No effect of obesity on limb and component alignment after computer-assisted total knee arthroplasty.

PURPOSE: This retrospective study aimed to determine if computer navigation provides consistent accuracy for limb and component alignment during TKA irrespective of body mass index (BMI) by comparing limb and component alignment and the outlier rates in obese versus non-obese individuals undergoing computer-assisted TKA. METHODS: Six hundred and thirty-five computer assisted total knee arthroplasties (TKAs) performed in non-obese individuals (BMI<30 kg/m(2)) were compared with 520 computer-assisted TKAs in obese individuals (BMI ≥ 30 kg/m(2)) for postoperative limb and component alignment using full length standing hip-to-ankle radiographs. RESULTS: No significant difference in postoperative limb alignment (179.7° ± 1.7° vs 179.6° ± 1.8°), coronal femoral (90.2° ± 1.6° vs 89.8° ± 1.9°) and tibial component (90.2° ± 1.6° vs 90.3° ± 1.7°) alignment and outlier rates (6.2% vs 7.5%) was found between non-obese and obese individuals. Similarly, alignment and the outlier rates were similar when non-obese individuals and a subgroup of morbidly obese individuals (BMI >40 kg/m(2)) were compared. CONCLUSIONS: Computer navigation can achieve excellent limb and component alignment irrespective of a patient's BMI. Although obesity may not be an indication per se for using computer navigation during TKA, it will help achieve consistently accurate limb and component alignment in obese patients. LEVEL OF EVIDENCE: Level II.

Factors contributing to inherent varus alignment of lower limb in normal Asian adults: role of tibial plateau inclination.

PURPOSE: This prospective study aimed to evaluate radiographically, mechanical or hip-knee-ankle (HKA) axis in healthy, asymptomatic, Asian (Indian and Korean) adults between 20 and 40 years of age to determine the incidence of inherent varus (mechanical limb alignment of >3° varus) and the factors influencing it. METHODS: Three hundred and eighty-eight lower limbs were evaluated using full length, standing hip-to-ankle radiographs in 198 healthy, asymptomatic, Asian (Indian and Korean) adults between 20 and 40 years of age to assess the hip-knee-ankle (HKA) angle, medial proximal tibial angle (MPTA), femoral bowing and femoral neck-shaft angle to determine the incidence of inherent varus (mechanical limb alignment of >3° varus) and the factors influencing it. RESULTS: Overall, the mean HKA angle was 177.6°±2.6° with 34.5% of limbs in inherent varus (mean HKA angle 174.9°±1.8°). The incidence of inherent varus was significantly higher (p=0.01) in males (40%) compared to females (28%) but similar among Indian (34%) and Korean subjects (35%). The hip-knee-ankle (HKA) angle showed significant positive correlation (r=0.82, p<0.001) with only the medial proximal tibial angle (MPTA). CONCLUSIONS: Inherent varus alignment of the lower limb is fairly common among asymptomatic, Asian adults. These results raise several pertinent questions regarding the role of inherent varus in the aetiopathogenesis of knee osteoarthritis and in lower limb realignment procedures.

Which factors increase risk of malalignment of the hip-knee-ankle axis in TKA?

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.

Computer guided restoration of joint line and femoral offset in cruciate substituting total knee arthroplasty.

PURPOSE: This prospective study aimed to evaluate radiographically, change in joint line and femoral condylar offset with the optimized gap balancing technique in computer-assisted, primary, cruciate-substituting total knee arthroplasties (TKAs). METHODS: One hundred and twenty-nine consecutive computer-assisted TKAs were evaluated radiographically using pre- and postoperative full-length standing hip-to-ankle, antero-posterior and lateral radiographs to assess change in knee deformity, joint line height and posterior condylar offset. RESULTS: In 49% of knees, there was a net decrease (mean 2.2mm, range 0.2-8.4mm) in joint line height postoperatively whereas 46.5% of knees had a net increase in joint line height (mean 2.5mm, range 0.2-11.2mm). In 93% of the knees, joint line was restored to within ± 5 mm of preoperative values. In 53% of knees, there was a net increase (mean 2.9 mm, range 0.2-12 mm) in posterior offset postoperatively whereas 40% of knees had a net decrease in posterior offset (mean 4.2mm, range 0.6-20mm). In 82% of knees, the posterior offset was restored within ± 5 mm of preoperative values. CONCLUSIONS: Based on radiographic evaluation in extension and at 30° flexion, the current study clearly demonstrates that joint line and posterior femoral condylar offset can be restored in the majority of computer-assisted, cruciate-substituting TKAs to within 5mm of their preoperative value. The optimized gap balancing feature of the computer software allows the surgeon to simulate the effect of simultaneously adjusting femoral component size, position and distal femoral resection level on joint line and posterior femoral offset.

How accurate are orthopaedic surgeons in visually estimating lower limb alignment?

This study aimed to determine the accuracy and reliability of visual estimation of limb alignment and knee flexion by orthopaedic surgeons when compared to recordings done by computed navigation. Orthopaedic surgeons attending a national conference were asked to place a lower limb synthetic bone model in 6 positions of the knee in the coronal and sagittal planes. These were simultaneously quantified and recorded by a computer navigation system. In the sagittal plane, 44%, 54% and 60% of the surgeons deviated by more than 5 degrees when positioning the knee in 0 degrees flexion, 10 degrees flexion and 90 degrees flexion respectively. In the coronal plane, 15%, 12% and 8% of the surgeons deviated by more than 5 degrees when positioning the knee in 0 degrees varus/valgus, 5 degrees varus and 5 degrees valgus respectively. Only 25% of the surgeons could position the knee both within 3 degrees of neutral varus/valgus and within 5 degrees of neutral flexion. Accuracy of visual estimation was not different when surgeons were compared based on time since residency, experience with TKA and experience with computer-assisted TKA. Visual estimation of knee alignment in both the sagittal and coronal plane is prone to error and may lead to inaccurate limb alignment during procedures such as TKA.

Simultaneous bilateral versus unilateral computer-assisted total knee arthroplasty: a prospective comparison of early postoperative pain and functional recovery.

Whether simultaneous bilateral TKAs (SBTKAs) are more painful and the postoperative functional recovery slower compared to staged bilateral TKAs or unilateral TKAs are issues that frequently concerns patients. The purpose of the current study was to compare the early postoperative pain, function and recovery in simultaneous bilateral versus unilateral computer-assisted TKA. In this prospective study, 50 consecutive patients undergoing unilateral computer-assisted total knee arthroplasties (TKAs) were compared with 50 consecutive patients undergoing SBTKAs in terms of pain, length of hospital stay and rehabilitative milestones during the immediate postoperative period. The mean visual analogue pain scores, mean knee range of motion, straight leg raising and extensor lag were equal in both the groups at the time of discharge. Patients in the SBTKA group lagged behind the unilateral group in stick walking by approximately 24 h. The results of this study demonstrate excellent pain relief and functional recovery with simultaneous bilateral computer-assisted TKAs comparable to unilateral TKAs. Patients eligible for bilateral TKAs can undergo them simultaneously without excessive pain or slower functional outcome.