A magnetic resonance imaging study of abnormalities of the patella and patellar tendon that predispose children to acute patellofemoral dislocation

    A magnetic resonance imaging study of abnormalities of the patella and patellar tendon that predispose children to acute patellofemoral dislocation ¨ ¨ un Barıs¸ Yılmaz, Esin Derin C¸ic¸ek, Evrim S¸irin, G¨uzelali Ozdemir, Ozg¨ Karakus¸, Hasan Hilmi Muratlı PII: DOI: Reference:

S0899-7071(16)30182-6 doi: 10.1016/j.clinimag.2016.11.010 JCT 8151

To appear in:

Journal of Clinical Imaging

Received date: Revised date: Accepted date:

31 July 2016 23 October 2016 15 November 2016

¨ Please cite this article as: Yılmaz Barı¸s, C ¸ i¸cek Esin Derin, S¸irin Evrim, Ozdemir G¨ uzelali, ¨ Karaku¸s Ozg¨ un, Muratlı Hasan Hilmi, A magnetic resonance imaging study of abnormalities of the patella and patellar tendon that predispose children to acute patellofemoral dislocation, Journal of Clinical Imaging (2016), doi: 10.1016/j.clinimag.2016.11.010

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A magnetic resonance imaging study of abnormalities of the patella and patellar tendon that predispose children to acute patellofemoral dislocation

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Barış Yılmaz1, Esin Derin Çiçek2 , Evrim Şirin3 , Güzelali Özdemir4 , Özgün Karakuş5, Hasan Hilmi Muratlı6

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Academic Affiliations and Authors Contributions

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1. MD, Assistant Professor, Fatih Sultan Mehmet Education and Research Hospital, Department of Orthopedic Surgery and Traumatology, Istanbul, Turkey; Designed the study, collected data, assessed the results, wrote the manuscript. 2. MD, Fatih Sultan Mehmet Education and Research Hospital, Department of Radiology, Istanbul, Turkey; Designed the study, collected data, assessed the results, wrote the manuscript. 3. MD, Assistant Professor, Fatih Sultan Mehmet Education and Research Hospital, Department of Orthopedic Surgery and Traumatology, Istanbul, Turkey; Designed the study, collected data, assessed the results, wrote the manuscript. 4. MD, Assistant Professor, Ankara Numune Education and Research Hospital, Department of Orthopedic Surgery and Traumatology, Ankara, Turkey; Designed the study, collected data, assessed the results, wrote the manuscript. 5. MD, Fatih Sultan Mehmet Education and Research Hospital, Department of Orthopedic Surgery and Traumatology, Istanbul, Turkey; Designed the study, collected data, assessed the results, wrote the manuscript. 6. MD, Professor, Trakya University Hospital, Department of Orthopedic Surgery and Traumatology, Edirne, Turkey; Designed the study, collected data, assessed the results, wrote the manuscript.

Declaration of conflicting interests Barış Yılmaz, Esin Derin Çiçek, Evrim Şirin, Güzelali Özdemir, Özgün Karakuş, Hasan Hilmi Muratlı declare that they have no conflict of interest. Compliance with Ethical Requirements

Ethical Board Review Statement: Procedures were fully compliant with Fatih Sultan Mehmet Education and Research Hospital Ethics Committee which approved the study with project number FSMEAH-KAEK 2013/33.

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ACCEPTED MANUSCRIPT Corresponding author: Barış Yılmaz Fatih Sultan Mehmet Research and Training Hospital,

Department of Orthopaedics and Traumatology,

E-mail: [email protected]

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Telephone: +90 505 800 60 60

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E-5 Karayolu üzeri, İçerenköy, İstanbul-Turkey

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ACCEPTED MANUSCRIPT A magnetic resonance imaging study of abnormalities of the patella and patellar tendon that predispose children to acute patellofemoral dislocation

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Abstract

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This study compared 20 children hospitalised with acute patellofemoral dislocation with an age-matched healthy control group with no history of knee problems or patellar dislocation. The following morphological parameters were significantly different between the groups: the

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mean patellar width and length, mean sulcus depth, mean patellar tendon width and total patellar volume. The magnetic resonance imaging findings of this study suggested that

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for acute patellofemoral dislocation.

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structurally smaller than normal patella and patellar tendon volumes are predisposing factors

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Keywords: patella, acute patellofemoral dislocation, patellar tendon, patellofemoral

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instability, patellofemoral joint INTRODUCTION

Acute patellofemoral dislocation of an anatomically normal knee joint requires high-

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energy trauma (1, 2). In the absence of serious trauma, the condition can be evaluated as patellofemoral instability (PFI) syndrome; these patients have definite underlying predisposing factors (3, 4) such as adolescent age, excessive weakness, tightness or imbalance of dynamic stabilizers, abnormally shaped trochlear groove, deficient medial patellofemoral ligament from a previous injury or congenital laxity, family history of patellar dislocation injuries, and patellar dislocation history of the contralateral knee. In addition, there are other rarer conditions that may influence patellar stability: rotational malalignment of the femur and tibia (femoral anteversion and external tibial torsion, known as “miserable malalignment”); a patella alta, in which an abnormally long patellar tendon affects the position of the patella; and problems due to previous surgery such as an overly extensive lateral release (5). 3

ACCEPTED MANUSCRIPT The assessment of PFI is predominantly based on X-rays, computed tomography, and magnetic resonance imaging (MRI) (6-8). MRI also provides a three-dimensional image of

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the joint allowing surgeons to make reliable measurements, to objectively determine the

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underlying abnormalities, and to compare abnormalities with their published thresholds. More

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recently, MRI has gained popularity for PFI imaging because of its superior evaluation of associated cartilage defects and ligamentous anatomy (9-13).

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In addition to the known predisposing factors in children who develop patella dislocation, that the volume of the patella and patellar tendon is smaller than that of other

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children is also a possibility. However, to date, no studies describing patellar volume and patellar tendon volume using MRI have been reported. This study aimed to determine the

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morphological features in the patella and patellar tendon that may predispose children to acute

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patellofemoral dislocation.

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METHODS

MRI data sets of 40 adolescent knees were acquired as approved by our Institutional

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Review Board (Research Ethics Committee no. FSM EAH-KAEK 2013/20). Radiology department records were reviewed to obtain details of adolescents aged 10–16 years with previous lower extremity MRI findings. The control group included patients without underlying PFI (MRI was performed due to suspected meniscal and/or ligament pathology); the study group patients had a history of acute traumatic patellofemoral dislocation. Forty randomly selected patients (20 in each group) suitable for radiological and MRI examinations were enrolled after obtaining informed consent. The control group included 8 (40%) males and 12 (60%) females (median age, 14.6 years); the study group included 7 (35%) males and 13 (65%) females (median age, 13.8 years). The body mass index (BMI) of the patients was evaluated in the belief that it could affect the study results.

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All patients underwent routine 1.5 T MRI, with all images were viewed upon a Picture

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Archiving and Communication System (PACS). T1 sequences were obtained in the sagittal

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plane, and T2 fat sat/Pd fat sat sequences were obtained in the coronal, sagittal, and axial

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planes. All studies were performed on a 1.5 T MRI 450w system (GE Healthcare, Milwaukee, WI, USA). The gradient strength and slew rate of the system were 33 mT/m and 150 T/m/sec, respectively. Routine knee examination was performed and measurements were taken on axial

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PD FS and sagittal PD FS images. Axial PD FS images were acquired using FOV of 16-

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17cm, Slice thickness/spacing of 4/1mm, Matrix of 192x192, NEX (or NSA) of 2, Receiver Bandwidth of 31 KHz and echo train length of 10. Sagittal PD FS images were acquired using

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FOV of 16-17cm, Slice thickness/spacing of 4/1mm, Matrix of 288x224, NEX (or NSA) of 2,

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Receiver Bandwidth of 41 KHz and echo train length of 11. All the measurements and evaluations of the MR images were made by a radiology

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specialist (EDC) with more than 10 years of experience. The trochlear sulcus angle was measured on the first craniocaudal image showing a

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complete cartilaginous trochlea and corresponding to the deepest depression of the intercondylar groove according to van Huyssteen et al (14) (Fig. 1a). For the trochlear sulcus depth, the most anterior edges of two femoral condyles were determined and joined on the axial view. A perpendicular line was drawn from the intersection of the deepest points of the medial and lateral facets, and from the length of this line, the depth was measured (Fig. 1b). Patella alta was defined based on the Insall–Salvati method (3). The patella and patellar tendon volumes were calculated from the data obtained. There are no standard methods for measuring the patella and patellar tendon volumes in the

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ACCEPTED MANUSCRIPT literature. We used ellipsoid formula in order to calculate the patellar volume (15-17). It is as follows;

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Ellipsoid Formula= height × width × length x π/6

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Since the longest craniocaudal (CC) dimension and anteroposterior (AP), mediolateral (ML) dimensions which are obtained from the widest axial slice were used to measure patellar volume (Fig. 2a-b), the formula changes into the following form,

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Patellar volume = height(AP)× width (ML) × length (CC) x π/6

(π/6 =0.523)

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In this study, patellar tendon volume was also calculated utilizing a standard volume formula. The tridimensional volume calculation was applied by multiplying three orthogonal

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dimensions. The tendon craniocaudal (TCC) length from the sagittal sequence multiplied by

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the tendon anteroposterior (TAP) and tendon mediolateral (TML) dimensions from the axial

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sequence was used to determine the patellar tendon volume (Fig. 3a-b). It was calculated using the following formula:

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Patellar tendon volume = height (TAP) × width (TML) × length (TCC) Data were analyzed using IBM SPSS Statistics 22 (IBM SPSS, Turkey). The Shapiro– Wilk and Kolmogorov–Smirnov tests were used to determine if the parameters obtained from the study data were normally distributed. In addition to the standard statistical measurements (median and standard deviation), Student’s t-test was used to compare the parameters between the groups. A value of p <0.05 was considered statistically significant. RESULTS BMI values were 21.01 ± 2.03 kg/m2 in the study group and 19.95 ± 1.81 kg/m2 in the control group. There were no statistically significant differences in age and BMI between the groups (p > 0.05; Table 1). 6

ACCEPTED MANUSCRIPT The trochlear sulcus angle obtained from axial images was significantly greater in the study group than in the control group (147.41° ± 8.31° vs. 135.71° ± 11.02°, respectively; p =

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0.001). The trochlear sulcus depth was significantly less in the study group than in the control

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group (4.81 ± 1.13mm vs. 7.28 ± 1.14 mm, respectively; p= 0.001).

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The patellar width was significantly smaller in the study group than in the control group (37.9 ± 3.23mm vs. 41.62 ± 3.73 mm, respectively; p = 0.002). Similarly, the median patellar length was significantly shorter in the study group than in the control group (38.44 ±

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4.05mm vs. 41.77 ± 4.2 mm, respectively; p=0.015). However, there was no statistically

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significant difference between the groups in respect of patellar height (19.8 ± 1.87mm vs. 19.35 ± 1.87 mm, respectively; p > 0.05). The patellar volume was significantly less in the

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respectively; p= 0.022) (Table 2).

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study group than in the control group (14632.26 ± 3925.83mm3 vs. 17881.32 ± 4674.45 mm3,

Assessments using the Insall–Salvati index showed that 16 (80%) patients in the study

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group and 3 (15%) patients in the control group had patella alta. The Insall–Salvati indices were 1.35 ± .21, in the study group and 1.13 ± .12, in the control group (p = 0.001). The

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Insall–Salvati index was measured as the ratio of the patellar tendon length to the patellar length. There was no significant difference between the groups in respect of patellar tendon length (49.97 ± 6.37mm vs. 47.91 ± 4.57 mm, respectively; p > 0.05). No significant difference was determined between the groups in respect of patellar height (p > 0.05). The mean patellar width was significantly smaller in the study group than in the control group (p = 0.011). However, there was no significant difference in the approximate volume obtained by multiplying the length, width, and height values (p > 0.05). Patellar tendon volume was determined to be approximately 12% smaller in the study group than in the control group (4677.9 ± 1286.53mm3 vs. 5281.15 ± 1645.41mm3, respectively).

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DISCUSSION

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The patellar articular surface is anatomically smaller than the trochlear articular

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surface, and thus the entire patellar articular surface is not in contact with the femur at any one time. This anatomical structure is the reason why the patellofemoral joint (PFJ) is one of the most incongruent joints in the body (18-20). These findings demonstrate and aid in

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quantifying the anatomic basis of this incongruity. The magnetic resonance imaging data

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obtained in this study suggested that structurally smaller than normal patella and patellar tendon volumes are predisposing factors for acute traumatic patellofemoral dislocation.

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The anatomical structure and unique relationship of the patella and trochlea are critical

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for normal knee flexion and extension (21). For example, in cases of trochlear dysplasia, dislocation can occur in knee flexion, with the patella subluxing out of the shallow groove.

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MRI is more sensitive in describing the morphology and characteristics of the trochlear sulcus than conventional radiography (22). A sulcus angle of >144° is a sign of hypoplasia (23). A

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recent study demonstrated that in addition to the sulcus angle, a depth measurement made 3 cm above the tibiofemoral joint line is very specific and sensitive for the diagnosis of trochlear dysplasia (24). A sulcus depth of <5 mm is accepted as hypoplasia, whereas a depth of <3 mm is considered as dysplasia (25). In a study by Dejour and Le Coultre, it was emphasized that 96% of patients with true patellar luxation have trochlear dysplasia (6). In 5 of every 6 patients, the pathology is located at the center or medial part of the trochlea (26). In the current study, the mean sulcus angle was significantly higher and the mean sulcus depth was significantly lower in the study group than in the control group; this condition appears to have originated from the femoral bony structure and led to PFI.

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There is very little descriptive information in literature regarding patellar dysplasia,

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which is one of the factors causing PFI. In the current study, as it was suspected that

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evaluating only the trochlear aspect of PFJ would not completely explain patellar dislocation, the morphology of the patella was analysed. The patellar volume was calculated and thus it was attempted to understand the patellar structure. Using the ellipsis formula, which is

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frequently used in radiological practice, the patellar volume was calculated and was found to

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be significantly lower in the study group than in the control group. This result demonstrates that in addition to trochlear dysplasia, patellar volume is also an important factor leading to PFI. Therefore, as demonstrated by the results of this study, most PFI cases have patellar

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anomalies accompanying trochlear dysplasia. If the articular surface of the trochlea is flat (trochlear hypoplasia), joint stability

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seems to rely on the retinaculum and muscle balance. This means that if the bony congruence is insufficient, stability would only be provided by soft tissues, with a reliance on muscle,

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ligament, and tendon structures around the patella. Many active forces affect the patella, such as those generated by the rectus femoris, vastus medialis, and lateralis muscles. Patellofemoral stability is mainly provided by the retinaculum, patellofemoral, and patellar ligaments, which is why soft tissue imbalance is another important factor causing PFI (27, 28). The peripatellar retinaculum becomes adaptively dysplastic as a result of chronic alignment disorder. Hallisey et al. demonstrated in a cadaveric study that there is variance in the insertion point of the vastus lateralis obliquus muscle (29). The excessive pulling action of this muscle can cause the patella to slide too far laterally. Conversely, there might be an abnormal inclination of the patella that might cause increased lateral pressure syndrome, a condition caused by the lateral patellar retinaculum being too tight, without subluxation.

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ACCEPTED MANUSCRIPT One of the most important structures stabilizing the patella is the patellar tendon. In cases of patellofemoral dislocation, attention has always been paid to the structure of the

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patellar tendon. However, the mass structure of the patellar tendon as a cause of

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patellofemoral dislocation has not been researched in literature. The clinical importance of

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patella alta, which is an important risk factor for PFI, is actually now believed to be more significant than previously thought (23, 30, 31) In fact, 24% of patients with PFI have patella alta, whereas this condition is present in only 3% of patients with a stable PFJ (32). This

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condition is seldom isolated and is usually associated with trochlear dysplasia (33). If a minor

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trauma causes patellar dislocation, the probability of associated patella alta is higher than it is in more severe trauma cases (34, 35). In the current study, patella alta was observed in 3 (15%) patients in the control group and 16 (80%) in the study group. Furthermore, the mean

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Insall–Salvati indices were significantly higher in the study group than in the control group. According to the results of the current study, no statistical difference was found

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between the two groups in respect of the patellar tendon volume. However, it was observed that the patellar tendon volume in the study group was found to be approximately 12%

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smaller than that of the control group. When this was examined more closely, although there was no significant difference in the mean length or thickness of the patellar tendon, the mean width of the patellar tendon in the study group was determined to be statistically significantly smaller than that of the control group. This finding may be explained by the fact that the width of the patella tendon is proportional to the width of the patella from which it arises; therefore a narrower patella tends to be associated with a narrower patellar tendon. Thus, as the patellar tendon holding the lower pole of the patella, is of a smaller width on a smaller width patella, the patellar tendon in the study group was weaker in volume. This finding obtained from the current study is important as it has not been previously shown in literature.

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ACCEPTED MANUSCRIPT There were some limitations to this study, primarily the limited number of patients. In addition, the patients were drawn from a Turkish paediatric population only.

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investigations based on all populations should be conducted to provide more complete data.

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which promising new PFI criteria are described in detail.

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Due to the limited number of patients, this study has been labelled as a preliminary report, in

CONCLUSIONS

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In conclusion, knee movements of the patella occur through the gathering of forces

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coming from the quadriceps, transferred to the tibia via the patellar tendon. The anatomic structure of the patella and patellar tendon appear to be equally important to that of the trochlea for normal function of the patellofemoral joint. This study suggests that the patella

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and patellar tendon tend to be structurally smaller in patients prone to patellofemoral dislocation. With methods used in radiology for the measurement of the approximate mass of

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structures and a standard orthopaedic method, the results of this study have shown that the patella and patellar tendon are smaller than normal in children with acute patellofemoral

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32. Dejour D, Saggin P (2010) The sulcus deepening trochleoplasty the Lyon's procedure. Int

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Orthop 34:311-316. doi: 10.1007/s00264-009-0933-8. 33. Caton JH, Dejour D (2010) Tibial tubercle osteotomy in patellofemoral instability and in

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patellar height abnormality. Int Orthop 34:305-309. doi: 10.1007/s00264-009-0929-4. 34. Geenen E, Molenaers G, Martens M (1989) Patella alta in patellofemoral instability. Acta Orthop Belg 55:387-393 35. Walker P, Harris I, Leicester A (1998) Patellar tendon-to-patella ratio in children. J Pediatr Orthop 18:129-131 FIGURE CAPTIONS Fig. 1: Measurement of the trochlear sulcus angle (1a) and trochlear sulcus depth (1b) Fig. 2: Measurement of the length of patellar joint surface and length (3a), thickness and patellar width (3b) 15

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Fig. 3: Measurement of the length (3a), thickness and width of the patellar tendon (3b)

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Fig. 1: Measurement of the trochlear sulcus angle (1a) and trochlear sulcus depth (1b)

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2b.

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Fig. 2: Measurement of the length of patellar joint surface and length (3a), thickness and patellar width (3b)

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Fig. 3: Measurement of the length (3a), thickness and width of the patellar tendon (3b)

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ACCEPTED MANUSCRIPT Table 1. Comparison of the study parameters between children with acute patellar dislocation (mm: milimeter) Control Group

Study Group

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(Mean ± SD)

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13.8 ± 2.26

0.222

21.01 ± 2.03

0.091

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(Mean ± SD)

14.6 ± 1.79

BMI

19.95 ± 1.81

Length of Patellar Tendon (mm)

47.91 ± 4.57

49.97 ± 6.37

0.248

Thickness of Patellar Tendon (mm)

4.29 ± 0.71

3.98 ± 0.83

0.219

25.92 ± 2.99

23.52 ± 2.62

0.011*

5281.15 ± 1645.41

4677.9 ± 1286.53

0.204

41.62 ± 3.73

37.9 ± 3.23

0.002**

Length of Patella (mm)

41.77 ± 4.2

38.44 ± 4.05

0.015*

Thickness of Patella (mm)

19.8 ± 1.87

19.35 ± 1.87

0.457

17881.32 ± 4674.45

14632.26 ± 3925.83

0.022*

1.13 ± 0.12

1.35 ± 0.21

0.001**

135.71 ± 11.02

147.41 ± 8.31

0.001**

7.28 ± 1.14

4.81 ± 1.13

0.001**

MA

NU

SC R

Age (years)

AC

CE P

Width of Patella (mm)

TE

Patellar Tendon Volume (mm3)

Patellar Volume (mm3) Insall–Salvati index

Trochlear Sulcus Angle (degree)

Trochlear Sulcus

Depth (mm)

D

Width of Patellar Tendon (mm)

20

ACCEPTED MANUSCRIPT

IP

T

Table 2: Patellar volumes in the two groups

Patella Volume

SC R

25000

15000

NU

10000 5000

MA

0

Control Group

CE P

TE

D

Study Group

AC

Mean+SD

20000

21