Kohler's Disease

                                      DR KS Dhillon

Introduction

Alban Kohler in 1908 first described Kohler disease. He referred to avascular necrosis of the navicular bone of the foot. Kohler disease is only seen in pediatric patients. The etiology is not fully understood. It is believed to be caused by the compression of the navicular bone prior to ossification. The compression leads to blood flow abnormalities resulting in avascular necrosis. Kohler disease is most often seen in males between the ages of 4 to 7 years. This disease is typically unilateral. There was one report in the literature which found that 25% of Kohler disease is bilateral. Patients usually present with medial-sided foot pain, swelling of the medial foot, and/or a limp. X-rays of the foot will show standard characteristics of avascular necrosis (AVN), including sclerosis, fragmentation, and flattening of the navicular bone. Kohler disease is a self-limiting condition. The prognosis is usually excellent. Kohler disease does not lead to long-term clinical or radiologic abnormalities (1,2,3).

Etiology

The navicular bone has a dual blood supply. The dorsal aspect of the bone is supplied by a branch of the dorsalis pedis artery. The plantar aspect is supplied by the medial plantar branch of the posterior tibial artery. Both the vessels enter the navicular bone and branch to supply the medial and lateral thirds of the bone. This leads to the creation of an avascular zone in the central third of the bone. There are vascular foramina that help to supply this avascular area.  They are found on the medial, dorsal, plantar,  and lateral surfaces of the navicular bone. In a study of 100 adult cadaveric navicular bones, 97% of vascular foramina were smaller than 1 millimeter. Any compression of these small vascular foramina can result in decreased blood flow and lead to avascular necrosis.

Abnormal strain on the navicular is believed to be the cause of Kohler disease. The navicular bone is the last of the tarsal bones to ossify in children. In boys, it ossifies between 30 to 36 months old, and in girls between 18 and 24 months. Because of the navicular bone’s slow ossification, it is weaker than the other tarsal bones. The navicular bone can be compressed between the already ossified talus and cuneiform bones as the child grows and becomes heavier. The compression of non-ossified navicular bone can lead to the squeezing of the perforating vessels in the central spongy bone. This can lead to ischemia and later avascular necrosis (4-7).

Epidemiology

Köhler disease is a rare condition. It is thought to occur in less than 2% of the population (8). There are however no accurate epidemiologic figures available for this condition. The disorder can begin very early in life. It can start after the age of 2 years. It is more often seen in children aged 5-10 years (9). Köhler disease is far more common in boys than in girls. Girls with this condition are usually younger than the boys. This is probably due to the earlier onset of ossification in girls. Ossification in girls occurs at the age of 18-24 months. In boys, ossification occurs at the age of 24-30 months.

Histopathology

A bone biopsy is not required for the diagnosis of Kohler disease. A biopsy is not recommended for the diagnosis unless there is a need to rule out malignancy or infection. Histologically Kohler disease looks similar to other forms of avascular necrosis. The main histologic feature of avascular necrosis is dead trabeculae with empty lacunae that stain deeper than healthy bone. The lacunae enlarge and with cystic changes. Bone marrow will show fat necrosis and calcium deposits. This is a more sensitive indicator for AVN than the bone itself. 

Clinical Presentation

Sometimes Kohler disease can be asymptomatic. Patients, however, often present to the pediatrician with dorsomedial midfoot pain. Examination shows point tenderness over the navicular with or without redness, swelling, and warmth. The patient may walk with an antalgic limp. They walk on the lateral side of their foot.

Evaluation

For the diagnosis of Kohler disease plain radiographic images are the imaging modality of choice. The X-rays will show that the navicular bone is wafer-thin with bony collapse. There will be fragmentation of the bone with a loss of a trabecular pattern. Patchy sclerosis of the bone with increased radiodensity will be seen. The X-rays will also show soft tissue swelling around the affected navicular bone. CT scan and MRI imaging are not required for diagnosis. They may become necessary if the patient's symptoms do not improve with treatment. Navicular sclerosis may be consistent with a normal variant in asymptomatic patients. It is important to correlate radiographic findings with clinical findings.

In patients where infection is suspected basic lab tests, such as a complete blood count (CBC), C-reactive protein (CRP), and erythrocyte sedimentation rate (ESR) are required.

Management

Patients in whom Kohler disease is suspected should be referred to a pediatric orthopedic surgeon (8). The treatment of Kohler disease is usually conservative. NSAIDs can be used to reduce the symptoms but NSAIDS have not been shown to shorten the duration of disease symptoms. A short leg walking cast for 4 to 6 weeks can be used to shorten the duration of symptoms. The effect of weight-bearing casts compared to non-weight bearing casts remains unclear. There have been some reports of using offloading orthotics for symptomatic relief. It does not appear, however, that orthotics shorten the duration of symptoms.

There are no indications for surgery for Kohler disease. If symptoms persist an alternative diagnosis should be considered. The symptoms and radiographs usually start to show improvement in around six months.

Differential Diagnosis

Kohler disease can often be misdiagnosed as osteomyelitis in kids. The basic lab tests (WBC, CRP, ESR) will, however, help to differentiate between the two diagnoses. If there is an elevated ESR or CRP, there should be a high index of suspicion for infection. Kohler disease will not have elevated inflammatory markers. If an infection is suspected there will be a need for bone aspiration, bone biopsy, or blood cultures.

Prognosis

The prognosis of Kohler disease is excellent. There have been no reports of long-term symptoms or disability with Kohler disease. X-rays usually improve around 6 to 48 months after the onset of symptoms. Without a cast, symptoms usually resolve within 6 to 9 months. Patients treated with plaster casts (non-weight bearing) are pain-free at an average of 3 months. With arch support pain is reduced but symptoms can last an average of 7 months.

Conclusion

Kohler disease is a disease taht is seen only in pediatric patients. The etiology of Kohler disease is not fully understood. It is believed to be caused by the compression of the navicular bone prior to ossification. This compression leads to blood flow abnormalities which leads to avascular necrosis. This disease is usually seen in males aged between 4 to 7 years.  It is typically unilateral, although one report in the literature found that 25% of Kohler disease is bilateral. Patients usually present with medial-sided foot pain, swelling of the medial foot, and/or a limp. Plain X-rays of the foot will show standard characteristics of avascular necrosis, including sclerosis, fragmentation, and flattening of the navicular bone. Kohler disease is a self-limiting condition. The prognosis is excellent. Long-term clinical or radiologic abnormalities do not develop in patients with Kohler disease. 

References

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4. Lechleitner M, Abrahamian H, Francesconi C, Sturm W, Köhler G. [The diabetic foot]. Wien Klin Wochenschr. 2016 Apr;128 Suppl 2:S80-4. 

5. Clements JR, Dijour F, Leong W. Surgical Management Navicular and Cuboid Fractures. Clin Podiatr Med Surg. 2018 Apr;35(2):145-159. 

6. Riaz S, Bashir H, Hassan A, Khan AH. Kohler disease: Imaging King Tut's foot in 21st century. J Pak Med Assoc. 2018 May;68(5):822. 

7. Alhamdani M, Kelly C. Kohler's disease presenting as acute foot injury. Am J Emerg Med. 2017 Nov;35(11):1787.e5-1787.e6.

8. Kohler disease. National Organization for Rare Disorders. Available at https://rarediseases.org/rare-diseases/kohler-disease/. November 7, 2018; Accessed: June 12, 2023.

9. Chan JY, Young JL. Köhler Disease: Avascular Necrosis in the Child. Foot Ankle Clin. 2019 Mar. 24 (1):83-88.