Anterior cruciate ligament (ACL) ruptures are debilitating injuries, often managed via ACL reconstruction (ACLR). Reduced range of motion (ROM), particularly loss of extension (LOE), is the most significant contributor to post-operative patient dissatisfaction. LOE may preclude return to sport, increase re-rupture rates and precipitate osteoarthritis. Passive LOE rates following ACLR have been reported at 15%. However, LOE incidence during active tasks are poorly characterised. Our review sought to determine knee extension angles for active tasks following an ACL injury or ACLR. We hypothesised greater incidences of active LOE following ACL injury or ACLR, compared to uninjured contralateral limbs or controls. We systematically searched MEDLINE, Embase, Cochrane Library, Scopus, SPORTDiscus, and relevant trials databases for English articles. Included were cohort, cross-sectional, case-controlled or randomised controlled trials analysing adults with ACL injury treated surgically or otherwise, with at least 12-weeks follow-up and reporting either active knee extension angle, active LOE angles or incidence of active knee LOE during functional tasks. The protocol was registered on PROSPERO (CRD42018092295). Subsequent meta-analysis was performed. After screening, 71 eligible articles were included. Studies were heterogenous in design and quality. Included tasks were overground walking (n=44), running (n=3), hopping/jumping/cutting (n=11) single-leg landing (n=7), and stair climbing (n=6). LOE incidence varied depending on functional activities (33.95-92.74%). LOE incidence did not vary depending on ACL status (67.26% vs. 65.90% vs. 62.57% for ACL intact, ACLD and ACLR, respectively). We observed no difference in active LOE incidence according to ACL status. Importantly, the observed incidence for active LOE was reliably higher than previously reported rates for passive measures. Given the discrepancy between active and passive LOE incidence, clinicians may advisably prioritise active ROM during ACL rehabilitation

After anterior cruciate ligament (ACL) rupture, reconstructive surgery with a hamstring tendon autograft is often performed. Despite overall good results, ACL re-rupture occurs in up to 10% of the patient population, increasing to 30% of the cases for patients aged under 20 years. This can be related to tissue remodelling in the first months to years after surgery, which compromises the graft's mechanical strength. Resident graft fibroblasts secrete matrix metalloproteinases (MMPs), which break down the collagen I extracellular matrix. After necrosis of these fibroblasts, myofibroblasts repopulate the graft, and deposit more collagen III rather than collagen I. Eventually, the cellular and matrix properties converge towards those of the native ACL, but full restoration of the ACL properties is not achieved. It is unknown how inter-patient differences in tissue remodelling capacity contribute to ACL graft rupture risk. This research measured patient-specific tissue remodelling-related properties of human hamstring tendon-derived cells in an in vitro micro-tissue platform, in order to identify potential biological predictors for graft rupture. Human hamstring tendon-derived cells were obtained from remnant autograft tissue after ACL reconstructions. These cells were seeded in collagen I gels on a micro-tissue platform to assess inter-patient cellular differences in tissue remodelling capacity. Remodelling was induced by removing the outermost micro-posts, and micro-tissue compaction over time was assessed using transmitted light microscopy. Protein expression of tendon marker tenomodulin and myofibroblast marker α-smooth muscle actin (αSMA) were measured using Western blot. Expression and activity of remodelling marker MMP2 were determined using gelatin zymography. Cells were obtained from 12 patients (aged 12–51 years). Patient-specific variations in micro-tissue compaction speed or magnitude were observed. Up to 50-fold differences in αSMA expression were found between patients, although these did not correlate with faster or stronger compaction. Surprisingly, tenomodulin was only detected in samples obtained from two patients. Total MMP2 expression varied between patients, but no large differences in active fractions were found. No correlation of patient age with any of the remodelling-related factors was detected. Remodelling-related biological differences between patient tendon-derived cells could be assessed with the presented micro-tissue platform, and did not correlate with age. This demonstrates the need to compare this biological variation in vitro - especially cells with extreme properties - to clinical outcome. Sample size is currently increased, and patient outcome will be determined. Combined with results obtained from the in vitro platform, this could lead to a predictive tool to identify patients at risk for graft rupture

Anterior cruciate ligament (ACL) rupture with associated meniscal pathology commonly occurs in a young, active population. Preserving a greater proportion of the meniscus may improve long-term outcomes by maintaining shock absorption and knee stability. However, meniscal repair procedures involve longer healing and rehabilitation than meniscal debridement, which could affect return to work and activity. The purpose of this study was to examine the functional outcomes and quality of life scores through two years in patients undergoing ACL reconstruction (ACL-R) who had meniscal repair, meniscal debridement, or no meniscal damage at the time of reconstruction. Data for 1814 skeletally mature patients with isolated primary ACL-R was prospectively collected at a single centre from January 2010 to December 2015. Functional testing of operative to non-operative limb performance was completed at one- and two-years following surgery and included single-leg balance, single-leg hop for distance, timed six-meter hop, triple-hop for distance, and triple cross-over hop for distance. ACL-Quality-of-life questionnaires (ACL-QoL) were completed pre-operatively and at 1- and 2-years post-operatively. Descriptive statistics were completed for patient demographics and intra-operative pathology. Unpaired t-tests using 95% confidence intervals were conducted to compare groups. The patient cohort was 45% female, with a mean age of 31 years (SD 11, range 14–66). Meniscal injury was detected in 1229/1814 knees (67.8%). There were 729 debridements and 538 repairs performed. Graft choice was hamstring autograft in 85.8% of cases, bone-patellar-tendon-bone autograft in 2.5%, allograft in 10.1% and other graft types in 1.5%. Pre-operative ACL-QoL scores were 29 and 28.5 for knees without and with meniscal damage, respectively (p>0.05). Of 1814 patients, 1269 (69.9%) completed the ACL-QoL at the two-year appointment, and 1225 (67.5%) completed the functional testing. At two years post-operative, patients with no meniscal damage at surgery demonstrated superior limb symmetry performance on triple-hop for distance compared to patients with meniscal damage (98.4% vs 97.1%, p < 0 .05, CI 0.1–2.5%). No other functional testing parameters showed statistical significance. There was no difference in functional outcome between patients undergoing an isolated meniscal repair versus debridement at one- or two-years. ACL-QoL scores were statistically significantly higher at one- and two-years post-operative for patients without meniscal damage (1-year: 73 vs 70.2, p < 0 .05, CI 0.51–5.1, 2-years: 79.2 vs 76.1, p < 0 .05, CI 0.79–5.4). ACL-QoL scores were minimally higher for isolated meniscal debridement compared to isolated meniscal repair at both time points (1-year: 71.4 vs 68, p < 0 .05, CI 0.4–6.4, 2-years: 78.3 vs 74, p < 0 .05, CI 1.3–7.3). Functional outcomes do not differ at one or two years post-operatively for patients undergoing meniscal repair versus debridement concomitant with ACL-R. Quality of life scores were statistically significantly higher for the patients with no meniscal pathology at both one- and two-years post-operative. ACL-QoL scores were also statistically significantly different for the meniscal repair and debridement groups however these differences are unlikely to be clinically significant. Extended follow-up is needed to determine if the differences detected in ACL-QoL scores are sustained over time, as well as the long-term role of meniscal injury on functional outcomes

With associated snow sports injury risks being well documented, the scope for preventative medicine is clear. This article focuses on potential precautions taken by skiers/snowboarders and how they vary between different snow sport groups. A total of 181 randomly selected individuals from the Whistler/Blackcomb Medical Centre, Canada, took part in this questionnaire-based cohort study, examining snow sports activity, preventive measures, and protective equipment use. Most individuals were ski area residents of advanced expertise, with 50% having had a previous snow-riding injury. The most commonly reported significant ski injury was anterior cruciate ligament (ACL) rupture, while in snowboarders, it was wrist fracture. Skiers were more likely to improve fitness levels before going onto the slopes, whereas crossover riders (both skiing and snowboarding) were more likely to take lessons. Most individuals used eye and sun protection and had adequately warm clothing. Beyond basic precautions, protective equipment and preventive measures are used infrequently. It is suggested that by increasing awareness and use of such equipment, injury rates may be reduced

Early stabilisation after an anterior cruciate ligament (ACL) rupture reduces future meniscal injury. We may therefore expect protection of articular cartilage from ACL reconstruction, but this has yet to be shown. Our aim wasto determine the effect of meniscal injury on the long term risk of osteoarthritis (OA) following ACL reconstruction using Single Photon Emission Computed Tomography (SPECT, a 3 dimensional radionuclide scan). We studied a prospective series of 31 patients (mean age at injury of 29 years) who had bone-patellar tendon-bone ACL reconstruction for unstable, ACL deficient knees. Mean follow-up was 10 years (range 9-13). Patients were separated into two groups according to the status of their menisci at the time of ACL reconstruction, those with intact menisci in group 1 (n=15) and those who required partial meniscectomy in group 2 (n=16). The contra-lateral normal knee was used as a control. All knees were clinically stable with high clinical scores (mean Lysholm score 93 and mean Tegner activity score 6). In group 1 (intact menisci) only one patient (7%) had clinical symptoms of OA and was the only patient with increased uptake on SPECT compatible with early OA. In group 2 (partial meniscectomy), two had clinical symptoms of osteoarthritis, and five patients (32%) had increased uptake on SPECT compatible with early OA. None of the control knees had early OA on SPECT. The prevalence of OA 10 years post ACL reconstruction, using the most sensitive investigation available, is very low in patients who had intact menisci (7%), but increases 5 fold (32%) if a meniscal tear was present. We recommend early ACL reconstruction to preserve the menisci to minimise the long term risk of OA

Introduction. Anterior cruciate ligament (ACL) rupture is a common sporting injury, often managed surgically with patella-tendon or hamstrings autograft. Surgeons are under increasing pressure for open transparent assessment of their performance. Scoring systems can be used to assess outcome. More than 50 different scoring systems have been identified to assess the ACL deficient knee. Aims. The survey is investigating the use of ACL scoring systems between knee surgeons in the United Kingdom as a method of assessing performance. Method. 134 knee surgeons in the United Kingdom, performing ACL reconstruction, were asked to complete a written questionnaire regarding their use of scoring systems & outcome measures. Written questionnaires were sent and responses were received by post. Results. 81 (60%) surgeons responded to the questionnaire by stating their preferred scoring system. 40 (49%) surgeons routinely use ACL scoring systems versus 41 (51%) surgeons who do not. The Lysholm (I and II) knee scoring scale (80%) and Tegner activity score (67.5%) were most commonly used (57.5% both of them) followed by the Knee injury and osteoarthritis outcome score (KOOS) (30%), International Knee Documentation Committee (IKDC) subjective knee score (22.5%), Medical Outcome Study 12 Item Short Form (SF12) (20%), the Medical Outcome Study 36 Item Short Form (SF 36) (12.5%), Cincinnati Knee Scoring System (10%), and ACL Quality of Life scoring system (7.5%). Recommendations. The routine use of ACL scoring systems by 49% of surgeons raises the question - should all surgeons be using scoring systems in their ACL practice? This would be relatively easy to do as most patients are followed up post operatively for 6 months. This will help to adopt a transparent assessment of the performance of every consultant to the procedure they perform

Aim: We conducted a prospective, randomised study of 50 patients, 40 (80%) male and 10 (20%) female, with anterior cruciate ligament (ACL) rupture to compare the results of ligament reconstruction by middle third patellar tendon graft (M) or synthetic Leeds-Keio (LK) ligament. Method: The patients were randomised into two groups. 26 (52%) underwent PTG repair and 24 (48%) LK repair. Subjective knee function was classified using the Lysholm score, Tegner activity score and IKDC grading. Laxity was tested by clinical examination including anterior draw, pivot shift and arthrometric measurements using the Stryker Laxometer (Stryker Corporation, Kalamazoo, Michigan, USA). Results: We present the early (two to five-year follow-up) results of this on-going trial. There was no statistical difference between the two groups in activity levels, both pre-injury and current. However, both pivot shift and anterior laxity were significantly greater in the LK group at two years and greater. Discussion: While the LK group did develop significantly greater laxity, it is demonstrated that the functional outcome is not affected. We conclude therefore that if the results of surgery were to be based on a functional outcome rather than objective measurements of laxity, it would seem logical that the LK is an acceptable alternative to autogenous PTG. However whilst function appears to be as good the less successful objective criteria do suggest reservations for the long term results of the Leeds-keio graft

The management of symptomatic single bundle Anterior Cruciate Ligament (ACL) ruptures is still a surgical dilemma. Preservation of the intact fibres of the ACL bundle is considered to be a possible source of reinnervation of the ACL autograft which reflects on better proprioceptive knee control after major ligament reconstruction. Results of a prospective study of 67 patients who had a double stranded but single bundle Anterior Cruciate Ligament (ACL) reconstruction for partial ACL ruptures are presented. There were 43 males and 24 females in this study with a mean age at the time of injury of twenty-five years (14 – 40). Eight played sport professionally and thirty-four played at a competitive level. A valgus twisting force was the most common mechanism of injury. Mean injury to operation time was 7.5 weeks (2–12). All procedures were done arthroscopically without using tourniquet, but using an arthroscopy pump and irrigation fluid containing adrenaline. The semitendinosis hamstring graft was used in all reconstructions. The mean follow-up period was 3.3 years (2–5.4). There was one major complication, who developed a reflex sympathetic dystrophy following a saphenous nerve neuroma. The Quality of Life (QOL) score was assessed using the Mohtadi index. The mean pre-operative QOL score of 30 (13–50) was improved to 93 (70–100) post-operatively. Fifty patients were able to return to their previous sporting level at a mean duration of 9 months (6–12). Preservation of mechanoreceptors by performing a double stranded, single bundle ACL reconstruction in partial ACL ruptures in high demand patients yields good results and enables early return to high demand sports

INTRODUCTION. Patellar tendon (PT) autograft is an excellent choice repairing anterior cruciate ligament (ACL) ruptures. Published studies testing the biomechanical characteristics after plasty usually refer to grafts with 10mm wide. The thickness of PT and geometry of the patella have been overlooked. The purpose of this study was to understand the geometry of PT and patella in our population, regarding their use in Bone - Patellar Tendon - Bone (BTB) technique, in order to evaluate their biomechanical efficiency and study their relationship with anthropometric parameters. MATERIAL. 100 individuals (50/50) who underwent knee MRI (3-Tesla). Ages between 18–65years. METHODS. Retrospective study. Standardized protocol for measuring the PT and patella based in MRI images. Interview to obtain personal data. Statistical analysis using SPSS®. RESULTS. Sample (mean ±SD): age 41 ±14years, weight 73 ±12kg, height 167 ±10cm, BMI 26,04 ±4,13; length PT/patella −41,3 ±6,1mm/29,6 ±4,2 mm, width PT/patella −25,3 ±3,2mm/43,4 ±4,14mm; thickness PT −3,79 ±1,01mm/22,8 ±2,2mm; Men have thicker and wider patella and PT than women (p<0.001). The patella is also longer in males (p<0.001). There is statistical significant relationship between weight and height to width, thickness and length of PT and patella (p<0.01). Body Mass Index (BMI) doesn't have statistical correlation with geometry of the PT and patella. DISCUSSION. The PT remains as an excellent option in ACL repair. The anatomy and quality of the graft are essential to achieving good functional results. The choice of middle third tendon to the BTB plasty does not always correspond to the 10mm width, as used in most biomechanical tests. Also patellar integrity can be at risk (when collecting the bone block) if patella geometry is not considered. To our knowledge, there is only one similar study in literature, preformed in Asian individuals. CONCLUSION. Preoperatively accessing the geometry of Patella and PT can be crucial in obtaining efficient grafts and decreasing morbidity over the extensor mechanism

Introduction: Anterior cruciate ligament (ACL) rupture leads to biomechanics disturbances of the knee joint which are reflected also in the plantar supports. Our hypothesis is that a redistribution of the sole bilateral charges will be produced to allows the feet to get a new control system to compensate ACL rupture. The aim of this research is to study the plantar support pressures disturbances in patients with ACL rupture before operation. Material and Methods: We analyzed the plantar pressure distribution in two populations: Group A: 39 males of 37 years average age (21–49 y.o), previous surgery of isolated ACL rupture, excluding patients with meniscal tear or serious cartilage damage, contralateral lesions and knee previous surgery as well. Group B (control group): 37 healthy males of 31 years average age (21–40 y.o) without any musculoskeletal disorders. We performed physical examination and walking through a pedography plate (Emed, Novel Munich, Germany). We studied global plantar support (pressure, forces and areas) of each foot and also divided each foot into six parts. Data obtained was compared between group A, patients (healthy leg and ACL rupture leg) and group B (control group). Statistical analysis was performed with a non-parametric Wilcoxon test. Results: Group A (healthy leg and ACL rupture leg) total support area of both feet were statistically superior than Group B total support area (p< 0,019 and p< 0,005 respectively). Evenly midfoot total support area was superior in Group A that in Group B, as well as midfoot force support (p< 0.089). Group A midfoot pressure was higher in ACL rupture leg than in healthy leg (p< 0.007) and it was also higher to the one obtained for group B (p< 0.046). Evenly the anterior-external region of Group A, healthy leg got the highest pressure (p< 0.076), followed by Group A, ACL rupture leg (p< 0.022) and finally Group B. Group B anterior-internal pressure was statistically superior to Group A, ACL rupture leg (p< 0.049) followed by Group A, healthy leg (p=0.022). During foot takeoff, first toe pressures were higher in Group B compared to Group A (p< 0.076). Conclusion: ACL rupture shows differences in plantar support pressures distribution of both legs (ACL rupture leg and healthy leg) compared with a control population. The injured leg seeks balance decreasing heel support and increasing the contact surfaces between floor, midfoot and forefoot

Introduction and Aims: There are more than 200,000 anterior cruciate ligament (ACL) ruptures each year in the United States. The replacements used for ACL repair do not fully recreate the ACL’s function and histological appearance. Therefore, a novel tissue-engineered ligament was designed and evaluated after ACL reconstruction in a rabbit model. Method: Rabbits received tissue-engineered ligaments or tissue-engineered ligaments seeded with primary rabbit ACL cells. The tissue-engineered ligaments were composed of multifilament poly-L-lactide yarn (70 denier) fabricated into novel 24 yarn 3-D braids. Scaffolds were designed to be easily handled and fixed by the surgeon in ACL reconstructions using the suture over the button technique. A continuous scaffold design accommodated the flexibility of intra-articular loads and the rigours of the bone tunnels. The contralateral legs were used as controls. A key parameter for tissue ingrowth was scaffold porosity at 58 ± 9% and mode pore diameter of 183 ± 83 μm. Results: Histological evaluations showed slow collagen tissue infiltration at the surface of the replacement at the four-week time point for both the tissue-engineered ligament and cell-seeded tissue-engineered ligament. At the 12-week time point, both replacements showed collagen ingrowth and remodelling across the entire implant occurred with a thin fibrous capsule. The cell-seeded tissue-engineered ligament demonstrated greater levels of mature collagen ingrowth and healing compared to the non-cell seeded tissue-engineered ligament. The initial tensile strength properties of the scaffold were 332 ± 20 N and 354 ± 68 MPa, which compared well to the rabbit ACL control (314 ± 66 N). The tensile properties of the tissue-engineered ligament and seeded tissue-engineered ligament at four weeks were 67% and 76%, respectively of control. The tensile properties of the biodegradable implant decreased with time for the tissue-engineered and cell seeded tissue-engineered ligament and by 12 weeks was 9% and 30% respectively, as compared to the rabbit ACL control. The 30% strength retention for the tissue-engineered ligament replacements at 12 weeks was greater than reported by others using poly(lactic acid) and polypropylene ligament augmentation devices (LAD) at 12 weeks, with values of 13% and 16% of control strength retention, respectively. Conclusion: The results of this study demonstrate the promise of a novel cell seeded tissue-engineered ligament for anterior cruciate ligament regeneration

Introduction: Anterior cruciate ligament (ACL) rupture impairs knee stability. Reconstruction of the ACL is therefore performed to restore knee stability and avert risk of subsequent ligament and meniscal injury. Bone-patellar tendon-bone autograft is the most commonly employed technique for ACL reconstruction and considered the “gold standard”. Although 10% postoperative patellar tendon shortening has been reported with this technique, there are no systematic studies assessing the effect of this shortening on patellofemoral joint (PFJ) biomechanics under loading conditions simulating normal physiologic activity. The purpose of this study was to determine if 10% shortening of the patellar tendon affected PFJ biomechanics. Methods: Patellofemoral contact characteristics were evaluated in cadaveric knees before and after patellar tendon shortening. Tendon shortening was performed using a specifically designed device that shortened the tendon without interfering with its anatomic and physiologic integrity. Conditions simulating light physical activity such as level walking were recreated by applying physiological quadriceps loads and corresponding angles of tibial rotation to the PFJ at 15°, 30° and 60° of knee flexion. PFJ contact areas were measured at each position of knee flexion before and after patellar tendon shortening using the silicone oil-carbon black powder suspension squeeze technique (3S technique, . Yao & Seedhom, . Proc Instn Mech Engrs. 1991. ;. 205. :. 69. –72. ). Differences were compared using the Wilcoxon signed rank t-test, with p< 0.05 required for statistical significance. Results: Twelve unembalmed cadaveric knees (median age 81.8 years, 8 female: 4 male) were available for study. Five knees had evidence of osteoarthritic changes, and were rejected. The remaining 7 knees were macroscopically intact and were considered adequate for the experimental procedure. The mean patellofemoral contact areas and stresses determined preoperatively were comparable to those reported in normal knees in previous studies. Following patellar tendon shortening, PFJ contact areas were displaced superiorly on the patellar articular surface and distally on the femoral articular surface. Although the PFJ contact area increased by 17% at 15° of knee flexion (p=0.04), no significant change occurred at 30° or 60° of knee flexion (p> 0.05). Patellofemoral contact stress did not differ before and after patellar tendon shortening (p> 0.05) at any angle of knee flexion. Conclusions: Our results suggest that with light activity such as level walking, a 10% postoperative shortening of the patellar tendon does not alter patellar tracking (in particular contact stresses) and therefore may not impact biomechanics of the patellofemoral joint. Extrapolating these results to the clinical scenario, deleterious consequences on the patellofemoral joint are unlikely after bone-patellar tendon-bone autograft reconstruction of the ACL despite the possibility of postoperative patellar tendon shortening

Anterior Cruciate Ligament (ACL) rupture is one of the commonest injuries in sports medicine. However, the rates of the reported graft re-rupture range from 2–10%, leading to around 3000 to 10000 revision ACL reconstructions in United States per annum. Inaccurate tunnel positions are considered to be one of the commonest reasons leading to failure and subsequent revision surgery. Additionally, there remains no consensus of the optimal position for ACL reconstructions. The positions of the bone tunnels in patients receiving ACL reconstruction are traditionally assessed using X-rays. It is well known that conventional X-ray is not a precise tool in assessing tunnel positions. Thus, there is a recent trend in using three-dimensional (3D) CT. However, routine CT carries a major disadvantage in terms of significant radiation hazard. In addition, it is both inconvenient and expensive to use CT as a regular assessment tools during the follow-up. The goal of the present work is to develop a novel 2D-3D registration method using single X-ray image and a surface model. By performing such registration for two post-operative X-rays, we can further calculate the 3D tunnel positions after ACL reconstructions. Our framework consists of five parts: (1) a surface model of the knee, (2) a 2D-3D registration algorithm, (3) a 3D tunnel position calculation, (4) a graphic user interface (GUI), and (5) a semi-transparency rendering. Among them, the crucial part is our 2D-3D registration method that estimates the relative position of the knee model in the imaging coordinate system. Once registered, the 3D position of an ACL tunnel in the knee model is calculated from the imaging geometry. The only interaction required is to mark the ACL tunnels on the X-rays through the GUI. We propose two 2D-3D registration methods. One is a contour-based method that uses pure geometric information. Most methods in this category accomplish the registration by extracting contours in X-rays, establishing their correspondences on the 3D model, and calculating the registration parameters. Unlike these methods, which need point-to-point correspondences, our method optimises the registration parameters in a statistical inference framework without giving or establishing point-to-point correspondences. Due to the use of the statistical inference, our method is robust to the spurs and broken contours that automatically extracted by the contour detector. The second method takes into account both the geometric shape of the object and the intensity property (intensity changes) of the image, where the intensity changes can be detected via image gradients. The use of gradient is based on the interpretation that two images are considered similar, if intensity changes occur at the same locations. The angles between the image gradients and the projected surface normals were used as a distance measure. The summation of the measures for all projected model points gives us the gradient term, which we multiply the contour-based measurement. Multiplication is preferred over addition because addition of the terms would require both terms to be normalised. To evaluate the feasibility of our methods, a simulation study was conducted using Digitally Reconstructed Radiographs (DRR) of a sawbone underwent a single-bundle ACL reconstruction performed by an experienced orthopedic surgeon. The real position of the bone tunnel entry point was obtained using the CT images, which were acquired using a custom-made well-calibrated cone-beam CT. The knee model was built by downsampling and smoothing the high-resolution CT reconstructions. It is important in our experiments to make the model different from the original reconstruction since this simulates the condition in which patient's CT is unavailable. Two DRRs generated from approximately anteroposterior and lateral viewpoints were used. For each DRR, 50 trials of 2D-3D registration were carried out for the femoral part using 50 different initialisations, which were randomly selected from the values independently and uniformly distributed within ±10 degrees and ±10 mm of the ground-truth. Compared with the ground-truth established using the CT images, our single image contour-based method achieved accurate estimations in rotations and in-plane translations, which were (−0.67±1.38, −0.98±0.84, −0.42±0.71) degrees and (0.11±0.26, −0.06±1.20) mm for the anteroposterior image, and (−0.78±0.76, −0.37±0.87, 0.70±0.88) degrees and (−0.14±0.22, 0.31±0.71) mm for the lateral one, respectively. The same experiments were also performed using the second method. However, it did not produce desirable results in our experiments. The tunnel entry point was then calculated using the averaged registration result of our contour-based method. The entry point of the tunnel was obtained with high accuracy of 1.25 mm distance error from the real position of the entry point. For the 2D-3D registration, the estimated off-plane translations showed relatively low accuracy. It is well known that the depth can be difficult to be accurately estimated using one single image. As the result showed, the accuracy in rotations and in-plane translations is more important for ACL tunnel position estimation in our framework. As for the image gradient, it is too sensitive to the small perturbation caused by image noises. A more robust way of integrating the gradient information into our contour-based method is required. We propose a novel approach for estimating the 3D position of bone tunnels in ACL reconstruction using two post-operative X-rays. It was tested in a sawbone study using DRRs. The most significant advantage of our approach is to potentially eliminate the necessity of acquiring a patient's CT. The success in developing and validating the proposed workflow will allow convenient and precise assessment of tunnel positions in ACL reconstruction with minimal risk of radiation hazard

Cite this article: Bone Joint Res 2022;11(8):514–517.

Aims

The aim of this study was to estimate the incremental use of resources, costs, and quality of life outcomes associated with surgical reconstruction compared to rehabilitation for long-standing anterior cruciate ligament (ACL) injury in the NHS, and to estimate its cost-effectiveness.

Objectives

The aim of this study was to investigate the biomechanical effect of the anterolateral ligament (ALL), anterior cruciate ligament (ACL), or both ALL and ACL on kinematics under dynamic loading conditions using dynamic simulation subject-specific knee models.

Objectives

Re-rupture is common after primary flexor tendon repair. Characterization of the biological changes in the ruptured tendon stumps would be helpful, not only to understand the biological responses to the failed tendon repair, but also to investigate if the tendon stumps could be used as a recycling biomaterial for tendon regeneration in the secondary grafting surgery.