1. Session 3 The Knee Anatomy of the knee Biomechanics – how it moves
Structure and function of ligaments
Review of common conditions of the knee, how they present and how they can be managed

3. Anatomy of the Knee joint
2 joints – patellofemoral joint more involved with bending and straightening, tibiofemoral joint more involved with weightbearing
Condyles of the femur covered with articular cartilage
Lateral condyle higher ridge orientated front to back, medial condyle more angled
Groove for the patella to slide up and down
Note ligaments medial, lateral, anterior cruciate, posterior cruciate and menisci
Posterior view with the knee straightened

4. Looking down into the knee joint
Medial tibial plateau has a larger circumference than the lateral
Medial meniscus is a more open C shape
Lateral meniscus nearly closed C
Made of fibrocartilage – more fibres arranged parallel to circumference
Tethered to the bone by the anterior and posterior horns
Attached around the outside edge to the joint capsule
The outer edge of the meniscus has a blood supply and nerve supply
Slow metabolic turnover therefore ability to repair limited

5. Side view of the knee joint
Femoral condyle seen as a wheel and wedge, more rounded surface in contact when knee bent, flatter when straight
Note the convex shape of the tibial plateau
Bursae – fluid filled sacks to lubricate movement. Pre-patellar bursa over the patella, if inflamed housemaid’s knee, deep infrapatellar bursa – lubricates movement of patellar tendon in flexion, superficial infrapatellar bursa – movement skin tibial tuberosity – clergyman's knee
Wedge shape of menisci in cross section
Capsule of the joint – collagen-elastin, network of blood vessels and nerves – mechanoreceptors and pain nerve endings (see later), lined with synovial membrane, ligaments blend with the capsule. Extends upwards 2-3 fingers breadths above the base of the patella – suprapatellar bursa

6. Lateral view of the knee
Note the lateral ligament of the knee from the femoral condyle to the head of the fibula
Rounded cord like ligament
Behind the lateral condyle there are thickenings in the capsule fabello-fibular ligament also the arcuate complex – all give stability to the lateral and posterolateral part of the joint
Warning – next slide is human dissection. As they say look away now if squeamish!

7. Medial view of the knee
Dissection of the knee to show the fan-shaped medial ligament from the medial condyle of the femur to the tibia
Some of the fibres extend a hands breadth down onto the tibia
Tendons of several muscles (sartorius, gracilis, semitendinosus) overlie the ligament, several bursae in this region can become swollen and painful

9. Vastus Medialis Oblique fibres
Vastus medialis oblique – particular function in producing the last few degrees of straightening of the knee but also they insert into the patellar retinaculum, thickening of the capsule which helps to guide the patella in the patellar groove
Must be in balance with the strong lateral structures such as the tensor fascia lata which tend to pull the patella laterally out of the groove

11. Popliteus Muscle
Originates from the outside of the lateral condyle of the femur
Inserts into the back of the inside edge of the tibia
Action – it is a weak flexor of the knee
More important role is to unlock the knee. With the foot on the ground contraction of shortening of the muscle rotates the femur laterally (outwards)

12. Biomechanics of movement
When moving from extension to flexion there is rolling and gliding of the articular surfaces

13. Rotation of the femur and tibia with movement
Because of the shape of the articular surfaces particularly the increased radius of the medial condyles when the knee is extended as in kicking a football the tibia spins (rotates) laterally
When the foot is fixed as in standing from a squatting position the femur spins medially

14. Behaviour of the ligaments with movement
Moving from squatting to standing looking at the inner (medial) side of the knee
Roll and glide of the femur lifts the point of origin of the ligaments tensioning them to provide stability
Diagram not quite correct as some of the ACL is taut in flexion
The medial ligament is fan shaped so the front and middle portions remain taut in flexion

15. Posterior cruciate ligament during movement
The ligament attaches to the back of the tibia and moves forwards and upwards to attach to the inside of the medial femoral condyle
As the knee straightens, the area of attachment to the femur is lifted and the posterior part of the ligament becomes taut
The anterior portion becomes taut in flexion, it also prevents the tibia moving further backwards

16. Meniscal movement during flexion and extension
Looking down on the menisci as they sit on the upper surface of the tibia
Movement occurs between the femoral condyles and the upper surface of the menisci
In flexion the lateral meniscus is carried backwards with the femoral condyle
It moves forwards with extension
In the last 20 degrees of extension the medial femoral condyle rotates medially taking the medial meniscus back slightly
The lateral meniscus slides forwards
As the knee extends the flatter surfaces of the condyles comes into contact squashing and elongating the menisci front to back
The menisci increase the contact area between the femur and tibia
They increase lubrication of the joint surfaces

17. Patellar movement extension to flexion
As the knee moves from full extension 0 degrees to full flexion the patella slides down in the trochlea surface of the femur
It also bends backwards on the patellar tendon
Looking from the front it also moves in a C shape open laterally

19. Microscopic structure of ligament
Ligament derived from Latin word ligare or binding
White, shiny band like structures connect bones to each other
Sinusoidal or wavy pattern referred to as crimp
Composed of small amounts of cells – fibroblasts and large extracellular matrix
Fibroblasts account for 20% of tissue volume
Fibrous component of ECM greater collagen component than elastin
Collagen fibres orientated in a range of directions reflecting the fact that bones can move in a number of directions
Combination of strength and extensibility enables ligaments to absorb more strain energy per unit weight than any other biological material, effective shock absorbers

20. Behaviour of the ligament under tension
As force is applied to stretch the ligament the crimp of the fibres is pulled out
permits stretching by 10-15% before failure

21. Role in joint proprioception

22. Type III and IV receptors
Type III - found on the surface of the ligament close to the bony attachment
Become active at the extremes of movement
Signal sent via the sensory nerve to the spinal cord
Reflex contraction of muscle to protect the joint
Information also sent to the sensory cortex in the brain
Type IV – Free nerve endings, fire with marked mechanical deformation or tension. Also a pain receptor

23. Spinal cord level

24. Receptors in the joint capsule
Type I – Ruffini adapt slowly to mechanical force
Sensitive to and stimulated by movement (velocity) also monitor the static position of the joint
Type II – Paccinian adapt quickly to mechanical force
Only stimulated by and sensitive to changes in position
Responsible for kinaesthetic motion sense
Also sensitive to pressure

26. Structure and function of the menisci
Thick collagen fibres distributed in proteoglycan matrix
Slightly compressible, very tough
Found in areas where high compressive forces are applied to joints

28. Vulnerability of the menisci
The medial meniscus is attached firmly and extensively to the capsule of the joint
The horns of the meniscus are widely separated as they insert into the tibial plateau
Its capacity for movement is limited
The lateral meniscus is more loosely attached to the capsule with the horns attached close together
Considerable movement of the meniscus is possible
The peripheral edge of the meniscus has a blood supply and is also innervated

29. Meniscal injuries
Usually associated with sport, particularly twisting with the foot fixed
The medial meniscus is more frequently involved as it is less mobile and more easily caught between the femoral condyle and tibial plateau
The joint can become locked as the torn section of the meniscus impedes normal movement
The knee can also give way
If the tear occurs around the periphery there is potential for healing

30. Arthroscopic knee surgery
If the knee is troublesome the torn section of meniscus can be removed using an arthroscope which is minimally invasive
Total removal of the meniscus is avoided as this leads on to degenerative changes within the joint

31. Mechanism of injury to the medial ligament

32. Injury to the medial collateral ligament
Usually a sporting injury where a force is applied to the outside of the thigh with the foot fixed
The ligament can also be damaged if the tibia is forcibly externally ( outwardly rotated)
A moderate strain will sprain or over stretch some of the fibres of the ligament
A stronger force can produce a partial tear of the ligament
The anterior cruciate ligament may also be stretched
A huge force will rupture the ligament completely
The anterior cruciate may also rupture
The medial meniscus can also be torn in this type of injury
Sprains and partial tears of the ligament are very painful as the ligament is highly innervated
Partial and complete tears make the joint unstable

33. Clinical examination
The examiner supports the leg and applies pressure to the outside of the thigh
The examiners right arm applies outward pressure to the lower leg
If the ligament is sprained this will produce pain
If there is a partial tear there will be some joint laxity with pain
If the ligament is completely torn there will be greater laxity of the joint
Sprains and partial tears will heal in 6 weeks
If the ligament is completely torn further investigations will be required to ascertain which other structures are damaged
Surgical intervention and rehabilitation is required to regain full function

34. Injury to the Lateral collateral ligament
The picture shows a severe injury where the knee is hyperextended which is likely to cause additional damage to the cruciate ligaments

35. Mechanisms of injury of the anterior cruciate ligament

36. Injury to the anterior cruciate ligament and management
The ACL lies within the joint capsule
Forces sufficient to partially tear or rupture the ligament cause bleeding into the joint – haemarthrosis. Swelling appears almost immediately
The joint may be unstable if there is major damage
Emergency department, orthopaedic clinic for assessment and management
MRI, arthroscopy
Surgical repair depends on age, occupation, level of participation in sport
Tendon graft taken from the patellar tendon with bone block, screwed into place
Physiotherapy to regain full range of movement, increase muscle strength, retrain proprioception

37. Sites of attachment of the tendon graft

38. Mechanism of injury to the posterior cruciate ligament
Injured by a direct blow to the front of the tibia with the knee flexed
Dash board injury – hitting the knee on the dash board during an RTA
At the bottom of a scrum when the leg is forced into flexion and rotation
The ligament originates outside the joint capsule therefore if it is torn bleeding appears in the calf muscle over several days

39. Mechanism of injury and appearance on examination

40. Posterior cruciate repair using patellar tendon graft
Reasoning for reconstruction as for ACL
Rehabilitation required to gain full movement, strength and function

41. OA knee
The knee is the most common site in the body for osteoarthritis, followed by the hip. Common to have it in more than one joint.  million people in England are estimated to have osteoarthritis of the knee (around 18% of the population aged 45 and over (Arthritis Research UK)
Risk factors – obesity, previous knee injury, selected physical activity, family history, presence of Heberden’s nodes in the hand
Higher numbers of population with OA knee than progress to surgery. Some people it can remain stable and manageable for many years

42. Presentation
Pain around the knee which can radiate into the shin and or thigh
Swelling noticeable at the front of the joint but can be at the back – bakers cyst (see later)
Restriction of flexion and extension, also less noticeable loss of rotation
X-ray changes – loss of joint space, formation of osteophytes
Presence of deformity – genu valgum (knock knees) genu varum (bandy legs), flexion deformity – unable to straighten the knee fully
Muscle wasting particularly the quadriceps muscle
Walking with a limp

43. Bakers cyst Note valve like connection with the knee joint
Quadriceps exercises can push fluid into the sack but not able to return after exercise

44. Management
Research finding that the most effective management is weight loss
Walking with a stick to off load the joint
Reduction of swelling – ice packs, cannot straighten knee fully in the presence of swelling greater than 10 mls
Careful specific exercise to strengthen the supporting muscles of the joint, primarily the quadriceps muscle
Careful exercise to increase range of movement without aggravating pain
NSAIDs with care due to gastric side effects

45. Management
Analgesics. However paracetamol found to be ineffective for arthritic pain
Transcutaneous Nerve Stimulation – TNS can be helpful
If debilitating and cannot be managed conservatively, or in the presence of significant deformity, referral for consideration of joint replacement - TKR
Important to undertake surgery at the right point, too soon and it will not last long enough, too late and the result may be poor
Up to 1 in 5 patients are dissatisfied with the outcome of TKR
Due to a number of factors – patient expectations, general health, mental status

46. Examples of joint replacement

47. Anterior knee pain
Pain over the front of the knee - made worse by prolonged sitting or going up and down stairs
In young people it can be associated with flat feet and knock knees with poor muscle function around the hip and knee
In older patients it is more likely to be associated with patello-femoral OA
Anterior knee pain can also be associated with patellar tendinopathy, bursitis, irritation of the fat pad or the presence of plicae

49. Management Arch supports if flat feet
Muscle function – strengthen vastus medialis oblique, gluteus medius, abdominals
Stretch tight muscles – tensor fasciae lata, hamstrings, gastrocnemius
Offload the patella – strapping may help to correct patellar tracking

50. Exercises to increase flexionB C
Diagram A and B show passive exercise to increase knee flexion
Diagram C shows active knee flexion against gravity which increases the strength of the knee flexors or hamstring muscles
Exercise C can be progressed by putting a weight onto the heel
Exercise C could also be used as an exercise to improve proprioception or balance for the right leg

51. Quadriceps exercises
Inner range quadriceps exercises are important to achieve full extension (straightening) of the knee. This is often very difficult to do post surgery due to inhibition of the quadriceps muscle due to pain or swelling
Extension through range in sitting works the quadriceps from middle range to inner range. This exercise can be progressed by adding a weight to give more resistance to muscle contraction. The muscle responds by laying down additional protein or hypertrophying

52. Exercises for vastus medialis oblique
Activation of vastus medialis oblique can be stimulated by contracting the adductors as they share the same nerve supply. Activation plus wall slide increases the difficulty of the exercises and enhances strengthening
Forward lunging and small knee bend maintaining correct alignment of the hip and knee is a progression of muscle co-ordination and strengthening

53. More advanced exercises
More advanced re-education of balance
High level re-education and strengthening if these activities are required for sport or work

54. Next session
Look at the ankle (talocrural joint) and the subtalar joint (hind foot)
Anatomy of the joints
Muscles and how the joints move (biomechanics)
Structure of tendons and Achilles tendinitis
Some common conditions including sprained ankle, involvement of the common peroneal nerve, the importance of retraining balance