Soft Tissue Envelope Preserving Technique for Computer Navigated Total Knee Arthroplasty

OBJECTIVES: Current techniques in Total Knee Arthroplasty(TKA) are utilitarian in that all patients are recommended to have the same alignment of neutral mechanical axis. It has been well established that the population has a varied natural alignment with less than 20% of patients naturally neutral. The ability to predictably individualise alignment for patients is hypothesised to result in greater patient satisfaction. This technique aims to modify mechanical axis technique to consider an individual’s soft tissue constraints. METHODS: Soft Tissue Envelope Preserving (STEP) is an operative technique for performing TKA that utilises the soft tissue data obtained intra-operatively from computer navigation registration to determine the optimal alignment to provide balanced positioning of implants without the need for soft tissue releases. Hence balance is achieved through bone cuts rather than altering the patient’s soft tissue balance. The technique will be described in detail. RESULTS: The last 100 patients performed with complete data sets including navigation files and both pre-op and one year post operative outcome measures were reviewed. The spread of overall alignments and bony resections have been compiled with no outliers outside 5 degrees of neutral. The clinical results were comparable with other series and patient satisfaction of greater than 90% was reported. There were no MCL or LCL releases performed. Ilio-tibial band partial releases were the only reported soft tissue releases made. CONCLUSIONS: This technique is a safe and effective method of performing TKA with good short term outcomes. It minimises the use of soft tissue releases by utilising the patient’s own soft tissue envelope to balance the knee whilst maintaining the basic principles of a measured resection mechanical axis technique. It has resulted in excellent patient satisfaction in the short term.