What is knee malalignment?
In a normal leg, an imaginary straight line drawn from the center of the hip to the center of the ankle should pass through the center of the knee. This straight line, called the mechanical axis, shows the way our bodies bear weight when standing. Even a tiny variance of a few millimeters can make a huge difference in the wear-and-tear on a knee joint. Malalignment of the bones that form the knee joint may be present at birth or may develop following trauma or arthritis. The two different types of malalignment in the knee include:
- Genu varum:
- Tibia turns inwards causing a bow-legged deformity
- More cartilage wear on the inside (medial side) of their knees
- Usually treated with high tibial osteotomy (HTO) i
- Genu valgus:
- Tibia turns outwards causing a knock-knee deformity
- More cartilage wear in the outside (lateral side) of their knees
- Usually treated with distal femoral osteotomy (DFO)
Who is a good candidate for surgery?
Knee osteotomies are most effective in active patients that are younger than 60 years old, and have pain on only one side of the knee that is aggravated with activity and standing for long periods of time
How are varus and valgus deformities treated?
An osteotomy of the knee involves cutting and repositioning bone to correct the knee’s alignment and improve its function with the goal of reducing the development of osteoarthritis. The primary objective of the surgery is to shift weight away from the painful, damaged side of the knee joint and onto the healthy side of the knee joint. This is made possible by strategically repositioning the bones and then securing them in proper alignment.
Dr. Potts will make precise measurements regarding your leg alignment to calculate the exact size of the bone wedge to be added or removed for an osteotomy. The wedge size will depend on each patient’s unique anatomy and degree of varus or valgus deformity. Typically, a 1 mm wedge will provide 1 degree of correction, so a 10 mm wedge will provide a 10-degree change in knee alignment.
- High Tibial Osteotomy (HTO) – most commonly performed to correct genu varum (bow-legged deformity). A wedge of bone is added or removed to an area of the tibia just below the knee
- Distal Femoral Osteotomy (DFO) – most commonly performed to correct genu varum (knock-knee deformity). A wedge of bone is added or removed to the femur, just above the knee. Less common than tibial osteotomies
- Closed osteotomy – A wedge of bone is cut and removed. The resulting gap in the bone is closed by bringing the two sides together and securing them with a plate and screws.
- Open osteotomy – A cut is made about three-quarters of the way across the bone. A wedge-shaped bone graft is inserted into the cut. The wedge is secured to the bone with a plate and screws. There are three types of bone graft: autograft, allograft, and artificial graft.
- Autograft. The inserted wedge is bone taken from another bone in the patient’s body, usually the pelvic bone, during the surgery.
- Allograft. The inserted wedge is bone from another person. Usually these grafts are procured from bone banks that harvest and freeze bone from cadavers.
- Artificial graft. The inserted wedge is made from a synthetic bone substitute.
What happens during the procedure?
Knee osteotomies are performed under general anesthesia and typically lasts between 1-2 hours. The following technique is used:
- An incision is made where the osteotomy is to be performed. A medial closing wedge osteotomy is performed on the inside while a lateral opening wedge osteotomy is performed on the outside
- A cut in the bone is made using an oscillating saw, and then a predetermined section of bone is removed
- For a medial closing wedge osteotomy, a wedge-shaped section of bone is removed, and the opening is closed by bringing the cut ends of the bones together, thus changing the alignment of the bones
- For a lateral opening wedge osteotomy, a wedge-shaped section of bone is removed, and the gap is opened further to change the alignment of the bones. A bone graft is inserted into the gap so that the bones fuse in the new alignment
- The bones are secured in position with the help of metal plates and screws
- The incision is closed, and healing occurs in the same fashion as a normal fracture
