*2.1. Patient Presentation and Examination*

A 45-year-old female with no medical history relevant to this injury underwent a motorcycle fall at low speed with the left lower extremity in hyperextension. She heard a snap, together with an acute intense cramping pain from the buttock region to the knee. Once at the hospital, the X-ray study did not show a bone fracture. She began a physiotherapy treatment, but, after a few days, the patient noticed a significant hematoma associated with a persistent pain (Figure 1a).

**Figure 1.** Preoperative description of the case. (**a**) Image of the haematoma two days after the accident, accompanied by lancinating pain with paresthesia similar to radicular pain. (**b**) MRI confirming the injury; the conjoint tendon was retracted 7 cm and the semimembranosus tendon 10 cm, with a significant accumulation of free fluid. (**c**,**d**) Ultrasound also showed complete disinsertion of both tendons, as well as their retraction.

In this second visit to the hospital, the performed US and MRI studies confirmed a complete detachment of conjoined tendon of biceps femoris and semitendinosus (JT), and the semimembranous tendon (SMT). After following a conservative treatment and 6 months after the accident, the patient came for the first time to our consultation reporting a significant

functional limitation. Physical examination showed a limitation in knee extension while walking, a gap distal to the left gluteal fold, and the impossibility of knee flexion against resistance with a positive Puranen–Orava test. New MRI (Figure 1b) and US (Figure 1c,d) studies showed that the JT was retracted 7 cm and the SMT 10 cm. This injury could be classified as type 5-B following the classification developed by Wood et al. [6], namely, a complete tendon avulsion from bone with a retraction of the tendon ends associated with sciatic nerve involvement.

After discussing treatment options and possible outcomes, the patient underwent a surgical intervention with a novel technique using a semitendinosus tendon allograft in a "V inversion" manner assisted with liquid PRGF injected intraosseous, intratendinously and within the suture areas, and a PRGF membrane that wrapped the sciatic nerve.
