Peter lawlor Flashcards
Describe the reinforcements of the knee joint capsule
Anteriorly
- Replaced by the patellar ligament and the patella itself.
-The patellar retinaculum; tendon extensions of the vastus medialis and lateralis muscles of thigh.
Medially/ Laterally
-The medial and lateral collateral ligaments.
Posteriorly
- The oblique popliteal ligament; tendon extension of the semimembranosus muscle (hamstring muscle)
Describe the anatomy of the menisci
Anatomy
-2x menisci in each knee; medial and lateral
-They are fibrocartilage, wedge shaped structures.
-They overlay the medial and lateral tibial plateau.
-They are thicker peripherally, and thinner on inner aspects.
-The medial meniscus is larger than the lateral.
-The transverse ligament runs between both anterior horns.
Medial meniscus
-Serves as an attachment point for the medial collateral ligament
–> This makes the medial meniscus less mobile and more susceptible to injury
-It is firmly attached to the fibrous capsule.
-It is firmly attached to tibial plateau by the coronary ligament.
Lateral meniscus
- Smaller than medial meniscus
- Is NOT firmly attached to fibrous cartilage.
- The tendon of the popliteus muscle prevents it from attaching to capsule
- The meniscofemoral ligament attaches the posterior horn to the medial tibial condyle
List 3 functions of the menisci
- Load bearing/Shock absorption
-> transmits >50% of weight applied to joint and more evenly spreads force so it is not being applied to a single point on the tibia. - Joint stability/Congruence
- The shape of the medial meniscus prevents anterior movement of the tibia.
- The menisci improve overall congruence of the femoro-tibial joint.
-It also acts as a point of attachment for ligaments thereby strengthening joint. - Proprioception.
What factor limits the healing capacity of the meniscus following injury?
The blood supply to the meniscus in an adult is limited.
The inner portion is particularly susceptible to permanent degenerative damage due to its lack of vasculature; for this reason it is called the “white zone”.
The peripheral portion has some but limited blood supply - for this reason it is called the red zone
What is the blood supply to the knee joint
Superior genicular arteries (from femoral)
Inferior genicular arteries (from popliteal)
These form an anastomosis around the joint
What characteristic of the knee capsule make it susceptible to effusions?
The capsule is fairly loose, and the synovial and fibrous component do not always coincide.
Some portions of the synovial membrane extend beyond the scope of the fibrous capsule to form fluid-filled bursae - these are communicating bursae as they are extensions of the synovial space. Therefore excess fluid in bursae can cause effusion.
Examples of communicating bursae include:
- Suprapatellar
- Popliteus
- Gastrocnemius.
Give an example of communicating and non-communicating bursae
Communicating:
-Suprapatellar
-Popliteus -> bakers cyst
-Gastrocnemius
Non-communicating
-Prepatellar -> housemaids knee
-Superficial infrapatellar -> clergymans knee
Outline the causative factors of OA
Causative factor can be described as varying but is thought to be due to: ageing, genetic factors and biomechanical stress on the joint -> contributes to the progressive loss of cartilage leading to bone on bone friction.
Ageing: chondrocytes lose capacity to maintain the cartilaginous matrix.
Biomechanical stress: obesity, joint injury, mal-alignment, poor stability -> can lead to increased unit load on the joint.
Outline the pathophysiology of OA
Initially
*Causative factor will result in chondrocyte injury
*Chondrocytes respond by releasing IL-1
*Other mediators involved include TNF-a, TGF-B
*These mediators will result in:
–> Increased aggrecanases -> proteoglycan breakdown
–> increased matrix metalloproteinases -> increased collagen breakdown
*These will result in loss of integrity of cartilage matrix -> becomes weaker.
* Chondrocyte injury eventually leads to chondrocyte death
Subsequently
* Cartilage gets worn away below the tide mark
-> neovascularisation as new vessels grow in from the epiphysis and fibrocartilage is laid down (this is influenced by VEGF)
* This fibrocartilage eventually gets worn away exposing the subchondral bone which become eburnated (smooth/polished due to friction)
* Fibrillation/cracking of the cartilage -> influx of synovial fluid forming subchondral cysts.
* disordered focal regrowth (influenced by TGF-B) leads to osteophyte formation.
list 4 findings on x-ray indicative of OA
Generally seen in DIP/PIP’s and first carpo-metacarpal joint
- Joint space narrowing
- Subchondral sclerosis -> thickening of subchondral bone just below hyaline cartilage - can show increased collagen deposition and abnormal mineralisation.
- Subchondral cysts
- Osteophytes
Describe the molecular composition of articular cartilage.
Main molecular components are:
(i) Collagen- mostly type II
(ii) Glycosaminoglycans- Chondroitin sulfate, keratin sulfate, hyalauronic acid
(iii) proteoglycans
(iv) link proteins.
Chondroitin sulfate is attached to a core proteins (aggrecans) forming a proteoglycan.
Link proteins bind the proteoglycans to hyalauronic acid forming negatively charged proteoglycan aggregates which attract water molecules.
Collagen fibrils (type II) surround the structures and restrain the proteoglycans thereby preventing them from maxing-out on their water uptake -> this means that the structure is turgid and compressible.
Cruciate ligament injuries - outline the mechanism of injury and name a test used to diagnose
ACL
-Planted foot, hyperextension and femur rotation independant of lower leg.
-Anterior drawer test
PCL
-Dashboard injury; sudden force to anterior proximal tibia forcing it posteriorly.
-Posterior drawer test
Outline the mechanism behind a medial and lateral meniscal tear - name test used to diagnose
Medial meniscus
-Valgus force to knee and external rotation
Lateral meniscus
-Varus force and internal rotation
Apley’s test or McMurrays test.
what is the unhappy triad injury
Ant cruciate lig
Medial collateral
Meniscus (typically medial but lateral now known to be involved often also)
What is meant by “congruity”
Congruity refers to how well aligned and how well fitted 2 opposing bones are within their joint.
