Quantitative study of the quadriceps muscles and trochlear groove geometry related to instability of the patellofemoral joint

Clinical and Computational Evaluation of an Anatomic Patellar Component

INTRODUCTION

Anatomic patellar components for total knee arthroplasty (TKA) have demonstrated favorable in vivo kinematics. A novel failure mechanism in patients implanted with anatomic patella components was observed, prompting a clinical and computational investigation to identify patient and implant-related factors associated with suboptimal performance.

METHODS

A retrospective evaluation was performed comparing 100 TKA patients implanted with anatomical versus 100 sex-, age-, and BMI-matched patients implanted with dome patellar components. All were implanted with the same posterior-stabilized (PS) TKA system with a minimum 1-year follow-up duration. Several radiographic parameters were assessed. A separate computational evaluation was performed using finite-element analysis, comparing components. Bone strain energy density was measured at the proximal and distal patellar poles.

RESULTS

Patients who had anatomic patellar components had a significantly higher prevalence of anterior knee pain (AKP; 18 versus 2%, P < 0.001), chronic effusions (18 versus 2%, P < 0.001), and superior patellar pole fragmentation (36 versus 13%, P < 0.001) versus those who had dome patellar components. The anatomic group also demonstrated more lateral patellar subluxation (2.3 versus 1.1 mm, P < 0.001) and lateral tilt (5.4 versus 4.0 mm, P = 0.013). There was a higher, but not significant, number of revisions in the anatomic group (7 versus 3, P = 0.331). In computational evaluation, all simulations demonstrated increased bone strain energy density at the superior patellar pole for the anatomic patella. Resection thickness < 13 mm resulted in an over 2-fold increase in strain energy density, while a negative 7° resection angle resulted in a 6-fold higher superior pole strain energy.

CONCLUSION

Patients who had this design of anatomic patellar component showed higher rates of AKP, effusion, and superior pole fragmentation than patients who had dome patellae, with higher superior patella pole strain energy confirmed on computational evaluation. Avoiding higher resection angles and excessive patellar resection may improve the performance and survivorship of the anatomic patella.

Specific considerations in female patients with patellar instability: current concepts

Prior literature suggests that patellofemoral instability (PFI) is significantly more prevalent in women than in men. This higher prevalence is commonly attributed to anatomical differences between sexes, particularly with patellofemoral alignment. These differences encompass a higher rate of trochlear dysplasia (TD), patella alta, an increased Q angle, and soft tissue imbalances. In recent years, worse outcomes have been reported in female patients after patellofemoral stabilization surgery using medial patellofemoral ligament reconstruction (MPFLr) alone or in combination with a tibial tubercle osteotomy (TTO), for this reason an "à la carte" plan (addressing the individuals anatomical risk factors) could be more appropriate for female patients.

Isometry of anteromedial reconstructions mimicking the deep medial collateral ligament depends on the femoral insertion

PURPOSE

This study aimed to investigate the length change patterns of the native deep medial collateral ligament (dMCL) and potential anteromedial reconstructions (AMs) that might be added to a reconstruction of the superficial MCL (sMCL) to better understand the control of anteromedial rotatory instability (AMRI).

METHODS

Insertion points of the dMCL and potential AM reconstructions were marked with pins (tibial) and eyelets (femoral) in 11 cadaveric knee specimens. Length changes between the pins and eyelets were then tested using threads in a validated kinematics rig with muscle loading of the quadriceps and iliotibial tract. Between 0° and 100° knee flexion, length change pattern of the anterior, middle and posterior part of the dMCL and simulated AM reconstructions were analysed using a rotary encoder. Isometry was tested using the total strain range (TSR).

RESULTS

The tibiofemoral distance of the anterior dMCL part lengthened with flexion (+12.7% at 100°), whereas the posterior part slackened with flexion (-12.9% at 100°). The middle part behaved almost isometrically (maximum length: +2.8% at 100°). Depending on the femoral position within the sMCL footprint, AM reconstructions resulted in an increase in length as the knee flexed when a more centred position was used, irrespective of the tibial attachment position. Femoral positioning in the posterior aspect of the sMCL footprint exhibited <4% length change and was slightly less tight in flexion (min TSR = 3.6 ± 1.5%), irrespective of the tibial attachment position.

CONCLUSION

The length change behaviour of potential AM reconstructions in a functionally intact knee is mainly influenced by the position of the femoral attachment, with different tibial attachments having a minimal effect on length change. Surgeons performing AM reconstructions to control AMRI would be advised to choose a femoral graft position in the posterior part of the native sMCL attachment to optimise graft length change behaviour. Given the high frequency of MCL injuries, sufficient restoration of AMRI is essential in isolated and combined ligamentous knee injuries.

LEVEL OF EVIDENCE

There is no level of evidence as this study was an experimental laboratory study.

Neuromuscular Responses and Perceptions of Health Status and Pain-Related Constructs in End-Stage Knee Osteoarthritis During Resistance Training With Blood Flow Restriction

ABSTRACT

Ogrezeanu, DC, López-Bueno, L, Sanchís-Sánchez, E, Carrasco, JJ, Cuenca-Martínez, F, Suso-Martí, L, López-Bueno, R, Cruz-Montecinos, C, Martinez-Valdes, E, Casaña, J, and Calatayud, J. Neuromuscular responses and perceptions of health status and pain-related constructs in end-stage knee osteoarthritis during resistance training with blood flow restriction. J Strength Cond Res 38(4): 762-772, 2024-We aimed to evaluate the neuromuscular responses and their relationship with health status, kinesiophobia, pain catastrophizing, and chronic pain self-efficacy in patients with end-stage knee osteoarthritis during acute resistance training with different levels of blood flow restriction (BFR). Seventeen patients with end-stage knee osteoarthritis participated in 3 experimental sessions separated by 3 days, performing 4 sets of knee extensions with low load and 3 levels of concurrent BFR performed in a random order: control (no BFR), BFR at 40% arterial occlusion pressure (AOP), and BFR at 80% AOP. Normalized root-mean-square (nRMS), nRMS spatial distribution (centroid displacement, modified entropy, and coefficient of variation), and normalized median frequency (nFmed) were calculated from the vastus medialis (VM) and lateralis (VL) using high-density surface electromyography. Subjects were asked to report adverse effects after the sessions. In the VM, nRMS was higher with 80% AOP than with 40% AOP ( p = 0.008) and control ( p < 0.001), whereas there were no differences between conditions in the VL. Normalized root-mean-square also showed an association with pain catastrophizing, chronic pain self-efficacy, and health status (VM: -0.50, 0.49, -0.42; VL: -0.39, 0.27, -0.33). Spatial distribution varied between conditions but mostly in the VL. Overall, nFmed did not vary, with only a slight increase in the VL with 40% AOP, between set 3 and 4. BFR during knee extensions at 80% AOP increases VM activity and VL amplitude distribution more than 40% AOP and control. Importantly, muscle activity increases are modulated by pain catastrophizing, chronic pain self-efficacy, and health status in these patients, and kinesiophobia seems to especially modulate entropy.

Effect of movement-evoked and tonic experimental pain on muscle force production

INTRODUCTION

When performing an exercise or a functional test, pain that is evoked by movement or muscle contraction could be a stronger stimulus for changing how individuals move compared to tonic pain. We investigated whether the decrease in muscle force production is larger when experimentally-induced knee pain is directly associated to the torque produced (movement-evoked) compared to a constant painful stimulation (tonic).

METHODS

Twenty-one participants performed three isometric knee extension maximal voluntary contractions without pain (baseline), during pain, and after pain. Knee pain was induced using sinusoidal electrical stimuli at 10 Hz over the infrapatellar fat pad, applied continuously or modulated proportionally to the knee extension torque. Peak torque and contraction duration were averaged across repetitions and normalized to baseline.

RESULTS

During tonic pain, participants reported lower pain intensity during the contraction than at rest (p < 0.001), whereas pain intensity increased with contraction during movement-evoked pain (p < 0.001). Knee extension torque decreased during both pain conditions (p < 0.001), but a larger reduction was observed during movement-evoked compared to tonic pain (p < 0.001). Participants produced torque for longer during tonic compared to movement-evoked pain (p = 0.005).

CONCLUSION

Our results indicate that movement-evoked pain was a more potent stimulus to reduce knee extension torque than tonic pain. The longer contraction time observed during tonic pain may be a result of a lower perceived pain intensity during muscle contraction. Overall, our results suggest different motor adaptation to tonic and movement-evoked pain and support the notion that motor adaptation to pain is a purposeful strategy to limit pain. This mechanistic evidence suggests that individuals experiencing prevalently tonic or movement-evoked pain may exhibit different motor adaptations, which may be important for exercise prescription.

Strength and passive stiffness of the quadriceps are associated with patellar alignment in older adults with knee pain

BACKGROUND

Maintaining normal patellar alignment is important for knee health. Altered activation of individual quadriceps muscles have been found related to patellar alignment. However, the relationships between strength and passive stiffness of the quadriceps and patellar alignment remains unexplored.

METHODS

Participants aged between 60 and 80 years with activity-induced knee pain were recruited. Knee pain was quantified using an 11-point numeric rating scale. Quadriceps strength was assessed using a Cybex dynamometer and passive stiffness of rectus femoris, vastus lateralis, and vastus medialis were measured by shear-wave ultrasound elastography. Patellar alignments were assessed using MR imaging. Linear regression was used to examine relationships between quadriceps properties and patellar alignments with and without controlling for potential covariates.

FINDINGS

Ninety-two eligible participants were assessed (71.7% females, age: 65.6 ± 3.8 years; pain scale: 4.6 ± 2.0), most of whom had knee pain during stair climbing (85.9%). We found that 17% of patellar lateral tilt angle could be explained by lower quadriceps strength (adjusted R2 = 0.117; P < 0.001), especially in females (R2 = 0.281; P < 0.001; adjusted R2 = 0.211; P < 0.001). In addition, a higher stiffness ratio of vastus lateralis/medialis accounted for 12% of patellar lateral displacement (adjusted R2 = 0.112; P = 0.008).

INTERPRETATION

Quadriceps strength and relative stiffness of lateral to medial heads are associated with patellar alignment in older adults with knee pain. It suggests that quadriceps weakness and relatively stiffer lateral quadriceps may be risk factors related to patellar malalignments in the elderly.

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.

A novel patella fracture fixation technique: finite element analysis

INTRODUCTION

Patella fractures account for approximately 1% of all bone fractures. The tension band wiring technique has been used in surgical treatment. However, there is no clear information about the location of the K-wires in sagittal plane. Thus, a transverse fracture line was created in the patella finite element model and fixed with Kirchner (k) wires and cerclage at different angles and compared with two different standard tension band models.

MATERIALS AND METHODS

A total of 10 finite element models were created to study AO/OTA 34-C1 patella fractures. Two models used the classical tension band method with either circumferential or 8-shaped cerclage wire. The other 8 models used K-wires placed at 45° or 60°, either alone or combination with cerclage wire. A force of 200 N, 400 N, and 800 N were applied at 45° knee angle and the resulting data fracture line opening, surface pressure and stress in the implants were analyzed through finite element analysis.

RESULTS

When all the results are considered, it was determined that the K-wires 60° crossing at the fracture line and with cerclage modeling was superior to the other models. The diagonal placement of the K-wires with cerclage (could be 45° or 60° medium) was superior to the reference models.

CONCLUSIONS

This study has shown that the new fixation method we propose could come to the fore as an alternative method to be used successfully in transverse patella fractures and lower complications. In transverse patellar fractures, the use of K-wires crossed at 60° may be a good alternative to the standard method.

Graft-Specific Surgical and Rehabilitation Considerations for Anterior Cruciate Ligament Reconstruction with the Quadriceps Tendon Autograft

Anterior cruciate ligament reconstruction (ACLR) with a bone-patellar tendon-bone (BPTB) or hamstring tendon (HT) autograft has traditionally been the preferred surgical treatment for patients returning to Level 1 sports. More recently, international utilization of the quadriceps tendon (QT) autograft for primary and revision ACLR has increased in popularity. Recent literature suggests that ACLR with the QT may yield less donor site morbidity than the BPTB and better patient-reported outcomes than the HT. Additionally, anatomic and biomechanical studies have highlighted the robust properties of the QT itself, with superior levels of collagen density, length, size, and load-to-failure strength compared to the BPTB. Although previous literature has described rehabilitation considerations for the BPTB and HT autografts, there is less published with respect to the QT. Given the known impact of the various ACLR surgical techniques on postoperative rehabilitation, the purpose of this clinical commentary is to present the procedure-specific surgical and rehabilitation considerations for ACLR with the QT, as well as further highlight the need for procedure-specific rehabilitation strategies after ACLR by comparing the QT to the BPTB and HT autografts.

Level of Evidence

Level 5.

The relationship between single muscle fibre and voluntary rate of force development in young and old males

PURPOSE

It is suggested that the early phase (< 50 ms) of force development during a muscle contraction is associated with intrinsic contractile properties, while the late phase (> 50 ms) is associated with maximal force. There are no direct investigations of single muscle fibre rate of force development (RFD) as related to joint-level RFD METHODS: Sixteen healthy, young (n = 8; 26.4 ± 1.5 yrs) and old (n = 8; 70.1 ± 2.8 yrs) males performed maximal voluntary isometric contractions (MVC) and electrically evoked twitches of the knee extensors to assess RFD. Then, percutaneous muscle biopsies were taken from the vastus lateralis and chemically permeabilized, to assess single fibre function.

RESULTS

At the joint level, older males were ~ 30% weaker and had ~ 43% and ~ 40% lower voluntary RFD values at 0-100 and 0-200 ms, respectively, than the younger ones (p ≤ 0.05). MVC torque was related to every voluntary RFD epoch in the young (p ≤ 0.001), but only the 0-200 ms epoch in the old (p ≤ 0.005). Twitch RFD was ~ 32% lower in the old compared to young (p < 0.05). There was a strong positive relationship between twitch RFD and voluntary RFD during the earliest time epochs in the young (≤ 100 ms; p ≤ 0.01). While single fibre RFD was unrelated to joint-level RFD in the young, older adults trended (p = 0.052-0.055) towards significant relationships between joint-level RTD and Type I single fibre RFD at the 0-30 ms (r² = 0.48) and 0-50 ms (r² = 0.49) time epochs.

CONCLUSION

Electrically evoked twitches are good predictors of early voluntary RFD in young, but not older adults. Only the older adults showed a potential relationship between single fibre (Type I) and joint-level rate of force development.

Numerical investigation of patellar instability during knee flexion due to an unbalanced medial retinaculum loading effect

Background and aim

Healthy patellofemoral (PF) joint mechanics are critical to optimal knee joint function. Patella plays a vital role in distributing quadriceps load during the knee extension. Patellar tracking, not physiological tracking, causes an increase of strains in PF ligaments, peaks of localized stress of soft tissues and articular cartilage and bony parts, and knee pain; these problems lead to complications such as bone abnormalities and osteoarthritis. This research aimed to develop a Finite Element (FE) model to evaluate patellar instability due to the medial retinaculum asymmetric loading effect.

Methods

A numerical model of the knee was obtained by matching nuclear magnetic resonance (MRI) for soft tissues and computerized tomography (CT) for bones, carried on a normal adult. Loading setup was chosen by using literature data. The intensity of the muscle forces was calculated by a static optimization taking into account ground reaction and knee flexion/extension during walking. The effect of patellar instability was obtained by gradually unbalancing this symmetry, one side was unloaded till 90 N, and the other loaded till 110 N.

Results

Unbalanced forces of 10 N acting on the retinaculum alone can produce a real difference in displacements of about 7 mm, and an increment of about 44% on patellar contact forces.

Conclusion

This research demonstrated how an unbalanced forces acting on the retinaculum can produce significant patellar instability. Patellar instability starts at 25-30° of the knee flexion angle but tends to appear at 15° when the unbalanced muscular loading conditions are acting.

Quantifying muscle strength, size, and neuromuscular activation in adolescent and young adult survivors of musculoskeletal sarcoma: Identifying correlates and responses to functional strengthening

BACKGROUND

Medical and surgical treatment for musculoskeletal sarcoma (MSS) place survivors at risk for impairments in muscle properties including muscle strength, muscle size, and neuromuscular activation. The purpose of this study was to explore muscle properties, gross motor performance, and quality of life (QoL) and the changes in response to a 6-week functional strengthening intervention (PT-STRONG) in MSS survivors of childhood cancer (CCS).

METHODS

Eight lower extremity MSS CCS (13-23 years old) performed baseline testing and three completed PT-STRONG. Participants completed measurements of knee extension strength using handheld dynamometry, vastus lateralis (VL) and rectus femoris (RF) muscle thickness using ultrasonography at rest, and neuromuscular activation using electromyography during strength testing and a step-up task. Participants also completed gross motor and QoL assessments.

RESULTS

Compared with the non-surgical limb, MSS CCS had lower surgical limb knee extension strength, VL muscle thickness, and RF step-up muscle rate of activation (RoA). Compared with normative values, MSS CCS had decreased bilateral knee extension strength, gross motor performance, and physical QoL. Positive correlations among muscle strength, muscle thickness, and gross motor performance were identified. After PT-STRONG, MSS CCS had improvements in VL muscle thickness, VL and RF RoA duing step-up, gross motor performance, and physical QoL.

CONCLUSIONS

Positive association between larger muscle thickness with greater knee extension strength, and higher knee extension strength with better gross motor performance indicate that comprehensive physical therapy assessment and interventions that identify and target impairments in muscle properties to guide clinical decision making should be considered for MSS CCS into survivorship.

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.

Change of the cross-sectional area of vastus medialis oblique in patients with recurrent patellar dislocation treated by tibial tubercle transfer combined with medial patellofemoral ligament reconstruction on axial CT

PURPOSE

To investigate the change of the cross-sectional area (CSA) of vastus medialis oblique (VMO) in patients with recurrent patellar dislocation (RPD) treated by tibial tubercle transfer combined with medial patellofemoral ligament (MPFL) reconstruction by imaging methods, and to guide clinical treatment and rehabilitation.

METHODS

From October 2015 to March 2022, 23 patients with RPD who underwent tibial tubercle transfer combined with MPFL reconstruction were retrospectively enrolled. All patients were assessed by CT in the supine position with the knee fully extended and the quadriceps relaxed. The CSA of VMO and the ratio of CSA of VMO to body weight (CSA/BW) were measured at the upper pole of the patella, 5 mm above the upper pole of the patella and 5 mm below the upper pole of patella. The differences of measured parameters were compared before surgery and at follow-up, including CSA of VMO and CSA/BW. Test level α = 0.05.

RESULTS

The tibial tubercle-trochlear groove (TT-TG) distance was significantly reduced at follow-up compared with that before surgery (27.91 ± 1.95 mm vs 12.33 ± 1.07 mm, P < 0.001). The CSA of VMO was significantly increased at follow-up compared with that before surgery at 5 mm below the upper pole of the patella (473.06 ± 106.32 mm² vs 562.97 ± 157.90 mm², P < 0.001), at the upper pole of the patella (641.23 ± 188.45 mm² vs 700.23 ± 177.55 mm², P = 0.029), and at 5 mm above the upper pole of the patella (788.25 ± 238.62 mm² vs 849.79 ± 180.84 mm², P = 0.018). The CSA/BW was significantly increased at follow-up compared with that before surgery at 5 mm below the upper pole of the patella (7.83 ± 2.52 mm²/kg vs 9.22 ± 3.54 mm²/kg, P < 0.001), at the upper pole of the patella (10.48 ± 3.62 mm²/kg vs 11.42 ± 4.14 mm²/kg, P = 0.020), and at 5 mm above the upper pole of the patella (12.86 ± 4.65 mm²/kg vs 13.68 ± 3.86 mm²/kg, P = 0.017).

CONCLUSION

After tibial tubercle transfer combined with MPFL reconstruction, CSA of VMO increased in patients with RPD, which will help to enhance patellar stability and reduce recurrence.

Neuromuscular and acute symptoms responses to progressive elastic resistance exercise in patients with chronic obstructive pulmonary disease: Cross-sectional study

Background

Quadriceps muscle training is a key part in the rehabilitation of chronic obstructive pulmonary disease (COPD) patients. However, exercise intensity prescription and progression with the typically used elastic bands is challenging. We aimed to evaluate neuromuscular, acute symptoms and cardiorespiratory responses (heart rate and dyspnea) during progressive elastic resistance exercise in patients with COPD.

Methods

Fourteen patients diagnosed with moderate-very severe COPD performed knee extensions at different elastic resistance levels (i.e., colors). The neuromuscular activity was recorded using surface electromyography for the rectus femoris, vastus lateralis and vastus medialis, together with rate of perceived exertion, perceived quadriceps fatigue, dyspnea, oxygen saturation and heart rate.

Results

For the vastus lateralis and rectus femoris, increase of muscle activity was evident from a two-level increment when using the red color. For the vastus medialis, there were no muscle activity progressions. Dyspnea, quadriceps fatigue and especially rate of perceived exertion increased in a dose-response fashion and were correlated with the resistance level and muscle activity at the three muscles.

Conclusion

Heavy elastic resistance exercise is feasible in COPD patients without excessive dyspnea and a stable cardiorespiratory response. In general, at least two elastic resistance increments are needed to enhance muscle activity for the vastus lateralis and rectus femoris, while there is no increase for the vastus medialis. These results may help to individualize exercise dosing during elastic resistance training in patients with COPD.

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.

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.

The Nonintuitive Contributions of Individual Quadriceps Muscles to Patellar Tracking

The purpose of this study was to quantify the contribution of the individual quadriceps muscles to patellar tracking. The individual and/or combined quadriceps muscles were activated in rabbits (n = 6) during computer-controlled flexion/extension of the knee. Three-dimensional patellar tracking was measured for the vastus lateralis, vastus medialis, and rectus femoris when activated alone and when activated simultaneously at different frequencies, producing a range of knee extensor torques. Patellar tracking changed substantially as a function of knee extensor torque and differed between muscles. Specifically, when all quadriceps muscles were activated simultaneously, the patella shifted more medially and proximally and rotated and tilted more medially compared with when vastus lateralis and rectus femoris were activated alone (P < .05), whereas vastus medialis activation alone produced a similar tracking pattern to that observed when all quadriceps muscles were activated simultaneously. Furthermore, patellar tracking for a given muscle condition shifted more medially and proximally and rotated and tilted more medially with increasing knee extensor torques across the entire range of knee joint angles. The authors conclude that patellar tracking depends crucially on knee extensor force/torque and that vastus medialis affects patellar tracking in a distinctly different way than vastus lateralis and rectus femoris, which produce similar tracking patterns.

SPATIAL DISTRIBUTION PATTERN OF THE ELECTROMYOGRAPHIC POTENTIAL IN THE VASTUS MEDIALIS AND LATERALIS MUSCLES FOR THREE KNEE FLEXION ANGLES DURING ISOMETRIC KNEE EXTENSION

Understanding the function of the vastus lateralis (VL) and vastus medialis (VM) muscles is important since these muscles are essential for daily and sport activities. The association between the knee flexion angle and spatial muscle activation is controversial. This study compares the distribution patterns of multi-channel electromyographic activities of the VL and VM muscles at three knee flexion angles for three intensities of isometric contraction. Sixteen men performed isometric knee extensions at 30%, 50% and 70% maximal voluntary contraction (MVC), at [Formula: see text], [Formula: see text] and [Formula: see text] knee flexion. Alterations in the spatial electromyographic potential distribution were determined by the root mean square (RMS), modified entropy, and coefficient of variation in the spatial electromyographic potential. Modified entropy and the coefficient of variation showed differences in the VM muscle between [Formula: see text] and [Formula: see text] knee flexion. The RMS at the three angles was similar between the VL and VM muscles, with no differences in contraction intensities at 30%, 50%, or 70% MVC. The VL and VM muscle function differed among knee flexion angles, as did activity in the distal and proximal VM muscles. These findings suggest the need for functional evaluation of the VL and VM muscles at each knee flexion angle.

Motor Unit Recruitment is Altered When Acute Experimental Pain is Induced at a Site Distant to the Contracting Muscle

Acute pain alters motor unit discharge properties in muscles that are painful or influence loading of painful structures. Less is known about the changes in discharge when pain is induced in distant tissues that are unable or have limited capacity to modify the load of the contracting muscle. We aimed to determine whether acute experimental pain alters quadriceps motor unit discharge when pain is induced in; (i) a muscle that is unlikely to be mechanically influenced by modified quadriceps activity (tibialis anterior: TA), or (ii) the antagonist muscle (biceps femoris: BF). Using a within-subject design, 16 adults performed force-matched isometric knee extension during pain-free control conditions, and trials after painful hypertonic saline injections into TA or BF. Surface and intramuscular electromyography recordings were made. Despite maintained force, discharge rate of quadriceps motor units was lower during Pain than Control conditions for TA and BF trials (both P < 0.001). Redistribution of motor unit activity was observed; some units were recruited in control or pain but not both. As modified quadriceps motor unit discharge has limited/no potential to modify load in the painful tissue to protect the painful part, the findings might support an alternative hypothesis that activity is redistributed to larger motor units.

Variation in the patellar tendon moment arm identified with an improved measurement framework

The mechanical advantage of the knee extensor mechanism depends heavily on the patellar tendon moment arm (PTMA). Understanding which factors contribute to its variation may help improve functional outcomes following arthroplasty. This study optimized PTMA measurement, allowing us to quantify the contribution of different variables. The PTMA was calculated about the instantaneous helical axis of tibiofemoral rotation from optical tracked kinematics. A fabricated knee model facilitated calculation optimization, comparing four data smoothing techniques (raw, Butterworth filtering, generalized cross-validated cubic spline-interpolation and combined filtering/interpolation). The PTMA was then measured for 24 fresh-frozen cadaveric knees, under physiologically based loading and extension rates. Combined filtering/interpolation enabled sub-mm PTMA calculation accuracy throughout the range of motion (root-mean-squared error 0.2 mm, max error 0.4 mm), whereas large errors were measured for raw, filtered-only and interpolated-only techniques at terminal flexion/extension. Before scaling, the mean PTMA was 46 mm; PTMA magnitude was consistently larger in males (mean differences: 5 to 10 mm, p < .05) and was strongly related to knee size: larger knees have a larger PTMA. However, while scaling eliminated sex differences in PTMA magnitude, the peak PTMA occurred closer to terminal extension in females (female 15°, male 29°, p = .01). Knee size accounted for two-thirds of the variation in PTMA magnitude, but not the flexion angle where peak PTMA occurred. This substantial variation in angle of peak PTMA has implications for the design of musculoskeletal models and morphotype-specific arthroplasty. The developed calculation framework is applicable both in vivo and vitro for accurate PTMA measurement.

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.

Total and partial knee arthroplasty implants that maintain native load transfer in the tibia

AIMS

Unicompartmental and total knee arthroplasty (UKA and TKA) are successful treatments for osteoarthritis, but the solid metal implants disrupt the natural distribution of stress and strain which can lead to bone loss over time. This generates problems if the implant needs to be revised. This study investigates whether titanium lattice UKA and TKA implants can maintain natural load transfer in the proximal tibia.

METHODS

In a cadaveric model, UKA and TKA procedures were performed on eight fresh-frozen knee specimens, using conventional (solid) and titanium lattice tibial implants. Stress at the bone-implant interfaces were measured and compared to the native knee.

RESULTS

Titanium lattice implants were able to restore the mechanical environment of the native tibia for both UKA and TKA designs. Maximum stress at the bone-implant interface ranged from 1.2 MPa to 3.3 MPa compared with 1.3 MPa to 2.7 MPa for the native tibia. The conventional solid UKA and TKA implants reduced the maximum stress in the bone by a factor of 10 and caused > 70% of bone surface area to be underloaded compared to the native tibia.

CONCLUSION

Titanium lattice implants maintained the natural mechanical loading in the proximal tibia after UKA and TKA, but conventional solid implants did not. This is an exciting first step towards implants that maintain bone health, but such implants also have to meet fatigue and micromotion criteria to be clinically viable. Cite this article: Bone Joint Res 2022;11(2):91-101.

Lateral release associated with MPFL reconstruction in patients with acute patellar dislocation

Objective

Medial patellofemoral ligament (MPFL) injury occurs in the majority of the cases of acute patellar dislocation. The role of concomitant lateral retinaculum release with MPFL reconstruction is not clearly understood. Even though the lateral retinaculum plays a role in both medial and lateral patellofemoral joint stability in MPFL intact knees, studies have shown mixed clinical outcomes following its release during MPFL reconstruction surgery. Better understanding of the biomechanical effects of the release of the lateral retinaculum during MPFL reconstruction is warranted. We hypothesize that performing a lateral release concurrent with MPFL reconstruction will disrupt the patellofemoral joint biomechanics and result in lateral patellar instability.

Methods

A previously developed and validated finite element (FE) model of the patellofemoral joint was used to understand the effect of lateral retinaculum release following MPFL reconstruction. Contact pressure (CP), contact area (CA) and lateral patellar displacement were recorded. abstract.

Results

FE modeling and analysis demonstrated that lateral retinacular release following MPFL reconstruction with tibial tuberosity-tibial groove distance (TT-TG) of 12 mm resulted in a 39% decrease in CP, 44% decrease in CA and a 20% increase in lateral patellar displacement when compared to a knee with an intact MPFL. In addition, there was a 45% decrease in CP, 44% decrease in CA and a 21% increase in lateral displacement when compared to a knee that only had an MPFL reconstruction.

Conclusion

This FE-based analysis exhibits that concomitant lateral retinaculum release with MPFL reconstruction results in decreased PF CA, CP and increased lateral patellar displacement with increased knee flexion, which may increase the risk of patellar instability.

Lower Extremity Kinetics and Kinematics in Runners with Patellofemoral Pain: A Retrospective Case–Control Study Using Musculoskeletal Simulation

Patellofemoral pain (PFP) is a common atraumatic knee pathology in runners, with a complex multifactorial aetiology influenced by sex differences. This retrospective case–control study therefore aimed to evaluate lower limb kinetics and kinematics in symptomatic and control male and female runners using musculoskeletal simulation. Lower extremity biomechanics were assessed in 40 runners with PFP (15 females and 25 males) and 40 controls (15 females and 25 males), whilst running at a self-selected velocity. Lower extremity biomechanics were explored using a musculoskeletal simulation approach. Four intergroup comparisons—(1) overall PFP vs. control; (2) male PFP vs. male control; (3) female PFP vs. female control; and (4) male PFP vs. female PFP—were undertaken using linear mixed models. The overall (stress per mile: PFP = 1047.49 and control = 812.93) and female (peak stress: PFP = 13.07 KPa/BW and control = 10.82 KPa/BW) comparisons showed increased patellofemoral joint stress indices in PFP runners. A significantly lower strike index was also shown in PFP runners in the overall (PFP = 17.75% and control = 33.57%) and female analyses (PFP = 15.49% and control = 40.20%), revealing a midfoot strike in control, and a rearfoot pattern in PFP runners. Peak rearfoot eversion and contralateral pelvic drop range of motion (ROM) were shown to be greater in PFP runners in the overall (eversion: PFP = −8.15° and control = −15.09°/pelvic drop ROM: PFP = 3.64° and control = 1.88°), male (eversion: PFP = −8.05° and control = −14.69°/pelvic drop ROM: PFP = 3.16° and control = 1.77°) and female (eversion: PFP = 8.28° and control = −15.75°/pelvic drop ROM: PFP = 3.64° and control = 1.88°) PFP runners, whilst female PFP runners (11.30°) exhibited a significantly larger peak hip adduction compared to PFP males (7.62°). The findings from this investigation highlight biomechanical differences between control and PFP runners, as well as demonstrating distinctions in PFP presentation for many parameters between sexes, highlighting potential risk factors for PFP that may be addressed through focused intervention modalities, and also the need, where appropriate, for sex-specific targeted treatment approaches.

Qualitative and Quantitative Anatomy of the Human Quadriceps Tendon in Young Cadaveric Specimens

Background:

A detailed understanding of the anatomy of the quadriceps tendon (QT) is clinically relevant, owing to its increased use as a graft in anterior cruciate ligament reconstruction.

Purpose:

To qualitatively and quantitatively describe the anatomy of the QT in younger adult specimens.

Study Design:

Descriptive laboratory study.

Methods:

A total of 18 nonpaired cadaveric knees with a mean age of 30.1 years (range, 18-38 years) were utilized for this study. A 3-dimensional coordinate measuring system was used to assess the structural relationships between the different layers of the QT and their attachments to the patella, and QT thickness was measured medially, centrally, and laterally at 2-cm intervals from the patellar eminence line (PEL; defined as a straight line between the medial and lateral patellar eminences) and proximally.

Results:

In all specimens, 3 distinct layers formed the QT. The first (superficial) layer was formed by the rectus femoris, which was fused to the second layer with an unclearly defined direct attachment to the patella. The median length of the QT was 86.9 mm (range, 68.4-98.9 mm). The second (middle) layer consisted of the vastus medialis and vastus lateralis and was found to have fibers running in an oblique direction that attached on the patella. A “fuse point,” where the proximal part of the rectus femoris started to merge to the second layer, was identified at a median of 48.7 mm (range, 27.9-62.6 mm) from the PEL. The third (deep) layer consisted of the vastus intermedius. The median thickness of the graft centrally at 20, 40, 60, 80, and 100 mm from the PEL was 8.5, 7.2, 7.5, 6.5, and 5.4 mm, respectively.

Conclusion:

Overall, 3 different layers of the QT were consistently found in all specimens. The first layer was fused with the second layer, and the direction of the fibers of the second layer or the vastus medialis and vastus lateralis was oblique. The median length of the QT was 86.9 mm, and the thickness of the tendon diminished proximally.

Clinical Relevance:

This study allows for a better understanding of QT anatomy when harvesting the tendon as a graft for ligamentous reconstruction.

Elongation and orientation pattern of the medial patellofemoral ligament during lunging

Unfavorable clinical outcomes after medial patellofemoral ligament (MPFL) reconstruction, such as early osteoarthritis of the patellofemoral joint, were considered to be associate with tunnel malpositioning. Length change studies have found that small changes in the femoral position can cause great changes in elongation trends. Further studying the MPFL kinematics may help us to understand the consequences of tunnel malpositioning and optimize the reconstruction techniques. Fifteen healthy subjects were studied with a combined computed tomography and biplane fluoroscopic imaging technique during a lunge motion. Five femoral and three patellar attachments were used to simulate different MPFL bundles. Kinematics of MPFL was defined as elongation and orientation changes (i.e., deviation angle and elevation angle). The mean deviation angle was 28.7° (95% confidence interval, 28.0°-29.4°) at full extension and remained nearly unchanged up to 60° of flexion, and increased to 56.5° (54.1°-58.9°) at 110°. The elevation angle decreased linearly from 12.6° (9.3°-15.9°) at full extension to -86.2° (-92.7-79.7°) at 110° of flexion. The MPFL was most stretched anteriorly and laterally relative to femur from full extension to 30° of flexion and remained near isometric beyond 30°. The current study found that proximal and anterior femoral attachments caused excessive lateral stretching of the MPFL at deeper flexion angles. Such abnormal MPFL kinematics may subsequently cause overconstraint and increased cartilage pressures of the medial patellofemoral joint.

Validity of repeated-measures analyses of in vitro arthroplasty kinematics and kinetics

In vitro models of arthroplasty enable pre-clinical testing and inform clinical decision making. Repeated-measures comparisons maximise resource efficiency, but their validity without testing order randomisation is not known. This study aimed to identify if there were any large testing order effects for cadaveric models of knee and hip arthroplasty. First, the effect of testing order on total knee arthroplasty (TKA) biomechanics was assessed. Extension moments for TKAs (N = 3) implanted into the native knee (TKA-only) were compared to a dataset of TKAs (N = 24) tested after different combinations of partial knee arthroplasty (TKA-last). The effect of repeatedly testing the same knee five times over 36 h on patellofemoral and tibiofemoral kinematics was also quantified. Second, the effect of testing order on capsular ligament function after total hip arthroplasty (THA) was assessed. Randomisation was removed from a previously published dataset to create increasing and decreasing head size groups, which were compared with t-tests. All three TKA-only extension moments fell within the 95% CI of the TKA-last knees across the full range of knee flexion/extension. Repeated testing resulted in root-mean-squared kinematics errors within 1 mm, 1°, or < 5% of total range of motion. Following THA, smaller head-size resulted in greater laxity in both the increasing (p = 0.01) and decreasing (p < 0.001) groups. Testing order did not have large effects on either knee or hip arthroplasty biomechanics measured with in vitro cadaveric models.

Safety, Fear and Neuromuscular Responses after a Resisted Knee Extension Performed to Failure in Patients with Severe Haemophilia

Background: low–moderate intensity strength training to failure increases strength and muscle hypertrophy in healthy people. However, no study assessed the safety and neuromuscular response of training to failure in people with severe haemophilia (PWH). The purpose of the study was to analyse neuromuscular responses, fear of movement, and possible adverse effects in PWH, after knee extensions to failure. Methods: twelve severe PWH in prophylactic treatment performed knee extensions until failure at an intensity of five on the Borg CR10 scale. Normalised values of amplitude (nRMS) and neuromuscular fatigue were determined using surface electromyography for the rectus femoris, vastus medialis, and vastus lateralis. After the exercise, participants were asked about their perceived change in fear of movement, and to report any possible adverse effects. Results: Patients reported no adverse effects or increased fear. The nRMS was maximal for all the muscles before failure, the median frequency decreased, and wavelet index increased during the repetitions. The vastus lateralis demonstrated a higher maximum nRMS threshold and earlier fatigue, albeit with a lower and more progressive overall fatigue. Conclusions: severe PWH with adequate prophylactic treatment can perform knee extensions to task failure using a moderate intensity, without increasing fear of movement, or adverse effects.

Do the quadriceps and hamstring muscles have an effect on patella stability in trochlear dysplasia?

Introduction

Trochlear dysplasia (TD) is a condition that is characterized by the presence of either a flat or convex trochlear, which impedes the stability of the patellofemoral joint (PFJ). The PFJ function is dependent on many different structures that surround the knee joint. The aim of this study was to analyse all the muscle components around the PFJ and identify whether gross muscle imbalance could contribute to the stability of the patella in TD.

Material and methods

The average cross-sectional area (CSA) and cross-sectional area ratio (CSAR) of each muscle of the thigh region in subtypes of TD was evaluated and compared to normal knee joints. Ninety-eight patients (196 knees in total) were included in the study.

Results

Of the 196 knee joints that were reviewed, 10 cases were found to be normal. In total, 186 cases were positive for TD. The majority consisted of type C. The hamstring muscles showed variable results. The vastus medialis muscle was larger in comparison to the vastus lateralis muscle over all the different TD subtypes; however, no statistical significance was identified. There was a marked statistical significance between the quadriceps and hamstring muscles, especially when comparing this to the normal knees within our cohort.

Conclusions

This study revealed no significant difference in the effect of the thigh muscle CSA on the stability of the PFJ in TD. Further research is required to establish the roles of the different muscles around PFJ in the prevention of TD dislocation.

The quantitative influence of current treatment options on patellofemoral stability in patients with trochlear dysplasia and symptomatic patellofemoral instability - a finite element simulation

BACKGROUND

Trochlear dysplasia is highly associated with patellofemoral instability. The goal of conservative and surgical treatment is to stabilize the patella while minimizing adverse effects. However, there is no literature investigating the quantitative influence of different treatment options on patellofemoral stability in knees with trochlear dysplasia. We created and exploited a range of finite element models to address this gap in knowledge.

METHODS

MRI data of 5 knees with trochlear dysplasia and symptomatic patellofemoral instability were adapted into this previously established model. Vastus medialis obliquus strengthening as well as double-bundle medial patellofemoral ligament reconstruction and the combination of medial patellofemoral ligament reconstruction and trochleoplasty were simulated. The force necessary to dislocate the patella by 10 mm and fully dislocate the patella was calculated in different flexion angles.

FINDINGS

Our model predicts a significant increase of patellofemoral stability at the investigated flexion angles (0°-45°) for a dislocation of 10 mm and a full dislocation after medial patellofemoral ligament reconstruction and the combination of medial patellofemoral ligament reconstruction and trochleoplasty compared to trochleodysplastic (P = 0.01) and healthy knees (P = 0.01-0.02). Vastus medialis obliquus strengthening has a negligible effect on patellofemoral stability.

INTERPRETATIONS

This is the first objective quantitative biomechanical evidence supporting the place of medial patellofemoral ligament reconstruction and medial patellofemoral ligament reconstruction combined with trochleoplasty in patients with symptomatic patellofemoral instability and trochlear dysplasia type B. Vastus medialis obliquus strengthening has a negligible effect on patellar stability at a low total quadriceps load of 175 N.

A Secondary Injury of the Anterolateral Structure Plays a Minor Role in Anterior and Anterolateral Instability of Anterior Cruciate Ligament-Deficient Knees in the Case of Functional Iliotibial Band

PURPOSE

To analyze the contribution of a secondary anterolateral structure (ALS) deficiency to knee instability based on anterior cruciate ligament (ACL) deficiency, in the condition of a functional iliotibial band (ITB).

METHODS

Nine freshly-frozen cadaveric knees were sectioned sequentially to create ACL deficiency and ACL-ALS deficiency, using intact knees before sectioning as controls. When ITB was tensioned with 30 N, 4 separate aspects of knee instability were tested as follows: anterior translation in 90 N anterior load, isolated internal rotation in 5 N·m internal rotational torque from 0° to 90° in 15° increments, and anterolateral translation and internal rotation during a simulated pivot-shift test at 0°, 15°, 30°, and 45°. The contribution of ACL deficiency alone and additional ALS deficiency to knee instability were evaluated.

RESULTS

The addition of an ALS lesion produced no significant exacerbation of either anterior translational or pivot shift instability in ACL-deficient knees. Additional ALS deficiency in an ACL-deficient knee resulted in a significant increase in isolated internal rotation from 45° to 90° (P = .001 at 45° and P < .001 in other cases). After sequentially sectioning, the contribution to instability of additional ALS deficiency to the entire instability in ACL-ALS-deficient knees was significantly smaller than that of ACL deficiency alone during anterior load and pivot-shift test (P < .001 in all cases), but significantly contributed more to isolated internal rotational instability at 60° (P = .011) and 90° (P = .015).

CONCLUSIONS

When ITB was tensioned, ALS played a minor role in controlling both anterior or pivot shift stability in ACL-deficient knees but a major role in restraining isolated internal rotation from 45° to 90°.

CLINICAL RELEVANCE

In the condition of functional ITB, concomitant ALS injury might not exacerbate anterior and pivot-shift instability after ACL rupture, while affecting isolated internal rotation stability at higher flexion.

Assessment and Trends of the Methodological Quality of the Top 50 Most Cited Articles on Patellar Instability

Background

Studies with a low level of evidence (LOE) have dominated the top cited research in many areas of orthopaedics. The wide range of treatment options for patellar instability necessitates an investigation to determine the types of studies that drive clinical practice.

Purpose

To determine (1) the top 50 most cited articles on patellar instability and (2) the correlation between the number of citations and LOE or methodological quality.

Study Design

Cross-sectional study.

Methods

The Scopus and Web of Science databases were assessed to determine the top 50 most cited articles on patellar instability between 1985 and 2019. Bibliographic information, number of citations, and LOE were collected. Methodological quality was calculated using the Modified Coleman Methodology Score (MCMS) and the Methodological Index for Non-Randomized Studies (MINORS). Mean citations and mean citation density (citations per year) were correlated with LOE, MCMS, and MINORS scores.

Results

Most studies were cadaveric (n = 10; 20.0%), published in the American Journal of Sports Medicine (n = 13; 26.0%), published between 2000 and 2009 (n = 41; 82.0%), and conducted in the United States (n = 17; 34.0%). The mean number of citations and the citation density were 158.61 ± 59.53 (range, 95.5-400.5) and 12.74 ± 5.12, respectively. The mean MCMS and MINORS scores were 59.62 ± 12.58 and 16.24 ± 3.72, respectively. No correlation was seen between mean number of citations or citation density versus LOE. A significant difference was found in the mean LOE of articles published between 1990 and 1999 (5.0 ± 0) versus those published between 2000 and 2009 (3.12 ± 1.38; P = .03) and between 2010 and 2019 (3.00 ± 1.10; P = .01).

Conclusion

There was a shift in research from anatomy toward outcomes in patellar instability; however, these articles demonstrated low LOE and methodological quality. Higher quality studies are necessary to establish informed standards of management of patellar instability.

Morphological study of the vastus medialis oblique in recurrent patellar dislocation based on magnetic resonance images

Background

To investigate the morphological parameters of the vastus medialis obliquus (VMO) muscle and delineate its importance in the maintenance of patellofemoral joint stability.

Methods

The magnetic resonance imaging data of seventy-five knees (fifty-four patients) with recurrent lateral patella dislocation (LPD) and seventy-five knees (seventy patients) without recurrent LPD were retrospectively analysed. Five morphological parameters related to the VMO (elevation in the sagittal plane and coronal plane, craniocaudal extent, muscle-fibre angulation, cross-sectional area ratio) and two patella tilt parameters (patella tilt angle, bisect offset ratio) were measured in MR images. The independent-samples t test or chi-square test was used for statistical comparisons.

Results

The mean ages of the patients in the recurrent LPD group and control group were 22.1 ± 9.9 years and 24.0 ± 6.5 years, respectively. Eighteen out of seventy-five (24%) patients MRI showed VMO injuries. Compared with the control group, the patients with recurrent LPD showed significantly higher sagittal VMO elevation (10.4 ± 2.3 mm vs. 4.1 ± 1.9 mm), coronal VMO elevation (15.9 ± 5.7 mm vs. 3.9 ± 3.7 mm), muscle-fibre angulation (35.4 ± 8.0° vs. 27.9 ± 6.3°), patella tilt angle (25.9 ± 10.7° vs. 9.1 ± 5.2°), and bisect offset ratio values (0.9 ± 0.3 vs. 0.5 ± 0.1) and significantly lower craniocaudal extent (13.7 ± 5.3 mm vs. 16.7 ± 5.1 mm) and cross-sectional area ratio values (0.05 ± 0.02 vs. 0.07 ± 0.02).

Conclusions

The results showed that abnormalities in the VMO and patella tilt were clearly present in recurrent LPD patients compared with normal people.

The extensor efficiency of unicompartmental, bicompartmental, and total knee arthroplasty

Aims

Unicompartmental knee arthroplasty (UKA) and bicompartmental knee arthroplasty (BCA) have been associated with improved functional outcomes compared to total knee arthroplasty (TKA) in suitable patients, although the reason is poorly understood. The aim of this study was to measure how the different arthroplasties affect knee extensor function.

Methods

Extensor function was measured for 16 cadaveric knees and then retested following the different arthroplasties. Eight knees underwent medial UKA then BCA, then posterior-cruciate retaining TKA, and eight underwent the lateral equivalents then TKA. Extensor efficiency was calculated for ranges of knee flexion associated with common activities of daily living. Data were analyzed with repeated measures analysis of variance (α = 0.05).

Results

Compared to native, there were no reductions in either extension moment or efficiency following UKA. Conversion to BCA resulted in a small decrease in extension moment between 70° and 90° flexion (p < 0.05), but when examined in the context of daily activity ranges of flexion, extensor efficiency was largely unaffected. Following TKA, large decreases in extension moment were measured at low knee flexion angles (p < 0.05), resulting in 12% to 43% reductions in extensor efficiency for the daily activity ranges.

Conclusion

This cadaveric study found that TKA resulted in inferior extensor function compared to UKA and BCA. This may, in part, help explain the reported differences in function and satisfaction differences between partial and total knee arthroplasty.

Cite this article: Bone Joint Res 2021;10(1):1–9.

Patellofemoral instability in trochleodysplastic knee joints and the quantitative influence of simulated trochleoplasty - A finite element simulation

BACKGROUND

Patellofemoral instability is a debilitating condition mainly affecting young patients and has been correlated with trochlear dysplasia. It can occur when the patella is insufficiently guided through its range of motion. Currently, there is no literature describing patellofemoral stability in trochleodysplastic knees and the effect of isolated trochleoplasty on patellofemoral stability.

METHODS

The effect of isolated trochleoplasty in trochleodysplastic knees of patients with symptomatic patellofemoral instability was investigated using a quasi-static finite element model. MRI data of five healthy knees were segmented, meshed and a finite element analysis was performed in order to validate the model. A second validation was performed by comparing simulated patellofemoral kinematics to in-vivo values obtained from upright- weight bearing CT scans. Subsequently, five trochleodysplastic knees were modelled before and after simulated trochleoplasty. The force necessary to dislocate the patella by 10 mm and to fully dislocate the patella was calculated in various knee flexion angles between 0 and 45°.

FINDINGS

The developed models successfully predicted outcome values within the range of reference values from literature. Lateral stability was significantly lower in trochleodysplastic knees compared to healthy knees. Trochleoplasty was determined to significantly increase the force necessary to dislocate the patella in trochleodysplastic knees to comparable values as in healthy knees.

INTERPRETATION

This is the first study to investigate lateral patellofemoral stability in patients with symptomatic patellofemoral instability and dysplasia of the trochlear groove. We confirm that patellofemoral stability is significantly lower in trochleodysplastic knees than in healthy knees. Trochleoplasty increases patellofemoral stability to levels similar to healthy.

Sexual and ethnic polymorphism result in considerable mismatch between native trochlear geometry and off-the-shelf TKA prostheses

PURPOSE

To determine if trochlear morphology in healthy knees depends on sex and ethnicity, and to compare it to off-the-shelf TKA prostheses.

METHODS

Three retrospective series of CT angiograms from France (female, 124; male, 135), China (female, 122; male, 137) and South Africa (female, 21; male, 62) were used to digitize osseous landmarks at the level of the femoral epicondyles. Sulcus angle, trochlear rotation, lateral trochlear inclination, trochlear asymmetry ratio, and trochlear depth index were quantified for each knee and for 10 total knee arthroplasty (TKA) models. Univariable regression analyses were performed to determine associations of the five trochlear parameters with sex and ethnicity. Interquartile ranges (IQR) of native trochlear parameters were compared to the trochlear parameters of 10 off-the-shelf TKA prostheses.

RESULTS

Compared to French knees, Chinese knees had greater sulcus angle (β = 6.3°, p < 0.001), trochlear rotation (β = 0.8°, p = 0.004) and trochlear depth index (β = 1.60, p < 0.001). Conversely, South African knees had greater trochlear rotation (β = 1.9°, p < 0.001) and lateral trochlear inclination (β = 3.7°, p < 0.001). Female knees had smaller trochlear asymmetry ratios (β =  - 0.03, p = 0.05) but greater trochlear rotation angles (β = 0.7, p = 0.005). Considerable mismatches in trochlear morphology were revealed between native knees and off-the-shelf TKA prostheses.

CONCLUSIONS

The findings suggest that thresholds used in the diagnosis of patellofemoral instability should be adapted to patient sex and ethnicity, and that standard off-the-shelf TKA may not restore native trochlear parameters in all patients.

LEVEL OF EVIDENCE

III, retrospective comparative.

Reliability of the Oswestry-Bristol Classification for trochlear dysplasia: expanded characteristics

Aims

The Oswestry-Bristol Classification (OBC) was recently described as an MRI-based classification tool for the femoral trochlear. The authors demonstrated better inter- and intraobserver agreement compared to the Dejour classification. As the OBC could potentially provide a very useful MRI-based grading system for trochlear dysplasia, it was the aim to determine the inter- and intraobserver reliability of the classification system from the perspective of the non-founder.

Methods

Two orthopaedic surgeons independently assessed 50 MRI scans for trochlear dysplasia and classified each according to the OBC. Both observers repeated the assessments after six weeks. The inter- and intraobserver agreement was determined using Cohen’s kappa statistic and S-statistic nominal and linear weights.

Results

The OBC with grading into four different trochlear forms showed excellent inter- and intraobserver agreement with a mean kappa of 0.78.

Conclusion

The OBC is a simple MRI-based classification system with high inter- and intraobserver reliability. It could present a useful tool for grading the severity of trochlear dysplasia in daily practice.

Cite this article: Bone Joint Open 2020;1-7:355–358.

Isolated Medial Patellofemoral Ligament Reconstruction Can Be an Effective Procedure in Patellofemoral Instability with Risk Factors

Patellofemoral instability is a severe problem in young and active patients. This pathology is influenced by ligamentous, bony, and neuromuscular parameters. The reconstruction of the medial patellofemoral ligament (MPFL) evolved to a primary procedure, but combined procedures were more frequently performed in the past years. However, additional operative procedures are associated with increased morbidity and no absolute indication can be identified in the literature. This study is intended to clarify whether addressing only ligamentous influence factors (MPFL) in chronic patellofemoral instability is sufficient to produce good clinical outcomes, or whether other risk factors influence the results negatively and should also be treated at some point. In 52 patients with chronic patellofemoral instability patellar height according to Caton-Deschamps, trochlear dysplasia according to Dejour, the leg axis, the femoral antetorsion, tibial tubercle (TT)-trochlear groove, and TT-posterior cruciate ligament distance were evaluated. All patients were treated with isolated MPFL reconstruction. After a minimum follow-up period of 24 months (24-36 months), the clinical outcome results were calculated using the scoring system according to Lysholm and Tegner. Correlation between clinical outcome scores and anatomic risk factors were calculated. The analysis was performed using a standard statistical software package (JMP version 12, SAS Institute, Cary, NC). The average postoperative Lysholm score increased significantly from 57.23 ± 19.9 to 85.9 ± 17.2 points (p < 0.0001) after isolated MPFL reconstruction. Moreover, the Tegner and Lysholm scores significantly improved both in patients without and with different risk factors postoperative. There were no significant differences in the outcome sores between the groups. Even the degree of trochlear dysplasia (types I-III) did not influence the results. Finally, there was no significant correlation found between all collected risk factors and the postoperative outcome scores. Isolated MPFL reconstruction can be an effective procedure in patients with patellofemoral instability and mild to moderate risk factors.

Sex differences in neuromuscular control of quadriceps

PURPOSE

Patellofemoral pain syndrome (PFPS) is twice as prevalent in females as males, yet a few studies have evaluated differences in quadriceps muscle control between sexes or across force levels. This study investigated sex differences in quadriceps EMG onset times and amplitude at different force levels during isometric knee extension in asymptomatic males and females and in females with PFPS.

METHODS

Thirteen healthy males, 12 healthy females, and 10 females with PFPS performed isometric knee extension ramp contractions at 25%, 50%, and 75% of maximal voluntary contraction (MVC). Surface EMG was recorded from the vastus lateralis (VL), vastus medialis oblique (VMO), vastus medialis (VM), and rectus femoris (RF).

RESULTS

Healthy females showed delayed VL (222 ± 67 ms, p = 0.002), VMO (357 ± 101 ms, p = 0.001), and VM (258 ± 62 ms, p < 0.001) recruitment in comparison with healthy males. Healthy males activated the VL earlier than the VM (156 ± 51 ms, p = 0.02) and RF (379 ± 74 ms, p < 0.001), and at a similar time as the VMO; healthy females activated the VL earlier than the VM (192 ± 53 ms, p = 0.004) and VMO (239 ± 73 ms, p = 0.01). A lower VMO:VL activation ratio was found at 25% MVC (p < 0.001) than at higher force levels.

CONCLUSIONS

Delayed activation of the VMO relative to the VL has been proposed as a risk factor for PFPS. This study confirms a delay in VMO onset time in females.

Muscular architecture of the popliteus muscle and the basic science implications

BACKGROUND

The function of the popliteus muscle is largely treated as a static stabilizer and has a lack of basic muscular architectural data to enable study of its dynamic function. A large volume of literature supports its static function and the essential need for reconstruction in the posterolateral knee when injured to restore knee stability.

HYPOTHESIS/PURPOSE

We hypothesize that the popliteus muscle is more significant as a dynamic presence in the knee.

METHODS

A collection of popliteus architectural data was collected from 28 cadaver specimens (mean (SD) 76 years (11)). Physiological cross-sectional area of the popliteus and semimembranosus muscles were calculated from muscle volume and fiber length to power future muscle force prediction models. Posterior knee muscle trajectories were measured with respect to the longitudinal axis of the tibia. A 2-tailed T test was performed.

RESULTS

Significant differences between males and females were found for both the popliteus (p = 1.1E-05) and semimembranosus (p = 2.0E-05) muscle volumes. Significant differences between males and females were also found in PCSA for the popliteus (p = 0.005) and semimembranosus (p = 4.1E-05) muscles. There were no significant differences in fiber length, overall muscle length (with tendon removed), age, and orientation.

CONCLUSION

Further consideration should be given to include the popliteus muscle as a dynamic entity in the knee given its mechanical properties, trajectory, and prior biomechanical evidence showing when and how it is activated. The present study provides data that may shape future directions of research and treatment with regard to posterolateral corner injuries and ligamentous balancing of the knee.

Repair of the medial patellofemoral ligament with suture tape augmentation leads to similar primary contact pressures and joint kinematics like reconstruction with a tendon graft: a biomechanical comparison

PURPOSE

To compare suture tape-augmented MPFL repair with allograft MPFL reconstruction using patellofemoral contact pressure and joint kinematics to assess the risk of patellofemoral over-constrainment at point zero.

METHODS

A total of ten fresh frozen cadaveric knee specimens were tested in four different conditions of the MPFL: (1) native, (2) cut, (3) reconstructed with tendon graft, and (4) augmented with suture tape. The patellofemoral mean pressure (MP), peak pressure (PP) and contact area (CA) were measured independently for the medial and lateral compartments using pressure-sensitive films. Patellar tilt (PT) and shift (PS) were measured using an optical 3D motion tracking system. Measurements were recorded at 0°, 10°, 20°, 30°, 60° and 90° of flexion. Both the tendon graft and the internal brace were preloaded with 2 N, 5 N, and 10 N.

RESULTS

There was no significant differences found between surgical methods for medial MP, medial PP, medial CA, lateral MP and PS at any preload or flexion angle. Significant differences were seen for lateral PP at 20° knee flexion and 10 N preload (suture tape vs. reconstruction: 1045.9 ± 168.7 kPa vs. 1003.0 ± 151.9 kPa; p = 0.016), for lateral CA at 10° knee flexion and 10 N preload (101.4 ± 39.5 mm² vs. 108.7 ± 36.6 mm²; p = 0.040), for PT at 10° knee flexion and 2 N preload (- 1.9 ± 2.5° vs. - 2.5 ± 2.3°; p = 0.033) and for PT at 0° knee flexion and 10 N preload (- 0.8 ± 2.5° vs. - 1.8 ± 3.1°; p = 0.040). A preload of 2 N on the suture tape was the closest in restoring the native joint kinematics.

CONCLUSIONS

Suture tape augmentation of the MPFL resulted in similar primary contact pressures and joint kinematics in comparison with MPFL reconstruction using a tendon graft. A pretension of 2 N was found to restore the knee joint closest to normal patellofemoral kinematics.

Length-change patterns of the medial collateral ligament and posterior oblique ligament in relation to their function and surgery

PURPOSE

To define the length-change patterns of the superficial medial collateral ligament (sMCL), deep MCL (dMCL), and posterior oblique ligament (POL) across knee flexion and with applied anterior and rotational loads, and to relate these findings to their functions in knee stability and to surgical repair or reconstruction.

METHODS

Ten cadaveric knees were mounted in a kinematics rig with loaded quadriceps, ITB, and hamstrings. Length changes of the anterior and posterior fibres of the sMCL, dMCL, and POL were recorded from 0° to 100° flexion by use of a linear displacement transducer and normalised to lengths at 0° flexion. Measurements were repeated with no external load, 90 N anterior draw force, and 5 Nm internal and 5 Nm external rotation torque applied.

RESULTS

The anterior sMCL lengthened with flexion (p < 0.01) and further lengthened by external rotation (p < 0.001). The posterior sMCL slackened with flexion (p < 0.001), but was lengthened by internal rotation (p < 0.05). External rotation lengthened the anterior dMCL fibres by 10% throughout flexion (p < 0.001). sMCL release allowed the dMCL to become taut with valgus rotation (p < 0.001). The anterior and posterior POL fibres slackened with flexion (p < 0.001), but were elongated by internal rotation (p < 0.001).

CONCLUSION

The structures of the medial ligament complex react differently to knee flexion and applied loads. Structures attaching posterior to the medial epicondyle are taut in extension, whereas the anterior sMCL, attaching anterior to the epicondyle, is tensioned during flexion. The anterior dMCL is elongated by external rotation. These data offer the basis for MCL repair and reconstruction techniques regarding graft positioning and tensioning.

Mechanical characterization of the ligaments in subject-specific models of the patellofemoral joint using in vivo laxity tests

BACKGROUND

The purpose of this study was to propose a methodology for mechanical characterization of the ligaments in subject-specific models of the patellofemoral joint (PFJ) of living individuals.

METHOD

PFJ laxity tests were performed on a healthy volunteer using a specially designed loading apparatus under biplane fluoroscopy. A three-dimensional (3D) parametric model of the PFJ was developed in the framework of the rigid body spring model using the geometrical data acquired from the subject's computed tomography and magnetic resonance images. The stiffness and pre-strains of the medial and lateral PFJ ligaments were characterized using a two-step optimization procedure which minimized the deviation between the model predictions and the calibration test results. Sensitivity analyses were performed to investigate the effect of mechanical properties of the non-characterized model components on the characterization procedure and its results.

RESULTS

The overall findings indicate that the proposed methodology is applicable and can improve the model predictions effectively. For the subject under study, ligament characterization reduced the root mean square of the deviations between the patellar shift and tilt predicted by the model and obtained experimentally for the validation laxity test (from 6.2 mm to 0.5 mm, and from 8.4° to 1.5°, respectively) and passive knee flexion test (from 1.4 mm to 0.3 mm, and from 2.3° to 1.3°, respectively). The non-characterized mechanical properties were found to have a minimal effect on the characterization procedure and its results.

CONCLUSION

The proposed methodology can help in developing truly patient-specific models of the PFJ, to be used for personalized preplanning of the clinical interventions.

When does the patella dislocate? A systematic review of biomechanical & kinematic studies

Background

Patellar dislocations are a significant injury with the potential for long term problems. Little work has been done on establishing the mechanism by which this injury occurs.

Objectives

To determine the mechanism of injury of a patella dislocation based on the available published literature and compare them to already proposed theories.

Methods

A systematic review of the literature was conducted following searches performed on MEDLINE, EMBASE and ProQuest from the earliest year of indexing using the following search terms in any combination: "patella", "dislocation", "mechanism of injury", "anatomy", "biomechanical" and "risk factor". A broad inclusion criteria was used that included studies that looked at patellar dislocations and instability with respect to the patellofemoral joint (PFJ) kinematics or altered kinematics of the PFJ. Studies that did not address the kinematics or biomechanics of the PFJ were excluded. Studies were appraised based on their methodology using a combination of the Critical Appraisal Skills Programme tool and the Quality Appraisal for Cadaveric Studies.

Results

113 studies were identified from a search of MEDLINE, EMBASE and ProQuest databases. Following application of our inclusion criteria, a total of 23 studies were included in our review. 18 of these studies were cadaveric biomechanical studies. The remaining studies were anatomical, imaging based, and a computer simulation based study.

Conclusions

These biomechanical and kinematic studies provide some evidence that a dislocation is likely to occur during early knee flexion with external rotation of the tibia and contraction of the quadriceps. There is limited evidence to support other elements of proposed mechanisms of dislocation.

Primary Medial Patellofemoral Ligament Repair Versus Reconstruction: Rates and Risk Factors for Instability Recurrence in a Young, Active Patient Population

PURPOSE

To comparatively evaluate the clinical outcomes and rates of recurrent instability in young patients with primary medial patellofemoral ligament (MPFL) repair or reconstruction, as well as to assess for radiologic risk factors for worse outcomes.

METHODS

A retrospective review identified all patients with lateral patellar instability who underwent either MPFL repair and/or imbrication or MPFL reconstruction without any additional osseous procedures between 2008 and 2015 at a single center. Demographic variables and preoperative magnetic resonance imaging were analyzed, and Kujala scores were obtained at a minimum 2-year follow-up. Risk factors for worse outcomes were assessed, including the Caton-Deschamps Index (CDI) Insall-Salvati Index, tibial tubercle-trochlear groove distance, and tibial tubercle-posterior cruciate ligament distance.

RESULTS

We identified 51 knees with isolated MPFL surgery (reconstruction in 32 and imbrication and/or repair in 19) at a mean of 59.7 months' follow-up (range, 24-121 months). The overall rate of recurrent dislocations was significantly greater in the repair group (36.9%) versus the reconstruction group (6.3%, P = .01), despite the average CDI being significantly higher in the reconstruction group (1.34 vs 1.23 in repair group, P = .04). No significant difference in the rate of return to baseline activity was found between the groups (77.8% in reconstruction group vs 70% in repair group, P = .62). The average Kujala score showed no significant difference between the repair and reconstruction groups (84.15 ± 14.2 vs 84.83 ± 14.38, P = .72). No imaging measurements were found to be predictive of a worse postoperative Kujala score; however, the average CDI among the MPFL repair failures (1.30 ± 0.05) was significantly higher than among the MPFL repair nonfailures (1.18 ± 0.12, P = .03).

CONCLUSIONS

MPFL reconstruction may provide improved midterm clinical outcomes and a decreased recurrence rate compared with MPFL repair. Increased patellar height as measured by the CDI may be a risk factor for recurrent patellar instability in patients who undergo isolated MPFL repair.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

Parametric finite element model of medial patellofemoral ligament reconstruction model development and clinical validation

Background

Currently, there is uncertainty regarding the long-term outcome of medial patellofemoral ligament reconstructions (MPFLr). Our objectives were: (1) to develop a parametric model of the patellofemoral joint (PFJ) enabling us to simulate different surgical techniques for MPFLr; (2) to determine the negative effects on the PFJ associated with each technique, which could be related to long-term deterioration of the PFJ.

Methods

A finite element model of the PFJ was created based on CT data from 24 knees with chronic lateral patellar instability. Patella contact pressure and maximum MPFL-graft stress at five angles of knee flexion (0, 30, 60, 90 and 120°) were analysed in three types of MPFLr: anatomic, non-anatomic with physiometric behaviour, and non-anatomic with non-physiometric behaviour.

Results

An increase in patella contact pressure was observed at 0 and 30° of knee flexion after both anatomic and non-anatomic MPFLr with physiometric behaviour. In both reconstructions, the ligament was tense between 0 and 30° of knee flexion, but at 60, 90 and 120°, it had no tension. In the third reconstruction, the behaviour was completely the opposite.

Conclusion

A parametric model of the PFJ enables us to evaluate different types of MPFLr throughout the full range of motion of the knee, regarding the effect on the patellofemoral contact pressure, as well as the kinematic behaviour of the MPFL-graft and the maximum MPFL-graft stress.

Electronic supplementary material

The online version of this article (10.1186/s40634-019-0200-x) contains supplementary material, which is available to authorized users.

Distal femoral torsional osteotomy increases the contact pressure of the medial patellofemoral joint in biomechanical analysis

PURPOSE

Torsional osteotomy of the distal femur allows anatomic treatment of patellofemoral instability and patellofemoral pain syndrome in cases of increased femoral antetorsion. The purpose of this study was to investigate the effects of distal femoral torsional osteotomy on pressure distribution of the medial and lateral patellar facet.

METHODS

Nine fresh frozen human knee specimens were embedded in custom-made 3D-printed casts and tested with a robotic arm. Torsional osteotomy could be simulated ranging from increased femoral antetorsion of 25° with a corresponding lateralization of the patella to an overcorrected value of 5° of femoral antetorsion. The peak and mean lateral and medial compartment pressure was measured in 0°, 15°, 30°, 45°, 60° and 90° flexion beginning with neutral anatomic muscle rotation.

RESULTS

The medial aspect of the patella showed a significant influence of femoral torsion with an increase of mean and peak pressure in all flexion angles with progressive derotation from 15° external rotation to 5° internal rotation (p = 0.004). The overall pressure difference was highest in near extension and stayed on a constant level with further flexion. On the lateral facet, the derotation resulted in decrease of pressure in near extension; however, it had no significant influence on the mean and peak pressure through the different torsion angles (n.s.). Unlike on the medial facet, a significant consistent increase of peak pressure from 0° to 90° flexion could be shown (p = 0.022) on the lateral patella aspect.

CONCLUSION

Distal femoral torsional osteotomy to correct pathological femoral antetorsion leads to a redistribution of retropatellar pressure. External derotation leads to an increased peak pressure on the medial patellar facet and can impair simultaneous cartilage repair. However, as the lateral patellofemoral load decreases, it has a potential in preventing patellofemoral osteoarthritis.