| September 2006 Case of the Month | |
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Compiled By: Dakshesh Patel, M.D.
History: 63-year-old male who complained of pain in the right calf. He was cleaning on his tip toes when he felt a pop and sharp pain in the posterior calf.
Exam: MRI of the right calf performed on open MRI.
Findings: Coronal T1 and T2 (Fig. 1 and 2) and Axial T2 (Fig. 3) and STIR (Fig. 3 and 4) images demonstrate fluid or dilute blood in the plantaris space located deep to the medial head of the gastrocnemius muscle. There is nonvisualization of the plantaris tendon consistent with rupture. The gastrocnemius and soleus muscles are intact and have normal signal.
Diagnosis: Plantaris Rupture.
Discussion: The plantaris is a thin, small superficial posterior leg muscle that lies just deep to the lateral head of the gastrocnemius muscle in the proximal portion of the lower leg. It has a long tendon that crosses the medial side of the leg and accompanies the Achilles tendon to the calcaneus. The muscle arises from the inferior aspect of the lateral supracondylar line of the femur just superior and medial to the lateral head of the gastrocnemius muscle and from the oblique popliteal ligament of the posterior aspect of the knee. It passes inferior and medially just posterior to the knee joint to become tendinous at the level of origin of the soleus muscle from the tibia in the proximal portion of the lower leg. The tendon lies between the medial head of the gastrocnemius and the soleus muscle in the midportion of the leg and courses distally along the medial aspect of the Achilles tendon. The distal tendon inserts with the Achilles tendon or occasionally separately into the medial side of the calcaneus.
Rupture of the plantaris occurs during forced dorsiflexion of the ankle with the knee in extension. The rupture is usually during a sudden forced activity in a middle aged adult or as a result of a sports related injury in a younger individual. After complete rupture, which occurs at the myotendinous junction, there is retraction of the plantaris muscle. On MRI, this proximal muscle retraction frequently appears as a mass between the popliteus tendon and the lateral head of the gastrocnemius muscle at the level of the knee joint. The retracted muscle may have high-signal intensity from associated edema or hemorrhage. An intermuscular hematoma may be seen between the medial head of the gastrocnemius and the soleus muscles.
Plantaris “Pearls”:
- The plantaris muscle is a vestigial structure that is absent in 7-10% of the population. Since its tendon is the longest in the body, it is commonly harvested as an autograft for ligament and tendon reconstructions.
- The plantaris tendon may rupture when the muscle is violently contracted causing lower leg pain in athletes, termed “tennis leg”. This clinical entity was first described in clay court tennis players.
- Plantaris rupture can mimic tears of the gastrocnemius or soleus muscles. The differentiation is important as the latter are more severe injuries and are treated for longer durations and may even require splinting. It can also be confused with deep venous thrombosis and occasionally Achilles tendon rupture.
- Posterior compartment syndrome is a possible complication due to edema, soft-tissue swelling and hematoma formation.
- Tennis leg may be associated with ACL rupture, arcuate ligament injury, and partial tear of the medial head of the gastrocnemius muscle.
- Aggressive rehabilitation therapy of plantaris rupture is recommended to prevent chronic hematoma formation with calcification and subsequent limitation of range of motion of the lower leg.
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Figure 1
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Figure 2
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Figure 3
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Figure 4
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Figure 5
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References:
- Helms CA, Fritz RC, Garvin GJ. Plantaris muscle injury: evaluation with MR imaging. Radiology 1995: 195:201-203.
- Allard JC, Bancroft J, Porter G. Imaging of plantaris muscle rupture. Clinical Imaging 1992; 16:55-58.
- Crenshaw AH, ed. Campbell's Operative Orthopedics, St. Louis: C.V. Mosby Co., 1987.
- Delgado GJ, Chung CB, Lektrakul N, Azocar P, Botte MJ, Coria D, Bosch E, Resnick D. Tennis Leg: Clinical US Study of 141 Patients and Anatomic Investigation of Four Cadavers with MR Imaging and US. Radiology 2002; 224:112-119.
- Stoller DW, Tirman PFJ, Bredella MA. Diagnostic Imaging: Orthopaedics. Salt Lake City: Amyrsis, 2004.
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