Knee Cartilage Injuries & Management

Anatomy & Function

Cartilage is a glistening white smooth tissue covering the ends of bones where it articulates with other bone and form a joint. It is toughened yet flexible enough to cushion the gliding of the bones forming the joint. Knee is a large weight bearing joint with forces up to 8 times body weight passing through it with every step.

Articular Cartilage helps in reducing friction by acting as a slippery cushion and a shock absorber. This allows for smooth movements of the knee joint.

MRI of the knee showing articular cartilage.

Cartilage Damage

Apart from the above mentioned unique properties it has a limited blood supply so any damage to the cartilage will not heal optimally on its own.

The most common form of cartilage damage is age related degeneration or wear and tear of the joint known as osteoarthritis.

Contrary to the age related degeneration, primary injuries to the articular cartilage usually occur in young and active population. It can lead to early deterioration of joint causing secondary osteoarthritis.

Symptoms

• Knee Pain: Damage to the articular cartilage of knee occurring in an otherwise healthy patient presents most commonly with knee joint pain.
• Swelling and Stiffness: The pain is usually associated with swelling, knee effusion and stiffness, especially worse during walking, jogging or sports activities.
• Feeling of Knee Giving Away: Patients may also experience symptoms of their knee giving away, catching, instability or may have a grinding sensation in the knee during day to day activities.
• Locking: Sometimes the cartilage breaks from the bony end and comes to lie freely in the joint known as a ‘loose body’. This loose body might cause episodes of locking of knee. The patient might not be able to extend (straighten) or bend their leg from a particular position.

These are all symptoms that slowly deteriorate over time, causing a significant morbidity in day to day activities. Young athletes may find themselves off field and may affect their career. Over time the condition may lead to degenerative changes secondary to the cartilage injury and altering of the normal biomechanics of the joint.

Causes

• Trauma/Injuries: The condition is particularly common among athletes and active adults engaging in sports. Here the injury is usually a result of the direct impact on the articular cartilage which may be small or large in size with a varying amount of depth of lesion. Lesions reaching the bone lying directly under the cartilage (called subchondral bone) are a result of significant trauma.
• Overuse: Other common cause is repetitive overuse of the joint in active adult population leading to microfractures of the underlying bone and cartilage which progresses to a full depth cartilage injury.
• Congenital(since birth): Some people with abnormalities of the joint by birth are predisposed to the cartilage injury as abnormal forces act on certain areas of the knee which would be otherwise distributed in a normal adult. Such individuals have altered biomechanics of the knee.
• Osteochondritis dissecans: Conditions such as Osteochondritis dissecans occur more frequently in children. Here the underlying bone loses its vascularity or blood flow. The bone upon losing the blood supply slowly dies or gets degraded. The body tries to form new bone and replace the dead bone but in the process the overlying piece of cartilage is damaged.

Certain endocrine/hormonal abnormalities, vascular diseases, unknown causes or simply hereditary factors predispose to the development of osteochondritis dissecans.

Diagnosis

• History & Examination:Physician will take a detailed history preceding your condition and any injuries or surgeries around the knee. They will conduct a thorough physical examination including clinical tests and measurements to check for instability.
• X-Ray/CT Scan: Usually a radiograph/X-ray is the first investigation done to check for bony integrity ruling out fractures which can be further aided with a superior CT scan.
• MRI: For cartilage injuries the best investigation is an MRI which can provide a detailed view of all the sectors of the cartilage and any damage to the surrounding ligaments and knee pads (meniscus) which stabilize the knee.
• Diagnostic Arthroscopy:  Arthroscopy when used for diagnosis is the gold standard. Here a tiny camera is inserted through a keyhole providing a telescopic view of the entire knee joint. Treatment of the condition can also be done at the same time using arthroscopic instruments.

Management

Treatment depends on a number of factors like age of the patient, the size of defect,demands of the patient and ability to tolerate rehabilitation.

NonSurgical Treatment

Nonoperative treatment usually consists of anti-inflammatory medications, physical therapy and braces to unload the injured cartilage. Some other options like steroid injections or viscosupplementation are controversial especially in young patients. All conservative options focus on relieving the pain and giving time for the cartilage to repair itself. But the defect rarely heals on its own and generally progresses over time.

Surgical Treatment

Surgical techniques can be compared to filling a pothole and options involve either the use of minimally invasive Arthroscopic technique or invasive open procedures called arthrotomy.

Generally arthroscopic surgeries provide earlier return to previous activity and lesser hospitalization. Most of them are day care procedures. Arthroscopic surgery utilizes 2-4 keyhole incisions through which a mini camera is inserted providing a telescopic view and fine pencil size instruments are inserted to do surgical procedure.

Debridement / Chondroplasty

In this surgery, usually performed with an arthroscope, the friable cartilage is simply removed and cleaned. Although it promises a very fast rehabilitation and recovery but success rates are variable and is successful in very small and superficial defects. The cleaned up area is filled with a tissue by the body but this tissue is not as good as the original cartilage itself.

Microfracture Technique

Several small micro-holes are created in the underlying bone through keyhole surgical techniques like arthroscope. Multiple drills cause marrow bleeding in the defect thereby allowing cells with regeneration potential to fill the defect and over time these cells form the new cartilage tissue.The technique is quite effective in small defects and is cost effective being a single stage procedure. But it requires the patients to remain non weight bearing for a long period of time.

Mosaicplasty

It involves filling of the defect from patients own cartilage as a graft taken from a non weight bearing portion. The defects are filled and the body’s own grafted cartilage incorporates into the defect along with bone plugs. The procedure can be done for small full thickness defects in weight bearing area and require the availability of normal cartilage for grafting.

This technique avoids the problems of graft rejection and high costs. The non weight bearing areas of the cartilage are accessed through keyhole surgery using arthroscopy and matched to shape exactly the size of the defect. Rehabilitation is expedited and offers good results. As there are multiple grafts planted in the defects hence looking like mosaic. The surgery is usually day-care and patients usually return to their previous activities after a period of physical therapy.

Allograft Osteochondral Transplantation

The bone and cartilage graft is taken from a cadaver i.e preserved cartilage and bones from a dead donor. The graft is matched and shaped to fill the defect. The graft is especially prepared and processed to prevent transfer of infections.

This is useful in patients with larger defects in young patients. It is done through open technique. A right size graft is shaped to exactly match the defect and fixed. The grafted cartilage is incorporated in the defect with time and the patient can then resume his daily activities.

Fixation of fragments

In case of children and young patients, especially those suffering from osteochondritis dissecans, a large fragment can be simply fixed back to the underlying bone with sutures or screws. Helpful in fresh cases when the cartilage fragment is usually hanging by a tissue in the joint.

This helps in retaining the patient’s anatomy and native bone and cartilage. The sutures and screw fixation can be done using arthroscopy technique which not only treats but helps to detect any other cartilage problems within the knee as the whole joint is inspected using the telescopic camera.

Autologous Chondrocyte Implantation

In this two step surgery usually spanning several weeks the patient’s own cartilage cells are first harvested from the non weight bearing areas of the joint and then grown in a special medium in the lab. Over the course of several weeks the cells multiply and they are then placed in the defect of the cartilage which is covered by periosteum (covering of the bones).

The cells have regeneration potential meaning they can form the native cartilage when placed in the defect. The surgery is usually performed using an open technique in which the knee joint is opened and the area is directly accessed. Rehabilitation takes several weeks and the patient can then resume his activities.

Knee replacement

Reserved for older age group with chronic cartilage damage leading to osteoarthritis changes. Here the joint surfaces are replaced with prosthetic material to re-create the normal motion of the knee. The joint is divided into two compartments one on the inner side and the other on the outer side. The inner side is more frequently involved and in patients with a normal outer side and undergo a semi knee transplant called Unicondylar knee arthroplasty using a minimally invasive technique. It offers an expedited rehabilitation and resumption of activities.

In patients with widespread osteoarthritic changes a total knee replacement is usually performed where both the bones forming the knee joint are replaced with prosthetic material and the normal axis and balance of the knee joint is restored to recreate the biomechanics.

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