Knee & Distal Lower Limb Written Learning Objectives

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1. Identify the joints of the knee region and associated structures. Explain what types of movement occur at these joints and other pertinent clinical information.

The knee joint is a complex of 3 articulations: 

• Patellofemoral,

• Medial tibiofemoral, & 

• Lateral tibiofemoral joints. 

When observing the articular surfaces of the medial and lateral condyles of the femur & the tibia, one can see the notable incongruence of the articulations. Due to this incongruence, accessory structures (muscles/tendons, ligaments, and menisci) are vital to the structural integrity of this joint.

Movements

• The knee joint is primarily a synovial hinge joint, with the major actions being flexion & extension.

• Additionally, there are slight medial & lateral rotational movements allowed at this joint

  • In a standing (extended knee) position, there is a slight amount of medial rotation of the femoral condyles on the tibial condyles - allowing the knee to ‘lock’ - often referred to as the ‘screw-home mechanism’

    • This allows increased weight bearing and muscles in the region to relax to an extent without totally decreasing knee stability

  • Lateral rotation occurs to ‘unlock’ the knee and allow flexion to occur

Muscles/Tendons

• Muscles/tendons provide structural integrity of the knee joint. Muscle conditioning can help prevent numerous injuries in the region.

• Quadriceps mm. (particularly vastus lateralis & medialis) are the most important set.

  • These muscles and the associated patellar ligament are the main source of stability and protection for the anterior portion of the joint.

Extracapsular Ligaments: located outside (or as a thickening) of the articular capsule

• Patellar ligament: distal expansion of the the quadriceps femoris tendon (from patella to tibial tuberosity)

  • Anterior portion of knee joint

• Fibular [lateral] collateral ligament (FCL; LCL): protect lateral side of knee joint

  • Taut during extension; more slack during flexion

• Tibial [medial] collateral ligament (TCL; MCL): protect medial side of knee joint

  • Taut during extension; more slack during flexion

  • The TCL/MCL and medial meniscus are attached and often damaged in unison

Intra-articular Ligaments: located within the articular capsule

• The cruciate ligaments are very characteristically ‘criss-crossed’ within the joint capsule, and these ligaments typically serve as the pivot for the slight rotational movements allowed at the knee joint

  • Anterior cruciate ligament (ACL): prevents tibial anterior displacement/femoral posterior displacement

    • The ACL is the weaker and more commonly injured of the two

    • If damaged/ruptured and anterior tibial displacement allowed: anterior drawer sign

• Posterior cruciate ligament (PCL): prevents tibial posterior displacement/femoral anterior displacement

  • In actions such as walking down stairs, the PCL plays a major role in femoral stabilization

  • If damaged/ruptured and posterior tibial displacement allowed: posterior drawer sign

Menisci: fibrocartilaginous structures that deepen the articular surfaces of the tibial condyles and play a role in shock absorption

• Medial meniscus: less mobile of the menisci; important attachment to the tibial (medial) collateral ligament

• Lateral meniscus

Clinical Considerations

• “Unhappy (terrible) triad” - term used for knee injuries that involve the anterior cruciate ligament (ACL), medial meniscus, and tibial (medial) collateral ligament

  • Recall that the tibial (medial) collateral ligament and medial meniscus have a close attachment

    • The ACL, as the weaker of the cruciate ligaments, are often also damaged during injuries that also affect the other 2 structures

  • More common in contact sports, particularly in direct blows to the lateral knee region

2. Describe the organization of neurovasculature in the popliteal fossa.

The popliteal fossa is located in the posterior knee region and while mostly filled with adipose tissue, it is also an important region for neurovasculature to traverse between the thigh and leg. It is located between the distal tendons of the hamstring mm. superiorly and the proximal tendons of the gastrocnemius m. inferiorly.

The neurovasculature is organized in the popliteal fossa from superficial to deep (or posterior to anterior):

• Sciatic n., splitting into its terminal branches:

  • Tibial n.: larger, medial branch

  • Common fibular (peroneal) n.: smaller, lateral branch

• Popliteal v.

• Popliteal a.: very deep - right at the surface of the femur

  • Divides into terminal branches: anterior & posterior tibial aa.

3. Identify the joints of the ankle region and major intertarsal joints and associated ligaments. Explain what types of movement occur at these joints and other pertinent clinical information.

The ankle region hosts 4 joints: 

• Inferior tibiofibular, 

• talocrural (ankle) - greatest range of motion, 

• subtalar, &

• transverse tarsal.

Distal Tibiofibular Joint

The distal tibiofibular joint is one of the 3 articulations between the tibia and fibula, in a similar arrangement to what was located between the radius and ulna of the forearm (a proximal joint, an interosseous membrane, and a distal joint.

The largest difference between the forearm and the leg is the degree of movement occurring, with only very slight movements occurring between the bones of the leg. However, the distal tibiofibular joint is important in helping maintain stability of the ankle joint, and damage to ligaments associated with a joint (and potentially the interosseous membrane) are often termed high ankle sprains.

Talocrural (Ankle) Joint

The talocrural (ankle) joint involves the:

• Distal tibia (primarily) and fibula 

  • The medial malleolus of the tibia and the lateral malleolus of the fibula flank and grip the talus on the sides to allow controlled movements of the joint.

• Superior surface of the talus. 

Talocrural Joint Actions

The ankle joint is a hinge joint allowing movement in one plane of motion, although it should be noted that these movements rarely occur in a vacuum and often occur in unison with action at intertarsal and other surrounding joints.

The actions at this joint include:

• Dorsiflexion (‘digging in your heels’; toes pointing up)

• Plantar flexion (occurs when standing on your toes; toes/ball of foot on ground & heels up)

Ligaments Supporting Talocrural Joint

Similar to most other hinge joints, there are ligaments located on the medial and lateral sides (types of collateral ligaments). However, at the ankle joint, they are not organized as one solid structure but instead an amalgamation of smaller ligaments.

• Medial (deltoid) ligaments are a complex of 4 parts all of which attach proximally to the medial malleolus of the tibia.

  • Stronger of the collateral ligaments

  • Important in stabilization during eversion

• Lateral ligament: 3 separate ligaments; all attach proximally to the lateral malleolus of the fibula, but do not interweave together as a unit

  • Weaker of the collateral ligaments and most commonly injured

  • Important in stabilization during inversion

  • Anterior talofibular ligament (ATFL): located between lateral malleolus and talar neck

    • Most commonly injured ligament during ankle sprains

Clinical Considerations

Ankle sprains are the most common injuries involving the ankle joint as well as one of the most common MSK injuries. These types of injuries are most common after over-inversion during plantarflexion and injury to the lateral ligaments of the ankle, in particular the anterior talofibular ligament (ATFL).

Intertarsal Joints

There are intertarsal joints between each articulating tarsal bone, but there are two that are involved in the movements of inversion (bring sole/plantar surface of the foot medially) & eversion (bring sole/plantar surface of the foot laterally). These joints include:

• Subtalar joint

• Transverse tarsal joint

Subtalar joint

The subtalar joint is the articulation between the talus and the calcaneus (e.g. the joint inferior to/below the talus). The majority of the mobility necessary for inversion and eversion occurs at this joint.

Transverse tarsal joint

The transverse tarsal joint is a complex joint involving 2 separate joints that are aligned on a similar plane. This includes the articulations between the talus and navicular (talonavicular) and the calcaneus and cuboid (calcaneocuboid). This complex of joints will augment and further allow the movements of inversion and eversion.

4. Identify the major muscles, innervation, actions, and clinical considerations of the anterior leg.

One of the three compartments of the leg, the anterior compartment is located anterior to the interosseous membrane located between the tibia and fibula. While it is called anterior, the compartment actually is oriented anterolaterally, with the shaft of the tibia oriented anteromedially.

There are 4 muscles in the anterior compartment:

• Tibialis anterior (TA) m.: most medial and superficial muscle of this compartment

• Extensor digitorum longus (EDL) m.: most lateral muscle of this compartment

  • Has 4 long tendons that will create extensor expansions for digits 2-5

• Extensor hallucis longus m.

• Fibularis (peroneus) tertius m.

Actions

• The primary action of this compartment is dorsiflexion of the ankle joint.

  • Think of this action as ‘digging in your heels and pointing toes up’

  • Tibialis anterior m. is typically the prime mover in this action

• The tibialis anterior m. (with the tibialis posterior m. in the posterior compartment of the leg) can cause inversion of the subtalar & transverse tarsal joints.

  • Inversion will move the sole of the foot (plantar surface) medially

  • Tibialis muscles = inversion; Fibularis muscles = eversion

• The extensor digitorum (digits 2-5) and hallucis longus (digit 1) mm. will extend the digits via the joints of the foot.

Innervation

• The deep fibular (peroneal) n. is the primary innervation for this muscle compartment. The deep fibular n. is one of the terminal branches of the common fibular (peroneal) n.

  • With injury/damage to this nerve, this may lead to the loss of the ability to dorsiflex the ankle, which is often referred to as foot drop.

Clinical Considerations

As previously discussed, this compartment is particularly susceptible to compartment syndrome due to relatively thick and unyielding deep fascia.

• Shin splints typically present as pain or edema in the distal portion of the anterior leg, and are typically caused by minor tears of the tibialis anterior m. and the closely associated periosteum of the tibia.

5. Identify the major muscles, innervation, and actions of the lateral leg.

The lateral compartment is the smallest of the 3 compartments of the leg. There are 2 muscles in this compartment:

• Fibularis (peroneus) longus m.: superficial 

• Fibularis (peroneus) brevis m.: deeper

Actions

• The primary action of this compartment is eversion of the subtalar and transverse tarsal joints. 

  • With this movement, the sole (plantar) surface of the foot is moved laterally (raising the lateral portion of the foot).

  • Remember: tibialis mm. - invert; fibularis mm. - evert

• The muscles can play a small role in plantar flexion of the ankle joint, but only synergistically

Innervation

• The primary innervation for the muscles in this compartment is the superficial fibular (peroneal) n.

  • One of the terminal branches of the common fibular n. 

6. Identify the major muscles, innervation, and actions of the posterior leg.

The largest of the leg compartments, the posterior compartment can be subdivided into larger, (superficial) and smaller (deeper) subcompartments.

Innervation

All muscles in the posterior compartment are innervated by the tibial n., the larger of the two terminal branches of the sciatic n.

Superficial Subcompartment

The superficial subcompartment consists of three muscles, but two are the largest in the overall posterior compartment and form most of the bulk in this region. The plantaris muscle is also included in the subcompartment but is relatively weak in actions.

The muscles include:

• Gastrocnemius m.: superficial; has 2 proximal heads/attachments

  • Crosses 2 joints: knee & ankle

• Soleus m.: deep and flatter

• Together these muscles are often referred to as ‘triceps surae’

• These muscles share a common distal tendon, the calcaneal (Achilles) tendon

  • This is the strongest & thickest tendon in the body

  • Attaches to the calcaneal tuberosity of the calcaneus

Actions

• The gastrocnemius & soleus mm. are the primary and powerful plantar flexors of the ankle joint. 

  • Plantar flexion involves bringing the hindfoot (heel region) superiorly off the ground with the ball of the foot firmly on the ground. This action is important in propelling the body forward during locomotion or jumping motions.

Deep Subcompartment

There are four muscles in the deep subcompartment, but these are small and tend to be weaker in terms of contraction power. Additionally, these muscles tend to be difficult to differentiate at the muscle belly region without following distal tendons to attachment sites.

The muscles in this compartment include:

• Popliteus m.

• Flexor hallucis longus (FHL) m.

• Flexor digitorum longus (FDL) m.

• Tibialis posterior m.

Actions

Many of these muscles work in synergistic roles with other more powerful muscles and play a role in flexion of the knee joint (e.g. popliteus m.), and plantar flexion of ankle joint (FHL, FDL, tibialis posterior mm.).

The tibialis posterior m. works with the tibialis anterior m. to invert the subtalar and transverse tarsal joints.

The flexor digitorum & hallucis longus mm. flex digits 1-5 of the foot. 

7. Describe the organization of deep fascia of the foot with an emphasis on the plantar aponeurosis.

The deep fascia of the foot is continuous with the crural fascia in the leg. It is relatively thin on the dorsum of the foot (superior surface), but is notably thicker on the plantar (inferior) surface of the foot - this is referred to as plantar fascia.

Plantar fascia

The plantar fascia is important in protecting the plantar surface of the foot from injury, and is divided into:

• Medial & lateral parts - thinner

• Central part - thicker; referred to as the plantar aponeurosis

The plantar aponeurosis extends from the calcaneus to form distal digital sheaths. The plantar aponeurosis plays an important role in supporting the medial longitudinal arch, utilizing its inherent tensile strength to prevent collapse of the arch of the foot upon vertical load.

Plantar fasciitis is inflammation of the plantar fascia.

8. Describe the main arches of the foot, function and structures that support them.

Arches of the foot are important in distributing weight and absorbing shock that occurs during locomotion. 

The medial longitudinal arch is the highest and most noticeable arch, located on the medial side of the foot.

The lateral longitudinal arch is located on the lateral side of the foot, is much flatter, and is typically in contact with the ground during weight bearing.

The transverse arch runs transversely between the longitudinal arches.

The integrity of the arches of the foot are maintained by numerous factors, including shape of articulating bones, tendons and intrinsic mm. that run along the sole of the foot, but of most importance, are the plantar aponeurosis and plantar ligaments (spring, long plantar, & short plantar).

Pes planus (‘flat feet’) involve relatively shallow medial longitudinal arches. These can be caused by bone and/or connective tissue deformities or acquired (which is often referred to as ‘fallen arches’).