• Juuso Heikkinen, Iikka Lantto, Juuso Piilonen, Tapio Flinkkilä, Pasi Ohtonen, Pertti Siira, Vesa Laine, Jaakko Niinimäki, Ari Pajala, and Juhana Leppilahti.
• 1Division of Orthopaedic and Trauma Surgery, Department of Surgery (J.H., I.L., J.P., T.F., P.O., A.P., and J.L.), Department of Physical Medicine and Rehabilitation (P.S. and V.L.), and Department of Diagnostic Radiology, Institute of Diagnostics (J.N.), Oulu University Hospital, Medical Research Center, University of Oulu, Oulu, Finland.
• J Bone Joint Surg Am. 2017 Sep 20; 99 (18): 1509-1515.

BackgroundIn this prospective study, we used magnetic resonance imaging (MRI) to assess long-term Achilles tendon length, calf muscle volume, and muscle fatty degeneration after surgery for acute Achilles tendon rupture.MethodsFrom 1998 to 2001, 60 patients at our center underwent surgery for acute Achilles tendon rupture followed by early functional postoperative rehabilitation. Fifty-five patients were reexamined after a minimum duration of follow-up of 13 years (mean, 14 years), and 52 of them were included in the present study. Outcome measures included Achilles tendon length, calf muscle volume, and fatty degeneration measured with MRI of both the affected and the uninjured leg. The isokinetic plantar flexion strength of both calves was measured and was correlated with the structural findings.ResultsThe Achilles tendon was, on average, 12 mm (95% confidence interval [CI] = 8.6 to 15.6 mm; p < 0.001) longer (6% longer) in the affected leg than in the uninjured leg. The mean volumes of the soleus and medial and lateral gastrocnemius muscles were 63 cm (13%; p < 0.001), 30 cm (13%; p < 0.001), and 16 cm (11%; p < 0.001) lower in the affected leg than in the uninjured leg, whereas the mean volume of the flexor hallucis longus (FHL) was 5 cm (5%; p = 0.002) greater in the affected leg, indicating FHL compensatory hypertrophy. The median plantar flexion strength for the whole range of motion ranged from 12% to 18% less than that on the uninjured side. Finally, the side-to-side difference in Achilles tendon length correlated substantially with the strength deficit (ρ = 0.51, p < 0.001) and with medial gastrocnemius (ρ = 0.46, p = 0.001) and soleus (ρ = 0.42, p = 0.002) muscle atrophy.ConclusionsIncreased Achilles tendon length is associated with smaller calf muscle volumes and persistent plantar flexion strength deficits after surgical repair of Achilles tendon rupture. Strength deficits and muscle volume deficits are partly compensated for by FHL hypertrophy, but 11% to 13% deficits in soleus and gastrocnemius muscle volumes and 12% to 18% deficits in plantar flexion strength persist even after long-term follow-up.Level Of EvidenceTherapeutic Level II. See Instructions for Authors for a complete description of levels of evidence.

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