Differential Diagnosis of Lateral Mid-foot Pain
When we talk about the lateral column of the foot, we’re referring to the
bones of the outside, or lateral aspect of the foot. Inherent in any discussion of the lateral column is the concept of load bearing. The lateral column is the Rodney Dangerfield of the foot, it just gets no respect. The reason I say that is that the lateral column bears the brunt of load bearing during gait as the body passes over the foot. The majority of that load bearing is focused in a small segment of the foot referred to as the calcaneo-cuboid joint (CC joint). Let’s hone in on the CC joint and look at what may cause pain in the region of the calcaneo-cuboid joint, and differential diagnoses specific to that area.
By default, when we speak of calcaneo-cuboid pain, the first diagnosis that most folks think of is cuboid syndrome. Cuboid syndrome is described as a subluxation of the calcaneo-cuboid joint. In my experience, I’ve always questioned cuboid syndrome as the primary cause of CC joint pain. The literature describes how in cases of cuboid syndrome, the CC joint can be physically manipulated and supported with taping and Rx orthotics. But the scientist in me is suspect of this diagnosis. The reason I’m suspect is that in the literature there is no documentation of studies that quantify cuboid syndrome. For instance, there are no MRI studies that show evidence of CC joint subluxation. Nor are there any CT scans that have been used to quantify the amount of subluxation.  Hmmmm. How come. Does that mean that cuboid syndrome is a bit nebulous? Maybe indeed, subluxation of the CC joint does occur, but when making a diagnosis, it’s important to be open to what in medicine we call a differential diagnosis. A differential diagnosis is simply other diagnosis that need to be considered when trying to make a definative diagnosis. Let’s take a look at the differential diagnosis of cuboid syndrome.
One of the often over looked aspects of the cuboid is how the peroneus longus tendon affects the function of the cuboid. The peroneus longus tendon originates in the lateral calf and descends the leg posterior to the lateral malleolus (outside ankle bone). The peroneus longus then takes an abrupt turn at the lateral aspect of the cuboid to insert into the base of the first metatarsal (bottom of the foot). The primary function of the peroneus longus is to plantarflex the medial aspect of the foot. So how does the peroneus longus affect the cuboid? In several ways, actually.
First, the peroneus longus traverses the cuboid in a small groove called the peroneal groove. In cases of an inversion sprain of the ankle, the function of the peroneus longus is to inhibit the sprain. It does so by contracting to inhibit the inversion of the ankle. But in some cases, the force of the peroneus longus tendon, focused in the peroneal groove, will be so strong that the tendon actually damages the cuboid. When seen with an MRI, abrupt force from the peroneus longus causes a bone contusion. A bone contusion is a bruise in the bone. So our first differential diagnosis for cuboid syndrome should be a bone contusion of the cuboid.
Second, a common finding specific to the lateral cuboid is a small little accessory ossicle called the os peroneum. Think of the os peroneum as functioning much like your knee cap (patella). When a tendon changes direction, this section of the tendon is subject to wear and subsequent failure. An accessory ossicle is used to decrease this wear zone. Just as the patella facilitates the transfer of force around the anterior knee, the os peroneum facilitates the transfer of force around the lateral wall of the cuboid. It is fairly common to see an irritation of the interface between the accessory bone and the underlying bone. This process is called chondromalacia. Chondromalacia of the articular surface of the os peroneum and cuboid is common and may be caused by wear (osteoarthritis) or acute injury. So our second differential diagnosis is chondromalacia of the os peroneum.
Our third differential is a fracture of the os peroneum. Again, let’s consider
the case of an inversion sprain of the ankle. As the ankle starts to roll, the peroneal muscle senses the stretch and responds by contacting. This contraction of the PL will help to inhibit the inversion sprain. But in the presence of an os peroneum (present in approx. 15% of the general population), that os peroneum can actually fracture into two or more parts. These fractures rarely heal in entirety. The resulting problem is chronic pain at the CC joint. Hence our third differential diagnosis.
Our fourth consideration should be a stress fracture of the cuboid. Stress fractures of the cuboid a somewhat rare and are often referred to as a ‘nutcracker fracture’ of the cuboid. These fractures rarely show up on plain x-ray and are most commonly diagnosed with an MRI.
Each of the previously described injuries are specific to the cuboid and peroneus longus tendon. But as we move out and away from the CC joint, we need to consider a few other conditions that may be included in our differential diagnosis. Those conditions include a fracture of the 5th metatarsal base and a tear in the peroneal tendons.
So, is all lateral mid-foot pain cuboid syndrome? No. Not in the least. That’s why it’s so important to keep an open mind when it come to making a diagnosis of lateral column pain. Be sure when making your diagnosis to incorporate a good history of the problem, noting the onset of pain and the mechanism of injury, if an injury is described.
Jeffrey A. Oster, DPM
The Cherry Valley Foot and Ankle Center, Newark, Ohio
Ohio Valley Sports Medicine, Chillicothe, Ohio
Dr. Oster cannot answer medical questions or provide medical care through this blog.
Tags: calcaneo-cuboid joint, cuboid, cuboid fracture, cuboid syndrome, os peroneum, peroneus longus
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