Influence of tibial tuberosity position and trochlear depth on patellar tracking in patellar instability: Variations with Patella Alta

Investigating patellar motion using weight-bearing dynamic CT: normative values and morphological considerations for healthy volunteers

BACKGROUND

Patellar instability is a well-known pathology in which kinematics can be investigated using metrics such as tibial tuberosity tracheal groove (TTTG), the bisect offset (BO), and the lateral patellar tilt (LPT). We used dynamic computed tomography (CT) to investigate the patellar motion of healthy subjects in weight-bearing conditions to provide normative values for TTTG, BO, and LPT, as well as to define whether BO and LPT are affected by the morphology of the trochlear groove.

METHODS

Dynamic scanning was used to acquire images during weight-bearing in 21 adult healthy volunteers. TTTG, BO, and LPT metrics were computed between 0° and 30° of knee flexion. Sulcus angle, sulcus depth, and lateral trochlear inclination were calculated and used with the TTTG for simple linear regression models.

RESULTS

All metrics gradually decreased during eccentric movement (TTTG, -6.9 mm; BO, -12.6%; LPT, -4.3°). No significant differences were observed between eccentric and concentric phases at any flexion angle for all metrics. Linear regression between kinematic metrics towards full extension showed a moderate fit between BO and TTTG (R2 0.60, β 1.75) and BO and LPT (R2 0.59, β 1.49), and a low fit between TTTG and LPT (R2 0.38, β 0.53). A high impact of the TTTG distance over BO was shown in male participants (R2 0.71, β 1.89) and patella alta individuals (R2 0.55, β 1.91).

CONCLUSION

We provided preliminary normative values of three common metrics during weight-bearing dynamic CT and showed the substantial impact of lateralisation of the patella tendon over patella displacement.

RELEVANCE STATEMENT

These normative values can be used by clinicians when evaluating knee patients using TTTG, BO, and LPT metrics. The lateralisation of the patellar tendon in subjects with patella alta or in males significantly impacts the lateral displacement of the patella.

KEY POINTS

Trochlear groove morphology had no substantial impact on motion prediction. The lateralisation of the patellar tendon seems a strong predictor of lateral displacement of the patella in male participants. Participants with patella alta displayed a strong fit between the patellar lateral displacement and tilt. TTTG, BO, and LPT decreased during concentric movement. Concentric and eccentric phases did not show differences for all metrics.

Adding Tibial Tuberosity Medialization to Medial Patellofemoral Ligament Reconstruction Reduces Lateral Patellar Maltracking During Multidirectional Motion in a Computational Simulation Model

Purpose

To determine whether adding tibial tuberosity medialization to medial patellofemoral ligament (MPFL) reconstruction reduces lateral patellar maltracking during a dynamic multidirectional activity and to investigate when medial patellofemoral contact pressures are elevated during daily activities, such as squatting.

Methods

Seven computational models representing knees with patellar instability, including lateral patellar maltracking, were evaluated following simulated MPFL reconstruction (bisect offset index > .75). Tibial tuberosity medialization was added to MPFL reconstruction for each model. Patellar tracking during multidirectional motion was evaluated by simulating pivot landing. Analysis of pivoting focused on early flexion (5° to 40°). Patellofemoral contact pressures during daily function were evaluated by simulating knee squatting. Data were analyzed with paired comparisons between MPFL reconstruction with and without tuberosity medialization.

Results

The patella dislocated during pivoting for 2 models with an isolated MPFL reconstruction and for 1 model including tibial tuberosity medialization. Adding tibial tuberosity medialization to MPFL reconstruction significantly decreased bisect offset index by ∼0.1 from 5° to 40° (P < .03). For knee squatting, medializing the tibial tuberosity significantly increased maximum medial contract pressure by ∼0.5 MPa from 30° to 85° (P < .05) but did not significantly influence maximum lateral pressure.

Conclusions

In this study of simulated multidirectional motion, MPFL reconstruction did not sufficiently constrain the patella for some knees. Adding tibial tuberosity medialization to MPFL reconstruction in these models reduced lateral patellar maltracking during multidirectional motion but increased pressure applied to medial cartilage during squatting.

Clinical Relevance

After establishing the influence of tibial tuberosity medialization on patellar maltracking for an idealized population, as was done in the current study, future simulation studies can be performed to better determine the anatomical characteristics of patients for whom tibial tuberosity medialization is needed to reduce the risk of postoperative patellar maltracking.

The Onset and Development of Patella Alta in Children With Patellar Instability

BACKGROUND

Patella alta is an anatomic risk factor for patellar instability in adolescents that is also linked to the risk factor of trochlear dysplasia. This study aims to determine the age of onset and age-related incidence of patella alta in a pediatric population of patients with patellar instability. We hypothesized that patellar height ratios would not increase with age, suggesting a congenital rather than the developmental origin of patella alta.

METHODS

A retrospective cross-sectional cohort of patients was collected with the following inclusion criteria: patients aged 5 to 18 who had a knee magnetic resonance imaging performed from 2000 to 2022 and the International Classification of Diseases code for patellar dislocation. Demographic information and details of the patellar instability episode(s) were collected with a chart review. Sagittal magnetic resonance imaging was used to measure Caton-Deschamps Index (CDI) and the Insall-Salvati Ratio (ISR) by 2 observers. Data were analyzed to assess for associations between patellar height ratios and age of the first dislocation and to assess if the proportion of patients categorized as having patella alta changed with age.

RESULTS

The 140 knees included in the cohort had an average age of 13.9 years (SD=2.40; range: 8-18) and were 55% female. Patella alta was present in 78 knees (55.7%) using CDI>=1.2 and in 59 knees (42.1%) using ISR>=1.3. The earliest age patella alta was observed was at age 8 using CDI>=1.2 and age 10 using ISR>=1.3. There were no statistically significant associations between CDI and age without adjustment (P=0.14) nor after adjustment for sex and body mass index (P=0.17). The proportion of knees above the CDI threshold for patella alta to the knees below the cutoff did not show a significant change with age (P=0.09).

CONCLUSIONS

Patella alta, as defined by CDI, is seen in patients as young as 8 years old. Patellar height ratios do not change with age in patients with patellar dislocation, suggesting that patella alta is established at a young age rather than developing during the adolescent years.

LEVEL OF EVIDENCE

Level III-diagnostic, cross-sectional.

Patellar Tendon Imbrication for the Treatment of Patella Alta in Skeletally Immature Patients

Patella alta is a major contributor to recurrent patellar instability, which is commonly seen in young athletes. Distalizing tibial tubercle osteotomy has been used for the correction of patella alta and patellar instability, but this procedure is contraindicated in the skeletally immature patient population, as it could lead to growth arrest of the proximal tibial physes. We propose a patellar tendon imbrication technique as a soft-tissue alternative to tibial tubercle osteotomy. When used with concomitant medial patellofemoral ligament reconstruction, we suggest this procedure may prove beneficial for the treatment of patellar instability in skeletally immature patients.

MODELING OF PATELLA HEIGHT WITH DISTAL FEMUR AND PROXIMAL TIBIA REFERENCE POINTS WITH ARTIFICIAL NEURAL NETWORK

The patellofemoral joint is one of the parts of the knee extension mechanism that plays a role in the stability of the knee by enlarging the force arm of the quadriceps muscle and changing the direction of the muscle strength. For the entire knee joint to perform its task painlessly and functionally, the positions and strength of the muscles, the strength of the ligaments, and their reaction to movement must be compatible. The Insall–Salvati (Ins-Sal) index is useful for showing changes in patellar height produced by repositioning the tibial plateau, in other words, showing changes in patellar tendon length. Patella height is an important value to be taken into account in knee prosthesis surgery, tibial osteotomy, and anterior cruciate ligament reconstruction. The morphometric relationship between the reference measurements of the distal femur and proximal tibia and the position of the patella will be useful in determining the natural anatomy. In this study, we aimed to determine the relationship between patella height and distal femur and proximal tibia reference areas by using the artificial neural network method as an alternative approach method. In order to assess the performance of the estimation of the Ins-Sal index, the four ANN model with six input combinations which included age, gender and the reference measurements for the right and left sides have been constructed and tested. The MSE and [Formula: see text] values are calculated for every four models for the training and test phase. The results show that the proposed approach for modeling of relation between reference measurements and the Ins-Sal index is a powerful approach.