CHAPTER 8

Knee

EPIDEMIOLOGY OF KNEE PAIN

KNEE PAIN IN THE GENERAL POPULATION

Prevalence

•  ~5% of adult population has nonspecific knee pain

Osteoarthritis (OA)

•  Most common (MC) cause of chronic knee pain in people >50 years old

•  Prevalence: 7% to 17% of people >45 years old from population-based studies (varies depending on the definition)

•  More common in aged population: 20% of adult population, 25% of 56 to 84 years old (Sweden) (1,2)

•  Higher in women, rural areas of developing countries

Other common causes

•  Overexertion, minor trauma (contact with objects), and falls

KNEE PAIN IN ATHLETES

Anterior knee pain

•  Occurs in 25% of athletes, 70% between 16 and 25 years old (3)

Knee injuries

•  Second MC cause of lost playing time after ankle injuries in sports (4)

Knee ligament injuries

•  MC sports injury leading to medical disability compensation

•  Anterior cruciate ligament (ACL) injury: MC, 70% during athletic activity, female > male by 2 to 8 times, noncontact pivoting injury (eg, skiing, football, soccer, and basketball)

•  Posterior cruciate ligament (PCL) injury from football (fall on flexed knee with plantar flexed foot)

Meniscal injury

•  Noncontact cutting, deceleration, hyperflexion, or landing from a jump (eg, football, basketball, wrestling, skiing, baseball) (5)

Knee OA

•  Higher prevalence in soccer players (7% vs 1.6% in control)

KNEE PAIN AT WORK (6)

Risk factors for chronic knee pain

•  Exposure to loading of the joints, such as heavy lifting, kneeling, and crawling in obese patients

•  Increased body weight correlates with knee pain in men and hip pain in women

Knee OA

•  Odds ratio 2.2 for jobs requiring knee bending and at least medium level of physical activity (7)

•  Relative risk two to three times higher in physically demanding jobs (shipyard workers, male farmers, male construction workers, firefighters, female janitors, and letter carriers)

DIFFERENTIAL DIAGNOSIS

MSK (MUSCULOSKELETAL) CAUSES OF KNEE PAIN BASED ON LOCATION (8) (FIGURE 8.1; FLOWCHART 8.1)

•  Localization of pain is not discrete in intra-articular lesions, such as osteoarthritis (more discrete when irritating soft tissue and superficial tendons/ligaments).

FIGURE 8.1

Surface anatomy of the knee.

FLOWCHART 8.1

Differential diagnosis of musculoskeletal knee pain.

AVN, avascular necrosis; Fx, fracture; MSK, musculoskeletal; OA, osteoarthritis.

MC, most common; OA, osteoarthritis

FIGURE 8.2

Bony and soft tissue anatomy (A) anterior aspect; (B) posterior aspect; (C) medial and lateral meniscus.

NEUROPATHIC CAUSES OF KNEE AND LEG PAIN (10) (FLOWCHART 8.2)

FLOWCHART 8.2

Differential diagnosis of neuropathic knee pain.

N, neuropathy; SI, sacroiliac.

N, nerve.

DIFFERENTIAL DIAGNOSIS OF KNEE SWELLING

Acute injury (hemarthrosis)

ACL, anterior cruciate ligament.

•  Acute knee injury without significant swelling: central meniscal tear, medial collateral ligament (MCL) tear/rupture, PCL rupture, cartilage lesion, epiphyseal injury, or posterolateral corner injury

Knee swelling without significant trauma

•  Osteoarthritis flare-up, inflammatory arthropathy (rheumatoid arthritis [RA], crystal-induced arthropathy, and other rheumatologic disease), and bursitis (suprapatellar, prepatellar, Baker’s cyst), ganglion cyst or tumor (soft tissue or bony)

DIFFERENTIAL DIAGNOSIS OF SUBJECTIVE KNEE INSTABILITY (11,12)

ACL, anterior cruciate ligament; OA, osteoarthritis; PCL, posterior cruciate ligament; RA, rheumatoid arthritis.

DIFFERENTIAL DIAGNOSIS OF PAINFUL KNEE SNAPPING (13,14)

Lateral knee snapping: discoid lateral meniscus, biceps femoris tendon snapping, popliteus tendon snapping, and iliotibial band friction syndrome

Medial knee snapping: medial plicae, meniscal pathology, and subluxation of the gracilis and semitendinous tendons

Others: intra-articular loose body, fabella, congenital snapping knee, patellar dysplasia

ANATOMY

BONE AND JOINT (15)

Patellofemoral joint

•  Patella: largest sesamoid bone, two facets with central ridge, lateral larger than medial (can be further divided into seven facets)

      Medial facet: smaller and steeper angle ( lateral subluxation and tilt of patella: more common). Thickest hyaline cartilage in our body

    º  With aging, the patellofemoral (PF) joint is reduced to a cylindrical outline with reduced the bone-to-bone contact area

      Complex arterial plexus supplies proximal two-thirds of the patella (16)

•  Trochlea of the femur: concavity between the condyles

      Lateral facet: larger, extends more proximally

      Trochlear dysplasia: a loss of the normal concave anatomy and depth of the groove, creating a flat trochlea patellar instability and/or PF syndrome

Femoro-tibial joint: condylar articulation, incongruent shape (17)

•  Allows transmission of body weight from the femur to the tibia while providing hinge-like sagittal rotation along with a small degree of tibial axial rotation

•  Medial condyle: larger, increased curvature and projects further distally than lateral condyle

      Femur slant medially (~6º)

      Allows full flexion without contact between the posterior joint margins of the tibia and the femur

•  Lateral condyle: more anterior than medial condyle

•  Articular cartilaginous layer

      Distributes reactive load over a wide area and helps contribute to cam shape of condyles, which maximizes the extensor lever arm

      Type 2 collagen and an abundance of proteoglycan versus type 1 collagen mostly in meniscus

Proximal tibiofibular joint (12)

•  Synovial joint, hyaline cartilage articulation, 10% to 12% communicates with the knee joint

•  Oblique articulation varies; angle can affect stability

•  Thicker capsule anteriorly

•  Posterior proximal tibiofibular ligament reinforced by posterolateral corner structures of the knee; for example, biceps femoris and popliteus tendons

Other structures

•  Capsule or capsular ligament (15)

      Retinaculum: in the anterior third of capsule, the combined fascia, and aponeurotic sheet

  Medial patellofemoral ligament (MPFL): just proximal and posterior to the medial epicondyle and distal to the adductor tubercle the proximal and medial surface of the patella: important stabilizer against lateral subluxation/dislocation of the patella

      Coronary ligament (meniscotibial ligament, deep layer of MCL): medial third, capsule between the tibia and the medial menisci (18)

      Oblique popliteal ligament: (middle layer of MCL): thickened capsule by an expansion from the semimembranosus

•  Synovial membrane and fluid

      The largest synovium in the body, lining fibrous capsule, suprapatellar pouch, infrapatellar fat pad, cruciate ligament, and meniscus

      Suprapatellar recess: up to 5 to 6 cm or above the patella; communicates with knee joint unless there is a complete plica

  Common location for intra-articular knee joint injection (supralateral approach)

      Knee joint synovial fluid: less than 1 mL physiologically

      Joint effusion (>15 mL) can inhibit quadriceps (vastus medialis more than rectus femoris, vastus lateralis)

      Popliteal bursa and semimembranosus bursa may communicate with knee joint

Blood supply

•  Popliteal artery (through adductor canal; anterior to posterior, medial and lateral genicular arteries: main suppliers), femoral artery (descending genicular artery, runs with saphenous nerve/infrapatellar branch), and anterior tibial artery (recurrent artery at the fibular neck)

      Adductor canal: sartorius, vastus medialis, adductor magnus tendon/fascia, 3 to 10 cm above the superior pole of the patella

•  Middle genicular artery: supplies the cruciate ligaments, synovial capsule, and the margin of the meniscus

•  Inferior lateral genicular artery: under the lateral collateral ligament (LCL) near the meniscus; caution during lateral joint line injection or arthroscopy

•  Inferior medial genicular artery: between the tibia and medial collateral ligament (MCL)

LIGAMENT AND MENISCUS

Intra-articular (Figure 8.2)

•  Cruciate ligament (anterior and posterior cruciate ligament) (19)

      Intra-articular and extrasynovial band of dense connective tissue

•  Anterior cruciate ligament (ACL)

      Lateral femoral condyle anterior portion of tibial eminence

      Two bundles based on the location of the tibial insertion

  Anteromedial bundle: taut in flexion, resists anterior tibial translation in 60° to 90° of flexion, and resists rotatory subluxation

  Posterolateral bundle: taut in extension; resists anterior subluxation in full extension. More important restraint at knee in full extension

      Function (20)

  Restraint to anterior translation of the tibia, internal rotation of tibia, and hyperextension of knee. Can cause rotational instability and limited knee full extension if impaired

  Secondary: resists varus and valgus force (can cause medial compartment overloading if impaired)

  Joint proprioception: repair does not improve proprioceptive deficit

           –  Chronic ACL deficiency: medial compartment degenerative joint disease (DJD); increased risk regardless of ACL repair

  Functionally, hamstring analog: 25% of impaired function by ACL injury are compensated by hamstrings

           –  Increased hamstring (biceps femoris) activity during midstance gait

      Blood supply by middle genicular artery, innervated by posterior articular nerve

•  Posterior cruciate ligament (PCL)

      Posterolateral bundle: medial femoral condyle posterolateral to the tibia 1 cm distal to joint line, checking larger and less curved medial condyle

      Stronger and thicker than ACL; more synovial tissue: better potential for healing than ACL

      Anterolateral bundle: taut in flexion, posterolateral stability at 90° flexion and posteromedial: tight in extension

    º  Primary restraint to posterior translation of the tibia, stabilize in varus, and valgus stress

•  Meniscus (21)

      Fibrocartilaginous structure, type 1 collagen

      Supplied by superior and inferior geniculate artery

  Vascular in the outer 10% to 25% of the lateral and 10% to 30% of the medial meniscus

      Collagen fibers in a circumferential pattern, much less proteoglycan (<1%)

      Function

  Shock absorption and load transmission (to articular cartilage) in knee joint movement. Static loading by the tensile strength of the meniscal matrix (hoop tension). Distributes stress over a large area. Increase joint congruence

           –  Fifty percent compressive force transmitted to the meniscus in extension increased to 85% in 90º knee flexion

           –  Increased OA in patients with meniscus injury

  Contributes to joint stability, proprioception, and joint lubrication (distributes synovial fluid)

           –  Primary stabilizer in ACL-deficient knee

  Mobility

           –  Lateral more mobile than medial meniscus

           –  Anterior horn more mobile than posterior, lateral meniscus more mobile than medial (due to joint capsule and deep MCL), peripheral more mobile than central; firmly attached to intercondylar area of tibia

  Varus alignment: potential risk factor for medial meniscal tear and extrusion

Extra-articular (22)

•  MCL (23) (Figure 8.3)

      Superficial MCL: one femoral and two tibial attachments (~1 and 6 cm from joint line)

  Primary restraint to valgus laxity: higher load response at 90° knee flexion

  MCL bursa under the superficial MCL

      Deep MCL: meniscofemoral and meniscotibial ligaments

  Secondary restraint to valgus loads: restraint against external rotation in 0 to 30° flexion

      Posterior oblique ligament: fibrous extension of the semimembranosus that blends with and reinforces the joint capsule

  Internal rotator and valgus stabilizer at between 0 and 30° flexion

      Abundant blood supply; good potential for healing

•  LCL (Figure 8.4)

      Single layer, cord-like structure (vs band-like structure in MCL): ~7 cm in length, proximal/posterior to the popliteus origin on the femoral condyle to the fibular head

  Primary static stabilizer to varus at knee from 0 to 30° of knee flexion

  No direct attachment to the meniscus

  Check rein to external rotation of the tibia and posterior tibial translation

FIGURE 8.4

Extra-articular structures—the lateral aspect of the knee.

M, muscle.

FIGURE 8.3

Extra-articular structures—the medial aspect of the knee.

M, muscle.

•  Arcuate ligament complex (posterolateral corner)

      LCL, arcuate ligament (variable, fibular head to oblique popliteal ligament, and lateral gastrocnemius muscle), joint capsule, popliteus muscle, fabello fibular ligament (variable), lateral gastrocnemius

      Popliteo fibular ligament, biceps femoris tendon, and iliotibial band (ITB): important stabilizer in posterolateral corner

      Arcuate sign: avulsion of tip of the fibular head (LCL or biceps tendon rupture) associated cruciate ligament injury (~90%)

      Missed posterolateral corner injury common cause of failed ACL reconstruction

•  Popliteus muscle

      Underneath the LCL (anterior/inferior to LCL) and inferior to (underneath) ITB when flexed. Intracapsular in the femoral insertion, and extrasynovial

      Attached to the lateral meniscus (post horn)/fibular allows the popliteus to withdraw the meniscus during knee flexion/stabilizes the meniscus and prevents medial entrapment of the meniscus when varus forces are applied

      Flexes and internally rotates the tibia concentrically; eccentric contraction resists extension and external rotation stability against external rotation. Unlocks the knee via externally rotating the femur on the tibia

  Hyperpronation: risk factor for popliteal tendinopathy and symptom (from popliteal tendinopathy) worse with walking downhill and stair negotiation

NERVE

Innervation of the Knee (24) (Figure 8.5)

N, nerve.

Local neuropathic pain (medial/lateral/posterior) can be secondary to the following

•  Mononeuropathy (or 1–2 nerves): local injury/entrapment along the course

•  Diffuse pain from local pathologies affecting the knee joint capsule complex (musculoskeletal etiology)

•  Lesion at level of root or higher (rather than focal peripheral nerve lesion)

FIGURE 8.5

Nerve innervation of the knee.

N, nerve.

BIOMECHANICS

KINEMATIC AND KINETIC

Patellofemoral joint (15) (Figure 8.6)

•  Zero to 20 degree knee flexion: accompanied by internal rotation of the tibia (by popliteus) and laterally directed quadriceps muscle vector PF contact is made; the initial contact at the lateral facet of the patella lateral PF joint and ITB pain at initial knee flexion

•  Further flexion of knee moves patella anterior relative to center of rotation of the knee, which improves the mechanical advantage of the quadriceps mechanism

•  Patella continues to move laterally at 90° of knee flexion, and lateral border of the patella provides the primary loading site

•  Loading of PF joint

      Increases with flexion (50% with 1º–15º, 300% in 60º, 800% of body weight in deep squatting)

      Different activities: ~3 times higher in stair climbing, ~7 times higher in squatting. Maximal contact at 45º flexion

      Q angle: angle of patellar ligament and pull of quadriceps (normal up to 10°–17°, female > male due to wider pelvis, genu valgum, femoral anteversion, abnormal if >20°)

  Increased Q angle increased lateral pull on patella

Tibiofemoral joint (27)

•  Knee extension from flexion

      Tibia externally rotates to accommodate the medial condyle (more anterior protruded medial condyle than lateral condyle in axial plane)

      Tibia externally rotates 5° in the last 15° of extension

•  Knee flexion from full extension preceded by the tibia internal rotation (if standing closed kinetic chain, the femur externally rotates) by the popliteus muscle contraction

      With knee flexion, the instant center of rotation on the femur moves posteriorly (posterior rollback), allows knee flexion without impingement

      Relaxes tension of collateral ligaments sufficient to permit flexion

•  Sagittal plane range 0° to 140°, other motions (transverse and frontal planes) limited by interlocking of the femoral condyles in extension; transverse plane motion: maximal at knee flexion (45° internal rotation, 30° external rotation)

•  Knee range of motion (ROM) during functional activities

      Level walking: 65° for swing phase, stairs 80°, sit to stand from low chair: 95°, and bath transfer 120° (in bath) to 130° (out of bath) (28)

      Flexion of 110°: reasonable goal for activities for daily living (ADLs) otherwise compensated by other joints

•  In osteoarthritis, greater femoral internal rotation, decreased tibial posterior translation dysfunction of “screw home” motion during extension (17)

•  Joint reaction force: three times during walking and four times with climbing

FIGURE 8.6

“Screw home” motion of knee (rotation of knee joint with flexion/extension movement).

Tibiofibular joint

•  Dissipate torsional loads applied at ankle, absorption of lateral tibial bending movement, and transmission of 1/6 body weight

•  Knee flexion and extension fibular anterior-posterior motion

      Knee extension: taut lateral collateral ligament (0°–30°) stabilizes tibiofibular joint. With knee flexion, proximal fibula moves anteriorly with relaxation of LCL (as well as biceps femoris); loose

•  Affected by ankle movement: ankle dorsiflexion external rotation of the fibula; forced ankle dorsiflexion increase torsional load, predisposing higher risk of fracture or ligament sprain, dislocation

Knee joint in a closed kinetic chain (on standing and walking)

•  Flexion and extension momentum depending on the center of mass and ground reaction force (GRF)

    º  If the GRF is posterior to the knee joint, flexion. If anterior, then extension momentum

•  Response to foot and ankle biomechanics (pronation–supination)

      Ankle dorsiflexed in standing (closed kinetic chain) flexion momentum to knee versus ankle plantar flexion in standing extension momentum

      Pronation response (from foot and ankle conditions; eg, flat foot or functional leg length discrepancy) tibia externally rotated (internal rotation moment proximally), genu valgum and slight knee flexion

  Heel lift can affect GRF to decrease excessive extension momentum (pain in knee extension)

      Adduction momentum diminished by medial heel/extended wedge

  Increased adduction moment partly by increased medial quadriceps muscle hyperactivity

  Medial wedge and extended wedge also can decrease tibia external rotation (pronation response)

  Lateral wedge can decrease adductor moment by moving GRF closer to the knee center

•  Response to hip biomechanics

      Increased hip anteversion (increased angle from femoral neck axis and transcondylar line) intercondylar groove rotates more internally and tibia also internally rotates supination response occurs

      Decreased hip anteversion or increased retroversion intercondylar groove face laterally (external rotation) pronation response occurs

Anterior cruciate ligament

•  Biomechanics and clinical application

      Gender differences in ACL injuries (29): female > male by three to six times (30), multifactorial

  Over activation of quadriceps versus hamstring on landing and cutting

  Posture: more upright during cutting (increased valgus of the knee and quadriceps activation)

           –  More crouched position: may reduce the risk of ACL injuries

      Jumping while fatigued: decreased hip flexion/knee flexion, decreased eccentric capacity, and increased knee valgus

•  ACL-deficient knee

      Compensation to avoid anterior displacement of the tibia during gait (during obstacle-crossing) decrease knee extensor moment (effort)/prevent quadriceps contracture

  Shift center of mass forward; increased anterior tilt of the pelvis and hip flexion

  Increased peak hip extensor and ankle plantar flexor moments

      Significant increases in the anterior tilt of the pelvis and flexion at both hips when the unaffected leading toe was above the obstacle

  To prevent quadriceps contraction, patients may have to shift the center of body mass forward and thus cause greater pelvic anterior tilt and hip flexion, in both the swing limb and the stance limb, with normal leading toe clearance for safe obstacle crossing (31)

Biomechanics in knee OA

•  Knee OA (medial tibiofemoral) associated with high external knee adduction moment, reflects compression of the medial compartment of the knee

      Biomechanical intervention: to reduce the knee adduction moment, AposTherapy^®, and foot inserts (32)

•  Increased pelvic anterior tilt, swing-pelvic list, decreased standing knee abduction, as well as decreased standing hip flexor and knee extensor moments

•  In severe bilateral medial knee OA: increased hip abduction, knee extension, and ankle plantar flexion

      Training of the hip muscles and pelvic control are essential for patients with knee OA, especially in severe OA (33)

KNEE STABILITY

Tibofemoral joint stabilizers (29)

•  Dynamic stabilizers: quadriceps, hamstring, gastrocnemius, and popliteus muscles

•  Static stabilizers: joint capsule, lateral/medial meniscus, and ligaments (ACL, PCL, MCL, LCL, and another small ligament)

•  Hamstring and ACL: resist anterior movement of tibia

•  Quadriceps and PCL: resist posterior movement of tibia

•  Posteromedial stabilizers: oblique ligament (semimembranosus), semitendinosus

•  Anterolateral: ITB, retinaculum

•  Posterolateral stabilizers: lateral collateral ligament, oblique trans-popliteal ligament (semimembranosus), arcuate ligament, fabellofibular ligament, and popliteus muscle

•  Posterior: oblique trans-popliteal ligament, arcuate ligament, joint capsule, and popliteal muscle

•  Medial and lateral knee-stabilizing structures by layer

ITB, iliotibial band, MCL, medial collateral ligament; M, muscle.

Patellofemoral joint stabilizers (34)

•  Medial: vastus medialis obliquus (VMO; primary dynamic restraint to lateral tracking of the patella), medial PF ligament (especially 0°–30° flexion) > patellotibial/meniscal ligament and retinaculum

•  Lateral: vastus lateralis oblique > anterior fibers of ITB and lateral retinaculum

Tibiofibular joint stabilizers (12,35)

•  Bony: angle of joint plane (from the coronal plane) and configuration variation of tibiofibular joint

•  Ligaments and muscles: capsule (thicker in anterior), tibiofibular ligament; anterior (three bands), posterior (two bands; weaker than anterior with reinforcement from posterolateral structures; LCL, arcuate ligament, fabellofibular ligament, popliteo fibular ligament, popliteus muscles), and biceps femoris muscle

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