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To investigate the diagnostic performance of preoperative MRI in evaluating posterolateral corner (PLC) structures after acute knee dislocation (KD) and determine the correlation of MRI with operative findings for grading structure integrity.Acute knee (femorotibial) dislocations between 2005 and 2020 with preoperative MRI and surgical posterolateral corner repair were identified from a single academic institution. From MRI, integrity was evaluated for PLC structures: lateral collateral ligament (LCL), popliteus tendon (PT), biceps femoris tendon (BFT), and ligamento-capsular complex (LCC). Frequency of injury to each structure and number of PLC structures torn in each case were tabulated. Diagnostic performance of MRI was determined using surgery as the reference standard. Correlation between MRI and surgery for each PLC structure was determined using kappa.Thirty-nine KD cases (19 right) in 39 patients (28 male) were included, with mean age of 33 years. Mechanism of injury was as follows: high energy 52%, low energy 38%, ultra-low energy 10%. LCL was most frequently torn, in 95% (37/39) of cases. Most commonly, three of four PLC structures were torn in 54% (21/39) of cases. Diagnostic accuracy of MRI was high for LCL 95%, BFT 87%, PT 82%, and LCC 92%. Correlation between MRI and surgical findings was variable: substantial for BFT, moderate for LCL and PT, and fair for LCC.MRI has high accuracy for detecting tears of posterolateral corner stabilizers in the setting of acute KD. However, for grading structure integrity, the correlation of MRI with surgical findings is variable, ranging from fair to substantial.• In acute knee dislocation, MRI has high diagnostic accuracy for detecting tears of posterolateral corner (PLC) structures. • Preoperative MRI should be considered by orthopedic surgeons when there is clinical concern for posterolateral corner instability following acute knee dislocation. • Although MRI is valuable in the preoperative investigation of knee dislocation, clinical assessment and intraoperative exploration may still be required for definitive diagnosis.

Cephalomedullary (CMN) implants are commonly used to address elderly intertrochanteric hip fractures. Multiple CMN implant systems exist with subtle variation between manufacturers. Multiple modes of CMN failure have been described in the literature. The present study assessed the local modes and rates of construct failure (nail fracture, cut-out and non-union) of two such implants, after a change in implant supply provided the opportunity for retrospective comparison. Additional investigation was undertaken to assess whether any predictors of failure could be identified based on common radiographic measurement parameters.Based on local implant records, all consecutive patients who suffered an intertrochanteric fracture, treated at a tertiary care hospital with a cephalomedullary nail from January 2014 to January 2018 were included. Patients were excluded if they received a CMN for pathologic fracture. Within the collection period all patients received either a Synthes Trochanteric Fixation Nail (TFN) or Zimmer Natural Nail (ZNN). Patients were retrospectively assessed for fracture reduction and implant technique parameters at the time of initial surgery. Radiographic data were assessed at minimum two years post-operatively to assess for union. Patient demographic data was followed to assess rate and mode of failure.Six hundred and sixty-two patients were included in the study, from which a propensity matched cohort was derived. Comparing across equivalent cohorts, no differences in the rate or mode of construct failure were identified between the TFN and ZNN. When assessing the entire cohort we observed 39 construct failures (5.9%), which included 31 instances of nail cutout (4.7%), 4 episodes of nail fracture (0.6%) and 4 failures related to non-union (0.6%). Tip to apex distance, sagittal malalignment and Cleveland zone were identified as significant predictors of nail failure.No difference in rates or modes of failure were identified between the TFN and ZNN constructs. Similar to previous reports we again identified the impact of tip to apex distance on construct failure and further identified Cleveland zone and sagittal malalignment as significant risks for failure.

OBJECTIVES Assess outcomes of acetabular open-reduction and internal fixation (ORIF) in the elderly; 2) Investigate factors influencing outcome; 3) Compare outcomes following low and high energy mechanisms of injury. DESIGN Retrospective case series. SETTING Level 1 trauma center. PATIENTS Seventy-eight patients over 60 (age:70.1±7.4; 73.1% males). INTERVENTION ORIF for acetabular fractures. MAIN OUTCOME MEASUREMENTS Complications, re-operation rates, and Oxford Hip Score (OHS), joint preservation and development of symptomatic OA. Cases with OA and OHS

Fragility fractures (FFs) are low-energy trauma fractures that occur at or below standing height. Among FFs, hip fractures are associated with the greatest morbidity, mortality and cost to Canadian health care systems. This review highlights the current state of medical care for hip fractures in Canada, with specific focus on the role of the multidisciplinary team. Gaps in care exist, as FFs represent a unique challenge requiring both acute and chronic management. Furthermore, there is a lack of ownership of FFs by a medical specialty. These gaps can be addressed through the use of multidisciplinary teams, which have been shown to be efficacious and cost-effective. This model of care also addresses numerous patient-identified barriers to treatment, including inadequate patient counselling. However, there is still room for improvement in both the identification of patients at risk for hip fracture and patient adherence to therapy.Les fractures de fragilisation (FF) sont des fractures qui surviennent lors d’un traumatisme léger se produisant depuis la position debout ou d’une hauteur moindre. Les fractures de la hanche sont les FF associées aux plus grands taux de morbidité et de mortalité et aux plus grands coûts pour les systèmes de santé au Canada. La présente revue s’intéresse à l’état actuel des soins médicaux pour une fracture de la hanche au pays et porte une attention spéciale au rôle de l’équipe multidisciplinaire. Des lacunes dans les soins existent et sont mises en évidence par les FF, qui posent un défi bien particulier en nécessitant une prise en charge à la fois aiguë et chronique. De plus, cette prise en charge ne relève d’aucune spécialité médicale. La correction de ces lacunes peut passer par le recours aux équipes multidisciplinaires, dont l’efficacité et la rentabilité ont été démontrées. Ce modèle de soins élimine également de nombreux obstacles au traitement signalés par les patients, y compris le counseling inadéquat. Des améliorations sont néanmoins encore nécessaires dans l’identification des patients à risque de fracture de la hanche et dans l’observance du traitement.

The REGAIN (Regional versus General Anesthesia for Promoting Independence after Hip Fracture) trial found similar ambulation and survival at 60 days with spinal versus general anesthesia for hip fracture surgery. Trial outcomes evaluating pain, prescription analgesic use, and patient satisfaction have not yet been reported.To compare pain, analgesic use, and satisfaction after hip fracture surgery with spinal versus general anesthesia.Preplanned secondary analysis of a pragmatic randomized trial. (ClinicalTrials.gov: NCT02507505).46 U.S. and Canadian hospitals.Patients aged 50 years or older undergoing hip fracture surgery.Spinal or general anesthesia.Pain on postoperative days 1 through 3; 60-, 180-, and 365-day pain and prescription analgesic use; and satisfaction with care.A total of 1600 patients were enrolled. The average age was 78 years, and 77% were women. A total of 73.5% (1050 of 1428) of patients reported severe pain during the first 24 hours after surgery. Worst pain over the first 24 hours after surgery was greater with spinal anesthesia (rated from 0 [no pain] to 10 [worst pain imaginable]; mean difference, 0.40 [95% CI, 0.12 to 0.68]). Pain did not differ across groups at other time points. Prescription analgesic use at 60 days occurred in 25% (141 of 563) and 18.8% (108 of 574) of patients assigned to spinal and general anesthesia, respectively (relative risk, 1.33 [CI, 1.06 to 1.65]). Satisfaction was similar across groups.Missing outcome data and multiple outcomes assessed.Severe pain is common after hip fracture. Spinal anesthesia was associated with more pain in the first 24 hours after surgery and more prescription analgesic use at 60 days compared with general anesthesia.Patient-Centered Outcomes Research Institute

➤ A preoperative computed tomography scan may be considered to improve surgical planning, as secondary fracture lines are poorly visualized on radiographs. ➤ Oblique internal and external rotation fluoroscopic views may be used intraoperatively to fully evaluate the medial and lateral facet articular reduction if direct assessment by visualization or palpation is not completed. ➤ Partial patellectomy for inferior pole fractures should be avoided, and bone-preserving procedures are recommended. ➤ A lateral arthrotomy may be used for direct visualization of the articular reduction for multifragmentary fractures. An inferomedial arthrotomy should be avoided to protect the dominant blood supply of the patella. ➤ Tension band fixation with cannulated screws yields a lower reoperation rate, improved functional outcome scores, and better performance in biomechanical studies than Kirschner wire-based tension band fixation. ➤ Preliminary studies of novel plate and screw constructs for osteosynthesis have shown promising results.

Background: Guidelines for urinary catheterization in patients with hip fracture recommend limiting catheter use and using intermittent catheterization preferentially to avoid complications such as urinary tract infection (UTI) and postoperative urinary retention (POUR). We aimed to compare current practices to clinical guidelines, describe the incidence of POUR and UTI, and determine factors that increase the risk of these complications. Methods: We retrospectively reviewed the charts of patients with hip fracture who presented to a single large tertiary care centre in southeastern Ontario between November 2015 and October 2017. Data collected included comorbidities, catheter use and length of stay. We compared catheter use to guidelines, and investigated the incidence of and risk factors for POUR and UTI. Results: We reviewed the charts of 583 patients, of whom 450 (77.2%) were treated with a catheter, primarily indwelling (416 [92.4%]). Postoperative urinary retention developed in 98 patients (16.8%); however, it did not affect length of stay (p = 0.2). Patients with indwelling catheters for more than 24 hours after surgery had a higher incidence of POUR than those who had their catheter removed before 24 hours (65/330 [19.7%] v. 10/98 [10.2%]) (odds ratio [OR] 2.2, 95% confidence interval [CI] 1.06–4.38). A UTI developed postoperatively in 62 patients (10.6%). Catheter use was associated with a 6.6-fold increased risk of UTI (OR 6.6, 95% CI 2.03–21.4). Patients with indwelling catheters did not have a significantly higher incidence of UTI than those with intermittent catheterization (57/416 [13.7%] v. 2/34 [5.9%]) (p = 0.2). Patients who developed a UTI had significantly longer catheter use than patients who did not (p < 0.002). Conclusion: Indwelling catheters were used frequently, which suggests low compliance with clinical guidelines. Longer duration of catheter use led to higher rates of UTI and POUR. Further investigation of the reasons for the common use of indwelling rather than intermittent catheterization is needed.

Summary Engaging patients—defined broadly as individuals with lived experience of a given condition, family members, caregivers, and the organisations that represent them—as partners in research is a priority for policymakers, funders, and the public. Nonetheless, formal efforts to engage patients are absent from most studies, and models to support meaningful patient engagement in clinical anaesthesia research have not been previously described. Here, we review our experience in developing and implementing a multifaceted patient engagement strategy within the Regional Versus General Anesthesia for Promoting Independence After Hip Fracture (REGAIN) surgery trial, an ongoing randomised trial comparing spinal vs general anaesthesia for hip fracture surgery in 1600 older adults across 45 hospitals in the USA and Canada. This strategy engaged patients and their representatives at both the level of overall trial oversight and at the level of individual recruiting sites. Activities spanned a continuum ranging from events designed to elicit patients' input on key decisions to longitudinal collaborations that empowered patients to actively participate in decision-making related to trial design and management. Engagement activities were highly acceptable to participants and led to concrete changes in the design and conduct of the REGAIN trial. The REGAIN experience offers a model for future efforts to engage patients as partners in clinical anaesthesia research, and highlights potential opportunities for investigators to increase the relevance of anaesthesia studies by incorporating patient voices and perspectives into the research process.

Background Acetabular fractures in the elderly frequently involve segmental quadrilateral plate injury, yet no consensus exists on how to best control the femoral head medial displacement. Quadrilateral surface plates (QSP) were developed to help buttress these challenging fractures. The study aims to 1) Determine the prevalence of segmental quadrilateral plate fractures (SQPF) in elderly patients; and 2) Assess if utilization of a QSP is associated with improved acetabulum fracture reduction and outcome. Methods This was a retrospective study conducted at a level-1 trauma centre. . All patients over 60-years that sustained an acetabular fracture between 2007 and 2019 were reviewed. Pre-operative pelvic radiographs and CT imaging were reviewed for 96 patients, to assess for SQPF. From the 96 patients reviewed, over one third of patients (n = 40, 41.6%) sustained a SQPF. Patients that had an acute-THA (n = 7) were excluded as were patients that underwent an ORIF but did not have a QSP or an anterior column buttress plate (n = 3). The remaining 30 formed the study’s cohort. We assessed the ability to achieve and maintain reduction in this elderly population, and compared outcomes using traditional anterior column buttress plates (ilioingual or intra-pelvic approach) versus an intra-pelvic pre-contoured buttress suprapectineal plate (QSP). Outcome measures included: fracture reduction using the Matta classification (desirable: anatomical/imperfect and poor), re-operations, conversion to THA and Oxford Hip Score (OHS) (for the preserved hips). Results Ten patients had an ORIF with utilization of a QSP (QSP-group), and 20 had an ORIF but did not have the QSP (non-QSP-group). There was no difference in patient demographics between groups. Fracture patterns were also similar (p = 0.6). Postoperative fracture reduction was desirable (anatomical/imperfect) in 17 patients and poor in 13. Improved ability to achieve a desirable reduction was seen in the QSP-group (p = 0.02). Conversion to THA was significantly lower in patients that had a desirable fracture reduction (appropriate: 3/17; poor: 7/13). No patients in the QSP-group have required a THA to-date, compared to 10/20 patients in the non-QSP-group (p = 0.01). The mean time to THA was 1.6 ± 2.1 year. There was no difference in OHS between the two groups (34.4 ± 10.3). Conclusion Elderly acetabulum fractures have a high incidence (approaching 40%) of segmental QPF. Desirable (anatomical/imperfect) fracture reduction was associated with improved outcome. The use of a QSP was associated with improved ability to achieve an appropriate reduction. A QSP should be considered as they are both reliable and reproducible with a significantly improved fracture reduction and lower conversion to THA.

OBJECTIVE To determine if geriatric intertrochanteric hip fracture patients achieve equivalent postoperative functional status after management with either a short (180-200 mm) or a long (260-460 mm) InterTAN intramedullary device. DESIGN Retrospective review of a prospective randomized control trial. SETTING Four Level I Trauma Centers. PATIENTS/PARTICIPANTS One hundred eight patients with OTA/AO classification 31A-1 and 31A-2 intertrochanteric hip fractures were included in the study. INTERVENTION Internal fixation using an IT device. MAIN OUTCOMES MEASURES Primary outcomes included Functional Independence Measure and Timed Up and Go. Secondary outcomes included blood loss, surgical time, length of stay, adverse events, and mortality. RESULTS Seventy-one short and 37 long IT patients met study inclusion criteria. Demographics were similar between groups. There was no difference in Functional Independence Measure or Timed Up and Go scores between the 2 IT groups at any of the time points collected. Mean operative time was lower in the short IT group than in the long IT group (60 vs. 73 minutes; P = 0.021). A higher proportion of long IT patients had reamed constructs (95% vs. 48% short IT, P < 0.001). Postoperative blood loss was significantly higher in the long IT group without a significant influence on the number of patients requiring transfusion (P = 0.582) or average units transfused (P = 0.982). There was no significant difference in the proportion of postoperative adverse events between the 2 cohorts despite a higher number of peri-implant femur fractures in the short IT group than in the long IT group (5 vs. 1, P = 0.350). CONCLUSIONS Postoperative functional status was not influenced by the length of IT device in the management of geriatric intertrochanteric hip fractures. LEVEL OF EVIDENCE Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Background: Negative-pressure wound therapy (NPWT) can improve fasciotomy wound closure, but its effects on skeletal muscle are largely unknown. The purpose of this study was to evaluate NPWT effects on skeletal muscle after fasciotomy for compartment syndrome in an animal model and to assess regional variability in muscle fiber regeneration. Methods: Compartment syndrome was induced in the hindlimb of twenty-two adult female pigs with use of a continuous intracompartmental serum-infusion model. Fasciotomy was performed after six hours, and animals were randomized to receive either wet-to-dry gauze dressings (control group) or NPWT dressings (−125 mm Hg, continuous suction) for seven days. Delayed primary wound closure was attempted at seven days, and the peroneus tertius was harvested for analysis seven days or twenty-one days after fasciotomy. Muscles were weighed, and hematoxylin and eosin-stained samples from four regions of the muscle (superficial central, deep central, lateral, and proximal) were mapped for different cellular morphologies. Results: Muscle weight was greater in the affected limb at all time points with no difference between treatment groups. At seven days, only the deep central samples in the NPWT group had a significantly greater cross-sectional area containing normal fibers as compared with that found in the controls. By twenty-one days, the deep central, lateral, and proximal regions of the NPWT-treated muscles had a smaller cross-sectional area containing normal fiber morphology and a greater cross-sectional area containing only mononucleated cells as compared with the controls. Conclusions: NPWT did not decrease muscle weight. At twenty-one days, the extent of muscle fiber regeneration after fasciotomy for compartment syndrome was reduced in muscles treated with NPWT for seven days compared with the values in the control group treated with wet-to-dry gauze dressings. Clinical Relevance: NPWT may be harmful to skeletal muscle after compartment syndrome requiring fasciotomy and local wound care.

Composite reconstruction of the pelvis in the setting of trauma is challenging. In addition to coverage and containment of the abdominal viscera, recreating a robust sitting surface is critical. However, there is a paucity of literature to guide the reconstructive surgeon. The authors present a case of traumatic hemipelvectomy, and describe their application of the ‘spare-parts’ concept to successfully reconstruct the bony pelvis and provide soft tissue coverage.

To assess the accuracy of a new radiographic measurement of the distal tibia and fibula on the lateral view of the ankle in normal adults: the anteroposterior tibiofibular (APTF) ratio.Thirty adults without history of trauma or disease of the ankle were included. Bilateral ankles were x-rayed with a true lateral view of the ankle. A line from the anterior tibial physis scar to the posterior tibial cortex, passing by the intersection of the physis and the fibula anterior cortex, was drawn. The APTF ratio was calculated as the ratio of the anterior segment to the posterior segment. The measurements were done by 3 independent evaluators. Intra- and interobserver reliability was obtained using intraclass correlation.The APTF ratio was 0.94 ± 0.13 with a range of 0.63-1.31. Sex and age had no effect on the results. Inter- and intraobserver reliability was good to very good with an intraclass correlation between 0.6 and 0.8. A strong correlation between the left and the right APTF ratio was observed (r = 0.501 and P = 0.001).The distal tibiofibular joint anatomy in the sagittal plane can be accurately assessed with a new reliable radiographic measurement, the APTF ratio. The reduction of this joint during surgery can be confirmed with a true lateral view of the ankle. The anterior fibula cortex crosses the tibial physeal scar at the center of the line crossing this point and the anterior cortex of the tibia at the level of the physeal scar in the normal ankle.

There have been no studies assessing the optimal biomechanical tension of suture button constructs. The purpose of this study was to assess optimal tensioning of suture button fixation and its ability to maintain reduction under loaded conditions using a stress computed tomography (CT) model.Ten cadaveric lower limbs disarticulated at the knee were used. The limbs were placed in a modified ankle load frame that allowed for the application of sustained torsional axial or combined torsional/axial loads. The syndesmosis and the deep deltoid ligaments complex were sectioned and the limbs were randomized to receive a suture button construct tightened at 4, 8, or 12 kg. The specimens were loaded under the 3 loading scenarios with CT scans performed after each and at the conclusion of testing. Multiple measurements of translation and rotation were compared with baseline CT scan taken before sectioning.Significant lateral (maximum 5.26 mm) and posterior translation (maximum 6.42 mm) and external rotation (maximum 11.71 degrees) was noted with the 4 kg repair. Significant translation was also seen with both the 8 and the 12 kg repairs; however, the incidence was less than with the 4 kg repair. Significant overcompression (ML = 1.69 mm, B = 2.69 mm) was noted with the 12 kg repair and also with the 8 kg repair (B = 2.01 mm).Suture button constructs must be appropriately tensioned to maintain reduction and re-approximate the degree of physiological motion at the distal tibiofibular joint. These constructs also demonstrate overcompression of the syndesmosis; however, the clinical effect of this remains to be determined.

Copyright © 2016 Wolters Kluwer Health, Inc. All rights reserved. Objectives: To compare outcomes in elderly patients with intertrochanteric hip fractures treated with either the sliding hip screw (SHS) or InterTAN intramedullary device (IT). Design: Prospective, randomized, multicenter clinical trial. Setting: Five level 1 trauma centers. Patients: Two hundred forty-nine patients 55 years of age or older with AO/OTA 31A1 (43) and OA/OTA 31A2 (206) fractures were prospectively enrolled and followed for 12 months. Intervention: Computer generated randomization to either IT (n = 123) or SHS (n = 126). Main Outcome Measurements: The Functional Independence Measure (FIM) and the Timed Up and Go test (TUG) were used to measure function and motor performance. Secondary outcome measures included femoral shortening, complications, and mortality. Results: Demographics, comorbidities, preinjury FIM scores and TUG scores were similar between groups. Patients (17.2%) who received an IT had limb shortening greater than 2 cm compared with 42.9% who received an SHS (P < 0.001). To determine the importance of preinjury function and fracture stability, we analyzed the subgroup of patients with the ability to walk 150 m independently preinjury and an OA/OTA 31A-2 fracture (n = 70). In this subgroup, patients treated with SHS had greater shortening and demonstrated poorer FIM and TUG scores compared with patients treated with an IT. Conclusions: Overall, most patients with intertrochanteric femur fractures can expect similar functional results whether treated with an intramedullary or extramedullary device. However, active, functional patients have an improved outcome when the InterTAN is used to treat their unstable intertrochanteric fracture. Level of Evidence: Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.

Knee dislocation is uncommon, but can be devastating and can include limb loss. The diagnosis of the multiligament injury may be missed entirely or mistaken for an isolated injury. The physical examination and magnetic resonance imaging primarily make the diagnosis. Based on the clinical examination, a classification such as Schenck may be made to develop the treatment plan.

Acetabular fracture patterns in the elderly, with increased involvement of the anterior column, quadrilateral plate comminution, medialization of the femoral head, and marginal impaction, differ from those noted among a younger cohort. Poor prognostic factors for open reduction and internal fixation (ORIF) are posterior wall comminution, marginal impaction of the acetabulum, a femoral head impaction fracture, a so-called gull sign, and hip dislocation. The rate of conversion to total hip arthroplasty following formal ORIF has been reported to be 22% at a mean of twenty-nine months. Total hip replacement after an acetabular fracture generally yields good clinical results; however, in the acute setting, it must be combined with proper stable fracture fixation.

Objective: This study was designed to evaluate the postimpact response of the articular cartilage in the rabbit knee after a single traumatic episode. Design: A novel servo-controlled Rabbit Impact Test System (RITS) was developed to apply a well-defined trauma to the femoral condyle in the rabbit knee. The RITS was first used in an in vitro study to determine an appropriate stress to cause cartilage damage without bone fracture. Viable rabbit knees (n = 18) were impacted with stresses of 15 to 50 MPa at a stress rate of 420 MPa/s, the latter corresponding to joint impact rates commonly seen in sports injuries and vehicular accidents. Based on the in vitro study, we performed an in vivo study by impacting the knees of rabbits (n = 9) with a 35 MPa peak stress at a stress rate of 420 MPa/s. The articular cartilage in these knees was analyzed at 0 and 3 weeks after impaction. Setting: Center for Laboratory Animal Services, Hospital for Special Surgery. Subjects: A total of 27 New Zealand White rabbits were used in this study. Intervention: A rabbit's knee was rigidly immobilized in the adjustable frame of the RITS. A small incision on the knee exposed the lateral condyle and the impactor was positioned perpendicular to the surface of the condyle. The lateral femoral condyle of the left knee was impacted, whereas the right knee was sham operated and used as a control. Main Outcome Measurements: Visual matrix damage, cell viability, and microscopic matrix damage was assessed. Results: In the in vitro study, matrix damage was observed at stress magnitudes ≥30 MPa. However, cell death was initiated at ∼20 MPa at the articular surface and increased in depth with increasing stress magnitude (2.8 ± 2% thickness/MPa,). In the in vivo study, visible surface damage was observed immediately after impaction but not at 3 weeks after impaction. At 3 weeks, the articular cartilage showed significant arthritic changes (matrix damage, chondrocyte death, and proteoglycan loss) typical of late-stage osteoarthritis. Conclusions: Our novel impact test system was able to accurately apply a quantifiable stress magnitude at a constant stress rate to rabbit femoral condyles in the in vitro and in vivo settings. At the time of impaction, the extent of cell death depended with the intensity of trauma (stress magnitude) in which complete cell death was observed in the impacted site at >40 MPa. Under in vivo conditions, the test system was able to consistently produce superficial matrix damage and cell death at 35 MPa stress magnitude at the time of impaction. This resulted in cartilage “arthritic” changes by 3 weeks postinjury.

Joint injuries in humans are frequent and similar to those seen in all mammalian species. The most commonly used method to study the correlation between trauma and cartilage survival (post-traumatic arthritis) has been conducted using in-vivo animal models. In a majority of these animal models a single or multiple impact was delivered to the patello-femoral joint (PFJ) using a drop tower type apparatus [1–6]. A main limitation of these models is with the drop tower itself and the impaction of a “whole joint”. A free-falling mass impacting the specimen abruptly decelerates, generating a nonlinear inertial force upon the tissue due to cartilage’s structural non-homogeneity. Haut et al. [2] specifically commented that it was difficult to control the impact stress using a drop tower apparatus. In addition, the rate of loading is difficult to control because changes in potential energy will generate different stress magnitudes and rates of loading. Thus, it is hard to correlate these high-loading rate experiments to slow loading rate experiments [6,7]. Only one study reported exposing and directly traumatizing the articular surface of the joint, but again utilized a drop tower device [4,5]. All these studies correlated “impact energy” or “impact force” to the amount of cartilage damage but did not evaluate the influence of stress magnitude or the rate of loading.