Mechanical Axis Line Research Articles

Three-Dimensional Bowing Measurement of Distal Femur at Actual Size and Clinical Implications of Total Knee Arthroplasty.

Background and Objectives: To assess femoral shaft bowing (FSB) in coronal and sagittal planes and introduce the clinical implications of total knee arthroplasty (TKA) by analyzing a three-dimensional (3D) model with virtual implantation of the femoral component. Materials and Methods: Sixty-eight patients (average age: 69.1 years) underwent 3D model reconstruction of medullary canals using computed tomography (CT) data imported into Mimics® software (version 21.0). A mechanical axis (MA) line was drawn from the midportion of the femoral head to the center of the intercondylar notch. Proximal/distal straight centerlines (length, 60 mm; diameter, 1 mm) were placed in the medullary canal's center. Acute angles between these centerlines were measured to assess lateral and anterior bowing. The acute angle between the distal centerline and MA line was measured for distal coronal and sagittal alignment in both anteroposterior (AP) and lateral views. The diameter of curve (DOC) along the posterior border of the medulla was measured. Results: The mean lateral bowing in the AP view was 3.71°, and the mean anterior bowing in the lateral view was 11.82°. The average DOC of the medullary canal was 1501.68 mm. The average distal coronal alignment of all femurs was 6.40°, while the distal sagittal alignment was 2.66°. Overall, 22 femurs had coronal bowing, 42 had sagittal bowing, and 15 had both. Conclusions: In Asian populations, FSB can occur in coronal, sagittal, or both planes. Increased anterolateral FSB may lead to cortical abutment in the sagittal plane, despite limited space in the coronal plane. During TKA, distal coronal alignment guides the distal femoral valgus cut angle, whereas distal sagittal alignment aids in predicting femoral component positioning to avoid anterior notching. However, osteotomies along the anterior cortical bone intended to prevent notching may result in outliers due to differences between the distal sagittal alignment and the distal anterior cortical axis.

Mechanical Axis Method to Determine First Intermetatarsal Angle and Tibial Sesamoid Position

Utilizing the mechanical axis can decrease load on the joint and be beneficial when analyzing bony deformities and planning surgical correction with osteotomies. The aim of this study was to identify the normal mechanical axes of the first and second metatarsals and use them to obtain the first/second mechanical intermetatarsal angle (mIMA). The mechanical axis of the first metatarsal was used to obtain the mechanical tibial sesamoid position (mTSP), which provides a mechanical relationship with the sesamoid apparatus. The angular difference between the anatomic and mechanical axis lines (anatomic-mechanical angle [AMA]) was determined for the first metatarsal and for the second metatarsal. The commonly used first/second anatomic intermetatarsal angle (aIMA) and anatomic tibial sesamoid position (aTSP) were also obtained and compared with the first/second mIMA and mTSP. In this retrospective analysis, radiographs of 50 normal feet (40 patients) were assessed. Pearson's correlation coefficients were used to measure reliability between obtained measurements. Mean first/second aIMA was 8.6 ± 3.0 degrees, and first/second mIMA was 8.6 ± 2.6 degrees. First metatarsal AMA was 1.1 ± 1.0 degrees; second metatarsal AMA was 2.0 ± 1.6 degrees. The mTSP was 2.8 ± 1.1, and aTSP was 2.9 ± 1.0. The TSP median was 3 (range, 1-5). Using the mechanical axis method to obtain the first/second mIMA and the mTSP is reproducible and not affected by anatomic changes to the shape of the metatarsal. Unlike the anatomical axis, the mechanical axis does not change, therefore we recommend using the mechanical axis during surgical planning and when obtaining preoperative and postoperative measurements for the long bones of the foot, particularly for forefoot conditions such as hallux valgus.

PERANAN PROYEKSI STITCH VIEW LONG LEG PADA PEMERIKSAAN KNEE JOINT DENGAN INDIKASI OSTEOARTHRITIS


 ABSTRACT
 Introduction: Long Leg View is an x-ray examination of all parts of the lower extremity using a long vertical cassette which aims to measure the angle between the mechanical axis of the femur and tibia. Knee Joint examination with indications of osteoarthritis at the Radiology Installation of RSUP Dr. Sardjito Yogyakarta uses supine AP projection, Lateral recumbent, Skyline, and Stitch View Long Leg.
 Methods: This research is a qualitative research with a case study approach. Collecting data by means of observation, documentation, and in-depth interviews with patients, sending doctors, radiologists, and radiographers. Data collection was carried out in March 2018 at the Radiology Installation of Dr. RSUP. Sardjito Yogyakarta. The data obtained were analyzed using an interactive model.
 Results: On the Stitch View Long Leg examination at the Radiology Installation, Dr. Sardjito Yogyakarta uses a collimation area from the pelvis to the ankle joint. According to the resident doctor of orthopedic surgery and traumatology, Dr. Sardjito Yogyakarta, Stitch View Long Leg is able to see the shape of the foot formation, namely the O formation or X formation. In addition, according to radiology specialists, looking at the alignment deviation of the lower extremities can be used to assess the grade of osteoarthritis. Under normal conditions, the anatomical axis of the femur and tibia forms an angle of 6º ± 2º, while the mechanical axis line under normal conditions is 8 mm ± 7 mm medial to the center of the knee joint line. The alignment of varus and valgus has been associated with the development of medial or lateral osteoarthritis.
 Conclusion: Stitch View Long Leg aims to assess the grade of osteoarthritis through assessment of lower extremity alignment deviations, see the overall mechanical and anatomical alignment of the lower extremities, help determine the calculation of the angle of bone cutting during Total Knee Replacement surgery, and see the right and left symmetrical balance of genu.

Evaluation of Accuracy of Preoperative Planning of the Femurofibular Angle in Open-Wedge High Tibial Osteotomy for Mild Medial Knee Osteoarthritis

Objective The purpose of this study was to evaluate the usefulness of preoperative planning of the femurofibular angle (FFA) in medial open-wedge high tibial osteotomy (OWHTO) for mild medial knee osteoarthritis. Methods Thirty-two patients (32 knees) with mild medial knee OA were retrospectively reviewed. The patients underwent preoperative planning of the FFA for OWHTO. For preoperative planning, a full-length weight-bearing X-ray photograph of the lower limb was opened within Adobe Photoshop Software, and a targeted corrective mechanical axis line of the lower limb and its intersecting point at the lateral tibial plateau surface was drawn using rectangle selection and filling tools. A frame, which encircled the tibia and fibula, was created around the predicted osteotomy plane and then rotated until the ankle center was on the targeted mechanical axis line. Subsequently, a distal femoral condyle line and a proximal fibula axis line were drawn, and the angle between the two lines was measured and defined as the femurofibular angle (FFA). During biplane OWHTO, the preoperatively determined FFA was used to complete the correction of the mechanical axis. During follow-up, the postoperative mechanical weight-bearing line (WBL) of the lower limb, the mechanical femorotibial angle (mFTA), and the FFA were measured and compared with the preoperatively determined values. Results The mechanical WBL shifted from a preoperative value of 25.36 ± 5.02% to a postoperative value of 56.19 ± 0.10% from the medial border along the mediolateral width of the tibial plateau, and it was 56.57 ± 0.08% at the final follow-up (P < 0.01). The preoperatively determined value was 56.25%, and no significant difference was found compared with postoperative week-one and final follow-up values (P > 0.05). The mFTA was corrected from a preoperative varus of 4.02 ± 0.63° to a postoperative week-one valgus of 2.37 ± 0.28°, and it had a valgus of 2.48 ± 0.39° at the final follow-up (P < 0.01). No significant difference in the valgus was found compared with the postoperative week-one, final follow-up and preoperatively determined valgus of 2.34 ± 0.26° (P > 0.05). The postoperative week-one and final follow-up FFAs were 90.34 ± 1.53° and 90.33 ± 1.52°, respectively, and no significant difference was found compared with the preoperatively determined value of 90.12 ± 1.72° and the intraoperative setting value of 90.25 ± 1.67° (P > 0.05). All corrected values were within the acceptable range of preoperative planning. Conclusion Preoperative planning of the FFA may be useful in OWHTO for patients with mild medial knee OA. Satisfactory correction of the postoperative targeted mechanical axis line of the lower limb can be obtained.

INFLUENCE OF LOWER EXTREMITY STATIC ALIGNMENT ON DYNAMIC KNEE VALGUS IN ADOLESCENTS FOLLOWING ACL RECONSTRUCTION

Background:Dynamic limb valgus, particularly high knee abduction moments, are a known risk factor for anterior cruciate ligament (ACL) injury. High knee abduction moments may result from poor static anatomic limb alignment, faulty biomechanics, or a combination of both. The distinction is important because anatomic limb alignment is difficult to change, while dynamic factors can be addressed through neuromuscular or biomechanical training.Hypothesis/Purpose:This study assessed the influence of static (lower extremity anatomic alignment) and dynamic (kinematic and kinetic) factors on external knee abduction moments during side-step cutting in uninjured adolescent athletes.Methods:This retrospective study included 43 adolescents with recent unilateral ACL reconstruction (mean age 15.3 years, SD 2.0, range 10-21; 17/43 female; 3-12 months post-surgery, mean 6.5, SD 2.1). Frontal plane hip to ankle imaging (EOS) was used to measure mechanical axis deviation (perpendicular distance from the center of the femoral condyles to the mechanical axis line connecting the center of the femoral head to the center of the talar dome) and tibial-femoral angle. Femoral anteversion was measured during physical examination. 3D motion capture provided lower extremity kinematics and kinetics during quiet standing and during the loading phase (initial contact to peak knee flexion) of an anticipated 45° side-step cut, with 2-3 trials per limb averaged for analysis. Relationships among imaging, static motion capture, and dynamic motion capture measures were investigated using correlation, and backward stepwise linear regression was used to evaluate potential predictors of average dynamic knee abduction moment.Results:Dynamic knee abduction moment was best predicted by a combination of dynamic measures: knee and hip abduction, external knee rotation, lateral trunk lean towards the planting foot, and ankle inversion during cutting (Table 1.1). Although EOS frontal plane tibial-femoral angle was correlated with dynamic knee abduction moment (r=0.24, p=0.02), no static/anatomic variables entered the model once the dynamic measures were included.Conclusion:Knee abduction moments during side-step cutting were related to dynamic factors reflecting frontal plane trunk, hip, knee, and ankle motion, as well as external knee rotation. Static (anatomic) lower limb alignment did not influence knee abduction moments once these dynamic factors were considered. Knee abduction moments and ACL injury risk are therefore not dictated by anatomic alignment and can be altered through neuromuscular/biomechanical training.Table 1.1.Multivariable prediction of average knee abduction moment during cutting (R2=0.69) βPDynamic ankle eversion-0.35<0.001Dynamic knee external rotation0.69<0.001Dynamic hip abduction0.180.004Dynamic trunk contralateral lean0.170.007Dynamic knee abduction0.39<0.001

Effect of Lower Extremity Static Alignment on Dynamic Valgus in Adolescents Following ACL Reconstruction

PURPOSE: Knee abduction moments may lead to valgus collapse, potentially causing ACL rupture. The contribution of static lower extremity alignment to knee abduction moments is unknown. This study assessed relationships among lower extremity static alignment and dynamic kinematics and kinetics during side-step cutting in uninjured adolescent athletes. METHODS: This retrospective study included 8 adolescents with recent unilateral ACL reconstruction (mean age 14.8 yr, SD 1.2; 3/8 female). Frontal plane hip to ankle imaging (EOS) was used to measure mechanical axis deviation (perpendicular distance from the center of the femoral condyles to the mechanical axis line connecting the center of the femoral head to the center of the talar dome) and tibial-femoral angle. 3D motion capture provided lower extremity kinematics and kinetics during quiet standing and loading (initial contact to peak knee flexion) of an anticipated 45° side-step cut; 2-3 trials per limb were averaged for analysis. Relationships among imaging, static motion capture and dynamic motion capture measures were investigated using correlation, and backward stepwise linear regression was used to evaluate potential predictors of average dynamic knee abduction moment. RESULTS: Regardless of surgical status, standing knee abduction angle was correlated with standing hip adduction (r=0.60, p=0.02) and ankle eversion (r=0.85, p<0.0001) along with larger mechanical axis deviations (r=0.83, p=0.0001) and higher knee abduction on EOS (r=0.44, p=0.09). Dynamic knee abduction moment was best predicted by a combination of EOS knee abduction angle, standing ankle eversion, standing knee abduction, standing knee rotation, ankle eversion during cutting, along with ground reaction force and age (R2=0.94; p<0.004). There was no significant relationship between knee abduction moment and side (surgical vs. contralateral) (p=0.63). CONCLUSIONS: In this small group of adolescent athletes with recent ACLR, knee abduction moment during side-step cutting was related to age and anatomic lower limb alignment in addition to dynamic factors such as ankle positioning and ground reaction force. Anatomic alignment or standing posture with greater hip adduction, knee abduction, and ankle eversion may indicate a higher risk for injury during dynamic activities.

Correction of distal femoral valgus deformities with fixator-assisted plating: How accurate is the correction?

ObjectiveThe aim of this study was to evaluate the results of fixator assisted correction of the distal femoral valgus deformities and the precision of the correction. MethodsSeventeen extremities of 13 patients (7 women and 6 men; mean age: 16 ± 5.4 years) who had fixator assisted plating of the distal femur for genu valgum deformity were evaluated. Mechanical axis deviation (MAD) and mechanical lateral distal femoral angles (mLDFA) were measured pre-operatively and post-operatively. mLDFA was graded as perfect if it is between 85° and 90°(85° ≤ x ≤ 90°); overcorrection if it is between 91° and 95° (91° ≤ x ≤ 95°) and undercorrection if it is between 80° and 85° (80° ≤ x < 85°). Measurements beyond those limits were graded as a poor result. The position of the mechanical axis line with respect to center of the knee was graded from zone 1 to zone 4 pre-operatively and post-operatively. ResultsThe mean follow-up period was 12.8 ± 3.7 months. The pre-operative and post-operative mLDFA was 70.5°±9.4° (range, 57°–82°) and 87.7° ± 3.5° (range, 80°–94°), respectively (p < 0.001). Based on post-operative standing radiographs, the correction was graded perfect in 12 femurs. The correction in three femurs were graded as overcorrection and graded as undercorrection in two femurs. Sagittal plane correction was also achieved in two femurs. Peroneal nerve decompression was done in three patients (5 extremities) with valgus deformity over 30°. The mechanical axes in all lower extremities were passing through zone 2 or more, pre-operatively, whereas the mechanical axes were in zone 2 or more in five extremities post-operatively. ConclusionFixator assisted plating is an effective treatment modality in patients with distal femoral valgus deformity. Although the technique enables to obtain significant correction in coronal plane it has the disadvantages of over- and undercorrection. Thus, we advise intraoperative confirmation of the correction under fluoroscopic control.Level of Evidence: Level IV Therapeutic Study.

Microdose acquisition in adolescent leg length discrepancy using a low-dose biplane imaging system.

Background Children with leg length discrepancy often undergo repeat imaging. Therefore, every effort to reduce radiation dose is important. Using low dose preview images and noise reduction software rather than diagnostic images for length measurements might contribute to reducing dose. Purpose To compare leg length measurements performed on diagnostic images and low dose preview images both acquired using a low-dose bi-planar imaging system. Material and Methods Preview and diagnostic images from 22 patients were retrospectively collected (14 girls, 8 boys; mean age, 12.8 years; age range, 10-15 years). All images were anonymized and measured independently by two musculoskeletal radiologists. Three sets of measurements were performed on all images; the mechanical axis lines of the femur and the tibia as well as the anatomical line of the entire extremity. Statistical significance was tested with a paired t-test. Results No statistically significant difference was found between measurements performed on the preview and on the diagnostic image. The mean tibial length difference between the observers was -0.06 cm (95% confidence interval [CI], -0.12 to 0.01) and -0.08 cm (95% CI, -0.21 to 0.05), respectively; 0.10 cm (95% CI, 0.02-0.17) and 0.06 cm (95% CI, -0.02 to 0.14) for the femoral measurements and 0.12 cm (95% CI, -0.05 to 0.26) and 0.08 cm (95% CI, -0.02 to 0.19) for total leg length discrepancy. ICCs were >0.99 indicating excellent inter- and intra-rater reliability. Conclusion The data strongly imply that leg length measurements performed on preview images from a low-dose bi-planar imaging system are comparable to measurements performed on diagnostic images.

Can Achilles tendon be used as a new distal landmark for coronal tibial component alignment in total knee replacement surgery? An observational MRI study.

BackgroundIn total knee arthroplasty, it is better to use more than one reference point for correct alignment of the components. By measuring the distances of Achilles tendon (AT) and other conventional landmarks from the mechanical axis in magnetic resonance imaging (MRI) of the ankle, we aimed to demonstrate that, as a novel landmark which can help for correct alignment in the coronal plane, AT is a better option than other landmarks.Materials and methodsThis retrospective study was done on 53 ankle MRIs that met the criteria for inclusion to the study among 158 ankle MRIs. After identification of the mechanical axis, the distances of distal landmarks, which were extensor hallucis longus tendon (EHLT), tibialis anterior tendon (TAT), dorsalis pedis artery (DPA), AT, extensor digitorum longus tendon (EDLT), and malleoli, were measured from the mechanical axis and were statistically evaluated.ResultsIn proximal measurements, the distances of the landmarks to the mechanical axis (on average) were AT, 2.64±1.62 mm lateral; EHLT, 3.89±2.45 mm medial; DPA, 4.69±2.39 mm medial; TAT, 8.24±3.60 mm medial; and EDLT, 14.2±4.14 mm lateral (P<0.001). In distal measurements, the distances of the landmarks to the mechanical axis (on average) were AT, 1.99±1.24 mm medial; EHLT, 4.27±2.49 mm medial; DPA, 4.79±2.10 mm medial; TAT, 12.9±4.07 mm medial; and EDLT, 12.18±4.17 mm lateral (P<0.001).ConclusionIn this study, the mechanical axis line, which is the center of talus, passes through the AT. Our MRI investigations showed that the AT, EHLT, DPA, and malleolar center (3–5 mm medial) may help in correct alignment.

Open wedge high tibial osteotomy using three-dimensional printed models: Experimental analysis using porcine bone

BackgroundThe purpose of this study was to evaluate the usefulness of three-dimensional (3D) printed models for open wedge high tibial osteotomy (HTO) in porcine bone. MethodsComputed tomography (CT) images were obtained from 10 porcine knees and 3D imaging was planned using the 3D-Slicer program. The osteotomy line was drawn from the three centimeters below the medial tibial plateau to the proximal end of the fibular head. Then the osteotomy gap was opened until the mechanical axis line was 62.5% from the medial border along the width of the tibial plateau, maintaining the posterior tibial slope angle. The wedge-shaped 3D-printed model was designed with the measured angle and osteotomy section and was produced by the 3D printer. The open wedge HTO surgery was reproduced in porcine bone using the 3D-printed model and the osteotomy site was fixed with a plate. Accuracy of osteotomy and posterior tibial slope was evaluated after the osteotomy. ResultsThe mean mechanical axis line on the tibial plateau was 61.8±1.5% from the medial tibia. There was no statistically significant difference (P=0.160). The planned and post-osteotomy correction wedge angles were 11.5±3.2° and 11.4±3.3°, and the posterior tibial slope angle was 11.2±2.2° pre-osteotomy and 11.4±2.5° post-osteotomy. There were no significant differences (P=0.854 and P=0.429, respectively). ConclusionThis study showed that good results could be obtained in high tibial osteotomy by using 3D printed models of porcine legs.

Measurement Variance in Limb Length Discrepancy

The purpose of this study was to assess interobserver and intraobserver variability in the assessment of clinical and radiographic measurement of lower limb length discrepancy. Clinical measurements included direct measurement with a tape measure from anterior superior iliac spine (ASIS) to lateral malleolus and ASIS to medial malleolus as well as block measurement. Slit scanogram radiographic measurement was also evaluated. All three clinical measurements had excellent reliability, but the relatively large mean differences and the large 95% confidence intervals for clinical measurements limit the usefulness of these techniques. Slit scanogram measurement was the most reliable measurement technique. The intraobserver variance of direct slit scanogram measurement included intraclass correlation coefficient of 0.99, mean difference of 0.1 cm, and 95% confidence interval of 0.4 cm. Results were not influenced by patient age or body mass index. Slit scanogram measurement is the preferred method for assessment of limb length discrepancy. The direct slit scanogram measurement described in the text follows the mechanical axis line of the leg in the "at ease" standing position described by Paley. Direct measurement using a measuring tape on a full-length slit scanogram is more reliable than indirect measurement using horizontal lines drawn to a radiolucent ruler that is positioned by a technician, since direct measurement avoids errors due to nonparallel positioning of the limb relative to the ruler, and direct measurement also avoids errors due to non-horizontal lines drawn from standard bony landmarks to the ruler. The ideal radiographic measurement technique would have high reliability and accuracy and would minimize or eliminate radiation.

Principles of deformity correction around the knee

Lower limb frontal and sagittal plane alignment and joint orientation have significant consequences for function and wear on the hip, knee and ankle. There is a normal range for the orientation of these joints relative to the mechanical and anatomic axis of the femur and/or tibia. We can use the normal joint orientation to accurately plan realignment of a deformed femur or tibia. In the frontal plane we use both anatomic and mechanical axis lines for planning. In the sagittal plane, the mechanical axis has less relevance and, therefore, only the anatomic axis is used for planning.

Definition, Quantification, and Correction of Translation Deformities Using Long Leg, Frontal Plane Radiography

The surgical realignment of mechanical axis deviation is necessary to prevent early joint degeneration. Modern types of external fixation systems allow alignment of the mechanical axis to exact degrees. Predominately, these are corrections of angulation deformities. In some cases, the analysis of the mechanical axis deviation does not show any angulation deformity, but rather a parallel staggering of the mechanical axis lines of a bone. Such parallel staggering of the mechanical axis lines is defined as a translation deformity of the bone. In combined deformities with angulation and translation, the center of deformity can be established proximal or distal to the limit of the bone. In translation deformities, the realignment of the mechanical axis requires a parallel restaggering made by a translation-osteotomy or by a counterangulated double osteotomy. In complex deformities with angulation and translation, the translation requires separate corrective planning. In frontal plane radiographs of the standing leg, the components of angulation and translation can be established graphically or by simple trigonometric formulas. The analysis and surgical procedure to realign translation deformities or a combination of translation and angulation deformities using an unilateral fixator device are discussed.

Definition, Quantification, and Correction of Translation Deformities Using Long Leg, Frontal Plane Radiography

The surgical realignment of mechanical axis deviation is necessary to prevent early joint degeneration. Modern types of external fixation systems allow alignment of the mechanical axis to exact degrees. Predominately, these are corrections of angulation deformities. In some cases, the analysis of the mechanical axis deviation does not show any angulation deformity, but rather a parallel staggering of the mechanical axis lines of a bone. Such parallel staggering of the mechanical axis lines is defined as a translation deformity of the bone. In combined deformities with angulation and translation, the center of deformity can be established proximal or distal to the limit of the bone. In translation deformities, the realignment of the mechanical axis requires a parallel restaggering made by a translation-osteotomy or by a counterangulated double osteotomy. In complex deformities with angulation and translation, the translation requires separate corrective planning. In frontal plane radiographs of the standing leg, the components of angulation and translation can be established graphically or by simple trigonometric formulas. The analysis and surgical procedure to realign translation deformities or a combination of translation and angulation deformities using an unilateral fixator device are discussed

Correction of leg deformities. Definition, estimation and realignment of axis deviation and misalignment

The operative realignment of mechanical axis deviations (MAD) is necessary to prevent early joint degeneration and to reach normal load-bearing. Modern types of external fixation systems allow an alignment of the mechanical axis to exact degrees. Predominantly this are corrections of angular deformities. In some cases the analysis of the MAD does not show any angular deformity, but a parallel staggering of the mechanical axis lines of a bone. Such parallel staggering of the mechanical axis lines is defined as a translation deformity of the bone. In combined deformities with angulation and translation the centre of deformity can be established proximal or distal out of the limit of the bone. In translation deformities the realignment of the mechanical axis requires a parallel re-staggering made by a translation-osteotomy or by a counter-angulated double osteotomy. In complex deformities with angulation and translation, the translation requires a separate corrective planning. By using external fixator systems to perform acute or progressive corrective osteotomies the position of the Axis of Correction of Angulation (ACA) in relation to the n-CORA of the deformity has to be considered. If ACA position is not conform with the n-CORA position relevant geometric effects in relation of length and translation occur. These geometric effects to corrective osteotomies can be calculated by using simple trigonometric formulas or graphical methods. Possibilities to compensate translation and length effects are shown by using unilateral external fixator systems.

Mechanical Axis Deviation of the Lower Limbs

Angular deformities of the tibia or femur in the frontal plane lead to mechanical axis deviation of the lower limb and malorientation of the joints above and below the level of deformity. Accurate correction of the malalignment and of the joint orientation is important for function and to prevent joint degeneration. An accurate yet simple method to determine the apex of deformity and the type of correction required is based on the joint reference lines of the hip, knee, and ankle, and the individual mechanical axis lines of each bone segment. If the osteotomy is performed at the level of the apex of the deformity, then the only correction needed is angulation. If the osteotomy is performed at a level proximal or distal to the apex, then translation in addition to angulation is necessary to accurately correct the deformity.