Proximal and mid-thigh fascia lata graft constructs used for arthroscopic superior capsule reconstruction show equivalent biomechanical properties: an in vitro human cadaver study

Abstract

Background: The proximal fascia lata (FL) graft construct used for arthroscopic superior capsule reconstruction (ASCR) is openly harvested, whereas the mid-thigh FL graft construct is minimally invasively harvested. The purpose of the current study was to compare the biomechanical properties of proximal thigh and mid-thigh-harvested FL graft constructs used for ASCR. The hypothesis was that, despite the different morphological characteristics of the proximal thigh and mid-thigh FL graft constructs used for ASCR, their biomechanical properties would not significantly differ. This information may assist orthopedic surgeons in the choice of the harvest location, technique, and type of graft construct for ASCR.

Methods: Forty FL specimens, 20 proximal thigh and 20 mid-thigh, were harvested from the lateral thighs of 10 fresh human cadavers (6 male, 4 female; average age, 58.60 ± 17.20 years). The thickness of each 2-layered proximal thigh and 6-layered mid-thigh FL graft construct was measured. Each construct was mechanically tested in the longitudinal direction, and the stiffness and Young's modulus were computed. Data were compared by Welch's independent t-test and analysis of variance, and statistical significance was set at P < .05.

Results: The average thickness of the proximal thigh FL graft construct (7.17 ± 1.97 mm) was significantly higher than that of the mid-thigh (5.54 ± 1.37 mm) [F (1,32) = 7.333, P = .011]. The average Young's modulus of the proximal thigh and mid-thigh graft constructs was 32.85 ± 19.54 MPa (range, 7.94 - 75.14 MPa; 95% confidence interval [CI], 23.71 - 42.99) and 44.02 ± 31.29 MPa (range, 12.53 -120.33 MPa; 95% CI, 29.38 - 58.66), respectively. The average stiffness of the proximal thigh and mid-thigh graft constructs was 488.96 ± 267.80 N/mm (range, 152.96 - 1086.49 N/mm; 95% CI, 363.63 - 614.30) and 562.39 ± 294.76 N/mm (range, 77.46 - 1229.68 N/mm; 95% CI, 424.44 - 700.34), respectively. There was no significant difference in the average Young's modulus or stiffness between the proximal thigh and mid-thigh graft constructs (P = .185 and P = .415, respectively).

Conclusion: Despite the different morphological characteristics of the proximal thigh and mid-thigh FL graft constructs used for ASCR, their Young's modulus and stiffness did not significantly differ.

Keywords: Arthroscopic superior capsular reconstruction; Autograft; Fascia lata; Harvest; Irreparable rotator cuff tear; Minimally invasive; Stiffness; Superior capsule reconstruction.

Figure 1

Picture of the (A) proximal thigh and (B) mid-thigh harvest of the fascia lata (FL) of the left thigh of subject 1. P, proximal thigh-harvested FL; M, mid-thigh-harvested FL.

Figure 2

Fascia lata (FL) specimens. Measurement of the mid-thigh FL (A) single layer and (B) final 6-layered thrice-folded graft construct using the digital caliper, positioned at one of the 6 random points. (C) Final proximal thigh graft construct with the mattress suturing in the middle of the graft and peripheral sutures (white-colored sutures), and (D) final mid-thigh graft construct with peripheral suturing, showing that the FL layers are folded so that the FL fibers are longitudinally directed (the white arrows point from proximal to distal in each graft construct).

Figure 3

Experimental setup. (A) Universal testing machine with the Standard Video Extensometer: the graft construct sample is centrally placed between the pneumatic grips; (B) the white arrows point to the markings of the 2 control points on the graft construct used for the optical strain measurement. (C) The proximal and distal ends of the graft construct are clamped on the pneumatic action grips of the universal testing machine, and the dashed arrow represents the longitudinal direction of the fibers of the graft and of the test. C, clamps of the pneumatic action grips; G, graft construct; SVE, Standard Video Extensometer.

Figure 4

(A) Stiffness and (B) Young’s modulus of the graft constructs according to the location of the harvest. The “X” inside the bars represent the mean values; the horizontal lines inside the bars represent the medians.