The Sagittal Tibial Tubercle-Trochlear Groove Distance as a Measurement of Sagittal Imbalance in Patients with Symptomatic Patellofemoral Chondral Lesions

Sagittal tibial tuberosity to trochlear groove distance measurements may reflect patellofemoral contact pressures

Tibial tubercle to trochlear groove (TTTG) distance is a commonly utilized measurement in the assessment of knees with patellar instability, representing malalignment in the form of tuberosity lateralization relative to the trochlear groove. More recently, the concept of the anteroposterior TTTG (AP-TTTG), renamed as the sagittal TTTG (sTTTG), has been studied as a measurement to assess the relationship between the two structures in a different direction, potentially representing patellofemoral contact pressures through its assessment in the sagittal plane. As we incorporate this measurement to capture how our surgical procedures can offload the joint and 'correct' the sTTTG distance, the utility of this measurement as a proxy for patellofemoral contact pressures will continue to grow, allowing us to better consider joint preservation in addition to stability in the management of patellar instability.

Risk Factors for Atraumatic Medial Patellar Facet Lesions

Background

Medial patellar facet lesions have been well-described in the setting of patellar instability. However, relatively little is known about risk factors for atraumatic medial patellar facet lesions.

Purpose/Hypothesis

To identify clinical and radiographic risk factors for medial patellar facet lesions in patients without a history of trauma or patellar instability. It was hypothesized that a posterior tibial tubercle relative to the trochlear groove would be a risk factor for atraumatic medial patellar facet lesions.

Study Design

Case-control study; Level of evidence, 3.

Methods

A total of 37 patients with atraumatic medial patellar facet lesions were matched by age, sex, and body mass index with 37 control patients without a history of patellofemoral dysplasia. Demographic and imaging characteristics were compared between groups. Plain radiography was used to evaluate Wiberg type, and magnetic resonance imaging was used to calculate Caton-Deschamps index, tibial tubercle-trochlear groove distance, trochlear facet asymmetry ratio, patellotrochlear index, sulcus depth, patellar bisect ratio, and tibial tubercle height. Statistically significant variables from univariate analysis were used as inputs to the multivariate regression model to assess independent risk factors.

Results

There were no differences between groups with respect to Wiberg type, Caton-Deschamps index, tibial tubercle-trochlear groove distance, sulcus depth, or patellotrochlear index (P > .05 for all). The medial facet lesion group had a larger medial trochlear facet (trochlear facet asymmetry ratio, 0.72 ± 0.11 vs 0.60 ± 0.09; P < .001), a more medial-lying patella in the trochlear groove (patellar bisect ratio, 0.57 ± 0.06 vs 0.55 ± 0.07; P = .035), and a more posterior tibial tubercle relative to the trochlear groove (tibial tubercle height, -3.13 ± 5.21 vs -0.23 ± 5.93 mm; P = .030) compared with the control group. Multivariate regression analysis identified trochlear facet asymmetry and tibial tubercle height as independent risk factors for medial patellar facet lesions (relative risk = 97.3 [95% CI, 14.9-635.1], P < .001 and relative risk = 0.95 [95% CI, 0.92-0.98], P = .004, respectively).

Conclusion

A relatively larger medial trochlear facet and a more posterior tibial tubercle relative to the trochlear groove were found to be risk factors for medial patellar facet lesions in patients without a history of trauma or patellar instability.

Decreased Effective Patellar Tendon Length following Distalization Tibial Tubercle Osteotomy without Patellar Tendon Tenodesis

Background

Distalization tibial tubercle osteotomy (TTO) is an effective treatment for improving patellar height in patients with patella alta associated with patellofemoral instability and cartilage lesions. The addition of a patellar tendon tenodesis has been suggested; nonetheless, concerns exist regarding possible increased patellofemoral cartilage stresses.

Purpose

To evaluate pre- and postoperative patellar tendon length and alignment parameters on magnetic resonance imaging (MRI), as well as patient-reported outcome measures (PROMs) after distalization TTO without patellar tendon tenodesis.

Study Design

Case series; Level of evidence, 4.

Methods

Twenty skeletally mature patients who underwent distalization TTO with or without anteromedialization at our institution between December 2014 and August 2021 were included. All patients underwent pre- and postoperative MRIs of the affected knee. The Caton-Deschamps index (CDI), the axial and sagittal tibial tubercle-trochlear groove (TT-TG) distances, the distances from the tibial plateau to the patellar tendon insertion and the tibial tubercle, and the patellar tendon length were assessed. PROMs included the International Knee Documentation Committee Subjective Knee Evaluation Form, the Knee injury and Osteoarthritis Outcome Score-Quality of Life subscale, the Kujala Anterior Knee Pain Scale, and the Veterans RAND 12-Item Health Survey mental and physical component scores.

Results

The mean patient age at surgery was 27.4 years (range, 14-42 years). Radiographic parameters demonstrated improved patellar height (CDI decreased from 1.36 to 1.11; P < .001) after distalization TTO. The distance from the tibial plateau to the patellar tendon insertion significantly decreased from 20.1 mm preoperatively to 17.9 mm postoperatively (P < .020), and the patellar tendon length decreased from 53.4 mm preoperatively to 46.0 mm postoperatively (P < .001). The patellar tendon insertion was not distalized after distalization TTO, likely because of scarring of the patellar tendon proximal to the osteotomy site. Patients demonstrated significant pre- to postoperative improvements on all PROMs (P≤ .024 for all ). There were 4 (20%) complications-2 cases of arthrofibrosis, 1 postoperative infection, and 1 osteotomy delayed union.

Conclusion

Distalization TTO without patellar tendon tenodesis was associated with improved radiographic outcomes and PROMs. It provides an additional tool for surgical management of patellofemoral pathology with associated patella alta.

Editorial Commentary: A Posterior Tibial Tubercle Relative to the Trochlear Groove Is Associated With Increased Risk of Patellofemoral Arthritis: The Sagittal Tibial Tubercle-Trochlear Groove Distance

Arthritis of the patellofemoral compartment affects up to 24% of women and 11% of men over the age of 55 years who have symptomatic osteoarthritis of the knee. Patellofemoral cartilage lesions have been associated with several different geometric measures of patellar alignment, including the tibial tubercle-trochlear groove (TTTG) distance, trochlear sulcus angle, trochlear depth, and patellar height. Recently, there has been interest in the sagittal TTTG distance, which measures the position of the tibial tubercle with respect to the trochlear groove. This measurement is now being used in patients presenting with patellofemoral pain and/or cartilage pathology and may help guide surgical decision making as we gain more data on how changing the tibial tubercle alignment relative to the patellofemoral joint can improve outcomes. For now, there are not enough data to support isolated anteriorization tibial tubercle osteotomy in patients with patellofemoral chondral wear based on the sagittal TTTG distance. However, as we better understand geometric measures as risk factors for patellofemoral arthritis, realignment at a young age might be recommended as a preventative measure against end-stage osteoarthritis.

Tibial Tubercle Osteotomy With Distalization for the Treatment of Patella Alta

One of the most common osseous abnormalities associated with patellar instability and patellofemoral osteochondral disease is patella alta, characterized by an Insall-Salvati ratio ≥1.2 or a Caton-Deschamps Index ≥1.2. Despite being the most common surgical treatment option for patella alta, tibial tubercle osteotomy with distalization raises concerns due to the complete detachment of the tubercle, which may lead to damage of local vascularity from periosteal detachment and increased mechanical stress at the attachment site. These factors are related to greater risk of complications, such as fractures, loss of fixation, delayed union, or nonunion of the tuberosity. We describe a technique for tibial tubercle osteotomy with distalization that aims to minimize these complications through care with the osteotomy, stabilization, bone cut thickness, and local periosteum.

A More Posterior Tibial Tubercle (Decreased Sagittal Tibial Tubercle-Trochlear Groove Distance) Is Significantly Associated With Patellofemoral Joint Degenerative Cartilage Change: A Deep Learning Analysis

PURPOSE

To perform patellofemoral joint (PFJ) geometric measurements on knee magnetic resonance imaging scans and determine their relations with chondral lesions in a multicenter cohort using deep learning.

METHODS

The sagittal tibial tubercle-trochlear groove (sTTTG) distance, tibial tubercle-trochlear groove distance, trochlear sulcus angle, trochlear depth, Caton-Deschamps Index (CDI), and flexion angle were measured by use of deep learning-generated segmentations on a subset of the Osteoarthritis Initiative study with radiologist-graded PFJ cartilage grades (n = 2,461). Kruskal-Wallis H tests were performed to compare differences in PFJ morphology between subjects without PFJ osteoarthritis (OA) and those with PFJ OA. PFJ morphology was correlated with secondary outcomes of mean patellar cartilage thickness and mean patellar cartilage T2 relaxation time using linear regression models controlling for age, sex, and body mass index.

RESULTS

A total of 1,626 knees did not have PFJ OA, whereas 835 knees had PFJ OA. Knees without PFJ OA had an increased (anterior) sTTTG distance (mean ± standard deviation, 11.1 ± 12.8 mm) compared with knees with PFJ OA (8.4 ± 12.7 mm) (P < .001), indicating a more posterior tibial tubercle in subjects with PFJ OA. Knees without PFJ OA had a decreased sulcus angle (127.4° ± 7.1° vs 128.0° ± 8.4°, P = .01) and increased trochlear depth (9.1 ± 1.7 mm vs 9.0 ± 2.0 mm, P = .03) compared with knees with PFJ OA. Decreased patellar cartilage thickness was associated with decreased trochlear depth (β = 0.12, P = .002) and increased CDI (β = -0.07, P < .001). Increased patellar cartilage T2 relaxation time was correlated with decreased sTTTG distance (β = -0.08, P = .01), decreased sulcus angle (β = -0.12, P = .04), and decreased CDI (β = -0.12, P < .001).

CONCLUSIONS

PFJ OA, patellar cartilage thickness, and patellar cartilage T2 relaxation time were shown to be associated with the underlying geometries within the PFJ. This large longitudinal study highlights that a decreased sTTTG distance (i.e., a more posterior tibial tubercle) is significantly associated with PFJ degenerative cartilage change.

LEVEL OF EVIDENCE

Level III, retrospective comparative prognostic trial.

Interobserver Reliability and Change in the Sagittal Tibial Tubercle-Trochlear Groove Distance with Increasing Knee Flexion Angles

The tibial tubercle-trochlear groove (TT-TG) distance is currently utilized to evaluate knee alignment in patients with patellar instability. Sagittal plane pathology measured by the sagittal tibial tubercle-trochlear groove (sTT-TG) distance has been described in instability but may also be important to consider in patients with cartilage injury. This study aims to (1) describe interobserver reliability of the sTT-TG distance and (2) characterize the change in the sTT-TG distance with respect to changing knee flexion angles. In this cadaveric study, six nonpaired cadaveric knees underwent magnetic resonance imaging (MRI) studies at each of the following degrees of knee flexion: -5, 0, 5, 10, 15, and 20. The sTT-TG distance was measured on the axial T2 sequence. Four reviewers measured this distance for each cadaver at each flexion angle. Intraclass correlation coefficients were calculated to determine interobserver reliability and reproducibility of the sTT-TG measurement. Analysis of variance (ANOVA) tests and Friedman's tests with a Bonferroni's correction were performed for each cadaver to compare sTT-TG distances at each flexion angle. Significance was defined as p < 0.05. There was excellent interobserver reliability of the sTT-TG distance with all intraclass correlation coefficients >0.9. The tibial tubercle progressively becomes more posterior in relation to the trochlear groove (more negative sTT-TG distance) with increasing knee flexion. The sTT-TG distance is a measurement that is reliable between attending surgeons and across training levels. The sTT-TG distance is affected by small changes in knee flexion angle. Awareness of knee flexion angle on MRI is important when this measurement is utilized by surgeons.

Posterior tibial tubercle measured by the sagittal TT-TG distance correlates with increased risk for patellofemoral chondral lesions

PURPOSE

To evaluate the variation in tibial tubercle sagittal alignment in patients with and without patellofemoral (PF) cartilage wear.

METHODS

This was a single-centre, retrospective review of patients that underwent a cartilage restoration procedure for isolated PF cartilage wear from 2014 to 2020. Patients were matched in a 1:2 ratio for age, sex and BMI to partial meniscectomy patients as controls. The sagittal TT-TG (sTT-TG) distance was measured on preoperative axial T2 magnetic resonance imaging (MRI) and was defined as the distance between a point at the nadir of the trochlear cartilage and the most anterior point of the tibial tubercle.

RESULTS

One hundred and forty patients (47 cartilage restoration, 94 meniscectomy) were included. Mean age, BMI, and height for the total cohort were 34.01 ± 8.7, 26.6 ± 6.4, and 173.0 ± 17.7 respectively, with 78 males (55%) and 63 females (45%). There were no significant differences between groups for age, BMI or sex (n.s). The cartilage restoration group (- 2.5 mm ± 5.9) was found to have a significantly more posterior (negative) sTT-TG compared to the meniscectomy group (1.72 mm ± 6.7) (p < 0.001). Interrater reliability was excellent (ICC = 0.931, p < 0.001). Patients with less than - 3.4 mm sTT-TG were 2.74 times more likely to have a cartilage restoration procedure compared to those with greater than - 3.4 mm (OR 2.7, 95% CI 1.3-5.85). Patients with < - 10 mm posterior translation were 13.7× (CI 1.6-111.1) more likely to have a cartilage restoration procedure.

CONCLUSION

Patients that underwent isolated cartilage restoration procedures had a significantly more posterior tibial tubercle than partial meniscectomy controls based on the sagittal TT-TG. The more posterior the tubercle, the more likely the patient had a cartilage restoration procedure. Surgeons should consider the sTT-TG measurement in patients presenting with anterior knee pain, particularly patellofemoral lesions.

LEVEL OF EVIDENCE

III.

[Patellofemoral cartilage repair]

Anterior knee pain is a frequent symptom in young athletes. Symptomatic patellofemoral cartilage defects can occur after trauma, especially after patellar dislocation. Numerous cartilage repair methods are currently available. Due to co-pathologies, the outcome after patellofemoral cartilage repair is inferior to the treatment of cartilage defects of the tibiofemoral joint. Adequate addressing of coexisting pathologies is essential for treatment success. This review provides an overview of the different techniques of patellofemoral cartilage repair.

Sagittal patellar flexion angle measurement determines greater incidence of patella alta in patellar tendinopathy patients

PURPOSE

The objective of this study was to compare patellar height and patella alta between a control cohort and patients with patellar tendinopathy by the sagittal patellar flexion angle (SPFA) measurement.

METHODS

Magnetic resonance imaging (MRI) scans of the knee were obtained from a sports imaging facility and screened to select patients with anterior knee pain. This symptomatic group was divided into two patient cohorts: those with and without MRI features of patellar tendinopathy. Lateral knee radiographs were reviewed and SPFA, knee flexion angle and Insall-Salvati ratio (IS) were measured from the radiographs by two independent reviewers.

RESULTS

A total of 99 patients consisting of 48 patellar tendinopathy patients and 51 control patients were included. There was a significantly higher mean patellar height (p = 0.002, d = 0.639) and a greater patella alta incidence in the patellar tendinopathy cohort (25.0%) compared to the controls (3.9%) (p = 0.022, d = 0.312). Insall-Salvati ratio measurements showed no difference in patella alta incidence between tendinopathy and control cohorts. There was excellent inter- and intra-observer reliability of SPFA measurements (ICC 0.99).

CONCLUSION

This is the first study to demonstrate a greater incidence of patella alta in patellar tendinopathy patients compared to controls. A greater patella alta incidence amongst patellar tendinopathy patients as defined by SPFA was found to be clinically relevant, as it suggests these patients may comprise the recalcitrant patient subgroup who do not improve with current surgical intervention and may therefore benefit from a biomechanical surgical solution.

LEVEL OF EVIDENCE

III.

Anteriorizing Tibial Tubercle Osteotomy for Patellofemoral Cartilage Lesions

Patellofemoral chondral lesions are common and can lead to significant pain. A tibial tubercle osteotomy (TTO) functions to mechanically unload the patellofemoral joint and improve the clinical success of cartilage restoration procedures. The type of TTO performed is based on several factors. There is a subset of patients with patellofemoral cartilage disease who would benefit from a pure anteriorization of the tibial tubercle. We describe our technique for a pure anteriorization TTO, which functions to safely unload the patellofemoral joint in the appropriately indicated patient.