Biomechanical and histological comparison between the cryopreserved and the lyophilized Gracilis tendon allograft for MPFL reconstruction, a cadaveric experimental study

BACKGROUND Medial patellofemoral ligament (MPFL) is the main restrictor of lateral shifting of the patella, contributing by 60 % in the first 20° flexion of the knee. MPFL reconstruction has been performed in order to restore the stability of the patella with good results.Lyophilized Gracilis tendon allograft (LGA) compared to Cryopreserved Gracilis tendon allograft (CGA) has a lower cost, does not require to maintain cooling chain or preparation. The purpose of this study is to compare the histological and biomechanical characteristics of an experimental model of reconstruction of the MPFL in porcine patellas with LGA versus CGA. METHODS Randomized controlled experimental study in porcine model conducted on 36 porcine patellas in which 18 were intervened with LGA and 18 were intervened with CGA. The confluent tunnel technique was used for MPFL reconstruction. Maximum tensile force, allograft elongation and stiffness of the construct were measured. The cellularity and collagen tissue distribution were evaluated in the allografts. The histological and biomechanical characteristics of the LGA were compared to those of the CGA. RESULTS The median of the maximum tensile force for the LGA group was 299.63 N and 280.86 N for the CGA group (p = 0.45). The median of the stiffness was 57.86 N/mm for the LGA and 54.23 N/mm for the CGA (p = 0.2). The median of the elongation for the LGA was 5.95 mm and 6.12 mm for the CGA (p = 0,29). The bone bridge failed in 88.88 % of the constructs with LGA and 94.44 % in those with CGA (p = 0.5). CONCLUSIONS No differences were observed between the LGA group and the CGA group in maximum tensile force, elongation, stiffness, site of rupture and histological characteristics. The use of a lyophilized Gracilis tendon allograft for MPFL reconstruction confers the same histological and biomechanical characteristics as a cryopreserved Gracilis tendon allograft.