Comparisons of the morbidities of a double gastrocnemius flap and a medial gastrocnemius flap in the orthoplastic reconstruction around the knee

Background: The pedicled gastrocnemius flap is commonly used to treat lower limb defects. Either the medial, lateral, or both heads can be used. When extended soft tissue defects are present, a double gastrocnemius (DG) flap may be used. However, no data of the additional donor site morbidity compared to a medial gastrocnemius (MG) flap are available. The aim of this study was to compare the donor site morbidity of a DG with that of a MG. Methods: Patients with a soft tissue defect around the knee, treated with a gastrocnemius flap between 2018 and 2021 at the University Hospital of Lausanne and Bari, with a minimum follow-up of 12 months, were included. According to the size and the position of the defect, it was decided whether one (10 patients) or two (9 patients) heads of the gastrocnemius were necessary for the coverage. The mean age was 61 years (range 42-82) in DG, and 63 years (range 45-78) in MG. The average defect size was 89.8 cm2 in the DG group and 53.4 cm2 in the MG group. The etiologies were trauma (n = 10), infection (n = 7) and sarcoma (n = 2). A medial approach or a posterior midline approach was used for the harvesting of the gastrocnemius muscle. Once the flap was harvested, it was rotated and transposed anteriorly over the defect, either through a subcutaneous tunnel or by dividing the intervening skin bridge, depending on the soft tissue defect. A split-thickness skin graft was used to close the skin over the remaining exposed muscle flap. The active range of motion of the ankle and knee joints was measured. Muscle strength was assessed with a hand-held dynamometer and by the ability to stand on tiptoe. Physical function was evaluated through the Lower Extremity Functional Scale (LEFS). Results: The two groups were homogeneous, with no significant difference in age, sex, and BMI. All flaps survived in both groups. Both groups showed lower values in strength and range of motion of the operated leg, when compared to contralateral side. In plantar flexion, this accounted for a reduction in MG by 3.8 ± 1.0 kg of strength and 8 ± 3° of ROM, and in DG by 4.7 ± 1.7 kg and 16 ± 4°, respectively. For knee flexion, the reduction in MG was 4.4 ± 0.6 kg and 16 ± 7°, while in DG 5.6 ± 1.0 kg and 28 ± 6°. In the MG group, 60% were able to stand on the tiptoe of the operated leg, as opposed to 0% in DG. The average LEFS score in DG was lower by 10.9 points (p < .05). Questions concerning running and jumping had a lower score in DG (p < .01). Conclusions: The harvesting of both gastrocnemii led to significant additional donor site morbidity compared to the harvesting of the medial gastrocnemius alone. However, the additional morbidity did not have an impact on activities of daily living and walking, even though it limited the ability to perform more demanding tasks such as running and jumping. Therefore, based on our study, the choice of a DG flap should be critically assessed in younger, more demanding patients.