Patellar height abnormalities: Patella Alta - Patella Infera. Diagnosis and treatment

To diagnose patella alta or patella infera, it is necessary to know the normal patellar height. Many techniques have been described in literature to measure patellar height but the most common and easiest is the method according to the Caton-Deschamps index. Since 1977 we have been using our assessment index (J. Caton) modified in 1982 (J. Caton -G. Deschamps). The measurement of patellar height is made on the X-ray sagittal view taken between 10 and 80 degrees of flexion. Material and method. The patella is high (patella alta) when the Caton-Deschamps index is superior or equal to 1.2 (normal index is 1) and the patella is low (patella infera) when the index is inferior or equal to 0.6. Patella alta is rarely an isolated finding and is most often part of a regional patello fermoral dysplasia with functional problems and knee instability. Patella infera is frequently a complication of a lesion of the knee. In the majority of cases patella infera is secondary to iatrogenic mechanical lowering of the patellar tendon. It can also occur as a consequence of a reflex inflammatory sympathetic dystrophy syndrome with a distinctive pathology dominated by pain and knee stiffness mainly in the inflammatory form. Treatment. In patella alta the lowering of the patellar with a normal index is necessary to obtain a good outcome but when associated with a patello-femoral dysplasia, the surgical treatment must absolutely take into account other abnormalities to obtain a satisfactory result: medial translation of the tibial tuberosity, groove osteotomy. In patella infera the preoperative planning requires assessment of the patellar vertical height but also of the patellar tendon length on MRI (normal length 4.5 cm). Surgery is useful when the patellar tendon appears satisfactory longer than 2.5 cm. The tibial tubercle is detached and raised according to the distance necessary as described by J. Caton in 1982. When the patellar tendon is retracted <= 2.5 cm it is often necessary to perform a patellar tendon lengthening as proposed by H. and D. Dejour in 1995. Results. 77% patella alta patients had a perfect postoperative stability with a very good outcome. The patella infera syndrome of tubercle origin gave 83% excellent and good results with the proximal transfer of the tubercle. Patella infera syndrome of quadricipital origin gave 75% good and very good results; in these cases the treatment is very difficult.