Differentials
Fracture of the tibial tubercle
SIGNS / SYMPTOMS
Onset of symptoms is typically sudden and associated with a traumatic event. Patients are unable to actively extend the knee and may be unable to bear weight.[1]
INVESTIGATIONS
Radiographs demonstrate irregular fracture line, usually without fragmentation of the tubercle (such as may be seen in cases of OSD). May be associated with physeal arrest of the tibial tubercle leading to recurvatum deformity.[6]
Fat pad hypertrophy/impingement (Hoffa disease)
Inferior patellar pole traction apophysitis (Sinding-Larsen and Johansson syndrome)
SIGNS / SYMPTOMS
Maximal tenderness is at the inferior pole of the patella, not at the tibial tubercle.[1]
Patellar stress fracture
SIGNS / SYMPTOMS
A very rare entity.
Patients may present with variable ability to bear weight, as well as pain, swelling, and localized tenderness over the anterior aspect of the patella (as opposed to the tenderness over the tibial tubercle in OSD).
Patients may report a sensation of crack or pop with activities.
INVESTIGATIONS
Plain radiographs may show a transverse fracture line, usually at the junction of the middle and distal thirds of the patella. Callus formation may also be noted, indicating reparative process at the site of injury. Typical findings of enlarged or fragmented tibial tubercle are absent.
Osteochondritis dissecans of the knee
SIGNS / SYMPTOMS
Patients typically present complaining of anterior or anteromedial knee pain, and intermittent knee swelling, sometimes accompanied by mechanical symptoms.
A history of minor trauma may precede the onset of symptoms, or the condition may be completely atraumatic.
Typically, tenderness is localized to the joint line (usually medial), with absence of tenderness at the tibial tubercle.
INVESTIGATIONS
Classic location for osteochondritis dissecans of the knee is the lateral aspect of the medial femoral condyle. The lesion may be visible on plain radiographs or may require MRI for diagnosis.[6]
Infrapatellar bursitis
SIGNS / SYMPTOMS
Clinically may be difficult to differentiate from early OSD.
Location of pain is similarly at or near patellar tendon insertion, although distinct tenderness to palpation over the tibial tubercle is usually absent.
INVESTIGATIONS
Radiographs are typically normal or demonstrate increased soft-tissue swelling in the infrapatellar region.
MRI shows normal tibial tubercle and fluid accumulation in the infrapatellar region.
Patellar tendonitis
SIGNS / SYMPTOMS
May be difficult to distinguish from early OSD, and may occur as secondary pathology in knees with OSD.
INVESTIGATIONS
Radiographs are typically normal or demonstrate increased soft-tissue swelling in the infrapatellar region.
MRI shows normal tibial tubercle and may demonstrate increased signal in the patellar tendon on T2-weighted images.
Osteoid osteoma
SIGNS / SYMPTOMS
Lesions of bone will often manifest as pain that occurs both at rest and with activity.
Night-time pain may be present.
INVESTIGATIONS
Plain radiographs identify a circular defect.
Osteosarcoma
SIGNS / SYMPTOMS
Lesions of bone will often manifest as pain that occurs both at rest and with activity.
Presents with systemic symptoms and signs such as fever, night sweats, and weight loss.
INVESTIGATIONS
Plain radiographs demonstrate radiolucent lesion with areas of mottled radiodensity and ill-defined margins.
CT or MRI is confirmatory.
Bone biopsy performed by an experienced orthopedic oncologist may be done to confirm the diagnosis.
Osteomyelitis
SIGNS / SYMPTOMS
Lesions of bone will often manifest as pain that occurs both at rest and with activity.
Presents with systemic symptoms and signs such as fever and chills.
INVESTIGATIONS
Laboratory markers such as ESR, CRP, and WBC count may be elevated.
Positive blood cultures for inciting organism.
The earliest changes seen on plain radiographs are soft-tissue swelling, periosteal thickening, and focal osteopenia.
MRI is confirmatory.
Slipped capital femoral epiphysis
SIGNS / SYMPTOMS
Patients with disorders of the hip may present with referred knee pain (via the posterior branch of the obturator nerve), typically on the medial aspect of the knee.
They may sometimes be unable to bear weight on the affected extremity and have a limp.
Physical examination of such patients often demonstrates limited range of motion of the ipsilateral hip, with a relatively normal range of motion of the knee.
An episode of minor trauma may precede this presentation.
INVESTIGATIONS
Radiographs of the hip and pelvis, including anteroposterior and frog-leg lateral views demonstrate abnormality of the hip joint.
Radiographs of the knee are usually normal.
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