Correction to: 3D-printed spine surgery implants: a systematic review of the efficacy and clinical safety profile of patient-specific and off-the-shelf devices.

Unfortunately, 3rd author's first name was incorrectly published in the original publication. The complete correct name is given below.

3D-printed spine surgery implants: a systematic review of the efficacy and clinical safety profile of patient-specific and off-the-shelf devices.

PURPOSE: Three-dimensional printing (3DP), or additive manufacturing, is an emergent fabrication technology for surgical devices. As a production method, 3DP enables physical realisation of surgical implants from geometrically complex digital-models in computer-aided design. Spine surgery has been an innovative adopter of 3DP technology for both patient-specific (PS) and market-available 'Off-The-Shelf' (OTS) implants. The present study assessed clinical evidence for efficacy and safety of both PS and OTS 3DP spinal implants through review of the published literature. The aim was to evaluate the clinical utility of 3DP devices for spinal surgery. METHODS: A systematic literature review of peer-reviewed papers featured on online medical databases evidencing the application of 3DP (PS and OTS) surgical spine implants was conducted in accordance with PRISMA guidelines. RESULTS: Twenty-two peer-reviewed articles and one book-chapter were eligible for systematic review. The published literature was limited to case reports and case series, with a predominant focus on PS designs fabricated from titanium alloys for surgical reconstruction in cases where neoplasia, infection, trauma or degenerative processes of the spine have precipitated significant anatomical complexity. CONCLUSION: PS and 3DP OTS surgical implants have demonstrated considerable utility for the surgical management of complex spine pathology. The reviewed literature indicated that 3DP spinal implants have also been used safely, with positive surgeon- and patient-reported outcomes. However, these conclusions are tentative as the follow-up periods are still relatively short and the number of high-powered studies was limited. Single case and small case series reporting would benefit greatly from more standardised reporting of clinical, radiographic and biomechanical outcomes. These slides can be retrieved under Electronic Supplementary Material.

Sagittal patellar flexion angle: a novel clinically validated patellar height measurement reflecting patellofemoral kinematics useful throughout knee flexion.

PURPOSE: Patellar height measurements on lateral radiographs are dependent on knee flexion which makes standardisation of measurements difficult. This study described a plain radiographic measurement of patellar sagittal height which reflects patellofemoral joint kinematics and can be used at all degrees of flexion. METHODS: The study had two parts. Part one involved 44 normal subjects to define equations for expected patellar position based on the knee flexion angles for three new patellar height measurements. A mixed model regression with random effect for individual was used to define linear and polynomial equations for expected patellar position relating to three novel measurements of patella height: (1) patellar progression angle (trochlea), (2) patellar progression angle (condyle) and (3) sagittal patellar flexion. Part two was retrospective and involved applying these measurements to a surgical cohort to identify differences between expected and measured patellar position pre- and post-operatively. RESULTS: All three measurements provided insight into patellofemoral kinematics. Sagittal patellar flexion was the most useful with the least residual error, was the most reliable, and demonstrated the greatest detection clinically. CONCLUSIONS: Clinically applied radiographic measurements have been described for patellar height which reflect the sagittal motion of the patella and can be used regardless of the degree of flexion in which the radiograph was taken. The expected sagittal patellar flexion linear equation should be used to calculate expected patellar height. LEVEL OF EVIDENCE: IV.

Head to head: the case for fighting behaviour in Megaloceros giganteus using finite-element analysis.

The largest antlers of any known deer species belonged to the extinct giant deer Megaloceros giganteus. It has been argued that their antlers were too large for use in fighting, instead being used only in ritualized displays to attract mates. Here, we used finite-element analysis to test whether the antlers of M. giganteus could have withstood forces generated during fighting. We compared the mechanical performance of antlers in M. giganteus with three extant deer species: red deer (Cervus elaphus), fallow deer (Dama dama) and elk (Alces alces). Von Mises stress results suggest that M. giganteus was capable of withstanding some fighting loads, provided that their antlers interlocked proximally, and that their antlers were best adapted for withstanding loads from twisting rather than pushing actions, as are other deer with palmate antlers. We conclude that fighting in M. giganteus was probably more constrained and predictable than in extant deer.

Computer simulations show that Neanderthal facial morphology represents adaptation to cold and high energy demands, but not heavy biting.

Three adaptive hypotheses have been forwarded to explain the distinctive Neanderthal face: (i) an improved ability to accommodate high anterior bite forces, (ii) more effective conditioning of cold and/or dry air and, (iii) adaptation to facilitate greater ventilatory demands. We test these hypotheses using three-dimensional models of Neanderthals, modern humans, and a close outgroup (Homo heidelbergensis), applying finite-element analysis (FEA) and computational fluid dynamics (CFD). This is the most comprehensive application of either approach applied to date and the first to include both. FEA reveals few differences between H. heidelbergensis, modern humans, and Neanderthals in their capacities to sustain high anterior tooth loadings. CFD shows that the nasal cavities of Neanderthals and especially modern humans condition air more efficiently than does that of H. heidelbergensis, suggesting that both evolved to better withstand cold and/or dry climates than less derived Homo We further find that Neanderthals could move considerably more air through the nasal pathway than could H. heidelbergensis or modern humans, consistent with the propositions that, relative to our outgroup Homo, Neanderthal facial morphology evolved to reflect improved capacities to better condition cold, dry air, and, to move greater air volumes in response to higher energetic requirements.

Three-dimensional kinematics of the canine carpal bones imaged with computed tomography after ex vivo axial limb loading and palmar ligament transection.

OBJECTIVE: To describe normal antebrachiocarpal joint kinematic motion during axial loading and to describe the effect of palmar radiocarpal ligament (PRL) and palmar ulnocarpal ligament (PUL) transection on this motion. SAMPLE POPULATION: Ten forelimbs from 5 adult greyhound cadavers. METHODS: Limbs were placed in a custom jig and computed tomography images of limbs were obtained in neutral and extended positions. The translation and rotation of the intermedioradiocarpal bone (RCB), ulnar carpal bone, and accessory carpal bone were described relative to the radius through rigid body motion analysis. Kinematic and load analysis was repeated after sequential transection of the PRL and the PUL. RESULTS: Sagittal plane extension with a lesser component of valgus motion was found in all evaluated carpal bones. RCB supination was also detected during extension. Compared with the normal intact limb, transection of either or both the PRL and the PUL did not influence mean translation or rotation data or limb load. However, the transection of the PRL and the PUL increased the variance in rotation data compared with intact limb. CONCLUSION: This study describes normal antebrachiocarpal kinematics as a foundation for determining carpal functional units. During axial loading, the PRL and the PUL may function to guide consistent motion in extension and flexion as well as pronation and supination. CLINICAL SIGNIFICANCE: Three-dimensional carpal kinematic analyses may improve our understanding of carpal injury and facilitate the development of novel treatments techniques.

Influence of Scan Resolution, Thresholding, and Reconstruction Algorithm on Computed Tomography-Based Kinematic Measurements.

Radiographic data, including computed tomography (CT) and planar X-ray, is increasingly used for human and animal kinematic studies. There is a tendency toward using as high-resolution imaging as possible. Higher resolution imaging is one factor (in conjunction with the reconstruction algorithm), which may increase the precision of reconstructed three-dimensional (3D) surface models in representing true bone shape. However, to date no study has tested the effects of scan resolution, threshold, and 3D model reconstruction algorithm on the accuracy of bone kinematic results. The present study uses a novel method to do this where canine tarsal bones were positioned on a radiolucent Lego™ board and scanned before and after undergoing known translations and/or rotations. The digital imaging and communications in medicine (DICOM) images were acquired using two different CT scanning resolutions and processed using three different segmentation threshold levels and three different reconstruction algorithms. Using one bone as the reference bone, an iterative closest point (ICP) algorithm was used to register bones to a global co-ordinate system and allow measurement of other bone kinematics in terms of translations and rotations in and around the x-, y-, and z-axes. The measured kinematics were compared to the "known" kinematics, which were obtained from the Lego™ board's manufacturing standards and tolerances, to give accuracy error metrics for all bones. The results showed error in accuracy of measured kinematics was at subvoxel levels (less than 0.5 mm). Despite altering the volume and surface area of the 3D bone models, variation in resolution, segmentation threshold and reconstruction algorithm had no significant influence upon the accuracy of the calculated tarsal bone kinematics.

Moa diet fits the bill: virtual reconstruction incorporating mummified remains and prediction of biomechanical performance in avian giants.

The moa (Dinornithiformes) are large to gigantic extinct terrestrial birds of New Zealand. Knowledge about niche partitioning, feeding mode and preference among moa species is limited, hampering palaeoecological reconstruction and evaluation of the impacts of their extinction on remnant native biota, or the viability of exotic species as proposed ecological 'surrogates'. Here we apply three-dimensional finite-element analysis to compare the biomechanical performance of skulls from five of the six moa genera, and two extant ratites, to predict the range of moa feeding behaviours relative to each other and to living relatives. Mechanical performance during biting was compared using simulations of the birds clipping twigs based on muscle reconstruction of mummified moa remains. Other simulated food acquisition strategies included lateral shaking, pullback and dorsoventral movement of the skull. We found evidence for limited overlap in biomechanical performance between the extant emu (Dromaius novaehollandiae) and extinct upland moa (Megalapteryx didinus) based on similarities in mandibular stress distribution in two loading cases, but overall our findings suggest that moa species exploited their habitats in different ways, relative to both each other and extant ratites. The broad range of feeding strategies used by moa, as inferred from interspecific differences in biomechanical performance of the skull, provides insight into mechanisms that facilitated high diversities of these avian herbivores in prehistoric New Zealand.

Evolution of neck vertebral shape and neck retraction at the transition to modern turtles: an integrated geometric morphometric approach.

The unique ability of modern turtles to retract their head and neck into the shell through a side-necked (pleurodiran) or hidden-necked (cryptodiran) motion is thought to have evolved independently in crown turtles. The anatomical changes that led to the vertebral shapes of modern turtles, however, are still poorly understood. Here we present comprehensive geometric morphometric analyses that trace turtle vertebral evolution and reconstruct disparity across phylogeny. Disparity of vertebral shape was high at the dawn of turtle evolution and decreased after the modern groups evolved, reflecting a stabilization of morphotypes that correspond to the two retraction modes. Stem turtles, which had a very simple mode of retraction, the lateral head tuck, show increasing flexibility of the neck through evolution towards a pleurodiran-like morphotype. The latter was the precondition for evolving pleurodiran and cryptodiran vertebrae. There is no correlation between the construction of formed articulations in the cervical centra and neck mobility. An increasing mobility between vertebrae, associated with changes in vertebral shape, resulted in a more advanced ability to retract the neck. In this regard, we hypothesize that the lateral tucking retraction of stem turtles was not only the precondition for pleurodiran but also of cryptodiran retraction. For the former, a kink in the middle third of the neck needed to be acquired, whereas for the latter modification was necessary between the eighth cervical vertebra and first thoracic vertebra. Our paper highlights the utility of 3D shape data, analyzed in a phylogenetic framework, to examine the magnitude and mode of evolutionary modifications to vertebral morphology. By reconstructing and visualizing ancestral anatomical shapes, we provide insight into the anatomical features underlying neck retraction mode, which is a salient component of extant turtle classification.

Rapid Personalised Virtual Planning and On-Demand Surgery for Acute Spinal Trauma Using 3D-Printing, Biomodelling and Patient-Specific Implant Manufacture.

Three-dimensional printing is a rapidly growing field, with extensive application to orthopaedics and spinal surgery. Three-dimensional-printed (3DP) patient-specific implants (PSIs) offer multiple potential benefits over generic alternatives, with their use increasingly being described in the spinal literature. This report details a unique, emergency case of a traumatic spinal injury in a 31-year-old male, acquired rurally and treated with a 3DP PSI in a tertiary unit. With increasing design automation and process improvements, rapid, on-demand virtual surgical planning (VSP) and 3DP PSIs may present the future of orthopaedics and trauma care, enabling faster, safer, and more cost-effective patient-specific procedures.

Combining Virtual Surgical Planning and Patient-Specific 3D-Printing as a Solution to Complex Spinal Revision Surgery.

With the advent of three-dimensional printing, rapid growth in the field and application in spinal and orthopedic surgery has been seen. This technology is now being applied in creating patient-specific implants, as it offers benefits over the generic alternative, with growing literature supporting this. This report details a unique application of virtual surgical planning and manufacture of a personalized implant in a case of cervical disc replacement failure with severe osteolysis and resultant hypermobility. Where this degree of degenerative bone loss would often necessitate a vertebrectomy to be performed, this case highlights the considerable customizability of 3D-printed patient-specific implants to contour to the bony defects, allowing for a smaller and safer operation, with the achievement of stability as early as 3 months after the procedure, by the presence of osseointegration. With increasing developments in virtual planning technology and 3D printing ability, the future of complex spinal revision surgery may adopt these technologies as it affords the patient a faster, safer, and less invasive and destructive procedure.

Standalone titanium/polyetheretherketone interbody cage for anterior lumbar interbody fusion: Clinical and radiological results at 24 months.

Context: Anterior lumbar interbody fusion (ALIF) is a common procedure for patients suffering degenerative, deformity, or posttraumatic pathologies of the lumbar spine. Aims: The aim of this study is to evaluate the clinical and radiological outcomes of a combination Titanium/Polyetheretherketone (Ti/PEEK) 3-screw fixation ALIF cage. Settings and Design: This was a prospective multisurgeon series of 87 patients (105 implants), with a minimum 24-month follow-up. Twelve patients (12/87) were supplemented with posterior percutaneous pedicle screw fixation for additional stability for pars defect spondylolisthesis correction. Radiological follow-up with fine-cut computed tomography (CT) scan occurred at 4-6 months, and again at 18-24 months if no fusion observed on initial CT, was performed to evaluate early and final fusion rates, and integration of the Ti/PEEK cage at the end-plate junction. Clinical follow-up included the subjective measures of pain and functional status and objective wearable device monitoring. Results: The fusion rate was 85% (97/105 implants) 6 months postoperatively, with no implant-related complications, and 95% at 24 months, based on independent radiological assessment. Patients experienced statistically significant improvement in subjective pain and functional outcomes compared to preoperative status. The objective measures revealed a daily step count with a 27% improvement, and gait velocity with a mean increase from 0.97 m/s to 1.18 m/s, at 3 months postoperatively. Conclusions: A Ti/PEEK cage, with allograft and bone morphogenetic protein-2 (BMP-2), achieved rapid interbody progression to fusion and is an effective implant for use in anterior lumbar surgery with high early fusion rates and no peri-endplate lucency. Supercritical CO2 allograft provided an osteoconductive scaffold and combined well with BMP-2 to facilitate fusion.

Inter- and intra-specific scaling of articular surface areas in the hominoid talus.

The morphology of postcranial articular surfaces is expected to reflect their weight-bearing properties, as well as the stability and mobility of the articulations to which they contribute. Previous studies have mainly confirmed earlier predictions of isometric scaling between articular surface areas and body mass; the exception to this is 'male-type', convex articular surface areas, which may scale allometrically due to differences in locomotor strategies within the analysed samples. In the present study, we used new surface scanning technology to quantify more accurately articular surface areas and to test those predictions within the talus of hominoid primates, including modern humans. Our results, contrary to predictions, suggest that there are no generalised rules of articular scaling within the talus of hominoids. Instead, we suggest that articular scaling patterns are highly context-specific, depending on the role of each articulation during locomotion, as well as taxon- and sex-specific differences in locomotion and ontogenetic growth trajectories within any given sample. While this may prove problematic for inferring body mass based on articular surface area, it also offers new opportunities of gaining substantial insights into the locomotor patterns of extinct species.

Opinion Piece: Patient-Specific Implants May Be the Next Big Thing in Spinal Surgery.

The emergence of 3D-Printing technologies and subsequent medical applications have allowed for the development of Patient-specific implants (PSIs). There have been increasing reports of PSI application to spinal surgery over the last 5 years, including throughout the spine and to a range of pathologies, though largely for complex cases. Through a number of potential benefits, including improvements to the implant-bone interface and surgical workflow, PSIs aim to improve patient and surgical outcomes, as well as potentially provide new avenues for combating challenges routinely faced by spinal surgeons. However, obstacles to widespread acceptance and routine application include the lack of quality long-term data, research challenges and the practicalities of production and navigating the regulatory environment. While recognition of the significant potential of Spinal PSIs is evident in the literature, it is clear a number of key questions must be answered to inform future clinical and research practices. The spinal surgical community must selectively and ethically continue to offer PSIs to patients, simultaneously allowing for the necessary larger, comparative studies to be conducted, as well as continuing to provide optimal patient care, thereby ultimately determining the exact role of this technology and potentially improving outcomes.

Revision of a Failed C5-7 Corpectomy Complicated by Esophageal Fistula Using a 3-Dimensional-Printed Zero-Profile Patient-Specific Implant: A Technical Case Report.

BACKGROUND: Esophageal fistulae are rare, though serious, complications of anterior cervical surgery. Hardware-related issues are important etiologic factors. Patient-specific implants (PSIs) have increasingly been adapted to spinal surgery and offer a range of benefits. Zero-profile implants are a recent development primarily aimed at combating postoperative dysphagia. We report the first use of a 3-dimensional (3D)-printed zero-profile PSI in managing implant failure with migration and a secondary esophageal fistula. METHODS: A 68-year-old female had a prior C5-7 corpectomy with cage and plate fixation, as well as posterior C3-T1 lateral mass fixation, complicated by anterior plate displacement, resulting in pseudoarthrosis and an esophageal fistula. A 3D-printed zero-profile PSI was designed and implanted as part of a revision procedure to assist in recovery, prevent recurrence, and facilitate bony fusion. RESULTS: Optimal implant placement was achieved on the basis of preoperative virtual surgical planning. By 1 month postoperatively the patient had significantly improved, with evidence of esophageal fistula resolution and radiographic evidence of optimal implant placement. CONCLUSIONS: Zero-profile 3D-printed PSIs may combat common and serious complications of anterior cervical surgery including postoperative dysphagia and esophageal fistulae. Further research is required to validate their widespread use for either cervical corpectomy or diskectomy and interbody fusion.

Effect of Bicortical Interfragmentary Screw Size on the Fixation of Metacarpal Shaft Fractures: A 3-Dimensional-Printed Biomechanical Study.

Purpose: Spiral metacarpal fractures fixed with 2 non-lagged, interfragmentary cortical screws were tested to failure. The effect of screw size (1.2 mm, 1.5 mm, 2.0 mm, and 2.3 mm) on construct strength was tested in 3-point bending. Methods: Three-dimensional-printed metacarpal test models were reproduced from computed tomography scans to reduce the confounding variables of bone density and anatomy, often encountered when using cadavers. Results: No significant difference was found between the screw sizes, and the peak failure force was similar. Drill bit fracture and deformation during the insertion of the smallest screw (1.2 mm) as well as model failure during the insertion of the largest screw (2.3 mm) were found in some cases. Conclusions: Screws of 1.5 mm and 2.0 mm in diameter were of sufficient strength and did not have the issues encountered with smaller or larger screws. Concerns from previous authors regarding intraoperative fracture were consistent with the pre-testing failure of some 2.3-mm models. Clinical Relevance: Screws of 1.5 mm or 2 mm appear adequate for the fixation of spiral fracture patterns in metacarpal shafts using bicortical non-lagged technique with a low risk of fixation complications.

Development of a Multivariate Prediction Model for Successful Oswestry Disability Index Changes in L5/S1 Anterior Lumbar Interbody Fusion for Degenerative Disc Disease.

OBJECTIVE: Lower back pain associated with degenerative disc disease (DDD) is a leading cause of disability worldwide. Anterior lumbar interbody fusion (ALIF) has been shown to be effective for treating refractory DDD, but it remains unclear which patients may benefit most from the procedure. This study aims to develop a predictive model for clinical success in L5/S1 ALIF for DDD. METHODS: A retrospective cohort study of 68 patients with refractory DDD who underwent L5/S1 ALIF was performed. Clinical success was defined as an improvement in Oswestry Disability Index (ODI) of 20 points postoperatively. Exploratory analyses were performed on 16 preoperative clinical and radiographic parameters, followed by a multivariate logistic regression. Evaluation of the predictive model was performed. RESULTS: After exploratory analyses, 4 parameters were suitable for inclusion in the multivariate model. Workers' compensation status (odds ratio [OR], 0.02; 95% confidence interval [CI], 0.001-0.262; P = 0.004) and preoperative ODI (OR, 1.13; 95% CI, 1.05-1.23; P = 0.002) were statistically significant parameters. Furthermore, posterior disc height and disc depth contributed significantly to the model variance (OR, 0.69, 95% CI, 0.44-1.09 and OR, 0.97, 95% CI, 0.81-1.15, respectively). The model had a sensitivity of 81.5%, specificity of 83.3%, C-statistic of 0.921, and a calibration plot similar to the 45° reference line. CONCLUSIONS: This analysis confirms workers' compensation and low preoperative ODI as risk factors for successful L5/S1 ALIF performed for DDD. It also identifies novel prognostic factors, namely posterior disc height and disc depth. This model can aid in patient counseling and selection in the management of L5/S1 DDD.

Fatigue implications for bending orthopaedic plates.

OBJECTIVES: - We aimed to investigate how pre-bending affects the mechanical properties, specifically fatigue, of stainless-steel plates. METHODS: - 3.5mm LCP 10-hole plates were pre-bent in 1, 2 and 3 locations to the same overall degree and fatigue testing performed. Finite Element Analysis (FEA) was performed in Strand7 (version 2.4.6) to better understand the failure point of the plates in four-point bending. RESULTS: - Six different plate pre-bending conditions were tested for resistance to fatigue failure. Increasing the number of pre-bends improved the fatigue resistance with two pre-bends having a mean 509,304 cycles to failure and three pre-bends 491,378 cycles to failure. The region of highest stress and the point of fatigue failure were at the plate's minimum cross-sectional area, which was predicted by the FEA and confirmed with mechanical testing. For plates pre-bent in two locations, the fatigue failure always occurred in the screw hole not in between the positions of the two pre-bends. Non-linear FEA simulation confirmed that work hardening occurs around pre-bend locations, conferring increased fatigue resistance to the holes next to, or between, pre-bend locations. CONCLUSIONS: We found that contrary to orthopaedic folklore, pre-bending of plates is not detrimental to fatigue resistance of the stainless-steel plates we tested. Pre-bending plates in a single plane increased the fatigue properties of the 10-hole stainless-steel plate tested.

Kinematics of the Feline Antebrachiocarpal Joint from Supination to Pronation.

OBJECTIVE: Cats rely on their forelimb mobility for everyday activities including climbing and grooming. Supination and pronation of the forelimb in cats are considered to primarily involve the antebrachium, rather than the carpus. Therefore, our null hypothesis was that there would be no movement of the carpal bones (radial carpal bone, ulnar carpal bone and accessory carpal bone) relative to the ulna during supination and pronation. STUDY DESIGN: Eight feline cadaveric forelimbs were rotated from supination to pronation in a jig and computed tomography was performed in the neutral, supinated and pronated positions. The individual carpal bones were segmented from computed tomography images of the supinated and pronated scans in each of the eight specimens. A feline ulna coordinate system was established and used to quantify the translations and rotations between bones of the proximal carpal row and antebrachium. RESULTS: After the carpus was rotated from the initial supinated position into pronation, there was significant translation (x, y and z axes) and rotation (x and y axes) of the proximal row of carpal bones based on absolute magnitude values. Given the differences in translations and rotations of the proximal row of carpal bones, our null hypothesis was rejected. CONCLUSION: The proximal row of carpal bones translate and rotate independently from the ulna in the cat during pronation of the antebrachium. This may have future implications in the diagnosis and management of feline carpal injuries involving the antebrachiocarpal joint.

Moment arm function dictates patella sagittal height anatomy: Rabbit epiphysiodesis model alters limb length ratios and subsequent patellofemoral anatomical development.

Patellofemoral anatomical dysplasia is associated with patellofemoral instability and pain. The closure of the knee physis occurs at the same age as the peak incidence of patellofemoral dislocation. This study determined the effect on the patellofemoral anatomical development in a rabbit epiphysiodesis model. Twenty-four skeletally immature New Zealand White rabbits were divided into three groups (a) distal femur epiphysiodesis (FE) (b) proximal tibia epiphysiodesis (TE) (c) control; no epiphysiodesis (C) performed at 6 weeks of age. The primary endpoint was shape analysis using three-dimensional reconstructions of micro-computed tomographys (CTs) performed at 30 weeks of age. The limb length ratios (femur:tibia) were significantly different for both FE (mean 0.72, SD 0.0381, P < .001) and TE (mean 0.91, SD 0.0383, P < .001) treatment groups compared to control (mean 0.81, SD 0.0073). Patella height, as measured from the most distal point of the patella to the tibial joint surface (modified Caton-Deschamps measurement), was lower (baja) in the FE and higher (alta) for the TE, compared with the control group. Our findings suggest femoral and tibial shortening can influence the development of the patellofemoral joint, which may be dictated by moment arm function and is potentially responsible for the etiology of patella alta. Future studies are warranted to explore this association further with the view for the development of treatment options for patella alta in human patients.