Learn: Lumbar Spine, Hip, Knee and Foot Biomechanics: Gait and Assessment

Lumbar facet joint alignment

Aligned primarily in the sagittal plane with an interlocking mechanism that allows only a few degrees of rotation.

Lumbar facet joint rotation

Normal rotation produces impaction of the facets, preventing more than 3% strain to the annulus.

Lumbar facet joint resistance

Provides significant resistance to shear stress, especially when the spine is in a lordotic posture.

Lumbar facet joint planes

Oriented at a 90-degree angle.

Fetal and infant lumbar zygapophyseal joints

Coronally oriented joints that later develop into curved or biplanar joints.

Adult lumbar facet joints

The anterior third has a coronal component, and the posterior two-thirds has a sagittal component.

Lumbar meniscoids

Linguiform and filiform fibroadipose synovial folds continuous with periarticular tissues.

Posterior longitudinal ligament (PLL) in the lumbar spine

Narrows as it courses down, covering only about 50% of the central portion of the lower lumbar discs.

Weakest area of the lumbar annulus

The posterolateral aspect, which is the most likely spot for a disc herniation.

Lumbar interpedicular zone space

Contains an average of 0.4 to 0.8 mm of space around each nerve root and dorsal root ganglion.

Lumbar capsular ligaments

Provide nearly 40% of the joint's resistance during full flexion.

Creep in the lumbar spine

Sustained lumbar flexion causes progressive deformation faster than repetitive flexion, potentially stretching the facet capsule and causing pain.

Load transmission in a healthy lumbar disc

The highest effective stresses occur in the center of the vertebral endplate.

Load transmission in a degenerated lumbar disc

Stresses shift to the lateral aspects of the endplates, the cortical wall, and the vertebral body rims.

Prone instability test

Patient lies prone with feet on the floor while the doctor applies posteroanterior (P-A) pressure to identify abnormal segmental translation.

Center of mass

In an upright human, it lies just anterior to the second sacral vertebra.

Sacroiliac function and leg length

Disturbances can induce torsion between the innominates, altering femoral head position or hip muscle tone, causing functional leg length inequality.

Close-packed position: Coxofemoral (Hip) joint

Maximal extension, internal rotation, and abduction.

Close-packed position: Tibiofemoral (Knee) joint

Maximal extension and external rotation.

Close-packed position: Tibiotalar (Ankle) joint

Maximal dorsiflexion.

Close-packed position: Tarsometatarsal (Foot) joints

Maximal inversion.

Close-packed position: Intermetatarsal (Foot) joints

Maximal opposition.

Close-packed position: Metatarsophalangeal (Toe) joints

Maximal extension.

Tensile fractures in the foot

Can occur at the base of the fifth metatarsal (from the peroneus brevis) or the calcaneus (from the Achilles tendon).

Shear fractures in the knee

Shear loading on cancellous bone makes the femoral condyles and tibial plateaus prone to fracture.

Shock absorption in the lower extremities

Primarily handled by the musculotendon system; failure can lead to shin splints, plantar fasciitis, and Achilles tendinitis.

Phases of gait

The stance phase (65% weight-bearing) and the swing phase (35% non-weight-bearing).

Causes of altered gait

Pain during weight-bearing, muscle weakness/imbalance, limited joint motion, incoordination, or structural deformities.

Lateral plumb line landmarks

The line should pass through the greater trochanter, just anterior to the midline of the knee joint, and slightly anterior to the lateral malleolus.

Posterior plumb line landmarks

The line should fall midway between the knees and midway between the ankles.

Prone leg length evaluation

Involves comparing the symmetry of the patient's heels or the inferior poles of the medial malleoli.

Derifield pelvic leg check

A common procedure used to assess functional leg length inequality, heavily affiliated with Activator and Thompson techniques.