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Remote Fellowship – Foot & Ankle Fundamentals – 11/2/2020

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Diagnosis

Plantar Plate Tear

Case Discussion

The plantar plate (plantar capsuloligamentous complex) is formed by the distal aspect of the plantar fascia and the plantar portion of the metatarsophalangeal joint capsule. It originates from the distal plantar aspect of the metatarsal neck and inserts on the plantar aspect of the proximal phalangeal base. It is considered the most important stabilizing structure of the metatarsophalangeal joint and when ruptured, causes great instability of the joint allowing for dorsal subluxation of the proximal phalanx onto the metatarsal head/neck.

On T1- and T2-weighted images, an intact plantar plate appears as a continuous low-signal structure between the plantar aspect of the metatarsal head and proximal phalangeal base. It is directly between the high-signal hyaline cartilage of the joint and overlying lower-signal flexor tendons.

MRI findings of a degenerated plantar plate include thinning of the plantar plate and both intrasubstance and surrounding increased signal intensity. Discontinuity of the plate itself may be difficult to appreciate. 

MRI findings of a torn plantar plate include increased signal intensity at and around the plantar plate on both T1- and T2-weighted images, discontinuity of the plantar plate, retraction of the plantar plate, and synovitis within the flexor tendon sheath and metatarsophalangeal joint.

Soft tissue thickening and capsulosynovitis surrounding the plantar plate are highly suggestive of a plantar plate tear (even if not directly visualized).

A synovial recess at the distal portion of the plate (at the phalangeal insertion) is a common pitfall. 

Any soft tissue swelling that is unexplained around the head of m2 in a woman should raise strong suspicion of 2nd mtp plantar plate tear until proven otherwise.

Key Images

A. Sagittal STIR image of the left foot shows near-complete rupture of the 2nd MPJ plantar plate (red arrow), moderate capsulosynovitis, and high signal pericapsular soft tissue edema/inflammation (green arrow).
B. Long axis T2 FSE image shows disruption of the lateral aspect of the plantar plate (red arrow), which is the most commonly injured part.
C. Short axis T1 image shows abnormal intermediate signal intensity at the plantar aspect of the 2nd MTPJ (red arrows). This is indicative of swelling and plantar plate injury, and is commonly the only sign on MRI of a plantar plate injury/tear.
D. Axial PD FSE image shows near-complete rupture of the 2nd MPJ at the lateral aspect (red arrow) with moderate capsulosynovitis (green arrow) and high signal pericapsular soft tissue edema/inflammation.
E. Long axis T2 FSE image again shows near-complete rupture of the lateral phalangeal collateral ligament (yellow arrow). There is also medial subluxation of the base of the 2nd toe.

References

  1. Yao L, Do HM, Cracchiolo A, Farahani K. Plantar plate of the foot: Findings on conventional arthrography and mr imaging. American Journal of Roentgenology 1994; 163:641-644
  2. Duan X, Li L, Wei D, Liu M, Yu X, Xu Z, Long Y, Xiang Z. Role of magnetic resonance imaging versus ultrasound for detection of plantar plate tear. Journal of Orthopaedic Surgery and Research 2017; 12:14