Coronal and Transverse Malalignment in Pediatric Patellofemoral Instability

[Patellofemoral instability in children and adolescents]

Patellofemoral instability is a common and clinically relevant disorder of multifactorial causes. Several concomitant problems such as genua valga, hyperlaxity, injuries or sports-related overuse may contribute to the development of instability and recurrent patellar dislocations. A thorough diagnosis is of paramount importance to delineate every contributing factor. This includes radiographic modalities and advanced imaging such as magnetic resonance imaging or torsional analyses. The authors recommend non-operative management (including physiotherapy, gait and proprioceptive training, orthoses) and, whenever non-operative measures fail, surgical patellar stabilization using, e.g. MPFL reconstruction.

Femoral internal torsion greater than twenty-five degrees and/or external tibial torsion greater than thirty degrees as measured by computed tomography are threshold values for axial alignment correction in patellofemoral instability

OBJECTIVES

Patellofemoral instability (PFI) has multiple predisposing anatomic factors, including ligamentous hyperlaxity, coronal and axial malalignment, patella alta, trochlea dysplasia, excessive lateral patellar tilt, and excessive lateral Q vector. Yet, few studies have analyzed surgical thresholds for performing axial alignment corrective osteotomies in the treatment of PFI and patella maltracking. The objective of this systematic literature review was to determine if there is a threshold for axial plane alignment that triggers surgical correction for the treatment of patellar instability in the published literature.

METHODS

Using a predetermined search strategy, a systematic literature search of 10 major databases and gray literature resources was completed. Only studies reporting on patellar instability and outcomes were included. Radiologic indications, additional procedures, outcomes, and complications were reported. Titles and abstracts were screened, and full-text manuscripts were then selected and extracted. Variables related to radiographic and clinical parameters, patient demographics, surgery performed, surgical correction, complications, and reoperations were recorded preoperatively and postoperatively.

RESULTS

A total of 1132 abstracts and titles were screened by two reviewers, yielding 15 eligible studies. The reported threshold identified in our study for axial plane alignment that triggers surgical correction in most of the published literature when discussing PFI was either tibial torsion greater than 30° and/or femoral anteversion greater than 25°. Following rotational osteotomy of one or both long bones, one study (7%) reported improvements in tubercle-sulcus angle, two studies (13%) reported improvements in femoral-tibial angle, and four studies (27%) reported decreases in tibial torsion. For patient-reported outcomes, seven studies (47%) reported improvement in the Kujala score, five studies (33%) reported postoperative improvement in Lysholm, and four studies (27%) reported improvement in the International Knee Documentation Committee (IKDC) score. Nine studies (60%) reported preoperative femoral anteversion; however, only two studies compared pre- and post-operative values (one study reported a decrease in anteversion and another study reported an increase in anteversion).

CONCLUSION

When treating PFI, the reported threshold for axial plane alignment that triggers surgical correction in most of the published literature was tibial torsion greater than 30° and/or femoral anteversion greater than 25° as measured by CT. However, there is no consensus on the axial alignment measurement technique.

LEVEL OF EVIDENCE

III.

Simultaneous MPFL reconstruction and guided growth result in low rates of recurrent patellofemoral instability

PURPOSE

Implant-mediated guided growth (IMGG) is used to address coronal plane deformity in skeletally immature patients. Few studies have reported on IMGG and simultaneous medial patellofemoral ligament (MPFL) reconstruction for paediatric patients with concurrent genu valgum and patellofemoral instability (PFI). This study aimed to report on the outcomes of these simultaneous procedures.

MATERIALS AND METHODS

This was a retrospective review of paediatric patients undergoing simultaneous MPFL reconstruction and IMGG between 2016 and 2023. Mechanical lateral distal femoral angle (mLDFA), hip-knee-ankle angle (HKA) and mechanical axis deviation (MAD) were measured on full-length hip-to-ankle plain radiographs. Measurements were taken preoperatively, prior to implant removal and/or at final follow-up with minimum 1-year clinical follow-up.

RESULTS

A total of 25 extremities in 22 patients (10 female) underwent simultaneous IMGG and MPFL reconstruction. The mean age at surgery was 12.6 ± 1.7 years. The mean duration of implant retention was 18.6 ± 11.3 months. Nineteen extremities (76%) underwent implant removal by final follow-up. Preoperative HKA corrected from a mean of 5.8 ± 2.3° to -0.8 ± 4.5° at implant removal or final follow-up (p < 0.001), with mLDFA and MAD similarly improving (both p < 0.001). HKA corrected a mean of 0.7 ± 0.9° per month, while mLDFA and MAD corrected a mean of 0.5 ± 0.6°/month and 2 ± 3 mm/month, respectively. At the time of implant removal or final follow-up, 88% of patients demonstrated alignment within 5° of neutral. Only one extremity experienced subsequent PFI (4%). For 14 patients who underwent implant removal with further imaging at a mean of 7.8 ± 4.9 months, only one patient (7%) had a valgus rebound to an HKA > 5°.

CONCLUSION

Simultaneous MPFL reconstruction and IMGG provided successful correction of lower extremity malalignment with only one recurrence of PFI. This approach is a reliable surgical option for skeletally immature patients with genu valgum and PFI.

LEVEL OF EVIDENCE

Level 4 case series.

Genu Valgum in Pediatric Patients Presenting With Patellofemoral Instability

BACKGROUND

Lower extremity valgus is a commonly described factor associated with patellofemoral instability (PFI) and, if identified before skeletal maturity, can be treated with guided growth. The prevalence of valgus alignment in the pediatric and adolescent PFI population is largely unknown.

PURPOSE

The aim of this study was to report the prevalence of valgus alignment in adolescent patients presenting with PFI; with secondary assessment of high-grade valgus (zone II or III), coronal asymmetry, and associations of these findings with body mass index (BMI).

STUDY DESIGN

A retrospective cohort study.

METHODS

A total of 279 consecutive patients (349 knees) with a diagnosis of PFI presenting to a single orthopedic pediatric sport medicine surgeon were identified. A retrospective chart review was performed to collect demographic and clinical data, chronologic and bone age, sex, BMI, mechanism of injury, and the presence of osteochondral fracture. Full-length standing hip-to-ankle alignment radiographs were graded for knee alignment mechanical zone utilizing standard linear femoral head center to talar center assessment. In addition, mechanical axis deviation, mechanical lateral distal femoral angle and medial proximal tibial angle (MPTA) were also calculated.

RESULTS

Mean patient age was 14.0±2.5 years. There were 162 (58.1%) females and mean BMI was 24.3±6.4. Seventy patients (25.1%) had bilateral PFI. Standing alignment radiographs were available for 81.4% of knees (n=284). Valgus alignment was present in 172 knees with PFI (60.6%). High-grade valgus, defined as zone 2 or greater, was present in 66 knees (23.3%). Overall, 48.9% had asymmetry of coronal alignment (n=139). The mean mechanical lateral distal femoral angle was 85.4±2.8 and the mean MPTA was 88.2±2.6. There was a greater MPTA in female patients (88.8±2.4 vs. 87.5±2.7, P <0.001). A higher BMI (24.87±6.95, P =0.03) was associated with valgus alignment.

CONCLUSIONS

There is a high (60%) prevalence of lower extremity valgus in adolescent patients presenting with PFI, with nearly 1 in 4 presenting with high-grade valgus. The treatment team should be aware of this association as it may be an important consideration in the pediatric and adolescent PFI populations.

LEVEL OF EVIDENCE

Level III.

Eye of the Carpenter: How Well do Orthopaedic Surgeons Estimate Angular Measurements in Derotational Osteotomies?

BACKGROUND

Femoral derotational osteotomies are used by orthopaedic surgeons to decrease version in a variety of pathologies. Intraoperatively, the goal of the surgery is to decrease the rotation of the femur to within physiological range. Surgeons generally visually estimate the angle of correction based on bone markers at the rotating cylindrical portion of the femur. This study sought first to assess the accuracy and inter-rater reliability of surgeons with respect to angle creation, and then to implement a training intervention.

METHODS

A rotational femur model was constructed and tested among surgeons and nonsurgeons. Surgeons were then randomized into an experimental and control cohort with training on the model as the intervention. Subjects were asked to create target angles of 15, 30, 45, and 60 degrees using only Kirschner wires and then only bone marks for reference. Independent and paired t -tests were performed to determine variability between cohorts.

RESULTS

The mean angle creation error and range of the surgeon cohort were significantly lower than those of the nonsurgeon cohort. Within the nonsurgeon cohort, the mean angle creation error and range of the wire modality were significantly lower than that of the mark modality. The mean angle creation error and range of the trained cohort were significantly lower than the untrained cohort.

CONCLUSIONS

The considerable inter-subject range within the surgeon cohort highlights a need for the reinforcement of basic geometric principles within orthopaedic instruction. This model allows for immediate, accurate feedback on angle creation, and training appears to be both time and cost-effective. The physiological range allows for a level of variability between surgical outcomes without consequence. However, the more than 20 degree range determined by this study does not fall within those bounds and should be addressed.

CLINICAL RELEVANCE

Moving forward, rotational estimation as a surgical skill should increase in prominence within orthopaedic instruction to maximize future joint health, and additional emphasis should be placed on fundamental spatial orientation during training.

Epidemiology of Lateral Patellar Dislocation Including Bone Bruise Incidence: Five Years of Data from a Trauma Center

OBJECTIVE

Systematic summary of the epidemiology of patellar dislocation is rare. This study aims to investigate sex-, age-, type-, injury causing events-, incidence of bone bruise and time from last injury (TFLI)-specific characteristics, and detail the epidemiological characteristics of patellar dislocation.

METHOD

In this descriptive epidemiological study, a total of 743 patients who have a history of lateral patellar dislocation with either first-time patellar dislocation (FPD) or recurrent patellar dislocation (RPD) between August 2017 and June 2022 at our institution met the inclusion criteria and were selected in this study. Patient characteristics including the type, gender, age, events leading to patellar dislocation, incidence of patellar bone bruise, and the time from last injury (TFLI) of patellar dislocation were retrospectively obtained and described. Magnetic resonance imaging scans (MRI) of the knee were reviewed for insuring bone bruise.

RESULTS

Among the 743 patients with patellar dislocation who required surgical reconstruction of the medial retinaculum, 418 (56.2%) had RPD and 325 (43.8%) had FPD. There were more females (65.0%) than males (35.0%) in patellar dislocation patients. Among the female patients, those aged <18 years had higher incidence (31.4%) of patellar dislocation. Among the male patients, those aged <18 and 19-28 years had higher incidence (16.8%) of patellar dislocation. Of all age groups, the prevalence rate of patellar dislocation was high in juvenile population and females, but with no statistical significance. The most common patellar dislocation-causing event was sport accidents (40.1%), followed by life accidents (23.2%). The incidence of left-knee patellar dislocation was slightly higher than that of right-knee patellar dislocation. The incidence of patellar bone bruise of RPD (63.2%) was significantly lower (p < 0.05) than that of FPD (82.2%). Patellar dislocation patients with bone bruise had shorter time from last injury (TFLI) than those without patellar bone bruise (p < 0.05).

CONCLUSIONS

The incidence of bone bruise of RPD was lower than that of FPD, and patients with patellar bone bruise may have a shorter time from last injury than those without bone bruise.

Management of patellar instability in skeletally immature patients

Surgical intervention is the treatment of choice for recurrent lateral patellar instability. Surgery should be considered for first time lateral patella dislocations with osteochondral fractures or underlying anatomical risk factors. Primary repair and nonanatomical imbrications/reconstructions have fallen out of favor due to abnormal biomechanics and high rates of recurrence. Anatomical reconstruction of the MPFL using a variety of auto and allograft tissues have yielded good outcomes and low redislocation rates. Physeal sparing MPFL reconstruction techniques under radiological control are safe and do not cause growth disturbance. Allografts may be indicated for hyperlax patients. Although no clear cutoff points exist, correction of valgus and excessive femoral anteversion should be considered when indicated. Osteochondral and chondral injuries are common and should be addressed during surgery for instability.

The tibial tubercle-trochlear groove distance: a comparison study between EOS and MRI in the paediatric population

OBJECTIVE

This study aims to compare the relative reliability and accuracy of TT-TG measurements in EOS with that of MRI in a paediatric population.

METHODS

Patients were included if they underwent both an MRI and EOS scans and were under the age of 16. Two authors recorded the TT-TG distances on each modality at two separate time points. In the EOS images, the distance between the two points was measured in the horizontal 2D plane. In the MRI images, it was done in the plane referenced by posterior femoral condylar axis. The intra- and inter-rater reliability was assessed in each modality and between modalities.

RESULTS

Twenty-seven patients (30 knees), 14 males, and 13 females with an average age of 13 years (range: 7-16 years) were included in the study. The mean TT-TG distance on EOS scan and MRI scan was 14 mm. On inter- and intra-observer analysis, both imaging modalities had excellent reliability (0.97 ICC for EOS and 0.98 ICC for MRI inter-observer) and repeatability (0.98-0.99 ICC for EOS and 0.99 ICC for MRI for intra-observer). However, on comparing the two imaging modalities (EOS vs MRI), the ICC was fair (0.56 ICC for rater 1 and 0.65 ICC for rater 2).

CONCLUSION

While the EOS TT-TG measurements were precise and reproducible, they were only moderately comparable to MRI TT-TG measurements. Consequently, EOS TT-TG measurements should not be used for decision-making without the development of EOS-specific TT-TG values that indicate the need for distal realignment surgery.

LEVEL OF EVIDENCE

Level II.

Patellar Dislocation: Workup and Decision-Making

Acute patellar dislocation (PD) is usually a problem of adolescents and young adults. In most cases, it is a sports-related injury. It is the result of an indirect force on the knee joint, which leads to valgus and external rotation of the tibia relative to the femur. PD is unlikely to occur on a knee with normal patellofemoral joint (PFJ) anatomy. Acute PD consists of an acute injury of the ligamentous medial patellar stabilizers in the background of factors predisposing to patellar instability. These factors are classified into three groups. The first group refers to the integrity of the ligamentous medial patellar restraints, particularly, the medial patellofemoral ligament (MPFL). The second group refers to an abnormal PFJ anatomy, which renders the patella inherently unstable inside the trochlea. The third group refers to the overall axial and torsional profile of the lower limb and to systemic factors, such as ligament laxity and neuromuscular coordination of movement. PD at a younger age is associated with an increased number and severity of patellar instability predisposing factors and lower stress to dislocate the patella. Acute primary PD is usually treated conservatively, while surgical treatment is reserved for recurrent PD. The aim of treatment is to restore the stability and function of the PFJ and to reduce the risk of patellar redislocation. Surgical procedures to treat patellar instability are classified into non-anatomic and anatomic procedures. Non-anatomic procedures are extensor mechanism realignment techniques that aim to center the patella into the trochlear groove. Anatomic procedures aim to restore the PFJ anatomy (ruptured ligaments, osteochondral fractures), which has been severed after the first incident of PD. Anatomic procedures, especially MPFL reconstruction, are more effective in preventing recurrent PD, compared with non-anatomic techniques. Theoretically, all factors that affect PFJ stability should be evaluated and, if possible, addressed. This is practically impossible. Considering that the MPFL ruptures in almost all PDs, MPFL reconstruction is the primary procedure, which is currently selected by most surgeons as a first-line treatment for patients with recurrent PD. Restoration of the axial and torsional alignment of the lower limbs is also increasingly implemented by surgeons. Non-anatomic surgical techniques, such as tibial-tuberosity osteotomy, are used as an adjunct to anatomic procedures. In the presence of multiple PFJ instability factors, acute MPFL reconstruction may be the treatment of choice for acute primary PD as well. Skeletal immaturity of the patient precludes osseous procedures to avoid premature physis closure and subsequent limb deformity. Unfortunately, restoration of the patient's previous activity level or participation in more strenuous sports is questionable and not easy to predict. In the case of competitive athletes, PD may prevent participation in elite levels of sports.

Comparison of Habitual Versus Recurrent Patellar Dislocation in Children and Adolescents: Differences in Radiological Features

Background

Recurrent patellar dislocation (RPD) and habitual patellar dislocation (HPD) in flexion are frequently encountered in children and adolescents.

Purpose

To compare the radiological features of RPD and HPD in children and adolescents.

Study Design

Cross-sectional study; Level of evidence, 3.

Methods

Imaging data were collected from patients aged 9 to 15 years who received surgical treatment for HPD or RPD at a single institution between June 2015 and September 2020. The prevalence of trochlear dysplasia, tibial tubercle lateralization, and lower limb rotational deformity was assessed through hip/knee/ankle computed tomography (CT) using the following quantitative indicators: trochlear depth index, lateral trochlear inclination, sulcus angle, tibial tubercle-trochlear groove (TT-TG) distance, ratio of TT-TG distance to femoral width, TT-TG angle, femoral anteversion angle, and tibial external rotation angle. The morphology of trochlea and patella were graded on knee CT using the Dejour and Wiberg classification. The Insall-Salvati index and Caton-Deschamps index were used to evaluate the height of the patella on lateral view radiographs. To evaluate lower limbs malalignment, the mechanical lateral distal femoral angle and medial proximal tibial angle were measured on weightbearing full-length radiographs. The collected data were analyzed and compared between the HPD and RPD groups.

Results

Enrolled were 15 patients (21 knees) diagnosed with HPD and 18 patients (22 knees) diagnosed with RPD. The age of first dislocation was significantly younger in the HPD group (7.6 ± 3.4 vs 11.2 ± 1.4 years; P = 0.003). Knees in the HPD group had a significantly higher proportion of Dejour type C dysplasia (57.1% vs 4.5%; P < .005) and Wiberg type 3 patella (66.7% vs 9.1%; P < .001). There were statistically significant differences between the groups in the trochlear depth index (HPD vs RPD: 1.1 ± 1.7 vs 2.2 ± 1.5 mm; P = .039), sulcus angle (170.3° ± 13.7° vs 157.3° ± 16.0°; P = .007), Insall-Salvati index (1.1 ± 0.2 vs 1.3 ± 0.2; P = .034), and tibial external rotation angle (31.3° ± 7.8° vs 38.4° ± 8.5°; P = .009).

Conclusion

Patients in the HPD group presented with poorer trochlear and patellar development, lower patellar height, and less tibial external rotation compared with patients in the RPG group.

Radiographic Changes After Medial Patellofemoral Ligament Reconstruction in Skeletally Immature Patients Compared With an Age- and Sex-Matched Cohort

BACKGROUND

Despite recent evidence that medial patellofemoral ligament reconstruction (MPFLR) in the skeletally immature patient is both safe and effective, there are limited data evaluating postoperative coronal- and sagittal-plane growth and radiographic patellofemoral parameters in this population.

PURPOSE

The primary purpose was to assess radiographic measures of coronal-plane alignment, longitudinal growth, patellar congruence, and trochlear dysplasia after MPFLR in a skeletally immature population. A secondary purpose was to assess this population compared with a matched cohort with a focus on trochlear dysplasia prevalence and the effect of MPFLR on patellar height.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

A total of 28 children with a minimum 1-year follow-up who underwent isolated MPFLR were identified. All patients were skeletally immature, defined as fully open physes on both sides of the knee joint, at the time of surgery. The development of a limb length discrepancy or angular growth abnormalities were assessed on standing hip-to-ankle radiographs, patellar tilt and congruence were measured on the Merchant view of the knee, and the grade of trochlear dysplasia and patellar height were assessed on lateral knee radiographs. A sex- and age-matched group of patients who underwent anterior cruciate ligament reconstruction was formed as a control for patellar height and trochlear dysplasia measurements.

RESULTS

The mean patient age was 11.71 ± 2.02 years at the time of surgery with a mean follow-up of 23.54 ± 12.49 months. All but 1 patient in the MPFLR group had preoperative features consistent with trochlear dysplasia. There was no significant difference in limb length or coronal-plane alignment at final follow-up (P = .725 and P > .999, respectively). Both the MPFLR and the anterior cruciate ligament reconstruction groups had a statistically significant decrease in the Caton-Deschamps index between the preoperative and postoperative time points (mean, 0.18 ± 0.20 and 0.11 ± 0.14, respectively; P = .161).

CONCLUSION

MPFLR may be safely performed utilizing an epiphyseal femoral socket in a skeletally immature cohort without affecting normal longitudinal growth or coronal limb alignment. The previously reported effect of MPFLR in reducing patellar height may be related to physiological growth based on similar changes noted in a comparison cohort that did not undergo the procedure.

Patellofemoral joint load and knee abduction/adduction moment are sensitive to variations in femoral version and individual muscle forces

Torsional profiles of the lower limbs, such as femoral anteversion, can dictate gait and mobility, joint biomechanics and pain, and functional impairment. It currently remains unclear how the interactions between femoral anteversion, kinematics, and muscle activity patterns contribute to joint biomechanics and thus conditions such as knee pain. This study presents a computational modeling approach to investigating the interactions between femoral anteversion, muscle forces, and knee joint loads. We employed an optimal control approach to produce actuator and muscle-driven simulations of the stance phase of gait for femoral anteversion angles ranging from -8° (retroversion) to 52° (anteversion) with a typically developing baseline of 12° of anteversion and implemented a Monte Carlo analysis for variations in lower limb muscle forces. While total patellofemoral joint load decreased with increasing femoral anteversion, patellofemoral joint load alignment worsened, and knee abduction/adduction magnitude increased with both positive and negative changes in femoral anteversion (p < 0.001). The rectus femoris muscle was found to greatly influence patellofemoral joint loads across all femoral anteversion alignments (R > 0.8, p < 0.001), and the medial gastrocnemius was found to greatly influence knee abduction/adduction moments for the extreme version cases (R > 0.74, p < 0.001). Along with the vastus lateralis, which decreased with increasing femoral anteversion (R = 0.89, p < 0.001), these muscles are prime candidates for future experimental and clinical efforts to address joint pain in individuals with extreme femoral version. These findings, along with future modeling efforts, could help clinicians better design treatment strategies for knee joint pain in populations with extreme femoral anteversion or retroversion.

Tibial Derotational Osteotomy for Patellofemoral Instability: A Systematic Review

Introduction

The etiology of patellofemoral (PF) instability is multifactorial. Excessive external tibial torsion has been associated with recurrent patellar subluxation and persistent anterior knee pain. Several surgical techniques have been historically used to correct this, including medial patellofemoral ligament reconstruction, tibial tuberosity transfer (TTT), trochleoplasty, and tibial derotation osteotomy (TDO). The purpose of this systematic review is to investigate the safety and efficacy of TDO for PF instability and pain.

Methods

A thorough search of the literature was conducted on July 15, 2022. Seven studies met the inclusion criteria for this systematic review.

Results

Among the included studies, there were 179 total subjects and 204 operative knees. Mean follow-up time was 66.31 months (range 11-192). Complication rate was low (12.8%) in studies that reported complications. Average degree of anatomical correction in the transverse plane was 19.9 degrees with TDO. This increased to 34 degrees when combined with TTT. All PROMs assessed were significantly increased postoperatively (p < 0.05). Age greater than 25 years and advanced PF chondromalacia may negatively affect postoperative outcomes.

Conclusion

The primary findings of this review were as follows: (1) TDO results in significantly improved pain and PROM ratings in patients with PF pain and/or instability, (2) the likelihood of complication, including recurrent patella subluxation after TDO, is low but may be increased by aging, and (3) the successful anatomical correction of TDO may be augmented by concurrent TTT in some cases.

Radiographic Evaluation of Pediatric Patients with Patellofemoral Instability

PURPOSE OF REVIEW

The purpose of this review is to highlight the radiographic assessments of utility in the evaluation of a pediatric patient with patellofemoral instability to facilitate a thorough work-up. Understanding of these measures is useful in understanding evolving research in this field, providing accurate patient risk assessment, and appropriately directing surgical decision-making.

RECENT FINDINGS

Recent literature has broadened the radiographic characterization of the pediatric patellar instability and its anatomic risk factors. Knee MRI can inform the assessment of skeletal maturity and novel axial alignment measurements may enhance our identification of patients at increased risk of recurrent instability. Additional improvements have been made in the objective measurement and classification of trochlear dysplasia. Knee MRI-based skeletal age assessments may obviate the need for hand bone age assessments in growing children with patellofemoral instability. Novel objective measures exist in the evaluation of pediatric patellar instability both in the assessment of axial alignment and trochlear dysplasia. Future work should focus on how these measures can aid in guiding surgical decision-making.

Alteration of patellar tendon morphology in patellofemoral instability (trochlear dysplasia)

INTRODUCTION

Trochlear Dysplasia (TD) is a condition that is characterized by the presence of an abnormally shaped trochlear groove, which hinders the patellofemoral joint (PFJ) stability. PFJ stability is determined by static and dynamic structures around the knee joint. We analysed whether the patellar tendon morphology is altered in patients with patellofemoral instability in Trochlear Dysplasia (TD).

MATERIAL AND METHODS

Magnetic Resonance Imaging (MRI) studies for 50 consecutive knees with TD and 50 consecutive knees with normal PFJ morphology were obtained for evaluation. For each MRI study, the cross-sectional area (CSA) of the medial and lateral components of the patellar tendon was measured and used to calculate the cross-sectional area ratio (CSAR) by two readers.

RESULTS

There was a statistically significant difference in the CSAR of the lateral-to-medial components of the patellar tendon between knees with normal PFJ morphology and knees with TD (one way ANOVA, F (4,95) = 7.743, p < 0.001). Pairwise comparisons amongst the Dejour subtypes of TD, revealed a statistically significance difference (p < 0.05) in the CSAR ratio between patients with normal PFJ morphology, and patients with type A (p = 0.007) and type C, TD. There was moderate correlation between the readers on Intraclass Correlation Coefficient (ICC) analysis (ICC- 0.7).

CONCLUSION

Our findings reveals hypertrophy of the medial part of the patellar tendon in patients with PFJ instability and TD. These differences could reflect the dynamic compensatory changes occurring at the PFJ to counteract the laterally directed instability vectors found in this condition.