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The human lower limb is structured for locomotion (gait cycle), posture (position of limbs and trunk), trunk stability and weight bearing. Trunk stability enables higher quality vision and hearing, plus more accurate manipulation of objects. Co-ordination of the limbs with the trunk allows for various positions of the upper body despite changes in lower body position.
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The limb is a module. The regions in the lower limb are extensor or flexor. The two groups are analogous to those in the upper limb but situated opposite those in its upper counterpart, due to embryological rotation (lateral in the upper limb and medial in the lower).
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The regions in the upper limb are grouped in the:
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i) Pelvic girdle (gluteal region including hip in floor)
ii) Thigh (3 compartments, femoral triangle, subsartorial canal)
iii) Knee (popliteal fossa)
iv) Leg (anterior, lateral, posterior)
v) Ankle (tarsal tunnel)
vi) Foot (dorsum, sole, toes)
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Assessment of the limb is made easier by its accessibility compared to trunk modules, usually providing clear symptoms and signs.
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Osteoarthritis of the hip develops when the articular cartilage becomes soft and fibrillated ('small fibered'). If subject to high pressure (highest in the weight-bearing area of the femoral head), it becomes worn and thin, producing changes in the underlying bone. The causes of osteoarthritis are:
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i) Abnormal stresses (subluxation, coxa vara, dysplasia)
ii) Abnormal cartilage (infection, rheumatoid, trauma, age)
iii) Abnormal bone (fracture, necrosis, Paget's disease)
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Age-related osteoarthritis is called 'primary', while if there is an underlying cause, it is called 'secondary'.
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Symptoms include pain (often radiating to the knee via a common neurosome), progressive stiffness and limp. Signs are the limp, positive Trendelenburg test, abnormal limb position, muscle wasting, tenderness, high greater trochanter and restricted, painful movements.
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Investigations are usually limited to plain x-ray, except where there is a possible underlying cause.
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Treatment is conservative (weight loss, drugs, aids, manipulation) or operative (when the patient's life is still significantly affected). The decision is made by assessing both hip and patient. Surgical options include osteotomy (used in the young to alter weight-bearing), arthrodesis (rarely performed) or arthroplasty (partial, total, surface). Complications of joint replacement include dislocation, loosening, infection, failure or malalignment.
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