Tibial Tubercle-posterior Cruciate Ligament Distance Research Articles

Impact of sex and age on the lateralisation of the tibial tubercle in normal paediatric and adolescent populations.

Numerous methods have been proposed to characterise tubercle lateralisation. However, their normal values and related changes remain unclear. Accordingly, it was aimed to determine the potential sex and age effects and determined the optimal individualised method of diagnosing lateralisation of the tibial tubercle in patients with recurrent patellar dislocation (RPD). Measurements included the tibial tubercle-trochlear groove (TT-TG) distance, tibial tubercle-posterior cruciate ligament (TT-PCL) distance and tibial tubercle lateralisation (TTL); and the proximal tibial width (PTW), trochlear width (TW) and trochlear dysplasia index (TDI), for adjustment. A two-way analysis of variance was used to determine the effect of age, sex and their interaction within the normal group. When the age effect was statistically significant, a nonlinear regression was created. Areas under the receiver-operating characteristic curve (AUCs) were calculated to assess diagnostic accuracy. A total of 277 normal participants (mean [SD] age, 13.5 [2.6] years; 125 [45.1%] female) and 227 patients with RPD (mean [SD] age, 13.5 [2.6] years; 161 [58.1%] female) were analysed. It was found that in the normal group, in patients aged 7-10, TT-PCL distance (p = 0.006), TTL (p = 0.007) and TT-PCL/PTW (p < 0.001) were significantly larger in females than in males. A significant sex effect was also detected on TT-TG/TW (p = 0.014). TT-TG distance, TT-PCL distance, TTL and TT-PCL/PTW (in male patients) approached an established normal adult value of 12.3 mm, 20.9 mm, 0.64 and 0.28, respectively, with increasing age (p < 0.001). The AUC was greater for TT-TG/TDI and TT-TG/TW (p ≤ 0.01) and TT-TG/TDI outperformed TT-TG/TW in patients aged 15-18 (p = 0.004). Tubercle lateralisation increased with age and was affected by sex, with the exception of TT-TG distance and TT-TG/TDI. TT-TG/TDI is the optimal method of diagnosing a lateralized tibial tubercle in patients with RPD. These findings assist with the evaluation of tubercle lateralisation in that they provide a proper protocol for paediatric and adolescent populations with RPD; and thus, will help determine whether medial tubercle transfer should be included among the tailored surgical procedures considered for the treatment of patients with RPD. Level III.

Normative Values of Tibial Tubercle–Trochlear Groove Distance and Tibial Tubercle–Posterior Cruciate Ligament Distance in Children

Background: Patellar instability is a common knee pathology in skeletally immature patients. In skeletally mature populations, a tibial tubercle–trochlear groove (TT-TG) distance of ≥20 mm is generally considered a pathological value. However, as pediatric patients grow and as the TT-TG distance varies with age, applying the same cutoff value as adult patients to them is unreasonable. Purpose/Hypothesis: This study aimed to analyze the normative values of the TT-TG and tibial tubercle–posterior cruciate ligament (TT-PCL) distances in children with no patellofemoral instability and to propose the cutoff value of the TT-TG and TT-PCL distances predictive of increased risk of patellofemoral instability in pediatric patients. We hypothesized that the TT-TG and TT-PCL distances increase with age in children and adolescents. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Magnetic resonance imaging scans of the knee were collected from the patellar instability group and the control group. The TT-TG and TT-PCL distances were measured. The normalized values of the TT-TG and TT-PCL distances were calculated by dividing them by the femoral width. Segmented analysis with 1 breakpoint was performed for both the TT-TG and the TT-PCL distances. The optimal cutoff values of the TT-TG and TT-PCL distances were calculated by maximizing the sum of the sensitivity and specificity. Results: A total of 87 patients had patellar instability, and 509 patients did not. The median values of TT-TG and TT-PCL distances in the control group (8.18 mm and 19.48 mm, respectively) were significantly smaller than those in the instability group (16.10 mm and 24.41 mm, respectively). For those aged <15 years, the TT-TG distance significantly increased by 0.39 mm as the age increased by 1 year. The TT-PCL distance increased by 1.14 mm/year until the age of 11 years. In our cohort, the cutoff value of the TT-TG distance of 14.90 mm yielded 66% sensitivity and 81.9% specificity for predicting an increased risk of patellar instability. The cutoff value of the TT-PCL distance of 23.68 mm yielded 63.9% sensitivity and 65.3% specificity for predicting an increased risk of patellar instability. Conclusion: In our cohort of 596 participants, we have documented the normative values of the TT-TG and TT-PCL distances in children aged <20 years. During the surgery for patellar instability in pediatric patients, orthopaedic surgeons should consider the normative values of the TT-TG and TT-PCL distances according to age to determine which patients need distal realignment surgery.

The Tibial Tuberosity–Rotational Angle as a Novel Predisposing Parameter for Patellar Dislocation

The tibial tuberosity (TT) in the axial plane is located on a curved line along the anterior cortex of the proximal tibia. Therefore, the linear measurement of TT position may not fully reflect TT malposition. To introduce TT-rotational angle (TT-RA) as a new anatomical parameter, which means the rotation of the TT relative to the dorsal condylar line of the tibia, and to validate its predictive value for patellar dislocation. Cross-sectional study; Level of evidence, 3. Included were 46 patients with a history of patellar dislocation and 46 age- and sex-matched controls who underwent axial magnetic resonance imaging. Seven radiological parameters were measured and compared between the 2 groups, including TT-trochlear groove (TT-TG) distance, tibial tubercle-posterior cruciate ligament (TT-PCL) distance, TT-PCL ratio, TT lateralization (TTL), trochlear groove medialization (TGM), TT-RA, trochlear groove-posterior condylar axis angle (TG-PCA), and knee rotation. The predictive values of parameters for patellar dislocation were assessed using multiple logistic regression analysis. The intra- and interobserver correlation coefficients for measuring the radiographic parameters showed good to excellent values., respectively. There were significant differences in the TT-TG distance (13.9 vs 6.8 mm; P < .001), TT-RA (16.0° vs 9.1°; P < .001), TG-PCA (93.7° vs 95.4°; P = .017), and knee rotation (0.9° vs 5.3°; P < .001) between the 2 groups. However, there was no significant difference in TT-PCL distance (20.7 vs 19.4 mm; P = .075), TT-PCL ratio (28.0% vs 26.6%; P = .136), TTL (65.7% vs 64.9%; P = .270), or TGM (54.9% vs 55.0%; P = .923). Multivariable analysis showed that 3 parameters were significantly associated with patellar dislocation: TT-RA (OR, 1.57; P < .001), TT-TG distance (OR, 1.52; P = .002), and knee rotation (OR, 0.75; P = .022). The TT-RA was a reliable predisposing parameter of patellar instability. It can be an alternative method of measurement when the TT-TG distance is not clearly defined.

The tibial tubercle-posterior cruciate ligament (TT-PCL) distance does not truly reflect the lateralization of the tibial tubercle.

The role of the tibial tubercle-posterior cruciate ligament (TT-PCL) and tibial tubercle-trochlear groove (TT-TG) in recurrent patellar instability (RPI) remains unclear. This study aims to confirm the validity of the TT-TG and TT-PCL in predicting RPI and to verify whether the TT-PCL can truly reflect the lateralization of the tibial tubercle. A total of 50 patients with RPI and 50 controls were recruited and underwent magnetic resonance imaging examinations. The TT-TG, TT-PCL, and tibial tubercle lateralization (TTL) were measured independently by two authors in a blinded and randomized fashion. T-test was used for parametric variances and the Mann-Whitney U and Chi-square tests were used for non-parametric variances. Pearson's product moment correlation coefficients were calculated to determine correlations between the defined measurements. The intraclass correlation coefficient was used to assess the reliability of the measurements. All defined measurements showed excellent intra- and inter-observer reliability. The TT-TG distance, TT-PCL distance, and TTL were significantly greater in the PI group than in the control group. The AUC was highest for the TT-TG distance compared with that for the TT-PCL distance, and TTL were 0.798, 0.764, and 0.769, with the calculated cut-off value of 12.5mm, 16.5mm, and 66.1 percentages. There was a moderate correlation (r = 0.595) between the TT-TG distance and TTL, and a weak correlation (r = 0.430) between the TT-PCL distance and TTL. Both the TT-TG distance and TT-PCL distance can be measured with excellent reliability on magnetic resonance imaging. The TT-TG distance, rather than the TT-PCL distance, has a better performance in predicting RPI. Most interestingly, the TT-PCL distance cannot reflect the real lateralization of TT. This study provides new information to evaluate TTL in patients with RPI. III.

Patellar dislocation is associated with increased tibial but not femoral rotational asymmetry.

Patellar dislocation is associated with a range of anatomical abnormalities affecting the trochlea, extensor mechanism and the tibia. The relationship between patellofemoral instability and rotational abnormalities of the posterior condyles, trochlear groove and proximal tibia has not been adequately determined. This study aimed to identify the frequency and severity of anatomical risk factors to determine their relative contribution to patellofemoral instability. A retrospective morphological study was undertaken comparing multiple anatomical measurements with magnetic resonance imaging of 50 patients with patellofemoral instability to an age- and gender-matched Control group (n = 50). Several techniques were assessed measuring both femoral and tibial axial asymmetry. A new measurement, tibial rotational asymmetry, comparing a line between the midpoints of the collateral ligaments to the axis between the patellar tendon and posterior cruciate ligament, was assessed for its association with patellofemoral instability. Compared to the controls, the patellofemoral instability group demonstrated a significant difference in tibial rotational asymmetry, with a mean of 2.9° (SD 3.2°) externally rotated vs -1.6° (SD 2.2°) in the control group. Significant differences were also demonstrated regarding the sulcus angle, tibial tubercle-trochlear groove distance, tibial tubercle-posterior cruciate ligament distance, patellar size and the Insall-Salvati ratio. There were no differences between groups regarding the lengths of the posterior condyles, the heights of the trochlear ridges or lateralisation of the trochlear groove. Further analysis of the patellofemoral instability group revealed a subgroup of males with normal anatomy (7/50) and a subgroup of females with isolated patella alta (7/50). Patellofemoral instability is associated with tibial rotational asymmetry due to lateralisation of the tibial tubercle. It is also associated with patella alta and reduced trochlear groove depth. The femoral axial shape is otherwise unchanged. III.

Accuracy of tibial tuberosity-trochlear groove distance and tibial tuberosity-posterior cruciate ligament distance in terms of the severity of trochlear dysplasia

PurposeIncreased tibial tubercle-trochlear groove distance (TT-TG) was proposed as one of the main risk factors for patellofemoral instability (PFI). The increased TT-TG distance indicated externalization of the tibial tubercle with the reference of the trochlear groove. However, in the case of severe trochlear dysplasia, the reference point on the trochlear groove was indistinct, and the accuracy of TT-TG was controversial. The purpose of this study was to evaluate the accuracy of TT-TG and TT-PCL in consideration of the mild and severe trochlear dysplasia.MethodsFrom 2015 to 2020, MRI findings of consecutive knee joints with PFI symptoms diagnosed in our hospital were retrospectively analyzed. All knees with trochlear dysplasia were diagnosed by longitudinal MRI scan and lateral radiograph. The knees were classified according to the four-type classification system described by Dejour et al. Twenty cases of type A (mild trochlear dysplasia); 20 cases of type B, C, and D (severe trochlear dysplasia); and 20 cases of normal type were selected and divided into normal group (normal trochlea), mild group (type A), and severe group (type B, type C, type D). Tibial tubercle-trochlear groove distance (TT-TG), tibial tubercle-posterior cruciate ligament distance (TT-PCL), and the Dejour classification of trochlear dysplasia were assessed by 2 experienced orthopedics. The reliability of TT-TG distance and TT-PCL distance was tested by intraclass correlation coefficients (ICCs).ResultsComparing the differences between TT-TG and TT-PCL in the normal, mild, and severe groups, the TT-TG and TT-PCL in the mild and severe groups show different meanings (normal, 8.83 ± 3.62 mm vs. 8.44 ± 4.57 mm, P > 0.05; mild, 17.30 ± 4.81 mm vs. 20.09 ± 5.05 mm, P < 0.05; severe, 10.79 ± 4.24 mm vs. 12.31 ± 5.43 mm, P > 0.05). The Pearson correlation coefficient of TT-TG and TT-PCL measurements of trochlear dysplasia were r = 0.480 (mild group, P = 0.032) and r = 0.585 (severe group, P < 0.001). The intra-observer ICCs of TT-TG were r = 0.814 (mild group) and r = 0.739 (severe group). The inter-observer ICCs of TT-TG were r = 0.810 (mild group) and r = 0.713 (severe group). In the normal knee, the Pearson correlation coefficient of TT-TG and TT-PCL was r = 0.787(P < 0.001), the intra-observer ICC of TT-TG was r = 0.989, and the inter-observer ICC of TT-TG was r = 0.978.ConclusionCompared with the mild trochlear dysplasia, the inter-observer and intra-observer correlations of TT-TG measurements decreased in the group of severe dysplastic trochlea (inter-observer ICC, 0.810 vs. 0.713; intra-observer ICC, 0.814 vs. 0.739). In the present study, the determination of TT-TG and TT-PCL distance are of great significance for patients with low-grade trochlear dysplasia. And TT-PCL, without referring to the abnormal trochlear groove, is an effective indicator to measure the lateralization of tibial tuberosity in patients with severe dysplastic trochlea.

Radiologic Measurements in the Assessment of Patellar Instability: A Systematic Review and Meta-analysis.

Background:Numerous diagnostic imaging measurements related to patellar instability have been evaluated in the literature; however, little has been done to compare these findings across multiple studies.Purpose:To review the different imaging measurements used to evaluate patellar instability and to assess the prevalence of each measure and its utility in predicting instability. We focused on reliability across imaging modalities and between patients with and without patellar instability.Study Design:Systematic review; Level of evidence, 4.Methods:We performed a systematic review of the literature using the PubMed, SCOPUS, and Cochrane databases. Each database was searched for variations of the terms “patellar instability,” “patellar dislocation,” “trochlear dysplasia,” “radiographic measures,” “computed tomography,” and “magnetic resonance imaging.” Studies were included if they were published after May 1, 2009, and before May 1, 2019. A meta-analysis using a random effects model was performed on several measurements, comparing instability and control groups to generate pooled values.Results:A total of 813 articles were identified, and 96 articles comprising 7912 patients and 106 unique metrics were included in the analysis. The mean patient age was 23.1 years (95% CI, 21.1-24.5), and 41% were male. The tibial tubercle–trochlear groove (TT-TG) distance was the most frequently included metric (59 studies), followed by the Insall-Salvati ratio and Caton-Deschamps index (both 26 studies). The interobserver intraclass correlation coefficients were excellent or good for the TT-TG distance and Insall-Salvati ratio in 100% of studies reporting them; however, for the Caton-Deschamps index and Blackburne-Peel ratio, they were excellent or good in only 43% and 40% of studies. Pooled magnetic resonance imaging values for TT-TG distance (P < .01), Insall-Salvati ratio (P = .01), and femoral sulcus angle (P = .02) were significantly different between the instability and control groups. Values for tibial tubercle–posterior cruciate ligament distance (P = .36) and Caton-Deschamps index (P = .09) were not significantly different between groups.Conclusion:The most commonly reported measurements for evaluating patellar instability assessed patellar tracking and trochlear morphology. The TT-TG distance was the most common measurement and was greater in the patellar instability group as compared with the control group. In addition, the TT-TG, tibial tubercle–posterior cruciate ligament, and patellar tendon–trochlear groove distances were highly reproducible measurements for patellar tracking, and the Insall-Salvati ratio had superior reproducibility for assessing patellar height.

Validating the Role of Tibial Tubercle–Posterior Cruciate Ligament Distance and Tibial Tubercle–Trochlear Groove Distance Measured by Magnetic Resonance Imaging in Patients With Patellar Dislocation: A Diagnostic Study

To (1) compare these parameters between patients with patellar dislocation and healthy individuals on magnetic resonance imaging measurements, (2) validate the diagnostic capacity of the tibial tubercle-posterior cruciate ligament (TT-PCL) distance and tibial tubercle-trochlear groove (TT-TG) distance, (3) define the pathologic threshold values of these parameters for tibial tubercle osteotomy indication, and (4) compare these values with those of previous studies. Seventy patients with patellar dislocation and 70 healthy volunteers were identified. The inter- and intraobserver reliability values were determined using Bland-Altman analysis and the intraclass correlation coefficient (ICC). The diagnostic capacity of the parameters was evaluated using receiver operating characteristic curves and the area under the receiver operating characteristic curve. The data of the control group were used to determine the pathologic threshold values of the measurements. Logistic regression analysis was performed with these pathologic threshold values. Significant differences in the TT-PCL distance (P= .01) and TT-TG distance (P < .001) were found between the study group (21.48 ± 3.18 and 12.91 ± 3.80, respectively) and the control group (20.07 ± 2.99 and 8.46 ± 3.16, respectively). Both the TT-PCL distance and TT-TG distance had excellent inter- and intraobserver agreement, with inter-ICCs >0.915 and intra-ICCs >0.932, respectively. However, the TT-TG distance had a higher area under the receiver operating characteristic curve than did the TT-PCL distance (0.820 vs 0.627). The pathologic threshold value of the TT-PCL distance was 24.76 mm. The pathologic threshold value of the TT-TG distance was 13.64 mm. Subjects with a TT-TG distance of >13.64 mm had a greater risk for patellar dislocation, with an odds ratio of 14.02 (95% confidence interval 4.00-49.08, P < .001). Both the TT-PCL distance and TT-TG distance can be measured reliably by magnetic resonance imaging; however, the TT-TG distance has a better diagnostic capacity than does the TT-PCL distance. Retrospective cohort study (diagnosis); Level of evidence, I.

Comparative study of the tibial tubercle-trochlear groove distance measured in two ways and tibial tubercle-posterior cruciate ligament distance in patients with patellofemoral instability

BackgroundA comparative analysis of the strengths and weaknesses of three different methods for radiologic evaluation of patellofemoral instability (PFI).MethodsComputed tomography (CT) and magnetic resonance imaging (MRI) were performed in 47 patients with or without PFI. The tibial tubercle-trochlear groove (TT-TG) distance was measured by two observers through conventional CT and three-dimensional CT reconstruction (TDR-TT-TG) respectively and the tibial tubercle-posterior cruciate ligament (TT-PCL) distance with MRI. The intraclass correlation coefficient (ICC) was used to evaluate the interobserver reliability. In addition, the differences of three measurements between different patients were compared. The consistency of TT-TG and TDR-TT-TG was analyzed by the Bland-Altman method.ResultsThe ICCs of three measurements were high between two observers; the results were TT-TG (ICC = 0.852), TDR-TT-TG (ICC = 0.864), and TT-PCL (ICC = 0.758). The values of PFI patients were significantly higher than those of non-PFI patients, and the mean TT-TG, TDR-TT-TG, and TT-PCL distance in patients with PFI were 19.0 ± 3.8 mm, 19.0 ± 3.7 mm, and 25.1 ± 3.6 mm, respectively. There was no statistically significant difference between the TT-TG distance and the TDR-TT-TG distance, we found no significant difference. The Bland-Altman analysis showed that the TDR-TT-TG distance was in good agreement with the TT-TG distance.ConclusionAll three methods can be used to assess PFI; the TDR-TT-TG measurement method has superior operability and better interobserver consistency. It may be an alternative method to the conventional TT-TG distance measurement.

New standardization method of tibial tubercle-posterior cruciate ligament distance according to patient size in patients with patellofemoral instability

BackgroundLarge differences in tibial tubercle–posterior cruciate ligament (TT-PCL) distance were described in several reports between countries, suggesting that abnormal TT-PCL distance is variable due to individual patient size. This study aimed to clarify the relationship between TT-PCL distance and patient size, and to determine a method for describing individualized TT lateralization. MethodsWe analyzed 41 patients with recurrent patellar dislocation (RPD) and 41 age-matched patients without patellar instability who underwent primary anterior cruciate ligament reconstruction (control). TT-PCL distance and tibia width (TW) were measured based on preoperative T2-weighted magnetic resonance imaging. Then, TT-PCL distance was standardized based on TW (TT-PCL ratio), and TT-PCL distance and ratio were compared between groups. Correlations were investigated among TT-PCL distance, TT-PCL ratio and each measurement (patient height, weight, TW). ResultsStrong positive correlations were observed between TW and patient height, and weak or moderate positive correlations were found between TT-PCL distance and each parameter. The mean TT-PCL distance was 21.2 and 20.6 mm (P = .39), while the mean TT-PCL ratio was 31.6% and 29.0% (P = .0093) in the RPD and control groups, respectively. The TT-PCL ratio was <34% in 39 of 41 knees (95.1%) in the control group. No correlation was indicated between the TT-PCL ratio and patient size. ConclusionsOur findings demonstrate that the TT-PCL ratio is not affected by patient size, although the TT-PCL distance is associated with knee size and patient height. The TT-PCL ratio could be an important index for identifying patients for whom distal realignment surgery should be considered.

Primary Medial Patellofemoral Ligament Repair Versus Reconstruction: Rates and Risk Factors for Instability Recurrence in a Young, Active Patient Population

To comparatively evaluate the clinical outcomes and rates of recurrent instability in young patients with primary medial patellofemoral ligament (MPFL) repair or reconstruction, as well as to assess for radiologic risk factors for worse outcomes. A retrospective review identified all patients with lateral patellar instability who underwent either MPFL repair and/or imbrication or MPFL reconstruction without any additional osseous procedures between 2008 and 2015 at a single center. Demographic variables and preoperative magnetic resonance imaging were analyzed, and Kujala scores were obtained at a minimum 2-year follow-up. Risk factors for worse outcomes were assessed, including the Caton-Deschamps Index (CDI) Insall-Salvati Index, tibial tubercle-trochlear groove distance, and tibial tubercle-posterior cruciate ligament distance. We identified 51 knees with isolated MPFL surgery (reconstruction in 32 andimbrication and/or repair in 19) at a mean of 59.7months' follow-up (range, 24-121months). The overall rate of recurrent dislocations was significantly greater in the repair group (36.9%) versus the reconstruction group (6.3%, P=.01), despite the average CDI being significantly higher in the reconstruction group (1.34 vs 1.23 in repair group, P=.04). No significant difference in the rate of return to baseline activity was found between the groups (77.8% in reconstruction group vs 70% in repair group, P= .62). The average Kujala score showed no significant difference between the repair and reconstruction groups (84.15 ± 14.2 vs 84.83 ± 14.38, P= .72). No imaging measurements were found to be predictive of a worse postoperative Kujala score; however, the average CDI among the MPFL repair failures (1.30 ± 0.05) was significantly higher than among the MPFL repair nonfailures (1.18 ± 0.12, P= .03). MPFL reconstruction may provide improved midterm clinical outcomes and a decreased recurrence rate compared with MPFL repair. Increased patellar height as measured by the CDI may be a risk factor for recurrent patellar instability in patients who undergo isolated MPFL repair. Level III, retrospective comparative study.

Tibial Tubercle Osteotomy: Anterior, Medial, and Distal Correction

For patients with patellofemoral pain who fail exhaustive nonoperative treatment, surgical intervention may be a viable option for selected patients who have pain on the bases of pathomechanics and/or cartilage lesions. Treatments may be directed at proximal soft tissues and distally at the tibial tubercle such as in a tibial tubercle osteotomy. Tibial tubercle osteotomies can include medialization, anteriorization and/or distalization of the tibial tubercle. Proximaltaization can also be performed in the setting of patella baja, however, it is rarely performed and is outside the scope of this article. Medialization may be used to improve force vectors and contact area, anteriorization can decrease contact pressures, and distalization can normalize patellar height. Factors influencing which techniques are used include concomitant chondral pathology and specific measurements on imaging such as the tibial tubercle-trochlear groove distance, tibial tubercle-posterior cruciate ligament distance, and Caton-Deschamps Index. The following article reviews the indications for and techniques of anteriorization, medialization, distalization, and combinations of the 3, for tibial tubercle osteotomies.

Isolated Medial Patellofemoral Ligament Reconstruction Can Be an Effective Procedure in Patellofemoral Instability with Risk Factors.

Patellofemoral instability is a severe problem in young and active patients. This pathology is influenced by ligamentous, bony, and neuromuscular parameters. The reconstruction of the medial patellofemoral ligament (MPFL) evolved to a primary procedure, but combined procedures were more frequently performed in the past years. However, additional operative procedures are associated with increased morbidity and no absolute indication can be identified in the literature. This study is intended to clarify whether addressing only ligamentous influence factors (MPFL) in chronic patellofemoral instability is sufficient to produce good clinical outcomes, or whether other risk factors influence the results negatively and should also be treated at some point. In 52 patients with chronic patellofemoral instability patellar height according to Caton-Deschamps, trochlear dysplasia according to Dejour, the leg axis, the femoral antetorsion, tibial tubercle (TT)-trochlear groove, and TT-posterior cruciate ligament distance were evaluated. All patients were treated with isolated MPFL reconstruction. After a minimum follow-up period of 24 months (24-36 months), the clinical outcome results were calculated using the scoring system according to Lysholm and Tegner. Correlation between clinical outcome scores and anatomic risk factors were calculated. The analysis was performed using a standard statistical software package (JMP version 12, SAS Institute, Cary, NC). The average postoperative Lysholm score increased significantly from 57.23 ± 19.9 to 85.9 ± 17.2 points (p < 0.0001) after isolated MPFL reconstruction. Moreover, the Tegner and Lysholm scores significantly improved both in patients without and with different risk factors postoperative. There were no significant differences in the outcome sores between the groups. Even the degree of trochlear dysplasia (types I-III) did not influence the results. Finally, there was no significant correlation found between all collected risk factors and the postoperative outcome scores. Isolated MPFL reconstruction can be an effective procedure in patients with patellofemoral instability and mild to moderate risk factors.

Lateralization of the Tibial Tubercle in Recurrent Patellar Dislocation: Verification Using Multiple Methods to Evaluate the Tibial Tubercle.

The tibial tubercle deviation associated with recurrent patellar dislocation (RPD) has not been studied sufficiently. New methods of evaluation were used to verify the extent of tubercle deviation in a group with patellar dislocation compared with that in a control group, the frequency of patients who demonstrated a cutoff value indicating that tubercle transfer was warranted on the basis of the control group distribution, and the validity of these methods of evaluation for diagnosing RPD. Sixty-six patients with a history of patellar dislocation (single in 19 [SPD group] and recurrent in 47 [RPD group]) and 66 age and sex-matched controls were analyzed with the use of computed tomography (CT). The tibial tubercle-posterior cruciate ligament (TT-PCL) distance, TT-PCL ratio, and tibial tubercle lateralization (TTL) in the SPD and RPD groups were compared with those in the control group. Cutoff values to warrant 10 mm of transfer were based on either the minimum or -2SD (2 standard deviations below the mean) value in the control group, and the prevalences of patients in the RPD group with measurements above these cutoff values were calculated. The area under the curve (AUC) in receiver operating characteristic (ROC) curve analysis was used to assess the effectiveness of the measurements as predictors of RPD. The mean TT-PCL distance, TT-PCL ratio, and TTL were all significantly greater in the RPD group than in the control group. The numbers of patients in the RPD group who satisfied the cutoff criteria when they were based on the minimum TT-PCL distance, TT-PCL ratio, and TTL in the control group were 11 (23%), 7 (15%), and 6 (13%), respectively. When the cutoff values were based on the -2SD values in the control group, the numbers of patients were 8 (17%), 6 (13%), and 0, respectively. The AUC of the ROC curve for TT-PCL distance, TT-PCL ratio, and TTL was 0.66, 0.72, and 0.72, respectively. The extent of TTL in the RPD group was not substantial, and the percentages of patients for whom 10 mm of medial transfer was indicated were small. Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Current evidence advocates use of a new pathologic tibial tubercle-posterior cruciate ligament distance threshold in patients with patellar instability.

To determine (1) whether a correlation exists between tibial tubercle-posterior cruciate ligament (TT-PCL) and tibial tubercle-trochlear groove (TT-TG) distances in patellar instability patients; (2) reliability when measuring TT-PCL distance; (3) whether TT-PCL distances measured on MRI are equivalent to those on CT; and (4) whether a correlation exists between TT-PCL distance and number of instability events or recurrence of instability following stabilization surgery. A systematic review was performed using PRISMA guidelines. Clinical studies investigating the relationships of TT-PCL with TT-TG on CT and/or MRI in patellar instability patients were sought. English language studies with Levels of evidence I-IV were eligible for inclusion. Four studies (285 subjects [300 knees] with patellar instability [74.2% female; mean age 26.1±8.2years]; 114 controls [144 knees; 77% female; mean age 23.1years]) were included. Mean TT-PCL of instability and control groups was 21.1±4.1 and 18.8±4.0mm (p<0.0001), respectively. Two studies reported significant positive (strong and moderate) correlations between TT-PCL and TT-TG MRI measurements in instability patients. All four investigations reported excellent interobserver and intraobserver reliability in MRI measurement of TT-PCL distance. No study compared TT-PCL distances on MRI and CT. No study assessed correlation between TT-PCL distance and number of instability events or recurrence of instability after surgery. A moderate-to-strong positive correlation exists between TT-PCL and TT-TG measurements taken from MRIs of patellar instability patients. There is excellent interobserver and intraobserver reliability when taking TT-PCL measurements using MRI. This review advocates use of a new pathologic TT-PCL threshold of 21mm. Level III, systematic review of Level II-III studies.

Evaluation of the Tibial Tubercle to Posterior Cruciate Ligament Distance in a Pediatric Patient Population.

Evaluation of distal extensor mechanism alignment continues to evolve in children with patella instability. Prior studies support the use of the tibial tubercle to trochlear groove (TT-TG) distance but limitations exist for this measurement including: changes in the TT-TG distance with knee flexion, difficulty with finding the deepest part of a dysplastic trochlea, and limitations regarding identification of the site of the anatomic abnormality. The tibial tubercle-posterior cruciate ligament (TT-PCL) distance has been introduced as an alternative measure to address the shortcomings in the TT-TG distance by quantifying the position of the TT independent of the trochlea and with respect to the tibia only. The objectives of this study were to (1) confirm that TT-PCL measurements in the pediatric population are reliable and reproducible; (2) determine whether normal TT-PCL distance changes with age; and (3) compare TT-PCL distances in patients with and without patellar instability to assess its utility in the workup of pediatric patellar instability. All knee magnetic resonance imaging performed for patients from birth to 15.9 years of age at our institution between December 2004 and February 2012 were retrospectively collected (total 566). Eighty-two patients had patellar instability and 484 patients did not have patellar instability. Two magnetic resonance imaging reviewers measured TT-PCL distance on T2-weighted axial images in a blinded manner. Intraobserver and interobserver agreement was measured. Correlation between TT-PCL distance and age as well as group differences between mean TT-PCL distances was evaluated. Intraobserver and interobserver agreement was excellent (0.93) and very good (0.80), respectively. The mean TT-PCL distance was 20.1 mm with a range of 5.8 to 32.1 mm. The mean age was 12.6 years with a range of 0.8 to 15.9 years. The average TT-PCL distance was 21 mm for the instability group and 19.9 mm for the control group. TT-PCL distance increased significantly as subject age increased; however, there was no significant measurement difference shown between the patellar instability group and the control group. TT-PCL distance increased with age in the pediatric population but did not correlate with recurrent patella instability in this pediatric cohort. Level III-diagnostic.

The contribution of the tibial tubercle to patellar instability: analysis of tibial tubercle-trochlear groove (TT-TG) and tibial tubercle-posterior cruciate ligament (TT-PCL) distances.

The purpose of this study is to assess the reliability of measuring the tibial tubercle to posterior cruciate (TT-PCL) distance compared to the tibial tubercle to trochlear groove (TT-TG) distance on magnetic resonance imaging (MRI), establish baseline TT-PCL values in patellar instability patients, and determine the predictive value of an excessive TT-PCL distance (≥24mm) for recurrent patellar instability compared to a TT-TG distance ≥20mm. TT-TG and TT-PCL distances were calculated on MRI in a randomized and blinded fashion by two reviewers on 54 patients (59 knees) with patellar instability. Interobserver reliability was assessed using interclass correlation coefficients (ICC). TT-PCL distances were also assessed to establish mean values in patellar instability patients. The ability of excessive TT-PCL and TT-TG distances to predict recurrent instability was assessed by comparing odds ratios, sensitivities, and specificities. Interobserver reliability was excellent for both TT-TG (ICC=0.978) and TT-PCL (ICC=0.932). The mean TT-PCL in these 59 knees was 21.7mm (standard deviation 4.1mm). Twelve (20%) of 59 knees had a single dislocation, and 47 (80%) exhibited 2 or more dislocations. The odds ratios, sensitivities, and specificities of a TT-TG distance ≥20mm for identifying patients with recurrent dislocation were 5.38, 0.213, and 1.0, respectively, while those of a TT-PCL distance ≥24mm were 1.46, 0.298, and 0.583, respectively. Of the 10 knees with a TT-TG distance ≥20mm, all 10 (100%) had recurrent instability, while 14 (73.7%) of the 19 knees with a TT-PCL ≥24mm experienced multiple dislocations (n.s.). Both TT-PCL and TT-TG can be measured on MRI with excellent interobserver reliability. In this series, the mean TT-PCL value in patients with patellar instability was 21.8mm, but the range was broad. A TT-PCL distance ≥24mm was found to be less predictive of recurrent instability in this series. For patients experiencing multiple episodes of patellar instability in the setting of a normal TT-TG distance, obtaining the TT-PCL measurement may provide a more focused assessment of the tibial contribution to tubercle lateralization. III.

Significant influence of rotational limb alignment parameters on patellar kinematics: an in vitro study.

Component malrotation has a major impact on patellar kinematics in total knee arthroplasty. The influence of natural rotational limb alignment on patellar kinematics is unclear so far. Based on recent clinical investigations, we hypothesized that rotational limb alignment significantly influences patellar kinematics. Patellar kinematics of ten cadaveric knees was measured using computer navigation during passive motion. Data were correlated with different rotational limb alignment parameters of preoperative CT scans. Femoral antetorsion showed a significant influence on patellar rotation, while tibial tubercle-posterior cruciate ligament distance additionally displayed a significant influence on patellar mediolateral shift (p<0.05). Femoral posterior condylar angle was sensitive to patellar epicondylar distance, rotation and tilt (p<0.05). Patellar rotation was influenced by five out of eight rotational limb alignment parameters (p<0.05). Rotational limb alignment should be paid more attention in terms of clinical evaluation of patellar tracking and future biomechanical and clinical investigations.

Tibial Tubercle–Posterior Cruciate Ligament Distance

Background: In patients with patellar instability, a pathological tibial tubercle–trochlear groove (TT-TG) distance is a risk factor. However, the TT-TG distance gives no information about the location of the malformation. Hypothesis: Not all patients with a pathological TT-TG distance (≥20 mm) had lateralization of the tibial tubercle. Study Design: Cohort study (diagnosis); Level of evidence, 2. Methods: Fifty-eight knees in 49 patients with 2 or more patellar dislocations and 60 knees in 30 volunteers with no history of dislocation were analyzed using magnetic resonance imaging (MRI). The tibial tubercle–posterior cruciate ligament (TT-PCL) distance was defined as the mediolateral distance between the tibial tubercle midpoint and the medial border of the posterior cruciate ligament. The distance was measured parallel to the dorsal aspect of the proximal tibia (dorsal tibia condylar line). Three observers performed the measurements. Significant differences in the TT-PCL distance between the patient and the control group were estimated using an unpaired t test. The inter- and intraobserver variability of the measurement was performed. Results: The intraclass correlation coefficients for inter- and intraobserver variability of the TT-PCL distance were higher than 0.74 and 0.93, respectively. A statistically significant difference (P < .05) was found between the TT-PCL distance in the control group (mean [SD], 18.4 [3.35] mm) and in patients (21.9 [4.30] mm). The mean (SD) TT-TG was 18.9 (5.16) mm in the patient group and 11.9 (4.67) mm in the control group (P < .05). In the control group, 95% had a TT-PCL distance <24 mm. In the patient group, 22 of 58 knee joints (38%) had a TT-PCL distance ≥24 mm. Seventeen of 40 knee joints (43%) with a TT-TG distance ≥20 mm had a TT-PCL distance <24 mm. Conclusion: Only 57% of the patients with a pathological TT-TG distance (≥20 mm) had lateralization of the tibial tubercle in relation to the posterior cruciate ligament. The TT-PCL distance is an alternative method for determining the position of the tibial tubercle.