Photography was used to study the geometry of the cartilaginous and osseous contours of the distal femur and the orientation of the trochlear groove in 9 fresh-frozen and 24 embalmed knees. The sulcus angle (146.1°±5.5°) decreased from 0° to 50° of femoral flexion then increased afterwards. The maximum slope of the lateral femoral condyle (20.2°±5.2°) also decreased with flexion. Both the sulcus angle (p =0.0007) and maximum slope (p =0.0001) were larger at 0° than they were for 60° cartilaginous surfaces. The lateral femoral condylar height decreased, whilst the medial femoral condylar height increased as the flexion increased. The femoral groove was midway between the two femoral epicondyles (49.5±3.9%), but deviated laterally as the flexion angle increased. The groove axis deviated distally and laterally from the femoral anatomical axis for both cartilaginous and bony surfaces, and the angle between the groove and anatomical axes was similar for both cartilaginous (19.1°) and osseous (16.8°) surfaces. Articular cartilage is not well represented on radiography yet it had a significant effect on the distal femoral geometry, and should be taken into account when evaluating the patellofemoral joint.

The cartilaginous and osseous geometry of the femoral trochlear groove

In 40 patients with patellofemoral pain, intra-osseous pressure measurements were recorded under anaesthesia with the knee first in extension and then in flexion prior to performing a longitudinal osteotomy of the patella. There was a statistically significant increase of pressure in painful knees compared with normal knees (29 mm Hg. vs 15 mm Hg.), and a marked increase when compared during sustained flexion (97 mm Hg. vs 60 mm Hg.). However wide variability of individual results made the diagnostic value of a single pressure measurement unreliable. A clinical test, based on reproduction of the characteristic pain by sustained knee flexion, proved to be reliable in predicting a good response to operation. The effect of the operation was encouraging, with significant relief of pain as measured by a visual analogue scale.

Osteotomy of the patella in the patellofemoral pain syndrome. The significance of increased intraosseous pressure during sustained knee flexion.

Eighty patients who complained of retropatellar pain underwent evaluation by bone scintigraphy, intraosseous pressure determination, radiography, arthroscopy and physical diagnostic tests. The bone scans showed that 48% of the painful knees had an increased uptake compared with 9% for the normal joints. A highly significant correlation was evident between an increased uptake and established chondromalacia. For the diagnosis of a high pressure patella, radiography was only 7% sensitive (6/88), compared with 44% (39/88) for bone scintigraphy and 78% for the clinical "sustained flexion" test. The positive predictive value of a bone scan for detecting a high pressure patella was 0.72 (39/54). The best predictor was a positive sustained flexion test with a predictive value of 0.85 (69/81).

Bone scan in the patellofemoral pain syndrome

In 150 normal subjects the distance (P) between the upper and lower limits of the articular surface of the patella, and the shortest distance (T) between this same lower limit and the tibial plateau, were measured in standard lateral views of the knee in about 30° of flexion The limits of confidence of the T/P ratio are shown in the Table The 5% upper limit of normality of this ratio is 111 (one-sided) This method of determining the position of the patella is accurate and more simple than those previously described

A method for assessing the height of the patella.

The Insall-Salvati ratio (ISR) is important for detecting two common clinical signs of knee disease: patella alta and patella baja. Furthermore, large inter-operator differences in ISR measurement make an objective measurement system necessary for better clinical evaluation. In this paper, we define three specific bony landmarks for determining the ISR and then propose an x-ray image analysis system to localize these landmarks and measure the ISR. Due to inherent artifacts in x-ray images, such as unevenly distributed intensities, which make landmark localization difficult, we hence propose a registration-assisted active-shape model (RAASM) to localize these landmarks. We first construct a statistical model from a set of training images based on x-ray image intensity and patella shape. Since a knee x-ray image contains specific anatomical structures, we then design an algorithm, based on edge tracing, for patella feature extraction in order to automatically align the model to the patella image. We can estimate the landmark locations as well as the ISR after registration-assisted model fitting. Our proposed method successfully overcomes drawbacks caused by x-ray image artifacts. Experimental results show great agreement between the ISRs measured by the proposed method and by orthopedic clinicians.

https://iopscience.iop.org/article/10.1088/0031-9155/55/22/012/pdf

Automatic Insall–Salvati ratio measurement on lateral knee x-ray images using model-guided landmark localization

X-rays of 71 patients operated on for chondromalacia patellae were examined in order to obtain a comprehensive picture of the radiographic changes in this disease. Ninety-seven patients with a normal patellofemoral joint - found at operation - were used as a control group. We found a significantly higher frequency of patella alta and the presence of Haglund's excavation in patients with chondromalacia but had to conclude that ordinary X-rays cannot be used to confirm the diagnosis chondromalacia patellae.

https://www.tandfonline.com/doi/pdf/10.3109/17453678208992190

Claus Perrild

Papers

Chondromalacia Patellae: A Radiographic Study of the Femoropatellar Joint