Stress fractures often occur in physically active individuals as a result of repetitive strenuous muscle and tendon forces acting on bones that have not adapted to such forces1-3. To our knowledge, the literature contains no reports of displaced longitudinal stress fractures of the patella requiring open reduction and internal fixation. The quadriceps muscle and patellar tendon produce extensive forces that can result in a displaced transverse patellar stress fracture2-7. The less strong vertical patellar restraints, including the medial patellofemoral ligament8, produce most of the ligamentous patellar stability in the lateral direction near knee extension8. In cases of acute traumatic patellar dislocation, the osseous structure of the patella is compromised mostly in the lateral direction—e.g., by avulsion of the medial patellofemoral ligament insertion—causing a medial margin fracture of the patella9. We are not aware of any previous reports of repetitive stress causing a displaced longitudinal patellar stress fracture.
Here, we describe a case of a displaced longitudinal stress fracture of the patella in a female athlete. The patient was informed that data concerning the case would be submitted for publication, and she consented.
Stress fractures typically occur in athletes or physically active individuals who participate in strenuous repetitive physical activities without allowing adequate adaptation of the bone to the stress forces1,3,11. Patellar stress fractures appear to be quite rare, but our ability to make the diagnosis in daily practice may also be poor. In fact, in the present case, nonsurgical care with rest might have been adequate treatment had the line of low signal intensity not been missed on the original magnetic resonance images.
Transverse patellar stress fractures are well described in the literature, and displacement is considered to be an indication for open reduction and internal fixation2-5,7,12. Many different sports activities have been described as causes of a transverse patellar stress fracture4,6,11,13-15. In the present case, repetitive pivoting stress forces across the knee joint related to participation in floorball16 may have predisposed the patient to extensive lateralizing forces of the patella and subsequently to displacement of the vertical stress fracture. We could not determine a specific traumatic event that might have caused displacement of the stress fracture, and we concluded that the medial restraints, including the medial patellofemoral ligament, had remained intact. If the medial restraints of the patella had been loose, the patient would have had difficulties with patellar instability and the lateralizing forces would have produced a dislocated or subluxated patella. Because the medial restraints remained intact, the lateralizing forces created the longitudinal stress fracture.
To our knowledge, four cases of longitudinal patellar stress fractures have been reported in the English-language literature; three occurred in children, were nondisplaced, and were treated successfully with conservative means13. One fracture in an adult was treated by excision of the small fracture fragment4. Because the knee is a common site of overuse injuries such as patellar tendinitis, patellofemoral pain syndrome, patellar subluxation, and unspecified anterior knee pain, a longitudinal patellar stress fracture may be an underlying cause of prolonged anterior knee pain and could go undetected on radiographs if it is not displaced. Therefore, we recommend that patients with persistent anterior knee pain and palpable patellar tenderness undergo magnetic resonance imaging11 if radiographs and clinical examination do not provide evidence of a cause of the prolonged pain.
Treatment options for a longitudinal patellar stress fracture should first include nonsurgical management with rest, which will likely be successful for the majority of nondisplaced fractures13. Use of a patellar support or brace for a few weeks after the diagnosis should be considered to minimize the risk of fracture displacement and to help relieve pain6,13. Controlled closed-chain quadriceps exercises with a brace may be performed initially, if the pain is tolerable. Our patient had symptoms over a long period, and eventually the fracture line became displaced, most likely because the patient exercised forcefully after the initial missed diagnosis.
Open reduction and internal fixation may be required if the fracture is displaced. Our patient first underwent internal fixation with bioabsorbable pins, but the fracture did not heal and it redisplaced five months after that operation. Because of this experience, we recommend fixing displaced vertical patellar stress fractures with screws that can apply compression across the fracture line to enhance fracture-healing. With rigid fixation, the patient may begin passive mobilization immediately and controlled quadriceps exercises within a few weeks after surgery. We recommended a four to six-month break from athletic participation and that healing of the fracture line be visible on radiographs before the patient is allowed to resume participation in sports.
Here, we presented a case of a displaced longitudinal patellar stress fracture, which, although rare, should be suspected in physically active patients with persistent anterior knee pain. We suggest careful clinical assessment of these patients and recommend magnetic resonance imaging for cases of persistent nonspecific anterior knee pain with palpable patellar tenderness. Activity restriction may permit healing of nondisplaced fractures. On the basis of this unique case, we suggest open reduction and internal screw fixation for the management of a displaced longitudinal stress fracture of the patella with a large lateral fracture fragment.