Kathryne J. Stabile

Importance of Tibial Slope for Stability of the Posterior Cruciate Ligament—Deficient Knee

Background Previous studies have shown that increasing tibial slope can shift the resting position of the tibia anteriorly. As a result, sagittal osteotomies that alter slope have recently been proposed for treatment of posterior cruciate ligament (PCL) injuries. Hypotheses Increasing tibial slope with an osteotomy shifts the resting position anteriorly in a PCL-deficient knee, thereby partially reducing the posterior tibial “sag” associated with PCL injury. This shift in resting position from the increased slope causes a decrease in posterior tibial translation compared with the PCL-deficient knee in response to posterior tibial and axial compressive loads. Study Design Controlled laboratory study. Methods Three knee conditions were tested with a robotic universal force-moment sensor testing system: intact, PCL-deficient, and PCL-deficient with increased tibial slope. Tibial slope was increased via a 5-mm anterior opening wedge osteotomy. Three external loading conditions were applied to each knee condition at 0°, 30°, 60°, 90°, and 120° of knee flexion: (1) 134-N anterior-posterior (A-P) tibial load, (2) 200-N axial compressive load, and (3) combined 134-N A-P and 200-N axial loads. For each loading condition, kinematics of the intact knee were recorded for the remaining 5 degrees of freedom (ie, A-P, medial-lateral, and proximal-distal translations, internal-external and varus-valgus rotations). Results Posterior cruciate ligament deficiency resulted in a posterior shift of the tibial resting position to 8.4 ± 2.6 mm at 90° compared with the intact knee. After osteotomy, tibial slope increased from 9.2° ± 1.0° in the intact knee to 13.8° ± 0.9°. This increase in slope reduced the posterior sag of the PCL-deficient knee, shifting the resting position anteriorly to 4.0 ± 2.0 mm at 90°. Under a 200-N axial compressive load with the osteotomy, an additional increase in anterior tibial translation to 2.7 ± 1.7 mm at 30° was observed. Under a 134-N A-P load, the osteotomy did not significantly affect total A-P translation when compared with the PCL-deficient knee. However, because of the anterior shift in resting position, there was a relative decrease in posterior tibial translation and increase in anterior tibial translation. Conclusion Increasing tibial slope in a PCL-deficient knee reduces tibial sag by shifting the resting position of the tibia anteriorly. This sag is even further reduced when the knee is subjected to axial compressive loads. Clinical Relevance These data suggest that increasing tibial slope may be beneficial for patients with PCL-deficient knees.

Biomechanical comparison of tibial inlay versus transtibial techniques for posterior cruciate ligament reconstruction: analysis of knee kinematics and graft in situ forces.

Background The tibial inlay technique for posterior cruciate ligament reconstruction has been proposed to provide a more anatomic reconstruction because it eliminates the sharp turn in the graft as it exits the proximal margin of the tibial tunnel in the transtibial technique. Hypothesis Reconstruction of the posterior cruciate ligament using the tibial inlay technique would more closely restore intact knee kinematics and in situ forces in the posterior cruciate ligament than would reconstruction using the transtibial technique. Methods Ten human cadaveric knees were tested in a controlled laboratory study. A robotic/universal force-moment sensor testing system was used to apply a 134-N posterior tibial load at 5 knee flexion angles: 0°, 30°, 60°, 90°, and 120°. Four knee conditions were tested: intact, posterior cruciate ligament–deficient, and the single-bundle tibial inlay reconstruction and transtibial posterior cruciate ligament reconstruction. Results Both reconstruction techniques restored posterior tibial translations to 1.7 to 2.1 mm of the intact knee, with no statistical differences between the techniques. In response to the posterior tibial load, in situ forces in both grafts were between 7 and 39 N less than those in the intact posterior cruciate ligament, with no significant differences between the grafts. Clinical Relevance The study suggests that either technique may be performed with similar biomechanical results at initial fixation under these loading conditions.

Biomechanical Analysis of a Combined Double-Bundle Posterior Cruciate Ligament and Posterolateral Corner Reconstruction

Background Failure to address both components of a combined posterior cruciate ligament and posterolateral corner injury has been implicated as a reason for abnormal biomechanics and inferior clinical results. Hypothesis Combined double-bundle posterior cruciate ligament and posterolateral corner reconstruction restores the kinematics and in situ forces of the intact knee ligaments. Study Design Controlled laboratory study Methods Ten fresh-frozen human cadaveric knees were tested using a robotic testing system through sequential cutting and reconstructing of the posterior cruciate ligament and posterolateral corner. The knees were subjected to a 134-N posterior tibial load and a 5-N.m external tibial torque at multiple flexion angles. The double-bundle posterior cruciate ligament reconstruction was performed using Achilles and semitendinosus tendons. The posterolateral corner reconstruction consisted of reattaching the popliteus tendon to its femoral origin and reconstructing the popliteofibular ligament with a gracilis tendon. Results Under the posterior load, the combined reconstruction reduced posterior translation to within 1.2 - 1.5 mm of the intact knee. The in situ forces in the posterior cruciate ligament grafts were significantly less than those in the native posterior cruciate ligament at all angles except full extension. Conversely, the forces in the posterolateral corner grafts were significantly higher than those in the native structures at all angles. Under the external torque with the combined reconstruction, external rotation as well as in situ forces in the posterior cruciate ligament and posterolateral corner grafts were not different from the intact knee. Conclusions A combined posterior cruciate ligament and posterolateral corner reconstruction can restore intact knee kinematics at time zero. In situ forces in the intact posterior cruciate ligament and posterolateral corner were not reproduced by the reconstruction; however, the posterolateral corner reconstruction reduced the loads experienced by the posterior cruciate ligament grafts. Clinical Relevance By addressing both structures of this combined injury, this technique restores native kinematics under the applied loads at fixed flexion angles and demonstrates load sharing among the grafts creating a potentially protective effect against early failure of the posterior cruciate ligament grafts but with increased force in the posterolateral corner construct.

RECONSTRUCTION OF THE INTEROSSEOUS LIGAMENT OF THE FOREARM REDUCES LOAD ON THE RADIAL HEAD IN CADAVERS

Excision of the radial head after fracture may be complicated by longitudinal radio-ulnar instability (Essex-Lopresti lesion) if the forearm interosseous ligament has also been torn. In such cases proximal migration of the radius occurs, and ulnar impaction at the wrist and radiocapitellar contact at the elbow may impair function. Although metal radial head arthroplasties are now used for irreparable radial head fractures, the long-term clinical outcome may still be unsatisfactory because of excessive radiocapitellar load causing pain. Interosseous ligament reconstruction might improve outcome by restoring normal load transfer from the radius to ulna, but the biomechanical effect of reconstruction has not been reported. This study evaluated forearm load transfer following interosseous ligament reconstruction with an Achilles tendon allograft in a cadaveric model with the radial head intact. Interosseous ligament reconstruction reduced proximal radius loading by transferring force to the proximal ulna, but force transfer by the reconstruction was only half that by the intact ligament.

An Acellular, Allograft-Derived Meniscus Scaffold in an Ovine Model

PURPOSE The purpose of this study was to develop a meniscus scaffold that has increased porosity and maintains the native meniscus extracellular matrix in an ovine model. METHODS The medial menisci of skeletally mature ovine (n = 16) were harvested; half were made into meniscus scaffolds (n = 8), and half remained intact (n = 8). Intact and scaffold meniscus tissues were compared by use of histology, DNA content analysis, in vitro cellular biocompatibility assays, and ultrastructural analysis. An additional 16 knees were used to investigate the biomechanics of the intact meniscus compared with the meniscus scaffold. RESULTS DNA content and histology showed a significant decrease in cellular and nuclear content in the meniscus scaffold (P < .003). Biocompatibility was supported through in vitro cellular assays. Scanning electron microscopy and micro-computed tomography showed a substantial increase in porosity and pore connectivity in the meniscus scaffold compared with the intact meniscus (P < .01). There was no statistical difference between the ultimate load or elastic modulus of the intact and meniscus scaffolds. CONCLUSIONS In this study a meniscus scaffold was evaluated for potential clinical application as a meniscus transplant construct in an ovine model. The data showed that a decellularized meniscus scaffold with increased porosity was comparable to the intact meniscus, with an absence of in vitro cellular toxicity. Although some compositional alterations of the extracellular matrix are to be expected during processing, it is evident that many of the essential structural components remained functional with maintenance of biomechanical properties. CLINICAL RELEVANCE This meniscus scaffold has potential for future clinical application as a meniscus transplant construct.

Reconstruction of Essex-Lopresti Injury of the Forearm: Technical Note

Longitudinal instability of the forearm resulting from an Essex-Lopresti injury is a surgical challenge, and no technique has yet met universal success. A new technique is presented here consisting of reconstruction of the radial head, leveling of the distal radioulnar joint, reconstruction of the central band of the interosseous membrane by using a pronator teres rerouting technique, and finally repair of the triangular fibrocartilage complex. It is hoped that by addressing all of the contributing longitudinal stabilizing structures, the longitudinal instability of the forearm will be controlled. The technique is challenging and requires much surgical experience.

Biomechanical analysis of titanium elastic nail fixation in a pediatric femur fracture model.

Background: Increasing weight in relation to total diameter of implanted titanium elastic nails has been found to be significantly associated with increasing sagittal angulation. However, the biomechanical literature has not well established the load at which failure of titanium elastic nails in the sagittal and coronal planes occurs. The purpose of this study was to determine load to failure in sagittal and coronal plane bending of transverse midshaft femur fractures stabilized with titanium elastic nails and correlate this with the maximum patient weight. Methods: Ten synthetic, pediatric-sized femurs 35 cm in length with an intramedullary canal diameter of 9.5 mm were used. Transverse midshaft fracture patterns were created with a handheld saw. Two 4.0-mm titanium elastic nails were then placed in a retrograde fashion through medial and lateral insertion sites in the distal metaphysis of the femur to stabilize the simulated fractures. A 4-point bending load to failure test was performed on each of the femurs. Five femurs were tested in the sagittal plane, and 5 femurs were tested in the coronal plane. Yield load, bending stiffness, and bending moments for both testing configurations were determined. Results: For the sagittal plane bending tests, the yield load was 628 ± 29 N. For the coronal plane bending tests, the yield load was 596 ± 20 N. The resulting bending moments in the sagittal and coronal planes were 20.4 ± 0.9 and 19.4 ± 0.6 Nm, respectively. From these data, we correlated bending moments with in vivo gait data to find a patient weight cutoff of 40 to 45 kg. Clinical Relevance: With the increasing rate of childhood obesity and tendency for sagittal and coronal angulation of femur fractures treated with titanium elastic nails, it is necessary to determine the load at which permanent sagittal and coronal deformation of the nails occurs because this may result in an unfavorable outcome. Conclusions: Our study provides biomechanical evidence that patients weighing more than 40 to 45 kg who undergo stabilization of a transverse midshaft femur fracture with titanium elastic nails are at risk for loss of reduction in the sagittal and coronal planes.

The Essex-Lopresti fracture-dislocation Factors in early management and salvage alternatives

Treatment recommendations for the Essex-Lopresti lesion have not come very far in 50 years. Although there have been multiple biomechanical studies, the biomechanics of forearm loading and stability remain somewhat elusive. Clinical studies have yielded some insight, but predictable outcomes are exceptional. More studies are needed to further understand the biomechanics of the forearm and provide a basis for reconstruction of the IOL. Although current clinical studies regarding IOL reconstruction and radial head replacement seem promising, long-term results with substantial patient numbers are needed. In the short term, the Essex-Lopresti lesion continues to challenge clinicians.

Development and Validation of a Computed Tomography-Based Methodology to Measure Carpal Kinematics

Motion of the wrist bones is complicated and difficult to measure. Noninvasive measurement of carpal kinematics using medical images has become popular This technique is difficult and most investigators employ custom software. The objective of this paper is to describe a validated methodology for measuring carpal kinematics from computed tomography (CT) scans using commercial software. Four cadaveric wrists were CT imaged in neutral, full flexion, and full extension. A registration block was attached to the distal radius and used to align the data sets from each position. From the CT data, triangulated surface models of the radius, lunate, and capitate bones were generated using commercial software. The surface models from each wrist position were read into engineering design software that was used to calculate the centroid (position) and principal mass moments of inertia (orientation) of (1) the capitate and lunate relative to the fixed radius and (2) the capitate relative to the lunate. These data were used to calculate the helical axis kinematics for the motions from neutral to extension and neutral to flexion. The kinematics were plotted in three dimensions using a data visualization software package. The accuracy of the method was quantified in a separate set of experiments in which an isolated capitate bone was subjected to two different known rotation/translation motions for ten trials each. For comparison to in vivo techniques, the error in distal radius surface matching was determined using the block technique as a gold standard. The motion that the lunate and capitate underwent was half that of the overall wrist flexion-extension range of motion. Individually, the capitate relative to the lunate and the lunate relative to the radius generally flexed or extended about 30 deg, while the entire wrist (capitate relative to radius) typically flexed or extended about 60 deg. Helical axis translations were small, ranging from 0.6 mm to 1.8 mm across all motions. The accuracy of the method was found to be within 1.4 mm and 0.5 deg (95% confidence intervals). The mean error in distal radius surface matching was 2.4 mm and 1.2 deg compared to the use of a registration block. Carpal kinematics measured using the described methodology were accurate, reproducible, and similar to findings of previous investigators. The use of commercially available software should broaden the access of researchers interested in measuring carpal kinematics using medical imaging.