Knee

Description[edit|edit source]

The knee joint is one of the largest and most complex joints in the body. It is constructed by 4 bones and an extensive network ofligamentsandmuscles.^[1]It is a bi-condylar type of synovial joint, which mainly allows for flexion and extension (and a small degree of medial and lateral rotation).^[2]

Image: Overview of the knee joint (anterior and posterior views)^[3]

Anatomy[edit|edit source]

Articulating Surfaces[edit|edit source]

The thigh bone (femur), the shin bone (tibia) and the kneecap (髌骨) articulate through tibiofemoral andpatellofemoraljoints. These three bones are covered in articular cartilage which is an extremely hard, smooth substance designed to decrease the friction forces. The medial and lateral condyles of the femur articulate with the tibia to form tibiofemoral joint. Similarly, the anterior and distal part of the femur articulate with the patella to form patellofemoral joint. The tibiofemoral joint is the weight bearing joint of the knee. The髌骨lies in an indentation of the femur known as the intercondylar groove.^[1][2]

The smallerfibularuns alongside thetibiaand is attached via the superior tibiofibular joint is not directly involved in the knee joint, but provides a surface for importantmusclesandligaments附着。^[1][4]

The distal aspect of thefemurforms the proximal articulating surface for the knee, which is composed of 2 large condyles. The medial and the lateral. These two condyles are separated inferiorly by the intercondylar notch although they are connected anteriorly by a small shallow groove which is known as either the femoral sulcus or the patella groove or patella surface. This engages the髌骨in early flexion.

Thetibiaalso has 2 asymmetrical condyles (medial and lateral) of which are relatively flat, These are also known as the tibial plateau. The medial tibial plateau is much longer than the lateral anteroposteriorly, and the diameter of the proximal tibia is much greater than the shaft posteriorly which is sloped at approximately 7 to 10^oto facilitate flexion of the femoral condyles on thetibia.

The two tibial condyles are separated by the intercondylar tubercles, these are two bony spines which are roughened and their role lies within knee extension. They become lodged in the intercondylar notch of the femur, adding to the stability of the joint. Overall the tibiofemoral joint is a relatively unstable joint as the plateaus are slightly convex anteriorly and posteriorly. This emphasizes the importance of the other structures of the knee such as the menisci.

Menisci[edit|edit source]

There are two menisci in the space between the femoral and tibial condyles. They are crescent-shaped lamellae, each with anterior and posterior horn, and are triangular in cross-section. The surface of each meniscus is concave superiorly, providing a congruous surface to the femoral condyles and is flat inferiorly to accompany the relatively flat tibial plateau.^[5]The horns of themedial meniscusare further apart and meniscus appears ‘C’ shaped, than those of the lateral one where meniscus appears more ‘O’ shaped. This is due to the increased size of themedial meniscus, which unfortunately leaves a large exposed area that in turn can be prone to injury.

半月板正确之间缺乏一致性the articular surfaces of tibia and femur, increase the area of contact and improve weight distribution and shock absorption. They also help to guide and coordinate knee motion, making them very important stabilizers of the knee.^[5]

The arrangement of the fibres in the menisci allows for axial loads to be dispersed radially decreasing the wear on the hyaline articular cartilage. This is essential as the compressive loads through the knee can reach 1-2 times body weight during gait and stair climbing and an astonishing 3-4 times body weight during running. The menisci are connected with the tibia by coronary ligaments. Themedial meniscusis much less mobile during joint motion than thelateral meniscusowing in large part to its firm attachment to the knee joint capsule andmedial collateral ligament (MCL). On the lateral side, the meniscus is less firmly attached to the joint capsule and has no attachment to thelateral collateral ligament (LCL). In fact, the posterior horn of thelateral meniscusis separated entirely from the posterolateral aspect of the joint capsule by the tendon of the腘肌肌肉as it descends from the lateral epicondyle of thefemur.^[6]

During the first year of life the menisci are fully vascularized but once weight bearing commences the vascularity diminishes to the outer third (red zone), the red zone being the only area having a slight ability to heal. The inner non-vascularized part (white zone) receives nutrition through diffusion of synovial fluid.^[5]The medial and lateral menisci are fibrocartilage structures in the knee that serve two main functions- To deepen the articular surface of the tibia and To act as shock absorbers.^[2]

Bursae[edit|edit source]

A bursa is synovial fluid filled sac, found between moving structures in a joint – with the aim of reducing wear and tear on those structures. There are four bursae found in the knee joint.^[2]

•Suprapatellar bursa

•Prepatellar bursa

•Infrapatellar bursa

•Semimembranosus bursa

Ligaments & Joint Capsule[edit|edit source]

The joint capsule has thick and fibrous layer superficially and thinner layers deeper. This along side the capsule ligaments enhances she stability of the knee. As with all of the structures that from the knee they are under most tension therefore more stable in an extended (closed packed) position in comparison to the laxity present in a flexed position (open packed). Inside this capsule is a specialized membrane known as the synovial membrane which provides nourishment to all the surrounding structures. The synovial membrane produces synovial fluid which lubricates the knee joint. Other structures include the infrapatellar fat pad and bursa which function as cushions to exterior forces on the knee.^[1]The synovial fluid which lubricates the knee joint is pushed anteriorly when the knee is in extension, posteriorly when the knee is flexed and in the semi flexed knee the fluid is under the least tension therefor being the most comfortable position if there is a joint effusion.

膝盖的韧带保持稳定f the knee. Each ligament has a particular function in helping to maintain optimal knee stability.

• Medial Collateral Ligament(MCL)- Thisligamentcan be divided into two sets of fibres - the superficial and the deep fibres. The general location of this band runs from the medial epicondyle of thefemurto the medial condyle and the superior part of the medial surface of thetibia. The superficial fibres originates from medial femoral condyle and attaches to the medial aspect of the proximal tibia distally to the pes anserinus. The deep fibres are continuous to the joint capsule and originates from the inferior aspect of the medial femoral condyle, and inserts to the proximal aspect of the medial tibial plateau. In the middle of the ligament the deep fibres are attached to themedial meniscus.^[4]TheMCLprimarily resists forces acting from the outer surface of the knee, valgus forces, but also resists the lateral rotation of thetibiaon thefemur. TheMCLis able to resist a valgus stress more effectively in the closed pack position (extension) due to the laxity of the ligament in the open packed position (flexed). TheMCLdoes have another role in restraining anterior translation of thetibiaon thefemur. Therefore when someone has anMCL injurythe protection of theanterior cruciate ligamentneeds to be considered.
• Lateral Collateral Ligament(LCL)– a cord likeligamentthat begins on the lateral epicondyle of thefemurand joins with the tendon of thebiceps femoris(hamstring muscle) to form the conjoined tendon. This ligament is different to theMCLand is considered to be an extracapsular ligament. Its main role is resisting varus forces on the knee, and similarly to the MCL is most effective in full extension. another similarity of theMCLand theLCLis the ability of theLCLto also resist lateral rotation of thetibiaon thefemur.
• Anterior Cruciate Ligament(ACL)- The ACL is an important structure in the knee for resisting anterior translation of thetibiaon thefemur. Thisligamentis a very well knownligamentdue to the high injury rate of athletes, which has resulted in a lot of research being done in the field of theACL. The cruciate ligaments are so called because they form a cross in the middle of the knee joint. TheACLruns from anterolateral aspect of the medial intercondylar tibal spine superolaterally and posteriorly to the posteromedial aspect of the lateral femoral condyle. TheACLtwists medially as it travels proximally. There are thought to be 2 bundles of fibres that form theACL- the anteromedial bundle (AMB) and the posterolateral bundel (PLB). TheACLis responsible for resisting anterior sheering forces on the knee. Dependant on the position of the knee, will depend on which bundle of theACLfibres will be taut. So when the knee close to full extension the PLB will be taut and resisting the force, but as the knee moves into a flexed position the PLB become lax and the AMB becomes taut taking over the role of resisting the anterior sheering forces. At approximately 30^oof the flexion neither of the bundles of theligamentare taut leading to the most anterior translation available at this range. It is most commonly injured in twisting movements.^[7]TheACLis also an accessoryligamentin resisting rotary forces medially and laterally as well as valgus and varus forces. The PLB of theACLis theorised to be most effective at providing rotary stability of the knee. In addition to this the AMB is under most tension at approximately 10-15^oof knee flexion with medial rotation.
• Posterior Cruciate Ligament(PCL)- Thisligamentruns from the posterior surface of the tibia between the two posterior horns of the menisci it then runs superiorly and anteriorly and attaches to the lateral aspect of the medial femoral condyle. ThePCLis much shorted and less oblique with a much larger cross sectional area in comparison to theACL. As thePCLblends with the posterior capsule as it crosses to the tibial attachment. Factors such as the size, shape and location possibly contribute to the increased strength of thePCLin comparison to theACLand is much less frequently injured. ThePCLsimilarly has 2 bundles of fibres the posteromedial (PMB) and the anterolateral bundle (ALB). When the knee is in near full extension the ALB which is much larger and stronger are lax and the PMB are taut whereas in 80-90^oof flexion the PMB are lax and the ALB are taut. The PCL is more adept for resisting posterior translation / sheering forces in knee when it is flexed despite there being the most posterior translation available at 75-90^oflexion. The secondary stabilisers at this point in the range are ineffective and relay upon thePCL. ThePCLalso plays an important role in resisting rotation and valgus / varus forces on the knee. ThePCLbest resists medial tibial rotation at 90^oflexion rather than extension, but is not very good at resisting lateral tibial rotation. If thePCLbecomes damaged the腘肌肌肉plays an important role in stabilising the knee from posterior sheering forces. In thePCLdeficient personhamstringcontraction can destabilise the knee joint alongside agastrocnemiuscontractions (at angles greater than 40^oknee flexion), whereasquadricepscontractions degrees the strain on thePCLbetween angles of 20 and 60^oflexion.^[8]
  

Muscles[edit|edit source]

Muscles	Function	周围神经	Spinal innervation
Quadriceps femoris	Strong extensor of the knee	Femoral	L2, L3, L4
Semitendinosus*	Flexor and internal rotator of the knee	Tibial	L5, S1, S2
Semimembranosus	Flexor and internal rotator of the knee	Tibial	L5, S1, S2
Gracilis*	Flexor and internal rotator of the knee	Obturator	L2, L3, L4
Sartorius*	Flexor and internal rotator of the knee	Femoral	L2, L3
Popliteus	Flexor and internal rotator of the knee Prevents the femur from slipping forwards on the tibia during squatting	Tibial	L4, L5, S1
Tensor fasciae latae	Weak extensor when knee is extended Weak flexor and external rotator of the knee in flexion greater than 30o	Superior gluteal	L4, L5
Gastrocnemius	Weak flexor of the knee Weak internal and external rotator of the knee Strong plantiflexor and inventor of the heel	Tibial	S1, S2
Biceps femoris	Strong flexor and external rotator of the knee	Sciatic	L5, S1

^[5]

*这三个musclesoriginate from different bones on the pelvis, they perform different actions at thehipand are innervated by different nerves. Regardless, they all attach to the proximal medialtibiathrough a broad sheet of connective tissue known as the pes anserinus and perform flexion and medial stability to the knee.^[1]

Function[edit|edit source]

Osteokinematics and range of motion[edit|edit source]

Theligamentsand menisci provide static stability and themusclesand tendons dynamic stability.

The main movement of the knee isflexion - extension. For that matter, knee act as a hinge joint, whereby the articular surfaces of thefemurroll and glide over the tibial surface. During flexion and extension,tibiaand髌骨act as one structure in relation to thefemur.^[5]The quadriceps muscle group is made up of four different individual muscles.^[1]They join together forming one single tendon which inserts into the anterior tibial tuberosity. embedded in the tendon is the髌骨, a triangular sesamoid bone and its function is to increase the efficiency of thequadricepscontractions. Contraction of thequadricepspulls the髌骨upwards and extends the knee.^[5]的活动范围:extension 0^o. Thehamstringmuscle group consists of thebiceps femoris,semitendinosusandsemimembranosus. They are situated at the back of the thigh and their function is flexing or bending the knee as well as providing stability on either side of the joint line.^[1][5]的活动范围:flexion 140^o.

Secondary movement isinternal - external rotationof the tibia in relation to the femur, but it is possible only when the knee is flexed.^[5]

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Arthrokinematics[edit|edit source]

Viewed in the sagittal plane, the femur's articulating surface is convex while the tibia's in concave. Knee arthrokinematics is based on the rules of concavity and convexity^[11]and is described in terms of open and closed chain:

Open kinetic chain^[12]- During knee extension,tibiaglides anteriorly onfemur. More precisely, from 20^oknee flexion to full extension,tibiarotates externally. During knee flexion,tibiaglides posteriorly onfemurand from full knee extension to 20^oflexion,tibiarotates internally.^[4]

Closed kinetic chain^[12]- During knee extension, femur glides posteriorly on tibia. To be more specific, from 20^oknee flexion to full extension, femur rotates internally on stable tibia. During knee flexion, femur glides anteriorly on tibia and from full knee extension to 20⁰flexion, femur rotates externally on stable tibia.^[11]

The "screw home mechanism"

The "screw-home" mechanism, considered to be a key element to knee stability, is the rotation between thetibiaandfemur. It occurs at the end of knee extension, between full extension (0^o) and 20^oof knee flexion. The tibia rotates internally during the open chain movements (swing phase) and externally during closed chain movements (stance phase). External rotation occurs during the terminal degrees of knee extension and results in tightening of both cruciate ligaments, which locks the knee. Thetibiais then in the position of maximal stability with respect to thefemur.

Pathology/Injury[edit|edit source]

• Anterior cruciate ligament injury
• Lateral collateral ligament injury
• Medial collateral ligament injury
• Posterior cruciate ligament injury
• Meniscal lesions
• Quadriceps muscle strain
• Quadriceps muscle contusion
• Patellar fractures
• Tibial plateau fractures
• Femur fractures
• Tibial fractures
• Articular cartilage lesions
• Baker's cyst
• Chondromalacia patellae
• Femoral fractures
• Hamstring strain
• Iliotibial band syndrome
• Sinding Larsen Johansson syndrome
• Knee osteoarthritis
• Knee bursitis
• Osteochondritis dissecans of the knee
• Osgood-Schlatter's disease
• Plica syndrome
• Quadriceps muscle strain
• Quadriceps muscle contusion
• Patellar tendinitis
• Popliteus tendinitis
• Popliteus strain
• Popliteus tendinitis
• Semimembranosus tendinopathy
• Pes anserinus bursitis
• Pre-patellar bursitis

Techniques[edit|edit source]

See the page forknee examination.

Special Tests[edit|edit source]

• McMurray's Test
• Apley's Test
• Steinman's Test
• Ege's Test
• Ely's Test
• LCL Test
• MCL Test
• Anterior Draw
• Lachman Test
• Pivot Shift
• Slocum's Test
• Posterior Drawer Test
• Dial Test
• Muller's Test
• Patellar Apprehension Sign
• Patellar Grind Test
• Thessaly's Test
• Ober's Test

Outcome Measures[edit|edit source]

• Knee Injury and Osteoarthritis Outcome Score
• Cincinnati knee rating system
• Knee Injury and Osteoarthritis Outcome Score
• Knee Injury and Osteoarthritis Outcome Score - Child
• Knee outcome survey
• Lower Extremity Functional Scale (LEFS)
• WOMAC Osteoarthritis Index
• Ibadan Knee/Hip Osteoarthritis Outcome Measure (IKHOAM)

Treatment[edit|edit source]

Surgical Management[edit|edit source]

• Arthroscopic meniscectomy
• Meniscal repair
• Articular cartilage debridement and microfracture
• ACL reconstruction
  • Patellar tendon autograph
  • Hamstring tendon autograph
  • Allograph
• PCL reconstruction
• Surgical fixation of fracture
• Arthroscopic debridement & manipulation
• Lateral release of the patella
• Tibial osteotomy
• Total knee replacement

Physiotherapy Management[edit|edit source]

• Therapeutic exercise: knee
• Manual therapy: knee
• ACL rehabilitation
• Rehabilitation post surgery (e.g. surgical fixation, arthroscopic surgery, total knee replacement)
• Patellar taping

References[edit|edit source]