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

Analysis of spatial patellofemoral alignment using novel three-dimensional measurements based on weight-bearing cone-beam CT

OBJECTIVES

To propose a reliable and standard 3D assessment method to analyze the effect of weight-bearing (WB) status on the location of patella and clarify the diagnostic performance of 3D parameters for recurrent patellar dislocation (RPD) in WB and non-weight-bearing (NWB) conditions.

METHODS

Sixty-five knees of RPD patients and 99 knees of controls were included. Eight landmarks, two lines and a coordinate system were defined on 3D bone models of knees based on weight-bearing CT and non-weight-bearing CT. The shift and tilt of patella in three orthogonal axes (Xshift, Yshift, Zshift, Xtilt, Ytilt, Ztilt) were evaluated.

RESULTS

Xshift and Yshift were significantly higher, Zshift, Xtilt and Ytilt were significantly lower in WB condition than NWB condition (p < 0.001, p < 0.001, p = 0.001, p = 0.002, p = 0.010). In both WB and NWB conditions, Xshift, Yshift and Ztilt were significantly higher, and Xtilt was significantly lower in the RPD group than the control group (WB/NWB: p < 0.001/p = 0.002, p < 0.001/p = 0.001, p < 0.001/p < 0.001, p < 0.001/p = 0.009). In WB condition, Zshift and Ytilt were significantly higher in the RPD group than the control group (p = 0.011, p < 0.001). Ztilt had the best diagnostic performance for RPD in both WB and NWB conditions, with AUC of 0.887 (95% CI: 0.828, 0.946) and 0.885 (95% CI: 0.822, 0.947), respectively.

CONCLUSIONS

The 3D measurement method reliably and comprehensively reflected the relative spatial position relationship of the patellofemoral joint. It can be applied to the 3D preoperative planning of patellofemoral procedures. In addition, patellofemoral evaluation under the WB condition was essential to detect subtle underlying risk factors for RPD, with axial lateral patellar tilt being the best predictor.

CRITICAL RELEVANCE STATEMENT

This 3D measurement method under weight-bearing conditions contributes to comprehensively describing the relative spatial position of the patellofemoral joint in a standardized way and can be applied to preoperative evaluation for recurrent patellar dislocation.

KEY POINTS

Patellofemoral alignment is a 3D problem, and the accuracy of 2D parameters has been questioned. 3D measurement was reliable and comprehensively reflected relative spatial relationships of the patellofemoral joint. 3D measurements under weight-bearing condition help preoperative evaluation for RPD.

Reliability of Tibial Tubercle-Trochlear Groove Distance for Assessing Tibial Tubercle Lateralization: A Study Comparing Different Anatomic References

Background

The tibial tubercle-trochlear groove (TT-TG) distance is a measurement used to quantitatively assess tibial tubercle lateralization (TTL), and it has important reference value for the treatment of patellar dislocation (PD). However, TT-TG distance accuracy has been questioned, so many new parameters have been proposed.

Purpose

To compare which of the TT-TG, tibial tubercle-midepicondyle (TT-ME), tibial tubercle-Roman arch (TT-RA), tibial tubercle-tibial intercondylar midpoint (TT-TIM), and tibial tubercle-mid inter-epicondyle trochlea intersection (TT-MIELTI) distances better reflect TTL in patients with PD.

Study Design

Cohort study (diagnosis); Level of evidence, 3.

Methods

A total of 96 patients who had undergone surgery for PD and 96 patients without PD (controls) were included in the study. The patients had all undergone computed tomography examination. The TT-TG, TT-ME, TT-RA, TT-TIM, TT-MIELTI distances and the TTL distance were measured independently by 2 surgeons in a blinded and randomized fashion. The t test was used to detect whether the parameters were significantly different between the 2 groups. The TTL distance was used as a reference value for lateralization of tibial tubercle. Pearson correlation coefficients were calculated to determine correlations between the defined measurements.

Results

The intra- and interobserver reliability of the defined measurements was excellent. All parameters except for TT-TIM distance were significantly larger in the PD group than the control group (P < .01 for all). There was a moderate correlation (r = 0.601) between the TT-TG distance and TTL, and other parameters were less correlated with TTL.

Conclusion

Among 5 the parameters tested, the TT-TG distance still had the highest correlation with TTL and was able to reflect TTL better in patients with PD. The role of TT-TIM distance in the assessment of PD needs further study.

Tibial Tubercle-Trochlear Groove Distance Has Better Diagnostic Reliability Than Tubercle-Posterior Cruciate Ligament Distance For Predicting Patellar Instability: A Systematic Review

OBJECTIVE

The tibial tubercle-trochlear groove (TT-TG) distance is now routinely utilized to help determine whether a realignment procedure is necessary for patients with patellar instability. The tibial tubercle-posterior cruciate ligament (TT-PCL) distance has been explored as an alternative measurement. The aim of this study is to compare the reliability of TT-TG and TT-PCL; to explore whether there is a relationship between the TT-PCL and the TT-TG distance; to determine whether there is a relationship between the TT-TG and TT-PCL distances and knee rotation; and to compare the abilities of the TT-PCL distance and the TT-TG distance with predicted patellar instability.

METHOD

This systematic review was performed in accordance with PRISMA guidelines. Three databases, PubMed, EMBASE, and Cochrane Central Register of Controlled Trials, were searched from inception to September 2021 to identify clinical studies comparing TT-TG and TT-PCL distances to patellar instability. Data on patient baseline characteristics, TT-TG and TT-PCL distances, inter-observer reliability, and area under the receiver-operating characteristic curve (AUC) were recorded. The methodological quality of the studies was assessed using the quality assessment form recommended by the Agency for Healthcare Research and Quality (AHRQ).

RESULT

Twenty studies were included in the final analysis, comprising 2330 knees from 2260 patients. The current study showed that TT-TG and TT-PCL have similar observer reliability. The inter- and intra-observer reliability of TT-TG ranged from 0.807 to 0.98 and 0.553 to 0.99, respectively. The inter- and intra-observer reliability of TT-PCL ranged from 0.553 to 0.99 and 0.88 to 0.981, respectively. Six studies compared the AUC for predicting patellar instability and showed that TT-TG had better predictive performance than TT-PCL. Three studies reported a correlation between TT-TG and knee rotation, but no such relationship was found for TT-PCL. Eight studies reported a weak or moderate correlation between TT-TG and TT-PCL.

CONCLUSION

TT-TG and TT-PCL have similar inter- and intra-rater reliability (as measured by ICC), but TT-TG has greater discriminatory power to predict patellar instability than TT-PCL (as measured by AUC values and odds ratio). However, considering trochlear dysplasia and individual variations, future studies need to find more accurate and individualized methods to predict patellar instability.

Patellar Tracking: An Old Problem with New Insights

Patellofemoral pain and instability are common indications for imaging that are encountered in everyday practice. The authors comprehensively review key aspects of patellofemoral instability pertinent to radiologists that can be seen before the onset of osteoarthritis, highlighting the anatomy, clinical evaluation, diagnostic imaging, and treatment. Regarding the anatomy, the medial patellofemoral ligament (MPFL) is the primary static soft-tissue restraint to lateral patellar displacement and is commonly reconstructed surgically in patients with MPFL dysfunction and patellar instability. Osteoarticular abnormalities that predispose individuals to patellar instability include patellar malalignment, trochlear dysplasia, and tibial tubercle lateralization. Clinically, patients with patellar instability may be divided into two broad groups with imaging findings that sometimes overlap: patients with a history of overt patellar instability after a traumatic event (eg, dislocation, subluxation) and patients without such a history. In terms of imaging, radiography is generally the initial examination of choice, and MRI is the most common cross-sectional examination performed preoperatively. For all imaging techniques, there has been a proliferation of published radiologic measurement methods. The authors summarize the most common validated measurements for patellar malalignment, trochlear dysplasia, and tibial tubercle lateralization. Given that static imaging is inherently limited in the evaluation of patellar motion, dynamic imaging with US, CT, or MRI may be requested by some surgeons. The primary treatment strategy for patellofemoral pain is conservative. Surgical treatment options include MPFL reconstruction with or without osseous corrections such as trochleoplasty and tibial tubercle osteotomy. Postoperative complications evaluated at imaging include patellar fracture, graft failure, graft malposition, and medial patellar subluxation. ©RSNA, 2023 Quiz questions for this article are available in the supplemental material.

Tibial tubercle to trochlear groove distance versus tibial tubercle to posterior cruciate ligament distance for predicting patellar instability: a systematic review

PURPOSE

To determine the reliability and diagnostic accuracy of tibial tubercle-trochlear groove (TT-TG) distance versus tibial tubercle-posterior cruciate ligament (TT-PCL) distance, and to determine cutoff values of these measurements for pathological diagnosis in the context of patellar instability.

METHODS

Three databases MEDLINE, PubMed and EMBASE were searched from inception to October 5, 2022 for literature outlining comparisons between TT-TG and TT-PCL in patellar instability patients. The authors adhered to the PRISMA and R-AMSTAR guidelines as well as the Cochrane Handbook for Systematic Reviews of Interventions. Data on inter-rater and intra-rater reliability, receiver-operating characteristic (ROC) curve parameters such as area under the curve (AUC), sensitivity and specificity, as well as odds ratios, cutoff values for pathological diagnosis and correlations between TT-TG and TT-PCL were recorded. The MINORS score was used for all studies in order to perform a quality assessment of included studies.

RESULTS

A total of 23 studies comprising 2839 patients (2922 knees) were included in this review. Inter-rater reliability ranged from 0.71 to 0.98 and 0.55 to 0.99 for TT-TG and TT-PCL, respectively. Intra-rater reliability ranged from 0.74 to 0.99 and 0.88 to 0.98 for TT-TG and TT-PCL, respectively. AUC measuring diagnostic accuracy of patellar instability for TT-TG ranged from 0.80 to 0.84 and 0.58 to 0.76 for TT-PCL. Five studies found TT-TG to have more discriminatory power than TT-PCL at distinguishing patients with patellar instability from patients who do not. Sensitivity and specificity ranged from 21 to 85% and 62 to 100%, respectively, for TT-TG. Sensitivity and specificity ranged from 30 to 76% and 46 to 86%, respectively, for TT-PCL. Odds ratio values ranged from 1.06 to 14.02 for TT-TG and 0.98 to 6.47 for TT-PCL. Proposed cutoff TT-TG and TT-PCL values for predicting patellar instability ranged from 15.0 to 21.4 mm and 19.8 to 28.0 mm, respectively. Eight studies reported significant positive correlations between TT-TG and TT-PCL.

CONCLUSION

TT-TG resulted in overall similar reliability, sensitivity and specificity as TT-PCL; however, TT-TG has better diagnostic accuracy than TT-PCL in the context of patellar instability as per AUC and odds ratio values.

LEVEL OF EVIDENCE

Level IV.