Balancing the knee: factors affecting outcomes after primary total knee replacement

© 2012 Dr. Sina BabazadehArthritis currently affects 15% of the Australian population and is the leading cause of pain and disability in the elderly. Knee joint arthroplasty is a successful way of providing patients with relief from debilitating end-stage arthritic knee pain. Unfortunately 5% of knee replacements will require revision surgery, which is technically and financially demanding with often inferior functional outcomes. Half of all knee revisions can be attributed to a preventable cause such as knee balancing. A balanced knee is defined as having a full range of motion, rectangular, even joint space, symmetrical soft-tissue tension and correct leg alignment. This thesis investigated the role of knee balance in primary knee arthroplasty. It helped establish and improve methods of measuring balance, identified ways to improve balance and investigated the effects of knee balancing on the patient’s functional outcome and quality of life. Chapter 2: The Accuracy of Measured Range of Motion of the Arthritic Knee - Chapter two assessed the validity of retrospective data and helped identify the most appropriate research strategy for the remainder of the thesis. The range of motion of forty-eight patients was assessed using a goniometer and compared to that entered in the patient notes by the examiner during a routine clinical examination, without the examiner being aware. The range of motion of a further twenty patients was subsequently assessed and compared to the findings of the same clinical examiners but this time with the examiner being aware. Accuracy of measurements improved significantly when the examiner was aware. Routinely measured range of motion was found to be inaccurate, implying inaccuracy of retrospective data. Chapter 3: Assessing Alignment - Chapter three compared alignment as measured by long-leg radiographs (LLRs) and computer tomography (CT) to intra-operative navigation measurements in 40 patients undergoing a primary total knee replacement. This study attempted to identify the most accurate way of measuring alignment. Inter-modality correlation proved to be higher when comparing LLRs and CT (>0.893), than when comparing either of these modalities with computer navigation (>0.643 and >0.671 respectively). Further investigation using reformatted computer tomography supported these findings. Given its availability and reduced radiation dose when compared to CT, LLRs should remain the mainstay of measuring the mechanical alignment of the lower limb. Chapter 4: The Joint-Line in Primary Knee Arthroplasty - Chapter four assessed the role of computer-assisted surgery in maintaining the level of the joint-line using a randomized controlled trial comparing computer-assisted to conventional primary total knee arthroplasty. No significant difference was found between computer-assisted and conventional surgery in terms of maintaining the joint line. Patients with depressed joint-lines post-operatively improved the least in terms of functional scores. Change in joint line was found to be related to change in alignment. Change in alignment was found to significantly effect change in joint line and functional scores. Chapter 5: Impact of Joint Distraction on Functional Outcome in Primary Total Knee Arthroplasty - Chapter five assessed over-distraction of the tibio-femoral and analyzed its effects on function and quality of life. Measures of knee joint distraction were devised using long-leg alignment radiographs and lateral radiographs. Seventy-three patients were prospectively recruited and their joint-distraction measured post-operatively. Twelve months follow-up was achieved. Those knees that were over-distracted post-operatively suffered significantly more pain, less flexion and a lower International Knee Society score compared to their counterparts. Chapter 6: A Comparison of Different Surgical Techniques of Primary Knee Arthroplasty - A total knee replacement can be completed using two standard techniques; measured resection and balanced resection. Direct comparisons between these techniques are few. In chapter six, a randomized controlled trial was completed with 103 patients randomized to either one of these techniques. Primary outcomes measured were coronal alignment, femoral component rotation and joint-line maintenance. Secondary outcomes were function and quality-of-life outcomes. A significant difference was found in coronal alignment, with the measured resection technique resulting in an average coronal alignment 1 degree varus to the balanced resection group. No significant difference was found in femoral component rotation or joint-line maintenance. Functional outcomes and quality-of-life were not significantly different between groups at 1 year. Future direction - This thesis hoped to investigate current concepts of knee balancing and introduce new concepts for future researchers. Future research should concentrate on techniques for maintaining the joint line and preventing joint over-distraction. These can involve more specific research into why the joint becomes distracted and hence find ways to prevent it. Research should concentrate on being less observational and more interventional, with more emphasis on tools such as computer navigation, and the newly introduced patient-specific guides. Future research could concentrate on how patient specific guides could be used to improve joint-line maintenance and prevent over-distraction. Larger cohorts would help identify even more minute effectors of knee function post-arthroplasty and cement the novel effectors introduced in this thesis. Longer follow-up of the current cohorts will allow determination of the long-term effects of attributes discussed in this thesis on the longevity of the prosthesis and achieving the ultimate goal of preventing the need for revision surgery