A plantaris injury typically occurs as a result of sudden acceleration or deceleration movements, usually seen in sports that require running or jumping, placing eccentric load on the ankle with an extended knee. These injuries will usually present as a tendinopathy or a tear (partial or full rupture) in the tendon.
 

Injury to the plantaris muscle can occur on its own but most often in combination with the gastrocnemius and/or soleus injury. 

1. A patient may report feeling as though they were struck in the back of the leg when the injury initially occurs. Patients with a plantaris injury will also report a sharp pain in the posterior calf with tenderness and swelling along the muscle course or tendon. 

   Patients may present with calf soreness during an activity that may force them to stop and report that the pain will be more severe when resting or the next day. Patients can also typically report a sharp pain in the posterior calf with tenderness and swelling along the muscle course or tendon. Plantaris injury presentations can sometimes be misdiagnosed as a medial gastrocnemius tear or an Achilles tendon injury due to similar presenting symptoms and the common course through the posterior compartment of the lower leg.

Despite both muscles being located in the posterior compartment of the lower leg and having similar insertions, an injury to the Achilles versus the plantaris will differ in terms of the mechanism of injury, clinical presentation, diagnosis and recovery.

Achilles injuries will normally occur from high-force activities such as sprinting, jumping and abrupt change of direction, whereas a plantaris injury will occur from eccentric loading on the calf, sudden dorsiflexion or from a hyper-extended knee during running. 

Due to having a limited biomechanical role, the severity of a plantaris injury will be significantly less than an Achilles injury.  Patients will normally present with sharp pain at the back of the ankle or mid-calf with significant weakness in plantarflexion and difficulty walking. A plantaris injury will have minimal functional deficits due to having a limited biomechanical role where other muscles will compensate i.e. a patient will still have normal function in plantarflexion and dorsiflexion, however these movements may be accompanied by pain along the course of the muscle or near the medial head of the gastrocnemius. 

The recovery for a plantaris injury is a relatively faster one with an approximate timeframe of 2-8 weeks unlike an Achilles injury, which may take up to 6 months for a tendinopathy and up to 12 months for a full rupture.

Diagnosis can be performed by a physiotherapy assessment where by the pain will be localised to the muscle tendon unit with the patient appearing to have normal Achilles function. Imaging via an MRI or ultrasound can be utilised to confirm a tear, the grade of tear and differentiate from other injuries, however is not required for treatment to proceed as the treatment for a plantaris injury is similar to that of a calf strain or Achilles tendon injury. 

Conservative treatment is usually sufficient as surgical intervention is very rarely required due to the minimal functional impact of the muscle. The protocol may be very similar to a calf injury or tendinopathy depending on the presentation as, most often, injury to the plantaris will occur in combination with either a gastrocnemius or soleus injury. Depending on the severity of the injury, most patients will fully recover within 1-3 months with no long-term complications. 

Acute management has a focus on preventing further damage, controlling inflammation cascade and pain management. Regeneration of the muscle tissue = isometrics. 

Strengthening and proprioceptive then sportspecific

Conservative management is most often more successful for these types of injuries through physiotherapy, however, if the injury is severe and persistent over an extensive time frrame, an appointment with orthopaedic specialist may be indicated to review if surgical intervention is required.