Lower extremity anatomy
Hip region
The hip region comprises two bony structures - the acetabulum and femur.
The angle of inclination (between the femoral neck and shaft) is normally 115-125 degrees. A larger angle is coxa valga; a smaller angle is coxa vara.
Normal femoral anteversion (the femoral neck angled forward relative to the femoral condyles) is about 10-15 degrees. An angle greater than about 15 degrees is excessive anteversion (associated with toe-in), and an angle less than about 10 degrees is retroversion (associated with toe-out).
The primary movements of the hip are:
- Hip flexion/extension
- Hip external rotation/internal rotation
- Hip abduction/adduction
The hip joint is a stable synovial joint due to the bony anatomy and strength of ligaments, capsule, and labrum.
- Capsule encloses the entire joint
- Labrum
- Attached to the acetabulum and serves to deepen the structure to allow for greater articulation
- Ligaments
- Iliofemoral
- Two bands that originate at the anterior inferior iliac spine (AIIS), run medially to the distal intertrochanteric line, and laterally to the proximal aspect of the intertrochanteric line
- Both bands tighten with extension and external rotation; the superior band tightens with adduction; the inferior band tightens with abduction
- Pubofemoral
- Band tightens with extension, external rotation, and abduction
- Ischiofemoral
- Band tightens with medial rotation, abduction, and extension
- Iliofemoral
Other pertinent structures of the hip joint are:
- Inguinal ligament - forms a tunnel for vital arteries, veins, and nerves in the lower extremity
- Bursae - fluid-filled sacs that provide cushioning and friction reduction between tendons, joints, muscles, and bone; present at the hip, knee, and ankle/foot
Knee region
The knee region is composed of four bones: the femur, tibia, fibula, and patella.
These bony structures then form three joints: tibiofemoral, patellofemoral, and proximal tibiofibular joint.
The primary movements of the knee that are aided by the three joints of the knee are:
- Knee flexion/extension
- Knee (tibial) internal/external rotation - available only when the knee is flexed; in the last degrees of extension the tibia externally rotates on the femur (the femur internally rotates on the fixed tibia in weight bearing) to lock the knee, called the screw-home mechanism
Other pertinent structures of the knee joint are:
- Capsule
- Tibiofemoral capsule covers the distal femur and proximal tibia - posteriorly divided into medial and lateral sections, anterior cut-out for the patella
- Ligaments
- Tibiofemoral and patellofemoral joints
- Medial collateral ligament
- Tightened in extension; slackened in flexion
- Resists valgus forces and external rotation of the tibia
- Lateral collateral ligament
- Tightened in extension; slackened in flexion
- Prevents external rotation and provides stability against varus forces
- Anterior cruciate ligament
- Prevents anterior displacement of the tibia on the femur and provides rotational stability
- Posterior cruciate ligament
- Prevents posterior displacement of the tibia on the femur
- Medial collateral ligament
- Tibiofemoral and patellofemoral joints
- Menisci
- Function
- Deepens the tibial fossa, increasing congruency between the tibia and femur
- Reduces friction between joints during movement
- Improves weight distribution
- Provides shock absorption and lubrication to the knee
- Provide stability to the tibiofemoral joint
- Lateral meniscus
- Outer side of joint
- Attached to the popliteus and the joint capsule but not to the lateral collateral ligament, so it is more mobile
- Helps restrain tibial rotation
- Medial meniscus
- Inner side of joint
- Attached to the medial collateral ligament and joint capsule, so it is less mobile and more easily trapped between the femur and tibia
- Secondary restraint to anterior tibial translation, most important when the ACL is torn
- Function
Foot and ankle region
The ankle/foot joint is composed of five major articulations: the talocrural, subtalar, midtarsal (transverse tarsal), metatarsophalangeal, and interphalangeal joints.
The primary movements of the foot/ankle joint are:
- Talocrural joint: plantarflexion/dorsiflexion
- Subtalar and midtarsal joints: inversion/eversion (components of supination/pronation)
- Metatarsophalangeal and interphalangeal joints: toe flexion/extension
Other pertinent structures of the ankle/foot joint are:
- Capsule
- Provides stability to the joints of the ankle/foot
- Ligaments
- Talocrural joint
- The medial collateral ligament (Deltoid ligament) has deep and superficial fibers
- Lateral collateral ligament: Anterior talofibular, calcaneofibular, posterior talofibular
- Syndesmosis tibiofibular joint (high ankle ligaments)
- Anterior inferior tibiofibular ligament
- Posterior inferior tibiofibular ligament
- Metatarsophalangeal joint
- Plantar ligaments
- Collateral ligaments
- Interphalangeal joint
- Plantar ligament
- Collateral ligament
- Talocrural joint
- Plantar fascia
- Runs from the medial calcaneal tubercle to the proximal phalanges
- Toe (MTP) extension during push-off tightens the fascia (the windlass mechanism), raising the arch and supinating the foot into a rigid lever
Lower extremity range of motion normals
As the PTA, you’ll measure these ranges with a goniometer, compare them to the normals below, and record strength with manual muscle testing (MMT) grades and function with standardized outcome measures such as the lower extremity functional scale (LEFS), Berg balance scale, and timed up and go (TUG) test. A value outside these normals, a side-to-side difference, or a finding such as increased valgus laxity after an MCL sprain is something you document precisely and report to the supervising PT - not something you interpret or use to adjust the plan of care. The ligament functions described above also show which structure is stressed during a valgus, varus, or anterior/posterior drawer test, covered in the knee special tests chapter.
- Hip flexion/extension goniometry: axis at the greater trochanter, stationary arm along the trunk, moving arm toward the lateral femoral condyle
- Knee flexion/extension goniometry: axis at the lateral epicondyle, stationary arm toward the greater trochanter, moving arm toward the lateral malleolus
- Ankle dorsiflexion/plantarflexion goniometry: axis at the lateral malleolus, stationary arm along the fibula, moving arm parallel to the fifth metatarsal