What is a Distal Femoral Osteotomy?
Distal femoral osteotomies involve changing the shape of the femur to make one become neutral to slightly bow-legged in alignment for somebody who has a knock-kneed alignment. This is called valgus alignment and is performed by creating a surgical fracture and plating the surgical fracture into a corrected alignment position.
What are the Different Indications of Distal Femoral Osteotomies?
There are usually 3 main indications for distal femoral osteotomies. The first one is in patients who may have developed arthritis either from a previous lateral meniscectomy or genetic causes and who are found to have fairly normal cartilage in the rest of their knee, but have arthritis on the outside of their knee. In these patients that are knock-kneed, straightening out the femur will shift the weight to the more normal cartilage surfaces on the inside of the knee and can be very beneficial to allow one to not have to undergo a total knee replacement or a partial knee replacement for the arthritis on the outside of their knee.
The next most common indication for a distal femoral osteotomy is when a patient is knock-kneed and needs a lateral meniscal transplant and/or a cartilage resurfacing procedure of the outside (lateral) compartment of their knee. The success rates for lateral meniscal transplants and cartilage resurfacing procedures are much less if the valgus alignment is not corrected with the surgical procedure (or before it).
The third most common reason for a distal femoral osteotomy is in patients who have a chronic MCL tear who are in valgus alignment. It is felt that if the valgus alignment is not corrected with a reconstruction of a chronic MCL tear, that there is a much higher risk the MCL tear will stretch out.
What is the Most Common Type of Distal Femoral Osteotomy?
The most common type of distal femoral osteotomy is one that involves an incision on the outside of the knee. The femur is cut with surgical instruments to about 1 cm away from the medial edge of the femur, commonly at a 45-degree angle and angling towards the adductor tubercle, and the bone is then slowly opened up to the point where the weightbearing goes through the center of the knee. Calculations of the specific amount of opening that is needed using the current digital x-ray systems are very accurate. Concurrent with this, a plate and screws are placed on the outside of the knee and bone graft is placed into the opening wedge which is created to assist with healing of the gap.
How to Recover from a Distal Femoral Osteotomy?
Patients who have a distal femoral osteotomy, which is basically a surgical fracture, need to be on crutches until the osteotomy heals sufficiently to start weightbearing. Otherwise, there is a risk that the hinge on the inside part of the knee could crack or the screws could break because too much weight is being placed on them from relying on the plate and screws to hold the fracture apart rather than allowing the bone to heal. In general, we keep patients non-weightbearing for 8 weeks for the distal femoral osteotomy, obtain x-rays at 8 weeks to ensure there is sufficient healing, and then initiate a partial protective weightbearing program, advancing it one-quarter body weight per week until the 3-month point. Further x-rays are obtained at that point to verify healing.
As part of the planning for a distal femoral osteotomy, we like to put most of our patients into a lateral compartment unloader brace. These braces help push the weight towards the inside of the knee, and by doing so, they can help serve as an excellent screen to determine if a patient would benefit from a distal femoral osteotomy. In our hands, almost all patients who benefit from the use of a lateral unloader brace do very well with a later performed distal femoral osteotomy.
The success rate of distal femoral osteotomies is felt to be about 70% to 75% at 10 years. The success rate also depends upon the amount of arthritis of the lateral compartment, if there is a concurrent meniscal transplant or cartilage resurfacing procedure, and also if the patient is not significantly overweight (with a high body mass index, BMI). In general, patients who smoke are not candidates for a distal femoral osteotomy because bone does not heal very well in smokers and this would generally be a contraindicated surgical procedure in this circumstance.