Osteotomies, or bone cutting and realignment procedures, have been used by orthopedic surgeons long before joint replacements were being done. The main indication for an osteotomy is to change one’s alignment and unweight one side of the knee joint that may be arthritic and painful. Today, we still perform osteotomies in people who are too young and active for knee replacement surgery.
In a neutrally aligned knee, approximately 70% of the weight bearing forces are transmitted through the inside or medial portion of the knee joint and only 30% through the outside or lateral aspect of the knee. However, some patients are excessively bow legged (varus malalignment) or knock kneed (valgus malalignment) and these forces are redistributed accordingly. Given enough years of malalignment and being active on one’s knee, a person will start to preferentially wear the cartilage on the side of the knee that is overloaded. A patient with varus malalignment overloads and wears the medial side of the knee, whereas a patient with valgus malalignment overloads and wears the cartilage on the lateral side of the knee. I tell my patients it is similar to wearing the tread on your tires on one side when the tire is out of alignment on your car.
Genu Valgum or knock kneed alignment usually occurs during development as there is diminished growth of the end of the femur bone on the outside of the knee. However, I also see a fair number of patients with acquired genu valgum, particularly in skiers. Alpine skiers load the downhill ski in order to turn. The forces of doing so year after year can eventually lead to a lateral meniscus tear and arthritis on the lateral side of the knee. The lateral meniscus bears a greater mechanical load than the medial meniscus due to the anatomy of the lateral compartment of the knee so once the lateral meniscus fails and starts to tear, arthritis then progresses at a much faster rate in the outer compartment of the knee.
In order to assess the mechanical alignment of one’s lower limb, a special xray is obtained whereby the hip, knee and ankle joint are all imaged while the patient is standing. A line can then be drawn from the center of the hip to the center of the ankle joint to determine whether the person is in varus or valgus. Basically, if the weightbearing line travels through the outer portion of the knee, the patient is in valgus and more of their weightbearing is being transmitted through the outer portion of the knee and vice versa in the case of a varus knee. In a valgus knee, there is accelerated arthritis in the lateral side of the knee and associated contractures of the IT band, lateral knee ligaments, and lateral knee tendons (such as the popliteus and biceps femoris).
Not infrequently, I see patients in their 30’s who already have lateral compartment arthritis of the knee with associated valgus malalignment. They typically complain of lateral sided and posterior knee pain, swelling, and catching in the knee. Once the diagnosis is established, I typically prescribe an unloader knee brace to unweight the lateral side of the knee as well as physical therapy to stretch out the lateral soft tissue structures. We may also consider injections such as steroid, viscosupplementation, PRP, or a stem cell injection.
As the arthritis worsens over time, these nonsurgical measures may fail to provide relief. If the patient is only in their 30’s or early 40’s, they are not a good candidate for a knee replacement as they will wear out the replacement prematurely and there will be limited options later in life for them. Given this, a corrective femoral osteotomy is a good option. In this surgery, a precise cut is made in the lower end of the femur, the bone is gently wedged open, bone graft is placed in the defect and a metal plate and screws holds the bone in this new position as it heals. In so doing, the patients valgus alignment is corrected into slight varus, thus unweighting the arthritic outer portion of the knee and transferring more of the load to the medial side of the knee where there is still healthy cartilage. This can alleviate much of the patient’s pain allowing them to resume the activities they enjoy, and it also prolongs the life of the native knee, forestalling the need for knee replacement surgery.