Mr Joel Melton
BM, MRCS, MSc (Orth Eng), FRCS (Trauma and Orth)
Consultant Knee Surgeon, Cambridge University Hospitals
Associate Lecturer, Cambridge University
The knee is required to sustain and transmit very large forces during load bearing. Any mal-alignment of the lower limb can have a further detrimental effect on the loading patterns across the knee joint. Mal-alignment can lead to increased loading in damaged areas of the joint and increase the symptoms experienced from an arthritic knee joint. Osteotomy can be undertaken as a primary procedure but if cartilage repair, meniscal repair/ replacement and joint stabilisation techniques are being considered, the alignment should always be considered in conjunction. Any abnormality of lower limb alignment should be corrected to optimise the chances of success of these biological interventions.
An osteotomy is a surgical procedure to cut or divide a bone. Around the knee joint, an osteotomy can be used to correct mal-alignment of the lower limb in order to improve the biomechanical loading patterns within the joint. Depending on the location of deformities of the bones around the knee, the area of damage within the joint and the extent of combined biological interventions in the knee, an osteotomy can be carried out in the tibial (shin) bone or in the bone of the distal femur (thigh bone).
Patients who have degenerative joint disease in part of the knee joint which is being subjected to abnormal loading patterns owing to mal-alignment and who have areas within the joint, which are not worn, may be candidates for osteotomy. Patients who have significant lower limb extra-articular mal-alignment may need corrective osteotomy. Intra-articular osteotomy is occasionally indicated after a mal-union of a fracture or other trauma has occurred at the knee joint. Osteotomy has higher failure rates in smokers and therefore all patients should commit to smoking cessation prior to surgery.
As arthritis of the knee joint develops, it often affects either the medial (inner) or lateral (outer) compartment of the joint only. When this is the case, it is frequently associated with a progressive mal-alignment of the leg, which further contributes to excessive loading and increased pain from the damaged area of the joint. The effect of this scenario is that the damaged area is taking increasing load while the non-arthritic parts of the joint are not being loaded during weight-bearing. In this situation, osteotomy can be used to redistribute loads back onto the remaining healthy cartilage and to ‘off-load’ the damaged cartilage. This can reduce pain and improve function for many patients and can delay the need for joint replacement (arthroplasty). Knee arthroplasty is still an option for those that need it but it may be possible to delay the need for this by employing a biological approach.
If cartilage repair techniques are to be considered, the alignment of the lower limb must be assessed. Given the challenges of biological tissue engineering (as described on the Articular Cartilage Repair pages of this site) the mechanical and biological environment within the knee must be optimised. If there is mal-alignment of the leg, the loading patterns on the repaired cartilage will be suboptimal. Osteotomy, in this context, will improve the mechanical loading conditions in the damaged compartment of the joint and improve the chances of successful cartilage repair.
The meniscal cartilages (shock absorbers) of the knee are important structures involved in load transmission, joint stabilisation, lubrication and nutrition of the joint surfaces. If these tissues are to be repaired or replaced (meniscal transplant) neutral alignment is preferred in order to optimise loading conditions and osteotomy may be required.
Both extra-articular and intra-articular deformity can be indications for osteotomy in selected patients.
As one compartment of the knee becomes progressively worn, the leg may become noticeably deformed causing either a varus (bow legged) or valgus (knock knee) deformity. This will often be evident clinically on critical visual inspection. The true anatomic and mechanical alignment of the leg is assessed using weight bearing, long leg alignment X-rays demonstrating the hip and ankle position in relation to the knee. From these X-ray views, the degree of mal-alignment can be assessed and the degree of correction that will be required can be calculated.
The preoperative images are critically assessed to calculate the position and obliquity of the joint line, the severity and location of the most degenerate areas of joint cartilage in order to plan whether the osteotomy should be undertaken by realigning the femur or the tibia (sometimes a double correction is required) to ensure that the joint line remains perpendicular to the weight bearing axis of the leg.
The surgery is undertaken in the operating theatre, usually under a general anaesthetic. Realignment can be achieved by removing a wedge shaped section of bone or by cutting the bone and opening a wedge, which will fill in with new bone. Bone grafting of the defect may be required and this can be autograft (patients own bone), allograft (donor human bone) or synthetic graft material designed to substitute for bone. Intraoperative fluoroscopy (like X-ray) is used during the surgery to guide the degree of correction. When the required correction in all planes is achieved, the bone must be fixed in position. Historically, this has included the use of wires, staples, screws and plates but, more recently, the availability of angle stable fixation (fixed angle plating options) has dramatically improved the stability of osteotomy fixation. Angle stable plating is now the preference for most modern-day osteotomy scenarios. The surgery is undertaken through small incisions on the inner or outer side of the leg.
Re-alignment can be undertaken as a ‘stand alone’ procedure or as a combined/staged procedure with concomitant joint stabilization (ligament reconstruction) procedures, meniscal repair/replacement and cartilage repair procedures.
The risks of the surgery include bleeding, infection, pain, stiffness, swelling, numbness, bruising, nerve and blood vessel damage, blood clots, anaesthetic risks, mal –union and non –union, failure and the need for further surgery. Every effort is made to reduce the risks of these occurrences.
Any patient undergoing osteotomy should attempt to regain as much muscle strength as possible prior to the surgery. This ‘pre-habilitation’ will optimise the readiness of the leg muscles for surgery. The procedure will generally require an inpatient stay in hospital and physiotherapy will be arranged to encourage early mobilisation post-operatively. If a nerve block injection has been used to control discomfort, the leg may feel numb and ‘heavy’ after surgery for 12-24 hours. A continuous passive motion (CPM) machine may be utilized to regain range of motion following the operation. The weight bearing status will be determined by the operating surgeon but usually, full weight bearing status is the goal. The patient will be discharged home when mobilising safely (usually crutches are provided) with analgesic medication (pain killers) and further instructions for rehabilitation. Bracing may be required and elevation and icing of the leg are valuable in the postoperative period. Out-patient physiotherapy is beneficial for most patients. Workers may return to light work after 1-2 weeks but manual labour may not be possible for between 6-12 weeks.
Surgeons will review the healing process and will monitor progression of bone union at the osteotomy site during rehabilitation with regular x-ray assessment in an outpatient setting.
The long-term goal of osteotomy surgery is to improve the biomechanical environment within the knee joint to prevent damage, where possible, and to reduce symptoms and progression of joint degeneration if it is already present. It can offer symptom relief to some, prevention of disease progression in others and can improve the chances of successful cartilage and meniscal repair/replacement. Osteotomy is a powerful tool in the hands of the specialist knee surgeon and plays a crucial role in the avoidance or deferment of the need for joint replacement in the context of biological knee preservation.