Huddleston, Hailey P.

Background: While the biomechanical properties of the native medial patellofemoral ligament (MPFL) have been well studied, there is no comprehensive summary of the biomechanics of MPFL reconstruction (MPFLR). An accurate understanding of the kinematic properties and functional behavior of current techniques used in MPFLR is imperative to restoring native biomechanics and improving outcomes. Purpose: To provide a comprehensive review of the biomechanical effects of variations in MPFLR, specifically to determine the effect of graft choice and reconstruction technique. Study Design: Systematic review. Methods: A systematic review was performed in accordance with the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. A total of 32 studies met inclusion criteria: (1) using ≥8 human cadaveric specimens, (2) reporting on a component of MPFLR, and (3) having multiple comparison groups. Results: Gracilis, semitendinosus, and quadriceps grafts demonstrated an ultimate load to failure (N) of 206.2, 102.8, and 190.0 to 205.0 and stiffness (N/mm) of 20.4, 8.5, and 21.4 to 33.6, respectively. Single-bundle and double-bundle techniques produced an ultimate load to failure (N) of 171 and 213 and stiffness (N/mm) of 13.9 and 17.1, respectively. Anchors placed centrally and superomedially in the patella produced the smallest degree of length changes throughout range of motion in contrast to anchors placed more proximally. Sutures, suture anchors, and transosseous tunnels all produced similar ultimate load to failure, stiffness, and elongation data. Femoral tunnel malpositioning resulted in significant increases in contact pressures, patellar translation, tilt, and graft tightening or loosening. Low tension grafts (2 N) most closely restored the patellofemoral contact pressures, translation, and tilt. Graft fixation angles variably and inconsistently altered contact pressures, and patellar translation and tilt. Conclusion: Data demonstrated that placement of the MPFLR femoral tunnel at the Schöttle point is critical to success. Femoral tunnel diameter should be ≥2 mm greater than graft diameter to limit graft advancement and overtensioning. Graft fixation, regardless of graft choice or fixation angle, is optimally performed under minimal tension with patellar fixation at the medial and superomedial patella. However, lower fixation angles may reduce graft strain, and higher fixation angles may exacerbate anisometry and length changes if femoral tunnel placement is nonanatomic.

Purpose To investigate the feasibility and accuracy of 3‐dimensional (3D) iPhone scans using commercially available applications compared with computed tomography (CT) for mapping chondral surface topography of the knee. Methods Ten cadaveric dysplastic trochleae, 16 patellae, and 24 distal femoral condyles (DFCs) underwent CT scans and 3D scans using 3 separate optical scanning applications on an iPhone X. The 3D surface models were compared by measuring surface‐to‐surface least distance distribution of overlapped models using a validated 3D‐3D registration volume merge method. The absolute least mean square distances for the iPhone‐generated models from each scanning application were calculated in comparison to CT models using a point‐to‐surface distance algorithm allowing regional “inside/outside” measurement of the absolute distance between models. Results Only 1 of the 3 scanning applications created models usable for quantitative analysis. Overall, there was a median absolute least mean square distance between the usable model and CT‐generated models of 0.18 mm. The trochlea group had a significantly lower median absolute least mean square distance compared with the DFC group (0.14 mm [interquartile range, 0.13‐0.17] vs 0.19 mm [0.17‐0.25], P = .002). iPhone models were smaller compared with CT models (negative signed distances) for all trochleae, 83% of DFCs, and 69% of patellae. Conclusions In this study, we found minimal differences between a 3D iPhone scanning application and conventional CT scanning when analyzing surface topography. Clinical Relevance Emerging 3D iPhone scanning technology can create accurate, inexpensive, real‐time 3D models of the intended target. Surface topography evaluation may be useful in graft selection during surgical procedures such as osteochondral allograft transplantation.