Bisect Offset Index Research Articles

Ratio of Tibial Tubercle-Trochlear Groove Distance to Patellar Width as a Predictor of Patellar Dislocation: Analysis of Individualized Tibial Tubercle Lateralization Parameters.

Available conventional tibial tubercle lateralization (TTL) parameters fail to account for individual patient size or anatomy. To evaluate the predictive ability of individualized TTL parameters and clarify the best predictor of patellar dislocation (PD) and to determine the relationship of the best predictor with other risk factors of PD with quadriceps isotonic contraction. Cohort study (diagnosis); Level of evidence, 2. A total of 15 patients with PD (28 knees) and 14 controls (28 knees) underwent 4-dimensional computed tomography, and the image with the knee fully extended and quadriceps isotonically contracted was selected for evaluation. The following TTL parameters were measured on the images: tibial tubercle-trochlear groove (TT-TG) distance, tibial tubercle-Roman arch distance, and tibial tubercle-posterior cruciate ligament distance, as well as their ratios to femoral condylar width and patellar width (PW). In addition, the following parameters were measured: Insall-Salvati ratio, Blackburne-Peel ratio, Caton-Deschamps ratio, modified Insall-Salvati ratio, bisect offset index, congruence angle, lateral patellar tilt, lateral trochlear inclination, sulcus depth, sulcus angle, trochlear groove medialization, patella-patellar tendon angle, patellofemoral axis angle (P-FAA), patellar articular facet-patellar tendon angle, patellar articular facet-femoral axis angle (PA-FAA), and patellar shape according to Wiberg type. The area under the receiver operating characteristic curve (AUC) was calculated to access the diagnostic accuracy of the TTL parameters for PD, and the TTL parameters with high diagnostic ability were evaluated for correlation with the remaining parameters. The TT-TG/PW ratio had the best diagnostic ability for PD (AUC = 0.890). The TT-TG/PW ratio was positively correlated with bisect offset index, congruence angle, lateral patellar tilt, P-FAA and PA-FAA (r = 0.610, 0.465, 0.635, 0.553 and 0.418, respectively; P≤ .027 for all), and TT-TG/PW ratio was greater in knees with type II versus type III patella (P = .017). With the knee fully extended and quadriceps isotonically contracted, the TT-TG/PW ratio was found to be the best predictor of PD and reflected individualized TTL, which helps with clinical preoperative planning.

Differences in Patellofemoral Alignment Between Static and Dynamic Extension Positions in Patients With Patellofemoral Pain.

Considering that patellofemoral pain (PFP) is related to dynamic factors, dynamic extension on 4-dimensional computed tomography (4-DCT) may better reflect the influence of muscles and surrounding soft tissue than static extension. To compare the characteristics of patellofemoral alignment between the static and dynamic knee extension position in patients with PFP and controls via 4-DCT. Cross-sectional study; Level of evidence, 3. Included were 39 knees (25 patients) with PFP and 37 control knees (24 participants). For each knee, an image of the dynamic extension position (a single frame of the knee in full extension [flexion angle of -5° to 0°] selected from 21 frames of continuous images acquired by 4-DCT during active flexion and extension) and an image of the static extension position (acquired using the same equipment with the knee fully extended and the muscles relaxed) were selected. Patellofemoral alignment was evaluated between the dynamic and static extension positions and between the PFP and control groups with the following parameters: patella-patellar tendon angle (P-PTA), Blackburne-Peel ratio, bisect-offset (BO) index, lateral patellar tilt (LPT), and tibial tuberosity-trochlear groove (TT-TG) distance. In both PFP patients and controls, the P-PTA, Blackburne-Peel ratio, and BO index in the static extension position were significantly lower (P < .001 for all), while the LPT and TT-TG distance in the static extension position were significantly higher (P ≤ .034 and P < .001, respectively) compared with values in the dynamic extension position. In the comparison between groups, only P-PTA in the static extension position was significantly different (134.97° ± 4.51° [PFP] vs 137.82° ± 5.63° [control]; P = .027). No difference was found in the rate of change from the static to the dynamic extension position of any parameter between the study groups. The study results revealed significant differences in patellofemoral alignment characteristics between the static and dynamic extension positions of PFP patients and controls. Multiplanar measurements may have a role in subsequent patellofemoral alignment evaluation.

The effects of different taping methods on patellofemoral alignment, pain and function in individuals with patellofemoral pain: A randomized controlled trial.

Athletic taping has long been a physiotherapeutic application in individuals with patellofemoral pain (PFP). However, the therapeutic effects of local and proximal taping have not been fully determined. To evaluate the effects of two different taping techniques applied in addition to exercise on patellofemoral alignment, pain, and function in individuals with PFP. Randomized controlled trial. An outpatient hospital clinic. Individuals with PFP aged 18-50 years (n = 36). Group 1 underwent only the exercise program. Group 2 underwent the exercise plus McConnell patellar taping (MPT), and Group 3 underwent the exercise plus femoral rotational taping (FRT) (6 weeks). Bisect offset index (BOI) and patellar tilt angle (PTA) were measured in relaxed and maximum voluntary contractions of the quadriceps muscle (MVCq) using magnetic resonance imaging. Pain intensity was assessed by the Visual Analog Scale for three conditions: at daytime rest, during activity, and at nighttime. Functional level was assessed by the Kujala Patellofemoral Scoring System. Significant improvements in the BOI of Group 2 at rest (p = .015; r = 0.593) and in PTA of Group 3 at MVCq (p = .010; r = 0.613) were found. Improvements in pain under all three conditions were significant within groups (all, p values < .050 and r > 0.5). The change in pain was similar between groups (all, p values > .05). All groups showed significant improvement in functional level (all, p values < .010 and r > 0.5). However, the increase in Group 3 was higher than that in Group 1 (p = .019). This study shows that MPT and FRT applications increase functionality and can affect patellofemoral alignment in different ways. In the treatment of PFP, more successful results can be obtained with appropriate taping techniques for the local and proximal region.

Adding Tibial Tuberosity Medialization to Medial Patellofemoral Ligament Reconstruction Reduces Lateral Patellar Maltracking During Multidirectional Motion in a Computational Simulation Model

To determine whether adding tibial tuberosity medialization to medial patellofemoral ligament (MPFL) reconstruction reduces lateral patellar maltracking during a dynamic multidirectional activity and to investigate when medial patellofemoral contact pressures are elevated during daily activities, such as squatting. Seven computational models representing knees with patellar instability, including lateral patellar maltracking, were evaluated following simulated MPFL reconstruction (bisect offset index > .75). Tibial tuberosity medialization was added to MPFL reconstruction for each model. Patellar tracking during multidirectional motion was evaluated by simulating pivot landing. Analysis of pivoting focused on early flexion (5° to 40°). Patellofemoral contact pressures during daily function were evaluated by simulating knee squatting. Data were analyzed with paired comparisons between MPFL reconstruction with and without tuberosity medialization. The patella dislocated during pivoting for 2 models with an isolated MPFL reconstruction and for 1 model including tibial tuberosity medialization. Adding tibial tuberosity medialization to MPFL reconstruction significantly decreased bisect offset index by ∼0.1 from 5° to 40° (P < .03). For knee squatting, medializing the tibial tuberosity significantly increased maximum medial contract pressure by ∼0.5 MPa from 30° to 85° (P < .05) but did not significantly influence maximum lateral pressure. In this study of simulated multidirectional motion, MPFL reconstruction did not sufficiently constrain the patella for some knees. Adding tibial tuberosity medialization to MPFL reconstruction in these models reduced lateral patellar maltracking during multidirectional motion but increased pressure applied to medial cartilage during squatting. After establishing the influence of tibial tuberosity medialization on patellar maltracking for an idealized population, as was done in the current study, future simulation studies can be performed to better determine the anatomical characteristics of patients for whom tibial tuberosity medialization is needed to reduce the risk of postoperative patellar maltracking.

Influence of medial patellofemoral ligament reconstruction on patellar tracking and patellofemoral contact pressures in patella alta

Knee squatting was simulated to characterize the influence of medial patellofemoral ligament (MPFL) reconstruction on patellar tracking and contact pressures for knees with mild patella alta (Caton-Deschamps index = 1.3-1.4). Eight computational models represented knees in the pre-operative condition and following MPFL reconstruction. MPFL reconstruction significantly reduced patellar lateral tracking at low flexion angles based on bisect offset index, significantly decreased the maximum lateral pressure in mid-flexion, and significantly increased the maximum medial pressure in mid-flexion. MPFL reconstruction improves patellar stability for knees with mild patella alta and can reduce the pressure applied to lateral cartilage on the patella.

The Increased Tibiofemoral Rotation: A Potential Contributing Factor for Patellar Maltracking in Patients with Recurrent Patellar Dislocation.

ObjectiveThe purpose of this study was to analyze the relationship between tibiofemoral rotation and patellar maltracking in patients with recurrent patellar dislocation.MethodsA total of 143 consecutive knees (118 patients) with clinically diagnosed recurrent patellar dislocation from January 2018 to December 2019 were retrospectively analyzed. Patellar tilt angle and bisect offset index were recorded on axial CT to assesses the severity of patellar maltracking. Tibiofemoral rotation angle is measured by comparing the angle between the posterior femoral and tibial condylar lines on three‐dimensional CT. The Pearson correlation was calculated to investigate the association between tibiofemoral rotation angle and patellar maltracking. Patients were divided into the rotation group (≥15°) and control group (<15°) based on the value of tibiofemoral rotation and a further comparison was performed. To further clarify the complicated relationship among tibial tubercle‐trochlear groove (TT‐TG), tibial tubercle‐posterior cruciate ligament distance (TT‐PCL), tibiofemoral rotation, and patellar maltracking, patients were divided into four subgroups according to the value of TT‐TG and TT‐PCL.ResultsThe mean preoperative tibiofemoral rotation angle was 12° ± 6° (range, 0°–31°). Pearson correlation between patellar maltracking parameters (bisect offset index, patellar tilt angle) and various bony deformities found that the tibiofemoral rotation angle was moderately correlated with bisect offset index (r = 0.451, p < 0.001) and patellar tilt angle (r = 0.462, p < 0.001). Further results demonstrated that bisect offset index (152.1 vs 121.2, p < 0.001) and patellar tilt angle (41.2° vs 33.5°, p < 0.001) were significantly higher in the rotation group than that in control group. For patients with a TT‐TG distance of >20 mm, the increased TT‐TG distance was mainly caused by tibiofemoral rotation angle in group C (TT‐TG > 20 mm, TT‐PCL < 24 mm) and predominantly induced by tibial tubercle lateralization in group D (TT‐TG > 20 mm, TT‐PCL > 24 mm). Bisect offset index and patellar tilt angle were significantly higher in the group C than group D.ConclusionThe increased tibiofemoral rotation angle is associated with patellar maltracking in patients with recurrent patellar dislocation. Patients with increased tibiofemoral rotation angle usually have more severe patellar maltracking.

Groove-deepening trochleoplasty reduces lateral patellar maltracking and increases patellofemoral contact pressures: Dynamic simulation.

Groove-deepening trochleoplasty is performed to restore patellar stability by increasing the lateral constraint applied to the patella by the trochlear groove. Multibody dynamic simulation of knee function was used to characterize the influence of groove-deepening trochleoplasty on patellar tracking and patellofemoral contact pressures. Computational models were created to represent seven knees with trochlear dysplasia, indicated by a flat trochlear groove and supratrochlear spur. The models were manipulated to remove the spur and deepen the trochlear groove to represent the average shape following a trochleoplasty. Knee squatting was simulated for the preoperative and postoperative conditions. Statistically significant (p < 0.05) differences in output parameters were identified with repeated measures comparisons at every 5° of knee flexion. Trochleoplasty significantly decreased lateral patellar tracking, particularly at low knee flexion angles. Trochleoplasty decreased the peak lateral shift of the patella (bisect offset index) with the knee extended from 0.87 ± 0.14 to 0.75 ± 0.12. Trochleoplasty also significantly decreased the contact area and increased the maximum contact pressure at multiple flexion angles. Trochleoplasty decreased the average contact area by approximately 10% in mid-flexion, with a corresponding increase in the average maximum contact pressure of 13%-23%. Decreased contact area and increased contact pressures are related to altered patellofemoral congruity due to reshaping the femur without a corresponding change to the patella. Clinical significance: The results indicate groove-deepening trochleoplasty decreases lateral patellar maltracking, reducing the risk of patellar dislocations, but can elevate patellofemoral contact pressures, which could contribute to long-term degradation of cartilage.

Tibia Tubercle Distalization Reduces Contact Pressures in Patella Alta and Instability

Patella alta is associated with patellar instability and arthritis. Tibial tuberosity distalization is commonly performed to treat recurrent patellar instability related to patella alta. The current study was performed to characterize the influence of tuberosity distalization on patellar tracking and the pressure applied to patellofemoral cartilage. High resolution 3T MRI scans of eight patients (1 male, 7 female, mean age 17, range 13-21) being treated for patellar instability were used to create individual multibody dynamic computer simulation models with patella alta (Caton-Deschamps index ≥ 1.3). Dynamic knee squatting was simulated for 3 conditions: the native knee with patella alta; following distalization (Caton-Deschamps index = 1.0); and following distalization combined with patellar tendon tenodesis. Lateral patella tracking was measured by the bisect offset index (percentage of the patella lateral to the deepest part of the trochlear groove) and the patellofemoral contact pressures and distribution were based on discrete element analysis). Repeated measures comparisons were used to identify significant (p < 0.05) differences between the conditions. : Tibial tuberosity distalization significantly reduced lateral patellar maltracking at 10°, 15° and 25° of knee flexion. At 10°, the average bisect offset index decreased from 0.85 to 0.78. Tuberosity distalization significantly decreased the maximum pressure applied to cartilage at 15°, 20°, 30°, and 35° of flexion, with the decrease more than 20% of the pre-operative pressure. Distalization also significantly increased contact area from 15° to 40° of flexion. Tenodesis had a relatively small influence on the kinematics and pressure, compared to distalization. Tibial tuberosity distalization improves patella tracking by decreasing lateral patellar maltracking at lower flexion angles. Additionally, this improved tracking is also associated with a reduction in peak patella contact pressure at low flexion angles.

Comparisons of patellar bone mineral density between individuals with and without patellofemoral pain

BackgroundAlthough bone stress injuries have been reported in individuals with patellofemoral pain (PFP), especially within the lateral patella, it remains unclear whether persons with PFP exhibit altered patellar regional bone mineral density (BMD). The primary purpose of this study was to compare BMD of the patella (lateral, medial, and total regions) between individuals with and without PFP using quantitative computed tomography (QCT). The secondary aim was to examine the associations between patellar regional BMD and patellofemoral joint (PFJ) alignment. MethodsTen individuals with retropatellar pain and 10 sex, age, weight, height, and activity matched pain-free controls underwent a QCT scan to obtain patellar BMD. To quantify PFJ alignment, patellar lateral displacement was measured using bisect-offset (BSO) index and patellar mediolateral tilt was quantified using patellar tilt angle (PTA). A two-factor repeated-measures ANOVA was used to compare BMD across the three patellar regions and between the two groups. Pearson correlation coefficient analyses were used to evaluate the associations between BMD and PFJ alignment of all participants. ResultsThere was no difference in BMD between the two groups. However, BMD was highest within the lateral patella and was lowest within the medial patella across both groups. There were significantly moderate to large correlations between BSO index/PTA and BMD within lateral, medial, and total regions. ConclusionsWhile individuals with PFP and pain-free controls have similar patellar BMD, the lateral patella exhibits the highest BMD. Additionally, higher patellar regional BMD is related to increased patellar lateral displacement and lateral tilt.

MPFL GRAFT TENSIONING TO TREAT PATELLAR INSTABILITY RELATED TO PATELLA ALTA: DYNAMIC SIMULATION

Background:Medial patellofemoral ligament (MPFL) reconstruction is a popular treatment for lateral patellar instability. For knees with patella alta, however, tibial tuberosity distalization is the most common approach due to concerns about graft tensioning. A MPFL graft is tensioned intra-operatively to prevent lateral subluxation without over-constraining the patella by allowing some translation.Purpose:To analyze the effects of MPFL reconstruction on lateral tracking and cartilage pressure for knees with patella alta using dynamic simulation of knee function.Methods:Knee function was simulated with 8 multibody dynamic simulation models (RecurDyn) constructed from 3.0 T MRI scans of subjects being treated for recurrent patellar instability. The models were validated in previous studies and included ligaments, tendons, and retinacular structures represented by tension-only springs (Fig1). Four models displayed patella alta; the remaining 4 models were made to reflect patella alta by lengthening the springs. Forces were applied to simulate a dual limb squat from 0º to 90º. Motion was simulated in a pre-operative condition and for three MPFL graft tensioning techniques (1.0, 0.5, and 0 patellar quadrants of lateral translation). The maximum bisect offset index during flexion was used as a measure of patellar instability and the maximum pressures applied to patellar cartilage (lateral, medial) as measures of the risk of overloading cartilage. Statistics were used to compare the parameters with significance set at p < 0.05. Post- and pre-operative maximum bisect offset index were also correlated.Results:MPFL reconstruction with 0.5 and 0 quadrants of allowed lateral translation significantly decreased the maximum bisect offset index compared to the pre-operative condition, but not for 1.0 quadrants (Table 1). MPFL reconstruction did not significantly influence the maximum pressure applied to medial or lateral cartilage. The maximum post-operative bisect offset index was significantly correlated with the pre-operative bisect offset index for 1.0 and 0.5 quadrants of lateral translation allowed (r2 = 0.80, 0.65, and 0.48 for grafts allowing 1, 0.5 and 0 quadrants of translation, respectively).Conclusion:For knees with patella alta, the influence of MPFL reconstruction on patellar tracking varied with the allowed patellar translation during graft tensioning. None of the graft tensioning conditions significantly decreased the maximum lateral pressure or increased the medial cartilage pressure.Significance:The graft tensioning process for MPFL reconstruction typically allows some lateral patellar translation to avoid overconstraining the knee. For knees with patella alta, reducing the allowed lateral translation seems to limit maltracking without overconstraining the knee.Table 1.Average (± standard deviation) output parameters (*p<0.05 compared to pre-op) Pre-opMPFL 1.0MPFL 0.5MPFL 0Maximum bisect offset0.92±0.180.86±0.170.81±0.14*0.74±0.13*Maximum lateral pressure4.2±0.93.9±0.93.7±0.93.8±1.0Maximum medial pressure3.0±1.73.4±1.23.4±1.43.7±1.2Fig1.Dynamic simulation of knee flexion and the patellofermoral pressure distribution.

Factors Influencing Graft Function following MPFL Reconstruction: A Dynamic Simulation Study.

Medial patellofemoral ligament (MPFL) reconstruction is currently the primary surgical procedure for treating recurrent lateral patellar instability. The understanding of graft function has largely been based on studies performed with normal knees. The current study was performed to characterize graft function following MPFL reconstruction, focusing on the influence of pathologic anatomy on graft tension, variations with knee flexion, and the influence on patellar tracking. Knee squatting was simulated with 15 multibody dynamic simulation models representing knees being treated for recurrent lateral patellar instability. Squatting was simulated in a preoperative condition and following MPFL reconstruction with a hamstrings tendon graft set to allow 0.5 quadrants of lateral patellar translation with the knee at 30 degrees of flexion. Linear regressions were performed to relate maximum tension in the graft to parameters of knee anatomy. Repeated measures comparisons evaluated variations in patellar tracking at 5-degree increments of knee flexion. Maximum graft tension was significantly correlated with a parameter characterizing lateral position of the tibial tuberosity (maximum lateral tibial tuberosity to posterior cruciate ligament attachment distance, r 2 = 0.73, p < 0.001). No significant correlations were identified for parameters related to trochlear dysplasia (lateral trochlear inclination) or patella alta (Caton-Deschamps index and patellotrochlear index). Graft tension peaked at low flexion angles and was minimal by 30 degrees of flexion. MPFL reconstruction decreased lateral patellar shift (bisect offset index) compared with preoperative tracking at all flexion angles from 0 to 50 degrees of flexion, except 45 degrees. At 0 degrees, the average bisect offset index decreased from 0.81 for the preoperative condition to 0.71. The results indicate that tension within an MPFL graft increases with the lateral position of the tibial tuberosity. The graft tension peaks at low flexion angles and decreases lateral patellar maltracking. The factors that influence graft function following MPFL reconstruction need to be understood to limit patellar maltracking without overloading the graft or over constraining the patella.

Tibial tuberosity anteriomedialization vs. medial patellofemoral ligament reconstruction for treatment of patellar instability related to malalignment: Computational simulation

BackgroundMedial patellofemoral ligament reconstruction and tibial tuberosity anteromedialization are common treatment options for recurrent lateral patellar instability, although ligament reconstruction is not commonly applied to knees with lateral malalignment. MethodsMultibody dynamic simulation was used to assess knee function following tibial tuberosity anteromedialization and medial patellofemoral ligament reconstruction for knees with lateral malalignment. Dual limb squatting was simulated with six models representing knees being treated for patellar instability with an elevated tibial tuberosity to trochlear groove distance. The patellar tendon attachment on the tibia was shifted medially (10 mm) and anteriorly (5 mm) to represent tibial tuberosity anteromedialization. A hamstrings tendon graft was represented for medial patellofemoral ligament reconstruction. Patellar tracking was quantified based on bisect offset index. The patellofemoral contact pressure distribution was quantified using discrete element analysis. Data were analyzed with repeated measures comparisons with post-hoc tests. FindingsBoth procedures significantly reduced bisect offset index, primarily at low flexion angles. The decrease was larger for tibial tuberosity anteromedialization, peaking at 0.18. Tibial tuberosity anteromedialization shifted contact pressures medially, significantly increasing the maximum medial contact pressure at multiple flexion angles, with the maximum pressure increasing up to 1 MPa. InterpretationThe results indicate tibial tuberosity anteromedialization decreases lateral patellar maltracking more effectively than medial patellofemoral ligament reconstruction, but shifts contact pressure medially. Tibial tuberosity anteromedialization is likely to reduce the risk of post-operative instability compared to medial patellofemoral ligament reconstruction. The medial shift in the pressure distribution should be considered for knees with medial cartilage lesions, however.

Lateral patellar maltracking due to trochlear dysplasia: A computational study

BackgroundThe study focuses on the influence of trochlear dysplasia on patellar tracking related to patellar instability. MethodsKnee extension against gravity and dual-limb squatting were simulated with seven models representing knees being treated for recurrent instability. Trochlear depth was altered to represent lateral trochlear inclination (LTI) values of 6°, 12° and 24°. Repeated measures analyses compared patellar lateral shift (bisect offset index) across different LTI values. Peak bisect offset index during extension and squatting was correlated with patella alta (Caton–Deschamps index) and maximum lateral position of the tibial tuberosity. ResultsBisect offset index varied significantly (p < 0.05) between different LTI values at multiple flexion angles throughout simulated knee extension and squatting. Average bisect offset values were 1.02, 0.95, and 0.86 for LTI = 6°, 12°, and 24°, respectively, at 0° of flexion for knee extension. The strongest correlation occurred between peak bisect offset index and lateral position of the tibial tuberosity for knee squatting with LTI = 6° (r2 = 0.81, p = 0.006). The strength of the correlation decreased as LTI increased. Caton–Deschamps was only significantly correlated with patellar tracking for LTI = 24° during knee squatting. ConclusionsA shallow trochlear groove increases lateral patellar maltracking. A lateral tibial tuberosity in combination with trochlear dysplasia increases lateral patellar tracking and the risk of patellar instability. Patella alta has relatively little influence on patellar tracking in combination with trochlear dysplasia due to the limited articular constraint provided by the trochlear groove.

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.