Mechanical Axis Of Lower Extremity Research Articles

Ten Flaws of Systematic Mechanical Alignment Total Knee Arthroplasty

Mechanical alignment (MA) and its tenets have been considered essential for total knee arthroplasty (TKA) success since they were introduced in 1973. However, over time, there have been colossal advances in our knowledge and understanding of the anatomy and kinematics of the knee, as well as in surgical precision and implants. However, the MA systematic principles of prosthetic arthroplasty and implant position related to the lower-extremity mechanical axis, have only recently been called into question. The high rates of dissatisfaction and residual pain reported after MA TKA prompted this questioning, and that leaves plenty of room for improvement. Despite the general consensus that there is great variability between patients’ anatomy, it is still the norm to carry out a systematic operation that does not consider individual variations. Evolving to a more personalized arthroplasty surgery was proposed as a rational and reasonable option to improve patient outcomes. Transitioning to a personalized TKA approach requires questioning and even disregarding certain MA TKA principles. Based on current knowledge, we can state that certain principles are erroneous or unfounded. The aim of this narrative review was to discuss and challenge 10 previously accepted, yet we believe, flawed, principles of MA, and to present an alternative concept, which is rooted in personalized TKA techniques.

Are All Unloader Braces Created Equal? Recommendations for Evidence-Based Implementation of Unloader Braces for Patients with Unicompartmental Knee OA

Unicompartmental knee osteoarthritis (UKOA) is a complex issue that is estimated to affect roughly 28% of patients with knee OA, and can result in severe cartilage degeneration, meniscus deficiency, and concomitant varus or valgus malalignment. This malalignment results in abnormally high joint reaction forces in the affected compartment, which can elicit pain, cause dysfunction, and exacerbate joint degradation. For more than two decades, the use of knee unloader braces has been advocated as a cost-effective option for symptomatic management of UKOA.During bipedal ambulation with a normal lower extremity mechanical axis, ground reaction forces create a knee adduction moment (KAM) such that the medial compartment of the knee experiences approximately 60% of joint loading and the lateral compartment experiences approximately 40% of joint loading. UKOA disrupts the mechanical axis, altering KAM and joint loading and causing pain, dysfunction, and disease progression. In theory, knee unloader braces were designed to mitigate the symptoms of UKOA by normalizing KAM via shifts in the lever arms about the knee. However, studies vary, and suggest that push-mechanism knee unloaders do not consistently provide significant biomechanical benefits for medial or lateral UKOA. Current evidence suggests that pull-mechanism unloaders may be more effective, though contrasting data have also been reported, such that further validation is necessary. The purpose of our study was to synthesize current best evidence for use of knee unloader braces for management of UKOA to suggest evidence-based best practices as well as gaps in knowledge to target for future studies. Unloader bracing for patients with UKOA appears to be a cost-effective treatment option for patients with medial UKOA who have insurance coverage. Pull-mechanism unloader bracing should be considered in conjunction with other nonoperative management therapies for those who are willing to adhere to consistent brace use for weight-bearing activities.

The effect of unicompartmental knee arthroplasty on lower extremity axis, tibiofemoral subluxation, and lateral knee joint distance

Purpose: The aim of this study was to investigate the corrective effect of Oxford phase 3 medial unicompartmental knee arthroplasty (UKA) on the lower extremity axis, tibiofemoral subluxation and lateral joint distance.
 Materials and Methods: The study included 105 knees that had undergone UKA. The Oxford Knee Score, EQ-5D-3LD and visual analog scale, and The Knee injury and Osteoarthritis Outcome Score were evaluated. Radiological evaluation was made of the lower extremity axis, tibiofemoral subluxation, and lateral knee joint distance.
 Results: The postoperative mean improvement in the mechanical axis was 1.4° and in the tibiofemoral subluxation distance, 1.59 mm compared to preoperative values. The difference between the preoperative and postoperative lateral joint distance values was on average 0.25 mm lateral inner joint distance, 0.08 mm in the lateral middle joint distance and 0.34 mm in the outer joint distance. There was no significant difference in clinical results between the groups.
 Conclusion: There were significant improvements in the postoperative period after cemented, cementless, and hybrid medial UKA in the measurements of lower extremity mechanical axis, tibiofemoral subluxation distance and lateral joint distances compared to the preoperative period.

Postural sway changes in genu recurvatum deformity during standing with manipulation of visual and proprioceptive systems

ObjectivesGenu recurvatum deformity shifts the mechanical axis of lower extremity posteriorly which may disturb the balance and lead to injury. The aim of this research was to compare postural sways in genu recurvatum subjects with healthy controls while manipulating visual and proprioceptive systems. Methods10 female subjects with genu recurvatum (20.04 ± 4.64 years) and 11 female healthy controls (20.11 ± 4.64 years) participated in the study. The back knee angle was measured using a goniometer. Dynamic BIODEX balance system was used to measure the total, anteroposterior, and mediolateral postural sways while manipulating the stability of the base of support (stable versus unstable) and visual system (open versus closed eyes). ResultDuring standing on the stable level, in both visual conditions, genu recurvatum subjects demonstrated greater total and anteroposterior postural sways than controls in both standing on the right and left foot (p<0.05). Similarly, when standing on the unstable base of support, in all conditions, the postural sways of genu recurvatum subjects were significantly greater than controls in both right and left foot (p<0.05). The vision had a main effect on postural control of genu recurvatum group (p=0.0001). There was a significant interaction between vision, the stability of the base of support and group factors (p=0.003). ConclusionThe results indicated that genu recurvatum subjects have a proprioceptive deficiency and they mainly rely on visual system inputs to control and maintain their balance. Thus, the proprioceptive system and balance control should be considered in assessment and designing an appropriate treatment regimen for genu recurvatum.

Correction of the Lower Extremity Mechanical Axis Deviation in Children with Angular Deformities of the Knee treated with Guided Growth Hemiepiphysiodesis

Correction of the Lower Extremity Mechanical Axis Deviation in Children with Angular Deformities of the Knee treated with Guided Growth Hemiepiphysiodesis

Correction of the Lower Extremity Mechanical Axis Deviation in Children with Angular Deformities of the Knee treated with Guided Growth Hemiepiphysiodesis

Background: Correction rate of angular deformities around the knee following hemiepiphysiodesis has been variable in the literature. This study aims to report the rate of mechanical axis after hemiepiphysiodesis around the knee. Factors associated with differences in correction rate are also reported. Methods: Records of skeletally immature patients, who underwent hemiepiphysiodesis for either genu valgum or genu varum between 2004 and 2018, were reviewed. For all patients, temporary hemiepiphysiodesis was performed using tension band plating. Radiographs at preoperative visit as well as each follow up visit were reviewed. Lower extremity mechanical axis deviation …

Osteochondritis Dissecans Lesion Location Is Highly Concordant With Mechanical Axis Deviation

Background: The cause of osteochondritis dissecans (OCD) is unknown. Purpose: To determine if mechanical axis deviation correlates with OCD lesion location in the knee, if degree of mechanical axis deviation correlates with size of OCD lesion, and if the deformity was primarily in the distal femur or proximal tibia. Study Design: Cross-sectional study; Level of evidence, 3. Methods: We identified 61 knees that underwent osteochondral allograft (OCA) transplantation for femoral condyle OCD lesions and used preoperative lower extremity alignment radiographs to measure lower extremity mechanical axis, mechanical lateral distal femoral angle (mLDFA), mechanical medial proximal tibial angle (mMPTA), and hip-knee-ankle angle. Lesion location and area were retrieved from operative records. Results: The location of the OCD lesion was the medial femoral condyle (MFC) for 37 knees and lateral femoral condyle (LFC) for 24 knees. Among knees with MFC lesions, alignment was varus in 25 (68%). Conversely, knees with LFC lesions had valgus alignment in 16 (67%). The mLFDA was significantly more valgus in the LFC group. mMPTA was not different between MFC and LFC groups. There was no significant correlation between degree of mechanical axis deviation and lesion size. Conclusion: In this cohort, two-thirds of patients with symptomatic OCD lesions had associated mechanical axis deviation. Lesion location correlated with mechanical axis deviation (LFC lesions were associated with a deformity in the distal femur). Degree of deformity was not correlated with lesion size. Mechanical axis deviation may play a role in OCD pathogenesis. These data do not allow analysis of the role of mechanical axis deviation in causation or prognosis of OCD lesions, but surgeons treating OCD should be aware of this common association.

P97. The varus knee phenomenon in spine deformity patients

BACKGROUND CONTEXT There is a paucity in the literature describing coronal compensatory mechanisms of the lower extremities in spine deformity patients. This study aims to report the prevalence of the varus knee phenomenon in spine deformity patients and assess the changes in the lower extremity mechanical axis after deformity correction surgery. PURPOSE Spine deformity patients are predisposed to having varus knees that will self-correct postoperatively with restoration of global spine alignment. STUDY DESIGN/SETTING Retrospective cohort. PATIENT SAMPLE A total of 361 patients undergoing spinal deformity surgery between July 2015 and July 2018. OUTCOME MEASURES The prevalence of varus knees on pre- and postoperative standing films was adjusted for patient demographics and diagnosis. METHODS A single center radiographic review of all patients undergoing spinal deformity surgery between July 2015 and July 2018 were included. All patients had full-length standing spine pre- and post-operative films with an identifiable lower extremity mechanical axis. The prevalence of varus knees on pre- and postoperative standing films was adjusted for patient demographics and diagnosis. RESULTS A total of 361 patients met the inclusion criteria. There was 268 adult (>18 years) and 93 pediatric ( CONCLUSIONS The adult spine deformity patients, particularly those with ADS, are predisposed to having preoperative varus knee posture compared to the pediatric patients. Spine deformity correction surgery corrected the lower extremity mechanical malalignment in more than half of the adult patients with preoperative varus knee postures and all of the pediatric patients with varus knees. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.

&lt;p&gt;Total knee arthroplasty associated with tibial tubercle and simultaneous femoral and tibial osteotomies for severe extra-articular deformity: a case report&lt;/p&gt;

The restoration of the lower extremity mechanical axis in patients with osteoarthritis in knee and extra-articular deformity requires careful pre-operative planning. An extra-articular deformity may be corrected inside the knee by arthroplasty with intra-articular correction or outside of the knee by osteotomy alone or by arthroplasty combined with extra-articular corrective osteotomy. In this study, we described a unique case of simultaneous femoral and tibial osteotomies at the time of primary total knee arthroplasty in a 45-year-old woman. To prevent unnecessary bone loss, the intra-articular bone resections were made parallelly to the preexisting joint obliquity prior to the corrective tibial and femoral osteotomies. After restoration of the mechanical axis and healing of all osteotomies, a successful clinical and radiological outcome was achieved during the mid-term 5-year follow-up. The preoperative analysis of patients with an extra-articular deformity is invaluable and should include long-standing radiographs from the center of the femoral head to the center of the ankle. Although different osteotomy principles (opening wedge vs closing wedge) and fixation methods (stemmed revision prosthesis, intramedullary nail, locking plates) have been reported in the literature, the use of a tapered fluted long stem offers several benefits, including ease of application, rotational control, and possible early weight bearing. Total knee arthroplasty in combination with simultaneous extra-articular osteotomy is technically difficult but effective. This technique helps to preserve bone stock and ligament stability. A single intervention leads to less recovery time, reduced risk to the patients by avoiding two separate applications of anesthesia, and reduced costs. Based on the literature search, this is the first report describing the detailed surgical technique of simultaneous femoral and tibial osteotomies at the time of primary total knee arthroplasty associated with tibial tubercle osteotomy, achieving a comprehensive correction.

A Computer Model Assessment of the Effect of Hindfoot Alignment on Mechanical Axis Deviation and Ankle Fractures

Category: Basic Sciences/Biologics Introduction/Purpose: Conventional mechanical axis is calculated from the center of the femoral head to the center of the ankle. Mechanical axis deviation of the lower limb can be associated with a pes planus hindfoot. Malalignment of the lower limb has been shown to increase progression of osteoarthritis of the knee and ankle and decrease joint arthroplasty longevity. Clinically, a pes planus hindfoot has also been seen with patients who present with a stress fracture of the lateral malleolus. This biomechanical study aims to utilize computer modeling to evaluate the hypothesis that altered force transmission on the lateral malleolus with resultant stress fractures in a pes planus model is attributable to mechanical axis deviation. Methods: A free-body diagram of the fibula in single leg stance was generated by modeling the fibula as a uniform cylinder. It includes the axially applied load and a single evertor muscle force as an eccentric load applied to the mid-diaphysis . Previously derived relationships between body weight (BW = 667 N, 150lbs) and a) normal axial fibula load (BW*0.17) and b) muscle force (BW*0.25) were used. Fibula length (286.5 mm) and diameter (8 mm) were derived from anthropological data. Mechanical axis deviation in pes planus was simulated in two manners: 1) increased (2 and 3 times normal) axial fibula load and 2) increased evertor muscle force. The compressive stress along the length of the bone was determined through static analysis and the total applied load was compared to theoretical Euler buckling load. Results: Increasing the load on the fibula, either by increasing the axial load (Figure 1A) or the muscle load (Figure 1B), increases the maximum compressive stress below the lateral muscle origins, namely the section between the distal tibiofibular ligaments and the evertor muscles. The compressive stress for both cases was less than the compressive yield stress of cortical bone (200 MPa) and cancellous bone (100 MPa) even as the force was increased to the critical buckling value. This model serves as a first attempt to relate the spatial distribution of stress in the fibula with muscle force, axial load, and compressive stress in light of distal fibular fractures associated with pes planus. Conclusion: The importance of lower extremity mechanical axis deviation is well established in the progression of arthritis in the knee and ankle. The role of the mechanical axis in the predisposition of stress fractures around the ankle has not been evaluated in the literature. This biomechanical study represents the first attempt to understand how deviation of the mechanical axis can result in stress fractures of the lateral malleolus. Future studies including a finite element analysis will provide further information and the results of these studies may alter how clinicians treat patients with stress fractures of the fibula.

Short-term results of the management of severe bone defects in primary TKA with cement and K-wires

ObjectiveThe aim of this study was to evaluate the results of cement and kirschner wire augmentation in the management of bone defects in primary TKA. MethodsTwenty-four patients (10 male, 14 female; mean age: 66 years) with uncontained unilateral medial tibial articular bone defect who underwent TKA between 2010 and 2014 were included in this study. The average follow up time was 33.7 months. Patients were divided to two groups according to the size of the bone defect (Group 1: <20 mm, Group 2: >20 mm). The tibial defect was reconstructed by using cement and K-wires. We used posterior stabilized prosthesis with no tibial stem extension. ResultsThe preoperative and postoperative lower extremity mechanical axis in Group I was in a mean varus of 15° and mean varus of 3°, respectively (p < 0.001). The preoperative and postoperative lower extremity mechanical axis in Group 2 was in a mean varus of 20° and mean varus of 3° respectively in Group II (p < 0.001). None of the patients neither suffered from failure of K-wires nor loosening. ConclusionThe use of cement and K-wires augmentation appears to be a simple and cost-effective treatment option for the tibial bone defects in primary TKA. Level of evidenceLevel IV, Therapeutic study.

Tibial osteotomy combined with arthroscopic condylar notch plasty to treat flexion deformity of knee varus osteoarthri-tis

Objective To explore the medial open wedge high tibial osteotomy (OWHTO) combined with arthroscopic condyle plasty with clinical flexion deformity in patients with osteoarthritis of knee varus. Methods From January 2014 to July 2015, 11 cases (11 knees) of varus knee joint flexion deformity were applied the procedure of OWHTO combined with arthroscopic condyle plasty, including 4 male and 7 female; the average age was 52.1 years old (ranged from 48 to 58 years). OWHTO could ad-just the line of force of the lower limbs in coronal plane (the connection line between femoral head center point and the center point of ankle joint) through lateral tibial plateau 62.5% position, and implant allogeneic bone to support posterior inclination an-gle, underwent arthroscopic condyle plasty to improve flexion deformity at the same time. Results 11 patients in this group were all followed up, and the follow-up time was 1-2.5 years, average 1.5 years. No case of fracture nonunion or delayed healing was found. Imaging data was measured to evaluate the mechanical axis of lower extremity by the relative position of tibial plateau, femo-ral tibial angle,femoral notch width index, tibial plateau posterior angle before operation and one year after the operation. The rela-tive position of the mechanical axis of the lower limb through the tibial plateau was 17.4% ± 4.9% preoperatively, and 58.9% ± 3.1% after operation, femoral tibial angle changed from 181.6°±1.2° to 170.3°±1.3°, tibial plateau posterior inclination angle: pre-operative 7.7°±2.2°, postoperative 7.9°±1.9°, femoral notch width index was increased from 0.221±0.007 to 0.272±0.009 after op-eration, flexion deformity angle of preoperative was 11.1°±3.1°, and 1.4°±1.5° one years after operation, VAS score was (6.5±1.1) points before surgery, and (2.5±0.8) points of postoperative, Lysholm score was (50.72±6.57) points before operation, and (75.72±7.41) points one year after operation, and the differences were all statistically significant. Conclusion OWHTO combined with arthroscopic condyle plasty can significantly improve the lower limb line and flexion deformity, and also maintain the posterior in-clination angle of tibial plateau,and can get a good short-term efficacy. Key words: Osteoarthritis, knee; Osteotomy; Genu varum; Treatment outcome

Combination of Accelerometer-Based Navigation and Force Sensor for Precise Bone Resection and Appropriate Soft Tissue Balancing in Total Knee Arthroplasty

Background: Precise bone resection and appropriate soft tissue balancing are considered indispensable in total knee arthroplasty (TKA). However, in most TKAs, only the experienced-based subjective physical “feel” of the surgeon, or either a computer-based navigation system or a soft tissue balancing system are applied to improve the results. In the present study, a combination of both an accelerometer-based navigation system and an electronic knee balancing force sensor were applied to attempt to obtain optimal outcomes.Materials and Methods: An accelerometer-based navigation system and an electronic knee balancing force sensor were applied in combination in 5 TKAs. Thereafter, the incidence of radiographical outliers of the lower-extremity mechanical axis and the alignments of femoral and tibial components, and the incidence of intraoperative lateral retinacular release were evaluated and compared against those of 5 TKAs performed with the force sensor alone as a control.Results: The posterior slope of the tibia was significantly improved in the TKAs performed with the combination of both devices (P=0.004). No lateral release was performed in any TKAs of either group.Conclusion: TKAs performed under the combination of an accelerometer-based navigation system and an electronic knee balancing force sensor can obtain greater the accuracy of bone resection and appropriate soft tissue balancing.

Repeatability of a Multi-Segment Foot Model with a 15-Marker Set in Healthy Children

Category: Basic Sciences/Biologics Introduction/Purpose: Recently, 3D multi-segment foot models using 15 marker set(Foot 3D model) was proposed . Our team demonstrated that this model had comparable intra-session/inter-session repeatability with other MFMs making it suitable for evaluation of segmental foot motion during gait. And also we have shown that this model had high intra-session/inter-session repeatability in the assessment of foot motion in healthy adults. Compared with adults, children have some specific character of gait. Mechanical axis of lower extremity and gait has changed over the course of growing up. And children has small bones and soft skin comparing with adults, so these can be some factors that induce bias of analysis. Then despite of verification of high intra- session/inter-session repeatability of Foot 3D model in healthy adults, it is necessary to validate the intra-session/inter-session repeatability of this model in healthy children. Methods: Participating subjects is made up of 40 feet of twenty healthy children (10 males, 10 females) of 10-15 years old. We utilized multi-segment foot model with 15-marker set used in previous study for healthy adults. We divided participants into two groups in tens. One group was tested by same operator in each test and the other group changed the operator in each test. The former is for inter-session analysis and the latter is for inter-rater analysis. In this study, we analyzed the intra-session, inter- session, and inter-rater repeatability. Coefficients of multiple correlation (CMC) and intra-class correlation (ICC) were calculated in order to assess the intra-session, inter-session and inter-rater session repeatability. The difference between the two sessions of each group was assessed for each time points of the gait cycle. Results: There is no significant difference pattern in gait analysis graph (Figure 1). The mean intra-session CMC (±Standard deviation) was 0.933 (± 0.034). The intra-session CMC values of all parameters were interpreted as excellent or very good repeatability. The intra-session ICC values of all parameters were interpreted as excellent. The mean inter-session CMC (±SD) was 0.794 (± 0.123). The mean inter-session ICC (±SD) was 0.866 (± 0.086). The inter-session ICC values of all parameters were interpreted as excellent except hindfoot rotation parameter. Inter-rater CMC (±Standard deviation) was 0.766 (± 0.214). The mean inter-rater ICC (±SD) was 0.839 (± 0.203). The inter-rater ICC values of all parameters were interpreted as good or excellent. Mean gap of all parameters is larger than the value of previous study for healthy adults. Conclusion: In this study, we used a multi-segment foot models using 15 marker set in order to evaluate segmental foot motion in healthy children as in case of adults. And we demonstrated that this model had high intra-session, inter-session and inter-rater repeatability in the assessment of foot motion except some cautions. We believe that our study for children is very important to understand the gait of childhood and this Foot 3D model can be applicable in clinical settings, which require further elucidation.

Alignment of the lower extremity mechanical axis by computer-aided design and application in total knee arthroplasty.

The success of total knee arthroplasty (TKA) depends on many factors. The position of a prosthesis is vitally important. The purpose of the present study was to evaluate the value of a computer-aided establishing lower extremity mechanical axis in TKA using digital technology. A total of 36 cases of patients with TKA were randomly divided into the computer-aided design of navigation template group (NT) and conventional intramedullary positioning group (CIP). Three-dimensional (3D) CT scanning images of the hip, knee, and ankle were obtained in NT group. X-ray images and CT scans were transferred into the 3D reconstruction software. A 3D bone model of the hip, knee, ankle, as well as the modified loading, was reconstructed and saved in a stereolithographic format. In the 3D reconstruction model, the mechanical axis of the lower limb was determined, and the navigational templates produced an accurate model using a rapid prototyping technique. The THA in CIP group was performed according to a routine operation. CT scans were performed postoperatively to evaluate the accuracy of the two TKA methods. The averaged operative time of the NT group procedures was [Formula: see text]min shorter than those of the conventional procedures ([Formula: see text] min). The coronal femoral angle, coronal tibial angle, posterior tibial slope were [Formula: see text], [Formula: see text], [Formula: see text] in NT group and [Formula: see text], [Formula: see text], [Formula: see text] in CIP group, respectively. Statistically significant group differences were found. The navigation template produced through mechanical axis of lower extremity may provide a relative accurate and simple method for TKA.

Proximal Tibial Valgus Osteotomy: Lateral Closing Wedge.

Valgus-producing high tibial osteotomy (HTO) is a well-accepted treatment modality in active patients with varus malalignment and symptomatic medial unicompartmental osteoarthritis (OA) of the knee. One of the key factors for long-term success of the osteotomy is the achievement of an even distribution of the mechanical load on the knee joint by obtaining an ideal alignment of the lower-extremity mechanical axis. Proper surgical techniques are very important, and lateral closing wedge proximal tibial valgus osteotomy (CWO) is highly effective in achieving the desired overcorrection of 3° to 7° of valgus. The major steps of CWO are (1) preoperative planning, in which the frontal plane varus knee deformity is assessed on a standard whole-leg radiograph; (2) a transverse anterolateral incision from the tubercle toward the posterior aspect of the proximal part of the fibular head; (3) exposure and snaring of the common peroneal nerve; (4) resection of the anterior aspect of the proximal part of the fibular head; (5) use of a calibrated slotted wedge resection guide to perform the osteotomy proximal to the tuberosity under fluoroscopic guidance; (6) removal of an osseous wedge and closure of the osteotomy site, with the medial opposite cortex acting as a hinge; and (7) fixation of the osteotomy site with two step staples. Complications (e.g., nonunion, deep infection, and peroneal neuropathy) are rare. At follow-up, CWO has been shown to improve knee function and reduce pain. Male patients with early-onset knee OA have an almost ten times lower probability of failure of a CWO than women with more degenerative disease. The survival rate, with knee replacement as the end point, is approximately 75% at ten years following CWO. CWO postpones primary total knee arthroplasty (TKA) for a median of seven years, and there is low-quality evidence that osteotomy does not compromise subsequent knee replacement.

Correlation of knee and hindfoot deformities in advanced knee OA: compensatory hindfoot alignment and where it occurs.

Many patients undergoing TKA have both knee and ankle pathology, and it seems likely that some compensatory changes occur at each joint in response to deformity at the other. However, it is not fully understood how the foot and ankle compensate for a given varus or valgus deformity of the knee. (1) What is the compensatory hindfoot alignment in patients with end-stage osteoarthritis who undergo total knee arthroplasty (TKA)? (2) Where in the hindfoot does the compensation occur? Between January 1, 2005, and December 31, 2009, one surgeon (JJC) obtained full-length radiographs on all patients undergoing primary TKA (N=518) as part of routine practice; patients were analyzed for the current study and after meeting inclusion criteria, a total of 401 knees in 324 patients were reviewed for this analysis. Preoperative standing long-leg AP radiographs and Saltzman hindfoot views were analyzed for the following measurements: mechanical axis angle, Saltzman hindfoot alignment and angle, anatomic lateral distal tibial angle, and the ankle line convergence angle. Statistical analysis included two-tailed Pearson correlations and linear regression models. Intraobserver and interobserver intraclass coefficients for the measurements considered were evaluated and all were excellent (in excess of 0.8). As the mechanical axis angle becomes either more varus or valgus, the hindfoot will subsequently orient in more valgus or varus position, respectively. For every degree increase in the valgus mechanical axis angle, the hindfoot shifts into varus by -0.43° (95% confidence interval [CI], -0.76° to -0.1°; r=-0.302, p=0.0012). For every degree increase in the varus mechanical axis angle, the hindfoot shifts into valgus by -0.49° (95% CI, -0.67° to -0.31°; r=-0.347, p<0.0001). In addition, the subtalar joint had a strong positive correlation (r=0.848, r2=0.72, p<0.0001) with the Saltzman hindfoot angle, whereas the anatomic lateral distal tibial angle (r=0.450, r2=0.20, p<0.0001) and the ankle line convergence angle (r=0.319, r2=0.10, p<0.0001) had a moderate positive correlation. The coefficient of determination (r2) shows that 72% of the variance in the overall hindfoot angle can be explained by changes in the subtalar joint orientation. These findings have implications for treating patients with both knee and foot/ankle problems. For example, a patient with varus arthritis of the knee should be examined for fixed hindfoot valgus deformity. The concern is that patients undergoing TKA, who also present with a stiff subtalar joint, may have exacerbated, post-TKA foot/ankle pain or disability or malalignment of the lower extremity mechanical axis as a result of the inability of the subtalar joint to reorient itself after knee realignment. A prospective study is underway to confirm this speculation. Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Three-dimensional reconstruction and reverse-engineering used to establish lower-extremity mechanical axes in healthy adults

Objective To present a method to establish lower-extremity mechanical axes by means of three-dimensional (3D) reconstruction and reverse-engineering.Methods Twenty healthy adult volunteers of Han ethnic group were enrolled in the present study.They were 10 men and 10 women,18 to 22 years of age (average,19.3 years).Continuous spiral CT scans were conducted on their both lower extremities.The original scan data in the.dicom format were imported into the Mimics Innovation Suite 14.0 software for 3D reconstruction of models of lower extremity bones which were saved in the.stl format.Next,the 3D models were imported into Geomagic Studio 2012 software before centers of the femoral head,the knee,the tibia and the ankle were defined and the mechanical axes of the tibia and femur were determined on the 3D reconstruction models.Results The average lower-extremity mechanical axis at the coronal view was 178.6° ± 2.4° for the male and 177.1°± 2.5° for the female; the included angles between the femoral and tibial mechanical axes averaged 2.1° ± 1.8° for the male and 2.2° ± 1.9° for the female; the average lower-extremity mechanical axis at the sagittal view was 178.5° ± 2.2° for the male and 177.6° ± 2.3° for the female.There were no significant differences between male and female or between the left and the right sides of the lower limb regarding the lower-extremity mechanical axis.Conclusion 3D reconstruction and reverse-engineering is a digital and individualized method that can be used to determine lower-extremity mechanical axes. Key words: Imaging, three-dimensional; Reverse-engineering; Mechanical axis

Patient specific cutting guides versus an imageless, computer-assisted surgery system in total knee arthroplasty

BackgroundPatient specific cutting guides (PSC) in total knee arthroplasty (TKA) have recently been introduced, in which preoperative 3-dimensional imaging is used to manufacture disposable cutting blocks specific to a patient's anatomy. The purpose of this study was to compare the alignment accuracy of PSC to an imageless CAS system in TKA. MethodsThirty-seven patients (41 knees), received a TKA using an imageless CAS system. Subsequently, 38 patients (41 knees), received a TKA using a MRI-based, PSC system.Postoperatively, standing AP hip-to-ankle radiographs were obtained, from which the lower extremity mechanical axis, tibial component varus/valgus, and femoral component varus/valgus mechanical alignment were digitally measured. Each measurement was performed by two blinded, independent observers, and interclass correlations were calculated. A student's two-tailed t test was used to compare the two cohorts (p-value<0.05=significant). ResultsIn the PSC cohort, 70.7% of patients had an overall alignment within 3° of a neutral mechanical axis (vs. 92.7% with CAS, p=0.02), 87.8% had a tibial component alignment within 2° of perpendicular to the tibial mechanical axis (vs. 100% with CAS, p=0.04), and 90.2% had a femoral component alignment within 2° of perpendicular to the femoral mechanical axis (vs. 100% with CAS, p=0.2). Interclass correlation coefficients were good to excellent for all radiographic measurements. ConclusionWhile PSC techniques appear sound in principle, this study did not demonstrate patient specific cutting guides to obtain the same degree of overall mechanical and tibial component alignment accuracy as a CAS technique. Level of evidenceIII: Retrospective cohort study.

Assessment of changes in the loading of menisci following femur structural deformities

Purpose: To evaluate the changes of maximum equivalent stresses (MES) on menisci following femur structural deformities. Materials and methods: Three- Dimensional (3D) solid models were created on MIMICS® by using DICOM formatted longitudinal computed tomography scans. +10° femur neck valgus osteotomy was simulated for coxa valga and -10° varus osteotomy was simulated coxa vara. ANSYS® WorkbenchTM (Version 12) was used to analyze the stress/load distribution on menisci.Results: In the reference model, the MES on medial meniscus was 17.362 Megapascal (MPa), lateral meniscus was 8.621 MPa. The MES was measured 10.632 MPa on medial meniscus and 9.487 MPa on lateral meniscus in coxa vara model. In coxa valga simulated model the MES on medial meniscus was 6.866 MPa while lateral meniscus was 21.854 MPa.Conclusion: Maxiumum equivalent stresses on menisci were affected according to changes in mechanical axis of lower extremity due to proximal femur geometric variations.