Layers of Articular Cartilage - Everything You Need To Know

Layers of Articular Cartilage - Everything You Need To Know 

 Dr. Nabil Ebraheim

https://www.youtube.com/watch?v=9g0TG249BDI

The articular cartilage is made up of many layers.  If you look at the joint, this will be the top of the articular cartilage.  If you magnify the joint, this is the articular surface, the subchondral bone and the cancellous bone.

 

How many layers are in the articular cartilage?

There are 4 layers in the articular cartilage.

1. Superficial zone

2. Middle zone

3. Deep zone

4. Calcified zone

In every layer there will be some changes.  These layers will differ in the chondrocytes, the morphology, size and in the orientation of the collagen bundles, and in the amount of water and proteoglycan present.

We start with the superficial zone which is about 10 to 15%.  Another name for the articular cartilage layer is the tangential layer.  The superficial zone is really a thin layer, but it is an important layer.  You find that the cartilage fibers are parallel to the surface.  The chondrocytes are elongated and parallel to the axis of the articular cartilage.  It has the highest concentration of collagen, which means it has the highest tensile strength, the highest concentration of water and the lowest concentration of proteoglycans.  It has less cells than the deep zone.  You do not want proteoglycans here because it will swell (do not want the cartilage to swell in this area).  This is the area connected to the motion of the articular cartilage, so you have to have a high tensile strength.  You have to have some collagen and some water, but you do not need proteoglycans because you do not need the cartilage to swell.  Both the cells and the collagen fibers are pounded by the pressure, becoming flattened and elongated along the long axis of the joint.

The middle zone is the transition zone (zone between the superficial and the deep zones).  The chondrocytes and the collagen fibers are oriented randomly.  In the middle cartilage layer, you will find the collagen in an oblique orientation.  You can see the disparity between the arrangement of the structures in the superficial zone and the arrangement of the structures in the deep zone.  You can imagine the transition zone is really disorganized because they do not know which zone they belong to.

The deep zone is about 30%.  The collagen fibers are perpendicular to the surface.  There are more cells, they are round and they are arranged in columns perpendicular to the joint.  The deep zone has the highest concentration of proteoglycans and the lowest concentration of water.  You do not need water inside of the cartilage.  In the deep zone, the chondrocytes are arranged in columns and the collagen fibers are oriented vertical to the articular cartilage.  The deep layer is strong in compression.

The fourth layer is the calcified cartilage and then the cancellous bone.  The calcified cartilage will start at the tidemark and it has Type X collagen (it is a transition zone to the bone).  The calcified zone is the transitional zone between the cartilage and the subchondral bone.  There is a tidemark that goes over the calcified zone.  The tidemark is the boundary between the calcified and uncalcified layers of articular cartilage. The tidemark separates the deep zone from the calcified zone.  The tidemark is seen mainly in the mature articular cartilage of the joint (for example: not cartilage of osteochondroma).  

Hip Fractures Mechanism of Injury

 

Low energy fracture occurs in the elderly from a fall onto the greater trochanter. The young will try to protect themselves by falling on the wrist. High energy fractures can occur in both the young or the elderly  form either a fall or a car accident.

Femoral Neck Fracture Anatomy

 

The neck shift angle is approximately 130 degrees. Anteversion is approximately 10 degrees. The calcar is an area of stress transfer. It is a posteromedial dense plate of bone. It forms an internal strut within the inferior part of the femoral neck and the intertrochanteric area. No periosteum in the femoral neck and no abundant callus. The fracture heals by endosteal proliferation. The medial femoral circumflex artery is the most important blood supply to the femoral head. In young patients, injury is usually high energy that may lead to avascular necrosis. Some believe that surgery should be urgent in the young patient in order to decompress the compressed vessels. The more displaced the fracture and the more vertical the fracture, then the more likely that the risk of complications will occur including disruption of the retinacular vessels, avascular necrosis, and nonunion. Femoral neck reduction should be anatomic, either by closed technique or open technique (if closed reduction technique fails).

Bipartite Patella

 

Bipartite patella is a failure of the ossification centers of the patella to fuse. Common types of bipartite patella include inferior pole, lateral margin, and superolateral pole. The accessory ossification center at the superolateral pole remains unfused. In the cases of bipartite patella, you can see that the patella has two parts: the smaller part is rounded and usually located laterally. It can be confused with a fracture. The superolateral pole is the most common type (occurs in about 75% of patients). Try to get an x-ray of the other knee (it is bilateral in about 50% of the time). Skyline view x-ray with a squatting position (weight-bearing) may show displacement and increased separation of the fragment. The bipartite patella is usually asymptomatic, and it is usually an incidental finding on the x-ray. It may cause symptoms that mimic those of a fracture. Minor trauma or injury can cause the fibrous tissue between the two segments to become inflamed and irritated. Localized tenderness over the separated fragments, usually the superolateral part of the patella. The most common presentation is pain at the area of the separated fragments, especially during or after heavy physical activity or sports. It is usually asymptomatic and does not require treatment or surgery. In general, the most common error with bipartite patella is mistaking the condition for a fracture and fixing it (the patient really does not need surgery). Treatment is usually reassurance and observation, rest, knee immobilizer, physical therapy, and nonsteroidal anti-inflammatory medication (NSAID). Nonoperative treatment should be done for at least 6 months. These patients will improve without surgery. Surgery is rare, and it is excision of the fragment if the fragment is small. If the fragment is large, painful, and conservative treatment fails, then you can do lateral release of the retinaculum to reduce the traction force on the unfused, smaller fragment. Internal fixation and possible bone graft is rarely done if the fragment is large and painful.

Hip Fractures History Exam Evaluation of Patients

 

Obtain adequate history from the patient such as any syncopal episodes and loss of consciousness. The preinjury ambulatory status may determine the treatment selected for the patient. Falls and low sodium will increase the risk of hip fractures. Check for comorbidities. The number of comorbidities is directly related to 1-year mortality rate. Patients with 4 or more comorbidities are reported to have a higher 1-year mortality rate than patients with 3 comorbidities or less. Position of the leg is usually shortening and external rotation. You will be able to tell which hip is broken by looking at the feet of the patient. If the leg is shortened and externally rotated, then this is the broken hip. AP view and cross-table lateral view. In cross-table lateral view, you move the uninjured hip away. Cross-table lateral view is better than frog leg lateral view. Consider doing traction-internal view if the fracture is occult or comminuted. Check for hip arthritis and pathological fracture. If you have a comminuted femoral shaft fracture, you may look for an associated femoral neck fracture. In patients with femoral shaft fracture, the rate of associated femoral neck fracture is precisely undetermined, however it is approximately 5%, and the fracture may be overlooked in about 30% of the time. Normal x-rays of the hip do not mean that the patient with hip pain does not have a hip fracture. 8% of the patients may have an occult hip fracture. It may be important to get a CT scan of the neck of the femur when you have a comminuted femoral shaft fracture. This will help to diagnose an occult femoral neck fracture. You may see the fracture in abdomen/pelvic CT scan cuts, usually before surgery. Good for occult and stress fractures (if the patient cannot bear weight- get an MRI). If there is contraindication for an MRI, get a CT scan or bone scan. Bone scan increases sensitivity by waiting up to 72 hours after the injury. Deep vein thrombosis (DVT) can occur in about 80% of patients. Patients will need chemical and mechanical prophylaxis. The duration and the type of prophylaxis is not determined (no unanimity). Get the patient out of bed and allow weight-bearing as tolerated. The patient will autoregulate their ambulation. Preoperative cognitive impairment will lead to a higher incidence of delirium in patients with hip fractures. Delirium and time of surgery affected the length of stay in the hospital. Most patients with hip fractures between the ages of 50-80 years old were able to regain their mobility and independence. If the patient is older than 80 years old, the patient was able to regain their independence, but not their mobility with 70% of these patients requiring a walking aid at 12 months. The factors associated with the increased ability to ambulate and to live independently 1 year after surgery for femoral neck fracture are patients age 50-80 years old, ASA class 1, and pre-fracture independence. Some patients may delay coming to the hospital. They may have been lying on the floor for many hours or even days. Check the patient for DVT, ulcers, dehydration, and malnutrition (the patient may be very sick). May need comedical management with the medical team. Early surgery (within 48 hours) is associated with a decreased one-year mortality. Expedited definitive surgery of less than 24 hours will reduce the mortality rate at 30 days and at 1 year. A delay of more than 24 hours of surgery significantly increased the incidence of 30 day mortality, and 1 year mortality, as well as increased incidence of pulmonary embolism, myocardial infarction and pneumonia. If the patient has ASA 3 and ASA 4, this will increase the mortality rate for the patient (means that the patient’s condition is medically complicated and the patient is high risk). Types of ASA is classification of American Society of Anesthesiologists. ASA 1 is a lot better than ASA 4. In younger trauma patients, the femoral neck fracture should be dealt with urgently and after the overall condition of the patient is thoroughly evaluated to exclude other injuries. Early surgery may decrease the incidence of osteonecrosis.

Hip Fractures Types & Classifications

 

Femoral neck fractures can occur as a result of low energy trauma as in the elderly. Femoral neck fractures can also occur due to high energy trauma, such as with falls or motor vehicle accidents. Anatomic classification of femoral neck fractures includes subcapital, transcervical, basicervical. Subcapital is common. There are two famous classifications of subcapital fractures: Garden classification and Pauwel’s classification. Garden classification classifies the fractures according to the amount or degree of displacement. There are four types. It relates the amount of displacement to the risk of vascular disruption. This classification applies to the geriatric and insufficiency fractures.it is classified into two groups: nondisplaced are type I and type II, and displaced are type III and type IV. Garden classification type I is incomplete and impacted in valgus. Type II fracture is complete and nondisplaced on at least two planes (anteroposterior & lateral). Type III is a complete fracture and partially displaced. The trabecular pattern of the femoral head does not line up with the acetabular trabecular pattern. Type IV is a completely displaced fracture with no continuity between the proximal and distal fragments. The trabecular pattern of femoral head remains parallel with the acetabulum trabecular pattern. There are three types within the Pauwel’s classification. Pauwel’s classification classifies the fracture according to the orientation and direction of the fracture line across the femoral neck. It relates to the biomechanical stability. The more vertical the fracture, the more shear forces, and the more complication rate. Type I has an obliquity ranging from 0-30 degrees. Type II has an obliquity ranging from 30-50 degrees. Type III has an obliquity between 50-70 degrees or more. As the fracture progresses from Type I- Type III, the obliquity of the fracture line increases. As the fracture line becomes more vertical, the shear forces increase and the instability increases. A horizontal fracture is good and stable. A vertical fracture is bad and unstable. The more displaced the fracture, the more disruption of the blood supply and the chance of avascular necrosis and nonunion (can occur in about 25% of displaced fractures). If nonunion occurs in a younger patient, you may help the patient by doing subtrochanteric osteotomy to reorient the fracture line from vertical to horizontal (will help the fracture healing). In femoral neck fractures associated with femoral shaft fractures, the typical neck fracture is vertical and nondisplaced. It may require internal rotation view x-rays to see this hip fracture (fracture could be missed). Fix the femoral neck fracture first, followed by the femoral shaft fracture. The usual combination is parallel screws in the femoral neck and a retrograde femoral rod for the fractured femur. Pipkin type II fracture is fracture of the femoral head, dislocation of the hip, and fracture of the femoral neck. Try to avoid reduction of the hip dislocation by closed means (especially in the young patients). You may want to do open reduction of the hip dislocation especially if the femoral neck fracture is not displaced. Stress fracture is more common in female athletes. It can be tension fractures. Fracture or callus is present on the superior aspect of the femoral neck. Adult bone is weak in tension, so stress fracture of the femoral neck needs to be fixed. This should be an emergency operation before the fracture displaces. With compression fractures, the compression or callus is present on the inferior aspect of the femoral neck. Some people believe that if the compression fracture is less than 50% across the neck, then the fracture could be stable and you can do protected crutch ambulation. If the compression fracture is more than 50% across the neck, then the fracture is unstable and you will do ORIF. Some surgeons fix all stress fracture of the femoral neck. A female runner with groin pain will rule out stress fracture. Get an MRI, and you will probably have to fix the fracture. Femoral neck fractures can also occur due to insufficiency fracture. This occurs due to weak bone because of osteoporosis or osteopenia. The patient will have groin pain, pain with axial compression, and the x-ray may be normal (MRI is helpful in diagnosing insufficiency fracture).

Causes of Hip Pain

 

Pain can arise from the structures that are within the hip joint or from the structures surrounding the hip joint. The most important thing is to ask the patient to locate the site of pain. ask the patient to point at the site of pain. When the patient states that their hip hurts, it doesn’t mean that the pain is coming from the hip joint itself, so ask the patient to point at the site of the pain. The pain can arise from structures that are within the hip joint or from structures surrounding the hip. The hip joint is a weight bearing joint. The joint consists of two main parts: femoral head (ball) and acetabulum (socket). The hip pain can be anterior hip pain (deep groin pain). The pain can be lateral hip pain. the pain can be posterior hip pain. The pain can be far posterior hip pain, coming from the sacroiliac joint and the lower spine. Anterior hip pain is usually deep within the groin, and it can result due to arthritis of the hip. Conservative treatment is physical therapy, anti-inflammatory medication, possible injections, and surgery is done in late cases, usually by total hip replacement. It is usually diagnosed by clinical examination with a provocative test of flexion, adduction, and internal rotation. The diagnosis is confirmed by an MRI arthrogram. Conservative treatment is therapy, anti-inflammatory medication, and injections. Surgical treatment provides good result and is usually done by arthroscopic debridement or repair of the tear. Stress fracture is usually diagnosed by an MRI. The x-ray may be normal. Early diagnosis is important before the fracture displaces and gives a bad result. Treatment of avascular necrosis is usually surgical fixation of the fracture. Fixation of the fracture is usually performed utilizing screws. Femoral head replacement is done in rare, late cases. Avascular necrosis means death of a segment of the bone. When the blood supply of the femoral head is interrupted, a segment of the bone dies and becomes necrotic (femoral head will collapse). Treatment for early stages of AVN without collapse of the femoral head include decompression by drilling of this segment in the femoral head to bring a new blood supply to the area. Vascularized fibular graft may be used also. In severe cases with collapse of the femoral head (usually diagnosed by an x-ray), the treatment is usually total hp replacement. Treatment of an inflamed bursa is usually conservative treatment of physical therapy, anti-inflammatory medication, and injection. Surgical treatment by excision of the bursa is rarely done. In case of chronic, resilient trochanteric bursitis, try to get an MRI to exclude a tear of the abductor muscles of the hip (gluteus medius and gluteus minimus muscle tear). Posterior hip pain is usually due to piriformis syndrome. The sciatic nerve can be irritated from the piriformis syndrome. Treatment is usually physical therapy, stretching, anti-inflammatory medications, and injections. Surgical treatment is usually rare. It is the last resort. It includes release of the piriformis tendon and exploration of the sciatic nerve. It is done in cases that fail to improve with conservative treatment. Far posterior pain may come from the sacroiliac joint or from the lower spine conditions. Sacroiliac joint (SI) problems is a challenging diagnostic and treatment entity. There are a lot of clinical diagnostic examinations that can be used to diagnose sacroiliac joint (SI) problems such as the Faber test and others. However, injection of the SI joint is probably the method to diagnose pain originating from the SI joint. If there is improvement of the condition of the patient after injection of the SI Joint, then we will probably consider that the problem is in the SI joint. The SI joint problems are usually under estimated and are unappreciated. Lower spine conditions can cause referred pain to the buttock and hip area. In fact, symptoms of hip and lower spine conditions can overlap or both of them can coexist in the same patient. You have to separate pain from the hip from pain that comes from the spine.