Chapter 18 The Knee Complex

Overview The knee joint complex is extremely elaborate and includes three articulating surfaces, which form two distinct joints contained within a single joint capsule: the patellofemoral and tibiofemoral joint Given the frequency of knee injuries and the intricate nature of this joint complex, clinicians caring for knee injuries must have an extensive knowledge base

Anatomy The tibiofemoral joint The tibiofemoral joint consists of the distal end of the femur and the proximal end of the tibia The distal aspect of the femur is composed of two femoral condyles that are separated by an intercondylar notch The intercondylar notch serves to accept the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL)

Anatomy Distal femur The femoral condyles project posteriorly from the femoral shaft The smaller lateral femoral condyle is ball-shaped and faces outward, while the elliptical-shaped medial femoral condyle faces inward The lateral epicondyle serves as the origin for the lateral head of the gastrocnemius, and the lateral collateral ligament (LCL) The medial condyle serves as the insertion site for the adductor magnus, and the medial collateral ligament (MCL)

Anatomy Femoral condyles The anterior-posterior length of the medial femoral condyle is greater than its lateral counterpart by about 1.7 cm The length of the articular surface of the medial femoral condyle is longer than the length of the lateral femoral condyle

Anatomy Proximal tibia The proximal tibia is composed of two plateaus separated by the intercondylar eminence, including the medial and lateral tibial spines The tibial plateaus are concave in a medial-lateral direction In the anterior-posterior direction, the medial tibial plateau is also concave, while the lateral is convex, producing more asymmetry, and an increase in lateral mobility The medial plateau has an approximately 50% greater surface area than the lateral plateau, and its articular surface is 3 times thicker

Anatomy Patellofemoral Joint The patellofemoral joint is a complex articulation, dependent on both dynamic and static restraints for its function and stability The patella is a very hard triangular-shaped bone, situated in the intercondylar notch, and embedded in the tendon of the quadriceps femoris muscle above, and the patella tendon below The posterior surface of the patella can include up to seven facets, with three on the medial and lateral surfaces

Anatomy The patellofemoral joint functions to: Provide an articulation with low friction Protect the distal aspect of the femur from trauma, and the quadriceps from attritional wear Improve the cosmetic appearance of the knee Improve the moment arm of the quadriceps Decrease the amount of anterior-posterior tibiofemoral shear stress placed on the knee joint

Anatomy The knee joint capsule is composed of a thin, strong fibrous membrane is the largest synovial capsule in the body A synovial membrane lines the inner portion of the knee joint capsule. By lining the joint capsule, the synovial membrane excludes the cruciate ligaments from the interior portion of the knee joint, making them extrasynovial yet intra-articular

Anatomy The proximal tibiofibular joint An almost plane joint with a slight convexity on the oval tibial facet and a slight concavity of the fibular head Has more motion than its distal partner

Anatomy Ligaments The static stability of the knee joint complex depends on four major knee ligaments, which provide a primary restraint to abnormal knee motion Anterior cruciate Posterior cruciate Medial collateral Lateral collateral

Anatomy The cruciate ligaments Are intra-articular/extra synovial because of the posterior invagination of the synovial membrane Are different from those of other joints, in that, they restrict normal motion, rather than restrict abnormal motion

Anatomy Both the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL) are each named according to their attachment sites on the tibia

Anatomy The anterior cruciate ligament One of the most important ligaments to knee stability Serves as a primary restraint to anterior translation of the tibia relative to the femur, and a secondary restraint to both internal and external rotation in the non-weight bearing knee

Anatomy The posterior cruciate ligament Provides 90-95% of the total restraint to posterior translation of the tibia on the femur, with the remainder being provided by the collateral ligaments, posterior portion of the medial and lateral capsules, and the popliteus tendon

Anatomy The medial collateral ligament (MCL) The anterior fibers of this ligament are taut in flexion, and can be palpated easily in this position The posterior fibers, which are taut in extension, blend intimately with the capsule and with the medial border of the medial meniscus, making them difficult to palpate

Anatomy The lateral collateral ligament (LCL) The main function of the LCL is to resist varus forces It offers the majority of the varus restraint at 25° of knee flexion, and in full extension

Anatomy Secondary restraints include: The structures in the posterior-lateral and posterior-medial corners of the knee The hamstrings and quadriceps The patellar ligament, oblique popliteal ligaments, and the fabella

Anatomy Menisci The crescent-shaped lateral and medial menisci, attached on top of the tibial plateaus, are pieces of fibrocartilage material that lie between the articular cartilage of the femur and the tibia

Anatomy Medial meniscus Semi-lunar or C-shaped Larger and thicker than its lateral counterpart Sits in the concave medial tibial plateau Wider posteriorly than anteriorly

Anatomy Lateral meniscus Rounder O-shaped Sits atop the convex lateral tibial plateau Smaller and thinner, than its medial counterpart More mobile than its medial counterpart Two mensicofemoral ligaments, the ligaments of Humphrey and Wrisberg attach to the lateral meniscus

Anatomy Menisci Function The menisci assist in a number of functions including load transmission, shock absorption, joint lubrication, joint stability and the guiding of movements

Anatomy Bursae There are a number of bursae situated in the soft tissues around the knee joint The bursae serve to reduce friction, and to cushion the movement of one body part over another

Anatomy Plica Synovial plica represents a remnant of the three separate cavities in the synovial mesenchyme of the developing knee

Anatomy Retinacula Formed from structures in the first and second layers of the knee joint The retinacula can be subdivided into the medial and the lateral retinacula for clinical examination and intervention purposes

Anatomy Muscles The major muscles that act on the knee joint complex are the quadriceps, the hamstrings (semimembranosus, semitendinosus, and the biceps femoris), the gastrocnemius, the popliteus, and the hip adductors

Anatomy Vascular supply The major blood supply to this area comes from the femoral, popliteal, and genicular arteries

Anatomy Neurology Femoral nerve Sciatic nerve Saphenous nerve Common peroneal Tibial

Biomechanics The tibiofemoral joint The tibiofemoral joint, or knee joint, is a ginglymoid, or modified hinge joint, which has six degrees of freedom The bony configuration of the knee joint complex is geometrically incongruous and lends little inherent stability to the joint Joint stability is therefore dependent upon the static restraints of the joint capsule, ligaments, and menisci, and the dynamic restraints of the quadriceps, hamstrings, and gastrocnemius

Biomechanics Patellofemoral joint To assist in the control of the forces around the patellofemoral joint, there are a number of static and dynamic restraints

Biomechanics The Quadriceps (‘Q’) angle Can be described as the angle formed by the bisection of two lines, one line drawn from the anterior superior iliac spine (ASIS) to the center of the patella, and the other line drawn from the center of the patella to the tibial tubercle The most common ranges cited are 8-14° for males and 15-17° for females Angles of greater than 20° are considered abnormal and may be indicative of potential displacement of the patella

Biomechanics Patella-Femur Contact and Loading The amount of contact between the patella and the femur appears to vary according to a number of factors including: The angle of knee flexion The location of contact The surface area of contact The patellofemoral joint reaction force

Biomechanics Patella Stability Patella stability is dependent on 2 factors: Static restraints Dynamic restraints

Biomechanics Patellar Tracking In the normal knee, the patella glides in a sinuous path inferiorly and superiorly during flexion and extension respectively, covering a distance of 5-7 cm with respect to the femur One proposed mechanism for abnormal patellar tracking is an imbalance in the activity of the of the vastus medialis obliquus (VMO) relative to the vastus lateralis (VL)

Biomechanics Open and Closed Kinetic Chain Activities An understanding of the forces generated and the muscle activity employed by different exercises is essential for determining how to achieve optimal balance of muscle force, ligament tension, and joint compression Whether the motion occurring at the knee joint complex occurs as a closed or open kinetic chain has implications on the biomechanics and the joint compressive forces induced

Examination History The diagnosis of tibiofemoral and patellofemoral joint disorders can often be made on the history and physical examination alone With the larger number of specific tests available for the knee joint complex, it is tempting to overlook the important role of the history, which can detail both the chronology, and mechanism, of events

Examination History The mechanism of the injury is one of the most important aids in making a diagnosis The position of the joint at the time of the traumatic force dictates which anatomic structures are at risk for injury The primary mechanisms of injury in the knee are direct trauma, a varus or valgus force (with or without rotation), hyperextension, flexion with posterior translation, a twisting force, and overuse

Examination History There is a significant temptation to cut corners with a patient who presents with anterior knee pain, and to proceed directly to the diagnosis of patellofemoral pain Particular activities can help with differential diagnosis Complaints of pain that occur when a patient arises from a seated position, negotiates stairs, or squats, are associated with patellofemoral dysfunction

Examination Systems Review Knee pain can be referred to the knee from the lumbosacral region (L 3 to S 2 segments), or from the hip

Examination Observation The observation component of the examination begins as the clinician meets the patient and ends as the patient is leaving This informal observation should occur at every visit

Examination Active Range of Motion with Passive Over pressure Normal knee motion has been described as 0° of extension to 135° of flexion, although hyperextension is frequently present to varying degrees Passive movements, as elsewhere, can determine the amount of motion and the end-feel Resisted testing is performed to provide the clinician with information about the integrity of the neuromuscular unit, and to highlight the presence of muscle strains

Examination Palpation For palpation to be reliable, the clinician must have a sound knowledge of surface anatomy, and the results from the palpation exam should be correlated with other findings

Examination Functional Tests Functional outcome following knee injury must consider the patient’s perspective, and not just objective measurements of instability Functional motion requirements of the knee vary according to the specific task A number of commonly used rating scales can be used to assess knee function

Examination Special Tests Special tests are merely confirmatory tests and should not be used alone to form a diagnosis The results from these tests are used in conjunction with the other clinical findings to help guide the clinician To assure accuracy with these tests, both sides should be tested for comparison

Intervention Acute Phase The goals during the acute phase are: Reduce pain and swelling Control inflammation Regain range of motion Minimize muscle atrophy/weakness Attain early neuromuscular control Maintain general fitness

Intervention Functional Phase The goals for this phase include: Attain full range of pain free motion Restore normal joint kinematics Improve muscle strength Improve neuromuscular control Restore normal muscle force couple relationships