Inoue, Nozomu

Background: Osteochondral allograft (OCA) transplantation is an important surgical technique for full-thickness chondral defects in the knee. For patients undergoing this procedure, topography matching between the donor and recipient sites is essential to limit premature wear of the OCA. Currently, there is no standardized process of donor and recipient graft matching. Purpose: To evaluate a novel topography matching technique for distal femoral condyle OCA transplantation using 3-dimensional (3D) laser scanning to create 3D-printed patient-specific instrumentation in a human cadaveric model. Study Design: Descriptive laboratory study. Methods: Human cadaveric distal femoral condyles (n = 12) underwent 3D laser scanning. An 18-mm circular osteochondral recipient defect was virtually created on the medial femoral condyle (MFC), and the position and orientation of the best topography-matched osteochondral graft from a paired donor lateral femoral condyle (LFC) were determined using an in silico analysis algorithm minimizing articular step-off distances between the edges of the graft and recipient defect. Distances between the entire surface of the OCA graft and the underneath surface of the MFC were evaluated as surface mismatch. Donor (LFC) and recipient (MFC) 3D-printed patient-specific guides were created based on 3D reconstructions of the scanned condyles. Through use of the guides, OCAs were harvested from the LFC and transplanted to the reamed recipient defect site (MFC). The post-OCA recipient condyles were laser scanned. The 360° articular step-off and cartilage topography mismatch were measured. Results: The mean cartilage step-off and graft surface mismatch for the in silico OCA transplant were 0.073 ± 0.029 mm (range, 0.005-0.113 mm) and 0.166 ± 0.039 mm (range, 0.120-0.243 mm), respectively. Comparatively, the cadaveric specimens postimplant had significantly larger step-off differences (0.173 ± 0.085 mm; range, 0.082-0.399 mm; P = .001) but equivalent graft surface topography matching (0.181 ± 0.080 mm; range, 0.087-0.396 mm; P = .678). All 12 OCA transplants had mean circumferential step-off differences less than a clinically significant cutoff of 0.5 mm. Conclusion: These findings suggest that the use of 3D-printed patient-specific guides for OCA transplantation has the ability to reliably optimize cartilage topography matching for LFC to MFC transplantation. This study demonstrated substantially lower step-off values compared with previous orthopaedic literature when also evaluating LFC to MFC transplantation. Using this novel technique in a model performing MFC to MFC transplantation has the potential to yield further enhanced results due to improved radii of curvature matching. Clinical Relevance: Topography-matched graft implantation for focal chondral defects of the knee in patients improves surface matching and has the potential to improve long-term outcomes. Efficient selection of the allograft also allows improved availability of the limited allograft sources.

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.

Purpose (1) To determine the area of posterior cruciate ligament (PCL) insertion sites on the lateral wall of the medial femoral condyle (LWMFC) that demonstrates the least amount of length change through full range of motion (ROM) and (2) to identify a range of flexion that would be favorable for graft tensioning for single‐bundle (SB) and double‐bundle (DB) PCL reconstruction. Methods Six fresh‐frozen cadaveric knees were obtained. Three‐dimensional computed tomography point‐cloud models were obtained from 0° to 135°. A point grid was placed on the LWMFC and the tibial PCL facet. Intra‐articular length was calculated for each point on the femur to the tibia at all flexion angles and grouped to represent areas for bone tunnels of SB and DB PCLR. Normalized length changes were evaluated. Results Femoral tunnel location and angle of graft fixation were significant contributors to mean, minimum, and maximum normalized length of the PCL (all p < .001). Tibial tunnel location was not significant in any case (all p < .22). A femoral tunnel in the location of the posteromedial bundle of the PCL resulted in the least length change at all tibial positions (maximum change 13%). Fixation of the anterolateral bundle in extension or at 30° flexion resulted in significant overconstraint of the PCL graft. The femoral tunnel location for a SB PCLR resulted in significant laxity at lower ranges of flexion. Conclusion PCL length was significantly dependent on femoral tunnel position and angle of fixation, whereas tibial tunnel position did not significantly contribute to observed differences. All PCL grafts demonstrated anisometry, with the anterolateral bundle being more anisometric than the posteromedial bundle. For DB PCLR, the posteromedial bundle demonstrated the highest degree of isometry throughout ROM, although no area of the LWMFC was truly isometric. The anterolateral bundle should be fixed at 90° to avoid overconstraint, and SB PCLR demonstrated significant laxity at lower ranges of flexion. Clinical Relevance Surgeons can apply the results of this investigation to surgical planning in PCLR to optimize isometry, which may ultimately reduce graft strain and the risk of graft failure. Additionally, DB PCLR demonstrated superiority compared with SB PCLR regarding graft isometry, as significant laxity was encountered at lower ranges of flexion in SB PCLRs. Fixation of the ALB at 90° flexion should be performed to avoid overconstraint in knee extension.

Objective To analyze the topography of the opposite condyle to treat focal femoral condyle articular defects with an osteochondral allograft (OCA). Design Three groups were created: Group 1, same condyle with same width; Group 2, opposite condyle with same width; Group 3, opposite condyle with different width. Computed tomography (CT) of 22 cadaveric femoral hemi-condyles was used to create 3-dimensional CT models that were exported into point-cloud models. Three zones of the donor condyle (anterior, middle, and posterior) were quantified. Four defect sizes were created (15, 18, 23, 25 mm) at the weight-bearing region. The defect was moved throughout each donor condyle zone and the least distance was calculated, defined as the shortest distance between the defect and the donor condyle. Results The mean least distance increased with larger defect size in all groups, yet there was a less than 0.2 mm difference in the least distance among defect sizes. The 15, 18, and 23 mm defect models in Group 1 exhibited greater least distances at the anterior than middle and posterior zones. The 15 mm defect model exhibited greater least distance at the anterior zone than posterior zone in Group 3. However, there was a less than 0.05 mm difference in the mean least distance between zones. There was no significant difference in the least distance between groups. Conclusion OCAs from opposite condyles yield similar topographic matching to OCAs from the same condyles, suggesting that opposite condyles can be utilized. Clinical correlation and outcomes are necessary.