Surgical parameters influence paediatric knee kinematics and cartilage stresses in anterior cruciate ligament reconstruction: Navigating subject-specific variability using neuromusculoskeletal-finite element modelling analysis.

PURPOSE: Anterior cruciate ligament (ACL) rupture is increasingly common in paediatric and adolescent populations, typically requiring surgical ACL reconstruction (ACLR) to restore knee stability. However, ACLR substantially alters knee biomechanics (e.g., motion and tissue mechanics) placing the patient at elevated risk of early-onset knee osteoarthritis. METHODS: This study employed a linked neuromusculoskeletal (NMSK)-finite element (FE) model to determine effects of four critical ACLR surgical parameters (graft type, size, location and pre-tension) on tibial articular cartilage stresses in three paediatric knees of different sizes during walking. Optimal surgical combinations were defined by minimal kinematic and tibial cartilage stress deviations in comparison to a corresponding intact healthy knee, with substantial deviations defined by normalized root mean square error (nRMSE) > 10%. RESULTS: Results showed unique trends of principal stress deviations across knee sizes with small knee showing least deviation from intact knee, followed by large- and medium-sized knees. The nRMSE values for cartilage stresses displayed notable variability across different knees. Surgical combination yielding the highest nRMSE in comparison to the one with lowest nRMSE resulted in an increase of maximum principal stress on the medial tibial cartilage by 18.0%, 6.0% and 1.2% for small, medium and large knees, respectively. Similarly, there was an increase of maximum principal stress on lateral tibial cartilage by 11.2%, 4.1% and 12.7% for small, medium and large knees, respectively. Knee phenotype and NMSK factors contributed to deviations in knee kinematics and tibial cartilage stresses. Although optimal surgical configurations were found for each knee size, no generalizable trends emerged emphasizing the subject-specific nature of the knee and neuromuscular system. CONCLUSION: Study findings underscore subject-specific complexities in ACLR biomechanics, necessitating personalized surgical planning for effective restoration of native motion and tissue mechanics. Future research should expand investigations to include a broader spectrum of subject-specific factors to advance personalized surgical planning. LEVEL OF EVIDENCE: Level III.

Sensitivity analysis of paediatric knee kinematics to the graft surgical parameters during anterior cruciate ligament reconstruction: A sequentially linked neuromusculoskeletal-finite element analysis.

BACKGROUND AND OBJECTIVE: Incidence of paediatric anterior cruciate ligament (ACL) rupture has increased substantially over recent decades. Following ACL rupture, ACL reconstruction (ACLR) surgery is typically performed to restore passive knee stability. This surgery involves replacing the failed ACL with a graft, however, surgeons must select from range of surgical parameters (e.g., type, size, insertion, and pre-tension) with no robust evidence guiding these decisions. This study presents a systemmatic computational approach to study effects of surgical parameter variation on kinematics of paediatric knees. METHODS: This study used sequentially-linked neuromusculoskeletal (NMSK) finite element (FE) models of three paediatric knees to estimate the: (i) sensitivity of post-operative knee kinematics to four surgical parameters (type, size, insertion, and pre-tension) through multi-input multi-output sensitivity analysis; (ii) influence of motion and loading conditions throughout stance phase of walking gait on sensitivity indices; and (iii) influence of subject-specific anatomy (i.e., knee size) on sensitivivty indices. A previously validated FE model of the intact knee for each subject served as a reference against which ACLR knee kinematics were compared. RESULTS: Sensitivity analyses revealed significant influences of surgical parameters on ACLR knee kinematics, albeit without discernible trend favouring any one parameter. Graft size and pre-tension were primary drivers of variation in knee translations and rotations, however, their effects fluctuated across stance indicating motion and loading conditions affect system sensitivity to surgical parameters. Importantly, the sensitivity of knee kinematics to surgical parameter varied across subjects, indicating geometry (i.e., knee size) influenced system sensitivity. Notably, alterations in graft parameters yielded substantial effects on kinematics (normalized root-mean-square-error > 10 %) compared to intact knee models, indicating surgical parameters vary post-operative knee kinematics. CONCLUSIONS: Overall, this initial study highlights the importance of surgical parameter selection on post-operative kinematics in the paediatric ACLR knee, and provides evidence of the need for personalized surgical planning to ultimately enhance patient outcomes.

Severe mucoid degeneration of the anterior cruciate ligament (ACL) treated with conservative arthroscopic debridement and platelet-rich plasma (PRP) injection.

Mucoid degeneration of the anterior cruciate ligament (ACL) can be treated with arthroscopic debridement, however, instability can ensue. Here, we present a fit and active woman in her 60s with severe mucoid degeneration of the ACL who underwent conservative arthroscopic debridement and treatment with intraligamentous administration of platelet-rich plasma (PRP). After 1 month, the patient demonstrated significant improvements in range of motion and pain symptoms, with nil resultant laxity. The patient was able to return to all recreational sporting activities and professional duties. Quantitative MRI conducted 6 months postoperatively revealed improved fibre orientation and formation of new parallel fibres. Compared with the preoperative scan, the mean grey value demonstrated darker pixel intensity with a smaller standard deviation (SD), potentially indicating a more uniform and less variable formation of ligamentous tissue. Therefore, PRP did not cause harm and was associated with benefit in combination with arthroscopic debridement.

Validation and evaluation of subject-specific finite element models of the pediatric knee.

Finite element (FE) models have been widely used to investigate knee joint biomechanics. Most of these models have been developed to study adult knees, neglecting pediatric populations. In this study, an atlas-based approach was employed to develop subject-specific FE models of the knee for eight typically developing pediatric individuals. Initially, validation simulations were performed at four passive tibiofemoral joint (TFJ) flexion angles, and the resulting TFJ and patellofemoral joint (PFJ) kinematics were compared to corresponding patient-matched measurements derived from magnetic resonance imaging (MRI). A neuromusculoskeletal-(NMSK)-FE pipeline was then used to simulate knee biomechanics during stance phase of walking gait for each participant to evaluate model simulation of a common motor task. Validation simulations demonstrated minimal error and strong correlations between FE-predicted and MRI-measured TFJ and PFJ kinematics (ensemble average of root mean square errors < 5 mm for translations and < 4.1° for rotations). The FE-predicted kinematics were strongly correlated with published reports (ensemble average of Pearson's correlation coefficients (ρ) > 0.9 for translations and ρ > 0.8 for rotations), except for TFJ mediolateral translation and abduction/adduction rotation. For walking gait, NMSK-FE model-predicted knee kinematics, contact areas, and contact pressures were consistent with experimental reports from literature. The strong agreement between model predictions and experimental reports underscores the capability of sequentially linked NMSK-FE models to accurately predict pediatric knee kinematics, as well as complex contact pressure distributions across the TFJ articulations. These models hold promise as effective tools for parametric analyses, population-based clinical studies, and enhancing our understanding of various pediatric knee injury mechanisms. They also support intervention design and prediction of surgical outcomes in pediatric populations.

Leg-Length and Alignment Changes in Children and Adolescents After Transphyseal Anterior Cruciate Ligament Reconstruction With Soft Tissue Graft: Results at 1-Year Follow-up.

Background: Growth disturbance to leg length or coronal plane alignment are important considerations in pediatric anterior cruciate ligament (ACL) reconstruction (ACLR). Purpose/Hypothesis: The purpose of this study was to investigate the lower limb alignment and leg length of pediatric patients preoperatively and at approximately 1 year after transphyseal ACLR. Our hypothesis was that there would be no significant change in leg-length discrepancy (LLD) or operated-side alignment at follow-up. Study Design: Case series; Level of evidence, 4. Methods: Data were extracted from the prospective Queensland Children's Hospital Pediatric ACL Injury Registry. Long-leg alignment radiographs were captured preoperatively and at an approximately 12-month postoperative follow-up. Radiographic measures included leg length, LLD (injured minus uninjured leg length), mechanical axis deviation (MAD), mechanical and anatomical lateral distal femoral angle (mLDFA and aLDFA, respectively), and medial proximal tibial angle. We evaluated the effect of time (annual vs baseline) on imaging measurements with analysis of covariance, using the covariates of age, sex, and body mass index. Results: Data were available for 104 patients, of whom 34 (33%) had >12 months of skeletal growth remaining based on skeletal age. At an average follow-up time of 14.5 months after ACLR, there were no significant differences in mean lower limb alignment or longitudinal growth compared with baseline. However, seven patients demonstrated clinically significant changes to their mechanical axis or LLD (>10 mm change). A subgroup analysis of patients with >12 months of growth remaining (n = 34) demonstrated no statistically significant changes in mean alignment or LLD. Before surgery, LLD was -1.39 mm and the injured limb was in significantly more valgus compared with the uninjured lower limb (mean difference: MAD, 4.79 mm [95% CI, 2.64 to 6.94 mm]; mLDFA, -0.93° [95% CI, -1.29° to -0.57°], and aLDFA, -0.91° [95% CI, -1.31° to -0.50°]). Conclusion: After ACLR, there were no statistically significant changes in mean alignment or longitudinal growth; however, 7 out of 104 patients (6.7%) demonstrated clinically significant changes in alignment or LLD. Preoperatively, the injured limb was statistically significantly in more valgus compared with the uninjured limb with lateralized MAD.

Chronic Recurrent Multifocal Q Fever Osteomyelitis in Children: An Emerging Clinical Challenge.

BACKGROUND: Clinical disease caused by Coxiella burnetii occurs infrequently in children. Chronic Q fever is particularly uncommon and endocarditis is rarely seen. A small number of cases of Q fever osteomyelitis have been described but the pathophysiology is not well understood and optimal treatment is unknown. METHODS: We describe a series of cases of chronic recurrent multifocal Q fever osteomyelitis cases diagnosed in children from a single region in Australia. RESULTS: Between 2011 and 2014, 9 cases of chronic recurrent multifocal Q fever osteomyelitis were diagnosed based on clinical findings, suggestive serology and detection of C. burnetii DNA by polymerase chain reaction testing of biopsy samples (8/9). All required surgical management; antibiotic and adjuvant therapies did not appear to be consistently effective and 2 cases had clinical resolution in the absence of directed antimicrobial therapy. CONCLUSIONS: Chronic recurrent multifocal osteomyelitis is a rare manifestation of chronic Q fever infection in children. The pathophysiology of this condition is poorly understood, and effective treatment options have not been established.

A Magnetic Resonance Imaging Study of the Significance of the Distal Femoral Physis During Medial Patellofemoral Ligament Reconstruction.

BACKGROUND: Medial patellofemoral ligament (MPFL) reconstruction in adults often utilizes screw fixation in the distal femur. The aim was to define the safety of similar fixation in young patients, with respect to their open physis. PURPOSE: To define the age-related relationship between the femoral insertion of the MPFL and the medial aspect of the distal femoral physis on magnetic resonance imaging (MRI) scans. The study investigates whether screw fixation at this point is safe with respect to patient age and screw inclination. STUDY DESIGN: Cross-sectional study. METHODS: Retrospective review of the MRI scans of 159 skeletally immature patients. The femoral insertion of the MPFL was defined with respect to the distal femoral physis. The predicted paths of 2-cm screw fixation were simulated both parallel to the joint line and 45° distally oblique; physeal and joint penetration were noted when present. Results are plotted against age and compared as quartile ranges. RESULTS: The femoral insertion of the MPFL was found to be distal to the distal femoral physis in all patients by an average of 10 mm (range, 2-16 mm). The mean distance increases slightly with age in a nonlinear relationship (r = 0.51, P < .001) from 9 mm at age 10 years to 12 mm by age 16 years. For the classic, parallel screw, the risk of physeal breach is high for all age groups (mean, 64%). For the novel, oblique screw, joint penetration and physeal breach were less prevalent (mean, 13%), and importantly, the vast majority of these breaches were in younger children (age <9 years 9 months). With oblique screws, older children were at significantly lower risk than younger children (<3% vs 48%; P < .001). CONCLUSION: This study accurately defines the relationship between the femoral insertion of the MPFL and the distal femoral physis in children and adolescents. A high risk of potentially poor outcomes was found during anatomic reconstruction of the MPFL in children utilizing classic (parallel) screw fixation, irrespective of age. However, in children older than 10 years, a 20-mm screw, from the anatomic MPFL insertion and directed 45° distally oblique, should be safe in 98% of patients.

MRI of traumatic patellar dislocation in children.

BACKGROUND: Traumatic patellar dislocations (TPD) are common injuries in children, and MRI is useful in evaluation of pediatric musculoskeletal injuries. However, no pediatric studies on the MR features of TPD have been reported. OBJECTIVE: To review the injuries after TPD in children. MATERIALS AND METHODS: Patients with clinical or radiological recognition of TPD and those with suggestive MR findings were selected. Bone, cartilage and soft-tissue injuries and patellofemoral relationships were assessed. RESULTS: A total of 26 patients (age range 10-18 years) were identified. The following injuries were seen: bone bruising of the inferomedial patella (81% of patients) and the lateral femoral condyle (81% of patients), cartilage injuries of the inferomedial patella (38% of patients) and the lateral femoral condyle (38% of patients), osteochondral fragments (42% of patients) and injuries of the medial patellar restraints (81% of patients). CONCLUSION: Pediatric manifestations of TPD seen on MRI are similar to those in adults. TPD is often occult in children. Early recognition of bone bruising of the patella and lateral femoral condyle, associated osteochondral injuries, and medial patellar stabilizer injury is important for timely diagnosis.