Abstract
Background
Lateral patellar compression syndrome (LPCS) is a common cause of anterior knee pain. Early diagnosis of LPCS using an accurate radiological examination is, therefore, important. However, the currently used radiological examinations for detecting LPCS are poor diagnostic indicators. Therefore, the aim of this study was to establish a new diagnostic imaging examination for LPCS and evaluate its accuracy in comparison with conventional examinations.
Methods
From June 2020 to May 2023, a retrospective analysis was conducted on 72 patients in the LPCS group and 140 patients in the Control group, all of whom underwent axial radiographs of the patella and knee MRI. The patellar compression angle (PCA), Tilting angle (TA), Congruence angle (CA), Grelsamer angle (AG), and Lateral patellofemoral angle (LPA) were used and compared statistically for their accuracy in terms of diagnosing LPCS.
Results
The area under the receiver operating characteristic curve (ROC) for the PCA was 0.87, which was the highest among the five examinations. ROC analysis revealed that a smaller PCA, less than 14.7°, was associated with LPCS, with the highest sensitivity (80.6%), specificity (82.9%), accuracy (82.1%), positive predictive value (PPV, 70.7%), negative predictive value (NPV, 89.2%), positive likelihood ratio (PLR, 4.71), and lowest negative likelihood ratio (NLR, 0.23) compared with the other four examinations. The interobserver reproducibility of the PCA was good, with an intraclass correlation coefficients (ICCs) of 0.85.
Conclusions
The PCA can detect LPCS with a moderate diagnostic performance and could, therefore, might be a new angle for the diagnosis of LPCS in clinical settings.
Keywords: Patellar compression angle, Lateral patellar compression syndrome, Axial radiograph, Patella
Introduction
Anterior knee pain, or patellofemoral pain, is one of the most common knee complaints encountered in sports medicine clinics, accounting for 25% [1], and accounts for 25 to 40% of all knee disorders [2]. Lateral patellar compression syndrome (LPCS) is the common cause of patellofemoral pain [3–5]. Early detection of LPCS using an accurate radiological examination is essential to avoiding expensive (such as magnetic resonance imaging) and invasive additional tests (such as arthroscopy). Unfortunately, only a few radiographic examinations that can detect LPCS are available in the clinical setting [6–9].
The commonly used imaging evaluations for diagnosing patellar tilt included Tilting angle (TA), Angle of Grelsamer (AG), Lateral patellofemoral angle (LPA), Patellar tilt angle (PTA), and Angle of Fulkerson (AF) [6–10]. The measurement method for detecting patellar lateralization included Congruence angle (CA) [11]. Among them, PTA and AF, need to be measured with reference to the tangential line to the posterior aspect of both femoral condyles [8, 10], were not applicable in axial radiographs of the patella. The four angles that can be measured by radiograph were: TA, AG, LPA, and CA [6–9].
LPCS occurs as a result of patellar instability, lateral tilt and/or lateralization, resulting in compression and malalignment of the lateral patellofemoral joint [12]. Therefore, the ideal imaging examination is to detect both patellar lateral tilt and lateralization. TA’s cut-off value of CT was 31.8°, and was affected by quadriceps muscle contraction [6]. CA was not sensitive to detect minor degrees of mal-alignment. Inoue et al. [13]. reported that only 30% of patients with patellar subluxation had an abnormal CA. The accuracy of AG depended heavily on whether the knee was in a horizontal position during the examination [8]. LPA had excellent accuracy in diagnosing patellar subluxation, but poor accuracy and sensitivity of only 10% in patients with chondromalacia of the patella without patellofemoral misalignment [9]. Overall, the four currently available commonly used radiographic examinations for LPCS are poor diagnostic indicators. They can only detect patellar tilt or lateralization, not both. A more accurate radiological examination is needed for use in a clinical setting.
Therefore, we developed a new angle, the “Patellar compression angle (PCA).” The purpose of this study was (1) to describe the PCA in axial radiographs of patella, (2) to compare accuracy with the other four conventional angle measurement methods, and (3) to determine the cut-off value. We hypothesize a more accurate detection in diagnosing LPCS than TA, AG, LPA, and CA (Fig. 1), owing to the fact that PCA (Fig. 1) can diagnose both lateral patellar tilt and lateralization, especially in patients with less severe patellar tilt.
Fig. 1.
Schematic diagram of PCA, TA, CA, AG and LPA measurement methods. a A line tangential to the lateral patellar facet through the lowest point of the patellar ridge (the top line); a line tangential to the lateral trochlear facet through the lowest point of the patellar ridge (the bottom line). PCA consists of the angle between both lines. As the patella tilts and/or displaces, the PCA decreases. b The red line represents the long axis of the patella, the top black line is parallel to the red line, and the bottom black line represents a line tangential to the anterior aspect of both lateral and medial trochlear facets, and TA consists of the two black lines. c The two black lines represent the tangential lines from the deepest point of the trochlear groove to the anterior aspect of lateral and medial trochlear facets. The dotted line represents the angular bisector of the angle which consists of the two black lines. The red line represents the line connecting the deepest point of the trochlear groove and the ridge of the patella, and CA consists of the dotted line and the red line. d The top line represents the long axis of the patella, the bottom line represents the horizontal line, and AG consists of the two lines. e The top line represents a line tangential to the lateral patellar facet, the bottom line represents a line tangential to the anterior aspect of both lateral and medial trochlear facets, and LPA consists of the two lines. PCA: Patellar compression angle; TA: Tilting angle; CA: Congruence angle; AG: Grelsamer angle; LPA: Lateral patellofemoral angle
Materials and methods
Subjects
This study was approved by the institutional review board. The study was carried out in accordance with the ethical standards described by the Local Ethics Committee of the National Health Commission and was approved by the Ethics Committee of Tianjin Hospital (Ethics No.: 2024 Medical Ethics 174).
This study was a diagnostic accuracy design, and it was retrospective. From June 2020 to May 2023, we retrospectively analyzed patients who made appointments for knee specialist outpatient department in Tianjin Hospital, the patients were consecutive over this period. Patients were screened based on inclusion and exclusion criteria. Inclusion criteria: (1) history of anterior knee pain, (2) clear axial patellar radiographs and MRI images of patellofemoral joint, and (3) complete medical records. Exclusion criteria: (1) unavailable imaging modalities, (2) history of knee surgery, (3) history of knee trauma, (4) knee joint bone tumors, and (5) other conditions that may affect the recognition of the knee bone morphology, such as a severe osteoproliferation. After screening by inclusion and exclusion criteria, a total of 212 patients remained.
Patients were reviewed with electronic charts and imaging examinations by a senior knee specialist surgeon (16 years of clinical experience). At present, the definition of LPCS diagnosis is still obscure. As reported by Chen et al. [14]. and Migliorini et al. [5]. , the following were the main clinical manifestations of LPCS patients [15], which can be used as the definition of LPCS in this study: (1) history of anterior knee pain, (2) axial radiographs of the patella showed lateral patellar tilt (in the axial radiograph, the angle formed by the line through the longest axis of the patella and a horizontal line represented patellar tilt, and when the angle was greater than 5°, it was defined as lateral patellar tilt [8]) and/or displacement (in the axial radiograph, the distance between the perpendicular lines passing through the ridge of the patella and the deepest point of the trochlear groove to the horizontal line represented the patellar displacement, when the distance was greater than 5 mm, it was defined as patellar displacement [16]), resulting in narrowing of the lateral patellofemoral joint space, and (3) MRI showed the lateral patellofemoral joint cartilage injury (in T2-weighted fat-suppressed axial sequence, the Recht cartilage injury grading was used as the reference, the cartilage injury in this study referred to Recht grade III and IV [17]).
The (2) and (3) definitions of LPCS used as reference standards to distinguish between two groups of cases. Those meeting the reference standards were included in the LPCS group, other patients were included in the Control group.
Imaging evaluations
All patients underwent axial radiographs of the patella and knee MRI. All examinations were performed using DR (DuraDiagnost, Philips, Amsterdam, Netherlands), 3.0-T MRI (MAGNETOM Skyra, Siemens, Erlangen, Germany). All patients used the same medical equipment and parameters. The imaging parameters used in this study were axial MRI (T2-weighted fat-suppressed axial sequence; TR 1613ms; TE 65ms; FOV 16 cm; matrix 320 × 224; slice thickness 5.5 mm) and axial radiograph (FOV 12 × 4 cm; 80 kV; 160 mA). For both groups, the following angles of axial radiographs of the patella were measured: PCA, TA, CA, AG, and LPA (Fig. 1). TA, CA, AG, and LPA were used to compare with PCA, as these four angles were commonly used to test patellar tilt and displacement in the patellar axial radiographs [6–9].
Radiographic technique: We referred to the Merchant´s view. The patient was in a supine position, the patient’s lower leg was placed on a brace at a pre-defined 30° flexion [8]. The radiology technician moved the X-ray tube and cassette, the X-ray tube was usually on the upper side of the head, tilted down 30° along the horizontal line and directed in the foot direction. The cassette was placed under the patient’s feet, parallel to their feet. The X-rays were parallel to the patellofemoral interspace, and the Cassette should be at 90° to the beam and to the patellofemoral interspace.
Our measurements were carried out using the image processing software (GCRIS, Carestream, Rochester, America) with an accuracy of 0.01°.
Measurements
Fig. 2 shows the axial radiographs of the patella of patients in the LPCS group, and Fig. 3 shows the radiographs of patients in the Control group. The patellar ridge, lateral patellar facet of the patella, and lateral trochlear facet can be clearly identified in Figs. 2 and 3. The tangent line of the lateral patellar facet and the tangent line of the lateral trochlear facet were made from the lowest point of the patellar ridge. The angle formed by the two tangent lines is called the patellar compression angle, and the lines open laterally. The results of five imaging examinations used to detect LPCS, including the PCA, TA, AG, LPA, and CA were retrospectively evaluated.
Fig. 2.
Measurement of PCA angles in LPCS group patients on axial radiographs of the patella. a, d Axial radiographs of the patella at the Merchant position; b, e The red point represents the lowest point of the patellar ridge, the green point represents the inflection point of the tangent line of the lateral patellar facet, and the yellow point represents the highest point of the lateral trochlea. The line connecting the red and green points represents the tangent line of the lateral patellar facet, and the line connecting the red and yellow points represents the tangent line to the lateral trochlear facet through the lowest point of the patellar ridge. PCA angle consists of the angle between both lines. c, f PCA were 4.96° and 9.06°, respectively. (a, b, and c show LPCS caused by patellar tilt, and d, e, and f show LPCS caused by patellar displacement). PCA: Patellar compression angle
Fig. 3.
Measurement of PCA angles in Control group patients on axial radiographs of the patella. a, d Axial radiographs of the patella at the Merchant position; b, e The red point represents the lowest point of the patellar ridge, the green point represents the inflection point of the tangent line of the lateral patellar facet, and the yellow point represents the highest point of the lateral trochlea. The line connecting the red and green points represents the tangent line of the lateral patellar facet, and the line connecting the red and yellow points represents the tangent line to the lateral trochlear facet through the lowest point of the patellar ridge. PCA angle consists of the angle between both lines. c, f PCA were 16.26° and 18.76°, respectively. PCA: Patellar compression angle
All the angle measurements were independently conducted by two authors, both authors were specialized knee surgeons, they were blinded to any clinical information of all cases. All patients were examined twice at different times. The interval between measurements was at least 4 weeks. All participants were examined twice at different times to determine the intraobserver reliability. The tests were independently performed by the senior author (25 years of clinical experience), and another trained author (4 years of clinical experience). Two authors independently read the radiographic measurements to determine the interobserver reliability.
Statistical analysis
Statistical significance was set at p < 0.05. All continuous variable data were performed by Kolmogorov–Smirnov test. The independent-samples T test was used for comparison of all continuous variables, including Age, Height, Weight, and BMI. The chi-square test was used for categorical variables, including Laterality and Gender. The accuracy of the angles was assessed by using sensitivity, specificity, accuracy, positive predictive value (PPV), negative predictive value (NPV), positive likelihood ratio (PLR), and negative likelihood ratio (NLR). The reproducibility of the PCA was assessed with the intraclass correlation coefficients (ICCs), which determined the interobserver and intraobserver variation. Receiver operating characteristic (ROC) curve was plotted, and the area under the curve (AUC) was calculated. The cut-off value was derived from the point with the maximal Youden index, which corresponds to the highest sum of sensitivity and specificity, it was exploratory rather than prespecified. The closer the AUC is to 1, the better the diagnostic value. 95% CI of 5 angles for sensitivity, specificity, accuracy, PPV, and NPV were also calculated. The statistical analyses were performed with the SPSS 21.0 software package (SPSS Inc., Chicago, Illinois, USA).
Results
All continuous variable data fit the normal distribution. Flowchart of cases enrollment was shown in Fig. 4. By distinguishing based on reference standards, there were 72 patients in the LPCS group, and 140 patients in Control group. In the LPCS group, there were 55 cases with grade III cartilage injury and 17 cases with grade IV. 62 cases had patellar tilt > 5°, 33 patients had patellar displacement > 5 mm, and 23 cases had both tilt > 5° and displacement > 5 mm. In the Control group, there were 7 cases with Recht grade 0 cartilage injury, 52 cases with grade I, 75 cases with grade II, and 6 cases with grade III. 105 cases had patellar tilt < 5°, 92 cases had patellar displacement < 5 mm, and 81 cases had both tilt < 5° and displacement < 5 mm. 15 cases had tilt > 5°, 17 cases had displacement > 5 mm, and 8 cases had both tilt > 5° and displacement > 5 mm. The demographic characteristics of the subjects are presented in Table 1.
Fig. 4.
Flowchart of cases enrollment. From June 2020 to May 2023, 529 cases who made appointments for knee specialist outpatient department and met the inclusion criteria. According to the exclusion criteria, a total of 212 cases remained, two groups were divided according to the reference standards. Finally, 72 cases were included in the LPCS group, and 140 cases in the Control group. LPCS: Lateral patellar compression syndrome
Table 1.
Demographic characteristics of the subjects
| Items | LPCS Group (n = 72) | Control Group (n = 140) | P value |
|---|---|---|---|
| Age, Y | 42.8 ± 22.4 | 40.7 ± 21.2 | 0.599a |
| Height, cm | 164.91 ± 8.70 | 166.26 ± 8.63 | 0.526a |
| Weight, kg | 64.19 ± 11.51 | 67.29 ± 11.27 | 0.270a |
| BMI, kg/m2 | 23.86 ± 2.76 | 24.30 ± 2.89 | 0.512a |
| Laterality, L/R | 33/39 | 61/79 | 0.754b |
| Gender, M/F | 52/20 | 94/46 | 0.449b |
BMI: Body mass index
Data was given as n or mean ± standard deviation. Significance was calculated using a two-tailed
a 2 independent-samples t-tests
b chi-square test
All parameters of axial radiographs of the patella measured in the two groups were summarized in Table 2.
Table 2.
Comparison of each measurement between groups
| Items | LPCS Group (n = 72) | Control Group (n = 140) | P value |
|---|---|---|---|
| PCA, ° | 11.7 ± 4.3 | 17.8 ± 4.3 | < 0.001a* |
| TA, ° | 17.0 ± 7.8 | 14.8 ± 6.3 | 0.024a* |
| CA, ° | 11.0 ± 20.5 | -5.3 ± 18.8 | < 0.001a* |
| AG, ° | 14.0 ± 8.1 | 11.6 ± 7.9 | 0.034a* |
| LPA, ° | 10.9 ± 7.5 | 13.1 ± 7.4 | 0.043a* |
PCA: Patellar compression angle; TA: Tilting angle; CA: Congruence angle; AG: Grelsamer angle; LPA: Lateral patellofemoral angle
Data was given as mean ± standard deviation. Significance was calculated using a two-tailed
a 2 independent-samples t-tests
*Significant difference
Cross tabulation for PCA diagnosis of LPCS can be found in Table 3. The diagnostic values of the five angles for detecting LPCS, detailed data were listed in Table 4, and the analysis of the ROC curve was shown in Fig. 5.
Table 3.
Cross tabulation for PCA diagnosis of LPCS
| PCA | Diagnostic criteria | Total | |
|---|---|---|---|
| LPCS patients | Control patients | ||
| Positive, n | True-positive, 58 | False-positive, 24 | 82 |
| Negative, n | False-negative, 14 | True-negative, 116 | 130 |
| Total | 72 | 140 | 212 |
PCA: Patellar compression angle; LPCS: Lateral patellar compression syndrome
Table 4.
The diagnostic values of the five angles for LPCS
| Items | PCA | TA | CA | AG | LPA |
|---|---|---|---|---|---|
| AUC, mean ± SE | 0.87 ± 0.03 | 0.58 ± 0.04 | 0.73 ± 0.04 | 0.59 ± 0.04 | 0.58 ± 0.04 |
| 95% CI for AUC | 0.813–0.923 | 0.498–0.663 | 0.657–0.798 | 0.505–0.668 | 0.497–0.655 |
| Youden index | 0.64 | 0.20 | 0.38 | 0.20 | 0.15 |
| OOP (°) | 14.7 | 18.1 | 3.5 | 17.3 | 13.5 |
| True-positive, n | 58 | 29 | 46 | 27 | 45 |
| True-negative, n | 116 | 111 | 103 | 115 | 74 |
| False-positive, n | 24 | 29 | 37 | 25 | 66 |
| False-negative, n | 14 | 43 | 26 | 45 | 27 |
| Sensitivity (%), 95% CI | 80.6 (0.7–0.9) | 40.3 (0.3–0.5) | 63.9 (0.5–0.8) | 37.5 (0.3–0.5) | 62.5 (0.5–0.7) |
| Specificity (%), 95% CI | 82.9 (0.8–0.9) | 79.3 (0.7–0.9) | 73.6 (0.7–0.8) | 82.1 (0.8–0.9) | 52.9 (0.4–0.6) |
| Accuracy (%), 95% CI | 82.1 (0.8–0.9) | 66.0 (0.6–0.7) | 70.3 (0.6–0.8) | 67.0 (0.6–0.7) | 56.1 (0.5–0.6) |
| PPV (%), 95% CI | 70.7 (0.6–0.8) | 50.0 (0.4–0.6) | 55.4 (0.4–0.7) | 51.9 (0.4–0.7) | 40.5 (0.3–0.5) |
| NPV (%), 95% CI | 89.2 (0.8–0.9) | 72.1 (0.6–0.8) | 79.8 (0.7–0.9) | 71.9 (0.6–0.8) | 73.3 (0.6–0.8) |
| PLR | 4.71 | 1.95 | 2.42 | 2.09 | 1.33 |
| NLR | 0.23 | 0.75 | 0.49 | 0.76 | 0.71 |
PCA: Patellar compression angle; TA: Tilting angle; CA: Congruence angle; AG: Grelsamer angle; LPA: Lateral patellofemoral angle; AUC: Area under the curve; SE: Standard error; CI: Confidence Interval; OOP: Optimal operating point; PPV: positive predictive value; NPV: Negative predictive value; PLR: Positive likelihood ratio; NLR: Negative likelihood ratio
The OOP was determined at the maximal Youden index in ROC, which was considered a cut-off value
ROC: Receiver operating characteristic; PCA: Patellar compression angle; TA: Tilting angle; CA: Congruence angle; AG: Grelsamer angle; LPA: Lateral patellofemoral angle
Fig. 5.
ROC curve analysis was performed to analyze the diagnostic accuracy of detecting LPCS at the 5 angles and to determine the cut-off value of 5 angles that were associated with LPCS. AUC can be used to compare the diagnostic accuracy of the 5 angles
The diagnostic values of other thresholds of the five angles for LPCS were shown in Table 5. The mean value in this study was used as the cut-off value for PCA and TA, as no cut-off value for TA was provided in the literature.
Table 5.
The diagnostic values of other thresholds of the five angles for LPCS
| Items | PCA | TA | CA | AG | LPA |
|---|---|---|---|---|---|
| Threshold value (°) | 11.7 | 17.0 | 4.0 [7] | 5.0 [8] | 0 [9] |
| True-positive, n | 32 | 32 | 45 | 62 | 7 |
| True-negative, n | 135 | 96 | 103 | 32 | 135 |
| False-positive, n | 5 | 44 | 37 | 108 | 5 |
| False-negative, n | 40 | 40 | 27 | 10 | 65 |
| Sensitivity (%) | 44.4 | 44.4 | 62.5 | 86.1 | 9.7 |
| Specificity (%) | 96.4 | 68.6 | 73.6 | 22.9 | 96.4 |
| Accuracy (%) | 78.8 | 60.4 | 69.8 | 44.3 | 67.0 |
| PPV (%) | 86.5 | 42.1 | 54.9 | 36.5 | 58.3 |
| NPV (%) | 77.1 | 70.6 | 79.2 | 76.2 | 67.5 |
| PLR | 12.33 | 1.41 | 2.37 | 1.12 | 2.69 |
| NLR | 0.58 | 0.81 | 0.51 | 0.61 | 0.94 |
PCA: Patellar compression angle; TA: Tilting angle; CA: Congruence angle; AG: Grelsamer angle; LPA: Lateral patellofemoral angle; PPV: positive predictive value; NPV: Negative predictive value; PLR: Positive likelihood ratio; NLR: Negative likelihood ratio
The threshold value of PCA is the mean value, and the cut-off value of TA is not found in the literature, so the mean value is also taken as the threshold value. TA, AG and LPA referred to thresholds in literature
The interobserver and intraobserver reliability of five angles was calculated by ICCs value. The interobserver reliability of TA was 0.92, indicating excellent. Other measurements (PCA, CA, AG, and LPA) in this study showed good interobserver reproducibility, with ICCs values of 0.85, 0.84, 0.89, and 0.86, respectively. The intraobserver of TA and AG were 0.91 and 0.90 respectively, indicating excellent. Other measurements (PCA, CA, and LPA) in this study showed good intraobserver reproducibility, with ICCs values of 0.87, 0.85, and 0.89, respectively.
Discussion
The most important finding of the present study is that PCA was a reliable angle to predict the diagnosis of LPCS. At present, the diagnostic accuracy of the conventional imaging examinations for detecting LPCS remain poor and variable, and a more accurate angle measurement for LPCS is needed in clinical practice. In our clinical practice, we developed a new angle, the “patellar compression angle,” to more accurately detect LPCS. The results of the present retrospective study demonstrated that the newly proposed angle can accurately detect LPCS with a high sensitivity, specificity and accuracy compared with the other four conventional angles mentioned above. In general, a diagnostic test is considered good when the AUC is above 0.8 [18]. In our study, the PCA yielded an AUC of 0.87 compared with the other 4 conventional angles in terms of diagnosing LPCS. Therefore, we can conclude that the discriminative ability of the PCA was higher than that of the conventional measurement methods. Furthermore, in terms of the most important clinical measures of accuracy by far [19, 20], the PPV (70.7%) and NPV (89.2%) of the PCA were high in the 5 examinations, which indicated that it is an accurate angle tool for detecting LPCS. The likelihood ratios are also good summaries of diagnostic accuracy [21, 22]. In the present study, the NLR of the PCA was the lowest (0.23) among the 5 angles, and the PLR was the highest (4.71), which indicates that the accuracy of the PCA is not significantly influenced by the prevalence of a disease. The reliability of a diagnostic angle depends not only on the accuracy but also on the reproducibility of the results [21]. In our study, the ICCs of 0.85 indicated that the PCA had a good agreement [22]. In our experience, the angle is very simple to measure and perform, which may explain the good reproducibility. According to the study of Ye et al. [23]. , the CA and AG showed inadequate inter-scan reliability in detecting patellar instability, with relatively lower ICCs of 0.33 and 0.38. The inter-scan reliability of CA was the poorest among all of the studied parameters.
Common diagnostic examinations for skeletal disorders include radiograph, CT, MRI, and arthroscopy [24]. CT and MRI have advantages in diagnosing musculoskeletal disorders, and these technological advances have primarily focused on providing higher quality and multiple tissue images [25], so that few people have recently focused on diagnostic methods of radiograph. However, CT and MRI are relatively expensive examination items and are contraindications for patients with claustrophobia [26]. Arthroscopy is a technology used not only for gold-standard confirmation of chondral patellofemoral lesions but also for treatment through different methodologies. As arthroscopy is an invasive procedure with possible complications [27], imaging evaluation prior to surgical therapy has become an important strategy [28, 29]. Therefore, radiographs remains a common method for detecting skeletal disorders [30], and as does the early diagnosis of LPCS.
An ideal radiograph measurement method for diagnosing LPCS requires simultaneous detection of patellar tilt and lateral displacement. In axial radiographs of the patella, the angle measurements we can use include those of the TA, CA, AG, and LPA. However, the above angles cannot meet the requirements. Interestingly, in LPCS patients, most patients did not have an obvious patellar tilt. As shown in Table 5, only 44.4% of LPCS patients had abnormal TA according to the mean value of 17.0° measured by this study as cut-off value. Compression of the lateral patellofemoral joint, resulting in cartilage injury, is more common in patients with LPCS. According to Aglietti et al. [7]. , 4.0° is used as the cut-off value, and 62.5% of LPCS patients have abnormal CA. Detecting only patellar tilt or displacement explains why the AUC is lower in ROC analysis at these four angles.
Patients with LPCS may have bone hyperplasia on the lateral side of the patella due to instability [14, 31–33], and in severe cases, tongue-shaped osteophytes may form, and eventually patellofemoral arthritis develops [34, 35], so early diagnosis and then receiving relevant treatment are important for preventing the aggravation of LPCS [36, 37]. This poses difficulties in measuring TA, AG, and LPA, as TA and AG measurements require reference to the longest axis of the patella [6, 8]. LPA includes a line tangential to the lateral patellar facet [9], and similarly, osteophytes may be troublesome to the operator [36]. We took some measures to reduce these effects in clinical practice. The measurement of PCA emphasizes how to avoid the disturbance of bone hyperplasia, as one of the marked points is the inflection point of the lateral patellar facet.
However, several limitations of the present study have to be noted. First, the retrospective design of the investigation leads to inevitable biases. Second, the limited number of analyzed patients is also an important limitation. Third, this was a single-center study, and only Chinese population were recruited in our investigation. Fourth, the patients in the study were managed in the orthopedics department, and their characteristics would not be representative of the population seen in medical practice. Fifth, the present study did not include more angles for measuring patellar instability, such as Patellar tilt angle and Angle of Fulkerson, nor did we consider the effect of patellar tendon length and patellar height on the results. Sixth, testing the PCA in Control group could overestimate the results, and using radiographs as the main inclusion criterion was a limitation and might have introduced selection bias by overestimating the results. Seventh, using radiographs as the index test and reference standard was one more limitation introducing incorporation verification bias and might have overestimated the results. Eighth, for the cut-off value 14.7° of PCA, the corresponding Youden index was 0.64, which was a moderate performance. Given these limitations, the conclusion may be optimistic, results from the present study must be interpreted with caution. Further multicenter research, large sample, more angles and other ethnic population to confirm the results are needed in the future.
Conclusions
The present retrospective study demonstrated that the newly proposed angle, the “patellar compression angle,” can detect LPCS with a moderate diagnostic performance and might be a new angle for the diagnosis of LPCS in clinical settings.
Acknowledgements
Not applicable.
Abbreviations
- LPCS
Lateral patellar compression syndrome
- PCA
Patellar compression angle
- TA
Tilting angle
- CA
Congruence angle
- AG
Grelsamer angle
- LPA
Lateral patellofemoral angle
- ROC
Receiver operating characteristic
- PPV
Positive predictive value
- NPV
Negative predictive value
- PLR
Positive likelihood ratio
- NLR
Negative likelihood ratio
- ICCs
Intraclass correlation coefficients
- PTA
Patellar tilt angle
- AF
Angle of Fulkerson
- CT
Computed tomography
- MRI
Magnetic resonance imaging
- DR
Digital radiography
- AUC
Area under the curve
- BMI
Body mass index
- SE
Standard error
- CI
Confidence Interval
- OOP
Optimal operating point
Author contributions
XG and WX designed the study. JL revised the manuscript. XG, ZX and CY drafted the manuscript. YY and LM interpreted and analyzed the data. XG and JZ collected the data. WX supported the study and approved the final version of the manuscript. All authors read and approved the final manuscript.
Funding
This work was supported by Medical Science Research Project Plan of Hebei Province (20251364), Tianjin Hospital Science and Technology Fund (TJYY2401) and, Science and Technology Project of Tianjin Health Commission (TJWJ2024MS027).
Data availability
No datasets were generated or analysed during the current study.
Declarations
Ethics approval and consent to participate
All procedures were performed in accordance with the Declaration of Helsinki. This retrospective study was approved by the Ethical Committee of the Tianjin Hospital. (Ethics No.: 2024 Medical Ethics 174)
Consent for publication
All the authors listed have approved the manuscript that is enclosed.
Competing interests
The authors declare no competing interests.
Footnotes
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Xiaokang Gao and Jinwei Liu contributed equally to this work.
References
- 1.Charles MD, Haloman S, Chen L, et al. Magnetic resonance imaging-based topographical differences between control and recurrent patellofemoral instability patients. Am J Sports Med. 2013;41(2):374–84. 10.1177/0363546512472441. [DOI] [PubMed] [Google Scholar]
- 2.Kasitinon D, Li WX, Wang EXS, et al. Physical examination and Patellofemoral Pain Syndrome: an updated review. Curr Rev Musculoskelet Med. 2021;14(6):406–12. 10.1007/s12178-021-09730-7. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Doucette SA, Goble EM. The effect of exercise on patellar tracking in lateral patellar compression syndrome. Am J Sports Med. 1992;20(4):434–40. 10.1177/036354659202000412. [DOI] [PubMed] [Google Scholar]
- 4.Smith BE, Selfe J, Thacker D, et al. Incidence and prevalence of patellofemoral pain: a systematic review and meta-analysis. PLoS ONE. 2018;13(1):e0190892. 10.1371/journal.pone.0190892. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 5.Migliorini F, Lüring C, Eschweiler J, et al. Isolated arthroscopic lateral retinacular release for lateral patellar Compression Syndrome. Life (Basel). 2021;11(4). 10.3390/life11040295. [DOI] [PMC free article] [PubMed]
- 6.Sasaki T, Yagi T. Subluxation of the patella. Investigation by computerized tomography. Int Orthop. 1986;10(2):115–20. [PubMed] [Google Scholar]
- 7.Aglietti P, Insall JN, Cerulli G. Patellar pain and incongruence. I: measurements of incongruence. Clin Orthop Relat Res 1983; (176):217–24. [PubMed]
- 8.Grelsamer RP, Bazos AN, Proctor CS. Radiographic analysis of patellar tilt. J Bone Joint Surg Br. 1993;75(5):822–4. 10.1302/0301-620x.75b5.8376449. [DOI] [PubMed] [Google Scholar]
- 9.Laurin CA, Lévesque HP, Dussault R, et al. The abnormal lateral patellofemoral angle: a diagnostic roentgenographic sign of recurrent patellar subluxation. J Bone Joint Surg Am. 1978;60(1):55–60. [PubMed] [Google Scholar]
- 10.Schutzer SF, Ramsby GR, Fulkerson JP. The evaluation of patellofemoral pain using computerized tomography. A preliminary study. Clin Orthop Relat Res. 1986;204:286–93. [PubMed] [Google Scholar]
- 11.Laurin CA, Dussault R, Levesque HP. The tangential x-ray investigation of the patellofemoral joint: x-ray technique, diagnostic criteria and their interpretation. Clin Orthop Relat Res. 1979(144):16–26. [PubMed]
- 12.Hamawandi SA, Amin HI, Al-Humairi AK. Open versus arthroscopic release for lateral patellar compression syndrome: a randomized-controlled trial. Arch Orthop Trauma Surg. 2022;142(10):1–7. 10.1007/s00402-021-03878-0. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 13.Inoue M, Shino K, Hirose H, et al. Subluxation of the patella. Computed tomography analysis of patellofemoral congruence. J Bone Joint Surg Am. 1988;70(9):1331–7. [PubMed] [Google Scholar]
- 14.Chen JB, Chen D, Xiao YP, et al. Efficacy and experience of arthroscopic lateral patella retinaculum releasing through/outside synovial membrane for the treatment of lateral patellar compression syndrome. BMC Musculoskelet Disord. 2020;21(1):108. 10.1186/s12891-020-3130-y. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 15.Yalfani A, Ahadi F, Ahmadi M. Effects of pain exacerbation on postural control in women with patellofemoral pain during single leg squat: a cross-sectional study. J Orthop Surg Res. 2024;19(1):462. 10.1186/s13018-024-04911-9. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 16.Schueda MA, Astur DC, Bier RS, et al. Use of computed tomography to determine the risk of patellar dislocation in 921 patients with patellar instability. Open Access J Sports Med. 2015;6:55–62. 10.2147/oajsm.s75243. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 17.Recht MP, Kramer J, Marcelis S, et al. Abnormalities of articular cartilage in the knee: analysis of available MR techniques. Radiology. 1993;187(2):473–8. 10.1148/radiology.187.2.8475293. [DOI] [PubMed] [Google Scholar]
- 18.Harrell FE Jr., Lee KL, Mark DB. Multivariable prognostic models: issues in developing models, evaluating assumptions and adequacy, and measuring and reducing errors. Stat Med. 1996;15(4):361–87. 10.1002/(sici)1097-0258(19960229)15:4. [DOI] [PubMed] [Google Scholar]
- 19.Van Nynatten LR, Miller MR, Patel MA, et al. A novel multiplex biomarker panel for profiling human acute and chronic kidney disease. Sci Rep. 2023;13(1):21210. 10.1038/s41598-023-47418-9. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 20.Jaeschke R, Guyatt GH, Sackett DL. Users’ guides to the medical literature. III. How to use an article about a diagnostic test. B. What are the results and will they help me in caring for my patients? The evidence-based Medicine Working Group. JAMA. 1994;271(9):703–7. 10.1001/jama.271.9.703. [DOI] [PubMed] [Google Scholar]
- 21.Gjørup T. Reliability of diagnostic tests. Acta Obstet Gynecol Scand Suppl. 1997;166:9–14. [PubMed] [Google Scholar]
- 22.Landis JR, Koch GG. The measurement of observer agreement for categorical data. Biometrics. 1977;33(1):159–74. [PubMed] [Google Scholar]
- 23.Ye Q, Yu T, Wu Y, et al. Patellar instability: the reliability of magnetic resonance imaging measurement parameters. BMC Musculoskelet Disord. 2019;20(1):317. 10.1186/s12891-019-2697-7. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 24.Pohlig F, Lenze U, Lenze FW, et al. Arthroscopic lateral retinacular release improves patello-femoral and femoro-tibial kinematics in patients with isolated lateral retinacular tightness. Knee Surg Sports Traumatol Arthrosc. 2022;30(3):791–9. 10.1007/s00167-021-06434-w. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 25.Kijowski R, Fritz J. Emerging Technology in Musculoskeletal MRI and CT. Radiology. 2023;306(1):6–19. 10.1148/radiol.220634. [DOI] [PubMed] [Google Scholar]
- 26.Malviya S, Voepel-Lewis T, Eldevik OP, et al. Sedation and general anaesthesia in children undergoing MRI and CT: adverse events and outcomes. Br J Anaesth. 2000;84(6):743–8. 10.1093/oxfordjournals.bja.a013586. [DOI] [PubMed] [Google Scholar]
- 27.Kuwabara A, Cinque M, Ray T, et al. Treatment options for Patellofemoral Arthritis. Curr Rev Musculoskelet Med. 2022;15(2):90–106. 10.1007/s12178-022-09740-z. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 28.Liu Y, Lu W, Ouyang K, et al. The imaging evaluation of acetabular labral lesions. J Orthop Traumatol. 2021;22(1):34. 10.1186/s10195-021-00595-7. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 29.Snow M, Singh N, Rix L, et al. No correlation exists between tibial-and femoral-based measurements of Patella Alta in a Population with Chronic Patellofemoral Pain or Instability undergoing Patella distalization. Arthroscopy. 2024;40(11):2706–14. 10.1016/j.arthro.2024.01.036. [DOI] [PubMed] [Google Scholar]
- 30.Mi C, Zhang X, Yang C, et al. Bone disease imaging through the near-infrared-II window. Nat Commun. 2023;14(1):6287. 10.1038/s41467-023-42001-2. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 31.Wu T, Tang S, Wang F. Treatment for lateral patellar impingement syndrome with arthroscopic lateral patelloplasty: a bidirectional cohort study. J Orthop Surg Res. 2017;12(1):173. 10.1186/s13018-017-0676-y. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 32.Wang CL, Chen JB, Li T. Outcome and experience of arthroscopic lateral retinacular release combined with lateral patelloplasty in the management of excessive lateral pressure syndrome. J Orthop Surg Res. 2021;16(1):80. 10.1186/s13018-021-02229-4. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 33.Hamawandi SA. Use of hyaluronic acid injection after arthroscopic release in lateral patellar compression syndrome with degenerative cartilage changes: randomized control trial. BMC Musculoskelet Disord. 2021;22(1):24. 10.1186/s12891-020-03876-0. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 34.Kayll SA, Hinman RS, Bryant AL, et al. Do biomechanical foot-based interventions reduce patellofemoral joint loads in adults with and without patellofemoral pain or osteoarthritis? A systematic review and meta-analysis. Br J Sports Med. 2023;57(13):872–81. 10.1136/bjsports-2022-106542. [DOI] [PubMed] [Google Scholar]
- 35.Neal BS, Bartholomew C, Barton CJ, et al. Six treatments have positive effects at 3 months for people with Patellofemoral Pain: a systematic review with Meta-analysis. J Orthop Sports Phys Ther. 2022;52(11):750–68. http://dx.doi.org/10.2519/jospt.2022.11359IF: 6.0 Q1. [DOI] [PubMed] [Google Scholar]
- 36.Kamel AM, Ghuiba K, Abd Allah DS, et al. Effect of adding short foot exercise to hip and knee focused exercises in treatment of patients with patellofemoral pain syndrome: a randomized controlled trial. J Orthop Surg Res. 2024;19(1):207. 10.1186/s13018-024-04688-x. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 37.Huo Z, Xu C, Li S, et al. The thickness change ratio and preservation ratio of the infrapatellar fat pad are related to anterior knee pain in patients following medial patellofemoral ligament reconstruction. J Orthop Surg Res. 2024;19(1):375. 10.1186/s13018-024-04853-2. [DOI] [PMC free article] [PubMed] [Google Scholar]
Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
No datasets were generated or analysed during the current study.