Foot and Ankle cases 18

You are asked to evaluate a 40-year-old man with medial forefoot pain. The patient’s primary care provider (PCP) tells you the patient has had the insidious onset of a chronic ache that is worsened with barefoot walking, particularly when pushing off, and made better by stiff shoe wear. No imaging studies are available, but the PCP would like to know what to do before sending the patient to your clinic.

You ask the primary care provider to:

1. Obtain an MRI of the foot

2. Obtain a bone scan

3. Obtain weight-bearing x-rays of the foot

4. Provide a Morton’s extension (rigid orthosis to protect the first metatarsophalangeal joint [MTPJ])

Discussion

The correct answer is (C). Weight-bearing views of the foot are requisite for the initial evaluation of medial forefoot pain. Additional views may include contralateral comparison radiographs, an axial sesamoid view, and lateral/medial oblique radiographs. MRI can be a very specific study in differentiating the various structures about the first MTPJ but is not an effective screening tool. Bone scan is a useful study but is not specific and is not the first-line of study for these patients. With a bone scan, uptake should be compared with the contralateral side given the occasional increased uptake in asymptomatic patients. A Morton’s extension may

eventually be employed, especially if hallux rigidus is identified, but a diagnosis should be established first.

Weight-bearing foot radiographs are obtained (Fig. 5–36). You do not notice a bipartite sesamoid.

 

 

 

Figure 5–36 Weight-bearing AP radiograph of the foot.

 

Regarding the findings of bipartite sesamoid(s), which is least accurate?

1. The medial sesamoid is bipartite in 50% of the population

2. The lateral sesamoid is rarely bipartite

3. The medial sesamoid is bipartite in 10% of the population

4. In patients with a bipartite sesamoid, the finding is bilateral in 25% of the population

Discussion

The correct answer is (A). The prevalence of a bipartite medial sesamoid is 10%, not 50%. A bipartite lateral sesamoid is rarely encountered and is less frequently noted than a bipartite medial sesamoid. One-quarter of patients found to have a bipartite sesamoid have a similar finding on the contralateral foot.

You evaluate the patient and note maximal tenderness at the lateral sesamoid with reproduction of plantar pain with passive dorsiflexion and resisted plantar flexion at the first MTPJ. Passive and active motion at the interphalangeal joint is not painful, and the medial eminence is not tender. There is no dorsal tenderness. Your initial treatment involves activity modification and orthotic wear with a recess under the first MTPJ. During this lengthy nonoperative course, an MRI is obtained (Fig. 5–37).

 

 

 

Figure 5–37 Sagittal STIR sequence MRI image demonstrating the lateral sesamoid.

 

Having failed nonoperative treatment, the patient requests surgical intervention. What is the most appropriate surgical intervention?

1. Microfracture of the lateral sesamoid

2. Excision of medial and lateral sesamoids

3. Plantar flexion osteotomy of the first metatarsal

4. Excision of the lateral sesamoid with flexor hallucis brevis (FHB) repair

 

Discussion

The correct answer is (D), excision of the lateral sesamoid with FHB repair (Fig. 5–

38). The physical examination and MRI findings suggest lateral sesamoiditis. The sesamoids act as pulleys for the FHB, thus placing the FHB on stretch or resisting its active function can reproduce the patient’s pain. The increased signal on MRI provides objective evidence to support the diagnosis.

 

 

 

Figure 5–38 AP radiograph demonstrating excision of the lateral sesamoid.

 

The mainstay of surgical intervention for lateral sesamoiditis is excision. A

plantar approach is employed. Care is taken to protect the flexor hallucis brevis tendon. The medial and lateral slips of the FHB envelope the plantar aspect of their respective sesamoids. After the lateral sesamoid is excised from the flexor hallucis brevis and surrounding plantar plate complex, it is of utmost importance to perform a meticulous soft tissue repair. If not performed, iatrogenic hallux varus may result. Alternatively, failure to perform this repair during a medial sesamoidectomy may result in the development of hallux valgus. Excision of both sesamoids may result in claw toe deformity, and is therefore not recommended. A plantar flexion osteotomy of the first ray would likely exacerbate the problem and load the sesamoids further. Those patients with a plantar-flexed first ray may benefit from a dorsiflexion osteotomy.

 

Objectives: Did you learn...?

 

Describe the prevalence of bipartite sesamoids?

 

Describe considerations for imaging studies used to assess the sesamoids?

 

Identify the anatomic location of the medial and lateral sesamoids within the medial and lateral slips of the flexor hallucis brevis?

 

Assess the considerations for surgical treatment of sesamoiditis?