A radiographic study of the distal femoral epiphysis

Physeal Location on the Distal Femoral Cortical Surface Is Consistently Proximal to Apparent Location on the Perfect Lateral Radiograph: A 3-Dimensional Digitally Reconstructed Radiograph Study

INTRODUCTION

The perfect knee lateral radiograph visualizes anatomic landmarks on the distal femur for clinical and scientific purposes. However, radiographic imaging is a two-dimensional (2D) representation of a three-dimensional (3D) physis. The aim of this study was to characterize the perceived radiographic projection of the femoral physis using perfect lateral digitally reconstructed radiographs (DRRs) and to evaluate discrepancies from this projection to the physis at the lateral and medial cortices.

METHODS

Pediatric patients from a cohort of CT scans were analyzed. Inclusion criteria were an open physis; exclusion criteria were any implant or pathology affecting the physis. CT scans were imported into 3D imaging software and transformed into lateral DRRs and 3D renderings of the femur. The physis was divided into four equal segments, with fiducial markers placed at the "anterior," "midpoint," and "posterior" points. Lines extended from these points in the lateral and medial direction. The vertical distance from these lines, representing the radiographic projection of the physis, was measured relative to the physis at the lateral and medial cortex of the femur on coronal CT slices.

RESULTS

Thirty-one patients were included. On the perfect lateral radiograph DRR, the physis on the medial cortex was located proximal to the visualized physis by 6.64 ± 1.74 mm, 11.95 ± 1.67 mm, and 14.30 ± 1.75 mm at the anterior (25%), midpoint (50%), and posterior (75%) locations, respectively. On the lateral side, the physis on the lateral cortex was proximal to the visualized physis by 2.19 ± 1.13 mm, 3.71 ± 1.19 mm, and 6.74 ± 1.25 mm at the anterior, midpoint, and posterior locations, respectively.

DISCUSSION

In this cohort of pediatric patients, the location of the cortical physis was, in all areas measured, proximal to the projection of the visualized physis as seen on the perfect knee lateral DRR. The distance from radiographic physis to cortical physis was greater at the medial cortex compared with the lateral cortex.

STUDY DESIGN

Descriptive laboratory study.

LEVEL OF EVIDENCE

III, observational radiographic anatomic study.

Improved epiphyseal socket placement with intraoperative 3D fluoroscopy: a consecutive series of pediatric all-epiphyseal anterior cruciate ligament reconstruction

PURPOSE

Disturbance of the growth plate during all-epiphyseal anterior cruciate ligament reconstruction (ACLR) socket placement is possible due to the undulation of the distal femoral physis and proximal tibial physis. Therefore, it is important to obtain intraoperative imaging of the guide wire prior to reaming the socket. The purpose of this study was to investigate the effect of the use of 3D intraoperative fluoroscopy on socket placement in patients undergoing all-epiphyseal ACLR. It was hypothesized that 3D imaging would allow for more accurate intraoperative visualization of the growth plate and hence a lower incidence of growth plate violation compared to 2D imaging.

METHODS

Patients under the age of 18 who underwent a primary all-epiphyseal ACL reconstruction by the senior authors and had an available postoperative MRI were retrospectively reviewed. Demographic data, surgical details, and the distances between the femoral socket and distal femoral physis (DFP) and tibial socket and proximal tibial physis (PTP) were recorded. Patients were split into two groups based on type of intraoperative fluoroscopy used: a 2D group and a 3D group. Interrater reliability of radiographic measurements was evaluated using intraclass correlation coefficient (ICC).

RESULTS

Seventy-two patients fit the inclusion criteria and were retrospectively reviewed. 54 patients had 2D imaging and 18 patients had 3D imaging. The mean age at time of surgery was 12.3 ± 1.5 years, 79% of patients were male, and 54% tore their left ACL. The mean time from surgery to postoperative MRI was 2.0 ± 1.1 years. The ICC was 0.92 (95% CI 0.35-0.98), indicating almost perfect interrater reliability. The mean difference in distance between the tibial socket and the PTP was significantly less in the 2D imaging group than the 3D imaging group (1.2 ± 1.7 mm vs 2.5 ± 2.2 mm, p = 0.03). The femoral and tibial sockets touched or extended beyond the DFP or PTP, respectively, significantly less in the 3D group than in the 2D group (11% vs 43%, p < 0.000, 17% vs 65%, p < 0.000).

CONCLUSION

There was a significantly increased distance from the PTP and decreased incidence of DFP violation with use of 3D intraoperative imaging for all-epiphyseal ACLR socket placement. Surgeons should consider utilizing 3D imaging prior to creating femoral and tibial sockets to potentially decrease the risk of physis violation in these patients.

LEVEL OF EVIDENCE

III.

Properties and Function of the Medial Patellofemoral Ligament: A Systematic Review

BACKGROUND

As the main passive structure preventing patellar lateral subluxation, accurate knowledge of the anatomy, material properties, and functional behavior of the medial patellofemoral ligament (MPFL) is critical for improving its reconstruction.

PURPOSE

To provide a state-of-the-art understanding of the properties and function of the MPFL by undertaking a systematic review and statistical analysis of the literature.

STUDY DESIGN

Systematic review.

METHODS

On June 26, 2018, data for this systematic review were obtained by searching PubMed and Scopus. Articles containing numerical information regarding the anatomy, mechanical properties, and/or functional behavior of the MPFL that met the inclusion criteria were reviewed, recorded, and statistically evaluated.

RESULTS

A total of 55 articles met the inclusion criteria for this review. The MPFL presented as a fanlike structure spanning from the medial femoral epicondyle to the medial border of the patella. The reported data indicated ultimate failure loads from 72 N to 208 N, ultimate failure elongation from 8.4 mm to 26 mm, and stiffness values from 8.0 N/mm to 42.5 N/mm. In both cadaveric and in vivo studies, the average elongation pattern demonstrated close to isometric behavior of the ligament in the first 50° to 60° of knee flexion, followed by progressive shortening into deep flexion. Kinematic data suggested clear lateralization of the patella in the MPFL-deficient knee during early knee flexion under simulated muscle forces.

CONCLUSION

A lack of knowledge regarding the morphology and attachment sites of the MPFL remains. The reported mechanical properties also lack consistency, thus requiring further investigations. However, the results regarding patellar tracking confirm that the lack of an MPFL leads to lateralization of the patella, followed by delayed engagement of the trochlear groove, plausibly leading to an increased risk of patellar dislocations. The observed isometric behavior up to 60° of knee flexion plausibly suggests that reconstruction of the ligament can occur at flexion angles below 60°, including the 30° and 60° range as recommended in previous studies.

Evaluation of Skeletal Maturity Using the Distal Femoral Physeal Central Peak Is Not Significantly Affected by Radiographic Projection

BACKGROUND

Accurate estimation of skeletal maturity is important in several pediatric orthopaedic conditions. The current gold standard for estimating skeletal maturity using the Greulich and Pyle Bone Atlas is complex and shown to have significant interobserver variability. Recent data have shown peak height velocity to occur on average at 90% of final adult height, providing an improved gold standard to quantify skeletal maturity, facilitating the investigation of different skeletal maturity systems. Measurement of topographical changes to the developing distal femoral physis on anteroposterior (AP) radiographs allow for calculation of the central peak value (CPV), a quantitative method shown to provide accurate prediction of 90% of final adult height. The purpose of this study was to assess the clinical tolerance of the CPV method to varying beam angles by comparing measurement reliability between AP radiographs of the knee versus standing hip-to-ankle leg-length radiographs.

METHODS

We searched our institution's pediatric orthopaedic clinical database for skeletally immature patients evaluated with both standard AP radiographs of the knee as well as standing hip-to-ankle radiographs. Patients included female individuals aged 7 to 16 years and male individuals aged 7 to 18 years with both radiographs within 6 months. CPV was measured using a previously published method. Intraclass correlation coefficient was calculated to determine the level of agreement between observers in all available radiographs. CPVs between AP radiographs of the knee and standing hip-to-ankle radiographs were compared using a paired t test to determine if there is a significant difference between radiographic projection and sex.

RESULTS

A total of 78 subjects meeting appropriate inclusion and exclusion criteria were identified. intraclass correlation coefficient value was 0.873, indicating excellent interobserver reliability for CPV measurements. The mean time between radiographs was 0.30 years for male and 0.27 years for female patients. CPV values between the 2 radiographic projections were not significantly different in male (P=0.37), female (P=0.22) or male+female patients (P=0.17). CPV values were significantly higher in male patients on both AP radiographs (P<0.001) and standing hip-to-ankle radiographs (P<0.001) when compared with female patients.

CONCLUSIONS

The CPV is a quick, quantitative method for estimating skeletal maturity. CPVs are not significantly different between standard AP radiographs of the knee versus standing hip-to-ankle leg-length radiographs, expanding the potential to utilize this method without the need for additional expense or radiation.

LEVEL OF EVIDENCE

Level III-retrospective comparative study.

An Anatomic and Radiographic Study of the Distal Tibial Epiphysis

BACKGROUND

Although the undulating shape of the distal tibial epiphysis is well recognized, its anatomic features have not been well quantified in the literature. To guide the placement of surgical implants about the distal tibial physis, we investigated the topographical anatomy of the distal tibial epiphysis and explored the ability of standard radiographs to visualize the physis.

METHODS

We studied 30 cadaveric distal tibial epiphyses in specimens 3 to 14 years of age. Anteroposterior (AP) and lateral radiographs were obtained of each specimen and then repeated after flexible radiopaque markers were placed on the major undulations. All radiographs were analyzed to determine the height or depth of each landmark, and measurements with and without markers for each landmark were compared using intraclass correlation coefficients (ICC). In 9 specimens, similar measurements were obtained on high-resolution 3-dimensional (3D) surface scans.

RESULTS

There were 4 distinct physeal undulations usually present: an anteromedial peak (Kump's bump), a posterolateral peak, an anterior central valley, and a posterior central valley. On the 3D scans, Kump's bump averaged 5.0 mm (range, 3.0 to 6.4 mm), the posterolateral peak 2.4 mm (range, 1.2 to 5.0 mm), the anterior valley 1.3 mm (range, 0 to 3.6 mm), and the posterior valley 0.77 mm (range, 0 to 2.7 mm). Lateral radiographs with markers correlated with measurements from 3D scans better than those without markers (ICC=0.61 vs. 0.24). For AP radiographs, correlation was good to excellent regardless of marker use (ICC=0.76 vs. 0.66).

CONCLUSIONS

There are 4 major undulations of the distal tibial physis. Kump's bump is the largest. A centrally placed epiphyseal screw in the medial/lateral direction or screws from anterolateral to posteromedial and anteromedial to posterolateral would tend to avoid both valleys. Particular caution should be taken when placing metaphyseal screws in the anteromedial or posterolateral distal tibia. Physeal undulations were more difficult to visualize on the lateral view.

CLINICAL RELEVANCE

This study provides quantitative data on the topography of the distal tibial physis to aid hardware placement. Lateral views should be interpreted with caution, as the physeal undulations are not as visible, whereas AP views can be interpreted with more confidence.

A quantitative method for the radiological assessment of skeletal maturity using the distal femur

Aims

Using 90% of final height as a benchmark, we sought to develop a quick, quantitative and reproducible method of estimating skeletal maturity based on topographical changes in the distal femoral physis.

Patients and Methods

Serial radiographs of the distal femoral physis three years prior to, during, and two years following the chronological age associated with 90% of final height were analyzed in 81 healthy children. The distance from the tip of the central peak of the distal femoral physis to a line drawn across the physis was normalized to the physeal width.

Results

A total of 389 radiographs of the distal femur with corresponding Greulich and Pyle bone ages and known chronological ages were measured. Children reached 90% of final height at a mean age of 11.3 years (sd 0.8) for girls and 13.2 years (sd 0.6) for boys. Linear regression analysis showed higher correlation coefficent in predicting the true age at 90% of final height using chronological age + gender + central peak value (R² = 0.900) than chronological age + gender (R² = 0.879) and Greulich and Pyle bone age + gender (R² = 0.878).

Conclusion

Chronological age + gender + central peak value provides more accurate prediction of 90% of final height compared with chronological age + gender and Greulich and Pyle bone age + gender. Cite this article: Bone Joint J 2018;100-B:1106-11.

Safe Drilling Paths in the Distal Femoral Epiphysis for Pediatric Medial Patellofemoral Ligament Reconstruction

BACKGROUND

Anatomic surgical reconstruction of the medial patellofemoral ligament (MPFL) has been popularized for the treatment of recurrent patellar instability in the skeletally immature population. Previous anatomic studies have found that the femoral attachment point of the MPFL is very close to the distal femoral physis.

PURPOSE

To establish the safe angles for drilling the distal femoral epiphysis for MPFL graft placement.

STUDY DESIGN

Descriptive laboratory study.

METHODS

A total of 23 cadaveric distal femoral epiphyses were scanned into high-resolution 3-dimensional images. Using computer-aided design, we identified and marked the femoral insertion site of the MPFL. Cylinders 8 mm in diameter were placed at varying angles to simulate the drill paths for placement of 6-mm interference screws with a 1-mm buffer. The distance from the MPFL footprint to where the tunnel first violated the physis, the intercondylar notch, or the distal cartilage was measured. We recorded the percentage of tunnels that caused violations before reaching 20 mm, the shortest length of a typical femoral tunnel socket.

RESULTS

Measurements indicated that 41% of tunnels angled distally less than 10° violated the physis, 40% of tunnels angled distally more than 10° but anteriorly less than 10° violated the notch, and 27% of tunnels angled distally and anteriorly more than 20° violated the distal femoral cartilage. At least 90% of the tunnels were safe at 20 mm when the drill was angled between 15° and 20° both anteriorly and distally.

CONCLUSION

Because of the anatomy of the distal femoral physis, drilling into the epiphysis from the MPFL attachment site at improper trajectories risks damage to sensitive structures. Angling the drill to an acceptable degree distally and anteriorly leads to less risk to the physis and notch, respectively, but angling too much leads to risk to the distal femoral cartilage. Small variations in the sagittal plane were better tolerated than variations in the coronal plane, so we recommend that more attention be paid to the radiographic anteroposterior view intraoperatively. It is safest to angle the drill distally and anteriorly approximately 15° to 20° in each plane from the MPFL attachment site.

CLINICAL RELEVANCE

During drilling into the distal femoral epiphysis at the MPFL origin in skeletally immature patients, angling the drill appropriately 15° to 20° both distally and anteriorly minimizes damage to the physis, notch, and distal femoral cartilage.