Offset Index Research Articles

Gamma angle, a measurement tool of the femoral head angular translation in adults hips with cam or mix form of impingement femoroacetabulare

Femoral head translation leads to the cam deformity development. It is formed on the femoral head-neck junction. Cam deformity produces femoroacetabular impingement. There are no particular techniques for femoral head translation assessment. The offset index is the most regularly applied. It quantifi es the relation between the femoral head and neck junction. We introduce the original method to test the femoral head translation.

The role of the femoral anterior offset index on the degree of flexion in total knee arthroplasty

<p class="abstract"><strong>Background:</strong> Anterior projection of the femoral condyles is often disregarded as an issue in knee arthroplasty. Overstuffing the patellofemoral joint may limit knee flexion and be a source of patellofemoral complications, thus having an impact in satisfaction rates after total knee arthroplasty (TKA). Our hypothesis is that excessive anterior projection of the femoral condyles as a negative effect in flexion range after TKA, introducing a new concept, the anterior offset index (AOI).</p><p class="abstract"><strong>Methods:</strong> From a group of 99 consecutive patients who underwent TKA using patient specific instrumentation (PSI), we selected the patients with good pre-operative flexion range (above 90º) and a 6-minute walk test (6 MWT) ≥ 0 meters, evaluating the correlation between the AOI and the flexion range. A total of 23 patients were included in the study.<strong></strong></p><p class="abstract"><strong>Results:</strong> A moderate and positive correlation (r=0.488; p=0.018) between AOI and flexion range was found.</p><p class="abstract"><strong>Conclusions:</strong> Our results seem to indicate that the AOI influences postoperative flexion in TKA, in patients with a good pre-operative flexion and good functional outcome. AOI is an important concept to retain when optimizing knee flexion and minimizing patellofemoral complications. However, more studies need to be done in order to clarify the role of all the factors influencing post op flexion after TKA.</p>

Relationship between post-operative residual patellar J sign and the laxity of reconstructed medial patellofemoral ligament in recurrent patellar instability adult patients

Objective To discover the relationship between the post-operative positive residual patellar J sign and the laxity of reconstructed medial patellofemoral ligament (MPFL) after MPFL reconstruction combined with tibial tubercle osteotomy (TTO). Methods A total of 39 consecutive recurrent patellar dislocation (RPD) adult patients who were performed MPFL reconstruction and TTO with more than 2 follow-up time were analyzed retrospectively in the present study. The patellar tracking of all the patients was evaluated and was classified into positive patellar J sign group and negative J sign control group during knee active flexion and extension at final follow up. The computed tomography (CT) examination was performed in all patients at 0° extension of the knee. The patellar laxity index measured by patellar glide test (PGT) and the radiographic parameters (tibial tuberosity-trochlear groove distance, bisect offset index, patella trochlear-groove distance, patella lateral tilt angle, femoral anteversion angle, tibial external angle and knee rotational angle) calculated by CT scans slices as well as the pre-/post- operative knee functional scores including International Knee Documentation Committee (IKDC) score, Kujala score, and Lysholm score were compared between the positive group and negative group at final follow up. Results The average follow-up duration was 26.3±6.7 months (range 24-31) and all the patients did not suffer from the RPD during the follow-up. Ten (26%, 10/39) patients performed positive J sign, and the remaining 29 (74%, 29/39) performed negatively. The two groups were compatible with no significant difference in age, gender, injury side, follow-up duration and preoperative knee function scores (P>0.05). At the final follow up, the patellar laxity index in the positive J sign group was 34.9%±6.9%, while that in the negative group was 24.6%±8.6%. There was significantly difference in the patellar laxity index between two groups (t=-3.413, P=0.002). The bisect offset index in the positive group was 102.9%±12.4%, while that in the negative group was 76.0%±18.4%. There was significantly difference in the bisect offset index between two groups (t=-4.268, P=0.000). The patella trochlear-groove distance in the positive group was 2.2±3.7 mm, while that in the negative group was -7.6±5.8 mm. There was significantly difference in the patella trochlear-groove distance between two groups (t=-4.233, P=0.000). The two groups were compatible with no significant difference in tibial tuberosity-trochlear groove distance, patella lateral tilt angle, femoral anteversion angle, tibial external angle and knee rotational angle (P>0.05). The IKDC, Kujala, and Lysholm in the positive group were 86.4±6.5, 85.3±1.1, 91.5±7.9 respectively with significantly differences compared with preoperative scores 53.3±2.4, 73.2±9.7, 76.7±6.6 (t=-10.163, P=0.000; t=-1.274, P=0.023; t=-8.533, P=0.018). The IKDC, Kujala, and Lysholm in the negative group were 87.3±8.6, 84.3±4.7, 93.1±4.3 respectively with significantly differences compared with preoperative scores 49.1±4.6, 71.4±6.5, 79.5±7.0 (t=-14.381, P=0.000; t=-0.068, P=0.037; t=-6.902, P=0.013). There were no significant difference in the postoperative knee function scores between the two groups (P>0.05). Conclusion RPD patients can recover the patellar instability from the surgical technique of MPFL reconstruction and TTO and none of them suffer from the RPD during the follow-up. However, the morbidity of post-operative positive residual patellar J sign was 26%. The positive J sign might increase the laxity of patella. Key words: Patellofemoral joint; Wounds and injuries; Arthroscopy; Joint instability

Excessive lateral patellar translation on axial computed tomography indicates positive patellar J sign.

The purpose of the study was to quantify the patellar J sign using traditional computed tomography (CT) scans. Fifty-three patients (fifty-three knees) who suffered from recurrent patellar instability were included and analyzed. The patellar J sign was evaluated pre-operatively during active knee flexion and extension. It was defined as positive when there was obvious lateral patellar translation, and negative when there was not. The CT scans were performed in all patients with full knee extension; and the parameters including bisect offset index (BOI), patellar-trochlear-groove (PTG) distance, and patellar lateral tilt angle (PLTA) were measured on the axial slices. All the three parameters were compared between the J sign-positive group (study group) and the J sign-negative group (control group). In addition, the optimal thresholds of the three CT scan parameters for predicting the positive patellar J sign were determined with receiver operating characteristic (ROC) curves, and the diagnostic values were assessed by the area under the curve (AUC). Among the fifty-three patients (fifty-three knees), thirty-seven (70%) showed obvious lateral patellar translation, which were defined as positive J sign (study group), and the remaining sixteen (30%) who showed no lateral translation were defined as negative J sign (control group). The mean values of the three CT parameters in the study group were all significantly larger compared to the control group, including BOI (121 ± 28% vs 88 ± 12%, P = 0.038), PTG distance (5.2 ± 6.6mm vs -4.4 ± 5.2mm, P<0.05), and PLTA (34.9 ± 10.5° vs 25.7 ± 3.4°, P = 0.001). Furthermore, the evaluation of ROC analysis showed that the AUC of BOI was the largest (AUC = 0.906) among the three parameters, and the optimal threshold of BOI to predict the positive patellar J sign was 97.5% (Sensitivity = 83.3%, Specificity = 87.5%). In this study, the prevalence of positive patellar J sign was 70%. The BOI measured from the axial CT scans of the knee joint can be used as an appropriate predictor to differentiate the positive J sign from the negative J sign, highlighting that the excessive lateral patellar translation on axial CT scan indicates positive patellar J sign. IV.

Dynamic tracking influenced by anatomy following medial patellofemoral ligament reconstruction: Computational simulation

BackgroundContinued patellar instability can occur following medial patellofemoral ligament (MPFL) reconstruction. Computational simulation of function was used to investigate the influence of the lateral position of the tibial tuberosity, trochlear dysplasia and patella alta on lateral patellar tracking following MPFL reconstruction. MethodsMultibody dynamic simulation models were developed to represent nine knees being treated for recurrent patellar instability. Knee extension against gravity and dual limb squatting were simulated with and without simulated MPFL reconstruction. Graft resting lengths were set to allow 10mm and five millimeters of patellar lateral translation at 30° of knee flexion. The bisect offset index, lateral tibial tuberosity to posterior cruciate ligament tibial attachment (TT–PCL) distance, lateral trochlear inclination, and Caton–Deschamps index were quantified at every five degrees of knee flexion to characterize lateral tracking, lateral position of the tibial tuberosity, trochlear dysplasia, and patella alta, respectively. For the pre-operative and post-operative conditions and each type of motion, bisect offset index was correlated with the anatomical parameters using stepwise multivariate linear regression. ResultsFor both motions, the pre-operative and post-operative bisect offset indices were significantly correlated with lateral trochlear inclination and lateral TT–PCL distance. For both motions, the adjusted r2 decreased with MPFL reconstruction, but was still approximately 0.5 for MPFL reconstruction allowing five millimeters of lateral translation. ConclusionMPFL reconstruction decreases but does not eliminate lateral maltracking related to trochlear dysplasia and a lateralized tibial tuberosity. Patients with these pathologies are likely at the highest risk for instability related to maltracking following MPFL reconstruction.

Evaluation of the Effect of the Sulcus Angle and Lateral to Medial Facet Ratio of the Patellar Groove on Patella Tracking in Aging Subjects with Stable Knee Joint.

Purpose To determine whether the sulcus angle and the lateral to medial facet ratio correlate with patella lateral displacement and tilt in patients without patella instability. Methods Computed tomography images of the lower limb of 64 patients without known arthropathy were collected. Three-dimensional models of the lower limb with a unified coordinate system were rebuilt by using Mimics software. The sulcus angle, lateral to medial facet ratio, lateral trochlear inclination of the patellar groove, tibial tuberosity-trochlear groove (TT-TG) distance, bisect offset index, and lateral tilt of the patella were measured. Pearson's correlation test was used to determine the relationship between the aforementioned parameters. Results Data from 51 patients were analyzed. The sulcus angle was negatively correlated with lateral tilt inclination (p < 0.001, r = 0.8406) and positively correlated with the bisect offset index (p = 0.003, r = 0.634) and patellar tilt (p = 0.03, r = 0.551); the lateral to medial facet ratio was positively correlated with TT-TG distance (p = 0.003, r = 0.643) and bisect offset index (p = 0.026, r = 0.559). Conclusion The sulcus angle and lateral to medial facet ratio of the patellar groove can influence patella tracking in patients with stable knee joints.

Correlation of 3D Shift and 3D Tilt of the Patella in Patients With Recurrent Dislocation of the Patella and Healthy Volunteers: An In Vivo Analysis Based on 3-Dimensional Computer Models

Background: The concepts of lateral deviation and lateral inclination of the patella, characterized as shift and tilt, have been applied in combination to evaluate patellar malalignment in patients with patellar dislocation. It is not reasonable, however, to describe the 3-dimensional (3D) positional relation between the patella and the femur according to measurements made on 2-dimensional (2D) images. Purpose: The current study sought to clarify the relation between lateral deviation and inclination of the patella in patients with recurrent dislocation of the patella (RDP) by redefining them via 3D computer models as 3D shift and 3D tilt. Study Design: Descriptive laboratory study. Methods: Altogether, 60 knees from 56 patients with RDP and 15 knees from 10 healthy volunteers were evaluated. 3D shift and tilt of the patella were analyzed with 3D computer models created by magnetic resonance imaging scans obtained at 10° intervals of knee flexion (0°-50°). 3D shift was defined as the spatial distance between the patellar reference point and the midsagittal plane of the femur; it is expressed as a percentage of the interepicondylar width. 3D tilt was defined as the spatial angle between the patellar reference plane and the transepicondylar axis. Correlations between the 2 parameters were assessed with the Pearson correlation coefficient. Results: The patients’ mean Pearson correlation coefficient was 0.895 ± 0.186 (range, –0.073 to 0.997; median, 0.965). In all, 56 knees (93%) had coefficients >0.7 (strong correlation); 1 knee (2%), >0.4 (moderate correlation); 2 knees (3%), >0.2 (weak correlation); and 1 knee (2%), <0.2 (no correlation). The mean correlation coefficient of the healthy volunteers was 0.645 ± 0.448 (range, –0.445 to 0.982; median, 0.834). A statistically significant difference was found in the distribution of the correlation coefficients between the patients and the healthy volunteers (P = .0034). When distribution of the correlation coefficients obtained by the 3D analyses was compared with that by the 2D (conventional) analyses, based on the bisect offset index and patellar tilt angle, the 3D analyses showed statistically higher correlations between the lateral deviation and inclination of the patella (P < .01). Conclusion: 3D shift and 3D tilt of the patella were moderately or strongly correlated in 95% of patients with RDP at 0° to 50° of knee flexion. Clinical Relevance: It is not always necessary to use both parameters when evaluating patellar alignment, at least for knees with RDP at 0° to 50° of flexion. Such a description may enable surgeons to describe patellar alignment more simply, leading to a better, easier understanding of the characteristics of each patient with RDP.

A knee brace alters patella position in patellofemoral osteoarthritis: a study using weight bearing magnetic resonance imaging

To assess using weight bearing magnetic resonance imaging (MRIs), whether a patellar brace altered patellar position and alignment in patellofemoral joint (PFJ) osteoarthritis (OA). Subjects age 40-70 years old with symptomatic and a radiographic Kellgren-Lawrence (K-L) evidence of PFJOA. Weight bearing knee MRIs with and without a patellar brace were obtained using an upright open 0.25T scanner (G-Scan, Easote Biomedica, Italy). Five aspects of patellar position were measured: mediolateral alignment by the bisect offset index, angulation by patellar tilt, patellar height by patellar height ratio (patellar length/patellar tendon length), lateral patellofemoral (PF) contact area and finally a measurement of PF bony separation of the lateral patellar facet and the adjacent surface on the femoral trochlea (Fig.1). Thirty participants were recruited (mean age 57 SD 27.8; body mass index (BMI) 27.8 SD 4.2); 17 were females. Four patients had non-usable data. Main analysis used paired t tests comparing within subject patellar position with and without brace. For bisect offset index, patellar tilt and patellar height ratio there were no significant differences between the brace and no brace conditions. However, the brace increased lateral facet contact area (P=.04) and decreased lateral PF separation (P=.03). A patellar brace alters patellar position and increases contact area between the patella and femoral trochlea. These changes would lower contact stress at the PFJ. Such changes in patella position in weight bearing provide a possible biomechanical explanation for the success of the PFJ brace in clinical trials on PFJOA.

Dynamic tracking influenced by anatomy in patellar instability

BackgroundThe current study was performed to correlate anatomical parameters related to trochlear dysplasia, tibial tuberosity position, and patella alta with in vivo patellar tracking for subjects with recurrent patellar instability. MethodsEight subjects with recurrent patellar instability that failed conservative treatment were evaluated using computational reconstruction of in vivo knee motion. Computational models were created from dynamic CT scans of the knee during extension against gravity. Shape matching techniques were utilized to position a single model of each bone (femur, patella and tibia) to represent multiple positions of knee extension. Patellar tracking was characterized by the bisect offset index (lateral shift) and lateral tilt. Anatomical parameters were characterized by the inclination of the lateral ridge of the trochlear groove, the lateral distance from the tibial tuberosity to the posterior cruciate ligament attachment (lateral TT–PCL distance), and the Caton–Deschamps index. Stepwise multivariable linear regression analysis was used to relate patellar tracking to the anatomical parameters at low (<20°) and high flexion angles. ResultsAt low flexion angles, both lateral trochlear inclination and lateral TT–PCL distance were significantly correlated with bisect offset index (p=0.02). Only lateral trochlear inclination was significantly correlated with lateral tilt (p<0.001). At high flexion angles, bisect offset index and lateral tilt were correlated with only lateral TT–PCL distance (p≤0.02). ConclusionParameters related to trochlear dysplasia and tibial tuberosity position were both related to patellar tracking, but the relationship changed with the flexion angle. Clinical relevanceThe anatomical parameters related to patellar tracking can be used to evaluate the risk of continued instability and guide surgical treatment.

Effect of leg press training on patellar realignment in patients with patellofemoral pain.

[Purpose] The purpose of this study was to investigate the effect of leg press and leg press with hip adduction exercise training on patellar alignment and pain in patients with patellofemoral pain (PFP). [Subjects and Methods] Seventeen patients participated in this study. Eight weeks of leg press or leg press with hip adduction training, including progressive lower-limb weight-training and stretching, was given. Patellar alignment (tilt and displacement) and pain measurements were conducted before and after leg press or leg press with hip adduction training. Patellar tilt angle and the bisect offset index were measured on axial computed tomography scans of the fully extended knee position with the quadriceps relaxed and contracted. Pain was assessed by using a 10-cm visual analog scale. [Results] No differences were found in patellar tilt and displacement with the quadriceps either relaxed or contracted after leg press and leg press with hip adduction. However, significant pain reduction was evident in both leg press and leg press with hip adduction. [Conclusion] The results indicated that patellar realignment does not appear to mediate pain alleviation. Furthermore, hip adduction in addition to leg press training had no additive beneficial effect on patellar realignment or pain reduction.

Anatomical factors influencing patellar tracking in the unstable patellofemoral joint.

The current study was performed to relate anatomical parameters to in vivo patellar tracking for pediatric patients with recurrent patellar instability. Seven pediatric patients with recurrent patellar instability that failed conservative treatment were evaluated using computational reconstruction of in vivo patellofemoral function. Computational models were created from high-resolution MRI scans of the unloaded knee and lower-resolution scans during isometric knee extension at multiple flexion angles. Shape matching techniques were applied to replace the low-resolution models of the loaded knee with the high-resolution models. Patellar tracking was characterized by the bisect offset index (lateral shift) and lateral tilt. Anatomical parameters were characterized by the inclination of the lateral ridge of the trochlear groove, the tibial tuberosity-trochlear groove distance, the Insall-Salvati index and the Caton-Deschamps index. Stepwise multivariable linear regression analysis was used to relate patellar tracking to the anatomical parameters. The bisect offset index and lateral tilt were significantly correlated with the lateral trochlear inclination (p≤0.002) and TT-TG distance (p<0.05), but not the Insall-Salvati index or the Caton-Deschamps index. For both the bisect offset index and lateral tilt, the standardized beta coefficient, used to identify the best anatomical predictors of tracking, was larger for the lateral trochlear inclination than the TT-TG distance. For this population, the strongest predictor of lateral maltracking that could lead to patellar instability was lateral trochlear inclination. Diagnostic study, Level II.

Maximum Likelihood Frequency Estimation and Preamble Identification in OFDMA-based WiMAX Systems

In multi-cellular WiMAX systems based on orthogonal frequency-division multiple-access (OFDMA), the training preamble is chosen from a set of known sequences so as to univocally identify the transmitting base station. Therefore, in addition to timing and frequency synchronization, preamble index identification is another fundamental task that a mobile terminal must successfully complete before establishing a communication link with the base station. In this work we investigate the joint maximum likelihood (ML) estimation of the carrier frequency offset (CFO) and preamble index in a multicarrier system compliant with the WiMAX specifications, and derive a novel expression of the relevant Cramer-Rao bound (CRB). Since the exact ML solution is prohibitively complex in its general formulation, suboptimal algorithms are developed which can provide a reasonable trade-off between estimation accuracy and processing load. Specifically, we show that the fractional CFO can be recovered by combining the ML estimator with an existing algorithm that attains the CRB in all practical scenarios. The integral CFO and preamble index are subsequently retrieved by a suitable approximation of their joint ML estimator. Compared to existing alternatives, the resulting scheme exhibits improved accuracy and reduced sensitivity to residual timing errors. The price for these advantages is a certain increase of the system complexity.

Lateral Patellar Translation Effects after Arthroscopic Partial Meniscectomy of Torn Discoid Lateral Meniscus

To investigate the effects of arthroscopic partial meniscectomy of torn discoid lateral meniscus on patellar tracking. In all, 112 patients (112 knees) who underwent arthroscopic partial meniscectomy participated in the study. All subjects were examined with standing weight-bearing magnetic resonance imaging (MRI) preoperatively and one month postoperation. Axial-plane images through the maximum width of the patella and the maximum dorsal area of the femoral condyles were superimposed and the bisect offset index used to quantify patellar translation. Differences between pre- and postoperation in the bisect offset indexes were calculated and compared by Student's paired t-test. P < 0.05 was considered statistically significant. Before surgery, the mean bisect offset index was 0.574 (0.437-0.692). One month postoperation, the mean bisect offset index was 0.622 (0.510-0.801). The postoperation bisect offset index increased by an average of 0.048 (-0.018 to 0.129) compared with the preoperation value; this difference is statistically significant result (t = 18.33, P < 0.01). After arthroscopic partial meniscectomy, the patella translates more lateral to the femoral trochlear groove. These results suggest that arthroscopic partial meniscectomy may result in patellar maltracking.

Complexity Effective Integer Frequency Offset and Sector Cell Detection Scheme for LTE Downlink System

This paper proposes a low-complexity integer frequency offset (IFO) and sector cell index (CID) detection scheme in a long term evolution downlink system. In the proposed detection scheme, the IFO and CID are estimated in a decoupled manner. In doing so, the detection scheme is designed to first estimate IFO without a priori knowledge of cell-specific reference signals and then detect the CID consecutively. We show via simulations that such a design achieves not only a low computational load but also comparable performance, when compared to the conventional detection scheme.

Tibiofemoral and patellofemoral mechanics are altered at small knee flexion angles in people with patellofemoral pain

ObjectivesTo test the hypothesis that, at 0° and 20° of knee flexion, patellofemoral contact area would be lower, while tibiofemoral rotation and patellofemoral malalignment would be higher in participants with patellofemoral pain (PFP) compared to pain-free participants. We hypothesized that no differences would be detected at 40° due to increasing patellar stability. DesignCross-sectional, descriptive study. MethodsTwenty-seven people with PFP and 29 pain-free people participated. Participants underwent magnetic resonance imaging at 0°, 20°, and 40° knee flexion with the limb in a simulated weight-bearing position. Patellofemoral contact area, tibiofemoral rotation angle, patellofemoral alignment (bisect offset index and patellar tilt angle) were quantified and compared between groups at each angle using Student's t-tests. An a-posteriori comparison was made between the pain-free group and a subgroup of 15 participants with patellofemoral pain who demonstrated a faulty lower limb movement pattern (“medial collapse”). ResultsIn the patellofemoral pain group, contact area was lower at 0° (203.8±45.5mm2 vs. 224.1±46.6mm2, p=0.05) and 20° (276.8±56.2mm2 vs. 316.7±82.8mm2, p=0.02), bisect offset index (BOS) and patellar tilt angle (PTA) were higher at 0° (bisect offset index: 0.69±0.13 vs. 0.64±0.09, p=0.04; patellar tilt angle: 12.5±7.6° vs. 9.2±5.8°, p=0.04). In the patellofemoral pain subgroup, tibiofemoral rotation was higher at 0° compared to pain-free participants (6.4±5.9° vs. 4.0±4.6°, p=0.07). ConclusionsWhile contact area and patellofemoral alignment were altered in people with patellofemoral pain, tibiofemoral rotation was altered in a subgroup of people who demonstrated medial collapse. Subgroup classification may help identify mechanisms of pain and assist in developing targeted interventions.

CSM 2010 Orthopaedic Section Platform Presentations (Abstracts OPL1-OPL67)

CSM 2010 Orthopaedic Section Platform Presentations (Abstracts OPL1-OPL67)

Computer-assisted antetorsion control prevents malrotation in femoral nailing: an experimental study and preliminary clinical case series

The effect of fluoroscopy-based navigation for femoral fracture reduction on the prevention of malrotation was examined in an experimental setting followed by a first case series. Eleven cadaver femurs were used. All femurs were reduced by closed methods. An optoelectronic navigation system was utilized to check for fragment reduction and alignment. Fluoroscopic control without navigation was used as the control group. The Six Sigma Analysis [offset capability index (C (pk)) = 1.3] was used to compare the probability of outliers of more than 15 degrees . In the clinical case series the same navigation tool was used in ten non-consecutive patients with femoral fractures. Torsional differences between both legs were measured postoperatively by CT scan. The highest malrotation in the navigated group was 7.0 degrees for the cadaver testings, while two femurs in the control group showed a difference of more than 10 degrees (10.3 degrees , 17.4 degrees). Only the navigated group showed a sufficient offset capability index (C (pk-navigated) = 1.83; C (pk-conventional) = 0.59). In the clinical series nine femurs were successfully reduced by navigation control. The average malrotation was 6.6 degrees . No patient had a torsional difference of more than 10 degrees. Navigated femoral nailing reduces the risk for outliers of postoperative torsional differences and might avoid revision surgery for malrotation. IV.

Optical mode properties of laterally offset gain and index guiding structures

We describe the mode properties of offset gain and index guided structures in which gain and index guiding effects are simultaneously present and oriented in parallel but laterally offset. Such structures can occur in semiconductor lasers, integrated optics, and optical waveguides. Within the parabolic approximation the resulting waveguide modes are found to be Hermite-Gaussian functions with complex-valued Gaussian mode parameters and centerlines. The lateral positions and far-field angles of these modes can be controlled by modifying the gain and index guiding parameters, permitting both transverse mode displacement and output beam steering.