External validation of machine learning predictive models is achieved through evaluation of model performance on different groups of patients than were used for algorithm development. This important step is uncommonly performed, inhibiting clinical translation of newly developed models. Recently, machine learning was used to develop a tool that can quantify revision risk for a patient undergoing primary anterior cruciate ligament (ACL) reconstruction (https://swastvedt.shinyapps.io/calculator_rev/). The source of data included nearly 25,000 patients with primary ACL reconstruction recorded in the Norwegian Knee Ligament Register (NKLR). The result was a well-calibrated tool capable of predicting revision risk one, two, and five years after primary ACL reconstruction with moderate accuracy. The purpose of this study was to determine the external validity of the NKLR model by assessing algorithm performance when applied to patients from the Danish Knee Ligament Registry (DKLR).

The primary outcome measure of the NKLR model was probability of revision ACL reconstruction within 1, 2, and/or 5 years. For the index study, 24 total predictor variables in the NKLR were included and the models eliminated variables which did not significantly improve prediction ability - without sacrificing accuracy. The result was a well calibrated algorithm developed using the Cox Lasso model that only required five variables (out of the original 24) for outcome prediction. For this external validation study, all DKLR patients with complete data for the five variables required for NKLR prediction were included. The five variables were: graft choice, femur fixation device, Knee Injury and Osteoarthritis Outcome Score (KOOS) Quality of Life subscale score at surgery, years from injury to surgery, and age at surgery. Predicted revision probabilities were calculated for all DKLR patients. The model performance was assessed using the same metrics as the NKLR study: concordance and calibration.

In total, 10,922 DKLR patients were included for analysis. Average follow-up time or time-to-revision was 8.4 (±4.3) years and overall revision rate was 6.9%. Surgical technique trends (i.e., graft choice and fixation devices) and injury characteristics (i.e., concomitant meniscus and cartilage pathology) were dissimilar between registries. The model produced similar concordance when applied to the DKLR population compared to the original NKLR test data (DKLR: 0.68; NKLR: 0.68-0.69). Calibration was poorer for the DKLR population at one and five years post primary surgery but similar to the NKLR at two years.

The NKLR machine learning algorithm demonstrated similar performance when applied to patients from the DKLR, suggesting that it is valid for application outside of the initial patient population. This represents the first machine learning model for predicting revision ACL reconstruction that has been externally validated. Clinicians can use this in-clinic calculator to estimate revision risk at a patient specific level when discussing outcome expectations pre-operatively. While encouraging, it should be noted that the performance of the model on patients undergoing ACL reconstruction outside of Scandinavia remains unknown.

Introduction

Tunnelwidening in failed anterior cruciate ligament reconstruction (ACLR) can result in the staged revision procedures with a need for bone transplantation prior to revision reconstruction. Limited knowledge exist regarding to quality of different transplantation methods. The present study used CT-scanning to evaluate tunnel bone density after allogenic bone chips and bone cylinder transplantation.

We hypothesized that bone chips transplantation resulted in higher bone density than bone cylinder transplantation due to possible voids between individual cylinders in the tunnels.

High tibial osteotomy (HTO) is an established treatment for medial compartment osteoarthritis of the knee; the aim being to achieve a somewhat valgus coronal alignment, thereby unloading the affected medial compartment. This study investigated knee kinematics and kinetics before and after HTO and compared them with matched control data.

A three dimensional motion analysis system and two force platforms were used to collect kinematic and kinetic data from eight patients with medial compartment knee osteoarthritis during walking preoperatively and 12 months following HTO (opening wedge). Nine control participants of similar age and the same sex were tested using the same protocol. Sagittal and coronal knee angles and moments were measured on both the operated and non-operated knees and compared between the two time points and between HTO participants and controls. In addition, preoperative and postoperative radiographic coronal plane alignments were compared in the HTO participants.

The point at which the mechanical axis passed through the knee joint was corrected from a preoperative mean of 10% tibial width from the medial tibial margin to 56% postoperatively. Stride length and walking speed both improved to essentially normal levels (1.57 m and 1.5 m/s) ostoperatively. In the coronal plane the mean peak adduction angle during stance reduced from 14.3° to 5.2° (control: 6.8°). Mean maximum adduction moments were similarly reduced to levels less than in control participants, in keeping with the aim of the surgical procedure: peak adduction moment 1: pre 3.8, post 2.7, control 3.6 peak adduction moment 2: pre 2.5, post 1.7 and control 2.6.

In the sagittal plane, both mean maximum flexion and extension during stance increased postoperatively—extension to greater than in control participants and flexion to almost control levels. The maximum external knee flexor moment during stance also increased to near normal postoperatively.

High tibial osteotomy appears to achieve the intended biomechanical effects in the coronal plane (reduced loading of the medial compartment during stance). At the same time there were improvements in sagittal plane kinematics and kinetics which may reflect a reduction in pain. The net effect was to reduce quadriceps demand.

Aim: In order to monitor the developments in anterior cruciate ligament (ACL) reconstruction and clinical outcome, a national clinical database for knee ligament surgery (Danish ACL Registry) was established in 2005. This study presents data for 2 years national production of ACL reconstructions from the Danish ACL registry.

Methods: All clinics performing ACL reconstructions in Denmark reports to the database. The database is divided into surgeon data and patient data. The surgeon reports anamnestic, objective knee laxity and operative data including graft and implant choices. At one year control, complications, reoperations and objective knee laxity are recorded. The patient registers the KOOS knee score and Tegner function score preoperatively and at 1, 5 and 10 years follow-up. A specific set of indicators that define good diagnostic procedures and clinical outcome have been specified.

Results: During the first 24months, more than 5000 knee-ligament reconstructions were registered. 84 % were primary ACL recontruction, 7,7 % were ACL revisions 8,4 %were multiligament reconstructions. 90 % of all departments reported to the database. 71 % of primary ACL reconstruction used hamstring tendon grafts and 21 % used patella tendon graft. Meniscus injuries were treated in 35 % of all patients. 17 % had significant cartilage lesions. Follow-up KOOS scores demonstrated specific differences between primary ACL, revision ACL and multiligament reconstructions.

Conclusion: This study presents epidiomiology and follow-up data a national ACL reconstruction registry. These data will become new international reference materials for outcome measures before and after ACL surgery. The database will enable future monitoring of developments in ACL reconstruction techniques and outcome.

Since the approval of parathyroid hormone (PTH) as an anabolic treatment for osteoporosis, PTH has increasingly been investigated for other potential clinical uses such as bone repair and regeneration. The microstructure of newly formed bone during distraction osteogenesis enhanced by PTH treatment has yet to be studied. Therefore, the purpose of the study was to investigate the effects of intermittent parathyroid hormone PTH (1–34) treatment on the microstructure of regenerated bone during distraction osteogenesis in rabbits. After tibial mid-diaphyseal osteotomy the callus was distracted 1 mm/day for 10 days. The rabbits were divided in to 3 groups, which daily received a PTH injection for 30 days, a saline injection for 10 days and a PTH injection for 20 days, or a saline injection for 30 days. The new-trabecular structure of the regenerate callus was assessed by micro computed tomography (μCT). In all 51 specimen obtained from the lengthened tibia were scanned and evaluated morphometrically using three different volume of interests. The investigated μCT parameters included trabecular number Tb.N*, trabecular thickness Tb.Th*, trabecular separation Tb.Sp*, bone volume fraction (BV/TV), bone volume (BV), connectivity density (CD), and degree of anisotropy (DA). The results showed that intermittent treatment with PTH during distraction osteogensis resulted in a significantly higher Tb.N*, a more isotropic trabecular orientation, a higher connectivity density, and a higher bone mass. We also found preliminary evidence suggesting that the newly regenerated calluses treated with PTH were more mature than the non-treated calluses. In conclusion: the study demonstrated that treatment with PTH resulted in an enhanced microstructure of the newly regenerated bone indicating that PTH has a potential role as a stimulating agent for distraction osteogenesis.

INTRODUCTION: Medial open-wedge HTO is an alternative in the treatment of medial knee OA for the young and active patient. However this technique leaves an open gap that requires stable fixation to achieve bony healing. As a bone substitute injectable calcium-phosphate-cements could be an alternative to autograft.

MATERIAL AND METHODS: Biomechanical testings were performed on open wedge HTO to investigate load to failure and displacement after cyclic loading (viscous and/or damaged material response). A medial 10 mm open-wedge osteotomy was performed on 7 pairs of composite (Sawbone) left tibiaes, and 8 pairs of preserved cadaver tibiaes. Osteosynthesis where performed with the Dynafix system. In half of the bones the gap was filled with 15 g of Calcibon®. The composite tibiaes were loaded at a ramp speed of 20 mm/min and failures of the constructs were recorded visually. On the cadaver tibiaes, cyclical loading were performed with a maximum load of 2250 N.

RESULTS: Filling of the gap with Calcibon® resulted in significant different load-to-failure patterns with failure at 10.2 kN compared to 2.7 kN in the group without Calcibon®. Displacement at the end of cyclical loading was 1.2 mm in the group with Calcibon® and 2.7 mm in the group without Calcibon®. This difference also was significant.

CONCLUSION: The injectable calcium-phosphate-cement Calcibon® enhances primary stability during load to failure and during cyclical loading in open wedge osteotomies on proximal tibia. Clinical studies are performed to investigate whether Calcibon® has any clinical advantage on wedge healing and stability.