Trochlear dysplasia is an important anatomical abnormality in symptomatic patellar instability. Our study assessed the mismatch between the bone and cartilaginous morphology in patients with a dysplastic trochlea compared with a control group.

MRI scans of 25 knees in 23 patients with trochlear dysplasia and in 11 patients in a randomly selected control group were reviewed retrospectively, in order to assess the morphology of the cartilaginous and bony trochlea. Inter- and intra-observer error was assessed.

In the dysplastic group there were 15 women and 8 men with a mean age of 20.4 years (14 to 30). The mean bony sulcus angle was 167.9⁰ (141⁰ to 203⁰), whereas the mean cartilaginous sulcus angle was 186.5⁰ (152⁰ to 214⁰; p < 0.001). In 74 of 75 axial images (98.7%) the cartilaginous contour was different from the osseous contour on subjective assessment; the cartilage exacerbated the abnormality.

Our study shows that the morphology of the cartilaginous trochlea differs markedly from that of the underlying bony trochlea in patients with trochlear dysplasia. MRI is necessary in order to demonstrate the pathology and to facilitate surgical planning.

Introduction: Trochlear dysplasia is an important anatomical factor in symptomatic patellar instability. The impression at surgery is that the dysplasia is predominantly an abnormality of the proximal trochlea. There is a mismatch between the bony and cartilaginous trochlear anatomy in normal knees. This study assessed the mismatch in dysplastic trochleas.

Methods: The MRI scans of 25 knees in 23 patients with patellar instability and trochlear dysplasia were reviewed retrospectively. Axial fat saturation images where used to assess cartilaginous and bony trochlear morphology. The following parameters were measured in the three most proximal images of each trochlea:

Cartilaginous and bony sulcus angles.

Inter and intra observer error was recorded.

Results: There were 15 females and 8 males with an average age of 20.4 years (14 30).

The average bony sulcus angle (SA) was 166.9 degrees (141 – 203) whereas the average cartilaginous SA was 184.8 degrees (152 – 222). In 74 of 75 axial images (98.6%) the cartilaginous SA was greater than the bony SA by an average of 17.6 degrees (3 45).

Conclusion: This study demonstrates that the cartilaginous trochlear morphology differs markedly from that of the underlying bony trochlea in patients with trochlear dysplasia. Although the bony trochlea was dysplastic, the cartilage morphology worsened this abnormal shape. Since cartilage is poorly represented on routine radiography and computed tomography, MRI is necessary to demonstrate both the bony and cartilaginous morphology to facilitate surgical planning.

The results of 34 knees with stage IV to VI Blount’s disease were reviewed. 24 patients were treated over the seven-year period from 1994 to 2000.

The surgical technique addressed the medial joint line depression with an elevating osteotomy maintained with a tricortical wedge from the iliac crest. The tibial varus and intorsion was corrected with an osteotomy proximal to the apophysis. In the more recent patients a proximal lateral tibial and fibular epiphyseodesis was done concomitantly. The average preoperative mechanical varus angle of 30.6°(range 14° to 60°) was corrected to 0–4° mechanical valgus in 29 knees. In five knees an undercorrection of 2–4° mechanical varus occurred. At follow-up a further 8 knees developed residual varus due to a delayed epiphyseodesis. The tibial varus angle (ie. angle subtended by the mechanical axis of the tibia with the lateral tibial joint line) increased at an average of 1°/ month due to the inevitable medial growth plate fusion.

The average pre operative joint depression angle of 49° (range 40° to 60°) was corrected to an average of 26°(mean 20°–30°). There was no significant preoperative frontal plane f emoral deformity to warrant a femoral correction. At long term follow up of 3.5 years (range 2 to 5 years) all knees had a full range of movement without any varus instability. However in eight cases a delay of more than six months occurred before a lateral epiphysiodesis was performed, and in these patient’s mechanical axis varus recurred although the joint line correction was maintained. Neutral or valgus mechanical axis was maintained in all patients who underwent an epiphysiodesis within six months.

We concluded that although the joint elevation correction was maintained in our series, mechanical axis varus recurs if lateral epiphysiodesis is not performed early.

We reviewed the results in 24 children (34 knees) following double-elevating osteotomy for late presenting infantile Blount’s disease.

The mean age of our seven male and 17 female patients was 9.1 years (7 to 13.5). Obesity was noted in 15 (above the 95th percentile). Previous valgus osteotomy had been performed on nine knees.

Ten knees were Langenskîld stages IV, six stage V and 18 stage VI. The surgical technique addressed the medial joint line depression with an elevating osteotomy, which was maintained by insertion of a tricortical wedge from the iliac crest and the excised fibula. The tibial varus and internal torsion was corrected with an osteotomy proximal to the apophysis. In the more recent patients, a proximal lateral tibial and fibular epiphysiodesis was done concomitantly.

The mean preoperative mechanical varus of 30.6( (14( to 60() was corrected to 0( to 4( mechanical valgus in 29 knees. In five knees there was under-correction to 2( to 4( mechanical varus. At follow-up a further eight knees developed varus owing to late epiphysiodesis. The tibial varus angle (the angle subtended by the mechanical axis of the tibia and a line along the lateral tibial joint line) increased at a mean of 1( a month due to inevitable medial growth plate fusion.

The mean preoperative joint depression angle of 49( (40( to 60() was corrected to 26( (20( to 30(), which was maintained at follow-up. There was no noteworthy femoral valgus or varus present preoperatively to warrant femoral osteotomy.