differences between genders. The mean TT-Te distance was 63.9 mm (range 49–79 mm) with there being signifi-cant differences between genders. The resulting mean TT-TG Index was 0.12 ± 0.05 (range 0–0.25). In the patient group, the average TT-TG distance was 13.5 ± 4.1 mm and the average TT-Te distance was 61.3 ± 6.8 mm. The resulting average TT-TG Index of 0.22 ± 0.07 in the patient group (PFI) approximates the threshold determined by the 95 % confidence interval in the healthy control group. A direct comparison between the control group and the patient group revealed a significant difference in the TT-TG distance (p = 0.0001), in the TT-Te distance (p < 0.0042) and in the resulting TT-TG Index (p < 0.0001).Conclusions The measurement of the TT-TG Index is a reliable and differentiated approach for determining the lateral displacement of the tibial tubercle in relation to the proximal trochlear groove. The pathological influence of the TT-TG distance in case of patella instability depends on individual joint size, confirming the initial hypothesis. We currently consider a TT-TG Index >0.23 to be pathological based on our findings. Particularly, in case of a marginal TT-TG distance, the additional relative TT-TG Index facili-tates a decision concerning an indication for a operative medial transfer of the tibial tubercle.Level of evidence II.
Because the genesis of patellofemoral instability is mul-tifactorial, diagnosing and treating it requires a differ-entiated approach when it comes to the individual risk
Abstract Purpose Medial transfer of the tibial tubercle has become a standard procedure in cases of patella instability caused by an increased tuberositas tibae-trochlear groove (TT-TG) distance. However, the TT-TG distance has always been assessed as an absolute value without taking individual joint size into consideration. It was assumed that the path-ological influence of the TT-TG distance correlates with individual joint size. Aim of the current study therefore was to develop a method to express TT-TG distance in relation to these joint variables.Methods Two hundred knee MRI scans of healthy indi-viduals (69 females and 131 males) were evaluated retro-spectively in a control group. First, the TT-TG distance was measured as described by Schoettle et al. To determine joint size, the proximal–distal distance between the entrance of the chondral trochlear groove (Te) and the onset of the patella tendon at the tibial tubercle (TT) was selected. Sub-sequently, the TT-TG/TT-Te ratio expresses the relation-ship between the TT-TG distance and the proximal–distal distance from the entrance of the chondral trochlear groove to the height of the tibial tubercle. The TT-TG Index can also be expressed as an angle (TT-TG angle). Likewise, in another patient group, 54 knee MRTs of patients with patellofemoral instability were evaluated.Results The average TT-TG distance of the control group was 7.5 ± 3.5 mm (range 0–17.4 mm) with no significant
Swen Hingelbaum and Raymond Best have contributed equally to this work.
S. Hingelbaum · R. Best · J. Huth (*) · D. Wagner · G. Bauer · F. Mauch Sportklinik Stuttgart, Taubenheimstr. 8, 70372 Stuttgart, Germanye-mail: [email protected]
Knee Surg Sports Traumatol Arthrosc
1 3
factors. Recently, there has been a rise in the number of publications looking at different diagnostic and treat-ment approaches for patellar instability. In principle, instability criteria can be differentiated into ligament, muscular (dynamic) and osseous risk factors. Dejour et al. first formulated the four main risk factors in 1994: (1) trochlear dysplasia; (2) quadriceps dysplasia, rep-resented by an increase in patellar tilt in extension; (3) patella alta with a Caton-Deschamps Index greater than or equal to 1.2; and (4) a TT-TG distance greater than or equal to 20 mm [3].
The TT-TG distance reflects the gold standard of the lateral pulley (M. quadriceps), in particular the patellar tendon, and in principle can differ depending on the size of the knee [2]. The tibial-tubercle-to-trochlear-groove distance (TT-TG distance) was first described by Goutal-lier [5]. Using superimposed axial CT scans, the position of the tibial tubercle (TT) can be measured precisely in relation to the trochlear groove (TG) [7]. The pathological relevance of this was demonstrated by Dejour et al. [3]. Comparing patients that have patellofemoral instability with healthy subjects, the CT scans of the healthy con-trol group showed an average TT-TG distance of 12 mm. In the group with patellar instability, 56 % of the patients exhibited a TT-TG value greater than 20 mm [3]. Later Schoettle et al. [9] demonstrated that the TT-TG distance can also be measured using an MRI. To evaluate the necessity of an operative medial transfer by determining an absolute value like the TT-TG distance with one ref-erence threshold of 15–20 mm according to Dejour and Walch (1994)/Koeter, Diks et al. (2007) seems critical, as individual joint measures, e.g., in relation to a patients, are not respected [3, 6].
In contrast, the pathological impact of the TT-TG dis-tance can be influenced by the prevailing proportions of the knee, and in particular, the patellofemoral joint. Spe-cifically, this means that a TT-TG distance of, for example, 20 mm in a large patellofemoral joint has a much lower pathological impact on the patellofemoral alignment than in a small patellofemoral joint. Hence, a more differentiated approach to medial tibial tubercle indication is necessary.
So far literature has lacked defined parameters that reflect these different proportions during TT-TG meas-urement. Against this backdrop, we formulate following hypothesis: The pathological influence of the TT-TG dis-tance correlates with individual joint size.
The aim of the present study was to develop a reliable MRI-based method for measuring TT-TG distance as a relative value, taking individual knee sizes into account. In clinical all-day practice, especially in case of a marginal TT-TG-distance, the additional relative TT-TG Index could facilitate a decision concerning an indication for a opera-tive medial transfer of the tibial tubercle.
Materials and methods
In order to take into account the individual size of the patel-lofemoral joint when measuring the TT-TG distance, this study not only uses the conventional method of determin-ing the lateral displacement of the tibial tubercle in relation to the proximal entry (TT-TG distance), but also measures the axial (proximal–distal) distance between the chon-dral proximal trochlear entrance (Te) and the height of the tibial tubercle (TT). The ratio between both distances is expressed by the TT-TG Index: TT-TG/TT-Te (Fig. 1). We focus on the TT-Te distance rather than the mediolat-eral dimension because it correlates more precisely with the patellofemoral function. The two anatomical landmarks of the TT-Te distance: The proximal chondral entrance of the trochlear groove and the height of the tibial tubercle determine substantially the biomechanical alignment of the patellofemoral joint.
Since both the TT-Te distance and the TT-TG Index rep-resent a new departure that has not yet been described in the literature, they were first determined in a healthy con-trol group in 200 knee joints without patellofemoral prob-lems. In addition to determining the respective standard value, the aim was to check the inter-observer and intra-observer reliability of this measuring approach.
Fig. 1 TT-Te distance: proximal–distal distance between entrance of the trochlea groove (Te) and height of the tibial tubercle (TT)
Knee Surg Sports Traumatol Arthrosc
1 3
Two hundred knee MRI examinations performed in our department between October 2009 and June 2010 were analyzed retrospectively. The average age of the 200 sub-jects (69 females and 131 males) was 27.9 ± 7.8 years. To obtain a standard TT-TG Index value, only MRIs of sub-jects without any anamnestic and clinical patellar insta-bility or patellofemoral disorder were taken into account. Indications for the retrospective MRIs were chondral, meniscal or cruciate ligament pathologies. exclusion cri-teria included patellofemoral arthrosis, surgery in the area of the patellofemoral compartment or the tibial tubercle.
All examinations were performed using the same scanners (esaote dedicated 0.25 Tesla G-Scan or esaote 0.2 Tesla e-Scan) and image program (VePRO eMR manager). A standard knee MRI examination protocol using a coronal Se-T1 and STIR sequence, a sagittal TSe-T2 and Ge-T1 sequence and an axial TSe-T2 sequence was used. The axial and sagittal planes included the entire femoral troch-lea and the tibial tubercle. First, the TT-TG distance was measured on axial MRI scans using the method described by Schoettle et al. [9]. The deepest point of the cartilagi-nous entrance of the trochlear groove showing a complete cartilaginous layer of the trochlea was marked in the first axial sequence. In the same axial image, a tangent baseline was drawn to the posterior chondral border of the poste-rior femur condyles. A perpendicular line was then drawn from this “baseline” to the deepest point of the trochlea mentioned above (Fig. 2). These lines were transferred to the first proximal axial sequence, which shows complete attachment of the patellar tendon to the tibial tubercle. In this sequence, a vertical line was drawn from the midpoint between the most external attachment points of the patella tendon to determine the center of insertion. From this point, another perpendicular line was drawn to the transferred baseline. The TT-TG distance was measured between both perpendicular lines.
Then, using the image program’s 3D linking func-tion, the deepest point of the cartilaginous trochlear entrance in the axial sequence was transferred to the sag-ittal T2-weighted sequence (Fig. 3). Similarly, the height of the most proximal, complete attachment of the patel-lar tendon to the tibial tubercle, was transferred to the sagittal sequences (Fig. 4), and the proximal–distal dis-tance between the height of these transferred points was
Fig. 2 Measurement of the TT-TG distance according to Schoettle et al. [9]
Fig. 3 Determination of the entrance of the chondral trochlear groove (Te) in the axial plane and transfer into the sagittal plane via 3D linking function of the image program
Knee Surg Sports Traumatol Arthrosc
1 3
measured in the sagittal plane (Fig. 5). Finally, The TT-TG Index: (TT-TG)/(TT-Te) was calculated. To determine intra-rater and inter-rater reliability, 30 subjects were ran-domly selected from the total study population (n = 200). This group was measured twice by two independent exam-iners with an interval of 6 weeks between measurements.
The measurements were blinded with regard to the other examiner and with regard to the results of the respective initial measurements.
By analogy, a second retrospective series of measure-ments, including the necessary TT-TG and TT-Te dis-tances, were made in 54 knee joints of 51 patients (33 female and 18 male) with established chronic patellofemo-ral instability to determine the TT-TG Index. The average age was 22 ± 11 years. The respective MRT examinations were carried out between March 2009 and August 2011. Unlike for the control group, the existing patellofemoral instability was the indication for the MRT. except for patel-lofemoral instability and trochlear dysplasia, the remain-ing exclusion criteria were the same as for the above-men-tioned control group from the beginning.
Inter-rater reliability was also determined by 2 examin-ers for all 54 measurements in a blinded procedure.
Data acquisition was performed as a retrospective analy-sis within the study “risk factors of patellar luxation in MRI examination in upright and supine position.” The study was approved by the Institutional Review Board of the respon-sible State Medical Association (F-2013-062).
Statistical analysis
The data were checked for normal distribution using the Shapiro–Wilk test. Because there was no normal data dis-tribution for the TT-TG and the TT-Te distances in both groups, significant differences were verified using the Wilcoxon–Mann–Whitney test. Based on the data from the control group, the “standard value” of the TT-TG Index was determined using the 95 % confidence interval (CI).
Fig. 4 Determination of the height of the tibial tubercle (TT) in the axial plane and transfer into the sagittal plane via 3D linking function of the image program
Fig. 5 Determination of the proximal–distal distance between the deepest point of the chondral entrance of the trochlea and the height of the tibial tubercle (TT): TT-Te distance
Knee Surg Sports Traumatol Arthrosc
1 3
To determine intra-rater reliability, the individual meas-urement results from the examiners were used to calculate an intra-class coefficient (ICC). The mean values of both measurements taken by an examiner were then used to cal-culate an additional ICC that reflected inter-rater reliability.
The a priori calculated sample size (Software G-Power 3.1—effect size 0.8, α-error 0.05, power 0.95) revealed a minimum of 42 subjects per group. In order to achieve standard value, the control group was increased consider-ably. Patient sample size was increased to eliminate unus-able measurements.
Results
Results of the control group
An average TT-Te value of 63.9 ± 5.9 mm (range 49.1–78.8 mm) was established for the first time in this study in the case of 200 knee joints without patellofemoral prob-lems. The mean cartilaginous tendon TT-TG distance was 7.5 ± 3.5 mm (range 0–17 mm). The difference between the genders was not statistically significant (p = n.s.). The resulting TT-TG Index was 0.12 ± 0.05 (Table 2).
In order to highlight the pathological relevance, a TT-TG Index was calculated using the control group’s smallest and largest TT-Te distances (smallest and largest knee joints) of 49 and 79 mm, respectively, and using the TT-TG dis-tance threshold of 20 mm described by Dejour and Walch. The result was a TT-TG Index of 0.41 for the smallest knee compared with one of 0.25 for the largest knee. Applying the co-tangent function resulted in a corresponding angle α of 23° for the smallest knee and only 15° for the larg-est knee (Fig. 1; Table 1). Measured based on the 95 % CI resulted in a threshold for the TT-TG Index of greater than or equal to 0.23.
The intra-observer reliability for the TT-Te distance for both rater 1 and rater 2 was highly significant with an ICC of 0.98 and 0.94, respectively. The inter-observer reliability for the TT-Te distance was also highly significant with an ICC of 0.88. The intra-observer reliability for the TT-TG Index was highly significant (ICC: rater 1 = 0.9 and rater 2 = 0.96). The inter-observer reliability was also signifi-cant (ICC: 0.83).
Results of the patient group
The inter-rater reliability was highly significant for all three parameters: ICC TT-TG distance: 0.9; ICC TT-Te distance: 0.94 and ICC TT-TG Index: 0.92.
The determined values in the group of patients with patellofemoral instability (PFI) were mentioned in Table 2. The average TT-TG distance was 13.5 ± 4.1 mm. As in the control group, there was no significant gender differ-ence (p = n.s.) with a TT-TG distance of 13.6 ± 4.4 mm in females and 13.4 ± 3.7 mm in males. There was a sig-nificant gender difference between females and males. The resulting TT-TG Index for the entire patient group was 0.22 ± 0.07, with an index value of 0.23 ± 0.08 in females and 0.20 ± 0.06 in males (p = n.s.) (Table 2).
Comparison of the patient group and the control group
The difference between the TT-Te distance of 63.9 mm in the control group and 61.3 mm in the PFI group was sig-nificant. Likewise the TT-TG distance of 7.5 mm (control group) and 13.5 mm in the PFI group revealed significant differences. This is also reflected in a significant difference between the TT-TG Index of 0.12 in the control group and 0.22 in the PFI group (Table 3). Females with smaller knee
Fig. 6 TT-TG Index of the biggest and smallest measured knee
Table 1 Illustration of the relative TT-TG Index using an absolute TT-TG value of 20 mm for the smallest and largest knee joint and the threshold (Fig. 6)
20-mm TT-TG TT-TG Index
Lateralizing angle in degrees
Possible threshold of the TT-TG Index based on the 95 % CI
“Smallest knee joint”:TT-Te = 49 mm 0.41 23 >0.23
“Largest knee joint”: TT-Te = 79 mm 0.25 15 >0.23
Knee Surg Sports Traumatol Arthrosc
1 3
joints exhibited the largest TT-TG Index of 0.23 (Table 1). The differences between genders in patient and control group are shown in Table 4.
Furthermore, we analyzed the PFI group for patients with a TT-TG distance >20 mm, which is considered an indication for medial transfer of the tibial tubercle and compared this with a TT-TG Index >0.23. In total, we found six patients with a TT-TG distance of more than
20 mm (male = 1 and females = 5) and a total of 20 patients (males = 4 and females = 16) with a TT-TG Index greater than 0.23.
Discussion
The most important finding of the present study was to evaluate the necessity for medial transfer of the tibial tuber-cle on a more individualized basis. The new TT-TG Index could reliably be assessed and measured in an MRI both in the control group and in the patient group. Inter-observer reliability and intra-observer reliability were highly signifi-cant in the control group as well as in the patient group. Hence, our work currently offers the only measuring approach that can reliably determine the TT-TG distance taking individual joint sizes into account. Other meas-urement approaches can be found in the literature, which describe the TT-TG distance or the lateral displacement of the tibial tubercle in relation to the epicondylar axis [1, 12]. These working groups, however, did not indicate that reli-ability had been reviewed. Applying the co-tangent func-tion revealed the varying pathological relevance in the con-trol group of the TT-TG distance in relation to the existing geometry of the (patellofemoral) joint through the resulting angle α. The application of TT-TG Index was reliable and, as a relative value because it includes the TT-TG and the TT-Te distances, takes into account the lateral and the axial distance of the tibial tubercle to the proximal entry of the trochlear groove.
Against the backdrop of a 95 % CI in the control group, we established a standard value of <0.23 for the TT-TG Index. When the TT-TG Index of the patient group was reviewed, a statistically significant difference could be found when compared to that of the control group. The average TT-TG Index of 0.22 in the patient group (PFI) approximates the threshold determined by the 95 % CI in the healthy control group. Thus, we regard that a relative threshold for the TT-TG Index can be determined, as being confirmed.
Based on the mentioned findings, we consider a TT-TG Index >0.23 to be unphysiological. Accordingly, medial transfer of the tibial tubercle possibly should have been indicated more frequently in individual cases in the patient group in retrospect than when only the TT-TG distance threshold of 20 mm was used. no significant gender dif-ference in terms of the absolute TT-TG distance was found in either the control group or the patient group. This find-ing is consistent with the findings of the working group of Balcarek et al. [1]. In contrast, the TT-Te distance in the control and patient groups differed significantly between genders with the smaller TT-Te distance being found in the female gender. Against this backdrop, the average shorter
Table 2 Illustration of the different values in the control and patient group (see text)
Males Females Significance
Control group
TT-Te (mm) 65.9 ± 5.5 60.2 ± 4.7 p < 0.001
TT-TG (mm) 7.5 ± 3.7 7.6 ± 3.1 n.s.
TT-TG Index 0.11 ± 0.06 0.13 ± 0.05 n.s.
Patient group
TT-Te (mm) 67.5 ± 6.7 58.2 ± 4.3 p < 0.0001
TT-TG (mm) 13.4 ± 3.7 13.6 ± 4.4 n.s.
TT-TG Index 0.20 ± 0.06 0.23 ± 0.08 n.s.
Table 3 Summary of the values of the patient group and control group
Control group (n = 200)
PFI group (n = 54)
Significance
All samples
TT-Te distance 63.9 ± 5.9 mm 61.3 ± 6.8 mm p = 0.0042
TT-TG distance 7.5 ± 3.5 mm 13.5 ± 4.1 mm p < 0.0001
TT-TG Index 0.12 ± 0.05 0.22 ± 0.07 p < 0.0001
Table 4 Summary of the values of the patient group and control group divided in genders
Control group (n = 200)
PFI group (n = 54)
Significance
Females
TT-Te distance (f)
60.2 ± 4.7 mm 58.2 ± 4.3 mm p = 0.0315
TT-TG distance (f)
7.6 ± 3.1 mm 13.6 ± 4.4 mm p < 0.0001
TT-TG Index (f)
0.13 ± 0.05 0.23 ± 0.08 p < 0.0001
Males
TT-Te distance (m)
65.9 ± 5.5 mm 67.5 ± 6.7 mm n.s.
TT-TG distance (m)
7.5 ± 3.7 mm 13.4 ± 3.7 mm p < 0.0001
TT-TG Index (m)
0.11 ± 0.06 0.20 ± 0.06 p < 0.0001
Knee Surg Sports Traumatol Arthrosc
1 3
TT-Te distance in females could be an explanation for two observations described in the literature: In the high-risk group (adolescents between the ages of 10 and 17), first-time patellar dislocation occurs 33 % more frequently in girls than in boys. Women who have already had a first-time patellar dislocation are three times more likely to have a relapse dislocation than men [4]. Since no significant difference in TT-TG distance could be found between the genders, an isolated analysis of the TT-TG distance has not provided any explanation so far. However, the TT-TG Index only represents a relative TT-TG distance. extraarticular pathologies, e.g., a genu valgum, or an increased antever-sion of the neck of femur remain unconsidered. These may also play an important role in chronic patellar instability and need thus to be excluded in case of luxations of the patella [13].
In the literature, only a few papers are mentioned, which describe the TT-TG distance in relation to the size of the knee joint. Tsujimoto et al. [12] describes in contrast the position of the tibial tubercle using the lateral deviation index (LDI) based on CT not in MRI. Considering Staeu-bli et al., significant differences exist between the articular joint surface geometry in correlation with the correspond-ing subchondral osseous anatomy of the patella and femo-ral trochlea [10]. The measurements are performed as rec-ommended by Dejour [11]. They describe a significantly higher average LDI value of 30.1 ± 5.6 in the instability group compared with 15.1 ± 5.6 in the healthy control group [12]. This is not consistent with the findings of Bal-carek et al. [1]. Balcarek et al. also use a trans-epicondylar axis in order to express the TT-TG distance as a relative value. In contrast to Tsujimoto et al., the measurement is MRT and not CT based. Furthermore, they did not select the deepest point on the trochlea for the trochlear exit point of the perpendicular lines, but rather the deepest point of the proximal trochlear entrance in the first axial cutting plane with complete cartilage surface. In their study, the absolute and the relative TT-TG distances differ signifi-cantly in the control and the patient groups. The absolute TT-TG distance in the dislocation group was an aver-age of 4 mm more than in the control group (14.6 ± 4.6 vs. 10.6 ± 4.0 mm). The relative TT-TG distance in the dislocation group was 18.8 ± 6.2 mm compared with 13.8 ± 5.2 mm in the healthy control group. Analogous to these finding, we also found a significantly increased TT-TG Index in the PFI group (0.22) compared with 0.12 in the control group. Thus, we also consider our third hypoth-esis, that the relative TT-TG Index differs significantly in the patient group, to be confirmed. In his statistical analy-sis, Balcarek was unable to verify any significant impact on patellar instability through the ratio of the TT-TG distance to the length of the trans-epicondylar axis. We see one pos-sible reason being that the trans-epicondylar axis is not a
reference point in the framework of patellofemoral func-tion. In contrast, we take two anatomical landmarks into consideration in our TT-Te distance: the proximal chondral entrance of the trochlear groove and the height of the tibial tubercle, which substantially determine the biomechanical alignment of the patellofemoral joint. Since patellar dislo-cation frequently occurs in a state of slight flexion of the knee joint [8], the anatomical configuration of the proximal part of the trochlea plays a superordinate role in the osse-ous stabilization of the patella.
The present study is limited in its explanatory power by the unconfirmed biomechanical validation of the change in the lateral vector in relation to the existing proportions which until now has only been analyzed from a geometric point of view. The TT-TG Index should be evaluated further in a larger group of patients with patellar dislocation. More-over, in the present study, 4-mm layer thicknesses were used. Thinner layer thicknesses would enable a much more precise determination of the TT-Te distance. Despite these limitations, we believe that applying the relative TT-TG Index results in a reliable and differentiated approach for determining the lateral displacement of the tibial tubercle in relation to the proximal trochlear groove. The clinical rele-vance of this could be, that particularly in cases where there is a threshold TT-TG distance between 15 and 20 mm or in patients with very large or very small knee joints, the neces-sity for medial transfer of the tibial tubercle can be indicated on a more individualized basis. We currently consider a value of >0.23 to be pathological based on our findings.
Conclusion
Clinical decision for operative distal patellar realignment procedures mostly are related to a TT-TG distance of 15–20 mm or more. Here, the TT-TG distance is an absolute reference not respecting individual variations, e.g., the size of the knee joint. The described TT-TG Index instead allows to evaluate the necessity for medial transfer of the tibial tubercle on a more individualized basis.
Conflict of interest The authors declare that they have no conflict of interest.
References
1. Balcarek P, Jung K, Frosch K-H, Stürmer MK (2011) Value of the tibial tuberosity–trochlear groove distance in patellar instabil-ity in the young athlete. Am J Sports Med 39(8):1756–1761
2. Cooney A, Kazi Z, Caplan n, newby M, Gibson ASC, Kader D (2012) The relationship between quadriceps angle and tibial tuberosity–trochlear groove distance in patients with patellar instability. Knee Surg Sports Traumatol Arthrosc 20(12):2399–2404
Knee Surg Sports Traumatol Arthrosc
1 3
3. Dejour H, Walch G, nove-Josserand L, Guier C (1994) Factors of patellar instability: an anatomic radiographic study. Knee Surg Sports Traumatol Arthrosc 2(1):19–26
4. Fithian DC, Paxton eW, Stone ML, Silva P, Davis DK, elias DA, White LM (2004) epidemiology and natural history of acute patellar dislocation. Am J Sports Med 32(5):1114–1121
5. Goutallier D, Bernageau J, Lecudonnec B (1977) The measure-ment of the tibial tuberosity. Patella groove distanced technique and results (author’s transl). Rev Chir Orthop Reparatrice Appar Mot 64(5):423–428
6. Koëter S, Diks M, Anderson P, Wymenga A (2007) A modified tibial tubercle osteotomy for patellar maltracking ReSULTS AT TWO YeARS. J Bone Joint Surg Br 89(2):180–185
7. Muneta T, Yamamoto H, Ishibashi T, Asahina S, Furuya K (1994) Computerized tomographic analysis of tibial tubercle position in the painful female patellofemoral joint. Am J Sports Med 22(1):67–71
8. nikku R, nietosvaara Y, Aalto K, Kallio Pe (2009) The mech-anism of primary patellar dislocation: trauma history of 126 patients. Acta Orthop 80(4):432–434
9. Schoettle PB, Zanetti M, Seifert B, Pfirrmann CW, Fucentese SF, Romero J (2006) The tibial tuberosity–trochlear groove dis-tance; a comparative study between CT and MRI scanning. Knee 13(1):26–31
10. Staeubli H, Bosshard C, Porcellini P, Rauschning W (2002) Mag-netic resonance imaging for articular cartilage: cartilage-bone mismatch. Clin Sports Med 21(3):417–433
11. Tecklenburg K, Dejour D, Hoser C, Fink C (2006) Bony and car-tilaginous anatomy of the patellofemoral joint. Knee Surg Sports Traumatol Arthrosc 14(3):235–240
12. Tsujimoto K, Kurosaka M, Yoshiya S, Mizuno K (2000) Radio-graphic and computed tomographic analysis of the position of the tibial tubercle in recurrent dislocation and subluxation of the patella. Am J Knee Surg 13(2):83
13. Wang J, Yue B, Wang Y, Yan M, Zang Y (2012) The 3D analysis of the sagittal curvature of the femoral trochlea in the Chinese population. Knee Surg Sports Traumatol Arthrosc 20(5):957–963
