Comparison of Initial Stability of Oblong, Large Circular, and Multiple-Plug “Snowman” Osteochondral Autografts for Elongated Focal Cartilage Lesions: A Biomechanical Study in a Porcine Model

Abstract

Background: Distal femoral osteochondral allograft transplantation (OAT) is an effective treatment of osteochondral lesions in the knee measuring >2 cm2 in select patients. Prior studies have demonstrated that the morphology of the plug can affect graft-host interference fit. To our knowledge, there are no data comparing the initial biomechanical stability of standard cylindrical plugs with multiple-plug and oblong-plug morphologies. Hypothesis: Large cylindrical single-plug (LCSP) and oblong single-plug (OSP) grafts will have greater pull-out strength, and therefore greater initial stability, than multiple-plug (MP) grafts in a cadaveric porcine femur model. Study Design: Controlled laboratory study. Methods: A total of 55 porcine distal femurs were divided into 3 groups—LCSP (n = 18), OSP (n = 19), and MP (n = 18)—according to the plug morphology used. The method of graft harvesting and implantation was based on technique guides for the respective implant systems. The sizes (length × width × depth) of the osteochondral defects created in each of the groups were approximately 20.2 × 20.2 × 9.4–mm for the LCSP group, 14.4 × 30.5 × 7.9–mm for the OSP group, and 14.8 × 14.8 × 9.9–mm for the MP group. Tensile testing was performed on each graft to determine pull-out strength. Results: The pull-out strength was significantly lower in the OSP group (65.7 N) versus the LCSP (133 N; P = .0005) and the MP (117.6 N; P = .001) groups. There was no statistically significant difference in pull-out strength between the LCSP and MP groups ( P = .42). There were no statistically significant differences in displacement at maximum load among any 2 of the 3 groups. Conclusion: These findings suggest that while initial stability may play a role in the clinical outcomes of osteochondral allograft (OCA) implantation, the biological milieu in vivo for each graft setting perhaps has a greater impact on the success of an OAT procedure. Further study is needed on the relationship between OCA biomechanics and clinical outcomes of OAT.

Humeral Head Reconstruction With Osteochondral Allograft: Bone Plug Optimization for Hill-Sachs Lesions Using CT-Based Computer Modeling Analysis

“…There is limited biomechanical evidence to compare single-plug and multiple-plug OCA transplantation for the treatment of HSLs. A biomechanical study in a porcine model by Dwivedi et al 5 demonstrated that there was no significant difference in pull-out strength and displacement in maximum load between the large cylindrical single plug and multiple plugs OCA transplantation. Results from their study showed good initial stability for the multiple plugs OCA; however, further in vivo study is needed to validate stability, healing process, and clinical outcomes.…”

Characterizing Osteochondral Allograft Biomechanics for Optimizing Transplant Success: A Systematic Review

“…Resistance to pull-out and push-in forces is higher in press-fit cylindrical single-plug grafts that are greater in diameter and depth and are "bottomed out." 54,62,63 For these grafts, larger diameter, thinner, perfect-depth grafts are more likely to resist subsidence. 63,64 Depths less than 7 mm are at greater risk for displacement and subsequent biomechanical failure, while greater depths are associated with biological failure mechanisms.…”

“…7 For autografts and allografts, using multiple plugs to treat a single articular defect is discouraged based on reduced graft stability, decreased ability to resist axial loading, poor restoration of articular surface contour, and inferior interface healing and integration. 13,54,56 Emerging techniques that include instrumentation to fabricate elliptical OCAs that may allow for a single graft to be used to treat defects that might otherwise require multiple overlapping plugs may be advantageous. 18 However, fabrication requires impacting the graft, indications are limited by graft size, shape, and anatomic locations, and early failures have been reported.…”

“…As OCA size and geometric complexity increase such that multiple-plug, elliptical, or custom-cut anatomic grafts are required, successful osteointegration becomes more challenging. [54][55][56] Thermal and/or impact energy delivered to the graft during fabrication and implantation can result in mechanical and/or biological failure. 57 Impact energy should not exceed 15 to 20 Mpa to prevent acute cartilage degeneration.…”