Capsulitis

Capsulitis is inflammation of the joint capsule — the sleeve of connective tissue that surrounds and stabilizes a metatarsophalangeal joint. It most commonly affects the second MTP joint, at the base of the second toe, though it can occur at any of the lesser toe joints. The condition produces pain, swelling, and tenderness at the affected joint — typically on the plantar surface of the ball of the foot — along with a progressive sense of instability or looseness in the toe.

The second MTP joint is uniquely predisposed to capsulitis for biomechanical reasons. Patients with a relatively long second metatarsal bear disproportionate forefoot pressure at the second MTP with every step. Patients with hallux valgus — a bunion — experience lateral force transfer from the first ray to the second toe, overloading the second MTP joint capsule over time. Patients with tight calf muscles, high heels, or other conditions that concentrate forefoot loading also place the second MTP under chronic stress. The result is a cycle of repetitive microtrauma to the joint capsule that produces the characteristic pain and swelling of capsulitis.

Capsulitis is frequently misdiagnosed — it is commonly mistaken for a neuroma, metatarsalgia, or simply 'ball of foot pain' without identification of the specific joint involvement. The distinction matters because capsulitis requires specific treatment targeting the affected joint and the biomechanical contributors driving the overload. Treating it as generic metatarsalgia produces incomplete results.

The most important clinical fact about capsulitis is its relationship to the plantar plate — the dense fibrocartilaginous ligament on the plantar surface of the MTP joint that prevents the toe from dorsiflexing abnormally and stabilizes the toe in its correct alignment. Capsulitis and the plantar plate share the same anatomical territory, and chronic capsular inflammation progressively weakens the plantar plate. If the inflammatory process is not arrested — through appropriate treatment of both the acute inflammation and the underlying biomechanical contributors — the plantar plate can partially or completely tear. A plantar plate tear is a structural injury that does not respond to the same conservative measures that manage capsulitis effectively at the inflammatory stage.

The clinical signs of plantar plate involvement developing within a capsulitis presentation are the toe beginning to drift upward, a positive Lachman test of the affected MTP joint, increasing instability, and the characteristic crossover deformity — the second toe drifting laterally and crossing over the big toe — in advanced cases. These signs indicate that the window for purely conservative management is closing.

Dr. Gunter evaluates capsulitis with careful attention to the plantar plate — assessing stability clinically and with imaging when indicated — to determine whether the condition is still in the inflammatory stage or whether plantar plate involvement has developed, as this significantly influences the management approach.