High Tibial Osteotomy

A joint is formed when two bones meet. Knee is a large weight bearing hinge joint formed by the thigh bone, kneecap and shin bone. The various structures forming the joint are:

• Cartilage: Articular 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 a joint thereby reducing friction and acting as a shock absorber.
• Meniscus: They are pads of tissue between the joint dampening the impact. Both the meniscus and cartilage have a very limited blood supply therefore limiting any healing if subjected to damage.
• Ligament:  These are tough tissues connecting one bone to another. Ligaments prevent slipping one bone over the other, maintaining stability.
• Synovium: A thin tissue lines the inside of the joint secreting a watery thin, sticky, clear lubrication called synovial fluid. Just like machine oil it helps in smooth movement of the joint.
• Bones and Muscles: End of the thigh bone(femur) and upper part of the shin bone(tibia) with muscles attached to them help to bend or straighten the knee joint. A proper alignment between both is necessary to perform the movements.

ALIGNMENT OF THE KNEE

In a normal individual the thigh bone and shin bone are aligned so the weight is transmitted equally among the inner and the outer side of the joint. Any malalignment or mismatch leads to excessive weight being placed on one side of the knee. With repetitive loading parts of the cartilage and meniscus get torn on the side placed under undue force. Bow legs or knock knees are examples of malalignment.

OSTEOARTHRITIS(OA)

With growing age the tissues forming the knee joint, including the bones, articular cartilage, tendons, ligaments, meniscus and muscles degenerate. The changes culminate into tears of the meniscus and cartilage leading to loss of smooth gliding of the joint. The joint(especially the synovium) becomes inflamed.  

Risk factors and causes: Degenerative OA also called wear and tear arthritis, it is common in middle aged to elderly individuals. Age and obesity are common risk factors but a malaligned knee such as knock knees or bow legs can lead to early osteoarthritis. Injuries to the structures forming the knee joint lead to early OA.

Symptoms: 

• Grinding/popping/clicking sensation in the knee.
• Inability to fully bend or straighten the knee.
• Knee Pain, especially with activity.
• Stiffness after periods of inactivity
• Swelling around the joint.

ROLE OF HIGH TIBIAL OSTEOTOMY(HTO) IN OSTEOARTHRITIS

It is a surgical procedure literally meaning cutting of bone. When performed near the upper end of the shin bone either on outer side or inner side is known as high tibial(shin bone) osteotomy.

Goals & Principles: Two compartments are mainly affected in OA of the knee joint, the outer or the inner compartment. In a malaligned knee the body weight force is transferred mainly through one compartment leading to excessive wear and tear. So the goal of HTO is to reshape and relieve the pressure of the damaged side.

Ideal candidates:

• Patients younger than 60 years of age.
• Knee joint movements are not restricted i.e can fully bend or straighten the knee.
• One compartment involvement either the inner or outer side.
• Normal knee ligaments which balance the knee.
• Patient who are not obese or having inflammatory diseases like rheumatoid arthritis.

Types and procedure:

• Lateral Closing Wedge: A predetermined wedge of bone is removed from the upper part of the shin bone to correct the alignment. Different methods such as casts or plate and screws may be used to fix the cut ends together.
• Medial Opening Wedge: Here a cut is made on the inner side of the upper shin bone. The cut is opened up and usually filled with a bone graft. Again it may be fixed with a plate and screws.

Post Surgery: Weight bearing is delayed and patient walks on crutches as long as 12 weeks with regular physical therapy.

Advantages: The anatomy of the knee is maintained. With corrected alignment the degenerative process of osteoarthritis halts or slows down. Younger age group of patients with limited single compartment involvement are to benefit more.

Disadvantages: Various complications may arise post surgery

• Full recovery is usually prolonged to many weeks or months.
• Pain relief at times is not predictable and many patients complain of residual pain.
• Postoperative complications such as infection and stiffness may occur.
• A potential damage to the nerves which make the foot work or the blood vessels supplying blood to the leg.
• Majority of patients opting for HTO end up having a total knee replacement in the coming years. Although the surgical technique for Total Knee Replacement becomes much more challenging after HTO.
• HTO requires cutting of the bone. The cutting site sometimes fail to heal and a second surgery is then needed to heal it. Moreover, when a bone graft from a person’s own body is used to fill in the gap of cutting, there could be potential complications of bone graft site.
• There could be problems of leg lengthening or leg shortening after the surgery.
• In case there is evidence of kneecap arthritis(patellofemoral arthritis) HTO cannot be performed in such cases.

ROLE OF TOTAL KNEE REPLACEMENT

Knee replacement surgeries have revolutionized the treatment of osteoarthritis. The joint ends are replaced or resurfaced with metal and plastic parts. The prosthetic parts recreate the joint movements.

The tibial post on the polyethylene insert allows femoral rollback during bending of the knee. The post along with the femoral cam reduplicates the function of the posterior cruciate ligament.

The prosthetic parts include metallic (cobalt chromium) femoral and tibial components and a highly cross linked polyethylene bearing insert. The femoral component fits in the lower end of the thigh bone on the cuts made during surgery. The tibial components sits on top the upper end of the shin bone. Both the metal components are fixed to the respective bones using bone cement.

Excellent stability is achieved as the parts reduplicate the function of ligaments and meniscus. Alignment of the joint line is created as it was before the disease process.

Advantages

• Can be performed even in individuals more than 60 years of age.
• Early rehabilitation as most patients start to bear weight the very next day
• Excellent survival of the implant even in second decade of surgery.
• Pain relief is complete and the patient satisfaction rates are very high.
• Most patients carry on their daily activities without feeling any difference from the native knee.
• Revisions are being carried out without any complications.

A primary total knee arthroplasty is emerging as a better option than high tibial osteotomy even in stages of early Osteoarthritis. The success rate of surgery and patient satisfaction rates are unparalleled.