Foot injuries are one of the most common injuries for athletes. Specifically, among all the joints and bones of the foot, the first metatarsophalangeal joint with its sesamoid complex is the most commonly affected. It is usually clear when an athletic injury involves the first metatarsophalangeal joint complex. However, identifying the specific injured structures and arriving at a precise diagnosis can be difficult.
Acute or chronic injures to the sesamoid bones or their associated tendon and joint capsule apparatus may cause pain, limping and difficulty wearing shoes, all aggravated by even a simple activity like walking. The resultant clinical impact makes both acute (traumatic) and overuse injuries major causes of competitive and recreational athletic disability.
Two hallucal sesamoids are situated under the first metatarsal head. The medial (tibial) sesamoid tends to be larger, oval-shaped and presents in a bipartite or multipartite form in 10 to 33 percent of feet. The lateral (fibular) sesamoid is smaller and rounder. Each sesamoid has an articular surface of hyaline cartilage, allowing it to articulate with the plantar aspect of the distal first metatarsal. While sesamoids elsewhere in the body occur variably, the hallucal sesamoids are virtually constant. These sesamoids function as an integral part of the first MPJ.
The hallucal sesamoids play an important role in great toe function as they absorb weightbearing pressure, reduce friction and protect tendons. The functional complexity and anatomic location of these small bones make them vulnerable to injury from shear and loading forces.
During running, more than half the weightbearing force travels through the great toe complex. Forces up to three times the athlete’s body weight may be transmitted across the sesamoids. The medial sesamoid bears most of this force and thus is more prone to injury than the lateral sesamoid. Injury to the hallucal sesamoids can cause incapacitating pain. Although you usually can diagnose traumatic injuries easily, you may overlook other pathologic conditions caused by overuse.
Careful physical and radiographic examinations (including bone scans) may be necessary to determine the structures damaged, extent of damage and the optimal treatment plan. Sesamoidal injures are divided into acute and chronic injures. Acute injuries are traumatic fracture/dislocations of the sesamoids and sesamoidal apparatus caused by trauma to the first MPJ complex. Chronic injuries of the sesamoids can be divided into three groups: Stress fractures, osteochondritis and sesamoiditis.
How To Detect And Treat Acute Injuries
Fracture dislocation of the sesamoids and sesamoidal apparatus is relatively rare. It usually results from a high-impact force like a fall, an injury which the pathological force of hyperextension of the MPJ causes.
The hallux is dorsiflexed, causing stretching of the plantar joint capsule. This causes distal distraction of the sesamoids due to their strong attachments to the plantar base of the proximal phalanx. As pathologic dorsiflexion continues, the capsule ruptures from its insertion at the plantar metatarsal neck. The hallux, with the sesamoids attached to the base of the proximal phalanx, dislocates dorsally to override the metatarsal head. The metatarsal head is then driven plantarly. The pathologic dorsiflexion may dislocate the sesamoids dorsally with the intersesamoidal ligament still intact. It also may result in either rupture of the intersesamoidal ligament or a transverse fracture of one of the sesamoids.
Jahss classified two types of first MPJ dislocation. Type I is a dorsal dislocation of the proximal phalanx and sesamoids on the first metatarsal head with the intersesamoidal ligament still intact. You cannot reduce this type of dislocation by closed means because of the intact intersesamoidal ligament. However, you can often use closed means to reduce the two groups of Type II dislocations. Type IIA is a dorsal dislocation of the proximal phalanx and sesamoids on the first metatarsal head with rupture of the intersesamoidal ligament, which results in wide separation of the sesamoids. Type IIB shows a transverse fracture of one of the sesamoids.
What About Sesamoid Stress Fractures?
Stress fractures occur when an athlete applies abnormal repetitive stress to normal bone or applies normal repetitive stress to a weakened bone. Fractures are more common in long-distance runners. Stress fractures account for 40 percent of all sesamoid injuries. These patients will complain of increasing pain and have point tenderness of the involved sesamoid. Keep in mind the pain usually develops gradually and is exacerbated by faster running or walking up and down stairs.
It’s important to differentiate sesamoid stress fractures from bipartite or multipartite sesamoids. Employing bone scans or CT scans may be necessary for early confirmation of an abnormal bony sesamoid process, as plain radiographs will not be abnormal until approximately three weeks after the injury has occurred.
As far as treatment goes, you would emphasize rest and use a 1/4- to 3/8-inch weight dispersion felt padding or a specially modified foot orthosis with a sesamoid “cutout” that decreases stress on the sesamoid while transferring weight along the shaft of the first metatarsal. Using a rigid soled shoe is also helpful. If the fracture has not united after six months of treatment and symptoms are sufficiently severe, you should consider surgical treatment. This may include performing open reduction with internal fixation of the fractured sesamoid or excising the involved sesamoid.
What To Look For In Osteochondritis Of The Sesamoids
Osteochondritis or avascular necrosis of the sesamoids may occur as a primary disorder, possibly related to recurrent stress, or as a secondary problem following a stress fracture and subsequent fragmentation. Be aware sesamoidal osteochondritis is less commonly a complication of traumatic fracture and more often the result of chronic stress. In either case, resulting avascular necrosis may lead to fragmentation and collapse of the sesamoid. You should treat such lesions conservatively for at least six months with splinting and activity modification.
Use functional orthoses and paddings similar to those you would use for sesamoid fractures. It may be necessary to fabricate a custom shoe with a protective toe box roomy enough to permit splinting of the toe. You also may emphasize other modalities such as icing, physical therapy and non-steroidal anti-inflammatory medications if necessary. If the symptoms continue to be disabling, you may use bone grafting from the adjacent first metatarsal. If the sesamoids are too fragmented for bone grafting, partial or complete excision may be a last resort.
How To Relieve Sesamoiditis
Sesamoiditis is a clinical diagnosis usually related to repetitive stress to the hallucal sesamoids. It occurs more frequently in the high arch or cavus foot type. In diagnosing sesamoiditis, keep in mind that it is marked by point tenderness on one or both of the sesamoids in the absence of radiographic evidence of a specific bony abnormality such as stress fracture or avascular necrosis.
At times, it’s tough to differentiate between a symptomatic and fractured partite sesamoid. In such cases, you may find contralateral X-rays or previous X-rays of the same foot valuable. Bipartite sesamoids have smoother edges and usually occur bilaterally.
Treatment options for curing or controlling sesamoiditis include temporary rest, icing, non-steroid anti-inflammatory drugs, physical therapy, splinting or foot orthoses. In severe cases, up to three weeks of rest and casting may be necessary to reduce symptoms in order to achieve pain-free foot function.
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Dr. Caselli (pictured) is Vice-President of the greater New York Regional Chapter of the American College of Sports Medicine and is a Professor in the Dept. of Orthopedic Sciences at the New York College of Podiatric Medicine.
Mr. Khoshneviszadeh is a podiatric orthopedic resident at the Veterans Affairs Hudson Valley Health Care System in Montrose, New York.