Ensuring correct rotation of the femoral component is a challenging aspect of patellofemoral replacement surgery. Rotation equal to the epicondylar axis or marginally more external rotation is acceptable. Internal rotation is associated with poor outcomes. This paper comprises two studies evaluating the use of the medial malleolus as a landmark to guide rotation.

We used 100 lower-leg anteroposterior radiographs to evaluate the reliability of the medial malleolus as a landmark. Assessment was made of the angle between the tibial shaft and a line from the intramedullary rod entry site to the medial malleolus. The femoral cut was made in ten cadaver knees using the inferior tip of the medial malleolus as a landmark for rotation. Rotation of the cut relative to the anatomical epicondylar axis was assessed using CT. The study of radiographs found the position of the medial malleolus relative to the tibial axis is consistent. Using the inferior tip of the medial malleolus in the cadaver study produced a mean external rotation of 1.6° (0.1° to 3.7°) from the anatomical epicondylar axis. Using the inferior tip of the medial malleolus to guide the femoral cutting jig avoids internal rotation and introduces an acceptable amount of external rotation of the femoral component.

A number of measurements of patella height exist all of which use a position on the tibia as a reference. The Patellotrochlear Index has recently been proposed as a more accurate reflection of the functional height of the patella and described in normal knees.

We aimed to compare patellar height measurements in patients with patellofemoral dysplasia.

In a retrospective analysis of the MRI scans of 33 knees in 29 patients with patellofemoral dysplasia we assessed the inter- and intraobserver reliability of four patellar height measurements: the Patellotrochlear Index (PTI), Insall-Salvati (IS), Blackburne-Peel (BP) and Caton-Deschamps (CD) ratios. We also assessed the correlation between the different measurements in predicting patella alta. Three blinded observers on two separate occasions performed the measurements.

There were 21 females and 8 males with a mean age of 21.4 years (13–33). Statistical analysis revealed good inter-observer reliability for all measurements (0.78 for PTI, 0.78 for IS, 0.73 for BP and 0.77 for CD). Intra-observer reliability was also good (0.80, 0.83, 0.75, 0.78 respectively). When comparing the different measurements for patella alta there was a weak correlation between the PTI and the others. There was a strong correlation between the CD and BP ratios (0.96) and a moderate correlation between IS and CD and IS and BP ratios (0.594 and 0.539 respectively).

All measurements are reproducible. The PTI however suggests patella alta exists in different patients to that suggested by the established measures. We propose the PTI as a more clinically relevant measure.

A number of measurements of patellar height are in clinical use all of which reference from the tibia. The patellotrochlear index has been proposed recently as a more accurate reflection of the functional height of the patella and described in normal knees.

We compared patellar height measurements in patients with patellofemoral dysplasia.

In a retrospective analysis of the MRI scans of 33 knees in 29 patients with patellofemoral dysplasia we assessed the inter- and intraobserver reliability of four patellar height measurements: the recently described Patellotrochlear Index (PTI), Insall-Salvati (IS), Blackburne-Peel (BP) and Caton-Deschamps (CD) ratios. We also assessed the correlation between the different measurements in predicting patella alta. Three blinded observers on two separate occasions performed the measurements.

There were 21 females and 8 males with a mean age of 21.4 years (13–33).

Statistical analysis revealed good inter-observer reliability for all measurements (0.78 for PTI, 0.78 for IS, 0.73 for BP and 0.77 for CD). Intra-observer reliability was also good (0.80, 0.83, 0.75, 0.78 respectively). There was weak correlation between the PTI and the other ratios for patella alta. There was a strong correlation between the CD and BP ratios (0.96) and a moderate correlation between IS and CD and IS and BP ratios (0.594 and 0.539 respectively).

We propose the PTI as a more clinically relevant measure.

A number of measurements of patella height exist all of which use a position on the tibia as a reference. The Patellotrochlear Index has recently been proposed as a more accurate reflection of the functional height of the patella and described in normal knees.

Aim: A comparison of patellar height measurements in patients with patellofemoral dysplasia.

Method: A retrospective analysis of the MRI scans of 33 knees in 29 patients with patellofemoral dysplasia to assess the inter- and intraobserver reliability of four patellar height measurements: the Patellotrochlear Index (PTI), Insall-Salvati (IS), Blackburne-Peel (BP) and Caton-Deschamps (CD) ratios. We also assessed the correlation between the different measurements in predicting patella alta. Three blinded observers on two separate occasions performed the measurements.

Results: There were 21 females and 8 males with a mean age of 21.4 years (13–33).

Statistical analysis revealed good inter-observer reliability for all measurements (0.78 for PTI, 0.78 for IS, 0.73 for BP and 0.77 for CD). Intra-observer reliability was also good (0.80, 0.83, 0.75, 0.78 respectively). When comparing the different measurements for patella alta there was a weak correlation between the PTI and the others. There was a strong correlation between the CD and BP ratios (0.96) and a moderate correlation between IS and CD and IS and BP ratios (0.594 and 0.539 respectively).

Conclusion: All measurements are reproducible. The PTI however suggests patella alta exists in different patients to that suggested by the established measures. We propose the PTI as a more clinically relevant measure.

Introduction: Patello-femoral instability (PFI) and pain may be caused by anatomical abnormality. Many radiographic measurements have been used to describe the shape and position of the patella and femoral trochlea. Some are difficult to apply when dysplasia is present.

This paper describes a simple new MRI measurement of the axial patellar tendon angle (APTA), and compares this angle in patients with and without patello-femoral instability.

Method: Axial MRI images of the knee of 20 patients with PFI and 20 normal knees (isolated acute ACL rupture) were used for measurement. The angle between the patellar tendon and the posterior femoral condylar line was assessed at three levels from the proximal tendon to its insertion.

Results: In normal knees, the APTA is 11 degrees of lateral tilt at all levels from the proximal tendon to its distal insertion. In PFI knees, the APTA is 32 degrees at the proximal tendon, 27 degrees at the joint line and 22 degrees at the distal insertion. The difference is significant (p< 0.001) at all levels.

Discussion: Measurement of the APTA is reproducible and is easier than many other indices of patello-femoral anatomy. In PFI, the APTA is increased by 21 degrees at the proximal tendon and by 11 degrees at its distal insertion.

In PFI, the patella is commonly tilted laterally. This is matched by the orientation of the patellar tendon. The increased tilt of the tendon is only partially corrected at its distal insertion with an abnormal angle of tibial attachment. When performing distal realignment procedures, angular correction as well as displacement may be appropriate.

Introduction: Patello-femoral instability (PFI) and pain may be caused by anatomical abnormality. Many radiographic measurements have been used to describe the shape and position of the patella and femoral trochlea.

This paper describes a simple new MRI measurement of the axial patellar tendon angle (APTA), and compares this angle in patients with and without patello-femoral instability.

Method: Axial MRI images of the knee of 20 patients with PFI and 20 normal knees (isolated acute ACL rupture) were used for measurement. The angle between the patellar tendon and the posterior femoral condylar line was assessed at three levels from the proximal tendon to its insertion.

Results: In normal knees, the APTA is 11 degrees of lateral tilt at all levels from the proximal tendon to its distal insertion. In PFI knees, the APTA is 33 degrees at the proximal tendon, 28 degrees at the joint line and 22 degrees at the distal insertion. The difference is significant (p< 0.001) at all levels.

Discussion: Measurement of the APTA is reproducible and is easier than many other indices of patello-femoral anatomy. In PFI, the APTA is increased by 21 degrees at the proximal tendon and by 11 degrees at its distal insertion.

In PFI, the patella is commonly tilted laterally. This is matched by the orientation of the patellar tendon. The increased tilt of the tendon is only partially normalized at its distal insertion with an abnormal angle of tibial attachment. When performing distal realignment procedures, angular correction as well as displacement may be appropriate.

Patello-femoral instability (PFI) and pain may be caused by anatomical abnormality. Many radiographic measurements have been used to describe the shape and position of the patella and femoral trochlea.

This paper describes a simple new MRI measurement of the axial patellar tendon angle (APTA), and compares this angle in patients with and without patello-femoral instability.

Method: Axial MRI images of the knee of 20 patients with PFI and 20 normal knees (isolated acute ACL rupture) were used for measurement. The angle between the patellar tendon and the posterior femoral condylar line was assessed at three levels from the proximal tendon to its insertion.

Results: In normal knees, the APTA is 11 degrees of lateral tilt at all levels from the proximal tendon to its distal insertion. In PFI knees, the APTA is 33 degrees at the proximal tendon, 28 degrees at the joint line and 22 degrees at the distal insertion. The difference is significant (p< 0.001) at all levels.

Discussion: Measurement of the APTA is reproducible and is easier than many other indices of patello-femoral anatomy. In PFI, the APTA is increased by 21 degrees at the proximal tendon and by 11 degrees at its distal insertion.

In PFI, the patella is commonly tilted laterally. This is matched by the orientation of the patellar tendon. The increased tilt of the tendon is only partially normalized at its distal insertion with an abnormal angle of tibial attachment. When performing distal realignment procedures, angular correction as well as displacement may be appropriate.

During Anterior Cruciate Ligament reconstruction, using bone- patellar tendon- bone graft, debris can accumulate in the joint. We assessed incidence and potential for complications, described the radiographic appearance and defined the natural history of these intrarticular debris in 50 consecutive reconstructions. The records and radiographs of 50 consecutive cases were reviewed. A stripe of radio-opaque material, resembling a comma, termed the “comma” sign, was noted behind the lateral femoral condyle on the early postoperative radiographs of 40 of the 50 cases. There was no statistically significant difference in loss of knee motion at six, twelve, twenty- six and fifty- two weeks postoperatively (P> 0.50) between the patients presenting the radio-opacity and those without it. A second set of radiographs was taken in 12 patients between 3 and 18 months postoperatively, revealing that this radio- opaque material was visible in 1 case only. No correlation was found between presence of radio- opacities and duration of pain, effusion, analgesia requirement, discharge timing, time to driving and time to work. A protocol of postoperative early weight- bearing mobilisation had been followed in all cases which may have played a role in promoting the faster dissolution of the debris.

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.