Which Factors Increase Risk of Malalignment of the Hip-Knee-Ankle Axis in TKA?

Abstract

Background Computer navigation has improved accuracy and reduced the percentage of alignment outliers in TKA. However, the characteristics of outliers and the risk factors for limb malalignment after TKA are still unclear. Questions/Purposes We therefore addressed the following questions: (1) What is the incidence and characteristics of outliers for postoperative limb mechanical axis (hip-knee-ankle [HKA] angle outside the conventional 180°± 3°range) and component alignment in TKA? And (2) what are the preoperative clinical or radiographic risk factors for limb mechanical axis malalignment in TKA? Methods We retrospectively reviewed the clinical and radiographic records of 1500 computer-assisted TKAs to identify outliers for postoperative HKA axis and component alignment and determined risk factors for malalignment. Full-length hip-to-ankle and knee radiographs were used to measure preoperative HKA angle, femoral coronal bowing, joint divergence angle, tibial subluxation, and tibial bone loss and postoperative HKA angle and femoral and tibial component angle. Results The incidence of outliers for postoperative limb mechanical axis, femoral component alignment, and tibial component alignment was 7% (112 of 1500 TKAs), 7%, and 8%, respectively, with 70% of limbs placed in excessive varus and 30% in excessive valgus. Preoperative varus deformity of more than 20°and femoral bowing of more than 5°were associated with increased risk of placing the limb mechanical axis outside the acceptable ± 3°range after computer-assisted TKA. Conclusions The presence of preoperative radiographic risk factors should alert the surgeon to increased chance of malalignment and every measure should be undertaken in such at-risk knees to ensure proper limb and component alignment and soft tissue balance.

Analysis of factors that affect the precision of the radiographic lateral femoral bowing angle using a three-dimensional computed tomography-based modelling technique

“…A preoperative RLFB angle >5° could result in a wrong judgment regarding force alignment; therefore, special attention should be paid to the bone section intraoperatively [3, 7, 16]. …”

Dynamic Alignment Analysis in the Osteoarthritic Knee Using Computer Navigation

“…29,30 We believe that the patients included in the present study may be considered a representative sample of the osteoarthritic population because the age, sex, BMI, and coronal FTMA match with the patients requiring knee replacement. 31 The conclusions are therefore applicable, at least in an investigational frame. The number of patients included and the method described allow the development of a powerful statistical analysis of the varus-valgus laxity in a total range of motion with potentially important implications.…”

“…In TKA, assessment of the laxity is critical information and a routine component during the surgical procedure. 3,4,13,15,16,[18][19][20][21]23,24,27,31,32,37,38 We have developed a reproducible method when using navigation systems, representing the first step in this line of investigation, and are committed to increasing the relevance of the quantitative data provided by navigation systems, especially in postoperative analysis.…”

Surgical Technique: Computer-assisted Sliding Medial Condylar Osteotomy to Achieve Gap Balance in Varus Knees During TKA

“…3A). The amount of lateral joint space opening was quantified as the joint divergence angle [20] measured as the angle made by the distal femur and the proximal tibial cut plotted perpendicular to the femoral and tibial mechanical axes (Fig. 3A).…”

“…Knee arthritic deformities in these patients are frequently confounded by an extraarticular deformity, such as excessive coronal bowing of the femur [18,27]. This adds to the complexity and difficulty of achieving deformity correction and mediolateral soft tissue balance during TKA, especially in the presence of substantial lateral laxity [17,20]. Hence, SMCO was used in rigid, recalcitrant varus deformities during TKA not amenable to full correction of alignment to normal and/or mediolateral soft tissue balance despite extensive release of medial soft tissue structures.…”