• Juuso Heikkinen, Iikka Lantto, Tapio Flinkkila, Pasi Ohtonen, Jaakko Niinimaki, Pertti Siira, Vesa Laine, and Juhana Leppilahti.
• Division of Orthopaedic and Trauma Surgery, Department of Surgery, Medical Research Center Oulu, Oulu University Hospital, University of Oulu, Oulu, Finland.
• Am J Sports Med. 2017 May 1; 45 (6): 1395-1404.

BackgroundIt remains controversial whether nonsurgical or surgical treatment provides better calf muscle strength recovery after an acute Achilles tendon rupture (ATR). Recent evidence has suggested that surgery might surpass nonsurgical treatment in restoring strength after an ATR.PurposeTo assess whether magnetic resonance imaging (MRI) findings could explain calf muscle strength deficits and the difference between nonsurgical and surgical treatments in restoring calf muscle strength.Study DesignRandomized controlled trial; Level of evidence, 1.MethodsFrom 2009 to 2013, 60 patients with acute ATRs were randomized to surgery or nonsurgical treatment with an identical rehabilitation protocol. The primary outcome measure was the volume of calf muscles assessed using MRI at 3 and 18 months. The secondary outcome measures included fatty degeneration of the calf muscles and length of the affected Achilles tendon. Additionally, isokinetic plantarflexion strength was measured in both legs.ResultsAt 3 months, the study groups showed no differences in muscle volumes or fatty degeneration. However, at 18 months, the mean differences between affected and healthy soleus muscle volumes were 83.2 cm3 (17.7%) after surgery and 115.5 cm3 (24.8%) after nonsurgical treatment (difference between means, 33.1 cm3; 95% CI, 1.3-65.0; P = .042). The study groups were not substantially different in the volumes or fatty degeneration of other muscles. From 3 to 18 months, compensatory hypertrophy was detected in the flexor hallucis longus (FHL) and deep flexors in both groups. In the nonsurgical treatment group, the mean difference between affected and healthy FHL muscle volumes was -9.3 cm3 (12%) and in the surgical treatment group was -8.4 cm3 (10%) ( P ≤ .001). At 18 months, Achilles tendons were, on average, 19 mm longer in patients treated nonsurgically compared with patients treated surgically ( P < .001). At 18 months, surgically treated patients demonstrated 10% to 18% greater strength results ( P = .037). Calf muscle isokinetic strength deficits for the entire range of ankle motion correlated with soleus atrophy (ρ = 0.449-0.611; P < .001).ConclusionTreating ATRs nonsurgically with a functional rehabilitation protocol resulted in greater soleus muscle atrophy compared with surgical treatment. The mean Achilles tendon length was 19 mm longer after nonsurgical treatment than after the surgical treatment of ATRs. These structural changes partly explained the 10% to 18% greater calf muscle strength observed in patients treated with surgery compared with those treated nonsurgically. Registration: NCT02012803 ( ClinicalTrials.gov identifier).

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