International
International Orthopaedics (SICOT) (1988) 12:223-227
Orthopaedics © Springer-Verlag 1988
CT-scan in the diagnosis of patellar malalignment J. J. Fernandez de Rota, L. Sanado, L. Laidler, E. Guerado, and A. Queipo de Llano Servicio de Cirugia Ortopedica y Traumatologia, Hospital Civil Provincial de Malaga, E-29009 Malaga (Spain)
Summary. Fifty-one knees with patellofemoral symptoms, but with normal conventional radiographs, were studied by CT-scan. All but five showed evidence of malalignment, and when operated on had an abnormality of the articular cartilage. The authors conclude that in many cases a CT-scan is the best diagnostic procedure for the evaluation of disorders of the patellofemoral joint. Cinquante et un genoux prbsentant une symptomatologie fbmoro-patellaire, mais dont les radiographies standard ktaient normales, ont bknkficib d'un examen par tomodensitombtrie. Tous, saul cinq, montraient une d~saxation ~vidente et prbsentaient, lors de l'intervention, des alt&ations cartilagineuses. Les auteurs concluent que dans de nombreux cas la tomodensitomktrie est le meilleur moyen de diagnostic en cas d'atteinte de l'articulation f~moro-pa tellaire. R6snmb.
Key words: Patella, Patellofemoral syndrome, Computerized tomography
L a t e r a l d i s p l a c e m e n t o f t h e p a t e l l a is a v e r y c o m mon problem. Clinically, there may be either an acute lateral dislocation of the patella, or pain in the knee suggesting the patellofemoral syndrome. Although the diagnosis can usually be made by clinical examination and skyline radiographs, patellar malalignment may not always be detecte d b y t h e s e m e a n s . W e h a v e i n v e s t i g a t e d t h e resuits of a CT-scan examination in these patients and correlated them with the operative findings.
Offprint requests to: A. Queipo de Llano Gimenez
Material and method Fifty-one knees in 49 patients with symptoms of patellar malalignment, but with normal radiographs, were studied by CTscan. The mean age of the patients was 21 years (range 11-52 years) and they were classified into four groups: 1) One episode of patellar dislocation. 2) Recurrent patellar dislocation with a subjective sensation of instability and clinical evidence of lateral displacement. 3) Recurrent patellar subluxation with a subjective sensation of instability but no apparent patellar displacement. 4) Patellofemoral pain without the subjective sensation of instability. Radiographs were taken of both knees. These included anteroposterior and lateral views in 45 ° of flexion and skyline views taken at 30 ° , 60 ° and 90 ° of flexion (4). Special attention was paid to the lateral patellofemoral angle (PFA) formed by the transverse axis of the femoral condyles and the lateral facet of the patella. Lateral widening of this angle is considered to be normal. The most significant results were obtained when the knee was flexed to 30 ° [13, 14]. A CT-scan was carried out with the patient lying face down and the knees flexed to 150 [15, 16, 18, 20]. An EMI 5005 device was used with the gantry situated perpendicularly to the proximal, medial and distal thirds of the patella. Examination was carried out with and without isometric contraction of the quadriceps muscle. Laurin's angle [14] was also measured, usually, at the medial third of the patella. The CT findings were classified [19] as follows; 1) Normal patella. 2) Patella tilted laterally without malalignment.
Fig. 1. Patellogemoral angle (PFA)
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J.J. Fernandez de Rota et al.: CT scan in the diagnosis of patellar malaligment
Fig. 2a, b. AG, A 19 year-old patient with bilateral patellar instability, a Skyline views: Normal alignement of the right patella and subluxation of the left side, seen in the 30° flexion projection; b CT-Scan: Severe bilateral subluxation Fig. 3a, b. A 23 year-old patient presenting with pain in both knees when climbing stairs. Occasional episodes of giving way. a Skyline views: Normal bilateral alignment; b Left column: Without contraction of the quadriceps muscle. Right column: With contraction of the quadriceps muscle 3) Patella tilted laterally with malalignment. 4) Complete lateral dislocation. All the cases with an abnormal CT-scan underwent operation. The findings were classified as; l) Normal cartilage. 2) "Closed" chondromalacia. 3) "Open" chondromalacia.
4) Complete cartilage destruction. 5) Other findings.
Results I n all cases t h e s y m p t o m s s u g g e s t e d a p a t e l l a r m a l a l i g n m e n t a n d t h e d e t a i l s are s h o w n i n T a b l e 1.
J. J. Fernandez de Rota et al.: CT scan in the diagnosis of patellar malaligment
225
Fig. 4 a - c . A 16 year-old patient with episodes of giving way. a Skyline views: Normal bilateral alignment; b CT-Scan: Bilateral subluxation; e CT-Scan (contraction of the quadriceps muscle): the subluxation increases
Three cases of patellar dislocation occurred, one when playing soccer, another during a high jump and the third after a fall. Lateral radiographs showed 29 cases of patella alta, with the Insall-Salvati index [9, 10] greater than 1.25; in 17 normal knees the index was between 1 and 1.25. In all the cases the skyline view was normal. In four knees the value of the lateral patellofemoral angle was 0 °, which is on the borderline of normal; two had recurrent dislocation and the others a recurrent subluxation of the patella. The CT-scan was abnormal in 46 cases and this varied from a simple lateral tilting of the patella to a complete lateral dislocation (Table 2). There was correlation between the severity of the symptoms and the CT-scan findings. Of the five knees with a normal CT-scan two had a tear of
Table 1. Clinical symptoms
No. of cases I. 2. 3. 4.
One episode of patellar dislocation Recurrent dislocation of the patella Recurrent subluxation of the patella Patellofemoral syndrome
3 16 15 17
Table 2. CT-scan findings
No. of cases 1. Normal patella 2. Lateral tilting without malalignment 3. Lateral tilting with malalignment 4. Lateral subluxation 5. Lateral dislocation
5 0 14 19 13
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J.J. Fernandez de Rota et al.: CT scan in the diagnosis of patellar malaligment
Table 3. Correlation between clinical symptoms and CT-scan findings Normal
Lateral tilting without malalignment
Lateral tilting with malalignment
Lateral subluxation
Lateral dislocation
One episode of patellar dislocation
0
0
1
2
0
Recurrent dislocation of the patella
0
0
1
6
9
Recurrent subluxation
0
0
3
8
4
Patellofemoral syndrome
5
0
9
3
0
Table 4. Surgical findings in knees with abnormal CT-scans
No. of cases 1. Normal patella 2. "Closed" chondromalacia 3. "Open" chondromalacia 4. Complete cartilage destruction 5. Other findings (osteochondral fractures)
0 19 22 4 1
the lateral meniscus, one a cyst of the lateral meniscus and no diagnosis could be made in the other two (Table 3). There were changes in the articular cartilage of all the knees which were operated on. The severity was related to the CT-scan findings (Table 4). More severe symptoms also corresponded to more severe changes in the articular cartilage (Table 5). Discussion
Hughston stressed the importance of the clinical history and examination in the diagnosis of patellar malalignment [7, 8]. Ficat claimed that the skyline view was a very reliable diagnostic method [4]. Hughston [7, 8], Merchant [17], Laurin [13, 14], Fukabayashi [5] and Aglietti [1, 2] demonstrated cases in which the diagnosis could be made using this radiographic projection. Laurin proposed the lateral patellofemoral angle (PFA) for the diagno-
sis of patellar malalignment. Ninety-seven per cent of the knees studied by him had a lateral widening of that angle, and only 3% had a 0 ° angle. All of the knees with a patellofemoral angle less than 0 ° were considered to be abnormal. Many of our patients with symptoms of malalignment had normal radiographs and these knees were chosen for a CT-scan examination. Insall et al. [9, 10] and Bandi [3] believe that patella alta is an underlying factor in subluxation or dislocation. Seventeen out of the 51 of our cases (36.9%) had a patella alta. Four (8.7%) were classified as within the normal range according to Laurin's criteria, but they all had either calcification in the medial patellar retinacula, an indirect sign of malalignment, or a PFA value of nearly 0 °. Goodfellow's biomechanical experiments showed that the most susceptible position for patellar displacement is at the beginning of knee flexion [6]. At this point the patella starts to adjust itself into the femoral groove. Judet [12], Passariello [18], Martinez [15, 16] and Sasaki [19], recommended the CT-scan as a very reliable diagnostic procedure. Passariello [18] recommended 10° of knee flexion as the best position to study the whole knee joint. Martinez performed the CT-scan in full extension, 20 ° and 45 ° of knee flexion. He agreed with Goodfellow's and Sasaki's conclusions and found better results be-
Table 5. Correlation between clinical symptoms and surgical findings Normal
Closed chondromalacia
One episode of patellar dislocation
0
2
Recurrent dislocation of the patella Recurrent subluxation
0
Patellofemoral syndrome
Open chondromalacia
Complete cartilage destruction
Other findings
0
0
1
6
7
3
0
0
4
10
1
0
0
7
5
0
0
J. J. Fernandez de Rota et al.: CT scan in the diagnosis of patellar malaligment
tween full extension and 30 ° of flexion. Schutzer showed that this is the best range of motion to study both patellar malalignment and the tilting element [20]. In our series the CT-scan was performed with the knees flexed to 15 ° as this was the position where patellar malalignment and tilting was maximal. Beyond 30 ° of flexion the patella becomes normally aligned. Sasaki studied the patellofemoral joint when the quadriceps muscle was contracted and found that bot the lateral displacement and the tilting component increased up to 27.7% and 8.8 degrees respectively. We agree with these findings. A correlation could be made between clinical symptoms and the CT-scan findings. Fifty-six per cent of those patients with symptoms suggesting recurrent dislocation had a complete dislocation, 37.5% a subluxation with tilting and the remaining 6.5% simple malalignment with tilting. Of the patients with symptoms of subluxation, 27% showed a dislocation, 53% a subluxation and 20% malalignment with tilting. All the patients with a CT-scan showing malalignment had articular cartilage lesions at operation. More severe lesions were found in those patients with the more marked signs of malalignment. Clinical examination and conventional radiological studies may enable a diagnosis to be made in many cases, but when there is doubt a CT-scan should be undertaken. References 1. Aglietti P, Cerulli G (1979) Chondromalacia and recurrent subluxation of the patella. A study of malaligment, with some indications for radiography. Ital J Orthop Traumatol 5:187-201 2. Aglietti P, Insall JN, Cerulli G (1983) Patellar pain and incongruence. I: Measurements of incongruence. Clin Orthop 176:217-224 3. Bandi W (1982) Die retropatellaren Kniegelenk-Schgden. Aktuelle Probleme in Chirurgie und Orthopgdie 4. Huber, Bern
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4. Ficat RP, Hungerford DS (1977) Disorders of the patello femoral joint. Masson, Paris 5. Fukabayashi T, Kurosawa H, Doki T (1977) Recurrent subluxation of the patella. Knee 3:37-45 6. Goodfellow JW, Hungerford DS, Woods C (1976) Patellofemoral joint mechanics and pathology. 2: chondromalacia Patellae. J Bone Joint Surg [Br] 58:291-299 7. Hughston JC (1962) Recurrent subluxation and dislocation of the patella. Thesis AOA 8. Hughston JC (1968) Subluxation of the patella. J Bone and Joint Surg [Am] 50: 1003-1026 9. Insall JN, Aglietti P, Trias AJ Jr (1983) Patellar pain and incongruence. II: Clinical Application. Clin Orthop 176: 225-232 10. Insall J, Salvati E (1977) Patella position.in the normal knee. Joint Radiology 101:101 11. Jensen CM, Roosen JU (1985) Acute traumatic dislocations of the patella. J Trauma 25:160-162 12. Judet J, Judet H, Massare CI (1979) Use of scanner for exploration of patella displacements. Chirurgie 105 : 535-539 13. Laurin CA, Dussault R, Levesque HP (1979) The tangential X-ray investigation of the patellofemoral joint; X-ray technique, diagnostic criteria and their interpretation. Clin Orthop 144:16-26 14. Laurin CA, Levesque HP, Dussault R, Labelle H, Peides JP (1979) The abnormal lateral patello-femoral angle; A diagnostic roentgenographic sign of recurrent subluxation. J Bone Joint Surg [Am] 60:55-60 15. Martinez S, Korobkin M, Fondren FB, Hedlung LW, Goldner JL (1983) Diagnosis of patellofemoral malaligment by computed tomography. J Comput Assist Tomogr 7:1050-1053 16. Martinez S, Korobkin M, Fondren FB, Goldner JL (1983) Computed tomography of the normal patellofemoral joint. J Comput Assist Tomogr 7: 1050-1053 17. Merchant AC, Mercer RL, Jacobsen RH (1975) Cool CR Roentgenographic analysis of patellofemoral congruence. J Bone Joint Surg 56 [Am]: 1391-1396 18. Passariello R, Trecco F, De Paulis F, De Amicis R, Bonanni G, Masciochi C (1983) Computed tomography of the knee joint: Clinical results. J Comput Assist Tomogr 7: 1043-1049 19. Sasaki T, Yagi T (1986) Subluxation of the patella, investigation by computarized tomography. Int Orthop 10: 115-120 20. Schutzer SF, Ramsby GR, Fulkerson JP (1986) The evaluation of patellofemoral pain using computerized tomography. Clin Orthop 204:286-293
