The Knee Joint - Anatomy & Function PDF

The knee joint  Outline A bit of revision. Review of synovial joint structure. Introduction to the structure of the knee. The patellofemoral joint. The knee locking mechanism. Neural and vascular structures. Bursae of the knee. Motions and abnormal positions of the k...

The knee joint  Outline A bit of revision. Review of synovial joint structure. Introduction to the structure of the knee. The patellofemoral joint. The knee locking mechanism. Neural and vascular structures. Bursae of the knee. Motions and abnormal positions of the knee.  Aims To study the structure of the knee joint. To study the structures and processes that aid knee stability. To study the movements at the knee. To introduce the student to some common injuries of the knee.  What is a synovial joint? A joint that moves freely. Surrounded by a fibrous joint capsule and synovial membrane. Synovial membrane secretes fluid to lubricate the joint. Ends of bones involved covered with hyaline cartilage, joint cavity between the bones involved. Fibrocartilage pads (menisci) between bone ends (not all joints). Ligaments, fatty pads and bursae  What is a synovial joint? 2  What is the knee? Largest (synovial) joint in the body. Synovial, diarthroidal, modified hinge. 2 joints not 1: – Tibiofemoral joint – Patellofemoral joint Remarkably stable (especially when straight) given lack of congruence between joint surfaces. Stability maintained maintained by passive and dynamic structures around the knee and the locking mechanism.  Bones Femur Tibia Patella  Cartilage Articular ‘hyaline’ – Absorbs and redistributes force. cartilage – Attached to and held in – Covers bone ends place by: Tibial plateau Joint capsule Fibrocartilage MCL – Forms menisci Transverse ligament – C shaped wedges that – Protects and stabilises bone ends fit in to. knee – Medial bigger than – Helps to lubricate knee lateral joint. Cartilage QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Medial meniscus Lateral meniscus  Ligaments Join bone to bone Intracapsular – The joint capsule (and other – ACL & PCL (cruciates) structures) – Transverse ligament Many in the knee. – M & L coronary Extracapsular Allow free motion in – Patella ligament some directions, – M & L collateral control or prevent – Oblique popliteal – Arcuate popliteal motion in others.  Ligaments Joint capsule – Tough fibrous connective tissue, continuous with periosteum. – Generally thicker and stronger at sides, thinner anteriorly and posteriorly. – Allows free AP motion – Has some other integral thickenings (eg. Patella retinacula) – Contains many small vascular structures and nerves.  Anterior cruciate ligament From: Anterior tibial intercondylar area (up and back). To: Posterolateral femoral intercondylar notch. Stops tibia moving forward in relation to femur, controls rotation assists pivoting  Posterior cruciate ligament From: posterior tibial intercondylar area (up and forward). To: anterior medial femoral intercondylar notch. Stops tibia sliding back on femur, hyperextension, controls rotation. Cruciate ligaments Ouch!  Transverse ligament Joins anterior horns Lateral meniscus of the medial and lateral menisci. Prevents motion of Medial meniscus menisci Transverse ligament  Medial and lateral coronary ligaments Expansion of joint Lateral coronary ligament capsule fibres around base of medial and lateral menisci. Fixes menisci to tibial plateau. Medial coronary ligament  Patella ligament From patella To tibial tuberosity. Continuous with quadriceps tendon. Causes knee extension (with quadriceps). Gives anterior knee stability. Patella ligament  Medial collateral ligament From medial epicondyle of the femur. To anteromedial tibial condyle and attached to medial meniscus. Broad strong band of tissue. Provides medial stability  Lateral collateral ligament From lateral epicondyle of femur. To head of fibula (passing over tendon of popliteus) doesn’t attach to lateral meniscus. Thinner, cord like structure. Provides lateral stability.  Oblique popliteal From tendon of semimembranosus. To posterior joint capsule. Provides strength to posterior capsule Oblique popliteal  Arcuate popliteal From posterior head of fibula. Forms Y shaped fan to tibial intercondylar area (passes over tendon of popliteus). Strengthens Arcuate popliteal posterolateral area of joint capsule. Anterior structures Anterior & Posterior Knee 1.Medial Collateral Ligament 2.Medial Condyle of Femur 3.Posterior Cruciate Ligament 4.Anterior Cruciate Ligament 5.Lateral Condyle of Femur 6.Lateral Collateral Ligament 7.Lateral Condyle of Tibia 8.Lateral Meniscus 9.Medial Meniscus 10.Medial Condyle of Tibia 11.Tibia 12.Fibula 13.Transverse Ligament Posterior structures Anterior & Posterior Knee 1.Medial Collateral Ligament 2.Medial Condyle of Femur 3.Posterior Cruciate Ligament 4.Anterior Cruciate Ligament 5.Lateral Condyle of Femur 6.Lateral Collateral Ligament 7.Lateral Condyle of Tibia 8.Lateral Meniscus 9.Medial Meniscus 10.Medial Condyle of Tibia 11.Tibia 12.Fibula  The patellofemoral joint The articulation of the patella and the femur. Patella is largest sesamoid in body. Sits in the tendon of the quadriceps group, between the femoral condyles. Held in place by M, I & L vasti and M & L patella retinacula. Hyaline cartilage on deep side of patella and joint surface of femur.  Muscles that act at the knee There are many muscles that act at the knee. You have already met some of them, you will meet one more today and the rest later this term. They can be broadly grouped as muscles that: – Act at the hip and knee – The knee only – Or the knee and ankle Similarly they may be grouped as: – Extensors, or – Flexors (and one special one).  Muscles that act at the hip and knee Extensors (of the knee) – Rectus femoris – Gluteus maximus / tensor fascia lata (via iliotibial band) Flexors (of the knee) – Biceps femoris (long head) – Semimembranosus – Semitendinosus – Sartorius – Gracilis  Muscles that act at the knee and ankle Flexors (of the knee) – Gastrocnemius – Plantaris  Muscles that act at the knee only Extensors – Vastus medialis – Vastus lateralis – Vastus intermedius Flexors – Biceps femoris (short head) PLUS ONE MORE!  The special one! Popliteus – Origin: Posterior tibia, above soleal line. – Insertion: Outer surface lateral femoral epicondyle. – Action: Unlocks straight knee by externally rotating femur. Controls locking of knee by slowing internal rotation of femur as knee extends. A bit of flexion. – Innervation: Tibial nerve, L4, L5, S1.  The knee locking mechanism There is a basic principle of knee mechanics which says, “a straight knee is a stable knee”. As the knee extends, the femur relatively internally rotates on the tibia, this improves joint stability and tightens ligaments, locking the knee straight. Popliteus works eccentrically to control this process. In order unlock the knee, popliteus contracts concentrically to externally rotate the femur, thus allowing flexors to do their jobs.  Surface anatomy Locate and mark the following: – The popliteal fossa – Patella – Tibial tuberosity – MCL – LCL – Joint margin  Nerve supply to the knee: motor nerves See notes on innervation of individual muscles that move the knee.  Nerve supply to the knee: Joint The joint is supplied by branches of: – Femoral – Tibial – Common peroneal – Obturator  Nerve supply to the knee: Cutaneous The skin surrounding the knee may be innervated by: Saphenous. Femoral cutaneous – Lateral – Intermediate – Medial – Posterior Lateral cutaneous calf. A bit of obturator  Vascular structures of the knee: arteries 8 arteries, supplied by 4 larger arteries. Form an anastomosis round knee. From the popliteal: – Superior lateral genicular. – Superior medial genicular. – Inferior lateral genicular. – Inferior medial genicular. From the tibial Posterior tibial – Anterior tibial recurrent recurrent – Posterior tibial recurrent. From the femoral – Descending genicular From lateral circumflex – Genicular Knee arteries: anterior view Descending genicular (branch of femoral) Genicular  Knee veins Broadly all the knee arteries have a companion vein which drains blood from the region. These drain into the popliteal vein. Short saphenous v Also draining into this vein are: – Posterior tibial – Anterior tibial – Small saphenous Long saphenous v communicates with the above v’s and drains medial knee.  Lymphatics 6 or 7 popliteal nodes, embedded in fatty tissue of popliteal fossa. – (Blue blobs in diagram) Drain proximally towards the deep inguinal nodes.  supra-patella pre-patella popliteal deep infra-patella superf. infra-patella  Pes anserinus Pes anserinus bursa Semimembranosus and tendinosus cross over further down. Tendons of sartorius, gracilis and semitendinosus overlie the bursa, insertion of semimembranosus is posterolateral to the bursa, MCL is anterior to the bursa.  Knee joint motion Predominantly flexion and extension. These happen in open and closed kinetic chain. Some medial and lateral rotation in association with knee Knee flexion(bending) locking mechanism.  Knee motion in gait STANCE PHASE SWING PHASE 180 EXT FLEX HS FFL MS HL TO HS  Abnormal knee positions Sagittal plane Genu Genu Genu – Genu recurvatum valgum varum recurvatum Hyperextended Frontal plane – Genu varum Bow legs – Genu valgum Knock knees Transverse plane – Squinting patellae  Patellofemoral joint cont. Lateral tracking can lead to chondromalacia patellae (softening of patellar cartilage), not always symptomatic, subluxation, dislocation... decreased VMO strength patella position – Tilt (med/lat movement) – Rotation (inf/sup patella poles not vertical) – Displacement (sup/inf movement) Basic Knee Joint Examination  Observation Need to adequately expose both knees Must have proper examination table Stance: eg. g.varum/valgum/recurvatum, Baker’s cyst – Posterior protrusion of the synovial membrane, seen as popliteal swelling prone and in stance – Spontaneous, sometimes associated with RA  Cruciate Ligaments Injury: often when leg is restricted from moving, and thigh excessively int/ext rotates upon it Tests: – anterior drawer sign – posterior drawer sign – Lachman test – pivot shift test (X) – posterior sag test  Anterior & Posterior Drawer Sign knee at 90 degrees flexion patient’s foot kept stable hamstrings need to be relaxed tibia drawn anteriorly to test ACL pushed posteriorly for PCL assess extent of movement and quality of end point – Reproduce any pain? Anterior & Posterior Drawer Sign Increasingly firm pull Pain/ROM/QOM Compare L to R Greater than or equal to 0.5cm displacement – Ruptured ACL  Lachman Test follows ACL and PCL test – More sensitive than, pt. Less able to contract hamstrings flex knee to 30°, grasp proximal tibia and support distal femur – Size of pt./practitioner - assistant/pillows? tibia then pulled anteriorly note difference in translation and the presence or absence of a firm end point when uninjured the ligament should have a crisp end point as it stops forward progression of the tibia  Lachman Test... complete rupture of the ligament results in a notable (>4mm) increase in translation & an absence of a firm end point if there is an increase in translation and an end point, then a partial rupture of the ACL or an injury to the PCL should be considered Lachman Test...  Posterior Sag PCL rupture test thigh muscles need to be relaxed patient supine flex knees to 90 degrees, hold heel when a PCL tear is present the tibia should sag posteriorly  Collateral Ligaments knee fully extended and at 30 degrees of flexion to relax posterior knee capsule – Extended +ve = MCL & cruciate damage – Flexed +ve = MCL damage only apply a varus (LCL) and a valgus (MCL) force do not allow the femur to rotate assess for pain, extent of movement and feel for an end point Muscle spasm can mask a low-grade tear Best if tested shortly after injury Collateral Ligaments Variation… Foot & ankle between chest wall and arm  Menisci Apley Compression Test Meniscal injury – Rotational force – Accompanied by a ‘pop’ sometimes – Often able to continue activity (unlike most other ligamentous injuries) – Swelling development in area – Sometimes unable to fully ‘lock’ the knee in extension - due to bits of torn meniscus  Apley Compression Test prone knee flexed to 90 degrees push down on foot – Int/ext rotate the tib – Like a ‘pepper grinder’ places pressure on to the posterior half of the menisci pain if a tear(s) are present Apley Compression Test  Patellofemoral joint syndrome Also called: anterior knee pain syndrome, overutilization syndrome Gradual onset of pain around the patella Incidence: high in: – Young athletic individuals – Obese adolescent females Observation – standing (biomechanics)- patellar position? – lying supine – Swelling - inf/sup, med/lat to patella?  PFJ Palpation – tenderness where? – Warmth? – tight lateral retinaculum – move medially, laterally, inferiorly and superiorly and check for pain and crepitus – active movement with quad. contraction – apprehension test Isn’t particularly good test Lots of false positives  Patellofemoral joint Tx Patella position – Displacement, tilt, rotation – McConnell taping where patella is taped medially (McConnell, 1986; Shelton & Thigpen, 1991) Muscle function – VMO strength and timing Foot Orthoses (Saxena, Amol and Haddad, 1998)  Summary The knee joint is complex! Podiatrists play an important role in managing chronic injuries, esp. patellofemoral joint syndrome Some structures of greater functional importance in the knee Homework: familiarise yourselves with surface anatomy of knee – Eg. patella, lat/med fem condyles, joint line, tib tuberosity, fibular head  Summary You should now be able to describe: – The structure of the knee. – How stability is maintained. – Normal movements of the knee. – The relationship of the medial meniscus and MCL. – The function of the menisci. – The location and function of the ACL & PCL.  Look forward Bus leaves for Leicester at 8.45 sharp. For next week: – Review the structure and function of the knee in today’s lecture. – Read supplementary notes on NILE regarding assessment of the knee. Next week: – The anterior leg and dorsum of the foot, me. – Posterior thigh and pop fossa, Leicester.