Knee Injuries in the Elite American Football Player: A Descriptive Pictorial Imaging and Mechanism of Injury Review.

ABSTRACT: Musculoskeletal injuries are common in American football, with an incidence ranging from approximately 10 to 35 per 1000 playing hours. Injuries occur more commonly in games than in practice. Although several studies have analyzed specific injury types in football, this review aims to describe the most common knee injuries sustained by American football players and to review the existing literature pertaining to the radiologic findings used in the diagnosis of these injuries.

Trends associated with distal biceps tendon repair in the United States, 2007 to 2011.

BACKGROUND: Current studies investigating surgical treatment of distal biceps tendon tears largely consist of small, retrospective case series. The purpose of this study was to investigate the current patient demographics, surgical trends, and postoperative complication rates associated with operative treatment of distal biceps tendon tears using a large database of privately insured, non-Medicare patients. METHODS: Patients who underwent surgical intervention for distal biceps tendon tears from 2007 to 2011 were identified using the PearlDiver database. Demographic and surgical data as well as postoperative complications were reviewed. Statistical analysis was performed using linear regression analysis and χ(2) tests, with statistical significance set at P < .05. RESULTS: A total of 1443 patients underwent surgical treatment for distal biceps tendon tears. Men and patients aged 40 to 59 years accounted for 98% and 72% of the cohort, respectively. Regarding surgical technique, reinsertion to the radial tuberosity was preferred (95%) over tenodesis to the brachialis (5%) (P < .01). In total, revision surgery for tendon rerupture occurred in 5.4% of treated patients. The incidence of revision surgery for rerupture in acute and chronic distal biceps tears was 5.1% and 7.0%, respectively (P = .36). Postoperative infection and peripheral nerve injury rates were 1.1% and 0.6%, respectively. CONCLUSION: Surgeons strongly preferred anatomic reinsertion to the radial tuberosity for treatment, regardless of the chronicity of the injury. Postoperative complication rates were similar to those found in prior studies, although the true rate of rerupture may be higher than previously thought.

Anatomic Factors that May Predispose Female Athletes to Anterior Cruciate Ligament Injury.

Female athletes are 2 to 10 times more likely to injure their anterior cruciate ligaments (ACL) than male athletes. There has been greater recognition of this gender discrepancy because female participation in competitive athletics has increased. Previous investigators have divided risk factors into hormonal, neuromuscular response, and anatomic subgroups. Gender variation within these groups may help explain the higher incidence of ACL injury in women. The purpose of this article is to review research examining female-specific anatomy that may predispose women to ACL injury. Specifically, we discuss how women may have increased tibial and meniscal slopes, narrower femoral notches, and smaller ACL, which may place the ACL at risk from injury. These anatomic factors, combined with other female-specific risk factors, may help physicians and researchers better understand why women appear to be more prone to ACL injury.

In vitro determination of the passive knee flexion axis: Effects of axis alignment on coupled tibiofemoral motions.

The natural passive flexion axis of human cadaveric knees was determined using a technique that minimized coupled tibiofemoral motions (translations and rotations), and the kinematic effects of mal-positioned flexion axes were determined. The femur was clamped in an apparatus that allowed unconstrained tibial motions as the knee was flexed from 0° to 90°. To establish the natural flexion axis, the femur's position was adjusted such that coupled tibiofemoral motions were minimized. Tests were repeated, first with the femur rotated internally and externally from its original position, and again after positioning the femur to flex the knee about the transepicondylar axis. Compared to the transepicondylar axis, flexion about the natural axis significantly reduced mean tibial translation by 66.4% (p < 0.01) and varus-valgus rotation by 70.1% (p <0.01). Mean varus-valgus rotation increased by 3.4° (factor of 4) when the femur was rotated 3° internally or externally from the optimum position. Differences in condylar location coordinates between the transepicondylar and natural flexion axes most likely indistinguishable clinically. Knee flexion about an axis that minimizes coupled tibiofemoral motions could be important for placement and orientation of a femoral total knee component and for specimen alignment during biomechanical knee testing.

Cyclic testing of tibialis tendon allografts for anterior cruciate ligament reconstruction using suture-post versus spiked washer tibial fixation.

BACKGROUND: The purpose of this study was to directly compare spiked washer and suture-post tibial-sided fixation techniques used for anterior cruciate ligament reconstruction by measuring anterior tibial translation during cyclic tests. METHODS: Fresh-frozen human knees were tested using a robotic system that applied 250 cycles of anterior-posterior tibial force (134 N) at 30° flexion, while recording tibial translation. Ten intact knees were tested to collect baseline data for native specimens. A single knee was selected to test ligament reconstructions using doubled tibialis tendon allografts. All grafts were fixed proximally using an EndoButton™, and the tibial end of the graft was fixed with either a spiked washer or with a suture post placed at two different locations (near and distant) relative to the tibial tunnel. FINDINGS: Mean first cycle translation for intact knees was 4.8 (sd 1.8) mm; means after reconstruction were 2.6 (sd 0.9) mm (spiked washer), 10.1 (sd 1.9) mm (suture post near), and 10.4 (sd 1.5) mm (suture post distant). Corresponding means for translation increase over 250 cycles were 0.3 (sd 0.2) mm, 3.6 (sd 1.3) mm, 7.2 mm (sd 0.9) mm, and 8.0 (sd 1.3) mm. All mean increases (first cycle and cyclic) after ACL reconstruction were significantly greater than those for the intact knees, and all means with a suture post were significantly greater than those with a spiked washer. There were no significant differences between mean translations for near and distant suture post locations. INTERPRETATION: Use of suture post fixation for anterior cruciate ligament reconstruction is questioned since increases in anterior tibial translation could lead to excessive post-operative knee laxity and possibly early clinical failure.

A novel method for determining sagittal pediatric patellar height with the Blumensaat-Epiphyseal Containment of the Knee Angle.

Defining normal pediatric patellar height is complicated. Current methods use ratios calculated from lateral radiographs, but often provide inconsistent results and are time-consuming. It has been observed that the angle formed by Blumensaat's line and the distal femoral physis, when extended, form an area of patellar containment throughout a range of knee flexion. Deemed the Blumensaat-Epiphyseal Containment of the Knee (BECK) Angle, the objective of this study was to investigate this as a simple alternative to identify normal pediatric patellar height. Lateral radiographs were taken every 15° from 0° to 90° flexion on 10 fresh-frozen cadaveric knees. Patellar height was measured as the percentage of pole-to-pole patellar length contained within the BECK angle. The method was then applied to normal lateral radiographs of 105 pediatric knees, divided into age groups of 7-9, 10-12, and 13-16 years old. BECK angle patellar containment was compared with previously described methods. For cadaveric specimens, at least 50% patellar containment occurred between 0° and 71° flexion without quadriceps tension and between 21° and 81° flexion with 30 N of quadriceps tension. For pediatric radiographs, flexion ranged from 9° to 81°. At least 50% patellar containment occurred in 96% of knees in all three age groups. Knee flexion fell within a range of 15°-60° in 92 of the 105 pediatric knees. Limiting the analysis to this range, at least 50% patellar containment occurred in 99% of knees in all three age groups. On the basis of this study, normal pediatric knee lateral radiographs between 15° and 60° flexion should show at least 50% patellar containment within the BECK angle. LEVEL OF EVIDENCE: Diagnostic Level II study.

Plate Versus Intramedullary Nail Fixation of Anterior Tibial Stress Fractures: A Biomechanical Study.

BACKGROUND: Anterior midtibial stress fractures are an important clinical problem for patients engaged in high-intensity military activities or athletic training activities. When nonoperative treatment has failed, intramedullary (IM) nail and plate fixation are 2 surgical options used to arrest the progression of a fatigue fracture and allow bone healing. HYPOTHESIS: A plate will be more effective than an IM nail in preventing the opening of a simulated anterior midtibial stress fracture from tibial bending. STUDY DESIGN: Controlled laboratory study. METHODS: Fresh-frozen human tibias were loaded by applying a pure bending moment in the sagittal plane. Thin transverse saw cuts, 50% and 75% of the depth of the anterior tibial cortex, were created at the midtibia to simulate a fatigue fracture. An extensometer spanning the defect was used to measure the fracture opening displacement (FOD) before and after the application of IM nail and plate fixation constructs. IM nails were tested without locking screws, with a proximal screw only, and with proximal and distal screws. Plates were tested with unlocked bicortical screws (standard compression plate) and locked bicortical screws; both plate constructs were tested with the plate edge placed 1 mm from the anterior tibial crest (anterior location) and 5 mm posterior to the crest. RESULTS: For the 75% saw cut depth, the mean FOD values for all IM nail constructs were 13% to 17% less than those for the saw cut alone; the use of locking screws had no significant effect on the FOD. The mean FOD values for all plate constructs were significantly less than those for all IM nail constructs. The mean FOD values for all plates were 28% to 46% less than those for the saw cut alone. Anterior plate placement significantly decreased mean FOD values for both compression and locked plate constructs, but the mean percentage reductions for locked and unlocked plates were not significantly different from each other for either plate placement. The percentage FOD reductions for all plate constructs and the unlocked IM nail were significantly less with a 50% saw cut depth. CONCLUSION: Plate fixation was superior to IM nail fixation in limiting the opening of a simulated midtibial stress fracture, and anterior-posterior placement of the plate was an important variable for this construct. CLINICAL RELEVANCE: Results from these tests can help guide the selection of fixation hardware for patients requiring surgical treatment for a midtibial stress fracture.

Location of the natural knee axis for internal-external tibial rotation.

BACKGROUND: Rotating hinge and mobile bearing tray knee replacement designs utilize a single fixed axis for tibial rotation, yet there is little published information regarding the natural internal-external axis (IEA) for tibial rotation. Identifying the IEA should provide an opportunity for reproducing normal knee kinematics and maintaining the balance of forces in the soft tissues that help control rotation of the tibia. METHODS: The location and orientation of the IEA relative to the tibial plateau were calculated in 46 fresh frozen human cadaveric specimens using an instant center of rotation analysis at fixed knee flexion angles ranging from five degrees to 105°. RESULTS: IEA location ranged from 4.0 to 4.9mm medial and 1.7 to 5.5mm posterior to the center of the tibial plateau (from 5° to 105° of knee flexion). IEA orientation was reported relative to a reference axis perpendicular to the plane of the tibial plateau. In the frontal plane, the IEA was not significantly different from the reference axis from five degrees to 45° flexion, and 2.0° to 2.7° valgus to the reference axis from 60° to 105° flexion. In the sagittal plane, the IEA was not significantly different from the reference axis from 5° to 15° flexion, and 3.0° to 7.0° extended from the reference axis from 30° to 105° flexion. CONCLUSIONS: The IEA moves posteriorly with increasing knee flexion on the tibial plateau. Placement of the IEA relative to the tibial plateau for a rotating hinge or mobile bearing tray implant may represent a compromise between design objectives for moderate and deeper knee flexion. CLINICAL RELEVANCE: This study has relevance for future knee implant designs.

Male-Female Differences in Knee Laxity and Stiffness: A Cadaveric Study.

BACKGROUND: It has been reported that over 70% of anterior cruciate ligament (ACL) injuries occur in noncontact situations and that females are at 2 to 8 times greater risk of ACL injury than males. Increased joint laxity and reduced knee stiffness in female knees have been suggested as possible explanations for the higher ACL injury rates in females. HYPOTHESIS: Compared with male knees, female knees will demonstrate increased laxity and reduced stiffness along the anterior-posterior (AP), internal-external (IE), and varus-valgus (VV) directions. STUDY DESIGN: Controlled laboratory study. METHODS: Forty-seven fresh-frozen human cadaveric knees were tested (22 male and 25 female) by use of a robotic system. Mean ages were 34.6 years (range, 19-45 years) for males and 28.4 years (range, 16-42 years) for females. Joint laxity and stiffness were measured from force-vs-displacement or torque-vs-rotation curves recorded for 3 modes of testing: ± 134 N AP force, ± 5 N · m IE torque, and ± 10 N · m VV moment. RESULTS: Compared with male knees, female knees had greater internal laxity from 0° to 50° flexion (P < .01; maximum difference of 8.3° at 50° of flexion) and greater valgus laxity from 0° to 50° of flexion (P < .05; maximum difference of 1.6° at 50° of flexion). However, female knees exhibited greater anterior laxity only at 50° of flexion (P < .03; difference of 1.3 mm). No significant male-female differences in anterior or posterior stiffness were found. Male knees had 42% greater internal stiffness from 0° to 30° of flexion (P < .03), 35% greater valgus stiffness at 10° of flexion (P < .03), and 19% greater varus stiffness at 50° of flexion (P < .03). CONCLUSION: Female knees demonstrated significantly increased laxity and reduced stiffness compared with males. This finding was not uniform but was dependent on the direction tested and the knee flexion angle. CLINICAL RELEVANCE: Understanding the risk factors for noncontact ACL injury is important for injury prevention. In combination with other female-specific risk factors, increased knee laxity may be a contributing factor associated with the higher rate of female ACL injuries.

Effect of Different Preconditioning Protocols on Anterior Knee Laxity After ACL Reconstruction with Four Commonly Used Grafts.

BACKGROUND: It is currently unknown if preconditioning an anterior cruciate ligament (ACL) graft prior to fixation is helpful in eliminating possible increases in anterior knee laxity. The purpose of this study was to measure cyclic increases in anterior tibial translation of four commonly used graft tissues subjected to four preconditioning protocols. METHODS: A robotic system was used to apply 250 cycles of anteroposterior force (134 N of anterior force followed by 134 N of posterior force) to ten intact knees (ACL controls) and then to a single knee reconstructed, for separate tests, with bone-patellar tendon-bone, bone-Achilles tendon, hamstring tendon, and tibialis tendon grafts following (1) no preconditioning, (2) preconditioning on a tension board (89 N of initial force held for twenty minutes), (3) preconditioning in situ (89 N of force applied to the tibial end of the graft during twenty-five flexion-extension cycles), and (4) a combination of protocols 2 and 3. RESULTS: Over the 250 cycles, all grafts were associated with a progressive increase in anterior tibial translation that was approximately an order of magnitude greater than that of the ACL, and preconditioning had no significant effect on this increase in translation. There were some significant differences in the progressive anterior tibial translation increase among the graft tissues within a given preconditioning protocol, but these differences were no greater than 1.1 mm. First-cycle and cycle-250 anterior tibial translation varied among the graft tissue types, possibly reflecting an initial "settling in" process. Regardless of the tissue type, ≥75% of the total increase in the anterior tibial translation occurred within the first 125 cycles. CONCLUSIONS: Preconditioning had no significant effect on the progressive increase of anterior tibial translation from the first cycle to cycle 250 for any of the graft tissues tested. CLINICAL RELEVANCE: On the basis of these results, current preconditioning methods appear to be ineffective in reducing progressive increases in anterior knee laxity from cyclic loading.

Use of inertial sensors to predict pivot-shift grade and diagnose an ACL injury during preoperative testing.

BACKGROUND: The pivot-shift (PS) examination is used to demonstrate knee instability and detect anterior cruciate ligament (ACL) injury. Prior studies using inertial sensors identified the ACL-deficient knee with reasonable accuracy, but none addressed the more difficult problem of using these sensors to determine whether a subject has an ACL deficiency and to correctly assign a PS grade to a patient's knee. HYPOTHESIS: Inertial sensor data recorded during a PS examination can accurately predict ACL deficiency and the PS score assigned by the examining physician. STUDY DESIGN: Cohort study (diagnosis); Level of evidence, 2. METHODS: A total of 32 patients with unilateral ACL deficiency and 29 with intact ACLs in both knees had inertial sensor modules strapped to the tibia and femur of each limb for preoperative PS testing under anesthesia. Support vector machine (SVM) methods assessed PS grades on the basis of these data, with the examiner's clinical grading shift used as ground truth. A fusion of regression and SVM classification techniques diagnosed ACL deficiency. RESULTS: The clinically determined PS grades of all 122 knees were as follows: 0 (n = 69), +1 (n = 23), +2 (n = 27), and +3 (n = 3). The SVM classification analysis was 77% accurate in correctly classifying these grades, with 98% of computed PS grades falling within ±1 grade of the clinically determined value. The system fusion algorithm diagnosed ACL deficiency in an individual with an overall accuracy of 97%. This method yielded 6% false negatives and 0% false positives. CONCLUSION: This study used inertial sensor technology with SVM algorithms to accurately determine clinically assigned PS grades in ACL-intact and ACL-deficient knees. By extending the assessment to a separate group of patients without ACL injury, the inertial sensor data demonstrated highly accurate diagnosis of ACL deficiency.