads of several times body weight in ordinary gait.
• The distal segment is not a manipulator but a platform and a lever: an arched, semi-rigid structure that must be compliant at heel strike and rigid at toe-off.

The price is written in the pattern of pathology:

• the hip does not dislocate without major trauma, but it develops osteoarthritis
• the knee is asked to be both mobile and stable and pays with the highest ligament injury burden in the body
• and the foot, loaded a million times a year, accumulates overuse pathology no upper limb structure sees

Learning outcomes

• Name the bones of the pelvic girdle and free lower limb and describe their principal features.
• Describe the hip bone, the acetabulum and the greater and lesser sciatic foramina.
• Compare the male and female pelvis and describe the pelvic inlet, outlet and diameters.
• Describe the femur in full, including neck-shaft and torsion angles, the trabecular systems and blood supply.
• Describe the patella, tibia and fibula and their weight-bearing contributions.
• Name the tarsal bones and describe the arches of the foot in skeletal terms.
• Explain the weight-bearing chain from sacrum to ground and the alignment angles that govern it.
• Explain the common fracture patterns of the lower limb and their functional consequences.
• Palpate and name at least eleven bony landmarks and state the clinical use of each.

The bones, in outline

Figure 2 · Bones of the lower limb

Compare with the upper limb’s 32: the counts are nearly identical, but the carpus has eight bones in two rows for mobility while the tarsus has seven, arranged in a longitudinal column for load transmission.

The hip bone and pelvis

The three components

Three bones fused at the triradiate cartilage in the acetabulum, which ossifies at 15–17 years — an important radiographic landmark in paediatric hip disease.

Obturator foramen: bounded by the pubic and ischial rami, closed by the obturator membrane except for the obturator canal, which transmits the obturator nerve and vessels.

The acetabulum

• Formed by ilium (~40%), ischium (~40%) and pubis (~20%).
• The articular lunate surface is horseshoe-shaped, deficient inferiorly at the acetabular notch, bridged by the transverse acetabular ligament.
• The central non-articular acetabular fossa contains the pulvinar (fat pad) and the ligamentum teres.
• Deepened by the acetabular labrum, which creates a fluid seal (Chapter 4).
• Normal orientation: anteversion ~15–20° and inclination (abduction) ~40–45°. Deviations produce impingement or instability, and both are measured routinely before hip arthroscopy or replacement.
• Centre-edge (Wiberg) angle: normally >25°; below 20° indicates acetabular dysplasia.

The greater and lesser sciatic foramina

Converted from notches by two ligaments — sacrospinous (to the ischial spine) and sacrotuberous (to the ischial tuberosity) — which also prevent the sacrum tilting backwards under load.

The pudendal nerve’s course — out of the greater foramen, around the ischial spine, back in through the lesser foramen — is the reason it can be blocked at the ischial spine and the reason it is compressed in pudendal neuralgia, an under-recognised cause of pelvic pain that physiotherapists working in pelvic health will meet.

Male and female pelvis

Caldwell–Moloy types: gynaecoid (~50%, the classic female form, most favourable for delivery), android (~20%, male-type), anthropoid (~25%, oval anteroposteriorly), platypelloid (~5%, flattened).

Clinically for physiotherapy, the wider female pelvis produces a greater Q angle at the knee, more pronounced femoral anteversion in some individuals, and a different hip abductor moment arm — factors that contribute (alongside neuromuscular and hormonal ones) to the higher female incidence of patellofemoral pain and ACL injury.

Pelvic diameters worth knowing: at the inlet, the anteroposterior (true conjugate ~11 cm) is the smallest and the transverse (~13 cm) the largest; at the outlet, the reverse — anteroposterior (~12.5 cm) largest and the interspinous transverse (~10.5 cm) smallest. Hence the fetal head engages transversely and delivers anteroposteriorly, rotating in between.

The femur

Figure 3 · The hip joint and the femoral neck

The longest, strongest and heaviest bone in the body — about 26–27% of standing height, which is the basis of stature estimation from a single bone in forensic work.

Proximal end

The angles — and why they matter

Craig’s (Ryder’s) test estimates anteversion clinically: with the patient prone and knee flexed 90°, rotate the hip until the greater trochanter is most laterally prominent; the angle of the tibia from vertical approximates the anteversion.

The combined effect of coxa vara or valga on the abductor moment arm is not academic. A varus neck lengthens the abductor moment arm and reduces the force needed; a valgus neck shortens it and increases both the abductor force required and the joint reaction force — which is one reason valgus hips wear.

Trabecular systems

Two principal systems cross in the femoral neck, mirroring the theoretical stress trajectories (Chapter 2):

• Principal compressive group — from the medial cortex and calcar, arching superiorly into the head
• Principal tensile group — from the lateral cortex, arching medially into the head. Between them lies Ward’s triangle, a bone-poor region that rarefies first in osteoporosis and is a standard DEXA region

Singh index grades osteoporosis radiographically by the progressive loss of these trabecular groups — a useful concept even where DEXA is unavailable.

Shaft and distal end

• The shaft is bowed anteriorly and carries the linea aspera posteriorly, with medial and lateral lips continuing proximally as the pectineal line and gluteal tuberosity and distally as the supracondylar lines enclosing the popliteal surface. The adductor tubercle sits at the end of the medial supracondylar line.
• Distally: medial and lateral condyles (the medial extending further distally, which is why the femoral shaft is oblique yet the knee joint line is horizontal), separated posteriorly by the intercondylar fossa, with the medial and lateral epicondyles for the collateral ligaments and the patellar (trochlear) surface anteriorly.

Blood supply and fracture

The femoral head’s supply is precarious and age-dependent:

Fracture

Location

Consequence

Intracapsular (subcapital, transcervical)

Within the capsule

Disrupts the retinacular vessels → high risk of avascular necrosis and non-union. Usually treated by replacement (hemiarthroplasty or THR) in the elderly

Extracapsular (intertrochanteric, subtrochanteric)

Outside the capsule

Good blood supply; heals well; treated by fixation (DHS or intramedullary nail)

The clinical picture of a displaced neck of femur fracture — the limb shortened, adducted and externally rotated — is produced by the pull of iliopsoas, the short external rotators and the adductors on the distal fragment.

Slipped capital femoral epiphysis (SCFE) — displacement through the hypertrophic zone of the proximal femoral physis in the adolescent (typically 10–16 years, often overweight); presents with hip, thigh or knee pain and an externally rotated limb with obligatory external rotation on hip flexion (Drehmann’s sign). Physiotherapists must know this: an adolescent with knee pain and a limp needs the hip examined and imaged.

The patella

The largest sesamoid, within the quadriceps tendon.

• Base superiorly, apex inferiorly; the articular surface is divided by a vertical ridge into a larger lateral and a smaller medial facet, plus a narrow odd facet on the extreme medial edge.
• Functions: increases the quadriceps moment arm by ~30–50%, thereby improving extension torque; protects the anterior knee; centralises the divergent pull of the quadriceps heads; reduces friction.
• Contact area migrates with knee flexion: distal facets contact near extension, and progressively more proximal facets contact with flexion, with the odd facet contacting only beyond ~120–135°. Patellofemoral joint reaction force rises steeply with flexion under load — roughly 0.5 × body weight in level walking, 3–4 × in stair climbing, and up to 7–8 × in deep squatting. This is why patellofemoral pain is graded by depth of knee flexion under load, not by activity name.
• Bipartite patella (usually a separate superolateral fragment, ~2% of people, often bilateral) is a normal variant mistaken for fracture.
• Patellar dislocation is almost always lateral, and injures the medial patellofemoral ligament (MPFL), the primary passive restraint (contributing ~50–60% of the medial restraining force).

The tibia and fibula

Tibia — the weight-bearing bone

The tibia transmits ~85–90% of the axial load through the leg; the fibula carries only ~10–15% — which is why a fibular shaft can be harvested for grafting with little functional loss, while a tibial shaft cannot.

Fibula — the muscle bone

• Head (with the styloid process for the fibular collateral ligament and biceps femoris), neck — around which the common fibular nerve winds subcutaneously, the commonest site of nerve injury in the lower limb (tight plaster, crossed legs, prolonged squatting, direct blow, proximal fibular fracture) producing foot drop and sensory loss over the dorsum.
• Shaft — extensive muscle attachment.
• Lateral malleolus — extends ~1 cm more distally and lies more posteriorly than the medial malleolus, which is why inversion sprains predominate and why the ankle is more stable against eversion.

Named leg fracture patterns:

The foot

Figure 4 · The foot skeleton and its arches

The tarsus

Mnemonic: Tall Californian Navy Medics In Long Coats — talus, calcaneus, navicular, medial/intermediate/lateral cuneiforms, cuboid.

Metatarsals and phalanges

• First metatarsal — short, thick, carrying the greatest load; bears two sesamoids under its head within the flexor hallucis brevis tendons, which are the load-bearing surface of the hallux and the site of sesamoiditis and turf toe injury.
• Fifth metatarsal base — the tuberosity (styloid) receives fibularis brevis. Three distinct fracture zones: zone 1 (tuberosity avulsion — heals well), zone 2 (Jones fracture, at the metaphyseal–diaphyseal junction — a watershed zone with a high non-union rate), zone 3 (proximal diaphyseal stress fracture). Distinguishing these three matters clinically, because the management differs from a walking boot to surgical fixation.
• Phalanges — as in the hand, but shorter and stouter; the hallux has two.

The arches, in skeletal terms

The passive supports (bone shape and ligaments) do most of the work in quiet standing; the muscles contribute increasingly with load and during propulsion. This is examined constantly and is treated functionally in Chapter 16.

The weight-bearing chain and lower limb alignment

Load descends from the fifth lumbar vertebra to the ground along a defined path:

L5 → sacrum → sacroiliac joints → ilium → acetabulum → femoral head → femoral neck (calcar) → femoral shaft → femoral condyles → tibial plateau → tibial shaft → tibial plafond → talus → calcaneus (posteriorly) and the forefoot (anteriorly) → ground.

Approximate weight distribution in the standing foot: 50% through the calcaneus, 50% through the forefoot, with the medial forefoot (first metatarsal head and sesamoids) carrying roughly twice the load of each lesser metatarsal head.

The alignment angles

The developmental sequence of knee alignment is worth knowing so that normal is not treated as pathology: infants are varus until about 18–24 months, become maximally valgus at about 3–4 years, and settle into the adult mild valgus by about 7 years. Parents frequently present a physiologically bow-legged toddler or knock-kneed four-year-old; recognising the normal trajectory prevents unnecessary intervention, while asymmetry, progression, short stature or pain warrants investigation (Blount disease, rickets, skeletal dysplasia).

Surface anatomy: the palpable landmarks

Leg length measurement:

• True length: ASIS to medial malleolus, with the pelvis square and the limbs in comparable positions
• Apparent length: xiphisternum or umbilicus to medial malleolus. Apparent shortening without true shortening indicates a pelvic obliquity or adduction contracture, not bone loss
• Interpretation requires Galeazzi’s test (to localise shortening to femur or tibia) and segmental measurement (ASIS→knee joint line, joint line→malleolus)

Where students consistently go wrong

• Forgetting the acetabulum’s triradiate cartilage and its fusion at 15–17 years.
• Confusing the capsular attachment on the femoral neck. All of the neck anteriorly, only the medial two-thirds posteriorly.
• Assuming the ligamentum teres supplies the adult femoral head. It is negligible after childhood.
• Not distinguishing intracapsular from extracapsular neck fractures. It determines replacement versus fixation.
• Missing SCFE in an adolescent presenting with knee pain.
• Forgetting that no muscle attaches to the talus.
• Treating all fifth metatarsal base fractures alike. Zone 2 (Jones) is the problem zone.
• Failing to palpate the proximal fibula in an ankle injury. Maisonneuve.
• Treating physiological toddler bowing or four-year-old knock knees as pathology.
• Forgetting the common fibular nerve at the fibular neck when applying a cast or positioning a patient.

Check yourself

15 questions on this chapter. Tap one to see the answer and the reasoning.

Quick review

Further reading

Chapter 13 of 24 · Human Anatomy · Physiotherapist India Next: Chapter 14 — Gluteal Region, Hip and Thigh: the hip as the shoulder’s opposite, the abductor mechanism, and the femoral triangle.

Reviewed by the Physiotherapist India Team. · Human Anatomy contents