Patellofemoral kinematics during knee flexion-extension: an in vitro study

Evaluating tibial rotation in recurrent patellar dislocation with four-dimensional computed tomography

OBJECTIVE

This study is to investigate the three-dimensional (3D) kinematic changes in the knee joint in patients with recurrent patellar dislocation using four-dimensional computed tomography (4DCT) imaging and the 3D-3D surface registration technique.

MATERIALS AND METHODS

Ten knees from nine patients with recurrent patellar dislocation and seven knees from seven controls (unaffected side of patients with unilateral anterior cruciate ligament injury) were analyzed using 4DCT. The patients were asked to extend their knees from 60° of flexion to full extension for 10 s in the CT gantry. We used the 3D-3D registration technique, and the 3D angles of the patella and tibia relative to the femur were evaluated.

RESULTS

In the dislocation group, the patellar lateral tilt increased as the knee extended. Significant differences were found between the two groups at 0°-20° of knee flexion. The tibia rotated externally as the knee extended in the dislocation group. Significant differences between the two groups were found at 0°-10° of knee flexion.

CONCLUSION

This study demonstrated significant differences in the timing and magnitude of tibial external rotation between patients with recurrent patellar dislocation and controls. Specifically, the tibia began to externally rotate during the early phase of knee extension in the dislocation group. These findings provide new insights into knee kinematics that may inform future treatment strategies for patellar dislocation.

Comparing Patellofemoral Kinematics Assessed With a Novel Muscle Actuator System and an Oxford Rig Using Noncadaveric Knees

Total knee replacement (TKR) failure, low patient satisfaction and high revision surgery rates may stem from insufficient preclinical testing. Conventional joint motion simulators for preclinical testing of TKR implants manipulate a knee joint in force, displacement, or simulated muscle control. However, a rig capable of using all three control modes has yet to be described in literature. This study aimed to validate a novel platform, the muscle actuator system (MAS), that can generate gravity-dependent, quadriceps-controlled squatting motions representative of an Oxford rig knee simulator and is mounted onto a force/displacement-control-capable joint motion simulator. Synthetic knee joint phantoms were created that comprised revision TKR implants and key extensor and flexor mechanism analogues, but no ligaments. The combined system implemented a constant force vector acting from simulated hip-to-ankle coordinates, effectively replicating gravity as observed in an Oxford rig. Quadriceps forces and patellofemoral joint kinematics were measured to assess the performance of the MAS and these tests showed high levels of repeatability and reproducibility. Forces and kinematics measured at a nominal patellar tendon length, and with patella alta and baja, were compared against those measured under the same conditions using a conventional Oxford rig, the Pennsylvania State Knee Simulator (PSKS). There was disagreement in absolute kinematics and muscle forces, but similar trends resulting from changing prosthesis design or patellar tendon length.

Medial patellofemoral ligament reconstruction normalizes patellar kinematics but fails to predict cartilage contact area: A prospective 3D MRI study

Introduction

The medial patellofemoral ligament (MPFL) is the main patellar stabilizer in low knee flexion degrees (0-30°). Isolated MPFL reconstruction (MPFLr) is therefore considered the gold standard of surgical procedures for low flexion patellofemoral instabilities (PFIs). Despite excellent clinical results, little is known about the effect of MPFLr on kinematic parameters (KPs) of the patellofemoral joint in vivo. This study investigates the effect of MPFLr on KP of patellofemoral articulation, using a three-dimensional (3D) in vivo magnetic resonance imaging (MRI) analysis at different flexion and loading positions, and analyzes the correlation of these parameters with the patellofemoral cartilage contact area (CCA).

Methods

In this prospective, matched-pair cohort study of 30 individuals, 15 patients with low flexion PFI and 15 knee-healthy individuals were included. Patients were analyzed pre and post-operatively after MPFLr. MRI images were obtained at 0°, 15° and 30° with and without muscle activation, using a custom-designed pneumatic loading device. Patellar shift, tilt and rotation were determined in 3D bone and cartilage models of each individual, guaranteeing the highest reliability. Subsequently, the KPs were correlated with patellofemoral CCA.

Results

Patients with low flexion PFI had a leg geometry of 0.5 ± 2.6° valgus and a TTTG of 11.4 ± 4.4 mm. Eleven patients had moderate (Type A/B) and 2 had severe (Type C/D) trochlear dysplasia. Without muscle activation, patients showed significantly increased patellar shift (0-30°; p 0° = 0.011, p 15° = 0.004 and p 30° = 0.015) and tilt (15°; p 15° = 0.041). Muscle activation did not compensate for maltracking in these patients, but even increased tilt and shift further in extension (p 0° = 0.002 and p 0° = 0.001). MPFLr statistically reduced patellofemoral tilt from 0° to 30° flexion during passive flexion and tended to approach the values of knee-healthy individuals (p ext = 0.008, p 15° = 0.006 and p 30° = 0.003). Post-operatively, muscle activation led to comparable tilt and shift as in healthy individuals. Tilt, shift and rotation did not correlate with CCA neither in healthy individuals nor in pre- or post-operative patients.

Conclusion

Isolated MPFLr can normalize patellar shift and tilt in patients with low flexion instability. Considering the influence of muscle activation, passive stabilization through MPFLr seems to be the basic precondition for physiologically active patella stabilization. The investigated KPs as easy-to-measure parameters in clinical practice cannot be used to assume normalized CCA for low flexion degrees. Therefore, methodologically demanding methods are still required to calculate the patellofemoral CCA.

Level of Evidence

Level II.

Three-Dimensional Imaging of the Patellofemoral Joint Improves Understanding of Trochlear Anatomy and Pathology and Planning of Realignment

Three-dimensional (3D) modeling using digital or printed models provides a unique perspective that caters to cognitive spatial ability in a way that can add to our understanding and mental representations of human anatomy. This is particularly useful in the setting of trochlear dysplasia, where the morphology of the groove can exhibit substantial variability and complexity. Using 3D reformatted images and models, a pragmatic understanding of how morphology influences patellofemoral pathology can be gleaned. Further, this perspective facilitates cognition of what patellar tracking may look like after realignment procedures. Using 3D modeling, concepts such as patella alta, trochlear depth, lateralization of the patellar entry point, trochlear curvature, and the presence of a proximal trochlear spur can help afford a better understanding of how trochlear anatomy may influence tracking while also providing insight as to the ideal tracking path. The use of 3D has recently emerged as a useful tool in multiple surgical subspecialties, particularly in situations involving surgical planning or complex anatomy. Given the complexity and variation in trochlear morphology in patients with trochlear dysplasia who develop either patellar instability or focal overloading, 3D modeling is well-suited to provide a perspective that can add to our understanding of trochlear dysplasia, and potentially even how we diagnose and treat it. LEVEL OF EVIDENCE: Level V, expert opinion.

Patellofemoral Instability in the Pediatric and Adolescent Population: From Causes to Treatments

BACKGROUND

Patella instability is one of the most common knee injuries in the adolescent patient. There are several pathoanatomic risk factors which should be assessed via several modalities, including X-rays, magnetic resonance imaging (MRI), or even CT scan.

OBJECTIVES

We intend to review these risk factors along with the nonsurgical and surgical techniques used to prevent recurrent dislocations.

METHODS

We completed an extensive review of the recent literature concerning pediatric and adolescent patellar dislocation and subsequent treatment modalities.

RESULTS

We review in detail the risk factors such as patella alta, trochlear dysplasia, lateralization of the tibial tubercle or medialization of the trochlear groove (increased tibial tubercle to trochlear groove (TT-TG) distance), lower limb malalignment, excessive femoral anteversion and/or tibial torsion, and hyperlaxity. There are classification systems for dislocators, and a natural progression of instability that patients often proceed through. Only after a patient has continued to dislocate after bracing and physical therapy is surgical treatment considered. Surgical techniques vary, with the workhorse being the medial patellofemoral ligament (MPFL) reconstruction. However, there are a variety of other techniques which add onto this procedure to address other anatomic risk factors. These include the tibial tubercle osteotomy to address a large TT-TG distance or trochleoplasty to address the lack of a trochlear groove.

CONCLUSIONS

Nonsurgical and surgical treatments for patella dislocators are tailored to the pathoanatomic risk factors in each patient.

Shallow trochlear groove and narrow medial trochlear width at the proximal trochlea in patients with trochlear dysplasia: A three-dimensional computed tomography analysis

PURPOSE

Although the Dejour classification is the primary classification system for evaluating trochlear dysplasia, concerns have been raised about its reliability owing to its qualitative criteria and challenges associated with obtaining accurate radiographs. This study aimed to quantify trochlear dysplasia using three-dimensional (3D) computed tomography (CT) reconstruction with novel parameters related to the transepicondylar axis (TEA).

METHODS

Sixty patients were enrolled, including 20 with trochlear dysplasia and 40 healthy controls. The 3D CT model was generated using the Materialise Interactive Medical Image Control System software. The following six parameters were measured in eight consecutive planes at 15° intervals (planes 0-105): the distance from the TEA to the most cortical point of the lateral condyle ('LP-TEA', where LP stands for lateral peak), medial condyle ('MP-TEA', MP for medial peak) and deepest point of the trochlea ('TG-TEA', TG for trochlear groove). The distances from the medial epicondyle (MEC) to the corresponding TEA points were measured ('LP-MEC', 'MP-MEC' and 'TG-MEC').

RESULTS

In the dysplasia group, TG-TEA (planes 0, 15 and 30) and MP-MEC (planes 0, 15 and 30) were significantly greater than those in the control group (all p < 0.05 for planes of TG-TEA and MP-MEC). For type A dysplasia, LP-MEC (plane 0) was greater than that in the control group. For type B dysplasia, the MP-MEC (planes 0 and 15) and TG-TEA (planes 0 and 15) were greater than those of the control group. For type D dysplasia, MP-MEC (planes 0, 15 and 30) and TG-TEA (planes 0 and 15) were elevated.

CONCLUSION

The 3D CT reconstruction analysis established a reproducible method for quantifying osseous trochlear morphology. Patients with trochlear dysplasia had a shallow TG and narrow medial trochlear width at tracking angles of 0°-30°. This finding corroborates the clinical manifestations of recurrent patellar instability that occur during early flexion.

LEVEL OF EVIDENCE

Level III.

Inferior patellar mobility before and after knee arthroplasty: A comparison with healthy knees

PURPOSE

The aim of this study was to evaluate patellar mobility in patients before and after knee arthroplasty (KA) and compare it with that of healthy subjects. It was hypothesised that patellar mobility is diminished in patients with osteoarthritis (OA) and remains unchanged after KA.

METHODS

A total of 101 patients (59 females and 42 males) with a mean age of 70.9 ± 9.9 years underwent KA and were compared with 25 healthy individuals (seven females and 18 males) with a mean age of 32.3 ± 9.3 years. Mediolateral patellar displacement was measured by applying a force of 10 N, and the medial and lateral patellar shifts were recorded separately using a validated novel patellostabilometer. Patients were examined preoperatively and at 3 months postoperatively, assessing the range of knee motion and the clinical and functional status based on the Oxford Knee Score (OKS), Kujala Score, subjective Knee Society Score (sKSS), Forgotten Joint Score (FJS) and Western Ontario and McMaster Universities Arthritis Index (WOMAC).

RESULTS

Total patellar displacement was 42.1 ± 6 mm for healthy subjects, 31 ± 6 mm before surgery and 32.8 ± 7.8 mm after surgery in osteoarthritic patients (p < 0.01). The mean lateral patellar shift differed significantly between healthy individuals (17.9 ± 4 mm) and osteoarthritic patients (15.1 ± 6 mm) (p < 0.01). The mean medial patellar mobility of healthy individuals (24.2 ± 7 mm) was significantly greater than that of osteoarthritic patients (15.8 ± 4.8 mm) (p < 0.01). All scores improved significantly postoperatively. No correlation was found between patellar mobility and OKS, Kujala Score, sKSS, FJS and WOMAC (r = -0.11). Improvement in patellar mobility also showed no correlation with clinical outcomes according to OKS, Kujala Score, sKSS, FJS and WOMAC (r = 0.08).

CONCLUSION

This study has demonstrated reduced patellar mobility in patients with OA. While patellar mobility significantly improved after KA, it may not hold clinical significance (p = 0.04). No impact on clinical outcome can be expected when the presurgical patella mobility is preserved in KA.

LEVEL OF EVIDENCE

Level IV.

Automated personalization of biomechanical knee model

PURPOSE

Patient-specific biomechanical models of the knee joint can effectively aid in understanding the reasons for pathologies and improve diagnostic methods and treatment procedures. For deeper research of knee diseases, the development of biomechanical models with appropriate configurations is essential. In this study, we mainly focus on the development of a personalized biomechanical model for the investigation of knee joint pathologies related to patellar motion using automated methods.

METHODS

This study presents a biomechanical model created for patellar motion pathologies research and some techniques for automating the generation of the biomechanical model. To generate geometric models of bones, the U-Net neural network was adapted for 3D input datasets. The method uses the same neural network for segmentation of femur, tibia, patella and fibula. The total size of the train/validation (75/25%) dataset is 18,183 3D volumes of size 512 × 512 × 4 voxels. The configuration of the biomechanical knee model proposed in the paper includes six degrees of freedom for the tibiofemoral and patellofemoral joints, lateral and medial contact surfaces for femur and tibia, and ligaments, representing, among other things, the medial and lateral stabilizers of the knee cap. The development of the personalized biomechanical model was carried out using the OpenSim software system. The automated model generation was implemented using OpenSim Python scripting commands.

RESULTS

The neural network for bones segmentation achieves mean DICE 0.9838. A biomechanical model for realistic simulation of patellar movement within the trochlear groove was proposed. Generation of personalized biomechanical models was automated.

CONCLUSIONS

In this paper, we have implemented a neural network for the segmentation of 3D CT scans of the knee joint to produce a biomechanical model for the study of knee cap motion pathologies. Most stages of the generation process have been automated and can be used to generate patient-specific models.

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

Background

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.

Purpose

To compare the characteristics of patellofemoral alignment between the static and dynamic knee extension position in patients with PFP and controls via 4-DCT.

Study Design

Cross-sectional study; Level of evidence, 3.

Methods

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.

Results

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.

Conclusion

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.

Medialized Dome and Anatomic Onlay Patella Designs in the Modern Posterior Stabilized Rotating Platform Total Knee Arthroplasty Demonstrate No Clinical or Radiological Differences at One Year

BACKGROUND

A successful outcome after total knee arthroplasty (TKA) includes the restoration of patellofemoral function. Modern patella component designs in TKA include a medialized dome and more recently, an anatomic design. There is a paucity of literature comparing these 2 implants.

METHODS

This prospective nonrandomized study examined 544 consecutive TKAs with patella resurfacing using a posterior-stabilized, rotating platform knee prothesis performed by a single surgeon. A medialized dome patella design was used in the first 323 cases and an anatomic design in the subsequent 221 cases. Patients were assessed preoperatively, at 4 weeks and 1-year post-TKA for Oxford Knee Score (OKS) (total, pain, and kneeling components) and range of movement (ROM). Radiolucent lines (RLLs), patellar tilts and displacements, as well as reoperations were assessed at 1-year post-TKA.

RESULTS

At 1-year post-TKA, both groups demonstrated similar improvements in ROM, OKS, pain, and kneeling scores, and had a similar incidence of fixed-flexion deformity (all P > .05). Radiographically, there was no clinically significant difference in the incidence of RLLs, patellar tilts, and displacements. The prevalence of reoperations (1.8 versus 3.2%, P = .526) was similar between the designs with no patella-related complications.

CONCLUSION

Both medialized dome and anatomic patella designs result in improved ROM and OKS with no patella-related complications. However, our study showed no differences between the designs at 1 year.

Development and Validation of a Novel In Vitro Joint Testing System for Reproduction of In Vivo Dynamic Muscle Force

In vitro biomechanical experiments utilizing cadaveric specimens are one of the most effective methods for rehearsing surgical procedures, testing implants, and guiding postoperative rehabilitation. Applying dynamic physiological muscle force to the specimens is a challenge to reconstructing the environment of bionic mechanics in vivo, which is often ignored in the in vitro experiment. The current work aims to establish a hardware platform and numerical computation methods to reproduce dynamic muscle forces that can be applied to mechanical testing on in vitro specimens. Dynamic muscle loading is simulated through numerical computation, and the inputs of the platform will be derived. Then, the accuracy and robustness of the platform will be evaluated through actual muscle loading tests in vitro. The tests were run on three muscles (gastrocnemius lateralis, the rectus femoris, and the semitendinosus) around the knee joint and the results showed that the platform can accurately reproduce the magnitude of muscle strength (errors range from -6.2% to 1.81%) and changing pattern (goodness-of-fit range coefficient ranges from 0.00 to 0.06) of target muscle forces. The robustness of the platform is mainly manifested in that the platform can still accurately reproduce muscle force after changing the hardware combination. Additionally, the standard deviation of repeated test results is very small (standard ranges of hardware combination 1: 0.34 N~2.79 N vs. hardware combination 2: 0.68 N~2.93 N). Thus, the platform can stably and accurately reproduce muscle forces in vitro, and it has great potential to be applied in the future musculoskeletal loading system.

What is the J-sign and why is it important?

PURPOSE OF REVIEW

Recurrent lateral patellofemoral instability is a complex condition that requires a thorough evaluation to optimize treatment. The J-sign test is classically part of the physical examination, but its significance and importance remain unclear. This review aims to describe how to perform the test and classify the observation as well as to analyze the most recent literature on its clinical applications.

RECENT FINDINGS

The J-sign test has been described as positive (present) or negative (absent), and classified using the quadrant method and the Donnell classification. Suboptimal inter-rater reliability has been shown for both classifications, making comparison between clinicians and studies challenging. The J-sign is most predominantly associated with patella alta, trochlear dysplasia, lateral force vector, and rotational abnormalities. A growing number of studies have shown a correlation between a positive J-sign and lower clinical outcome scores and higher rate of surgical failure.

SUMMARY

The J-sign is an important aspect of the physical examination in patients with recurrent lateral patellofemoral instability. Although there is no consensus on how to perform or classify the test, it can be used as a marker of severity of patellofemoral instability and is one of the tools available to guide the treatment plan.

The Patellostabilometer: A New Device for Quantification of Mediolateral Patella Displacement

Mediolateral patella displacement is of interest for diagnostics and clinically relevant research questions. Apart from manual testing, no standardized method is currently available. Proper quantification of patella mobility is necessary to better understand pathologies at the patellofemoral joint. Patella mobility was assessed in 25 healthy individuals using a Patellostabilometer, a new prototype instrument for quantification of the mediolateral patella displacement. The participants underwent measurements of the mediolateral displacement three times using the Patellostabilometer. A maximal force of 10 N was applied for patella movement. Additionally, leg length and circumference of the knee, upper- and lower-leg were measured. Lateral patella displacement of 18.27 ± 3.76 mm (range 15.85-20.64 mm, interquartile range (IQR) of 4.79) was measured. The medial patella displacement showed 24.47 ± 6.59 mm (range 19.29-29.76 mm, IQR of 10.47). The test-retest measurement error was 2.32 ± 1.76 mm (IQR of 2.38 mm), with five outliers. There was greater test-retest variability between the measurements of the medial displacement compared to the lateral one. The test-retest variability reached 7% of the patella displacement. Other parameters provided no significant correlations. Based on the natural patellofemoral mobility, a precise and clinically relevant quantification of patella mobility is allowed.

Fully automatic extraction of knee kinematics from dynamic CT imaging; normative tibiofemoral and patellofemoral kinematics of 100 healthy volunteers

BACKGROUND

Accurate assessment of knee kinematics is important in the diagnosis and quantification of knee disorders and to determine the effect of orthopaedic interventions. Despite previous studies showing the usefulness of dynamic imaging and providing valuable insights in knee kinematics, dynamic imaging is not widely used in clinics due to a variety of causes. In this study normative knee kinematics of 100 healthy subjects is established using a fully automatic workflow feasible for use in the clinic.

METHODS

One-hundred volunteers were recruited and a dynamic CT scan was made during a flexion extension movement. Image data was automatically segmented and dynamic and static images were superimposed using image registration. Coordinate systems for the femur, patella and tibia were automatically calculated as well as their dynamic position and orientation.

RESULTS

Dynamic CT scans weremade withan effective radiation dose of 0.08 mSv. The median tibial internal rotation was 4° and valgus rotation is 5° at full flexion. Femoral rollback of the lateral condyle was 7 mm versus 2 mm of the medial condyle. The median patella flexion reached 65% of tibiofemoral flexion and the median tilt and rotation were 5° and 0° at full flexion, respectively. The median mediolateral translation of the patella was 3 mm (medially) in the first 30° of flexion.

CONCLUSION

The current study presents TF and PF kinematic data of 97 healthy individuals, providing a unique dataset of normative knee kinematics. The short scanning time, simple motion and, automatic analysis make the methods presented suitable for daily clinical practice.

The Influence of Surgical Realignment Procedures on Dynamic Patellar Tracking: A Dynamic Magnetic Resonance Imaging-Controlled Feasibility Study

Persisting patellar maltracking following surgical realignment often remains unseen. The aim of this study was to analyze the effects of realignment procedures on patellofemoral kinematics in patients with patellofemoral instability (PFI) and patellofemoral maltracking (PM) by using dynamic magnetic resonance imaging (MRI). Patients planned for surgical patellar realignment due to PFI and a clinically and radiologically apparent PM between December 2019 and May 2022 were included. Patients without PM, limited range of motion, joint effusion, or concomitant injuries were excluded. Dynamic mediolateral translation (dMPT) and patella tilt (dPT) were measured preoperatively and three months postoperatively. In 24 patients (7 men, 17 women; mean age 23.0 years), 10 tibial tubercle transfers, 5 soft tissue patella tendon transfers, 6 trochleoplasties, 3 lateral lengthenings, 1 varizating distal femoral osteotomy (DFO), and 1 torsional DFO were performed. At final follow-up, dMPT (from 10.95 ± 5.93 mm to 4.89 ± 0.40 mm, p < 0.001) and dPT (from 14.50° ± 10.33° to 8.44° ± 7.46°, p = 0.026) were significantly improved. All static radiological parameters were corrected to physiological values. Surgical patellar realignment contributed to the significant improvement of patellofemoral kinematics, with an approximation to normal values. The postoperative application of dynamic MRI allowed for a quantification of the performed correction, allowing for a postoperative control of success.

Simultaneous Measurement of Patellofemoral Joint Kinematics and Contact Mechanics in Intact Knees: A Cadaveric Study

OBJECTIVE

Patellofemoral kinematics and contact mechanics are important measurements for the assessment of patellofemoral joint (PFJ) problems. Simultaneously measuring PFJ contact pressures and kinematics is a challenging task. The purpose of this study was to simultaneously measure the kinematics and mean/peak contact pressures in the PFJs of cadaveric knees.

METHODS

This was a comparative study performed on fresh cadaveric knees. The kinematic data was acquired for nine cadaveric knees using an optical tracking system. Data about the contact pressure and contact area in the PFJ was obtained at knee flexion angles of 0°, 30°, 60°, 90°, and 120° using a pressure sensor. Intraclass correlation coefficients (ICCs) and minimal detectable differences (MDDs) of six degrees of freedom (6 DOF) in the PFJs were calculated. ICCs and the MDDs of contact pressure, peak pressure, and contact area in the PFJs were also analyzed. We also compared the kinematics of the cadaveric knees before and after the insertion of the pressure sensor.

RESULTS

All ICC values of 6 DOF in the PFJs were found to be greater than or equal to 0.924. Regarding medial-lateral rotation, the patellar showed a simplified movement pattern that demonstrated progressive lateral rotation of 4.8° ± 3.4° at 120° of knee flexion. While for patellar tilting, the patella showed medial tilting that peaked at 7.2 ± 2.5° at 30° of knee flexion. Whereas no significant differences in PFJ kinematics were found between with and without the placement of the pressure sensor at all knee flexions (P > 0.05). Most of the ICC values for contact pressure, peak contact pressure, and contact area ranged from 0.8 to 0.9. The MDDs for rotational displacement were 0.9° and 0.6 mm for translational displacement. No statistical differences in patellar kinematics were found before and after the insertion of the pressure sensor.

CONCLUSIONS

The setup in the present study enables researchers to simultaneously and synchronously collect real-time PFJ kinematics and tibiofemoral joint (TFJ) biomechanical kinematic data with high reliability. The low MDDs enabled the researchers to obtain an accurate interpretation of the kinematic and contact mechanics measurement using the experimental setting used in the present study.

Inter-rater Reliability of the Classification of the J-Sign Is Inadequate Among Experts

OBJECTIVE

The purpose of this study was to determine the inter-rater and intra-rater reliability of the symmetry, classification, and underlying pathoanatomy associated with the J-sign in patients with recurrent lateral patellofemoral instability.

STUDY DESIGN

Blinded, inter-rater reliability study.

SETTING

N/A.

PARTICIPANTS

Thirty patellofemoral joint experts.

INTERVENTIONS

Thirty clinicians independently assessed 30 video recordings of patients with recurrent lateral patellofemoral instability performing the J-sign test.

MAIN OUTCOME MEASURES

Raters documented J-sign symmetry and graded it according to the quadrant and Donell classifications. Raters indicated the most significant underlying pathoanatomy and presence of sagittal plane maltracking. Intra-rater reliability was assessed by 4 raters repeating the assessments. Mean pairwise simple and/or weighted Cohen's kappa were performed to measure inter-rater and intra-rater reliability, as well as calculation of percent agreement.

RESULTS

J-sign symmetry demonstrated fair inter-rater reliability (k = 0.26), whereas intra-rater reliability was moderate (k = 0.48). Inter-rater reliability for the quadrant and Donell classifications indicated moderate agreement, k = 0.51 and k = 0.49, respectively, whereas intra-rater reliability was k = 0.79 and k = 0.72, indicating substantial agreement. Inter-rater reliability of the foremost underlying pathoanatomy produced only slight agreement (k = 0.20); however, intra-rater reliability was substantial (k = 0.68). Sagittal plane maltracking demonstrated slight inter-rater agreement (k = 0.23) but substantial intra-rater agreement (k = 0.64).

CONCLUSIONS

The symmetry, classification, and underlying pathoanatomy of the J-sign demonstrated fair to moderate inter-rater reliability and moderate to substantial intra-rater reliability among expert reviewers using video recordings of patients with recurrent lateral patellofemoral instability. These findings suggest individual raters have a consistent standard for assessing the J-sign, but that these standards are not reliable between assessors.

LEVEL OF EVIDENCE

III.

Dynamic versus static medial patellofemoral ligament reconstruction technique in the treatment of recurrent patellar dislocation: a randomized clinical trial protocol

BACKGROUND

The redislocation rate of conservatively treated patella instability is high. One of the leading surgical strategies is medial patellofemoral ligament reconstruction. Over-tensioning is one of the most challenging complications in static medial patellofemoral ligament reconstruction as the graft used for reconstruction is isometric and the anatomical MPFL is a mostly dynamic structure. As an alternative to established static reconstruction techniques, dynamic graft techniques have been introduced for stabilizing the patella with the aim of providing a more physiological reconstruction of the medial patellofemoral ligament. To date, data on clinical outcomes are scarce and on biomechanical outcomes of the dynamic MPFL reconstruction are lacking. Here, we present the protocol of a randomized clinical trial for comparing clinical and biomechanical outcomes of dynamic versus static medial patellofemoral ligament reconstruction.

METHODS

This study is a prospective, single blinded, randomized, multicenter, multimodal (clinical and biomechanical) clinical trial. Patients with recurrent patella dislocation requiring isolated MPFL reconstruction will be recruited and randomized to the dynamic or static reconstruction technique. Participants will be followed up for 2 years with a total of five follow-ups. Preoperative magnetic resonance imaging, upright radiographs, surgical reports and patient records will be evaluated, and clinical and functional outcomes will be measured. Patient-reported knee function and anterior knee pain as assessed with the Kujala score will serve as primary outcome. For biomechanical outcome, pre- and postoperative evaluations will be performed to assess isokinetic muscle strength, gait asymmetry, joint kinematics and kinetics, and timing of muscle activity.

DISCUSSION

The results of the study will clarify whether the reported surgery success for patella stabilization via dynamic MPFL reconstruction is due to muscle contraction or to the passive tenodesis effect combined with clinical outcome measures. With this study, we will provide much needed information on knee biomechanics after dynamic versus static MPFL reconstruction to provide evidence to support orthopedic surgeons in evidence-based decision-making in their quest for surgical techniques most favorable for their patients. Trial registration The study protocol was registered at clinicaltrials.gov (NCT04849130). Registered 19 April 2021, https://clinicaltrials.gov/ct2/show/NCT04849130 .

Lateral Patellar Dislocation: A Critical Review and Update of Evidence-Based Rehabilitation Practice Guidelines and Expected Outcomes

»

Nonoperative treatment of a lateral patellar dislocation produces favorable functional results, but as high as 35% of individuals experience recurrent dislocations.

»

Medial patellofemoral ligament reconstruction is an effective treatment to prevent recurrent dislocations and yield excellent outcomes with a high rate of return to sport.

»

Both nonoperative and postoperative rehabilitation should center on resolving pain and edema, restoring motion, and incorporating isolated and multijoint progressive strengthening exercises targeting the hip and knee.

»

Prior to return to sports, both functional and isolated knee strength measurements should be used to determine leg symmetry strength and to utilize patient-reported outcome measures to assess the patient's perceived physical abilities and patellofemoral joint stability.

Dynamic Mediolateral Patellar Translation Is a Sex- and Size-Independent Parameter of Adult Proximal Patellar Tracking Using Dynamic 3 Tesla Magnetic Resonance Imaging

PURPOSE

To provide normal values for physiological patellofemoral tracking in a representative group of healthy individuals, as well as sex differences, using real-time 3T-magnetic resonance imaging (MRI) and to test for the reliability of the presented technique.

METHODS

One hundred knees of healthy individuals with no history of patellofemoral symptoms were scanned with dynamic MRI sequences, during repetitive cycles of flexion (40°) and full extension. Within a 30-seconds time-frame, three simultaneous, transverse slices were acquired. Dynamic mediolateral patellar translation (dMPT) and dynamic patellar tilt (dPT) were measured on two occasions by two independent examiners. Common radiological parameters were measured using static MRI, and correlations were calculated.

RESULTS

100 knees (53 right, 47 left; age: 26.7 ± 4.4 years; BMI: 22.5 ± 3.1) of 57 individuals (27 females, 30 males) were included. Mean height was 170.1 ± 7.7 cm in women and 181.8 ± 6.4 cm in men. Average patella diameter was 37.9 ± 2.7 (95% CI 37.1-38.7) mm in women and 42.4 ± 3.2 (95% CI 41.5-43.3) mm in men. In females, the patellar diameters and intercondylar distances were significantly smaller than in males (P < .001). Radiological parameters for patellar maltracking were within the normal range. During the range of motion, mean dMPT was 1.7 ± 2.4 (95% CI .9-2.5) mm in females and 1.8 ± 2.7 (95% CI 1.1-2.6) mm in males (P = .766). Mean dPT was 1.3 ± 2.9° (95% CI .4-2.1°) in females and -0.2 ± 3.8° (95% CI -1.2-.9°) in males (P = .036). Neither dMPT nor dPT was correlated with height, BMI, or patellar diameter. Intercondylar distance correlated weakly with dPT (r = -.241; P = .041). Intra- and interrater reliability were excellent for dMPT and dPT.

CONCLUSION

Dynamic mediolateral patellar translation is a size- and sex-independent parameter for proximal patellar tracking. In healthy individuals without patellofemoral abnormalities normal dMPT proximal to the trochlea groove was 1.7 ± 2.5 (1.2-2.2) mm, independent of size or sex. Normal dPT showed a dependency on sex and was 1.3 ± 2.9 (.4-2.1)° in women and -0.2 ± 3.8 (-1.2-0.9)° in men.

LEVEL OF EVIDENCE

Level II, diagnostic study.

Influence of Menisci on Tibiofemoral Contact Mechanics in Human Knees: A Systematic Review

Purpose: Menisci transfer axial loads, while increasing the load-bearing tibiofemoral contact area and decreasing tibiofemoral contact pressure (CP). Numerous clinical and experimental studies agree that an increased CP is one predominant indicator for post-traumatic osteoarthritis (PTOA) of the knee joint. However, due to the immense variability in experimental test setups and wide range of treatment possibilities in meniscus surgery, it is difficult to objectively assess their impact on the CP determination, which is clearly crucial for knee joint health. Therefore, the aim of this systematic review is to investigate the influence of different meniscal injuries and their associated surgical treatments on the CP. Secondly, the influence of different test setups on CP measurements is assessed. On the basis of these results, we established the basis for recommendations for future investigations with the aim to determine CPs under different meniscal states. Methods: This review was conducted in accordance with the PRISMA guidelines. Studies were identified through a systematic literature search in Cochrane, PubMed and Web of Science databases. Literature was searched through pre-defined keywords and medical subject headings. Results: This review indicates a significant increase of up to 235% in peak CP when comparing healthy joints and intact menisci with impaired knee joints, injured or resected menisci. In addition, different test setups were indicated to have major influences on CP: The variety of test setups ranged from standard material testing machines, including customized setups via horizontal and vertical knee joint simulators, through to robotic systems. Differences in applied axial knee joint loads ranged from 0 N up to 2,700 N and resulted unsurprisingly in significantly different peak CPs of between 0.1 and 12.06 MPa. Conclusion: It was shown that untreated traumatic meniscal tears result in an increased CP. Surgical repair intervention were able to restore the CP comparable to the healthy, native condition. Test setup differences and particularly axial joint loading variability also led to major CP differences. In conclusion, when focusing on CP measurements in the knee joint, transparent and traceable in vitro testing conditions are essential to allow researchers to make a direct comparison between future biomechanical investigations.

[When nothing else works: patellofemoral joint arthroplasty]

Patellofemoral joint replacement is the best treatment option available for isolated patellofemoral arthritis. Especially young patients should be operated on with bone-sparing techniques that also preserve the soft tissues, since these patients are very likely to be revised at some point in their lifetime. Correct patient selection is important for the success of surgery and should include a meticulous clinical examination and imaging. Special attention should be paid to additional pathologies that may also need to be addressed. For the trochlea, there are two different options for treatment with the inlay and onlay system. The retropatellar surface should be replaced. Patellofemoral joint replacement is still rarely performed, so treatment in specialised centres is recommended. National joint registry data show high revision rates, while data from centres show promising results.

Clinical outcomes and predictive factors for failure with MPFL reconstruction combined with tibial tubercle osteotomy and lateral retinacular release for recurrent patellar instability

BACKGROUND

Medial patellofemoral ligament (MPFL) reconstruction combined with tibial tubercle osteotomy (TTO) and lateral retinacular release (LRR) is one of the main treatment methods for patellar instability. So far, few studies have evaluated the clinical effectiveness and assessed potential risk factors for recurrent patellar instability.

PURPOSE

To report the clinical outcomes of MPFL reconstruction combined with TTO and LRR at least three years after operation and to identify potential risk factors for recurrent patellar instability.

METHODS

A retrospective analysis of medical records for patients treated with MPFL, TTO and LRR from 2013 to 2017 was performed. Preoperative assessment for imaging examination included trochlear dysplasia according to Dejour classification, patella alta with the Caton-Deschamps index (CDI), tibial tubercle-trochlear groove distance. Postoperative assessment for knee function included Kujala, IKDC and Tegner scores. Failure rate which was defined by a postoperative dislocation was also reported.

RESULTS

A total of 108 knees in 98 patients were included in the study. The mean age at operation was 19.2 ± 6.1 years (range, 13-40 years), and the mean follow-up was 61.3 ± 15.4 months (range, 36-92 months). All patients included had trochlear dysplasia (A, 24%; B, 17%; C, 35%; D, 24%), and 67% had patellar alta. The mean postoperative scores of Tegner, Kujala and IKDC were 5.3 ± 1.3 (2-8), 90.5 ± 15.5 (24-100) and 72.7 ± 12.1 (26-86). Postoperative dislocation happened in 6 patients (5.6%). Female gender was a risk factor for lower IKDC (70.7 vs 78.1, P = 0.006), Tegner (5.1 vs 6.0, P = 0.006) and Kujala (88.2 vs 96.6, P = 0.008). Age (p = 0.011) and trochlear dysplasia (p = 0.016) were considered to be two failure factors for MPFL combined with TTO and LRR.

CONCLUSION

As a surgical method, MPFL combined with TTO and LRR would be a reliable choice with a low failure rate (5.6%). Female gender was a risk factor for worse postoperative outcomes. Preoperative failure risk factors in this study were age and trochlear dysplasia.

LEVEL OF EVIDENCE

Level IV; Case series.

Can Computer-Assisted Total Knee Arthroplasty Support the Prediction of Postoperative Three-Dimensional Kinematics of the Tibiofemoral and Patellofemoral Joints at the Replaced Knee?

The aim of this study was to analyze the extent to which postoperative patellofemoral joint (PFJ) kinematics assessed at 6-month follow-up after total knee arthroplasty (TKA) mimics the intraoperative kinematics after final component implantation. The study hypothesis, already proved in terms of tibiofemoral joint (TFJ) kinematics, is that the intraoperative assessment of PFJ kinematics after component implantation is also capable of predicting postoperative knee kinematics during activities of daily living. Twenty patients selected for TKA with patellar resurfacing were implanted using surgical navigation, including patellar component positioning via a novel computer-assisted procedure. This allowed for intraoperative TFJ and PFJ kinematic assessment after final component implantation. At 6-month follow-up, all patients were contacted for follow-up control; in addition to clinical examination, this implied postoperative kinematics assessments by three-dimensional video fluoroscopy of the replaced knee during standard activities of daily living. Several traditional PFJ, as well as TFJ, rotations and translations were calculated intra- and postoperatively and then statistically compared. Good postoperative replication of the intraoperative measurements was observed for most of PFJ variables analyzed, as well as those for TFJ. Relevant statistical analysis also supported the significant consistency between the intra- and postoperative measurements. Pertaining to the present findings on a statistical basis, intraoperative measurements performed at both TFJ and PFJ kinematics using a surgical navigation system under passive conditions, are predictive of the overall knee kinematics experienced at postoperative follow-ups by the same replaced knees in typical activities of daily living.

Common Physical Examination Tests for Patellofemoral Instability Demonstrate Weak Inter-Rater Reliability

Purpose

The purpose of this study was to assess the inter-rater reliability of 3 common physical examination assessments, the Q-angle, J-sign, and apprehension test, used to evaluate patients presenting with recurrent lateral patellofemoral instability.

Methods

A consecutive sample of 38 subjects with recurrent lateral patellofemoral instability in 2013 were included in this reliability study. Two orthopaedic surgeons performed the physical examination maneuvers blinded to each other. The physical examination tests were performed bilaterally and included the Q angle, the J-sign, and the apprehension test. To measure the inter-rater reliability, an intraclass correlation coefficient (ICC 2,κ) was used for both legs independently for Q-angle measurements. A Cohen’s kappa was used to measure the inter-rater reliability for the J-sign and the apprehension test.

Results

The measurement of the Q-angle demonstrated poor reliability (ICC 2,κ 0.18-0.44). The assessment of the J-sign demonstrated fair to moderate reliability (κ = 0.31 – 0.41), and the evaluation of apprehension demonstrated fair to substantial reliability (κ = 0.30 – 0.65). All 3 clinical tests demonstrated substantial variability comparing the reliability on the right and left limbs. Assessment of the quality of apprehension demonstrated good agreement between the examiners.

Conclusions

In this study of patients with recurrent lateral patellofemoral instability the common physical examination tests, Q-angle, J-sign, and apprehension demonstrated weak inter-rater reliability. These results indicate that these tests are not reliable for communication between health care practitioners or as evaluations for clinical research.

Level of Evidence

Level IV, therapeutic case series.

Posterior Tibial Loading Results in Significant Increase of Peak Contact Pressure in the Patellofemoral Joint During Anterior Cruciate Ligament Reconstruction: A Cadaveric Study

BACKGROUND

Inappropriate posterior tibial loading and initial graft tension during anterior cruciate ligament (ACL) reconstruction may cause altered patellofemoral joint (PFJ) contact mechanics, potentially resulting in pain and joint degeneration.

HYPOTHESIS

PFJ contact pressure would increase with the increases in posterior tibial loading and graft tension during ACL reconstruction.

STUDY DESIGN

Controlled laboratory study.

METHODS

Nine fresh-frozen, nonpaired human cadaveric knees were tested in a customized jig from 0° to 120° of knee flexion. First, the knee was tested in the ACL-intact state. Second, reconstruction of the ACLs using different posterior tibial loadings and graft tensions were performed. The posterior tibial loading was evaluated at 2 levels: 33.5 and 67 N. Graft tension was assessed at 3 levels: low tension (20 N), medium tension (60 N), and high tension (80 N). Maximum values of peak contact pressure in the medial and lateral patellar facets were compared between ACL-intact and ACL-reconstructed knees. The PFJ kinematics between ACL-intact knees and ACL-reconstructed knees were compared during knee flexion at 30°, 60°, 90°, and 120°.

RESULTS

Reconstruction of ACLs with both low and high posterior tibial loading resulted in significant increases of peak contact pressure in the medial (range of differences, 0.46-0.92 MPa; P < .05) and lateral (range of differences, 0.51-0.83 MPa; P < .05) PFJ compared with the ACL-intact condition. However, no significant differences in PFJ kinematics were identified between ACL-reconstructed knees and ACL-intact knees. In ACL-reconstructed knees, it was found that a high posterior tibial loading resulted in high peak contact pressure on the medial patellar side (range of differences, 0.37-0.46 MPa; P < .05). No significant difference in peak contact pressure was observed among the differing graft tensions.

CONCLUSION

In this cadaveric model, ACL reconstruction resulted in significant increases of peak contact pressure in the PFJ facet when compared with the ACL-intact condition. A high posterior tibial loading can lead to high medial PFJ peak contact pressure. Graft tension was found to not significantly affect PFJ contact pressure during ACL reconstruction.

CLINICAL RELEVANCE

An excessive posterior tibial loading during ACL reconstruction resulted in increased PFJ contact pressures at time of surgery. These data suggest that a low posterior tibial loading might be preferred during ACL reconstruction surgery to reduce the PFJ contact pressure close to that of the ACL-intact condition.

Relationship between patellofemoral finite helical axis and femoral trans-epicondylar axis using a static magnetic resonance-based methodology

Background

To manage patellofemoral joint disorders, a complete understanding of the in vivo patellofemoral kinematics is critical. However, as one of the parameters of joint kinematics, the location and orientation of the patellofemoral finite helical axis (FHA) remains unclear. The purpose of this study is to quantify the location and orientation of the patellar FHA, both in vivo and non-invasively at various flexion angles, and evaluate the relationship of the FHA and the trans-epicondylar axis (TEA).

Methods

The magnetic resonance (MR) images of 18 unilateral knees were collected at full extension, 30°, 60°, 90°, and maximum angle of knee flexion. Three-dimensional models of the knee joint at different flexion angles were created using the MR images, and then used to calculate the patellar tracking and FHA with a spline interpolation algorithm. By using a coordinate system based on the TEA, the FHA tracking was quantified. Six parameters concerning the location and orientation of the patellar FHA were analysed.

Results

The average patellar FHA drew an L-shaped tracking on the midsagittal plane moving from the posteroinferior to the anterosuperior side of the TEA with knee flexion. Before 90° flexion, the patellar rotational radius decreased slightly, with an average value of 5.65 ± 1.09 cm. During 20° to 90° knee flexion, the average angle between the patellar FHA and the TEA was approximately 10° and that between the FHA and the coronal plane was maintained at about 0°, while that between the FHA and the level plane fluctuated between − 10° and 10°.

Conclusions

This study quantitatively reported the continuous location and direction of the patellar FHA during knee flexion. The patellar FHA was close to but not coincident with the femoral TEA both in location and orientation, and the patellar rotational radius decreased slightly with knee flexion. These findings could provide a clear direction for further studies on the difference in patellofemoral FHA among various types of patellofemoral disorders, and provide a foundation for the application of FHA in surgical evaluation, preoperative planning and prosthesis design, thereby assisting in the diagnosis and treatment of patellofemoral disorders.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13018-021-02328-2.

[Patellar dislocation : Causes and treatment]

The causes of patellofemoral instability (PFI) are complex. In accordance with the current literature a classification was developed which clearly weights all entities and derives diagnostic and therapeutic consequences. It considers patellar instability and patellar maltracking or the complete loss of patellar tracking and differentiates into 5 types. Type 1: patellar dislocation without maltracking or instability with a low risk of redislocation. Type 2: high risk of redislocation, no maltracking. Type 3: instability and maltracking; reasons for maltracking are a) soft tissue contracture, b) patella alta, c) pathological tibial tuberosity trochlear groove (TTTG) distance, c) valgus deformities and e) torsional deformities. Type 4: massively unstable floating patella, which is based on a high-grade trochlear dysplasia. Type 5: maltracking without instability.

Development of an innovative measurement method for patellar tracking disorder

In this study, we investigated whether the measurement of patellar tracking can be used as a diagnostic parameter of patellofemoral joint disease. Patellar tracking is defined as the movement of the patella in relation to the femorotibial joint within the full range of flexion and extension of the knee joint. The PubMed, EMBASE, Medline, PsychINFO, and AMED databases were used to find relevant articles. Analyzed were the patellar tracking coordinate system and the measurement objects, precision, methods used in those studies, as well as the results obtained. Origin points for coordinate systems varied across the studies. The research object and methods of patellar tracking varied in the studies. Most studies focused on a static description of the internal and external displacement and the internal and external inclination. The in vivo, noninvasive, and six degrees of freedom evaluation of patellar tracking reflect patellar motion more comprehensively, though each of these methods does so in different ways. Dynamic and quantitative evaluation of patellar tracking is still lacking in clinical work. Accurate and quantitative patellar tracking measurement could provide clinicians with a comprehensive evaluation of the stability of the knee joint.

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.

Computational framework for population-based evaluation of TKR-implanted patellofemoral joint mechanics

Differences in patient anatomy are known to influence joint mechanics. Accordingly, intersubject anatomical variation is an important consideration when assessing the design of joint replacement implants. The objective of this study was to develop a computational workflow to perform population-based evaluations of total knee replacement implant mechanics considering variation in patient anatomy and to assess the potential for an efficient sampling strategy to support design phase screening analyses. The approach generated virtual subject anatomies using a statistical shape model of the knee and performed virtual implantation to size and align the implants. A finite-element analysis simulated a deep knee bend activity and predicted patellofemoral (PF) mechanics. The study predicted bounds of performance for kinematics and contact mechanics and investigated relationships between patient factors and outputs. For example, the patella was less flexed throughout the deep knee bend activity for patients with an alta patellar alignment. The results also showed the PF range of motions in AP and ML were generally larger with increasing femoral component size. Comparison of the 10-90% bounds between sampling strategies agreed reasonably, suggesting that Latin Hypercube sampling can be used for initial screening evaluations and followed up by more intensive Monte Carlo simulation for refined designs. The platform demonstrated a functional workflow to consider variation in joint anatomy to support robust implant design.

Sagittal patellar flexion angle: a novel clinically validated patellar height measurement reflecting patellofemoral kinematics useful throughout knee flexion

PURPOSE

Patellar height measurements on lateral radiographs are dependent on knee flexion which makes standardisation of measurements difficult. This study described a plain radiographic measurement of patellar sagittal height which reflects patellofemoral joint kinematics and can be used at all degrees of flexion.

METHODS

The study had two parts. Part one involved 44 normal subjects to define equations for expected patellar position based on the knee flexion angles for three new patellar height measurements. A mixed model regression with random effect for individual was used to define linear and polynomial equations for expected patellar position relating to three novel measurements of patella height: (1) patellar progression angle (trochlea), (2) patellar progression angle (condyle) and (3) sagittal patellar flexion. Part two was retrospective and involved applying these measurements to a surgical cohort to identify differences between expected and measured patellar position pre- and post-operatively.

RESULTS

All three measurements provided insight into patellofemoral kinematics. Sagittal patellar flexion was the most useful with the least residual error, was the most reliable, and demonstrated the greatest detection clinically.

CONCLUSIONS

Clinically applied radiographic measurements have been described for patellar height which reflect the sagittal motion of the patella and can be used regardless of the degree of flexion in which the radiograph was taken. The expected sagittal patellar flexion linear equation should be used to calculate expected patellar height.

LEVEL OF EVIDENCE

IV.

When is Trochleoplasty a Rational Addition?

Trochlear dysplasia has been recognized as a dominant anatomic risk factor in patients with recurrent patellar instability. Sulcus-deepening trochleoplasty is a very effective and powerful procedure for correcting trochlear dysplasia and, specifically, eliminating the supratrochlear spur. However, it must be emphasized that trochleoplasty is not appropriate for patients with mild trochlear dysplasia or those without a large supratrochlear spur or bump. We discuss the characteristics and classification of trochlear dysplasia and discuss specific indications for sulcusdeepening trochleoplasty.

The Effect of Patellar Tendon Release on the Characteristics of Patellofemoral Joint Squat Movement: A Simulation Analysis

Objectives: This paper studies the patellar tendon release’s effect on the movement characteristics of the artificial patellofemoral joint squat to provide reference data for knee joint surgery. Methods: Firstly, the dynamic finite element model of the human knee joint under squatting was established. Secondly, in the above no-release models, the release of 30% of the attachment area at the upper end, the lower end, or both ends of the patellar tendon were conducted, respectively. Then the simulations of all above four models were conducted. Finally, the results of the simulation were compared and analyzed. Results: The simulation results show that, after releasing the patellar tendon (compared with the no-release simulation’s results), the relative flexion, medial-lateral rotation, medial-lateral tilt, and superior-inferior shift of the patella relative to the femur increased; the medial-lateral shift and anterior-posterior shift of the patella relative to the femur decreased. Conclusion: In this paper, the maximum flexion angle of the patella increased after the patellar tendon being released (compared with the no-release model), which indicated that the mobility of knee joint was improved after the patellar tendon release. The simulation data in this paper can provide technical reference for total knee arthroplasty.

Patellar calcar: morphometric analysis by knee magnetic resonance imaging and three-dimensional reconstruction software-assisted

PURPOSE

Patellar calcar corresponds to a greater trabecular bone density area in the patella lateral facet, whose morphometry is uncertain. This study aimed to describe patellar calcar morphometry by knee MRI and develop a 3D reconstruction software-assisted.

MATERIALS AND METHODS

Consecutive adult patients, submitted to knee MRI, between 2014 and 2017, were entered in IMPAX software. Exclusion criteria are history of patellar surgical intervention, trauma, chondromalacia, bone edema or bipartite patella. All MRI images were retrospectively reviewed by three readers. MRI patellar calcar measurements are height, width, thickness and posterior distance. 3D model protocol reconstruction: 3D Slicer software was used to design a preliminary model for each patient, and then all were automatically merged into one, which was finalized using the software segmentation tools. For 3D patellar calcar location, the transpolar axis was designed.

RESULTS

250 MRI were analyzed, patellar calcar was present in 208 (83.2%); 101 men and 107 women. Mean age was 44.3 ± 15.6 years.

MEASUREMENTS

height 13.84 ± 2.42 mm (male: 14.50 ± 2.42; female: 13.21 ± 2.26) (p < 0.0001), width 12.21 ± 2.26 mm (male 13.14 ± 2.22; female 11.33 ± 1.93) (p < 0.0001). No statistically significant difference of thickness 0.56 ± 0.22 mm (male: 0.56 ± 0.25; female: 0.56 ± 0.20) and posterior distance 2.37 ± 0.80 mm (male: 2.46 ± 0.89; female: 2.29 ± 0.69) between genders was found. 3D model results: transpolar axis went through the patellar calcar in all the cases.

CONCLUSIONS

This study shows in a 3D model reconstruction, what was previously described in the literature, determining for the first time the patellar calcar morphometry in the knee MRI and identifying it as a regular finding in this imaging test.

Length of stay after introduction of a new total knee arthroplasty (TKA)-results of a German retrospective database analysis

BACKGROUND

Although total knee arthroplasty (TKA) procedures are increasing, patient satisfaction is still inferior compared to total hip arthroplasty. The ATTUNE^® Knee System was designed to reduce pain and improve function, leading to greater patient satisfaction and decreased resource utilization in TKA. The objective of this study was to compare length of stay (LOS) of TKA with ATTUNE knee versus LCS^® knee implants.

METHODS

A retrospective chart review analysis in a German center was conducted between 2008 and 2016. All patients without prior ipsilateral knee operation, treated with a cemented LCS or ATTUNE knee were included. Endpoints captured included gender, age, availability of home support, prior contralateral TKA, ASA grade and LOS. Statistical analyses included chi-squared test for differences in patient demographics and Welch two-sample t-test for difference in LOS.

RESULTS

Mean LOS in the ATTUNE Knee group (N=85) was 8.3 days (SD: 1.79) compared to 10.4 days (SD: 1.91) in the LCS knee group (N=85). No significant differences in gender, age, availability of home support, prior contralateral TKA, or ASA grade between both cohorts were observed. The 2.1 days reduction was statistically significant (P<0.001; 95%CI: 2.7-1.6). A sensitivity analysis outlined the impact of the study duration: even when assuming that 1.3 days reduction resulted from the observed national LOS decrease, the remaining 0.8 reduction in days LOS reduction was still significant (P<0.01).

CONCLUSION

When comparing two cohorts with similar sociodemographic and medical factors, LOS of ATTUNE knee patients was 2.1 days shorter than patients treated with the LCS knee.

Evaluation of predicted patellofemoral joint kinematics with a moving-axis joint model

The main objectives of this study were to expand the moving-axis joint model concept to the patellofemoral joint and evaluate the patellar motion against experimental patellofemoral kinematics. The experimental data was obtained through 2D-to-3D bone reconstruction of EOS images and segmented MRI data utilizing an iterative closest point optimization technique. Six knee model variations were developed using the AnyBody Modeling System and subject-specific bone geometries. These models consisted of various combinations of tibiofemoral (hinge, moving-axis, and interpolated) and patellofemoral (hinge and moving-axis) joint types. The newly introduced interpolated tibiofemoral joint is calibrated from the five EOS quasi-static lunge positions. The patellofemoral axis of the hinge model was defined by performing surface fits to the patellofemoral contact area; and the moving-axis model was defined based upon the position of the patellofemoral joint at 0° and 90° tibiofemoral-flexion. In between these angles, the patellofemoral axis moved linearly as a function of tibiofemoral-flexion, while outside these angles, the axis remained fixed. When using a moving-axis tibiofemoral joint, a hinge patellofemoral joint offers (-5.12 ± 1.23 mm, 5.81 ± 0.97 mm, 14.98 ± 2.30°, -4.35 ± 1.95°) mean differences (compared to EOS) while a moving-axis patellofemoral model provides (-2.69 ± 1.04 mm, 1.13 ± 0.80 mm, 12.63 ± 2.03°, 1.74 ± 1.46°) in terms of lateral-shift, superior translation, patellofemoral-flexion, and patellar-rotation, respectively. Furthermore, the model predictive capabilities increased as a direct result of adding more calibrated positions to the tibiofemoral model (hinge-1, moving-axis-2, and interpolated-5). Overall, a novel subject-specific moving-axis patellofemoral model has been established; that produces realistic patellar motion and is computationally fast enough for clinical applications.

No difference in joint awareness after TKA: a matched-pair analysis of a classic implant and its evolutional design

PURPOSE

Total knee arthroplasty (TKA) designs continuously evolve with the aim of improving patient outcomes. The purpose of the current study was to compare clinical and patient-reported outcome (PRO) results of a new TKA implant to its predecessor. The hypothesis of this study was that joint awareness and range of motion (ROM) of the newer design would be better than the classic design.

METHODS

One hundred patients undergoing TKA using the newer design (Attune^®) were matched by age and gender to 200 patients with the classic design (LCS^®). All patients underwent computer-navigated (Vector Vision, Brain-Lab, Germany) primary TKA by the same surgeon using the same technique. Data (FJS-12, WOMAC and ROM) were collected preoperatively and at 12 months follow-up at our implant registry.

RESULTS

Compared to preoperative scores, FJS-12, WOMAC and ROM improved significantly at 12 months follow-up. In the Attune group, mean FJS-12 and WOMAC at follow-up were 67.6 (SD 27.8) and 14.8 (SD 14.9) respectively, compared to 70.8 (SD 33.8) and 15 (SD 17.9) in the LCS group. Mean postoperative ROM was similar in both groups (Attune 120°, range 90°-140°, SD 10.4 and LCS 120°, range 85°-140°, SD 10.3).

CONCLUSION

The newer TKA and the predecessor design achieved comparable joint awareness, WOMAC scores and ROM at 1-year follow-up. The benefits expected of the newer design could not be observed in early clinical and PROs. The clinical relevance of this study is that it questions the importance of implant design as the single most important factor for patient outcomes.

LEVEL OF EVIDENCE

III.

Research Methods and Progress of Patellofemoral Joint Kinematics: A Review

Patellofemoral pain syndrome has a high morbidity, and its pathology is closely associated with patellofemoral joint kinematics. A series of in vivo and in vitro studies have been conducted to explore patellofemoral kinematics, and the findings are relevant to the diagnosis, classification, and management of patellofemoral diseases and even the whole knee joint. However, no definite conclusion on normal patellofemoral kinematics has been established. In this study, the measurement methodologies of patellofemoral kinematics (including data collection methods, loading conditions, and coordinate system) as well as their advantages and limitations were reviewed. Motion characteristics of the patella were analyzed. During knee flexion, the patellar flexion angle lagged by 30–40% compared to the tibiofemoral joint flexion. The patella tilts, rotates, and shifts medially in the initial stage of knee flexion and subsequently tilts, rotates, and shifts laterally. The finite patellar helical axis fluctuates near the femoral transepicondylar axis or posterior condylar axis. Moreover, factors affecting kinematics, such as morphology of the trochlear groove, soft tissue balance, and tibiofemoral motion, were analyzed. At the initial period of flexion, soft tissues play a vital role in adjusting patellar tracking, and during further flexion, the status of the patella is determined by the morphology of the trochlear groove and patellar facet. Our findings could increase our understanding of patellofemoral kinematics and can help to guide the operation plan for patients with patellofemoral pain syndrome.

Patellofemoral kinematic characteristics in anterior cruciate ligament deficiency and reconstruction

Background

It is very important to dynamically evaluate the functional outcome in the knee after anterior cruciate ligament (ACL) reconstruction under physiological weight bearing. The objective of the current study is that we would like to compare the patellofemoral joint kinematics in three ACL status: ACL intact, ACL deficiency, ACL reconstruction.

Methods

Twenty patients with unilateral ACL deficient knees were recruited as preoperative group. Six months after ACL reconstruction, these ten subjects were included as postoperative subjects. Ten normal subjects with healthy knees as the control group. Each subject was asked to walk up a custom set of stairs and a single-plane fluoroscopic imaging system was used to determine the 6DOF kinematics of the injured knees, ACL reconstructed knees, and intact knees.

Results

ACL deficient knees showed reduced patellar flexion angle and reduced distal patellar translation during knee flexion. ACL reconstructed knees showed abnormal patellofemoral joint kinematics compared to ACL intact and ACL deficient knees, exhibiting increased patellar external rotation, lateral tilt, lateral translation during knee flexion.

Conclusion

These findings imply that some alterations persist after ACL deficiency and ACL reconstruction. These abnormal changes will be the onset of degeneration in patellofemoral joint even if the ACL is reconstructed in a way that restores the clinical anteroposterior stability of the knee. Some biomechanical changes should be made to improve the outcome of intervention especially in surgical treatment like ACL reconstruction.

Can stretch sensors measure knee range of motion in healthy adults?

Study aim: There are currently limited methods available to access dynamic knee range of motion (ROM) during free-living activities. This type of method would be valuable for monitoring and progressing knee rehabilitation. Therefore, the aim of this study was to evaluate the functioning of stretch sensors for the measurement of knee ROM and to assess the level of the measurement error. Material and methods: Nine healthy participants were included in the study. Three stretch sensors (StretchSense™, Auckland, NZ) were attached on the participants’ right knees by Kinesiotape®. A Cybex dynamometer was used to standardise movement speed of the knee joint. Data was recorded through the StretchSense™ BLE application. Knee angles were obtained from the video clips recorded during the testing and were analysed by MaxTraq® 2D motion analysis software. The knee angles were then synchronised with the sensor capacitance through R programme. Results: Seven out of the nine participants presented with high coefficient of determination (R2) (>0.98) and low root mean square error (RMSE) (<5°) between the sensor capacitance and knee angle. Two participants did not confirm good relationship between capacitance and knee angle as they presented high RMSE (>5°). The equations generated from these 7 participants’ data were used individually to predict knee angles. Conclusions: The stretch sensors can be used to measure knee ROM in healthy adults during a passive, non-weight-bearing movement with a clinically acceptable level of error. Further research is needed to establish the validity and reliability of the methodology under different conditions before considered within a clinical setting.

Relationship between patellar mobility and patellofemoral joint cartilage degeneration after anterior cruciate ligament reconstruction

Patellofemoral cartilage degeneration is a potential complication of anterior cruciate ligament reconstruction (ACLR) surgery. Hypomobility of the patella in the coronal plane is often observed after ACLR. Few studies, however, have examined the relationship between cartilage degeneration in the patellofemoral joint and mobility after ACLR. The present study investigated 1) the coronal mobility of the patella after ACLR, 2) the relationship between patellar mobility and cartilage degeneration of the patellofemoral joint, and 3) the relationship between patellar mobility and knee joint function after ACLR. Forty patients who underwent medial hamstring-based ACLR participated in the study. Lateral and medial patellar displacements were assessed with a modified patellofemoral arthrometer, and the absolute values of the displacements were normalized to patient height. The International Cartilage Repair Society (ICRS) cartilage injury classification of the patellar and femoral (trochlear) surfaces, and the Lysholm Knee Scoring Scale were used to evaluate knee function. Lateral and medial patellar displacements were reduced compared with the non-operated knee at the second-look arthroscopy and bone staple extraction operation (second operation; 24.4 ± 7.9 months after ACLR, P<0.01). The ICRS grades of the patellofemoral joint (patella and trochlea) were significantly worse than those pre-ACLR. Neither lateral nor medial patellar mobility, however, were significantly correlated with the ICRS grade or the Lysholm score. Although patellar mobility at approximately 2 years after ACLR was decreased compared to the non-operated knee, small displacement of the patella was not related to cartilage degeneration or knee joint function at the time of the second operation.

Patellar tracking should be taken into account when measuring radiographic parameters for recurrent patellar instability

PURPOSE

To date, many radiographic parameters on patellar instability have their measurements taken statically, and have not been studied in various degrees of flexion according to the patellar tracking. There are also limited data regarding the use of these parameters in predicting recurrent patellar dislocation. The current study aims to review the radiographic parameters of the patellofemoral joint in different degrees of knee flexion and to correlate them with the presence of recurrent instability.

METHODS

A 10-year retrospective study was conducted on all patients who had computed tomography patellar-tracking scan done for patellar instability when aged 18 years or younger. The computed tomography patellar-tracking scans were performed with the knee in extension, 10° flexion, and 20° flexion. The axial radiographic parameters were evaluated at the patellar equator, roman arch, and distal patellar pole. Sagittal and coronal parameters were noted. Radiographic parameters were then correlated with recurrent patellar instability.

RESULTS

The femoral sulcus angle and trochlear groove depth at the distal patellar pole in 10° knee flexion (p value 0.04 and 0.03, respectively) and patellar equator in 20° knee flexion (p value 0.02 and 0.03, respectively) had the most significant clinical correlations with recurrent instability on multivariate analysis. Other radiographic parameters found to have significant clinical correlation on univariate analysis include the patellar tilt angle, congruence angle, femoral sulcus angle, trochlear groove depth, and Wiberg's classification.

CONCLUSIONS

As per the knee dynamics, axial radiographic parameters had the most significant correlation with recurrent patellar instability when measured at the distal patellar pole in 10° knee flexion and at the patellar equator in 20° knee flexion. Future axial radiographic evaluation of patellofemoral instability should then be performed at these degrees of knee flexion and axial cuts. Trochlear dysplasia, as measured by the femoral sulcus angle and trochlear groove depth, was the most significant predictor of recurrent patellar instability in the skeletally immature. Wiberg's classification was also a novel factor found to have clinical correlation with patellofemoral instability.

LEVEL OF EVIDENCE

III.

Patella tracking calculation from patellofemoral positions at finite angles of knee flexion

Patellofemoral (PF) pain is a common knee disease. Patella tracking has a significant correlation with PF pain, therefore it could be used as an index for diagnosis and treatment evaluation. Previous research has proposed a method for measuring in vivo patella tracking by means of an interpolation algorithm. The present study aimed to quantify the effect of the interpolation parameters on the accuracy of the patella tracking with a motion capture experiment. The precise patella tracking of 5 knee specimens was collected and compared with the interpolated tracking. The results showed that the total interpolation error decreased to 2 mm with the number of interpolation angles increasing to 6. The number of interpolation reference points had a slight influence on the accuracy. The findings consolidated the feasibility of using interpolation to measure the in vivo patella tracking, and can help to optimize the accuracy and efficiency of the methodology.

In vivo comparison of medialized dome and anatomic patellofemoral geometries using subject-specific computational modeling

Successful outcome following total knee arthroplasty (TKA) with patella resurfacing is partly determined by the restoration of patellofemoral (PF) function and recovery of the quadriceps mechanism. The current study compared two patellar TKA geometries (medialized dome and anatomic) to determine their impact on PF mechanics and quadriceps function. In-vivo, subject-specific patellar mechanics were evaluated using a sequential experimental and modeling approach. First, stereo radiography, marker-based motion capture, and force plate data were collected for TKA patients (10 dome, 10 anatomic) performing a knee extension and lunge. Second, subject-specific, whole-body, musculoskeletal models, including 6 degrees-of-freedom (DOF) knee joint kinematics, were created for each subject and activity to predict quadriceps forces. Last, finite element models of each subject and activity were created to predict PF kinematics, patellar loading, moment arm, and patellar tendon angle. Differences in mechanics between dome and anatomic patients were highlighted during load-bearing (lunge) activity. Anatomic subjects demonstrated greater PF flexion angles (avg. 11 ± 3°) compared to dome subjects during lunge. Similar to the natural knee, contact locations on the patella migrated inferior to superior as the knee flexed in anatomic subjects, but remained relatively superior in dome subjects. Differences in kinematics and contact location likely contributed to altered mechanics with anatomic subjects presenting greater load transfer from the quadriceps to the patellar tendon in deep flexion (>75°), and dome subjects demonstrating larger contact forces during lunge. Although there was substantial patient variability, evaluations of PF mechanics suggested improved quadriceps function and more natural kinematics in the anatomic design. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1910-1918, 2018.

Impact of Simulated Knee Injuries on the Patellofemoral and Tibiofemoral Kinematics Investigated with an Electromagnetic Tracking Approach: A Cadaver Study

Purpose

The purpose of this study was to evaluate the approach of using an electromagnetic tracking (EMT) system for measuring the effects of stepwise, simulated knee injuries on patellofemoral (PF) and tibiofemoral (TF) kinematics.

Methods

Three cadaver knees were placed in a motion rig. EMT sensors were mounted on the patella, the medial/lateral femoral epicondyles, the tibial condyle, and the tibial tuberosity (TT). After determining the motion of an intact knee, three injuries were simulated and the resulting bony motion was tracked.

Results

Starting with the intact knee fully extended (0° flexion) and bending it to approximately 20°, the patella shifted slightly in the medial direction. Then, while bending the knee to the flexed position (90° flexion), the patella shifted progressively more laterally. After transecting the anterior cruciate ligament (ACL), the base of the medial menisci (MM) at the pars intermedia, and the medial collateral ligament (MCL), individual changes were observed. For example, the medial femoral epicondyle displayed a medial lift-off in all knees.

Conclusion

We demonstrated that our EMT approach is an acceptable method to accurately measure PF joint motion. This method could also enable visualization and in-depth analysis of in vivo patellar function in total knee arthroplasty, if it is established for routine clinical use.

Trochleoplasty: Indications and Technique

PURPOSE OF REVIEW

Trochlear dysplasia is a well-described risk factor for patellar instability. Trochleoplasty has emerged as a procedure within the surgical armamentarium for patellar instability, yet its role is unclear. A variety of trochleoplasty procedures have emerged. The purpose of this review is to clarify indications for trochleoplasty, outline the technical steps involved in performing common trochleoplasties and report the published outcomes and potential complications of these procedures.

RECENT FINDINGS

Patellar instability with severe trochlear dysplasia is the main indication for trochleoplasty. Three types of trochleoplasty have emerged: (1) lateral facet elevation; (2) sulcus deepening; and (3) recession wedge. Deepening and recession wedge trochleoplasties are the most commonly performed. Trochleoplasty is a surgical option for addressing patellar instability in patients with severe trochlear dysplasia. Deepening and recession wedge trochleoplasties that address Dejour B and D dysplastic trochleas are the most studied, with both short- and midterm outcomes reported. Long-term outcomes are lacking and comparative studies are needed.

Protecting the PCL During Total Knee Arthroplasty Using a Bone Island Technique

BACKGROUND

Prior studies have shown that the posterior cruciate ligament (PCL) may be partially resected during cruciate retaining (CR) total knee arthroplasty (TKA) using highly experienced hands and standard surgical technique; therefore, proper surgical technique is aimed at preservation and balance of the PCL during CR TKA. The central objective of this study is to evaluate the effectiveness of a simple surgical technique to prevent PCL damage during performance of a CR TKA.

METHODS

Sixty embalmed cadaver specimens were randomized into 2 groups, experimental and control. The control group consisted of standard tibial resection without the use of an osteotome. The experimental group utilized an osteotome in addition to standard technique to preserve a bone island anterior to the tibial attachment of the PCL.

RESULTS

In the control group, PCL damage was noted in 73% (22/30) of specimens. In the experimental group, where an osteotome was used, PCL damage was found in 23% (7/30) of specimens. The use of an osteotome was found to have an absolute risk reduction of 50% when compared to the control group which did not use an osteotome to protect the PCL.

CONCLUSION

In the setting of minimal surgical experience, the use of an osteotome to preserve the PCL during CR TKA by forming a bone island was found to be an effective means of protecting the PCL over standard technique. In addition, standard technique with the use of a Y-shaped PCL retractor was found to provide questionable protection to the PCL.

Impact of the patella height on the strain pattern of the medial patellofemoral ligament after reconstruction: a computer model-based study

PURPOSE

Medial patellofemoral ligament (MPFL) reconstruction is a key procedure for treating patellofemoral instability. However, controversy exists regarding the correct graft placement in different patellar heights. Therefore, our study aimed to investigate the influence of patellar height on MPFL insertion points.

METHODS

Strain patterns of the reconstructed MPFL were calculated using a dynamic musculoskeletal multibody simulation. Numerous patellar (proximal, central, distal) and femoral attachment sites (around the radiological point according to Schöttle) were analysed in the presence of different patella heights [Insall-Salvati (IS) indices 0.74, 1.0, 1.5] during dynamic knee flexion from 0° to 120°.

RESULTS

The reconstructed MPFL showed an almost isometric behaviour at the anatomic insertion (IS 1.0). Slight variation (<5 mm) around the ideal femoral insertion point resulted in only small changes in MPFL tension. However, a displacement of 10 mm led to a significant increase in MPFL tension, especially in the more anteriorly/proximally located femoral attachment points. Depending on the patella height, there exists an area of absolute isometry of the MPFL (length change <3 %) on the femoral condyle, which did not necessarily coincide exactly with the radiological point, but was located within a radius of 5 mm around it.

CONCLUSIONS

When reconstructed in the radiological femoral insertion point, MPFL strain patterns were only slightly affected by different patella heights (IS 0.74-1.5) suggesting that MPFL reconstruction could be safely performed using the radiological insertion. However, in case of a patella alta (IS 1.5), a slightly more proximal femoral insertion is beneficial for the biomechanical behaviour of the reconstructed MPFL.