Arthroscopic evaluation of trochlear dysplasia as an aid in decision making for the treatment of patellofemoral instability.

PURPOSE: Trochlear dysplasia is an important aetiological factor for the development of patellofemoral instability (PFI). The aim of the study was to identify the arthroscopic morphology of trochlear dysplasia that can be helpful when planning operative treatment for PFI. METHODS: Magnetic resonance imaging (MRI) scans and strict lateral radiographs of 46 patients treated for PFI were assigned according to Dejour and matched with arthroscopic views from the lateral superior arthroscopic portal. On arthroscopy, signs of trochlear dysplasia were identified and classified into two types. Intra- and inter-observer agreements of the arthroscopic evaluation were assessed. RESULTS: Arthroscopically, 2 major types of trochlear dysplasia could be distinguished. Type I shows a flat trochlear groove with an elevated trochlear floor in relation to the anterior femoral cortex. In type II, the proximal trochlea was convex with a lateral trochlear bump. Arthroscopic evaluation was not consistent with the Dejour's radiographic and axial MRI classification. Arthroscopic grading showed excellent intra- and inter-observer agreements (81-92%). CONCLUSION: Arthroscopic evaluation can give additional information about the severity of trochlear dysplasia. This additional information can be used as an aid in decision making for the treatment of PFI. LEVEL OF EVIDENCE: II.

Evaluation of trochlear dysplasia using MRI: correlation between the classification system of Dejour and objective parameters of trochlear dysplasia.

PURPOSE: Trochlear dysplasia is considered to be one of the major factors causing patellofemoral instability (PFI). Dejour's classification is widely used to assess the severity of trochlear dysplasia. Additionally, in current literature, different quantitative parameters are recommended to distinguish between a normal trochlea and a dysplastic trochlea. In order to achieve a more objective evaluation of the trochlea, the aim of this study was to evaluate whether specific measurements of the femoral trochlea can be assigned to the qualitative classification system of Dejour. METHODS: Transverse MRI T2-weighted scans of 80 knees with symptomatic PFI and varying severity of trochlear dysplasia were classified according to Dejour (type A to D). For all MRI scans, quantitative measurements with parameters as described in the literature were applied. The values were then allocated to Dejour's classification. In addition to the four-grade analysis, two-grade analysis was also performed (Dejour type A against type BCD). Dependent on the cut-off values, specificity, sensitivity and Youden index for each parameter was defined. RESULTS: The allocation resulted in the following distribution: type A trochlear dysplasia n = 25, type B n = 23, type C n = 18 and type D n = 14. In descriptive statistics, none of the measurements proposed in the literature could be assigned to the four-grade classification system of Dejour. For the two-grade analysis at the cut-off, sensitivity ranged from 75 to 86 % and specificity from 76 to 84 % for lateral trochlear inclination, trochlear facet asymmetry and depth of trochlear groove. All other measurements showed a poor sensitivity ranging from 49 to 67 % and specificity from 40 to 72 %. Interobserver and intraobserver repeatability for the measured parameters was fair to moderate (ICC values 0.34-0.58) in high-grade dysplasia (type BCD) and substantial to almost perfect (ICC values 0.71-0.88) in low-grade trochlear dysplasia (type A). CONCLUSION: Quantitative measurements of the femoral trochlea have shown to be of limited value for the assessment of trochlear dysplasia. None of the quantitative measurements of the trochlea on transverse images could be assigned to the four-grade descriptive classification of trochlear dysplasia of Dejour. Additionally, measurements could not be reliably performed in high-grade trochlear dysplasia. However, trochlear inclination, trochlear facet asymmetry and depth of trochlear groove may help to distinguish between low-grade and high-grade dysplasia.

The effects of femoral external derotational osteotomy on frontal plane alignment.

PURPOSE: Femoral osteotomies are the preferred treatment in significant torsional deformity of the femur. The influence of torsional osteotomies on frontal plane alignment is poorly understood. Therefore, the aim of the present study was to evaluate the effects of external derotational osteotomies on proximal, mid-shaft and distal levels onto frontal plane alignment. METHODS: The effect of rotation around the anatomical axis of the femur on frontal plane alignment was determined with a 3D computer model, created from CT data of a right human cadaver femur. Virtual torsional osteotomies of 10°, 20° and 30° were performed at proximal, mid-shaft and distal levels under five antecurvatum angles of the femur. The change of the frontal plane alignment was expressed by the mechanical lateral femoral angle. RESULTS: Proximal derotational osteotomies resulted in an increased mechanical lateral distal femoral angle (mLDFA) of 0.8°-2.6° for 10°, of 1.6°-5.1° for 20° and of 2.3-7.9° for 30° derotational osteotomy, indicating an increased varus angulation. Supracondylar derotational osteotomy resulted in a decreased mLDFA of -0.1° to -1.7° for 10°, of -0.2 to -3.7° for 20° and of -0.7 to -6.9° for 30° derotational osteotomy, indicating an increased valgus angulation. The effect increased with the amount of torsional correction and virtually increased antecurvatum angles. Mid-shaft torsional osteotomies had the smallest effect on frontal plane alignment. CONCLUSION: This three-dimensional computer model study demonstrates the relationship between femoral torsional osteotomies and frontal plane alignment. Proximal external derotational osteotomies tend to result in an increased varus angulation, whilst distal external derotational osteotomies tend to result in an increased valgus angulation. As a clinical consequence, torsional osteotomies have an increased risk of unintentional implications on frontal plane alignment.

Anatomical reconstruction of the medial patellofemoral ligament in children with open growth-plates.

Recurrent lateral patellar dislocation is a common knee injury in the skeletally immature adolescent. In adults, anatomical reconstruction of the medial patellofemoral ligament (MPFL) is recommended, but due to the open physis, operative therapy in children is more challenging. We present a minimal invasive technique for anatomical reconstruction of the MPFL in children respecting the distal femoral physis. This technical note considers the important fact that the femoral insertion is distal to the femoral physis. Since the importance of an anatomical reconstruction respecting the femoral insertion of the ligament has been proven an insertion proximal of the physis has to be strictly avoided.

The relation of the distal femoral physis and the medial patellofemoral ligament.

PURPOSE: The purpose of this study was to analyse true lateral radiographs of children and adolescents to determine the relation of the origin of the MPFL and the distal femoral physis considering the complex anatomy of the physis. The hypothesis was that the femoral insertion of the MPFL is distal to the growth plate. METHODS: Antero-posterior and true lateral radiographs from PACS computer records of 27 patients with a history of patellofemoral instability were assessed. To determine the femoral origin of the MPFL, the method by Schöttle et al. and the method by Redfern et al. were applied independently. On the anteroposterior radiograph, the distance between the medial most part of the physis and the central part of the physis was measured to quantify the concave curvature of the physis. To cross-reference the femoral insertion of the MPFL onto an ap view, the projected MPFL origin-physis distance was subtracted from the distance between the most medial part of the physis and the central part of the physis. RESULTS: The projected median origin of the MPFL as measured on a lateral radiograph was located 3.2 mm (1.2-5.8 mm) proximal to the physis. The median distance between the most medial part of the physis and the physeal line on the anteroposterior radiograph was 9.9 mm (4.1-12.0 mm). Subtracting the two measured values, the median origin of the MPFL as seen on the ap view was 6.4 mm (2.9-8.5 mm) distal to the femoral physis. CONCLUSION: Considering the concave curvature of the distal femoral physis, it can be assumed that the femoral insertion of the MPFL is distal to the femoral physis. As a too proximal insertion of the graft can cause unintentional tightening of the MPFL in knee flexion, these results have to be considered when performing reconstruction of the MPFL in children and adolescents with open growth plates.

[Patellar fracture after patellar stabilization]. / Patellafraktur nach MPFL-Rekonstruktion bei femoropatellarer Instabilität.

We report on a 20-year-old female patient with a fracture of the patella after she fell on"black ice" 2 months after medial patellofemoral ligament (MPFL) reconstruction for patellar instability. For reconstruction of the MPFL, a single hamstring tendon graft was passed through the medial intermuscular septum and was fixed to the superomedial pole of the patella. The fracture was reduced by wire cerclage. Intraoperatively it was shown that the fracture line went through the patellar drill hole. No complications occurred during the further postoperative period. The literature contains only a few case reports describing fractures of the patella after MPFL reconstruction without any specific trauma. In this case, an interruption in blood supply with resulting avascular necrosis was suspected as a causal factor.

Correction of malformative patellar instability in patients with nail-patella syndrome: a case report and review of the literature.

Nail-patella syndrome (NPS) or hereditary onycho-osteodysplasia is a relatively rare autosomal dominant disorder with the classic tetrad of fingernail abnormalities, hypoplastic patellae, radial head dislocation and iliac horns. The anatomic abnormalities in NPS often lead to subluxation or dislocation of the patellaeca causing knee instability and pain. Although most existing literature regarding the knee manifestation of this syndrome has focused on the clinically and radiological changes, only a few articles discussed the surgical treatment. This study reports the clinical, radiological and arthroscopical findings and a 24-month follow-up after operative stabilisation considering the underlying pathomorphology of malformative patellar instability in an 11-year-old girl. The findings of this study confirm the unique pathology of NPS with a synovial band preventing the engagement of the patella into the trochlear groove. NPS is a rare disorder and has to be considered in cases with untypical patella dislocation. The underlying pathology differs completely from patients with patellofemoral instability. The aim of orthopaedic surgery should be correction of the underlying pathology with resection of the synovial band and an additional realignment of the patella by recentering of the quadriceps muscle. Considering the underlying pathology good clinical results can be expected.