Mueller–Weiss syndrome, also known as Mueller–Weiss disease, is a rare idiopathic degenerative disease of the adult navicular bone characterized by progressive collapse and fragmentation, leading to mid- and hindfoot pain and deformity. It is most commonly seen in females, ages 40–60.
The exact cause of MWD is unknown, but it has traditionally been thought to be due to spontaneous bone cell death (osteonecrosis) of the navicular bone. The navicular bone is commonly described as “comma shaped” on X-ray and may be fragmented in later stages of disease.
Both triple fusion and TNC arthrodesis are reasonable methods to treat Mueller-Weiss disease. If the subtalar and/or calcaneocuboid joints are involve, triple fusion may be an effective and reliable operative option.
Müller-Weiss disease (MWD) is a rare condition of unclear pathogenesis that causes navicular bone collapse and fragmentation. MWD can be challenging to diagnose and presents with midfoot and hindfoot pain and deformities. Although its incidence is unknown, MWD more commonly affects women aged between 40 and 60 years.
As with osteoarthritis, navicular syndrome is a degenerative condition that worsens over time. It is therefore not possible to cure navicular syndrome.
Prognosis. Navicular syndrome is a lifelong condition, however, many horse can return to athletic function and soundness for long periods of time. Once the initial lameness is resolved, then corrective farriery can keep a horse from having repeated flare ups.
This normally takes six weeks to heal, but you may still have pain and swelling for up to six months after your injury. During this period, it is important that you follow the rehabilitation plan on the following page.
Damage can occur to the deep flexor tendon, navicular bursa, or navicular ligaments all resulting in pain and lameness.
When looking at treatments, it's important to remember that navicular is a degenerative disease and therefore is not curable. Most procedures are to designed to help the horse feel less pain while being worked. Phenylbutazone, an anti-inflammatory and pain reducer, is used for short periods.
Treating Mueller-Weiss syndrome
Because the degenerative disease is incurable, the goal for a Mueller-Weiss sufferer is to manage the pain.
Lameness is the classic sign of navicular syndrome. This can appear suddenly, but a more common pattern is mild lameness that becomes progressively worse over time. A horse with navicular syndrome feels pain in the heels of the front feet, and its movements reflect attempts to keep pressure off this area.
Mueller-Weiss syndrome more commonly occurs in women and favors a bilateral distribution. Kohler's disease, on the contrary, tends to be unilateral in presentation. For Mueller-Weiss syndrome, X-rays reveal a comma-shaped or wedge-shaped navicular bone on the anteroposterior view.
The navicular is the last of the tarsal bones to ossify with variable radiographic appearance between 2.7 to 4 years. The secondary ossification center does not appear until 9 through 13 years of age, occurring two years earlier in females than males.
There is no proven genetic heritability to navicular syndrome, although there are predispositions due to breed, conformation, discipline and training.
Magnetic Resonance Imaging (MRI)
An MRI is a highly sensitive tool for visualizing bones and joints and can detect early signs of osteonecrosis before they are seen on an x-ray. An MRI may even pick up signs of osteonecrosis before you experience symptoms.
Symptoms of accessory navicular syndrome include: Pain or throbbing in the midfoot and arch—typically during/after activity. Visible prominence or bump on the inner side of the foot, above the arch. Redness and swelling of the bony prominence.
Signs and Symptoms
Rarely, navicular syndrome lameness comes on suddenly. Usually, it is a gradual, intermittent lameness. What starts as a horse being somewhat “off” progresses over time.
Symptoms of a navicular stress fracture usually involve a dull, aching pain in the ankle or at the middle or top of the foot. In the early stages, pain often occurs only with activity. In the later stages, pain may be constant.
Medication Summary
Often, acetaminophen or an NSAID (eg, ibuprofen) suffices for the acute pain of a navicular stress fracture because immobilization and rest should considerably improve the pain.
Treatment for Navicular Syndrome
injecting the coffin joint and/or navicular bursa with corticosteroids to reduce inflammation; long-term pain medication such as Equioxx to minimize inflammation; a bisphosphonate such as Osphos; corrective shoeing.
Surgical intervention requires an excision of the accessory navicular and reattachment of the posterior tibial tendon to the navicular. Oftentimes, this is the only procedure necessary. However, if there are other deformities, such as a flat foot or forefoot that is abducted, other procedures may be required.
Navicular fractures are common due to trauma, stress, or chronic overuse. They account for about 14 to 35% of all types of foot stress fractures. The symptoms include extreme pain, limited motion range, and swelling. If you feel a sudden pain in your midfoot, immediately get it CT scanned for the diagnosis.
Navicular syndrome is a chronic and often progressive disease affecting the navicular bone and bursa, deep digital flexor tendon (DDFT), and associated soft tissue structures composing the navicular apparatus.