CASE 42 patellar fractures

A 48-year-old woman presents to the emergency department complaining of acute left knee pain and inability to bear weight after falling on a flexed knee. She is unable to perform a straight leg raise. Figure 6–45A and B shows a lateral and AP radiographs of her left knee.

 

 

 

Figure 6–45 A–B

 

All of the following suggest disruption of the extensor mechanism EXCEPT:

1. With the knee flexed 90 degrees, the superior pole of the patella lies superior to the anterior surface of the femur

2. With the knee flexed 30 degrees, the inferior pole of the patella is aligned with the level of Blumensaat’s line

3. An Insall–Salvati ratio of greater than 1.0

4. An Insall–Salvati ratio of less than 1.0

 

Discussion

The correct answer is (B). With the knee flexed 30 degrees, the inferior pole of the patella normally is aligned to the level of Blumensaat’s line. Thus answer B describes a normal anatomic relationship. With the knee flexed 90 degrees, the superior pole of the patella should normally lie inferior to the anterior surface of the femur. The Insall–Salvati ratio compares the height of the patella to the length of the patellar tendon. A ratio of less than 1.0 suggests patella alta and disruption of the patellar tendon, while a ratio of greater than 1.0 suggests patella baja and disruption of the quadriceps tendon.

Which of the following is NOT an indication for operative treatment of patellar fractures?

1. Stellate fracture pattern with 1 mm of intra-articular incongruity

2. Transverse fracture pattern with 3 mm of displacement

3. Osteochondral fracture associated with an intra-articular loose body

4. Compromised extensor mechanism function

 

Discussion

The correct answer is (A). Choices B, C and D all accurately describe relative indications for operative treatment of patellar fractures. A stellate fracture pattern with a relatively small amount of intra-articular incongruity, however, may be treated nonoperatively, provided that the extensor mechanism remains intact.

Regarding partial patellectomy, all of the following are true EXCEPT:

1. Partial patellectomy is indicated in the setting of comminuted superior or inferior pole fractures measuring less than 50% of the patella’s height.

2. As the size of the resected inferior pole increases so too do the contact stresses increase across the patellofemoral joint.

3. Partial patellectomy has been demonstrated to offer superior clinical results compared to internal fixation for fracture patterns with extensive inferior pole comminution.

4. Repair of associated medial and lateral retinacular injuries may lead to altered patellofemoral mechanics and an increase in patellar subluxation.

Discussion

All are true except for answer “D.” Partial patellectomy is a reasonable treatment approach for fractures of either the superior or inferior pole measuring less than 50% of the patellar height, especially in the setting of significant comminution. As the size of the resected portion of the inferior pole increases so too do the contact stresses across the patellofemoral joint. Partial patellectomy has been shown to offer superior outcomes in the setting of extensive inferior pole comminution. Repair of the medial and lateral retinacular injuries is a critical aspect of addressing associated soft tissue injuries to ensure optimization of patellofemoral mechanics.

 

Objectives: Did you learn...?

 

Operative indications for fixation of patellar fractures?

 

The role of partial patellectomy in the setting of comminuted superior or inferior pole fracture patterns?

 

The importance of restoring extensor mechanism function?