Non-invasive computer-assisted measurement of knee alignment

The quantification of knee alignment is a routine part of orthopaedic practice and is important for monitoring disease progression, planning interventional strategies, and follow-up of patients. Currently available technologies such as radiographic measurements have a number of drawbacks. The aim of this study was to validate a potentially improved technique for measuring knee alignment under different conditions. An image-free navigation system was adapted for non-invasive use through the development of external infrared tracker mountings. Stability was assessed by comparing the variance (F-test) of repeated mechanical femoro-tibial (MFT) angle measurements for a volunteer and a leg model. MFT angles were then measured supine, standing and with varus-valgus stress in asymptomatic volunteers who each underwent two separate registrations and repeated measurements for each condition. The mean difference and 95% limits of agreement were used to assess intra-registration and inter-registration repeatability. For multiple registrations the range of measurements for the external mountings was 1° larger than for the rigid model with statistically similar variance (p=0.34). Thirty volunteers were assessed (19 males, 11 females) with a mean age of 41 years (range: 20-65) and a mean BMI of 26 (range: 19-34). For intra-registration repeatability, consecutive coronal alignment readings agreed to almost ±1°, with up to ±0.5° loss of repeatability for coronal alignment measured before and after stress maneuvers, and a ±0.2° loss following stance trials. Sagittal alignment measurements were less repeatable overall by an approximate factor of two. Inter-registration agreement limits for coronal and sagittal supine MFT angles were ±1.6° and ±2.3°, respectively. Varus and valgus stress measurements agreed to within ±1.3° and ±1.1°, respectively. Agreement limits for standing MFT angles were ±2.9° (coronal) and ±5.0° (sagittal), which may have reflected a variation in stance between measurements. The system provided repeatable, real-time measurements of coronal and sagittal knee alignment under a number of dynamic, real-time conditions, offering a potential alternative to radiographs

Radiographic Outcomes of Adult Spinal Deformity Correction : A Critical Analysis of Variability and Failures Across Deformity Patterns

Study Design: Multicenter, prospective, consecutive, surgical case series from the International Spine Study Group. Objectives: To evaluate the effectiveness of surgical treatment in restoring spinopelvic (SP) alignment. Summary of Background Data: Pain and disability in the setting of adult spinal deformity have been correlated with global coronal alignment (GCA), sagittal vertical axis (SVA), pelvic incidence/lumbar lordosis mismatch (PI-LL), and pelvic tilt (PT). One of the main goals of surgery for adult spinal deformity is to correct these parameters to restore harmonious SP alignment. Methods: Inclusion criteria were operative patients (age greater than 18 years) with baseline (BL) and 1-year full-length X-rays. Thoracic and thoracolumbar Cobb angle and previous mentioned parameters were calculated. Each parameter at BL and 1 year was categorized as either pathological or normal. Pathologic limits were: Cobb greater than 30 , GCA greater than 40 mm, SVA greater than 40 mm, PI-LL greater than 10 , and PT greater than 20 . According to thresholds, corrected or worsened alignment groups of patients were identified and overall radiographic effectiveness of procedure was evaluated by combining the results from the coronal and sagittal planes. Fondation Paristech, ISS

Correlation and reliability of cervical sagittal alignment parameters between lateral cervical radiograph and lateral whole-body EOS stereoradiograph

STUDY DESIGN:  Retrospective analysis. OBJECTIVE:  To evaluate the correlation and reliability of cervical sagittal alignment parameters obtained from lateral cervical radiographs (XRs) compared with lateral whole-body stereoradiographs (SRs). METHODS:  We evaluated adults with cervical deformity using both lateral XRs and lateral SRs obtained within 1 week of each other between 2010 and 2014. XR and SR images were measured by two independent spine surgeons using the following sagittal alignment parameters: C2–C7 sagittal Cobb angle (SCA), C2–C7 sagittal vertical axis (SVA), C1–C7 translational distance (C1–7), T1 slope (T1-S), neck tilt (NT), and thoracic inlet angle (TIA). Pearson correlation and paired t test were used for statistical analysis, with intra- and interrater reliability analyzed using intraclass correlation coefficient (ICC). RESULTS:  A total of 35 patients were included in the study. We found excellent intrarater reliability for all sagittal alignment parameters in both the XR and SR groups with ICC ranging from 0.799 to 0.994 for XR and 0.791 to 0.995 for SR. Interrater reliability was also excellent for all parameters except NT and TIA, which had fair reliability. We also found excellent correlations between XR and SR measurements for most sagittal alignment parameters; SCA, SVA, and C1–C7 had r > 0.90, and only NT had r < 0.70. There was a significant difference between groups, with SR having lower measurements compared with XR for both SVA (0.68 cm lower, p < 0.001) and C1–C7 (1.02 cm lower, p < 0.001). There were no differences between groups for SCA, T1-S, NT, and TIA. CONCLUSION:  Whole-body stereoradiography appears to be a viable alternative for measuring cervical sagittal alignment parameters compared with standard radiography. XR and SR demonstrated excellent correlation for most sagittal alignment parameters except NT. However, SR had significantly lower average SVA and C1–C7 measurements than XR. The lower radiation exposure using single SR has to be weighed against its higher cost compared with XR

Non-invasive assessment of lower limb alignment is accurate for pre-operative planning and post-operative follow up

Knee alignment is a fundamental measurement in the assessment, monitoring and surgical management of patients with OA. In spite of extensive research into the consequences of malalignment, there is a lack of data regarding the potential variation between supine and standing (functional) conditions. The purpose of this study was to explore this relationship in asymptomatic, osteoarthritic and prosthetic knees. Our hypothesis was that the change in alignment of these three groups would be different. Infrared position capture was used to assess knee alignment for 30 asymptomatic controls and 31 patients with OA, before and after TKA. Coronal and sagittal mechanical femorotibial (MFT) angles in extension (negative values varus/hyperextension) were measured supine and in bi-pedal stance and changes analysed using a paired t-test. To quantify this change in 3D, vector plots of ankle centre displacement relative to the knee centre were produced. Alignment in both planes changed significantly from supine to standing for all three groups, most frequently towards relative varus and extension. In the coronal plane, the mean±SD(°) of the supine/standing MFT angles was 0.1±2.5/−1.1±3.7 for asymptomatic (p=0.001), −2.5±5.7/−3.6±6.0 for osteoarthritic (p=0.009) and −0.7±1.4/ −2.5±2.0 for prosthetic knees (p<0.001). In the sagittal plane, the mean±SD(°) of the supine/standing MFT angles was −1.7±3.3/−5.5±4.9 for asymptomatic (p<0.001), 7.7±7.1/1.8±7.7 for osteoarthritic (p<0.001) and 6.8±5.1/1.4±7.6 for prosthetic knees (p<0.001). The vector plots showed that the trend of relative varus and extension in stance was similar in overall magnitude and direction between the groups. The similarities between each group did not support our hypothesis. The consistent kinematic pattern for different knee types suggests that soft tissue restraints rather than underlying joint deformity may be more influential in dynamic control of alignment from lying to standing. This potential change should be considered when positioning TKA components on supine limbs as post-operative functional alignment may be different

Cervical spine sagittal alignment variations following posterior spinal fusion and instrumentation for adolescent idiopathic scoliosis

The aim of this study is to quantify the changes in the sagittal alignment of the cervical spine in patients with adolescent idiopathic scoliosis following posterior spinal fusion. Patients eligible for study inclusion included those with a diagnosis of mainly thoracic adolescent idiopathic scoliosis treated by means of posterior multisegmented hook and screw instrumentation. Pre and post-operative anterior-posterior and lateral radiographs of the entire spine were reviewed to assess the changes of cervical sagittal alignment. Thirty-two patients (3 boys, 29 girls) met the inclusion criteria for the study. The average pre-operative cervical sagittal alignment (CSA) was 4.0°±12.3° (range −30° to 40°) of lordosis. Postoperatively, the average CSA was 1.7°±11.4° (range −24° to 30°). After surgery, it was less than 20° in 27 patients (84.4%) and between 20° and 40° in 5 patients (15.6%). The results of the present study suggest that even if rod precontouring is performed and postoperative thoracic sagittal alignment is restored, improved or remains unchanged after significant correction of the deformity on the frontal plane, the inherent rigidity of the cervical spine limits changes in the CSA as the cervical spine becomes rigid over tim

Change of sagittal spinal alignment and its association with pain and function after lumbar surgery augmented with an interspinous implant

Background: Interspinous spacer/implants like the Device for Intervertebral Assisted Motion (DIAM™) are controversially yet commonly used in the surgical treatment of lumbar degenerative pathologies. Criticism is based on ill-defined indications, lack of superiority over decompression, and a poorly understood mechanical effect. Yet, continued use by surgeons implies their perceived clinical merit. We examined radiographic spinal alignment for 12 months, and pain and function for 24 months, after DIAM-augmented surgery to improve the understanding of the mechanical effect relating to clinical outcomes in patients. Methods: We undertook a single-surgeon prospective, longitudinal study of 40 patients (20 F, 20 M) who received DIAM-augmented surgery in treatment of their symptomatic lumbar degenerative condition. Outcomes measured included sagittal spinal alignment (lumbar lordosis, sacral inclination, primary (PDA), supradjacent (SDA) disc angles, and regional sagittal balance (RSB; standing lateral radiographs), and back and leg pain (visual analogue scale; VAS) and function (Oswestry Disability Index; ODI). Responders were identified as those with clinically meaningful improvement to pain (>20%) and function (>15%) at 24 months postoperatively; features of sagittal spinal alignment between responders and non-responders were examined. Results: Sagittal alignment was unchanged at 12 months. At 6 weeks postoperatively, PDA (mean (SD)) reduced by 2.2° (4.0°; p < 0.01) and more-so in back pain non-responders (3.8° (3.2°)) than responders (0.7° (4.4°); p < 0.05). Positive preoperative RSB in responders (26.7Rmm (42.3Rmm); Rmm is a system-relative measure) decreased at 6 weeks (by 3.1Rmm (9.1Rmm)). Non-responders had a negative RSB preoperatively (−1.0Rmm (32.0Rmm)) and increased at 6 weeks (11.2Rmm (15.5Rmm); p < 0.05). Clinically meaningful improvement for the whole cohort for back pain and function were observed to 24 months (back pain: 25.0% (28.0); function: 15.4% (17.6); both p < 0.0001). Conclusions: Unaltered sagittal alignment at 12 months was not related to symptoms after DIAM-augmented lumbar surgery. Subtle early flattening at the index disc angle was not maintained. Preoperative and early post-operative sagittal alignment may indicate response after DIAM-augmented surgery for mixed lumbar pathologies. Further investigation toward defining indications and patient suitability is warranted

ISSLS PRIZE IN BIOENGINEERING SCIENCE 2019: biomechanical changes in dynamic sagittal balance and lower limb compensatory strategies following realignment surgery in adult spinal deformity patients.

Study designA longitudinal cohort study.ObjectiveTo define a set of objective biomechanical metrics that are representative of adult spinal deformity (ASD) post-surgical outcomes and that may forecast post-surgical mechanical complications. Current outcomes for ASD surgical planning and post-surgical assessment are limited to static radiographic alignment and patient-reported questionnaires. Little is known about the compensatory biomechanical strategies for stabilizing sagittal balance during functional movements in ASD patients.MethodsWe collected in-clinic motion data from 15 ASD patients and 10 controls during an unassisted sit-to-stand (STS) functional maneuver. Joint motions were measured using noninvasive 3D depth mapping sensor technology. Mathematical methods were used to attain high-fidelity joint-position tracking for biomechanical modeling. This approach provided reliable measurements for biomechanical behaviors at the spine, hip, and knee. These included peak sagittal vertical axis (SVA) over the course of the STS, as well as forces and muscular moments at various joints. We compared changes in dynamic sagittal balance (DSB) metrics between pre- and post-surgery and then separately compared pre- and post-surgical data to controls.ResultsStandard radiographic and patient-reported outcomes significantly improved following realignment surgery. From the DSB biomechanical metrics, peak SVA and biomechanical loads and muscular forces on the lower lumbar spine significantly reduced following surgery (- 19 to - 30%, all p &lt; 0.05). In addition, as SVA improved, hip moments decreased (- 28 to - 65%, all p &lt; 0.05) and knee moments increased (+ 7 to + 28%, p &lt; 0.05), indicating changes in lower limb compensatory strategies. After surgery, DSB data approached values from the controls, with some post-surgical metrics becoming statistically equivalent to controls.ConclusionsLongitudinal changes in DSB following successful multi-level spinal realignment indicate reduced forces on the lower lumbar spine along with altered lower limb dynamics matching that of controls. Inadequate improvement in DSB may indicate increased risk of post-surgical mechanical failure. These slides can be retrieved under Electronic Supplementary Material

Comparison of extramedullary versus intramedullary referencing for tibial component alignment in total ankle arthroplasty.

BACKGROUND: The majority of total ankle arthroplasty (TAA) systems use extramedullary alignment guides for tibial component placement. However, at least 1 system offers intramedullary referencing. In total knee arthroplasty, studies suggest that tibial component placement is more accurate with intramedullary referencing. The purpose of this study was to compare the accuracy of extramedullary referencing with intramedullary referencing for tibial component placement in total ankle arthroplasty. METHODS: The coronal and sagittal tibial component alignment was evaluated on the postoperative weight-bearing anteroposterior (AP) and lateral radiographs of 236 consecutive fixed-bearing TAAs. Radiographs were measured blindly by 2 investigators. The postoperative alignment of the prosthesis was compared with the surgeon's intended alignment in both planes. The accuracy of tibial component alignment was compared between the extramedullary and intramedullary referencing techniques using unpaired t tests. Interrater and intrarater reliabilities were assessed with intraclass correlation coefficients (ICCs). RESULTS: Eighty-three tibial components placed with an extramedullary referencing technique were compared with 153 implants placed with an intramedullary referencing technique. The accuracy of the extramedullary referencing was within a mean of 1.5 ± 1.4 degrees and 4.1 ± 2.9 degrees in the coronal and sagittal planes, respectively. The accuracy of intramedullary referencing was within a mean of 1.4 ± 1.1 degrees and 2.5 ± 1.8 degrees in the coronal and sagittal planes, respectively. There was a significant difference (P < .001) between the 2 techniques with respect to the sagittal plane alignment. Interrater ICCs for coronal and sagittal alignment were high (0.81 and 0.94, respectively). Intrarater ICCs for coronal and sagittal alignment were high for both investigators. CONCLUSIONS: Initial sagittal plane tibial component alignment was notably more accurate when intramedullary referencing was used. Further studies are needed to determine the effect of this difference on clinical outcomes and long-term survivability of the implants. LEVEL OF EVIDENCE: Level III, retrospective comparative study

Anatomical landmark based registration of contrast enhanced T1-weighted MR images

In many problems involving multiple image analysis, an im- age registration step is required. One such problem appears in brain tumor imaging, where baseline and follow-up image volumes from a tu- mor patient are often to-be compared. Nature of the registration for a change detection problem in brain tumor growth analysis is usually rigid or affine. Contrast enhanced T1-weighted MR images are widely used in clinical practice for monitoring brain tumors. Over this modality, con- tours of the active tumor cells and whole tumor borders and margins are visually enhanced. In this study, a new technique to register serial contrast enhanced T1 weighted MR images is presented. The proposed fully-automated method is based on five anatomical landmarks: eye balls, nose, confluence of sagittal sinus, and apex of superior sagittal sinus. Af- ter extraction of anatomical landmarks from fixed and moving volumes, an affine transformation is estimated by minimizing the sum of squared distances between the landmark coordinates. Final result is refined with a surface registration, which is based on head masks confined to the sur- face of the scalp, as well as to a plane constructed from three of the extracted features. The overall registration is not intensity based, and it depends only on the invariant structures. Validation studies using both synthetically transformed MRI data, and real MRI scans, which included several markers over the head of the patient were performed. In addition, comparison studies against manual landmarks marked by a radiologist, as well as against the results obtained from a typical mutual information based method were carried out to demonstrate the effectiveness of the proposed method

Is Sacral Extension a Risk Factor for Early Proximal Junctional Kyphosis in Adult Spinal Deformity Surgery?

Study designRetrospective cohort study.PurposeTo investigate the role of sacral extension (SE) for the development of proximal junctional kyphosis (PJK) in adult spinal deformity (ASD) surgery.Overview of literatureThe development of PJK is multifactorial and different risk factors have been identified. Of these, there is some evidence that SE also affects the development of PJK, but data are insufficient.MethodsUsing a combined database comprising two propensity-matched groups of fusions following ASD surgery, one with fixation to S1 or S1 and the ilium (SE) and one without SE but with a lower instrumented vertebra of L5 or higher (lumbar fixation, LF), PJK and the role of further parameters were analyzed. The propensity-matched variables included age, the upper-most instrumented vertebra (UIV), preoperative sagittal alignment, and the baseline to one year change of the sagittal alignment.ResultsPropensity matching led to two groups of 89 patients each. The UIV, pelvic incidence minus lumbar lordosis, sagittal vertical axis, pelvic tilt, age, and body mass index were similar in both groups (p &gt;0.05). The incidence of PJK at postoperative one year was similar for SE (30.3%) and LF (22.5%) groups (p =0.207). The PJK angle was comparable (p =0.963) with a change of -8.2° (SE) and -8.3° (LF) from the preoperative measures (p =0.954). A higher rate of PJK after SE (p =0.026) was found only in the subgroup of patients with UIV levels between T9 and T12.ConclusionsInstrumentation to the sacrum with or without iliac extension did not increase the overall risk of PJK. However, an increased risk for PJK was found after SE with UIV levels between T9 and T12