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

Qualitative visual assessment of the J-sign demonstrates high inter-rater reliability

OBJECTIVES

To assess the inter- and intra-rater reliability of the classification of the J-sign as "large" versus "small or none" as compared to another two-level system ("present" versus "absent") and a three-level system ("large," "small," or "none") and to identify anatomical and patient factors associated with the presence of a large J-sign.

METHODS

Forty patients (40 knees) with recurrent patellar instability were prospectively enrolled and recorded on video actively extending their knee while seating. Four raters classified patellar tracking on two separate occasions using three systems: 1) two groups: J-sign versus no J-sign; 2) three groups: large J-sign, small J-sign, or no J-sign; and 3) two groups: large J-sign versus small or no J-sign. The intra- and inter-rater reliability of each system was assessed using kappa statistics. Anatomical (trochlear dysplasia, tibial tubercle-trochlear groove (TT-TG) distance, patellar height) and patient (Beighton score) factors as well as Knee Injury and Osteoarthritis Outcome Score (KOOS) subscales were compared between patients with a large J-sign and patients with a small or no J-sign.

RESULTS

Inter- and intra-rater reliability were found to be highest with the two-level classification system of a large J-sign versus a small or no J-sign (inter-rater kappa ​= ​0.76, intra-rater kappa ​= ​0.75). Patients with a large J-sign had more severe trochlear dysplasia as assessed with the sulcus angle (p ​= ​0.042) and were more likely to have a tight lateral retinaculum (p ​= ​0.032) and an elevated Beighton score (p ​= ​0.009). No significant differences in KOOS subscales were noted based on the presence of a large J-sign versus a small J-sign or no J-sign.

CONCLUSION

Qualitative visual assessment of patellar tracking with the J-sign demonstrates substantial inter- and intra-rater reliability, particularly when utilizing a two-group classification system to identify knees with a large J-sign. Patients with a large J-sign demonstrate an increased incidence of a tight lateral retinaculum, generalized ligamentous laxity, and trochlear dysplasia.

LEVEL OF EVIDENCE

Level III - cross-sectional study.

Computational comparison of medializing tibial tubercle osteotomy and trochleoplasty in patients with trochlear dysplasia

Medial patellofemoral ligament reconstruction (MPFLR) has emerged as the procedure of choice for recurrent patellar dislocation. This addresses soft tissue injury but does not address underlying anatomic factors, including trochlear dysplasia, that are commonly present and increase risk of dislocation. Quantification of the stability offered by other surgical interventions, namely, medializing tibial tubercle osteotomy (mTTO) and trochleoplasty, with and without MPFLR, may provide insight for surgical choices in patients with trochlear dysplasia. We developed subject-specific finite element models based on magnetic resonance scans from a cohort of 20 patients with trochlear dysplasia and recurrent patellar dislocation. The objectives of this study were (1) to compare patella stability after mTTO and trochleoplasty procedures; (2) to evaluate whether it is necessary to perform an MPFLR in combination with the mTTO or trocheoplasty procedure; and (3) to quantify the robustness of patellar stability to variability in knee kinematics. Trochleoplasty performed better than mTTO at stabilizing the patella between 5° and 30° flexion. For both mTTO and trochleoplasty procedures, it was beneficial to also perform MPFLR-inclusion of MPFLR halved the magnitude of patellar laxity predicted in the simulations. Simulations that did not include any medial patellofemoral ligament restraint were also more sensitive to variation in tibiofemoral internal-external kinematics.

Patella height influences patellofemoral contact and kinematics following cruciate-retaining total knee replacement

The role of patella height is discussed controversially in total knee arthroplasty (TKA). Therefore, this computational study aims to systematically analyze the biomechanical effect of different patella heights on patellofemoral (PF) forces and kinematics after cruciate-retaining (CR) TKA. We implemented a CR bicondylar TKA with a dome patellar button in a validated dynamic musculoskeletal multibody model of a male human knee joint. Retropatellar dynamics (contact force [N], shear force [N], patellar shift [mm], tilt [°], and rotation [°]) were evaluated during dual-limb squat motion (flexion from 0° to 90°) with simulated active muscle forces and the effects of different patella heights (Blackburne-Peel [BP] ratio of 0.39, 0.49, 0.65, 0.85, 1.01, and 1.1 were systematically examined). As active knee flexion increased, PF contact force also increased. Patella alta (BP = 1.1) resulted in higher PF contact forces compared to normal patella height (BP = 0.65) by up to 16%. Contrarily, patella baja was associated with decreased PF forces by 7%. Compared to patella baja (BP = 0.39), patella alta (BP = 1.1) considerably increased the contact force by up to 25%. Different patellar heights mainly affected PF shear forces during early knee flexion. Concerning PF kinematics, patella alta (BP = 1.1) yielded a greater lateral tilt of more than 4° and higher patellar rotation by up to 3° during deep knee flexion, compared to normal patella height (BP = 0.65). Our computational study indicates that patella alta is associated with the highest PF contact and shear force after the implantation of a CR bicondylar TKA. This should be considered in PF disorders following TKA.

When Should Bony Correction Be Considered in Addition to Medial Patellofemoral Ligament Reconstruction? Results of a Clinically Derived 2-Group Classification of Lateral Patellar Instability Based on 122 Patients at 2- to 5-Year Follow-up

Background

The need for concomitant bony procedures to realign pathoanatomic risk factors in addition to medial patellofemoral ligament reconstruction (MPFL-R) remains unclear.

Purpose

To evaluate a clinically derived 2-part classification of lateral patellar instability aimed at identifying patients indicated for a concomitant bony procedure.

Study Design

Cohort study; Level of evidence, 3.

Methods

The study included 122 patients (42 male, 80 female; mean ± SD age, 22 ± 6 years) who were assigned to a mild instability group (mIG) and a complex instability group (cIG) based on the reversed dynamic patellar apprehension test (ReDPAT) and J-sign. The mIG had a positive ReDPAT result <40° to 50° of knee flexion and an absent or low-grade J-sign (grade 1), and the cIG had a positive ReDPAT result >40° of knee flexion and/or a high-grade J-sign (grade 2 or 3). The mIG underwent isolated MPFL-R, and the cIG underwent MPFL-R and concomitant bony procedures depending on the established risk factor assessment. For evaluation, the BANFF Patellar Instability Instrument 2.0 (BPII 2.0) and numeric analog scale (0-10) for patellofemoral pain and subjective knee function were used. The minimal clinically important difference for the BPII 2.0 was ascertained by calculating half the standard deviation of baseline scores.

Results

Radiographic analysis confirmed a significantly more pronounced pathoanatomic risk factor constellation in the cIG regarding severity of trochlear dysplasia, distal malalignment, and patellar height (all P < .05). At final follow-up, no patellar redislocation occurred in either group; 2 patients in the cIG reported patellar subluxation. Within both groups, all outcome scores improved significantly pre- to postoperatively (all P < .0001); no between-group difference was found regarding BPII 2.0 score and numeric analog scale for function. The minimal clinically important difference for the BPII 2.0 was met by 84% (32/38) of the mIG and 90% (76/84) of the cIG (P = .36), but the cIG experienced more patellofemoral pain than the mIG (1.3 ± 1.6 vs 2.1 ± 2.1; P = .036).

Conclusion

Patients with a high-grade J-sign and/or a positive ReDPAT finding beyond 40° to 50° of knee flexion exhibited a significantly more pronounced pathoanatomic risk factor constellation; however, the correction of modifiable risk factors led to similarly good outcomes to patients who underwent isolated MPFL-R. A slightly higher level of patellofemoral pain after bony procedures was evident in these patients.

Lateral retinacular release in concordance with medial patellofemoral ligament reconstruction in patients with recurrent patellar instability: A computational model

BACKGROUND

The aim of this study was to develop and validate a finite element (FE) model of the patellofemoral joint to analyze the biomechanics of lateral retinacular release after medial patellofemoral ligament (MPFL) reconstruction in patellar malalignment (increased tibial tubercle-trochlear groove distance (TT-TG)). We hypothesized that lateral retinacular release is not appropriate in patellar instability addressed by MPFL reconstruction due to decreased lateral stability and inappropriate adjustment in patellofemoral contact pressures.

METHODS

A FE in-silico model of the patellofemoral joint was developed and validated. The model was used analyze the effect of lateral retinacular release in association with MPFL reconstruction on patellofemoral contact pressures, contact area, and lateral patellar displacement during knee flexion.

RESULTS

MPFL reconstruction alone results in restoration of patellofemoral contact pressures throughout the entire range of motion (0-90°), mimicking the results from healthy condition. The addition of the lateral retinacular release to the MPFL reconstruction resulted in significant reductions in both patellofemoral contact pressure and contact area. Lateral retinacular release resulted in more lateral patellar displacement during the mid-flexion knee range of motion.

CONCLUSIONS

Combination of lateral retinacular release with MPFL reconstruction in patients with increased TT-TG is not recommended as MPFL reconstruction alone for first-line management of recurrent patellar instability offers a greater biomechanical advantage and restoration of contact forces to resemble that of the healthy knee. The presented biomechanical data outlines the effect of concomitant MPFL reconstruction and lateral retinacular release to help guide surgical planning for patients with recurrent patellar instability due to malalignment.

Combined distal femoral osteotomy and tibial tuberosity distalization is effective in patients presenting with patellar instability and patellofemoral pain due to patella alta and femoral malalignment

INTRODUCTION

Patellar malalignment has been considered one of the major pathomechanical causes of patellofemoral instability and pain. The results have been reported after femoral varization/torsional osteotomy and tibial tuberosity distalization osteotomy (TTD-O). However, the combination of a femoral deformity (genu valgum/increased femur antetorsion) and patella alta remains underreported. Therefore, the aim of this study was to investigate the clinical outcomes of patients simultaneously treated by distal femoral osteotomy and TTD-O. The hypothesis was that restoration of patellofemoral (PF) alignment via the abovementioned osteotomies would achieve good patient-reported outcome measures.

MATERIALS AND METHODS

Between 2016 and 2019, a series of 25 knees in 20 patients were treated by a distal femoral osteotomy combined with a TTD-O aiming to correct patellofemoral malalignment consisting of genu valgum and/or increased femur antetorsion and patella alta. Six patients were lost to follow-up, and one patient refused to participate. Thus, 17 knees in 13 patients (male/female 1/12; age 27.4 ± 5.4 years) were included and comprised the study group for this investigation. Patients were evaluated after a mean of 3.1 ± 0.9 years postoperatively. The Kujala anterior knee pain scale and the PF-subscale of the Knee Osteoarthritis and Outcome score (KOOS-PF) were used to assess patients' reported outcome measures from pre- to postoperatively.

RESULTS

The mean amount of torsional correction, valgus correction, and tibial tuberosity distalization averaged 14° (10°-18°), 5.2° (3.8°-8°), and 9 mm (6°-15 mm), respectively. The Kujala score increased by an average of 24.18 points from a mean of 66.6 ± 18.3 points (34-93 points) preoperatively to 90.8 ± 14.2 points (44-100 points) postoperatively (95% CI - 33.0 to - 15.3; p < 0.0001). The KOOS-PF score increased by an average of 33.7 points from a mean of 49.5 ± 24.5 points (9.1-88.6 points) preoperatively to 83.2 ± 21.6 points (15.9 -100 points) postoperatively (95% CI - 47.5 to - 19.9; p < 0.0001).

CONCLUSION

The findings of this study indicate that the combination of a distal femoral osteotomy and a tibial tuberosity distalization osteotomy is effective in patients presenting with patellar instability and patellofemoral pain due to patella alta and femoral malalignment.

Combined MPFL reconstruction and tibial tuberosity transfer avoid focal patella overload in the setting of elevated TT-TG distances

PURPOSE

Objectives are (1) to evaluate the biomechanical effect of isolated medial patellofemoral ligament (MPFL) reconstruction in the setting of increased tibial tuberosity-trochlear groove distance (TTTG), in terms of patella contact pressures, contact area and lateral displacement; (2) to describe the threshold of TTTG up to which MPFL reconstruction should be performed alone or in combination with tibial tuberosity transfer.

METHODS

A finite element model of the knee was developed and validated. The model was modified to simulate isolated MPFL reconstruction, tibial tuberosity transfer and MPFL reconstruction combined with tibial tuberosity transfer for patella malalignment. Two TT-TG distances (17 mm and 22 mm) were simulated. Patella contact pressure, contact area and lateral displacement were analysed.

RESULTS

Isolated MPFL reconstruction, at early degrees of flexion, restored normal patella contact pressure when TTTG was 17 mm, but not when TTTG was 22 mm. After 60° of flexion, the TTTG distance was the main factor influencing contact pressure. Isolated MPFL reconstruction for both TTTG 17 mm and 22 mm showed higher contact area and lower lateral displacement than normal throughout knee flexion. Tibial tuberosity transfer, at early degrees of flexion, reduced the contact pressure, but did not restore the normal contact pressure. After 60° of flexion, the TTTG distance was the main factor influencing contact pressure. Tibial tuberosity transfer maintained lower contact area than normal throughout knee flexion. The lateral displacement was higher than normal between 0° and 30° of flexion (< 0.5 mm). MPFL reconstruction combined with tibial tuberosity transfer produced the same contact mechanics and kinematics of the normal condition.

CONCLUSION

This study highlights the importance of considering to correct alignment in lateral tracking patella to avoid focal patella overload. Our results showed that isolated MPFL reconstruction corrects patella kinematics regardless of TTTG distance. However, isolated MPFL reconstruction would not restore normal patella contact pressure when TTTG is 22 mm. For TTTG 22 mm, the combined procedure of MPFL reconstruction and tibial tuberosity transfer provided an adequate patellofemoral contact mechanics and kinematics, restoring normal biomechanics. This data supports the use of MPFL reconstruction when the patient has normal alignment and the use of combined MPFL reconstruction and tibial tuberosity transfer in patients with elevated TT-TG distances to avoid focal overload.

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.

The J-sign and the body mass index determine the disease-specific quality of life in patients with lateral patellar instability

PURPOSE

To determine which risk factors for patellar instability contribute most relevantly to patients' subjective disease-specific quality of life, aiming to provide implications on the overall treatment decision-making process.

METHODS

A total of 182 consecutive patients (male/female 70/112; mean age 23.6 ± 7.3 years) with a history of patellar instability were prospectively enrolled in this study. Patient age, body mass index (BMI), number of dislocations, reversed dynamic patellar apprehension test (ReDPAT), J-sign severity, and pathoanatomic risk factors of patellar instability were assessed. The statistical analysis evaluated the relationships among those variables and determined their ability to predict the Banff Patellofemoral Instability Instrument 2.0 (BPII 2.0) as a disease-specific quality of life measure. Using Spearman correlation, ANOVA and Fisher's exact test, all variables with ANOVA p ≤ 0.1 or Spearman's abs (rho) > 0.1 were entered into a multivariate linear model using backward-stepwise selection.

RESULTS

Analysis of the individual variables' ability to predict BPII 2.0 score values revealed 'age', 'BMI', 'ReDPAT', 'high grade of trochlear dysplasia', and 'high-grade J-Sign' as possible relevant factors. Backward-stepwise multivariate regression analysis yielded a final parsimonious model that included the factors 'BMI' and 'J-Sign (Grade II and III)' as the most relevant parameters influencing BPII 2.0 score values (adjusted R² = 0.418; p < 0.001), with a cutoff value for BMI found at 28 kg/m² (p = 0.01).

CONCLUSION

The results of this study indicate that in patients with lateral patellar instability, a high-grade J-sign and an increased BMI significantly impact subjective disease-specific quality of life.

LEVEL OF EVIDENCE

Level IV.

Lateral Release With Tibial Tuberosity Transfer Alters Patellofemoral Biomechanics Promoting Multidirectional Patellar Instability

PURPOSE

The purpose of this study was to develop and validate a finite element (FE) model of the patellofemoral (PF) joint to characterize patellofemoral instability, and to highlight the effect of lateral retinacular release in combination with tibial tuberosity transfer with respect to contact pressures (CP), contact area (CA), and kinematics during knee flexion.

METHODS

A comprehensive, dynamic FE model of the knee joint was developed and validated through parametric comparison of PF kinematics, CP, and CA between FE simulations and in vitro, cadaveric experiments. Using this FE model, we characterized the effect of patellar instability, lateral retinacular release (LR), and tibial tuberosity transfer (TTT) in the setting of medial patellofemoral ligament injury during knee flexion.

RESULTS

There was a high level of agreement in CP, CA, lateral patellar displacement, anterior patellar displacement, and superior patellar displacement between the FE model and the in vitro data (P values 0.19, 0.16, 0.81, 0.10, and 0.36, respectively). Instability conditions demonstrated the greatest CP compared to all of the other conditions. During all degrees of flexion, TTT and concomitant lateral release (TTT + LR) decreased CP significantly. TTT alone shows a consistently lower CA compared to nonrelease conditions with subsequent lateral release further decreasing CA.

CONCLUSIONS

The results of this study demonstrate that the FE model described reliably simulates PF kinematics and CP within 1 SD in uncomplicated cadaveric specimens. The FE model is able to show that tibial tubercle transfer in combination with lateral retinacular release markedly decreases patellofemoral CP and CA and increases lateral patellar displacement that may decrease bony stabilization of the patella within the trochlear groove and promote lateral patellar instability.

CLINICAL RELEVANCE

The goal of surgical correction for patellar instability focuses on reestablishing normal PF kinematics. By developing an FE model that can demonstrate patient PF kinematics and the results of different surgical approaches, surgeons may tailor their treatment to the best possible outcome. Of the surgical approaches that have been described, the biomechanical effects of the combination of TTT with lateral retinacular release have not been studied. Thus, the FE analysis will help shed light on the effect of the combination of TTT with lateral retinacular release on PF kinematics.

[Primary and recurrent patellar dislocation: recommendation for diagnostic evaluation, risk stratification and treatment]

The dogma that (every) primary patellar dislocation should be treated non-operatively is considered outdated. Therefore, every first-time dislocation, as well as every recurrent dislocation, should be fully diagnosed with regard to the injury pattern and anatomically predisposing risk factors. This enables the use of risk stratification models to assess the risk of recurrent episodes of instability, thereby supporting the clinical decision-making process. The reconstruction of the MPFL can be considered an established and successful treatment strategy for patellar instability. However, the additional correction of bony risk factors is often useful. In this context, the preoperative grading of the J sign and dynamic assessment of patellar instability (dynamic apprehension test) are of utmost importance. These findings, combined with the radiographic imaging findings, can be used as a clinical decision aid for a bony correction procedure.

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.

Influence of tibial tuberosity position and trochlear depth on patellar tracking in patellar instability: Variations with Patella Alta

BACKGROUND

Patella alta reduces articular constraints acting on the patella from the trochlear groove with the knee extended. The current study was performed to address how patella alta alters the influence of tibial tuberosity position and trochlear depth on patellar tracking in patients being treated for patellar instability.

METHODS

Fifteen subjects with recurrent patellar instability participated in knee extension within a dynamic CT scanner. Computational models were reconstructed from the motions to characterize patellar lateral shift, patellar tilt, patellar height, trochlear depth and lateral position of the tibial tuberosity at 0° and 30° of knee flexion. Linear regressions were used to correlate patellar tracking with anatomy for an alta group (7 knees, Caton-Deschamps index > 1.2) and a non-alta group.

FINDINGS

For the alta group, lateral patellar shift and tilt increased with increasing lateral position of the tibial tuberosity at 0° (r² > 0.8, P < 0.005). For the non-alta group, lateral patellar shift and tilt increased as depth of the groove decreased at 0° (r² > 0.8, P = 0.001). Lateral patellar tilt also increased with increasing lateral position of the tibial tuberosity at 30° for the non-alta group (r² = 0.55, P = 0.04).

INTERPRETATION

For patients with patellar instability, lateral patellar maltracking with the knee extended can be largely attributed to either a shallow trochlear groove or a combination of patella alta and a lateral position of the tibial tuberosity. These relationships should be considered in both conservative and surgical treatment planning.

Femoral Origin Anatomy of the Medial Patellofemoral Complex: Implications for Reconstruction

PURPOSE

To report the shape and orientation of the medial patellofemoral complex (MPFC) footprint on the medial femur and describe the difference between the proximal (medial quadriceps tendon femoral ligament, MQTFL) and distal (medial patellofemoral ligament, MPFL) fibers.

METHODS

In 20 cadaveric knees, the MPFC footprint on the medial femur was exposed. Images of the medial femur were analyzed using ImageJ software. The length and width of the MPFC footprint were described to the nearest 0.1 mm; the angle of its long axis was described relative to the axis of the femoral shaft (0.1°). The footprint's most proximal and distal margins were described in relation to the adductor tubercle and medial epicondyle. The differences between each were compared using paired t tests.

RESULTS

17 knees from 10 cadavers were included in this study. The MPFC footprint had a length of 11.7 ± 1.8 mm and a width of 1.7 ± 0.4 mm. The long axis of the footprint was at an angle 14.6° ± 16.6° anterior to the axis of the femoral shaft. The most proximal (MQTFL) fibers originated 7.4 ± 3.8 mm anterior and 1.8 ± 4.7 mm distal to the adductor tubercle and 4.1 ± 2.9 mm posterior and 8.4 ± 5.6 mm proximal to the medial epicondyle. The most distal (MPFL) fibers originated 4.9 ± 4.2 mm anterior and 12.7 ± 4.3 mm distal to the adductor tubercle, as well as 7.1 ± 2.4 mm posterior and 0.5 ± 5.6 mm distal to the medial epicondyle. The distal margin of the femoral MPFC footprint was 10.9 ± 1.7 mm distal (p < .001) and 2.6 ± 3.2 mm more posterior (p = .005) than the proximal margin.

CONCLUSIONS

The femoral footprint of the MPFC has a length almost 7 times greater than its width, with the distal margin being 10.9 mm distal and 2.6 mm posterior to the proximal margin.

CLINICAL RELEVANCE

This differential anatomy within the femoral origin suggests that MPFL and MQTFL reconstruction may require separate positions of femoral fixation to recreate the anatomy of these fibers.

Objective assessment of patellar maltracking with 3 T dynamic magnetic resonance imaging: feasibility of a robust and reliable measuring technique

Patellofemoral maltracking predisposes the patellofemoral joint to instability. The purpose of this study was to provide a reliable dynamic magnetic resonance imaging (MRI) measuring technique for patellofemoral maltracking, and to investigate the influence of anatomical risk factors (AF) on patellar maltracking. Ten patients (2 males,8 females, average 19 years) with clinical maltracking and 20 controls (10 males,10 females,average 28 years) were examined with a dynamic, multi-slice gradient-echo MRI sequence, during repetitive flexion(40°) and full extension, in an open-chain-active-movement. In a 30-s time frame three simultaneous transverse slices were acquired. Dynamic mediolateral translation and dynamic tilt were measured at defined positions, by two independent examiners. Reproducibility was tested in a set of five knees. Common AFs for patellar maltracking (tibial-tuberosity-to-trochlear-groove-(TT-TG)-distances, trochlea-sulcus-angle, trochlea-sulcus-depth, lateral-trochlear-inclination and Caton-Deschamps-Index) were analyzed in consensus, using standard static MRI sequences. In patients, dynamic mediolateral translation was significantly greater in patients (12.4 ± 6.9 mm vs. − 0.1 ± 2.3 mm, p < 0.001) and the patella was positioned significantly more laterally (17.5 ± 6.9 mm vs. 3.1 ± 2.4 mm, p < 0.001) compared to controls. During movement, the patella tilted 16.3 ± 13.1° laterally in patients and 1.9 ± 4.3° medially in controls (dynamic tilt) (p < 0.002). All AFs were significantly different between patients and controls. Pathological TT-TG-distances, Caton-Deschamps-Indices and trochlea-sulcus-angles strongly correlated with dynamic patellar translation and dynamic patellar tilt (p < 0.001). In the patient population, the primary pathologies for maltracking were lateralized-tibial-tubercle (n = 5), trochlea dysplasia n = 2, patella alta (n = 3). Interrater-reliability for translation and tilt-measurement was excellent (0.971/0.976, 95% CIs 0.939–0.986/0.950–0.988). Dynamic MRI reliably differentiates between abnormal and physiological patellar tracking. Dynamic tracking and tilt strongly correlate with measurable AFs, which reinforces their clinical use and validates the presented technique.

Modified Langenskiöld procedure for chronic, recurrent, and congenital patellar dislocation

PURPOSE

Langenskiöld described a reconstructive soft-tissue procedure for irreducible lateral congenital patellar dislocations. Paley further detailed the technique in the surgical management of congenital femoral deficiency. The aim of this study was to evaluate the outcomes of patients with congenital, chronic and recurrent patellar dislocations treated with the modified Langenskiöld procedure.

METHODS

This is a retrospective case series. Between 2011 and 2018, 18 knees in 13 patients (mean age 15.8 years (sd 4.4; 12 to 29.9), nine female) with diagnoses of recurrent (six patients, eight knees), chronic (four patients, six knees) and congenital (three patients, four knees) patellar dislocations were treated with the modified Langenskiöld procedure.

RESULTS

There were no recurrent lateral dislocations in the congenital or recurrent groups. One of the patients in the congenital group had an overcorrection with some medial patellar maltracking but until this time has not required any further surgery. In the chronic group two of the six knees developed further dislocations; these were both on the same patient, who had no dislocations until one year after surgery. Mean Kujala score was 83.7 (sd 17; 47 to 100) for all groups. In spite of preoperative knee flexion contractures of up to 30° in three patients (six knees), all patients had full extension postoperatively. Eight patients reported being satisfied with their outcome, one was somewhat satisfied, two were very dissatisfied, and two did not respond.

CONCLUSION

The modified Langenskiöld reconstruction provides a powerful correction for challenging cases of congenital and recurrent patellar dislocations. Re-dislocation as well as overcorrection can occasionally occur.

LEVEL OF EVIDENCE

Level IV.

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

BACKGROUND

Medial 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.

METHODS

Multibody 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.

FINDINGS

Both 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.

INTERPRETATION

The 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.

Computational approach to correcting joint instability in patients with recurrent patellar dislocation

Patellar dislocation is a debilitating injury common in active adolescents and young adults. Conservative treatment after initial dislocation is often recommended, but almost half of these patients continue to suffer from recurrent dislocation. The objective of this study was to compare preoperative patellofemoral joint stability with stability after a series of simulated procedures, including restorative surgery to correct to pre-injury state, generic tibial tubercle osteotomy, patient-specific reconstructive surgery to correct anatomic abnormality, less invasive patient-specific surgery, and equivalent healthy controls. Three-dimensional, subject-specific finite element models of the patellofemoral joint were developed for 28 patients with recurrent patellar dislocation. A 50 N lateral load was applied to the patella to assess the lateral stability of the patellofemoral joint at 10° intervals from 0° to 40° flexion. Medial patellofemoral ligament reconstruction, along with reconstructive procedures to correct anatomic abnormality were simulated. Of all the simulations performed, the healthy equivalent control models showed the least patellar internal-external rotation, medial-lateral translation, and medial patellofemoral ligament restraining load during lateral loading tests. Isolated restorative medial patellofemoral ligament reconstruction was the surgery that resulted in the most patellar internal-external rotation, medial-lateral translation, and medial patellofemoral ligament reaction force across all flexion angles. Patient-specific reconstruction to correct anatomic abnormality was the only surgical group to have non-significantly different results compared with the healthy equivalent control group across all joint stability metrics evaluated. Statement of clinical significance: This study suggests patient-specific reconstructive surgery that corrects underlying anatomic abnormalities best reproduces the joint stability of an equivalent healthy control when compared with the pre-injury state, generic tibial tubercle osteotomy, and less invasive patient-specific surgery. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:768-776, 2020.

Arthroscopic assessment of patella tracking correlates with recurrent patellar instability

PURPOSE

For recurrent lateral patellar instability surgical algorithm, an arthroscopic assessment of patellar tracking can aid with the decision of adding a tibial tubercle transfer procedure based on knee flexion angle at which patella centrally engages in its groove. Tibial tubercle-trochlear groove distance is variable in normal values and has discrepancies between imaging modalities. The aims of our study were to assess correlation of arthroscopic patellar tracking technique with recurrent patellar instability, and to assess the accuracy and reproducibility of this technique.

METHODS

157 patients were evaluated, 64 control patients with no patellar instability, and 93 patients with recurrent patellar instability. This included 57 consecutive knee arthroscopy procedures evaluated for accuracy and reproducibility of our technique. The technique involved low flow arthroscopy and anterolateral viewing portal. Patients' knees were extended from a flexed position of 120°, and paused when the patella disengaged from its groove. The KFA was then estimated by the primary surgeon, and compared with a goniometer measurement. The assisting surgeon, blinded to the primary surgeon measurements, repeated this process. For the primary outcome, goniometer readings for KFA from the primary surgeon were used to correlate with patellar instability diagnosis.

RESULTS

Patients with patellar instability had a mean KFA of 118° compared to 44°for patients without patellar instability (p < 0.001). The mean difference between goniometer reading and estimation of KFA by each surgeon was 5° (p < 0.001) with intra-class correlation of 0.99. The mean difference between the two surgeons' goniometer readings was 8° (p < 0.001) with intra-class correlation of 0.99.

CONCLUSION

This study confirms arthroscopic assessment of patella tracking is accurate, reproducible, and a knee flexion angle of greater than 44° correlates with patellar instability diagnosis. Patella tracking can be used as an adjunct or an alternative assessment method to tibial tubercle-trochlear groove distance to determine the need for tibial tubercle transfer in patellar stabilisation surgery.

LEVEL OF EVIDENCE

Prospective Cohort Study, Level III.

Closed-wedge Patelloplasty for the Treatment of Distal Patellofemoral Maltracking and Instability due to Severe Patellar Dysplasia: Case Report and Surgical Technique

Background

Patellofemoral maltracking is caused by different anatomical factors. Most of them are associated with a proximal maltracking, which alters the patella's engagement into the trochlear groove and predisposes the patellofemoral joint for instability. Different surgical techniques have been described to realign patellar tracking, however, most of which address proximal patellar maltracking.

Aim

The aim of this article is to demonstrate the influence of patella-related deformities on patellar tracking and to present a novel surgical technique for the treatment of distal patellar maltracking, caused by a severe patellar dyplasia.

Case Description

We report the case of a 23-year-old patient with a severe patellar dysplasia, presenting a distal patellar maltracking with recurring dislocations in deep flexion. Due to her instability, the patient was immobilised and dependent on the constant use of walking aids. Radiological images showed a concavely shaped patellar, which articulated exclusively with the lateral epicondyle and caused the patella to dislocate laterally, starting at a flexion angle of 60°. An anterior closing-wedge osteotomy was used to reshape and recenter the patella, which was complemented by a medial patellofemoral ligament reconstruction. At the 18-month follow-up, the patient presented pain free and fully remobilised, without the use of walking aids. Patellar tracking was reestablished, with a possible knee flexion until 140°. No redislocation of the patella had occurred.

Conclusion

Distal patellofemoral maltracking, caused by a severe patellar dysplasia, can successfully be treated with an anterior closed-wedge osteotomy of the patella. In combination with a medial patellofemoral ligament reconstruction, patellofemoral stability can be reestablished, to prevent further dislocations.

Clinical Significance

There are multiple factors, which may cause patellar maltracking. A thorough clinical and radiological preoperative analysis is mandatory, in order to clearly identify the underlying pathologies, as these may affect patellar tracking proximally or distally.

How to cite this article

Frings J, Freudenthaler F, Krause M, et al. Closed-wedge Patelloplasty for the Treatment of Distal Patellofemoral Maltracking and Instability due to Severe Patellar Dysplasia: Case Report and Surgical Technique. Strategies Trauma Limb Reconstr 2020;15(3):184-192.

Lateral patellar maltracking due to trochlear dysplasia: A computational study

BACKGROUND

The study focuses on the influence of trochlear dysplasia on patellar tracking related to patellar instability.

METHODS

Knee 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.

RESULTS

Bisect 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.

CONCLUSIONS

A 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.

Computational simulation of medial versus anteromedial tibial tuberosity transfer for patellar instability

The study utilizes dynamic simulation of knee function to determine how tibial tuberosity medialization and anteromedialization influence patellar tracking and contact pressures for knees with patellar instability. Dual limb squatting was simulated with six multibody dynamic simulation models representing knees being treated for patellar instability. Each knee exhibited lateral patellar maltracking in the pre-operative condition based on the bisect offset index. The patellar tendon attachment points on the tibia were medialized by 10 mm to represent tibial tuberosity medialization, with an additional 5 mm of anteriorization applied for anteromedialization. The patellofemoral contact pressure distribution was quantified using discrete element analysis. Data were analyzed with repeated measures analysis of variance with post-hoc tests and linear regressions. Tibial tuberosity medialization and anteromedialization significantly (p < 0.05) decreased the bisect offset index for nearly all flexion angles up to 80°, with the largest changes near full extension. Both procedures significantly decreased the maximum lateral pressure at 55°, but increased the maximum medial pressure from 30 to 80°. The pre-operative to post-operative increase in the maximum contact pressure was significantly correlated with the maximum pre-operative bisect offset index for tuberosity medialization (r²  = 0.84), but not for anteromedialization. Statement of Clinical Significance: The results indicate tibial tuberosity medialization decreases patellar lateral maltracking and lateral patellofemoral contact pressures, but increases medial contact pressures. When pre-operative patellar maltracking is relatively low, tibial tuberosity medialization is likely to increase maximum contact pressures. Tibial tuberosity anteromedialization lowers the risk of elevated post-operative contact pressures compared to medialization. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:3231-3238, 2018.