In Focus
– out of the curve and into the straight
Author: Marketing Department, Brisbane Private Hospital
Advances in computer navigated knee surgery and medical imaging are giving patients with arthritic deformity a better chance of ‘getting the knee out straight again’.
Brisbane Private Hospital orthopaedic surgeon John Gallagher, who in 2008 was the first surgeon in Australia to perform knee replacement using patient-specific cutting jigs, is utilising some of the most advanced operating techniques to help correct the deformity when performing knee replacements.
Dr Gallagher said patients tended to lose the normal alignment of the knee with progressive arthritis and quite often developed a bowed leg across the knee, and less commonly, a “knock knee” – both of which resulted in a painful and inefficient gait, with shortening of the overall leg length.
“The leg length inequality can lead to secondary deformities and patterns of wear in major joints above and below the knee, including the hip and ankle joints and, on occasion, the spine,” he said.
“For this reason, when performing knee replacement surgery, one of the priorities is to remove the abnormal curvatures of the knee and restore the correct physiological alignment and length, often referred to by patients as “getting the knee out straight again”.
Whilst computer navigation in knee replacement surgery has been around for many years, recent advances in medical imaging technology has made it possible to use MRI, in conjunction with computer programming, to image the entire lower limb and create tailor-made devices for knee replacement. In addition to being radiation free, computer navigated surgery using MRI has many benefits for patients.
“The MRI allows a three dimensional joint reconstruction to be achieved with knowledge of the existing alignment deformities,” Dr Gallagher said.
“Computer generated, customised cutting jigs are then created using this data and fitted directly onto the specific anatomy of the patient’s knee joint through a small, single incision. This technology negates the need to drill down into the intramedullary canal, resulting in less blood loss, cuss, drill holes and pins.”
Dr Gallagher said traditional techniques of computer navigation using antennae-like external arrays were helpful for guidance, but were cumbersome and required additional equipment, extra theatre space and more time.
“These techniques also need additional incisions above and below the knee, as well as drilling pins into the femur and tibia for the navigation arrays,” he said. “All of these factors are added risks for unwanted complications including infection, fracture and blood clots.”
Before computer navigation, traditional techniques of aligning the knee involved long rods that were either passed inside the medullary canal of the femur and tibia (intramedullary technique), or positioned outside the bones and lined up with landmarks on the front of the ankle and thigh (extramedullary technique). Once the rods were positioned and secured, cutting jigs were attached and critical bony cuts were made by eye, allowing the knee replacement implants to be positioned correctly to restore lower limb alignment.
Dr Gallagher said while he continued to use traditional techniques for many of his knee replacements, he found the patient-matched cutting jigs were excellent tools to have at his disposal for more complex cases.
“Many cases are straightforward enough to use the simple, traditional method, but for patients with deformity due to fractures where their leg is sometimes bent in many directions, the alignment rods do not readily work and computer precision is necessary,” he said. “An example is a previous case where a patient underwent bilateral total knee replacements, having sustained both femoral and tibial fractures in a motorbike accident in 1982. He had pronounced, varus (bowing) deformity, partly due to his arthritis and partly due to the poor positioning of his malunited fractures, and had great difficulty walking. Traditional knee replacement techniques could not be reliably used as his intramedullary canals were obliterated from the old fractures and landmarks for extramedullary technique were difficult to access,” he said.
“With a small incision and using the MRI navigated technique, he was able to mobilise without the use of any aids, walk freely on his fourth day after surgery and discharged home the next day. He now has two straight legs in spite of the deformities across his old malunited fractures in his thigh and shin, with well sized and positioned knee replacements courtesy of this new technique.”
